1 July 1998
 
 

1-RINGING ABOVE THE AURORA
Behind the shimmering curtains of light in an aurora tremendously
energetic events take place. 12 years ago researchers studying the
electrons and ions whizzing through and above auroras came across
puzzling electric field patterns that have taken years to explain.
One current theory is a new phenomenon in plasma physics: an
electric field oscillation that stays put, rather than propagating
away, as a normal electromagnetic wave would. In the 29 June PRL a
team claims to provide the most convincing evidence to date of
these localized "knots" of resonating fields.
(Phys. Rev.Lett. 80, 5734; posted 29 June 1998.)

Also in PRL this week: LIFE EXTINCTIONS BY COSMIC RAY JETS.
See AIP's Physics News Update story here
 
 

(Physics News Update is a weekly physics news bulletin, also
available by e-mail. See their home page here)
 

8 July 1998
 

1-CHARGED-UP ICE CRYSTALS
Snowflakes and many other crystals normally grow in fingerlike,
"dendritic" patterns that physicists do not yet fully understand.
In the 6 July PRL a team reports a new type of hypercrystallization
process caused by electric fields: they describe ice "needles" that
can grow at more than 10 times the normal rate. They show that a
simple extension of crystallization theory explains many features
of the accelerated growth and suggest the new method could be
useful for controlling crystal growth in materials applications.
(Phys. Rev. Lett. 81, 176; posted 29 June 1998.)

Also in PRL this week: TURNING SOLID METAL INTO A TRANSPARENT,
HIGHLY REFRACTIVE FLUID. See AIP's Physics News Update story here
 

16 July 1998
 

1-THE QUANTUM OF HEAT FLOW
Physicists have known for over a decade that electrical
conductance can be quantized: Under the right conditions it cannot
have just any value, but comes only in units of the universal
conductance quantum. In the past year, researchers have discovered
that a similar quantization should occur for the conduction of
heat. For an extremely thin wire at temperatures close to absolute
zero, the heat conduction quantum should be "universal"--
independent of the shape and size of the wire and even the
material it is made of. In the 6 July PRL a pair of theorists puts
this concept on an even firmer footing by showing that it should
be observable in practical experiments.
(Phys. Rev. Lett. 81, 232; posted 9 July 1998.)

2-LANDING IN THE TRENCHES OF GALLIUM ARSENIDE
A helicopter pilot flying over midtown Manhattan would find it
easiest to land on top of a building, but a report in the 13 July
PRL suggests that in some cases molecules hitting a surface
perform the equivalent of flying between the skyscrapers to land
on the streets. According to the authors, bromine molecules (Br2)
hitting a particular gallium arsenide (GaAs) surface bind
exclusively with atoms in the second layer, which are only exposed
at narrow "trenches" and breaks in the top layer of the crystal.
They explain the surprising finding with a simple bonding theory.
The result could be important for semiconductor processing in the
future, as techniques are developed to more precisely control
surface properties.
(Phys. Rev. Lett. 81, 413; posted 13 July 1998.)
 
 

24 July 1998
 

1-LEVITATING LIQUID BORON
Probing the innards of a material to determine its structure is no
problem for physicists, but they run into trouble if that material
is a liquid which attacks any container. That difficulty was
recently overcome by ingeniously eliminating the need for a
container. Now, in the 20 July PRL, a team sheds some light on the
structure of liquid boron, by performing the first successful x-ray
diffraction on this complex material's liquid form--as it floats on
a cushion of gas. (Phys. Rev. Lett. 81, 586; posted 20 July 1998.)

2-SIGNALS FROM AN ARTIFICIAL MOLECULE
Physicists can now probe a puddle of 100 or fewer electrons isolated
in a small slab of semiconducting material. They have even detected
individual electrons coming and going from these "quantum dots." Now
a team reports in the 20 July PRL that they can detect a single
electron hopping back and forth between two adjacent dots and
potentially follow its motion in detail. Similar experiments may
allow new detailed studies of single electrons in these structures
and bring physicists a step closer to developing computers based on
them. (Phys. Rev. Lett. 81, 689; posted 24 July 1998.)

Also in PRL this week: THE PERSISTENCE OF WEATHER.
See AIP's Physics News Update story here

 31 July 1998

ATOMS PROBE AN UNNATURAL FORCE FIELD
One of the oldest problems in physics is predicting the motion of
objects influenced by gravity--cannon balls, planets, or satellites--
and then verifying the predictions. The force of gravity varies as
the inverse square of the distance between the objects, but how
would Earth's orbit look if the Sun's attraction depended on the
inverse third power of distance? That question is answered
theoretically in a typical college physics course, but in the 27
July PRL an Austrian team reports the first observation of objects
moving under the influence of such a force. They show that cold
atoms fall toward a thin, charged wire in the predicted manner and
suggest that using small material objects to influence atomic
motions, rather than using lasers, could allow for new types of
atomic physics experiments.
(Phys. Rev. Lett. 81, 737; posted 28 July 1998. For link to the paper click here )
 
 
 

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