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第七届全国青年计算物理学术交流会

作者： T P Yu Z M Sheng A Pukhov Y Yin H B Zhuo YY Ma X H Xu F Q Shao C T Zhou College of Science National University of Defense TechnologyChangsha 410073People's Republic of Ch Key Laboratory for Laser Plasmas (MoE) and Department of Physics Shanghai Jiao Tong UniversityShang Institut fǖr Theoretische Physik I Heinrich-Heine-Universit(a)t Dǖsseldorf40225 DüsseldorfGermany College of Science National University of Defense TechnologyChangsha 410073People's Republic of Ch State Key Laboratory of High Performance Computing National University of Defense TechnologyChangsh Institute of Applied Physics and Computational Mathematics PO Box 8009Beijing 100088People's Repub

With the help of three-dimensional particle-in-cell simulations, we study the electron dynamics in radiation pressure acceleration of a mass-limited foil *** a mass-limited foil is irradiated by a circularly polarized laser pulse, the wing parts of the laser overtake the foil from the foil *** the laser propagation direction, electrons are significantly accelerated by the laser radiation *** the laser polarization direction, electrons are subjected to a strong radial space-charge force and oscillate in the overtaking laser *** their combined actions, electrons execute a betatron-like oscillation and a spatially helix electron bunch is thus formed.A simple analytical model is proposed for interpreting the high electron energies and large oscillating *** is shown that, when the electron oscillation frequency coincides with the laser frequency as witnessed by the electron, betatron-like resonance occurs, resulting in hundreds of MeV electron generation.

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Thrust augmentation of flapping airfoils in low reynolds number flow using a flexible membrane 53

Thrust augmentation of flapping airfoils in low reynolds num...

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53rd AIAA/ASME/ASCE/AHS/ASC Structures, Structural Dynamics and Materials Conference 2012

作者： Jaworski, Justin W. Gordnier, Raymond E. University of Cambridge Department of Applied Mathematics and Theoretical Physics Cambridge CB3 0WA United Kingdom Air Force Research Laboratory Computational Sciences Branch Wright-Patterson AFB OH 45433-7913 United States

ISBN: (数字)9781600869372

ISBN: (纸本)9781600869372

Designers of micro air vehicles (MAVs) are currently looking to biological flight to address the technical challenges of low Reynolds number fliers. These challenges include the aerodynamics of transitional flow, flight vehicle resilience to gusty environments, lightweight design, and propulsion. Recent biological observations and high-fidelity computations indicate that deformable membrane wing airfoils may offer an engineering solution to these design issues, and that the existence of membrane flexibility may enable and enhance the thrust production of flapping wings in low Reynolds number flows. To this end, the unsteady aerodynamic and aeroelastic responses of a two-dimensional membrane airfoil under prescribed harmonic motions are investigated computationally with a well-validated, robust, sixth-order Navier-Stokes solver coupled to a nonlinear membrane structural model. The effects of membrane prestress and elasticity are examined parametrically for selected plunge and pitch-plunge motions at a chord-based Reynolds number of 2500. The importance of inertial membrane loads resulting from the prescribed flapping is also assessed for pure plunging motions. This study compares the period-averaged aerodynamic loads of flexible versus rigid membrane airfoils and highlights the vortex structures and salient fluid-membrane interactions that enable more efficient flapping thrust production in low Reynolds number flows.

关键词： Membranes

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Flash-lamp-induced lateral solidification of thin Si films

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2011 MRS Spring Meeting

作者： Omori, K. Ganot, G.S. Chung, U.J. Chitu, A.M. Limanov, A.B. Im, James S. Program in Materials Science and Engineering Department of Applied Physics and Applied Mathematics Columbia University New York NY United States Technical Development Department Japan Steel Works LTD. Yokohama Japan Department of Materials Science and Engineering College of Engineering Korea Advanced Institute of Science and Technology Korea Republic of

ISBN: (纸本)9781605112985

In this paper we show that a flash lamp can be employed to induce controlled lateral solidification of a-Si thin films. Specifically, a dual xenon-arc-lamp-based system was utilized to induce location-controlled complete melting by shaping the incident beam using a contact mask. The resulting laterally solidified microstructure consisted of exceptionally long grains (∼10s to ∼100s of μm) that were relatively free of intragrain-defects. With further development and optimization, the approach may lead to cost-effective/high-throughput processes and systems that can capture and enhance the advantages of laser-based/melt-mediated crystallization techniques. © 2011 Materials Research Society.

关键词： Cost effectiveness

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Alignment-free sequence comparison based on next generation sequencing reads: Extended abstract

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16th Annual International Conference on Research in computational Molecular Biology, RECOMB 2012

作者： Song, Kai Ren, Jie Zhai, Zhiyuan X., Liu M., Deng F., Sun School of Mathematics Peking University Beijing China School of Mathematics Shandong University China School of Physics South China University of Technology Guangzhou China TNLIST Department of Automation Tsinghua University Beijing China Molecular and Computational Biology Program University of Southern California Los Angeles CA United States

ISBN: (纸本)9783642296260

Next generation sequencing (NGS) technologies have generated enormous amount of shotgun read data and assembly of the reads can be challenging, especially for organisms without template sequences. We study the power of genome comparison based on shotgun read data without assembly using three alignment-free sequence comparison statistics,D2D2* , and D2S , both theoretically and by simulations. Theoretical formulas for the power of detecting the relationship between two sequences related through a common motif model are derived. It is shown that both D2* and D2Soutperform D2 for detecting the relationship between two sequences based on NGS data. We then study the effects of length of the tuple, read length, coverage, and sequencing error on the power of D2* and| D2S. Finally, variations of these statistics, and , respectively, are used to first cluster 5 mammalian species with known phylogenetic relationships and then cluster 13 tree species whose complete genome sequences are not available using NGS shotgun reads. The clustering results using dS2 are consistent with biological knowledge for the 5 mammalian and 13 tree species, respectively. Thus, the statistic dS2 provides a powerful alignment-free comparison tool to study the relationships among different organisms based on NGS read data without assembly. © 2012 Springer-Verlag Berlin Heidelberg.

关键词： Statistics

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Josephson dynamics of a spin-orbit-coupled Bose-Einstein condensate in a double-well potential

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Physical Review A 2012年第4期85卷 043609-043609页

作者： Dan-Wei Zhang Li-Bin Fu Z. D. Wang Shi-Liang Zhu Laboratory of Quantum Information Technology School of Physics and Telecommunication Engineering South China Normal University Guangzhou China Science and Technology Computational Physics Laboratory Institute of Applied Physics and Computational Mathematics Beijing 100088 China Department of Physics and Center of Theoretical and Computational Physics The University of Hong Kong Pokfulam Road Hong Kong China Center for Quantum Information IIIS Tsinghua University Beijing China

We investigate the quantum dynamics of an experimentally realized spin-orbit-coupled Bose-Einstein condensate in a double-well potential. The spin-orbit coupling can significantly enhance the atomic interwell tunneling. We find the coexistence of internal and external Josephson effects in the system, which are moreover inherently coupled in a complicated form even in the absence of interatomic interactions. Moreover, we show that the spin-dependent tunneling between two wells can induce a net atomic spin current referred as spin Josephson effects. Such spin Josephson effects can be observable under realistic conditions.

关键词： Statistical mechanics

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Towards optimization of a human-inspired heuristic for solving explore-exploit problems

Towards optimization of a human-inspired heuristic for solvi...

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IEEE Annual Conference on Decision and Control

作者： Paul Reverdy Robert C. Wilson Philip Holmes Naomi E. Leonard Department of Mechanical and Aerospace Engineering Princeton University Department of Psychology and Neuroscience Institute Princeton University Program in Applied and Computational Mathematics Princeton University

ISBN: (纸本)9781467320658

Motivated by models of human decision making, we consider a heuristic solution for explore-exploit problems. In a numerical example we show that, with appropriate parameter values, the algorithm performs well. However, the parameters of the algorithm trade off exploration against exploitation in a complicated way so that finding the optimal parameter values is not obvious. We show that the optimal parameter values can be analytically computed in some cases and prove that suboptimal parameter tunings can provide robustness to modeling error. The analytic results suggest a feedback control law for dynamically optimizing parameters.

关键词： optimal parameter Heuristics numerical example control law Solve modeling error Exploration

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Orientation dependence of structural transition in fcc Al driven under uniaxial compression by atomistic simulations

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Chinese physics B 2011年第4期20卷 391-396页

作者：李莉邵建立段素青梁九卿 Institute of Theoretical Physics and Department of Physics Shanxi University Institute of Applied Physics and Computational Mathematics

By molecular dynamics simulations employing an embedded atom method potential, we have investigated structural transformations in single crystal A1 caused by uniaxial strain loading along the [001], [011] and [111] directions. We find that the structural transition is strongly dependent on the crystal orientations. The entire structure phase transition only occurs when loading along the [001] direction, and the increased amplitude of temperature for [001] loading is evidently lower than that for other orientations. The morphology evolutions of the structural transition for [011] and [111] loadings are analysed in detail. The results indicate that only 20% of atoms transit to the hcp phase for [011] and [111] loadings, and the appearance of the hcp phase is due to the partial dislocation moving forward on {lll}fcc family. For [011] loading, the hcp phase grows to form laminar morphology in four planes, which belong to the {111}fcc family; while for [111] loading, the hcp phase grows into a laminar structure in three planes, which belong to the {111}fcc family except for the （111） plane. In addition, the phase transition is evaluated by using the radial distribution functions.

关键词： single crystal Al molecular dynamics simulations uniaxial compression phase transition

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Excimer-laser-induced melting and solidification of PECVD a-Si films under partial-melting conditions

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2011 MRS Spring Meeting

作者： Hu, Q. Lee, Catherine S. Li, T. Deng, Y. Chung, U.J. Limanov, A.B. Chitu, A.M. Thompson, M.O. Im, James S. Program in Materials Science and Engineering Department of Applied Physics and Applied Mathematics Columbia University New York NY United States Department of Materials Science and Engineering College of Engineering Korea Advanced Institute of Science and Technology Daejeon Korea Republic of Department of Materials Science and Engineering College of Engineering Cornell University Ithaca NY United States

ISBN: (纸本)9781605112985

This paper reports on new experimental findings and conclusions regarding the pulsed-laser-induced melting-and-solidification behavior of PECVD a-Si films. The experimental findings reveal that, within the partial-melting regime, these a-Si films can melt and solidify in ways that are distinct from, and more complex than, those encountered in microcrystalline-cluster-rich LPCVD a-Si films. Specifically (1) spatially dispersed and temporally stochastic nucleation of crystalline solids occurring relatively effectively at the moving liquid-amorphous interface, (2) very defective crystal growth that leads to the formation of fine-grained Si proceeding, at least initially after the nucleation, at a sufficiently rapidly moving crystal solidification front, and (3) the propensity for local preferential remelting of the defective regions and grain boundaries (while the beam is still on) are identified as being some of the fundamental factors that can participate and affect how these PECVD films melt and solidify. © 2011 Materials Research Society.

关键词： Nucleation

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Charge-Transfer-Induced Cesium Superlattices on Graphene

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Physical Review Letters 2012年第15期108卷 156803-156803页

作者： Can-Li Song Bo Sun Yi-Lin Wang Ye-Ping Jiang Lili Wang Ke He Xi Chen Ping Zhang Xu-Cun Ma Qi-Kun Xue Beijing National Laboratory for Condensed Matter Physics Institute of Physics Chinese Academy of Sciences Beijing 100190 China State Key Laboratory of Low-Dimensional Quantum Physics Department of Physics Tsinghua University Beijing 100084 China Institute of Applied Physics and Computational Mathematics Beijing 100088 China

We investigate cesium (Cs) adsorption on graphene formed on a 6H-SiC(0001) substrate by a combined scanning tunneling microscopy and density functional theory study. Individual Cs atoms adsorb preferentially at the rim region of the well-defined 6×6 substrate superstructure and on multilayer graphene. By finely controlling the graphene thickness and Cs coverages (1/3 ML and 1 ML), we here demonstrate two intriguing and well-ordered Cs superlattices on bilayer and multilayer graphene (<6 layers). Statistical analysis of the Cs-Cs interatomic distance reveals a hitherto unobserved Cs-Cs long-range electrostatic potential caused by charge transfer from Cs to graphene, which couples with the inhomogeneous substrate potential to stabilize the observed Cs superlattices. The present study provides a new avenue to fabricate atomic and molecular superlattices for applications in high-density recording and data storage.

关键词： Cesium

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Low Yield of Near-Zero-Momentum Electrons and Partial Atomic Stabilization in Strong-Field Tunneling Ionization

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Physical Review Letters 2012年第9期109卷 093001-093001页

作者： Hong Liu Yunquan Liu Libin Fu Guoguo Xin Difa Ye Jie Liu X. T. He Yudong Yang Xianrong Liu Yongkai Deng Chengyin Wu Qihuang Gong Department of Physics and State Key Laboratory for Mesoscopic Physics Peking University Beijing 100871 China National Key Laboratory of Science and Technology on Computation Physics Institute of Applied Physics and Computational Mathematics 100088 Beijing China Center for Applied Physics and Technology Peking University 100084 Beijing China School of Science Beijing Institute of Technology Beijing 100081 China Department of Physics Northwest University Xian Shaanxi 710069 China

We measure photoelectron angular distributions of single ionization of krypton and xenon atoms by laser pulses at 1320 nm, 0.2–1.0×1014 W/cm2, and observe that the yield of near-zero-momentum electrons in the strong-field tunneling ionization regime is significantly suppressed. Semiclassical simulations indicate that this local ionization suppression effect can be attributed to a fraction of the tunneled electrons that are released in a certain window of the initial field phase and transverse velocity are ejected into Rydberg elliptical orbits with a frequency much smaller than that of the laser; i.e., the corresponding atoms are stabilized. These electrons with high-lying atomic orbits are thus prevented from ionization, resulting in the substantially reduced near-zero-momentum electron yield. The refined transition between the Rydberg states of the stabilized atoms has implication on the THz radiation from gas targets in strong laser fields.

关键词： Electrons

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