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Excitation and ionization of a simple two-level system by a harmonic force

JOURNAL OF PHYSICS A-MATHEMATICAL AND GENERAL 2005年第40期38卷 8681-8701页

作者： Rokhlenko, A Lebowitz, JL Rutgers State Univ Dept Math Piscataway NJ 08854 USA

A simple one-dimensional quantum system with two attractive delta-function potentials of strength q at x +/- 1 is subjected to a spatially asymmetric (as in the dipole interaction) harmonic forcing with frequency omega. The time evolution of the system, which has two discrete energy levels -omega(s), < -omega(a) (depending on q) and a continuum spectrum, exhibits a rich dynamics including regimes where the rate of ionization becomes very small due to the 'inverse' Ramsauer effect in electron-atom collisions. The two-photon ionization with omega approximate to omega(s)/2 can be enhanced when omega(a) = omega(s)/2 though the one-photon ionization is not affected significantly by the location of excited level. When omega is very close to the oneor two-photon resonance the ionization rate can differ greatly from that given by the low order perturbation theory even for small forcing amplitude. This is caused in part by the fact that the dynamic Stark effect has a strong dependence on omega and may shift the resonance frequencies omega(s) omega(a), up and down. When the ground state decays faster than the excited state and omega is not close to omega(s) - omega(a), the excited level at late times becomes and remains more populated than the ground state. The occupations of the bound states oscillate with a frequency that can be quite low compared with omega, in particular in the case omega approximate to omega(a) approximate to omega(s)/2, but it approaches omega when omega >> omega(s). Our analysis is based on the analytic structure of the wavefunction's Laplace transform in time. It considers one- and two-'photon' processes;the higher order multiphoton processes can also be treated by our computational scheme which goes beyond the low order perturbation theory.

关键词： MODEL QUANTUM SYSTEM MULTIPHOTON-IONIZATION MICROWAVE IONIZATION TIME EVOLUTION HYDROGEN FIELDS SURVIVAL RATES ATOMS PULSE ionization Atoms harmonic force Excitation Survival Hydrogen computational scheme

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Low-energy electron bremsstrahlung from metal clusters

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PHYSICS OF THE SOLID STATE 2004年第3期46卷 557-562页

作者： Kurkina, LI Russian Acad Sci Kutateladze Inst Thermal Phys Siberian Div Novosibirsk 630090 Russia

Expressions are derived allowing numerical calculation of the matrix element of the dipole moment between states that belong to a continuous spectrum for the case where a charged particle in an arbitrary orbital state is scattered by a spherically symmetric short-range potential. The calculation scheme is based on expanding a diverging matrix element into a sum of converging integrals. The method is used to study static bremsstrahlung of a slow electron scattered by sodium clusters. The bremsstrahlung cross section is shown to be resonant. The resonances arise at certain energies (depending on a cluster) of an electron having emitted a photon and are due to electron capture on quasi-steady-state levels. (C) 2004 MAIK "Nauka / Interperiodica".

关键词： Photon Electrons computational scheme metal clusters Bremsstrahlung Ions dipole moments LOW ENERGY Matrix Element Electron capture continuous spectra Metals Countries (nations) Clusters numerical calculation

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Methodological aspects of the tolerable windows approach

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CLIMATIC CHANGE 2003年第1期56卷 73-89页

作者： Bruckner, T Petschel-Held, G Leimbach, M Toth, FL Potsdam Inst Climate Impact Res D-14473 Potsdam Germany Tech Univ Berlin Inst Energy Engn D-10587 Berlin Germany

The tolerable windows approach (TWA) allows the climate policy formulation process to be safeguarded in the following way. First, guardrails are defined in order to exclude intolerable climate change impacts, on the one hand, and unacceptable socioeconomic consequences of climate change mitigation measures, on the other. Second, a scientific analysis is conducted to investigate the features of those emission paths that are compatible with the guardrail constraints. The fundamental methodology of the TWA is best described in terms of the theory of differential inclusions. This emerging mathematical theory already provides numerical methods applicable as long as the underlying integrated assessment models are of limited complexity. In order to identify emissions corridors, we propose a novel calculation scheme applicable also for large-scale integrated assessment models.

关键词： Climate-change Model FENSTER windows order Time-weighted average (TWA) large sizes Guardrails climate change computational scheme Emissions

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Combination of finite and boundary element methods in investigation and prediction of load-controlled noise of power transformers

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JOURNAL OF SOUND AND VIBRATION 2002年第2期250卷 323-338页

作者： Rausch, M Kaltenbacher, M Landes, H Lerch, R Anger, J Gerth, J Boss, P Univ Erlangen Nurnberg Dept Sensor Technol D-91052 Erlangen Germany ABB Transformatoren GmbH D-53585 Bad Honnef Germany ABB Secheron SA CH-1211 Geneva Switzerland

A recently developed calculation scheme for the computer modelling of the load-controlled noise of oil-insulated three-phase power transformers is presented. This modelling scheme allows the precise and efficient computation of the coupled electromagnetic, mechanical and acoustic fields. The equations are solved using the finite element method (FEM) as well as the boundary element method (BEM), resulting in a separation of the calculation of the winding and tank surface vibrations (using FEM) and the computation of the acoustic free-field radiation (using BEM). The complex dynamic behaviour of the loaded transformer can then be studied and, furthermore. an appropriate computer-aided design including an investigation and optimization of design parameters can be established. The validity of the computer simulations has been verified by means of appropriate measurements. Simulated and measured values for winding and tank surface vibrations as well as sound power levels of the loaded transformer are found to be in good agreement. The applicability of the calculation scheme with respect to the computer-aided design of power transformers is demonstrated by reporting two practical applications the influence of the stiffness of winding supports and the influence of the tap changer positions. (C) 2002 Academic Press.

关键词： sound power levels computational scheme load transformer ELECTRIC TRANSFORMERS design parameter windings Finite Surface dynamics Finite element method Tap changers Transformer winding (process) Computer-Aided Design load control Boundary element methods

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Nonempirical quantum-chemical calculation of the electric field gradient at the ⁵¹V nucleus sites in alkali metavanadates

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PHYSICS OF THE SOLID STATE 2002年第10期44卷 1864-1868页

作者： Vorotilova, LS Dmitrieva, LV Lavrov, SA Shchegolev, BF Russian Acad Sci IV Grebenshchikov Silicate Chem Inst St Petersburg 199155 Russia

The electric-field gradient tensor at the vanadium nucleus site was calculated ab initio within a cluster model for chained vanadates XVO3 (X = Li, Na, K). A comparison with experiment showed that it suffices to consider only small (VO4)(3-) and (V3O10)(5-) clusters in crystals of this type. The calculation scheme stability with respect to increasing cluster size was analyzed. (C) 2002 MAIK "Nauka/Interperiodica".

关键词： nuclei (nuclear physics) field gradient Cluster model Tensor Crystal structure types Clusters vanadates crystals Lithium computational scheme comparative experiment Vanadium

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Adaptive FE analysis of RC shells. I: Theory

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JOURNAL OF ENGINEERING MECHANICS-ASCE 2001年第12期127卷 1203-1212页

作者： Lackner, R Mang, HA Tech Univ Vienna Inst Strength Mat A-1040 Vienna Austria Vienna Tech Univ Inst Strength Mat A-1040 Vienna Austria

This paper contains the description of an adaptive calculation scheme for nonlinear (elastoplastic) finite element (FE) analysis. The underlying error estimator accounts for the error in the elastic regime as well as for the one arising from plastic loading. It is based on the stress recovery scheme proposed by Zienkiewicz and Zhu in 1992. The adaptation of the FE mesh is performed by means of the h-version of mesh refinement. The advancing front method is employed for remeshing. Before restart of the analysis after mesh refinement, the transfer of variables from the old to the new mesh must be performed. Unlike as for commonly used transfer schemes, the presented mode of transfer employs stresses and displacements for the evaluation of the state variables for the new mesh. All ingredients of the adaptive calculation scheme (i.e., error estimation, mesh generation, and the transfer of variables) are extended for application to the layer concept and to curved surfaces. Both extensions are necessary for adaptive analyses of reinforced concrete (RC) shells (see companion paper).

关键词： Restarting computational scheme Self tuning Ritchey-Chretien telescope State variable GTF2E1 gene Iron CURVES (GEOMETRY) Medical Subject Headings

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Adaptive FE analysis of RC shells. II: Applications

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JOURNAL OF ENGINEERING MECHANICS-ASCE 2001年第12期127卷 1213-1222页

作者： Lackner, R Mang, HA Vienna Tech Univ Inst Strength Mat A-1040 Vienna Austria

This paper deals with the application of an adaptive calculation scheme to ultimate load analyses of reinforced concrete (RC) plates and shells. The influence of the user-prescribed accuracy on the numerical results, especially on the ultimate load, is investigated. Three examples are considered: (1) a shear wall panel;(2) a circular plate, and (3) an RC cooling tower subjected to dead load and wind load. In addition to adaptive finite element (FE) analyses, single-mesh calculations on the basis of uniformly refined meshes are performed.

关键词： Static loads WALLBOARD Ritchey-Chretien telescope GTF2E1 gene Iron computational scheme ultimate loads LOAD Self tuning

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An efficient algorithm for calculating the heat capacity of a large-scale molecular system

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MACROMOLECULAR THEORY AND SIMULATIONS 2001年第8期10卷 756-761页

作者： Yang, C Noid, DW Sumpter, BG Sorensen, DC Tuzun, RE Oak Ridge Natl Lab Div Chem & Analyt Sci Oak Ridge TN 37831 USA Univ Calif Berkeley Lawrence Berkeley Lab Natl Energy Res Sci Comp Ctr Berkeley CA 94720 USA Rice Univ Dept Computat & Appl Math Houston TX 77005 USA SUNY Coll Brockport Dept Computat Sci Brockport NY 14420 USA

Full Paper: We present an efficient algorithm for computing the heat capacity of a large-scale molecular system. The new algorithm is based on a special Gaussian quadrature whose abscissas and weights are obtained by a simple Lanczos iteration. Our numerical, results have indicated that this new computational scheme is quite accurate. We have also shown that this method is at least a, hundred times faster than the earlier approach that is based on estimating the density:of states and integrating with a simple quadrature formula.

关键词： large sizes efficient algorithm computational scheme Quadrature Formula Abscissa Heat capacity

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Prediction of ductile fracture in axisymmetric tension by void coalescence

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INTERNATIONAL JOURNAL OF FRACTURE 2000年第4期105卷 391-409页

作者： Ragab, AR Cairo Univ Dept Mech Design & Prod Engn Giza Egypt

Fracture strains are predicted for ductile materials undergoing void growth and coalescence. The calculation scheme is based on Gurson-Tvergaard yield function and its associated flow rule. Fracture condition is identified by vanishing stress-carrying capacity of the material. The plastic flow parameters are all determined from experimental evidences for a variety of alloys. Comparison among predicted fracture strains and experimental ones is given for a wide range of conventional and superplastic materials as well as powder compacts. Finally an approximate fracture criterion is proposed.

关键词： A.R.RAGAB ductile material fracture criterion computational scheme STRAIN AT BREAK Powder compacts plastic flow Coalescence flow interval Micturition Bone Fracture flow law cracks

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Diradicaloids: Description by the spin-restricted, ensemble-referenced Kohn-Sham density functional method

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JOURNAL OF PHYSICAL CHEMISTRY A 2000年第28期104卷 6628-6636页

作者： Filatov, M Shaik, S Hebrew Univ Jerusalem Inst Chem IL-91904 Jerusalem Israel Hebrew Univ Jerusalem Lise Meitner Minerva Ctr Computat Quantum Chem IL-91904 Jerusalem Israel

A Kohn-Sham-type computational scheme capable of treating systems with strong nondynamic correlation is presented. The scheme, dubbed the spin-restricted, ensemble-referenced Kohn-Sham (REKS) method, is based on the representation of the density and energy for a strongly correlated system as weighted sums of densities and energies of several Kohn-Sham (KS) determinants. An optimal set of orthonormal KS orbitals and occupation numbers is obtained by minimizing the ground-state energy as a function of the density. Results of REKS calculations are reported and cover the following chemically important situations: (1) avoided crossing of potential energy surfaces, (2) bond-breaking processes, and (3) electronic structure of diradicals. The results of REKS calculations are compared with the available Kohn-Sham solutions for cases in which the exact density is known, as well as with results of conventional multireference ab initio methods and with the currently available density functional approaches.

关键词： .Strongly correlated occupation ab initio situations ground-state quantum chemistry diradicals Spin-restricted computational scheme REKS Ensemble-Referenced Kohn-Sham strong nondynamic correlation KS determinants KS orbitals multireference

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