From: LARRY KLAES (ljk4_at_msn.com)
Date: Tue Oct 09 2007 - 06:34:43 PDT
>From: physnews_at_aip.org
>Reply-To: physnews_at_aip.org
>To: ljk4_at_MSN.COM
>Subject: Physics News Update 842
>Date: Tue, 9 Oct 2007 09:19:44 -0400
>
>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)
>
>***********
>PHYSICS NEWS UPDATE is a digest of physics news items arising
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