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

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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Performance of a rack of liquid-cooled servers

Performance of a rack of liquid-cooled servers

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2007 Winter Meeting of the American Society of Heating, Refrigerating and Air-Conditioning Engineers

作者： Cader, Tahir McAllister, Herley Westra, Levi Regimbal, Kevin Marquez, Andres Government Computing Group Isothermal Systems Research Liberty Lake WA Applied Computer Science Department Computational Sciences and Mathematics Division Pacific North-west National Laboratory Richland WA

Electronics densification is continuing at an unrelenting pace at the server, rack, and facility level. With increasing facility density levels, airflow management has become a major challenge and concern. In an effort to deal with the resulting thermal management challenges, manufacturers are increasingly turning to liquid cooling as a practical solution. The majority of manufacturers have turned to liquid-cooled enclosed racks or rear-door heat exchangers, in which chilled water is delivered to the racks. Some manufacturers are now looking to cold plate cooling solutions that take the heat directly off problem components, such as the CPUs, to get it directly out of the facility. This paper describes work done at the Pacific Northwest National Labs (PNNL) under a Department of Energy-funded program titled "Energy Smart Data Center." An 8.2 kW (27,980 Btu/h) rack of HP rx2600 2U servers has been converted from air-cooling to liquid spray cooling (CPUs only). The rack has been integrated into PNNL's main cluster and subjected to a suite of acceptance tests. Under the testing, the spray-cooled CPUs ran an average of 10°C (18°F) cooler than the air-cooled CPUs. Other peripheral devices, such as the memory D1MMs, ran an average of 8°C (14.4°F) cooler, and the power pod board was measured at 15°C(27°F) cooler. Since installation in July 2005, the rack has been undergoing a one-year uptime and reliability investigation. As part of the investigation, the rack has been subjected to monthly robustness testing and ongoing performance evaluation while running applications such as High Performance Linpack, parts of the NASA NPB-2 Benchmark Suite, and NW Chem. The rack has undergone three months' worth of robustness testing with no major events. Including the robustness testing, the rack uptime is at 95.54% over 299 days. While undergoing application testing, no computational performance differences have been observed between the liquid-cooled and standard air-cooled racks. A sm

关键词： Electronic equipment

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An information theoretic framework for eukaryotic gradient sensing 19

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20th Annual Conference on Neural Information Processing Systems, NIPS 2006

作者： Kimmel, Joseph M. Salter, Richard M. Thomas, Peter J. Computer Science Program Oberlin College Oberlin OH 44074 United States Department of Mathematics Biology and Cognitive Science Case Western Reserve University Cleveland OH 44106 United States Computational Neuroscience Graduate Program University of Chicago United States Center for Computation and Modeling United States

ISBN: (纸本)9780262195683

Chemical reaction networks by which individual cells gather and process information about their chemical environments have been dubbed "signal transduction" networks. Despite this suggestive terminology, there have been few attempts to analyze chemical signaling systems with the quantitative tools of information theory. Gradient sensing in the social amoeba Dictyostelium discoideum is a well characterized signal transduction system in which a cell estimates the direction of a source of diffusing chemoattractant molecules based on the spatiotemporal sequence of ligand-receptor binding events at the cell membrane. Using Monte Carlo techniques (MCell) we construct a simulation in which a collection of individual ligand particles undergoing Brownian diffusion in a three-dimensional volume interact with receptors on the surface of a static amoeboid cell. Adapting a method for estimation of spike train entropies described by Victor (originally due to Kozachenko and Leonenko), we estimate lower bounds on the mutual information between the transmitted signal (direction of ligand source) and the received signal (spatiotemporal pattern of receptor binding/unbinding events). Hence we provide a quantitative framework for addressing the question: how much could the cell know, and when could it know it? We show that the time course of the mutual information between the cell's surface receptors and the (unknown) gradient direction is consistent with experimentally measured cellular response times. We find that the acquisition of directional information depends strongly on the time constant at which the intracellular response is filtered.

关键词： Ligands

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Predicting secret keys via branch prediction

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Cryptographers Track at the RSA Conference, CT-RSA 2007

作者： Acıiçmez, Onur Koç, Çetin Kaya Seifert, Jean-Pierre School of Electrical Engineering and Computer Science Oregon State University CorvallisOR97331 United States Information Security Research Center Istanbul Commerce University Eminönü Istanbul34112 Turkey Applied Security Research Group The Center for Computational Mathematics and Scientific Computation Faculty of Science and Science Education University of Haifa Haifa31905 Israel Institute for Computer Science University of Innsbruck Innsbruck6020 Austria

ISBN: (纸本)9783540693277

This paper announces a new software side-channel attack — enabled by the branch prediction capability common to all modern high-performance CPUs. The penalty paid (extra clock cycles) for a mispredicted branch can be used for cryptanalysis of cryptographic primitives that employ a data-dependent program flow. Analogous to the recently described cache-based side-channel attacks our attacks also allow an unprivileged process to attack other processes running in parallel on the same processor, despite sophisticated partitioning methods such as memory protection, sandboxing or even virtualization. In this paper, we will discuss several such attacks for the example of RSA, and experimentally show their applicability to real systems, such as OpenSSL and Linux. Moreover, we will also demonstrate the strength of the branch prediction side-channel attack by rendering the obvious countermeasure in this context (Montgomery Multiplication with dummy-reduction) as useless. Although the deeper consequences of the latter result make the task of writing an efficient and secure modular exponentiation (or scalar multiplication on an elliptic curve) a challenging task, we will eventually suggest some countermeasures to mitigate branch prediction side-channel attacks. © Springer-Verlag Berlin Heidelberg 2007.

关键词： Side channel attack

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Promoting holistic problem-solving in mechanics pedagogy

Promoting holistic problem-solving in mechanics pedagogy

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114th Annual ASEE Conference and Exposition, 2007

作者： Papadopoulos, Chris Bostwick, Josh Dressel, Andrew University of Wisconsin Milwaukee United States Cornell University United States Department of Civil Engineering and Mechanics University of Wisconsin Milwaukee United States UWM Computer Science Engineering and Mathematics Scholarship Program Brazil Department of Theoretical and Applied Mechanics Cornell University United States

The authors propose three strategies that are designed to enhance students' understanding and problem-solving ability in introductory mechanics courses: (1) employing multiple-method problem-solving, in which students solve a given problem using more than one method;(2) organizing systems of linear equations into a standard "tabular" format which resembles matrix format;and (3) emphasizing the discussion and use of assumptions in problem-solving activities. The authors give a rationale for each strategy, present a review of several mechanics textbooks to determine the prevalence of these strategies, and provide local student performance data that, while as yet inconclusive, suggests a possible method for assessment of the strategies' efficacy. © American Society for Engineering Education, 2007.

关键词： Mechanics

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Convergence properties of preconditioned hermitian and skew-hermitian splitting methods for non-hermitian positive semidefinite matrices

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mathematics of Computation 2007年第257期76卷 287-298页

作者： Bai, Zhong-Zhi Golub, Gene H. Li, Chi-Kwong Department of Mathematics Fudan University Shanghai 200433 China State Key Laboratory of Scientific Acad. of Math. and Syst. Sci. Chinese Acad. of Sci. Beijing 100080 P.O. BOX 2719 China Scientific Computing and Computational Mathematics Program Department of Computer Science Stanford University Stanford CA 94305-9025 United States Department of Mathematics College of William and Mary Williamsburg VA 23187-8795 P.O. Box 8795 United States

For the non-Hermitian and positive semidefinite systems of linear equations, we derive necessary and sufficient conditiorrs for guaranteeing the unconditional convergence of the preconditioned Hermitian and skew-Hermitian splitting iteration methods. We then apply these results to block tridiagonal linear systems in order to obtain convergence conditions for the corresponding block variants of the preconditioned Hermitian and skew-Hermitian splitting iteration methods. © 2006 American Mathematical Society.

关键词： Convergence Hermitian and skew-Hermitian splitting Non-Hermitian matrix Positive semidefinite matrix Splitting iteration method

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A weighted k-nearest neighbor method for gene ontology based protein function prediction

A weighted k-nearest neighbor method for gene ontology based...

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2nd International Multi-Symposiums on computer and computational sciences 2007, IMSCCS'07

作者： Kharsikar, Saket Mugler, Dale Sheffer, Daniel Moore, Francisco Duan, Zhong-Hui Department of Biomedical Engineering University of Akron Akron OH 44236 United States Department of Theoretical and Applied Mathematics University of Akron Akron OH 44236 United States Integrated Bioscience PhD Program University of Akron Akron OH 44236 United States Department of Biology University of Akron Akron OH 44236 United States Department of Computer Science University of Akron Akron OH 44236 United States

ISBN: (纸本)0769530397

Numerous genome projects have produced a large and ever increasing amount of genomic sequence data. However, the biological functions of many proteins encoded by the sequences remain unknown. Protein function annotation and prediction become an essential and challenging task of post-genomic research. In this paper, we present an automated protein function prediction system based on a set of proteins of known biological functions. The functions of the proteins are characterized with gene ontology (GO) annotations. The prediction system uses a novel measure to calculate the pair-wise overall similarity between protein sequences. The protein function prediction is performed based on the GO annotations of similar sequences using a weighted k-nearest neighbor method. We show the prediction accuracies obtained using the model organism yeast (Sacchyromyces cerevisiae). The results indicate that the weighted k-nearest neighbor method significantly outperforms the regular k-nearest neighbor method for protein molecular function prediction. © 2007 IEEE.

关键词： Proteins

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Oscillator models and collective motion

IEEE Control Systems Magazine

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IEEE Control Systems Magazine 2007年第4期27卷 89-105页

作者： Paley, Derek A. Leonard, Naomi Ehrich Sepulchre, Rodolphe Grünbaum, Daniel Parrish, Julia K. Princeton University Department of Mechanical and Aerospace Engineering Princeton NJ 08544 United States Department of Mechanical and Aerospace Engineering Program in Applied and Computational Mathematics Princeton University Princeton NJ 08544 United States Department Electrical Engineering and Computer Science University of Liège Liège Belgium School of Oceanography Department of Biology University of Washington Seattle WA United States Biology Department School of Aquatic and Fishery Sciences University of Washington Seattle WA United States

A description of the so called "particles with coupled oscillator dynamics" (PCOD) is presented which is used to model, analyze and synthesize collective motion. An oscillator model with spatial dynamics is presented to help describe how to design steering control laws while it is being used to study biological collectives. Lastly, both engineering and biological analysis were described.

关键词： Oscillators (mechanical)

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Instantaneous radar polarimetry with multiple dually-polarized antennas

Instantaneous radar polarimetry with multiple dually-polariz...

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40th Asilomar Conference on Signals, Systems, and computers, ACSSC '06

作者： Calderbank, A.R. Howard, S.D. Moran, W. Pezeshki, A. Zoltowski, M. Program in Applied and Computational Mathematics Princeton University Princeton NJ United States Defence Science and Technology Organization Edinburgh Australia Electrical Engineering and Computer Science University of Melbourne Melbourne Australia Electrical and Computer Engineering Purdue University West Lafayette IN United States

ISBN: (纸本)1424407850

Fully Polarimetric radar systems are capable of simultaneously transmitting and receiving in two orthogonal polarizations. Instantaneous radar polarimetry exploits both polarization modes of a dually-polarized radar transmitter and receiver on a pulse by pulse basis, and can improve the radar detection performance and suppress range sidelobes. In this paper, we extend the use of instantaneous radar polarimetry for radar systems with multiple dually-polarized transmit and receive antennas. Alamouti signal processing is used to coordinate transmission of Golay pairs of phase codes waveforms across polarizations and multiple antennas. The integration of multi-antenna signal processing with instantaneous radar polarimetry can further improve the detection performance, at a computational cost comparable to single channel matched filtering.

关键词： Polarimeters

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Learning representation and control in continuous Markov decision processes

Learning representation and control in continuous Markov dec...

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21st National Conference on Artificial Intelligence and the 18th Innovative Applications of Artificial Intelligence Conference, AAAI-06/IAAI-06

作者： Mahadevan, Sridhar Maggioni, Mauro Ferguson, Kimberly Osentoski, Sarah Department of Computer Science University of Massachusetts 140 Governor's Drive Amherst MA 01003 Program in Applied Mathematics Department of Mathematics Yale University New Haven CT 06510

ISBN: (纸本)1577352815

This paper presents a novel framework for simultaneously learning representation and control in continuous Markov decision processes. Our approach builds on the framework of proto-value functions, in which the underlying representation or basis functions are automatically derived from a spectral analysis of the state space manifold. The proto-value functions correspond to the eigenfunctions of the graph Laplacian. We describe an approach to extend the eigenfunctions to novel states using the Nyström extension. A least-squares policy iteration method is used to learn the control policy, where the underlying subspace for approximating the value function is spanned by the learned proto-value functions. A detailed set of experiments is presented using classic benchmark tasks, including the inverted pendulum and the mountain car, showing the sensitivity in performance to various parameters, and including comparisons with a parametric radial basis function method. Copyright © 2006, American Association for Artificial Intelligence (***). All rights reserved.

关键词： Knowledge representation

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