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171.
172.
非简并拉曼过程中交流斯塔克位移对原子反转的影响 总被引:2,自引:0,他引:2
利用修正后的有效哈密顿量计算非简拉曼过程中原子反转的演化,并研究交流斯塔克位移对拉比振荡崩溃和再生的影响。结果发现:交流斯克位移的存在使得非简并拉曼过程中原子反转的崩溃与再生现象呈现较好的周期性,并且拉比振荡的频率和幅均受交流斯塔克位移的影响。 相似文献
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T. Yazawa J. J. Rabbers B. ten Haken H. H. J. ten Kate Y. Yamada 《Physica C: Superconductivity and its Applications》1998,310(1-4):36-41
The current density distribution of high temperature superconducting (HTS) tapes is modeled for the combined case of an alternating self and applied magnetic field. This numerical analysis is based on the two-dimensional Poisson equation for the vector potential. A one-dimensional current (z-direction) and a one-dimensional applied field (y-direction) are assumed. The vector potential is rewritten into an equation of motion for the current density J(x,y,t). The model covers the finite thickness of the conductor and an n-power E–J relation. The magnetic field dependence of Jc is also included in this E–J relation. A time-dependent two-dimensional current distribution that is influenced by the aspect ratio of the conductor and the material properties in E=f(J,B) is calculated numerically. The numerical results are compared with the experimental results for the AC loss of a tape driven by a transport current. Finally, a total AC loss factor is given for two cases in magnetic field direction, perpendicular and parallel to the conductor broad side. 相似文献
176.
Svetlomir Stavrev Bertrand Dutoit 《Physica C: Superconductivity and its Applications》1998,310(1-4):86-89
The AC self-field loss in Bi(2223)Ag-sheathed tapes with different number of filaments has been measured between 59 and 2500 Hz by means of a dual lock-in amplifier. Due to the wide frequency range of the measurements, we have been able to dissociate quantitatively the different self-field loss contributions: hysteretic, eddy current and resistive loss (near Ic). This is an important advantage compared to single frequency measurements where such loss dissociation is only qualitative. The hysteresis losses of the different tapes fall between Norris' predictions for elliptical and strip cross-section. The relative weight of eddy current loss is found to be inversely proportional to the current ratio—the higher the i, the less is their contribution. Frequency-independent resistive loss due to flux-creep is observed for high currents at low frequencies; this loss becomes quickly negligible with the increasing frequency. 相似文献
177.
利用固相反应法制备了名义成分为Ca(Mn2Cu1)Mn4O12的类钙钛矿锰氧化物.x射线衍射表明,为了获得较为致密的样品和减小杂相含量,可以采用高温烧结再在1073K长时间空气中退火的制备方法.样品在低温下同时存在铁磁相和反铁磁相,由于反铁磁相的存在导致样品在4.5K时的磁化强度显著降低,并在8T的高磁场下仍未达到饱和.样品呈半导体导电性质,在85K和6T磁场下磁电阻比的最大值可达-46%.
关键词:
[AC3](B4)O12类钙钛矿锰氧化物
庞磁电阻效应
铁磁性
反铁磁性 相似文献
178.
The phenomenological model of the track formation processes during a heavy ion passing through materials is discussed. This model is based on the scanning tunneling and electronic microscopy investigations of diamond single crystals and stainless steel subjected to 40Ar, 84Kr and 129Xe ion irradiation with energies in the MeV region. The energy and temperature criteria when crater formation on the surface during the heavy ion irradiation takes place are introduced. 相似文献
179.
The current method for modelling magnetic core coils involves the use of an ohmic resistance connected in parallel to the ideal inductance to describe the related hysteresis and eddy-current losses. 相似文献
180.
M. P. Oomen J. Rieger M. Leghissa B. Fischer Th. Arndt 《Physica C: Superconductivity and its Applications》1998,310(1-4):137-141
In AC power-engineering applications, a large part of the AC loss in the superconductor is due to magnetization by the external field. This magnetic AC loss has been well described for the low-Tc conductors. In Bi-2223 tapes the picture is different due to strong anisotropy, granularity and flux creep. Magnetic AC loss in various twisted and non-twisted Bi-2223 tapes has been measured at power frequencies by a pickup method. The results are compared to theoretical models of magnetization loss. When the field is parallel to the tape plane, the filaments in twisted tapes can be decoupled and the AC loss is decreased even when the matrix is pure silver. The extra effect of higher-resistance matrix materials is studied. In perpendicular field it is more difficult to decouple the filaments, due to the particular tape geometry. Contrary to a wire, there are essential differences between the AC loss mechanisms in a long twisted tape and those in a short piece of non-twisted tape. Finally, the dynamic resistance caused by the AC magnetic field is examined. 相似文献