Search results for " approximation"
showing 10 items of 575 documents
Electronic structure and optical, mechanical, and transport properties of the pure, electron-doped, and hole-doped Heusler compound CoTiSb
2012
The Heusler compound CoTiSb was synthesized and investigated theoretically and experimentally with respect to electronic structure and optical, mechanical, and vibrational properties. The optical properties were investigated in a wide spectral range from 10 meV to 6.5 eV and compared with ab initio calculations. The optical spectra confirm the semiconducting nature of CoTiSb, with a strong exciton absorption at 1.83 eV. The calculated phonon dispersion as well as elastic constants verify the mechanical stability of CoTiSb in the cubic $C{1}_{b}$ system. Furthermore, solid solution series of CoTi${}_{1\ensuremath{-}x}$${M}_{x}$Sb ($M=\text{Sc}$, V and $0\ensuremath{\leqslant}x\ensuremath{\le…
First-principles calculations of perovskite thin films
2002
Abstract The results of the electronic structure calculations for different surface terminations of SrTiO3 (1 0 0) perovskite thin films are discussed. These calculations are based on ab initio Hartree–Fock method with a posteriori electron correlation corrections and density functional theory with a number of different exchange-correlation functionals, including hybrid (B3PW, B3LYP) exchange techniques. Results are compared with previous ab initio plane-wave local density approximation and classical shell model calculations. Calculated considerable increase of the Ti–O chemical bond covalency nearby the surface is confirmed by experimental data. We predict also the band-gap reduction, espe…
Temperature-dependent resistivity and anomalous Hall effect in NiMnSb from first principles
2019
We present implementation of the alloy analogy model within fully relativistic density-functional theory with the coherent potential approximation for a treatment of nonzero temperatures. We calculate contributions of phonons and magnetic and chemical disorder to the temperature-dependent resistivity, anomalous Hall conductivity (AHC), and spin-resolved conductivity in ferromagnetic half-Heusler NiMnSb. Our electrical transport calculations with combined scattering effects agree well with experimental literature for Ni-rich NiMnSb with 1--2% Ni impurities on Mn sublattice. The calculated AHC is dominated by the Fermi surface term in the Kubo-Bastin formula. Moreover, the AHC as a function o…
Some considerations on the transmissivity of trirefringent metamaterials
2016
Nonlocal effects in metal–dielectric (MD) periodic nanostructures may typically be observed when the plasmonic particles and gaps are on the scale of a few tens of nanometers, enabling under certain conditions (succinctly for epsilon near zero) a collimated beam to split into three refracted signals. We developed a method for precisely evaluating the categorized transmissivity in an air/trirefringent metamaterial interface, which uses a fast one-dimensional Fourier transform and finite element solvers of Maxwell’s equations. In periodic arrays of MD nanofilms, it is proved a tunable transmissivity switch of the multirefracted beams under varying angle of incidence and wavelength, while keep…
Ab initio studies on the lattice thermal conductivity of silicon clathrate frameworks II and VIII
2016
The lattice thermal conductivities of silicon clathrate frameworks II and VIII are investigated by using ab initio lattice dynamics and iterative solution of the linearized Boltzmann transport equation(BTE) for phonons. Within the temperature range 100-350 K, the clathrate structures II and VIII were found to have lower lattice thermal conductivity values than silicon diamond structure (d-Si) by factors of 1/2 and 1/5, respectively. The main reason for the lower lattice thermal conductivity of the clathrate structure II in comparison to d-Si was found to be the harmonic phonon spectra, while in the case of the clathrate structure VIII, the difference is mainly due to the harmonic phonon spe…
PAINT–SiCon: constructing consistent parametric representations of Pareto sets in nonconvex multiobjective optimization
2014
We introduce a novel approximation method for multiobjective optimization problems called PAINT–SiCon. The method can construct consistent parametric representations of Pareto sets, especially for nonconvex problems, by interpolating between nondominated solutions of a given sampling both in the decision and objective space. The proposed method is especially advantageous in computationally expensive cases, since the parametric representation of the Pareto set can be used as an inexpensive surrogate for the original problem during the decision making process. peerReviewed
Functional A Posteriori Error Estimates for Time-Periodic Parabolic Optimal Control Problems
2015
This article is devoted to the a posteriori error analysis of multiharmonic finite element approximations to distributed optimal control problems with time-periodic state equations of parabolic type. We derive a posteriori estimates of the functional type, which are easily computable and provide guaranteed upper bounds for the state and co-state errors as well as for the cost functional. These theoretical results are confirmed by several numerical tests that show high efficiency of the a posteriori error bounds. peerReviewed
Fully Polynomial Time Approximation Scheme for the Two-Parallel Capacitated Machines Scheduling Problem Under Unavailability Constraint
2010
Abstract Decision Support Systems (DSS) ensure the computer-based support for the conscientious decision-making in solving problems that require a large amount of information processing and complex scenarios. DSS for Transportation (DSST) are intelligent systems that are used at operational and organizational management levels. Operating a DSST in a public transportation web-based monitoring system is presented in this paper.
Moving Least Squares Innovative Strategies For Sheet Forming Design
2011
In the last years a great interest in optimization algorithms aimed to design forming processes was demonstrated by many researches. Proper design methodologies to reduce times and costs have to be developed mostly based on computer aided procedures. Response surface methods (RSM) proved their effectiveness in the recent years also for the application in sheet metal forming aiming to reduce the number of numerical simulations. Actually, the main drawback of such method is the number of direct problem to be solved in order to reach good function approximations. A very interesting aspect in RSM application regards the possibility to build response surfaces basing on moving least squares appro…
A contribution on the optimization strategies based on moving least squares approximation for sheet metal forming design
2012
Computer-aided procedures to design and optimize forming processes are, nowadays, crucial research topics since industrial interest in costs and times reduction is always increasing. Many researchers have faced this research challenge with various approaches. Response surface methods (RSM) are probably the most known approaches since they proved their effectiveness in the recent years. With a peculiar attention to sheet metal forming process design, RSM should offer the possibility to reduce the number of numerical simulations which in many cases means to reduce design times and complexity. Actually, the number of direct problems (FEM simulations) to be solved in order to reach good functio…