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81.
加强农村广播电视的发展,提高其覆盖率是关键,针对这一问题,阐述了解决农村广播电视覆盖的手段,对农村广播电视覆盖现状做了详细的分析,并提出建议和措施。 相似文献
82.
83.
正向设计了一种适合于听觉神经刺激的可编程双相恒流脉冲发生器,它可根据耳聋患者的要求和不同的语音信号,控制刺激电流脉冲的幅度和宽度,以及脉冲之间的间隙。本文阐述了电路的设计要求和方法,并给出了实验结果。采用标准3μmp阱CMOS工艺,在上海贝岭微电子制造有限公司流片。目前已成功地用于多道人工电子耳蜗接收刺激器中。 相似文献
84.
85.
A. N. Iyer U. Balachandran L. R. Motowidlo J. G. Hoehn P. Haldar 《Journal of Electronic Materials》1994,23(11):1087-1091
Pb0.4Bi1.8Sr2Ca2.2Cu3Ox (Bi-2223) precursor powder was prepared by a solid-state reaction of carbonates and oxides of lead, bismuth, strontium, calcium,
and copper, and the powder was then used to fabricate silver-clad tapes by the powder-in-tube technique. Transport critical
current density (Jc) values>4×104 A/cm2 at 77K and 2×105 A/cm2 at 4.2 and 27K have been achieved in short tape samples. Long lengths of tape were tested by winding them into pancake coils.
Recently, we fabricated a test magnet by stacking ten pancake coils, each containing three 16m lengths of rolled tape, and
tested it at 4.2, 27 and 77K. A maximum generated field of 2.6 T was measured in zero applied field at 4.2K and the test magnet
generated significant self-field in background fields up to 20 T. The results are discussed in this paper. 相似文献
86.
A. Goyal E. D. Specht Z. L. Wang D. M. Kroeger J. A. Sutliff J. E. Tkaczyk J. A. Deluca L. Masur G. N. Riley 《Journal of Electronic Materials》1994,23(11):1191-1197
Microstructural origins for reduced weak-link behavior in high-Jc melt-processed YBCO, spray pyrolyzed thick films of Tl-1223, metallic precursor Y-124 polycrystalline powder-in-tube (PIT)
wires and PIT Bi-2212/2223 are discussed. Since the materials studied are the highest Jc, polycrystalline, high-Tc superconductors fabricated worldwide, the results provide important guidelines for further improvements in superconducting
properties, thereby enabling practical applications of these materials. It is found that strongly linked current flow within
domains of melt-processed 123 occurs effectively through a single crystal path. In c-axis oriented, polycrystalline Tl-1223
thick films, local in-plane texture has been found to play a crucial role in the reduced weak-link behavior. Formation of
“colonies” of grains with a common c-axis and modest in-plane misorientation was observed. Furthermore, a colony boundary
in general has a varying misorientation along the boundary. Large regions comprised primarily of low angle boundaries were
observed. Percolative transport through a network of such small angle boundaries appears to provide the nonweak-linked current
path. Although powder-in-tube BSCCO 2212 and 2223 also appear to have a “colony” microstructure, there are some important
differences. Colonies in BSCCO consist of stacks of grains with similar c-axis orientation in contrast to colonies in Tl-1223
films where few grains are stacked on top of one another. Furthermore, most grains within a colony in BSCCO have the same
lateral dimensions as that of the colony, resulting largely largely in “twist” boundaries. Further microstructural characterization
of high-Jc PIT 2212 and 2223 is currently underway. In the case of Y-124 wires, weak macroscopic in-plane texture is found. Additional
measurements are underway to determine if a sharper, local in-plane texture also exists. It is found that in three of the
four types of superconductors studied, reduced weak-link behavior can be ascribed to some degree of biaxial alignment between
grains, either on a “local” or a “global” scale. 相似文献
87.
88.
近年来,大电流的监测成了人们十分关心的问题,这是由于大电流有强磁、高压、电流大等一系列的直接监测所不能克服的问题。这就需要把高压大电流的强电信号,经过提取后变成能在实验室中直接观测的弱电信号。为此,如何从高压大电流的信号中提取出随实时信号变化而实时变化的小信号就变成了一个关键问题。详细介绍了监测信号提取的光收发电路原理和后续信号处理电路,分析了各部分的作用,给出了必要的分析结果。 相似文献
89.
90.
Yang Lingxia Ge Debiao Wei Bing 《International Journal of Infrared and Millimeter Waves》2003,24(11):1893-1897
A modified formulation for fringe component of diffraction coefficient is implemented to TD-EEC method. An example of diffraction by perfectly conducting plate is used to illustrate our scheme. Comparing with the FDTD results we observe that the improved expression for fringe component is more accurate than that of Michaeli's formulation. This high frequency time domain technique is available for treating the bistatic scattering problems for millimeter waves. 相似文献