检索结果-内蒙古大学图书馆

Physical Review E 2012年第2期85卷 021130-021130页

作者： Adam B. Hopkins Frank H. Stillinger Salvatore Torquato Department of Chemistry Department of Physics Princeton Center for Theoretical Science Princeton Institute for the Science and Technology of Materials Program in Applied and Computational Mathematics Princeton University Princeton New Jersey 08544 USA

The densest binary sphere packings in the α-x plane of small to large sphere radius ratio α and small sphere relative concentration x have historically been very difficult to determine. Previous research had led to the prediction that these packings were composed of a few known “alloy” phases including, for example, the AlB2 (hexagonal ω), HgBr2, and AuTe2 structures, and to XYn structures composed of close-packed large spheres with small spheres (in a number ratio of n to 1) in the interstices, e.g., the NaCl packing for n=1. However, utilizing an implementation of the Torquato-Jiao sphere-packing algorithm [Torquato and Jiao, Phys. Rev. E 82, 061302 (2010)], we have discovered that many more structures appear in the densest packings. For example, while all previously known densest structures were composed of spheres in small to large number ratios of one to one, two to one, and very recently three to one, we have identified densest structures with number ratios of seven to three and five to two. In a recent work [Hopkins et al., Phys. Rev. Lett. 107, 125501 (2011)], we summarized these findings. In this work, we present the structures of the densest-known packings and provide details about their characteristics. Our findings demonstrate that a broad array of different densest mechanically stable structures consisting of only two types of components can form without any consideration of attractive or anisotropic interactions. In addition, the structures that we have identified may correspond to currently unidentified stable phases of certain binary atomic and molecular systems, particularly at high temperatures and pressures.

关键词： Spheres

来源：评论

学校读者我要写书评

暂无评论

Maximally dense packings of two-dimensional convex and concave noncircular particles

引用

Physical Review E 2012年第3期86卷 031302-031302页

作者： Steven Atkinson Yang Jiao Salvatore Torquato Department of Chemistry Department of Physics Princeton Center for Theoretical Science Program of Applied and Computational Mathematics Princeton Institute for the Science and Technology of Materials Princeton University Princeton New Jersey 08544 USA

Dense packings of hard particles have important applications in many fields, including condensed matter physics, discrete geometry, and cell biology. In this paper, we employ a stochastic search implementation of the Torquato-Jiao adaptive-shrinking-cell (ASC) optimization scheme [Nature (London) 460, 876 (2009)] to find maximally dense particle packings in d-dimensional Euclidean space Rd. While the original implementation was designed to study spheres and convex polyhedra in d≥3, our implementation focuses on d=2 and extends the algorithm to include both concave polygons and certain complex convex or concave nonpolygonal particle shapes. We verify the robustness of this packing protocol by successfully reproducing the known putative optimal packings of congruent copies of regular pentagons and octagons, then employ it to suggest dense packing arrangements of congruent copies of certain families of concave crosses, convex and concave curved triangles (incorporating shapes resembling the Mercedes-Benz logo), and “moonlike” shapes. Analytical constructions are determined subsequently to obtain the densest known packings of these particle shapes. For the examples considered, we find that the densest packings of both convex and concave particles with central symmetry are achieved by their corresponding optimal Bravais lattice packings; for particles lacking central symmetry, the densest packings obtained are nonlattice periodic packings, which are consistent with recently-proposed general organizing principles for hard particles. Moreover, we find that the densest known packings of certain curved triangles are periodic with a four-particle basis, and we find that the densest known periodic packings of certain moonlike shapes possess no inherent symmetries. Our work adds to the growing evidence that particle shape can be used as a tuning parameter to achieve a diversity of packing structures.

关键词： Geometry

来源：评论

学校读者我要写书评

暂无评论

Using a level set to model multiple myeloma induced bone loss

Using a level set to model multiple myeloma induced bone los...

引用

6th European Congress on computational Methods in applied Sciences and Engineering, ECCOMAS 2012

作者： Ayati, Bruce P. Graham, Jason M. Holstein, Sarah A. Department of Mathematics and Program in Applied Mathematical and Computational Sciences University of Iowa Iowa City IA 52242-1419 United States Department of Internal Medicine University of Iowa Iowa City IA 52242-1081 United States

ISBN: (纸本)9783950353709

Multiple myeloma is a hematological malignancy characterized by proliferation of malignant plasma cells and derangement of bone homeostasis. Myeloma bone disease results in significant morbidity as a result of bone pain, hypercalcemia, diffuse osteopenia, and pathologic fractures. We present a spatially explicit mathematical model of multiple myeloma and bone remodeling, synthesizing the existing model of local "microenvironment" interactions in Ayati et al. 2010 [1] with a level set approach for representing the sharp interface been bone and marrow introduced in [6]. computational results show the feasibility of using a level set to capture the spatial structure in the context of a geometrically straightforward interface, but one that nonetheless captures the essence of the rich geometries seen in bone marrow biopsy slides. In particular, we are able to model the formation of an osteolytic lesion in the case of multiple myeloma dysregulated bone remodeling, but not, using the same remodeling parameter set, in the case of normal bone remodeling.

关键词： Bone

来源：评论

学校读者我要写书评

暂无评论

Recollision Dynamics and Phase Diagram for Nonsequential Double Ionization with Circularly Polarized Laser Fields

引用

Physical Review Letters 2012年第10期108卷 103601-103601页

作者： L. B. Fu G. G. Xin D. F. Ye J. Liu National Laboratory of Science and Technology on Computational Physics Institute of Applied Physics and Computational Mathematics Beijing 100088 China Center for Applied Physics and Technology Peking University Beijing 100084 China School of Science Beijing Institute of Technology Beijing 100081 China Department of Physics Northwest University Xian Shaanxi 710069 China

A semiclassical quasistatic model is used to investigate the recollision dynamics in circularly polarized laser fields. A velocity window for recollision to occur is found. Only when the return electron’s orbits are irregular does significant double ionization take place. The model reproduces the experimental results for magnesium and explains the apparently conflicting experimental results in terms of an analytical formula that demarcates the phase diagram for the nonsequential double ionization in circularly polarized laser fields.

关键词： Circular polarization

来源：评论

学校读者我要写书评

暂无评论

Nonlinear Schrödinger equation: Generalized Darboux transformation and rogue wave solutions

引用

Physical Review E 2012年第2期85卷 026607-026607页

作者： Boling Guo Liming Ling Q. P. Liu Institute of Applied Physics and Computational Mathematics Beijing 100088 P.R. China Department of Mathematics China University of Mining and Technology Beijing 100083 P.R. China

In this paper, we construct a generalized Darboux transformation for the nonlinear Schrödinger equation. The associated N-fold Darboux transformation is given in terms of both a summation formula and determinants. As applications, we obtain compact representations for the Nth-order rogue wave solutions of the focusing nonlinear Schrödinger equation and Hirota equation. In particular, the dynamics of the general third-order rogue wave is discussed and shown to exhibit interesting structures.

关键词： Nonlinear equations

来源：评论

学校读者我要写书评

暂无评论

Sparsity reconstruction in electrical impedance tomography: An experimental evaluation

Sparsity reconstruction in electrical impedance tomography: ...

引用

作者： Gehre, Matthias Kluth, Tobias Lipponen, Antti Jin, Bangti Seppnen, Aku Kaipio, Jari P. Maass, Peter Center for Industrial Mathematics University of Bremen D-28334 Bremen Germany Department of Physics and Mathematics University of Eastern Finland P.O. Box 1627 FIN-70211 Kuopio Finland Department of Mathematics Institute for Applied Mathematics and Computational Science Texas AandM University College Station TX 77843-3368 United States Department of Mathematics University of Auckland 38 Princes Street 1142 Auckland New Zealand

We investigate the potential of sparsity constraints in the electrical impedance tomography (EIT) inverse problem of inferring the distributed conductivity based on boundary potential measurements. In sparsity reconstruction, inhomogeneities of the conductivity are a priori assumed to be sparse with respect to a certain basis. This prior information is incorporated into a Tikhonov-type functional by including a sparsity-promoting 1-penalty term. The functional is minimized with an iterative soft shrinkage-type algorithm. In this paper, the feasibility of the sparsity reconstruction approach is evaluated by experimental data from water tank measurements. The reconstructions are computed both with sparsity constraints and with a more conventional smoothness regularization approach. The results verify that the adoption of 1-type constraints can enhance the quality of EIT reconstructions: in most of the test cases the reconstructions with sparsity constraints are both qualitatively and quantitatively more feasible than that with the smoothness constraint. © 2011 Elsevier B.V. All rights reserved.

关键词： Water tanks

来源：评论

学校读者我要写书评

暂无评论

Effect of film thickness variation on (100)-surface texturing of MPS processed polycrystalline Si films

Effect of film thickness variation on (100)-surface texturin...

引用

2012 MRS Spring Meeting

作者： Chahal, Monica Van Der Wilt, P.C. Van Gestel, D. Limanov, A.B. Chitu, A.M. Im, James S. Program in Materials Science and Engineering Department of Applied Physics and Applied Mathematics Columbia University New York NY United States IMEC Solar Cell Tech. Group Leuven Belgium Korea Republic of Coherent GmbH Göttingen Germany

ISBN: (纸本)9781605114033

We have investigated the effect of varying the film thickness on the surface orientation texturing in polycrystalline Si films obtained via mixed-phase solidification (MPS) of initially a-Si precursor films on SiO 2. It is found that, for a given number of MPS exposure cycles, the degree of (100)-surface texturing is reduced as the film thickness is increased. We discuss how this trend can be accounted for by the previously proposed thermodynamic model of MPS, wherein a decreasing local solid/liquid interface curvature with increasing film thickness is identified as the primary cause for decreasing the influence which anisotropic solid-Si/SiO2 interfacial energies have on the survivability of the grains. This, in turn, leads to other factors becoming more significant in determining the grains that survive the MPS cycle, thereby reducing the degree of (100)-surface texturing in the resulting films. © 2012 Materials Research Society.

关键词： Film thickness

来源：评论

学校读者我要写书评

暂无评论

Investigation of the generation of high-order harmonics through Bohmian trajectories

引用

Physical Review A 2012年第3期86卷 033424-033424页

作者： Yang Song Fu-Ming Guo Su-Yu Li Ji-Gen Chen Si-Liang Zeng Yu-Jun Yang Institute of Atomic and Molecular Physics Jilin University Changchun 130012 China Department of Physics and Materials Engineering Taizhou University Taizhou 318000 China Institute of Applied Physics and Computational Mathematics Beijing 100088 China

We theoretically investigated the generation progress of high-order harmonics utilizing Bohmian trajectories, which are calculated from the accurate numerical wave function. It is found that the harmonic emission spectrum from atoms in an intense laser field calculated by Bohmian trajectories agrees well with that found by numerically solving the time-dependent Schrödinger equation. Through the analysis of the dynamic behavior of Bohmian trajectories, we investigated the ionization process, the acceleration of the ionized electron in the laser field, and its recollision with the parent ion in the progress. Furthermore, the individual behavior and the coherent contribution of these trajectories to the harmonic emission are discussed.

关键词： Wave functions

来源：评论

学校读者我要写书评

暂无评论

Computation of sparse low degree interpolating polynomials and their application to derivative-free optimization

Computation of sparse low degree interpolating polynomials a...

引用

作者： Bandeira, A.S. Scheinberg, K. Vicente, L.N. Program in Applied and Computational Mathematics Princeton University Princeton NJ 08544 United States Department of Industrial and Systems Engineering Lehigh University Harold S. Mohler Laboratory 200 West Packer Avenue Bethlehem PA 18015-1582 United States CMUC Department of Mathematics University of Coimbra 3001-501 Coimbra Portugal

Interpolation-based trust-region methods are an important class of algorithms forDerivative-Free Optimizationwhich rely on locally approximating an objective function by quadratic polynomial interpolation models, frequently built from less points than there are basis components. Often, in practical applications, the contribution of the problem variables to the objective function is such that many pairwise correlations between variables are negligible, implying, in the smooth case, a sparse structure in the Hessian matrix. To be able to exploit Hessian sparsity, existing optimization approaches require the knowledge of the sparsity structure. The goal of this paper is to develop and analyze a method where the sparse models are constructed automatically. The sparse recovery theory developed recently in the field of compressed sensing characterizes conditions under which a sparse vector can be accurately recovered from few random measurements. Such a recovery is achieved by minimizing the l1-norm of a vector subject to the measurements constraints. We suggest an approach for building sparse quadratic polynomial interpolationmodels byminimizing the l1-norm of the entries of themodel Hessian subject to the interpolation conditions. We show that this procedure recovers accurate models when the function Hessian is sparse, using relatively few randomly selected sample points. Motivated by this result, we developed a practical interpolation-based trust-region method using deterministic sample sets and minimum l1-norm quadratic models. Our computational results show that the new approach exhibits a promising numerical performance both in the general case and in the sparse one. © Springer and Mathematical Optimization Society 2012.

关键词： Interpolation

来源：评论

学校读者我要写书评

暂无评论

Timing of the x-ray burst from paralleled X-pinches

Timing of the x-ray burst from paralleled X-pinches

引用

IEEE Symposium Power Modulator

作者： Shen Zhao Haiyun Luo Xinlei Zhu Ran Zhang Xiaobing Zou Xinxin Wang Chuang Xue Cheng Ning Ning Ding Xiaojian Shu Department of Electrical Engineering Tsinghua University Beijing China Institute of Applied Physics and Computational Mathematics Beijing China

The current and the voltage of an X-pinch were measured. The inductance of the X-pinch was assumed to be a constant and estimated by the calculation of the magnetic field based on the well-known Biot-Savart's Law. The voltage of the inductance was calculated with Ldi/dt and subtracted from the measured voltage of the X-pinch. Then, the resistance of the X-pinch was determined and the following results were obtained. At the start of the current the resistance of the exploding wires is several tens of Ohms, and then it falls down quickly to about 1Ω, which reflects a current transition from the overheated and highly resistive wire core to the highly conductive plasma. The resistance is only a little bit lower than the impedance. It seems that the material and diameter of the wires have no strong influence on the resistance.

关键词：

来源：评论

学校读者我要写书评

暂无评论

建议与咨询留下您的常用邮箱和电话号码，以便我们向您反馈解决方案和替代方法

时间限定

文献类型

馆藏选择

核心期刊

语言

文献类型

帮助

文字说明：

检索规则说明：

检索范例：

分类表

所选分类

限定检索结果

文献类型

馆藏范围

日期分布

学科分类号

主题

机构

作者

语言

请选择保存的检索档案：

请选择收藏分类：

通借通还

建议与咨询 留下您的常用邮箱和电话号码，以便我们向您反馈解决方案和替代方法

时间限定

文献类型

馆藏选择

核心期刊

语言

文献类型

帮助

文字说明：

检索规则说明：

检索范例：

分类表

所选分类

限定检索结果

文献类型

馆藏范围

日期分布

学科分类号

主题

机构

作者

语言

请选择保存的检索档案： 新增检索档案 确定 取消

请选择收藏分类： 新增自定义分类 确定 取消

通借通还

建议与咨询留下您的常用邮箱和电话号码，以便我们向您反馈解决方案和替代方法

请选择保存的检索档案：

请选择收藏分类：