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由于高温超导材料的临界温度较高,可以运行在一个较宽的温度范围内,因此高温超导磁体被看作是稳定性较好的磁体,它在超导电力、超导磁体方面的应用占着日益重要的地位.YBCO带材作为第二代高温超导体的代表,近年来其生产工艺水平也得到了迅速发展和提高.磁体失超是影响超导磁体运行稳定性的重要问题之一.本文研究了YBCO单饼线圈在液氮环境中因由热扰动诱发的失超特性,设计了一套高温超导线圈在液氮浸泡下的失超测量系统,通过软件LABVIEW和数据采集卡对线圈的温度和电压进行采集和记录,测量YBCO单饼线圈在不同运行条件下的失超特性. 相似文献
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高温超导体的交流损耗直接影响超导电力装置的运行成本和稳定性,是判断超导电力设备设计是否合理的重要特性之一.在阐述准各向同性高温超导股线结构特点的基础上,首先对准各向同性高温超导股线的交流损耗和磁滞损耗进行仿真研究,利用有限元软件Comsol Multiphysics分析了交流背景磁场下的损耗,然后在对光纤布拉格光栅(optical fiber Bragg grating,简称FBG)波长与损耗关系标定的基础上,使用光纤布拉格光栅测量交流背景磁场下的交流损耗.理论计算与实验结果相吻合,表明在工频和液氮温度下股线的交流损耗以磁滞损耗为主. 相似文献
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YBCO线圈的交流损耗直接关系到YBCO设备的运行成本及稳定性。实现对YBCO线圈交流损耗的快速、准确测量,对于开展YBCO涂层导体的应用研究具有重要的意义。文中采用电测量法,在77K、零场和不同频率条件下,对YBCO线圈通以不同运行电流时产生的交流传输损耗进行测量。构建了YBCO线圈交流损耗的数值计算模型,对YBCO线圈交流损耗进行理论研究,最后将实验数据与理论计算结果进行比较,两者结果基本一致。可以发现,YBCO线圈在频率低于75Hz时,交流传输损耗随频率的增大而减小,当频率从75Hz增加到195Hz时,交流传输损耗随频率的增大而增加。 相似文献
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Due to the deformation of electronic charge clouds, the Dick-Overhauser exchange charge in ionic materials is shown to have quadratic temperature dependence as T tends to zero in non-centrosymmetric crystals. It follows that the pyroelectric coefficient π has a linear temperature dependence in the same low temperature limit. The order of magnitude of π obtained theoretically by a simple model at T = 5 K is 2 × 10?7 μC cm?2 K?1, which is in fairly good agreement with that obtained experimentally on LiTaO3 by Lines. 相似文献
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Arthur Komar 《General Relativity and Gravitation》1995,27(11):1185-1206
A measurement theory for the temperature of relativistic systems is developed. The resulting operational approach is shown to be quasi-local and therefore may be applicable in general Riemannian manifolds even when there are temperature gradients which induce heat flows. The surprising feature of our analysis is that it leads to a bifurcation of the temperature concept into two distinctly different measurable quantities: one a frame invariant scalar field which a local co-moving observer would tend to identify with the local temperature and employ in the definition of entropy, the other a frame dependent, but nevertheless locally determinable quantity which governs the flow of heat and the ability to extract work. The two quantities differ by the bookkeeping methodology employed to calibrate the thermometer. A simple relationship between the two temperatures can be established if a preferred Killing vector field is available in the Riemannian manifold. 相似文献
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A. H. Cai X. Xiong Y. Liu H. Chen W. K. An X. S. Li Y. Zhou Y. Luo 《The European Physical Journal B - Condensed Matter and Complex Systems》2008,64(2):147-151
We propose expressions for the estimation of the isenthalpic temperature T
0 (T
0 = αT
m
, α is a semi-empirical parameter and 0 ⩽ α < 1, T
m
is the solidus temperature) and the Kauzmann temperature T
k
(T
k
= T
m
exp(α−1)) for glass forming alloys. It is found that T
k
estimated by T
k
= T
m
exp(α−1) is in agreement with that directly calculated from the heat capacity data, indicating that T
k
= T
m
exp(α − 1) can be used to estimate T
k
of glass forming alloys. T
0 estimated by T
0 = αT
m
, on the other hand, widely deviates from that of directly calculated from the heat capacity data. This suggests that the
enthalpy difference of the under-cooled liquid and the crystal might be a nonlinear function of the temperature below T
k
. Moreover, the Gibbs free energy difference ΔG is not sensitive to the deviation of α. 相似文献
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Non-equilibrium carrier distributions were obtained in CdS at various temperatures from 77 to 400K. A study is made of the influence of the lattice temperature on the carrier temperature. It is found that the higher the lattice temperature the lower is the difference between carrier and lattice temperatures, though carriers are always thermalized among themselves. The results can be accounted for by carrier relaxation through optical polar phonon emission. 相似文献
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《Physica A》2005,358(1):49-57
The expressions for the nonequilibrium temperature derived from the fluctuation–dissipation theorem and from the differential of the informational nonequilibrium entropy for ideal gases under shear flow are compared. Both temperatures are different, in particular, the thermodynamic temperature derived from the entropy is lower than the local-equilibrium temperature, whereas the effective temperature defined from the fluctuation–dissipation expression is higher than the local-equilibrium temperature. 相似文献
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Ying Lu Zuying Zhang Wei Guo 《International Journal of Infrared and Millimeter Waves》1996,17(9):1567-1571
Based on the transmission-line theory, this paper describes a new procedure to calculate the radiation from layered media with nonuniform temperature profile. The result is compared with those obtained through the incoherent method and the analysis of the electromagnetic fields. 相似文献
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The transit times of ultrasonic waves have been measured in single crystal NbO2 from 295 K down to 1.5 K for quasilongitudinal and shear waves propagating in the [100] direction and down to 160 K for eight other waves. Values are obtained for the C44 elastic constant and for an elastic constant combination which is approximately equal to C11 for temperatures down to 1.5 K and for C11, C12, C13, C16, C33, and C66 down to 160 K. These results are used to deduce 0 K values for the elastic constants and an elastic Debye temperature of 596 ± 7 K at 1.5 K. The acoustic mode heat capacity calculated from the latter is significantly smaller than the heat capacity measured by Wenger and Keesom at low temperatures. Following Wenger and Keesom, the difference is attributed to phasons (excitations involving the phase modulation of charge density waves). An average velocity is deduced for the phasons. 相似文献