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Ergodic directional switching in mobile insect groups

Physical Review E 2010年第1期82卷 011926-011926页

作者： Carlos Escudero Christian A. Yates Jerome Buhl Iain D. Couzin Radek Erban Ioannis G. Kevrekidis Philip K. Maini ICMAT (CSIC-UAM-UC3M-UCM) Departamento de Matemáticas Facultad de Ciencias Universidad Autónoma de Madrid Ciudad Universitaria de Cantoblanco 28049 Madrid Spain Centre for Mathematical Biology Mathematical Institute University of Oxford 24-29 St. Giles’ Oxford OX1 3LB United Kingdom School of Biological Sciences and Centre for Mathematical Biology Heydon-Laurence Building A08 The University of Sydney Sydney New South Wales Australia Department of Ecology and Evolutionary Biology Princeton University Princeton New Jersey 08544 USA Oxford Centre for Collaborative Applied Mathematics Mathematical Institute University of Oxford 24-29 St. Giles’ Oxford OX1 3LB United Kingdom Department of Chemical Engineering Program in Applied and Computational Mathematics and Mathematics Princeton University Princeton New Jersey 08544 USA Department of Biochemistry Oxford Centre for Integrative Systems Biology University of Oxford South Parks Road Oxford OX1 3QU United Kingdom

We obtain a Fokker-Planck equation describing experimental data on the collective motion of locusts. The noise is of internal origin and due to the discrete character and finite number of constituents of the swarm. The stationary probability distribution shows a rich phenomenology including nonmonotonic behavior of several order and disorder transition indicators in noise intensity. This complex behavior arises naturally as a result of the randomness in the system. Its counterintuitive character challenges standard interpretations of noise induced transitions and calls for an extension of this theory in order to capture the behavior of certain classes of biologically motivated models. Our results suggest that the collective switches of the group’s direction of motion might be due to a random ergodic effect and, as such, they are inherent to group formation.

关键词： Fokker Planck equation

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Origin of broad polydispersion in functionalized dendrimers and its effects on cancer-cell binding affinity

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Physical Review E 2010年第3期82卷 036108-036108页

作者： Jack N. Waddell Douglas G. Mullen Bradford G. Orr Mark M. Banaszak Holl Leonard M. Sander Department of Mathematics University of Michigan Ann Arbor Michigan 48109 USA Program in Macromolecular Science and Engineering Ann Arbor Michigan 48109 USA Michigan Nanotechnology Institute for Medicine and Biological Sciences Ann Arbor Michigan 48109 USA Michigan Nanotechnology Institute for Medicine and Biological Sciences University of Michigan Ann Arbor Michigan 48109 USA Program in Applied Physics University of Michigan Ann Arbor Michigan 48109 USA Department of Physics University of Michigan Ann Arbor Michigan 48109 USA Department of Chemistry University of Michigan Ann Arbor Michigan 48109 USA Michigan Center for Theoretical Physics University of Michigan Ann Arbor Michigan 48109 USA

Nanoparticles with multiple ligands have been proposed for use in nanomedicine. The multiple targeting ligands on each nanoparticle can bind to several locations on a cell surface facilitating both drug targeting and uptake. Experiments show that the distribution of conjugated ligands is unexpectedly broad, and the desorption rate appears to depend exponentially upon the mean number of attached ligands. These two findings are explained with a model in which ligands conjugate to the nanoparticle with a positive cooperativity of ≈4 kT, and that nanoparticles bound to a surface by multiple bonds are permanently affixed. This drives new analysis of the data, which confirms that there is only one time constant for desorption, that of a nanoparticle bound to the surface by a single bond.

关键词： Nanoparticles

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Phase behavior of colloidal superballs: Shape interpolation from spheres to cubes

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Physical Review E 2010年第6期81卷 061105-061105页

作者： Robert D. Batten Frank H. Stillinger Salvatore Torquato Department of Chemical Engineering Princeton University Princeton New Jersey 08544 USA Department of Chemistry Princeton University Princeton New Jersey 08544 USA Department of Physics Princeton University Princeton New Jersey 08544 USA Princeton Center for Theoretical Science 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 School of Natural Sciences Institute for Advanced Study Princeton New Jersey 08544 USA

The phase behavior of hard superballs is examined using molecular dynamics within a deformable periodic simulation box. A superball’s interior is defined by the inequality |x|2q+|y|2q+|z|2q≤1, which provides a versatile family of convex particles (q≥0.5) with cubelike and octahedronlike shapes as well as concave particles (q<0.5) with octahedronlike shapes. Here, we consider the convex case with a deformation parameter q between the sphere point (q=1) and the cube (q=∞). We find that the asphericity plays a significant role in the extent of cubatic ordering of both the liquid and crystal phases. Calculation of the first few virial coefficients shows that superballs that are visually similar to cubes can have low-density equations of state closer to spheres than to cubes. Dense liquids of superballs display cubatic orientational order that extends over several particle lengths only for large q. Along the ordered, high-density equation of state, superballs with 1

关键词： Spheres

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Dislocation climb strengthening in systems with immobile obstacles: Three-dimensional level-set simulation study

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Physical Review B 2010年第5期81卷 054104-054104页

作者： Zi Chen Kevin T. Chu David J. Srolovitz Jeffrey M. Rickman Mikko P. Haataja Department of Mechanical and Aerospace Engineering Princeton University Princeton New Jersey 08540 USA Princeton Institute for the Science and Technology of Materials (PRISM) Princeton University Princeton New Jersey 08540 USA Vitamin D Inc. Menlo Park California 94025 USA Institute of High Performance Computing Singapore Singapore Department of Materials Science and Engineering Lehigh University Bethlehem Pennsylvania 18015 USA Department of Physics Lehigh University Bethlehem Pennsylvania 18015 USA Program in Applied and Computational Mathematics (PACM) Princeton University Princeton New Jersey 08540 USA

We employ a parallel, three-dimensional level-set code to simulate the dynamics of isolated dislocation lines and loops in an obstacle-rich environment. This system serves as a convenient prototype of those in which extended, one-dimensional objects interact with obstacles and the out-of-plane motion of these objects is key to understanding their pinning-depinning behavior. In contrast to earlier models of dislocation motion, we incorporate long-ranged interactions among dislocation segments and obstacles to study the effect of climb on dislocation dynamics in the presence of misfitting penetrable obstacles/solutes, as embodied in an effective climb mobility. Our main observations are as follows. First, increasing climb mobility leads to more effective pinning by the obstacles, implying increased strengthening. Second, decreasing the range of interactions significantly reduces the effect of climb. The dependence of the critical stress on obstacle concentration and misfit strength is also explored and compared with existing models. In particular, our results are shown to be in reasonable agreement with the Friedel-Suzuki theory. Finally, the limitations inherent in the simplified model employed here, including the neglect of some lattice effects and the use of a coarse-grained climb mobility, are discussed.

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Constructions and existence of tight fusion frames

Constructions and existence of tight fusion frames

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Wavelets XIII

作者： Casazza, Peter G. Fickus, Matthew Mixon, Dustin G. Wang, Yang Zhou, Zhengfang Department of Mathematics and Statistics Air Force Institute of Technology Wright-Patterson Air Force Base OH 45433 United States Program in Applied and Computational Mathematics Princeton University Princeton NJ 08544 United States Department of Mathematics Michigan State University East Lansing MI 48824 United States Department of Mathematics University of Missouri Columbia MO 65211 United States

ISBN: (纸本)9780819477361

Fusion frames are an emerging topic of frame theory, with applications to communications and distributed processing. However, until recently, little was known about the existence of tight fusion frames, much less how to construct them. We discuss a new method for constructing tight fusion frames which is akin to playing Tetris with the spectrum of the frame operator. When combined with some easily obtained necessary conditions, these Spectral Tetris constructions provide a near complete characterization of the existence of tight fusion frames. © 2009 SPIE.

关键词： Optical engineering

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Simultaneous tracking of movement and gene expression in multiple Drosophila melanogaster flies using GFP and DsRED fluorescent reporter transgenes

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BMC Research Notes 2009年第1期2卷 1-11页

作者： Grover, Dhruv Yang, Junsheng Ford, Daniel Tavaré, Simon Tower, John Molecular and Computational Biology Program Department of Biological Sciences University of Southern California Los Angeles CA 90089-2910 United States Department of Applied Mathematics and Theoretical Physics University of Cambridge Cambridge CB3 0WA United Kingdom

Background. Fluorescent proteins such as GFP (Green Fluorescent Protein) and DsRED (Discosoma *** Fluorescent Protein) are often used as reporter molecules for transgene expression in Drosophila and other species. We have recently reported methods that allow simultaneous tracking of animal movement and GFP expression in real time, however the assay was limited to single animals and a single transgene. Numerous studies would be facilitated by methods that allow for assay of multiple animals and multiple transgenes. Findings. Here we report an improved fly video tracking system that allows multiple transgenic flies to be tracked simultaneously using visible light, GFP fluorescence and DsRED fluorescence. The movement of multiple flies could be accurately tracked at real time rates, while simultaneously assaying the expression level of two different transgenes marked with GFP and DsRED. The individual flies could be accurately tracked and distinguished even during periods when transgene fluorescence was undetected. For example, characteristic patterns of hsp70 and hsp22 transgene induction could be simultaneously quantified and correlated with animal movement in aging flies, and as groups of flies died due to dessication/starvation. Conclusion. The improved methods allow for more efficient assay of the correlation between gene expression, behavior, aging and mortality: multiple animals can be assayed with simultaneous quantification of multiple transgenes using GFP and DsRED fluorescence. These methods should allow for increased flexibility in experimental designs. For example, in the future it should be possible to use gene expression levels to predict remaining life span more accurately, and to quantify gene expression changes caused by interactions between animals in real time. © 2009 Tower et al.

关键词： Green Fluorescent Protein Extended Kalman Filter Green Fluorescent Protein Expression Green Fluorescent Protein Fluorescence Daily Activity Pattern

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Transient response of a vertical Axis wind turbine to abrupt change of wind speed

Transient response of a vertical Axis wind turbine to abrupt...

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European Wind Energy Conference and Exhibition 2009, EWEC 2009

作者： Hayashi, Tsutomu Hara, Yutaka Azui, Tomoya Kang, In-Seung Department of Applied Mathematics and Physics Tottori University 4-101 Koyama-Minami Tottori 680-8552 Japan Center of International Exchange Program Tottori University 4-101 Koyama-Minami Tottori 680-8550 Japan

ISBN: (纸本)9781615677467

The transient responses of the vertical axis wind turbines (VAWT) are influenced by the abrupt change of the natural wind velocity, although these are not sensitive to the change of the wind direction. The basic transient response of a wind turbine in the abrupt change of the wind velocity is analyzed experimentally using a special wind tunnel that generates the flow with step like velocity increase. The wind turbine has a rotor with 4 straight blades of NACA 0015 symmetry aerofoil. A series of experiments was accomplished in the uniform flow with instantaneous increased velocity from V0 to V 1 (V01), under the two kind of conditions of the wind turbine, that is, a constant rotational speed and a constant load torques. In the experiments, the initial velocities V0=10.0 m/s, the final velocities V1=10.5, 11.0, 11.5, 12.0 m/s were selected. The result under the condition of a constant rotational speed revealed the flow around a rotor of the wind turbine, which followed the wind velocity change of the main flow very quickly. In the case of constant load torque condition, the effective torque of the wind turbine abruptly increased up to the value on the torque curve of the final wind velocity V1, with turbine rotational speed kept almost constant. After that, the effective torque decreased along the torque curve of final wind level to reach the final stage.

关键词： Transient analysis

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Efficient nonce-based authentication scheme for session initiation protocol

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International Journal of Network Security 2009年第1期9卷 12-16页

作者： Tsai, Jia Lun Degree Program for E-learning Department of Applied Mathematics National Chiao Tung University 1001 University Road Hsinchu 300 Taiwan

In recent years, Session Initiation Protocol (SIP) is more and more popular. However, there are many security problems in the Session Initiation Protocol. In 2005, Yang et al. [9] proposed a secure authentication scheme for Session Initiation Protocol. This authentication scheme is based on Diffie-Hellman [2] concept, so the computation cost of this authentication scheme is very high. In order to improve this shortcoming, Durlanik et al. [3] also proposed an authentication Scheme using ECDH in 2005. However, the computation cost of this authentication scheme is still very high. In this paper, we propose an efficient nonce-based authentication scheme. The computation cost of this authentication scheme is lower than Yang et al.s authentication scheme and Durlanik et al.s authentication scheme, and it is very suitable for low computation power equipment.

关键词： Costs

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A Nearly-Linear Time Algorithm for Approximately Solving Linear Systems in a Symmetric M-Matrix

A Nearly-Linear Time Algorithm for Approximately Solving Lin...

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Combinatorial Scientific Computing 2009

作者： Daitch, Samuel I. Spielman, Daniel A. Yale University Department of Computer Science PO Box 208285 New HavenCT06520-8285 United States Yale University Program in Applied Mathematics and Department of Computer Science PO Box 208285 New HavenCT06520-8285 United States

We present an algorithm for solving a linear system in a symmetric M-matrix. In particular, for n × n symmetric M-matrix M, we show how to find a diagonal matrix D such that DMD is diagonally-dominant. To compute D, the algorithm must solve O (log n) linear systems in diagonally-dominant matrices. If we solve these diagonally-dominant systems approximately using the Spielman-Teng nearly-linear time solver [1], then we obtain an algorithm for approximately solving linear systems in symmetric M-matrices, for which the expected running time is also nearly-linear. © 2009 Combinatorial Scientific Computing. All Rights Reserved.

关键词： Linear systems

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Executive Summary of Dagstuhl Seminar on Structured Decompositions and Efficient Algorithms (08492)

Executive Summary of Dagstuhl Seminar on Structured Decompos...

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Structured Decompositions and Efficient Algorithms 2008

作者： Dahlke, Stephan Daubechies, Ingrid Elad, M. Kutyniok, Gitta Teschke, Gerd Philipps-Universität Marburg FB12 Mathematik und Informatik Hans-Meerwein Straße Lahnberge Marburg35032 Germany Princeton University Program in Applied and Computational Mathematics Fine Hall Washington Road PrincetonNJ08544-1000 United States Technion Computer Science Department Haifa Technion City32000 Israel Universität Osnabrück Institute of Mathematics Osnabrück49069 Germany Hochschule Neubrandenburg University of Applied Sciences Institute for Computational Mathematics in Science and Technology Brodaer Str. 2 Neubrandenburg17033 Germany

New emerging technologies such as high-precision sensors or new MRI machines drive us towards a challenging quest for new, more effective, and more daring mathematical models and algorithms. Therefore, in the last few years researchers have started to investigate different methods to efficiently represent or extract relevant information from complex, high dimensional and/or multimodal data. Efficiently in this context means a representation that is linked to the features or characteristics of interest, thereby typically providing a sparse expansion of such. Besides the construction of new and advanced ansatz systems the central question is how to design algorithms that are able to treat complex and high dimensional data and that efficiently perform a suitable approximation of the signal. One of the main challenges is to design new sparse approximation algorithms that would ideally combine, with an adjustable tradeoff, two properties: a provably good 'quality' of the resulting decomposition under mild assumptions on the analyzed sparse signal, and numerically efficient design. The topic is driven by applications as well as by theoretical questions. Therefore, the aim of this seminar was to bring together a good mixture of scientists with different backgrounds in order to discuss recent progress as well as new challenging perspectives. In particular, it was intended to strengthen the interaction of mathematicians and computer scientists. © 2009 Dagstuhl Seminar Proceedings. All Rights Reserved.

关键词： Clustering algorithms

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