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Green's Function Method (green + function_method)
Selected AbstractsQuasiperiodic impurity energy spectra of GaAs/GaxAl1,xAs superlatticesPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue S2 2004M. S. Vasconcelos Abstract In this work we consider a generalized Fibonacci quasiperiodic superlattice (GFQPSL), within a tight-binding model, in which its nearest-neighbor-hopping matrix elements are distributed according to the generalized Fibonacci sequence. The electronic density of states (DOS) is then determined by using a Green function method based on Dyson's equation together with a transfer-matrix treatment. The resulting energy spectrum is then determined, considering initial physical parameters according to the scheme used in the experimental realization of a GFQPSL. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] A comparison of two spectral approaches for computing the Earth response to surface loadsGEOPHYSICAL JOURNAL INTERNATIONAL, Issue 2 2000E. Le Meur Summary When predicting the deformation of the Earth under surface loads, most models follow the same methodology, consisting of producing a unit response that is then con-volved with the appropriate surface forcing. These models take into account the whole Earth, and are generally spherical, computing a unit response in terms of its spherical harmonic representation through the use of load Love numbers. From these Love numbers, the spatial pattern of the bedrock response to any particular scenario can be obtained. Two different methods are discussed here. The first, which is related to the convolution in the classical sense, appears to be very sensitive to the total number of degrees used when summing these Love numbers in the harmonic series in order to obtain the corresponding Green's function. We will see from the spectral properties of these Love numbers how to compute these series correctly and how consequently to eliminate in practice the sensitivity to the number of degrees (Gibbs Phenomena). The second method relies on a preliminary harmonic decomposition of the load, which reduces the convolution to a simple product within Fourier space. The convergence properties of the resulting Fourier series make this approach less sensitive to any harmonic cut-off. However, this method can be more or less computationally expensive depending on the loading characteristics. This paper describes these two methods, how to eliminate Gibbs phenomena in the Green's function method, and shows how the load characteristics as well as the available computational resources can be determining factors in selecting one approach. [source] Numerical analysis of a new Eulerian,Lagrangian finite element method applied to steady-state hot rolling processesINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN ENGINEERING, Issue 5 2005Josef Synka Abstract A finite element code for steady-state hot rolling processes of rigid,visco-plastic materials under plane,strain conditions was developed in a mixed Eulerian,Lagrangian framework. This special set up allows for a direct calculation of the local deformations occurring at the free surfaces outside the contact region between the strip and the work roll. It further simplifies the implementation of displacement boundary conditions, such as the impenetrability condition. When applied to different practical hot rolling situations, ranging from thick slab to ultra-thin strip rolling, the velocity,displacement based model (briefly denoted as vu-model) in this mixed Eulerian,Lagrangian reference system proves to be a robust and efficient method. The vu-model is validated against a solely velocity-based model (vv-model) and against elementary methods based on the Kármán,Siebel and Orowan differential equations. The latter methods, when calibrated, are known to be in line with experimental results for homogeneous deformation cases. For a massive deformation it is further validated against the commercial finite-element software package Abaqus/Explicit. It is shown that the results obtained with the vu-model are in excellent agreement with the predictions of the vv-model and that the vu-model is even more robust than its vv-counterpart. Throughout the study we assumed a rigid cylindrical work roll; only for the homogeneous test case, we also investigated the effect of an elastically deformable work roll within the frame of the Jortner Green's function method. The new modelling approach combines the advantages of conventional Eulerian and Lagrangian modelling concepts and can be extended to three dimensions in a straightforward manner. Copyright © 2004 John Wiley & Sons, Ltd. [source] Redox-induced configuration conversion for thioacetamide dimer can function as a molecular switchJOURNAL OF COMPUTATIONAL CHEMISTRY, Issue 14 2010Haiying Liu Abstract The electronic switching properties of thioacetamide dimer (TAD) were investigated using the nonequilibrium Green's function method combined with density functional theory for design of a novel molecular switch. The H-bonded TAD can be converted upon hole-trapping to a three-electron (3e)-bonded configuration with a S,S linkage which could provide a more favorable channel for charge transfer than the before. The redox-induced configuration conversion between the H-bonded and the 3e-bonded TADs could govern the charge migration through the molecular junction with a considerable difference in conduction currents. The calculated I,V characteristic curves of two configurations exhibit a switching behavior with an On-Off ratio in a range of about 4.3,7.6 within the applied voltages. Clearly, this hypothetical scheme provides a potential way to explore the novel conformation-dependent molecular switch. © 2010 Wiley Periodicals, Inc. J Comput Chem 2010 [source] Theoretical Simulation of Oxygen Transport to Brain by Networks of Microvessels: Effects of Oxygen Supply and Demand on Tissue HypoxiaMICROCIRCULATION, Issue 4 2000T.W. SECOMB ABSTRACT Objective: Simulations of oxygen delivery by a three-dimensional network of microvessels in rat cerebral cortex were used to examine how the distribution of partial pressure of oxygen (PO2) in tissue depends on blood flow and oxygen consumption rates. Methods: Network geometry was deduced from previously published scanning electron micrographs of corrosion casts. A nonlinear least-squares method, using images obtained at three different angles, was used to estimate vessel locations. The network consisted of 50 segments in a region 140 µm × 150 µm × 160 µm. A Green's function method was used to predict the PO2 distribution. Effects of varying perfusion and consumption were examined, relative to a control state with consumption 10 cm3O2/100 g per min and perfusion 160 cm3/100 g per min. Results: In the control state, minimum tissue PO2 was 7 mm Hg. A Krogh-type model with the same density of vessels, but with uniform spacing, predicted a minimum tissue PO2 of 23 mm Hg. For perfusion below 60% of control, tissue hypoxia (PO2 <1 mm Hg) was predicted. When perfusion was reduced by 75%, the resulting hypoxia could be eliminated by a 31% reduction in oxygen consumption rate. Conclusions: The simulations suggest that tissue hypoxia resulting from a severe decrease in brain perfusion, as can occur in stroke, may be avoided by a moderate decrease in oxygen consumption rate. [source] Improvement of the resonant characteristics of the short-ended stub by the optimal arrangement positions of via-holesMICROWAVE AND OPTICAL TECHNOLOGY LETTERS, Issue 3 2007Ifong Wu Abstract A method for improving the resonant characteristic of the short-ended stub is proposed by locating the via-holes on the optimal position on the ground. In the first step, the optimal length of the stub at 1 GHz is evaluated by comparing the numerical calculated result and the measured result (used the fabricated stub), which is based on the theoretical calculation, and the resonant characteristics shifted to the lower frequency regions. These shifting phenomena of the resonant characteristics are caused by the via-hole. When the via-hole is arranged on the substrate, the via-hole becomes part of the stub, and the length of the stub becomes longer than the theoretical calculation. As a result, a good agreement between both results is achieved when the stub length is 27.43 mm, and hence the optimal length of the stub is confirmed. For the second step, the optimal arrangement position of the via-holes is evaluated by using current distribution on the stub model. In this study, we applied the Green's function method to obtain the current distribution. The improvement of resonant characteristic is achieved by arranging the via-holes on the place where the currents concentrate. © 2007 Wiley Periodicals, Inc. Microwave Opt Technol Lett 49: 642,645, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.22202 [source] Optical nanometrology of Au nanoparticles on a multilayer filmPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 5 2008Yia-Chung Chang Abstract Ellipsometric measurements coupled with efficient theoretical modeling are used to determine the size and distribution density of Au nanoparticles on a multilayer film. The rigorous coupled-wave analysis (RCWA) and finiteelement Green's function method were used to model the polarization-dependent reflectivity, and the model calculations are in reasonable agreement with the measurements. This demonstrates that the spectroscopic ellipsometry could be a useful optical tool for nondestructive nanometrology. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] | ||||||||||