August 29, 2011
Physics News Highlights of the American Institute of Physics (AIP) contains summaries of interesting research from the AIP journals, notices of upcoming meetings, and other information from the AIP Member Societies. Copies of papers are available to journalists upon request.
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TOPICS IN THIS ISSUE:
1. Scientists put a new spin on traditional information technology
Sending information by varying the properties of electromagnetic waves has served humanity well for more than a century, but as our electronic chips steadily shrink, the signals they carry can bleed across wires and interfere with each other, presenting a barrier to further size reductions. A possible solution could be to encode ones and zeros, not with voltage, but with electron spin, and researchers have now quantified some of the benefits this fresh approach might yield. In a paper in the AIP’s journal Applied Physics Letters, a team from the University of Rochester and the University of Buffalo has proposed a new communications scheme that would use silicon wires carrying a constant current to drive electrons from a transmitter to a receiver. By changing its magnetization, a contact would inject electron spin (either up or down) into the current at the transmitter end. Over at the receiver end, a magnet would separate the current based on the spin, and a logic device would register either a one or a zero. The researchers chose silicon wires because silicon’s electrons hold onto their spin for longer than other semiconductors. The team calculated the bandwidth and power consumption of a model spin-communication circuit, and found it would transmit more information and use less power than circuits using existing techniques. The researchers did find that the latency, or the time it takes information to travel from transmitter to receiver, was longer for the spin-communication circuit, but its other benefits mean the new scheme may one day shape the design of many emerging technologies.
Article: “Silicon spin communication” is accepted for publication in Applied Physics Letters.
Authors: Hanan Dery (1,2), Yang Song (2), Pengke Li (1), and Igor Žutić (3).
(1) Department of Electrical and Computer Engineering, University of Rochester
2. Magnetic memories manipulated by voltage, not heat
In their search for smaller, faster information-storage devices, physicists have been exploring ways to encode magnetic data using electric fields. One advantage of this voltage-induced magnet control is that less power is needed to encode information than in a traditional system. But earlier this year, researchers reported that a key element of magnetization called coercivity is not controlled by voltage at all, but rather by an unfortunate byproduct of applying electricity to a material – that is, by heat. (Coercivity is the tendency of a magnetic material to resist becoming demagnetized.) To further explore whether voltage or heating is responsible for changes to a magnet’s coercivity, scientists from Tsinghua University in Beijing, China, tested three structures commonly used in magnetic memory experiments. Their verdict: It’s not the heat. In a paper accepted for publication in the AIP’s Journal of Applied Physics, the authors show that the voltage is directly controlling changes in the magnetic properties of all three of the tested materials. For example, the researchers demonstrate that the effect can be turned on and off almost instantaneously, whereas the changes should lag if heat is the cause. This is a good thing for the field, since a system that produces too much heat would slow down the performance of any real-world device made from this technology.
Article: “Switchable voltage control of the magnetic coercive field via magnetoelectric effect” is accepted for publication in the Journal of Applied Physics.
Authors: Jing Wang (1), Jing Ma (1), Zheng Li (1), Yang Shen (1), Yuanhua Lin (1), and C.W. Nan (1).
(1) Tsinghua University
3. New microscope might see beneath skin in 4-D
A new type of laser scanning confocal microscope (LSCM) holds the promise of diagnosing skin cancer in a single snapshot. Typical LSCMs take 3-D images of thick tissue samples by visualizing thin slices within that tissue one layer at a time. Sometimes scientists supplement these microscopes with spectrographs, which are devices that measure the pattern of wavelengths, or “colors,” in the light reflected off of a piece of tissue. This pattern of wavelengths acts like a fingerprint, which scientists can use to identify a particular substance within the sample. But the range of wavelengths used so far with these devices has been narrow, limiting their uses. Not so with the new microscope developed by physicists from the Consiglio Nazionale delle Ricerche (CNR) in Rome, and described in a paper accepted to the AIP’s new journal AIP Advances. Unlike other combination “confocal microscope plus spectrograph” devices, the new machine is able to gather the spectrographic information from every point in a sample, at a wide range of wavelengths, and in a single scan. To achieve this, the authors illuminate the sample with multiple colors of laser light at once – a sort of “laser rainbow” – that includes visible light as well as infrared. This allows scientists to gather a full range of information about the wavelengths of light reflected off of every point within the sample. Using this method, the researchers took high-resolution pictures of the edge of a silicon wafer and of metallic letters painted onto a piece of silicon less than half a millimeter wide. They also demonstrated that it is possible to apply this technique to a tissue sample (in this case, chicken skin) without destroying it. With further testing, the researchers say the microscope could be used to detect early signs of melanoma; until then, it may be useful for non-medical applications, such as inspecting the surface of semiconductors.
Article: “Supercontinuum ultra wide range confocal microscope for reflectance spectroscopy of living matter and material science surfaces” is accepted for publication in AIP Advances.
Authors: Stefano Selci (1), Francesca R. Bertani (1), and Luisa Ferrari (1).
(1) Instituto dei Sistemi Complessi, Consiglio Nazionale delle Ricerche, Rome
4. What was that again? A mathematical model of language incorporates the need for repetition
As politicians know, repetition is often key to getting your message across. Now a former physicist studying linguistics at the Polish Academy of Sciences has taken this intuitive concept and incorporated it into a mathematical model of human communication. In a paper in the AIP’s journal Chaos, Łukasz Dębowski mathematically explores the idea that as humans we often repeat ourselves in an effort to get the story to stick. Using statistical observations about the frequency and patterns of word choice in natural language, Dębowski develops a model that shows repetitive patterns emerging in large chunks of speech. Previous researchers have noted that long texts have more entropy, or uncertainty, than very brief statements. This tendency to higher entropy would seem to suggest that only through brevity could humans hope to build understanding – uttering short sentences that won’t confuse listeners with too much information. But as long texts continue to get longer, the increase in the entropy starts to level off. Dębowski connects this power-law growth of entropy to a similar power-law growth in the number of distinct words used in a text. The two concepts – entropy and vocabulary size – can be related by the idea that humans describe a random world, but in a highly repetitive way. Dębowski shows this by examining a block of text as a dynamic system that moves from randomness toward order through a series of repetitive steps. He theorizes that if a text describes a given number of independent facts in a repetitive way then it must contain at least the same number of distinct words that occur in a related repetitive fashion. What this reveals is that language may be viewed as a system that fights a natural increase in entropy by slowly constructing a framework of repetitive words that enable humans to better grasp its meaning. For now the research is theoretical, but future work could experimentally test how closely it describes real texts, and maybe even candidates’ stump speeches.
(1) Institute of Computer Science, Polish Academy of Sciences
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