PHYSICS NEWS UPDATE A digest of physics news items by Phillip F. Schewe, American Institut

PHYSICS NEWS UPDATE
A digest of physics news items by Phillip F. Schewe, American
Institute of Physics
Number 179  May 17, 1994

THE RELAXATION OF A SINGLE DNA MOLECULE has been studied by attaching
to it a 1-micron latex bead which then can be manipulated in a special
configuration of lasers known as an "optical tweezers."  Lit up by an
infrared laser and viewed in a microscope, the DNA molecule can be
sent through a series of maneuvers (including spelling out the letters
"DNA") designed to measure the molecule's mechanical properties.
Stanford physicist Steven Chu and his colleagues were also able to
corroborate a theory of 1991 Nobel Laureate Pierre-Gilles de Gennes,
who asserted that the movement of single polymer strand among other
strands was analogous to one snake crawling past other snakes.
(Thomas T. Perkins et al., Science, 6 May.)

AN ION TEMPERATURE OF 429 MILLION K (37 keV) was achieved in the
fusion experiments last December at Princeton's TFTR Tokamak, which
for the first time used a fuel of 50% deuterium and 50% tritium in
order to produce a record 6.2 megawatts of power (the 1991 experiments
at the Joint European Torus, which produced the previous record of 1.7
MW, used a fuel of approximately 90% deuterium and 10% tritium).  The
central region of the TFTR plasma achieved a power density (from
fusion reactions) of just over 1 megawatt/m**3, comparable to that
expected in the first commercial reactors.  There are encouraging
signs that the alpha (helium-4) particles produced in the D-T
reactions are directly heating electrons in the plasma.  Alpha
particle confinement and heating will be the focus of ongoing
experiments at TFTR this year.  (Upcoming articles in Physical Review
Letters, May 23: J.D. Strachan et al., and R.J. Hawryluk et al.)

A THOUSANDFOLD INCREASE IN THE MAGNETORESISTANCE (MR) in superlattice
films has been observed by scientists at AT&T Bell Labs.  The MR
phenomenon, in which a material's electrical resistance is altered by
a changing magnetic field, has already been used in magnetic recording
heads.  One figure of merit, the MR ratio, is the percentage change in
resistance as an external magnetic field is switched between high and
low values.  The highest previous MR ratio was about 150% in a Fe- Cr
multilayer film.  The new MR ratio, obtained for 100 to 200-nm thick
La-Ca-Mn-O films (grown epitaxially on a LaAlO3 substrate), is
127,000% at a temperature of 77 K and 1300% at room temperature.  The
field used was 6 Tesla.  (S. Jin et al., Science, 15 April.)

THE 1995 RESEARCH BUDGET REQUEST, submitted to Congress by President
Clinton, calls for a 4% increase in R&D spending.  Among physics
programs at the Department of Energy, the 1995 request for high energy
physics is $621.9 (all amounts are in millions of dollars), about the
same as in 1994.  The '95 request for nuclear physics is $300.8, down
14% from '94.  The Basic Energy Sciences program, at $741.3, is down
6.2% from the previous year.  The new request for magnetic fusion is
$372.6, up 8.4% from '94, while the figure for inertial fusion is
$176.5, down from $185.5.  At the National Science Foundation, the
1995 figure for physics is $141.7 ($133.7 in '94), for materials
research $185.5 ($175.6 in '94), and for geoscience $443.1 ($403.9 in
'94).  At NASA the physics and astronomy program calls for $1058.7 in
1995 ($1076.6 in '94), including $226.7 for the Hubble Space Telescope
and $234.5 for the AXAF x-ray telescope.  The planetary exploration
request was $707.3, compared to $654.3 in '94.  (Physics Today, April
1994.)