Message-ID: <Pine.NEB.4.63.0507281438390.17925@panix3.panix.com>
From: Alan Sondheim <sondheim@panix.com>
To: Cyb <cybermind@listserv.aol.com>,
"WRYTING-L : Writing and Theory across Disciplines" <WRYTING-L@LISTSERV.UTORONTO.CA>
Subject: Physics News Update 739 (fwd)
Date: Thu, 28 Jul 2005 14:38:43 -0400 (EDT)
---------- Forwarded message ---------- Date: Thu, 28 Jul 2005 13:58:28 -0400 From: physnews@aip.org To: sondheim@PANIX.COM Subject: Physics News Update 739 PHYSICS NEWS UPDATE The American Institute of Physics Bulletin of Physics News Number 739 July 28, 2005 by Phillip F. Schewe, Ben Stein NEW SPINTRONIC SPEED RECORD. Spintronics is the science devoted to gaining greater control over digital information processing by exploiting electron spin along with electron charge in microcircuits. One drawback to implementing a scheme of magnetic-based memory cells for computers has been the relatively slower speed of spin transistors. Hans Schumacher of the Physikalisch-Technische Bundesanstalt, Braunscheig, Germany, has now devised the fastest yet magnetic version of a random access memory (MRAM) cell, one that switches at a rate of 2 GHz, as good as or better than the fastest non-magnetic semiconductor memories. The MRAM architecture is a sandwich, consisting of two magnetic layers, with a tunneling layer in between. When the magnetic layers are aligned (their spin orientation is the same) resistance in the cell is low; when they are counter-aligned resistance is high. These two conditions establish the binary 1 or 0 states. The speed of writing or reading data to and from the cells has, for MRAMs, been limited to cycle times of 100 MHz by magnetic excitations in the layers. This problem has now been overcome, according to Hans Schumacher (hans.w.schumacher@ptb.de), through a novel approach referred to as ballistic bit addressing. In the case of the new MRAM architecture, the influence of magnetic excitations is eliminated through the use of very short (500 picosecond) current pulses for carrying out the write operation and that even a bit whose value will remain the same undergoes a complete 360-degree precession, whereas a change of status (say, from a 0 to a 1) will be achieved by pivoting the magnetic status of the cell through 180 degrees. The 2-GHz switching speed (the rate at which writing can be accomplished) is faster than static RAM (or SRAM) memories, currently the fastest memories, can accomplish. Furthermore, the magnetic memories are non-volatile, which means that the status of the memory does not disappear if the computer is shut down. (Schumacher, Applied Physics Letters, 25 July 2005; and Journal of Applied Physics, August 1; general MRAM website at www.mram-info.com) VIBRATION AS A FORM OF ARTIFICIAL GRAVITY. French scientists have studied how the transition from liquid to gas and back again slows down in a weightless environment and how an artificial form of gravity can be simulated using high-speed vibration of the sample. This work has implications for work in space, where fluids don't behave the way they do on the ground.. Past studies have shown that vibrating an astronauts' legs and feet help to prevent muscle decay or bone decalcification. Daniel Beysens, a researcher at the Commissariat a l'Energie Atomique (CEA, dbeysens@cea.fr) and his colleagues study this problem at the much more basic level of individual bubbles and droplets, and what happens to them when you add or subtract the effects of gravity. Movement between liquid and vapor states is aided by buoyancy: bubbles rise and droplets fall. But without gravity these actions cease and liquids condense only by the haphazard and slower process of collision between droplets or bubbles. In the new experiment a 20-cubic-millimeter sample of liquid/gaseous hydrogen was levitated in a strong magnetic field; the field grabs onto the magnetic moments of the H2 molecules, helping to suspend them. This essentially creates an artificial weightlessness (only about 1% of Earth's gravity remains) and this allows one to see how capillary forces and "wetting" (the process by which a liquid layer builds up on a surface) are dominant in a freefall environment. Then some of the effects of gravity are artificially added back in, this time in the form of high-speed but low-amplitude vibrations. The vibrations cause motion in the fluid, which induces effects that resemble gravity. Bubbles and droplets go "up" and "down" again when the vibration is turned on. As far as simulating gravity, vibrations seem to work (Beysens et al., Physical Review Letters, 15 July 2005) GEONEUTRINOS DETECTED. Neutrinos have very little mass and interact but rarely, but are made in large numbers inside the sun as a byproduct of fusion reactions. They are also routinely made in nuclear reactors and in cosmic ray showers. Terrestrial detectors (usually located underground to reduce the confusing presence of cosmic rays) have previously recorded these various kinds of nu's. Now, a new era in neutrino physics has opened up with the detection of electron antineutrinos coming from radioactive decays inside the Earth. The Kamioka liquid scintillator antineutrino detector (KamLAND) in Japan has registered the presence of candidate events of the right energy; uncertainty in the model of the Earth's interior makes the exact number vague, but it might be dozens of geo-nu's. The neutrinos presumably come from the decays of U-238 or Th-232. They are sensed when they enter the experimental apparatus, where they cause a 1000-ton bath of fluid to sparkle. Scientists believe the Earth is kept warm, and tectonic plates in motion, by a reservoir of energy deriving from two principal sources: residual energy from the Earth's formation and additional energy from subsequent radioactive decays. The rudimentary inventory of geoneutrinos observed so far is consistent with the theory. (Araki et al., Nature, 28 July 2005.) *********** 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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