University of Stuttgart

About: University of Stuttgart is a education organization based out in Stuttgart, Germany. It is known for research contribution in the topics: Laser & Finite element method. The organization has 27715 authors who have published 56370 publications receiving 1363382 citations. The organization is also known as: Universität Stuttgart.

Improved PO-MM hybrid formulation for scattering from three-dimensional perfectly conducting bodies of arbitrary shape

Abstract: The method of moments (MM) represents a suitable procedure for dealing with electromagnetic scattering problems of arbitrary geometrical shape in the lower frequency range. However, with increasing frequency both computation time and memory requirement often exceed available computer capacities. Therefore a current based hybrid method combining the MM with the physical optics (PO) approximation suitable for three-dimensional perfectly conducting bodies is proposed in this paper. The hybrid formulation allows a substantial reduction of computation time and memory requirement, while the results are in reasonable agreement with those based on an application of the MM alone. Further improvement can be achieved for flat polygonal parts of the scattering body by a heuristic modification of the PO current density taking into account the effects of edges. As opposed to the physical theory of diffraction (PTD), no additional electric and magnetic line currents along the edges are necessary. >

Transport of cargo by catalytic Janus micro-motors

Abstract: Catalytically active Janus micro-spheres are capable of autonomous motion and can potentially act as carriers for transportation of cargo at the micron-scale. Focusing on the cases in which a single or a pair of Janus micro-motors is used as carrier, we investigate the complex dynamics exhibited by various active carrier–cargo composites.

Geostatistical interpolation using copulas

Abstract: [1] In many applications of geostatistical methods, the dependence structure of the investigated parameter is described solely with the variogram or covariance functions, which are susceptible to measurement anomalies and implies the assumption of Gaussian dependence Moreover the kriging variance respects only observation density, data geometry and the variogram model To address these problems, we borrow the idea from copulas, to depict the dependence structure without the influence of the marginal distribution The methodology and basic hypotheses for application of copulas as geostatistical methods are discussed and the Gaussian copula as well as a non-Gaussian copula are used in this paper Copula parameters are estimated using a division of the observations into multipoint subsets and a subsequent maximization of the corresponding likelihood function The interpolation is carried out with two different copulas, where the expected and median values are calculated from the copulas conditioned with the nearby observations The full conditional copulas provide the estimation distributions for the unobserved locations and can be used to define confidence intervals which depend on both the observation geometry and values Observations of a large scale groundwater quality measurement network in Baden-Wurttemberg are used to demonstrate the methodology Five groundwater quality parameters: chloride, nitrate, pH, sulfate and dissolved oxygen are investigated All five parameters show non-Gaussian dependence The copula-based interpolation results of the five parameters are compared to the results of conventional ordinary and indicator kriging Different statistical measures including mean squared error, relative differences and probability scores are used to compare cross validation and split sampling results of the interpolation methods The non-Gaussian copulas give better results than the geostatistical interpolations Validation of the confidence intervals shows that they are more realistic than the estimation variances obtained by ordinary kriging

The Parallel Grammar project

Abstract: We report on the Parallel Grammar (ParGram) project which uses the XLE parser and grammar development platform for six languages: English, French, German, Japanese, Norwegian, and Urdu.

An efficient local coupled cluster method for accurate thermochemistry of large systems

Abstract: An efficient local coupled cluster method with single and double excitation operators and perturbative treatment of triple excitations [DF-LCCSD(T)] is described All required two-electron integrals are evaluated using density fitting approximations These have a negligible effect on the accuracy but reduce the computational effort by 1–2 orders of magnitude, as compared to standard integral-direct methods Excitations are restricted to local subsets of non-orthogonal virtual orbitals (domain approximation) Depending on distance criteria, the correlated electron pairs are classified into strong, close, weak, and very distant pairs Only strong pairs, which typically account for more than 90% of the correlation energy, are optimized in the LCCSD treatment The remaining close and weak pairs are approximated by LMP2 (local second-order Moller-Plesset perturbation theory); very distant pairs are neglected It is demonstrated that the accuracy of this scheme can be significantly improved by including the close pair LMP2 amplitudes in the LCCSD equations, as well as in the perturbative treatment of the triples excitations Using this ansatz for the wavefunction, the evaluation and transformation of the two-electron integrals scale cubically with molecular size If local density fitting approximations are activated, this is reduced to linear scaling The LCCSD iterations scale quadratically, but linear scaling can be achieved by neglecting some terms involving contractions of single excitations The accuracy and efficiency of the method is systematically tested using various approximations, and calculations for molecules with up to 90 atoms and 2636 basis functions are presented