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41.
H. Altenbach I. Brigadnov K. Naumenko 《ZAMM - Journal of Applied Mathematics and Mechanics / Zeitschrift für Angewandte Mathematik und Mechanik》2009,89(10):823-832
The rotation of an inertialess ellipsoidal particle in a shear flow of a Newtonian fluid has been firstly analyzed by Jeffery [17]. He found that the particle rotates such that the end of its axis of symmetry describes a closed periodic orbit. In the special case of a slender particle the Jeffery solution predicts the particle alignment parallel to the streamlines. In a recent publication [3] it was shown that the orbits are no longer observable if the rotary inertia is taken into account. Furthermore, in the case of a slender particle the inertia may cause the jump over the equilibrium alignment. In this paper we address a detailed analysis of the slender particle behavior in the shear flow. We recall the constitutive equation for the hydrodynamic moment and formulate equations of rotary motion. For a special initial condition we reduce the problem to a single second‐order ordinary differential equation with respect to the angle of rotation about a fixed axis. The phase portrait of this equation illustrates different cases of the particle behavior depending on the initial conditions and the “inertia” parameter. They include the particle alignment to a semi‐stable equilibrium position, the non‐uniform rotation about a fixed axis as well as the quantization effect (the particle locates in the neighborhood of the first equilibrium point over a relatively long time and then rotates towards the next equilibrium point). 相似文献
42.
In numerically simulating heat and mass transport processes in an unconfined domain involving synthetic open (inflow and/or outflow) boundaries, how to properly specify flow conditions at these boundaries can become a challenging issue. In this work, within the context of a pressure‐based finite volume method under an unstructured grid, a solution procedure without the need for explicit specification of flow profiles at any of these boundaries when simulating incompressible fluid flow is proposed and numerically examined. Within this methodology, the flow at any open boundary is not necessarily assumed to be unidirectional or fully developed; indeed, the sole information required is the mass flow rate crossing the boundary. As a result, one can select the specific region of interest to perform simulations, rather than having to artificially increase the flow domain so as to invoke fully developed flow at all open boundaries. This not only greatly reduces computational costs (both in terms of memory requirements and simulation run‐time) but provides the means to engage with flow problems, which otherwise cannot be solved with currently available methods for handling the flow conditions at open boundaries. The proposed methodology is demonstrated by simulating laminar flow of an incompressible fluid in a two‐dimensional planar channel with a 90° T‐branch, a known inflow rate, and flow splits for the two outflow channels. The results obtained by placing the entrance and the two exits at different locations show that the flow behavior predicted is completely unaffected by using a highly truncated domain. Copyright © 2015 John Wiley & Sons, Ltd. 相似文献
43.
Jonathan A. Mettes J. Brandon Keith Richard B. McClurg 《Acta Crystallographica. Section A, Foundations and Advances》2004,60(6):621-636
A method is described to produce global phase diagrams for single‐component molecular crystals with separable internal and external modes. The phase diagrams present the equilibrium crystalline phase as a function of the coefficients of a general intermolecular potential based on rotational symmetry‐adapted basis functions. It is assumed that phase transitions are driven by orientational ordering of molecules with a fixed time‐averaged shape. The mean‐field approximation is utilized and the process begins in a high‐temperature disordered reference state, then spontaneous symmetry‐breaking phase transitions and phase structure information at lower temperature are sought. The information is mapped onto phase diagrams using the intermolecular expansion coefficients as independent variables. This is illustrated by global phase diagrams for molecules having tetrahedral symmetry (e.g. carbon tetrachloride, adamantane and white phosphorus). Uses of global phase diagrams include crystal structure data mining, guidance for crystal design and enumeration of likely or missing polymorphic structures. 相似文献
44.
Hsiao‐Ping Hsu Simon C. Lin Ulrich H. E. Hansmann 《Acta Crystallographica. Section A, Foundations and Advances》2002,58(3):259-264
The efficiency of a recently proposed novel global optimization method, energy landscape paving (ELP), is evaluated with regard to the problem of crystal structure determination from simulated X‐ray diffraction data comprising integrated diffraction intensities. The new approach has been tested using the example of 9‐(methylamino)‐1H‐phenalen‐1‐one 1,4‐dioxan‐2‐y1 hydroperoxide solvate (C14H11NO·C4H8O4). The results indicate that, for this example, ELP outperforms standard techniques such as simulated annealing. 相似文献
45.
求解非线性方程组的一种新的全局收敛的Levenberg-Marquardt算法 总被引：10，自引：0，他引：10
本文提出了求解非线性方程组的一种新的全局收敛的Levenberg-Marquardt算法,即μk=ακ(θ||F_k|| (1-θ)||J_k~TF_k||),θ∈[0,1],其中ακ利用信赖域技巧来修正.在不必假设雅可比矩阵非奇异的局部误差界条件下,证明了该算法是全局收敛和局部二次收敛的.数值试验表明该算法能有效地求解奇异非线性方程组问题. 相似文献
46.
世界正面临着第二次世界大战以来最严重的全球危机。不仅各国政府正在尽其所能改善国内公共卫生管理,而且国际社会也迫切需要改善全球治理。然而,面对这场全球性危机,世界没有应有的团结。相反,美国推进对抗性竞争战略以维护世界霸权,其政客试图将预防和控制政治化,破坏全球协调机制。这使得全球治理的缺陷进一步暴露,碎片化趋势进一步呈现,大国竞争及权势转移的趋势更为明显。可预见的未来,全球治理进程更有可能采用区域形式。适应全球治理的迫切需求,中等强国在全球治理中的多重作用空间显著扩大,多数选择平衡外交政策,力主践行多边主义,扮演“催化剂”“搭桥者”角色,赢得全球影响力;不过“追随者”角色也让部分中等强国暴露出能力上的弱点与外交独立性的不足。 相似文献
47.
在全球治理危机频现和大国战略竞争加剧的背景下,“国家中心主义”回归引发了人们对经济全球化走势的担忧。本轮国家中心主义回归的逻辑是：此前自由主义全球化的过度发展导致国家功能隐退;而当全球治理状况恶化时,国家的重要性再度凸现,成为各国社会谋求自我体系安全的唯一“阀门”,民族主义、保护主义思潮亦大行其道。从中期看,未来的全球体系重建过程将充满国家中心主义与自由主义两种理性的持续角力,国家与市场的作用都将在“拉锯战”相互影响与重塑。从远期看,新型全球化将是国家与市场关系再平衡的产物,国家仍是兼具服务本民族发展及其外部性的主要工具。国家处理内外发展与治理多重挑战的“灵活度”即为评判其核心竞争力的最终标准。 相似文献
48.
49.
In this paper, we explore the complete synchronization and quasi-projective synchronization in a class of stochastic delayed quaternion-valued neural networks, utilizing a state-feedback control scheme. The studied neural networks into real-valued networks are short of known decomposing, by designing a very general nonlinear controller, according to the quaternion form It^{o} formula with a number of inequality techniques in the configuration of quaternion domain, we obtained a quasi-projective synchronization criterion for drive-response networks. Moreover, we estimate the error margin for quasi-projective synchronization. At last, the theoretical results are confirmed by a numerical simulation. 相似文献
50.
Jerry L. Bona & Min Chen 《数学研究》2016,49(3):205-220
Studied here is the Boussinesq system $$η_t+u_x+(ηu)_x+au_{xxx}-bη_{xxt}=0,$$ $$u_t+η_x+frac{1}{2}(u²)_x+cη_{xxx}-du_{xxt}=0,$$of partial differential equations. This system has been used in theory and practice as amodel for small-amplitude, long-crested water waves. The issue addressed is whetheror not the initial-value problem for this system of equations is globally well posed.The investigation proceeds by way of numerical simulations using a computer codebased on a a semi-implicit, pseudo-spectral code. It turns out that larger amplitudesor velocities do seem to lead to singularity formation in finite time, indicating that theproblem is not globally well posed. 相似文献