Conference decwet::physics

PHYSICS NEWS UPDATE                         
The American Institute of Physics Bulletin of Physics News
Number 304 January 23, 1997    
by Phillip F. Schewe and Ben Stein

IS THE UNIVERSE CRYSTALLINE?  As astronomers measure
redshifts for additional galaxy superclusters, the three-dimensional 
architecture of the universe becomes more evident. 
New redshift surveys, reaching ever further into space, are
benefiting from fiber optics and increasing automation.  A fresh
analysis of current redshift catalogs offers some evidence for a
periodic arrangement of superclusters, separated by voids, on a
scale of 120 megaparsecs (about 390 million light years).  Great
walls of galaxies on this scale have been discerned before but the
apparent periodicity is new.  The researchers suggest that a new
theory might be needed to explain the sort of immense 3D-
chessboard structure they seem to be finding in the data.   
(J. Einasto et al., Nature 9 January 1997.)

OUR LOCAL CLUSTER OF GALAXIES IS STILL
FORMING.  For decades astronomers have wondered about the
origin of certain fast-moving clouds of atomic hydrogen in the
vicinity of the Milky Way.  In some cases the clouds appeared to
be plunging into the plane of the galaxy (at speeds as large as 500
km/sec), and could not be considered as rotating with the galaxy. 
Later observations showed that some clouds actually seemed to be
moving away from the Milky Way.  A synthesis of new radio-
telescope measurements plus re-evaluated data from COBE and
the Hubble Space Telescope indicates that the clouds may be raw
material left over from the formation of the entity known as the
Local Group of galaxies, whose largest shareholders are the
Andromeda galaxy (with 65% of the mass of the group) and our
own Milky Way (30%). Reporting at last week's American
Astronomical Society meeting in Toronto, Leo Blitz of UC
Berkeley and David Spergel of Princeton said that the high
velocity clouds will continue of feed the Milky Way (providing
fuel for future star formation) and might even harbor dark matter,
a hypothesis which would account for the continued stability of
the clouds and their unexplained large internal velocities. 
Spergel said that the features of his theory for nearby high
velocity clouds might apply also to larger, more distant hydrogen
clouds in the cosmos.

METAL INCLUSIONS COME IN SPECIAL SIZES.  Gold does
not come out of the ground as ingots, but rather as misshapen
lumps ensconced in a rocky ore.  One can ask whether, in
general, nature dictates the size and shape of chunks of one
element embedded in another solid.  This issue is especially
important at the microscopic level since the melting point of
some materials can be raised or lowered considerably by burying
particles of one type within the sample.  A Berkeley-Copenhagen-
Rio de Janeiro collaboration (contact Uli Dahmen,
[email protected]) has now shown, for the first time,
that nanoscopic three-dimensional lead inclusions, having come
to equilibrium inside an aluminum matrix, assume only special
("magic") sizes.  These preferred shapes, the researchers believe,
are imposed by the crystalline mismatch between the two
elements. In time, this magic-size phenomenon might be useful
for tailoring specific thermodynamic, magnetic, electronic, or
optical properties.  (U. Dahmen et al., Physical Review Letters,
20 January 1997.)

PHYSICS NEWS UPDATE                         
The American Institute of Physics Bulletin of Physics News
Number 305  January 27, 1997    
by Phillip F. Schewe and Ben Stein

A RUDIMENTARY ATOM LASER has been created at MIT,
promising significant improvements in high precision
measurements with atoms and offering the prospect of future
nanotechnology applications, such as atom lithography, in which
lines are drawn on integrated circuits (by directly depositing
atoms) with greater precision than ever before. In an atom laser
the output beam consists of a single coherent atom wave, just as
in a regular laser the beam consists of  a coherent light wave. 
The working substance for the atom laser is a Bose-Einstein
condensate (BEC) of sodium atoms, cooled and contained within
an atom trap by a shaped magnetic field.   BEC itself was
achieved for the first time only as recently as 1995 (see Update
233). It is a condition in which atoms are chilled to such low
energies that, in a wavelike sense, the atoms begin to overlap and
enter into a single quantum state.
   Wolfgang Ketterle and his colleagues at MIT make their claim
of producing the first atom laser on the basis of two experimental
developments, as reported in two journals this week.  In the first
effort (M.-O.Mewes et al., Physical Review Letters, 27 January
1997) a portion of a sodium condensate was successfully
extracted under controlled conditions.  They achieve  "output
coupling" by applying radiofrequency radiation to the BEC; this
"tips" the atoms' spins by  an adjustable amount, putting the
atoms in a superposition of quantum states.  Thereafter some of
the atoms feel the effect of the surrounding magnetic field in a
different way and are able to leave the atom trap.  It is these
departing atoms, still enjoying the coherent properties of the BEC
state, that constitute an atom laser beam. Pulled downward by
gravity, the beam was observed over a distance of millimeters,
although in principle it could travel further in an undisturbed
vacuum environment.
    The second development was to verify that the atom waves are
indeed coherent (M.R. Andrews et al., Science, 31 January
1997). At the time of the original BEC discovery, many
physicists expected the atoms in the condensate to fall into a
single quantum state; some hypothesized that it could take a time
equal to the age of the universe for true coherence to come about. 
The MIT group addressed this issue by creating two BEC clouds
in a special trap. Turning off the trap allows the clouds to
expand, overlap, and interfere, producing a pattern of light and
dark fringes.  The observed patterns (viewed with an electronic
camera) could only exist if each BEC was an intense coherent
wave.  The MIT team determined that the atom wave associated
with each BEC had a wavelength of 30 microns, a million times
larger than the wavelengths associated with room-temperature
atoms. 
   In addition to coherence, the atom laser waves are analogous to
the light waves in an optical laser in another respect as well.  Just
as a laser beam is more intense than an equivalent stream of light
from the Sun, the MIT atom beam is also more intense (for a
given beam spotsize) than ordinary atom beams (whose atoms
possess a variety of energies) since it delivers a powerful,
directional stream of atoms in a single quantum state. In other
ways, the atom lasers and light lasers are different.  According to
Ketterle, "Photons can be created but not atoms.  The number of
atoms in an atom laser is not amplified.  What is amplified is the
number of atoms in the lowest-energy quantum state, while the
number of atoms in other states decreases."
   Graphics and more text can be viewed on the World Wide Web
at this address: www.aip.org/physnews/special.htm. 

PHYSICS NEWS UPDATE                         
The American Institute of Physics Bulletin of Physics News
Number 306 February 4, 1997    by Phillip F. Schewe and Ben
Stein

ATOM WAVES CAN BE USED TO DETECT ROTATIONAL
EFFECTS, such as the revolution of the Earth, with as much
sensitivity as most commercial laser gyroscopes, new experiments
have demonstrated.  David Pritchard ([email protected]) and
his coworkers at MIT pass a beam of sodium atoms through an
atom interferometer, a device which splits individual atoms into
wavelets and recombines them to form interference patterns of
light and dark fringes.  Rotating the interferometer itself while
the atom waves travel freely through the device makes the fringes
shift from their usual positions. The MIT device can detect
rotation rates as slow as one-hundredth of a degree per minute,
comparable to the sensitivity of good-quality commercial laser
gyroscopes used to detect rotational effects in autos and tanks,
but only about one-tenth the sensitivity of laser gyroscopes used
in inertial guidance systems in aircraft.  With further
improvements, atom interferometers may one day easily surpass
the sensitivity of laser interferometers because atom wavelengths
can be tens of thousands of times smaller (potentially making
them more sensitive to smaller changes) and the atoms' much
slower speeds compared to light means the interferometer has
more time to rotate while the particles travel through the device
and thereby can create more appreciable fringe shifts. (A.Lenef
et al., Physical Review Letters, 3 February 1997.)

PHOTONS AND LEPTONS SHALL INHERIT THE
UNIVERSE.  The Copernican principle that the Earth does not
occupy a privileged place in space can be extended to the time
domain.  Carbon-based homo sapiens live some 10^10 years after
the big bang, but this is a mere preface to the vast timespan yet to
come. Using the latest models of proton decay, stellar evolution,
and black holes, Fred Adams and Greg Laughlin of the
University of Michigan have prophesied a dim future for the
cosmos.  They have wound up the clock of the universe and let it
tick forward in steps they call "cosmological decades," periods of 
tenfold increase in the number of years since the big bang. (They
also assume the continuing cosmological expansion.)  In the
current "stelliferous" age (10^6--10^14 years along, or decades
n=10-14) regular stars like ours are succeeded by longer-lived
red and white dwarf stars.  In the "degenerate era" (n=15-37)
galaxies fall apart as their inhabitants are reduced to stellar
remnants such as brown dwarfs and as more matter falls into
black holes. Remnant stars are replenished somewhat by soaking
up dark matter but ordinary baryonic matter inexorably
disappears through proton decay (a white dwarf generates about
400 watts of energy via proton decay).  In the next era (n=38-
100) even the last large repositories of mass, black holes,
succumb to evaporation (whereby particle-pair production at the
hole's event horizon allows some particles to escape): stellar-
mass black holes evaporate in 10^65 years, galaxy-mass black
holes in 10^98 years. In the "Dark Era" (n>100) almost nothing
is left but electrons, positrons, neutrinos and photons, most of
which are so spread out that encounters are rare. (Talks at the
American Astronomical Society meeting and April issue of Rev.
of Modern Physics.)

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PHYSICS NEWS UPDATE                         
The American Institute of Physics Bulletin of Physics News
Number 307 February 12, 1997    
by Phillip F. Schewe and Ben Stein

LASER COOLING OF BULK MATTER.  For many years laser
light has been used to slow down and thereby cool individual
atoms in traps.  But laser light can now also be used to cool bulk
matter.  This happens by a process called anti-Stokes
fluorescence.  In the solid certain molecules reside in vibrational
states which make them somewhat warmer than their neighbors. 
If now specially tuned laser light hits these molecules, they will
emit a photon whose energy is greater than the one they
absorbed.  Thus heat energy is carried away as light energy (New
Scientist, 18 January 1997).  In this way gases and liquids have
been cooled, and now  researchers at Los Alamos have cooled a
solid ytterbium-doped optical fiber from a temperature of 298 to
282 K, a difference of 16 K.  Applied on a large scale, this
principle could lead to a laser refrigerator.  (C.E. Mungan et al.,
Physical Review Letters, 10 February 1997.)

SONOLUMINESCENCE BUBBLES COLLAPSE AT MORE
THAN FOUR TIMES THE SPEED OF SOUND, new
experiments have shown.  Sonoluminescence is the still-
mysterious process in which sound waves aimed at a water tank
cause bubbles to collapse and generate ultrashort light flashes
which represent a trillionfold concentration of the original sound
energy.  UCLA researchers (Seth Putterman, 310-825-2269)
determine the speed of bubble collapse by measuring the amount
of laser light scattered from a bubble during different points of its
implosion.  The amount of scattered light is proportional to the
square of the bubble radius.  Previous experiments could only
establish that the bubble collapsed faster than the speed of sound;
using ultrashort (100-fsec) laser pulses has now enabled the
researchers to ascertain that the bubble collapses at a speed
greater than Mach 4 (more than 1 km/s for this tiny bubble). 
This confirms a major prediction of the leading explanation for
sonoluminescence known as the shock-wave model but does not
rule out competing explanations because this and other
experiments to date can only probe the outer surface of the
bubble, not what is happening inside.  In addition, the UCLA
team determined that the bubble accelerates by at least 10^11 g
when the bubble stops compressing and starts expanding;
amazingly, the bubble remains intact during this massive
acceleration.  (K.R. Weninger et al., upcoming article in
Physical Review Lett.)

POLYMER QUANTUM WIRES.  By restricting the spatial
motions of electrons in semiconductors, one also begins to
restrict the electron's allowable energies.  With this comes
greater control over the way in which the electrons' wave
properties can be used in practical devices such as diode lasers,
the ones used in CD players.  So far "quantum confinement"
structures that restrict motion in one dimension (quantum wells),
two dimensions (quantum wires), and all three dimensions
(quantum dots) have been made with inorganic semiconductors
such as GaAs.  But now scientists at Rochester (Samson Jenekhe,
[email protected]) report that they have made light-
emitting quantum wires using a blend of two polymers.  The
linear chain structure and electronic properties of polymers make
them a sort of natural quantum wire to begin with.  It's rather
early to compare to GaAs optical devices, but the polymer
versions might have better stability in high electric fields. 
Furthermore, as an organic material, the polymer wires could be
"grown" rather than built up in an expensive epitaxial process
using particle beams in vacuum chambers. (Chen and Jenekhe,
Applied Physics Letters, 27 January 1997.)

PHYSICS NEWS UPDATE                         
The American Institute of Physics Bulletin of Physics News
Number 308 February 20, 1997    by Phillip F. Schewe and Ben
Stein

SURFACE ENHANCED RAMAN SCATTERING (SERS) can
be used to detect single molecules.  In Raman spectroscopy the
light scattered inelastically from a molecule provides information
about the molecule's vibrational quantum states. The rather weak
Raman effect can be greatly strengthened (by a factor of up to 14
orders of magnitude)  if the molecules are attached to nm-sized
metal structures. (The way in which the enhancement occurs is
still not known for sure.)  In this way, an MIT-Berlin group
(Katrin Kneipp, [email protected]) has detected
single dye molecules attached to colloidal silver particles in an
aqueous solution.  The advantages of this method are that it is
fast, it can supply some structural information about the
molecules, and it doesn't bleach the molecules.  Single-molecule
detection is of great practical interest in chemistry, biology, and
medicine, and pollution monitoring; examples include DNA
sequencing and the tracing of biomedically interesting molecules. 
(Kneipp et al., upcoming article in Physical Review Letters.)

THE HUBBLE SPACE TELESCOPE UPGRADE has been
successfully carried out by Space Shuttle astronauts. The two
major newly installed devices are the Near-Infrared Camera and
Multi-Object Spectrometer (NICMOS), which will permit a look
at the infrared radiation (doppler shifted from the ultraviolet)
from young stars in very early (and far out in space) galaxies,
and the Space Telescope Imaging Spectrograph (STIS), which
replaces the Faint Object Spectrograph and the Goddard High
Resolution Spectrograph.  STIS will be valuable for studying
exotic objects like black holes and violent galaxies, and for
searching for extrasolar planets.

A ROOM-TEMPERATURE SINGLE-ELECTRON MEMORY
has been developed at the University of Minnesota. In
electronics, smaller usually means faster response, less power
consumption, and greater component density. In the tiny
Minnesota transistor a bit of information is stored in the form of
a single electron which, resident on a dot of silicon (acting as a
"floating gate"), has the power to influence the current flow in a
silicon channel connecting the transistor's source and drain. This
single-electron arrangement is orders of magnitude smaller than
the kind of metal-oxide-semiconductor (MOS) transistor used in
conventional computer memories.  (Lingjie Guo et al., Science,
31 January 1997.)

NAKED SINGULARITIES COULD EXIST, concedes Stephen
Hawking. In cosmological terms, a singularity is a place of
incalculably large---essentially infinite---mass density.
Singularities are supposed to reside inside black holes but could
never be observed because light is forever bottled up within the
black hole's event horizon.  In 1991 Hawking bet Caltech
physicists Kip Thorne and John Preskill that such singularities
must always be thus imprisoned within a black hole.  But a
computer study has since shown that singularities unencumbered
with any event horizon could, at least in principle, exist. 
Although he doubts whether a naked singularity could ever
actually form, Hawking has now paid up on his bet.  (Caltech
press release, 6 February 1997.)

PHYSICS NEWS UPDATE                         
The American Institute of Physics Bulletin of Physics News
Number 309 February 27, 1997  
by Phillip F. Schewe and Ben Stein

LEPTOQUARKS AT DESY?  At the HERA collider at the
DESY lab in Hamburg, Germany, 820-GeV protons smash into
27.5-GeV electrons or positrons.  At these very high energies, a
positron essentially scatters not from the proton as a whole but
from individual quarks inside the proton.  Two important
parameters help to characterize such interactions: x, the fraction
of the proton's momentum carried by the struck quark, and Q^2,
the square of the momentum transferred between proton and
positron.  The two large collaborations at HERA, the H1 and
Zeus groups, have searched their three-year data inventory for a
class of events at high x and high Q^2. Both groups report an
excess of very-high-Q^2 events compared to predictions based on
the standard model of particle physics.  For Q^2 events above a
value of 15,000 GeV^2, the H1 group found 12 events, against
an expected background of 4.7 events.  Meanwhile, the Zeus
group observed that their data agreed with theory for Q^2 up to
15,000.  Above that, however, agreement worsens; above a Q^2
of 35,000, where only one-tenth of an event would be expected,
2 events were recorded; one of them represents the highest Q^2
(46,000) value ever observed for a lepton-proton interaction. 
These surplus events at high Q^2 (if confirmed by more data---
the groups expect to double their data sample in the coming year)
could be a sign of some new phenomenon beyond the standard
model.  In one scenario, the electron and quark fuse into a
"leptoquark," a particle (with a mass around 200 GeV/c^2) that
would, among other things, help to facilitate proton decay. 
(Information on DESY website;US contacts for the Zeus group
include Malcolm Derrick, Argonne, 630-252-6272,
[email protected]; Frank Sciulli, Columbia,
[email protected])

THE HIPPARCOS STAR CATALOG offers new  measurements
of the distances to thousands of stars.  Of special interest are the
distances to Cepheid variable stars, whose luminosity behavior is
used as a yardstick for deducing the distances to far-away
galaxies. Launched in 1989, the Hipparcos satellite records the
position on the sky of more than 100,000 stars with milli-
arcsecond accuracy (a 100-fold improvement over present
catalogs) and lesser positional accuracy for a million more stars
(Science, 21 February 1997). This greater knowledge of star
locations is quickly being put to use.  For example, stellar age
and distance revisions based on the Hipparcos results, announced
on February 14 at a meeting of the Royal Astronomical Society
in London, suggest that the globular cluster stars, thought to be
the oldest stars in our galaxy, may be only 11 (not 15) billion
years old and, furthermore, that the universe as a whole is
perhaps 10% older than earlier studies implied.  Thus the
embarassing dilemma in which globular cluster stars appeared to
be older than the universe itself may now be resolving itself.
(Science News, 15 Feb.)

IRON AGE OF SUPERCONDUCTORS. When type-II
superconductors are placed in a magnetic field, the flux lines
organize themselves into small bundles. When the current
flowing through high-temperature superconductors is high
enough, these flux lines can move, causing an unwanted voltage
drop, a major impediment to the industrial use of these materials.
New images of the bundles, produced by Swiss scientists, show
that the bundles can entwine into stable "vortex twisters," offering
a possible way out of the flux problem. David Nelson of Harvard
compares this to the advent of the Iron Age, when smiths
strengthened iron by adding dislocation defects through bending.
(Nature, 20 Feb.)

Number 310 March 6, 1997    
by Phillip F. Schewe and Ben Stein

1ST-GRADE MATH---PRIMITIVE QUANTUM COMPUTERS
have arrived earlier than expected, and they have already performed
simple calculations, researchers announced at last month's AAAS
meeting in Seattle.  Whereas ordinary computers essentially
manipulate on-off switches each representing a 0 or a 1, quantum
computers are potentially more powerful because they employ
quantum systems which can exist in two states simultaneously to
represent both 0 and 1 at the same time.  Independently, an
MIT-Los Alamos team and a Harvard-MIT group have proposed an
unexpected way to make a quantum computer: use a cup of liquid. 
When exposed to a magnetic field, one in a million of the atoms
will settle into a "spin" state in which the atoms' internal magnets
are aligned with the field.  One can then cause each of these spins
to act as a "quantum bit" (or "qubit") by firing electromagnetic
pulses which cause each spin to enter two states simultaneously. 
Subsequent pulses can then perform logic operations, by exploiting
the fact that the spin state of a particular kind of atom can affect the
spin state of a different atom in the same molecule or in a
neighboring one.  By manipulating the spins in three distinct types
of quantum systems that exist within the liquid, the MIT-Los
Alamos group has constructed a three-qubit system that has
successfully executed the mathematical calculation 1+1=2.  With
their current approach, the researchers believe 10-qubit systems
may be possible. (Science, 17 January; The Economist, February
22, 1997; also see
http://physics.www.media.mit.edu/projects/spins)

DECELERATION CAN BE AS IMPORTANT AS
ACCELERATION when doing atom-trap experiments.  A team of
physicists at the Max Planck Institute (Heidelberg; contact Rudolf
Grimm, [email protected]) and the Ecole  Normale
Superieure (Paris) have succeeded in slowing cesium atoms, just out
of the oven, from a velocity of 160 m/sec down to a speed (8
m/sec) where they can easily be captured in a trap, all in a space of
only 10 cm, rather than the customary 1 m. Just as important as the
slowdown are the tight beam focus and the narrow range of final
velocities among atoms in the beam.  This is potentially important
for future atom lithography applications and for Bose-Einstein
condensate studies. The deceleration is accomplished through the
palpable force of laser light.  Besides producing an efficient
collimation of cold atom beams, this laser scheme can be used to
"clean" beams by removing unwanted isotopes and might help to
manipulate exotic atoms which cannot be controlled by other means. 
(J. Soding et al., Physical Review Letters, 24 February 1997.)

THE NAMES OF ELEMENTS 104-109 have finally been accepted
by nuclear scientists and certified by the International Union of Pure
and Applied Chemistry.  The delay over the names was caused
partly by  rival claims to priority; the pertinent experiments
rendered  mere handfuls of atoms.  Physics and chemistry students
worldwide will now have to memorize the following additions to the
Periodic Table: Rutherfordium (abbreviated Rf, element 104),
Dubnium (Db, 105), Seaborgium (Sg, 106), Bohrium (Bh, 107),
Hassium (Hs, 108), and Meitnerium (Mt, 109).  (The New York
Times, 4 March 1997.)

COMET HALE-BOPP, inherently brighter than last year's Comet
Hyakutake, should put on a brilliant display from March on into
May.  During the best viewing, late March to early April, the
comet is in the evening sky to the northwest.  (Sky & Telescope,
April 1997.)

PHYSICS NEWS UPDATE                         
The American Institute of Physics Bulletin of Physics News
Number 311 March 13, 1997    
by Phillip F. Schewe and Ben Stein

EXPLOSIONS OF ATOM CLUSTERS YIELD HIGH ENERGIES.
Femtosecond lasers can be used to convert chemical energy into
kinetic energy with great pyrotechnic effect.  For example, they can
blow up molecules, imparting a kinetic energy of 100 eV to
individual outgoing ions.  Aiming fsec pulses at a solid can produce
ions with keV energies.  Now scientists at Imperial College
(London) have observed much higher energy ions (up to 1 MeV)
flying away from the miniature fireball caused by shooting
ultrashort (150 fsec), high-intensity (2 x 10^16 W/cm^2) laser
pulses at clusters of xenon atoms. It is not yet understood why
clusters explode so much more violently than molecules. The
researchers look on their explosions as a novel and modest way of
achieving high-temperature plasmas in a gas of clusters.  They point
to the possibility of tabletop fusion experiments.  (T. Ditmire et al.,
Nature, 6 March 1997.)

ARE STANDARD SOLAR MODELS RELIABLE?  Yes, says John
Bahcall of the Institute for Advanced Study.  Fewer than expected
solar neutrinos register in terrestrial detectors.  This solar neutrino
problem is usually attributed to the hypothetical transmutation of
neutrinos from one type into another en route from sun to earth. 
One alternative is to propose that helium-3 from the cooler outer
layer of the sun sinks to the lower, warmer depths, thus moderating
neutrino production (Update  295).  This  modification in the model
of the sun is undesirable, Bahcall believes (Bahcall et al., Physical
Review Letters, 13 Jan. 1997).  He cites recent helioseismic
measurements of the velocity of sound waves inside the sun; the
velocity  in turn depends on the ratio of the temperature to the mean
molecular weight at any particular depth inside the sun.  Bahcall's
analysis finds a very good agreement (for all depths in the sun) 
between the measured values of sound velocity and the values
predicted using the standard solar model, and a much poorer
agreement for models including helium-mixing.  (Physics Today,
March 1997.)

DNA CHIPS are silicon- or glass-based surfaces which are split up
into regions onto which have been deposited (by, for example,
lithographic or ink-jet-printing techniques) known sequences of
DNA nucleotides (adenine, cytosine, guanine, and thymine)
corresponding to those in genes of specific interest, such as the
cancer-prone gene p53.  The aim is that this DNA probe sequence
should combine with a complementary sequence (an A nucleotide
always binding with T, C always binding with G, etc.) of single
strands of DNA from a sample injected onto the chip. These strands
can be tagged with fluorescent chemicals so that they light up after
being combined with the appropriate probe sequence positioned on
the test bed. Thus, like a forensic comparison of fingerprints, the
optical matchup of known and unknown genetic sequences can be
performed in a methodical way and can rapidly detect such things
as gene mutations in a sample of cells. And from this one can study
genetically-based diseases. Researchers at Affymetrix, a company 
in California, have made chips with up to a million different
chemical sequences.  Scientists foresee the possibility of using
several, or even single, DNA chips to detect  mutations in perhaps
all 100,000 human genes. For simpler organisms such as yeast, a
DNA chip coded for the entire genome (6000 in this case) will be
available soon.  (Science News, March 8, 1997; San Jose Mercury
News, November 26, 1996.)

PHYSICS NEWS UPDATE                         
The American Institute of Physics Bulletin of Physics News
Number 312 March 21, 1997    
by Phillip F. Schewe and Ben Stein

IMPORTANT PROCESSES IN SINGLE DNA MOLECULES
have been observed for the first time by using the atomic force
microscope (AFM), in which the deflections of a tiny stylus over
the contours of a surface can be turned into molecular-scale
images.  At the APS Meeting this week in Kansas City, Carlos
Bustamante of the University of Oregon (541-346-1537) and his
colleagues presented movies showing the first stages of DNA
replication, in which a protein is seen to slide on DNA like a
bead on a string to find the exact site where it could attach and
start the replication process.   Binding DNA and RNA
polymerase (the protein that mediates the transcription of DNA
into RNA) to a mica surface, Neil Thomson of UC-Santa Barbara
(805-893-4544) and his colleagues produced 5-nm-resolution
movies of the transcription process, in which RNA polymerase
pins down the middle of a single DNA strand and then pulls the
strand through as it starts transcribing the DNA into RNA using
RNA-building-blocks called NTPs  (Biochemistry, 21 Jan. 1997). 
Using an AFM, Gil Lee of the Naval Research Laboratory (202-
763-5383) found that a force of about 600 piconewtons was
required to tear apart two complementary strands of DNA,
namely a 20-base-pair-long strand of polycytosine (a form of
single-strand DNA) from single strands of polyinosine averaging
160 base-pairs long.

NANOTUBES, stiffer than steel, only a nanometer wide but
many microns long, are essentially rolled-up sheets of carbon
hexagons. The following are highlights from a dozen APS
sessions on the subject: Richard Smalley (713-527-4845) of Rice
University, winner of the 1996 Nobel Prize in chemistry for his
discovery of Buckyballs in 1985, reported that his lab currently
produces nanotubes ("more precious than platinum") at a rate of
grams/day but that within 5 to 10 years this could be increased
(on a commercial basis) to tons/day.  Smalley showed pictures of
nanotubes that swallow their own tails, forming closed Bucky
toruses (see also Nature, 27 Feb.), and diagrams of bundles of
nanotubes in which one tube stuck out further than its neighbors. 
Nested stages of such bundles, he said, could be used to fashion
pointers---macroscopic at one end but tapering down to a single
carbon cell at the other end---with which one could (like an artist
dipping a paintbrush into a palette of colors) "write" patterns of
molecules on a substrate.  Electrically, the versatile nanotubes
can be insulators, semiconductors, or conductors and are
expected to exhibit magnetoresistance qualities . The pointy
nanotubes have been used as field emitters in flat panel displays.
Attaching a semiconducting nanotube to a metallic nanotube one
gets a nano-diode. If, furthermore, the joint is angled, the
composite tube can actually conduct better in a bent state than
straight up; this property makes the structure into a possible
nanoswitch or strain gauge.  Cees Dekker of Delft University is
able to study the electron transport properties of single nanotubes
by draping them across a pair of electrodes; the current-versus-
voltage plot is a series of steps, indicative of a "quantum wire."
In general one would expect this behavior when the movement of
electrons through a conductor is restricted to one dimension.
Steven Louie of LBL (510-642-1709) studies nanotubes made of
boron and nitrogen, or of carbon mixed with B and N.   In one
configuration, a ribbon of conducting carbon hexagons forms a
corkscrew pattern up the length of the tube.  The current flow
through such a tube is therefore helical; in effect this nanotube is
the world's smallest solenoid magnet. 

PHYSICS NEWS UPDATE                         
The American Institute of Physics Bulletin of Physics News
Number 313 March 24, 1997    
by Phillip F. Schewe and Ben Stein

FORCE DETECTION WITH ATTO-NEWTON PRECISION
has been achieved by an IBM-Stanford team of physicists led by
Daniel Rugar (408-927-2027) at IBM. This work, reported at last
week's APS meeting in Kansas City, was carried out with a
magnetic resonance force microscope (MRFM), a device that
combines nuclear magnetic resonance technology with probe
microscope technology. The goal here is nothing less than the
ability to make 3-dimensional, non-destructive, in-situ atomic-
resolution images of atoms, molecules, defects in solids, dopants
in semiconductors, and binding sites in viruses.  In the IBM-
Stanford setup, a thin silicon cantilever, 230 microns long but
only 60 nm thick, is poised above a tiny sample. A magnetic
particle mounted on the cantilever interacts (under the additional
influence of fields from an RF coil) with tiny volumes of
magnetic atoms in the sample.  Under just the right circumstances
the particle on the cantilever (like a diver on a diving board) will
begin to resonantly oscillate; the cantilever's movement shifts a
laser interference pattern viewed through an optical fiber. In this
way Rugar can measure tiny magnetic interaction with a
resolution of 7 x 10^-18 Newtons, the most sensitive force
measurement ever made with a probe microscope.  (An
attoNewton is to the weight of a feather as the weight of the
feather is to that of the Hoover Dam.) With further refinement
the MRFM process will detect single spins; Rugar hopes to map
the spins of electrons in dispersed defect sites in silica. Another
speaker at the APS meeting, John Sidles (206-543-3690) of the
University of Washington, emphasized possible medical and
biological research applications. The first person to suggest the
MRFM approach, Sidles observed that the structure of some
proteins can be worked out with nearly atomic resolution by
crystallizing a sample and then interpreting the pattern of x rays
diffracted by the crystal.  Other notable proteins, however, do
not lend themselves to this process.  Moreover, ordinary force
microscopes cannot image interesting molecules residing in clefts
of biological structures. MRFM, by contrast, will supply 3D
images of the hardest-to-get-at molecules, providing information
for medical and drug-design research.  A Los Alamos-Caltech
group, represented by Chris Hammel of Los Alamos (505-665-
0759) is applying MRFM to the study of multi-layer electronic
devices.  Eventually his probe will be able to map buried
structures, such as defects in circuit elements.  He uses a stiffer,
faster-oscillating tip than the IBM version; this does not
necessarily improve the force sensitivity but would greatly speed
up data acquisition. (Some MRFM figures will soon be available
at this website: http://www.aip.org/physnews/graphics/)

SINGLE MAGNETIC ATOMS DISRUPT
SUPERCONDUCTIVITY on an atomic scale.  As part of their
microscopic study of magnetism, Ali Yazdani and his colleagues
at IBM Almaden deposit single manganese (Mn) and gadolinium
(Gd) atoms, each of which exerts magnetic forces, onto a
niobium metal, which is a superconductor at low temperatures. 
By measuring the tunneling current that flows from the surface to
the probe of a scanning tunneling microscope, the researchers
detected the loss of superconductivity in the vicinity of the
isolated magnetic atoms. This represents the first time a local loss
of the superconducting state at the atomic scale has been detected.
The researchers theorize that the atoms break up nearby electron
pairs which constitute supercurrents. (Talk at the APS meeting;
also Science, 14 March 1997.)

PHYSICS NEWS UPDATE                         
The American Institute of Physics Bulletin of Physics News
Number 314 March 28, 1997    
by Phillip F. Schewe and Ben Stein

STARDUST WITH RED GIANT FINGERPRINTS. Heavier
elements are assembled out of lighter elements inside stars.  For
roughly half the nuclei heavier than iron-56, nucleosynthesis
proceeds slowly (hence the name "s process") by the addition of
one neutron at a time.  The observed and calculated (based on 
s-process models) abundances of elements mostly agree; one
notable exception is the isotopically anomalous neodymium found
in carbonaceous meteorites. Partly to investigate this discrepancy
and partly to accommodate the latest theories which hold that the
s process is prevalent at solar energies of 6-8 keV (corresponding
to temperatures of 69-93 million K) rather than 30 keV as was
previously thought, scientists at Oak Ridge have performed
difficult new scattering experiments in the lab.  Using neutrons
from the Oak Ridge Electron Linear Accelerator (ORELA) they
have re-measured with much greater precision the likelihood of a
neutron being captured by the nuclides Nd-142 and Nd-144 and
have translated this into reaction rates within stars. Their findings
(contact Klaus Guber,[email protected]) help to explain
the Nd anomaly, confirming that the Nd-142 isotopic distribution
in certain microscopic dust grains in some meteorites originated
in low mass red giant stars under the auspices of the s process.
This work may have implications for "r-process" models, which
prescribe how even heavier nuclei are made rapidly in
supernovas, and for theories of how our solar system came about. 
(K. Guber et al., Physical Review Letters, 31 Mar.)

A ONE-SIZE-FITS-ALL UNIVERSAL SUBSTRATE for
semiconductors has been created, potentially allowing researchers
to deposit crystals of many previously incompatible materials
onto a semiconductor surface.  If the unit cell of a crystal differs
in dimensions by as little as 1% from the dimensions of the
surface onto which it is deposited, defects can form which
prevent the proper functioning of the material. Yu-Hwa Lo (607-
255-5077) and his colleagues at Cornell have created a thin
gallium arsenide film whose crystal axis is rotated slightly
relative to that of the gallium arsenide substrate onto which it was
deposited.  The resulting surface, known as a "compliant
surface," became more receptive to bonding with crystals of
different materials, with the interface between the substrate and
the deposited crystals forming a "twist boundary."  Onto the
GaAs surface, the researchers successfully deposited crystals of
InGaP, GaSb, and InSb. The lattice mismatches between crystal
and surface were as high as 15 percent, but the density of defects
was reduced by a factor of 10^5 compared to that for regular
substrates.  Moreover, if  gallium nitride (mismatch of 20%)
could be deposited onto this surface, the researchers believe that
high-quality blue and ultraviolet semiconductor lasers might
result. They expect that their approach could allow computer
chips of many different types to exist on the same motherboard. 
(Applied Physics Letters, 31 March 1997.)

THE ANAPOLE MOMENT OF A NUCLEUS IS DETECTED. 
Parity violation---the differentiation between left and right---was
first observed (1957) in transitions between nuclear states.  Later
certain transitions in atoms too were seen to violate the
conservation of parity.  Now an experiment at the University of
Colorado not only makes the most accurate measurement of this
effect in cesium atoms but also observes, for the first time, the
anapole moment for a nucleus, the internal electromagnetic
moment in the nucleus which comes about because of the weak
force.  (C.S. Wood et al., Science, 21 March.)

Physics News Update
The American Institute of Physics Bulletin of Physics News

Number 315 April 3, 1997 by Phillip F. Schewe and Ben Stein
---------------------------------------------------------------------------

THE WORLD'S SMALLEST FOCUSED BEAM OF LIGHT is a 50-nm-diameter x-ray beam
created at the Brookhaven National Synchrotron Light Source in New York. At
the APS March Meeting Janos Kirz and Chris Jacobsen at SUNY-Stony Brook
reported that they and their colleagues had for the first time produced
images showing the distribution of DNA and protein in sperm from bulls and
other mammals. Using a 5-micron-diameter x-ray beam at the Brookhaven
synchrotron, Slade Cargill at Columbia reported the first real-time
measurements of the stresses that occur when electric current traveling
through an aluminum wire displaces atoms in the wire; this
"electromigration" effect is expected to be a problem in the ever-
shrinking aluminum-based wires of future-generation computer chips.
(Associated graphics can be seen at Physics News Graphics.)

FRACTAL MAGNETORESISTANCE. Canadian and Australian physicists have
performed an experiment in which electrons enter a two-dimensional square
enclosure (made from GaAs) through one tiny opening and leave by another.
Voltage applied to an overlying electrode controls the electron flow. An
additional electrode serves to squeeze off a circular region in the middle
of the square, transforming the enclosure into a "Sinai billiard," so named
because the ensuing labyrinthine electron trajectories resemble Moses'
multifoliate trek through the desert. A plot of resistance through the
device as a function of the applied magnetic field exhibits, for the first
time in a billiards-type experiment, a fractal shape; that is, the
resistance plot looks the same at several different magnifications
(R.P.Taylor et al., Physical Review Letters, 10 March). The source of the
geometry-induced fractal resistance is not known. This peculiar billiard
table should provide an excellent laboratory for studying quantum chaos.
(Nature, 13 March.)

A GALAXY HAS BEEN OPTICALLY SIGHTED at the same apparent location as a
gamma ray burst object. In February the new orbiting telescope BeppoSAX
spotted one of the mysterious gamma bursts that have baffled astronomers;
do the bursts originate in our own galaxy or much further away? But quick
follow-up measurements by optical telescopes located a galaxy at what seems
to be the same position. BeppoSAX expects to find one burst a month, so
future searches at optical wavelengths may settle the issue of whether some
bursts are extragalactic. ( Science News, 22 March 1997.)

TENTH ANNIVERSARY OF THE WOODSTOCK OF PHYSICS. High-temperature
superconductivity (HTSC) became famous at a late-night session at the March
1987 APS meeting. Paul Grant of the Electric Power Research Institute
reviews the matter a decade along. First, HTSC wire is manufactured now in
km lengths and should be ready to carry industrial electric power on a test
basis within two years, Grant believes. Thin films of HTSC materials are
used in SQUID detectors and communications devices. No HTSC theory has yet
emerged victorious, and HTSC supercurrents may be both s-wave and d-wave
in nature. Government spending on research is currently $150 million per
year in the U.S. and $200 million in Japan. The highest confirmed
transition temperature seen so far, 164 K, occurs in a Hg-based material
under pressure. (Nature, 13 March 1997.)

PHYSICS NEWS UPDATE                         
The American Institute of Physics Bulletin of Physics News
Number 316 April 10, 1997  by Phillip F. Schewe and Ben Stein

ICEBERGS AND OCEANS ON EUROPA.  Previous pictures
suggested that Jupiter's moon was covered with an Arctic-like
fractured ice sheet.  Now ever sharper images reveal what look
like detached icebergs that can be traced back to earlier
lodgements.  Scientists associated with the Galileo spacecraft,
which viewed Europa on the closest-ever encounter (586 km) in
February, believe that the turned-around ice blocks are probably
floating on an ocean kept at least partially liquid by tidal forces
from Jupiter or possibly from heat generated by internal
radioactivity.  The relative lack of impact craters and the
extensive scarring imply, furthermore, that the icy surface is
young (millions of years) and in places thin (several km).  The
last time a new ocean was reported, one scientist mused, was five
hundred years ago when Balboa supposedly discovered the
Pacific.  (Jet Propulsion Lab press conference and press release,
9 April; images at www.jpl.nasa.gov/galileo/.)

SQUEEZED PHONONS HAVE BEEN PRODUCED for the
first time, allowing researchers to temporarily reduce the
uncertainties in the positions of atoms in a crystal. Classically,
atoms in a crystal are like little balls which vibrate around their
equilibrium positions in a lattice. The quantum-mechanical
description of this motion is given in terms of  particles called
"phonons" which carry specific bundles of vibrational energy. 
According to quantum mechanics, an atom does not have a
definite position, but a spread of possible positions. To
temporarily reduce these fundamental uncertainties, a University
of Michigan team (Roberto Merlin, 313-763-9759) has
successfully altered the state of the phonons in a crystal to
produce "squeezed" phonons, which act to momentarily reduce
the uncertainty in the atoms' positions at the expense of greater
uncertainties in the atoms' momenta. In the experiment,
described at the March APS Meeting, researchers shine two
70-femtosecond laser pulses on a potassium tantalate crystal.  The
first pulse momentarily perturbs the frequencies of the individual
phonons in the crystal.  In classical terms, the net result is to
return far-flung atoms closer to their central positions on the
lattice while not affecting as much the others which are already
close to their central positions.   The second pulse measures the
change of refractive index in the crystal caused by squeezing and
this tells how much the atoms as a whole stray from their central
positions.  Theoretically predicted since the early 1990s (Update
261) by various groups, squeezed phonons are similar to the
previously demonstrated phenomenon of squeezed light (Update
82).  (Science, 14 March 1997.)
     
PROTON TRANSISTOR MEMORY. Electrons do most of the work in electronic
devices; indeed heavier, mobile, positively-charged ions are usually a
nuisance.  A Sandia experiment, however, has made hydrogen ions (protons
buried inside a semiconductor sandwich) into the primary carriers of
information in a Si/SiO2/Si device. Judged as a storage device, this
transistor did pretty well: it retained its state (on or off) for up to 25
hours, it successfully underwent 10,000 write-erase cycles, and could be
switched on a 50-msec timescale. Its chief virtue may prove to be its ease
of construction.  (K. Vanheusden et al., Nature, 10 April 1997.)

PHYSICS NEWS UPDATE                         
The American Institute of Physics Bulletin of Physics News
Number 317 April 17, 1997 
by Phillip F. Schewe and Ben Stein

IS THE UNIVERSE BIREFRINGENT? That is, does universe
behave like a crystal in which light moving in one direction acts
differently from light going in another direction?  Radio waves
from distant galaxies must pass through the vast reaches of an
intergalactic medium filled with stray magnetic fields and a
tenuous plasma of ions and electrons. Through a well-known
phenomenon called the Faraday effect, these ions and fields in
the cosmic prairie subtly rotate the polarization of the radio
waves (the orientation of their electric fields) on their way toward
Earth. This is a very slight effect but it has been measured in the
case of light coming from many galaxies; the effect is
proportional to the magnetic field strengths and ion densities, as
well as the square of the light's wavelength. (Typically about 5-
8% of the light from a galaxy is plane polarized, most of this in
the form of synchrotron radiation.)  Now two researchers, Borge
Nodland at the University of  Rochester ([email protected].
edu; 716-275-5772) and John Ralston at the University of Kansas
([email protected]; 913-864-4020), have studied 
polarization rotation data for 160 galaxies and have perceived that 
in addition to the Faraday effect, there seems to be an extra 
mysterious angular dependency at work. Indeed, the rotation varies 
consistently with the angle across the sky, as if the universe had an 
axis. That is, the amount of polarization rotation depends on the 
distance to a galaxy as well as on the cosine of the angle between 
the incoming radio waves and an axis that apparently lies in the 
direction of the constellation Sextans. This anomaly would seem 
to challenge some important physics concepts, such as the notion 
that there is no preferred direction in space and the notion that 
space itself is isotropic (the same in all directions) or homogeneous 
(the same in all places). One possible explanation might be the 
existence of "domain walls" between different realms of the 
cosmos, as prescribed in certain particle physics theories.  The 
soundness of their study depends, among other things, on the 
quality and amount of  polarization observations, and Nodland 
and Ralston therefore look forward to acquiring additional data.  
(To appear in Physical Review Letters, 21 April 1997; see figures at
www.aip.org/physnews/graphics. Reminder---science journalists
can obtain a copy of PRL articles by contacting AIP Public
Information at [email protected])

SPRINGTIME FOR COMET HALE-BOPP.  Now past its prime
in the dusk sky, Hale-Bopp was first spotted two years ago as far
away as seven astronomical units, allowing astronomers to
observe the thawing process at an earlier stage than is usual for
comet watches. This in turn permitted the detection of trace
species not before seen on comets, such as SO2 and H2CS
(Science News, 21 April).  What else do we know? First of all,
the size of the comet nucleus is estimated to be 27-42 km, at least
three times bigger than that of Comet Halley.  Of the cometary
products vaporized on the inward trip toward the sun, the chief
gases are H2O, CO, and CO2, which seem to be the main
constituents of interstellar ice as well.  Dust jets are rich in
crystalline olivine, and dust production in general was more than
100 times stronger than with Halley at comparable distances.
Variations in the vented jet activity will be used to determine
Hale-Bopp's rotation rate. Chemical composition suggests that
the comet comes from the Oort Cloud rather than the Kuiper
Belt.  (Several articles in Science, 28 March.)

PHYSICS NEWS UPDATE                         
The American Institute of Physics Bulletin of Physics News
Number 318 April 23, 1997  by Phillip F. Schewe and Ben Stein

AN EXCESS OF TeV-ENERGY GAMMA RAYS from galaxy
Markarian 421 may oblige astronomers to revise their models of
active galactic nuclei (AGN).  Many suspect that AGNs, quasars,
and indeed all the most violent celestial objects in the universe
share a common energy-production architecture---a black hole,
supplied by a surrounding accretion disk, broadcasting powerful
jets of matter in two polar directions. Mrk421 (400 million light
years away) is the closest such object whose jet axis is aimed
directly at us. Last year Mrk421 rewarded patient observers with
the most explosive gamma display ever, with a flux ten times
higher than that of the much closer Crab Nebula, the strongest
known steady gamma source in the sky.  At last week's
APS/AAPT meeting in Washington, DC, Trevor Weekes of the
Whipple Observatory presented a detailed spectrum for Mrk421.
The flux of gammas falls off at the highest energies (up past 6
TeV), but not nearly as fast as one would have expected. 
Weekes suggested that the anticipated effect of two sources of
attenuation, dust near the AGN and the amorphous population of 
infrared photons in intergalactic space, may have been
overestimated. 

A SUPERFLUID ANALOGUE OF A JOSEPHSON JUNCTION
has been devised by Richard Packard at UC Berkeley.  One of
the peculiar properties of superconductors is that the amount of
magnetic flux penetrating a sample can only be a multiple of a
basic flux unit. At the heart of a superconducting quantum
interference device (SQUID) is a pair of insulating barriers which
interrupt a ring-shaped superconducting sample. Electron pairs
tunneling through the barriers interfere with each other in a way
that depends on the amount of flux threading the superconducting
circuit; thus the quantization of flux can be exploited to measure
tiny magnetic fields. In a superfluid, by contrast, fluid circulation
is quantized, and this property can be exploited to measure very
tiny rotations.  In the Berkeley experiment, the flow of superfluid
helium through a ring-shaped vessel is interrupted by a barrier
containing a micron-sized pinhole. When the vessel is rotated, the
helium must squirt back through the hole to maintain its place in
space (like an icecube in your drink wanting to stay where it is
when you turn the glass).  With this scheme the rotation of the
earth can be detected to a precision of 0.5%. (Nature, 10 April
1997.)

FIRST RESULTS FROM JEFFERSON LAB.  This new nuclear
physics facility in Newport News, Virginia explores the interface
between the physics of the nucleus (made of protons and
neutrons) and the physics of individual protons and neutrons
(made of quarks held together by particles known as gluons). 
The main machine at Jefferson Lab is the Continuous Electron
Beam Accelerator Facility (CEBAF), which accelerates
continuous streams of electrons to energies of 4 GeV (with a
maximum energy of 8 GeV planned for the future); the electrons
are then diverted to one of three experimental halls where they
collide with fixed targets containing nuclei.  At the APS meeting
Rolf Ent of Jefferson Lab described how electron collisions with
nuclei are ejecting protons from nuclei at a greater rate than
anticipated by the present theories on the subject.  Exploring how
gamma rays break up deuterons (containing a proton and
neutron), Haiyan Gao of Argonne presented measurements
showing that the quark substructure inside the deuteron must be
taken into account to properly understand the breakup
process.(CEBAF illustration at www.aip.org/physnews/graphics)

PHYSICS NEWS UPDATE                         
The American Institute of Physics Bulletin of Physics News
Number 319 April 29, 1997   by Phillip F. Schewe and Ben Stein

A NEW CELESTIAL SOURCE OF POSITRONS has been
identified. Positrons (antielectrons) are routinely made on Earth
at several labs (SLAC, LEP, HERA) and in deep space (the
galactic center and cosmic rays).  The Gamma Ray Observatory
(GRO) has now found a new positron source.  At a meeting in
Williamsburg, VA yesterday, GRO scientists announced the
observation of a diffuse fountain of positron-emitting material
projecting 3000 light years out of the plane of our galaxy. The
researchers are happy to have found a new galactic feature but
are puzzled as to why the flare, starting near or at the core of the
Milky Way, flows north out of the plane but not south. (See
figure at osse-www.nrl.navy.mil/dermer/annih.html)

SOUND WAVES AND SUPERNOVAS IN BOSE-EINSTEIN
CONDENSATES (BECs).  Since 1995, scientists have been
creating the BEC state, in which a cloud of atoms is cooled to
near-absolute-zero temperatures, falling into the same quantum
state and acting as a single entity (Update 233).  At this month's
APS/AAPT meeting in Washington, three researchers spoke on
this subject. (1) Randy Hulet of Rice University reported that
BECs of lithium atoms--different from other BECs in that the
lithium atoms attract rather than repel each other--are limited to a
size of approximately 1500 atoms.  According to some
predictions, adding more atoms than this would cause the BEC to
undergo a "macroscopic quantum tunneling" in which the
condensate would collectively transform from a low-density to a
high-density state, forming molecules which would then release
excess heat and cause the BEC to blow apart like a supernova. (2)
Studying BECs of rubidium atoms, Eric Cornell of NIST and the
University of Colorado discussed experiments confirming that
BECs are significantly more uniform in density than comparable
clouds of cold atoms in a non-BEC state. (3) Using laser light to
excite a specific spot on his cigar-shaped BEC of sodium atoms,
Wolfgang Ketterle of MIT described how the resulting
disturbance in a typical condensate propagates at about 5
millimeters per second, roughly 70,000 times slower than the
speed of sound in air.  (Writeup and figure from Hulet's group at
aps.org/BAPSAPR97/vpr/laylanguage.html)

ONE HUNDRED YEARS OF ELECTRONS.  On April 30,
1897, at a meeting of the Royal Institution in London, physicist
Joseph John (J.J.) Thomson declared that cathode rays lighting up
a fluorescent screen were made of negatively charged particles. 
Thomson boldly proclaimed that these particles--which we now
know as electrons--could be found in all atoms.  The term
"electron" as it applied to electricity actually came about in 1891
to describe the unit of electric charge in a chemical reaction. The
electron was the first known subatomic corpsucle and its
discovery marks the advent of particle physics. Michael Riordan
(editor of SLAC Beamline, whose Spring 1997 issue is devoted
to the electron centennial) refers to the electron as a truly
"industrial strength" particle, since it is the workhorse of
electronics, including television, telephones, and personal
computers. (Many of these devices organize electrons inside
transistors which were themselves developed exactly half a
century ago.) Labor saving devices aside, electrons are of course
the outer constitutents of all atoms and the principal currency of
exchange in all chemical reactions. (See also the AIP History
Center's web exhibit at www.aip.org/history/electron)

PHYSICS NEWS UPDATE                         
The American Institute of Physics Bulletin of Physics News
Number 320  May 6, 1997   by Phillip F. Schewe and Ben Stein

SINGLE-PHONON CALORIMETRY, including the measurement of heat flow at the 
10^-27 joule level, now appears possible through the combination
of nano-engineering and thermometry in the milli-kelvin realm.
Michael Roukes and his colleagues at Caltech begin by making a
tiny GaAs plate 1-3 microns on a side and only 100 nm thick,
supported by 4 bridges each about 100 nm wide. On top of this
monocrystalline structure are separate sets of GaAs fingers for
gently adding heat to the plate and measuring the subsequent flow
of heat. With this setup the group has made the first direct
thermal conductance measurements on a nanostructure (to appear
in Applied Physics Letters, 19 May). Their present efforts are
directed towards measuring the extremely small heat capacity (the
energy needed to raise the temperature of an object by 1 K) of
their sample, estimated to be about 10^-22 J/K at a temperature
of 10 mK. Roukes is in the process of switching from currently-
used resistance-based thermometry (a method which itself adds
heat to samples at low temperatures) to much less-intrusive
measurements based on the thermal noise induced in a SQUID
detector.  Speaking at the March APS meeting in Kansas City,
Roukes projected that with this scheme he expects to track the
movement of single phonons---single pulses of thermal energy--
-in parcels as small as 10^-26 joules.  Physics has not yet seen fit
to give a name to a unit as tiny as this. In this single-phonon
regime, Roukes pointed out, many analogies exist between the
thermal transport of phonons and the quantum optics of photons.

AN EXCITED ATOMIC STATE WITH A 10-YEAR LIFETIME
has been discovered in the ytterbium atom, raising
hopes for atomic clocks 1000 times more accurate than now
possible. The Heisenberg uncertainty principle states that the
longer a system can be observed, the smaller the uncertainty in its
energy can be; therefore, it is extremely desirable to tune an
atomic clock to a long-lived high-energy (excited) state. 
Researchers at the National Physical Laboratory in the UK laser
cool and trap a single ytterbium ion.  They then use a laser
photon to boost the atom's outermost electron to the long-lived
state.  With additional laser light, the researchers subsequently
induce the electron to return to its lowest-energy (ground) state. 
By noting the characteristics of the laser light interacting with the
electron, the researchers determine a 3700-day lifetime for the
state.  In addition to being the longest living excited energy state
yet detected in an atom, it is the first observed "octupole"
transition, a very rare transition in which the electron changes its
angular momentum by a relatively large amount of three units. 
Once in this state, the electron (in the absence of external
perturbations) can only decay via the octupole transition, which is
why the state lasts so long. An atomic clock based on the
transition would be very precise but requires much additional
development.  (M.  Roberts et al., Physical Review Letters, 10
March 1997; see also Nature, 20 March 1997.)

A GIANT PIEZOELECTRIC EFFECT has been observed in
strontium titanate at low temperatures.  The piezoelectric process,
by which mechanical energy in a crystal is converted into
electricity (and vice versa), generally gets worse below 50 K, but
in the case of SrTiO3, it gets better.  At 1.6 K, in fact, STO
competes with the best room-temperature piezoelectrics.  The
ultralow-temperature manifestation of this effect might result in
new forms of microscopy or thermometry.  (Science, 18 April
1997.)

PHYSICS NEWS UPDATE                         
The American Institute of Physics Bulletin of Physics News
Number 321 May 13, 1997   by Phillip F. Schewe and Ben Stein

A PHOTON CONVEYOR BELT has been created using sound
waves and lasers, bringing about a new method for processing and
storing light signals on a chip.  In some opto-electronic devices it
is desirable to delay or store an optically-encoded message by
dispatching it down kilometer-long fiber cul-de-sacs.  In a device
developed at the University of Munich, the delay can be
accomplished more compactly by first converting the light into a
splash of excitons (electron-hole pairs) which propagate at a more
leisurely pace, the electrons and holes surfing along on different
parts of a guiding acoustic wave.  Later the electron-hole pairs
recombine into photons, which are read out at the other end of the
sample.  In effect the signal has been converted from a speed-of-
light wave into a speed-of-sound wave, and back again.  This
technique is also a way of prolonging the lifetime of excitons,
which typically live for mere nanoseconds before recombining; in
this experiment they have now been preserved for microseconds.
(C.  Rocke et al., Physical Review Letters, 19 May 1997; contact
Achim Wixforth, Achim.Wixforth @physik.uni-muenchen.de;
animation at www.aip.org/physnews/graphics)

THE QUANTUM WAVEFUNCTION OF A MATTER WAVE,
the complete mathematical description of a quantum system, has
been experimentally reconstructed for the first time.   Trapping a
single beryllium ion in electric fields, Dietrich Leibfried and his
colleagues at NIST created a state in which the ion has exactly one
quantum of vibrational energy. Determining the wavefunction,
which contains all the knowable information about this system, is
difficult because the uncertainty principle says that measuring its
position alters its momentum and vice versa.   But by preparing the
same quantum state 500,000 times and making a different
measurement each time, the researchers sidestepped this limitation
and reconstructed piecemeal the probability for the ion to have
certain values of position and momentum.  Known as the Wigner
function, this "quasiprobability" distribution can be mathematically
transformed into an average quantum wavefunction for the system
which, the researchers argue, is nearly identical to the actual
wavefunction. The NIST researchers were the first to measure
negative Wigner function values for certain coordinates of position
and momentum--something that can only happen for quantum
systems; this reflects the fact that the system can exist in many
states simultaneously. (Physical Review Letters, 18 November
1996.)   Subsequently, physicists at the University of Konstanz in
Germany measured the Wigner function of a matter wave traveling
in free space--a helium atom traversing a pair of slits.  (Nature, 13
March; also Science News, March 15.)

PHYSICISTS ARE 46 YEARS OLD AND MAKE $65,000 A
YEAR.  These are median values for a PhD physicist in  the U.S.
in 1996.  Those who work at federal labs made the most (median 
$78,500), even more than in industry (median $77,000); those at 
4-year colleges made the least, with a median of $49,200. 
Geographically, median salaries ranged from $70,000 (Pacific
states) to $56,200 (East South Central). New PhD's earn $31,000
at universties and $39,600 at federal labs.  Salaries for female
physicists who have earned the PhD in the past 10 years are
comparable to salaries for male physicists with similar experience
("Society Membership Survey: Salaries 1996," a report issued in
April by the AIP Education and Employment Statistics Division;
contact Ray Chu, [email protected])

PHYSICS NEWS UPDATE                         
The American Institute of Physics Bulletin of Physics News
Number 322 May 20, 1997   by Phillip F. Schewe and Ben Stein

IN QUANTUM CASCADE LASERS electrons are put in a
barrel, as it were, and sent over a series of waterfalls.  Instead of
recombining with holes to create photons, as in conventional
semiconductor lasers (one injected electron resulting in one
photon), electrons in a QC laser pass through a succession of
closely coordinated quantum wells---each well consisting of a
sandwich of semiconductor layers---unloading energy as they go,
in the form of photons (one electron creating 25 photons, one for
each stage in the stack). QC lasers are unique in that the output
light wavelength is determined not by semiconductor chemistry
(the type of materials used) but by the thickness and spacing of
the layers (sometimes only a few atoms thick). Cascade lasers,
first developed in 1994 by Federico Capasso and Jerome Faist at
Bell Labs, can operate in the mid infrared wavelength region (4-
12 microns).  This technologically important range is currently
being served primarily by low-power lasers which can only work
at low temperatures. By contrast, Bell Labs' new QC laser can
not only operate at room temperature with high output power (60
mW, with even higher power evident in recent experiments) but
can also be tuned to a single wavelength through the use of
gratings within the laser.  These features will allow scientists in
the field to carry out remote chemical sensing (of, say, pollutants
present at parts-per-billion levels)  by selectively exciting, and
detecting, specific chemical species. (Jerome Faist et al., Applied
Physics Letters, 19 May 1997; and a talk at this week's
Conference on Lasers and Electro-Optics in Baltimore.)

ZERO-DIMENSIONAL METALS are studied by physicists at
Harvard.  In general, reducing the dimensionality of an object
makes its quantum nature more manifest.  In a semiconductor,
for example, confining mobile electrons to a plane (2D) or a wire
(1D) or a dot (0D) enforces an ever sharper limit on the allowed
energies, and this can be exploited in producing compact and
highly controllable electronic devices.  The Harvard scientists
(contact Dan Ralph, now at Cornell, [email protected])
have succeeded in attaching leads to 10-nm-sized metal particles;
this allows them to apply a gate voltage which turns the tiny
particle into a transistor. Unlike semiconductor dots, the metal
nanoparticle can be made magnetic or superconducting, allowing
forces inside the sample to be analyzed. Indeed, with this speck
of aluminum, the discrete quantum-mechanical spectrum of
electrons in a metal have been measured more accurately than
ever before. One can watch the electron spectrum even as
magnetic fields break up the superconducting state. (D.C. Ralph
et al., upcoming in Physical Review Letters, 26 May 1997.)

GAMMA RAY BURSTERS HAVE REVEALED
THEMSELVES at optical and radio wavelengths.  Astronomers
have sought to establish whether these once-only gamma sources
were near at hand (in the halo of our galaxy) or resident in distant
galaxies.  On May 8 the BeppoSAX satellite spotted a new GRB
at gamma wavelengths.  Alert Caltech scientists soon viewed the
same object with the Palomar and Keck optical telescopes,
establishing from the redshift that the object was some billions of
light years away.  Meanwhile, the Very Large Array radio
telescope has also glimpsed the object.  As of last week the
visible signal was decreasing and the radio signal increasing in
intensity.  (Press releases from Caltech (May 14) and VLA (May
15).)

PHYSICS NEWS UPDATE                         
The American Institute of Physics Bulletin of Physics News
Number 323 May 28, 1997   by Phillip F. Schewe and Ben Stein

AN AMORPHOUS SOLID BEHAVING LIKE A CRYSTAL. 
Amorphous silicon, a solid in which atoms are arranged in a non-
periodic jumble, rivals crystalline silicon for photovoltaic
applications.  Unfortunately, atoms in the amorphous state often
have unfulfilled (dangling) bond sites which interfere with
electric currents. To cure this problem hydrogen atoms are
introduced into the solid to bind to these sites; but too much
hydrogen itself leads to a deterioration of electrical properties. 
Now a collaboration of physicists from Cornell (Robert Pohl,
607-255-3303, [email protected]) and the National
Renewable Energy Labs (Golden, CO) has succeeded in
implanting a smaller, more judicious amount of hydrogen, greatly
improving the stability of the material and, in the process,
revealing something unexpected.  If you shake a pure silicon
crystal (chilled to low temperatures) it will ring for an hour at
many different frequencies.  In amorphous silicon, by contrast,
the tangled-atom nature of the sample quickly (in a second or
two) soaks up the vibrations at all different energies.  In the
NREL hydrogenated amorphous silicon, however, some vibration
modes (the low-energy ones) persist for an hour, just as in
crystalline silicon. This as-yet-unexplained property gives the
researchers an experimental tool for exploring the role of
hydrogen in these solids and for studying amorphous solids in
general. For example, one can observe what happens to these
low-energy excitations as impurities are added to the material. 
(Xiao Liu et al., upcoming article in Physical Review Letters,
probably June 9.)

THE EARLY FAINT SUN PARADOX goes as follows: 4
billion years ago the sun (its fusion fire not yet having worked up
to present levels) was 25-30% cooler than now.  Terrestrial
temperatures would have been sub-freezing,  precluding liquid
water.  How then did life form in these early eras?  Carl Sagan,
in a posthumous paper co-authored by Chris Chyba (Science, 22
May) suggests a possible scenario. Ultraviolet radiation from the
sun, they argue, would combine with existing methane to form
solid hydrocarbons in the upper atmosphere. This in turn would
shield ammonia (otherwise broken up by the UV) long enough
for the ammonia to produce a greenhouse warming adequate for
liquid water.  Sagan and his interest in life in extreme
environments was the subject of a session yesterday at the
meeting of the American Geophysical Union in Baltimore.
According to David Morrison of NASA Ames, there are only
two places on Earth where life has not been found---on the
Antarctic ice sheet and in the upper atmosphere.  Everywhere
else, whether in hot springs (even above boiling temperatures) or
a kilometer below the surface, life seems to thrive.  One speaker,
Todd Stevens of the Pacific Northwest Lab, asserted that some
subsurface "rock-eating" microbes constituted an ecosystem
independent of photosynthesis and that their metabolism (in some
cases amounting to a biomass doubling time of millennia) was
perhaps the slowest of all life forms.

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PHYSICS NEWS UPDATE                         
The American Institute of Physics Bulletin of Physics News
Number 324, June 4, 1997    by Phillip F. Schewe and Ben Stein

A PREVIOUSLY UNDETECTED STREAM OF COMETS
buffets the Earth.  Apparently up to 30 comets per minute
approach our planet, where they innocuously break up, releasing
a river of water and organic compounds into the atmosphere. 
The trajectories of the comets are heralded by visible tracks
(sunlight reflecting from OH molecules) observed by the Polar
Spacecraft, parked in an eccentric orbit, the better to view the
whole Earth.  Louis Frank of the University of Iowa reported this
new finding at last week's AGU meeting in Baltimore. In 1986
Frank proposed that not only were tiny ice comets arriving in
great numbers but that their cumulative cargo of water might
have fully stocked the oceans. This hypothesis, mostly dismissed
at the time, will be re-examined now. The issues of exactly how
many comets, how much water, and which organic molecules
will be addressed by further observations, perhaps by military
satellites.

MORE QUALMS ABOUT EXTRASOLAR PLANET
DISCOVERIES. The presence of planets around a number of
stars has been inferred from the slight doppler wobble in the
stars' spectra. One critic, David Grey of the University of
Western Ontario, contends that the wobble, at least in the case of
the star 51 Pegasi, may be due to the unstable nature of the star
itself (Nature, 27 February).  A second reservation has since
surfaced.  Caltech scientists, using an interferometer, suspect that
51 Pegasi is really a binary star system, and that this would
account for the wobble (Science, 30 May).

CELESTIAL HEAVYWEIGHTS.  The following items are a
selection from a list compiled in the June 1997 issue of
Astronomy.  The largest known star is Mu Cephei (with a radius
of 11 AU).  The most massive star is Eta Carinae (100 solar
masses).  The largest known meteorite in the ground (an
estimated 60 tons) lies in a farm in Namibia.  The largest dug-up
meteorite, the "Ahnighito" (34 tons), is on view in New York's
American Museum of Natural History.  The furthest galaxy (a
distinction which changes frequently) is an unnamed object in
Virgo with a redshift of 4.38. The most distant known object is
the quasar PC 1247+3406, with a redshift of 4.897. The
brightest recorded supernova occurred in the year 1006.  As
bright as a quarter moon, the object was visible in daylight and
cast shadows at night.

THE MOST EXTENSIVE USE OF PERMANENT MAGNETS
at an accelerator will be an important part of Fermilab's upgraded
beamline system.  The magnets (which provide stable fields and
require no input current)  will be used to help shuttle protons
through beampipes prior to injection into the main accelerator
ring.  The magnets will also be used in the Antiproton Recycler
Ring, a sort of waiting area for antiprotons.  Expert machining of
the pole faces ensures that the magnets meet the exacting
tolerances required for steering high-speed particles. (CERN
Courier, May 1997.)

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