PHYSICS NEWS UPDATE
The American Institute of Physics Bulletin of Physics News
Number 656 October 7, 2003 by Phillip F. Schewe, Ben Stein, and
James Riordon

THE 2003 PHYSICS NOBEL PRIZE goes to Alexei A. Abrikosov (Institute
for Physical Problems in Moscow and now at Argonne National
Laboratory near Chicago), Vitaly L. Ginzburg (Lebedev Physical
Institute, Moscow) and Anthony J. Leggett (University of Illinois,
Urbana) The award goes for work done on systems that operate under
two regimes very far from human experience: the quantum realm and
the low-temperature realm. In superconductivity, a current of
electrons flowing through a material undergoes a change in behavior:
normally reluctant to associate with each other, the electrons at
low temperature can form pairs. These pairs act like particles and
are so gregarious that they can enter into a single unified quantum
state. In this state the electron pairs are no longer just a
current, but a "supercurrent." This supercurrent flows without
dissipating energy. It flows without resistance. The practical
benefit is that energy loss through dissipation can be eliminated.
An additional feature is that much higher currents can flow through
some superconductor materials than through normal metal wires. The
price to pay for producing the weird quantum state of
superconductivity in the first place is having to chill the material
down to temperature close to absolute zero, which usually means
about 4 K.

Practical applications of wire made from superconducting material
include medical scanners (this year's Nobel for medicine rewards MRI
research; here potent magnetic fields inside the scanner are usually
produced with superconducting cables), levitated trains (still at an
early state of deployment), and the chilling of some components in
cell-phone networks.

In some superconductors (type I) magnetic fields are anathema to the
superconducting state. In other superconductors (type II), magnetic
fields are tolerated, and this makes possible the applications just
mentioned. Abrikosov and Ginzburg are being recognized for their
work in explaining how type II superconductors work.
When a sample of helium-3 atoms is chilled to very low temperature,
the atoms (which like electrons in a superconductor, are "fermions,"
particles reluctant to associate) can pair up, and the pairs in turn
may enter into a single quantum state in which (analogous to the
loss-less flow of supercurrents in superconductors) the fluid will
flow without losing energy via friction. Just as superconductors
have no electrical resistance, so superfluids have no viscosity, and
can flow freely. Leggett is being recognized for his work in
explaining He-3 superfluidity. Superfluidity also appears in
samples of helium-4 atoms (although the superfluid mechanism is much
different than in He-3), and possibly in Bose Einstein condensates.
(Some background articles: Physics Today---May 1989, Jul 95, Dec 96,
Jan 98, Dec 87, May 96; Scientific American---Dec 77, Nov 60, Dec
76, Nov 88, Jun 90, Jul 82, May 66, Dec 93, Aug 94; Physics World,
Feb 2000; Nature 13 Mar 97; Leggett, Review of Mod Physics, 1999;
Abrikosov, PRL, 1 July 1958; Nobel website:
www.nobel.se/physics/laureates/2003)

THE 2003 NOBEL PRIZE IN PHYSIOLOGY/MEDICINE goes to Paul C.
Lauterbur of the University of Illinois at Urbana-Champaign and
Peter Mansfield of the University of Nottingham for their work in
developing magnetic resonance imaging, or MRI. In the medical
world, MRI has become a major imaging technique, but its roots lie
in the most basic magnetic physics in the nuclei at the heart of
every atom and molecule. Taking advantage of the fact that the
body is two-thirds water, MRI obtains images of the hydrogen nuclei
in water molecules inside our bodies. In the early 1970s, while
working at the State University of New York at Stony Brook,
Lauterbur exploited the magnetic properties of atomic nuclei to
yield a two-dimensional image of matter, by introducing gradients in
the external magnetic field that surrounds the object to be imaged.
Shortly thereafter, Peter Mansfield helped to make MRI a practical
imaging procedure, in part by coming up with mathematical methods
for processing the radio waves released by hydrogen during the
technique. The origins of MRI go back further, to the late 1930s,
when physicist I.I. Rabi of Columbia University demonstrated that
one could obtaining abundant information about lithium chloride
molecules by manipulating the magnetic "spins" of the molecules'
nuclei (Nobel Prize, 1944). Later, physicists E.M. Purcell
(Harvard) and Felix Bloch (Stanford) developed nuclear magnetic
resonance (NMR) in hydrogen (Nobel Prize, 1952). Two Nobel Prizes
in Chemistry (1991 and 2002) have been awarded for achievements in
nuclear magnetic resonance. MRI has been so successful that the
original technique has spawned numerous offshoots, such as
functional MRI (fMRI), which measures brain activity by detecting
oxygen levels in specific brain areas. MRI advances continue at a
feverish pace: low-field MRI (Some background articles: Physics
Today---Jun 1995, Sep 2001, Jun 92, Oct 2003; Scientific
American---May 82, Oct 2001, Jan 83; Review of Mod. Physics, Jan 95)

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