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101.
102.
B. A. Albiss I. M. Obaidat M. Gharaibeh W. Hatamleh S. A. Barhoum M. K. Hasan 《Crystal Research and Technology》2009,44(9):930-936
The magnetic and transport properties of polycrystalline YBa2 (Cu1‐xMx)3 O7‐δ (M = B and Mn) superconductor was investigated. Samples of YBa2(Cu1‐xBx)3O7‐δ doped with several concentrations of boron B(x = 0.05 and 0.1) were investigated using magnetization measurements. A YBa2(Cu1‐xMnx)3O7‐δ sample doped with Mn with concentration of x = 0.02 was investigated using current‐voltage (I‐V) measurements. Our results on the YBa2(Cu1‐xBx)3O7‐δ samples reveal a considerable increase in the hysterisis width of the magnetization, M versus the applied magnetic field H with increasing boron concentration. The lower critical field was also found to be enhanced by boron doping. The critical current density, Jc was found to be significantly enhanced in the Mn‐doped sample. The enhancement of Jc was found to be more significant at the lower temperatures for all applied magnetic fields used (0 Oe, 300 Oe, and 500 Oe). Thus, chemical doping is suggested to enhance the vortex pinning forces in the YBCO samples. From the resistivity (R‐T) measurements, chemical doping of the samples was found to have no significant effect on the critical temperature, Tc. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
103.
The effect of magnetic field strength and orientation on two types of electromagnetically influenced turbulent flows was studied numerically under the Reynolds averaged Navier–Stokes (RANS) framework. Previous work (Wilson et al., 2014) used an electromagnetically extended linear eddy-viscosity model, whilst the current paper focuses on the performance of a more advanced Reynolds stress transport type model both with and without electromagnetic modifications proposed by Kenjereš et al. (2004). First, a fully-developed 2D channel flow is considered with a magnetic field imposed in either the wall-normal or streamwise direction. Both forms of the RSM gave good agreement with the DNS data for the wall-normal magnetic field across the range of Hartmann numbers with the additional electromagnetic terms providing a small, but noticeable, difference. For the streamwise magnetic field, where electromagnetic influence is only through the turbulence, the electromagnetically extended RSM performed well at moderate Hartmann numbers but returned laminar flow at the highest Hartmann number considered, contrary to the DNS. The RSM results were, however, significantly better than the previous eddy-viscosity model predictions. The second case is that of unsteady 3D Rayleigh–Bénard convection with a magnetic field imposed in either a horizontal or vertical direction. Results revealed that a significant reorganization of the flow structures is predicted to occur. For a vertically oriented magnetic field, the plume structures increase in number and become thinner and elongated along the magnetic field lines, leading to an increase in thermal mixing within the core in agreement with Hanjalić and Kenjereš (2000). With a horizontal magnetic field, the structures become two-dimensional and a striking realignment of the roll cells’ axes with the magnetic field lines occurs. The results demonstrate the capability of the Reynolds stress transport approach in modelling MHD flows that are relevant to industry and offer potential for those wishing to control levels of turbulence, heat transfer or concentration without recourse to mechanical means. 相似文献
104.
基于概率断裂力学理论和Mome Caflo模拟方法,本文进行了自紧身管临界裂纹尺寸的可靠性研究。自紧身管内表面的疲劳裂纹考虑为半椭圆形式。裂纹尖端处的应力强度因子由内压和自紧残余应力共同产生。自紧残余应力采用了符合身管材料具有强化和包辛格效应性能推导的公式计算,它产生的应力强度因子通过权函数方法得到。根据断裂准则,可计算出自紧身管的临界裂纹尺寸。实例分析表明,对数正态分布为临界裂纹尺寸的最佳分布,同时给出了在各种置信度和可靠度下自紧身管的临界裂纹尺寸。 相似文献
105.
通过对拱顶储罐罐壁承受轴向载荷、初始几何缺陷及轴压失稳状况研究,指出在固定顶罐设计、建造和运行各阶段都应进行罐壁轴压稳定性校核. 根据圆柱薄壳稳定性理论和轴压失稳临界应力数值分析计算结果,提出固定顶罐罐壁轴压稳定性校核方法和数学模型,并运用回归分析方法建立罐壁轴压失稳临界应力计算公式. 对几种常用规格的拱顶罐有初始挠度缺陷罐壁轴压稳定性分析表明：随储罐容积和罐壁初始挠度增大,罐壁轴压稳定性呈减弱趋势. 相似文献
106.
This paper presents a micromechanical study on the behavior of granular materials under confined shear using a three-dimensional Discrete Element Method （DEM）. We consider rotational resistance among spherical particles in the DEM code as an approximate way to account for the effect of particle shape. Under undrained shear, it is found rotational resistance may help to increase the shear strength of a granular system and to enhance its resistance to liquefaction. The evolution of internal structure and anisotropy in granular systems with different initial conditions depict a clear bimodal character which distinguishes two contact subnetworks. In the presence of rotational resistance, a good correlation is found between an analytical stress-force-fabric relation and the DEM results, in which the normal force anisotropy plays a dominant role. The unique properties of critical state and liquefaction state in relation to granular anisotropy are also explored and discussed. 相似文献
107.
M.M. Kassem 《ZAMM - Journal of Applied Mathematics and Mechanics / Zeitschrift für Angewandte Mathematik und Mechanik》2008,88(8):661-673
The heat and mass transfer of a non‐Newtonian fluid past a continuous moving vertical sheet subjected to constant heat flux is analyzed using the group similarity transformation method. The nonlinear coupled partial differential equation governing the flow and the boundary conditions are transformed to a system of ordinary differential equations with appropriate boundary conditions. Two cases for the external flow are analytically obtained during the transformation process. One is new; uw = x/t, while the other corresponds to Falkner–Skan case. For both cases the ordinary differential equations are solved numerically using the shooting method. The effect of Prandtl and Reynolds numbers as well as the fluid flow index n on the velocity and temperature of the boundary‐layer, is investigated. A comparison with previous numerical work is then presented. 相似文献
108.
109.
Xiaotao Qian 《偏微分方程(英文版)》2022,35(4):382-394
In this paper, we are interested in the following nonlocal problem with critical exponent begin{align*} begin{cases} -left(a-bdisplaystyleint_{Omega}|nabla u|^2{rm d}xright)Delta u=lambda |u|^{p-2}u+|u|^{4}u, &quad xinOmega, u=0, &quad xinpartialOmega, end{cases} end{align*} where $a,b$ are positive constants, $20$ is a parameter. By variational methods, we prove that problem has a positive ground state solution $u_b$ for $lambda>0$ sufficiently large. Moreover, we take $b$ as a parameter and study the asymptotic behavior of $u_b$ when $bsearrow0$. 相似文献
110.
Wei Han 《偏微分方程(英文版)》2013,26(2):138-150
This paper is devoted to studying the following initial-boundary value problemfor one-dimensional semilinearwave equationswith variable coefficients andwith subcritical exponent: $u_{tt}-∂_x(a(x)∂_xu)=|u|^p, x > 0, t > 0, n=1,$ where $u=u(x,t)$ is a real-valued scalar unknown function in $[0,+∞)×[0,+∞)$, here a(x) is a smooth real-valued function of the variable $x∈(0,+∞)$. The exponents p satisfies $1 < p < +∞$ in (0.1). It is well-known that the number $p_c(1)=+∞$ is the critical exponent of the semilinear wave equation (0.1) in one space dimension (see for e.g., [1]). We will establish a blowup result for the above initial-boundary value problem, it is proved that there can be no global solutions no matter how small the initial data are, and also we give the lifespan estimate of solutions for above problem. 相似文献