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PHYSICS NEWS UPDATE
The American Institute of Physics Bulletin of Physics News
Number 667  December 30, 2003   by Phillip F. Schewe, Ben Stein, and
James Riordon

WORLD'S FIRST LIGHT EMITTING TRANSISTOR.  Researchers at the
University of Illinois at Urbana-Champaign have developed the
world's first light emitting transistor (LET). Unlike conventional
transistors, which include an electrical input port and an
electrical output port, the new LET also has an infrared optical
output port (see image at http://www.aip.org/mgr/png/2003/210.htm).
The LET is built of indium gallium phosphide and gallium arsenide,
rather than the silicon and germanium used in many conventional
transistors. Although the LET produces light in essentially the same
way that light emitting diodes (LEDs) operate, the transistor can
modulate light at much higher speeds. To date, the researchers (N.
Holonyak, Jr., blpayne@.uiuc.edu,  217-333-4149)  have managed to
modulate the optical LET output at a frequency of one megahertz, but
much higher speeds are theoretically possible. Although it's too
early to predict the various applications for LETs, the hybrid
device should help integrate electrical and optical circuitry
designs with one convenient, high speed package. It is only fitting
that the research team that developed the LET include the inventor
of the first visible LED (Holonyak) and the developer of the world's
fastest bipolar transistor (Feng). (M. Feng et al., Applied Physics
Letters, 5 January 2004)

GLIAL CELLS AND EPILEPSY: is there a connection?   Neurons are not
the only cells in the brain.  In fact, 90% of brain matter consists
of glial cells.  Astrocytes, the most common glial cell type, don't
have enough sodium channels to carry on the active electro-chemical
signaling characteristic of neurons, but they can communicate with
other cells through the diffusion of messenger molecules.
Furthermore, astrocytes can partially or wholly enwrap neuronal
synapses, the message sending or receiving ends of the neuron.  This
facilitates neutron-astrocyte interactions, and even neuron-neuron
communications via astrocytes.   Formerly glia were thought to play
a passive role in the nervous system---cleaning up the potassium
needed in the neural firing mechanism.  But increasingly scientists
believe that glia play a more active role in enhancing or inhibiting
action in the synapse.
Suhita Nadkarni and Peter Jung at Ohio University believe that glia
participate in the making of epilepsy.  There is no accepted theory
of epilepsy; does it arise from neurons talking in synchrony or is
it a sort of "thunderstorm" of spontaneous activity among neurons?
Jung argues that under some conditions the neuron might "listen" so
much to its astrocyte environment (by an overexpression of of
certain receptor molecules) that it enters into a bistable state;
even in the absence of outside (normal) stimulation the neuron could
fire indiscriminately in the manner characteristic of epilepsy.  It
is therefore necessary to undertake a sort of electrical engineering
study of neural-glial circuitry.  Jung, a physicist (presently at
the Kavli Institute for Theoretical Physics at UC Santa Barbara,
805-893-7333, jungp@kitp.ucsb.edu), has demonstrated some of this
glial-neural behavior in computer simulations and is working with
neuro-biologists who might shortly put the model to an experimental
test.  (Physical Review Letters, upcoming article)

IMPROVED TANDEM ORGANIC LEDs.  Stacking organic light emitting
diodes (OLEDs) leads to brighter, stabler, longer lived light
sources than individual OLEDs. Unfortunately, the metal layers
typically used to connect the individual elements are not very
transparent, reducing the resulting brightness of underlying OLEDs
in a tandem configuration. Researchers in the Display Technology
Laboratory at Eastman Kodak Company have now managed to stack OLEDs
that are connected through optically transparent, organic
semiconductor materials. The improvement in brightness in the new,
tandem OLED is essentially linearly related to the number of
individual light emitting segments included in the device, that is,
a three-segment tandem OLED is roughly three times as bright as a
conventional OLED. High brightness, high efficiency tandem OLEDs
could lead to brighter TV's and computer screens. They could also
make it easier to read cell phone displays in bright sunlight, which
often renders existing cell phone displays unintelligible. The
researchers (contact: L. S. Liao, liang-sheng.liao@kodak.com)
propose that tandem OLEDs may also be useful as lighting sources for
liquid crystal display backlighting or as solid-state room lights.
In addition, varying the number of units in a tandem OLED stack
changes the operating voltage, allowing  the possibility of
tailoring the devices to match different electrical sources, such as
household 110 volt systems. Conventional LED lighting, on the other
hand, typically requires transformers to adjust power sources to
meet the lighting element's electrical specifications. (L. S. Liao
et al., Applied Physics Letters, 5 January 2004 )

PHYSICS NEWS UPDATE
The American Institute of Physics Bulletin of Physics News
Number 665 December 10, 2003 by Phillip F. Schewe, Ben Stein, and
James Riordon

LIGHT FROZEN IN A HALL OF ATOMIC MIRRORS. In a new experiment a
pulse of light has been stopped without losing its optical energy.
A few years ago, two different Harvard groups succeeded in slowing
and then storing a pulse of light in atomic vapor. In that work the
propagation of light pulses was halted by vesting the properties of
incoming photons into the spin orientations of the atoms in the
vapor. Thus light pulses had been stopped by ceasing to exist in
the form of electromagnetic energy while ceding all of its signal
qualities to the atomic vapor. Later they could be reconstituted
into propagating light beams
(http://www.aip.org/enews/physnews/2001/split/521-1.html). Now, a
new experiment, also conducted at Harvard, brings light to a halt
but leaves the pulse intact as an optical entity. Mikhail Lukin and
his colleagues begin as before by converting the incoming light
pulse into a corresponding ensemble of spins in a vapor. But then
something else is added: a pair of counter-propagating laser beams
ease the pulse back into existence. But the control beams also
serve to herd the atoms in just such a way as to cause them to act
like a stack of mirrors. In this hall of atomic mirrors, the
original pulse still exists as electromagnetic radiation, but it
cannot move---it persists within a fixed stationary envelope. Thus
the light pulse containing optical photons is literally frozen in
space. It can be held and released into motion again on command.
The present experimental work follows a theoretical proposal
published last year in Physical Review Letters (89, 143602, 2003).
Researchers believe that the new phenomenon that they demonstrated
may be used to controllably localize, shape and guide stationary
photonic pulses in three spatial dimensions. This can create ideal
conditions for different light beams to interact or "talk" to each
other since localized light electromagnetic energy can be held in
one place for a relatively long time. Such techniques may enable
nonlinear interactions between faint laser pulses that could be
useful for processing light signals. For example, this process might serve in
optical computing, where calculations are carried out not with
electrons but with photons. Another ambitious goal would be to
perform logic operations between individual photons in future
quantum computers. But the researchers say that much further work
is still needed to determine if the present work can aid of any of
these applications.
For now, its just another step toward ultimate control of light.
(Bajcsy, Zibrov, and Lukin, Nature, 11 December 2003.)

DO QUANTUM MEASUREMENTS CHANGE IF THE DETECTOR MOVES? For example,
could a count of the number of photons in a burst of light depend on
the location of the detector in an extreme gravitational field?
These ideas, long pondered by physicists, might be verifiable in the
lab, according to a new theory in which a Bose Einstein condensate
(BEC) of cold atoms acts as a stand-in for the universal vacuum.
The related notion that potential energy residing in the vacuum can
influence the geometry of spacetime and thus the expansion of the
cosmos could also be testable in a tabletop experiment here in
Earth.
The pertinent phenomenon that would facilitate this line of research
is called the Unruh-Davies effect, which suggests that a detector
accelerating (not just moving at a constant speed but actually
moving ever faster) through a vacuum will effectively encounter
photons coming out of the vacuum. (A related phenomenon is the
Gibbons-Hawking effect, in which photons, "Hawking radiation," can
be detected in the gravitationally intense region of a black hole).
In the Unruh effect the energy needed to turn virtual photons into
real photons would be supplied by the accelerating detector itself.
The detector would see the vacuum not as an empty space but as a
thermal bath of photons. The same effect can disrupt quantum
teleportation (see the Update from a few weeks
ago---http://www.aip.org/enews/physnews/2003/split/660-2.html ). The
"temperature" of this bath would be proportional to the detector's
acceleration. Actually observing such a thermal bath (equivalent to
an effective temperature of something like 10^-15 K for a detector
acceleration one hundred thousand times more than that felt by us on
the surface of the Earth) with any foreseeable manmade detector is
close to impossible, but two physicists at the
Leopold-Franzens-Universitaet in Innsbruck, Petr Fedichev
(peter.fedichev@uibk.ac.at) and Uwe Fischer
(uwe.fischer@uni-tuebingen.de), believe the effect could be probed
by studying how sound waves ripple through BECs in the lab. The
superfluid condensate of atoms would correspond to the vacuum and
phonons would be analogous to photons moving through a curved
space-time. Before the experiment can be performed, larger BECs
than used so far will be needed, as well as sharper optical
manipulation of atoms in the BEC. (Physical Review Letters, 12
December 2003)

PHYSICS NEWS UPDATE
The American Institute of Physics Bulletin of Physics News
Number 664 December 2, 2003 by Phillip F. Schewe, Ben Stein, and
James Riordon

THE TOP PHYSICS STORIES OF 2003. The first three on our list
concern the sharpening of our understanding of the big bang era,
evidence for new quark groupings, and progress in manipulating
quantum gases. At the largest size scale, new observations from
the Wilkinson Microwave Anisotropy Probe (WMAP), the Sloan Digital
Survey and other telescopes have reduced the uncertainties in the
values of such cosmic parameters as the Hubble constant, the age of
the universe, and the fractions of total energy vested in the form
of dark and luminous matter
(www.aip.org/enews/physnews/2003/split/624-1.html;
www.aip.org/enews/physnews/2003/split/659-1.html ). Going to the
opposite extreme, at the level of elementary matter, new data
indicate that quarks needn't appear only in clumps of three
(baryons) or two (mesons). Work at SLAC (US) and KEK (Japan) hint
that quarks might also exist in "tetraquark" states
(http://www.aip.org/enews/physnews/2003/split/643-1.html), while
experiments in Japan, the US, Russia, and elsewhere provide evidence
for a "pentaquark" state
(http://www.aip.org/enews/physnews/2003/split/644-1.html ). The
third top story concerns the creation of the first ever Bose
Einstein condensate (BEC) consisting of paired-fermion-atom
molecules. This work is potentially important because mastering the
interactions between fermion atoms in the BEC state might provide
insights into the nature of superconductivity and superfluids
(http://www.aip.org/enews/physnews/2003/split/663-1.html ). Other
notable physics stories from the past year include the controversy
over the use gravitational lensing of distant radio waves by Jupiter
to measure the speed of gravity
(http://www.aip.org/enews/physnews/2003/split/620-1.html ); advances
in the use of attosecond laser pulses in studying chemical reactions
(http://www.aip.org/enews/physnews/2003/split/625-1.html ); the use
of microfluidics---essentially the science of fluids on a chip---in
processing bio-particles such as blood cells and DNA molecules
(http://www.aip.org/enews/physnews/2003/split/627-1.html ); evidence
for the focusing of light in left-handed materials, materials with a
negative index of refraction, and vindication of earlier research in
this area (http://www.aip.org/enews/physnews/2003/split/628-1.html
); first fusion reactions in Sandia's Z machine
(http://www.aip.org/enews/physnews/2003/split/632-1.html ); LIGO's
first scientific publications report no gravity wave events but do
succeed in establishing new upper limits on various wave production
processes (http://www.aip.org/enews/physnews/2003/split/632-2.html
); building a laser based on a single atom at rest
(http://www.aip.org/enews/physnews/2003/split/654-1.html );
amphoteric refraction, both positive and negative refraction, in a
single material
(http://www.aip.org/enews/physnews/2003/split/657-3.html ); and new
work with photonic crystals, including the effects of shock waves
(http://www.aip.org/enews/physnews/2003/split/634-1.html) and energy
shifting (http://www.aip.org/enews/physnews/2003/split/646-1.html).

RELATIVISTIC CHAOS. A new study shows that general relativity, a
theory in which observers in different reference frames measure time
differently, is not incompatible with chaos theory, in which events
unfold in absolute time. Chaos is an ordinary word with lots of
meanings. In physics, however, the meaning is more precise: a
system---a weather system, say---is chaotic if a very slight change
in initial conditions sends the system off into a very different
history. How different? The degree to which a system is chaotic
can be encapsulated in a parameter called the Lyapunov exponent:
when it is positive the system is chaotic and to some extent
unpredictable; for a negative value, the system becomes
nonchaotic---a small perturbation will not radically change its
history. What has worried physicists for many years was the fear
that a shift in a frame of reference might so alter the time
parameter as to change the Lyapunov exponent from null or negative
to positive or vice versa. In other words, the change of frame
would seem to make a chaotic system nonchaotic or vice versa. Now,
the work of Adilson Motter of the Max Planck Institute for Complex
Systems in Dresden, Germany lays this matter to rest. He shows
(motter@mpipks-dresden.mpg.de,
http://www.mpipks-dresden.mpg.de/~motter ) that over a wide range of
conditions, a change of time parameter does not alter the Lyapunov
exponent enough to change chaos in a system. Motter believes that
this is good news since the equations of general relativity are
nonlinear, as are those of chaotic systems, and many common
situations described by general relativity, such as the motion of
massive bodies near black holes or a nonuniform expansion of the
universe at the time of the big bang ("mixmaster universe model,"see
http://www.aip.org/enews/physnews/1993/split/pnu158-3.htm ) are
expected to be highly chaotic. (Physical Review Letters, 5 December
2003)

PHYSICS NEWS UPDATE
The American Institute of Physics Bulletin of Physics News
Number 663 November 25, 2003 by Phillip F. Schewe, Ben Stein, and
James Riordon

BEC MADE FROM FERMION MOLECULES. The study of quantum gases, gases
that display spectacular quantum effects, has come under sharp
scrutiny over the past decade, partly because they offer the chance
to study a model quantum system in which the interaction among atoms
can possibly be tuned at will by the researcher. Chilled gases are
not all alike. Cold clouds of boson atoms (atoms with an overall
spin with a whole-number value) can fall into a single quantum state
known as a Bose Einstein condensate (BEC). BEC was first observed
in 1995 for the case of bosonic rubidium atoms (at NIST/Colorado,
http://www.aip.org/enews/physnews/1995/split/pnu233-1.htm ), lithium
atoms (Rice Univ,
http://www.aip.org/enews/physnews/1995/split/pnu237-1.htm ), and
sodium atoms (MIT,
http://www.aip.org/enews/physnews/1995/split/pnu248-1.htm ).
Meanwhile, fermion atoms (with half-integral overall spin) must
avoid consorting with each other in any unified quantum state (a
behavior enforced by the Pauli exclusion principle, which also
dictates how electrons in atoms group into discrete shells---a
grouping with implications for all chemical relationships). This
means condensation is out of the question. Fermi atoms can,
however, show off their quantum nature by piling up into all
possible quantum energy levels allowed by the ambient temperature
inside an atom trap. This feat was achieved in 1999 by another NIST
group (http://www.aip.org/enews/physnews/1999/split/pnu447-1.htm ).
In 2002, BECs were formed from molecules of bosonic rubidium atoms
(http://www.aip.org/enews/physnews/2002/split/581-1.html ). Now, in
the latest chapter in the saga of quantum gases, two research groups
have succeeded in producing a BEC of molecules made from pairs of
fermion atoms. Note that the atoms are fermions but considered as
pairs they are bosons and therefore able to condense in
Bose-Einstein fashion. The two groups involved: Rudolf Grimm and
his colleagues at the University of Innsbruck (publishing last week
online in Science) used lithium atoms, and Deborah Jin and her
colleagues at NIST (publishing online in Nature) used potassium
atoms.
Researchers will next want to tinker with the force between the
pairs of atoms. At the one extreme is the strong interaction
typical of the atomic BECs. At the other extreme is an interaction
in which the atoms forming the pair are correlated but essentially
unbound (in the chemical sense). The best example of this fragile
arrangement is the special correlation, "Cooper pairing" between
electrons, forming the essence of superconductivity. Such Cooper
pairing of fermion atoms (at work in bringing about the superfluid
state in liquid helium-3) does not seem to have occurred yet in the
present BEC experiments with gases.

MAGNETIC GRAPHITE. Physicists at the University of Leipzig have
irradiated graphite with protons to produce a lightweight,
pure-carbon, metal-free, room temperature magnet. Pure carbon comes
in several notable solid forms---graphite (powdery because with its
two dimensional planes of atoms are so loosely bound--hence the use
of graphite as a lubricant or pencil lead), diamond (hard because
its constituents are well connected to atoms in all 3 dimensions),
buckyballs (60-atom soccerballs), and nanotubes. All have important
electrical properties, but in general they are not magnetic. Until
now no pure-carbon sample was known to be magnetic, except when
doped and held at temperatures close to absolute zero. In the
Leipzig experiment, the protons were supplied by a nearby
accelerator, and their presence in the sample in small amounts was
just enough to inspire a small magnetic ordering among the carbon
atoms. The magnetism was then measured by sensitive SQUID detectors
and magnetic force microscopy at the surface. According to one of
the researchers, Pablo Esquinazi (esquin@physik.uni-leipzig.de,
+49-341-9732751), room-temperature magnetic graphite might have
interesting applications in spintronics (some theoretical work
suggests that atoms in a 2-dimensional graphite layer sprinkled
with protons might be 100% spin polarizable) or as a data storage
medium in which magnetic bits could be inscribed in a pure carbon
film rather than in metal or metal-semiconductor films. Weak
magnetism in graphite might also have implications for the study of
biomolecules, which are rich in carbon-hydrogen bonds, or for
astronomy since space is rich in carbon-filled gas clouds undergoing
irradiation. (Esquinazi et al., Physical Review Letters, 28
November)

DO MICROFLUID PUMPS GIVE HUMANS THEIR SENSITIVE HEARING? New images
of movements inside the cochlea, the part of the inner ear
responsible for auditory function, suggest that the incredible
sensitivity of mammalian hearing may be the result of hair cells
that act as electromechanical fluid pumps. Arranged in a spiral
structure known as the organ of Corti, the cochlea's outer hair
cells exhibit voltage changes in response to sound, and change their
length in response to an electrical voltage. At the Acoustical
Society of America in Austin earlier this month, researchers (David
Mountain, Boston University, dcm@bu.edu, and Domenica Karavitaki,
now at Harvard Medical School, domenica@alum.mit.edu) presented
visual evidence of contracting hair cells pushing fluid back and
forth. The fluid traveled through a tiny channel in the sensory
organ known as the tunnel of Corti. According to theoretical
calculations by Mountain and colleagues, hearing sensitivity is
increased 100-fold if this fluid flow is properly synchronized with
sound-induced motions in the cochlea. To image small but very rapid
vibrations in the cochlea, Karavitaki used stroboscopic illumination
flashing at rates 10,000 times a second to "freeze" the motion of
the cells. This visual evidence of outer hair cells acting as
electromechanical fluid pumps supports the researchers' theory of
cochlear function, which states that an increase in hearing
sensitivity cannot take place without fluid flow through the tunnel
of Corti. Among all vertebrates, only mammals have a tunnel of
Corti, and only mammal ears have hair cells that change their
lengths in response to an electrical voltage. (Paper 4pABa1 at
meeting; lay-language paper with diagrams and movies at
http://www.acoustics.org/press/146th/mountain.htm )

PHYSICS NEWS UPDATE
The American Institute of Physics Bulletin of Physics News
Number 662 November 18, 2003 by Phillip F. Schewe, Ben Stein, and
James Riordon

A LIQUID WALL IN A FUSION ENERGY DEVICE has improved the performance
of fusion fuel, and may lead to more resilient fusion devices. At
last month's American Physical Society Division of Plasma Physics
meeting in Albuquerque, Princeton Plasma Physics Laboratory
researchers (Dick Majeski, PPPL, 609-243-3112, rmajeski@pppl.gov and
Bob Kaita, PPPL, 800-777-5732, kaita@pppl.gov) described how they
tested this idea on the Current Drive Experiment-Upgrade (CDX-U).
CDX-U is a spherical torus, a more rotund version of the well-known
tokamak. Like the donut-shaped tokamak, the device uses magnetic
fields to confine hot plasma. At the bottom of their tubby tokamak,
the researchers placed a pool of liquid lithium. Meanwhile, they
applied electrical current to the plasma both to create strong
magnetic fields that confine it and also to heat the plasma to
desired hot temperatures. In contact with the fusion plasma, the
liquid lithium increased the efficiency of transferring the current
to the plasma, leading to less wasted energy. It also does an
excellent job of absorbing impurities, such as carbon and oxygen,
which could otherwise cool the plasma. What's more, it absorbs
hydrogen plasma that reaches it, requiring the researchers
continually to pump in hydrogen gas. This is actually a good thing,
as it prevents an undesirable buildup of cool hydrogen at the plasma
boundary which could return to the plasma and lower its
temperature. Finally, since the liquid surface can be continually
replenished, the liquid wall is not subject to the same degradation
and damage that would occur by neutrons that bombard a solid metal
wall. The liquid wall can conceivably be applied to future magnetic
fusion reactors, whether a spherical torus, a tokamak, or another
design. (Meeting paper RI1.004; see picture at
http://www.aps.org/meet/DPP03/baps/press/press1.html; also see R.
Majeski et al., Journal of Nuclear Materials, March 2003.)

ELECTRON SPINS CAN CONTROL NUCLEAR SPINS in a semiconductor when
trapped in a very confined space, a recent experimental development
which calls upon laser science, solid-state physics, and nuclear
magnetic resonance. David Awschalom and his colleagues at the Center for
Spintronics and Quantum Computation at UC Santa Barbara begin by
lithographically creating a quantum well, an extremely thin,
practically two-dimensional region inside a semiconductor
capable of trapping electrons. First, a laser pulse injects
polarized electrons (their spins have a definite orientation
determined by the laser's polarization) into the well. Once in the
well, the tiny disk of electrons (with a radius of about 20 microns
but a thickness of only 20 nm) can be controllably moved along one
axis, much as an abacus bead can be slid along a wire, by simply
changing a voltage. In this case, the disk can be positioned with
nm-accuracy. The nuclei of atoms residing within the thin
volume occupied by the spin-polarized
electrons will in turn be polarized; that is, the spin of these
nuclei will tend to align themselves with the spin of the
electrons. The result is an extremely thin region---equivalent to
the thickness of several tens of atoms--- of polarized nuclei
which can be precisely positioned by changing a single voltage.
These thin sheets of nuclear polarization could constitute the basic
elements of an information storage device in which nuclear spin
determines the logical state of the system. One may ask, why not
take out the "middle man" and just use the electron spin to encode
information? The answer: nuclear spins have a weaker interaction
with the surrounding environment than electron spins. While harder
to flip, once oriented, nuclear spins preserve their state longer
than do electrons. One may also wonder, why not just use some large
magnet to orient the nuclear spins? Why use electrons as
intermediaries? The answer: all-electronic control of spin is
desirable because electric fields are so much easier to control and
create on a small scale than magnetic fields. They are scalable and
easy to implement, while it is notoriously hard to produce large and
localized magnetic fields. In addition, all of our current
integrated circuit technology is based on charge and electric field;
it would certainly be helpful to manipulate spin using "knobs" which
are well developed and familiar to engineers. Awschalom
(awsch@physics.ucsb.edu, 805-893-2121) believes this current result
is the first step toward the establishment of an all-electrical
manipulation of countable numbers of nuclear spins.(Poggio et al.,
Physical Review Letters, 14 November 2003)

PHYSICS NEWS UPDATE
The American Institute of Physics Bulletin of Physics News
Number 661 November 11, 2003 by Phillip F. Schewe, Ben Stein, and
James Riordon

THE FURTHEST MANMADE THING, the Voyager 1 spacecraft, has recently
detected a change in its local environment in the form of a greatly
enhanced density of energetic particles. Two papers published last
week in Nature give different interpretations of the change.
Krimigis et al. believe that Voyager has finally begun to encounter
(at a distance of 85 astronomical units or 85 times the Earth-Sun
distance) our solar system's "termination shock," the region of
space where the outward going river of solar particles flags from
supersonic to subsonic speeds in its confrontation with the
interstellar medium. One would expect the shock front to be a good
accelerator of particles, and the observed upswing in fast particles
is suggestive. McDonald et al., however, argue that Voyager has
not yet reached the termination shock, citing the relatively
unimpressive presence of one species of energetic particles, namely
so called anomalous cosmic rays. (Nature 6 November 2003.) Voyager
1 and its twin, Voyager 2 (some 20 AU behind in the effort to leave
the solar system) were launched way back in 1977.

ITER TOPS THE DOE LIST OF FACILITY PRIORITIES. Yesterday the US
Department of Energy released a list specifying priorities for
construction or upgrading of science facilities over the next 20
years. The International Thermonuclear Experimental Reactor (ITER),
which would represent the next big generation in fusion reactor
design, occupied the number one slot on the list, followed by the
Ultrascale Scientific Computing Capability, a network which aims at
greatly enhancing high-end scientific computing. Four facilities
were grouped together as the number three priorities among near-term
projects. They are the Joint Dark Energy Mission, the Linac
Coherent Light Source, the Protein Production and Tags Facility, and
the Rare Isotope Accelerator. (The full report and list can be see
at http://www.sc.doe.gov/. )

A BETTER LOOK AT ATOMIC VIBRATIONS. The atoms that make up liquids,
gases, and even solids are constantly in motion. And in many
substances, slight differences in the vibrations of the constituent
atoms may have important effects on macroscopic material properties.
For example, the motions of impurity atoms can determine whether a
material is a useful semiconductor, and measuring the motions of
atoms is critical to understanding high-temperature
superconductivity, colossal magnetoresistance (which has led to new,
high capacity hard drives), and numerous other important effects.
Recently, a group of researchers from Kyoto University, the Japan
Synchrotron Radiation Research Institute, the Japan Atomic Energy
Research Institute, and Osaka University of Education developed a
new method that reveals differences in the quantum oscillations of
atoms that have, until now, been beyond detection by conventional
measurement techniques. The new approach is a refinement of nuclear
resonant inelastic scattering, which relies on x-ray radiation from
particle beam machines known as synchrotrons to excite atoms, which
in turn emit characteristic gamma radiation. Although previous
techniques could identify various elements in a material, they were
unable to distinguish between identical atoms bound in different
atomic configurations.
The researchers have found that by exciting atoms with a pulse of
synchrotron radiation and observing oscillations, or quantum beats,
in the time spectrum of radiation that the atoms emitted, they could
measure the ratio of atoms in various environments in a material.
Specifically, the group studied iron atoms in a common iron oxide
known as magnetite. Two thirds of the atoms in the magnetite sample
are surrounded by six oxygen atoms, and the remaining third are
surrounded by only four oxygen atoms. The quantum beats in the gamma
radiation signal, which was emitted as a result of the nuclear
resonant inelastic scattering, clearly revealed the ratio of iron
atoms in the two different atomic environments. The researchers
(Makoto Seto, +81-724-51-2445, seto@rri.kyoto-u.ac.jp) explain that
the new method can be extensively applied to studying the
differences in the dynamical properties of atoms in complex
condensed matter and large biological molecules, among other
substances, leading to a better understanding of the characteristics
of such materials. (M. Seto et al., Physical Review Letters, 31
October 2003)
 

GALLIUM CLUSTERS ARE TOO SMALL TO MELT. Nanoscopic clusters of
gallium atoms, consisting of as few as 17 atoms, melt at much higher
temperatures than bulk gallium, according to recent research at the
Indiana University. The observation runs counter to theoretical
expectations of melting points for small clusters. In fact, current
theory suggests that the melting point should fall as a cluster size
is reduced, and that nanoscopic lumps of many materials should be
liquid at room temperature. In previous work, the researchers
(Martin Jarrold, 812-856-1182, mfj@indiana.edu) discovered similar
trends in the melting of tin clusters, but did not observe melting
transitions directly. Instead they monitored the shapes of small
clusters to determine their state. In the recent experiment, the
researchers launched the gallium clusters through a high pressure
collision cell where they were heated in collisions with a helium
buffer gas. By monitoring the portion of dissociated clusters that
exited the collision cell, the researchers could directly determine
the clusters' melting temperatures. While bulk gallium melts at 303
K, thirty-nine and forty atom gallium clusters melt at about 550 K,
and seventeen atom clusters show no sign of melting at temperatures
as high as 800 K. No theoretical framework currently exists to
explain the high melting temperatures of gallium clusters. The
researchers explain that their measurements may have important
implications for nanotechnology and material science. In particular,
nanoscopic clusters may not sinter at low temperatures if they don't
melt as predicted by established theory. (G. A. Breaux et al.,
Physical Review Letters, 31 October 31)

PHYSICS NEWS UPDATE
The American Institute of Physics Bulletin of Physics News
Number 660 November 4, 2003 by Phillip F. Schewe, Ben Stein, and
James Riordon

MICRO-ORIGAMI FABRICATED MICROMIRRORS. Microelectromechanical
systems (MEMS) are becoming increasingly important as researchers
develop miniaturized mechanical devices for communications,
biotechnology, and a variety of measurement applications. Often
these machines include hinged parts that must be set in place before
operation, which can lead to challenging and time consuming manual
manipulation of components at ever decreasing scales. Recently,
researchers from the ATR Adaptive Communications Research
Laboratories in Japan proposed a technique that they call
micro-origami to fabricate MEMS devices that automatically move into
position. The group has now tested the technique, in collaboration
with researchers at Konan University and Osaka City University, by
creating hinged micromirrors that lift themselves up following the
final fabrication stage. The key to the micro-origami technique is
to manufacture hinges out of a pair of material layers with slightly
different atomic spacings. This lattice mismatch causes a stress
that in turn bends the hinge (see figure at www.aip.org/mgr/png )
and, in this case, raises a mirror above the substrate. (The effect
is reminiscent of the bimetallic strips in some thermostats, which
consist of bonded layers of metals that expand at different rates
when heated, leading to stresses that bend the strips as
temperatures change.) Once a mirror was in place, the researchers
could move it on its hinge by illuminating the mirror with a high
power argon laser. It is not yet entirely clear what mechanism
caused the illuminated mirror to move; the force due to radiation
pressure, in particular, was too small and in the wrong direction to
account for the effect. Nevertheless, the researchers (Jose M.
Zanardi Ocampo, 81-774-95-1582, zanardi@atr.co.jp) were able to use
the motion of the micromirror to control the position of a reflected
helium-neon laser beam. Potentially, the micro-origami mirror could
lead to optical MEMS switches or other small devices that
automatically pop into place without human or mechanical
intervention, dramatically speeding and simplifying construction of
miniature machines. (J. M. Zanardi Ocampo et al., Applied Physics
Letters, 3 November 2003)

ACCELERATION DISRUPTS QUANTUM TELEPORTATION,
(Paul Alsing, University of New Mexico, 505-277-9094,
alsing@ahpcc.unm.edu). In quantum teleportation (see
http://www.aip.org/enews/physnews/1997/split/pnu350-1.htm),
researchers create a pair of particles (such as photons) and cause
them to interact so their properties become interrelated (a process
called "entanglement"). Subsequently, after the particles go their
separate ways, one can measure the first particle's properties (such
as the direction its electric field is wiggling), destroy the
particle (a requirement), and then instantly transmit (or
"teleport") its exact properties to the second particle, even if it
ends up being light years away. Quantum teleportation is different
from Star Trek teleportation in that real-life physicists are only
teleporting a particle's properties, rather than the particle
itself. Now, a new analysis has shown that quantum teleportation
would malfunction if the receiver of the second particle is
accelerating relative to the first particle. (Coincidentally,
spaceships in Star Trek usually don't teleport crew members when
they accelerate into warp drive.) The disruption to quantum
teleportation arises from the Davis-Unruh effect (see
http://focus.aps.org/story/v8/st19), in which acceleration, even in
empty space, creates a bath of hot particles resulting from the
energy of the acceleration. This thermal bath of particles
inextricably disrupts the receiver's ability to perfectly recreate
(with the second accelerated particle) the properties of the first
(unaccelerated) particle that have been teleported from the sender.
While this effect is small for typical accelerations in Earthly labs
the result shows an interesting relationship between the effects of
space-time motion and the quantum world. (Alsing and Milburn,
Physical Review Letters, 31 October 2003)

A CLOSE LOOK AT HAGFISH SLIME. Hagfish are primitive, eel-like fish
that are nearly blind and lack jaws or true vertebrae. One thing
they do have is the unnerving ability to produce copious amounts of
slime when disturbed. Researchers from the Cambridge Polymer Group
in Boston and the University of British Columbia are now taking a
close look at hagfish slime, in an attempt to understand how the
slime protects the fish in nature and to determine if the slime
could lead to practical materials for industry or medicine. Hagfish
slime is a concoction of mucus and threadlike fibers, and is
produced in concentrated form from a series of pores that line the
sides of the fish's body. Upon contact with seawater, the
concentrated slime expands into a sticky gel that can ensnare and
sometimes suffocate an attacker. Unlike the mucous produced by the
membranes of humans and other animals, which functions best at body
temperature, the researchers (Gavin Braithwaite, 617-629-4400,
gavin@campoly.com; Douglas Fudge, dfudge@interchange.ubc.ca) found
that the properties of hagfish slime are relatively temperature
independent over a broad range (from roughly 5 to 30 degrees
Celsius). The insensitivity to temperature ensures that slime is an
effective defense in a variety of conditions, and also suggests that
artificial materials that mimic hagfish slime chemistry might make
good space-filling gels. One potential application for such gels,
explain the researchers, is as a way to curtail bleeding in an
accident victim or during surgery. In addition, studying the slime
may help us understand how mucins, the components of mucous,
function in our own bodies and elsewhere. There is currently some
debate regarding the relative importance of the fibers and the
mucous in the material properties of hagfish slime. The recent
research, which was presented earlier this month at the 75th Annual
Society of Rheology meeting in Pittsburgh
(http://www.rheology.org/sor/annual_meeting/2003Oct/default.htm),
focused on characterizing the properties of the mucous after the
fibers had been removed from the slime.

PHYSICS NEWS UPDATE
The American Institute of Physics Bulletin of Physics News
Number 659 October 28, 2003 by Phillip F. Schewe, Ben Stein, and
James Riordon

A MAP OF THE UNIVERSE produced by the Sloan Digital Sky Survey
contains 200,000 galaxies at distances of up to two billion light
years, and spread out across 2400 square degrees of sky. According
to Sloan astronomer Michael Blanton (NYU), this is "the best
three-dimensional map of the universe to date." The Sloan effort
uses a telescope in New Mexico optimized to record spectra from many
galaxies at the same time. One of the standout features of the map
is the Sloan Great Wall of galaxies, some 1.37 billion light years
long and the "largest observed structure in the universe"
(preprint:astro-ph 0310/0310571) Combined with data from other
telescopes, such as the Wilkinson Microwave Anisotropy Probe (WMAP),
the new Sloan observations help tamp down uncertainties in several
pivotal astronomical numbers. The new best value for the Hubble
constant is 0.70 with an uncertainty of about 0.04; the amount of
energy in the universe vested in matter is 30% with an uncertainty
of 4%; the upper limit on neutrino mass is 0.6 eV; and the age of
the universe is 14.1 billion years with an uncertainty of 1 billion
(Preprint astro-ph/0310/0310723; Sloan website at
http://www.sdss.org/news/releases/20031028.powerspectrum.html ).

AN ELECTRICAL MICRO-GENERATOR might provide electric power for
portable microscale devices. At a modern power station, high
pressure fluids (water, steam, or gas) are dashed against turbine
blades, thus turning a shaft which cranks out electricity. At an
MIT lab, all of this is done on a centimeter-size scale. At an
upcoming meeting of the AVS Science and Technology Society in
Baltimore, Carol Livermore will describe a micromotor with a 4-mm
rotor which puts out 20 milliwatts of power, far more power than any
other existing rotating micromotor. The motor may be incorporated
into a microscale gas turbine generator. This is, in effect, a tiny
jet engine: air and gas mix in a small combustion chamber and the
resultant explosion powers the turbine (figure at
http://www.aip.org/mgr/png/2003/204.htm ). The MIT researchers
expect that soon the output will be at the level of 300 volts, and 1
watt of mechanical power or 0.5 watt of electrical power. The
device might not yet be as compact as the best micro-batteries
currently available, but it will be able to do what batteries
cannot, namely supply power over long periods. (Paper MM-TuA3,
Carol Livermore, 617-253-6761, livermor@mit.edu; meeting will be
held November 2-7; website at
http://www.avs.org/symposium/baltimore/default.asp ; background
article, http://www.aip.org/tip/INPHFA/vol-7/iss-6/p20.pdf )

THE HIGH AND LOW NOTES OF THE UNIVERSE. The Cornell nano-guitar,
first built in 1997 but only now played for the first time, twangs
at a frequency of 40 megahertz, some 17 octaves (or a factor of
130,000) higher than a normal guitar (see figure at
http://www.aip.org/mgr/png/2003/205.htm ). Researchers at Cornell
University used laser light to set the delicate silicon "strings"
(actually slender planks of silicon) of the 10-micron-long guitar in
motion (see figure at www.aip.org/mgr/png ). There is no practical
microphone available for picking up the guitar sounds, but the
reflected laser light could be computer processed to provide an
equivalent acoustic trace at a much lower frequency. The laser
light could excite more than one string, creating megahertz
"chords." The playing of the nano-guitar will be described by
Lidija Sekaric (now at IBM) at the AVS meeting (paper MM-WeM1;
lidija@us.ibm.com, 914-945-1802;
www.avs.org/symposium/baltimore/default.asp ).
If the nano-guitar's natural tones are among the most high-pitched
sounds in the universe, some of the lowest pitched are to be found
in the vicinity of the black hole in the Perseus galaxy cluster.
The Chandra x-ray telescope recently saw concentric circles in the
inter-galactic gas cloud surrounding the cluster core; some
astronomers interpret the ripples as being sound waves (with a
frequency some 57 octaves below human hearing, and possibly "the
deepest note ever detected from an object in the universe") caused
by jets from the black hole shooting outwards into the nearby
matter.
(http://chandra.harvard.edu/press/03_releases/press_090903.html )

PHYSICS NEWS UPDATE
The American Institute of Physics Bulletin of Physics News
Number 658 October 21, 2003 by Phillip F. Schewe, Ben Stein, and
James Riordon

DIRECT IMAGING OF EXTRASOLAR PLANETS might be easier than
astronomers thought, a new study shows. Evidence for the existence
of planets around nearby stars comes mostly in the form of tiny
Doppler shifts in the star's spectra as one or more orbiting planets
tug on the star. In a few cases the transit of a planet across the
face of a star can be detected from a minute dimming of the star's
emission. These approaches are indirect. The problem of imaging
extrasolar planets directly is that the planet is far outshone by
the nearby star. One proposed way of getting around this glare
problem is to use nulling interferometry. In ordinary interferometry
the light waves from two or more telescopes are added together in
such a way that the resulting observation is equivalent to one made
with a single telescope with a much wider diameter than any of the
component scopes. But instead of maximizing the composite signal
from the distant object, it can be minimized (see past Update item
at http://www.aip.org/enews/physnews/1998/split/pnu397-3.htm ). By
doing this, a weaker nearby object, like a planet, might suddenly
emerge from what had been irrepressible glare.
In a new paper, William Danchi (Goddard Space Flight Center) and his
colleagues have performed extensive studies of the interferometry
nulling technique, especially the way in which increasing the
precision of component detectors increases the degree to which the
star's image is truly nulled, the better to see either smaller
planets or planets that are closer in toward their parent star.
Both the smaller and closer criteria are pertinent when searching
for earth-like extrasolar planets. Danchi (wcd@iri1.gsfc.nasa.gov,
301-286-4586) says that the new study shows that with the right
configuration of detectors, the spatial resolution of the overall
interferometer (which is related to its size) can be less than have
been thought, an important consideration for what would be an
orbiting space-based observatory. Danchi envisions that a
first-round nulling interferometer using two half-meter-sized
telescopes separated by a 12-meter boom could observe already
discovered extrasolar planets (including spectroscopic studies of
atmospheres). With a later, larger version of the nulling
interferometer one could hope to search for earthlike planets
harboring characteristic molecules such as ozone, and/or oxygen,
plus carbon dioxide, water, and methane. Detecting these molecules
could help determine the age of the planet and what life processes
might be occurring there. (Danchi, Deming, Kuchner, and Seager,
Astrophysical Journal Letters, 1 November 2003; preprint
astro-ph/0309361)

EVIDENCE FOR AN UNUSUALLY ACTIVE SUN since the 1940s comes from a
new estimation of sunspots back to the ninth century. Many natural
phenomena such as solar radiance and sunspots vary according to
natural cycles. The variation is subject also to additional
fluctuations (arising from as yet unexplained effects) which
complicate any study which examines only a short time interval.
The longer the baseline, the more confident one can be in drawing
out historical conclusions. In the case of sunspots, the direct
counting goes back to Galileo's time, around 1610. But earlier
sunspot activity can be deduced from beryllium-10 traces in
Greenland and Antarctic ice cores. The reasoning is as follows: more
sunspots imply a more magnetically active sun which then more
effectively repels the galactic cosmic rays, thus reducing their
production of Be-10 atoms in the Earth's atmosphere. Be-10 atoms
precipitate on Earth and can be traced in polar ice even after
centuries. Using this approach, scientists at the University of Oulu
in Finland (Ilya Usoskin, ilya.usoskin@oulu.fi, 358-8-553-1377) and
the Max Planck Institute in Katlenburg-Lindau in Germany have
reconstructed the sunspot count back to the year 850, nearly
tripling the baseline for sunspot studies. They conclude that over
the whole 1150 year record available, the sun has been most
magnetically active (greatest number of sunspots) over the recent 60
years. (Usoskin et al., Physical Review Letters, upcoming article)

CAN A SINGLE GAS BUBBLE SINK A SHIP? Yes, according to an
experimental and theoretical analysis performed by researchers at
Monash University in Australia (David May and Joseph Monaghan,
Joe.Monaghan@sci.monash.edu.au). The ocean floor contains vast
quantities of methane gas hydrates, ice-like crystals of methane
surrounded by cages of water molecules. If disturbed, these methane
gas hydrates can erupt from the floor and rise to the surface as gas
bubbles, some of which can be very large. Copious amounts of methane
hydrates exist in the North Sea, which lies in between the United
Kingdom and continental Europe. At a large eruption site in the
North Sea known as the Witches Hole off the coast of Aberdeen, a
sonar survey recently uncovered the presence of a sunken vessel, but
the cause of the wreck remains undetermined. Simple experiments
have previously shown that many small bubbles rising to the surface
could sink a cylinder of water (and conceivably a ship), by causing
a loss of buoyancy (Denardo et al., American Journal of Physics,
October 2001). But could a single large gas bubble do the trick?
The Monash researchers investigated this possibility in a simple,
roughly two-dimensional system. Trapping water between a pair of
vertical glass plates, and launching single gas bubbles from the
bottom, they used a video camera to observe a single large bubble's
effect on a small piece of acrylic shaped like the hull of a boat.
Along with numerical simulations of this scenario, the experiments
showed that the bubble could sink the ship, if the bubble's radius
was comparable to or greater than the ship's hull. Sinking would
occur because a mound of water formed above the bubble as it
approached the surface. As the bubble reached the surface, it would
temporarily lift the ship. However, water in the mound would then
flow off the sides of the bubble, forming deep troughs at either
side, and the water flow would carry the boat to one of the
troughs. In addition, the eventual rupture of the bubble would
create high-velocity jets of fluid that moved into the troughs,
creating vortices that further pulled down the boat. The
researchers say that their numerical simulations could test other
scenarios, including those involving multiple large bubbles, more
realistic boats, and ultimately a full three-dimensional simulation.
(American Journal of Physics, September 2003).

PHYSICS NEWS UPDATE
The American Institute of Physics Bulletin of Physics News
Number 657 October 14, 2003 by Phillip F. Schewe, Ben Stein, and
James Riordon

COSMOLOGY THEORIES COME AND GO as new information becomes
available. The geometry and nature of the universe must be one of
the most fascinating questions for the human species. Early
Egyptians thought the universe was a rectangular box. Alexandrian
Greeks pictured the cosmos as a set of concentric crystalline
spheres, a view adopted by the medieval Catholic Church, which
executed Giordano Bruno for holding that the universe was infinite
in extent. In the 20th century Hubble's surveys of receding
galaxies supported the idea of an expanding spacetime scaffolding.
This model, now called the big bang, is generally the accepted
overarching theory, but it has been amended several times to include
an early "inflationary" phase and, more recently, the existence of
dark energy, an entity or mechanism which apparently allows the
expansion of the universe visible to our telescopes to be speeding
up, and not slowing down. Also not slowing down is the list of new
cosmological ideas. Last year's entrant was the "ekpyrotic" model
(http://www.aip.org/enews/physnews/2002/split/588-2.html ),
according to which our universe and all the energy and matter
residing therein arises from the collision of two immense membranes
embedded in an even larger multi-dimensional volume. Last week's
interesting new cosmology development was the suggestion that the
universe is finite and has a dodecahedral (soccerball) geometry
(Luminet et al., Nature, 9 October 2003). Meanwhile, this week's
leading cosmology news, presented at a meeting in Cleveland,
featured observations of very distant (8 to 10 billion light years
away) and unusually bright supernovas, recorded by the Hubble Space
Telescope. This accords with the dark energy model which holds that
the general expansion of the universe was relatively slow 10 billion
years ago and afterwards got much faster, owing to the propulsive
effects of the dark energy winning out over the attractive and
slowing effects of gravity (paper by Adam Reiss,
http://www.phys.cwru.edu/events/cosmol03.php; also see Science News
Online, 11 October ).

WHY DON'T ALCOHOL AND WATER MIX VERY WELL? Bartenders who make
cocktails shouldn't worry about trying to get alcohol and water to
mix completely. Nature prevents even the most patient drink-makers
from fully blending the two. Studying methanol, a simple
non-drinkable alcohol that nonetheless can provide insights into
ethanol, or drinking alcohol, a US-Swedish collaboration (Jinghua
Guo, LBL, 510-495-2230, jguo@lbl.gov) has obtained new
molecular-level details of why water and alcohol don't mix very
well. Using LBL's Advanced Light Source, the researchers performed
x-ray emission (XE) and x-ray absorption (XA) spectroscopy, which
allowed them to study such things as the chemical bonds that form
between molecules in the liquid over timescales of picoseconds to
femtoseconds. Looking first at a liquid of pure methanol, the
researchers observed the presence of rings and chains made of 6-8
methanol molecules. When they mixed methanol and water, they found
that the 6-8 molecule chains connected with water molecules to form
larger water/methanol clusters (see image at
http://www.aip.org/mgr/png/2003/203.htm ). These clusters are very
stable, because of the (hydrogen) chemical bonds that hold them
together. But the water/methanol clusters also have a high amount of
order, thereby reducing the liquid's overall disorder (entropy).
Yet entropy must stay the same or increase in the liquid. So nature
discourages the formation of more clusters in the liquid, and this
can explain why alcohol and water don't like to mix completely. In
addition, the research sheds light on a 40-year controversy over the
molecular structure of pure methanol liquid, and the structures that
are formed when water and methanol combine. For example, other
researchers had suggested that water surrounded methanol in a
static, ice-like structure. (Guo et al., Physical Review Letters,
10 October 2003).

A NEW TYPE OF MEDIUM INTERFACE FEATURES NEGATIVE REFRACTION or,
depending on the angle of incidence, positive (conventional)
refraction. This switch-hitting optical ability (the technical name
for it is "amphoteric" refraction) is a first. Furthermore, the
same type of interface can be used to refract (negative or positive)
a ballistic beam of electrons (electrons traveling, as waves, over a
very short distance in a straight line). Refraction, a change in
direction, is what happens when light waves (or other kinds of
waves) move from a material with one index of refraction (say, air)
into a medium (water, say) with a different index. Physicists at
the National Renewable Energy Lab in Colorado have devised their
material sample not from a collection of tiny rods and split rings
mounted on boards, as was the case with previously reported
negative-refraction materials. Instead they used a YVO4 bicrystal.
Negative-refraction materials are also called "left handed
materials," or LHM, because they refract light in a way which is
contrary to the normal "right handed" rules of electromagnetism (for
a past summary in Update, see
http://www.aip.org/enews/physnews/2003/split/628-1.html ).
LHM researchers hope that the peculiar properties will lead to
superior lenses, and might provide a chance to observe some kind of
negative analog of other prominent optical phenomena, such as the
Doppler shift and Cerenkov radiation. According to Yong Zhang
(303-384-6617, yzhang@nrel.gov), an additional feature of their
material is that it inhibits all reflection. When considering the
refraction process, reflection can be thought of as a sort of
energy-loss penalty paid by waves when they are refracted, and so a
reflection-less lens would be of enormous value in, for example, the
transport of high-power laser beams. (Zhang et al., Physical Review
Letters, 10 October 2003; see figure at
http://www.aip.org/mgr/png/2003/202.htm)

PHYSICS NEWS UPDATE
The American Institute of Physics Bulletin of Physics News
Number 656 October 7, 2003 by Phillip F. Schewe, Ben Stein, and
James Riordon

THE 2003 PHYSICS NOBEL PRIZE goes to Alexei A. Abrikosov (Institute
for Physical Problems in Moscow and now at Argonne National
Laboratory near Chicago), Vitaly L. Ginzburg (Lebedev Physical
Institute, Moscow) and Anthony J. Leggett (University of Illinois,
Urbana) The award goes for work done on systems that operate under
two regimes very far from human experience: the quantum realm and
the low-temperature realm. In superconductivity, a current of
electrons flowing through a material undergoes a change in behavior:
normally reluctant to associate with each other, the electrons at
low temperature can form pairs. These pairs act like particles and
are so gregarious that they can enter into a single unified quantum
state. In this state the electron pairs are no longer just a
current, but a "supercurrent." This supercurrent flows without
dissipating energy. It flows without resistance. The practical
benefit is that energy loss through dissipation can be eliminated.
An additional feature is that much higher currents can flow through
some superconductor materials than through normal metal wires. The
price to pay for producing the weird quantum state of
superconductivity in the first place is having to chill the material
down to temperature close to absolute zero, which usually means
about 4 K.
Practical applications of wire made from superconducting material
include medical scanners (this year's Nobel for medicine rewards MRI
research; here potent magnetic fields inside the scanner are usually
produced with superconducting cables), levitated trains (still at an
early state of deployment), and the chilling of some components in
cell-phone networks.
In some superconductors (type I) magnetic fields are anathema to the
superconducting state. In other superconductors (type II), magnetic
fields are tolerated, and this makes possible the applications just
mentioned. Abrikosov and Ginzburg are being recognized for their
work in explaining how type II superconductors work.
When a sample of helium-3 atoms is chilled to very low temperature,
the atoms (which like electrons in a superconductor, are "fermions,"
particles reluctant to associate) can pair up, and the pairs in turn
may enter into a single quantum state in which (analogous to the
loss-less flow of supercurrents in superconductors) the fluid will
flow without losing energy via friction. Just as superconductors
have no electrical resistance, so superfluids have no viscosity, and
can flow freely. Leggett is being recognized for his work in
explaining He-3 superfluidity. Superfluidity also appears in
samples of helium-4 atoms (although the superfluid mechanism is much
different than in He-3), and possibly in Bose Einstein condensates.
(Some background articles: Physics Today---May 1989, Jul 95, Dec 96,
Jan 98, Dec 87, May 96; Scientific American---Dec 77, Nov 60, Dec
76, Nov 88, Jun 90, Jul 82, May 66, Dec 93, Aug 94; Physics World,
Feb 2000; Nature 13 Mar 97; Leggett, Review of Mod Physics, 1999;
Abrikosov, PRL, 1 July 1958; Nobel website:
www.nobel.se/physics/laureates/2003)

THE 2003 NOBEL PRIZE IN PHYSIOLOGY/MEDICINE goes to Paul C.
Lauterbur of the University of Illinois at Urbana-Champaign and
Peter Mansfield of the University of Nottingham for their work in
developing magnetic resonance imaging, or MRI. In the medical
world, MRI has become a major imaging technique, but its roots lie
in the most basic magnetic physics in the nuclei at the heart of
every atom and molecule. Taking advantage of the fact that the
body is two-thirds water, MRI obtains images of the hydrogen nuclei
in water molecules inside our bodies. In the early 1970s, while
working at the State University of New York at Stony Brook,
Lauterbur exploited the magnetic properties of atomic nuclei to
yield a two-dimensional image of matter, by introducing gradients in
the external magnetic field that surrounds the object to be imaged.
Shortly thereafter, Peter Mansfield helped to make MRI a practical
imaging procedure, in part by coming up with mathematical methods
for processing the radio waves released by hydrogen during the
technique. The origins of MRI go back further, to the late 1930s,
when physicist I.I. Rabi of Columbia University demonstrated that
one could obtaining abundant information about lithium chloride
molecules by manipulating the magnetic "spins" of the molecules'
nuclei (Nobel Prize, 1944). Later, physicists E.M. Purcell
(Harvard) and Felix Bloch (Stanford) developed nuclear magnetic
resonance (NMR) in hydrogen (Nobel Prize, 1952). Two Nobel Prizes
in Chemistry (1991 and 2002) have been awarded for achievements in
nuclear magnetic resonance. MRI has been so successful that the
original technique has spawned numerous offshoots, such as
functional MRI (fMRI), which measures brain activity by detecting
oxygen levels in specific brain areas. MRI advances continue at a
feverish pace: low-field MRI (Some background articles: Physics
Today---Jun 1995, Sep 2001, Jun 92, Oct 2003; Scientific
American---May 82, Oct 2001, Jan 83; Review of Mod. Physics, Jan 95)

PHYSICS NEWS UPDATE
The American Institute of Physics Bulletin of Physics News
Number 655 September 26, 2003 by Phillip F. Schewe, Ben Stein, and
James Riordon

AN ULTRABRIGHT TUNABLE PHOTON-PAIR SOURCE created at MIT is the best
generator so far of entangled photon pairs, a development which
should help quantum communications systems to do their job more
smoothly. Entangled photons possess a special correlation unlike
anything in classical physics: if, say, we measure the spin
(polarization) of one photon, then we automatically know the
polarization of the other photon, even though it might be on the
other side of the galaxy and even if, until the moment of
measurement, the spins of both photons had been indeterminate. This
weird property of quantum reality, it is hoped, will be a boon to
encryption (perhaps in a "quantum teleportation" scheme---see
Physics News Update 350,
http://www.aip.org/enews/physnews/1997/split/pnu350-1.htm ) and
future quantum computers. Indeed, for some time now quantum effects
have been an important factor in communications engineering
applications, especially insofar as quantum fluctuations
(uncertainty in our knowledge of where an electron is or the value
of its energy) can produce levels of electrical noise that can
limit the effectiveness of practical devices. The use of entangled
photons might be able to mitigate this problem. Quantum limitations
are already a problem in such devices as optical amplifiers (whose
amplified spontaneous emission noise limits communication
performance) or soliton pulses (supposedly non-dispersing light
pulses that are subject to quantum-induced timing jitter
accumulation) used in fiber-optic communications. MIT's Research
Laboratory of Electronics is a place where quantum aspects of
electrical engineering are taken very seriously. The head of the
lab, Jeffrey H. Shapiro (jhs@mit.edu, 617-253-4179), will report on
progress in a program aimed at developing a system for
long-distance, high-fidelity teleportation of photon states at the
upcoming Frontiers in Optics meeting of the Optical Society of
America. As part of this work the MIT team has developed a source
of entangled photons some ten times brighter than previous sources.
The correlated photons are engendered by shooting a laser beam into
a nonlinear optical crystal, where incoming photons are, in effect,
split into two related photons of half the wavelength. This
"down-conversion" process is even tunable over a certain wavelength
range. Up to 12,000 photon pairs per second per milliwatt of input
power have been produced. (Paper MI3, OSA meeting 5-9 October in
Tucson, AZ; meeting website at http://www.osa.org/meetings/annual/ )

THE RELATIVITY OF TIME, as set forth in Einstein's theory, has been
affirmed once again, with new higher precision. Time dilation is
the name for the notion that elapsed time as recorded by two
observers with identical clocks will differ if one of the observers
is traveling at a velocity v with respect to the other. The amount
of dilation will become more noticeable as v becomes a larger
fraction of the speed of light. In an experiment performed by
Gerald Gwinner, Dirk Schwalm and their colleagues at the Max Planck
Institute for Nuclear Physics in Heidelberg the clocks are lithium
ions. The ions are struck by laser light from in front and from the
back, putting them temporarily into an excited state and inducing
fluorescence. By comparing the resonant laser wavelengths with the
transition wavelength of
the stationary ion, and by taking into account the Doppler effect
(the apparent wavelength of a wave emitted from a traveling source
will always be different from a stationary source owing to bunching
or thinning of the wave crests---but this has nothing to do with
relativity) the researchers can arrive at a value for time dilation.
In the Heidelberg experiment, the lithium ions moved with a speed of
19,000 km/sec, or about 6.4 % of the speed of light (and
corresponding to an energy of 13.3 MeV, the largest energy
obtainable at the local heavy-ion storage ring). The precision of
the new time dilation measurement, an
uncertainty of 2.2 x 10^-7, is about a factor of four better than
the best previous value. (Saathoff et al., Physical Review Letters,
upcoming article; contact Guido Saathoff,
guido.saathoff@mpi-hd.mpg.de49-6221-516-547; website at
http://www.mpi-hd.mpg.de/ato/rel/)

MALLEABILITY OF SPACETIME, as set forth in Einstein's general
relativity theory, has been affirmed, once again, by watching radio
waves from the Cassini spacecraft, on its way toward Saturn, be
deflected by the sun. Einstein said that a massive object would
distort the fabric of spacetime in its vicinity, and that this
distortion would slightly redirect the trajectory of light waves
passing the object. Scientists from three Italian universities
(those of Pavia, Rome, and Bologna) have carefully scrutinized
Cassini's radio report and found that the observed light deflection
is in accordance with the conventional form of relativity.
Furthermore, the sensitivity of their measurements is at a level
where some alternative gravity models can be probed for veracity.
(Bertotti et al., Nature, 25 November 2003.)

PHYSICS NEWS UPDATE
The American Institute of Physics Bulletin of Physics News
Number 653 September 12, 2003 by Phillip F. Schewe, Ben Stein, and
James Riordon

NANOTUBE VELCRO. Joining two or more nanochips, such as
nano-electromechanical systems (NEMS), can be done by welding or
gluing or with tiny nuts and bolts. But what if you could gently
just fasten them the way fabrics are fastened, with velcro?
Conventional velcro fastening works by pairing one patch of mm-scale
hooked protuberances with a patch of looped protuberances. In the
microscopic version, both patches would bristle with carbon
nanotubes, grown upright except for a hook on the top end. David
Tomanek and his colleagues at Michigan State (tomanek@pa.msu.edu,
517-355-9702) are studying how to make nano-velcro work (see movies
as www.pa.msu.edu/cmp/csc/simulvelcro.html ). His calculations so
far show that the nanotubes will remain in place on each separate
substrate (they can be grown on selective pieces of surface geometry
using lithographic-like patterning techniques) and will also remain
locked together when mated with its counterpart on another
substrate. A typical application for nano-velcro would be to fasten
a diamond coating onto specific parts of a metal surface. (Berber
et al., Physical Review Letters, upcoming article; co-authors, Savas
Berber,
berber@pa.msu.edu and Young-Kyun Kwon, ykkwon@nano.com )

GOOD VIBRATIONS HELP A FROG LOCATE TASTY PREY. Living in southern
Africa, the aquatic frog Xenopus catches insects by detecting
critters' vibrations on the water surface. Not able to see well in
a liquid environment, the frog gets a wealth of information from the
water waves that insects produce as they slosh around. The waves
tell Xenopus the direction in which the insect is located. They even
give the frog a general idea of the type of insect that is making
the waves. To detect the water waves on its skin, the frog has
about 180 receptors known as "lateral-line" organs, which are found
on the skin along both sides of the body, around the eyes, and also
on the head and neck. Now, researchers in Germany (Leo van Hemmen,
TU Munich, LvH@ph.tum.de, +49-89-289.12362) have developed a simple
model that explains how the lateral-line organs enable Xenopus to
locate and classify its prey. Strikingly, the model suggests that
the frog can reconstruct the shape of the water wave (its
"waveform") from limited information, namely the movement of water
recorded by the 180 simple sensory organs. In the frog, water gets
deflected by 4-8 flag-like structures (called "cupulae") in the
lateral line organs. Each deflection stimulates nearby hair cells to
generate electrical spikes that are synchronized in time with the
deflection. The timed electrical spikes from the 180 sensory
organs, the researchers show, contain enough information for the
frog to "estimate" the shape of the water wave pretty accurately.
This is true even if some of the lateral-line organs are not
functioning properly. Furthermore, they show how the frog can
localize and distinguish between two different water waves coming
simultaneously from two insects in different directions. This model
may also be applicable to the mechano-sensory systems of other
animals, such as crocodiles (Soares, Nature, 16 May 2002), which
have similar receptor organs (Franosch et al., Physical Review
Letters, upcoming).

HORIZONTAL BRAZIL NUT EFFECT. A new twist on the Brazil-nut effect
appears to be a good way to harvest large particles from a granular
mixture, according to recent experiments and simulations performed
at the University of Texas at Austin. The Brazil-nut effect is an
odd but well-known phenomenon in agitated granular mixtures.
Depending on the conditions, shaking containers filled with grains
of various sizes will cause the larger grains to rise to the top of
the mixture (Update 132), or sink to the bottom. The Texas
researchers (contact: Sung Joon Moon, moon@Princeton.edu,
609-258-2977), however, showed that they could also control the
horizontal distribution of large grains by using kinks that
spontaneously arise in granular layers for sufficiently large
container accelerations. A kink separates two regions oscillating
with opposite phase: the granular layer on one side of a kink is
moving up while the layer on the other side is moving down. Larger
particles flow from the two oscillating regions and collect in the
kink. The researchers can control the location of a kink by
adjusting the driving signal, and harvest the large grains by
sweeping the kink to one side of the container. The research shows
that trapping results from avalanches that form at the kink as
falling fluid-like regions move past rising, effectively solid,
regions. The avalanches lead to internal convection rolls that carry
the large particles toward a kink. The horizontal Brazil-nut effect
may eventually lead to new commercial methods for segregating
granular material by size. (S. J. Moon et al., Phys. Rev Lett.,
date)

PHYSICS NEWS UPDATE
The American Institute of Physics Bulletin of Physics News
Number 652 September 4, 2003 by Phillip F. Schewe, Ben Stein, and
James Riordon

A SPINLESS BEC, a Bose-Einstein condensate that is insensitive to
any external magnetic field, has been created by researchers at
Kyoto University (contact Yosuke Takasu,
takasu@scphys.kyoto-u.ac.jp, or Yoshiro Takahashi,
yitk@scphys.kyoto-u.ac.jp), potentially offering a route to improved
atomic clocks, more precise atom interferometry, and more highly
controlled means of depositing atoms on surfaces. In all previous
Bose-Einstein condensates, the raw ingredients have either been
alkali metals (such as rubidium and cesium) or helium, all of which
have been sensitive to magnetic fields. In contrast, the
researchers decided to make a BEC of ytterbium (Yb), a rare-earth
element that has two outer (valence) electrons, whose "spins"
determine the atom's response to a magnetic field. When the spins
of Yb's two electrons are in opposite directions, the total spin is
zero and the atom assumes a "singlet" state, in which it is
unresponsive to a magnetic field. In their setup, the researchers
trap approximately 1 million Yb atoms in the singlet state with
light beams. The hotter atoms evaporate away, leaving a chilly gas
cloud of about 5000 atoms that form a BEC at temperatures of below
790 nanokelvins. Since the Yb BEC is insensitive to stray magnetic
fields in its surroundings, it may allow for more precise atomic
deposition and atom interferometry. Moreover, the very heavy mass
of Yb compared to other BEC atoms means that certain fundamental
physics effects, such as atomic parity violation and time symmetry
violation, are more pronounced, making a Yb BEC desirable for such
studies. Furthermore, lasers interacting with the Yb atoms can be
tuned to a very narrow frequency range, potentially enabling a Yb
BEC to be the basis of an atomic clock with unprecedented
precision. Finally, the many stable isotopes of Yb (5 are bosons, 2
are fermions) facilitates the possibility of creating a BEC and a
Fermi degenerate gas in the same cloud. (Takasu et al., Physical
Review Letters, 25 July 2003)

PRESSING FORWARD FROM TEETH TO SUPERCONDUCTORS. Found in teeth and
bones as well as fertilizers and DNA, phosphorus is an insulator at
room temperature. However, exerting a large amount of pressure on a
stable specimen of phosphorus changes its crystalline structure,
enabling it to superconduct at temperatures of around 10 K.
Exerting even more pressure (2.5 Mbar, about 30,000 times greater
than the pressure of clenching your teeth) can transform it again,
to a body-centered-cubic (bcc) crystal structure (Akahama et al.,
Phys Rev B, 1 Feb 2000). Now, Sergey Ostanin of the University of
Warwick in the UK (phsgv@warwick.ac.uk) and his colleagues have
shown that bcc phosphorus crystals achieve superconductivity at
higher temperatures, somewhere between 14-22 K. This is still much
lower than the temperature of your mouth, even after an ice-cream
headache. But such phosphorus superconductors might be very useful
in spintronics. For example, they could be help in the construction
of a superconducting spin switch, specifically one in which the
phosphorus layer would lie in between a pair of ferromagnets, an
arrangement that could alter its identity from superconductor to
regular conductor (L. R. Tagirov, Phys. Rev. Lett, 6 September
1999). Furthermore, high pressures might not even be needed to make
bcc phosphorus crystals: they could possibly be grown by depositing
the atoms onto a substrate of iron, which itself organizes into a
bcc structure. (Ostanin et al., Physical Review Letters, 22 August
2003)

NON-CONTACT FRICTION can be artificially enhanced. Usually for two
bodies in relative motion to feel friction the respective surface
atoms have to be in contact. There is a type of friction, however,
which can act between two surfaces not actually in contact. This
dilute friction is attributed to the van der Waals force, a common
but weak attractive force which arises when an atom or molecule
spontaneously develops a dipole moment (that is, although it is
neutral, a small region of net negative charge can develop, offset
slightly from a comparable positive region) owing to a thermal
fluctuation (related to the random motion of the electrons and ions)
or a quantum fluctuation (the very positions of the particles varies
from moment to moment owing to the uncertainty relations built into
quantum reality). This short-lived polarity can in turn induce a
dipole moment in a neighboring atom or molecule, some distance
away. A new study of van der Waals friction by Alexander Volokitin
and Bo Persson at the Institut fur Festkorperforschung (Julich,
Germany) accounts for recent odd friction experiments conducted
with STM probes. The theory holds that van der Waals friction can
be greatly enhanced (by up to a factor of ten million at a
separation of 10 angstroms in comparison with the case of good
conductors with clean surfaces) by adsorbing certain molecules onto
one or both of the surfaces. This increases the resonant
electromagnetic force (which can be viewed as the tunneling of
photons) between the objects, especially if they are made of the
same material. The adsorbate atoms can be thought of as tiny
antennas, one acting as an emitter and one as a receiver; when the
two antennas are in tune the electromagnetic interaction between
them will be greatly enhanced (see figure at
http://www.aip.org/mgr/png/2003/201.htm ).
A better understanding of this kind of non-contact friction will, at
the fundamental level, help physicists to study the quantum behavior
of atoms at surfaces and, at the level of applications, to prepare
"brakes" for micromachines where large friction is not needed.
(Volokitin and Persson, Physical Review Letters, 5 September 2003,
alevolokitin@yandex.ru)

PHYSICS NEWS UPDATE
The American Institute of Physics Bulletin of Physics News
Number 651 August 28, 2003 by Phillip F. Schewe, Ben Stein, and
James Riordon

THE BIG RIP: A NEW COSMIC DOOMSDAY scenario takes the present
acceleration of the expansion of the universe to new extremes.
Dartmouth physicist Robert Caldwell and his colleagues Marc
Kamionkowski and Nevin Weinberg at Caltech have determined that if
the supposed dark energy responsible for the acceleration is potent
enough not only will the space between galaxies continue to increase
but that the galaxies themselves will fly apart as will, at
successive times stars, planets, and even atoms and nuclei. Since
the acceleration idea became established with astronomers a few
years ago in the wake of observations of distant supernovae, it has
been conventional to apportion the supposed energy inventory of the
universe as follows: 5% in the form of conventional baryon matter
(out of which atoms are made), 25% in the form of dark matter, and
the biggest part, 70%, in the form of dark energy. Not a lot is
known about dark matter, and even less about dark energy.
Cosmologists have taken to discussing the enigmatic properties of
the dark energy with the use of a new parameter, w, which is the
ratio of its average pressure to energy density. The degree of this
runaway expansion impulse is expressed by w. What is the nature of
dark energy and how does it overcome the attractive pull of
gravitation in order to speed up the cosmic expansion, and what is
the proper value of w? In the best known model, the "cosmological
constant" in Einstein's famous equations of general relativity
corresponds to energy and pressure of the universal quantum vacuum,
and is constant in space and time. Here the value of w is -1. In a
second popular model, the "quintessence"model, the dark energy is
associated with a universal quantum field relaxing towards some
final state. Here the energy density and pressure of the dark
energy are slowly decreasing with time, and the value of w is
somewhere between -1/3 and -1 (w must be smaller than -1/3 in order
for cosmic acceleration to occur).
In Caldwell's "phantom energy" model, there is no stable vacuum
quantum state and the energy density and the expansionary pressure
exerted on the universe seems to increase even as the spacetime
itself expands (with ordinary gases, pressure falls with
expansion). In this scenario w is less than -1. The implications
of this new type of cosmology are that bound systems should in the
course of time be ripped up (see figure at
http://www.aip.org/mgr/png/2003/200.htm ). For example, at a w
value of -1.5 the universe would last for 35 billion years before
being ripped apart. About 60 million years before the end, the Milky
Way would be torn apart. About 3 months before the end the solar
system would become undone. About 30 minutes before that the Earth
would explode. And about 10^-19 seconds before the ultimate
moment of doom, atoms would be pulled apart. Caldwell
(robert.r.caldwell@dartmouth.edu, 603-646-2742) suggests that
deciding between this model and the others might be possible in
coming years with much better data coming from microwave background,
supernovae, and galaxy measurements. (Caldwell et al., Physical
Review Letters, 15 August 2003; text at www.aip.org/physnews/select
)

ULTRACOLD MOLECULAR BOSE GASES, where the gas consists of diatomic
molecules of fermionic atoms (atoms with an overall half-integral
spin value), provide two important opportunities---the chance to do
high-precision spectroscopy of molecules and the chance to study the
process by which fermions (normally unable to form into coherent
quantum condensates) amalgamate into pairs. The pairs are bosons
(entities with a whole-number valued spin) and can form
condensates. Randy Hulet and his colleagues at Rice University, the
first to engineer a Bose Einstein condensation (BEC) in lithium-7
atoms (http://www.aip.org/enews/physnews/1995/split/pnu237-1.htm ),
have gotten a batch of Li-6 atoms to pair up (at least 50% of them
at a time) at micro-kelvin temperatures by manipulating an external
magnetic field. Although the group does not yet have evidence that
the pairs, or molecules, have taken the final plunge by forming a
BEC, the atoms have held together (in an optical trap) in their
paired state for as long as 1 second, compared to millisecond times
for previous experiments of this type. Hulet hopes that as the
molecular gas hangs together long enough, it will cool off
sufficiently through the evaporative process to form a BEC. Having
a true BEC of molecules would give researchers the chance to study
the Cooper pairing mechanism at work in superconductivity and in
superfluidity of liquid helium-3. In ordinary molecules (joined by
chemical forces) the constituents (atoms) are very close together.
In the Cooper pairs characterizing superconductivity, the
constituents (electrons) are only weakly coupled and are far apart
from each other. Hulet and his group hope to dissociate the
molecular condensate in order to produce Cooper pairs that fall in
between these two cases, both as to the size and in the strength of
the force holding the pairs together. One might even be able to
simulate high-temperature superconductivity by loading ultracold
fermion gases into an "optical lattice" consisting of crossed laser
beams. (Strecker et al., Physical Review Letters, 22 August 2003;
see figure at http://www.aip.org/mgr/png/2003/199.htm and lab
website at http://atomcool.rice.edu; text at
www.aip.org/physnews/select )

PHYSICS NEWS UPDATE
The American Institute of Physics Bulletin of Physics News
Number 650 August 20, 2003 by Phillip F. Schewe, Ben Stein, and
James Riordon

GIANT HELIUM MOLECULES, containing only two atoms but assuming a
size as large as a small virus, have been created by researchers at
the École Normale Supérieure in Paris. At sizes ranging from 10 to
100 nanometers, these helium molecules are the largest diatomic
(two-atom) molecules ever created by a factor of 5 (and comparable
to the size of viruses, which vary in length from 5-300 nm). What's
more, helium is an inert gas that does not normally form molecules.

To observe the new giant molecular states, one needs to start from
an ultracold gas of atoms. At the École Normale Supérieure,
researchers trap a cloud of helium atoms with magnetic fields. Each
helium atom is in a long-lived "metastable" state and carries nearly
20 eV of internal energy, which is more than 10 billion times its
average energy of motion. In the confines of a magnetic trap, the
hottest He atoms evaporate and the colder atoms remain, lowering the
temperature of the cloud to 10 microkelvins (millionths of a degree
above absolute zero). Then, a laser pairs up He atoms through a
process called "photoassociation," in which light of a precise
color changes the state of the atoms so that they attract each other
more strongly. This attraction comes about through light-induced
"dipoles" (momentary separations of positive and negative charge in
each He) to cause the atoms to bind to each other. To detect the
molecules, the researchers record a temperature rise in the cloud
that results from the successful absorption of the laser light. In
a typical experiment, one percent of the atoms absorbs the light,
corresponding to the formation of about 100,000 molecules. In each
of the molecules, the atoms are sufficiently far apart that they
resist destructive "auto-ionization" effects, in which an electron
jumps from one atom to the other and breaks apart the molecule. In
fact, the atoms are so distant from each other that the researchers
had to account for the finite speed of light: each atom of the pair
sees the other the way it was a femtosecond earlier. The
researchers had to include this "retardation" effect in their
calculations to get agreement with the measured data. The
molecules last for an average of 50 nanoseconds--a remarkably long
time due to the huge amounts of internal energy in each He atom.
In precisely measuring the forces that bind the molecule, the
researchers can obtain detailed information about the helium atom.
In addition, the metastable helium molecule can sensitively test the
accuracy of calculations in quantum chemistry, the application of
quantum mechanics to chemical systems such as molecules. (Léonard
et al., Physical Review Letters,15 August 2003; contact Allard Mosk,
a.p.mosk@utwente.nl or Jérémie Léonard, Leonard@lkb.ens.fr).

LIKE-CHARGED BIOMOLECULES CAN ATTRACT EACH OTHER, in a biophysics
phenomenon that has fascinating analogies to superconductivity.
Newly obtained insights into biomolecular "like-charge attraction"
may eventually help lead to improved treatments for cystic fibrosis,
more efficient gene therapy and better water purification. The
like-charge phenomenon occurs in "polyelectrolytes," molecules such
as DNA and many proteins that possess an electric charge in a water
solution. Under the right conditions, polyelectrolytes of the same
type, such as groups of DNA molecules, can attract each other even
though each molecule has the same sign of electric charge. Since the
late 1960s, researchers have known that like-charge attraction
occurs through the actions of "counterions," small ions also present
in the water solution but having the opposite sign of charge as the
biomolecule of interest. But they have not been able to pin down
the exact details of the phenomenon. To uncover the mechanism
behind like-charge attraction, a group of experimenters (led by
Gerard Wong, Univ of Illinois at Urbana-Champaign, 217-265-5254,
gclwong@uiuc.edu) found that counterions organize themselves into
columns of charge between the protein rods. Along these 'columns',
the ions are not uniformly distributed, but rather are organized
into frozen "charge density waves."
Remarkably, these tiny ions cause the comparatively huge actin
molecule to twist, by 4 degrees for every building block (monomer)
of the protein. This process has parallels to superconductivity, in
which lattice distortions (phonons) mediate interactions between
pairs of like-charged particles (electrons). In the case of actin,
charge particles (ions) mediate attractions between like-charged
distorted lattices (twisted actin helix). (Angelini et al.,
Proceedings of the National Academy of Sciences, July 22, 2003).
In the next experiment, they investigated what kinds of counterions
are needed to broker biomolecular attraction. Researchers have long
known that doubly charged (divalent) ions can bring together actin
proteins and viruses, and triply charged (trivalent) ions can make
DNA molecules stick to one another, but monovalent ions cannot
generate these effects. Studying different-sized versions of the
molecule diamine (a dumbbell-shaped molecule with charged NH3 groups
as the "ends" and one or more carbon atoms along the handle) to
simulate the transition between divalent and monovalent ion
behavior, they found that the most effective diamine counterions for
causing rodlike M13 viruses to attract were the smallest ones.
These small diamine molecules had a size roughly equal to the "Gouy-
Chapman" length, the distance over which its electric charge exerts
a significant influence. Nestled on the M13 virus surface, one end
of the short diamine molecule neutralizes the virus's negative
charge, while the other end supplies a positive charge that can then
draw another M13 virus towards it (Butler et al., Physical Review
Letters, 11 July 2003; also see Phys. Rev. Focus, 21 July 2003,
http://focus.aps.org/ ).
In a third experiment, researchers noticed that the like-charge
attractions could cause actin molecules to organize themselves into
a novel phase of liquid crystal (a structure with both liquid-like
and solid-like properties). Adding small amounts of magnesium ions
to a solution of actin rods caused the rods to arrange themselves
into a stack of 2-dimensional rafts ((see figure at
http://www.aip.org/mgr/png/2003/198.htm ). This discovery may
revise notions of how cells control the actin cytoskeleton..
Previously, researchers assumed that only proteins could do all the
work in assembling this structure, which helps the cell to move,
shape itself and divide. However, this newly discovered phase opens
the possibility that physical interactions--electrostatics, electric
charge, and entropy--could work synergistically with proteins to
regulate the cytoskeleton in a wide range of cellular functions
(Wong et al., Phys. Rev. Lett., 4 July 2003).

PHYSICS NEWS UPDATE
The American Institute of Physics Bulletin of Physics News
Number 649 August 13, 2003 by Phillip F. Schewe, Ben Stein, and
James Riordon

DETECTING PLASTIC EXPLOSIVES IN AIR at the parts-per-trillion level
has been achieved by researchers at Oak Ridge National Laboratory
and the University of Tennessee (Thomas Thundat, 865-574-6201,
thundattg@ornl.gov), potentially leading to a fast, portable, and
ultrasensitive plastic-bomb "sniffer." Plastic explosives such as
pentaerythritol tetranitrate (PETN) and hexahydro-1,3,5-triazine
(RDX) pose serious threats because (1) they are easily to mold into
desired shapes, (2) they remain highly stable until detonated, and
(3) they can inflict significant damage even in small amounts. In
fact, the infamous shoe bomber had PETN in his footwear. Most
current plastic-bomb sensors are bulky and expensive. In contrast,
the new sensor is a microelectromechanical system (MEMS), or a tiny
mechanical device with microscopic dimensions. Potentially cheap
and easy to mass-produce, the bomb-sniffing MEMS device is a
microcantilever, a 180-by-25-micron slab of silicon attached to a
spring-loaded wire. Similar in structure to a diving board attached
to a pool, the microcantilever is coated on one side with gold. On
one end of the gold-coated surface is a single layer of 4-MBA
(4-mercaptobenzoic acid), to which PETN and RDX both attach. Like
hair that curls up on a humid day as water molecules adsorb to it,
this specially coated cantilever will bend by significant amounts
when PETN and RDX molecules attach to it. A laser-microscope system
can detect the degree of bending to nanometer precision. Placed in a
vacuum-tight glass cell, the cantilever was exposed to a stream of
ambient air with tiny traces of plastic explosive. Using a modified
atomic force microscope to measure the deflections of the
cantilever, the researchers determined that their MEMS device could
detect the explosives at a level of 14 parts per trillion, after
only 20 seconds of operation. By another measure, the device becomes
sensitive to plastic explosives even if only a few femtograms (1
fg=10^-15 g) impinges upon it. A future step is to take the device
out of the laboratory and develop it into a portable sensor. While
much activity has centered on the development of sensors for
detecting vapors from all kinds of explosives, this is, to the
authors' knowledge, only the third device of its kind that uses
MEMs. (Pinnaduwage et al., Applied Physics Letters, 18 August 2003)

BARIUM SHIELD TO PROTECT THE FETUS DURING CT SCANS. Computed
tomography (CT) on a pregnant woman's chest puts the fetus at risk
owing to the adverse effects of radiation. However, researchers from
the University of Chicago propose that it may be possible to protect
the fetus if the mother ingests barium sulfate before CT radiation
exposure. Because the fetal dose during chest scans is mainly due to
internal scatter of incident radiation, the barium compound acts as
an internal shield that absorbs errant radiation. A study that
simulated a CT scan of a pregnant woman showed that ingesting a 40
percent solution of barium sulfate would decrease the fetal dose to
a negligible level, so that even high-quality CT imaging could be
performed with minimal risk. Chester Reft presented data from the
study and discussed the potential for barium sulfate internal
shields at this week's meeting of the American Association of
Physicists in Medicine in San Diego
(http://www.aapm.org/meetings/03AM/, Paper WE-C23A-4:
creft@radonc.bsd.uchicago.edu, 773-702-6873)

CELLOPHANE AND 3D DISPLAYS. New research on ordinary cellophane
shows that it can be used to convert a laptop screen image into a
seemingly three-dimensional display. Cellophane is birefringent:
its index of refraction is not the same in all directions in the
material. This means that the polarization of an entering light
wave can be rotated. Keigo Iizuka's lab at the University of
Toronto verified that a cellophane sample 25 microns thick was
better at rotating the polarization direction of white light than a
commercially available device (called a half-waveplate) designed for
a specific wavelength. Taking
advantage of the fact that light emitted from a laptop display is
naturally polarized to begin with, a 3D stereoscopic effect can be
achieved by covering half the screen with a cellophane sheet in
order to construct orthogonally polarized left and right scenes
while the viewer wears eyeglasses holding two polarizers oriented 90
degrees apart (see series of figures at
http://www.keigo-iizuka.com/research/cellophane.htm ). Actually,
the crossed polarizers could be suspended between the screen and the
observer, obviating the need for the viewer to wear the glasses.
According to Iizuka (keigo.iizuka@utoronto.ca, 416-978-8657), this
"cellography" method for producing 3D effects will be
far cheaper than those using commercially available half-waveplates,
and should be amenable to arcade gaming applications and for medical
and scientific imaging applications. Iizuka is now at work on
converting liquid crystal displays on cellular phones to 3D.
(Review of Scientific Instruments, August 2003)

PHYSICS NEWS UPDATE
The American Institute of Physics Bulletin of Physics News
Number 648 July 31, 2003 by Phillip F. Schewe, Ben Stein, and
James Riordon

A WATER MOLECULE'S CHEMICAL FORMULA IS REALLY NOT H2O, at least from
the perspective of neutrons and electrons interacting with the
molecule for only attoseconds (less than 10^-15 seconds). According
to new and recent experiments, neutrons and electrons colliding with
water for just attoseconds will see a ratio of hydrogen to oxygen of
roughly 1.5 to 1, so a more accurate formula for water under these
circumstances would be H1.5O. According to the experimenters (Aris
Chatzidimitriou-Dreismann, Technical University-Berlin,
dreismann@chem.TU-Berlin.de, 011-49-30-314-22692), this "opening of
the attosecond time window" may be revealing dramatic quantum
effects that were once too short-lived to catch. Nonetheless, such
effects may revise conventional textbook notions of water and other
everyday molecules. Moreover, these experiments can provide new
insights on chemical reactions at the 100-500 attosecond scale: the
neutron and electron probes break apart the chemical bonds in
molecules, as compared to laser-based attosecond studies, which have
just ejected electrons from atoms at this point.
The story begins in 1995. At the ISIS neutron spallation facility in
the UK, a German-British collaboration collided epithermal neutrons
(those with energies of up to a few hundred electron volts) with a
target that included water molecules (Chatzidimitriou-Dreismann et
al., Physical Review Letters, 13 October 1997). Detecting the number
and energy loss of the scattered neutrons in the resulting
attosecond-scale collisions, the researchers noticed that neutrons
were scattering from 25% fewer protons than expected. Apparently,
the protons in hydrogen were sometimes "invisible" to the neutron
probes. While the exact details are still being debated by
theorists, the researchers' own theoretical considerations suggest
the presence of short-lived (sub-femtosecond) entanglement, in which
protons in adjacent hydrogen atoms (and possibly the surrounding
electrons) are all interlinked in such a way as to change the nature
of the scattering results. Realizing that water itself has anomalous
properties, the researchers repeated the neutron experiments in
other more typical molecules, for instance in benzene
(conventionally noted as C6H6). In that case, they found that the
neutrons saw a ratio of hydrogen to carbon of 4.5 to 6! Meanwhile,
this effect was also confirmed in various hydrogen-containing
metals, in a collaboration with Uppsala University in Sweden.
Now, the researchers (with new colleagues in Australia) have decided
to use an independent experimental method to verify this effect. In
experiments at Australian National University in Canberra, the
researchers used electron probes instead of neutrons, as the two
particles interact with protons via fundamentally different forces
(strong and electromagnetic interactions). Scattering electrons
from a solid polymer called formvar (with basic building block
C8H14O2), they observed the exact same shortfall in scattered
electrons from hydrogen nuclei, comparable to the shortfall of
scattered neutrons in accompanying neutron experiments on the same
polymer. This supports the earlier results on water and other
systems. (Chatzidimitriou-Dreismann et al., Physical Review Letters,
1 August 2003)

A NANOSCOPIC THERMOMETER, consisting of a magnesium oxide nanotube
filled with gallium metal, may dramatically increase the temperature
range of tiny thermometers. Researchers at the National Institute
for Materials Sciences (contact: Prof. Yoshio Bando, phone number
+81-29-860-4426; bando.yoshio@nims.go.jp ) announced the creation of
a carbon nanotube thermometer last year, but the device had at least
one shortcoming: nanoscopic carbon tubes rapidly degrade in air at
temperatures of 600-700 degrees Celsius. The new nanotubes are made
of magnesium oxide cylinders with inner diameters of 20-60
nanometers, or about a thousandth the thickness of a human hair.
Magnesium oxide nanotubes, in contrast to carbon versions, can
withstand high temperatures. Often, there is a gap in a nanotube's
gallium filling, and because gallium expands as it's heated, the
temperature of the thermometer is read out by measuring changes in
the gap between the two portions of the metal. The tiny thermometers
are expected to function well up to about 1000 degrees Celsius.
Eventually, miniature thermometers such as these could be important
for measuring temperature in the vicinity of nanoscopic motors and
other tiny devices. (Y.B. Li, Y. Bando, D. Golberg, and Z.W. Liu,
Applied Physics Letters, 4 August 2003)

PHYSICS NEWS UPDATE
The American Institute of Physics Bulletin of Physics News
Number 647 July 23, 2003 by Phillip F. Schewe, Ben Stein, and
James Riordon

THE PROTON HAS A DIFFERENT SIZE IN DIFFERENT NUCLEI. The electron,
which is mostly impervious to the nuclear forces, can penetrate deep
inside a nucleus. Therefore, scattering high energy electrons from
a nucleus is an excellent way of exploring the electric and magnetic
properties of the nucleus as a whole and of its constituent protons
and neutrons, especially when the electron transfers some of its
spin to a proton in a telltale way. For example, recent results
from such an experiment, conducted at the Jefferson Lab, gave
evidence that the proton is not necessarily spherical. Now a new
experiment at Jlab, comparing electrons scattering from single
protons (a hydrogen nucleus) with electron scattering from helium
nuclei, suggests that each nucleus "kneads" its protons in a
different way (see figure at www.aip.org/mgr/png/2003/197.htm ).
The kneading allows the constituent quarks inside the proton to
spread out a bit at time, perhaps into a peanut shape, even though
its average shape is round. (Strauch et al., Physical Review
Letters, upcoming article)

NMR WITHOUT THE MAGNET OR RF COILS. To image an object's interior
with nuclear magnetic resonance (NMR) a magnetic field of several
tesla (1 T =10,000 gauss) is usually required to polarize protons in
the sample and then radio waves are used to tip the protons and to
detect a weak signal as they upright themselves again. The strength
of the signal depends on the size of the magnetic field and the
degree of polarization, which is often only one part in 10^5, and
somewhat limits the use of NMR (including its medical application,
MRI) because of the need for a bulky, expensive magnet. One way of
improving things is to use laser light to produce a polarization as
high as 10% in a gas of xenon atoms. The Xe atoms can then be
injected into an empty space, such as lungs, and used to image their
interior, which couldn't be done using conventional NMR (see Update
398, http://www.aip.org/enews/physnews/1998/split/pnu398-1.htm ).
Another NMR advance has been the use of ultrasensitive SQUID
detectors for picking up the magnetic fields produced by protons,
greatly reducing the need for large magnets (see Update 528,
http://www.aip.org/enews/physnews/2002/split/582-1.html ) but at the
expense of weak signals, with a proton polarization of only one part
in 10^8.
Now, Princeton physicist Michael Romalis and co-workers, while
studying whether the Xe nucleus is slightly nonspherical (equivalent
to saying that the nucleus possesses a nonzero electric dipole
moment, which would imply the existence of "new physics" beyond the
Standard Model), have worked out a way to combine different
techniques to obtain a strong NMR signal in a very weak 1
micro-tesla magnetic field. They transfer polarization from
laser-polarized Xe to protons in an organic liquid and then use
SQUID detectors to measure the magnetic field produced by the
polarized protons. Romalis (romalis@princeton.edu, 609-258-5586)
expects that this low-field NMR technique would work for any
sample---whether liquid, surface, or biological tissue---with good
solubility for xenon. (Heckman et al., Physical Review Letters,
upcoming article; see also website atomic.princeton.edu/romalis )

MILLING DIAMOND FILMS can be performed with gallium beams. Diamond
films, created by first installing tiny diamonds in a pitted silicon
surface and then laying down subsequent atoms to form a near-planar
diamond surface, have many of the electrical properties of
semiconductors, but can operate at much higher temperatures,
voltages, and power. Because of its resistance to hostile
environments and its bio-compatibility, diamond films are also
expected to be act as handy protective coatings in microfluidic
research Because of its hardness, however, diamond films are
difficult to sculpt through micromachining, during which stresses on
the sample can crack the film. Now scientists at the Nanyang
Technological University in Singapore have devised a versatile way
of making possible micro-optical elements out of diamond films by
wielding a carefully focused gallium ion beam. Optical tests of the
resultant structures show that such properties as transmission and
index of refraction were not distorted by the milling process. By
the way, this research was undertaken as part of the Singapore-MIT
Alliance, an innovative engineering education and research
collaboration established in 1998 among three top engineering
research universities: National University of Singapore (NUS),
Nanyang Technological University (NTU), and Massachusetts Institute
of Technology (MIT). (Fu et al., Review of Scientific Instruments,
August 2003; contact Yongqi
Fu, yqfu@ntu.edu.sg )

PHYSICS NEWS UPDATE
The American Institute of Physics Bulletin of Physics News
Number 646 July 16, 2003 by Phillip F. Schewe, Ben Stein,
and James Riordon

PHOTONIC CRYSTAL SHIFTS ENERGY. Photonic crystals are
artificial structures, sometimes consisting of stacked rods, or arrays
of holes bored into a solid, which permit light in some wavelength
bands to pass through while rejecting light at other bands. New work
at Sandia National Lab indicates that a photonic crystal made from
half-micron-diameter tungsten rods, excited by thermal heating,
suppresses light at longer wavelengths and re-emits light at a shorter
wavelength band, one that may be more useful for such technological
applications as photovoltaic power generation, or building a better lightbulb.
Shawn Lin and his Sandia colleagues, in the course of their studies of
photonic crystals, have seemed to challenge the venerable formulation,
made by Max P
lanck a hundred years ago, of what kind
of emission spectrum a body should have. The Sandia photonic crystal
seems to emit between 4 and 10 times as much radiation in the near infrared
than a body at that temperature (the sample had been heated to 1250 C)
should be emitting. (Lin et al., Applied Physics Letters, 14 July 2003;
Lin et al., Applied Physics Letters, 14 July 2003; Lin et al.,
Optics Letters, Sep. 15 2003)

PICOSECOND X-RAY CRYSTALLOGRAPHY of a protein has been
demonstrated for the first time, by a multinational collaboration
(Philip Anfinrud, NIH, PhilipA@intra.niddk.nih.gov), enabling
atom-scale movies of an important biomolecule as it performs a
speedy function. This accomplishment will be presented at the
upcoming American Crystallographic Association meeting from
July 26-31 in Cincinnati (http://www.che.uc.edu/aca/index.html ;
see also Schotte et al., Science, 20 June 2003). While crystallographers
have previously obtained frozen snapshots of thousands of proteins,
they have yet to capture the full range of motion in even a single protein.
Previous x-ray movies of proteins have been on the nanosecond time scale,
which is too slow for capturing the steps
of many protein processes.
Recently, however, at the European Synchrotron and Radiation Facility
(ESRF) in France, researchers made picosecond-scale movies of a mutant
myoglobin molecule getting rid of a toxic carbon monoxide (CO) molecule.
Myoglobin is the protein that stores oxygen in muscle tissue. The
researchers chose to study a mutant version of the protein because the
highly strained atomic structure in part of the protein causes it to get
rid of a CO molecule much more quickly than does ordinary myoglobin.
To capture this process, they first sent a 1-ps pulse of laser light to the
protein to eject the CO. Immediately afterward, they illuminated the
protein with intense, 150-ps x-ray pulses from the ESRF synchrotron.
Crucial to this process was the ability to isolate singl
e x-ray pulses from the synchrotron. A CCD camera recorded the patterns
from the successive x-ray pulses as they passed through the protein.
The resulting movie showed the CO migrating to various sites in the
protein, with the myoglobin rearranging its shape to accommodate
the expulsion of the CO. In addition to enabling researchers to study
many important transitions in proteins, the picosecond time-scale of
these movies is commensurate with the timescale of many molecular
dynamics simulations, allowing for closer comparison between theory
and experiment.

TUMOR FLY-THROUGH MOVIES. Researchers at Purdue University
and the Imperial College of Science in London have created a real-time
holographic system to acquire a fly-through movie of living tissue using
infrared light and a special, semiconductor holographic film. The acquired
images showed structure inside rat tumors that, with conventional techniques,
would only be visible if the tumor was sectioned into thin slices or imaged
with ionizing radiation. The researchers created the fly-through movie
using optical coherence imaging (OCI). OCI is related to the more widely
known optical coherence tomography (OCT). However, OCT involves
scanning a laser beam through a sample and gathering information point
by point, which then must be assembled into a complete
image. OCI, on the other hand, captures complete images of thin tissue
sections that can be recorded directly with a video camera.
The key to the holographic OCI technique is a dynamic holographic film
that filters out the scattered, incoherent background light but passes the
coherent, full-frame images to a camera. Tissue readily reflects image-bearing
infrared light, but it also strongly scatters the light, and without coherence
filtering the scattered light would overwhelm the coherent pictures.
By adjusting the relative delay between the image beam and the reference
beam in the OCI system's imaging interferometer, the researchers
(Ping Yu, 765-494-3004, pingyu@physics.purdue.edu, David Nolte, 765-494-3013
nolte@physics.purdue.edu) could control the depth of the images and
assemble a slice-by-slice tour through a tumor while leaving the tissue intact.
Application of the OCI technique to cultured rat tumors revealed structures
that appeared to be necroses
(regions of dead tissue) and calcifications much like those found in human
cancers (see image at www.aip.org/mgr/png). Ultimately, the researchers
explain, holographic OCI could offer a nondestructive alternative to x-rays
and microsectioning methods for studying living tissue. (P. Yu et al., Applied
Physics Letters, 21 July 2003.)

PHYSICS NEWS UPDATE
The American Institute of Physics Bulletin of Physics News
Number 645 July 9, 2003 by Phillip F. Schewe, Ben Stein, and
James Riordon

ULTRA-INTENSE LIGHT FILAMENTS have successfully been sent through
laboratory "fog" that approximates atmospheric conditions. This is
an important step which should benefit several laser applications,
such as free-space laser communication, monitoring of pollution, and
range finding (see figure at http://www.aip.org/mgr/png/2003/194.htm)
Open-air laser light shows feature bright beams seemingly
traveling interminably through the sky. But in general water
droplets are an avid absorber of laser light. Now a group of
physicists at the Universite Claude Bernard Lyon in France have used
ultra intense (10^14 watts/cm^2), ultrashort (120 femtosecond) laser
pulses to create "light filaments," streaks of light only 150
microns wide but hundreds of meters long, which can propagate
through an artificial cloud of water droplets without losing much
energy. The filaments form up through two competing nonlinear
optical effects: the "Kerr effect" in which high intensity light
modifies the index of refraction in the transmission medium (in this
case air and water vapor) in such a way as to cause self-focusing;
and the creation of a defocusing plasma effect. The French
researchers now plan to test their scheme in the open atmosphere
under controlled conditions. (Courvoisier et al., Applied Physics
Letters, 14 July 2003; contact Jean-Pierre Wolf,
wolf@lasim.univ-lyon1.fr, 04072-43-13-01; text at
www.aip.org/physnews/select )

"MOTTNESS" MIGHT HELP TO EXPLAIN CUPRATE BEHAVIOR. One of the
biggest problems in condensed matter physics is the effort to
understand the behavior of copper oxide (or cuprate for short)
superconductors. One of the most studied materials in all of
science, cuprates are layer cakes consisting of copper-oxygen planes
alternating with planes in which other elements, such as strontium
or lanthanum, are stocked in varying ratios. For instance, the
alternating layer might consist entirely of La, or it might contain
10% Sr. Like chefs looking for just the right recipe of spices,
physicists have tried different levels of doping in an effort both
to understand the underlying physics and to enhance the movement of
electrons through their samples. At moderate doping levels, the
cuprates are superconducting: moving electrons pair up and
constitute a resistance-less current of electricity. Ironically,
the cuprates are much less hospitable to electricity at ultra-low
doping levels. In fact, they are insulators when they are not
doped. A material's conductivity is determined by the ease with
which electrons can move around. In a conductor, there is an
abundance of free electrons. (Hotel analogy: there are plenty of
guests and plenty of hotel rooms.) In an ordinary insulator
electrons are bound two by two (the Pauli exclusion principle
insures that no two electrons, except those with opposite values of
spin, can occupy the same state) and there are very few if any free
electrons. (In an insulating hotel all the rooms are filled with
two guests, with no room for more guests.) In a Mott insulator
(named for Sir Neville Mott) conditions are even more inhospitable:
all electron energy states are filled with single electrons, and
these interact so strongly as to preclude even the arrival of a
second electron. (In a Mott hotel all the rooms are single rooms,
and all are filled.). Many scientists believe that one of the keys
to understanding why the cuprates are such good superconductors in
the cold regime is to learn why they are Mott insulators in the warm
regime and how such physics manifests itself when they are doped.
One more oddity about the cuprates is the issue of "pseudogaps." In
a superconductor, the energy required to break up a pair of
electrons is termed the "energy gap." But in the cuprates, a
partial gap still persists even when superconductivity is
destroyed. Some have interpreted this as evidence that some pairs
can exist even when the material is warmed above its superconducting
transition temperature (see figure at
http://www.aip.org/mgr/png/2003/195.htm ). However, the pseudogap is
observed in Mott insulators that never became superconducting in the
first place, indicating that the pseudogap is of a more general
origin. Maybe there is more to superconductivity than the pairing
of electrons. (See Nature, 4 January 2001 for background on this
topic.)
Now, a new theory addresses the problem of cuprate superconductivity
by suggesting that the existence of the curious pseudogap behavior
can be explained by the same physics that makes cuprates Mott
insulators. Tudor Stanescu (Rutgers Univ) and Philip Phillips (Univ
Illinois) argue that "Mottness," involving the collective
interaction among many electrons, is still present even when some
of the hotel rooms are empty, to use the hotel analogy. They
propose that the pseudogap arises simply because transport of
electrons in a doped Mott insulator will still involve two electrons
temporarily occupying the same site (the same room in the hotel
analogy). Such events remind the doped state of its Mottness and
this produces a pseudogap. They argue that such an effect
disappears when roughly 25% of the hotel rooms are vacant. At such
an occupancy rate, an electron can move, on average, throughout a
layer without the inhospitability of Mottness. (Physical Review
Letters, 4 July 2003; text at www.aip.org/physnews/select ; contact
Philip Phillips, 216-751-7348, philip@wirth.physics.uiuc.edu )

SEMICONDUCTORS ARE COOL. One of the problems with electronic
circuitry is what to do with heat dissipation. One attempt to deal
with this would be to improve the thermoelectrical
properties of the intrinsic circuitry material and use the material
to make coolers for on-site chilling. The conventional typical
thermoelectric materials, such as Bi2Te3, do not fit easily
with the common integrated circuit semiconductors----Si, GaAs, and
InP---because of a mismatch of the atomic spacing. Now, a group of
scientists at the University of Massachusetts at Amherst, with a
colleague at the Hong Kong University of Science and Technology, has
tried to
solve the problem by making coolers using the GaAs-based material
itself. With this approach they have been able to bring about
cooling of 0.8 degrees at a temperature of 25 C and 2 degrees at a
temperature of 100 C. (Zhang et al., Applied Physics Letters, 14
July 2003; contact Jizhi Zhang, 413-545-0712,
jizhang@ecs.umass..edu; text at www.aip.org/physnews/select )

PHYSICS NEWS UPDATE
The American Institute of Physics Bulletin of Physics News
Number 644 June 30, 2003 by Phillip F. Schewe, Ben Stein, and
James Riordon

A FIVE-QUARK STATE HAS BEEN DISCOVERED, first reported by a group of
physicists working at the SPring-8 physics lab in Japan. All
confirmed particles known previously have been either
combinations of three quarks (baryons, such as protons or neutrons)
or two quarks (mesons such as pions or kaons). Although not
forbidden by the standard model of particle physics, other
configurations of quarks had not been found until now. The
"pentaquark" particle, with a mass just above 1.5 GeV, was
discovered in the following way. At the SPring-8 facility a laser
beam is scattered from a beam of 8-GeV electrons circulating in a
synchrotron racetrack. These scattered photons constitute a beam of
powerful gamma rays which were scattered from a fixed target
consisting of carbon-12 atoms. The reaction being sought was one in
which a gamma and a neutron inside a carbon nucleus collided,
leaving a neutron, a K+ meson, and a K- meson in the final state.
Efficient detectors downstream of the collision area looked for the
evidence of the existence of various combinations of particles,
including a
short-lived state in which the K+ and the neutron had coalesced
(drawing will be posted soon at www.aip.org/mgr/png ). In this
case the amalgamated particle, or resonance, would have consisted of
the three quarks from the neutron (two "down" quarks and one "up"
quark) and the two quarks from the K+ (an up quark and a strange
antiquark). The evidence for this collection of five quarks would
be an excess of events (a peak) on a plot of "missing" masses
deduced from K- particles seen in the experiment. The
Laser-Electron Photon Facility (LEPS) at the SPring-8 machine
(http://www.rcnp.osaka-u.ac.jp/Divisions/np1-b/index.html ) is
reporting exactly this sort of excess at a mass of 1540 MeV with an
uncertainty of 10 MeV. The statistical certainty that this peak is
not just a fluctuation in the natural number of background events,
and that the excess number of events is indicative of a real
particle, is quoted as being 4.6 standard deviations above the
background. This, according to most particle physicists, is highly
suggestive of discovery. (Nakano et al., Physical Review Letters, 4
July 2003; contact Takashi Nakano, nakano@rcnp.osaka-u.ac.jp,)
Confirmation of this discovery comes quickly. A team of physicists
in the US, led by Ken Hicks of Ohio University (hicks@ohio.edu,
740-593-1981) working in the CLAS collaboration at the Thomas
Jefferson National Accelerator Facility, has also found evidence for
the pentaquark. A photon beam (each photon being created by
smashing the Jefferson Lab electron beam into a target and then
measuring the energy of the scattered electron in order to determine
the energy of the outgoing gamma) was directed onto a nuclear
target. The photon collides with a deuteron target and the
neutron-kaon (nK+) final state is studied in the CLAS detector
(http://www.jlab.org/Hall-B/ ). The Jefferson Lab result was
announced at the Conference on the Intersections of Nuclear and
Particle Physics (http://www.cipanp2003.bnl.gov ) held on May 19-24,
2003, at New York City. Stepan Stepanyan (stepanya@jlab.org,
757-269-7196) reported at this meeting that the mass measured for
the pentaquark, 1.543 GeV (with an uncertainty of 5 MeV), is very
close to the LEPS value. The statistical basis of the CLAS
measurement is an impressive 5.4 standard deviations. (This result
is about to be submitted to Physical Review Letters.) These
results, together with the previous results from SPring-8, now
provide firmer evidence for the existence of the pentaquark. The
HERMES experiment at the DESY lab in Germany is also pursuing the
pentaquark particle.
The discovery of a 5-quark state should be of compelling interest to
particle physicists, and this might be only the first of a family of
such states. Not only that but a new classification of matter, like
a new limb in the family tree of strongly interacting particles:
first there were baryons and mesons, now there are also
pentaquarks. According to Ken Hicks, a member of both the SPring-8
and Jefferson Lab experiments, this pentaquark can be considered as
a baryon. Unlike all other known baryons, though, the pentaquark
would have a strangeness value of S=+1, meaning that the baryon
contains an anti-strange quark. Past searches for this state have
all been inconclusive. Hicks attributes the new discovery to better
beams, more efficient detectors, and more potent computing analysis
power. (Additional website:
http://www.phy.ohiou.edu/~hicks/thplus.htm )

HIGH-T SQUIDS PRODUCE MAGNETOCARDIOGRAMS that are clinically
practical. SQUIDs (superconducting quantum interference devices)
can detect incredibly small magnetic fields, even those produced by
nerve signals in the brain or heart. Arrays of SQUIDs have been
used to make magnetic maps of the heart in the past but only with
models using the lower-critical-temperature superconductors that
must be chilled in liquid helium, and operated in a room-sized
enclosure needed to shield against extraneous magnetic fields. Now,
for the first time, a group of scientists at Hitachi in Japan has
produced a magnetocardiograph machine based on high-temperature
superconductors which can be chilled with much more tractable liquid
nitrogen, and magnetically shielded by a much smaller cylindrical
enclosure. The Hitachi device employs a 4 x 4 SQUID array to map
the heart's magnetism at field strengths as small as 50 pico-tesla,
a million times weaker than Earth's field. One of the authors,
Koichi Yokosawa (yokosawa@rd.hitachi.co.jp, 81-423-23-111-39),
suggests that magnetocardiography will prove to be one of the
forefront applications of high-Tc superconductor technology.
(Yokosawa et al., Applied Physics Letters, 30 June 2003)

PHYSICS NEWS UPDATE
The American Institute of Physics Bulletin of Physics News
Number 643 June 26, 2003 by Phillip F. Schewe, Ben Stein, and
James Riordon

THE MESON Ds(2317), discovered a couple of months ago in high energy
electron-positron collisions at SLAC, possesses a mass of 2.317 GeV,
some 170 MeV lighter than expected, at least according to prevalent
theories of quark interactions. Hence physicists need a new
explanation of how a charm quark attached to an antistrange quark
should have this particular mass. In general, Ds and D mesons are a
class of particles, each consisting of a charm quark attached to a
light antiquark. (The subscript "s" pertains to all those D's
containing a strange antiquark; "ordinary" D mesons consist of a
charm quark and a down antiquark.) The Babar detection group at SLAC
responsible for the experimental discovery (Aubert et al., Physical
Review Letters, 20 June 2003, text at www.aip.org/physnews/select;
also see press release at
http://www.slac.stanford.edu/slac/media-info/20030428/index.html )
suggests that the Ds(2317) might be a novel particle made of 4
quarks. But a pair of physicists in Portugal claim that in their
model, assuming that the meson is indeed a charm/antistrange
combination, the mass comes out in the right range if the
strong-nuclear-force interactions responsible for the creation and
annihilation of extra quark-antiquark pairs are taken into account.
Using this model, Eef van Beveren (University of Coimbra) and George
Rupp (CFIF Lab, IST, Lisbon) have successfully predicted meson
masses in the past (such as the kappa meson, discovered at Fermilab
(E791) at a mass of 800 MeV), while in the case of Ds mesons they
predict a mass very near the Ds(2317) found already, and another at
about 2.9 GeV (yet to be found). As to D mesons, they predict the
equivalent of the Ds(2317) at a mass range of 2.1-2.3 GeV (for which
preliminary evidence exists), and a heavier one at about 2.8 GeV
(still undetected). According to van Beveren and Rupp, both pairs of
Ds and D mesons are, in some sense, different aspects of the same
underlying quark-antiquark state. (Physical Review Letters, upcoming
article, see website http://cft.fis.uc.pt/eef/default.htm or contact
George Rupp at george@ist.utl.pt, +351-21-841-9103)

MOUNTAIN-CLIMBING ATOMS. Atoms that are deposited on crystal
surfaces, through a method known as molecular beam epitaxy, often
form surfaces covered with numerous small mounds rather than smooth
layers, if the substrate temperature is sufficiently low. For higher
temperatures, an atom near the top of a mound can often move about
and diffuse down toward the crystal surface. Conventional wisdom
holds that upward diffusion, on the other hand, is essentially
negligible. Recently, however, a collaboration of researchers at the
INFM-Università di Genova in Italy, the Chinese Academy of Sciences,
and Oak Ridge National Laboratory has found that deposited atoms may
sometimes diffuse upward spontaneously, forming faceted mountains
that tower over the surrounding crystal plane. Although the
formation of faceted nanocrystals has been observed before, these
were generally thought to be due to a mismatch between a crystal
substrate and the crystal structure of the deposited atoms (for
example, when germanium atoms are deposited on silicon, differences
in the spacing of the two types of crystals lead to a strain that
encourages the growth of large, hut-shaped crystals). The new
research, by contrast, reveals for the first time that the
crystalline mountains (see image soon to be posted at
www.aip.org/mgr/png ) can form even when the deposited atoms and the
substrate crystal consist of the same element, and no strain energy
is involved. Specifically, aluminum atoms deposited on an aluminum
crystal substrate may diffuse upward into crystal structures that
rise upward as much as ten times higher than the thickness of the
surrounding planes.
Computer simulations seem to indicate that the growth may be caused
by processes thought to be insignificant in previous deposition
studies. In particular, an atom sitting at the inner corner near the
base of a crystal protrusion may jump out of place and onto the
crystal facet, or a pair of atoms can conspire to exchange positions
as they leapfrog up a crystal slope. The counterintuitive
formation of tall nanocrystals via upward diffusion of aluminum
atoms only occurs within a temperature window of about 330 K to 500
K, when the total crystal surface coverage exceeds critical values
of about 10 or more deposited layers, depending on the specific
temperature. The researchers (Francesco Buatier de Mongeot,
buatier@fisica.unige.it, +39-10-3536324, and Zhenyu Zhang,
zhangz@ornl.gov) predict that the often neglected processes leading
to upward atom diffusion are likely to be important for other
crystals grown via molecular beam epitaxy, leading to much richer
dynamics in the growth of thin films than previously suspected. (F.
Buatier de Mongeot et al., Physical Review Letters, upcoming
article, probably 4 July)

PHYSICS NEWS UPDATE
The American Institute of Physics Bulletin of Physics News
Number 642  June 18, 2003   by Phillip F. Schewe, Ben Stein, and
James Riordon

INTRIGUING ODDITIES IN HIGH-ENERGY NUCLEAR COLLISIONS.  Missing
debris in the smashup between gold nuclei going at close to the
speed of light suggests the creation of a highly unusual plasma
environment, researchers have announced at Brookhaven National
Laboratory.  By smashing together gold ions at Brookhaven's
Relativistic Heavy Ion Collider (RHIC), scientists are attempting to
make and study a state of matter that existed only millionths of a
second after the big bang.  Called a quark-gluon plasma (QGP), it is
a hot, dense soup of individual quarks and gluons. In today's
universe, by contrast, quarks come in groups of twos and threes,
held together by gluons.  This spring, Brookhaven researchers
performed a "control" experiment, in which they collided a gold
nucleus with a deuteron, a light nucleus consisting of just a proton
and neutron. In these and other kinds of nuclear collisions, a pair
of quarks from a proton or neutron occasionally gets ejected.  In
turn each ejected quark produces a stream or "jet" of particles in
its wake.  In some of the gold-deuteron collisions, the researchers
indeed observed pairs of jets flying in opposite directions.  But in
head-to-head collisions between two gold nuclei, researchers
observed only one, rather than two, jets.  This property, called jet
quenching, suggests that the particle jet traveling in the direction
of the collision region is getting absorbed by a hot, dense state of
matter.  Jet quenching is predicted to occur in the correspondingly
hot, dense environment of a quark-gluon plasma, but RHIC
experimentalists are not ready to claim the QGP prize quite yet.  To
verify its presence and rule out rival scenarios, they are planning
numerous other experiments for finding other signatures of a QGP.
However, the new data has convinced Columbia theorist Miklos
Gyulassy that the RHIC team is already seeing a QGP (see
http://www-cunuke.phys.columbia.edu/people/gyulassy/Welcome.html).
The gold-gold collisions, he and his colleagues calculate, produce
an environment 100 times denser than ordinary nuclear matter and
display properties predicted in QGP models based on quantum
chromodynamics (QCD), the theory of the strong force which holds
nuclei together.  On June 18, three of the four RHIC experimental
groups have submitted papers on the new results to Physical Review
Letters and researchers discussed these new results at a special
Brookhaven colloquium today. (Brookhaven press release, June 11,
http://www.bnl.gov/bnlweb/pubaf/pr/2003/bnlpr061103.htm.)

SOLAR FLARES AND GLOBAL WARMING.  A recent study by researchers at
Duke University and the Army Research Office has  found new evidence
of a link between solar flare activity and the earth's temperature.
The work is another contribution to the ongoing debate over global
warming and its causes. A strong link between solar flares and our
climate, if it exists, could override the influence humans have on
the temperature of our environment. One of the challenges of
determining the connection between solar flare activity and the
atmosphere stems from the fact that the motion of the air that
blankets our planet is turbulent and complex. A sudden burst of
solar activity would, in effect, be smeared out by moving air and
its interaction with the earth's surface. Any temperature increase
caused by a given period of solar flare activity would be difficult
to determine, at best. Rather than focus on such challenging
one-to-one correlations, the new study compares the form of the
statistical fluctuations in solar flare activity with the form of
the statistical fluctuations of the earth's temperature. The
researchers (contact: Bruce J. West, Bruce.J.West@us.army.mil,
919-549-4257) explain that solar flare activity can be characterized
by a type of statistics described by a Levy distribution, which is
generated by a "Levy-walk." (Many natural phenomena, from foraging
patterns of spider monkeys to complex hydrodynamic flows, are well
described by Levy walks, although the coefficients in the relevant
equations typically vary from one phenomenon to another. See Update
510-3 for one example.) Analyses of global and local temperature
fluctuations are also well described by a Levy-walk. In fact, a
comparison of the mathematical coefficients that describe the
fluctuations suggest to the researchers that the atmosphere directly
inherits its temperature fluctuations from the variation in solar
flare activity.  Unless some other underlying cause is responsible
for the unlikely
correspondence between solar flares and the earth's temperature, the
research suggests that for the large part variations in global
temperatures are beyond our control and are instead at the mercy of
the sun's activity. (Nicola Scafetta and Bruce J. West, Physical
Review Letters, 20 June 2003)

STAR OUT OF ROUND.  The Very Large Telescope Interferometer (VLTI),
an array of 2 telescopes which combine their light signals to
achieve a higher angular resolution than is possible with any one
scope, has determined that the star Achernar is the flattest star
ever studied.  The VLTI, which does not provide an actual image of
the star but can provide an accurate estimate of the star's profile,
has determined that Achernar's equatorial radius is 50% larger than
its polar radius.  This is quite oblate compared to most other
celestial bodies, such as our Earth, whose equatorial radius is only
0.3% larger than its polar radius.  Theorists do not yet know how to
explain how a star like this could turn fast enough to adopt with
such a shape without flying apart. Achernar is about 145 light years
away from Earth in the southern sky and has a mass of about 6 solar
masses.  The telescopes used to make the interference map were not
the giant 8.2-m VLT telescopes, but more modest 40-cm reflectors set
at various configurations with separations as large as 140 m.
(European Southern Observatory press release, 11 June,
www.eso.org/outreach/press-rel/pr-2003/pr-14-03.htm )

PHYSICS NEWS UPDATE
The American Institute of Physics Bulletin of Physics News
Number 641 June 12, 2003   by Phillip F. Schewe, Ben Stein, and
James Riordon

THE TWISTED ORIGIN OF SPHEROMAKS.  Researchers at the California
Institute of Technology have made important progress in solving a
long-standing mystery concerning the formation of spheromaks,
self-organizing toroidal plasma configurations that are
superficially reminiscent of smoke rings. It is well known that
current-carrying plasmas embedded in an initial seed magnetic field
can form spheromaks.  The formation process is believed to involve
some kind of dynamo process, whereby the internal  magnetic fields
become re-arranged or even amplified so as to achieve a stable
minimum energy state for the internal magnetic forces. (Similar
minimal-energy state arguments help explain why soap bubbles, for
example, tend to be spheres rather than cubes or other shapes.) But
until now, no one has definitively demonstrated just how a plasma
transforms from an unstable, high internal energy configuration into
a spheromak. The new experiment sheds light on the phenomenon by
capturing images of plasmas as spheromaks form. The images show that
plasma currents initially flow in straight lines along a confining
magnetic field. Owing to an effect known as the kink instability,
the plasma currents develop bends that twist into a helix (see image
at www.aip.org/mgr/png ). The helix acts like a coiled current
element, or solenoid, which amplifies the original, straight
magnetic field. Above a certain threshold in the initial magnetic
field, detached plasma spheromaks are formed. The researchers
(contact: Paul Bellan, pbellan@its.caltech.edu, 626-395-4827)
confirmed the theory behind the effect by measuring the rapid
amplification of the magnetic field inside developing plasma
solenoids. Spheromaks are potentially promising routes to
plasma-based nuclear fusion, and insight into their formation will
help in the design of future experiments-and possibly even a clean,
safe energy source. In addition, spheromak formation is important
for explaining the behavior of plasma in the solar corona, as well
as understanding the physics of jets that sprout from black holes,
galactic nuclei, and other astrophysical objects. (S. C. Hsu and P.
M. Bellan, Physical Review Letters, 30 May 2003)

A CARBON NANOTUBE COMPOSITE FIBER, made by injecting single-walled
nanotubes into a pipe filled with polyvinyl alcohol to form a gel,
can be spun out into100-meter strands.  According to the scientists
at the University of Texas at Dallas who created the spinning
process, the resulting fibers are "tougher than any natural or
synthetic organic fibre described so far," with a tensile strength
of 1.8 gigapascals.  The 50-micron-diameter fibers are 60% nanotube
by weight and has been woven into a fabric.  In textile form, the
researchers suggest, their composite material could be used for
making distributed sensors, antennas, capacitors, and even
batteries.  (Dalton et al., Nature, 12 June 2003.)

"COLOR FILTERING" AT THE ATOMIC LEVEL.  One of the most astounding
inventions of the late 20th century, the scanning tunneling
microscope, or STM, yields atomic-scale landscapes of electrically
conducting surfaces such as metals. Now, researchers at the Colorado
School of  Mines (Peter Sutter, psutter@mines.edu) have demonstrated
a new technique, called "energy-filtered STM," which is analogous to
putting a color filter on an ordinary microscope.  Just as color
filters make it easier to discern desired features in a photograph,
color-filtered STM makes it easier to distinguish between chemically
similar atoms, something that's usually very difficult to do.  It
can even identify specific chemical bonds on a surface. Conventional
STMs employ a metal tip, which, as it turns out, is generally most
sensitive to the highest-energy electrons on the surface.  These
electrons jump or "tunnel" to the tip, giving scientists data to
reconstruct an image of the surface.  This preference for the
highest-energy electrons can be a problem, because it can obscure
the signal from lower-energy electrons, which may be associated with
different atoms or different kinds of chemical bonds.  To address
this issue, the new technique employs an indium arsenide (InAs) tip.
InAs is a semiconductor, and all semiconductors have a "fundamental
bandgap," a range of energies that no electrons can possess because
of the 3D atomic structure of the material.  In the case of a
semiconductor tip very close to a conducting surface, what's more
important is something called a "projected gap," a range of
forbidden energies that appears when the 3D electronic structure is
seen along the tip axis.  So because of the projected gap, electrons
in a certain energy range cannot tunnel to the tip.  Adjusting the
voltage between the tip and sample can shift this projected gap so
that it blocks off the high-energy electrons, making the tip more
sensitive to electrons in lower-energy bonds at the sample surface
(see images at http://www.aip.org/mgr/png ). Researchers can shift
this range of forbidden electron energies repeatedly, to build up,
for example, maps of specific chemical bonds on a surface, and to
analyze how abundant one type of chemical bond is compared to
others.  This technique is now being explored for 'atom-by-atom'
mapping of the composition of alloys of chemically similar elements,
which is important for certain technologies such as thin-film
growth, which often involve nanometer scale variations in the
composition of alloys (Sutter et al., Physical Review Letters, 25
April 2003)

PHYSICS NEWS UPDATE
The American Institute of Physics Bulletin of Physics News
Number 640 June 5, 2003 by Phillip F. Schewe, Ben Stein, and James
Riordon

FEMTOSECOND LASERS FOR CUTTING AND IMAGING BRAIN TISSUE have been
demonstrated in a research collaboration that includes physicists
and pharmacologists. Speaking at this week's CLEO/QELS meeting in
Baltimore, Jeff Squier of the Colorado School of Mines
(squier@mines.edu) described an automated, all-optical technique for
performing histology, the study of biological tissue at the
microscopic level. Used widely in clinical settings (e.g., to
examine biopsied tissue from a suspected breast tumor) and in
biological research (e.g, to study the anatomy of muscle), histology
is presently a manual process, requiring a skilled technician to
slice frozen tissue samples into thin pieces, and then view them
with an optical microscope. Now, Squier and colleagues have
demonstrated a way to do histology by using femtosecond lasers,
which deliver light pulses that last just quadrillionths of a
second. Compared to present methods, the femtosecond-laser
technique does not require the freezing of biological samples (which
can damage the specimen) and it can even slice and image very soft
tissue (which is a challenge with standard histological
techniques). In the new technique, the researchers first stain a
tissue specimen with a layer of fluorescent dye to label desired
structures (such as nerve cells) in tissue. Then, they use the
laser beam at relatively low power (about 100 gigawatts per square
centimeter) to obtain a picture (through various optical techniques)
of these structures in a tissue specimen's first layer. The
resolution of the image can approach 30 microns. After taking this
first picture, the researchers increase the laser power (to levels
of about 7000 terawatts per cm^2) so that the light ablates (wears
away) a 100-micron-deep layer of the tissue. To this newly exposed
layer of tissue, the researchers add more fluorescent dye, and they
lower the laser intensity to take another image. This process is
repeated until no tissue remains. Stacking up the successive images
to create a 3D picture, Squier and colleagues have obtained
high-quality images of animal brain tissue, for example as blood
vessels in rat neocortex. Since the femtosecond technique completely
destroys its tissue samples, it may not be appropriate for certain
clinical applications such as biopsies of breast tissue, as
physicians may wish to preserve the tissue for future reference.
However, the technique may be especially suited for many other
applications, including studies in the burgeoning field of
transgenic animals, which include genetically altered mice. For
example, researchers could inject a fluorescently labeled gene into
a mouse, and then obtain high-quality images showing how the gene
gets expressed in mouse tissue (Paper CMN3 at the meeting).

A PLASMA VALVE, a device that uses electrically charged particles to
act as a barrier between air and vacuum, has been invented by a
Brookhaven-Argonne collaboration. These two DOE labs joined forces
to provide a needed component for Argonne's Advanced Photon Source
and similar facilities worldwide. Inside the walls of
accelerators, synchrotrons and storage rings, a good vacuum--empty
space mostly devoid of matter--enables particle beams to travel
unimpeded for hours. However, if a leak causes air to rush into the
vacuum, the particle beam spreads out and deposits its energy onto
surrounding walls, disrupting the beam and damaging valuable
equipment. The faster the leak can be closed, the less
damage will be done to the walls. The plasma valve, which has no
moving parts, can activate in a nanosecond, a million times faster
than mechanical valves. To keep air from rushing in, the
Brookhaven-Argonne team create a dense, high-temperature plasma
(collection of charged particles) held together by electric and
magnetic fields. Housed inside a hollow copper cylinder, the plasma
reaches a temperature of 15,000 degrees Kelvin (about 50 times
greater than room temperature)--making the plasma particles bounce
around so vigorously that they collide with air molecules and
prevent them from passing into the vacuum. Moreover, the valve's
confining electromagnetic fields prevent the plasma itself from
rushing into the vacuum. (Brookhaven press release, May 28,
http://www.bnl.gov/bnlweb/pubaf/pr/2003/bnlpr052803.htm ). A much
faster, more complex version of a previously introduced "plasma
window" (see New Scientist, 12 April 2003), the plasma valve is the
latest example of novel uses of plasma for particle-beam
applications; other recent ones include plasma acceleration of
antimatter (Update 634), a plasma lens (Update 508), and plasma
deflection of high-energy beams (Update 540).

PHYSICS NEWS UPDATE
The American Institute of Physics Bulletin of Physics News
Number 639 May 30, 2003 by Phillip F. Schewe, Ben Stein, and James
Riordon

OPTICAL PERISTALSIS. Part of the digestion process consists of the
massaging movement of powerful esophageal muscles urging food
particles along the alimentary track. The same sort of
"peristalsis" can also be carried out at the nanoscopic level with
small objects in the grip of cleverly crafted light pulses. David
Grier and Brian Koss at the University of Chicago use the optical
tweezer method of controlling particles with multiple laser beams,
but instead of a static array of beams, they use computer-generated
holograms to convert a single beam of light into large numbers of
optical traps. Each hologram may be considered to be a specialized
diffraction grating, producing intricately articulated networks of
hundreds of optical traps. Objects can fall into these light traps
and then the traps can be moved, thus transporting the objects. The
aim is to move and position sub-micron things in 3D space.
Applications include inserting the object into a microscopic
reservoir and pulling it back (parallelism is one of the technique's
strengths), or centering or rotating a biological cell in a
microscope's field of view. Grier's work has led to a commercial
version of this holographic optical tweezers, one in which a pattern
of 200 optical traps can be refreshed or modified at a rate of 100
times per second. (By the way, how forefront research is turned
into saleable products is an interesting story by itself. For
example, the company Grier started, Arryx,
Inc.---http://arryx.com---has a scientific advisory board (SAB) with
notable scientists from Princeton, NIH, the Whitehead Institute,
Harvard, and Northwestern.) In the "peristalsis" mode of
operation, particles are deliberately handed off from
one optical trap to another, as in a bucket brigade. In a separate
"thermal ratchet" mode of operation, the transfer from trap to trap
might involve intervals of free diffusion; this mode should be
useful for fractionating DNA molecules (see previous Update story at
http://www.aip.org/enews/physnews/2003/split/627-1.html ) as part of
the process of sequencing a gene.
Speaking as a physicist, Grier says the most important aspect of his
group's holographically generated tweezer patterns is the ability to
implement time-varying potential energy landscapes for moving tiny
objects in a "force-free" way. Speaking as a biophysicist, Grier
points to the ability to reach into a microscopic environment and to
position samples just where you want them. (Koss and Grier, Applied
Physics Letters, 2 June 2003; d- grier@uchicago.edu, 773-702-9176,
lab website at http://griergroup.uchicago.edu/~grier/hot/ )

A NEW OPTICAL GEOMETRIC PHASE has been measured for the first time,
by a group of physicists at Colgate University. The new geometrical
phase is associated with light beams carrying orbital angular
momentum. This development can be considered yet another step toward
understanding and exploiting the weirdness of quantum reality for
performing novel feats of computation. To see the meaning behind
the new effect, we shall break the explanation into parts,
considering in turn the issues of phase, orbital angular momentum in light,
and then geometrical
phase in light. First, phase. Many common periodic things have phase. The
orientation or phase of a minute hand on a clock is the amount by
which the hand has swept around the clock face: a quarter past the
hour, half past the hour, etc. Except when going into a new time
zone the phase of the clock regularly returns to its original
position every sixty minutes. The phase of a water wave specifies
where along the wave's crest-to-trough cycle it might be at any
moment. Now consider a different kind of phase. Picture a sign with
an arrow on it, oriented north. Starting at the equator, and
without changing its orientation, push the sign along the ground one
fourth of the way around the world. Next push the sign due north
until you reach the north pole, where, without changing the sign's
orientation, you move directly south again to return to your
starting point. Even though you will have traced a closed loop the
sign will now have a westerly orientation. In other words, because
of the intrinsic curved geometry of the path, a change in phase will
have occurred. This kind of phase change can occur in a quantum
system.
Second, orbital angular momentum. The ordinary forward momentum of
a particle of light is equal to Planck's constant divided by the
wavelength of the equivalent light wave. Furthermore, the light is
said to possess an intrinsic angular momentum, or "spin." The spin
angular momentum can be oriented by polarizers so that the electric
field of the light wave is oscillating vertically up and down, or
horizontally back and forth. Equivalently, if the light wave is
circularly polarized (the electric field precesses in corkscrew
fashion as the wave moves along) the two contrary states of the spin
would then correspond to the light wave's electric field precessing
clockwise (in a "right-handed" way) or anticlockwise (in a"left
handed" way). For the purposes of data processing a 0 or 1 bit can
be associated respectively with vertical and horizontal polarizations or,
equivalently, with
clockwise or anticlockwise polarizations. But what does it mean for
light to have "orbital" angular momentum? What is it that orbits?
To ponder this issue, picture the electric field values for a vertical
planar slice
of the light beam. For vertically-polarized light, the electric
field at all the points on the slice are vertically oriented. Look
at the sameslice at a later time and the fields are still vertically
oriented.
For circularly polarized light, the fields in the slice will, at a
certain moment, also be oriented in the same way. A moment later,
however, the electric field will have precessed a bit (from the one o'clock
position, say, to the three o'clock position; another way of saying
this is that the phase of the electric field will have advanced a
bit) but the orientation of the field at each point on the vertical
slice will be the same. With the use of special gratings one can
produce an entirely different mode of light, one in which the
electric field phase coils around the beam axis, and the light is
said to possess an orbital angular momentum, or OAM. This condition
is visualized at the following website prepared by physicists at
Colgate University:
departments.colgate.edu/physics/research/optics/oamgp/gp.htm. This
extra property of "coiled light" might be exploitable for future
quantum computing. For instance, recently a group at the University
of Vienna used OAM in light to create a three-dimensional entangled
state, or "qutrit" (Vaziri et al., Physical Review Letters, 9 Dec
2002). Third issue: geometrical phase. When a light pulse is made
to follow a closed loop path in real space, the phase of the
returning beam might be slightly off from the phase of light
starting off at that point. This disparity (which can result in an
interference effect) can be modified by changing the path length.
It can also be modified by changing the path geometry. In addition,
the space does not need to be real space. When the "mode" (set of
standing waves in the beam) is changed, it can also produce a phase
when changing the geometry of the path in "mode space," and it is
this that the Colgate physicists have measured. (see a schematic of
the setup at this website:
departments.colgate.edu/physics/research/optics/oamgp/geomph.htm ).
The change in phase that a quantum system undergoes in going around
a closed path in a space of states or parameters is called a
"geometrical phase," and can be measured when the light emerges from
the path to form a spiral shaped interference pattern at an external
detector (Galvez et al., Physical Review Letters, 23 May 2003;
contact Kiko Galvez, egalvez@mail.colgate.edu, 315-228-7205). (For
further background, see Physical Review Focus item at
focus.aps.org/story/v9/st29 and an article on geometric phase in
Physics Today, Dec 1990.)

PHYSICS NEWS UPDATE
The American Institute of Physics Bulletin of Physics News
Number 638 May 22, 2003 by Phillip F. Schewe, Ben Stein, and James
Riordon

A SOLID STATE PLASMA, a lattice of beryllium ions (atoms from which
2 or 3 of the 4 electrons have been removed) remaining in solid
state form for a few nanoseconds, has been studied by physicists at
Livermore National Lab. This is done in two steps. First, intense x
rays created by a powerful laser striking the outside of the coated
beryllium sweep into the beryllium and strip electrons as they go
by. But in the short time before the solid dissipates, a second
laser striking a metal foil creates a beam of diagnostic x rays.
The scattered x rays reveal an electron density of more than 2 x
10^23 per cubic centimeter and an electron temperature of 600,000
K. These conditions are hard to come by for plasmas in
low-atomic-number atoms like beryllium and the hydrogen isotopes
that will be the fuels in inertial confinement fusion. Siegfried
Glenzer (glenzer1@llnl.gov) and his colleagues do their research as
part of the lead-up to fusion work at the National Ignition
Facility, where target pellets will undergo a compression up to 1000
times the normal solid state density. (Glenzer et al., Physical
Review Letters, upcoming article; associated website,
http://www.llnl.gov/nif/ )

THE CONVENTIONAL THEORY OF DARK MATTER just got some potent support
from a new batch of observations to be reported by scientists from
the Sloan Digital Sky Survey (SDSS) this week at a meeting in the
Canary Islands. One of the main reasons for believing in the
existence of non-luminous matter is that the motions of galaxies
within galaxy clusters and the motions of matter around individual
galaxies seems to defy conventional celestial mechanics. Either
plenty of extra (but unconventional) mass must lurk in the vicinity
of the galaxies (the dark matter theory) or the known laws of
physics might be in need of amendment (the theory known as modified
Newtonian dynamics, or MOND). Scrutinizing a subset of 3000
galaxies (from Sloan's inventory of 250,000 galaxies) with satellite
galaxies in tow, the researchers' profile of satellite velocities
supported the dark matter theory and discounted the MOND idea. (See
the Sloan website at www.sdss.org )

ORCA ACOUSTICS. Echo-locating marine mammals help maneuver in the
deep by sending out sounds and listening for the response, a feat
requiring exquisite time resolution in distinguishing emitted clicks
from echos. Recently a team of scientists from the Russian Academy
of Sciences and the University of Hawaii studied this process by
recording the auditory brainstem responses (ABRs) in a false killer
whale (Pseudorca crassidens). The test animal was trained to
cooperate to the extent of accepting a suction-cup electrode (placed
behind the blowhole) for providing EEG signals and a willingness to
indicate whether it had detected the presence or absence of a
target. The intensity of the emitted clicks is of course much
higher than the intensity of the returning echos but the amplitude
of the respective brainstem response (the animal listening to its
own clicks and to the echos) was roughly the same. This suggested
to the researchers that some mechanism is at work helping to mask
out the emitted clicks while allowing the echos to be heard. (Supin
et al., Journal of the Acoustical Society of America, May 2003;
contact Alexander Supin, a.supin@g23.relcom.ru)

A SPACE MISSION TO THE EARTH'S CORE is a project worth considering,
argues David Stevenson of Caltech. Space, in this case, is not
empty vacuum but dense rock, and the "spacecraft" is not of the
Voyager class, but something like a grapefruit-sized seismic
detector. It might work like this: With an explosive device of some
kind, a downward going crack in the Earth would be initiated. Into
this crack would be pored a large supply of molten iron containing
the probe. The metal-filled crack would "fall" downward owing to
gravity with a speed of about 5 m/sec and would close up behind as
it went. As Stevenson points out, cracks in the Earth regularly
relay magma from the lower depths to the surface. The probe, made
of a high-melting-point alloy, would essentially communicate with
the surface by sending out seismic waves. Stevenson
(djs@gps.caltech.edu) advances the whole idea of directly probing
the Earth's core not as a well formulated plan but as a provocation
to scientific thinking. The mission, he allows, might cost as much
as the unmanned space program but the scientific rewards could be
high: learning more about energy sources (such as radioactivity) at
great depths or the origin of hot spots (responsible, say, for
creating the Hawaiian islands), and other material properties of the
terrestrial core. (Nature, 15 May 2003; website,
www.gps.caltech.edu/faculty/stevenson/coremission )

PHYSICS NEWS UPDATE
The American Institute of Physics Bulletin of Physics News
Number 637 May 14, 2003 by Phillip F. Schewe, Ben Stein, and James Riordon

PLASMA WAKEFIELDS ACCELERATE POSITRONS. An experiment conducted at SLAC
features a number of firsts: the first time positrons have been accelerated
by the plasma wakefield method (for background, see
http://www.aip.org/enews/physnews/1998/split/pnu385-2.htm ); the first time
wakefield acceleration has been achieved with meter-size plasmas (previous
efforts have taken place in 10 cm cells); and the first to operate under
realistic accelerator conditions (in this case a 30-GeV beam of positrons).
In this UCLA/SLAC/USC collaboration, positron bursts are sent into a
1.4-meter-long chamber filled with a lithium plasma. The first two-thirds
of the burst sets up powerful electric fields in the plasma which then serve
to accelerate the trailing one-third of the b
urst to higher energy. The boosted positrons increased their energy by
about 80 MeV over a length of 1.4 m, for an acceleration gradient of about
50 MeV/m. This is comparable to the best acceleration that can be
accomplished with conventional RF techniques in which electrons or positrons
are taken up to higher energies by soaking up radio energy coupled into the
beam pipe. But the wakefield researchers expect that the gradient can be
enhanced a hundredfold to 5 GeV/m if the size of the beam pulses can be
shrunk by a factor of 10. According to Chan Joshi of UCLA (contact Chan
Joshi, joshi@ee.ucla.edu, 310-825-7279) the wakefield approach may not be
fully mature by the time the next electron-positron collider is built, but
its benefit could be tested by
installing two plasma accelerator sections, one for positrons and one for
electrons, just before the interaction point for some final energy boosting
in an existing collider. (Blue et al., Physical Review Letters, upcoming
article)

TURNING BUBBLES INTO MICROSCOPIC SYRINGES through the use of sound has been
experimentally shown by researchers in the Netherlands (Claus-Dieter Ohl,
University of Twente, 011-31-53-489-5604. c.d.ohl@tn.utwente.nl),
demonstrating a potential method for injecting drugs and genes into specific
regions of a patient's body. Taking high-speed microscopic photographs, the
researchers revealed that even bubbles much smaller than the thickness of a
human hair could transform into a needle-like tube, delivering a billionth
of a millionth of a gallon of liquid. While this sub-nanofluidic volume
seems very small, it is more than enough to transfer large molecules (such
as DNA and most drugs) into desired cells for medical therapy.
In their experiment, the researchers start with a room-temperature container
of water that was slightly "degassed," or had some oxygen gas removed from
it. Inside the water container, they create tiny bubbles between 7 and 55
microns in size. Next, they broadcast high-intensity ultrasound into the
liquid, creating supersonic disturbances known as shock waves. Slamming
against the microscopic bubbles and squeezing them into needle-like shapes,
the shock waves also introduce small amounts of surrounding liquid into the
bubble. The liquid shoots through the bubble at very high speed, punctures
its opposite end, and continues outside as a high-speed stream of fluid
resembling a syringe. Based on the speed of the flow, the researchers
expect that this liquid
stream could easily penetrate a nearby cell membrane. Dissolved drugs or
genetic material surrounding specially designed microbubbles could therefore
be injected into targeted cells. Long suspected but now confirmed, the
acoustically driven metamorphosis of bubbles into micro-syringes could
someday become a useful medical tool. (Ohl and Ikink, Physical Review
Letters, upcoming).
While this work aims to inject material deeply into living cells, other
U-Twente researchers have just introduced a new acoustic method for
manipulating cells: they devised a "sonoporation" technique which uses
gently oscillating bubbles attached to a surface to deform or even puncture
cell membranes (Marmottant and Hilgenfeldt, Nature, 8 May 2003).

FIRST-YEAR PHYSICS GRADUATE STUDENTS are on the rise at US universities, a
new AIP study shows. The number of first-year physics/astronomy students
for the year 2000 (2697) was some 5% higher than the recent low in 1997.
(In still more recent numbers for 2002, about to be published, the number of
first year grad students is some 15% higher than in 1997.) In the 1999/2000
beginning-grad cohort, foreign students (52%) outnumber US students (48%).
Chinese students (25%) make up the largest single international component,
with Eastern European students accounting for 22%, up from about 5% in the
early 1980s. Women constitute 19% of the 1999/2000 first-year physics grad
students and 29% in astronomy. Age is a factor: about 64% of the foreign
students were 2
4 or older when they began physics grad school, whereas the number for US
students is 41%. What kind of employment do these students hope for? A
majority indicated their long-term desire was an academic job. ("Graduate
Student Report: First-Year Students in 1999 and 2000," prepared by the
Statistical Research Center, AIP; www.aip.org/statistics, contact Patrick J.
Mulvey, 301-209-3070.)

PHYSICS NEWS UPDATE
The American Institute of Physics Bulletin of Physics News
Number 636 May 7, 2003 by Phillip F. Schewe, Ben Stein, and James Riordon

ULTRA-LOW-ENERGY ELECTRONS CAN BREAK UP URACIL, a new study shows. How
injurious is radiation (alpha, beta, and gamma rays or heavy ions) to living
cells? This important question has been addressed in many ways. Much
attention has centered on the secondary particles produced in the wake of
the intruding primary radiation, especially electrons (about 40,000
electrons are produced for each MeV of energy deposited) with typical
energies of tens of electron volts. Many of these secondary particles
quickly lose their energy and become attached (solvated) to water molecules
in the cell. What is the general effect of electron energies below 20 eV?
A report from three years ago (Boudaiffa et al., Science 287, 1658, 2000)
showed that electrons in the 3-20 eV range are able to produce substantial
genotoxic damage, including breakin
g single- and double-stranded DNA? What about secondary electrons with even
smaller energies?
To look at this energy range for the first time, Tilmann Maerk and his
colleagues at the Universitat Innsbruck (Austria) and the University Claude
Bernard Lyon (France) scattered a beam of sub-eV electrons from a beam of
gaseous uracil molecules. Uracil is one of the base units of RNA molecules,
and is thus a crucial component in cells. These scientists found that
uracil is efficiently fragmented by electrons with energies as small as
milli-electron-volts. It's not the electron's kinetic energy that causes
the disruption, but the electron's charge, which changes the uracil's
internal potential energy environment. Furthermore, in the process a very
mobile atomic hydrogen can be freed, which on its own, as a radical (a free
chemical unit by itself), can do
damage to biomolecules (see a movie of this process at
http://info.uibk.ac.at/ionenphysik/ClusterGroup/Uracil.html; schematic at
http://www.aip.org/mgr/png/2003/187.htm ). Maerk (tilmann.maerk@uibk.ac.at,
43-512-507-6240) says that this low-energy damage seems to be a general
result since his group has since performed similar work with thymine (a DNA
base) and have seen similar fragmentation. (Hanel et al., Physical Review
Letters, 9 May 2003; Innsbruck website,
http://info.uibk.ac.at/c/c7/c722/e-index.html )

PERFECT INSULIN CRYSTALS. Perfection is elusive both in nature and in the
laboratory, but researchers at the University of Houston have found that
crystals of insulin often grow in a perfect fashion. It is a discovery that
may lead to improvements in future microelectronics, as well as higher
quality medicines, chemicals, or devices that can benefit from improved
crystal-growing methods. The researchers (Peter Vekilov, 713-743-4315,
vekilov@uh.edu) found that as insulin proteins crystallize around a screw
dislocation defect in an existing insulin crystal, they form spiraling
hillocks of perfect crystalline insulin (see image at www.aip.org/mgr/png ).
(Screw dislocations are a common type of crystal defect that results when
there is a slight angular misalig
nment between crystal layers.) In most crystals, interactions between
stepped layers that make up the edges of a growing crystal cause the steps
to bunch up, which in turn leads to striated crystals. In addition,
competition for dissolved material carried in the surrounding solution can
also cause step bunching. Insulin, however, is unusual in that there is
there is little interaction between steps. Although the researchers say that
it is not clear whether such perfection is possible in many other
substances, by coming to understand the factors that lead to perfect growth
of insulin crystals we may soon learn how to tweak growing conditions to
improve dramatically other crystals. For example, by properly stirring a
solution, it may be possible to reduce step
bunching that results from competition for dissolved material between
different crystal regions. Alternatively, manufacturers may choose to
introduce screw dislocations to induce crystal growth, rather than allowing
crystals to form around other types of defects that tend to generate
imperfect structures. Microelectronics is one field that could benefit from
better crystal growing techniques. In particular, microchips built of
gallium arsenide are frequently much faster that ones built of silicon, but
it is currently very difficult to grow the perfect gallium arsenide crystals
necessary for chip manufacturing.. Lessons learned from studying factors
that lead to perfect insulin crystals may help solve the problem. (O. Gliko
et al., Physical Review Letters, u
pcoming article)

THE TINIEST SOLID-STATE LIGHT EMITTER, produced by Phaedon Avouris and his
colleagues at IBM, consists of a single-walled carbon nanotube (NT) strung
between two electrodes, and controlled by a third. The business part of
this minuscule transistor is a nanotube only 1.4 nm wide and tailored to be
semiconducting. In this arena electrons coming from one electrode meet with
positively charged "holes" coming from the other electrode. When the two
species meet they combine and emit a tiny burst of light. This light is
conveniently engineered to be at a wavelength of 1.5 microns, invisible to
the human eye but perfect for photonic applications. Why use a NT when a
larger piece of bulk semiconductor could also produce light? Because of the
potentially much gr
eater energy efficiency and compactness of the light emitting region.
Single-molecule light emission has been instigated before, but not under the
auspices of solid state wiring. The NT wire also seems to be robust: it is
able to carry 6 micro-amps of current, for a current density of more than
100 million amps per square cm. (Misewich et al., Science 2 May 2003.)

PHYSICS NEWS UPDATE
The American Institute of Physics Bulletin of Physics News
Number 635 May 1, 2003 by Phillip F. Schewe, Ben Stein, and James Riordon

A "WATER HAMMER" POWERS UP SONOLUMINESCENCE. In household plumbing, a water
hammer can occur when the flow of water suddenly slows, generating a
temporary vacuum and a shock wave that together violently shake the
plumbing. At this week's meeting of the Acoustical Society of America in
Nashville, Seth Putterman of UCLA (310-825-2269) described a new "water
hammer" method for generating sonoluminescence (SL), the transformation of
sound into light. This new approach yields SL flashes with much higher
powers than before. In the ordinary SL process, a sound wave enters a
liquid tank, and produces bubbles that collapse and release ultrashort
flashes of light. In the SL version of the water hammer, researchers shake a
20-inch-long, 1.5 inch diameter cylindrica
l tube with a force of 2 g's. Filled with water and a small amount of xenon
gas, the tube shakes so that water in each half of the tube travels in an
opposite direction and temporarily creates a centimeter-long region of
vacuum in the center. As the vacuum closes, it launches a large shock wave
that generates SL in the water, producing an output of approximately 300
million photons (about a hundred times greater than earlier SL experiments)
that add up to a peak power of about half a watt. The scaled-up photon
output, Putterman says, makes it possible to perform more and better
measurements of the hard-to-understand SL phenomenon. (Su et al., Physics
of Fluids, tentatively June 2003.) In a separate experiment that uses the
traditional approach of aiming
sound at a liquid tank, Putterman and colleagues have successfully achieved
SL with 1 MHz sound waves, as opposed to the 20-40 kHz waves that are
conventionally used. While MHz sound waves are currently used in various
acoustics applications, megahertz SL from a single bubble has not been
achieved before: The small wavelength of a MHz acoustical wave makes it very
challenging to control the local sound field in water to the point that a
single bubble can collapse synchronously with sound. Compared to the
kilohertz version, megahertz SL produces a markedly different spectrum of
light, and therefore the researchers are planning further investigations in
this new high-frequency realm.

NICARAGUA IS WET UNDERNEATH. A new seismic study of a rock slab deep
underneath Nicaragua shows that the slab has the highest concentration of
water of any comparable slab associated with volcanoes. Just as radar can
be used to tell you about landforms and vegetation at the surface, so
seismic waves can tell you about the lay of the land 150 km down. Geoffrey
Abers and Terry Plank, scientists from Boston University, and their
collaborator from UCSB, Bradley Hacker, observed that seismic waves at
depths of 100-150 km beneath a string of Nicaraguan volcanoes traveled as if
the rock slab down there were acting like a waveguide. From the wave
speeds, the researchers deduced that the water content of the slab was about
5%, some 2 to 3 times greater than for o
ther subducted slabs. Since water subducted along with oceanic crust
sometimes returns to the surface along with lava, one can check the elevated
water content finding. Indeed, the fluid concentration of Nicaraguan lavas
is quite high. Abers (abers@bu.edu) says that the Nicaraguan slab, and
another very "wet" slab he has studied near Guam, are quite steep (the angle
of subduction in the Nicaraguan case is about 70 degrees), which he believes
makes the slab a better conduit for fluids. (Geophysical Research Letters,
1 April 2003.)

CARBON NANOWIRE (CNW), a one-dimensional string of carbon atoms threaded
through a carbon nanotube, has been observed for the first time. Carbon
chains have been observed before, but never inside a nanotube. Yosinori
Ando and his colleagues at Nagoya University (Japan) produced the CNWs amid
a welter of nanotube whiskers by shooting an electrical arc between two
carbon electrodes, and employ not the usual helium atmosphere but one of
hydrogen. (This same team has produced the smallest nanotubes---only 0.4 nm
in diameter---and multiwalled nanotubes with the thinnest inner
diameter---only 1 nm.) Carbon nanowires should have interesting mechanical
properties; e.g., as ultrastrong fibers they might serve in Space Shuttle
nosecones or as friction-free rotati
onal bearings (see figure at http://www.aip.org/mgr/png/2003/186.htm ).
Their chemistry is also new. The allotropes of carbon are usually
classified according to the type of chemical bonding, whether of the "s"
type (the electron residing in a spherical orbital cloud) or the "p" type
(dumbbell shaped orbital). The three known carbon bondings are sp^3
(diamond), sp^2 (graphite, fullerene, and nanotubes), and sp (carbon chain).
The CNW allotrope, however, partakes of both the sp and sp^2 bondings. In
the electronic realm, CNWs might provide the smallest possible metal-metal
junction, or provide highly coherent point sources of mono-energetic
electron beams. Finally, CNWs provide a quick way to study 1-dimension
carbon chains, which might account for some
of the mysterious emissions from interstellar space. (Zhao et al.,
Physical Review Letters, upcoming article; contact Yoshinori Ando,
81-52-832-1151, x5280, yando@ccmfs.meijo-u..ac.jp; website,
http://www.meijo-u.ac.jp/ST/coe/ENGLISH/index2.html )

PHYSICS NEWS UPDATE
The American Institute of Physics Bulletin of Physics News
Number 634 April 23, 2003 by Phillip F. Schewe, Ben Stein, and James
Riordon

SHOCKING COLOR EFFECTS. A photonic crystal is a lattice of structures
(sometimes an arrangement of rods or a solid filled with a pattern of holes)
with a periodic alteration in the index of refraction. In such a material
waves with only a select band of frequencies may propagate successfully.
Other frequencies are forbidden. What happens, though, when a shock wave
moves through the lattice, momentarily compressing or expanding the
characteristic spacings? A new "computational experiment" (detailed
computer simulation) provides an intriguing answer. Evan J. Reed, Marin
Soljacic, and John Joannopoulos at MIT determine that a light beam moving in
a shock-modified photonic crystal will undergo two unexpected changes: a
Doppler shifting hundreds or even 10,000 times bigger than usual and a
bandwidth narrowing. There are plenty of phenomena that can broaden a
signal's bandwidth but none yet known that would narrow the bandwidth of an
arbitrary signal in this way (and by factors of 4 or more). As for the
Doppler shift (a change in the frequency of the light owing to its
reflection from a moving target), the light reflecting from the shock wave
can be "up converted" (e.g., turned from red light into green light) with
an efficiency that should match or exceed the up conversions achieved with
nonlinear optical materials. Furthermore, the shock conversion process is
tunable and independent of light intensity.
According to Evan Reed (evan@mit.edu, 617-253-5482) the MIT research should
generate great surprise and interest among those who work with photonic
crystals. The next step will be to implement the computational results in
the laboratory with samples and actual shock waves, although for the sake of
eventual commercial applications (frequency conversion and signal
modulation) future modifications in photonic crystals will not have to be
initiated with guns or laser pulses but with less destructive acousto-optic
effects. The photonic-crystal modulations might even be actuated with some
kind of MEMS (microelectromechanical systems) device. (Reed et al.,
Physical Review Letters, upcoming article; website http://ab-initio.mit.edu
)

FEMTOGRAM MASS DETECTION has been achieved with cantilever oscillators at
Oak Ridge National Lab. Once set to vibrating at MHz frequencies with a
diode laser, the tiny cantilevers (tiny slivers of silicon as small as 2
microns long and 50 nm thick) are exposed to an atmosphere of small
particles or molecules. Depending on how the cantilever is coated, some of
the particles will be absorbed onto the surface of the cantilever, altering
its resonance frequency in a measurable way. In a recent test the vapor
used was an acidic substance, which was absorbed with a mass change that was
noticeable at the 5 fg mass scale. Other subject particles, such as DNA,
proteins, cells, or trace amounts of various chemical contaminants, should
be detectable by this process. The experiment was carried out at ambient
conditions, with no vacuum or cryogenic temperatures. According to Panos
Datskos of Oak Ridge (pgd@ornl.gov, 865-574-6205) the mass sensitivity of
the device can be sharpened to the molecular level if the resonance
frequency can be raised from about 2 MHz at present up to 50 MHz. (Lavrik
and Datskos, Applied Physics Letters, 21 April; figure at
http://www.aip.org/mgr/png/2003/184.htm; website at www.ornl.mnl.gov )

BECs UNDERGO BRAGG EXPLOSION. Bose Einstein condensates (BEC) provide a
versatile testbed for looking at quantum phenomena. And maybe cosmology
too. In their calculations, physicists at the University of Nottingham
first load an alkali BEC into an optical lattice, a honeycomb of laser light
which holds atoms in a 3D gridwork. (For another recent BEC-in-a-lattice
story, see www.aip.org/enews/physnews/2003/split/626-1.html ) Then they jar
the cloud of atoms, setting the BEC into motion, and have it scatter from
the same "crystal" of light beams. Instead of x rays undergoing Bragg
scattering from crystallized protein, the BEC waves scatter from a crystal
of light. But as it threads through the optical lattice, the pattern of
Bragg reflections can create traveling zones (essentially self-perpetuating
solitons and local whirlpools, or vortices) where atoms in the condensate
are actually excluded (see figure at http://www.aip.org/mgr/png/2003/185.htm
). These solitons can in turn destabilize the BEC, causing it to explode
outward. The Nottingham researchers have been trying to model this explosion
using a nonlinear Schrodinger equation, a modified version of the equation
that governs electron waves inside atoms. According to Mark Fromhold
(mark.fromhold@nottingham.ac.uk, 44-0115-9515192), similar equations are
being used in the statistical study of galaxy distribution. (See for
example, Scott et al., Physical Review Letters, 21 Mar 2003)

PHYSICS NEWS UPDATE
The American Institute of Physics Bulletin of Physics News
Number 633 April 16, 2003 by Phillip F. Schewe, Ben Stein, and James
Riordon

THE FIRST SINGLE-MOLECULE, SINGLE-BASE-RESOLUTION DNA SEQUENCING has been
carried out by a Caltech group. In this new approach, the bases forming
the backbone of the typical DNA molecule are viewed one by one in the act of
replicating. To be more exact, a DNA polymerase molecule, acting as a
genetic xerox machine, copies a single strand of DNA by adding complementary
base units to it; the "fuel" for this process, the base molecules being
added, were fluorescently labeled beforehand (by attaching site-specific,
light-producing fluorophore molecules), so the DNA sequence could be
observed by microscope observations (schematic setup figure at
www.aip.org/mgr/png ). Sequencing single-molecule DNA strands is
intrinsically difficult because of the high linear data storage density: the
bases are only about 3.4 angstroms apart along the DNA helix. Past efforts
to sequence bases through their fluorescence have been complicated by
background noise, a problem avoided by the Caltech scientists through
careful use of two laser pulses, one for producing pinpoint fluorescence and
another for nulling or "bleaching" the fluorescence in order to prepare for
the next base identification.
Stephen Quake (quake@caltech.edu) and his colleagues can currently identify
no more than about 6 bases in a row, so this research is still at the
proof-of-principle stage. However, within about two years or so, Quake
believes, his process should be a factor of ten faster than standard
gel-electrophoresis techniques used to sequence DNA molecules on a wholesale
level, and several orders of magnitude cheaper. (Braslavsky et al., Proc.
Natl. Acad. Sci., 1 April 2003.)

CHARGE SYMMETRY BREAKING has been observed in two experiments reported at
the recent American Physical Society meeting in Philadelphia. In the 1930s,
physicist Werner Heisenberg proposed that the neutron and proton are simply
slightly different manifestations of the same particle, called the
"nucleon." Modern nuclear physics endorses this view: plenty of nuclear
reactions proceed exactly the same way if a proton takes the place of a
neutron, or vice versa. However, this close similarity breaks down in some
cases, leading to a situation known as "charge symmetry breaking" (CSB). In
separate experiments at the Indiana University Cyclotron Facility (IUCF) and
the TRIUMF cyclotron in Canada, researchers have made groundbreaking new
measurements of CSB (which, incidentally, is a nuclear-physics phenomenon
completely different from charge [C] conjugation in particle physics). Such
CSB measurements can provide deep insights into why nature gave the neutron
and proton slightly different masses. At an even more fundamental level, the
CSB measurements can potentially yield more precise values of the mass
difference between the up and down quarks that make up protons and neutrons.
Nuclear theorists are busily analyzing these new experimental results to
put tighter constraints on the up-down mass difference.
At the APS meeting, Ed Stephenson of Indiana University
(stephens@iucf.indiana.edu) announced the first unambiguous
identification of a rare process: the fusion of two nuclei of heavy hydrogen
to form a nucleus of helium and an uncharged pion, one of the subatomic
particles responsible for the strong force that binds nuclei together. This
process would not exist at all were it not that nature allowed a small
violation of charge symmetry. Over a two-month period, researchers observed
this rare reaction several dozen times, giving physicists enough data to
test theories of charge-symmetry breaking.
Representing a collaboration at TRIUMF, Allena Opper of Ohio University
(opper@ohiou.edu) discussed the detection of CSB in another nuclear
reaction: the fusion of a proton and neutron, which produces a charged pion
as one of its products. Viewed from a perspective or ("reference frame") at
which the proton and neutron meet at the center, the reaction, repeated man
times, produces a small excess of pions (0.17%) in a preferred direction.
Such an asymmetry is a hallmark of CSB. Taken together, these new CSB
results promise a wealth of information on such things as the slightly
different electromagnetic fields inside each nucleon. As it turns out, such
fields may contribute to the proton-neutron mass difference, as they carry
energy which convert into a small amount of mass.

TUNABLE PHOTONIC CRYSTALS. Photonic crystals affect the flow of photons in
much the same way that electronic devices affect the flow of electrons. Most
photonic crystals, however, have specific properties that cannot be varied
once the crystals are made. A few types of photonic crystals, such as fluid
suspensions of colloidal silica, can be modified on the fly, but the time
required to change configurations is inconveniently long. Researchers at
Brown University have now made photonic crystals that can be modified in
milliseconds. The tunable photonic crystals consist of a class of materials
known as holographic-polymer dispersed liquid crystals (H-PDLCs). Complex
structures are defined in the material by exposing it to an interference
pattern produced by a set of four laser beams. Liquid crystal droplets form
in regions where the laser light interferes coherently; these droplets
constitute a photonic crystal. An electric field applied to the suspension
of liquid crystals modifies the refraction index of the droplets, which
changes the spectrum of light that the photonic crystals transmits. The new
photonic crystals are easily constructed on a wide range of scales, which
allows them to affect a wide spectrum of light, and can replicate
sophisticated structures including diamond lattices as well as anisotropic
lattices that affect light differently depending on the direction of
propagation through the crystal. Potential applications of the tunable
photonic crystals include filters to selectively block certain light
frequencies. With further improvement, they may also lead other optical
devices such as to novel lasers and optical waveguides. Jun Qi of Brown
University (jun_qi@brown.edu, 401-863-3078) described the tunable photonic
crystals in a paper he presented recently at the Optical Fiber and
Communication Conference in Atlanta (for more information on the conference,
see the website www.ofcconference.org ) .

PHYSICS NEWS UPDATE
The American Institute of Physics Bulletin of Physics News
Number 632 April 9, 2003 by Phillip F. Schewe, Ben Stein, and James
Riordon

FIRST FUSION AT THE Z MACHINE was announced this week at the April meeting
of the American Physical Society in Philadelphia. For the first time,
Sandia National Laboratories' Z facility in New Mexico has created a hot
dense plasma that produces neutrons associated with nuclear fusion.
According to Sandia's Ray Leeper (rjleepe@sandia.gov), the neutrons emanate
from fusion reactions within a BB-sized deuterium capsule placed within the
central target in the Z facility, itself about a third of a football field
in diameter. While tokamaks cause fusion reactions to occur by confining
plasmas in large magnetic fields, and laser facilities focus intense beams
on or around a target, Z applies a huge pulse of electricity (about 12
million joules) with very sophisticated timing. The pulse creates an intense
magnetic field which crushes an array of 360 tungsten wires into an
ultra-light foam cylinder to produce x rays. Striking the surface of the
fuel capsule embedded in the cylinder, the x-ray energy produces a shock
wave that compresses deuterium gas within the capsule, fusing enough
deuterium to produce neutrons. Sandia researchers measured a yield of
approximately 10 billion neutrons, around the expected energy of 2.45 MeV,
corresponding to a very modest level of nuclear fusion (about 4 millijoules
of energy). The deuterium capsule reached a temperature of about 11.6
million Kelvin and was compressed from a diameter of 2 mm to 160 microns.
The whole compression took about 7 nanoseconds. Providing outside
commentary, Cornell University's David Hammer (hammer@ece.cornell.edu) said
the Sandia group performed pretty much a full set of tests to verify that
they had achieved nuclear fusion. The ZR (Z-Refurbished) facility, an
upgrade scheduled to go online in 2006, is slated to attempt scaled-up
fusion experiments. While the Z approach to fusion is a promising,
straightforward, and potentially robust method, researchers caution that
they are at the start of a very long road in investigating its feasibility
as a fusion power source.

FIRST LIGO SCIENTIFIC RESULTS. With two controlling partners, MIT and
Caltech, and two branch offices (two completely independent detectors)
located in Washington State and Louisiana, the Laser Interferometer
Gravitational-Wave Observatory (LIGO) is essentially a giant strain gauge.
In the LIGO setup laser light reflects repeatedly in each of two
perpendicularly oriented 4-km-long pipes. A passing gravity wave will
distort the local spacetime, stretching very slightly one of the paths while
shrinking the other, causing the interference pattern of the two merging
laser light beams to shift in a characteristic way. LIGO does not measure
static gravitational fields, such as those from the sun or the Earth itself.
Rather it strives to see ripples in spacetime radiated by such events as
the inspiral of two neutron stars toward each other, a phenomenon which
would typically produce a strain in the LIGO apparatus as large as one part
in 10^20. That is, a passing gravity wave is expected to change the
distance between mirrors some 4 km apart by about 10^-18 meters, a
displacement 1000 times smaller than a proton. Such a measurement
represents a physics and engineering feat of great delicacy. But at long
last the LIGO team has prepared its instrument and at this week's APS
meeting, reported its first official results from the initial "science" run
conducted over 17 days in September 2002.
In this first run no gravitational wave events were observed, but palpable
knowledge was gained as to what the sky should look like when viewed in the
form of gravity waves. So great is LIGO's sensitivity that it has been able
to set the best upper limit on the output of gravitational waves from three
of the four prime source categories. These four expected waveforms are as
follows: bursts from sources such as supernovas or gamma bursters; chirps
from inspiraling objects such as coalescing binary stars; periodic signals,
perhaps from sources like spherically asymmetric pulsars; and a stochastic
background source arising from gravity waves originating from the big bang
itself. LIGO deputy director Gary Sanders (Caltech,
sanders_g@ligo.caltech.edu) said that in three of these four categories,
had set new upper limits on the rate at which gravitational waves were being
produced. In the coalescing binary category, for instance, LIGO has
established an upper limit of 164 per year from the Milky Way, a factor of
26 better than the previous limit. Erik Katsavounidis (MIT,
kats@ligo.mit.edu) said that LIGO could establish an upper limit on
periodic signals from bright pulsars with a sensitivity of about 10^-22.
Sheila Rowan (Stanford Univ and Univ Glasgow) spoke of future operations at
LIGO. First of all, the second scientific run currently underway will be
some ten times more sensitive than the first run, the one being reported at
the meeting. If in the first science run LIGO was essentially sensitive to
gravity waves from the whole of the Milky Way, then in the second science
run (conducted Feb-Apr 2003), featuring a ten-times improvement in
sensitivity, the region of space patrolled would effectively reach out to
about 15 million light years, a realm that includes the nearby Andromeda
galaxy. (For more information about LIGO and a complete collaboration list,
see www.ligo.caltech.edu ) In its search for gravity waves, LIGO (which with
about 440 scientists is as big as the large particle physics experiments
underway at accelerators) is also collaborating with other interferometer
devices such as GEO (in Germany, www.geo600.uni-hannover.de ) and TAMA
(Japan).

PHYSICS NEWS UPDATE
The American Institute of Physics Bulletin of Physics News
Number 631 April 2, 2003 by Phillip F. Schewe, Ben Stein, and James
Riordon

THE FIRST-EVER LARGE CHINA-TAIWAN SCIENTIFIC COLLABORATION has carried out
a reactor experiment which puts a new upper limit on the neutrino magnetic
moment. Consider first the electron; it not only has electrical charge but
also spin, which means that it will act like a tiny
magnet. Even a neutral atom, because of its internal distribution of
negative and positive charge, can have a nonzero magnetic moment.
Consequently neutral atoms can be controlled, to some extent, by magnetic
fields. But what about a neutrino? Neutrinos may well possess a small
amount of mass, But what about magnetism? Can they effectively have a tiny
bit of charge or internal structure? A nonzero neutrino magnetic moment
provides the neutrino with a way to interact electromagnetically with the
world; generally the neutrino is thought to interact only via the weak
nuclear force. Evidence for nonzero magnetic moment would show up in
several ways: in anomalous electron-neutrino scattering, in radiative decays
in which the neutrino casts off a gamma ray, and in various astronomical
settings, such as supernovas. The TEXONO collaboration, using neutrinos
from the 2.9-GW Kuo-Sheng Nuclear Power Station in Taiwan, looked for a
characteristic anomalous electron energy spectrum arising from
electron-neutrino scattering. They did not see any such evidence, and from
this they derive the best direct-laboratory upper limit on neutrino magnetic
moment, 1.3 x 10^-10 times the magnetic moment of the electron (a unit also
known as the Bohr magneton). The team also derives an indirect bound on
neutrino radiative decays. (Li et al., Physical Review Letters, April 4
2003; contact Henry Wong, Academia Sinica, Taiwan, 886-2-2789-6789,
htwong@phys.sinica.edu.tw ) The TEXONO Collaboration is supported by
several research institutions (see the website at
hepmail.phys.sinica.edu.tw/~texono ) and their respective funding agencies
from Taiwan and China. An efficient flow of students and scientists moves in
both directions.

SPACESHIP TRAVEL TO ANOTHER UNIVERSE THROUGH A BLACK HOLE may be highly
improbable, but it cannot be ruled out, according to a new analysis that
explores the idea of "hybrid singularity." As science fiction fans know,
anyone who wishes to fall into a black hole and re-emerge at some distant
location or even an another universe would have to go through a forbidding
region inside the black hole known as a "space-time singularity."
Traditionally this means negotiating a region of infinite density exerting
destructive, tide-like distortions on any "extended object" such as a
spaceship, molecule, or anything that is not truly point-like. Physicists
now suspect this picture is incomplete and that a second and potentially
milder type of singularity might exist. Known as a "Cauchy horizon
singularity," it would impart only finite tidal distortions on extended
objects.
The kinder, gentler singularity should only develop when a regular stream
of matter or energy falls into the hole. Previous analyses have considered
only streams that were brief bursts. But long-duration "non-compact" streams
of radiation, like the cosmic microwave background, can also fall into the
black hole. In a more comprehensive analysis that takes these
"non-compact" sources into account, Lior Burko of the University of Utah
(burko@physics.utah.edu) explores how a black hole's interior is affected
by such infalling radiation. If the non-compact sources are weak, Burko
shows, a hybrid singularity forms: a strong sector (inevitably destructive)
and a weak sector (finite tidal distortions). Conceivably, a spaceship
entering through the weak sector could travel unscathed to another part of
space-time. If the perturbations due to non-compact sources are large,
however, Burko shows that the singularity ends up being strong, and
destructive, everywhere in the black hole. Whether black hole singularities
in our universe are strong-only or hybrid in nature depends on incompletely
known cosmological parameters (such as the expansion rate of the universe
and the nature of dark energy). Several factors may ultimately rule out the
possibility of hyperspace travel. They include: (1) the possibility that
"weak" sectors may still be much too hazardous for travel; (2) overwhelming
effects on the black hole from actual non-compact sources and (3) a working
theory of quantum gravity, which may reveal other factors that rule out
hyperspace travel. But for now, Burko says, the possibilities are open.
(Burko, Physical Review Letters, 28 March 2003)

STRETCHABLE GOLD CONDUCTORS. New, stretchable gold conductors have been
developed by Princeton University researchers. The conductors may be the
answer to problems that arise when engineers build oddly shaped devices
(such as retina-inspired photosensor arrays, for example), or when making
connections to sensors attached to the skin or other flexible surfaces. The
researchers (Stephanie Lacour, 609-258-3582, slacour@princeton.edu) built
their new conductors by depositing layers of gold about 100 nanometers thick
on a substrate of poly-dimethyl siloxane (PDMS), a type of plastic material
commonly used in microelectronics-related research and manufacture. (An
underlying 5-nanometer layer of chromium helped to ensure that the gold
would adhere to the PDMS.) Once they had deposited the gold, the researchers
found that compressive stresses in the metal caused the film to buckle,
forming parallel wrinkles in strips of the material. The wrinkles smooth
out, as expected, when the film is stretched by a few tenths of a percent,
but surprisingly the material remained conducting as the film was stretched
up to twenty-three percent beyond its relaxed length. Simple strips of gold
film, on the other hand, break when stretched as little as one percent. As
it was stretched, cracks developed in the gold layer, but current continued
to flow along the strip. The researchers suspect that a thin conductive
metal layer, perhaps only a single molecule thick, may bridge the cracks and
account for the conductivity of the stretched film, although confirmation of
this hypothesis is still forthcoming. (Lacour et al., Applied Physics
Letters, 14 April 2003)

PHYSICS NEWS UPDATE
The American Institute of Physics Bulletin of Physics News
Number 630 March 27, 2003 by Phillip F. Schewe, Ben Stein, and James
Riordon

SUPERCONTINUUM LIGHT IS RED-HOT. Lasers usually produce a single pure
color, or more precisely, light with a narrow range of wavelengths. But
laser light traveling through special optical fibers can produce
"supercontinuum light," multicolored light with many of the same desirable
properties as ordinary laser light, including a bright, narrow, beam, and
coherence, in which the individual light waves in the beam have a precisely
defined interrelationship. Many new advances in the production of
supercontinuum light were presented at this week's Optical Fiber
Communication Conference and Exposition (OFC) in Atlanta. To generate
supercontinuum light at the 1550-nm wavelength used in telecom applications,
Jeff Nicholson (jwn@ofsoptics.com) of OFS, Inc. and his colleagues use an
erbium-doped fiber laser, in which erbium atoms in an optical fiber amplify
incoming laser light to the desired level. With this laser, the researchers
send intense, 100-femtosecond pulses through several meters of highly
nonlinear optical fiber, which interacts with the light to produce the
multiple colors. With this all-fiber design, based on standard telecom
manufacturing technology, Nicholson and colleagues produced low-noise
supercontinuum light that spans an octave of bandwidth (the frequencies at
the high end of its spectrum are twice that of the low-end). This is the
widest supercontinuum ever produced with an all-fiber laser.
In a different approach that employs continuous streams of laser light
rather than short pulses, Akheelesh Abeeluck of OFS (abeeluck@ofsoptics.com)
and co-workers use a Raman fiber laser, in which an optical signal is
amplified by a second, lower-wavelength light source. In their work,
Abeeluck splices the Raman fiber laser to a nonlinear fiber in order to
produce supercontinuum light. With 821 mW of power launched into 4.5 km of
fiber, they achieved a continuum with a bandwidth greater than 247 nm.
While not as wide a continuum as with the all-fiber laser, it is a
potentially high-power continuous source of light. In a third example,
Zulfadzli Yusoff of the University of Southampton (zuy@orc.soton.ac.uk) and
colleagues send intense picosecond pulses through a fiber with a special
geometric pattern of holes running along its length, causing the light to
interact with the fiber in a nonlinear fashion, converting the
single-colored laser light into a broad spectrum of colors. In his work,
Yusoff then carries out a "spectral slicing" method that uses a filter to
separate these colors. The separated colors then travel through individual
fibers. This approach might reduce the complexity of producing the multiple
colors of light that travel down modern transmission systems, leading to
cost savings. Among other applications, supercontinuum light could provide
high-quality broadband light for a medical imaging technique known as
"optical coherence tomography" which can yield detailed images of human
tissue.

WATCHING BRICKS AGE. Civil engineers and materials scientists have long
known that clay bricks and other fired ceramics expand as they age owing to
the absorption of water from the atmosphere. In general, however, studies of
moisture expansion in bricks have been limited to freshly fired bricks over
short timescales. Now researchers from the University of Manchester
Institute of Science and Technology and the University of Edinburgh have
experimentally investigated expansion in bricks over periods extending back
to Roman times, about 1900 years ago. They conclude that brick expansion is
governed by a power law. Specifically, bricks expand in proportion to time,
raised to the quarter power, as opposed to the logarithmic expansion with
time predicted by studies over shorter time scales. The researchers (M. A.
Wilson, 44-0161-200-4245, moira.wilson@umist.ac.uk) propose that the power
law moisture expansion is consistent with the ceramics absorbing water that
diffuses through atomic scale pathways in the material. The new theory
should help in the engineering of brick structures intended to last a
century or more by allowing designers to account for expansion that might
otherwise lead to cracks. The power law may also be handy for archeological
dating of bricks and ceramics. For example, archeologists could measure the
dimensions of a piece of ceramic, and then bake out any moisture it may have
absorbed to determine its size at the time that it was first fired. The age
of the sample can be inferred from the contraction as the ceramic dries out.
(M. A. Wilson et al., Physical Review Letters, 28 March 2003)

GAMMA RAY BURSTERS AND SUPERNOVAS go together, at least in one instance.
GRBs represent some of the most violent events in the universe and have been
the subject of intense study and conjecture. One theory holds that GRBs are
associated with supernovas
(http://www.aip.org/enews/physnews/2000/split/512-3.html ) This
hypothesis is bolstered by new observations by the Chandra X-Ray Observatory
of GRB 020813, a burster object discovered previously by the High-Energy
Transient Explorer (HETE). The x-ray spectrum contains characteristic
signs---the presence of ionized silicon and sulphur---of supernovas. The
new results were announced this week at the meeting of the High Energy
Division of the American Astronomical Society (AAS). (chandra.harvard.edu
)

THE PHYSICS OF SPEAR THROWING. Atlatl is the Mexican name for a spear
thrower, a stone age weapon used now not so much for hunting or warfare but
for sport (www.worldatlatl.org ). As with a bent bow or a stretched rubber
band, an atlatl enhances the hurling power of the human arm by storing
energy in a storage medium (in this case a spring). It also extends the
lever arm between the spear and wrist, imparting more velocity. Recently
Richard A. Baugh used high-speed video to study the performance of a modern
atlatl over a variety of values for wrist torque, hand position, and other
factors. The typical speed for a hurled 50-gram dart was 25 m/sec. The mean
thrown distance in one test was 66 meters. (Baugh, American Journal of
Physics, April 2003)

PHYSICS NEWS UPDATE
The American Institute of Physics Bulletin of Physics News
Number 629 March 19, 2003 by Phillip F. Schewe, Ben Stein, and James
Riordon

THE SHARPEST EVER OPTICAL IMAGE OF MOLECULAR VIBRATIONS, revealing details
as small as 20 nanometers, has been produced by a Rochester-Harvard-Portland
State collaboration (Lukas Novotny, 585-275-5767 ,
novotny@optics.rochester.edu). The image shows individual carbon
nanotubes with single-atom-thick walls (see figure at www.aip.org/mgr/png ).
Looking beyond this result, the researchers are striving for even higher
sensitivity, which could supply very useful images of proteins, only 5-20
nanometers in size. Other, non-optical imaging techniques, such as scanning
tunneling microscopy, can show smaller details, but this is the highest
resolution image that uses light, a probe that can potentially extract lots
more information. The researchers employed a sophisticated version of
"near-field optical microscopy," in which a small probe (in this case, a
gold wire with an extremely narrow tip) is placed very close to the surface.
With the wire only a few nanometers away from the surface, researchers
circumvented the usual roadblock to resolution, known as the "diffraction
limit," in which optical details are ordinarily limited to half the
wavelength of the light being used. In their technique, called "near-field
Raman spectroscopy," the researchers shine laser light at the gold wire. The
light strikes the wire's electrons, which then generate electric fields.
These fields interact with vibrating atoms in the sample, which then release
light of specific colors (frequencies). The spectrum of frequencies provides
information on the chemical composition and molecular structure of the
sample. From this information, an image can be created. In designing their
probe, the researchers made use of the "surface-enhanced Raman scattering
effect," in which the interaction with atomic vibrations is greatly
increased by the use of nanometer-sized metal particles (in this case, the
tip itself). In the future, researchers hope to use their technique to
determine presently unknown structural details of carbon nanotubes, such as
the different ways the nanotubes can interconnect with one another. With
better resolution, the researchers hope to take detailed pictures of
proteins in cell membranes. Such data can potentially shed new insights on
how proteins act in a cell membrane and offer clues for designing better
drugs. (Hartschuh et al., Physical Review Letters, 7 March 2003)

HOW DOES THE SUN SHINE? The SNO and Super-Kamiokande detectors have done a
handy job of accounting for the neutrinos coming from the decay of boron-8
nuclei in the sun. But the flux from B-8 decays represents a mere 0.02% of
the predicted flux of solar neutrinos, and one
wants to study other types of nu production in order to get a better grip
on nuclear physics in the sun's core. One would especially like to know
more about neutrinos from Be-7, N-13 and O-15 decays (catalyzed by
carbon-12), and from proton-proton reactions. (The p-p neutrinos, probably
amounting to 90% of the sun's nu flux, have relatively low energies, below
0.5 MeV, whereas the nu's seen directly in terrestrial detectors typically
have been in excess of 5 MeV.) In the 1930's, nuclear pioneer Hans Bethe
argued that energy produced in the nuclear reactions involving the heavier
elements (the CNO cycle) were a more important energy-producing mechanism
for the Sun than was the fusion of the lighter elements (the p-p cycle).
Nowadays solar scientists believe the CNO reactions are predominant for
stars a bit heavier than our sun but that in the sun itself the p-p cycle
will be more important. A new paper by John Bahcall and Carlos Pena-Garay
(Institute for Advanced Study) and Concha Gonzales-Garcia (Stony Brook)
addresses this issue using recent data from solar neutrino and reactor
experiments. Bahcall and his colleagues determine that the fraction of
energy produced in the sun via CNO reactions is less than 7.3%. This is a
tenfold improvement over the best previous estimation for the CNO
contribution. (Physical Review Letters, upcoming article; contact John
Bahcall, jnb@ias.edu, 609-734-8054; see neutrino website at
www.sns.ias.edu/~jnb )

BLOOD VESSEL NETWORKS. A new mathematical model is leading to insights
about the formation of blood vessel networks. The model, proposed by
researchers from several Italian institutions (contact A. de Candia,
decandia@na.infn.it, 011+39-081676805), accurately mimics vascular
structures formed by cells randomly spread on a gel matrix. Chemical cues
entice cells on a growing medium to migrate and aggregate into groups. Below
a certain cell density, the model and related experiments show many
disconnected groups are formed. Above a critical density known as the
percolation limit, a spanning cluster of cells connected across large
distances is formed (images at www.aip.org/mgr/png/2003/182.htm ). Exactly
at the percolation threshold, such a cluster exhibits a fractal structure
with a fractal dimension of about 1.9. (The fractal dimension specifies how
much of the available space is filled. For a 2-dimensional gel plate, the
surface is entirely filled at a fractal dimension of 2.) In addition, both
experiment and the new model point out that the fractal dimension is
different when the cells are observed at different scales. At scales of
about 0.8 millimeters or less, the fractal dimension of the cell networks
drops to about 1.5. The researchers speculate that the change in dimension
may be indicative of the dynamics that led to the formation of the cellular
networks in the first place. The good agreement between the model and
in-vitro experiments on gel growing media suggests that we may soon gain a
better understanding of the formation of vascular networks in living
creatures, as well as the pathological vascular formation that accompanies
certain cancers and other ailments. (A. Gamba et al., Physical Review
Letters, 21 March 2003)

PHYSICS NEWS UPDATE
The American Institute of Physics Bulletin of Physics News
Number 628 March 13, 2003 by Phillip F. Schewe, Ben Stein, and James
Riordon

LEFT HANDED MATERIALS (LHM), materials with a negative index of refraction,
can in principle focus light without the need for curved surfaces. The first
observation of such a "meta-material" (consisting of alternating layers of
metal rods and "C" shaped rings lodged on a honeycomb array of printed
circuit boards) came three years ago (see Update 476,
www.aip.org/enews/physnews/2000/split/pnu476-1.htm ). Then some
theorists said it couldn't be done. Now scientists at several labs say it
can be done. At last week's meeting of the American Physical Society (APS)
in Austin, Texas, two labs reported devising LHMs of their own and
demonstrating a negative-index behavior when microwaves were sent into a
wedge-shaped LHM "prism." A group from MIT (represented at the meeting by
Andrew Houck) said that microwaves entered an LHM sample and, sure enough,
the light waves were refracted according to Snell's law, the classic
equation for prescribing what happens when light goes from one medium into
another, but with a negative sign. The MIT experiment also provides
evidence that light from a point source can be focused with a flat
rectangular slab of LHM material (see also Houck et al., upcoming article
in Physical Review Letters). Patanjali Parimi (Northeastern Univ.) also
reported at the meeting that his team of scientists had observed
negative-index propagation on microwaves through a LHM sample (for
background and some simple movies, see sagar.physics.neu.edu/ ).
Two theorists present at the meeting, Clifford Krowne (Naval Research Lab)
and Alexandre Pokrovski (Univ. Utah), affirmed that the experimental results
had indeed established the existence of working left handed meta-materials
but that an earlier criterion thought necessary for LHM behavior, namely
that the material's permittivity (a measure of the material's response to an
applied electric field) and its permeability (a measure of the material's
response to an applied magnetic field) both had to be negative, was not
strictly required. Potential applications in the cell-phone industry alone
are many: LHM devices would be handy for filtering, steering, and focusing
microwaves. Furthermore, one would expect novel optical effects if negative
index-of-refraction materials could be extended into the visible light
range.

THE GIANT PLANAR HALL EFFECT is the name for a new type of
magnetoresistance (MR) seen in an experiment with ferromagnetic
semiconductors performed by a Caltech-UC Santa Barbara team of physicists.
MR effects are important in the huge magnetic read-head industry (where a
tiny magnetic artifact, such as a magnetic bit written in a storage medium,
is transformed into a large electrical artifact signal, such as an abrupt
change in resistance) and are also central to the development of
spintronics, the new form of electronics in which electron spin and not just
electron charge is instrumental in conducting high-speed transactions. In
the usual Hall effect, current flowing along a planar conductor is slightly
swept to the side when a magnetic field, oriented perpendicular to the
current and to the plane, is turned on. In the Caltech-UCSB experiment, the
applied magnetic field lies in the conducting plane, and the result is to
lower resistivity along several specific directions, encouraging a
corresponding pattern of current flow. This type of anisotropic MR has
previously been seen in magnetic metals, but the effect was weak. In the
present experiment, carried out with a magnetic semiconductor (GaMnAs), the
effect is 10^4 times stronger. For this reason Michael Roukes
(roukes@caltech.edu, 626-395-2916) believes that once the temperature at
which the materials can no longer retain a magnetic orientation (the "Curie
temperature") can be raised to more practical levels (this experiment was
carried out at below 45 K), the giant planar Hall effect could hasten the
onset of better magnetic resonance microscopy and magnetic random access
memory (MRAM) components, advanced magnetic sensors and memory components,
and, perhaps ultimately elements for solid-state quantum computers. (Tang et
al., Physical Review Letters, 14 March 2003, contact also David Awschalom,
awsch@physics.ucsb.edu).

DNA FUEL FOR FREE-RUNNING NANOMACHINES. More than just a blueprint for
life, DNA is proving to be one of the most versatile materials in
nanotechnology. A DNA molecule is made from 4 building blocks--the chemical
bases A, C, G, and T. Nanotechnologists take advantage of the fact that
they can obtain DNA strands with any sequence of bases to design strands
that bind together to make novel structures. G always binds to C, and A is
similarly complementary to T. Researchers at Bell Labs/Lucent Technologies
and the University of Oxford (contact Bernie Yurke, Yurke@lucent.com and
Andrew Turberfield, a.turberfield@physics.ox.ac.uk) have previously
constructed short strands of synthetic DNA that bind together to make a
simple molecular machine---a pair of molecular tweezers that can be opened
and closed by adding additional DNA strands (Yurke et al., Nature, 10 August
2000; see http://www.nature.com/nsu/000810/000810-10.html). Now, they have
made a fuel, consisting of DNA loops, that can act as a source of energy for
DNA-based molecular motors. The loops react very slowly unless a specially
designed DNA strand is present to catalyze the reaction by forcing loops
open. They propose that this principle could be used to make a molecular
motor (not yet built). The motor would act as a catalyst,pulling open two
complementary DNA loops. The opened loops would bind to each other,
exerting a force in the process which could for example cause the motor to
rotate or move down a track. The motor would slowly deplete the DNA
fuel--and run freely until the fuel was exhausted. Possible applications of
artificial molecular motors include nanoscale conveyor belts that carry
molecular cargo in a nanoscale asssembly line. (Turberfield et al., Physical
Review Letters, upcoming article).

PHYSICS NEWS UPDATE
The American Institute of Physics Bulletin of Physics News
Number 627 March 7, 2003 by Phillip F. Schewe, Ben Stein, and James
Riordon

MICROFLUIDICS is a traffic control system for sampling, sorting, and mixing
mesocopic objects. The objects are often biological---cells, proteins,
chromosomes in a solvent---and the platform is often a lithographically
patterned chip on which fluids are urged through microchannels using volts,
heat, or even peristaltic pressure. Microfluidics was a large topic at this
week's March Meeting of the American Physical Society (APS) in Austin, Texas
(http://www.aps.org/meet/MAR03/baps/index.html ). Here are some
highlights.
Carl Hansen (Caltech) described a device with the largest degree of
integration yet achieved: a chip with 1000 250-picoliter chambers with
attendant valves for controlling flow and mixing (see also Science, 18
October 2002). Another device in the Caltech lab of Stephen Quake allows
the careful metering of reagents in order to facilitate protein
crystallization under a variety of conditions (pH, viscosity, surface
tension, 48 different solvents, etc.) on a huge scale (144 parallel
reactions can take place) and with a minimum of means---only 10 nl of
precious protein samples are needed, 100 times less than with usual methods
(see also Proc. Natl. Acad. Sci., 24 Dec 2002). In this way, many proteins
have been turned into crystals, often in the space of hours rather than
days. Indeed some protein species were crystallized for the first time.
The crystals can then be bombarded with x rays in order to determine
molecular structure.
David Grier (Univ. Chicago) reported on a method called holographic optical
tweezers, in which a beam of laser light, sent into a hologram, is divided
into a myriad of sub-beams which can independently suspend and manipulate
numerous tiny objects for possible transportation, mixing, or reacting.
Grier showed movies of ensembles of micro-spheres moved into patterns and
even set to spinning by the holographically sculpted light fields. Applied
to fluid samples of biomolecules, the holographic multiplexing produces what
Grier calls "optical fractionation," an optical equivalent of gel
electrophoresis, in which electric fields are used differentially to drive
and separate macromolecules. In the flexible Chicago approach, there is no
viscous gel, and a deft change in the computer-generated hologram or the
laser wavelength can quickly bring about sorting of objects ranging from the
100-nm size (viruses) up to the 100-micron size scale.
Meanwhile, Jochen Guck (Univ. Leipzig) subjects fluid-borne cells to a pair
of laser beams which stretch the cells and probe their elasticity. In
general sick cells are softer (by a factor of 2 to 10) than healthy cells.
In this way, Guck's "optical stretcher" can "feel" the difference between
normal and abnormal at a rate of hundreds of cells per hour, compared to
typical rates of 10 cells per day using other elasticity-measuring methods,
thus reducing the need for biopsies requiring larger tissue samples. The
Leipzig device might even be able to tell the difference between ordinary
cancerous cells from the even softer metastasizing-capable cells.

THE SEARCH FOR AN RNA "EVE," a hypothetical ancestor of some or all of the
types of RNA now known, might be possible using a technique pioneered by
scientists at MIT's Whitehead Institute. Just as DNA samples are used by
paleo-anthropologists to study the spread of humans to different part of the
world, and by evolutionary biologists to study connections among various
lineages on the tree of living organisms, so too there might be ways of
studying the origins of RNA, or at least the relation between RNA foldedness
and biochemical function. Unlike DNA, its double-stranded cousin, RNA
starts out single-stranded, but can at many places along its length double
over on itself to arrive at complicated, twisted shapes.
Speaking at the APS March Meeting, Erik Schultes (MIT-Whitehead) reported
on an experiment in which a particular sequence of RNA bases could, by
altering one base at a time, take on rather quickly the identity of either
of two very different ribozymes (RNA molecules that can catalyze reactions)
with two very different functions, one for cleavage and one for ligation.
Continuing to substitute different bases in a clever way, the researchers
noticed that they could retain the functionality of the two RNA species
(that is, the ribozymes went on performing their cleavage or ligation jobs)
even though the two were getting progressively further apart in "sequence
space." At the end one could look at the two contrasting ribozymes, with
different function and very different sequences, and hardly suspect that
they had a common origin. Schultes (schultes@wi.mit.edu) compared this to
transforming the word cat into the word dog through a sequence of
single-letter "mutations," each one of which resulted in a legitimate word:
cat-cot-cog-dog (for background see Science, 21 July 2000).
At the same RNA session Ranjan Mukhopadhyay (ranjan@research.nj.nec.com)
reported that he and his colleagues at NEC Laboratories in New Jersey have
found that a typical RNA sequence with its 4-base chemical code folds more
predictably and stably than would hypothetical RNA sequences based on a
two-base or six-base "alphabet. Both 4-base and 6-base RNA proved to be
more stable than 2-base RNA. Furthermore, 4-base RNA possessed more stable,
foldable structures than 6-base RNA (just as it is easier to form 4-letter
Scrabble words than it is to form 6-letter words).
In other theoretical work, Ralf Bundschuh of Ohio State
(bundschuh@mps.ohio-state.edu) and Terence Hwa of UC-San Diego have
showed that RNA could exhibit several different "phases," just as water can
exist on a pressure-versus-temperature phase diagram in the solid, gaseous,
or liquid forms. In the case of RNA, Bundschuh showed mathematically, RNA
could exist in a normal, glassy, molten, or denatured phase. At low
temperatures, for instance, in the "glassy" phase, a given RNA sequence can
get stuck in a random structure. At higher temperatures, RNA can assume a
more flexible molten state, in which it is free to fold into a variety of
different shapes.

PHYSICS NEWS UPDATE
The American Institute of Physics Bulletin of Physics News
Number 626 February 26, 2003 by Phillip F. Schewe, Ben Stein, and James
Riordon

3600 ATOMS IN TWO PLACES AT ONCE. Bose Einstein condensates (BEC), clouds
of ultracold atoms which fall together into a single coherent state,
continue to be a marvelous working material for studying subtle quantum
effects. Last year physicists at the Max Planck Institute for Quantum
Optics (MPQ) managed to load a BEC of rubidium atoms into a
three-dimensional optical lattice, an artificial crystalline environment in
which crossing laser beams provide the forces needed to pinion atoms in the
3D equivalent of an egg crate. Moreover, by a delicate modification of the
laser light the resident atoms could be made to undergo a quantum transition
between two phases. In one phase the atoms constitute a superfluid: all the
atoms have a coordinated wave function, but the number of atoms in any one
"well" in the egg carton is unknown. In the other phase the atoms
constitute an insulator: the number of atoms in each well is known exactly
to be equal to one, but the atoms are all uncoordinated with respect to each
other (that is, they no longer can be considered a coherent quantum
material). These were the results as of a year ago (see Greiner et al.,
Nature, 3 January 2003.) Speaking at last week's meeting of the American
Association for the Advancement of Science (AAAS) in Denver, Immanuel Bloch
reported that he and his MPQ colleagues have exploited the fact that the Rb
atoms possess two magnetic substates and have succeeded, by a further
adjustment of the confining laser beams, to separate each atom into two
entangled spatially separated parts. The researchers are also attempting
to get the different diploid atoms (an average of 3600 per plane in the
lattice) to interact; one aim is to engineer an unprecedented degree of
quantum entanglement, possibly for computational purposes.

TUNABLE OPTICAL FIBERS. Optical fibers regularly carry billions of phone
conversations and other data transmissions every day and are a fundamental
part of optical sensing and numerous medical applications. The photonic
devices responsible for all this traffic are being made even more efficient
and versatile by handing over some of the switching and reconfiguring chores
to the fibers themselves---the trunk lines linking all the optical nodes. An
active optical fiber, which can tunably filter light at different
frequencies, has been created by infusing microfluidic plugs, spaced at
characteristic (periodic) intervals along the fiber, into air holes running
parallel to the passageway for the light at the center of the fiber (see
figure at http://www.aip.org/mgr/png/2003/180.htm ). The arrays of
microfluidic plugs along the light path serves as a diffraction grating for
producing the photonic-crystal effect. In other words, the presence of the
fluids is used to change the refractive index periodically, and hence the
transmission properties, of the fiber. The creators of this new
microstructured optical fiber (MOF), Charles Kerbage (OFS Laboratories in
Murray Hill, NJ; kerbage@ofsoptics.com) and Ben Eggleton (University of
Sydney, egg@physics.usyd.edu.au), say that this is the first time a tunable
grating has been achieved with microfluids, and that this provides (in
addition to the switchability) a very high index of refraction when compared
to conventional gratings. (Applied Physics Letters, 3 March 2003)

SHAKEN NOT STIRRED. The progression toward smaller and smaller electrical
and mechanical components presents tremendous challenges to engineers and
scientists as they strive to create devices on scales measured in microns
and nanometers. One solution may be to develop materials that automatically
arrange themselves in useful patterns. Now a collaboration of researchers
(Igor Aronson, aronson@msd.anl.gov, 630-252-9725) at Argonne National
Laboratory and Institute of Physics for Microstructures of the Russian
Academy of Sciences has developed a new method for encouraging microscopic
particles to self assemble into desired complex patterns. The technique is
inspired by the patterns formed in shaken mixtures of much larger granular
materials.
Numerous, beautiful experiments involving agitated containers of sand, ball
bearings, or other granular materials have shown that the combination of
gravity and inter-particle forces from collisions can lead to a rich variety
of patterns, ranging from particle-like localized excitations known as
oscillons to honeycomb shapes to chaotic swirls (Update 264). Other studies
have helped to explain why large and heavy brazil nuts sometimes rise to the
top in shaken containers of mixed nuts (Update 132). The new research
extends such experiments into microscopic regimes.
Rather than mechanically agitating tiny grains to create self assembled
patterns, however, the method relies on electrostatic fields to drive
metallic microparticles immersed in liquids. The researchers placed
120-micron bronze spheres in a mixture of toluene and ethanol trapped
between glass plates. The plates were coated with thin layers of transparent
conducting material, and an electric field of up to 3 kilovolts per
millimeter was applied between them. Particles that contacted the lower
plate acquired a charge and were repelled toward the upper plate. If the
upward electrostatic force is sufficient to overcome gravity, the particles
fly upward, contact the upper plate where their charge is reversed, and then
are forced back down again. In effect, the alternating charge on the
particles is analogous to shaking a container of macroscopic grains. As in
the classic granular material experiments, varying the conditions causes the
particles to form vortices, pulsating rings, honeycomb patterns, or other
structures (see figure at www.aip.org/mgr/png ). Ultimately, say the
researchers, studies such as this may allow us to design systems that
spontaneously self assemble into useful structures on increasingly tiny
scales. (M. V. Sapozhnikov, Physical Review Letters, upcoming article)

PHYSICS NEWS UPDATE
The American Institute of Physics Bulletin of Physics News
Number 625 February 19, 2003 by Phillip F. Schewe, Ben Stein, and James
Riordon

FROM FEMTOCHEMISTRY TO ATTOPHYSICS. Amid a fast game in a vast venue,
sports photography seeks to freeze motion and isolate small portions of
space for special consideration. In the scientific world of the ultrafast
and ultrasmall, stroboscopic effects are achieved with greatly attenuated
laser pulses. The advent of laser light served up in femtosecond (or 10^-15
second) bursts has helped to elucidate the molecular world by freezing
their vibrational and rotational motions. Scientists would of course like
to instigate and monitor even shorter times and distances.
A collaboration between scientists at the Technical University of Vienna
and the Max Planck Institute for Quantum Optics (MPQ) has now done precisely
this. They have produced a series of 2.5-fsec pulses, each consisting of
only a few cycles of a carrier light signal modulated within an amplitude
envelope. In the case of the Vienna-MPQ experiment, however, all the pulses
are identical (a feat not achieved previously) and the phase of the carrier
wave within the envelope is controlled with a time resolution of about 100
attoseconds.
When the intense (100 GW) few-cycle pulse strikes an atom, an electron can
be stripped away quickly, and reabsorbed just as quickly. This violent
excursion results in the emission of a sharp x-ray spike with a duration
even shorter than the pulse that excited the reaction. In fact the x-ray
pulses are about 500 attoseconds long. Moreover, because all the waveforms
of the optical pulse are identical, and controlled, the subsequent electron
motions and x-ray emissions are also highly controlled and reproducible. At
a talk at this week's meeting of the American Association for the
Advancement of Science (AAAS) in Denver, Vienna physicist Ferenc Krausz said
that this sub-femtosecond control of electron currents represented true
attophysics, a new technique for directing and watching atomic processes at
unprecedentedly short time intervals. (See Baltuska et al., Nature, 6
February 2003.)

A NEW LIMIT ON PHOTON MASS, less than 10^-51 grams or 7 x 10^-19 electron
volts, has been established by an experiment in which light is aimed at a
sensitive torsion balance; if light had mass, the rotating balance would
suffer an additional tiny torque. This represents a 20-fold improvement
over previous limits on photon mass. Photon mass is expected to be zero by
most physicists, but this is an assumption which must be checked
experimentally. A nonzero mass would make trouble for special relativity,
Maxwell's equations, and for Coulomb's inverse-square law for electrical
attraction. The work was carried out by Jun Luo and his colleagues at
Huazhong University of Science and Technology in Wuhan, China
(junluo@mail.hust.edu.cn, 86-27-8755-6653). They have also carried out a
measurement of the universal gravitational constant G (Physical Review D, 15
February 1999) and are currently measuring the force of gravity at the
sub-millimeter range (a departure from Newton's inverse-square law might
suggest the existence of extra spatial dimensions) and are studying the
Casimir force, a quantum effect in which nearby parallel plates are drawn
together. (Luo et al., Physical Review Letters, upcoming article, probably
28 Feb)

A MOLECULAR SWITCH TOOK ONLY 47 ZEPTO-JOULES (47 x 10^-21 joules, or 0.3
eV) to operate in a recent experiment, some 10,000 times less than
transistor switches used in current high-speed computers. The molecular
switch in question consists of rotating one of the four phenyl legs attached
to a complicated porphyrin molecule (abbreviated as Cu-TBPP) from one stable
position to another. A group of scientists from the University of Basle,
IBM Zurich, and the CEMES-CNRS Lab in Toulouse used an atomic force
microscope (AFM) tip both to rotate the leg and to measure the force
expended and energy used. The use of a single chemical bond as a switch
would greatly reduce the power dissipation in electronic circuits, but this
new development will take time to implement, along with other
molecular-electronic elements. (Loppacher et al., Physical Review Letters,
14 February 2003; contact Christian Loppacher, loppacher@iapp.de,
49-351-4633-4903; http://www.iapp.de/iapp/index.php )

PHYSICS NEWS UPDATE
The American Institute of Physics Bulletin of Physics News
Number 624 February 13, 2003 by Phillip F. Schewe, Ben Stein, James
Riordon

A PINPOINT PRECISION MAP of the cosmic microwave background, reported this
week at a press conference by scientists associated with the orbiting
Wilkinson Microwave Anisotropy Probe (WMAP), brings the early universe into
sharper focus. The credibility of WMAP's pronouncement rests on three
things: its angular resolution is some 40 times better than that of its
microwave predecessor, the Cosmic Background Explorer (COBE); it
comprehensively surveyed the entire sky for a whole year (3 more years of
data is yet to come); and it measures the polarization of the microwave
radiation; the orientation of the radiation arises partly from the last
scattering of light at the time of "recombination," when stable atoms
formed for the first time, and partly from the time when ultraviolet
radiation strewn by the first generation of stars ionized once again a lot
of atoms in space. Here are a few of the salient numbers coming out of the
WMAP analysis: the time of recombination was 380,000 years after the big
bang; the era of the first stars was about 200 million years along
(surprisingly early); the age of the universe is 13.7 billion years; and the
accounting of matter in the universe is as follows: atomic matter makes up
about 4%, dark matter about 23%, and dark energy 73%. (Websites:
http://map.gsfc.nasa.gov/;

http://www.gsfc.nasa.gov/topstory/2003/0206mapresults.html
)

SALT: THE MOVIE. Solid, liquid, melting, and freezing are concepts that
refer to bulk matter, and not to individual atoms. But what about a cluster
of a dozen atoms? Louis Bloomfield (University of Virginia) has assembled a
nano-sized grain of salt, a seven-atom blob of consisting of 4 cesium atoms
and 3 iodide atoms. Compare this to an ordinary salt grain, with a size of
.2 mm and about 1.5 million atoms along each side of its cubical structure.

By spraying this cluster with picosecond pulses of light, Bloomfield has
been able to make a "movie" of sorts showing how the cluster rearranges its
geometry: sometimes a 2x2x2 cube, sometimes a flat 2x4 ladder, sometimes an
octagonal ring, all by virtue of the cluster's own internal thermal energy;
they don't image the cluster directly, but their locations can be inferred
from a mixture of measurement and theory (for figures and cool movie, see
http://rabi.phys.virginia.edu/research/ ). Separate laser pulses are
used to heat or to view the clusters. One outcome of the experiment:
"melting" of the tiny crystal begins at a "temperature" of 225 C rather than
626 C, the melting temperature of the bulk material. Studies like this are
pertinent to the production of nm-sized circuitry since one should know
whether a wire or some other structure will retain its basic shape or shift
into something else over time. (Dally and Bloomfield, Physical Review
Letters, 14 February 2003 bloomfield@virginia.edu, 434-924-4576; see also
http://htw.wiley.com/htw/, chapter 15)

ULTRAVIOLET LITHOGRAPHY can produce lines for integrated circuits as small
as 39 nm in one recent test. To help sustain Moore's law and cram more and
more gates and memory units into a given space, manufacturers of microchips
must make the lines in their circuitry ever smaller. This usually means
working with a shorter-wavelength light beam for creating the patterns used
for inscribing fine features on silicon or metal surfaces. The form of
lithography currently in mass production now can produce a half-pitch size
(equal lines and spaces in between) of 90 nm and isolated line widths of 65
nm. To produce a later generation after that you would need even shorter
wavelengths. At the Advanced Light Source at the Lawrence Berkeley National
Lab (LBNL) a government-industry consortium of scientists is trying out this
future lithography. Using a beam of synchrotron radiation in the extreme
ultraviolet range they have produced 70-nm line/space intervals and isolated
lines 39 nm wide (see figure at http://www.aip.org/mgr/png/2003/179.htm ).
By the time this type of lithography comes into play, by about 2007, these
numbers should be 45 and 25 nm, respectively. The consortium consists of a
government side, the "Virtual National Lab" (LBNL, Livermore, and Sandia),
and an industrial component comprising Intel, AMD, IBM, Infineon, Micron,
and Motorola. (Naulleau et al., Journal of Vacuum Science Technology,
Nov/Dec 2002; contact Patrick Naulleau, pnaulleau@lbl.gov)

PHYSICS NEWS UPDATE
The American Institute of Physics Bulletin of Physics News
Number 623 February 5, 2003 by Phillip F. Schewe, Ben Stein, and James
Riordon

NEW SUPERBURST THEORY. When a neutron star pulls matter from a nearby
companion onto itself, powerful x-ray bursts, visible to telescopes in Earth
orbit, can result. Some astronomers believe the bursts leave behind an
ocean of debris, heavy nuclei mostly, on the neutron star's surface.
Occasionally much larger "superbursts," with up to 1000 times the amount of
x rays than other bursts, can flare up. Henrik Schatz of Michigan State
University (schatz@nscl.msu.edu, 517-333-6397) and his collaborators Lars
Bildsten from UCSB and Andrew C-u-m-m-i-n-g of UCSC believe that an energy
blitz is generated when high energy photons strike the heavy nuclei in the
debris ocean, springing free either a proton, neutron, or alpha particle,
which then recombine with the residual nuclei forming lighter, stronger
bound nuclei and free energy. This photodisintegration process is triggered
by the thermonuclear explosion of a small amount of carbon, but may then
proceed subject to positive feedback: the warmer the surface temperature the
more disintegration, which in turn leads to warmer temperatures. The
runaway production of energy through the conversion of heavy nuclei into
lighter nuclei could be unique in astrophysics: all other thermonuclear
energy generation (such as those inside our sun) proceeds by fusing lighter
nuclei into heavier nuclei. (Upcoming article in Astrophysical Journal
Letters; see also http://groups.nscl.msu.edu/nero/ )

LORENTZ VIOLATIONS? NOT YET. Lorentz invariance, the idea that the
result of a physics experiment should stay the same whether the apparatus is
motionless or traveling at some great constant speed relative to a reference
point, is taken for granted in the theory of special relativity. Yet in
recent years some scientists have come to question this pillar of physics,
and to suggest theoretical models (called "standard model extensions," or
SMEs ) incorporating Lorentz violations and experimental ways of settling
the matter (see Update 578, www.aip.org/enews/physnews/2002/split/578-2.html
). In these models, the speed of light is not universal but will have
extra terms dependent on the speed or orientation of the apparatus (see
http://media4.physics.indiana.edu/~kostelec/faq.html ).
Even before the advent of Einstein's relativity, the Michelson-Morley
experiment tried to perceive (unsuccessfully) a difference in the speed of
light when the Earth was traveling in two different directions in space
while on opposite sides of its orbit around the sun. Now scientists
have to be more subtle in their approach. In one new laboratory
experiment, just completed by Stanford physicists (John Lipa, 650-723-4562,
john.lipa@stanford.edu ) microwaves in two resonant cavities (one
oriented east-west, the other pointing vertically) are monitored as the
Earth sweeps around the sun. Any orientation- or speed-dependent changes in
the speed of light would alter the resonant conditions of the cavities in a
measurable way. The geometry of the experiment gives it optimal sensitivity
to a number of coefficients in a generalized SME. The Stanford group sees
no such anisotropy at the level of 10^-13 for velocity-independent terms,
and at the 10^-9 level for velocity-dependent terms. (Lipa et al., Physical
Review Letters, upcoming article; text at www.aip.org/physnews/select )

GROUND TEMPERATURES SINCE THE YEAR 1500 can be read back by examining the
temperatures in deep boreholes. Temperatures in the Earth's crust are
determined by a combination of surface climate effects and internal heat
flow. The general trend is a linear rise in temperature with depth, but
this is modulated by heat perturbations which act in a nonlinear way;
typically perturbations penetrate about 20 meters of depth per year or about
150 m in 100 years. Hugo Beltrami (St. Francis Xavier University in Nova
Scotia) has examined temperature-depth profiles from 826 places around the
world. Taking into account the known temperature anomalies, he is able to
work out the average surface energy flux and temperature for many localities
and for the world as a whole back for a period of 500 years. Beltrami
(902-867-2326, hugo@stfx.ca) finds that global average surface temperature
has increased by 0.45 K in the last 200 years. During this time, however,
some places have experienced more dramatic average temperature swings: for
example, parts of Africa show a cooling while northern Canada is warmer (3-4
K) during the same period. (Geophysical Research Letters, vol 29, 23, 2111;
also see http://geophysics.stfx.ca/public/index.html )

PHYSICS NEWS UPDATE
The American Institute of Physics Bulletin of Physics News
Number 622 January 27, 2003 by Phillip F. Schewe, Ben Stein, and James
Riordon

BUTTERFLIES AND PHOTONIC CRYSTALS. In recent years, scientists have
discovered that the iridescence of various colorful creatures, from beetles
to birds to butterflies, is often due to microscopic structures known as
photonic crystals. Unlike pigments, which absorb or reflect certain
frequencies of light as a result of their chemical composition, the way that
photonic crystals reflect light is a function of their physical structure.
That is, a material containing a periodic array of holes or bumps of a
certain size may reflect blue light, for example, and absorb other colors
even though the crystal material itself is entirely colorless. Because a
crystal array looks slightly different from different angles (unlike
pigments, which are the same from any angle), photonic crystals can lead to
shifting shades of iridescent color that may help some animals attract mates
or establish territories.
A collaboration of researchers from Hungary and Belgium (Jean-Pol Vigneron,
Universitaires Notre-Dame de la Paix, Brussels,
jean-pol.vigneron@fundp.ac.be, 011+32-81 724711) may have discovered why
the males in certain populations of lycaenid butterflies carry the striking,
photonic crystal coloration, and males in other lycaenid populations do not.
The researchers examined butterfly scales through high-resolution scanning
electron microscopes (see image at www.aip.org/mgr/png ), and confirmed that
indeed the colorful butterflies' scales included arrays of submicron-sized
holes that formed natural photonic crystals. Their closely related brethren
from higher elevations did not have the hole arrays in their scales, and
their wings were dull brown rather than iridescent blue. The difference, it
seems, may be due to a question of survival. The researchers found that the
plain brown butterfly wings warmed much more than the iridescent blue wings
when each were exposed to identical illumination. The researchers believe
that the butterflies at high elevations trade flashy iridescence for
light-absorbing brown so that they can withstand colder temperatures, and
survive long enough to mate.
If photonic crystals can have such a dramatic impact on butterfly thermal
management, suggest the researchers, manmade photonic crystals may someday
provide flexible thermal protection in extreme environments, possibly being
incorporated into such things as space suits or desert garments. (L. P. Biro
et al, Physical Review E, February 2003)

SYNCHRONIZATION TOMOGRAPHY. A new brain imaging method pioneered by a
German research group from several institutions can now produce images that
localize the areas of the brain involved when test subjects perform physical
activities, and can show how portions of the brain interact with each other.
The technique, dubbed synchronization tomography, involves mapping the
fluctuating magnetic fields produced by tiny electrical currents in the
brain, and determining which brain regions are synchronized with an activity
- such as a test subject's tapping finger. The researchers (Peter Tass,
Institute of Medicine, Research Center, Juelich, p.tass@fz-juelich.de,
011+49-2461-61-2087) asked test subjects to tap their finger in time to a
rhythmic tone, and to continue tapping at the same rate after the tone was
switched off. Meanwhile, their brain activity was mapped with a
magnetoencephalography (MEG) machine. The maps showed that the same regions
of the brain areas are active both as people tapped to a beat and as they
paced the tapping themselves, but that the synchronization between the
different brain areas changes dramatically. Other brain imaging methods,
including functional magnetic resonance imaging (fMRI) and positron emission
tomography (PET), can also provide insight into which regions of the brain
are involved during various activities, but they take too long to acquire
images to disclose how the brain regions interact with each other, and
therefore overlook important details of brain function which are clearly
revealed with synchronization tomography. In addition, a related
synchronization technique may help in the study of rapidly changing signals
in the heart detected with magnetocardiography systems. (P. A. Tass et al.,
Physical Review Letters, upcoming article)

THE PHYSICS OF STONE THROWING. Prompted by his son's questions on the
subject and the need to furnish his mechanics textbook with commonplace
examples, physicist Lyderic Bocquet of the Universite Claude Bernard Lyon
(France) has investigated the science behind stone skipping. The chief
parameters that determine whether your stone goes right in or skims across
the lake are as follows: the mass of the stone, its angle with respect to
the horizon, its angle with respect to the water surface (lower is better),
its spin rate (more is generally better, for stability), and its horizontal
velocity. Armed with calculations on energy loss, Bocquet (33-472-43-2796,
lyderic.bocquet@lpmcn.univ-lyon1.fr) has worked out an expression for the
maximum number of skips one can expect. According to Bocquet, the world's
record for stone rebounds is 38. (American Journal of Physics, February
2003; see also http://lpmcn.univ-lyon1.fr/~lbocquet )

PHYSICS NEWS UPDATE
The American Institute of Physics Bulletin of Physics News
Number 621 January 17, 2003 by Phillip F. Schewe, Ben Stein, and James
Riordon

SCATTERED CHATTER. Tall buildings are often the bane of cell phone users
when making calls in big cities, but such scattering structures may someday
enhance communication. Researchers at the Laboratoire Ondes et Acoustique in
Paris recently demonstrated the effect with ultrasonic antennas in a
water-filled tank. When the space between a 23-element transmitter array and
an array of
5 receivers was devoid of scattering structures, the error rate in
transmission of a set of 5 messages sent simultaneously to the receivers was
about 28%. By placing a forest of randomly arranged steel rods between the
transmitter and receivers, the researchers found that they could transmit
the same messages without any error at all. The effect is due to the fact
that, without scatterers, there is a substantial amount of cross-talk
between the receivers - that is, each antenna detects some of the data
intended for its neighbors, and has no way to distinguish between the
message it is supposed to receive and the messages it should ignore. By
adding scatterers, the researchers ensured that signals intended for
different antennas were distinct. The situation can be understood by
imagining a single antenna sending a signal to multiple receivers. Without
scatterers, each receiver detects
very nearly the same thing. Adding scatterers distorts the signal, and each
antenna detects something slightly different. In fact, by reversing the
experiment and sending signals from each of the receivers back to the
transmitter (an arrangement known as a time-reversal antenna, Update 190) it
is possible to ensure that with the scatterers, a transmitter array can send
multiple unique signals that are only detectable by the intended receivers.
In essence, scatterers make it possible to establish multiple communication
channels, and the more scatterers between the transmitters and receivers,
the more channels that are available. For the time being, the communication
technique is limited to ultrasonic communication - the electronics necessary
for exploiting scatterers with wide-band time-reversal antennas at cell
phone frequencies simply don't yet exist. But when they
are developed, the buildings that currently hamper wireless communication
will become a cell phone user's boon. (A. Derode et al, Physical Review
Letters, 10 January 2003)

A STRONGLY INTERACTING DEGENERATE FERMI GAS, an ultracold lithium-6 gas
which expands in a strangely lopsided fashion, has been produced for the
first time by Duke University researchers (John Thomas, 919-660-2508,
jet@phy.duke.edu). Performed on a tabletop, these results can provide
universal insights into all strongly interacting fermions, including the
neutrons in neutron stars, the quarks in atomic nuclei, and the electrons in
superconductors. In
addition to producing never-before-seen behavior in fermions, this
experiment may have provided the first evidence of a previously unseen
fermion-pairing phenomenon called "resonance superfluidity." The specially
prepared lithium-6 gas behaves in a markedly different fashion from ordinary
gases, those whose atoms essentially do not interact with one another. When
a cloud of ordinary gas expands in a vacuum, it usually spreads out with
equal speed in all directions. This means that a spherical cloud becomes a
larger sphere. Even a cigar-shaped cloud smooths out the differences in
its dimensions and adopts a spherical shape.
But something very different occurs in the lithium-6 gas, whose atoms
interact with the maximum amount allowed by the laws of quantum mechanics.
Trapped in a laser beam and cooled to 800 nanokelvins by optical methods,
the gas cloud started off with the shape of a vertical cigar. But when
released from its laser trap, the cloud hardly expanded in the vertical
direction, but it spread out rapidly in the horizontal direction. The
cloud ended up as a wide, horizontal ellipsoid (a 3D ellipse; see figures at
http://www.aip.org/mgr/png/2002/175.htm).
What had happened? The researchers had created a special version of a
degenerate Fermi gas (see Updates 447,
http://www.aip.org/enews/physnews/1999/split/pnu447-1.htm, and
580, http://www.aip.org/enews/physnews/2002/split/580-1.html). "Degenerate"
means that the deBroglie wavelength of the fermion atoms is greater than the
average distance between them, causing the atoms to "overlap" with each
other just as bosons overlap with each other in a Bose-Einstein condensate.
But in previous degenerate Fermi gases, the atoms did not interact strongly
with one another.
In this experiment, the researchers used a magnetic field that caused the
lithium atoms to interact quite strongly with one another, to an extent
never before reached in a degenerate Fermi gas. As a result, each atom
interacted with its kin over a region significantly larger than the average
distance between atoms. Because of the strong interactions among the atoms,
Thomas says, the gas completely changed its own shape while spreading out.
To explain fully this
"anisotropic expansion," the researchers suggest two possibilities, neither
of which they can distinguish at the present time: Either they were
observing a new kind of long-range collision between atoms, or they
witnessed resonance superfluidity, a relatively high-temperature form of
superfluidity that would be triggered by tuning the interactions between
fermions. (O'Hara et al., Science, 13 December 2002.)

PHYSICS NEWS UPDATE
The American Institute of Physics Bulletin of Physics News
Number 620 January 10, 2003 by Phillip F. Schewe, Ben Stein, and James
Riordon

CAN THE SPEED OF GRAVITY be measured directly through the observation of
gravitational lensing effects? Two scientists who monitored the deflection
of quasar light as it passed very near Jupiter argue that they have derived
an experimental value for the speed of gravity equal to 1.06 times the speed
of light (with an uncertainty of 20%). But two other scientists claim that
the lensing experiment only served as a crude measurement of the speed of
light itself.
Physicists have long taken for granted that the effect of gravitational
force, like the effect of electromagnetic force, is not instantaneous but
should travel at a finite velocity. A familiar example of this delay is the
fact that when we see the sun, we see it as it was 8 minutes ago. Many
believe that gravity also travels at the speed of light. The trouble is,
while it is relatively easy to gauge the strength of gravity (one can
measure gravity even near a black hole, where orbiting matter emits telltale
x rays), it is difficult to study the propagation of gravity.
Although not as heavy as a star, Jupiter still has considerable gravity,
and when on September 8, 2002, it swept very near the position of quasar
J0842 + 1835, the theory of general relativity suggests that the apparent
quasar position on the sky would execute a small loop over the course of
several days owing to the lensing of quasar light by the passing planet.
Sergei Kopeiken (University of Missouri) and Ed Fomolont (National Radio
Astronomy Observatory, or NRAO) have now seen just such a loop, as they
reported this week at the meeting of the American Astronomical Society (AAS)
in Seattle. For this purpose they employed the Very Long Baseline Array
(VLBA) of radio telescopes, a configuration of dish detectors providing an
angular resolution of 10 micro-arcseconds. Actually the observed lensing
loop was slightly displaced from what one would expect if gravity propagated
instantaneously. Kopeiken and Fomolont interpret this slight displacement
as providing an experimental handle on the speed of gravity itself, and
thereby calculate the value of 1.06 times c.
Other scientists disagree with this interpretation, and say that the radio
lensing data can do little more than provide a measurement of the speed of
light, not gravity. Two such opinions, by scientists who did not report at
the AAS meeting, are as follows: Clifford Will of Washington University in
the US (preprint at (www.arxiv.org/abs/astro-ph/0301145 ) and Hideki Asada
of Hirosaki University in Japan (www.arxiv.org/abs/astro-ph/0206266 )