PHYSICS NEWS UPDATE
The American Institute of Physics Bulletin of Physics News
Number 464 December 27, 1999 by Phillip F. Schewe and Ben Stein

SUPERCONDUCTING BALLS, a new phenomenon, have been
observed by physicists at Southern Illinois University. Rongjia
Tao (618-536-2117, rtao@physics.siu.edu) and his colleagues
began by wanting to observe the motion of micron-sized copper
oxide (e.g., Br-Sr-Ca-Cu-O) superconducting particles (suspended
in liquid nitrogen) in an electric field running between two
electrodes. Metal particles in this situation would bounce between
the two electrodes or tend to line up; after all, an electric field helps
to define a preferred direction in space. The superconducting
particles ignored this hint and, to the researchers' great surprise,
formed themselves into a ball. The ball, about .25 mm across and
containing over a million particles, formed quickly and was quite
sturdy, surviving constant collisions with the electrodes (see figure
at www.aip.org/physnews/graphics). What binds the ball together
against the dictates of the rectilinear field? Tao and his
collaborator, Princeton theorist Philip Anderson, have concluded
that the effect is an artifact of superconductivity (the same
particles, above their superconducting transition temperature, do
not ball up but instead queue into lines), perhaps something to do
with the way in which the surface energy of the particle ensemble
is reduced by self-assembly into a ball. This unprecedented new
surface energy is related to the acquired surface charges on the
particles and the reactions among the layers of the balls. Granular
properties of the particles might also play a role in the process and
in the ball's internal structure, but this is difficult to gauge since the
inter-particle interactions (frictional dissipation being the hallmark
of granular materials) are mitigated by the liquid nitrogen needed
in the experiment to neutralize gravity. A way around this is to do
the experiment in the microgravity of space. The basic scientific
novelty of this new phenomenon is paramount, but Tao is also
turning his attention to possible applications in the area of
superconducting thin films and unusual forms of wetting. (Select
Tao et al., Physical Review Letters, 27 Dec.)

TWO-DIMENSIONAL COLLOIDAL CRYSTALS SEEMINGLY
DEFY COULOMB'S LAW as they form, experiments have shown.
A colloidal crystal is a regular arrangement of tiny particles
suspended in a liquid. Three-dimensional examples have long been
known. Now free-floating 2D "crystallites" of colloidal particles,
lashed together by bilayer membranes similar to those surrounding
living cells, have been created, offering intriguing possibilities for
using them as templates for artificial biomaterials and industrial
catalysts. University of Pennsylvania researchers (Laurence Ramos,
now at Universite de Montpellier, France, ramos@gdpc.univ-
montp2.fr) created the system by adding negatively charged latex
beads to a suspension of positively charged soaplike (surfactant)
membranes in water. As expected, initially the beads avidly stuck
to the membranes. To the researchers' surprise, though, in many
cases the beads formed rafts floating on the membrane. Outside the
raft the membrane actually repelled additional beads, even though
they were highly oppositely charged. The researchers argued that
the source of this paradoxical behavior lay in the migration of
negative ions trapped on the side of the membrane opposite to the
beads. With time the fluid rafts solidify into rigid, flat crystallites,
near-perfect 2D crystalline structures some tens of microns on a
side. (Ramos et al., Science, 17 December 1999; and Aranda-
Espinoza et al., 16 June.)

PHYSICS NEWS UPDATE
The American Institute of Physics Bulletin of Physics News
Number 463 December 22, 1999 by Phillip F. Schewe and Ben
Stein

THE SOLAR WIND DISAPPEARED for a day back on May
10/11, allowing Earth's magnetosphere to balloon out to the orbit
of the Moon. Ironically, the greatly lowered solar wind flux of
particles and solar magnetic field allowed high-energy electrons
from the sun's corona to penetrate directly to our upper
atmosphere unadulterate, where the electrons' characteristic x-ray
emissions were observed by satellites over the North Pole for the
first time. Such a "polar rain" had been predicted years before.
Normally the coronal electrons (with energies of tens of keV,
corresponding to temperatures of millions of degrees) lose much of
their energy through scatterings with other particles on their ride
from sun to Earth and in the topsy-turvy trajectories experienced at
our magnetosphere. At last week's meeting of the American
Geophysical Union in San Francisco, these results were reported
by a number of speakers, including David Chenette of Lockheed,
Jack Scudder of the University of Iowa, and Keith Ogilvie of
NASA Goddard. (Images available at www-
spof.gsfc.nasa.gov/istp/news/9912)

SPONGELIKE STRUCTURES NEAR THE SUN'S SURFACE,
newly observed by the TRACE satellite (at extreme ultraviolet
wavelengths) and the SOHO satellite (in x rays), lie between the
10,000-K chromosphere and the corona at a temperature of several
million K. These filamentary structures (dubbed "solar moss" by
Lockheed scientists reporting at the AGU meeting) are typically
6000-12,000 miles in size and about 1000-1500 miles above the
photosphere, occur at various places around the sun's surface,
usually near the footprint of huge coronal loops. The moss blobs
seem to be stable for hours but can also change brightness over
periods as short as 30 seconds. Thomas Berger of Lockheed said
that the new structures may provide information on how the corona
gets so hot, an issue that remains one of the great unsolved
mysteries of solar physics.

THE RAREST NATURALLY OCCURRING ISOTOPE,
tantalum-180, is rare because it is bypassed in the two processes
that produced most of the heavy elements we dig out of the ground
here on Earth: the so called s process (slow neutron capture in
stars) and the r process (rapid neutron capture in supernova
explosions). What little Ta-180 that is produced (in stars or in
reactors) is quite robust; its halflife is more than 10^15 years. Ta-
180 is also unique in being the only naturally occurring isomer; it
is essentially a nucleus in a perpetual excited state. A group of
German physicists (Peter Mohr, 011-49-615-116-3221,
mohr@ikp.tu-darmstadt.de), essentially working with the world's
supply of this priceless substance, about 7 milligrams, try to jar the
tantalum nuclei out of their customary states by shooting them with
gamma photons, thus re-creating stellar conditions. They observed
that depending on the temperature the Ta-180 halflife varied over a
range of more than 10^17! This rules out the nucleosynthesis of
Ta-180 within the "canonical" s process; however, in a more
realistic version of the theory, the tantalum can survive if it rapidly
mixes with cooler layers of the star. (Belic et al., Physical Review
Letters, 20 December 1999. Select Article.)

PHYSICS NEWS UPDATE
The American Institute of Physics Bulletin of Physics News
Number 462 December 17, 1999 by Phillip F. Schewe and Ben Stein

COMPETING ARROWS OF TIME. Lawrence S. Schulman of
Clarkson University has found that time might actually flow backwards
in certain regions of space. This time reversal has nothing to do with
quantum fluctuations or the spacetime-warping effects of a black hole.
It's just ordinary matter obeying the ordinary and mostly time-
symmetric laws of physics. The difference lies in its statistics. If the
laws of physics have no preferred direction then why do we never see a
shattered wineglass jump back up on the table and reassemble itself?
The "arrow of time" concept enshrines this domestic disaster in the
form of a law, the second law of thermodynamics. The arrow describes
the tendency for macroscopic systems consisting of many particles (the
falling wineglass) to evolve in time in such a way that disorder grows
and information decreases. This tendency is statistical and does not
prevail at the microscopic level, where a movie of two atoms colliding
would seem credible if run in the forward or reverse direction. The
wineglass, however, consists of zillions of atoms. The reason we never
see the glass re-assemble and lift itself (courtesy of the warmth of the
original breakage returning from the floor and air) back onto the table
is that this highly specialized (and, as we would say, unlikely) scenario
is but one of a myriad of possible configurations, in most of which the
glass shards stay on the floor. This statistical explanation leads to two
puzzles.
First, why does this arrow point the way it does? Why not the other
way? And second, why should it point at all? On the first question,
Schulman subscribes to the view that the "thermodynamic" arrow of
time is a consequence of the "cosmological" arrow reflected in the one-
way expansion of the universe, a theory advanced some years ago by
Thomas Gold of Cornell. As to the second question, that's exactly
where Schulman's (schulman@clarkson.edu) new results have their
impact. The prevailing view holds that if opposite-arrow systems came
into even the mildest of contact, the order in at least one of them would
be destroyed. This is because from the perspective of one observer the
coordination needed to reassemble the other's wineglass would be so
fantastic that even a single photon could disrupt it. Not so, says
Schulman who, in his computer modeling of the universe, specifies not
one boundary condition in time (the big bang) but two, the other being
a supposed "big crunch" when the universe would contract (or so it
would seem to us; from the perspective of that arrow, the universe
would be expanding). In his model the two arrows of time (one
growing out of either end of the "timeline"; see the figure at
www.aip.org/physnews/graphics) can be mildly in contact and
nevertheless each have its wineglasses break and its rain fall
appropriately. Observers associated with either arrow might even
watch the other grow young---from a distance.
Some relatively-isolated relics of matter subject to the opposite arrow
might be found in our vicinity. By its own clock such a region would
be very old and no longer luminous, although gravitationally it would
not be anomalous, exactly the hallmark of dark matter. Or we might
see an opposite-arrow black hole giving matter back to an accretion
disk, which in turn would feed it back to a companion star which
would seem (to us) to be coming into existence. Schulman concedes
that recent observations may rule out a final crunch in our actual
universe but argues that there is still a lot we don't understand about
our thermodynamic arrow, and that a competing time arrow might arise
from another, as yet unknown, cause. (Physical Review Letters, 27
Dec.)

STARLIGHT REFLECTED FROM AN EXTRASOLAR PLANET has
been reported by University of St. Andrews astronomers. Roughly 30
planets have been detected around nearby stars through an indirect
method which monitors fluctuations in the stars' positions. More
recently the shadow of an extrasolar planet was observed to transit
across the face of its star (Update 458). Now light has been detected
which apparently comes to us directly from a planet circling the star tau
Bootis, some 50 light years away. The main difficulty was of course
discerning the reflected light while blocking out the glare of the star
itself. The planet seems to be blue-green in color, is twice the size of
Jupiter, and 8 times as massive. (Cameron et al., Nature, 16 December
1999.)

PHYSICS NEWS UPDATE
The American Institute of Physics Bulletin of Physics News
Number 461 December 10, 1999 by Phillip F. Schewe and Ben Stein

NATURALLY OCCURRING RADIATION LEVELS ARE MUCH
LOWER TODAY on Earth than when life first appeared, a new
analysis has shown (Andrew Karam,716-275-1473,
Andrew_Karam@URMC.Rochester.edu), suggesting that all living
organisms--which have mutation-repair mechanisms very similar to
those first developed by primordial life forms were once equipped to
handle larger doses of background nuclear radiation than modern life
forms. Presently, humans receive a dose of about 360 millirems per
year of radiation from natural sources, plus typically about 63 mrem/yr
from anthropogenic sources. Perhaps surprisingly, a major source
(about 40 mrem/yr) of naturally occurring radiation is inside our
bodies--in the form of potassium, a nutrient essential for many things
such as generating signals between cells. All natural sources of
potassium contain some radioactive potassium-40 (K-40). But life first
began about 4 billion years ago--about 3 K-40 half-lives ago--meaning
that the radiation dose from potassium today is about one-eighth of
what it was 4 billion years ago. Geologic sources of radiation (about
28 mrem/yr) include uranium, thorium, and potassium present in rocks
and minerals in the earth's crust. Studying published data of 1100
rocks, and assuming that the continental crust had formed early (a
scenario favored by the rock record), the researchers estimated that
radiation from these sources is now about one-half of what it was 4
billion years ago, because many of these radioisotopes decayed in the
intervening time. Not considered in the present study were cosmic
sources (about 27 mrem/yr) and radon (typically about 200 mrem/yr);
the authors are making these the subject of ongoing research. (Karam
and Leslie, Health Physics, December 1999.)

MAXWELL'S DEMON MADE OF SAND. The second law of
thermodynamics states that within a closed system heat cannot flow
unassisted from a cold to a warm place. To ponder this issue, James
Clerk Maxwell, one of the pioneers of statistical mechanics, posed
this thought experiment: could not a clever microscopic creature,
poised at a pinhole in a baffle dividing an insulated box into two
equal chambers, sort molecules in such a way that the hotter (faster)
molecules would be directed into one chamber while cooler (slower)
molecules would be directed into the other. "Maxwell's demon," as
the sorter came to be known, itself requires energy to operate, and so
the segregation of hot from cold cannot really happen as advertised.
And yet in an experiment conducted at the University of Essen in
Germany in which agitated sand in a two-chamber vessel (the halves
being connected by a hole) "hot," quickly moving sand migrated to
one side while cool sand spontaneously condensed and congregated
on the other side (see sketch at www.aip.org/physnews/graphics).
Jens Eggers (011-49-201-183-3941, eggers@theo-phys.uni-
essen.de) explains that, no, the second law is not violated in this case
since although moving sand can be considered as a gas, individual
grains can absorb heat and dissipate heat (that is, individual grains
can gain temperature), unlike the ideal gas molecules described by
Maxwell, whose "temperature" is a measurement of gas motion.
Thus when sand grains start to congregate in one chamber (the
segregation begins as an act of spontaneous symmetry breaking)
more and more grains will partake of a growing ordered state
consisting of grains falling to the bottom of the container (where the
grains are denser there are more collisions and hence faster cooling,
leading to more congregation, etc.), while the unaffiliated grains will
tend to be on the other side, still in "gaseous" form. (Eggers,
Physical Review Letters, 20 December; Select Articles.)

THE TOP PHYSICS STORIES FOR 1999, as recorded in the pages
of Physics News Update: Making tentative landfall on the nuclear
island of stability with the discovery of elements 114, 116, 118
(Updates 412, 432); the dramatic slowing of light to automobile
speeds in Bose Einstein condensates and in gases (415); the
achievement of a Fermi-degenerate gas, a cloud of fermion atoms
chilled so much that the exclusion principle inflates the size of the
cloud relative to a cloud of otherwise-comparable boson atoms
(447); tabletop fusion carried out with powerful lasers (421); the
observation of direct CP violation in the decay of K mesons at
Fermilab and CERN (420, 435); non-destructive photon
observations (439); extrasolar planet transits and other observations
(458, 462); three-photon entanglement (414); measuring the
frequency of visible light to a precision of 120 parts per billion
(434); and gravitational self-energy obeys the equivalence principle
(454).

PHYSICS NEWS UPDATE
The American Institute of Physics Bulletin of Physics News
Number 460 December 7, 1999 by Phillip F. Schewe and Ben Stein

MEASUREMENTS OF THE COSMIC MICROWAVE
BACKGROUND (CMB) provide new evidence that the expansion of
the universe is accelerating. One of the greatest issues in cosmology
is whether the current expansion will continue, reverse, or proceed at
a diminishing rate. Supernova observations two years ago suggested
that not only would the expansion not reverse but that it was in fact
getting faster (Update 361). The new CMB mappings, carried out
with telescopes on mountains and on balloons, reveal that the
temperature of the microwave background varies in clumps with an
angular size of about one degree on the sky, a result indicative of an
overall "flat" geometry for the universe (New York Times, 26
November 1999). Another way of saying this is that the observed
energy density of the universe is apparently equal to the critical
density value of about 10^-29 gm/cm^3. But the amount of known
matter (luminous and dark) is insufficient for producing a flat
geometry, so additional energy, probably hiding in the universal
vacuum, is needed. This energy, according to many theorists, would
exert an effect equivalent to a repulsive form of gravity, thus working
against the mutual gravitational attraction of galaxies. Much of the
new work is available only in preprint form. For example, papers for
one of the experiments, the "Boomerang" collaboration, which
measures the CMB with a balloon-mounted detector, can be found on
the Los Alamos server (Melchiorri et al.,
http://xxx.lanl.gov/abs/astro-ph/9911445.)

COOPERATIVE EVAPORATION, a process whereby droplets on
a substrate do not evaporate independently but in a coordinated
fashion, has been observed for the first time by physicists at the
University of Konstanz (Claudia Schafle, claudia.schaefle@uni-
konstanz.de). The researchers begin by laying down a periodic
array of diethylene glycol drops 0.75 microns in radius and spaced
by 2.5 microns (see figure at www.aip.org/physnews/graphics).
(Condensing the droplets out of a supersaturated vapor onto a
patterned grid of adsorption sites imposed on the surface with
microcontact-printing was itself something of a feat). The
Konstanz scientists found that some rows of droplets evaporated
faster than other rows, leading to a sort of "superstructure." In
other words, some drops would survive at the expense of the
preferential evaporation of other drops in a methodical way.
Previously scientists have considered how gas sensors comprised
of liquid droplet arrays could be designed. The droplet size in such
sensors can be made sensitive to environmental conditions by
selective uptake of certain molecules. When monitoring the
average droplet size by light scattering techniques, the
concentration of the molecules can be determined. But for this to
work the cooperative evaporation effect will have to be taken into
effect. (Schafle et al., Physical Review Letters, 20 December
1999; Select Article.)

ATOM TRAP TRACE ANALYSIS, the search for tiny isotope
fractions among atoms using a magneto-optic trap, may soon be
preferable to accelerator mass spectrometry (in which atoms are
heated, accelerated, and sent through a strong magnet, which sorts the
atoms by mass) for certain radio-dating purposes. To demonstrate this
idea, physicists at Argonne (Zheng-Tian Lu,
630-252-0583, lu@anl.gov) have detected traces of krypton-85 (with
an abundance of only 10^-11) and krypton-81 (abundance of 10^-13)
in an atom trap with an efficiency of 1 part in 10^7; accelerator mass
spectrometry, which requires an accelerator, currently has a counting
efficiency of a part in 10^5. Keeping track of Kr-85 atoms is
important since they are produced chiefly in nuclear-fuel
reprocessing plants, and (arising mostly since the 1950s) are used as a
tracer of air and ocean currents. Kr-81, in contrast, is made in
cosmic-ray showers in the upper atmosphere and (with a half life 40
times longer than C-14's) is preferable to carbon-dating for
calibrating the antiquity of million-year-old samples of ice and
ground water. (Chen et al., Science, 5 November 1999.)

PHYSICS NEWS UPDATE
The American Institute of Physics Bulletin of Physics News
Number 459 November 29, 1999 by Phillip F. Schewe and Ben
Stein

UNDERSEA VOLCANO. Like astronomers who team up to view
supernova eruptions at a variety of wavelengths, geophysicists have
been able to mount an in-depth study of the eruption in January 1998
of the Axial Volcano, lying 1500 m underwater about 200 miles off
the Oregon-Washington coast (see figure at
www.aip.org/physnews/graphics). Axial, which is a large volcanic
edifice lying along a rift zone in the Northeast Pacific where new
ocean floor is being created, is one of the few places on the
worldwide 60,000-km mid-ocean ridge system (Iceland and the
Azores are other examples) where volcanic activity can be monitored
in real time. In this case the coverage consisted of Navy hydrophone
arrays (listening for quakes rather than subs), surface ships, moored
sensors, and instruments placed on the very summit of the caldera in
anticipation of an eruption. The 1998 event is chronicled in a variety
of ways in a series of articles in the December 1 and 15 issues of
Geophysical Research Letters. For example, C.G. Fox reports (via
on-the-spot seafloor measurements) a 3-meter drop in the caldera
floor; Baker et al. provide the first in-situ observation of the water
temperature change above an erupting rift zone (constituting the
"largest vent field heat flux yet measured"); Embley et al estimate
that up to 76 million cubic meters of lava were produced, modest by
land volcano standards, but the largest outpouring in 20 years of
monitoring along the Juan de Fuca Ridge. (Robert Embley, Pacific
Marine Environmental Laboratory, embley@pmel.noaa.gov, 541-
867-0275.)

SWIRLED SPHERE MAGIC NUMBERS. Physicists love to
detect patterns in nature, whether in the crystalline structures of
atoms in solids, or the groupings into "shells" of electrons inside
atoms or protons and neutrons within nuclei. Even in a system as
simple as a bunch of spheres swirled around in a dish patterns can
emerge. Scientists at the Max Planck Institute in Dortmund,
Germany (Karsten Kotter, koetter@mpi-dortmund.mpg.de, and
Mario Markus), and the University of Chile (Eric Goles) have
determined that for certain "magic" numbers of spheres, such as
19, 21, or 30, the spheres congregate into solid-like shell structures
with stable rings (see figure at www.aip.org/physnews/graphics).
The swirled balls are a form of granular material. Studies of
agitated grains had uncovered stable structures before (such as
"oscillons") but not any that had depended on the number of
particles present. The researchers noticed that when they increased
the size of the dish a puzzling transition between stable and
disordered states would occur intermittently. (Kotter et al.,
Physical Review E, December 1999; Select Article.)

THE TOP PHYSICISTS IN HISTORY are, according to a poll of
scientists conducted by Physics World magazine, 1. Albert Einstein,
2. Isaac Newton, 3. James Clerk Maxwell, 4. Niels Bohr, 5. Werner
Heisenberg, 6. Galileo Galilei, 7. Richard Feynman, 8. Paul Dirac, 9.
Erwin Schrodinger, and 10. Ernest Rutherford. Other highlights of
Physics World's millennium canvas: the most important physics
discoveries are Einstein's relativity theories, Newton's mechanics, and
quantum mechanics. Most physicists polled (70%) said that if they
had to do it all over again, they would choose to study physics once
more. Most do not believe that progress in constructing unified field
theories spells the end of physics. Ten great unsolved problems in
physics: quantum gravity, understanding the nucleus, fusion energy,
climate change, turbulence, glassy materials, high-temperature
superconductivity, solar magnetism, complexity, and consciousness.
(December issue of Physics World, published by the Institute of
Physics, the British professional organization of physicists
celebrating its 125th anniversary this year.)

PHYSICS NEWS UPDATE
The American Institute of Physics Bulletin of Physics News
Number 458 November 18, 1999 by Phillip F. Schewe and Ben
Stein

THE SHADOW OF A PLANET slipping across the face of a distant
star has been detected, for the first time, by veteran extrasolar-planet
stalkers Geoffrey Marcy of UC Berkeley and Paul Butler of the
Carnegie Institution, working with Greg Henry of Tennessee State
University. Prior indirect "sightings" of extrasolar planets consisted
of small feints in the apparent position of the stars caused by the
suspected gravity pull of an orbiting planet. Astronomers have felt
that from among the growing sample of such planets (up to 25 as of
now) a few (whose orbits would be viewed at Earth edge-on) might
be detected directly as they pass in front of the star. One such
candidate was HD 209458. Prediction of a planetary transit for the
night of November 7 proved accurate and a 1.7% dimming in the
star's light was seen. (Announcement made in an International
Astronomical Union circular.)

MICROFLUIDICS CAN BE DRIVEN BY HEAT rather than by
electric fields. Microfluidics is to the mixing of fluids (including
studies of blood, DNA, etc.) what integrated circuits are to the
processing of electrical signals: transactions occur quickly,
controllably, in a very small space. But instead of excavating
small channels in a substrate and propelling tiny fluid volumes
around the nano-sized system of aqueducts customary in
microfluidics (see Update 367), Princeton professor Sandra M.
Troian and Dawn Kataoka, now at Sandia Laboratories(CA), have
moved tiny liquid rivulets around a silicon wafer using temperature
gradients. The capillary movement of the micro-fluids can be
programmed because (1) the liquid surface tension varies with
temperature and even a gradient of 3 or 4 K will cause a fluid to
seek out a cold region, and (2) a lithographically applied pattern of
chemical modifications on the substrate (the equivalent of an
invisible scent marker or a chemical levee) further constrains the
droplet rivercourses. Thus streams of hydrophilic and hydophobic
molecules, zooming across the substrate along neighboring lanes,
can be shunted together at some desired meeting point. The
advantages of thermo-capillary action over electronic-driven
fluidics are that the use of high electric fields and the precision
carving of channels are not necessary; everything happens on a
plane, making easier the task of building micro-electromechanical
(MEMS) "labs-on-a-chip." Troian (609-258-4574,
stroian@princeton.edu) will report on her research at the APS
division of fluid dynamics meeting in New Orleans, November 21-
23: http://www.nd.edu/~apsnd/)

HYDROGEN STORAGE IN NANOTUBES. Hydrogen is a potent
fuel: combined with oxygen it can power spacecraft to the Moon.
Storing such a dangerous substance, however, is difficult. Physicists
at MIT have now succeeded in canning hydrogen inside carbon
nanotubes. Actually, hydrogen sausage has been encased in a carbon
skin before, but the MIT efforts are the first to achieve reliably such a
high hydrogen uptake (one hydrogen for every two carbons) at room
temperature. And like a jack-in-the-box, the hydrogens came
shooting out of the tubes (80% of them anyway) when the packing
pressure was relaxed. (Liu et al., Science, 5 November 1999.)

THE ONLINE JOURNAL PUBLISHING SERVICE (OJPS)
constitutes a shopping mall for the physics journals published by the
American Institute of Physics (AIP), many of its member societies,
and other scientific and engineering societies. From this site
(http://ojps.aip.org/) one can handily visit the homepage for such
journals as Physical Review, Applied Physics Letters, Optics Letters,
and Chaos. Nonsubscribers can view tables of contents and look at
all the abstracts, including those from some issues not yet published.
(You can even search the full SPIN database of abstracts if you have
a subscription to at least one of the OJPS journals.) In general the
full texts are available only to subscribers, although a few prominent
articles are supplied to science writers via a separate website called
Physics News Select Articles.

PHYSICS NEWS UPDATE
The American Institute of Physics Bulletin of Physics News
Number 457 November 12, 1999 by Phillip F. Schewe and Ben
Stein

LASER LIGHT IN, 50-MEV PROTONS OUT. At next week's
meeting of the American Physical Society Division of Plasma
Physics in Seattle, three groups will independently announce their
ability to generate powerful, intense streams of ions by shining
ultrashort laser pulses on tiny spots of solid material. Potentially, this
approach offers an alternative to bulky, expensive ion accelerators for
producing high-velocity ions useful for cancer therapy and
electronics manufacturing. Using a single pulse of light from
Livermore's Petawatt laser, the most powerful in the world,
researchers at that laboratory (Scott Wilks, 925-422-2974,
wilks@icf.llnl.gov) have reported generating 30 trillion protons with
energies up to 50 MeV, from a tiny spot approximately 400 microns
in size. Using a tabletop terawatt laser one-thousandth the power of
the Petawatt, University of Michigan researchers (Donald Umstadter,
734-764-2284, dpu@umich.edu) produce 10 billion protons with
about a tenth the energy of those reported at Livermore. In addition,
the Michigan team has announced that they can produce a confined
beam of ions pointing roughly in the direction of the laser beam.
Employing the VULCAN laser at the Rutherford Appleton
Laboratory, researchers there (Karl Krushelnick, Imperial College,
kmkr@ic.ac.uk, 011-44-594-76-35), generated lead ions with
energies up to 420 MeV (and protons up to 17 MeV). The
mechanism behind each demonstration is similar. A single laser pulse
strikes a thin target, ejecting electrons which form a cloud of negative
charge around the back of the target. The cloud pulls positively
charged ions from the back of this target and rapidly accelerates the
ions to high energies. All of this occurs over a very short distance--
almost 1 MeV/micron for protons in the Livermore case, which is
orders of magnitude higher than conventional ion accelerators.
(Papers FI2.04, O1.11, QO1.12, QO1.13, JP1.74 at meeting; Meeting
program at http://www.aps.org/meet/DPP99/baps/; Figures at
www.aip.org/physnews/graphics.)

20,000 LEAGUES UNDER THE FERMI SEA. Recently Stanford
and UC Santa Barbara physicists used two alternating-current voltage
sources to skew the quantum states in a tiny semiconducting quantum
dot in such a way as to produce (without any net applied bias) a
nonzero current through the dot. This was an experimental
realization of a "Thouless pump" (named for David Thouless), which
pumps electrons much as an Archimedian screw pump lifts water
(Switkes et al., Science, 19 March 1999; see also the commentary in
the same issue by Altshuler and Glazman). Now, Mathias Wagner
(Hitachi Cambridge Laboratory, 011-44-1223-44-2911,
wagner@phy.cam.ac.uk) and Fernando Sols (Universidad Aut¢noma
de Madrid) predict that a similar principle will also apply to electrons
far beneath the Fermi-sea surface. The Fermi surface or Fermi level
represents (in an abstract space in which all electrons are described
by their momentum vectors) the highest energy an electron may
possess--at zero temperature--in the conduction band of a metal or
semiconductor material. Conduction electrons, those that stray from
their home atoms, are usually drawn from electrons very near the
Fermi surface. Electrons with lesser energies, and occupying rungs
further down on an energy-level diagram, are said to reside in the
"Fermi sea" and normally do not effectively contribute to the current.
Wagner and Sols suggest that with high enough ac power, the
resulting pump current might actually consist mostly of electrons
from far beneath the Fermi-sea surface. These subsea currents would
be largely immune from temperature effects (just as submarines are
less vulnerable to surface storms), a very useful property in the
electronics world. (Wagner and Sols, Physical Review Letters, 22
November 1999; see figure at www.aip.org/physnews/graphics.)

PHYSICS NEWS UPDATE
The American Institute of Physics Bulletin of Physics News
Number 456 November 9, 1999 by Phillip F. Schewe and Ben Stein

ULTRASOUND IMAGING WITHOUT PHYSICAL CONTACT
between device and patient has been achieved, providing a potential
solution to an unmet medical need--determining the depth and
severity of serious burns in a convenient, accurate, and pain-free
fashion. At the present time, physicians usually diagnose burns by
inspecting them visually; however, such visual observation cannot
provide direct information on whether there is damage to underlying
blood vessels, a condition which requires surgery. Technologies such
as conventional ultrasound or MRI are either too slow, time-
consuming, or cumbersome. In addition, they are painful for the
patient if they require direct contact with the burn area. This is
certainly the case with conventional ultrasound, which requires direct
contact with the body, or must at least be connected to the body via
water. That's because generating ultrasound in a device and sending
it through air causes a large proportion of the sound to bounce right
back into the device. This results from a great mismatch between air
and the device in the values of their "impedance," the product of the
density of the substance and the velocity of sound through it. By
more closely matching the impedance values between the device and
air, a significantly greater proportion of sound can be transmitted to
the body, and reflected back, to obtain enough of a signal for an
image. In a non-contact ultrasound device described at last week's
meeting of the Acoustical Society of America in Columbus, Joie
Jones of UC-Irvine (949-824-6147, jpjones@uci.edu) and his
colleagues pass the sound wave through a multilayered material, with
each succeeding layer having an impedance value closer to that of air.
The transmission is improved to the point that the researchers could
image burns by holding their device about two inches away from the
skin, in about a minute or so. Having tested this device on over 100
patients, the researchers plan to move to larger clinical studies and
develop a device that can take images in real time.

THE OXYGEN RED PHASE gets its name from the fact that this
form of solid oxygen comprised of oxygen-4 molecules is deeply
red in color, and gets more red at higher pressures. The red phase
has now been studied in detail by physicists in Italy and their
results suggest that at pressures above 10 GPa two O2 molecules
combine into an O4 molecule. The pressure is necessary for
altering (by brute force) the chemical bonds at work inside this
molecular solid. By recording the vibrational properties of oxygen
solids at pressures up to 63 GPa, Roberto Bini (bini@chim.unifi.it,
011-39-055-230-7864) and his colleagues at the European
Laboratory for Nonlinear Spectroscopy in Florence have concluded
that the process whereby O2 molecules form into O4 units could be
a kind of prelude to oxygen's transformation into longer chains
(polymers) and then into a metal (superconducting oxygen was
reported by Shimizu et al., in Nature, 25 June 1998).(Gorelli et al.,
Physical Review Letters, 15 November.)

IO SODIUM JET. Astronomers have previously known of a
sodium cloud which precedes the moon Io in its orbit around
Jupiter. The cloud is believed to arise from slow escape of sodium
from Io. Now the Galileo spacecraft is providing details of another
sodium feature at Io, more of a fast-escaping spray or jet, thought
to come about when Io plows through Jupiter's potent magnetic
field, a process which induces mega-amp currents through Io's
atmosphere (see schematic at www.aip.org/physnews/graphics).
New pictures, reported by scientists at the University of Colorado
(Matthew Burger, burger@ganesh.colorado.edu, 303-492-3395,
and Nicholas Schneider) and Boston University (Jody Wilson),
localize the source of the sodium to a region smaller than Io's
diameter, suggesting that Io's atmosphere might not be global; that
is, the atmosphere might be patchy and not extend all the way to
the poles. (Geophysical Research Letters, 15 November.)

PHYSICS NEWS UPDATE
The American Institute of Physics Bulletin of Physics News
Number 455 November 2, 1999 by Phillip F. Schewe and Ben Stein

ORIGIN OF RADIO JETS NEAR A BLACK HOLE. Black holes
don't just sit there spiderlike swallowing stars. They also fling out vast
plumes of light-emitting material; these collimated streams can stretch
for hundreds of thousands of light years. One of the closest of these
conspicuous jets is to be found at the heart of galaxy M87, about 50
million light years away from Earth. Presumably the jet originates at
an accretion disk surrounding a supermassive black hole. Previously
radio mapping of this spot in the sky did not possess sufficient
resolving power to see precisely where the jet begins. But now, by
pooling the extended radiowave gathering power of the Very Long
Baseline Array (VLBA), the Very Large Array (VLA), and telescopes
in Italy Sweden, Finland, Germany, and Spain, astronomers have
nailed down the jet origin to within tenths of a light year of the black
hole's location. The resulting image (see
www.aip.org/physnews/graphics) shows that the jet's initial opening
angle is 60 degrees, the widest ever seen for a jet, although the jet
becomes much more focused (6 degrees) further downstream. (Junor et
al., Nature, 28 Oct.)

GOLD CHAINS ARE PRIZED not only as jewelry but also for their
atomic properties. By plunging a scanning microscope probe into a
gold surface and then retracting the tip a string of several (perhaps as
many as seven) gold atoms can be produced. The binding strength
between atoms in the chain is at least about half that between atoms in
bulk gold and so the chain is somewhat stable. Transmission electron
microscope (TEM) pictures of the chains seem to indicate that the
atoms are much as 4 to 5 angstroms apart, but other measurements,
such as conductance tests, imply the gap was more like 3 angstroms or
less. So what are the gold atoms doing? This puzzle is addressed by a
group of scientists from several Spanish labs (plus a contingent at the
University of Illinois contact Daniel Sanchez-Portal,
daniel@roma.physics.uiuc.edu) whose computer simulations suggest
that the atoms lie not on a straight line but on a zig-zag (spaced about
2.5 angstroms apart) and that, furthermore, the chain should be
spinning around its long axis (see a figure at
www.aip.org/physnews/graphics). The TEM pictures would then be
explained as capturing only a misleadingly averaged position for the
gold atoms. Knowledge of where the gold atoms are and what they're
doing is important to those hoping to develop circuitry using
nanowires. (Sanchez-Portal et al., Physical Review Letters, 8
November 1999; Select Article.)

MACH CONES: SHOCK WAVES IN DUSTY PLASMAS. Plasmas-
-collections of charged particles such as ions and electrons--usually
behave as a gaslike substance, with particles dancing around each other
with little deflection. But under the right conditions, physicists can
make plasmas act like liquids and solids, in which particles sit almost
stationary, interacting almost exclusively with their nearest neighbors.
This is especially true when plasmas are mixed with dust, as is the case
in interstellar space. In laboratory experiments at the University of
Iowa (John Goree, 319-335-1843, john-goree@uiowa.edu), the "dusty
plasmas" are micron-sized spheres loaded up with approximately
10,000 electrons apiece. When illuminated by an intense sheet of
light, the researchers can see the microscopic structure and movements
of these particles in a way that is not possible with conventional atomic
matter. For this reason, plasmas can serve as a model system for
investigating condensed matter physics. By firing a particle at the
dusty plasma at supersonic speeds, the researchers produced a Mach
cone (figure at www.aip.org/physnews/graphics), similar to the V-
shaped shock wave produced by a supersonic airplane. Mach cones
are well known in gases (airplanes, for example), but almost unknown
in solids. One of the only other known examples is in seismology: a
sound wave traveling down the surface of a liquid-filled borehole
moves faster than the sound speed in the surrounding rock, causing a
Mach cone to be produced in the rock. (D. Samsonov et al, Phys. Rev.
Letters, 1 November 1999; also see paper H12.02 in the upcoming
American Physical Society Division of Plasma Physics meeting--
http://www.aps.org/meet/DPP99/baps/; also Select Article.)

PHYSICS NEWS UPDATE
The American Institute of Physics Bulletin of Physics News
Number 454 October 26, 1999 by Phillip F. Schewe and Ben Stein

GRAVITY'S GRAVITY. A new experiment at the University of
Washington seeks to determine whether the gravitational binding
energy of an object generates gravity of its own. As formulated by
Albert Einstein, the Equivalence Principle (EP) states that if we stand
in a closed room we cannot tell whether the weight we feel is the
result of gravity pulling down or the force of a rocket carrying us
forward through otherwise empty space. All of this gets complicated
in some theories of gravity, which predict that the EP will be violated
to a small degree since in addition to the usual gravity, carried from
place to place by spin-two particles called gravitons, there should
exist another, fainter kind of gravity carried by spin-zero particles
(sometimes called dilatons). For this reason, and because recent
observations of supernovas suggest that some repulsive gravitational
effects might be at work in the cosmos, scientists want to explore the
possibility of EP violations. Three decades of lunar laser ranging
(bouncing light off reflectors placed on the Moon) show that the
Moon and the Earth fall toward the Sun with the same acceleration to
within half a part in a trillion (10^12). What the Washington
physicists (Eric Adelberger, 206-543-4294,
eric@gluon.npl.washington.edu) have done is focus attention on the
subject of gravitational binding energy, or self-energy, and whether it
too obeys the EP. To illustrate the concept of binding energy,
consider that the mass of an alpha particle is actually about 28 MeV
less than the sum of its constituents. This energy (about 7.6 parts in a
thousand of the alpha mass) represents the energy (vested in the
strong nuclear force) needed to hold two protons and two neutrons
together inside the alpha. Gravity being very much weaker than the
strong nuclear force, the gravitational binding energy, the self-energy
of gravity attraction, is almost infinitesimal. For example, self-
energy effectively reduces the mass energy of the Earth by a factor of
only about 4.6 parts in 10^10. Is this tiny "mass" also subject to the
EP? Supplementing existing lunar laser ranging results with new data
from special test masses mounted on a sensitive torsion balance (see
www.aip.org/physnews/graphics) to take into account the different
compositions of the Earth and Moon, the Washington physicists show
that gravitational self energy does obey the equivalence principle at
the level of at least one part in a thousand. Thus gravitational self
energy does indeed generate its own gravity. (Baessler et al., Physical
Review Letters, 1 November; see also Clifford Will's article, Physics
Today, Oct 1999.)

VACUUM TUBES ATTEMPT A COMEBACK. Vacuum tubes were
the backbone of the electronics industry until the 1960s, when their
large size, excessive power dissipation, and lack of integration
allowed solid-state technology to win out. Now forests of 100-nm
sized nanotriodes might bring vacuum designs back, at least for niche
applications. Researchers at the University of Cambridge (Alexander
Driskill-Smith, David Hasko, and Haroon Ahmed,
aagd100@cus.cam.ac.uk, 011-44-1223-337556) have made an anode-
gate-cathode device in which the cathode consists of multiple
nanopillars which can be crowded together in a dense formation. This
will eventually enable nanotriode densities of 10^9 per cm^2
(including interconnects) to be reached, comparable with the best
packing densities for metal-oxide-semiconductor (MOS) transistors,
the electronics industry workhorse. Shooting electrons through
vacuum rather than a semiconductor not only makes switching fast
(the ballistic electrons always travel without scattering), but gives
nanotriodes a few advantages over MOS technology: the nanotriodes
are radiation resistant, operate well at high and low temperatures,
and, because they are vertically-oriented, will permit integration in
the third dimension, allowing even greater packing densities.
Electrons (or, more accurately, the electron waves) issuing from the
nanopillars are coherent and highly focused, and might be useful for
doing holography or nanolithography. Remaining problems with this
vacuum design include a relatively high operating voltage (10 V) for
large scale integration applications and the reproducibility and
longevity of the nanotriodes. (Applied Physics Letters, 1 November
1999.)

CORRECTIONS: 1. Diamonds precipitated from methane in an anvil
press (Update 451) squeezed up to pressures of 50 GPa, equivalent to
0.5 (not 10) million atm. 2. One can contemplate, at least in
principle, the wave behavior of bowling balls (not bawls; Update
453).

PHYSICS NEWS UPDATE
The American Institute of Physics Bulletin of Physics News
Number 453 October 19, 1999 by Phillip F. Schewe and Ben Stein

EXTRA INVISIBLE DIMENSIONS are for particle physicists what
they are for Star Trek captains: a device for covering a lot of ground
quickly and explaining anomalous behavior. In physics the
importation of extra dimensions into the standard theory helps to make
peace between quantum mechanics and general relativity, but it doesn't
explain the great disparity (the "hierarchy problem") between the
temperature at which the weak and electromagnetic forces fuse
together (10^2 GeV, expressed in energy units) and the temperature at
which gravity joins up with the other forces (10^18 GeV), a
temperature so hot, or an energy so high, that such conditions have not
prevailed since a tiny moment after the big bang. Some theories
contend that we are not aware of the extra dimensions because they
extend only a very short distance, far smaller than the size of an atom.
Yet another way of playing with spacetime is to introduce a new
dimension essentially infinite in extent but one in which gravitons, the
carriers of gravity, would largely be locked up in localized regions, at
least in the extra dimension. This exciting new idea, advanced by Lisa
Randall of Princeton (609-258-4322, randall@feynman.princeton.edu;
on leave from MIT, randall@baxter.mit.edu, 617- 253-4818) and
Raman Sundrum, now at Stanford, has the effect of fusing gravity
with the other known forces at the more reasonable energy of 10^3
GeV (rather than at 10^18 GeV), thus solving the hierarchy problem.
One testable implication of the new hypothesis would be the existence
of exotic new particles which could be detectable at energies to be
available in a few years at the Large Hadron Collider (LHC) under
construction in Geneva. (Two articles by Randall and Sundrum in
upcoming Physical Review Letters.)

WAVE PROPERTIES OF BUCKYBALLS have been observed in an
experiment at the University of Vienna. Physical objects from quarks
to planets have wavelike attributes. The quantum nature of a bowling
bowl, unfortunately, is not manifest since its equivalent quantum (or de
Broglie) wavelength is so tiny that interference effects (for example,
the left part of the ball negating the right part of the ball) cannot be
detected in a practical experiment. However, the wave properties of
some composite entities, such as atoms and even small molecules,
have previously been demonstrated. Now Anton Zeilinger at the
University of Vienna (zeilinger-office@exp.uniwire.ac.at) has been
able to perform the same feat for fullerenes, the largest objects (by a
factor of ten) for which wavelike behavior has been seen. The
researchers send a beam of the soccerball-shaped C-60 molecules (with
velocities of around 200 m/sec) through a system of baffles and a
grating (with slits 50 nm wide,100 nm apart) which yields a striking
interference pattern characteristic of quantum behavior. Ironically the
pattern indicating wave behavior is built up from an ensemble of
individual sightings, each of which depends upon a buckyball's
particle-like ability to make itself felt in an electrode. The interference
is not negated thereby since it is not known by which path the C-60
came to be at the electrode.(Arndt et al., Nature, 14 October 1999.)

STRIPED SUPERCONDUCTIVITY. In high-temperature ceramic
superconductors, currents flow mostly in the plane. But if special
dopants (such as neodymium) are added to La-Sr-Cu-O materials, the
supercurrents seem to be further restricted to narrow lanes or stripes.
In these materials rows of charges are separated by insulating
antiferromagnetic regions (in which neighboring atomic spins oppose
each other), so they are referred to as charge-ordered or spin-ordered
materials. Since the stripes occur preferentially at lower temperatures,
physicists are not sure whether the stripes help or hurt
superconductivity. Two new experiments (in which the
superconductivity is turned off, the better to study underlying
electronic properties) add some fresh perspective. A University of
Tokyo team (Noda et al.) uses a strong magnetic field to produce a
Hall effect, in which electrons should be pushed sideways by the field.
A resistance to this effect is taken as evidence for a "self-organized"
one-dimensional charge flow. Meanwhile a Stanford-LBL-Tokyo team
(Zhou et al.) shoots UV photons into their samples and observe the
ejected electrons that come flying out. The telltale photo-electron
pattern maps back to charge flows in the sample that must have been
organized into stripes. (Both articles appear in Science, 8 Oct.)

PHYSICS NEWS UPDATE
The American Institute of Physics Bulletin of Physics News
Number 452 October 12, 1999 by Phillip F. Schewe and Ben Stein

THE 1999 NOBEL PRIZE FOR PHYSICS goes to Gerardus 't
Hooft of the University of Utrecht and Martinus Veltman, formerly
of the University of Michigan and now retired, for their work
toward deriving a unified framework for all the physical forces.
Their efforts, part of a tradition going back to the nineteenth
century, centers around the search for underlying similarities or
symmetries among disparate phenomena, and the formulation of
these relations in a complex but elegant mathematical language. A
past example would be James Clerk Maxwell's demonstration that
electricity and magnetism are two aspects of a single electro-
magnetic force.
Naturally this unification enterprise has met with various
obstacles along the way. In this century quantum mechanics was
combined with special relativity, resulting in quantum field theory.
This theory successfully explained many phenomena, such as how
particles could be created or annihilated or how unstable particles
decay, but it also seemed to predict, nonsensically, that the
likelihood for certain interactions could be infinitely large.
Richard Feynman, along with Julian Schwinger and Sin-Itiro
Tomonaga, tamed these infinities by redefining the mass and charge
of the electron in a process called renormalization. Their theory,
quantum electrodynamics (QED), is the most precise theory known,
and it serves as a prototype for other gauge theories (theories which
show how forces arise from underlying symmetries), such as the
electroweak theory, which assimilates the electromagnetic and weak
nuclear forces into a single model.
But the electroweak model too was vulnerable to infinities and
physicists were worried that the theory would be useless. Then 't
Hooft and Veltman overcame the difficulty (and the anxiety)
through a renormalization comparable to Feynman's. To draw out
the distinctiveness of Veltman's and 't Hooft's work further, one
can say that they succeeded in renormalizing a non-Abelian gauge
theory, whereas Feynman had renormalized an Abelian gauge theory
(quantum electrodynamics). What does this mean? A mathematical
function (such as the quantum field representing a particle's
whereabouts) is invariant under a transformation (such as a shift in
the phase of the field) if it remains the same after the transformation.
One can consider the effect of two such transformations, A and B.
An Abelian theory is one in which the effect of applying A and then
B is the same as applying B first and then A. A non-Abelian theory
is one in which the order for applying A and B does make a
difference. Getting the non-Abelian electroweak model to work was
a formidable theoretical problem.
An essential ingredient in this scheme was the existence of
another particle, the Higgs boson (named for Peter Higgs), whose
role (in a behind-the-scenes capacity) is to confer mass upon many
of the known particles. For example, interactions between the Higgs
boson and the various force-carrying particles result in the W and Z
bosons (carriers of the weak force) being massive (with masses of
80 and 91 GeV, respectively) but the photon (carrier of the
electromagnetic force) remaining massless.
With Veltman's and 't Hooft's theoretical machinery in hand,
physicists could more reliably estimate the masses of the W and Z,
as well as produce at least a crude guide as to the likely mass of the
top quark. (Mass estimates for exotic particles are of billion-dollar
importance if Congress, say, is trying to decide whether or not to
build an accelerator designed to discover that particle.) Happily,
the W, Z, and top quark were subsequently created and detected in
high energy collision experiments, and the Higgs boson is now itself
an important quarry at places like Fermilab's Tevatron and CERN's
Large Hadron Collider, under construction in Geneva.
(Recommended reading: 't Hooft, Scientific American, June
1980, excellent article on gauge theories in general; Veltman,
Scientific American, November 1986, Higgs bosons. More
information is available at the Swedish Academy website:
http://www.nobel.se/announcement-99/physics99.html)

THE 1999 NOBEL PRIZE IN CHEMISTRY goes to Ahmed H.
Zewail of Caltech, for developing a technique that enables scientists
to watch the extremely rapid middle stages of a chemical reaction.
Relying on ultra-fast laser pulses, "femtosecond spectroscopy" can
provide snapshots far faster than any camera--it can capture the
motions of atoms within molecules in the time scale of
femtoseconds (10^-15 s).
An atom in a molecule typically performs a single vibration in
just 10-100 femtoseconds, so this technique is fast enough to discern
each and every step of any known chemical reaction. Shining pairs
of femtosecond laser pulses on molecules (the first to initiate a
reaction and the second to probe it) and studying what type of light
they absorb yields information on the atoms' positions within the
molecules at every step of a chemical reaction. With this technique,
Zewail and his colleagues first studied (in the late 1980s) a 200-
femtosecond disintegration of iodocyanide (ICN-->I+CN),
observing the precise moment at which a chemical bond between
iodine and carbon was about to break.
Since then, femtochemistry has revealed a whole new class of
intermediate chemical compounds that exist less than a trillionth of a
second between the beginning and end of a reaction. It has also
provided a way for controlling the courses of chemical reaction and
developing desirable new materials for electronics. It has provided
insights on the dissolving of liquids, corrosion and catalysis on
surfaces (see Physics Today, October 1999, p. 19); and the
molecular-level details of how chlorophyll molecules can efficiently
convert sunlight into useable energy for plants during the process of
photosynthesis. (Official announcement and further info at
http://www.nobel.se/announcement-99/chemistry99.html; see also
Scientific American, December 1990.)

PHYSICS NEWS UPDATE
The American Institute of Physics Bulletin of Physics News
Number 451 October 8, 1999 by Phillip F. Schewe and Ben Stein

SANDSTONE TORTUOSITY. In conventional nuclear magnetic
resonance (NMR) imaging, a liquid is the working substance. For
example, the hydrogen nuclei in watery living tissue are weakly
oriented by a powerful magnet, and then these nuclei signal their
positions by emitting radio waves. By contrast, gas-phase NMR
imaging has been difficult because of the low density of gases,
which yields only a weak NMR signal. Recently, however,
practical NMR imaging has been realized for noble-gas atoms by
strongly orienting the nuclei (with polarized laser light) outside the
sample and then injecting them into, say, the lungs, where they
rapidly diffuse into the deepest of alleyways, providing data that
can't be collected in any other way. In a new extension of gas-phase
NMR to the study of porous materials such as oil-bearing sandstone
and carbonate rocks, the aim right now is not so much to provide
images (the rapid diffusion of the gas atoms limits the spatial
resolution, as one would expect for a moving target, to about one
millimeter) as it is to characterize internal topology. Ronald
Walsworth (617-495-7274, rwalsworth@cfa.harvard.edu) and his
colleagues at the Harvard-Smithsonian Center for Astrophysics and
Schlumberger-Doll inject xenon atoms into various porous rock
samples filled with countless pores and connections, which affect
the rate of gas diffusion and flow in the porous solid. They
determine such things as the pore surface-area-to-volume ratio and a
property called 'tortuosity,' which is an indication of how the
structure of the porous medium restricts the flow of gases or liquids
through the material. In this sense, tortuosity is to fluid flow what
the structure of a wire (cross-section, length, etc.) is to the flow of
electricity. Noble gases may be handier to use than liquids in NMR
studies of rocks and other porous materials since the gas can flow
further and faster through the pores without losing its orientation.
(R.W. Mair et al., Physical Review Letters, 18 October 1999.)

WAVY MICROSTRUCTURES, induced to grow in a polymer
surface by a stressful puckering process, might be useful as a
diffraction grating or as a part of various microelectromechanical
systems (MEMS). George Whitesides (617-495-9430,
gwhitesides@gmwgroup.harvard.edu), Ned Bowden (617-495-
9434), and their colleagues at Harvard begin by heating a film of the
elastic polymer material PDMS (polydimethylsiloxane) attached to a
glass slide. The top coating of the film expands when heated, after
which it is exposed to an oxygen plasma, which makes a silica-like
crust. When the whole sample is cooled, the silica layer relieves the
stress by puckering (see the figure at
www.aip.org/physnews/graphics). The waves are locally ordered
but will be rather disorderly on a global level unless an extra
organizational rule can be imposed, in this case in the form of a bas-
relief pattern (see the second figure) on the PDMS surface. The
resulting wavy structures can be made with wavelengths as small as
half a micron. This might facilitate a variety of uses, such as being
part of a detection system for microfluidic devices, as stamps for
microcontact printing, as masks for photolithography, or as surfaces
on which cells can be grown and oriented. (Bowden et al., Applied
Physics Letters, 25 October 1999.)

NEPTUNE DIAMONDS. The crushing conditions inside Neptune
and Uranus are recreated at UC Berkeley, where a tiny sample of
methane is squeezed in a diamond anvil press up to pressures of 30-
50 GPa (more than 10 million atm) and heated with laser light to
temperatures to 3000 K. Scattered x rays and infrared light indicate
that some of the methane is being converted into 10-micron-sized
diamonds and certain polymers at pressures much below what had
been expected. This result might lead to some re-assessment of
planetary interiors since a widespread dissociation of methane would
release considerable energy, affecting the dynamics and evolution of
the planet in a big way. (Benedetti et al., Science, 1 October 1999.)

PHYSICS NEWS UPDATE
The American Institute of Physics Bulletin of Physics News
Number 450 September 30, 1999 by Phillip F. Schewe and Ben
Stein

CHILLING MIRRORS WITH LIGHT. In astronomy the effect of
atmospheric turbulence on the quality of images acquired by
ground-based telescopes can be greatly reduced by "adaptive
optics," a corrective process in which parts of the telescope mirror
are flexed mechanically by piezoelectric motors in an amount
typically equal to a fraction of the wavelength of the incoming light.
In interferometric measurements adjustments in mirrors are also
desirable, not because of turbulence in the intervening medium but
because of thermal noise in the mirror itself. The LIGO and VIRGO
interferometers (Update 442), searching for gravity waves, need
very still mirrors, the better to observe the flexing of space-time on a
scale far smaller than the size of an atom. A new technique might
help in this regard. Physicists at the Ecole Normale Superieure and
Universit‚ P. et M. Curie in Paris (Antoine Heidmann and Michel
Pinard, heidmann@spectro.jussieu.fr, 011-33.1-4427-4405), can
measure the thermal agitation of mirrors and reduce this unwanted
noise by a factor of 20, with pressure from laser light. This
corresponds to a spatial sensitivity of the mirror at a level of a
billionth of an angstrom. (P.F. Cohadon et al., upcoming article in
Physical Review Letters; see figure at
www.aip.org/physnews/graphics.)

COUNTING UP TO 100 MILLION. The science of measurement,
metrology, has been moving away from standards based on artifacts
such as a meter stick and toward the use of quantum phenomena to
provide reliable, accurate and, if possible, portable calibrations that
can be used by researchers in the field. Examples are resistance
defined in terms of the quantum Hall effect (Update 205) and
voltage in terms of the Josephson effect (Update 406). Consider
capacitance, the measure of how well a tiny reservoir can store
electrical charge. NIST already has the best capacitance standard,
accurate to 0.02 parts per million (ppm). But this device is
cumbersome and, more importantly, its accuracy is frequency
dependent. For rendering the value of capacitance in circuits
operating outside a certain frequency range, the standard is no better
than 2 ppm. A promising new approach to capacitance (pioneered at
NIST; contact Mark Keller, 303-497-5430) uses a single-electron
transistor (SET), which contains at its heart a tiny refuge for
electrons where the arriving charges can be counted one at a time,
all the way up to 100 million or more. When combined with an
accurate voltage measurement this becomes an accurate capacitance
standard (C=Q/V). The SET approach has now achieved a
measurement accuracy of about 2 ppm, and the NIST researchers
hope soon to reach 0.1 ppm. The setup is relatively portable and its
output is largely independent of frequency. (Keller et al., Science
10 Sept.)

QUANTUM COOL. Physicists at Simon Fraser University in
Vancouver are trying to get electrical circuits to cool themselves
electrostatically. To do this they employ both quantum and classical
physics. First, the classical: a gas can cool down by pushing against
a piston; some of the gas's thermal energy is converted into
mechanical energy. Second, the quantum: electrons flowing from
one GaAs layer into another via another a thin layer of AlGaAs will
move with optimum efficiency if the electron energy matches a
preferred "resonant" energy in the AlGaAs layer. This three-layer
setup, called a quantum well, is at the heart of grocery-store laser
scanners and CD players. As circuitry shrinks, disposing of waste
heat from even tiny electric currents becomes an ever greater
problem. The Simon Fraser researchers are proposing that the
electrons in a quantum well cool themselves by moving against not a
piston but against an opposing electric field, a field in addition to the
one moving the electrons through their circuit. This way of
combining the quantum (the electrons as waves tunneling through a
thin layer) and the classical (the electrons as a working fluid in a sort
of Carnot heat engine) might lead to a completely new category of
microelectronic quantum device. (Luis Rego and George
Kirczenow, kirczenow@sfu.edu, Applied Physics Letters, tent. 11
Oct.)

PHYSICS NEWS UPDATE
The American Institute of Physics Bulletin of Physics News
Number 449 September 23, 1999 by Phillip F. Schewe and Ben
Stein

ARE BOSE-EINSTEIN CONDENSATES SUPERFLUID?
Previously physicists have demonstrated that Bose Einstein
condensates (BEC is created when trapped atoms are chilled so low
that they begin to overlap) constitute a single macroscopic
quantum state, which implies superfluidity. However, physicists
would like to see frictionless flow more directly. Two new
experiments pave the way toward this goal. A NIST/Colorado
group has observed quantized vortices in a condensate of rubidium
atoms, while an MIT group has observed that excitations can move
through a condensate of sodium atoms and lose little or no energy
if the velocity is below a certain critical value. In the
Colorado/NIST work (Carl Wieman, 303-492-6963,
cwieman@jila.colorado.edu) the BEC state consists of atoms
residing in two separate spin states (referred to as 1 and 2). Using
microwaves and a separate probe laser beam working at the fringe
of the condensate, the spins of 1-state atoms are flipped, turning
them into 2-state atoms in one sector of the condensate after
another. This sets a vortex of 2-state atoms into motion around the
outer part of the condensate while 1-state atoms remain at rest at
the core of the vortex (see the figures at
www.aip.org/physnews/graphics). Thus the vortex is like a smoke-
ring of 2-state atoms (with a filling of 1-state atoms) rotating about
every 3 seconds. Furthermore, it has exactly one unit of angular
momentum. Meanwhile the MIT group (Wolfgang Ketterle,
ketterle@mit.edu, 617-253-4876) uses a focused laser beam to
punch a hole in the BEC blob (the light repels atoms from its
focus) and then scans the hole along at various speeds. The
moving hole is equivalent to a moving object. Below a scan
velocity of about 2 mm/sec, no energy dissipation was observed.
The existence of such a critical velocity for frictionless motion is
an attribute of superfluidity. One reason for this kind of BEC
research, other than for studying fundamental aspects of a novel
form of atomic matter, is that it might afford a new way of learning
about superfluidity and superconductivity. (Both reports appear in
the 27 Sep issue of Physical Review Letters: Colorado/NIST in
M.R. Matthews et al. and the MIT work in C. Raman et al.)

SEPARATING CHEMICAL ISOTOPES WITH A TABLETOP
TERAWATT LASER has been demonstrated by researchers at the
University of Michigan, providing a more compact alternative to
the bulky techniques for extracting isotopes, and introducing a new
method for making ultrapure thin films which can be used in
electronic devices. Using a technique known as chirped pulse
amplification (Update 154), University of Michigan researchers
(Peter Pronko, 734-763-6008) produced laser pulses that deliver
between 10 trillion and 1 quadrillion watts (10-1000 terawatts) of
power per square centimeter for an extremely short instant--
between 150 and 200 quadrillionths (10^-15) of a second. Aimed
at a target inside a vacuum chamber containing the isotopes of
interest, the pulse vaporized some of the isotopes, which escaped
in the form of ions (charged atoms). Intense magnetic fields
associated with the pulses exerted forces on the ions which
deposited them at different locations on a nearby silicon disk
depending on the isotope's weight. With their technique, the
researchers separated boron-10 from boron-11 and gallium-69 from
gallium-71. It's an open question if their technique will be feasible
on the large scales required for separating isotopes at nuclear
facilities, but the researchers are initially setting their sights on
other applications, such as depositing pure thin films of isotopes
directly onto microelectronic devices. (Pronko et al., Physical
Review Letters, 27 September 1999; figure at
www.aip.org/physnews/graphics)

PHYSICS NEWS UPDATE
The American Institute of Physics Bulletin of Physics News
Number 448 September 16, 1999 by Phillip F. Schewe and Ben
Stein

LIQUID CRYSTAL ACOUSTICS. Penn State physicist Jay Patel
seeks to understand the optical properties of liquid crystals which,
consisting of rod shaped molecules with the ability to polarize
light, are regularly employed in electronic displays; an applied
voltage lines up the rods and shuts off or turns on transmitted light.
So it came as a big surprise when Patel discovered that liquid
crystals also have acoustic properties. To be precise, an applied
voltage imparts energy to the rod molecules which in turn cause
the cavity in which the liquid crystal resides to vibrate. The cavity
resonates with an audible frequency that could be heard with the
unaided ear. (An analogy: the stings of a violin aren't what make
sound; rather they transmit the energy of the bow to the body of the
violin whose vibrations are source of the music we hear.) Unsure
of the implications of liquid crystal sound (tiny speakers, delay
lines for circuits?), Patel and his colleagues suspect that this
discovery will lead to a fruitful new research area. (Kim and Patel,
Applied Physics Letters, 27 Sept. 1999; contact Patel at
jayp@phys.psu.edu; 814-863-8999.)

CLAY OSCILLONS. Nature often sorts energy into certain
preferred forms such as the unique spectrum of colors emitted by
heated atoms or the characteristic note sounded by an organ pipe.
This energy sorting can even turn up in a granular material. For
example, a few years ago (Update 286) scientists discovered that
collections of tiny metal balls, when shaken slightly up and down,
vested some of their energy in the form of tiny waterspout heaps
called "oscillons" Now physicists at the Hebrew University in
Jerusalem (Jay Fineberg, jay@vms.huji.ac.il) have observed a
similar effect in a colloid, a fluid material (e.g., milk) in which tiny
particles (in this case small bits of clay) are suspended in a solvent
(see www.aip.org/physnews/graphics). Granular media and
suspensions are very different in nature---grains are discrete
objects that collide directly with each other whereas the particles in
colloids interact via the medium of the solvent fluid---so the
appearance of oscillons in both materials might represent some
universal manifestation of driven nonlinear systems. The
researchers are not yet sure where localized oscillon states would
turn up in the natural world. One possibility is earthquakes.
Oscillon-like states may explain the localized and highly variable
damage (or intense ground acceleration) which, in many cases,
occurs in poorly consolidated sediments (in analogy to the clay
sediments used in the experiments) at relatively large distances
from an earthquake's epicenter. (Lioubashevski et al., Physical
Review Letters, tent. 11 Oct.)

VISUALIZING ELECTRONIC ORBITALS. The image of an
atom is really the image of its outermost electrons or, to be more
precise still, the image of the averaged likelihood that the electrons
will be at various places. For any but the innermost electrons, the
shape of this likelihood surface (or orbital) will be non-spherical in
shape. Physicists at Arizona State have now actually imaged these
orbitals for the first time and shown that they look just the
drawings used in quantum textbooks for decades. Using a
combination of x-ray diffraction and electron microscopy the ASU
scientists produced a 3D map of the orbitals of copper atoms and
their bonds with neighboring atoms in a cuprite (Cu2O) compound
(see figure at www.aip.org/physnews/graphics). The images of
Cu-O and Cu-Cu bonds might provide insight into the workings of
high temperature superconductors, in which the whereabouts of
electrons and holes (the voids left by vacated electrons) are crucial.
(J.M. Zuo et al., Nature, 2 Sept. 1999.)

CORRECTION. Fermionic atoms (Update 447) are atoms with an
odd number of constituents (electrons, protons, or neutrons), but it
should be emphasized that these constituents are themselves
fermions, namely half-integral-spin entities. Dysprosium (Update
443) is element 66, not element 62.

PHYSICS NEWS UPDATE
The American Institute of Physics Bulletin of Physics News
Number 447 September 9, 1999 by Phillip F. Schewe and Ben
Stein

A "FERMI-DEGENERATE" ATOMIC GAS, a gas of fermion
atoms (atoms composed of an odd number of particles) which
essentially overlap with one another, has been created for the first
time, promising tabletop insights into the basic properties of neutron
stars, superfluid helium and all forms of superconductivity.
Preparing this gas of fermions requires the exact same conditions as
for preparing a Bose-Einstein condensate (BEC) of boson atoms,
atoms composed of an even number of particles. One must cool a
gas of atoms to the point that they exhibit wavelike properties and
pack them densely enough so that the average distance between
atoms is comparable to their "deBroglie wavelength." At this point,
individual atoms become impossible to distinguish. If the atoms are
bosons, they fall collectively into the lowest-energy (ground) state to
form a BEC (Update 233). If the atoms are fermions, however, this
cannot happen. The Pauli exclusion principle prohibits two
fermions from occupying the same state. Instead, the fermions
dutifully occupy different quantum states on the lowest available
energy levels, just as water fills a bottle from the bottom up to some
top level. (See figures at www.aip.org/physnews/graphics.) This
ensemble of atoms is called a "quantum degenerate gas" owing to
the fact that the differences between bosons and fermions only
become important in this low-temperature, high-density regime. A
Fermi degenerate gas has more energy than predicted by classical
physics, because fermions have to occupy higher and higher energy
levels once the lower ones get filled up. Achieving this state has
been difficult because cooling fermions is more difficult than
cooling bosons: placed in a trap made with magnetic fields, fermions
in similar states tend to repel each other and avoid the energy-
transferring collisions required for "evaporative cooling." To combat
this, researchers in Colorado (Deborah Jin, 303-492-5735,
NIST/University of Colorado) prepared potassium-40 atoms in two
different states of spin, a quantity which describes how the atoms
respond to an external magnetic field. The two species could collide
with one another and this enabled evaporative cooling to occur.
Then, one spin species was removed by a radio-frequency field,
leaving about a million of atoms in the other spin species for study.
The Colorado group deduced their temperature to be approximately
290 nanokelvins--the lowest ever recorded for a gas of fermions.
They witnessed that the fermion nature of the atoms dramatically
inhibited evaporative cooling. This is due in part to the Fermi
pressure--the repulsion of atoms in the trap--which resists the
compression necessary for effective evaporative cooling.
(Therefore, this system can provide insights into how the fermions
that make up white dwarfs and neutron stars remain buoyant instead
of collapsing by the force of gravity.) In the future, researchers
hope to study superconductivity by forming Cooper pairs with the
fermions, at even lower temperatures than presently achieved.
Creating such a "Fermi superfluid" will enable investigations into all
forms of superfluidity and superconductivity. (DeMarco and Jin,
Science, 10 September 1999.) Other groups are pursuing these and
similar states with other fermion atoms (Phys. Rev. Focus, 24 May
1999).

ANOMALOUS ACCELERATION UPDATE. Last year a team of
scientists published an assessment of the longterm trajectories of
certain spacecraft, including Pioneer 10 and 11, showing that even
after all known sources of gravity (sun, planets, comets, etc.) and
other forces were taken into account, an extra acceleration seemed to
be present (Anderson et al., Physical Review Letters, 5 Oct 98;
Update 391). Now a series of letters concerning this assessment
appears in the same journal (30 August 1999). John Murphy of
Johns Hopkins (301-953-6214) argues that the explanation lies in
the asymmetric radiation given off by the crafts' electronics as waste
heat. Jonathan Katz of Washington University (314-935-6202)
implicates the recoil of radiation (from radioactive thermal
generators, or RTG, powering the craft) off the rear of the high-gain
antenna. The authors of the original paper (contact John Anderson,
JPL, 818-354-3956) basically assert that these two particular
explanations fall short of accounting for the anomalous acceleration
by roughly a factor of five or more. (All PRL papers are available
to journalists from AIP Public Information.)

PHYSICS NEWS UPDATE
The American Institute of Physics Bulletin of Physics News
Number 446 September 1, 1999 by Phillip F. Schewe and Ben Stein

DARK MATTER ANNIHILATION AT THE GALACTIC CENTER.
How does the presumed massive black hole at the center of our galaxy
shape the distribution of the presumed halo of dark matter in its
vicinity? Paolo Gondolo of the Max Planck Institute of Physics
(Munich, Germany) and Joseph Silk of Oxford (UK; also UC
Berkeley) suggest the black hole sculpts the dark matter into a dense
spike where particle annihilation (or, more to the point, self-
annihilation, since one of the leading hypothetical dark-matter particles
is the "neutralino," which is its own antiparticle) would be enhanced.
Of all the annihilation products (e.g., electrons, positrons, protons,
etc.) issuing from the galactic center (a region half a light year wide)
neutrinos would be the most serviceable since they can travel to Earth
undeflected by magnetic fields. Gondolo and Silk have calculated
how present and future neutrino telescopes can probe the density of
inner halo dark matter. (Physical Review Letters, 30 August;
gondolo@mppmu.mpg.de, 011-49-893-235-4427.)

TO MEASURE LOCAL GRAVITY WITH AN UNCERTAINTY of
3 parts per billion, Steven Chu uses an atom interferometer, in which
cesium atoms are treated like waves, split apart into two wavelets, each
of which takes a separate path. When the wavelets are brought back
together they produce an interference pattern which depends
sensitively on the local force (gravity) tugging on the atoms. Not only
is this an improvement (by a factor of a million) in accuracy over
previous atom interferometers but represents, according to Chu, "the
best confirmation of the equivalence principle between a quantum and
macroscopic object." (Peters et al., Nature, 26 August 1999.)

NERVE CELLS MAY HOLD THEIR FIRE to allow their neighbors to
send electrical signals, researchers have proposed, potentially
explaining how interconnected networks of nerve cells send
information with high fidelity, and providing insights into how to
design better signal-processing devices for electronic equipment such
as CD players. At a cocktail party, many people talk simultaneously,
and one is able to hear several nearby conversations at once. In a
conference call, on the other hand, people generally take turns to speak.
Researchers (Doug Mar, Boston University, 617-353-5463) have
proposed that an interconnected network of nerve cells is similar to a
conference call: when a nerve cell fires, its neighbors are inhibited and
do not fire until it is done. One consequence is that the nerve cells fire
in rapid succession, permitting the network to transmit signals at higher
frequencies. Moreover, the pattern of random firings of nerve cells,
corresponding to noise, is smoothed out, enabling the cells to convey
information with higher fidelity. Finding direct evidence for these
phenomena in biological systems will be challenging, because it is
currently difficult to measure accurately the firing patterns of several
interconnected neurons simultaneously. In the meantime, the
researchers are working with Analog Devices, Corp. in Massachusetts
to apply the lessons from the theory to creating biologically inspired
networks of interconnected electric circuits with improved
characteristics, such as an extended range of operating frequencies.
(Mar et al., Proceedings of the National Academy of Sciences, 31
August.)

US HIGH-SCHOOL PHYSICS ENROLLMENTS AT A POSTWAR
HIGH. The percentage of US high-school students taking physics has
risen by eight percent in the last decade, reaching an all-time high of
28% since the end of World War II. In the late 1990s, girls now
represent almost half (47%) of students taking high-school physics (as
opposed to 39% in 1987). However, African-American and Hispanic
students remain underrepresented in physics classes; the same holds
true for women and non-white physics teachers. These statistics come
from a new AIP report entitled "Maintaining Momentum: High School
Physics For A New Millennium." (Contact Mark McFarling at
mmcfarli@aip.org. Full report at
www.aip.org/statistics/trends/reports/hsreport.pdf.)

PHYSICS NEWS UPDATE
The American Institute of Physics Bulletin of Physics News
Number 445 August 25, 1999 by Phillip F. Schewe and Ben
Stein

NEW THEORY OF EPILEPSY. Epilepsy is a sort of hurricane in
the brain; its onset is marked by a transition from the customary
uncoordinated (perhaps even chaotic) firings of neighboring
neurons into (ironically enough) a periodic common firing. A
hurricane's awesome organization comes from rising tropical heat
entraining surrounding air masses in a cyclonic motion. The
organizing principle behind epileptic seizures, by contrast, is not
yet known. At present the main way of studying seizures is with
electroencephalograms (EEGs) which, useful as they are, can
provide only a superficial (the electrodes sit on the scalp),
averaged signal map blurred by the passage of the electrochemical
currents through tissue, blood, and bone. To monitor a seizure
with greater detail, one would like to fly right into the center of
the storm. In recent years this has been possible with the
implantation of "depth electrodes" in the "focus" region of the
hippocampus (the staging point for some of the most intractable
forms of epilepsy). This provides a spatial resolution of one to
two orders of magnitude better than conventional electrodes.
Such work is being carried out at Indiana University Purdue
University at Indianapolis (contact Raima Larter, 317-274-6882,
larter@chem.iupui.edu), where researchers are now presenting a
new theory of epilepsy. Epilepsy is a "dynamical disease," arising
not from any structural abnormality or from any chemical
deficiency or surplus, but rather from the temporary excursion of
a critical parameter outside of some acceptable window of
behavior. Knowing what this parameter is could lead to new
therapies. The IUPUI scientists suspect the mystery parameter
might be the speed of communication among the synchronized
neurons. And this speed, in turn, might be related to how glial
cells (once thought of being no more than the "glue" between
neurons) process calcium ions. Indeed, the glia are now known to
be sensitive to neurotransmitters, which initiate waves of calcium
concentration among the glia like water waves rolling around a
swimming pool. Thus the coming and going of epilepsy might be
related to a chemical wave in the brain. (Larter et al., Chaos,
September 1999; copies of the article can be obtained from AIP
Public Information; figures at www.aip.org/physnews/graphics.)

A LINEAR DECELERATOR FOR NEUTRAL MOLECULES,
identical in principle to a linear accelerator (LINAC) for charged
particles, has been demonstrated by researchers in the Netherlands
(Gerard Meijer, University of Nijmegen, 011-31-24-365-2277,
gerardm@sci.kun.nl), providing a new way to cool molecules to
ultralow temperatures. Previous methods for cooling molecules
either depend upon the presence of a cold background gas and
magnetic fields (Update 393), or they are restricted to those
molecules which can be formed by combining already cold trapped
atoms. In their demonstration, the researchers constructed a 35-
centimeter long "Stark decelerator," containing a succession of 63
pulsed electric fields. The decelerator can slow down any neutral
molecule with a permanent dipole moment, i.e., a permanent
separation of electric charge within the molecule. This includes
any diatomic molecule composed of two different elements (such
as NaCl), but also molecules like H2O and NH3. The researchers
chose to demonstrate their technique with carbon monoxide (CO).
When a pre-cooled mixture of CO in xenon gas entered the linear
decelerator, each molecule experienced the Stark effect; at every
electric field, their internal energy shifted upward and caused them
to lose some kinetic energy. After passing through all 63 electric-
field stages, a subset of the CO molecules was slowed down from
225 m/s to 98 m/s, with an equivalent temperature of 30
millikelvin. Additional electric field stages could in principle cool
the molecules further. This technique promises to be useful for
cold-molecule physics, a field which is "expected to bloom in the
next decade," says Meijer. (Bethlem, Berden and Meijer, Phys.
Rev. Lett., 23 August 1999.)

PHYSICS NEWS UPDATE
The American Institute of Physics Bulletin of Physics News
Number 444 August 19, 1999 by Phillip F. Schewe and Ben
Stein

SUPERSYMMETRY IN ATOMIC NUCLEI. A new experiment
provides solid evidence that fermions (objects with half-integral
spin) and bosons (objects with integral-valued spin) are both
governed by the same nuclear physics laws. (The operative term
for this egalitarianism, supersymmetry, should not be confused
with a similar word used in particle physics to denote the
equivalence of fundamental bosons and fermions such as photons
and quarks, and of all the physical forces, at energies approaching
10^19 GeV.) The nuclear shell model, dating from 1948,
attempts to describe the nucleons (protons and neutrons) in an
atomic nucleus as sorting themselves into shells much as electrons
do in the atom as a whole. A further innovation in nuclear theory,
the interacting boson model (c1974), holds that nucleons can even
pair up within their shells, protons with protons and neutrons with
neutrons. Individual nucleons are fermions but nucleon pairs are
effectively bosons and as such are immune from Pauli's exclusion
principle. This allows the pairs to fall into a sort of ground state,
leaving only the outermost nucleons to determine the nature of the
nucleus's energy level diagram (again analogous to an element's
chemistry being determined mostly by its outermost "valence"
electrons). In atomic energy diagrams the levels are separated by,
at most, electron volts; in nuclear diagrams the levels are
typically separated by100 keV or so. Studying these diagrams
involves shooting beams (often of protons or deuterons) into a
sample, in which nuclei can be promoted into a variety of excited
states, and then detecting the telltale particles and high energy
photons (gammas) that come out. Nuclei that have an even
number of protons and an even number of neutrons possess
perhaps a dozen excited energy levels below an energy of 2 MeV,
and are relatively easy to probe experimentally. Pt-194 is an
example. When the target nucleus has an odd number of either
protons (eg, Au-195) or neutrons (eg, Pt-195), the number of low-
energy excited states might be 20, making it harder to predict an
energy diagram. Extending the interacting boson model further to
nuclei with an odd number of both protons and neutrons (a
nucleus which would consist, in effect, of many bosons and at
least two unpaired fermions) entails another level of difficulty.
Harder still is experimentally mapping the energy level diagram
for such a nucleus since it would have one hundred or more low-
lying excited states. Nevertheless, an intrepid Swiss-German
collaboration has now done exactly this for Au-196, a nucleus
with 79 protons and 117 neutrons. (Contact Jan Jolie, University
of Fribourg, Switzerland, 41-26-300-9097, jan.jolie@unifr.ch;
Gerhard Graw, University of Munich, Germany, 49-892-891-
4155, gerhard.graw@physik.uni-Muenchen.de.) Using high-
resolution detectors they were able to sort through the complex
energy-level terrain of Au-196, as well as those for the other three
nuclei mentioned above, with results very close to theoretical
predictions, demonstrating thereby that a single set of equations
could indeed account for nuclei with all the different combinations
of even or odd number of neutrons and protons. This is evidence
for supersymmetry in nuclei: nuclear forces seem to treat fermions
and bosons equivalently, at least for these four nuclei. According
to Richard Casten of Yale (rick@riviera.yale.edu, 203-432-6174),
who is not a team member, this new research represents an
important step forward in applying the interacting boson model.
(Metz et al., Physical Review Letters, 23 August 1999.)

FACULTY POSITIONS FOR WOMEN are increasing slowly in
number at US university physics departments. A new AIP report
(1997-98 Academic Workforce Report) shows that in the recent
half decade (from 1994 to 1998) the percentage of full professors
who are women stayed the same (3%) but the percentage of
women associate professors increased from 8 to 10% and assistant
professors increased from 12 to 17%. Where do these new slots
come from? Partly from a very modest increase (2%) in the overall
size of the faculty and partly through retirement, which for several
years has held steady at a rate of 2% (43% of these came as a result
of retirement incentives). For more information contact Rachel
Ivie at AIP, 301-209-3081, rivie@aip.org.

PHYSICS NEWS UPDATE
The American Institute of Physics Bulletin of Physics News
Number 443 August 16, 1999 by Phillip F. Schewe and Ben
Stein

NUCLEAR THERMOMETER. How hot is it inside the nucleus
of a dysprosium atom (element 62, abbreviated Dy)? Temperature
is a statistical concept that normally applies to an ensemble of
many particles, such as air molecules or a gas of atoms kept in a
bottle. Inside a heavy nucleus, swarming with protons and
neutrons (collectively called nucleons) it's not so easy to define
temperature, owing to the many pairing and other inter-nucleon
interactions that take place, but it can be done. The nuclear
environment can be sampled by colliding nuclei together and then
carefully measuring the photons that fly out: high energy gamma
rays, in this case, rather than the visible and infrared photons that
come out of heated-up atomic gases. In this way, physicists at the
University of Oslo have deduced the temperature inside a Dy
nucleus (in effect, a gas of 162 nucleons) to be 6 billion K. It can
be said, therefore, that even in winter parts of Norway (very small
parts) remain quite warm. This is the first time a nuclear
temperature has been measured strictly on the basis of the spectrum
of gammas emitted. (E. Melby et al., Physical Review Letters,
tent. 30 August 1999; contact Magne Guttormsen,
magne.guttormsen@fys.uio.no, 011-47-2285-6460.)

GALAXY FORMATION IN AMOEBAS. Dictyostelium
discoideum is the hydrogen atom of developmental biology.
Depending on available nutrients the organism can exist in a uni-
cellular or multi-cellular state (in which cells differentiate
themselves as spore or stalk cells). Dictyostelium cells like to
huddle together. A new experiment at UC San Diego shows,
furthermore, that when constrained to two dimensions the
ensemble will also start rotating and persist in this motion for tens
of hours. Self-organized vortex states in biological systems
(flocking birds, schools of fish, bacteria) have been seen before but
not in deformable units as here. A chemical wave (of the organic
molecule cyclic AMP) probably brings the cells together in the
first place, but thereafter the vortex behavior seems to be guided by
inter-cellular cohesion. There is so far no explanation why the
cells proceed in this manner, but the vortex motion might aid in the
process of sorting cell types following differentiation. (Rappel et
al., Physical Review Letters, 9 August 1999; contact Herbert
Levine, 858-534-7697, levine@herbie.ucsd.edu; movies and
simulations at http://herbie.ucsd.edu/~levine/dicty.html.)

X-RAY CRYSTALLOGRAPHY OF NON-CRYSTALS has been
carried out by a group at Stony Brook. X rays have long been used
to determine the structure of crystalline objects: when the waves
strike periodic arrays of atoms or molecules the waves diffract into
patterns which, when analyzed by Fourier-transformation
algorithms, provide a map of the sample's structure with
approximately angstrom resolution. In the Stony Brook
experiment x rays are shone onto a non-crystalline micron-sized
specimen (a tiny array of letters spelled out with 100-nm gold
nanoparticles). By pushing the algorithms a bit, images could be
formed from the x rays scattered from this patently non-crystal
object. The resolution, about 75 nm, is not nearly as good as for
traditional x-ray crystallography, but still much better than could
be achieved with visible light. The researchers believe their
method can be applied to imaging biological specimens at the level
of cells or even subcelluar objects. (Miao et al., Nature, 22 July
1999.)

PHYSICS NEWS UPDATE
The American Institute of Physics Bulletin of Physics News
Number 442 August 9, 1999 by Phillip F. Schewe and Ben Stein

GRAVITY WAVE ANALYSIS FROM LIGO PROTOTYPE. The
Laser Interferometer Gravitational-wave Observatory (LIGO),
when fully deployed, will consist of two facilities (Hanford, WA
and Livingston, LA). At each site laser beams pass up and down
two perpendicular 4-km-long vacuum pipes, reflecting repeatedly
from mirrors hung from wires. The presence of a passing
gravitational wave would announce itself by a flexing of space-
time which would very slightly lengthen the path of light in one
arm and shorten the path in the other arm, causing a subtle change
in the interference pattern made by the converging light beams
from the two arms. The full LIGO, by about November 2001,
should be able to detect a strain, defined as the fractional change in
the position of the mirrors divided by the length of the arm (4 km),
of 10^-21. This is the expected disturbance one expects from the
gravity waves emitted by the coalescence of two solar-sized stars at
a distance from Earth of 30-50 million light years. But before
LIGO scientists possess their full instrument, they do have a 40-m
prototype at Caltech, built for doing engineering studies but also
capable of sensing gravity waves, albeit with the lesser strain
sensitivity of a few times 10^-19. Thus the LIGO team, while
testing methods for searching (directly via gravity waves) for
binary coalescences, have thereby rendered an upper limit for such
events of less than one every two hours in our galaxy. This result
is useful for the test of the procedures, but is not significant for
astronomers, who have previously established more stringent upper
bounds with electromagnetic waves (visible and radio). (Contact
Barry Barish at Caltech, 626-395-3853 or 818-601-2643; Stan
Whitcomb 626-395-2131; or Bruce Allen, University of
Wisconsin-Milwaukee, 626-893-2003 or 414-229-6439; Allen et
al., Physical Review Letters, 16 August 1999.)

AT THE INTERNATIONAL PHYSICS OLYMPIAD, held in
July, the US team had its second-best showing since it started
competing in 1986, with 3 gold medals and 2 silver medals brought
home by the 5 high school students who participated. In informal
rankings, the US placed 3rd out of the 62 countries that competed,
after Russia and Iran. Taking place this year in Padua, Italy, where
Galileo discovered the 4 Jupiter moons named after him, the
Olympiad contains two days of grueling theoretical and
experimental problems amounting to what is the world's most
difficult high-school physics test. For example, the students had
to compute the precise trajectory of a space probe that uses
Jupiter's gravity as a slingshot--a technique used in real-life
spacecraft such as Cassini. Gold medalists included Peter Onyisi
(Arlington, VA), who had the tenth highest overall score out of the
approximately 300 competitors at the Olympiad, Benjamin
Mathews (Dallas, TX), and Andrew Lin (Wallingford, CT). Silver
medalists include Jason Oh (Baltimore, MD) and Natalia Toro
(Boulder, CO), who earlier this year also became the youngest
person (at 14 years of age) ever to win the top prize of the Intel
(formerly Westinghouse) Science Talent Search. (More
information at http://www.aip.org/releases/1999/release05.html)

IN-PLANE-GATE (IPG) TRANSISTORS can be excavated using
nanomachining techniques. IPG transistors, in which the source,
drain, and gate all lie in a plane rather than in a sandwich, might be
especially useful for high-frequency applications. Scientists at the
University of Hannover (Hans Werner Schumacher, 011-49-511-
762-2523, schumach@nano.uni-hannover.de) have carved out an
IPG structure in a semiconductor surface using the probe from an
atomic force microscope (see figure at
www.aip.org/physnews/graphics). The probe makes an incision
into the material extending down about halfway toward a buried
interface where, lodged between GaAs and AlGaAs layers, a
reservoir of electrons is confined to a plane. The incisions from
above do not penetrate into this two-dimensional electron gas
(2DEG) but they do shape (and can even pinch off) the conduction
of the electrons. The Hannover researchers have also used their
inscribing approach to make single-electron transistors (SETs),
devices that register the coming and going of single electrons.
(Schumacher et al., Applied Physics Letters, 23 August 1999.)

PHYSICS NEWS UPDATE
The American Institute of Physics Bulletin of Physics News
Number 441 July 30, 1999 by Phillip F. Schewe and Ben Stein

THE CHANDRA X-RAY TELESCOPE is now installed in its
highly elliptical orbit, where the Earth itself, and not just its
atmosphere, will not interfere with x-ray reception. Named for
astrophysicist Subrahmanyan Chandrasekher, the 14-m-long
telescope is considered one of NASA's three "great observatories";
the other telescopes in this battleship class are the Hubble Space
Telescope and the Compton Gamma Ray Observatory. Chandra
will have superb angular resolution (half an arc-second, 8 times
better than previous x-ray telescopes), sensitivity to faint objects
(20 times better), and spectral resolution (1 eV). The object of the
mission is unflinchingly to explore graphic violence wherever it can
be found at x-ray wavelengths: quasars, black holes, pulsars,
supernovas, and intergalactic plasmas.
(http://www1.msfc.nasa.gov/NEWSROOM/background/facts/cxoqu
ick.htm)

BLOCH STATES: NOT FOR ELECTRONS ONLY. It is often
essential to consider an electron traveling through a solid as being a
wave that spreads out through the whole of the solid. The quantum
description of this spread-out electron was formulated by Felix
Bloch in the 1920s. Physicists have since sought to extend this idea
of a "Bloch state" to guest atoms in a crystal, but an atom's mass is
so large (and its equivalent wavelength so small) that a Bloch state
for an atom has been difficult to observe. Now, physicists from
Japan (Ryosuke Kadono, KEK, ryosuke.kadono@kek.jp) have seen
clear signs of a Bloch state for a muonium "atom," in effect a light
isotope of hydrogen whose proton is replaced by a positively
charged muon particle having 1/9 of the proton's mass. Performing
experiments at the Rutherford Appleton lab in England, the
researchers studied spin-polarized muonium (Mu) atoms in a KCl
crystal cooled down to 10 mK. Measuring how long it took the
atoms to lose their initial polarization in the presence of an external
magnetic field provided information on their energy state and
matched the predictions of a Bloch model. Further studies may
offer new insights into the energy bands of atoms in crystals.
(Kadono et al., Physical Review Letters, 2 August 1999.)

PARTICLE ACCELERATOR TURN-ONS. The concrete poured
and the magnets tuned, several important new machines are about to
take up important physics matters. The Main Injector at Fermilab,
dedicated in June, is an additional 2-mile racecourse for getting
protons up to speed in much greater numbers. What this means is
that the proton-antiproton collider run starting in 2000 will record in
one year as much data as was taken in the earlier 10-year era. This is
crucial since beam intensity is no less important than the energy of
collision when producing rare objects, such as supersymmetric
particles (hypothetical cousins of the known leptons and quarks) and
the much sought Higgs boson (playing a sort of midwife role in the
life of many other particles, the Higgs should also exist in its own
right). New theoretical estimates for the mass of the Higgs suggest
that Fermilab might just have enough energy to discover the Higgs
(Science, 25 June). Meanwhile, two accelerator schemes dedicated
to studying CP violation through the agency of B-meson decays, are
nearly ready. The Asymmetric B Factory at SLAC in California is
now smashing 9-GeV electrons into 3.1-GeV positrons to produce
pairs of Bs. The decay products are absorbed in a detector called
BaBar. A comparable setup at the KEK lab in Japan will soon
collide 8-GeV electrons with 3.5-GeV positrons inside a detector
called BELLE. By the way, the cost of these detectors is a not-
inconsiderable portion of the accelerators themselves. BaBar and
BELLE cost, respectively $80 million and $70 million (Physics
World, May 1999). Finally, at the DAFNE electron-positron
collider in Frascati, Italy, CP violation is also the subject matter, but
the approach is different. Here the collisions are dedicated to
making phi mesons, which then decay into a pair of K mesons,
which in turn break up (amid the KLOE detector) in a process that
violates charge-parity invariance (CERN Courier, June 1999.)

PHYSICS NEWS UPDATE
The American Institute of Physics Bulletin of Physics News
Number 440 July 23, 1999 by Phillip F. Schewe and Ben Stein

ANTIPROTONS AT SOLAR MAXIMUM. The solar wind is an
electron-proton plasma blowing away from the Sun at 400-800
km/sec and can be thought of as a tenuous atmosphere (called the
heliosphere) of the Sun extending over most of the solar system.
The charged particles in this gust both envelope and are influenced
by the Sun's magnetic field. This field, because it rotates with the
Sun, gets pretty tangled up (see figure at
www.aip.org/physnews/graphics). When now cosmic rays from
outside the solar system venture in they are buffeted by wind and
field. During the present solar cycle of the 1990s, the configuration
of the field is such that positively charged cosmic-ray protons drift
into the inner heliosphere via solar polar regions and exit in
equatorial regions. After the soon approaching peak period of solar
activity (solar maximum), however, the Sun's field will be reversed.
Then the negatively charged cosmic-ray antiprotons preferentially
follow the polar route and more easily enter the inner heliosphere to
be detected by earthbound or satellite detectors. Thus in the period
2001-2010 we should see relatively more antiprotons than in the
previous cycle, which is now ending. Physicists at the Bartol
Research Institute at the University of Delaware (Thomas Gaisser,
gaisser@bartol.udel.edu, 302-831-8113) have calculated when and
by how much this antiproton surplus should manifest itself, telling
us how well we understand the solar cycle. They have also sought
ways of understanding the source of the antiprotons. Most
antiprotons are made when commonplace protons strike interstellar
dust, but some might have a more spectacular birth in the
annihilation of dark matter or in the evaporation of primordial black
holes. (Bieber et al., Physical Review Letters, 26 July 1999.)

WHY IS THE SAHARA A DESERT? Fossil pollen, rock art, and
other hints indicate that the Sahara was much greener 6000 years
ago in the mid-Holocene period. Neolithic peoples seemed to have
hastened desertification at the northern and southern edges of the
Sahara, but German geophysicists believe the main causes were
natural. They point to the fact that precession (wobble) in the
Earth's orbit causes changes in the timing of perihelion (closest
Earth-Sun approach) and our planet's rotational tilt. These
combined to promote a milder climate in most regions of the mid-
Holocene northern hemisphere. Since then the climate has become
cooler and more arid. The subtle alterations in northern hemisphere
cooling, however, were amplified by a feedback between
atmosphere and vegetation causing climate change in the Sahara
region to be far more drastic than elsewhere. Indeed what occurred
was "the largest change in land cover during the last 6000 years,"
according to Martin Claussen (Potsdam Institute for Climatology,
claussen@pik-postdam.de, 011-49-331-288-2522). He and his
colleagues have now confirmed this hypothesis with computer
modeling. (Claussen et al., Geophysical Research Letters, 15 July;
http://www.pik-potsdam.de/)

THE MOST POWERFUL FREE ELECTRON LASER (FEL), as of
this week, is the one at Jefferson Lab in Virginia. In an FEL
amplified laser light comes from a beam of electrons passing
through a cavity. The advantages of FEL's are their tunability (with
output from microwaves up into the ultraviolet), their high "duty
cycle" (they deliver light continuously) and the fact that the light is
produced in closely spaced picosecond bursts tied to the pulselike
nature of the parent electron beam. This makes the light useful for
doing fast things, such as melting metals and then watching as they
re-freeze into non-crystal solids, or roughening up sheets of
polymer fabric so that they will accept glues or dyes. Jefferson's
FEL has an average power of 1.7 kilowatts; the best previous
continuous FEL power was 11 watts. (Jefferson press release, 20
July; contact George Neil, 757-269-7443.)

PHYSICS NEWS UPDATE
The American Institute of Physics Bulletin of Physics News
Number 439 July 16, 1999 by Phillip F. Schewe and Ben Stein

HAVING YOUR PHOTON AND SEEING IT TOO. Measuring a
photon repeatedly without destroying it has been achieved for the
first time, enabling researchers to study an individual quantum object
with a new level of non-invasiveness. Physicists have long realized
that it is possible to perform non-destructive observations of a
photon with a difficult-to-execute technique known as a "quantum
non-demolition" (QND) measurement. After many years of
experimental effort, researchers in France (Serge Haroche, Ecole
Normale Superieure, 011-33-1-4432-3420,
haroche@physique.ens.fr) have demonstrated the first QND
measurement of a single quantum object, namely a photon bouncing
back and forth between a pair of mirrors (a "cavity"). A
conventional photodetector measures photons in a destructive
manner, by absorbing the photons and converting them into electrical
signals. "Eating up" or absorbing photons to study them is not
required by fundamental quantum mechanics laws and can be
avoided with the QND technique demonstrated by the French
researchers. In their technique, a photon in a cavity is probed
without absorbing any net energy from it. (Of course, Heisenberg's
Uncertainty Principle ensures that counting a photon still disturbs the
"phase" associated with its electric and magnetic fields.) In the
experiment, a rubidium atom passes through a cavity. If a photon is
present, the atom acquires a phase shift which can easily be detected.
Sending additional rubidium atoms through the cavity allowed the
researchers to measure the photon repeatedly without destroying it
or, as the French would say, "Avoir le beurre et l'argent du beurre"
("Getting the butter and money out of it at the same time"). This
technique can allow physicists to study the behavior of a photon
during its natural lifespan; it can potentially allow researchers to
entangle (Update 414) an arbitrary number of atoms and build
quantum logic gates (Update 250). (Nogues et al., Nature, 15 July;
see also Scientific American, April 1993; figure at
www.aip.org/physnews/graphics.)

IMPLEMENTATION OF MOLECULAR SWITCHES. In order to
plan for integrated circuits of ever greater complexity and
compactness, computer engineers would like "grow" components
and interconnections with chemical self-assembly instead of building
them with lithography. The next step toward creating such nano-
scale computer circuits, once the discrete molecular units have been
assembled, is to wire them up and configure them into logic gates
(OR, AND, etc.). This has now been done by a Hewlett
Packard/UCLA/Berkeley team, which has set itself the task of
producing a working 16-bit memory cell, no larger than a square 100
nm on a side, within two years. In the 16 July issue of Science, the
team reports on an experiment in which an array of rotaxane
molecules, grown on a substrate, are controlled by a grid of wires
which, through a system of applied voltages trigger local chemical
reactions at each rotaxane. These reactions serve to configure the
rotaxanes which become in effect molecular-scale switches whose
resistivity in the "on" state is 80-100 times less than in the "off"
position. Furthermore, addressing the rotaxanes and reading out
their condition will require only two wires per molecule rather than
the four wires typically needed in conventional integrated circuits
based on the metal oxide semiconductor (CMOS) design.

VERSATILE CARBON NANOTUBES are (1) now observed to be
superconducting. A group at the Universite Paris-Sud has detected the
flow of supercurrents through single nm-wide nanotubes and through
bundles of 100 nanotubes at temperatures below 1 K (Kasumov et al.,
Science, 28 May). (2) Nanotubes have been used to produce muscle-
like actuators. A cantilever consisting of two sheets of nanotubes
separated by a layer of Scotch tape could, when a voltage was applied
across the sandwich, produce stresses higher than natural muscle
(Baughman et al., Science, 21 May). (3) Nanotubes, which can be
only nm in width but microns or longer in length, are expected to be
an ideal strengthening agent in composite materials (Nature, 20 May.)
Finally, (4) alkali-doped nanotubes are expected to be great for
storing hydrogen, perhaps for use as fuel (Science, 2 July 1999.)

PHYSICS NEWS UPDATE
The American Institute of Physics Bulletin of Physics News
Number 438 July 9, 1999 by Phillip F. Schewe and Ben Stein

CLUSTERING IN GRANULAR GASES. Granular materials
(e.g., salt, sand, sugar) share properties with solids (they support a
load) and liquids (they pour) but have unique properties of their
own owing to the complex ways in which thousands to millions of
grains collide with each other. To understand better the ways in
which grains move and organize themselves, it would be nice if
gravitational interactions could be minimized so that only inter-
grain and grain-wall interactions were important. For this reason,
French researchers (Eric Falcon, Ecole Normale Superieure, 011-
33-1-44-323501, eric.falcon@ips.ens.fr) resorted to outer space.
They have performed the first experiment with vibrated granular
media in a low-gravity environment. On board a sounding rocket,
inelastic frictional collisions among the grains themselves and with
the container walls were the only interaction mechanisms at work.
Once fluidized (agitated) the grains form a uniform gas. At higher
densities, though, the grains formed dense, motionless, 3-
dimensional clusters surrounded by low-density regions. (Falcon
et al., Physical Review Letters, 12 July 1999.)

QUANTUM COMPUTERS PERFORM THEIR FIRST
SIMULATION. Until now, quantum computers have done simple
arithmetic (Update 310) and searched small databases (Update
367). But one of the first applications envisioned for them,
proposed in 1982 by Richard Feynman, was that they could
simulate quantum-mechanical processes better and more efficiently
than classical computers. Demonstrating Feynman's idea for the
first time,
researchers (David Cory, MIT, 617-253-3806, dcory@mit.edu)
have used a quantum computer to solve a senior-year
undergraduate physics problem. Namely, they simulated a
"truncated harmonic oscillator," the series of energy levels--
assumed to be finite for simplicity--experienced by a quantum
particle such as an electron which is bound to another object such
as a proton. To simulate this system, they used an NMR quantum
computer, a device in which an external magnetic field aligns a
group of atomic nuclei in a liquid, solid, or gas, so that the tiny
magnet associated with each atom's nucleus is either along the field
(a state known as "spin-down," which can represent a 0 in binary
code) or opposed to it ("spin-up," which can represent a 1). Like
previous designs, the NMR computer consisted of molecules in the
liquid state; in this case the researchers manipulated the spins of
two atomic nuclei within each molecule. The manipulation results
in the possible energy states for this two-spin system exactly
simulating the possible energy states for the quantum particle.
Future steps could include modeling the somewhat more
sophisticated real-world system of an electron in a hydrogen atom.
(Somaroo et al., Physical Review Letters, 28 June 1999.)

AIRLINER CONTRAILS, the thin line-shaped ice clouds formed
from water vapor in exhaust gases, account for about 0.1% of the
worldwide cloud cover, and as much as 0.5-2% over parts of
Europe and the Eastern Northern Atlantic. A group of atmospheric
scientists (Patrick Minnis, NASA Langley Research Center,
p.minnis@larc.nasa.gov) have made of a study of these clouds in
order to forecast their possible future radiative forcing effect, that
is, the amount by which contrails would enhance (through
greenhouse action) the solar and earth-emitted infrared radiation
retained on Earth. The conclusion: between 1992 and 2050
contrail cloud cover will increase by a factor of 6. During this
period the contrail fraction of anthropogenic radiative forcing may
increase from about 1% (1992) to 2 or 3%. These are global
estimates; regional averages (such as for the northern temperate
zone) will be greater still. (Minnis et al., Geophysical Research
Letters, 1 July 1999.)

PHYSICS NEWS UPDATE
The American Institute of Physics Bulletin of Physics News
Number 437 July 2, 1999 by Phillip F. Schewe and Ben Stein

STAR MATERIAL DISCOVERED IN SOUTH PACIFIC.
Interstellar matter formed in a supernova has been discovered on
Earth now for the first time. Light coming to Earth from distant
supernovas is recorded all the time. Likewise, a dozen or so
neutrinos from nearby Supernova 1987A have been detected. But
atoms from supernovas are a different matter. In a sense, all the
heavy atoms on Earth have been processed through or created in
supernovas long ago and far away. But now comes evidence of
atoms from a supernova that may have been deposited here only a
few million years ago. An interdisciplinary team of German
scientists from the Technical University of Munich (Gunther
Korschinek, 011-49-89-289-14257, korschin@physik.tu-
muenchen.de), the Max-Planck Institute (Garching), and the
University of Kiel have identified radioactive iron-60 atoms in an
ocean sediment layer from a seafloor site in the South Pacific.
First, several sediment layers were dated, and only then were
samples scrutinized with accelerator mass spectroscopy, needed to
spot the faintly-present iron. The half-life of Fe-60 (only 1.5
million years), the levels detected in the sample, and the lack of
terrestrial sources point to a relatively nearby and recent supernova
as the origin. How recent? Several million years. How close? An
estimated 90-180 light years. If the supernova had been any closer
than this, it might have had an impact on Earth's climate. The
researchers believe traces of the Fe-60 layer (like the iridium layer
that signaled the coming of a dinosaur-killing meteor 65 million
years ago) should be found worldwide but have not yet been able
to search for it. (K. Knie et al., Physical Review Letters, 5 July
1999.)

ELECTROPHOSPHORESCENCE GETS THE GREEN LIGHT.
In organic light emitting devices (OLEDs) electrical energy
injected onto a host molecule is often transferred to luminescent
"guest" molecules which then light up. Using this approach,
OLEDs have been fabricated to emit colors ranging from violet to
the near infrared and have been incorporated into displays already
on the market. So far OLED researchers have concentrated on
maximizing fluorescent emission of light. Fluorescent OLEDs use
a process whereby the energy transfer occurs between a singlet-
state (total spin of zero) host molecule and a singlet-state guest
molecule. Phosphorescent OLEDs, by contrast, transfer energy
from a triplet-state (total spin value of one) host to a triplet-state
guest, which subsequently emits the energy as light.
Phosphorescence is inherently a slower and less efficient process,
but triplet states constitute the majority of electrically excited
states, so putting them to
work can increase the overall luminescence. This is exactly what
scientists at Princeton (Stephen Forrest,
forrest@ee.princeton.edu,609-258-4532) and the University of
Southern
California have now done. Using both singlet and triplet states for
producing green light, they have achieved quantum efficiencies
(photons out divided by electrons in) of up to 8% and power
efficiencies (optical power out divided by electrical power in) of up
to 30 lumens/Watt. These high efficiencies are unprecedented and
may have a great impact on display technology. (Baldo et al.,
Applied Physics Letters, 5 July 1999).

A RUDIMENTARY MUON MAP OF THE SKY has been carried
out by the Soudan-2 detector, located deep in a Minnesota mine
and built originally to look for proton decay. To be exact, Soudan
records muons produced by incoming cosmic rays hitting the
atmosphere. The muon imaging process clearly senses the shadow
cast by the passing Moon, which temporarily blocks cosmic rays
coming from that position in the sky. (Science, 18 June.)

PHYSICS NEWS UPDATE
The American Institute of Physics Bulletin of Physics News
Number 436 June 28, 1999 by Phillip F. Schewe and Ben Stein

PERCEIVING MUSICAL PITCHES may require much less neural
processing and occur at a lower level of the nervous system than
previously thought, according to a new explanation, offering
possible insights into designing better hearing aids. A musical note
is defined mainly by its lowest pitch, known as its "fundamental
frequency," but a note also typically contains higher-pitched
"overtones" with frequencies that are some multiple of the
fundamental. Even when the fundamental frequency is completely
removed from a note, the overtones often allow listeners to
perceive the missing fundamental anyway. Being able to perceive
missing frequencies may explain why hearing a classical symphony
through a tiny radio, which cannot satisfactory reproduce the
lowest-frequency pitches, sounds reasonably faithful to a live
version heard in a concert hall. Recent explanations of how we
perceive "residue tones" require extensive amounts of neural
processing, which can only take place in the cerebral cortex.
However, researchers in Spain and Italy (Julyan Cartwright, Higher
Council for Scientific Research, Spain, 011-34-958-243360,
julyan@galiota.uib.es) propose that residue perception may result
from a "nonlinear" process, involving the generation of frequencies
that are not multiples of the original signal. Much more efficient
than previous linear models, their proposed mechanism can take
place at neural centers much earlier than the cerebral cortex.
Specifically, they propose a "three-frequency resonance" that takes
place in some neural processing center before the cerebral cortex,
in which the electrical signals generated by two overtones stimulate
a population of nerve cells to fire electrical signals at a third
frequency different from those of the two overtones. Better
understanding of pitch perception may lead to applications in
medicine; it is already known, for example, that hearing aids which
concentrate on making the fundamental frequencies more
intelligible produce better results than simple amplification alone.
(Cartwright et al., Physical Review Letters, 28 June; sound samples
at http://www.imedea.uib.es/~piro/PitchPage/ )

LONG BASELINE NEUTRINO OSCILLATION
EXPERIMENTS have now gotten underway with the
announcement that the Super-Kamiokande detector (near Tokyo)
has recorded the arrival of a neutrino launched in its direction from
the KEK proton accelerator 250 km away (near Tsukuba). Last
year Super-Kamiokande established the important fact that
neutrinos (made by cosmic rays striking the atmosphere)
transform, or oscillate, from one type to another on their way
through the Earth (see last week's Update 436 for more recent
results). In the new experiment (dubbed "K2K") physicists
attempt to confirm the oscillation phenomenon by allowing
neutrinos made artificially at an accelerator to pass through a
nearby detector and also the much more distant Super-Kamiokande
detector, aligned so as to receive the same neutrino beam. If, for
example, muon neutrinos oscillate into another type of neutrino,
adjusted event rates would be different for the two detectors. (K2K
website: http://neutrino.kek.jp; for background see Physics Today,
February 1996.)

FIRE OR ICE IN CALIFORNIA. A new study shows that
episodic volcanism and glaciation have alternated in holding sway
over the California-Nevada borderlands during the past 800,000
years. Scientists at the University of North Carolina and Duke,
who examined 112 different geological ages in documenting their
study, suggest that the anti-correlation comes about because of
climate-related issues, including perhaps the loading effect of lakes
or overlying ice (300 m thick in places) or the stress on the
lithosphere by changes in atmospheric circulation. (Glazner et al.,
Geophysical Research Letters, 15 June.)

PHYSICS NEWS UPDATE
The American Institute of Physics Bulletin of Physics News
Number 435 June 21, 1999 by Phillip F. Schewe and Ben Stein

HELIUM-6 NUCLEI SHARE DI-NEUTRONS. Helium-6 nuclei,
formed into beams for the first time only last year, are thought to be
"Borromean" structures (so named for the heraldic symbol of the
Princes of Borromeo, and consisting of three interlinking rings which
fall apart if any one ring is removed). The He-6 nucleus, theorists
believe, is really a He-4 core surrounded by two extra, loosely bound
neutrons which can reside in one of two configurations: (1) one
neutron on either side of the He-4 core or (2) both neutrons close
together (comprising a "di-neutron") far from the He-4 core. To test
this theory and to demonstrate the existence of di-neutrons, Yuri
Oganessian and his colleagues at the Joint Institute of Nuclear
Research (JINR) near Moscow (oganessian@flnr.jinr.ru, 011-7-
09621-62151) collided a He-6 beam with a He-4 target and observed
that some of the He-4 nuclei had been converted into He-6, proving
that in some of the high-energy collisions di-neutrons had jumped
from one nucleus to the other. This also holds true when He-6 beams
hit hydrogen targets (the target nucleus being a single proton). In this
case a di-neutron joined the proton to form a tritium nucleus. These
results seem to favor the picture in which di-neutrons are the rule
rather than the exception in He-6 nuclei. Now the JINR scientists are
using He-8 beams to study in more detail how neutrons correlate with
each other within nuclei and to search for signs of "tetra-neutron"
states. (Oganessian, Zagrebaev, and Vaagen, Physical Review
Letters, 21 June 1999; figures at www.aip.org/physnews/graphics)

DETECTION OF EARTH'S MAGNETIC FIELD USING
NEUTRINOS has been accomplished at the Super-Kamiokande
detector located underneath Mt. Ikenoyama in Japan. Here is the
sequence of events: a cosmic ray proton strikes an oxygen or nitrogen
atom in Earth's upper atmosphere, creating a neutrino which passes
freely into the Earth where it may find its way into Super-
Kamiokande, a device consisting chiefly of 50,000 tons of pure
water. In the water the neutrino (when it bothers to interact at all)
will typically convert into a muon or electron, plus light, which is
recorded in surrounding photodetectors. In this process, the neutrino
and its daughter muon or electron track pretty closely the trajectory of
the original cosmic ray proton. But the incoming cosmic ray flux,
which would otherwise be isotropic, is shaped by the Earth's
magnetic field. This acts as a sort of prevailing wind which sets up
an east-west anisotropy in cosmic rays. This anisotropy, measured as
long ago as the 1930s, should be matched by a corresponding
anisotropy in neutrinos, which is precisely what the Super-
Kamiokande team now finds. This measurement, while it says
nothing new about Earth's magnetic field, does reassure the
researchers that their detection of neutrino oscillation (one of the top
physics stories of 1998, see Update 375) stands on a firm
understanding of the complex chain of events whereby a cosmic ray
in outer space leads to a burst of light in a cavern beneath Japan.
(Futagami et al., Physical Review Letters, 28 June 1999; team leader,
Y. Totsuga, totsuga@suketto.icrr.u-tokyo.ac.jp, Tokyo University;
some US contacts: Henry Sobel, UC Irvine, 949-824-6911,
sobel@uci.edu; Lawrence Sulak, Boston University, 617 353- 9454,
sulak@bu.edu; paper available to science writers from AIP public
information; www.aip.org/physnews/graphics)

DIRECT CP VIOLATION AT CERN. The NA48 experiment at
CERN reports a new detection of direct CP violation (partly
responsible for the slight asymmetry between matter and anti-matter)
in the decay of K mesons. The value they measure for the ratio
epsilon prime over epsilon (roughly the ratio of direct to indirect CP
violation see Update 420) is 18.5 +/-7 x 10^-4. The value reported
by a Fermilab group earlier in the year was 28+/-4 x 10^-4.
(http://www.cern.ch/Press; for background see Physics Today, May
1999.)

PHYSICS NEWS UPDATE
The American Institute of Physics Bulletin of Physics News
Number 434 June 18, 1999 by Phillip F. Schewe and Ben Stein

MEASURING THE FREQUENCY OF LIGHT TO NEW
LEVELS OF PRECISION is now possible, opening a new chapter
in metrology which may lead to greatly improved determinations
of fundamental constants and one way of making powerful optical
versions of atomic clocks. Even the most advanced electronic
equipment cannot directly measure electromagnetic frequencies
higher than roughly 100 GHz (in the microwave range, where
frequencies can be counted in terms of the number of oscillations
induced in an electrical circuit). Now, researchers at the Max
Planck Institute for Quantum Optics (Thomas Udem, 011-49-89-
32905-257, Thomas.Udem@mpq.mpg.de) have shown that a
femtosecond laser pulse can be used as a "ruler" for precisely
determining the frequencies of visible light (which goes up to
roughly a million GHz). A femtosecond pulse does not contain a
single frequency; rather, its spectrum consists of many frequency
peaks which give the appearance of a comb with the tips pointing
upwards. The researchers have now shown that the very regular
spacing of these peaks can potentially be used to measure
differences of at least 20 THz between two electromagnetic waves
with a precision as high as 3 parts in 10^17 (Udem et al., Optics
Letters, 1 July 1999). For comparison, the best atomic clocks
today, based on measuring radio-frequency atomic transitions,
have accuracies of 2 parts in 10^15. Locking the wave of interest
to the low-frequency end of the femtosecond comb and locking a
reference wave to the high-frequency end can determine the
frequency difference between the two waves and ultimately allow
one to reconstruct the frequency of the visible-light wave. Using
femtosecond lasers, the researchers have already measured the
frequency of visible light emitted by a cesium atom undergoing a
specific transition (specifically, its "D1 line") to a precision of 120
parts per billion, almost 1000 times more precise than previous
measurements of that light. (Udem et al, Phys. Rev. Lett., 3 May
1999). The D1 frequency can be plugged into a formula for
precisely calculating the fine structure constant, which dictates the
strength of the electromagnetic force.

HOW DO COMPLEX ORGANISMS FORM? A Darwinian
mechanism of natural selection plus random mutation is not quite
enough to explain the complex features of life on earth. For
example, it does not predict or anticipate the fact that an ecosystem
or a global community has a hierarchical structure, with
interactions that take place at several size scales. For example,
people communicate with each other in an organization; and
organizations communicate with each other in a larger community.
Barbara Drossel of the University of Manchester in England (011-
44-161-275-4201, barbara.drossel@man.ac.uk) has introduced a
simple mathematical model for describing how originally
independent units may develop into a complex organism with a
hierarchical structure. In her model hierarchy comes about because
of the increase of a quantity she calls "productivity" (similar to
"fitness" in biology and "utility" in economics). Individual units
communicate with each other to increase productivity which leads,
at the very least, to larger groups. Drossel's model incorporates
the additional idea that the size of a group is restricted by the
limited capacity of individuals to communicate and to travel.
Therefore, she introduces a "communication cost" per partner and
per unit distance to the partner. This encourages the formation of
groups and ultimately the formation of supergroups and groups of
supergroups which interact with each other. (Drossel, Physical
Review Letters, 21 June 1999.)

PHYSICS NEWS UPDATE
The American Institute of Physics Bulletin of Physics News
Number 433 June 15, 1999 by Phillip F. Schewe and Ben Stein

ZERO-POINT MOTION IN A BOSE-EINSTEIN CONDENSATE
has been quantitatively measured for the first time, allowing
researchers, in effect, to study matter at a temperature of absolute
zero. According to quantum mechanics, objects cooled to absolute
zero do not freeze to a complete standstill; instead they jiggle
around by some minimum amount. MIT researchers (Wolfgang
Ketterle, 617-253-6815) measured such "zero-point motion" in a
sodium BEC, a collection of gas atoms that are collectively in the
lowest possible energy state (Update 233). According to Ketterle,
"the condensate has no entropy and behaves like matter at absolute
zero." The MIT physicists measured the motion (or lack thereof)
by taking advantage of the fact that atoms absorb light at slightly
lower (higher) frequencies if they are moving away from (towards)
the light. To determine these Doppler shifts (100 billion times
smaller than those of moving galaxies), the researchers used a
technique known as Bragg scattering. In this technique, atoms
absorb photons at one energy from a laser beam and are stimulated
by a second laser to emit a photon at another energy which can be
shifted upward or downward depending on the atoms' motion
towards or away from the lasers. Measuring the range in energies
of the emitted photons allowed the researchers to determine the
range of momentum values in the condensate. Multiplying this
measured momentum spread (delta p) by the size of the condensate
(delta x) gave an answer of approximately h-bar (Planck's constant
divided by 2 pi)--the minimum value allowed by Heisenberg's
uncertainty relation and quantum physics. While earlier BECs
surely harvested this zero-point motion, previous measurements of
BEC momentum spreads were done with exploding condensates
having energies hundreds of times larger than the zero-point
energy. (J. Stenger et al., Physical Review Letters, 7 June 1999.)

ACOUSTIC-DEPENDENT FRICTION. Studies of friction are
often carried out at modest relative speeds: the two moving
surfaces in question typically slide past each other at 1 cm/s.
However, researchers at UCLA (Anders Johansen, 310-825-2863)
wondered if new mechanisms might appear when surfaces slide
against each other at higher velocities, such as those associated
with friction between tectonic plates during earthquakes.
Observing the jerky "stick-slip" motion of a steel block riding on a
rotating steel table, the researchers carefully measured the friction
forces for relative velocities up to 0.35 m/s, by monitoring the
expansion and compression in a spring attached to the steel block.
At these high velocities, they noted that the significantly increased
production of sound waves (largely neglected in past analyses)
dissipates a large amount of energy, stealing away some of the
energy of motion required for two surfaces to slide past each other
and thereby amounting to an increase in friction. This suggests
that the generation of sound waves between two sliding fault
surfaces during an earthquake may provide a significant feedback
mechanism that mitigates a quake's effects, by converting energy
of motion (friction which might otherwise have caused fracturing
in the Earth) into sound energy. (Johansen and Sornette, Physical
Review Letters, 21 June 1999.)

PHYSICS NEWS UPDATE
The American Institute of Physics Bulletin of Physics News
Number 432 June 7, 1999 by Phillip F. Schewe and Ben Stein

ELEMENTS 118 AND 116 have been discovered at Lawrence
Berkeley Lab by crashing a beam of krypton atoms into lead atoms.
The three detectable atoms of element 118 have nuclei possessing
118 protons and 175 neutrons for a mass total of 293. The new
elements are even further along in the Periodic Table than element
114, whose existence was announced back in January 1999 by
scientists in Russia (see Update 412), and further into the "island of
stability," the supposed nuclear regime in which certain
combinations of neutrons and protons lead to a relatively long life.
For all that, the atoms of element 118 still decay after less than a
millisecond into element 116 plus an alpha particle. Element 116
then promptly decays into element 114 plus another alpha particle.
Ken Gregorich (510-486-7860) led the LBL group that discovered
the new nuclei. Four of the team members are German nationals,
which prompted DOE secretary Bill Richardson to emphasize the
continuing value of international scientists working at US national
labs. (LBL press release, June 7.)

THE SPEED OF LIGHT IS INDEPENDENT OF FREQUENCY to
within a factor of 6x10^-21. Bradley Schaefer of Yale (203-432-
3806, schaefer@grb2.physics.yale.edu) bases this estimate on the
observed arrival of gamma rays from distant explosive events in the
cosmos, such as gamma-ray bursters. If the speed of light (c) were
slightly different for the different frequency ranges, then some light
waves would show up before the others, but this is not the case. The
best previous effort to locate a frequency dependency for c, deduced
from light coming from the Crab pulsar, was at the 5x10^-17 level.
Why would c vary with frequency? Einstein's theory of relativity,
and its insistence on a universal light speed, might be at fault. Or
photons might have mass. Schaefer's analysis addresses this issue,
and puts an upper limit of 10^-44 g on any putative photon mass,
not quite as sharp a limit as those based on the observed strength of
the galactic magnetic field (a nonzero photon mass would allow the
fields to decay away). The new sharper limits on any possible
frequency-dependency for c is a vindication of relativity. By the
way, the prefix for anything as small as 10^-21 is "zepto." (Physical
Review Letters, tent. 21 June; journalists can obtain the article from
AIP.)

THE SURFACE OF MARS has been mapped to 13-meter precision,
better than for some places on Earth. Laser light sent from and
returning to the orbiting Mars Global Surveyor spacecraft reveals
that the southern hemisphere is one big highland (6 km higher)
compared to the northern hemisphere. Surface water, if there was
any, would have collected in the North, although there is not yet
definitive proof of any boreal ocean. One thing that is known about
the northern lowland: it is the flattest place in the solar system. The
South's elevation is due at least in part to an immense amount of
material raised during an ancient impact which fashioned a huge
crater known as the Hellas basin. (Science, 28 May 1999.)

THE PAINTINGS OF JACKSON POLLACK, famous for their
seemingly random distribution of drips and streaks, are fractal in
nature. Physicists at the University of New South Wales (Australia)
subjected Pollack's handiwork to the kind of mathematical scrutiny
usually given to fractures in crystals and distributions of galaxies.
They found that the paintings bore similar features at each of many
size scales, the hallmark of fractalness. The object's characteristic
"fractal dimensionality" is roughly related to the indentedness of the
object's texture. Apparently the dimensionality of Pollack's work
increased through the years. (Nature, 3 June 1999.)

PHYSICS NEWS UPDATE
The American Institute of Physics Bulletin of Physics News
Number 431 June 2, 1999 by Phillip F. Schewe and Ben Stein

THIRD-HARMONIC MICROSCOPE. Imaging biological
samples often involves telling apart one wet thing from another. A
relatively new way of gaining the needed contrast is to exploit the
nonlinear optical features of the sample itself by using a process in
which a high-power laser beam can, when it is brought to a tight
focus in certain media, generate subsidiary light waves at twice the
original frequency (second harmonic), three times the frequency
(third harmonic), and so on. If the detector is sensitive to just the
third harmonic radiation, say, then by scanning the laser focus
across the face of the sample, an image can be built up with a
spatial resolution as small as the focal size. Jeff Squier at UC San
Diego (619-534-0290, jsquier@chem.ucsd.edu) and his colleagues
have used this scheme to produce the first 3-dimensional third-
harmonic image of a living system. (Paper JTuA2, May 25, at the
electro-optics and quantum electronics meeting in Baltimore; see
figure at www.aip.org/physnews/graphics.)

METHANE DWARFS is the name for a new type of celestial
object. Actually they are a subclass of brown dwarf. With a mass
of less than 80 times that of Jupiter, Brown dwarfs cannot sustain
the fusion reactions that burn in our sun. At this week's meeting in
Chicago of the American Astronomical Society, Zlatan Tsvetanov
and Wei Zheng of Johns Hopkins University reported seeing
several very red objects very like one observed (Gliese 229B) in
1995. The new objects, glimpsed with the Sloan Digital Sky
Survey telescope, are red not because their spectrum has been red
shifted owing to great distance, but because they are nearby and
very cool. In fact they are cool enough to permit the presence of
methane, which normally dissociates amid the heat of stars and
even in other, warmer, brown dwarfs. (Fermilab press release, 31
May; www.aas.org/meetings/aas194/program/index.html)

PH.D. PHYSICISTS IN THE U.S. REPORTED A MEDIAN
SALARY OF $70,000 in 1998, an increase of 8 percent over the
past two years, and salary gaps appear to be narrowing between
physicists with master's ($57,000) and bachelor's degrees
($54,000). This information comes from approximately 9,250
respondents to an American Institute of Physics survey of members
belonging to its ten member societies. Moreover, the
unemployment rate of the respondents is 0.7%, the lowest this
decade. However, physics master's recipients who teach at high
schools reported only a 3 percent increase in their salary, not
keeping up with the pace of inflation. The highest median salary
belongs to those in the healthcare industry ($87,500). Although
median salaries differed across employment sectors for
respondents in their early- and mid-career, those working in many
sectors reach a median salary of $90,000-100,000 after 25 years of
experience, especially when one considers supplemental income,
such as consulting and summer teaching often done by physicists
with 9-10 month contracts at colleges and universities. ("1998
Salaries: Society Membership Survey," issued in April by the AIP
Education and Employment Statistics Division; single copies can
be ordered by going to www.aip.org/statistics/; reporters seeking
more information should contact Amanda Benedict,
abenedic@aip.org, 301-209-3388)

PHYSICS NEWS UPDATE
The American Institute of Physics Bulletin of Physics News
Number 430 May 26, 1999 by Phillip F. Schewe and Ben Stein

INSTANT HOLOGRAPHY. Polaroid succeeded in creating
instant photography, the appearance of an image very soon after
exposure. Now scientists at the Risoe National Lab in Denmark
have done the same for holography. They have devised a
photosensitive polymer (azobenzene) in which blue-green laser
light can record an image in a matter of nanoseconds without any
chemical processing. Applications for this type of process would
be 3D hologram movies, waveguides for instantly reconfigurable
optical switching, and for tracking the movement of particles.
(P.S. Ramanujam et al., Applied Physics Letters, 24 May 1999;
p.s.ramanujam@risoe.dk, 011-45-4677-4507.)

HELIUM ATOMS SHOOT DOWN HOLLOW FIBERS in an
experiment at the Australian National University (Maarten
Hoogerland, maarten.hoogerland@anu.edu.au). Previously
rubidium atoms had been sent down fibers (see Update 245) but
alkali atoms are prone to stick along the way. The helium atoms
flow more smoothly (guided by "evanescent light" impinging upon
the fibers from outside) since they have first been put into a long-
lived excited state which is almost impervious to interactions with
the walls of the fiber. Possible applications include atom
interferometers useful for gyroscopes or gravity wave detectors
(after all, the working substance of the interferometer, atoms, are
sensitive to gravity), and for atom-optics handling of Bose-Einstein
condensates. (Paper QTuH2, May 25, at the Conference on Lasers
and Electro-Optics (CLEO) in Baltimore.)

THE TEMPERATURE OF THE WORLD is 14.0 C. At least
that's the global average surface temperature. The average for the
northern hemisphere, 14.6 C, is somewhat warmer and the
southern a bit cooler, 13.4. A team of scientists (contact Phil
Jones, University of East Anglia, UK, p.jones@uea.ac.uk) has
gathered data from across a 150-year record and from points
around the globe looking for trends. This is what they found:
Over the period 1861-1997 the average global temperature rose
0.57 C. The warmest years of the century have all occurred in the
1990s: 1998 (the warmest), 1997, 1995, and 1990. The two
periods of greatest warming were 1925-1944 and 1978-1997.
Much of the net warming occurred at night; for the period 1950-93,
nighttime average minimum temperatures increased 0.18 C per
decade while daytime average high temperatures increased 0.08 C
per decade. (P.D. Jones et al., Reviews of Geophysics, May 1999.)

MEASURED VALUES FOR THE HUBBLE CONSTANT are
converging nicely. At a press conference on May 25, Wendy
Freedman of the Carnegie Institution reported a new value of 70
km/sec/megaparsec (with an uncertainty of 10%), down from a
value of 80 reported back in 1994. She is one of the leaders of a
group that uses the Hubble Space Telescope (HST) to track the
light emission of Cepheid variable stars in nearby galaxies.
Another Carnegie astronomer, Allan Sandage, has been a leader of
a group that consistently measures a smaller value for the Hubble
constant, the latest number being about 59, up from an earlier value
of 57. Thus the observed Hubble constant, which is a measure of
the overall expansion of the cosmos, is now providing an estimate
for the age of the universe about 12 billion years that is no
longer in contradiction with the apparent age of the oldest stars.
(NASA press release, 25 May 1999.)

PHYSICS NEWS UPDATE
The American Institute of Physics Bulletin of Physics News
Number 429 May 20, 1999 by Phillip F. Schewe and Ben Stein

THE BIGGEST LAVA OUTPOURING in history probably took
place about 200 million years ago. A team of geophysicists has just
put together the final jigsaw piece in a puzzle relating separated
basaltic layers in spots as far flung as the Hudson River Palisades,
Brazil, Europe, and Africa. What started out as an Australia-sized
blacktop in the heart of the ancient super-continent Pangea was later
torn asunder by the tectonic forces, which carried the fragments to
places all around the Atlantic rim, making discovery difficult until
now. The immense flow, now referred to as the Central Atlantic
Magmatic Province, might have played a part in the mass
extinctions occurring at the boundary between the Triassic and
Jurassic eras. (Marzoli et al., Science, 23 April 1999.)

RYDBERG SCULPTING is a new technique for placing an atom (a
highly excited, or "Rydberg," atom) in many energy states
simultaneously. Applications could include improved designs for
quantum computers, which presently call for collections of
rudimentary 2-level quantum systems, similar to the 2-state (0 and
1) classical binary computers used today. But how would an atom
be in, say, 10 energy states at one time? By being struck by laser
pulses of very short duration. Such a pulse is itself really a
superposition of coherent light waves at many different energies.
This multi-personality existence is transferred to the atom when it
absorbs the laser pulse. In Philip Bucksbaum's lab at the University
of Michigan (734-764-4348), actively shaped ultrashort light pulses
hit atoms in a beam. This creates within the atom what Bucksbaum
calls "wave packet sculpting," a bundle of electron waves dancing in
a complex pattern as they go around the nucleus, at times interfering
with each other. This interference can already be controlled so
carefully that it can be used to store several bits of information.
More complex versions will allow the type of factoring or searching
exercises (e.g., hunting for a pea hidden under one of several cups)
used in quantum computations. Bucksbaum estimates that a number
as large as 2^10 could be factored by setting a single atom to work.
Factoring larger numbers would require additional atoms. (Paper
QTHA1, May 27, at the Conference on Lasers and Electro-Optics
(CLEO) meeting in Baltimore. View movie at
www.aip.org/physnews/graphics; meeting website:
http://www.osa.org/Mtg_Conf/cleo/; also see Physical Review
Focus, 22 June 1999.)

SUPERCONDUCTIVITY GOES PLATINUM. It is ironic that
some of the best insulators (e.g., perovskite ceramics) should make
the best superconductors while some of the best conductors (the
noble metals gold, silver, and copper) should be bad
superconductors. Indeed the electron-phonon interactions that bring
about low-temperature superconductivity is so weak in these metals
that they have never been seen to superconduct. Recently, though,
physicists at the University of Bayreuth (Reinhard Koenig, 011-49-
921-55-3340, reinhard@btp9x5.phy.uni-bayreuth.de) in Germany
have overcome the recalcitrance of one of those metals, platinum,
which became superconducting only at milli-kelvin temperatures.
The platinum was studied in the form of a compacted powder which
contained only very few magnetic impurities (magnetism being
detrimental to superconductivity). Furthermore, it has a much larger
surface area, and it is thought that surface vibrations (phonons) may
also be important for superconductivity in the platinum powder.
This work allows the chance to see how magnetism and
superconductivity compete with each other and to study the
mechanism of the coupling between superconducting grains of the
powder (R. Koenig, A.Schindler, T. Herrmannsdoerfer, Physical
Review Letters, 31 May 1999).

PHYSICS NEWS UPDATE
The American Institute of Physics Bulletin of Physics News
Number 428 May 14, 1999 by Phillip F. Schewe and Ben Stein

PI AND RANDOM NUMBERS. Pi is a "quark" of mathematics: it
is one of the basic building blocks out of which various
geometrical and algebraic relations are built. Normally thought of
as the ratio of a circle's circumference to its diameter, pi keeps
turning up in odd places. For example, Georges Leclerc, Count de
Buffon, was the first to show a connection between pi and the
occurrence of random events. In 1777 he performed an experiment
in which needles are randomly dropped onto a surface covered
with ruled lines spaced apart by an amount equal to the size of the
needle; the fraction of times the needle comes down astride a line
is related to pi. Mathematicians have exploited this relation to
make random number generators. Sylvan Bloch (813-961-0778), of
the University of South Florida does the converse of this. He and
Robert Dressler developed software (for the classroom) for using
random numbers to generate a statistical estimation of pi. By the
way, in warped spacetime pi is not necessarily equal to the ratio of
a circle's circumference to its diameter. As an appendix to his
article in the April issue of the American Journal of Physics, Bloch
shows how "pi" varies as space becomes increasingly curved. (As
usual science journalists can obtain copies of articles from AIP
public information. For pi lore, see
http://forum.swarthmore.edu/dr.math/faq/faq.pi.html.)

ATOMIC STEERING COMMITTEE. Even the smoothest-
looking coatings are very rough on the atomic scale, with islands
of atoms peppered abundantly across the microscopic landscape.
Depositing copper atoms on a Cu surface, researchers (Sebastiaan
van Dijken, University of Twente, the Netherlands,
s.vandijken@tn.utwente.nl) have identified a largely ignored
mechanism which contributes to introducing roughness in films of
atoms being deposited onto surfaces. Known as steering, it arises
when surface atoms, including already deposited ones, exert
chemical forces on incoming atoms and cause them to veer towards
the surface. This is reminiscent of how static electricity can cause
some of the milk poured from a glass to drip down the sides rather
than fall freely from the glass. Steering causes incoming atoms,
especially those approaching the surface at grazing angles, to arrive
preferentially on the top of protruding islands of atoms. Therefore,
steering can make already rough surfaces even rougher. Besides
providing insights into the causes of roughness, understanding this
effect may help researchers to prepare arrays of surface ridges,
which could serve as templates for making magnetic nanowires
and other customized materials. (S. van Dijken et al., Physical
Review Letters, 17 May 1999; figures at
www.aip.org/physnews/graphics)

KING EDWARD III of England (1312-1377) has, back to the time
of Charlemagne, about 1000 perches on his family tree. Of course
in the relatively closed world of medieval royalty, many names on
that tree appear more than once; indeed the repetition of ancestors
conforms to a predictable pattern. A new study of the statistical
properties of genealogical trees, using Edward III's pedigree as a
case history, concludes that by going about 30 generations into
your past, you and all your contemporaries will be related to
everyone who lived then, at least to those who had offspring and
who lived within that particular geographical or cultural realm.
Bernard Derrida of the Ecole Normale Superieure in Paris
(bernard.derrida@lps.ens.fr), Susanna Manrubia of the Max Planck
Institute in Berlin, and Damian Zanette (Barlioche, Argentina),
have discovered that the factors shaping the patterns of repetitions
of individuals in family trees have traits in common with the forces
that govern the behavior of granular materials and can,
furthermore, be understood using the mathematical tools applied to
a variety of phase transitions in physics. They expect their work to
have applications in the study of population genetics and
evolutionary biology. (Physical Review Letters, 1 March 1999;
view Edward's family tree at
http://uts.cc.utexas.edu/~churchh/edw3chrt.html; see figure at
www.aip.org/physnews/graphics )

PHYSICS NEWS UPDATE
The American Institute of Physics Bulletin of Physics News
Number 427 May 10, 1999 by Phillip F. Schewe and Ben Stein

WATCHING PACEMAKERS FORM IN A PETRI DISH. The
bandleaders of biological systems, pacemakers are cells or groups
of cells capable of generating regularly repeating activity on their
own or in response to outside signals. In humans, roughly 5000
cells in the sinoatrial node, located in the right roof of the atrium,
generate the signals that regulate the rhythmic contractions of the
heart. In efforts that may improve understanding of how natural
pacemakers form and provide steady signals, researchers at
Technion University in Israel (Yoav Soen, yoav@technion.ac.il)
excised muscle cells and connective tissue (fibroblasts) from the
ventricles of rats. Spreading these cells on a petri dish under the
proper conditions caused the cells to proliferate, move around and
eventually form a hardy network of fibers after 1-3 weeks. Using a
CCD camera and real-time computer processing , the researchers
detected rhythmic contractions in the cells. They also noticed
rhythm disorders, such as alternations between irregular and
regular rates of contraction. This suggested to them that one or
more pacemakers had formed within the network. While in-vitro
pacemaker activity has been observed before, the Technion optical
technique is the first that monitors the cells noninvasively and
continuously long enough to watch a cell network evolve and form
a pacemaker system. Although the cell network is very different
from a biological heart, it can provide insights into how its
structure and density affects the development of a pacemaker.
(Soen et al., Physical Review Letters, 26 April; figure at
www.aip.org/physnews/graphics)

CONTROLLING STOCHASTIC RESONANCE. In some
systems, such as radio receivers, turning up the volume in order to
hear a faint signal amidst much noise usually only results in
turning up the noise as well. However, in other systems increasing
the amount of ambient noise actually enhances (up to a certain
point) the signal-to-noise ratio through a complicated nonlinear
cooperation between the system and detector. This effect, known
to operate in neurons, lasers, and tunnel diodes, is called stochastic
resonance: the noise fluctuations might be stochastic (meaning
totally random) but the detection of a desired signal can be
maximized by tuning the noise. Now, researchers at Georgia Tech
(Bill Ditto, 404-894-5216, wditto@acl.gatech.edu) have not only
adjusted the noise knob to advantage but also the detector
threshold. This can make the signal-to-noise ratio even better, with
a bearing on the study of how sensory systems such as touch or
hearing can pick out faint signals. Conversely the extra control
mechanism can be used to undo the stochastic resonance effect,
which just might be a desirable step in, for example, military
applications (jamming) or in the suppression of unwanted
interactions between electromagnetic radiation and biological
tissue. (Gammaitoni et al., Physical Review Letters, tent. 31 May.)

FERMI QUESTIONS, named for the Enrico Fermi who reveled in
the exercise, are problems that call upon the art of approximation.
Example: How many liters of water are drunk in the US per year?
Answer---10^11 liters (250 x 10^6 people times 1.5 liters of water
per day times 365 days). How long would it take to walk the
distance between Earth and Moon? 10^4 days (2.4 x 10^5 miles
divided by 24 miles/day). The number of postage stamps covering
a football field? 10^7 (stamp area of 4 cm^2 over a field of 100 x
50 m^2). (The Physics Teacher magazine, May 1999; contact
columnist Karen Bouffard, at kbouff@aol.com.)

PHYSICS NEWS UPDATE
The American Institute of Physics Bulletin of Physics News
Number 426 May 3, 1999 by Phillip F. Schewe and Ben Stein

MARS MAGNETISM. The Mars Global Surveyor spacecraft has
discovered patterns of magnetized surface rock, broad stripes of
magnetic material pointing in one direction alternating with
magnetic material pointing in the opposite direction, somewhat
like the patterns seen at mid-ocean rift zones on Earth. On our
planet the alternating stripes testify to the changing nature of
Earth's magnetic field and to the recurring upwelling of magma
resulting from the movement of tectonic plates above a seething
molten planetary core. The conclusion: Mars too might have
experienced tectonic activity. (Science, 30 April 1999.)

HIGH-PRECISION STUDIES OF ANTIPROTONS can be carried
out in an ion trap. Harvard physicist Gerald Gabrielse takes
antiprotons from a beam at CERN, reduces their energy by a factor
of 10 billion (in a series of slowing and cooling steps), and then
inserts them into the final trap, where their motions are compared
with commonplace protons. Strictly speaking what is measured is
q/m, the ratio of the particle's charge to its mass. In this respect
q/m proves to be identical for protons and antiprotons to within an
uncertainty of 90 parts per trillion, a tenfold improvement over
Gabrielse's previous best measurement. (Gabrielse et al., Physical
Review Letters, 19 April 1999; for a dossier on other antiproton
properties see the article by John Eades in Review of Modern
Physics, 1 Jan 1999.)

PATTERNED NANOTUBE ARRAYS. Nanometer-wide tubes of
carbon atoms, made amid fiery arc discharges, have been used in a
number of ways, such as for tips in scanned probe microscopes.
Researchers at ATMI, a company in Danbury, CT, produce films
of nanotubes in a chemical process that uses catalysts carefully
deposited on large-area substrates. Mats of nanotubes grow only
atop the catalyst in predetermined places to form desired nanotube
patterns. The tubes are good emitters of electrons and thus the
process lends itself to the job of enabling flat-panel displays, and
is, fortunately, compatible with silicon processing. (Xu and
Brandes, Applied Physics Letters, 26 April.).

WRITING THE WORD "OPTICS" ON A SINGLE ATOM is
possible, scientists have shown, demonstrating the huge
information capacity that exists even in an individual hydrogen
atom. The trick is to sculpt the electron cloud surrounding an atom
into the letters of this word. Shining an ultrashort UV laser pulse
and lower-frequency electromagnetic waves on an atom can send
one of its electrons to a high-lying "Rydberg state," in which it no
longer exists as a cloud of charge enshrouding the nucleus but
instead becomes a "wavepacket" that circles the atomic nucleus
like a planet around a sun (Update 234). Applying a series of
pulses can create a set of wavepackets that combine with each
other like water waves and cancel each other out at specific places
to form patterns around the atom, such as the word "optics," in
which points on each letter correspond to possible places for
finding the electron after measurement. Although neither this feat,
nor the act of accurately measuring such spatial patterns, can yet be
achieved technologically, Carlos Stroud of the University of
Rochester (716-275-2598) and Michael Noel of the University of
Virginia (804-924-6599) point out that an electron in an n=50
Rydberg state (49 energy levels higher than the lowest state) has
2,500 possible states of angular momentum, and have shown that
the states can be combined in many ways, such as to form this
word. (Optics & Photonics News, April 1999; figure at
www.aip.org/physnews/graphics)

PHYSICS NEWS UPDATE
The American Institute of Physics Bulletin of Physics News
Number 425 April 27, 1999 by Phillip F. Schewe and Ben Stein

THE COSMIC NEUTRINO BACKGROUND can in principle be
detected. There are almost as many neutrinos loose in the universe
as photons, and almost as much energy vested in neutrinos as in
photons. Yet, owing to the extreme reticence of neutrinos to
interact with other particles, detecting the neutrino background is
not easy as detecting the cosmic photon (microwave) background.
Indeed, dedicated neutrino detectors struggle just to record a
handful of incoming neutrinos from potent nearby sources like the
sun. Nevertheless, there might be a chance to map the background
indirectly. The pattern of lumps in the microwave background,
which will be measured by the upcoming MAP and PLANCK
orbiting detectors, encodes information about the neutrino
background. Scott Dodelson of Fermilab (630-840-2426), Michael
Turner and Robert Lopez of the University of Chicago, and
Andrew Heckler of Ohio State show these measurements will
accurately establish the time at which slow-moving matter (protons
and later atoms) became predominant over fast-moving radiation
(photons and neutrinos), and that this in turn determines precisely
how much early annihilation energy (arising from electrons and
positrons smashing up) was apportioned among photons and
neutrinos. (Lopez et al., upcoming article in Physical Review
Letters.)

PROGRESS TOWARDS A DICK TRACY WATCH. Introduced
in a Jan. 13, 1946 comic strip, the Dick Tracy watch is a techie's
dream: it is a two-way, voice-activated video phone that fits around
a wrist. In work that may lead to some components for a real-life
Dick Tracy watch, Peter Gammel and his colleagues at Bell
Labs/Lucent Technologies have constructed a tiny (100-micron)
pyramid-shaped microphone on a silicon chip. According to
Gammel, this is the first microphone built by surface
micromachining techniques, in which various thin films are
deposited on a silicon surface and some of the features are etched
away to result in movable parts. This process is to be
distinguished from bulk micromachining, in which features are
carved out of a silicon surface itself. The researchers have also
built a very small rf filter, which blocks unwanted radio
frequencies and prevents signals from a phone's transmitter from
disrupting its receiver. Made of aluminum nitride on a silicon
surface, it is 100 times smaller than conventional ceramic filters,
by far the largest single component in a cell phone. The Bell Labs
researchers also built a micron-scale version of an inductor, a
simple loop of wire that helps determine the proper frequency for
communications. Most important of all, these components can all
be built on the same silicon chip. Describing these results at the
New York State section meeting of the APS held at Lucent last
week, Gammel speculates that all of the components for a Dick
Tracy watch should be technologically available by 2005. (See
www.aip.org/physnews/graphics)

APS CENTENNIAL PHOTOGRAPHS. The American Physical
Society (APS) Centennial meeting in Atlanta, Georgia, March 20-
26, 1999 was attended by 11,400 physicists, making it the largest
physics meeting in history. Highlights included the presence of
more than 40 Nobel laureates, a talk by Stephen Hawking, the
unveiling of the Centennial physics wall chart, an international
banquet attended by physicists from over 60 nations, a series of
public lectures on everyday physics, and numerous symposia and
press conferences on some of the most important physics topics of
the day. A gallery of photographs from these events can be viewed
at:
http://www.aip.org/physnews/graphics/aps100/apsphoto.html

PHYSICS NEWS UPDATE
The American Institute of Physics Bulletin of Physics News
Number 424 April 20, 1999 by Phillip F. Schewe and Ben Stein

DOES GOD EXIST? This age-old question was the subject of an
AAAS-sponsored symposium in Washington, DC last week.
Actually, to accommodate a very ecumenical council of scientists
(mostly physicists) and religious thinkers, the session organizers
framed the debate in terms of three tactful "cosmic questions" (one
for each day of the meeting): Did the universe have a beginning?
Was the universe designed? Are we alone? The colloquy reached
its dramatic climax in the matchup between John Polkinghorne of
Cambridge and Steven Weinberg of Texas. Their collision of
views was reminiscent of the famous Oxford debate of 1860
(sponsored by the British Association for the Advancement of
Science) between biologist Thomas Huxley, staunch defender of
the-then new theory of evolution, and Bishop Samuel Wilberforce,
who argued that the notion of human descent from the apes was
absurd. One thing, at least, has changed in 129 years. Nowadays
most clerics are comfortable with the terminology and methods of
modern cosmology. Indeed, Polkinghorne is (like Wilberforce) an
Anglican minister and (like Weinberg) a particle physicist.
Nevertheless, the surface compatibility of science and religion
could not cover up the sense that the essence of the AAAS meeting
lay in the atheism/theism dichotomy as exemplified by Weinberg
and Polkinghorne respectively. Addressing the issue of a designed
universe, Weinberg asked about the designer: Who would he be?
What is his nature? Why are miracles no longer performed? "The
evidence for miracles is weaker than for cold fusion," he said.
Polkinghorne asserted that the idea of a cosmic designer was an
unanswerable metaphysical question; metaphysics, he continued,
could be constrained but not determined by science. Weinberg
countered by suggesting that recent cosmological models (e.g.,
"eternal inflation") and certain interpretations of quantum
mechanics (e.g., the "many-universes" hypothesis) demonstrated
that physics, and not just metaphysics, might one day assimilate all
of the above-named cosmic questions. Polkinghorne listed things
that reductionist science could not account for---beauty, art, and
ethics. "Consciousness is an intrinsic sign of a creator," he said. In
defense of a designer-less universe, Weinberg cited a possible
connection between the human disposition for beauty and the
seeming symmetries of nature as manifested in the laws of physics.
(For the full meeting agenda see this website:
http://www.aaas.org/spp/dspp/dbsr/events/cosmo/cosmic.htm.)

AN EXTENDED EXTRASOLAR PLANETARY SYSTEM, a star
orbited by three satellites, has been mapped by two separate teams
of astronomers, one using the Lick Observatory in California
(http://www.physics.sfsu.edu/~gmarcy/planetsearch
/upsand/upsand.html) and one using Harvard-Smithsonian's
Whipple Observatory in Arizona. The innermost planet circling
the star Upsilon Andromedae (44 light years from Earth) had been
known previously but the discovery of its two siblings is new. The
presence of the planets is inferred from irregularities in the star's
light emission. The masses for the three planets (working
outwards, 0.75, 2, and 4 Jupiter masses) and the orbital radii (0.06,
0.83, and 2.5 times the Earth-Sun distance) are puzzling since
according to some theories a Jupiter-sized planet (much less three
of them) should not have formed so close to a star. (The two
groups of astronomers have submitted their findings to the
Astrophysical Journal.)

PHYSICS NEWS UPDATE
The American Institute of Physics Bulletin of Physics News
Number 423 April 13, 1999   by Phillip F. Schewe and Ben Stein

THE SCIENCE OF GAMMA RAY BURSTERS has now
advanced to the point where a robot optical telescope, responding
to signals from orbiting gamma-ray and x-ray telescopes, can
within seconds swivel to a spot on the sky and photograph the
visible component of the burst.  Thus the object GRB990123 (with
a redshift of 1.6) was glimpsed at optical wavelengths on January
23, 1999 at the crucial early stage of its eruption.  Indeed this was
the first time a GRB was detected optically while still belting out
gammas.  Judging by its gamma emissions it was either the most
energetic GRB yet observed (if its energy were being spewed the
same in all directions) or the observations constitute the first
evidence for a beaming effect in GRB's.  The object's afterglow
was also watched by radio and infrared telescopes.  These prompt
measurements are important for understanding the burster's energy
engine, which operates at full throttle for only about 100 seconds.
(Science, 26 March 1999; Nature, 1 April 1999.)

THE MIGRATION OF PLUTONIUM is one of the gravest
concerns for those planning long-term underground storage of
nuclear waste.  Plutonium, one of most toxic substances known,
has a very low solubility in water and so it was once thought that
this hazardous material would not move via groundwater.  A new
Livermore-Los Alamos study, however, suggests that plutonium
might be making an aqueous journey aboard colloids (clays and
zeolites).  This is the chief explanation for the presence of
plutonium in groundwater found 1.3 km away from a the scene of a
Nevada nuclear test conducted 30 years before.  The Department of
Energy is now taking colloid transport into account in its
formulation of a strategy for permanent waste storage.  (Physics
Today, April 1999.)

PHYSICS DEPARTMENT RANKINGS are almost always unfair,
skewed, out of date, and misleading, but they're fun to look at
anyway.  US News and World Report recently ranked  a multitude
of professional schools and graduate departments in US
universities.  Their top graduate physics departments, in
descending order, are Caltech, Stanford, Harvard, MIT, Princeton,
Berkeley, Cornell, Chicago, and Illinois.  Some subdisciplines are
ranked too. In particle physics the top departments are Harvard,
Berkeley, Stanford, Caltech, and Princeton.  Nuclear physics: MIT,
Michigan State, Univ Washington, Indiana, and Caltech.
Condensed matter: Illinois, MIT, Stanford, Cornell, and Harvard.
Atomic/molecular: MIT, Harvard, Stanford, Colorado, and
Michigan.  Astrophysics/space: Caltech, Harvard, Berkeley,
Princeton, Chicago.  Nonlinear/chaos: Maryland, Texas, Cornell,
Chicago, and Georgia Tech. (For more rankings and for an
explanation of the US News methodology, see this website:
http://www.usnews.com/usnews/edu/beyond/bchome.htm.)

POWDER LASER.  Physicists at Northwestern have for the first
time observed laser action in zinc oxide and gallium nitride
powders (Cao et al., Physical Review Letters, 15 March).
Semiconductor powders would normally absorb or even "halt"
light (see Update 356), but because in the Northwestern samples
the average length between scattering from the tiny (100 nm)
grains is less than the light's wavelength, the light can propagate
and even augment itself by stimulating further emission from
atoms in the powder (Science, 2 April). This is laser action and the
powder constitutes a sort of "random laser," one in which light
moves not between the fixed mirrors of a cavity but, in random
directions, among trillions of grains.

PHYSICS NEWS UPDATE
The American Institute of Physics Bulletin of Physics News
Number 422 April 6, 1999   by Phillip F. Schewe and Ben Stein

A CONTINUOUS ATOM LASER BEAM has been demonstrated
for the first time by researchers at the Max Planck Institute for
Quantum Optics in Munich (Bloch, Haensch, and Esslinger,
Physical Review Letters, 12 April 1999). The first atom laser
(Update 305) produced pulses of atoms, rather than continuous
beams. Secondly, the atoms quickly spread out in a moon-like
crescent, instead of forming a more desirable narrow beam.  At the
APS Centennial Meeting, Theodor Haensch (011-49-893-290-
5702) described a design that produces a continuous stream of
atoms lasting as long as 100 milliseconds.  In addition, the beam
can potentially have a radius of a nanometer, thousands of times
narrower than the focus of an optical laser beam.  Using a specially
designed magnetic trap, placed inside a magnetic shield enclosure,
the researchers created a Bose-Einstein condensate (Updates 233,
362) of rubidium in a well-defined magnetic field which
experienced a minimal amount of fluctuations from the
environment.  In such a low-noise setup, a radio wave can address
a specific magnetic-field region of the condensate.  Since every
atom acts like a wave and is spread out over the entire condensate,
each atom eventually gets affected by the radio wave, becoming
converted from a trapped to an untrapped state.  The conversion
process occurs gradually, with a beam emerging at a slower and
more controlled rate than in previous atom-laser demonstrations.
The escaping rubidium atoms fall under the influence of gravity.
Also at the APS Centennial, Bill Phillips of NIST discussed an
atom laser that can produce beams in any direction, not just
downwards.  (Hagley et al., Science, 12 Mar. 1999).  The
researchers applied a pair of optical laser beams to a sodium BEC;
the atoms absorbed some of the momentum of the beams and could
be kicked in the desired direction to form a beam. Their design
actually generates a "quasi-continuous beam," pulses of atoms so
close together in succession that they overlap.  In addition, the
beam is narrowly collimated, spreading out just a tenth of a degree,
comparable to a laser pointer.  These beams provide an excellent
source of atoms for devices which can measure tiny amounts of
rotation (Update 306) and precision measurements of gravitational
acceleration (Update 384) and time; they may also allow
researchers to make very sophisticated nanostructures.
Interestingly, even the pioneers in this new frontier do not know
how physics concepts such as coherence will be redefined for the
case of these laser-like matter waves. (Image at Physics News
Graphics; see also Physics Today, April 1999)

NONLINEAR ATOM OPTICS.  Four-wave mixing of atom
waves, a process in which three matter waves combine to produce
a fourth wave while conserving energy and momentum, has been
demonstrated by researchers at NIST.  This experiment provides
the first example in atoms of "non-linear optics" effects which are
important in laser beams.  In lasers, these effects arise when the
light is so intense that it changes the index of refraction of the
material through which it traverses.  The behavior of the material
thereby depends on the intensity of light, and this non-linearity can
lead to the self-focusing of light and the creation of new colors of
light from a single color.  The NIST researchers created three
overlapping Bose-Einstein condensates of sodium atoms moving at
different velocities relative to one another.  The three BECs
interfered to create a fourth condensate moving at a different
velocity.  This four-wave mixing phenomenon, which also occurs
in light waves, can be used to explore the uniquely quantum
mechanical properties of matter waves.  (Deng et al., Nature, 18
March 1999 and report at the Atlanta APS meeting.)

PHYSICS NEWS UPDATE
The American Institute of Physics Bulletin of Physics News
Number 421 March 31, 1999  by Phillip F. Schewe and Ben Stein

CREATING ANTIMATTER WITH LASER LIGHT.  Intense
light from the Petawatt laser at Livermore, the world's most
powerful laser, has been directed onto a thin gold film where it
creates a plasma plume which acts as a sort of messy wakefield
accelerator.  In particular the laser electric fields rip electrons from
the gold atoms and send the electrons shooting off with energies as
high as 100 MeV.  Some of these electrons radiate gamma rays
which in turn can create electron-positron pairs (the first antimatter
made in laser-solid interactions) and can also induce fission.  Thus
laser photons at the electron-volt level can, by teaming up, initiate
the sort of million-electron-volt nuclear reactions that normally
take place only at an accelerator.  Moreover, the femtosecond laser
pulses can be focused to a much smaller spot size than is possible
with any conventional particle beam.  Tom Cowan (925-422-9678,
tcowan@llnl.gov) reported these results at last week's APS
centennial meeting in Atlanta (see figure at
www.aip.org/physnews/graphics).

TABLETOP THERMONUCLEAR FUSION.  Yet another
Livermore photonuclear breakthrough was reported at the APS
meeting.  Todd Ditmire described an experiment in which laser
pulses (35 fsec long and intensities as high as 10^17 W/cm^2)
were absorbed by a gas jet of deuterium molecules.  These
molecules actually resided in clusters (average size of 5 nm) which
exploded under the laser bombardment.  Some of the rocketing D's
fused into helium-3 nuclei plus energetic neutrons.  The neutrons,
showing up with a characteristic energy of 2.45 MeV, were
detected (about 10,000 per laser shot) via a time-of-flight
technique.  Ditmire said that this new approach to promoting
fusion reactions  (executed with a setup that fits on a 4'x11' table)
could probably not be scaled up to provide commercial power, but
that it might provide a cheap source of neutrons.  The whole
process is highly efficient: virtually all the laser energy was
converted into ion kinetic energy.

MOLECULAR ASTROPHYSICS.  To understand how molecules
form in space, earthbound scientists are performing laboratory
experiments that simulate the cold interstellar dust and gas clouds
where molecules are manufactured.  Some researchers study the
formation of H2, the universe's simplest and most abundant
molecule. Other researchers study the properties of polycyclic
aromatic hydrocarbons (PAHs), flat rings of carbon and hydrogen
which seem to exist in the interstellar clouds.  At the APS meeting,
Gianfranco Vidali of Syracuse (315-443-9115) presented studies
on how two hydrogen atoms join together on an interstellar dust
grain.  Shooting H atoms onto a solid target (playing the role of an
interstellar dust grain, with a temperature of 10 K) and observing
how many of the atoms would react on the cold surface to form
molecular hydrogen, he and his colleagues found that the rate of
H2 formation was higher on amorphous carbon than on olivine (a
silicon-oxygen based material), suggesting that the former is a
more likely candidate for interstellar dust, whose composition is
still unknown.  Louis Allamandola (650-604-6890) and his
colleagues at NASA-Ames discussed recent experiments showing
that shining UV light on PAHs can convert them to organic
compounds that are present in henna, aloe, and St. John's wort.
Combined with spectroscopic measurements that support the
existence of PAHs in interstellar clouds, these experiments
advance the notion that PAHs may be the precursors of
biologically important molecules on our planet and possibly others.

PHYSICS NEWS UPDATE
The American Institute of Physics Bulletin of Physics News
Number 420 March 29, 1999  by Phillip F. Schewe and Ben Stein

DIRECT CP VIOLATION has been observed at Fermilab by the
KTeV collaboration. An important way of apprehending the basic
nature of time and space (in the finest tradition of Greek
philosophy) is to ask "what if" questions. For example, will a
collision between particles be altered if we view the whole thing in
a mirror?  Or what if we turn all the particles into antiparticles?
These propositions, called respectively parity (P) and charge
conjugation (C) conservation,  are upheld by all the forces of
nature except the weak nuclear force. And even the weak force
usually conserves the compound proposition of CP. In only one
small corner of physics---the decay of K mesons---has CP violation
been observed, although physicists suspect that CP violation must
somehow operate on a large scale since it undoubtedly helped
bring about the present-day preponderance of matter over
antimatter.
    K mesons (kaons) are unstable and do not exist outside the
interiors of neutron stars and particle accelerators, where they are
artificially spawned in K-antiK pairs amidst high energy collisions.
K's might be born courtesy of the strong nuclear force, but the rest
of their short lives are under control of the weak force, which
compels a sort of split personality: neither the K nor anti-K leads a
life of its own.  Instead each transforms repeatedly into the other. A
more practical way of viewing the matter is to suppose that the K
and anti-K are each a combination of two other particles, a short
lived entity called K1 which usually decays to two pions (giving
K1 a CP value of +1) and a longer-lived entity, K2, which decays
into three pions (giving K2 a CP value of -1). This bit of
bookkeeping enshrined the idea then current that CP is conserved.
   All of this was overthrown when in 1964 the experiment of Jim
Cronin and Val Fitch showed that a small fraction of the time
(about one case in every 500, a fraction called epsilon) the K2
turns into a K1, which subsequently decays into two pions.  This
form of CP violation is said to be indirect since the violation
occurs in the way that K's mix with each other and not in the way
that K's decay. One theoretical response was to say that this lone
CP indiscretion was not the work of the weak force but of some
other novel "superweak" force.  Most theorists came to believe,
however, that the weak force was responsible and, moreover, that
CP violation should manifest itself directly in the decay of K2 into
two pions.  The strength of this direct CP violation, characterized
by the parameter epsilon prime, would be far weaker than the
indirect version.  For twenty years detecting a nonzero value of
epsilon prime has been the object of large-scale experiments at
Fermilab and for nearly as long at CERN.  In each case, beams of
K's are sent down long pipes in which the K-decay pions could be
culled in sensitive detectors.
    At the APS Centennial meeting in Atlanta last week, both
groups discussed their work. The KTeV group at Fermilab reported
a definite result: a ratio of epsilon prime to epsilon equal to 28 (+/-
4) x 10^-4, larger than the theoretical expectation. As for the NA48
group at CERN, Lydia Iconomidou-Fayard (lyfayard@in2p3.fr)
said that data analysis was still proceeding and no definite
measurement could be reported at this time. The principal
conclusion was stated by KTeV co-spokesman Bruce Winstein
(bruce@uchep.uchicago.edu, 773-702-7594): Before the new
experiments direct CP violation had not been established, owing to
the large uncertainty in the early measurements of epsilon prime;
the new experiment, by contrast, does succeed in establishing a
nonzero value for epsilon prime, thus providing a new way to
probe (a parameter that can be measured in the lab) this
cosmologically-important and most mysterious feature of particle
physics.  (See figure at www.aip.org/physnews/graphics;
background article: Physics Today, October 1988.)

PHYSICS NEWS UPDATE
The American Institute of Physics Bulletin of Physics News
Number 419 March 19, 1999 by Phillip F. Schewe and Ben
Stein

NANOMETER-SCALE IMAGES OF SOUND WAVES on
surfaces have been achieved by
several groups, enabling researchers to observe oscillations of
single atoms and promising ordinarily difficult-to-obtain
nanoscopic information on material properties beneath the surface.
At this week's international joint meeting in Berlin of the
Acoustical Society of America, the European Acoustics
Association, and the German Acoustical Society
(ASA/EAA/DAGA '99), Ute Rabe of the Frauenhofer Institute for
Nondestructive Testing in Germany showed that such images are
possible by generating ultrasound waves on a surface and detecting
them with a scanning probe microscope. Eduard Chilla of the Paul
Drude Institute in Berlin used atomic force microscopy techniques
to image insulators and a scanning tunneling microscope to image
conductors. The STM in particular could record oscillations of
single atoms responding to a sound wave. Using an AFM in
various operating modes, Andrew Kulik of the Federal Polytechnic
Institute of Lausanne, Switzerland showed images of sound waves
coursing through a tin sample. Different features in the image
corresponded to regions of increased stiffness or flexibility, and
likely were the sites of grain boundaries in the tin sample. In
general, these techniques can potentially provide nanoscopic
details on the elastic properties of a material and other subsurface
information, such as the stress between different layers of a
material.

SPACE-TIME FUZZINESS, the notion that space is like an
irregular foam at the smallest of size scales (the Planck scale,
10^-35 m) foreseen in current theories, should be detectable with
gravity-wave detectors now under construction. So says Giovanni
Amelino-Camelia of CERN, who believes that high-precision
instruments like the Laser Interferometer Gravitational
Observatory (LIGO), being built to detect the infinitesimal
distortions of space caused by a passing gravitational wave, would
also be able to probe the fundamental "noise" of the Planck froth.
(Nature, 18 March 1999.)

THE ANTARCTIC MUON AND NEUTRINO DETECTOR
ARRAY (AMANDA) watches the sky for TeV neutrinos. It does
this by looking inward: using the whole of the earth to screen out
all other particles, the detection scheme counts on the fact that only
neutrinos can navigate safely through our planet. Emerging into the
south polar ice mass, the high energy neutrinos (coming from
uncharted violent astrophysical processes) will occasionally
interact with atoms, creating muons whose potent energy is partly
converted into cones of (Cerenkov) light that can be seen by strings
of photodetectors buried in the ice. (The holes for the detectors,
stretching down as far as 2.4 km, are the deepest ever carved with
hot water.) Neutrino interactions are rare under any circumstance;
20 unambiguous neutrino scattering events have been fully
analyzed so far, but up to 100 per year are expected shortly. These
events are in a neutrino energy range, above 50 GeV, far different
from that of detectors such as Super Kamiokande, in which
oscillations of lower-energy neutrinos (less than 10 GeV) were
observed in 1998. With AMANDA the muon trajectory (and
essentially that of the parent neutrino) can be determined to within
about three degrees. Neutrinos with energies below 1 TeV would
probably come from cosmic ray events in our atmosphere. For
energies above 1 TeV, the neutrinosources are expected to be
gamma-ray bursters and active galactic nuclei. (Physics Today,
March 1999.)

PHYSICS NEWS UPDATE
The American Institute of Physics Bulletin of Physics News
Number 418 March 15, 1999 by Phillip F. Schewe and Ben Stein

CHAOTIC GRANULAR MIXING has been observed for the first
time. Studies of chaos in the mixing of fluids is common, but it
was thought that grains mixed by a combination of steady motion
and diffusion. Now an experiment by Troy Shinbrot, Fernando
Muzzio, and Albert Alexander at Rutgers
(shinbrot@sol.rutgers.edu, 732-445-6710), using identical (initially
segregated) red and green particles in a cylindrical drum being
gently tumbled, shows that grains can spontaneously interpenetrate
chaotically, and the green-red interface was fractal in nature. Even
more unexpected was the speed at which the interface grew in
complexity---many orders of magnitude greater than expected.
These results should have an impact on the mixing industry, which
worries about how long and how hard to mix commodities such as
pharmaceuticals, explosives, makeup, and powdered foods. (Troy
Shinbrot et al., Nature, 25 February 1999; see also
www.aip.org/physnews/graphics/.)

PINPOINT POLYMERIZATION, in which laser light is absorbed
two photons at a time within tiny volumes, can be used to turn
chemical reactions on and off and to fabricate microstructures from
the inside out. An Arizona-Caltech collaboration (Joseph Perry,
jwperry@u.arizona.edu, 520-626-9331) has developed a new
highly sensitive resin which when bombarded by intense laser light
is converted into polymer, but only within the tiny micron-sized
laser focus. By scanning the laser, a pattern of chemical changes is
imposed on the sample. Although not exactly a holographic
process since interference effects are not at work, the photo-
polymerization does result in permanent changes in the local
environment, such as index of refraction. The implications of this
are chemical (reactions can be activated in tiny zones and not in
neighboring zones), optical (rows of fluorescent binary bits can be
encoded), and mechanical (microstructures can be built, including
waveguides, photonic crystals, and arrays of cantilevers---see the
figure at www.aip.org/physnews/graphics). For example, the
photonic crystal (honeycomb structures which exclude or trap light
at select wavelengths) was built by polymerizing some sections of
the solid and then washing away the unwanted parts with solvents,
a process not unlike photo-lithography except that it's done in three
dimensions and with two-photon excitation. (Cumpston et al.,
Nature, 4 March 1999.)

WHERE DOES FRICTIONAL HEAT GO? Rub your hands
together and they get warm. How does this come about, at the
atomic level? Miquel Salmeron and his colleagues at LBL (510
-486-6230, salmeron2stm.lbl.gov) addressed this problem by
running a nanoscopic hoe (an atomic force microscope probe)
through a field of pliant stalks (a monolayer of closely packed,
upright alkylsilane molecules, strandlike molecules used in
lubrication) self-assembled on a mica prairie. When the probe
pushed harder, the contact area increased and so did the friction.
The surface molecules had to tilt and to do that they had to unlock
from each other, and this consumes energy, energy which is not
recovered when the probe passes, allowing the molecules to untilt.
This is the energy of friction. (The same AFM tip bends and
images the sample; see figures at www.aip.org/graphics.) By
adjusting the loading force of the probe, the researchers could get
the molecules to tilt in discrete steps (cramped atoms displacing
into new notches along the molecule, one at a time) resulting in a
quantized form of friction. The exertion felt by the probe provides
a measure of this energy dissipation, thus quantifying, for the first
time, the direct relation between physics at the molecular level and
macroscopic friction. (Barrena et al., Physical Review Letters,
upcoming article.)

PHYSICS NEWS UPDATE
The American Institute of Physics Bulletin of Physics News
Number 417 March 8, 1999 by Phillip F. Schewe and Ben Stein

WEIGHING VIRUSES. A nanobalance, a vibrating carbon
nanotube that can directly weigh microscopic organisms and
particles piggybacked onto it, has been demonstrated by
researchers at Georgia Tech (Walt de Heer, 404-894-7879). First
discovered in 1991, a carbon nanotube is essentially a sheet of
carbon atoms (arranged in a hexagonal pattern) rolled up into a
nanometer-diameter tube that is capped at both ends with carbon
hemispheres. In the present experiment, the researchers viewed
their nanotubes, protruding from a carbon fiber, with an electron
microscope. The fiber in turn was attached to a gold wire, mounted
on an insulator. This setup allowed the researchers to send an
electrical current through the nanotubes. Putting the whole
assembly on a special sample holder put it only 5-20 microns away
from an oppositely charged electrode. Applying an oscillating
electrical voltage to the wire, opposed to this electrode, caused the
tubes to vibrate; the vibration was a maximum at the resonant
frequency. Attaching a particle to such a nanotube would change
this resonance frequency, enabling researchers to deduce the mass
of the particle. With this technique, the researchers measured a
graphite particle to be 22 femtograms (22 quadrillionths of a
gram). In general, this technique can determine the mass of
particles with similar dimensions in the femtogram to picogram
range. This includes viruses. (Poncharal et al., Science, 5 March
1999.)

PARITY NONCONSERVATION (PNC) IN ATOMS is an area of
fundamental physics---testing parity conservation, or the
proposition that interactions are the same even if you view them in
a mirror ---carried out not at an immense particle accelerator but on
a tabletop. Atoms are chiefly governed by the electromagnetic
force, an ally of parity conservation but, according to current
theory, also feel a very faint tug from the weak nuclear force, a
notorious abuser of parity. Evidence for this has been the
observation of rare "forbidden" transitions between particular
atomic levels. For example, Carl Wieman of the University of
Colorado (303-492-6963, cwieman@jila.colorado.edu) sees such
transitions in cesium by detecting the fluorescence from 6S atoms
boosted into the 7S state (see Physics Today, April 1997). In
chemistry class, one learns of S and P states, in which
configurations of the atoms' electrons is such as to give the atom
spherical and dumbbell shapes, respectively. (Other states,
corresponding to even higher angular momentum levels, also
exist.) A photon, with an angular momentum unit of one, cannot
link to S states, but a Z boson (one harbinger of the weak force)
can. Now new precision in theoretical calculations of the
transitions have progressed to a point where the theory of the
electroweak force can be put to the test. The Colorado comparison
reveals a small but intriguing discrepancy between theory and
observation. Added impetus for these studies is the fact that
atomic PNC is sensitive to electron-quark interactions different
from those explored in high energy experiments. (S.C. Bennett
and C.E. Wieman, upcoming article in Physical Review Letters;
see also www.aip.org/physnews/graphics)

THE AMERICAN PHYSICAL SOCIETY CENTENNIAL will be
celebrated in two weeks in Atlanta. This largest physics meeting
in history will feature gatherings of more than 50 Nobel laureates
and representatives of physical societies worldwide, and an array
of important physics announcements, which will be featured in
future Physics News Updates. For more information see
http://www.aps.org/meet/CENT99/BAPS/index.html

PHYSICS NEWS UPDATE
The American Institute of Physics Bulletin of Physics News
Number 416 February 26, 1999 by Phillip F. Schewe and Ben
Stein

WIRE-GUIDED ATOMS. The development of "atom optics" is
part of the effort to store, guide, focus, reflect, and perform
calculations with atoms in analogy with the ways electrons are used
in electronics and photons in photonics. In a new innovation cold
lithium atoms from a magneto-optic trap (MOT) were nudged in the
direction of a thin current-carrying wire. Although the atoms are
neutral, they still feel the magnetic force field which can be used to
send the atoms in two types of trajectory. In one case the atoms
spiral in "Kepler" like orbits around and along the wire. In the
second case the use of an extra field helps to create a "potential
tube" parallel to the wire in which the atoms are guided along the
side of the wire. This second guide is especially interesting since
the wires can be mounted on a surface, allowing for easy
miniaturization of these guides and traps. Physicists at the
University of Innsbruck (Joerg Schmiedmayer,
joerg.schmiedmayer@uibk.ac.at, 011-43-512-507-6306) expect that
this will allow them to design guides and traps for cold atoms with a
variety of different geometries. These can be used to manipulate
atoms from Bose-Einstein condensates, or serve as beam splitters or
interferometers for guided atoms. Even more complicated
integrated atom optics devices and networks, similar to integrated
circuits for electrons, can be devised. Some mesoscopic
experiments which now use electrons in solids might, with this new
atom optics tool, be able to use guided atoms moving above a
surface. (Denschlag et al., Physical Review Letters, 8
March 1999; see www.aip.org/physnews/graphics, also
http://info.uibk.ac.at, and Physical Review Focus for 28 July 1998.)

HOLOGRAMS OF TRANSISTOR INTERIORS can provide maps
of electrostatic potentials in that crucial zone beneath the transistor's
gate, where the passage of electrons from emitter to drain can be
made difficult or easy, just as a water tap can switch a faucet on and
off. Why are such maps necessary? "Within a decade, integrated
circuits will consist of transistors 150 atoms long and 50 atoms
deep," according to researchers at the Institute for Semiconductor
Physics in Frankfurt (Oder), Germany, and knowledge of the precise
whereabouts of dopant atoms will be vital. To this end, the
Frankfurt scientists (Wolf-Dieter Rau, rau@ihp-ffo.de, 011-49-335-
562-5432) can now produce a subsurface sectional map of the
transistor. Electron waves from a transmission electron microscope
(in which the quantum wavelike properties of electrons are more
important than their particle properties) pass through the thin
transistor, where they scatter slightly. These waves are recombined
with some unscattered electron waves to form a holographic signal
which encodes information about local conditions throughout the
section. The electron data can be processed into 2-dimensional
images with 10-nm resolution and high sensitivity. (Rau et al., Phys
Rev Lett, tent. 8 Mar; see www.aip.org/physnews/graphics.)

A SINGLE-PHOTON TURNSTILE, a device in which photons are
emitted one at a time under controlled circumstances, has been
created by a team of scientists from Stanford (US), Hamamatsu
Photonics (Japan), and NTT (Japan). Essentially the researchers use
the quantization of electrical conductance to produce a quantization
of photon emission. They put together a quantum well (the frontier
between two thin semiconductor layers) containing a single electron
(other electrons are dissuaded from entering because of a "Coulomb
blockade" effect) with a quantum well containing a lone
(comparably Coulomb blockaded) hole, and then cycle the voltage
across the whole stack of layers in such a way that the lone electron
and lone hole meet, mate, and make a lone photon. The resulting
device, which operates at mK temperatures, is typically a tiny post
some 700 nm tall and with a diameter of 200-1000 nm. (J. Kim et
al., Nature, 11 February 1999.)

PHYSICS NEWS UPDATE
The American Institute of Physics Bulletin of Physics News
Number 415 February 18, 1999   by Phillip F. Schewe and Ben
Stein

LIGHT HAS BEEN SLOWED TO A SPEED OF 17 m/sec by
passing it through a Bose-Einstein condensate (BEC) of sodium
atoms at nK temperatures.  In general light is slowed in certain
materials, a property exploited in making optical lenses.  As the
index of refraction of these materials gets higher, however,
absorption increasingly takes its toll on the light beam.  In an
experiment at Harvard (Lene Vestergaard Hau, hau@rowland.org),
physicists have used a BEC (and its enormous index of refraction)
as the optical medium, but with the following important
modification.  They contrived a system of laser beams whose
pattern of interference created an effect called electromagnetically
induced transparency, allowing light to propagate unabsorbed but
at greatly reduced speeds, in this case a factor of twenty million
compared to the speed of light in vacuum; greater light-speed slow
downs are expected, to as low as cm/sec.  The researchers also
observed unprecedentedly large intensity-dependent light
transmission.  Such an extreme nonlinear effect can perhaps be
used in a number of opto-electronic components (switches,
memory, delay lines) and in converting light from one wavelength
to another.  (Hau et al., Nature, 18 February 1999.)

TUNABLE X-RAY WAVEGUIDE WITH AN AIR GAP.  At
synchrotron light sources, electron beams make floods of x rays
which must be tamed before they can be used in experiments
where typically they probe the structure of some tiny biological
sample.  One of the ways to focus the beam onto the sample is to
compress it and guide the x rays through a thin strip of material
sandwiched between reflecting surfaces.   Usually the guiding
material, often carbon, absorbs a substantial portion of the x rays.
Researchers at the University of Amsterdam (Friso van der Veen,
vdveen@wins.uva.nl,  011-31-20-525-6330) have now produced a
waveguide out of two parallel reflecting plates with only air in
between.  This not only greatly reduces x ray losses but also, when
the gap is filled with liquid, permits the x-ray study of lubricants
and colloids.  In optics geometry is destiny; the coherent wave
pattern in the Amsterdam device can be tuned by prising apart the
two flat plates which form the body of the waveguide.  For the
whole process to work the plates (only about 250 nm apart) must
be extremely parallel, the equivalent of suspending one soccer field
over another at a height of about 5 mm.  (M.J. Zwanenburg et al.,
Physical Review Letters, 22 Feb; see figure at
www.aip.org/physnews/graphics.)

A TWO DIMENSIONAL BOSE EINSTEIN CONDENSATE
(BEC) has been observed by a University of Turku (Finland)--
Kurchatov Institute (Russia) collaboration.  The condensate
occurred in hydrogen atoms sitting on top of a layer of liquid
helium-4 at a temperature of 120-200 mK (Safonov et al., Physical
Review Letters, 23 November 1998). Strong magnetic fields force
the nuclei and electron spins of the hydrogen atoms to align.
Magnetic fields also help to herd the atoms together into a small
portion of the helium surface, achieving the density needed to
begin the process of atom overlap at the heart of the BEC process.
Explanations for this type of 2D quantum fluid are lacking.
(Physics World, Feb 1999.)

PHYSICS NEWS UPDATE
The American Institute of Physics Bulletin of Physics News
Number 414 February 11, 1999 by Phillip F. Schewe and Ben
Stein

THE FIRST ENTANGLEMENT OF THREE PHOTONS has been
experimentally demonstrated by researchers at the University of
Innsbruck (contact Harald Weinfurter,
harald.weinfurter@uibk.ac.at, 011-43-512-507-6316).
Individually, an entangled particle has properties (such as
momentum) that are indeterminate and undefined until the particle
is measured or otherwise disturbed. Measuring one entangled
particle, however, defines its properties and seems to influence the
properties of its partner or partners instantaneously, even if they
are light years apart. In the present experiment, sending individual
photons through a special crystal sometimes converted a photon
into two pairs of entangled photons. After detecting a "trigger"
photon, and interfering two of the three others in a beamsplitter, it
became impossible to determine which photon came from which
entangled pair. As a result, the respective properties of the three
remaining photons were indeterminate, which is one way of saying
that they were entangled (the first such observation for three
physically separated particles). The researchers deduced that this
entangled state is the long-coveted GHZ state proposed by
physicists Daniel Greenberger, Michael Horne, and Anton
Zeilinger in the late 1980s. In addition to facilitating more
advanced forms of quantum cryptography, the GHZ state will help
provide a nonstatistical test of the foundations of quantum
mechanics. Albert Einstein, troubled by some implications of
quantum science, believed that any rational description of nature is
incomplete unless it is both a local and realistic theory: "realism"
refers to the idea that a particle has properties that exist even before
they are measured, and "locality" means that measuring one
particle cannot affect the properties of another, physically
separated particle faster than the speed of light. But quantum
mechanics states that realism, locality--or both--must be violated.
Previous experiments have provided highly convincing evidence
against local realism, but these "Bell's inequalities" tests require
the measurement of many pairs of entangled photons to build up a
body of statistical evidence against the idea. In contrast, studying a
single set of properties in the GHZ particles (not yet reported)
could verify the predictions of quantum mechanics while
contradicting those of local realism. (Bouwmeester et al., Physical
Review Letters, 15 Feb.)

A NEW ONLINE EXHIBIT DEVOTED TO WERNER
HEISENBERG traces the birth of quantum mechanics, the wartime
effort to build a German atom bomb, and other episodes from a
remarkable life. Prepared by leading Heisenberg biographer David
Cassidy, the exhibit is available now on the website
(www.aip.org/history/heisenberg) of the Center for History of
Physics, the premier clearinghouse of physics-related archived
papers, photos, and taped interviews (3000 hours' worth). Located
at the American Institute of Physics in College Park, Maryland, the
Center houses the Niels Bohr Library (nbl@aip.org, 301-209-
3184), strong in books from the mid-19th century to the present,
and the Emilio Segre Visual Archives (containing 25,000 items).
The Center itself possesses several valuable collections of papers
and provides support to other institutions in their efforts to archive
the papers of important physicists (contact Spencer Weart or Joe
Anderson at chp@aip.org). The Center has a prominent place on
the Internet (www.aip.org/history), where it maintains the
International Catalog of Sources for History of Physics and Allied
Sciences. In addition to the Heisenberg site, the Center website is
also home to two other widely popular exhibits, one devoted to
Albert Einstein and one to JJ Thomson's discovery of the electron.
Soon an exhibit devoted to Andrei Sakharov will also be available.

PHYSICS NEWS UPDATE
The American Institute of Physics Bulletin of Physics News
Number 413 February 4, 1999 by Phillip F. Schewe and Ben
Stein

THE FIRST 3D PHOTONIC CRYSTAL operating at a
wavelength of 1.5 microns, the all-important preferred wavelength
for light traveling down optical fibers, has been devised by
scientists at Sandia (Shawn Lin, slin@sandia.gov). Basically, a
photonic crystal is to light what a semiconductor is to electrons:
some photon energies are permitted while others are excluded.
The exclusion comes about by a careful interleaving of materials
with very different indices of refraction. The Sandia crystal is
actually a tiny pile of criss-crossed polysilicon rods with air in
between. Photonic crystals will be ingredients in future optical
transistors---by deflecting light they will be able to act as optical
switches at THz speeds; by trapping light they will be able to
produce optical amplification within cavities. The crystals will
also be part of other optical integrated circuit components such as
low-power nanolasers and as waveguides. (Optics Letters, 1 Jan
1999; see also Physics Today, Jan 1999.)

MAGNETOELECTRONICS, SPIN ELECTRONICS, AND
SPINTRONICS are different names for the same thing: the use of
electrons' spins (not just their electrical charge) in information
circuits. One magnetoelectronic device is the magnetic hard drive
based on the giant magnetoresistance (GMR) effect. In a GMR
material, consisting of a stack of alternating layers of magnetic and
nonmagnetic atoms, a small magnetic field can produce a large
change in electrical resistance. Already a billion dollar business,
GMR read heads will boost disk drive densities from 1 to 20 Gbits,
and GMR might be incorporated into random access memory units
as well (Gary Prinz, Science, 27 Nov 1998). The latest
demonstration of spin versatility is the organized movement of a
herd of spins over a lateral distance of 100 microns. In an
experiment at UC Santa Barbara, David Awschalom first aligned
the spins of a swarm of electrons and then nudged them across a
semiconductor strip without the spin bunch falling apart. Such
coherence will be necessary if spin currents are to transport
information from place to place, particularly in quantum
computers. (Nature, 14 Jan 1999.)

THE ROLE OF PHYSICS IN BIOLOGY is a venerable one. The
lead article in the 14 January issue of Nature describes how the
borrowing continues, chiefly through application of versatile
sensors and data management in such areas as genetic sequencing.
But more than technology transfer is at work, and several new
multidisciplinary institutes are being built (Stanford, Berkeley,
Princeton, and Chicago) to cross-fertilize physics and bio/medical
research (Nature, 7 Jan 1999). One of the leaders at Stanford, for
example, is Steven Chu, who has used his pioneering mageto-optic
traps methods to study the physics of DNA molecules. The
biology/physics connection was one of the themes of last week's
AAAS meeting in Anaheim, where Hans Frauenfelder of Los
Alamos described his motto as "Ask not what physics can do for
biology but what biology can do for physics." To illustrate his
point he cited the use of research on "energy landscapes"
(essentially energy-level diagrams depicting transitions among
various possible folded geometries, or conformations, of proteins)
in the study of physics systems as "spin glasses," in which
magnetic atoms are dispersed in an alloy with their spins oriented
at haphazard angles. The evolving relation of physics and biology
is even being felt at the high school level, where some schools are
reversing the traditional biology-chemistry-physics sequence of
courses, the better to introduce certain concepts, such as energy
and force, needed for understanding the new higher biology (New
York Times, 24 Dec 1998).

PHYSICS NEWS UPDATE
The American Institute of Physics Bulletin of Physics News
Number 412 January 27, 1999 by Phillip F. Schewe and Ben
Stein

ELEMENT 114, representing the beachhead of what might be an
"island of stability" among heavy nuclei, has been successfully
created, according to scientists at Russia's Joint Institute for
Nuclear Research in Dubna. Artificially made elements heavier
than uranium are generally unstable, but theorists have for some
time thought that elements in the vicinity of number 114 and
above might well possess a configuration of neutrons and protons
that makes for longer life. The Dubna result seems to be evidence
for this. Made by shooting atoms of calcium-48 into a target of
plutonium-244, atoms of element 114 (with a nuclear weight of
289) were detected through their decay into element 112. The
lifetimes for elements 114 and 112 are 30 seconds and 280 msec,
respectively. Element 113 has not yet been discovered. (News
items in Science, 22 January 1999.)

QUANTUM HOLOGRAPHY, in which a pair of laser pulses
reveals detailed information about an atom's state, has been used
for the first time to control the shape of an atom wave, advancing
prospects for tailoring an atom's exact properties. Classical
holography, which makes 3D pictures, involves the use of an
"object" and a "reference" laser beam. How these beams combine
in a piece of film provides information on their relationship
(specifically, their relative "phases"), allowing the eye to build up a
3D scene. In quantum holography, an ultrashort laser pulse
(playing the role of an object beam) first puts an atom into a
combination of wavelike states, forming a "wavepacket." Shortly
thereafter, a subsequent pulse (acting as the reference beam)
creates a second wavepacket within the atom. These two
wavepackets interfere. Ionizing the atoms and then measuring
them at a detector can provide information about the phase
relationships between the wavepackets, ultimately yielding details
on the individual wavelike states. University of Michigan
researchers (Tom Weinacht, 734-764-2344) have now
demonstrated a feedback approach, in which they shine a pair of
pulses on a gas of cesium atoms, measure the effect, and modify
subsequent pairs of pulses until they get the cesium wavepacket
they want. Such "wavepacket engineering" may enable scientists
to prepare atoms and molecules which undergo precisely desired
chemical reactions. (Weinacht et al., Nature, 21 January 1999; see
also Phys. Rev. Focus, 23 June 1998.)

THE ADVANCED COMPOSITION EXPLORER (ACE)
satellite measures isotope and ionization abundances in the solar
wind. On two recent occasions (6 Nov 1997 and 2-3 May 1998)
explosions on the sun spewed clouds of particles whose isotope
profiles departed from the norm. For the Nov 1997 event, for
instance, the presence of higher-than-normal ionized states of
certain isotopes indicated that regions of hotter-than-normal
portions of the solar corona were involved, and this in turn
suggested that several particle-acceleration mechanisms were
operating in the sun's atmosphere. The May 1998 event
featured charge states, such as triply ionized oxygen and nitrogen,
not seen before in solar wind. These comparatively modestly
ionized atoms are indicative of the relatively cool (100,000 K) gas
in solar prominences; this cooler gas must have gotten caught up in
the much hotter coronal-mass-ejection material making its way
toward ACE. (Series of articles in the 15 January 1999 issue of
Geophysical Research Letters.)

PHYSICS NEWS UPDATE
The American Institute of Physics Bulletin of Physics News
Number 411 January 19, 1999 by Phillip F. Schewe and Ben
Stein

QUANTUM GAMES. Star Trek's Captain Picard (fictional
commander of the USS Enterprise) and Q (his mischievous, all
-powerful adversary) are beamed onto the pages of Physical Review
Letters for the first time to engage in a hypothetical contest that
represents the extension of game theory to the quantum world.
With these characters, physicist David Meyer of the math
department (Project in Geometry and Physics) at UC-San Diego
(619-534-5524; dmeyer@chonji.ucsd.edu) illustrates how playing
nanoscopic versions of familiar games with atoms (or any other
object which obeys the peculiar rules of quantum mechanics) may
reveal new information-processing tasks (beyond already known
ones) that quantum computers would perform more efficiently than
classical computers. In Meyer's scenario, Q promises Picard that
he will help get the Enterprise out of its latest emergency if Picard
wins a game. Specifically, the contest amounts to a quantum
version of a penny-flipping game, in which an atomic nucleus with
"spin-up" and "spin-down" energy states takes the place of the
familiar zinc coin with heads and tails. Through this game, Meyer
shows that players like Q who exploit the unique properties of
quantum-mechanical objects (such as the ability to put it in a
simultaneous combination or "superposition" of two states) enjoy a
distinct advantage over those who (like Picard) just treat the
objects like everyday items such as balls or coins (which can only
be in one state or the other). Through his use of superpositions, Q
manipulates the nucleus in such a way that ensures he always wins,
even though the chances of winning the classical version of the
game are only 50-50. Such a contest, Meyer points out, can be
easily demonstrated with existing quantum computers, and may
provide insights on such things as quantum-error correction.
(Upcoming article in Physical Review Letters; as usual, journalists
can obtain the article from AIP Public Information.)

X RAYS IN, GAMMA RAYS OUT. A laser is a machine for
pumping energy (electrical, light, chemical, etc.) into a medium
(liquid, gas, solid, etc.) whose atoms subsequently relax in a
concerted way, producing coherent light. One of the obstacles to
creating an x-ray or gamma laser is the inability to pack enough
energy into the medium and have it sit there long enough until it
can be extracted under the right circumstances. One candidate
medium for the job is isomeric hafnium. In nuclear physics isomers
are nuclei that have the same number of neutrons and protons but
differ in that for one nucleus one or more nucleons (protons or
neutrons) are placed in an excited state. Physicists at the
University of Texas at Dallas (Carl Collins, 972-883-2864,
cbc@utdallas.edu) and their colleagues in Russia, Romania,
Ukraine, and the US begin with a sample (prepared at Los Alamos)
of a metastable (31-year lifetime) isomer of Hf-178 with 4
participating nucleons, possessing a stored energy of 2.5 MeV.
Then, like a transistor triggered by the merest of gate signals, the
isomer material can, with the input of some x rays (amounting to
only 1.6% of the output energy), produce induced gamma emission
(IGE); thus x ray energy is stockpiled in the Hf and later extracted
at higher gamma-ray energy. The emitted rays are not coherent,
however, so this is not yet an example of gamma lasing. IGE
research also has astrophysical implications since isomer states are
expected to behave differently in gamma-intense environments
such as supernovas. (C.B. Collins et al., Physical Review Letters,
upcoming article; see http://www.utdallas.edu/research/quantum.)

PHYSICS NEWS UPDATE
The American Institute of Physics Bulletin of Physics News
Number 410 January 13, 1999 by Phillip F. Schewe and Ben
Stein

IS THE FINE STRUCTURE CONSTANT CHANGING? The
inherent strength of the electromagnetic force is characterized by a
parameter called the fine structure constant (denoted by the Greek
letter alpha), defined as the charge of the electron squared divided
by the product of Planck's constant and the speed of light. The
size of alpha determines how well atoms hold together and what
types of light atoms will emit when heated up. And just as the
elastic band keeping a swimsuit snug will gradually relax with
time, so it is reasonable to ask whether an atoms' elasticity (or
alpha) might also vary with time, an idea broached by Paul Dirac
in 1937. A group of scientists at the University of New South
Wales in Australia (John Webb, jkw@edwin.phys.unsw.edu.au)
test this proposition by sampling ancient light emitted by ancient
atoms, and comparing them to modern light from modern atoms.
In particular they looked at the relative spacing of doublets of
absorption lines in the spectra of several types of atoms in distant
gas clouds lying in front of still more distant quasars. The
spacings, not easy to tease out from the faint spectra, are
proportional to alpha squared. After taking into account Doppler
effects owing to the expansion of the universe, the Australian
scientists find that there is a consistent change in alpha with
increasing redshift (z), especially above a z of one. Owing to the
caution needed in claiming a "measurement" of alpha change, the
researchers prefer to think of their result as constituting a new
upper limit on the fractional alpha change for z>1 of about 2 parts
in 10,000. (Webb et al., Physical Review Letters, tent. 25 Jan.
1999.)

HYDROGEN BONDS IN WATER HAVE COVALENT
PROPERTIES, new experiments have shown directly for the first
time, confirming a controversial prediction of great importance to
understanding water and the many other structures such as DNA
which contain hydrogen bonds. Within a single water molecule,
hydrogen and oxygen are held together by "sigma" bonds, which
are strongly covalent, meaning that electrons are shared between
atoms. Between groups of water molecules, however, are much
weaker "hydrogen bonds." These bonds are principally
electrostatic attractions between positively charged hydrogen---
which readily gives up its electron in water---and negatively
charged oxygen--which receives these electrons--in a neighboring
molecule. In the 1930s, after quantum mechanics had forever
changed the world view of physics, famous chemist and Nobel
Laureate Linus Pauling proposed that electron clouds associated
with hydrogen and sigma bonds would somewhat overlap with one
another, affecting each other's properties. However, the extent of
this effect has been contentious and experimentally untested--until
now. Shining intense synchrotron x rays on a single crystal of ice
from several different directions, and plotting the energy spectrum
of the scattered x rays, a US-France-Canada team (Eric Isaacs,
Lucent Technologies) observed wavelike interference fringes. The
presence of these fringes means that the electrons participating in
the hydrogen bond are at least in part quantum mechanically shared
(covalently) between neighbors just as Pauling had predicted.
Since hydrogen bonds play a significant role in determining
water's properties, this experiment is likely to shed light on the
mysteries of water (such as the fact that water expands upon
freezing) which have been so important to the advent and evolution
of life on this planet. (Isaacs et al., Physical Review Letters, 18
January 1999; additional information at
www.aip.org/physnews/preview)

PHYSICS NEWS UPDATE
The American Institute of Physics Bulletin of Physics News
Number 409 January 5, 1999 by Phillip F. Schewe and Ben
Stein

WHAT MAKES OBJECTS SO STICKY? Removing one's finger
from a sticky surface often requires an unexpectedly large amount
of work, sometimes up to 10,000 times more than simple
theoretical considerations would suggest. The forces primarily
involved in making objects sticky are the weak attractions between
molecules known as van der Waals forces, but their effect is
enhanced by mechanisms whose exact nature and role have
remained a mystery. Moreover, in controlled experiments where a
metallic probe is removed from a sticky polymer at a constant rate,
no one has explained the observed sequence of forces, which
quickly reach a peak value, then remain roughly constant before
dropping to zero. Now, researchers in France (Cyprien Gay and
Ludwik Leibler, CRNS-Elf Atochem, cgay@pobox.com, 011-33-
147-59-1494) suggest that a combination of surface roughness and
air suction effects is what makes things sticky. In their theory, air
bubbles are trapped as the rough, wavy surfaces of the metallic
probe and of the deformable polymer touch each other. Pulling
apart the surfaces causes the bubbles to change shape. At first this
creates a suction-cup effect which makes it harder to separate the
surfaces (corresponding to the force peak), until air rushes in.
Then, isolated bubbles connect and evolve into a network of
contact points between the probe and polymer. Fractures that
propagate through this network reduce the force required to
separate the surfaces, and keep it at a plateau before the probe is
finally removed, dropping the force to zero. Developing a more
sophisticated understanding of stickiness will help researchers
better design adhesives, coatings and paints. (Gay and Leibler,
upcoming paper in Physical Review Letters.)

THE TOP PHYSICS STORIES FOR 1998 were, according to us,
the realization (based on observations of distant supernovas) that
the cosmological expansion of the universe is not only not slowing
but actually accelerating (Updates 355, 361) and the observation of
neutrino oscillation (Update 375). Other highlights from last year
included the mapping of the cosmic infrared background (Update
354), the localization of near-visible light (Update 356), Bose-Einstein
research (Updates 362, 382, 402), progress in quantum
teleportation (Update 356), the complementarity principle
demonstrated for electrons (Update 362), quantum computing used
to perform simple searches (Update 367), the detection of gamma
rays from a high-magnetic-field pulsar (or "magnetar," Updates
374, 394), the idea of chaos-based computing (Update 389),
Physics Nobel Prize (Update 396), low-field MRI (Update 398),
direct observation of time-reversal asymmetry (Update 402), no
end in sight for cosmic-ray energies (385), and some indication of
CP violation in B meson decays (405).

FURLONGS PER FORTNIGHT is not an acceptable unit for
velocity in the study of physics. This is because such mongrel
units do not abet the sort of consistency needed for carrying out
scientific research, which is already complicated enough. Instead
the Systeme International (SI) dictates a strict code of kilograms,
meters, and seconds. Nevertheless, physicists are human and
(especially in the largely non-metric US) surround themselves with
many non-SI units like miles-per-hour and atmospheres. Robert
Romer, editor of the American Journal of Physics, argues that this
is inevitable and partly desirable since we all, even scientists,
continue to live in a world where BTU's, horsepower, and barrels
of oil are still common parlance. (Editorial, AJP, Jan 1999.)