Hanging by a magnetic thread.Hanging by a magnetic thread The sight of a superconducting pellet floating above the surface of a magnet is a striking demonstration that superconductors repel magnets. Now two research groups report that it's possible to suspend a superconducting pellet below or to either side of a magnet (see photo). The observation of this unusual type of levitation levitation (lĕvĭtā`shən), the raising of a human or other body in the air without mechanical aid. The idea is ancient; holy men, both pagan and Christian, were reputed to have had the power of becoming light at will and of moving suggests the presence of an attractive force in addition to the normal repulsive interaction between superconductors and magnets. "It's a curious and interesting effect," says Allen M. Hermann of the University of Arkansas The University of Arkansas strives to be known as a "nationally competitive, student-centered research university serving Arkansas and the world." The school recently completed its "Campaign for the 21st Century," in which the university raised more than $1 billion for the school, used in Fayetteville. Hermann and his colleagues demonstrated the effect in a thallium-based superconducting compound (SN: 4/2/88, p.213). A team including scientists from NASA's Marshall Space Flight Center The George C. Marshall Space Flight Center (MSFC), the original home of NASA, is a lead center for propulsion, Space Shuttle propulsion, Shuttle external fuel tank, crew training and payloads, International Space Station (ISS) design and construction, for computers, networks, and in Huntsville, Ala., has observed similar behavior in a superconductor A material that has little resistance to the flow of electricity. Traditional superconductors operate at absolute zero (-459.67 degrees Fahrenheit or -273.15 degrees Celsius). Experiments in the 1980s raised the temperature to -321 degrees Fahrenheit. made from yttrium-barium-copper oxide mixed with silver oxide. Both groups will report their findings in APPLIED PHYSICS LETTERS Applied Physics Letters is a weekly peer-reviewed scientific journal published by the American Institute of Physics devoted to the publication of new experimental and theoretical papers about applications of physics to science, engineering, and modern technology. . The unusual levitation effect appears to arise because the magnet's field penetrates certain types of superconductors, generating currents within the material. However, because the superconducting material contains impurities, these currents and the magnetic field they generate somehow become trapped. Hence, the superconductor retains this induced magnetic field. With a magnet nearby, the result is both an attractive and a repulsive interaction that combine to keep the superconductor a certain distance away from the magnet. "To calculate that effect and make it a quantitative explanation is extremely difficult and probably impossible," says Hermann. "It's not so much a question of computational difficulty. It's that we don't know Don't know (DK, DKed) "Don't know the trade." A Street expression used whenever one party lacks knowledge of a trade or receives conflicting instructions from the other party. the configuration of how the [magnetic field] threads itself around inside the superconductor." |
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