---------- Forwarded message ---------- Date: Wed, 9 Nov 2005 11:07:07 -0500 From: [EMAIL PROTECTED] To: [EMAIL PROTECTED] Subject: Physics News Update 753
PHYSICS NEWS UPDATE The American Institute of Physics Bulletin of Physics News Number 753 November 9, 2005 by Phillip F. Schewe, Ben Stein GUIDED, SLOW LIGHT IN AN ULTRACOLD MEDIUM has been demonstrated by Mukund Vengalattore and Mara Prentiss at Harvard. Slowing light pulses in a sample of atoms had been accomplished before (see for example http://www.aip.org/pnu/2001/split/521-1.html) by sending light pulses into a highly dispersive medium, that is, a medium in which the index of refraction varies greatly with frequency. Previously this dispersive quality had come about by tailoring the internal states of the atoms in the medium. In the present Harvard experiment, by contrast, the dispersive qualities come about by tailoring the external qualities of the atoms, namely their motion inside an elongated magnetic trap (see figure at www.aip.org/png/2005/238.htm). In the lab setup two pump laser beams can be aimed at the atoms in the trap; depending on the frequency and direction of the pump light, the atomic cloud (at a temperature of about 10 micro-K) can be made more or less dispersive in a process called recoil-induced resonance, or RIR. If now a separate probe laser beam is sent along the atom trap central axis, it can be slowed by varying degrees by adjusting the pump laser beam. Furthermore, the probe beam can be amplified (the intensity of the light can be increased by a factor of up to 50) or attenuated depending on the degree of dispersiveness in the atoms. This process can be used as a switch for light or as a waveguide. According to Mukund (now working at UC Berkeley, [EMAIL PROTECTED]), slowing light with the recoil induced resonance approach may be a great thing for nonlinear-optics research. Normally nonlinear effects come into play only when the light intensities are quite high. But in the RIR approach, nonlinear effects arise more from the strong interaction of the two laser beams (pump and probe) and the fact that the slow light spends more time in the nonlinear medium (the trap full of atoms). All of these effects are enhanced when the atoms are very cold. Moreover, because the slow light remains tightly focused over the length of the waveguide region, intensity remains high; it might be possible to study slowed single-photon light pulses, which could enhance the chances of making an all-optical transistor. The light in this setup has been slowed to speeds as low as 1500 m/sec but much slower speeds are expected when the atoms are chilled further. (Vengalattore and Prentiss, Physical Review Letters, upcoming article; MIT-Harvard Center for Ultracold Atoms at atomsun.harvard.edu) ZEN AND THE ART OF TEMPERATURE MAINTENANCE. Scientists at the Iwate University in Japan have shown that the skunk cabbage---a species of arum lily and whose Japanese name, Zazen-sou, means Zen meditation plant---can maintain its own internal temperature at about 20 C, even on a freezing day (picture at www.aip.org/png/2005/239.htm). The plant occurs in East Asia and northeastern North America, where its English name comes from its bad smell and from the fact that its leaves are like those of cabbage. Unlike the case of mammals, which maintain their body temperature by constant metabolism in cells all over the body, heat in the skunk cabbage is produced chiefly in the spadix, the plant's central spike-like flowering stalk through chemical reactions in the cells' mitochondria. According to one of the authors of the new study, Takanori Ito ([EMAIL PROTECTED]), only one other plant species, the Asian sacred lotus, is homeothermic, that is, able to maintain its own body temperature at a certain level. Most other plants do not produce heat in this way because they seem to lack the thermogenic genes (the technical name for which, in abbreviated form, is SfUCPb). Moreover, the researchers, studying subtle oscillations in the plant's internal temperature, claim that the thermo-regulation process is chaotic and that this represents the first evidence for deterministic chaos among the higher plants. The resultant trajectory in the abstract phase space (where, typically, one plots the plant's temperature at one time versus the temperature at another time) is a strange attractor, which the authors refer to as a Zazen attractor, a "Zen meditation" attractor. (Physical Review E, November 2005) DROWNING IN QUICKSAND IS IMPOSSIBLE, according to a new study, relegating this popular plot device in adventure stories to the category of pure folklore. Consisting of a mixture of sand, salt water, and clay, quicksand captured the attention of University of Amsterdam physicist Daniel Bonn when he went on a family trip to Iran, the birthplace of his wife. Collecting a sample of quicksand near a body of water in Iran, and bringing it to his laboratory for study, Bonn and his colleagues showed that shaking aluminum beads, designed to have the same density as human beings, would partially, but never fully, submerge them. Since quicksand is twice as dense as water, the beads (and humans) only sink about halfway. Shaking or otherwise disturbing the quicksand liquefies it, increasing the downward flow of the beads by a factor of a million. This is how humans can get stuck in it. Since quicksand is often located near bodies of water, Bonn speculates that high tidal floods passing over individuals stuck in quicksand may have caused casualties incorrectly ascribed to sinking fully in it. Bonn says his conclusions apply to all kinds of quicksand. Nonetheless, the force required to lift a foot out of quicksand can be equal to that required to raise a car. His solution: wiggling the stuck foot will cause water to trickle down, allowing the hapless adventurer to get out of it. (Khaldoun et al., Nature, September 29, 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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