Search

Your search keyword '"Römer S"' showing total 272 results
Start Over Author "Römer S"
272 results on '"Römer S"'

1. Asymptotic Behavior of Bohmian Trajectories in Scattering Situations

Author

Roemer, S., Duerr, D., and Moser, T.

Subjects
Mathematical Physics
Abstract

We study the asymptotic behavior of Bohmian trajectories in a scattering situation with short range potential and for wave functions with a scattering and a bound part. It is shown that the set of possible trajectories splits into trajectories whose long time behavior is governed by the scattering part of the wave function (scattering trajectories) and trajectories whose long time behavior is governed by the bound part of the wave function (bound trajectories). Furthermore the scattering trajectories behave like trajectories in classical mechanics in the long time limit. As an intermediate step we show that the asymptotic velocity v_{infty}:=lim_{t to infty}Q/t exists almost surely and is randomly distributed with the density |hat{Psi}^{out}|^2, where Psi^{out} is the outgoing asymptote of the scattering part of the wave function., Comment: 24 pages, 2 figures; added references in section 1

Published
2005
Full Text
View/download PDF

15. Gaussian-based multiconfiguration time-dependent Hartree: A two-layer approach. II. Application to vibrational energy transport in a molecular chain.

Author

Eisenbrandt, P., Ruckenbauer, M., Römer, S., and Burghardt, I.

Subjects
GAUSSIAN processes, GAUSSIAN basis sets (Quantum mechanics), WAVE packets, WAVE functions, ENERGY transfer
Abstract

We report on first applications of the Two-Layer Gaussian-based Multi-Configuration Time-Dependent Hartree (2L-GMCTDH) method [Römer et al., J. Chem. Phys. 138, 064106 (2013)] for high-dimensional quantum propagation using variational Gaussian basis sets. This method circumvents the limitations of conventional variational Gaussian wavepacket (GWP) methods by introducing a hierarchical wavefunction representation with a fully flexible first layer composed of orthogonal single-particle functions, which are in turn expressed as superpositions of GWPs of fixed width. The method is applied to a model Hamiltonian describing vibrational energy transport through a molecular chain. The model combines bilinear site-to-site couplings with site-local couplings induced by cubic anharmonicities. We report on simulation results for realizations comprising 5 sites with 35 vibrational modes and 18 sites with 90 vibrational modes, which are shown to be in excellent agreement with reference calculations by the Multi-Layer MCTDH method. [ABSTRACT FROM AUTHOR]

Published
2018
Full Text
View/download PDF

31. Anal Fistulas

Author

Staimmer, D., primary, Römer, S., additional, Bergmann, U., additional, and Hoffmann, T., additional

Published
1991
Full Text
View/download PDF

33. Gaussian-based multiconfiguration time-dependent Hartree: A two-layer approach. I. Theory.

Author

Römer, S., Ruckenbauer, M., and Burghardt, I.

Subjects
*GAUSSIAN processes, *STOCHASTIC convergence, *QUANTUM theory, *PARTICLES, *MATHEMATICAL functions
Abstract

We describe a novel two-layer variant of the Gaussian-based multiconfiguration time-dependent Hartree (G-MCTDH) approach which improves on the performance and convergence properties of quantum propagation based on variationally evolving frozen Gaussians (FGs). While the standard scheme uses factorizable multi-dimensional FGs, the present approach combines these into flexible, MCTDH-like single-particle functions. At the same time, the expensive variational evolution of the Gaussian parameters is reduced to low-dimensional subspaces. As a result, the novel scheme significantly alleviates the current bottleneck to accurate propagation in G-MCTDH and its variational multiconfigurational Gaussian (vMCG) variant. Since the first-layer single-particle functions are chosen to be orthogonal, the present approach can be straightforwardly combined with existing multi-layer MCTDH schemes. [ABSTRACT FROM AUTHOR]

Published
2013
Full Text
View/download PDF

38. A common haplotype of protamine 1 and 2 genes is associated with higher sperm counts

Author

Frank Tüttelmann, Joerg Gromoll, Aleksandra Nestorovic, Macek M, Manuela Simoni, Mila Ljujic, P. Krenkova, Römer S, Stambergová A, and Eberhard Nieschlag

Subjects
Linkage disequilibrium, urogenital system, Urology, Endocrinology, Diabetes and Metabolism, Haplotype, Semen, Biology, Teratozoospermia, medicine.disease, Sperm, Protamine, Male infertility, Andrology, Reproductive Medicine, medicine, biology.protein, Spermatogenesis
Abstract

Sperm chromatin compaction in the sperm head is achieved when histones are replaced by protamines during spermatogenesis. Haploinsufficiency of the protamine 1 (PRM1) or PRM2 gene causes infertility in mice. However, the published data remain inconclusive about a role of PRM1/2 variants in male infertility and their association with semen parameters. By full sequence analysis, we assessed the frequency of sequence variations in PRM1 and PRM2 in three groups of Caucasian patients with idiopathic teratozoospermia and normal (n = 88) or reduced sperm concentration (n = 83) and in men with a high percentage of normal sperm morphology and normal concentrations (n = 77). Two rare (c.54G>A and c.102G>T) and one common SNP (c.230A>C) were identified in PRM1. In PRM2, some rare heterozygous mutations and the two common intronic SNPs 298G>C and 373C>A were detected. None of the PRM1/2 variants was associated with teratozoospermia or individually with other semen parameters. However, significant linkage disequilibrium was detected between the common SNPs of PRM1 and PRM2 which formed haplotypes. Analysis of the pooled group (n = 248) revealed that homozygous carriers of the common haplotype ACC had a twofold higher sperm concentration and count than men lacking this haplotype, with sperm counts of heterozygotes for ACC being midway between the homozygotes. This markedly decreased sperm output might either be caused by spermatozoa lacking the ACC haplotype not being viable, or subject to negative selection. In addition, a significant deviation from Hardy-Weinberg-Equilibrium of these SNPs might indicate natural selection in favour of the ACC allele which leads to higher sperm output and therefore better fertility. In conclusion, for the first time we describe an association of a common haplotype formed by PRM1 and PRM2 with sperm output in a large group of men.

Published
2009
Full Text
View/download PDF

Catalog

Books, media, physical & digital resources
See catalog results