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Nature’s Microfluidic Transporter: Rotational Cytoplasmic Streaming at High Péclet Numbers

Physical Review Letters 2008年第17期101卷 178102-178102页

作者： Jan-Willem van de Meent Idan Tuval Raymond E. Goldstein Department of Applied Mathematics and Theoretical Physics Centre for Mathematical Sciences University of Cambridge Wilberforce Road Cambridge CB3 0WA United Kingdom Cambridge Computational Biology Institute Centre for Mathematical Sciences University of Cambridge Wilberforce Road Cambridge CB3 0WA United Kingdom

Cytoplasmic streaming circulates the contents of large eukaryotic cells, often with complex flow geometries. A largely unanswered question is the significance of these flows for molecular transport and mixing. Motivated by “rotational streaming” in Characean algae, we solve the advection-diffusion dynamics of flow in a cylinder with bidirectional helical forcing at the wall. A circulatory flow transverse to the cylinder’s long axis, akin to Dean vortices at finite Reynolds numbers, arises from the chiral geometry. Strongly enhanced lateral transport and longitudinal homogenization occur if the transverse Péclet number is sufficiently large, with scaling laws arising from boundary layers.

关键词： Reynolds number

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The Elastic Continuum Limit of the Tight Binding Model

引用

Chinese Annals of mathematics,Series B 2007年第6期28卷 665-676页

作者： Weinan E Jianfeng LU Department of Mathematics and Program in Applied and Computational Mathematics Princeton University Princeton NJ 08544 USA Program in Applied and Computational Mathematics Princeton University Princeton NJ 08544 USA

The authors consider the simplest quantum mechanics model of solids, the tight binding model, and prove that in the continuum limit, the energy of tight binding model converges to that of the continuum elasticity model obtained using Cauchy-Born rule. The technique in this paper is based mainly on spectral perturbation theory for large matrices.

关键词： Continuum limit Elasticity theory Cauchy-Born rule Tight binding model

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Modeling heterogeneous materials via two-point correlation functions. II. Algorithmic details and applications

引用

Physical Review E 2008年第3期77卷 031135-031135页

作者： Y. Jiao F. H. Stillinger S. Torquato Department of Chemistry Princeton University Princeton New Jersey 08544 USA Princeton Institute for the Science and Technology of Materials Princeton University Princeton New Jersey 08544 USA Program in Applied and Computational Mathematics Princeton University Princeton New Jersey 08544 USA Princeton Center for Theoretical Physics Princeton University Princeton New Jersey 08544 USA and School of Natural Sciences Institute for Advanced Study Princeton New Jersey 08540 USA

In the first part of this series of two papers, we proposed a theoretical formalism that enables one to model and categorize heterogeneous materials (media) via two-point correlation functions S2 and introduced an efficient heterogeneous-medium (re)construction algorithm called the “lattice-point” algorithm. Here we discuss the algorithmic details of the lattice-point procedure and an algorithm modification using surface optimization to further speed up the (re)construction process. The importance of the error tolerance, which indicates to what accuracy the media are (re)constructed, is also emphasized and discussed. We apply the algorithm to generate three-dimensional digitized realizations of a Fontainebleau sandstone and a boron-carbide/aluminum composite from the two-dimensional tomographic images of their slices through the materials. To ascertain whether the information contained in S2 is sufficient to capture the salient structural features, we compute the two-point cluster functions of the media, which are superior signatures of the microstructure because they incorporate topological connectedness information. We also study the reconstruction of a binary laser-speckle pattern in two dimensions, in which the algorithm fails to reproduce the pattern accurately. We conclude that in general reconstructions using S2 only work well for heterogeneous materials with single-scale structures. However, two-point information via S2 is not sufficient to accurately model multiscale random media. Moreover, we construct realizations of hypothetical materials with desired structural characteristics obtained by manipulating their two-point correlation functions.

关键词： RECONSTRUCTING RANDOM-MEDIA TOPOLOGY OPTIMIZATION MICROSTRUCTURES COMPOSITES DESIGN TRANSPORT

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Non-Markovian noise mediated through anomalous diffusion within ion channels

引用

Physical Review E 2008年第4期78卷 041920-041920页

作者： Sisir Roy Indranil Mitra Rodolfo Llinas Physics and Applied Mathematics Unit Indian Statistical Institute 203 Barrackpore Trunk Road Kolkata 700108 India Brain & Behavior Program Department of Physics Georgia State University 29 Peachtree Center Avenue Atlanta Georgia 30303 USA New York University School of Medicine 530 First Avenue New York New York 10016 USA

It is evident from a wide range of experimental findings that ion channel gating is inherently stochastic. The issue of “memory effects” (diffusional retardation due to local changes in water viscosity) in ionic flow has been recently addressed using Brownian dynamics simulations. The results presented indicate such memory effects are negligible, unless the diffusional barrier is much higher than that of free solute. In this paper using differential stochastic methods we conclude that the Markovian property of exponential dwell times gives rise to a high barrier, resulting in diffusional memory effects that cannot be ignored in determining ionic flow through channels. We have addressed this question using a generalized Langevin equation that contains a combination of Markovian and non-Markovian processes with different time scales. This approach afforded the development of an algorithm that describes an oscillatory ionic diffusional sequence. The resulting oscillatory function behavior, with exponential decay, was obtained at the weak non-Markovian limit with two distinct time scales corresponding to the processes of ionic diffusion and drift. This will be analyzed further in future studies using molecular dynamics simulations. We propose that the rise of time scales and memory effects is related to differences of shear viscosity in the cytoplasm and extracellular matrix.

关键词： Molecular dynamics

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Rate-achievability strategies for two-hop interference flows

Rate-achievability strategies for two-hop interference flows

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Annual Allerton Conference on Communication, Control, and Computing

作者： P.S. Chandrashekhar Thejaswi Amir Bennatan Junshan Zhang Robert Calderbank Douglas Cochran Department of Electrical Engineering Arizona Stare University Tempe 85287 USA Program in Applied and Computational Mathematics (PACM) at Princeton University Princeton NJ USA Department of Electrical Engineering Arizona State University Tempe AZ USA Department of Electrical Engineering Arizona Stare University Tempe AZ USA

We consider a basic model for two-hop transmissions of two information flows which interfere with each other. In this model, two sources simultaneously transmit to two relays (in the first hop), which then simultaneously transmit to two destinations (in the second hop). While the transmission during the first hop is essentially the transmission over a classical interference channel, the transmission in the second hop enjoys an interesting advantage. Specifically, as a byproduct of the Han-Kobayashi transmission scheme applied to the first hop, each of the relays (in the second hop) has access to some of the data that is intended to the other destination, in addition to its own data. As recently observed by Simeone et al., this opens the door to cooperation between the relays. In this paper, we observe that the cooperation can take the form of distributed MIMO broadcast, thus greatly enhancing its effectiveness at high SNR. However, since each relay is only aware of part of the data beyond its own, full cooperation is not possible. We propose several approaches that combine MIMO broadcast strategies (including ldquodirty paperrdquo) with standard non-cooperative strategies for the interference channel. Numerical results are provided, which indicate that our approaches provide substantial benefits at high SNR.

关键词： Relays Interference channels Decoding MIMO Broadcasting Context Wireless networks mathematics Electronic mail

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Stationary rotating strings as relativistic particle mechanics

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Physical Review D 2008年第2期78卷 023525-023525页

作者： Kouji Ogawa Hideki Ishihara Hiroshi Kozaki Hiroyuki Nakano Shinya Saito Department of Mathematics and Physics Graduate School of Science Osaka City University Osaka 558-8585 Japan Department of Applied Chemistry and Biotechnology Niigata Institute of Technology Kashiwazaki Niigata 945-1195 Japan Center for Computational Relativity and Gravitation School of Mathematical Sciences Rochester Institute of Technology Rochester New York 14623 USA

Stationary rotating strings can be viewed as geodesic motions in appropriate metrics in two-dimensional space. We obtain all solutions describing stationary rotating strings in flat spacetime as an application. These rotating strings have infinite length with various wiggly shapes. Averaged value of the string energy, the angular momentum, and the linear momentum along the string are discussed.

关键词：

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Detect the Carrier-Envelope Phase and Field Strength of a Few-Cycle Pulse by Non-Sequential Double Ionization

Detect the Carrier-Envelope Phase and Field Strength of a Fe...

引用

International Conference on Ultrahigh Intensity Lasers Development,Science and Emerging Applications(第三届超强激光科学和应用国际会议)

作者： Hongyun Li Bingbing Wang Jing Chen Hongbing Jiang Jie Liu Qihuang Gong Panming Fu Department of Physics State Key Laboratory for Artificial Microstructures and Mesoscopic Physics Peking University Beijing 100871 China Laboratory of Optical Physics Institute of Physics Chinese Academy of Sciences Beijing 100080 China Laboratory of Optical Physics Institute of Physics Chinese Academy of Sciences Beijing 100080 China Center for Nonlinear studies Institute of Applied Physics and Computational Mathematics Beijing 100088 China Department of Physics State Key Laboratory for Artificial Microstructures and Mesoscopic Physics Peking University Beijing 100871 China

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Block ignition Inertial Confinement Fusion (ICF) for space propulsion

Block ignition Inertial Confinement Fusion (ICF) for space p...

引用

作者： Miley, George H. Hora, H. Cang, Yu Osman, F. Badziak, J. Wolowski, J. Sheng, Zheng-Ming Zhang, Jie Zhang, Weiyan He, Xia Department of Nuclear Plasma and Radiological Engineering University of Illinois Urbana 61801 United States Department of Theoretical Physics University of New South Wales Sydney Australia School of Computer Sciences University of Western Sydney Penrith Australia Institute of Plasma Physics and Laser Microfusion Warsaw Poland Beijing National Laboratory for Condensed Matter Physics Institute of Physics Chinese Academy of Science Beijing 100080 China Institute of Applied Physics and Computational Mathematics Beijing China Nuclear Plasma and Radiological Engineering 216 Talbot Lab. 104 S. Wright Urbana IL 61801 United States Emeritus Theoretical Physics Sydney Australia Prollerweg 4 Garching/Munich Germany Dept. Mathematics Trinity College Summerville/Sydney Australia Institute of Plasma Physics and Laser Fusion Warsaw Poland Inst. Physics Chinese Academy of Sciences Beijing China Shanghai Jiao Tong University Shanghai China China Academy of Engineering Physics Beijing China Chinese Academy of Science Beijing China

ISBN: (纸本)9781563479434

Use of laser-driven Inertial Confinement Fusion (ICF) for space propulsion has been examined in several earlier conceptual design studies. However, these designs used older ICF target technology. Important new directions opened following the development of "chirped" lasers capable of ultra-short ps pulses with powers of PWs. This allows fast ignition (FI) for high energy gain ICF power plants1. The FI approach uses a conventional laser to pre-compress the target to high density. The PW laser is then fired on the compressed target, creating an internal electron beam that ignites fusion in a central core of the target. It is estimated that using a 10 TW-ps laser for FI can achieve fusion energy gains >103. Here a new type of FI, termed block ignition, is considered2-4. This approach can further increase the fusion gain offered through FI. Application of block ignition to the earlier VISTA design for ICF space propulsion unit is considered here. With the improved performance obtained, it becomes feasible to bypass DT fusion and use tritium-lean D targets as a first step for development of fusion propulsion technology.

关键词： Inertial confinement fusion

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Compressible Rayleigh-Taylor Instability with Preheat in Inertial Confinement Fusion

引用

Chinese physics Letters 2007年第8期24卷 2308-2311页

作者：范征锋罗纪生叶文华 Department of Mechanics Tianjin University Tianjin 300072 Laboratory of computational physics Institute of Applied Physics and Computational Mathematics Beijing 100088

The compressible Rayleigh-Taylor instability of accelerated ablation front is analysed in consideration of the preheat effects, and the corresponding eigen-problem is solved numerically using the fourth-order accurate two- point compact difference scheme. Both the growth rate and perturbation profiles are obtained, and the obtained growth rate is close to the results of direct numerical simulation. Our results show that the growth rate is more reduced and the cutoff wave length becomes longer as preheat increases.

关键词： CONSISTENT STABILITY ANALYSIS ABLATION FRONTS GROWTH-RATE

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Nonlinear laser focusing using a conical guide and generation of energetic ions

引用

Physical Review E 2008年第3期78卷 036405-036405页

作者： Lihua Cao Wei Yu M. Y. Yu Han Xu X. T. He Yuqiu Gu Zhanjun Liu Jinghong Li Chunyang Zheng Institute of Applied Physics and Computational Mathematics P.O. Box 8009 Beijing 100088 China Shanghai Institute of Optics and Fine Mechanics Chinese Academy of Sciences Shanghai 201800 China Institute for Fusion Theory and Simulation Department of Physics Zhejiang University Hangzhou 310027 China Institut für Theoretische Physik I Ruhr-Universität Bochum D-44780 Bochum Germany National University of Defense Technology Institute of Computer Science Changsha 410073 China Center for Applied Physics and Technology Peking University Beijing 100871 China Laser Fusion Research Center China Academy of Engineering Physics Mianyang 621900 China

Using conventional methods, a laser pulse can be focused down to around 6–8μm, but further reduction of the spot size has proven to be difficult. Here it is shown by particle-in-cell simulation that with a hollow cone an intense laser pulse can be reduced to a tiny, highly localized, spot of around 1μm radius, accompanied by much enhanced light intensity. The pulse shaping and focusing effect is due to a nonlinear laser-plasma interaction on the inner surface of the cone. When a thin foil is attached to the tip of the cone, the cone-focused light pulse compresses and accelerates the ions in its path and can punch through the thin target, creating highly localized energetic ion bunches of high density.

关键词： HIGH-INTENSITY LASER SUBPICOSECOND LASERS ULTRAINTENSE LASER PROTON GENERATION DENSITY PLASMA ACCELERATION IRRADIATION IGNITION TARGETS DRIVEN focusing action High intensity lasers Ignition TAIL IONS thin foil acceleration spot size Irradiation Pulsed lasers

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