Message-ID: <Pine.NEB.4.63.0607251641490.16988@panix3.panix.com>
From: Alan Sondheim <sondheim@panix.com>
To: Cyb <cybermind@listserv.aol.com>,
Wryting-L <WRYTING-L@LISTSERV.UTORONTO.CA>, WRYTING-L@listserv.wvu.edu
Subject: Physics News Update 786 (fwd)
Date: Tue, 25 Jul 2006 16:42:01 -0400 (EDT)
---------- Forwarded message ---------- Date: Tue, 25 Jul 2006 08:35:26 -0400 From: physnews@aip.org To: sondheim@PANIX.COM Subject: Physics News Update 786 PHYSICS NEWS UPDATE The American Institute of Physics Bulletin of Physics News Number 786 July 25, 2006 by Phillip F. Schewe, Ben Stein, and Davide Castelvecchi www.aip.org/pnu CHEMICAL TRANSISTOR. A new device, the chemical equivalent of a transistor, might make possible ultrasensitive bio-medical single-antigen detection. The things we associate with transistors, the closing or opening of a switch or the amplification of a signal, are normally carried out by injecting a tiny electric signal into a gate electrode which then changes the environment of a nearby channel region. This allows a current to be shut off or to be amplified. In an experiment carried out by physicists at the University of California at Irvine, the same things are done through chemical reactions. Philip Collins (collinsp@uci.edu, 949-824-9961) and his colleagues use carbon nanotubes as the central working substance of their device. The nanotubes, immersed in a liquid, can be switched from a conducting state to an insulating state by oxidizing them---that is, by chemically removing the free electrons. The chemical reactions are triggered by an electrical potential applied across the interaction area (figure at www.aip.org/png/2006/262.htm ). What the Irvine researchers (Philip Collins, collinsp@uci.edu, 949-824-9961) show is that this process can be performed reversibly and over short periods of time, as fast as 10 microseconds. This is quite slow by today�s transistor standards; the more important promise for prospective chemical field effect transistors (or ChemFETs) is the potentially large amplifications. It looks as if only a few electrons� worth of oxidation can be used to switch currents as large as microamps. In a future bio-detector the switching would be provided not by an applied electrochemical signal but by the trace presence of antigens docking with antibodies attached to the nanotubes. In previous detectors, chemical actuation has required the presence of tens of antigens; here, a single antigen might be enough to change the state of the nanotube. (Mannik et al., Physical Review Letters, 7 July 2006; lab website www.physics.uci.edu/~collinsp/) ASTEROID ENCOUNTER ENHANCEMENT. Just what you wanted to know: that the likelihood of an encounter between the earth and an asteroid is enhanced by the gravitational pull between the two bodies. The formula for the enhancement is worked out in a new paper by University of Iowa physicist James Van Allen, the same man who, a half century ago, predicted the existence (later confirmed) of plasma-particle radiation belts around the earth. The enhancement of the collision cross section, which Van Allen admits leaves out additional forces exerted by the sun and other planets in the solar system, equals 1 plus the square of the ratio of the escape velocity for the planet (Van Allen worked out the case Earth, Mars, Jupiter, and Saturn) to the approach velocity of the asteroid (starting far away). (American Journal of Physics, August 2006) ASIAN STORMS PUSH THE EARTH AROUND. Earth�s axis of rotation undergoes several gyrations, such as the precession of the equinoxes, which takes about 26,000 years. Recently two of the most important axis gyrations inadvertently cancelled each other, allowing geophysicists to measure other, subtler gyrations that would normally be difficult to detect. The two larger wobbles are the 433- day-cycle Chandler Wobble (whose origin is not very well known) and the wobble caused by annual weather oscillations. Their combined effect is normally to cause the rotational axis to migrate by as much as 10 meters. But from December 2005 to February 2006 their mutual nullification reduced the axis excursion to less than 1 meter. This allowed Belgian scientists to study fainter, lesser forces whose exertions could briefly be measured. The scientists saw signs of what they believe to be an influence on Earth�s wobble day by day triggered by storms over Asia and northern Europe. (Geophysical Research Letters, July 2006) *********** PHYSICS NEWS UPDATE is a digest of physics news items arising from physics meetings, physics journals, newspapers and magazines, and other news sources. It is provided free of charge as a way of broadly disseminating information about physics and physicists. For that reason, you are free to post it, if you like, where others can read it, providing only that you credit AIP. Physics News Update appears approximately once a week. 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