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4th International Symposium on Communications, Control, and Signal Processing, ISCCSP-2010

作者： Beltrani, Vincent Dominy, Jason Ho, Tak-San Rabitz, Herschel Department of Chemistry Princeton University NJ 08544 United States Program in Applied and Computational Mathematics Princeton University NJ 08544 United States

ISBN: (纸本)9781424462858

A controlled quantum system possesses a search landscape defined by the observable value as a functional of the control field. Within the search landscape, there exist level sets of controls giving the same observable value. This paper focuses on level sets of the transition probability P i→f. For transition probabilities 0 i→fi→f = 1, a second order D-MORPH algorithm is presented that can explore the perfect control level set. D-MORPH is utilized to identify level set members that exhibit certain desirable secondary characteristics, e.g., minimal pulse ftuence. Numerical simulations for finite level systems are presented to illustrate the variety of control behavior found across level set members. ©2010 IEEE.

关键词： Quantum optics

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Positron-Impact Excitation of Hydrogen Atoms in Debye Plasmas

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Chinese physics Letters 2010年第1期27卷 111-114页

作者：张松斌祁月盈屈一至陈向军王建国 Hefei National Laboratory for Physical Sciences at Microscale and Department of Modern Physics University of Science and Technology of China Hefei 230026 Key Laboratory of Computational Physics Institute of Applied Physics and Computational Mathematics PO Box 8009 Beijing 100088 School of Electrical Engineering Jiaxing University Jiaxing 314001 College of Material Sciences and Optoelectronic Technology Graduate School of the Chinese Academy of Sciences PO Box 4588 Beijing 100049

The positron-impact excitation of hydrogen atoms embedded in plasma environments is investigated using the close-coupling approximation from the low to intermediate energy region without including any positronium formation channel, and the excitation cross sections for 1s→2s, 1s→2p and 2s→2p processes are calculated in a wide Debye parameter range. The screening interactions, described by the Debye-Hückel model, decrease the coupling matrix elements, resulting in the reduction of the excitation cross sections from a few percent to one magnitude of ten. This will alter remarkably the spectroscopy of hydrogen in intensity and position, which should be considered in the simulation and diagnostics under some specific plasma conditions.

关键词： Chinese climate network complex systems small world community

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A new note on spectra of optimal and superoptimal preconditioned matrices

A new note on spectra of optimal and superoptimal preconditi...

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2010 International Conference on Computer Application and System Modeling, ICCASM 2010

作者： Zhang, Li-Tao Huang, Ting-Zhu Cheng, Shao-Hua Gu, Tong-Xiang Department of Mathematics and Physics Zhengzhou Institute of Aeronautical Industry Management Henan China School of Mathematical Sciences University of Electronic Science Technology of China Chengdu China Laboratory of Computationary Physics Institute of Applied Physics and Computational Mathematics Beijing China

ISBN: (纸本)9781424472369

Recently, Cheng et al. [Lin. Alg. Appl. 422 (2007): 482-485] proposed the spectral comparison of optimal preconditioner in Chan [SIAM J. Sci. Statist. Com put. 9 (1988): 766-771] and superoptimal preconditioner in Tyrtyshnikov [SIAM J. Matrix Anal. Appl. 13 (1992): 459-473]. In this paper, based on the work of Cheng et al., we further compare the spectra of optimal and superoptimal preconditioned matrices. © 2010 IEEE.

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On the mechanism of nucleation in pulsed-laser quenched Si films on Si02

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作者： Deng, Y. Hu, Q. 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 10027 United States

ISBN: (纸本)9781605112220

We have investigated the solid nucleation mechanism in laser-quenched Si films on SiO2. Previously neglected experimental steps, consisting of BHF-etching and irradiation in vacuum, were implemented to reduce potential extrinsic influences. The resulting experimental findings and computational analysis lead us to conclude that solid nucleation consistently takes place heterogeneously at, and only at, the bottom liquid Si-SiO2 interface. © 2010 Materials Research Society.

关键词： Nucleation

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Efficient and accurate linear algebraic methods for large-scale electronic structure calculations with nonorthogonal atomic orbitals

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Physical Review B 2011年第16期83卷 165103-165103页

作者： H. Teng T. Fujiwara T. Hoshi T. Sogabe S.-L. Zhang S. Yamamoto Center for Research and Development of Higher Education The University of Tokyo Bunkyo-ku Tokyo 113-8656 Japan Core Research for Evolutional Science and Technology Japan Science and Technology Agency (CREST-JST) Japan Department of Applied Mathematics and Physics Tottori University Tottori 680-8550 Japan School of Information Science and Technology Aichi Prefecture University Nagakute-cho Aichi 480-1198 Japan Department of Computational Science and Engineering Nagoya University Chikusa-ku Nagoya 464-8603 Japan School of Computer Science Tokyo University of Technology Katakura-machi Hachioji Tokyo 192-0982 Japan

The need for large-scale electronic structure calculations arises recently in the field of material physics, and efficient and accurate algebraic methods for large simultaneous linear equations become greatly important. We investigate the generalized shifted conjugate orthogonal conjugate gradient method, the generalized Lanczos method, and the generalized Arnoldi method. They are the solver methods of large simultaneous linear equations of the one-electron Schrödinger equation and map the whole Hilbert space to a small subspace called the Krylov subspace. These methods are applied to systems of fcc Au with the NRL tight-binding Hamiltonian [F. Kirchhoff et al., Phys. Rev. B 63, 195101 (2001)]. We compare results by these methods and the exact calculation and show them to be equally accurate. The system size dependence of the CPU time is also discussed. The generalized Lanczos method and the generalized Arnoldi method are the most suitable for the large-scale molecular dynamics simulations from the viewpoint of CPU time and memory size.

关键词： LINEAR algebraic groups CONJUGATE gradient methods APPROXIMATION theory NUMERICAL solutions to equations HILBERT space

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Extending FSNPC to handle data points with fuzzy class assignments

Extending FSNPC to handle data points with fuzzy class assig...

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18th European Symposium on Artificial Neural Networks, computational Intelligence and Machine Learning, ESANN 2010

作者： Geweniger, Tina Villmann, Thomas University of Leipzig Working Group Computational Intelligence Semmelweisstrasse 10 04103 Leipzig Germany University of Applied Sciences Mittweida Department of Mathematics/Physics/Informatics Computational Intelligence Group Technikumplatz 17 09648 Mittweida Germany

ISBN: (纸本)2930307102

In this paper we present an advanced Nearest Prototype Classification to handle data points with unsharp class assignments. Therefore we extend the Soft Nearest Prototype Classification as proposed by Seo et al. and its further enhancement working with fuzzy labeled prototypes as introduced by Villmann et al. We adapt the cost function and derive appropriate update rules for the prototypes. We assess the performance on a toy data set and a real-world problem and compare the classification result with the results obtained by Fuzzy Robust Soft LVQ by means of Fuzzy Cohen's Kappa.

关键词： Cost functions

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Hydrogen in tungsten: Absorption, diffusion, vacancy trapping, and decohesion

Hydrogen in tungsten: Absorption, diffusion, vacancy trappin...

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作者： Johnson, Donald F. Carter, Emily A. Department of Chemistry Princeton University Princeton NJ 08544 United States Department of Mechanical and Aerospace Engineering Program in Applied and Computational Mathematics Princeton University Princeton NJ 08544 United States

Understanding the interaction between atomic hydrogen and solid tungsten is important for the development of fusion reactors in which proposed tungsten walls would be bombarded with high energy particles including hydrogen isotopes. Here, we report results from periodic density-functional theory calculations for three crucial aspects of this interaction: surface-to-subsurface diffusion of H into W, trapping of H at vacancies, and H-enhanced decohesion, with a view to assess the likely extent of hydrogen isotope incorporation into tungsten reactor walls. We find energy barriers of (at least) 2.08 eV and 1.77 eV for H uptake (inward diffusion) into W(001) and W(110) surfaces, respectively, along with very small barriers for the reverse process (outward diffusion). Although H dissolution in defect-free bulk W is predicted to be endothermic, vacancies in bulk W are predicted to exothermically trap multiple H atoms. Furthermore, adsorbed hydrogen is predicted to greatly stabilize W surfaces such that decohesion (fracture) may result from high local H concentrations. © 2010 Materials Research Society.

关键词： Tungsten

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Why Gabor frames? Two fundamental measures of coherence and their role in model selection

Why Gabor frames? Two fundamental measures of coherence and ...

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作者： Bajwa, Waheed U. Calderbank, Robert Jafarpour, Sina Department of Electrical Engineering Program in Applied and Computational Mathematics Princeton University Princeton NJ 08544 United States Department of Computer Science Princeton University Princeton NJ 08544 United States

The problem of model selection arises in a number of contexts, such as subset selection in linear regression, estimation of structures in graphical models, and signal denoising. This paper studies non-asymptotic model selection for the general case of arbitrary (random or deterministic) design matrices and arbitrary nonzero entries of the signal. In this regard, it generalizes the notion of incoherence in the existing literature on model selection and introduces two fundamental measures of coherence- termed as the worst-case coherence and the average coherence-among the columns of a design matrix. It utilizes these two measures of coherence to provide an in-depth analysis of a simple, model-order agnostic one-step thresholding (OST) algorithm for model selection and proves that OST is feasible for exact as well as partial model selection as long as the design matrix obeys an easily verifiable property, which is termed as the coherence property. One of the key insights offered by the ensuing analysis in this regard is that OST can successfully carry out model selection even when methods based on convex optimization such as the lasso fail due to the rank deficiency of the submatrices of the design matrix. In addition, the paper establishes that if the design matrix has reasonably small worst-case and average coherence then OST performs near-optimally when either (i) the energy of any nonzero entry of the signal is close to the average signal energy per nonzero entry or (ii) the signal-to-noise ratio in the measurement system is not too high. Finally, two other key contributions of the paper are that (i) it provides bounds on the average coherence of Gaussian matrices and Gabor frames, and (ii) it extends the results on model selection using OST to low-complexity, model-order agnostic recovery of sparse signals with arbitrary nonzero entries. In particular, this part of the analysis in the paper implies that an Alltop Gabor frame together with OST can successfully carr

关键词： Recovery

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Temporal evolution of financial-market correlations

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Physical Review E 2011年第2期84卷 026109-026109页

作者： Daniel J. Fenn Mason A. Porter Stacy Williams Mark McDonald Neil F. Johnson Nick S. Jones Mathematical and Computational Finance Group Mathematical Institute University of Oxford Oxford OX1 3LB United Kingdom CABDyN Complexity Centre University of Oxford Oxford OX1 1HP United Kingdom FX Quantitative Strategy HSBC Bank 8 Canada Square London E14 5HQ United Kingdom Oxford Centre for Industrial and Applied Mathematics Mathematical Institute University of Oxford Oxford OX1 3LB United Kingdom Department of Physics University of Miami Coral Gables Florida 33146 USA Department of Physics Clarendon Laboratory University of Oxford Oxford OX1 3PU United Kingdom Oxford Centre for Integrative Systems Biology University of Oxford Oxford OX1 3QU United Kingdom

We investigate financial market correlations using random matrix theory and principal component analysis. We use random matrix theory to demonstrate that correlation matrices of asset price changes contain structure that is incompatible with uncorrelated random price changes. We then identify the principal components of these correlation matrices and demonstrate that a small number of components accounts for a large proportion of the variability of the markets that we consider. We characterize the time-evolving relationships between the different assets by investigating the correlations between the asset price time series and principal components. Using this approach, we uncover notable changes that occurred in financial markets and identify the assets that were significantly affected by these changes. We show in particular that there was an increase in the strength of the relationships between several different markets following the 2007–2008 credit and liquidity crisis.

关键词： FINANCIAL market reaction SECURITIES markets MATRICES LIQUIDITY (Economics) MARKETS

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Geometrical ambiguity of pair statistics. II. Heterogeneous media

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Physical Review E 2010年第1期82卷 011106-011106页

作者： Yang Jiao Frank H. Stillinger Salvatore Torquato Department of Chemistry and Department of Physics Princeton Institute for the Science and Technology of Materials Program in Applied and Computational Mathematics and Princeton Center for Theoretical Science Princeton University Princeton New Jersey 08544 USA

In the first part of this series of two papers [Y. Jiao, F. H. Stillinger, and S. Torquato, Phys. Rev. E 81, 011105 (2010)], we considered the geometrical ambiguity of pair statistics associated with point configurations. Here we focus on the analogous problem for heterogeneous media (materials). Heterogeneous media are ubiquitous in a host of contexts, including composites and granular media, biological tissues, ecological patterns, and astrophysical structures. The complex structures of heterogeneous media are usually characterized via statistical descriptors, such as the n-point correlation function Sn. An intricate inverse problem of practical importance is to what extent a medium can be reconstructed from the two-point correlation function S2 of a target medium. Recently, general claims of the uniqueness of reconstructions using S2 have been made based on numerical studies, which implies that S2 suffices to uniquely determine the structure of a medium within certain numerical accuracy. In this paper, we provide a systematic approach to characterize the geometrical ambiguity of S2 for both continuous two-phase heterogeneous media and their digitized representations in a mathematically precise way. In particular, we derive the exact conditions for the case where two distinct media possess identical S2, i.e., they form a degenerate pair. The degeneracy conditions are given in terms of integral and algebraic equations for continuous media and their digitized representations, respectively. By examining these equations and constructing their rigorous solutions for specific examples, we conclusively show that in general S2 is indeed not sufficient information to uniquely determine the structure of the medium, which is consistent with the results of our recent study on heterogeneous-media reconstruction [Y. Jiao, F. H. Stillinger, and S. Torquato, Proc. Natl. Acad. Sci. U.S.A. 106, 17634 (2009)]. The analytical examples include complex patterns composed of building blo

关键词： Inverse problems

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