Search results for " approximation"
showing 10 items of 575 documents
A reliable incremental method of computing the limit load in deformation plasticity based on compliance : Continuous and discrete setting
2016
The aim of this paper is to introduce an enhanced incremental procedure that can be used for the numerical evaluation and reliable estimation of the limit load. A conventional incremental method of limit analysis is based on parametrization of the respective variational formulation by the loading parameter ? ? ( 0 , ? l i m ) , where ? l i m is generally unknown. The enhanced incremental procedure is operated in terms of an inverse mapping ? : α ? ? where the parameter α belongs to ( 0 , + ∞ ) and its physical meaning is work of applied forces at the equilibrium state. The function ? is continuous, nondecreasing and its values tend to ? l i m as α ? + ∞ . Reduction of the problem to a finit…
A Comparison between Three Meta-Modeling Optimization Approaches to Design a Tube Hydroforming Process
2012
Computer aided procedures to design and optimize forming processes have become crucial research topics as the industrial interest in cost and time reduction has been increasing. A standalone numerical simulation approach could make the design too time consuming while meta-modeling techniques enables faster approximation of the investigated phenomena, reducing the simulation time. Many researchers are, nowadays, facing such research challenge by using various approaches. Response surface method (RSM) is probably the most known one, since its effectiveness was demonstrated in the past years. The effectiveness of RSM depends both on the definition of the Design of Experiments (DoE) and the acc…
Triangular Bézier Approximations to Constant Mean Curvature Surfaces
2008
We give a method to generate polynomial approximations to constant mean curvature surfaces with prescribed boundary. We address this problem by finding triangular Bezier extremals of the CMC-functional among all polynomial surfaces with a prescribed boundary. Moreover, we analyze the $\mathcal{C}^1$ problem, we give a procedure to obtain solutions once the tangent planes for the boundary curves are also given.
Modelling of defects and surfaces in perovskite ferroelectrics
2003
The results of electronic structure calculations for different terminations of SrTiO 3 (100) and (110) perovskite thin films are discussed. These calculations are based on the ab initio Hartree-Fock (HF) method and Density Functional Theory (DFT). Results are compared with previous ab initio plane-wave LDA and classical Shell Model (SM) calculations. Calculated considerable increase of the Ti-O chemical bond covalency nearby the surface is confirmed by experimental data. Our quantum chemical calculations performed by means of the intermediate neglect of differential overlap (INDO) method confirm the existence of self-trapped electrons in KNbO 3 , KTaO 3 and BaTiO 3 crystals. The relevant la…
Size dependent light absorption modulation and enhanced carrier transport in germanium quantum dots devices
2015
Quantum confinement in closely packed arrays of Ge quantum dots (QDs) was studied for energy applications. In this work, we report an efficient tuning mechanism of the light harvesting and detection of Ge QDs. Thin films of SiGeO alloys, produced by rf-magnetron sputtering, were annealed at 600 degrees C in N-2 to induce precipitation of small amorphous Ge QDs into the oxide matrix. Varying the Ge content, the QD size was tailored between 2 and 4 nm, as measured by high resolution transmission electron microscopy. X-ray photoelectron spectroscopy (XPS) measurements indicate the formation of pure SiO2, as well as the presence of a sub-stoichiometric Ge oxide shell at the QD interface. Light …
Measurement of proton electromagnetic form factors in the time-like region using initial state radiation at BESIII
2021
Physics letters / B 817, 136328 (2021). doi:10.1016/j.physletb.2021.136328
A New Approach to Deriving Interatomic Many-Body Interactions in Metals
1998
An original method of treating the kinetic and exchange-correlation en- ergies functionals in terms of many particle interactions was developed. It is based on utilizing the local density approximation. The total electron density, extracted from the ab initio . band structure calculations, is expressed as a lin- ear superposition of contributions from the individual pseudoions embedded in the uniform background. The explicit expressions for the pair and triplet potentials are presented. The general form for the part of the pair interatomic interactions caused by the kinetic and. the exchange-correlation effects is ob- tained. Relationship between the developing approach and the perturbation…
Small-sample characterization of stochastic approximation staircases in forced-choice adaptive threshold estimation
2007
Despite the widespread use of up—down staircases in adaptive threshold estimation, their efficiency and usability in forced-choice experiments has been recently debated. In this study, simulation techniques were used to determine the small-sample convergence properties of stochastic approximation (SA) staircases as a function of several experimental parameters. We found that satisfying some general requirements (use of the accelerated SA algorithm, clear suprathreshold initial stimulus intensity, large initial step size) the convergence was accurate independently of the spread of the underlying psychometric function. SA staircases were also reliable for targeting percent-correct levels far …
An Improved Iterative Nonlinear Least Square Approximation Method for the Design of SISO Wideband Mobile Radio Channel Simulators
2012
In this paper, we present an improved version of the iterative nonlinear least square approximation (INLSA) method for designing measurement-based single-input single-output (SISO) wideband channel simulators. The proposed method aims to fit the time-frequency correlation function (TFCF) of the simulation model to that of a measured channel. The parameters of the simulation model are determined iteratively by minimizing the Frobenius norm, which serves as a measure for the fitting error. In contrast to the original INLSA method, the proposed approach provides a unique optimized set of model parameters, which guarantees a quasi-perfect fitting with respect to the TFCF. We analyze the perform…
The Lang–Vojta Conjectures on Projective Pseudo-Hyperbolic Varieties
2020
These notes grew out of a mini-course given from May 13th to May 17th at UQAM in Montreal during a workshop on Diophantine Approximation and Value Distribution Theory.