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Time-dependent information transmission in a model regulatory circuit

Physical Review E 2013年第2期88卷 022708-022708页

作者： F. Mancini C. H. Wiggins M. Marsili A. M. Walczak International School for Advanced Studies (SISSA) Trieste Italy Department of Applied Physics and Applied Mathematics Center for Computational Biology and Bioinformatics Columbia University New York New York 10027 USA The Abdus Salam International Centre for Theoretical Physics (ICTP) Trieste Italy CNRS and Laboratoire de Physique Théorique de l’École Normale Supérieure Paris France

Many biological regulatory systems respond with a physiological delay when processing signals. A simple model of regulation which respects these features shows how the ability of a delayed output to transmit information is limited: at short times by the time scale of the dynamic input, at long times by that of the dynamic output. We find that topologies of maximally informative networks correspond to commonly occurring biological circuits linked to stress response and that circuits functioning out of steady state may exploit absorbing states to transmit information optimally.

关键词： Timing circuits

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AMUSE: Empowering Users for Cost-Aware Offloading with Throughput-Delay Tradeoffs

AMUSE: Empowering Users for Cost-Aware Offloading with Throu...

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IEEE INFOCOM Conference

作者： Youngbin Im Carlee Joe-Wong Sangtae Ha Soumya Sen Ted "Taekyoung" Kwon Mung Chiang School of Computer Science and Engineering Seoul National University Seoul Korea Program in Applied and Computational Mathematics Princeton University Princeton NJ USA Department of Electrical Engineering Princeton University Princeton NJ USA

ISBN: (纸本)9781467359443

Mobile users face a tradeoff between cost, through-put, and delay in making their offloading decisions. To navigate this tradeoff, we propose AMUSE (Adaptive bandwidth Management through USer-Empowerment), a practical, cost-aware WiFi offloading system that takes into account a user's throughput-delay tradeoffs and cellular budget constraint. Based on predicted future usage and WiFi availability, AMUSE decides which applications to offload to what times of the day. To practically enforce the assigned rate of each TCP application, we introduce a receiver-side TCP bandwidth control algorithm that adjusts the rate by controlling the TCP advertisement window from the user side. We implement AMUSE on Windows 7 tablets and evaluate its effectiveness with 3G and WiFi usage data obtained from a trial with 25 mobile users. Our results show that AMUSE improves user utility.

关键词： tradeoffs UNLOADING Wi-Fi third generation rate control

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Role of Ga-doping in iron-gallium alloy clusters

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Chinese physics B 2012年第2期21卷 461-468页

作者： Tang Pei-Zhe Liu Hai-Tao Zhu Jie Wang Shan-Ying Duan Wen-Hui Department of Physics Tsinghua UniversityBeijing 100084China The Key Laboratory of Computational Physics Institute of Applied Physics and Computational MathematicsBeijing 100088China State Key Laboratory for Advanced Metals and Materials University of Science and Technology BeijingBeijing 100083China

The structural and magnetic properties of Fen-mCam （n = 3 - 6, m = 0 - 2; n = 13, m = 0 - 3） alloy clusters have been studied using density functional theory. The substitutional doping is favourable for small clusters with up to six atoms at low Ga concentration and substitutional Ga atoms in 13-atom clusters prefer surface sites. The Ca-doping generally could reduce the energetic stability but enhance the electronic stability of Fe clusters, along with a decrease of the local magnetic moments of Fe atoms around Ca dopants. These findings provide a microscopic insight into Fe-Ga alloys which are well：known magnetostriction materials.

关键词： iron gallium alloy clusters density functional theory stability magnetic properties

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Correlation and relativistic effects in U metal and U-Zr alloy: Validation of ab initio approaches

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Physical Review B 2013年第23期88卷 235128-235128页

作者： Wei Xie (谢玮) Wei Xiong Chris A. Marianetti Dane Morgan Materials Science Program University of Wisconsin-Madison Madison Wisconsin 53706 USA Department of Materials Science and Engineering University of Wisconsin-Madison Madison Wisconsin 53706 USA Department of Applied Physics and Applied Mathematics Columbia University New York New York 10027 USA Department of Engineering Physics University of Wisconsin-Madison Madison Wisconsin 53706 USA

Ab initio calculations have been performed on all solid phases of U metal and U-Zr alloy, the basis of a promising metallic fuel for fast nuclear reactors. Based on generalized gradient approximation, both density functional theory (DFT) in its standard form and the so-called DFT plus Hubbard U (DFT+U) modification are evaluated. The evolution of calculated energetics, volume, magnetic moments, electronic structure, and f-orbital occupation as functions of the effective Hubbard U parameter, Ueff, is carefully examined at Ueff from 0 to 4 eV. DFT is found to overestimate energetics, underestimate volume, downward shift some f bands near Fermi level and overestimate f-orbital occupation against existing experimental and/or computational data. The error is ∼0.07 eV/atom in terms of enthalpy, which affects phase stability modeling for δ(U,Zr) and γ(U,Zr). DFT+U at Ueff=1−1.5 eV offers clear improvement on these calculated properties (∼0.05 eV/atom in terms of enthalpy) and in general still neither promotes ordered magnetic moments nor opens unphysical band gaps, which occur at higher Ueff values. The empirical Ueff values of 1–1.5 eV are close to but smaller than the theoretical estimations of 1.9–2.3 eV that we obtain from the linear response approach. Ueff is found to vary only slightly (≤0.24 eV) between different phases and at different compositions of U and U-Zr; thus, a single Ueff=1.24 eV, which is the statistical optimal from energetic fitting, is suggested for both U and U-Zr. Besides correlation, the relativistic effect of spin-orbit coupling (SOC) is also systematically explored. SOC is found to lower energy, increase volume, and split the 5f shell above Fermi level and reduce f-orbital occupation. The effect predominates in the unoccupied states and is very small on all these calculated ground state properties (∼0.02 eV/atom in terms of enthalpy).

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Linear instability and adiabaticity of a dark state during conversion of two species of fermionic atoms to stable molecules

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Chinese physics B 2012年第4期21卷 99-105页

作者：孟少英陈希浩吴炜傅立斌 Department of Physics Liaoning UniversityShenyang 110036China Science and Technology Computation Physics Laboratory Institute of Applied Physics and Computational MathematicsP.O.Box 8009Beijing 100088China Center for Applied Physics and Technology Peking UniversityBeijing 100871China

In the present paper, we investigate the linear instability and adiabaticity of a dark state during conversion of two species of fermionic atoms to stable molecules through the stimulated Raman adiabatic passage aided by Feshbach resonance. We analytically obtain the regions for the appearance of linear instability. Moreover, taking 40K and 6Li atom molecule conversion systems as examples, we give the unstable regions numerically. We also attempt to obtain the adiabatic criterion for this nonlinear system with classical adiabatic dynamics and study the adibaticity of the dark state with the adiabatic condition.

关键词： linear instability adiabaticity dark state atom molecule conversion

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Completeness of solutions of Bethe's equations

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Physical Review E 2013年第5期88卷 052113-052113页

作者： Wenrui Hao Rafael I. Nepomechie Andrew J. Sommese Mathematical Biosciences Institute The Ohio State University 1735 Neil Avenue Columbus Ohio 43210 USA Physics Department P.O. Box 248046 University of Miami Coral Gables Florida 33124 USA Department of Applied and Computational Mathematics and Statistics University of Notre Dame 163 Hurley Hall Indiana 46556 USA

We consider the Bethe equations for the isotropic spin-1/2 Heisenberg quantum spin chain with periodic boundary conditions. We formulate a conjecture for the number of solutions with pairwise distinct roots of these equations, in terms of numbers of so-called singular (or exceptional) solutions. Using homotopy continuation methods, we find all such solutions of the Bethe equations for chains of length up to 14. The numbers of these solutions are in perfect agreement with the conjecture. We also discuss an indirect method of finding solutions of the Bethe equations by solving the Baxter T-Q equation. We briefly comment on implications for thermodynamical computations based on the string hypothesis.

关键词： Chains

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Double-exchange theory of ferroelectric polarization in orthorhombic manganites with twofold periodic magnetic texture

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Physical Review B 2013年第14期87卷 144424-144424页

作者： I. V. Solovyev S. A. Nikolaev Computational Materials Science Unit National Institute for Materials Science 1-2-1 Sengen Tsukuba Ibaraki 305-0047 Japan Department of Theoretical Physics and Applied Mathematics Ural Federal University Mira str. 19 620002 Ekaterinburg Russia

We argue that many aspects of improper ferroelectric (FE) activity in orthorhombic manganites can be rationalized by considering the limit of infinite intra-atomic splitting between majority- and minority-spin states (or the double-exchange limit), which reduces the problem to the analysis of a spinless double-exchange (DE) Hamiltonian. We apply this strategy to the low-energy model, derived from the first-principles electronic-structure calculations, and combine it with the Berry-phase theory of electric polarization. We start with the analysis of the simplest two-orbital model, describing the behavior of the eg bands, and apply it to the E-type antiferromagnetic (AFM) phase, which in the DE limit effectively breaks up into one-dimensional zigzag chains. We derive an analytical expression for the electronic polarization (Pel) and explain how it depends on the orbital ordering and the energy splitting Δ between eg states. Then, we evaluate parameters of this model for the series of manganites. For these purposes, we start from a more general five-orbital model for all Mn 3d bands and construct a new downfolded model for the eg bands. From the analysis of these parameters, we conclude that the behavior of Pel in realistic manganites always corresponds to the limit of large Δ. This property holds for all considered compounds even in the local-density approximation, which typically underestimates Δ. We further utilize this property in order to derive an analytical expression for Pel in a general twofold periodic magnetic texture, based on the five-orbital model and the perturbation-theory expansion for the Wannier functions in the first order of 1/Δ. This expression explains the functional dependence of Pel on the relative directions of spins. Furthermore, it suggests that Pel is related to the asymmetry of transfer integrals, which should have simultaneously symmetric and antisymmetric components in the crystal-field representation. The main contribution to this asymm

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Alignment-Dependent Fluorescence Emission Induced by Tunnel Ionization of Carbon Dioxide from Lower-Lying Orbitals

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Physical Review Letters 2013年第13期111卷 133001-133001页

作者： Jinping Yao Guihua Li Xinyan Jia Xiaolei Hao Bin Zeng Chenrui Jing Wei Chu Jielei Ni Haisu Zhang Hongqiang Xie Chaojin Zhang Zengxiu Zhao Jing Chen Xiaojun Liu Ya Cheng Zhizhan Xu State Key Laboratory of High Field Laser Physics Shanghai Institute of Optics and Fine Mechanics Chinese Academy of Sciences Shanghai 201800 China University of Chinese Academy of Sciences Beijing 100049 China Quantum Optoelectronics Laboratory Southwest Jiaotong University Chengdu 610031 China Key Laboratory of High Energy Density Physics Simulation Center for Applied Physics and Technology Peking University Beijing 100084 China Institute of Applied Physics and Computational Mathematics Beijing 100088 China Department of Physics National University of Defense Technology Changsha 410073 China State Key Laboratory of Magnetic Resonance and Atomic and Molecular Physics Wuhan Institute of Physics and Mathematics Chinese Academy of Sciences Wuhan 430071 China

The study of the ionization process of molecules in an intense infrared laser field is of paramount interest in strong-field physics and constitutes the foundation of imaging of molecular valence orbitals and attosecond science. We show measurement of alignment-dependent ionization probabilities of the lower-lying orbitals of the molecules by experimentally detecting the alignment dependence of fluorescence emission from tunnel ionized carbon dioxide molecules. The experimental measurements are compared with the theoretical calculations of the strong field approximation and molecular Ammosov-Delone-Krainov models. Our results demonstrate the feasibility of an all-optical approach for probing the ionization dynamics of lower-lying orbitals of molecules, which is until now still difficult to achieve by other techniques. Moreover, the deviation between the experimental and theoretical results indicates the incompleteness of current theoretical models for describing strong field ionization of molecules.

关键词： Molecules

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Jammed lattice sphere packings

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Physical Review E 2013年第6期88卷 062151-062151页

作者： Yoav Kallus Étienne Marcotte Salvatore Torquato Princeton Center for Theoretical Science Princeton University Princeton New Jersey 08544 USA Department of Physics Princeton University Princeton New Jersey 08544 USA Department of Chemistry Princeton University Princeton New Jersey 08544 USA Program in Applied and Computational Mathematics Princeton University Princeton New Jersey 08544 USA Princeton Institute of the Science and Technology of Materials Princeton University Princeton New Jersey 08544 USA

We generate and study an ensemble of isostatic jammed hard-sphere lattices. These lattices are obtained by compression of a periodic system with an adaptive unit cell containing a single sphere until the point of mechanical stability. We present detailed numerical data about the densities, pair correlations, force distributions, and structure factors of such lattices. We show that this model retains many of the crucial structural features of the classical hard-sphere model and propose it as a model for the jamming and glass transitions that enables exploration of much higher dimensions than are usually accessible.

关键词： Spheres

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Atomistic simulation of fcc-bcc phase transition in single crystal Al under uniform compression

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Chinese physics B 2012年第2期21卷 425-430页

作者： Li Li Shao Jian-Li Li Yan-Fang Duan Su-Qing Liang Jiu-Qing Institute of Theoretical Physics and Department of Physics Shanxi UniversityTaiyuan 030006China Institute of Applied Physics and Computational Mathematics Beijing 100088China College of Materials Science and Engineering Taiyuan University of TechnologyTaiyuan 030024China

By molecular dynamics simulations employing an embedded atom model potential, we investigate the fcc-to-bcc phase transition in single crystal Al, caused by uniform compression. Results show that the fcc structure is unstable when the pressure is over 250 GPa, in reasonable agreement with the calculated value through the density flmctional theory. The morphology evolution of the structural transition and the corresponding transition mechanism are analysed in detail. The bcc （011） planes are transited from the fcc （111） plane and the （111） plane. We suggest that the transition mechanism consists mainly of compression, shear, slid and rotation of the lattice. In addition, our radial distribution flmction analysis explicitly indicates the phase transition of Al from fee phase to bce structure.

关键词： molecular dynamics simulations phase transition microstructure

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