Physics News Update 662 (fwd)
-- Forwarded message -- Date: Tue, 18 Nov 2003 11:34:46 -0500 From: [EMAIL PROTECTED] To: [EMAIL PROTECTED] Subject: Physics News Update 662 PHYSICS NEWS UPDATE The American Institute of Physics Bulletin of Physics News Number 662 November 18, 2003 by Phillip F. Schewe, Ben Stein, and James Riordon A LIQUID WALL IN A FUSION ENERGY DEVICE has improved the performance [SSZ: text deleted] ELECTRON SPINS CAN CONTROL NUCLEAR SPINS in a semiconductor when trapped in a very confined space, a recent experimental development which calls upon laser science, solid-state physics, and nuclear magnetic resonance. David Awschalom and his colleagues at the Center for Spintronics and Quantum Computation at UC Santa Barbara begin by lithographically creating a quantum well, an extremely thin, practically two-dimensional region inside a semiconductor capable of trapping electrons. First, a laser pulse injects polarized electrons (their spins have a definite orientation determined by the laser's polarization) into the well. Once in the well, the tiny disk of electrons (with a radius of about 20 microns but a thickness of only 20 nm) can be controllably moved along one axis, much as an abacus bead can be slid along a wire, by simply changing a voltage. In this case, the disk can be positioned with nm-accuracy. The nuclei of atoms residing within the thin volume occupied by the spin-polarized electrons will in turn be polarized; that is, the spin of these nuclei will tend to align themselves with the spin of the electrons. The result is an extremely thin region---equivalent to the thickness of several tens of atoms--- of polarized nuclei which can be precisely positioned by changing a single voltage. These thin sheets of nuclear polarization could constitute the basic elements of an information storage device in which nuclear spin determines the logical state of the system. One may ask, why not take out the "middle man" and just use the electron spin to encode information? The answer: nuclear spins have a weaker interaction with the surrounding environment than electron spins. While harder to flip, once oriented, nuclear spins preserve their state longer than do electrons. One may also wonder, why not just use some large magnet to orient the nuclear spins? Why use electrons as intermediaries? The answer: all-electronic control of spin is desirable because electric fields are so much easier to control and create on a small scale than magnetic fields. They are scalable and easy to implement, while it is notoriously hard to produce large and localized magnetic fields. In addition, all of our current integrated circuit technology is based on charge and electric field; it would certainly be helpful to manipulate spin using "knobs" which are well developed and familiar to engineers. Awschalom ([EMAIL PROTECTED], 805-893-2121) believes this current result is the first step toward the establishment of an all-electrical manipulation of countable numbers of nuclear spins.(Poggio et al., Physical Review Letters, 14 November 2003) *** 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. AUTO-SUBSCRIPTION OR DELETION: By using the expression "subscribe physnews" in your e-mail message, you will have automatically added the address from which your message was sent to the distribution list for Physics News Update. If you use the "signoff physnews" expression in your e-mail message, the address in your message header will be deleted from the distribution list. Please send your message to: [EMAIL PROTECTED] (Leave the "Subject:" line blank.)
News update
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Physics News Update 619 (fwd)
-- Forwarded message -- Date: Fri, 3 Jan 2003 12:37:30 -0500 From: [EMAIL PROTECTED] To: [EMAIL PROTECTED] Subject: Physics News Update 619 PHYSICS NEWS UPDATE The American Institute of Physics Bulletin of Physics News Number 619 January 3, 2003 by Phillip F. Schewe, Ben Stein, and James Riordon X-RATED INTERFEROMETRY. The appearance of an x-ray interference pattern in [SSZ: text deleted] FEASIBLE CHAOTIC ENCRYPTION. Encryption schemes that hide messages in chaotic signals have attracted attention in recent years as a means to transmit information securely (Update 170, 361), but most work has been either theoretical or strictly limited to laboratory experiments. Now a group of researchers in Beijing have managed to demonstrate chaotically encrypted, two-way voice transmission through the Beijing Normal University computer network. With a 32-bit encryption structure, a 750 MHz personal computer can encode information at speeds comparable to the widely recognized Advanced Encryption Standard, and support voice communication at typical telephone speeds and quality. While no encryption technique is absolutely impenetrable, the researchers (Hu Gang, Beijing Normal University, [EMAIL PROTECTED], 86-10-62208420) explain that their communication scheme is reasonably secure (it would take an intruder armed with a personal computer more than a million times the lifetime of the universe to break the code) as well as being feasible in realistic, commercial settings. (S. Wang et al., Physical Review E, December 2002.) *** 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. AUTO-SUBSCRIPTION OR DELETION: By using the expression "subscribe physnews" in your e-mail message, you will have automatically added the address from which your message was sent to the distribution list for Physics News Update. If you use the "signoff physnews" expression in your e-mail message, the address in your message header will be deleted from the distribution list. Please send your message to: [EMAIL PROTECTED] (Leave the "Subject:" line blank.)
Physics News Update 618 (fwd)
-- Forwarded message -- Date: Mon, 23 Dec 2002 11:16:47 -0500 From: [EMAIL PROTECTED] To: [EMAIL PROTECTED] Subject: Physics News Update 618 PHYSICS NEWS UPDATE The American Institute of Physics Bulletin of Physics News Number 618 December 23, 2002 by Phillip F. Schewe, Ben Stein, and James Riordon TUNING CARBON NANOTUBE RESONANCE FREQUENCIES can be achieved by varying a [SSZ: Text deleted] QUANTUM SIMULATIONS WITH CONTINUOUS VARIABLES. Furthering efforts to answer hard-to-test questions about the quantum world, a NIST ion-trap computer can now simulate how the unique rules of quantum mechanics can affect a microscopic particle's "continuous variables," quantities such as position and momentum which can have a smooth continuum of values. Acting as a form of quantum computer, the NIST ion trap might only need a couple of seconds to simulate a quantum physics experiment that can take days to carry out. Moreover, the ion trap can simulate experiments that require rare commodities, like entangled photons, which are created relatively infrequently. Since quantum computers embrace the unusual logic of the microscopic world, they can perform powerful simulations of its often counterintuitive phenomena. First envisioned by Richard Feynman, quantum simulators are perhaps the earliest practical application of quantum computing--in fact, they have been around for several years now. However, previous versions (Update 438, http://www.aip.org/enews/physnews/1999/split/pnu438-2.htm ) have only re-created quantum phenomena involving "discrete variables," such as an electron's energy in an atom, which can only have certain prescribed values. The new version recreates quantum processes involving both discrete and continuous variables. To construct their simulator, NIST researchers in Colorado trap a single beryllium-9 ion with electric fields. As the ion vibrates in the trap, its position and momentum are continuous. This allows the researchers to easily simulate any other complementary pair of continuous variables-such as an electric field's amplitude and phase-which have the exact same mathematical interrelationship. To perform simulations, the researchers shine a series of carefully engineered light pulses on the ion. The pulses cause the ion to act like something it's not, such as an electron bound by an atom, or even a photon as it hits a beamsplitter. Under the influence of the pulses, the ion's quantum states evolve in a way identical to the situation the researchers want to study. For now, the researchers have performed simple, proof-of-principle demonstrations. As an example, they have investigated how a photon would behave if entangled with other photons by sending it through a beamsplitter. Shining light pulses on the ion to simulate the effects of a beamsplitter on a photon, the researchers have demonstrated that interferometry with up to three other entangled photons would be three times as precise as interferometers using single photons, in line with the recent experimental results on bi-photon interferometry (Update 613, http://www.aip.org/enews/physnews/2002/split/613-1.html ). (Leibfried et al, Physical Review Letters, 9 December 2002; Dietrich Leibfried, 303-497-7880, [EMAIL PROTECTED]) PRL CHANGES ITS PUBLICATION DATES. Instead of appearing on Monday each week, the print version of Physical Review Letters will now appear on Friday. The print issue will comprise all the articles that were published online during that week. It had already been the case for more than a year that online publication marked the official publication date for each article, and so the new print-version schedule does not affect this policy. (http://prl.aps.org/edannounce/PRLv89i26.html ) *** 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. AUTO-SUBSCRIPTION OR DELETION: By using the expression "subscribe physnews" in your e-mail message, you will have automatically added the address from which your message was sent to the distribution list for Physics News Update. If you use the "signoff physnews" expression in your e-mail message, the address in your message header will be deleted from the distribution list. Please send your message to: [EMAIL PROTECTED] (Leave the "Subject:" line blank.)
AIP News Update: update.582 (fwd)
-- Forwarded message -- Date: Tue, 26 Mar 2002 13:46:24 -0500 (EST) From: AIP listserver <[EMAIL PROTECTED]> To: [EMAIL PROTECTED] Subject: update.582 PHYSICS NEWS UPDATE The American Institute of Physics Bulletin of Physics News Number 582 March 26, 2002 by Phillip F. Schewe, Ben Stein, and James Riordon MICRO-TESLA MRI was reported at last week's APS March meeting in Indianapolis by Robert McDermott, a member of John Clarke's group at UC Berkeley. The principle behind MRI is nuclear magnetic resonance (NMR), a process in which a magnetic field (often a strong one), is used to orient atomic nuclei in space while a burst of radio waves explores the nuclear energy levels by charting the frequencies at which energy is absorbed resonantly. In addition to establishing chemical identity NMR can also be turned into an imaging method by carefully watching the timing and the location of the re-emitted radio waves. A tumor, say, will have a slightly different water density (as revealed, in this case, by the presence of protons in the NMR survey) from surrounding healthy tissue. Computer processing and contrast enhancement will disclose the tumor's position to a trained observer. Generally large magnets are required to produce sharp NMR images, and the development of a low-field version would benefit medical and scientific studies. McDermott reported an experiment in which an array of four columns of fluid were imaged with a field of 10 micro-Tesla over the period of several hours. (See also McDermott et al., Science 22 March 2002.) Also at the APS meeting, Mark Haacke of the MRI Institute for Biomedical Imaging in St. Louis (314-961-9105, [EMAIL PROTECTED]) discussed a new MRI technique called susceptibility weighted imaging (SWI). The technique measures differences among brain tissue in its magnetic susceptibility, essentially its magnetic response to the applied magnetic field of the MRI machine. Yielding unique information from veins and blood products, SWI has already provided more sharply detailed MRI images of blood vessels in the brain than previously possible and the presence of small hemorrhages in heretofore unavailable detail. SWI can potentially detect angiogenesis, the growth of blood vessels caused by cancer, and may improve diagnosis of Parkinson's and Alzheimer's diseases, through its ability to monitor iron deposits in the brain. ELECTRICAL MEASUREMENTS OF INDIVIDUAL LIVING CELLS [SSZ: Text deleted] ATOMIC FORCE MICROSCOPY YIELDS 3D PROTEIN STRUCTURE. Despite its name, atomic force microscopy (AFM) does not produce atomic-resolution images of proteins or other large molecules. When imaging macromolecules, a large region, about 100 square nanometers, of the AFM tip makes contact with the molecule. This region is comparable in size to the entire molecule and makes the tip a blunt probe by atomic standards. To extract more detailed information from AFM images of macromolecules, one can directly subtract the effects of the tip but the results are often inaccurate. At the March APS Meeting, Steven Eppell and Brian Todd of Case Western Reserve University (216-368-4067, [EMAIL PROTECTED]) presented a new technique for obtaining submolecular information about proteins. Investigating aggrecan, a cartilage protein important in osteoarthritis, the researchers used a technique that combined AFM with genome information and transmission electron microscopy data. All of the data were integrated by using a sophisticated image processing technique to provide a best guess at the 3D structure. The resulting refined structure yielded new information on the molecule, showing distinct locations of kinks as well as regions of mechanical flexibility. The researchers hope to combine their results with AFM-measured force fields around cartilage proteins to link the biological and mechanical properties of cartilage with its molecular structure. This approach has the potential to provide information on molecular-scale mechanisms for arthritis and lead to intelligent drug design and other interventions to prevent or alleviate the disease.
