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【正文】 ansitions into the superconducting state ejection of magic field lines ?The occurrence of the Meissner effect indicates that superconductivity cannot be understood simply as the idealization of perfect conductivity in classical physics. ?The electrical resistivity of a metallic conductor decreases gradually as temperature is lowered. In ordinary conductors, such as copper or silver, this decrease is limited by impurities（ 雜質(zhì) ） and other defects（ 缺陷 ） . Even near absolute zero, a real sample of a normal conductor shows some resistance. In a superconductor, the resistance drops abruptly to zero when the material is cooled below its critical temperature. critical temperature Tc， critical magic field Hc， critical current Jc（ 臨界溫度 、 臨界磁場(chǎng) 、 臨界電流密度 ） the characteristics of superconductivity disappear when the temperature Tc is higher than the critical temperature Tc。 or higher than the critical magic field Hc, critical current Jc ,the regions separateed by Tc、 Hc， Jc. Josephson effect（約瑟夫森效應(yīng)） The Josephson effect is the phenomenon of supercurrent—. a current that flows indefinitely（ 無(wú)限期的 ） long without any voltage applied—across a device known as a Josephson junction (JJ), which consists of two superconductors coupled by a weak link. ? The weak link can consist of a thin insulating barrier (known as a superconductor–insulator–superconductor junction, or SIS), a short section of nonsuperconducting metal (SNS), or a physical constriction that weakens the superconductivity at the point of contact (SsS). development of superconductor 77 K ?By material: ? chemical elements ? alloys ? ceramics ? anic superconductors Applications ?Superconducting mags(超導(dǎo)磁體 ) are some of the most powerful electromags(電磁鐵 ) known. They are used in Magic Resonance Imaging(MRI， 磁共振成像 ) /nuclear magic resonance(NMR， 核磁共振成像 ) machines, mass spectrometers(質(zhì)譜儀 ), and the beamsteering mags (光束轉(zhuǎn)向磁體 )used in particle accelerators(粒子加速器 ). 粒子加速器 內(nèi)部溫度： 4萬(wàn)億攝氏度 工作溫度是 ℃ ，比外太空還冷 ?In the 1950s and 1960s, superconductors were used to build experimental digital puters using cryotron switches（ 低溫開(kāi)關(guān) ） . More recently, superconductors have been used to make digital circuits based on rapid single flux quantum （ 快速單量子通量 ） technology and RF （ radio frequency， 無(wú)線電頻率 ） and microwave filters（ 微波過(guò)濾器 ） for mobile phone base stations. ?Superconductors are used to build Josephson junctions which are the building blocks of SQUIDs (superconducting quantum interference devices), the most sensitive magometers（ 磁力計(jì) ） known. ?SQUIDs are used in scanning SQUID microscopes and magoencephalography（ 腦磁圖 ） ?highperformance smart grid（ 智能電網(wǎng) ） , electric
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