[tt] Physics News Update 842

Tue Oct 9 13:37:05 UTC 2007

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From: physnews at aip.org
Date: Tue, 9 Oct 2007 09:19:44 -0400
To: eugen at LEITL.ORG
Subject: Physics News Update 842
Reply-to: physnews at aip.org

PHYSICS NEWS UPDATE
The American Institute of Physics Bulletin of Physics News
Number 842  October 9, 2007  by Phillip F. Schewe
www.aip.org/pnu

THE 2007 NOBEL PRIZE IN PHYSICS WILL BE AWARDED TO Albert Fert
(Université Paris-Sud, Orsay, France) and Peter Grünberg
(Forschungszentrum Jülich, Germany) for the discovery of giant
magnetoresistance, or GMR for short.  GMR is the process whereby a
tiny magnetic field, such as that of an oriented domain on the
surface of a computer hard drive can, when the proper read head is
brought nearby, trigger a large change in electrical resistance,
thus *reading* the data vested in the magnetic orientation.  This
is
the heart of modern hard drive technology and makes possible the
immense hard-drive data storage industry.  Fert and Grünberg
pioneered the making of stacks consisting of alternating thin layers
of magnetic and non-magnetic atoms needed to produce the GMR
effect.  GMR is a prominent example of how quantum effects (a large
electrical response to a tiny magnetic input) come about through
confinement (the atomic layers being so thin.); that is, atoms
interact differently with each other when they are confined to a
tiny volume or a thin plane.
All these magnetic interactions involve the spin of an electron.
Spin is a quantum attribute that shouldn*t be associated too closely
in the mind with the electron literally spinning (in the way that a
top spins).  Still more innovative technology can be expected
through quantum effects depending on electrons* spin.  Most of the
electronics industry is based on manipulating the charges of
electrons moving through circuits.  But the electrons* spins might
also be exploited to gain new control over data storage and
processing.  Spintronics is the general name for this budding branch
of electronics.  (Nobel Prize website:
http://nobelprize.org/nobel_prizes/physics/laureates/2007/info.html)

NEW THEORY EXPLAINS HOW CELLULAR COMPASSES WORK.  Scientists from
the Politecnico di Torino in Italy and the Landau Institute of
Theoretical Physics in Russia have derived a theory to describe how
eukaryotic cells (such as those found in all higher organisms)
respond to chemical signals in their environments.  Considering that
coordinated sensing of and movement toward chemical signals is a
vital processes in embryology (how cells know where to go in
fashioning the organism), inflammation, and immune response,
directional maneuvering at the cellular level is quite important.
Here's what happens.  First, receptors in the membranes of the cells
become activated by the presence of trace amounts of
chemicals---even down to the
nano-molar level or about one molecule in a cubic micron---in the
cells' vicinity.   Not only do the receptors sense the presence of
the attractants but, through the differential activation of 10,000
or more receptors distributed along the body of the cell, the
direction of the source of the attractant can be located to within a
few degrees.  Ability to train upon a 5% chemical gradient allows
the cell to know where it should be going, whether to find food,
antigens, or to take up
its place in a larger multi-cellular structure.  Second, a cascade
of polymerization steps now ensues within a few minutes.
Consequently the cell develops head and tail structures, the better
to make possible travel along the chemical gradient (chemotaxis).
In nature, cells have also been known to plan their travel by
exploiting thermal gradients (thermotaxis) and electrical gradients
(galvanotaxis).  According to Andrea Gamba (andrea.gamba at polito.it)
and coauthors the new results consist of being able now to
demonstrate in a mech
anistic way how the cell's directional sensing
and response comes about through a kind of  self-organized phase
transition; when the chemical gradient exceeds a certain threshold
level the dynamic of growth of clusters of signaling molecules on
the cell surface fine-tunes to sense the slight unbalance in
activated receptors and provides a fast polarization in the
direction of the gradient, thus providing a compass bearing which is
able to initiate the modification in
the cellular structure.  The scientists argue that the physical
amount of space along the body of large eukaryotic cells needed for
making such an astute directional assessment might explain why
bacteria (with much smaller bodies) do not have a spatial system of
directional sensing.  (Gamba et al., Physical Review Letters, 12
October 2007)

***********
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