PHYSICS NEWS UPDATE
The American Institute of Physics Bulletin of Physics News
Number 703 October 5, 2004
by Phillip F. Schewe and Ben Stein

THE 2004 PHYSICS NOBEL PRIZE goes to David J. Gross (Kavli Institute,
University of California, Santa Barbara), H. David Politzer (Caltech), and
Frank Wilczek (MIT) for their discovery of asymptotic freedom, according to
which the interaction between quarks inside nuclear particles such as
protons and neutrons actually gets weaker the closer the quarks are to each
other and stronger the farther they are apart.  This hypothesis helped lead
to the establishment of quantum chromodynamics (QCD) as a firm theory of
the strong nuclear force, somewhat, but not exactly, in analogy with the
quantum electrodynamics (QED), the theory of the electromagnetic force. The
Work of Gross/Politzer/Wilczek explained why individual quarks could never
be observed in the lab.  In their picture, quarks are connected by lines of
force embodied in the form of particles called gluons.  The quarks
themselves possess a "color charge" analogous to electrical
charge.  That is why the strong force among quarks is referred to also as
the color force (whence the name "chromo" dynamics).  The energy
that could be used to free quarks from each other's embrace---energy in the
form, say, of a fast-moving incoming beam particle---would indeed force the
quarks farther apart for a while, but this energy (imagine a rubber band
being stretched) would eventually be converted into the creation of a new
quark-antiquark pair. One or the other of these newly made quarks would
immediate ally itself with one of the two separating quarks, resulting not
in any free quarks but only in two quark pairs.  (This process has been
compared to trying to saw a bar magnet in half attempting to create two
isolated magnetic poles; you only succeed in creating two new bar magnets.)
 Conversely, quarks very close together are practically free of each
other's influence. QCD has passed every confirmed experimental test so far,
but physicists continue to look for oddities that might signify a departure
from this theory.
(Background: Physics News Update has carried many items relating to
QCD---for example, see PNU's 533, 585, 549, 642, 600, 666, 216, 699, 554,
526 at www.aip.org/pnu.  Some pertinent magazine articles: Physics Today
(PT), April 88, Georgi, flavor symmetries; Scientific American (SA), Oct
75, Glashow, color and flavor; SA, Dec 80, Wilczek, matter-antimatter
asymmetry; PT, Oct 04, Wilczek, essay on forces of nature; SA, Jun 03,
beyond the standard model; Nature, 28 Jan 99, Wilczek, lattice gauge
theory; PT Aug 00, QCD made easy; PT Feb 04, lattice QCD; PT, Mar 95,
Witten, confinement; CERN Courier, free quarks in nuclear collisions; CERN
Courier, tests of QCD; PT, Aug 00, Wilczek; SA, Apr 81, grand unified
theories; SA, Dec 99, Weinberg, theory of everything; SA, Apr 85, Quigg,
standard model; SA, Jun 80, 't Hooft, fields; CERN Courier, Jun 04,
Wilczek; SA, Feb 83, lattice theory; SA, Jul 93, calculation of masses; PT,
Feb 04, QCD; Physics World, May 03, QCD and string theory; SA, Nov 76,
quark confinement; SA, Nov 98, glueballs.  Websites: Nobel Prize website:
www.nobel.se/physics/laureates/2004; germane Physics Today articles will be
posted at this site: physicstoday.org/vol-57/iss-10/nobel.html;
webphysics.davidson.edu/mjb/qcd.html, QCD website;
www.cpt.dur.ac.uk/qcdnet/, QCD website; fafnir.phyast.pitt.edu/exotica/,
QCD website; http://www-cdf.fnal.gov/physics/new/qcd/QCD.html, QCD
website.)
                        
AN MRI WIND TUNNEL.  The subject of last year's Nobel prize for physiology
or medicine, magnetic resonance imaging (MRI) is well known for making
beautiful images of the inside of the body. MRI is less recognized for its
ability to track movement, such as clinical studies of blood flow. Now,
researchers in Canada (Benedict Newling, University of New Brunswick,
bnewling{at}unb.ca) have invented a new MRI method  suitable for measuring
much faster fluid speeds, ten times more rapid than the fastest human blood
flow. Their approach uses a constant, shorter-than-usual measurement
interval (six milliseconds).  In effect, the MRI scanner becomes a new type
of practical wind tunnel, one that's non-invasive too. An obstruction of
any shape can be placed in the flow at the center of the scanner. The
resulting flow of liquid or gas around the object is readily measured. As
an example, the researchers measure gas flow past a wing at realistic
speeds (corresponding to a stalled aircraft) and compare them with
computer-based calculations of the expected flow (see figure at
www.aip.org/png). The flows they measure are highly turbulent, which means
the fluid velocity at every position varies rapidly around some average
value. The MRI measurement contains information about both the average
velocity and fluctuations. MRI is naturally three-dimensional and works
just as well in opaque or transparent fluids.  Furthermore, MRI can measure
several positions simultaneously, unlike most conventional wind-tunnel
measurements, and therefore has the potential to deliver measurements in
substantially reduced times. (Newling et al., Physical Review Letters, 8
October 2004; text at www.aip.org/physnews/select)

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