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排序方式: 共有1727条查询结果,搜索用时 15 毫秒
21.
A. Kiliç K. Kiliç H. Yetiş M. Olutaş A. Altinkok H. Sözeri O. Çetin 《The European Physical Journal B - Condensed Matter and Complex Systems》2006,50(4):565-569
The flux dynamics in a polycrystalline sample of
Bi1.7Pb0.3Sr2Ca2Cu3Ox with a macroscopic
cylindrical hole (CH) drilled was investigated by slow transport relaxation
(V-t curves) and magnetovoltage measurements (V-H curves). It was monitored that
there are several discontinuities in the time evolution of quenched state in
V-t curves, which was attributed to the leaving of quantized flux lines
trapped through CH together with surface superconducting effects. We
observed that asymmetric V-H curves demonstrate unusual remarkable counter
clockwise hysteresis effects upon cycling of field. This interesting result
was correlated mainly to the flux trapping inside the CH that acts as a
macroscopic attractive pinning center for flux lines. Further, the
hysteresis effects in V-H curves for a fixed transport current provide a direct
evidence that the number of flux lines, measured dissipation and relative
decrease/increase in irreversibilities could be determined by sweeping rate
of external magnetic field (dH/dt) which leads also to peculiar time effects. 相似文献
22.
23.
福布斯下降(Forbush decrease,FD)是银河宇宙线(galactic cosmic rays,GCRs)受短期剧烈太阳活动调制的重要现象之一.本文设GCRs进入由行星际日冕物质抛射(interplanetary coronal mass ejection,ICME)及其前沿激波共同形成的扰动区时,其径向扩散系数κ_(rr)受抑制变为μ(r)·κ_(rr)(0μ(r)1),且抑制强度与粒子位置处的太阳风等离子体速度正相关.对任意时刻的扰动区,抑制系数μ(r)在激波处最小为μ(r_(sh)),并按指数规律增大,在ICME尾部归一.CME爆发时,μ(r_(sh))取全局最小值μm.在扰动区向日球层外传播的过程中,μ(r_(sh))逐步恢复为1.在此基础上,根据GOES和ACE卫星观测确定模型参数,用一维随机微分方程描述GCRs在日球层内的传播,并采用倒向随机方法模拟了一个由独立Halo ICME调制GCRs引起的2005年5月15日FD事件.计算所得地面中子通量的主相、恢复相及其在CME到达地球前的增加过程,均与Oulu中子探测器观测结果一致. 相似文献
24.
Variable fluid properties and variable heat flux effects on the flow and heat transfer in a non-Newtonian Maxwell fluid over an unsteady stretching sheet with slip velocity 下载免费PDF全文
Ahmed M. Megahed 《中国物理 B》2013,(9):480-485
The effects of variable fluid properties and variable heat flux on the flow and heat transfer of a non-Newtonian Maxwell fluid over an unsteady stretching sheet in the presence of slip velocity have been studied. The governing differential equations are transformed into a set of coupled non-linear ordinary differential equations and then solved with a numerical technique using appropriate boundary conditions for various physical parameters. The numerical solution for the governing non-linear boundary value problem is based on applying the fourth-order Runge-Kutta method coupled with the shooting technique over the entire range of physical parameters. The effects of various parameters like the viscosity parameter, thermal conductivity parameter, unsteadiness parameter, slip velocity parameter, the Deborah number, and the Prandtl number on the flow and temperature profiles as well as on the local skin-friction coefficient and the local Nusselt number are presented and discussed. Comparison of numerical results is made with the earlier published results under limiting cases. 相似文献
25.
Heat transfer in boundary layer stagnation-point flow towards a shrinking sheet with non-uniform heat flux 下载免费PDF全文
Krishnendu Bhattacharyya 《中国物理 B》2013,(7):328-333
In this paper, the effect of non-uniform heat flux on heat transfer in boundary layer stagnation-point flow over a shrinking sheet is studied. The variable boundary heat fluxes are considered of two types: direct power-law variation with the distance along the sheet and inverse power-law variation with the distance. The governing partial differential equations (PDEs) are transformed into non linear self-similar ordinary differential equations (ODEs) by similarity transformations, and then those are solved using very efficient shooting method. The direct variation and inverse variation of heat flux along the sheet have completely different effects on the temperature distribution. Moreover, the heat transfer characteristics in the presence of non-uniform heat flux for several values of physical parameters are also found to be interesting. 相似文献
26.
27.
Pierre Gaspard 《Journal of statistical physics》1996,88(5-6):1215-1240
We describe a mechanism leading to positive entropy production in volume-preserving systems under nonequilibrium conditions.
We consider volume-preserving systems sustaining a diffusion process like the multibaker map or the Lorentz gas. A continuous
flux of particles is imposed across the system resulting in a steady gradient of concentration. In the limit where such flux
boundary conditions are imposed at arbitrarily separated boundaries for a fixed gradient, the invariant measure becomes singular.
For instance, in the multibaker map, the limit invariant measure has a cumulative function given in terms of the nondifferentiable
Takagi function. Because of this singularity of the invariant measure, the entropy must be defined as a coarse-grained entropy
instead of the fined-grained Gibbs entropy, which would require the existence of a regular measure with a density. The coarse-grained
entropy production is then shown to be asymptotically positive and, moreover, given by the entropy production expected from
irreversible thermodynamics. 相似文献
28.
本文用傅里叶及边缘泰勒展开的方法,导出了非圆截面托卡马克等离子体边缘磁面的解析解及其重构的方法。最后作为例子,给出了在TEXT-U装置中按实际参数重构的等离子体边缘磁面结构及重构的误差。 相似文献
29.
对于球解高对称性静磁场,如果仅应用安培环路定理和高斯定理,在解答中会存在一些不能唯一确定的常量,为了研究确定这些常量的规律,本讨论了穿过一个无限大平面的磁通量并用得到了一个有意义的结论。 相似文献
30.
Ke-Hui Song Zhen-Gang ShiShao-Hua Xiang Xiong-Wen Chen 《Physica B: Condensed Matter》2012,407(17):3596-3599
Based on superconducting flux qubits coupled to a superconducting resonator. We propose a scheme for implementing multi-qubit controlled-NOT (C-NOT) gates and Greenberger–Horne–Zeilinger (GHZ) state with one flux qubit simultaneously controlling on n qubits. It is shown that the resonator mode is initially in the vacuum state, a high fidelity for operation procedure can be obtained. In addition, the gate operation time is independent of the number of the qubits, and can be controlled by adjusting detuning and coupling strengths. We also analyze the experimental feasibility that the conditions of the large detuning can be achieved by adjusting frequencies of the resonator and pulses. 相似文献