Number 179, May 17, 1994 by Phillip F. Schewe and Ben Stein
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 1994.)
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 $443.1 for geoscience
($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.)
|
