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Electron Acceleration During the Mode Transition from Laser Wakefield to Plasma Wakefield Acceleration with a Dense-Plasma Wall

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Plasma Science and Technology 2013年第9期15卷 841-844页

作者：刘明萍刘三秋何俊刘杰 College of Information Engineering Nanchang University Key Laboratory of Beam Technology and Materials Modification of the Ministry of Education Beijing Normal University Department of Physics Nanchang University Institute of Applied Physics and Computational Mathematics

The wake bubble expansion and contraction by adding a dense-plasma wall in the background plasma during the mode transition from laser wakefield to plasma wakefield accel- eration is investigated by particle-in-cell simulations. The electrons are injected continuously into the cavity until the lateral bubble size equals the inner diameter of the wall. The injected electron bunch from the laser wakefield acceleration （LWFA） scheme is quasi phase-stably accel- erated forward because of the longitudinal contraction of the bubble. After the laser pulse is depleted completely, the electron bunch generated from the LWFA scheme drives a plasma wake- field. The electrons remaining in the channel are trapped and accelerated by the plasma wakefield. Ultimately, two energetic electron bunches with a narrow energy spread and low emittance are obtained.

关键词： quasi phase-stable acceleration monoenergetic electron bunch dense-plasmawall

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A lower bound on the Rényi entropy of convolutions in the integers

A lower bound on the Rényi entropy of convolutions in the i...

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IEEE International Symposium on Information Theory

作者： Liyao Wang Jae Oh Woo Mokshay Madiman Department of Physics Yale University New Haven CT USA Applied Mathematics Program Yale University New Haven CT USA Department of Mathematical Sciences University of Delaware Newark DE USA

A simple new lower bound is provided for the Rényi entropy of the convolution of probability distributions on the integers in terms of certain (discrete) rearrangements of these distributions. This inequality may... 详细信息

关键词： Entropy Random variables Information theory Educational institutions Additives Convex functions

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Spin dependence of ferroelectric polarization in the double exchange model for manganites

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Physical Review B 2014年第18期90卷 184425-184425页

作者： I. V. Solovyev S. A. Nikolaev Computational Materials Science Unit National Institute for Materials Science 1-1 Namiki Tsukuba Ibaraki 305-0044 Japan Department of Theoretical Physics and Applied Mathematics Ural Federal University Mira str. 19 620002 Ekaterinburg Russia

The double exchange (DE) model is systematically applied for studying the coupling between ferroelectric (FE) and magnetic orders in several prototypical types of multiferroic manganites. The model itself was constructed for the magnetically active Mn 3d bands in the basis of Wannier functions and includes the effect of screened onsite Coulomb interactions in the Hartree-Fock approximation. All model parameters were derived from the first-principles electronic-structure calculations. The essence of our approach for the FE polarization is to use the Berry-phase theory, formulated in terms of occupied Wannier functions, and to evaluate the asymmetric spin-dependent change of these functions in the framework of the DE model. This enables us to quantify the effect of the magnetic symmetry breaking and derive several useful expressions for the electronic polarization P, depending on the relative directions of spins. The spin dependence of P in the DE model is given by the isotropic correlation functions ei·ej between directions of neighboring spins. Despite formal similarity with the magnetostriction mechanism, the magnetoelectric coupling in the proposed DE theory is not related to the magnetically driven FE atomic displacements and can exist even in compounds with the centrosymmetric crystal structure, if the spatial distribution of ei·ej does not respect the inversion symmetry. The proposed theory is applied to the solution of three major problems: (i) the magnetic-state dependence of P in hexagonal manganites, using YMnO3 as an example; (ii) the microscopic relationship between canted ferromagnetism and P in monoclinic BiMnO3; (iii) the origin of FE activity in orthorhombic manganites. Particularly, we will show that for an arbitrary noncollinear magnetic structure, propagating along the orthorhombic b axis and antiferromagnetically coupled along the c axis, the polarization is induced by an inhomogeneous distribution of spins and can be obtained by scaling the one o

关键词： MANGANITE MULTIFERROIC materials POLARIZATION (Electricity) ELECTRONIC structure GEOMETRIC quantum phases

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Calibrated Langevin-dynamics simulations of intrinsically disordered proteins

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Physical Review E 2014年第4期90卷 042709-042709页

作者： W. Wendell Smith Po-Yi Ho Corey S. O'Hern Department of Physics Yale University New Haven Connecticut 06520-8120 USA Integrated Graduate Program in Physical and Engineering Biology Yale University New Haven Connecticut 06520-8114 USA Department of Mechanical Engineering and Materials Science Yale University New Haven Connecticut 06520-8286 USA Department of Applied Physics Yale University New Haven Connecticut 06520-8267 USA Program in Computational Biology and Bioinformatics Yale University New Haven Connecticut 06520 USA

We perform extensive coarse-grained (CG) Langevin dynamics simulations of intrinsically disordered proteins (IDPs), which possess fluctuating conformational statistics between that for excluded volume random walks and collapsed globules. Our CG model includes repulsive steric, attractive hydrophobic, and electrostatic interactions between residues and is calibrated to a large collection of single-molecule fluorescence resonance energy transfer data on the interresidue separations for 36 pairs of residues in five IDPs: α−, β−, and γ-synuclein, the microtubule-associated protein τ, and prothymosin α. We find that our CG model is able to recapitulate the average interresidue separations regardless of the choice of the hydrophobicity scale, which shows that our calibrated model can robustly capture the conformational dynamics of IDPs. We then employ our model to study the scaling of the radius of gyration with chemical distance in 11 known IDPs. We identify a strong correlation between the distance to the dividing line between folded proteins and IDPs in the mean charge and hydrophobicity space and the scaling exponent of the radius of gyration with chemical distance along the protein.

关键词： LANGEVIN equations SIMULATION methods & models CONFORMATIONAL analysis MICROTUBULE-associated proteins HYDROPHOBIC compounds

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Alignment and pulse-duration effects in two-photon double ionization of H2 by femtosecond XUV laser pulses

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Physical Review A 2014年第4期90卷 043416-043416页

作者： Xiaoxu Guan Klaus Bartschat Barry I. Schneider Lars Koesterke Department of Physics and Astronomy Drake University Des Moines Iowa 50311 USA Applied and Computational Mathematics Division Information Technology Laboratory National Institute of Standards and Technology Gaithersburg Maryland 20899 USA Texas Advanced Computer Center University of Texas at Austin Austin Texas 78758 USA

We present calculations for the dependence of the two-photon double ionization (DI) of H2 on the relative orientation of the linear laser polarization to the internuclear axis and the length of the pulse. We use the fixed-nuclei approximation at the equilibrium distance of 1.4 a0, where a0=0.529×10−10m is the Bohr radius. Central photon energies cover the entire direct DI domain from 26.5 to 34.0 eV. In contrast to the parallel geometry studied earlier [X. Guan, K. Bartschat, B. I. Schneider, and L. Koesterke, Phys. Rev. A 83, 043403 (2011)], the effect of the pulse duration is almost negligible for the case when the two axes are perpendicular to each other. This is a consequence of the symmetry rules for dipole excitation in the two cases. In the parallel geometry, doubly excited states of 1Σu+ symmetry affect the cross section, while in the perpendicular geometry only much longer-lived 1Πu states are present. This accounts for the different convergence patterns observed in the calculated cross sections as a function of the pulse length. When the photon energy approaches the threshold of sequential DI, a sharp increase of the generalized total cross section (GTCS) with increasing pulse duration is also observed in the perpendicular geometry, very similar to the case of the molecular axis being oriented along the laser polarization direction. Our results differ from those of Colgan et al. [J. Colgan, M. S. Pindzola, and F. Robicheaux, J. Phys. B 41, 121002 (2008)] and Morales et al. [F. Morales, F. Martín, D. A. Horner, T. N. Rescigno, and C. W. McCurdy, J. Phys. B 42, 134013 (2009)], but are in excellent agreement with the GTCSs of Simonsen et al. [A. S. Simonsen, S. A. Sørngård, R. Nepstad, and M. Førre, Phys. Rev. A 85, 063404 (2012)] over the entire domain of direct DI.

关键词： PHOTONS RESEARCH PULSE-width modulation IONIZATION of gases HYDROGEN FEMTOSECOND pulses ULTRAVIOLET lasers

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Density-based and transport-based core-periphery structures in networks

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Physical Review E 2014年第3期89卷 032810-032810页

作者： Sang Hoon Lee Mihai Cucuringu Mason A. Porter Oxford Centre for Industrial and Applied Mathematics Mathematical Institute University of Oxford Oxford OX2 6GG United Kingdom Program in Applied and Computational Mathematics (PACM) Princeton University Fine Hall Washington Road Princeton New Jersey 08544-1000 USA Department of Mathematics University of California Los Angeles Los Angeles California 90095 USA CABDyN Complexity Centre University of Oxford Oxford OX1 1HP United Kingdom

Networks often possess mesoscale structures, and studying them can yield insights into both structure and function. It is most common to study community structure, but numerous other types of mesoscale structures also exist. In this paper, we examine core-periphery structures based on both density and transport. In such structures, core network components are well-connected both among themselves and to peripheral components, which are not well-connected to anything. We examine core-periphery structures in a wide range of examples of transportation, social, and financial networks—including road networks in large urban areas, a rabbit warren, a dolphin social network, a European interbank network, and a migration network between counties in the United States. We illustrate that a recently developed transport-based notion of node coreness is very useful for characterizing transportation networks. We also generalize this notion to examine core versus peripheral edges, and we show that the resulting diagnostic is also useful for transportation networks. To examine the properties of transportation networks further, we develop a family of generative models of roadlike networks. We illustrate the effect of the dimensionality of the embedding space on transportation networks, and we demonstrate that the correlations between different measures of coreness can be very different for different types of networks.

关键词： MESOSCALE convective complexes -- Computer simulation COMMUNITY organization TRANSPORTATION SOCIAL networks DENSITY MARKOV processes DEPENDENCY (Imperialism)

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Effect of Electron Initial Longitudinal Velocity on Low-Energy Structure in Above-Threshold Ionization Spectra

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Chinese physics Letters 2013年第7期30卷 60-63页

作者： WU Ming-Yan WANG Yan-Lan LIU Xiao-Jun LI Wei-Dong HAO Xiao-Lei CHEN Jing State Key Laboratory of Magnetic Resonance and Atomic and Molecular Physics Wuhan Institute of Physics and MathematicsChinese Academy of SciencesWuhan 430071 University of Chinese Academy of Sciences Beijing 100190 Department of Physics and Institute of Theoretical Physics Shanxi UniversityTaiyuan 030006 HEDPS Center for Applied Physics and TechnologyPeking UniversityBeijing 100871 Institute of Applied Physics and Computational Mathematics Beijing 100088

Using a semiclassical model,we investigate the effect of the initial longitudinal velocity of the tunnel-ionized electron on low-energy structure(LES)in above-threshold ionization(ATI)*** analysis shows that the effect(reduction or enhancement)of the initial longitudinal velocity pz0 on the LES is dependent on the direction of the initial longitudinal *** the initial longitudinal velocity along the direction of the laser electric field at the moment of tunneling(i.e.,pz0>0),the Coulomb interaction between the photoelectron and ion core is enhanced,while for the initial longitudinal velocity in the opposite direction(i.e.,pz0<0),the Coulomb effect is *** work provides solid evidence that the initial electron longitudinal velocity has considerable effect on the photoelectron dynamics in the ATI process.

关键词： process. spectra. photoelectron

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Orbital magnetization of insulating perovskite transition-metal oxides with a net ferromagnetic moment in the ground state

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Physical Review B 2014年第6期89卷 064428-064428页

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

Modern theory of the orbital magnetization is applied to the series of prototype insulating perovskite transition metal oxides (orthorhombic YTiO3, LaMnO3, and YVO3, as well as monoclinic YVO3), carrying a net ferromagnetic (FM) moment in the ground state. For these purposes, we use an effective Hubbard-type model, derived from the first-principles electronic structure calculations and describing the behavior of magnetically active states near the Fermi level. The solution of this model in the mean-field Hartree-Fock approximation with the relativistic spin-orbit coupling typically gives us a distribution of the local orbital magnetic moments, which are related to the site-diagonal part of the density matrix D̂ by the “classical” expression μ0=−μBTr{L̂D̂}. These moments are usually well quenched by the crystal field. In this work, we evaluate “itinerant” corrections ΔM to the net FM moment, suggested by the modern theory. We show that these corrections are small and in most cases can be neglected. Nevertheless, the most interesting aspect of our analysis is that, even for these compounds, which are frequently regarded as prototype Mott insulators, the “itinerant” corrections reveal a strong k dependence in the reciprocal space, following the behavior of Chern invariants. Therefore, the small value of ΔM is the result of strong cancellation of relatively large contributions, coming from different parts of the Brillouin zone. We discuss details as well as possible implications of this cancellation, which depends on the crystal structure as well as the type of the magnetic ground state.

关键词： TRANSITION metals PEROVSKITE FERROMAGNETIC materials MAGNETIC moments FERMI level SPIN-orbit coupling CRYSTAL structure

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Detecting on forward error correction codes

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2nd International Conference on Opto-Electronics Engineering and Materials Research, OEMR 2013

作者： Lai, Zong Li Xu, Wen Tao Department of Software Development Institute of Applied Physics and Computational Mathematics Beijing 100083 China

ISBN: (纸本)9783037857731

Under the development of society, the dissemination of information plays an increasingly significant role. How to achieve the goal of continually reducing the error rate and enhance the quality of communication and construct a highly reliable, efficient and high-speed Broadband Communication System is really a tough task. Here comes the FEC that is one particular type of error correction codes which is introduced to protect the process of data transmitting. In addition to a brief introduction to FEC, this article covers the categories of FEC and their applications along with comparisons and also describes the latest development of these error correction algorithms. © (2013) Trans Tech Publications, Switzerland.

关键词： Convolutional codes

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Quantum Effects in Double Ionization of Argon below the Threshold Intensity

Quantum Effects in Double Ionization of Argon below the Thre...

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SFPUP 2014 International Workshop on Strong Field physics and Uitrafast Phenomena(2014年国际强场物理与超快现象研讨会)

作者： XiaoLei Hao Jing Chen WeiDong Li Bingbing Wang Xiaodong Wang Wilhelm Becker Institute of Applied Physics and Computational Mathematics P.O.Box 8009 Beijing 100088 China Institute of Theoretical Physics and Department of Physics Shanxi University Taiyuan 030006 China Institute of Applied Physics and Computational Mathematics P.O.Box 8009 Beijing 100088 China Institute of Theoretical Physics and Department of Physics Shanxi University Taiyuan 030006 China Laboratory of Optical Physics Beijing National Laboratory for Condensed Matter Physics Institute of Physics Chinese Academy of Sciences Beijing 100190 China College of Physics and Electronic Engineering Northwest Normal University Lanzhou 730070China Max Born Institute for Nonlinear Optics and Short-Pulse Spectroscopy Max-Born-Strasse 2a 12489 Berlin Germany

So far, nonsequential double ionization (NSDI) of atoms can be well understood within a semiclassical or even classical *** quantum effect appears to be required to explain the data *** theoretically study electron correlation resulting from NSDI of argon in a low-intensity laser field using a quantum-mechanical S-matrix *** show that quantum interference between the contributions of different intermediate excited states of the singly charged argon ion produces a transition from back-to-back to side-by-side emission with increasing laser intensity, which is in close agreement with the experimental *** higher intensities, this transition is enhanced by the consequences of depletion of the excited states.

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