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.

Fluctuation-dissipation theorem in nonequilibrium steady states

Abstract: In equilibrium, the fluctuation-dissipation theorem (FDT) expresses the response of an observable to a small perturbation by a correlation function of this variable with another one that is conjugate to the perturbation with respect to energy. For a nonequilibrium steady state (NESS), the corresponding FDT is shown to involve in the correlation function a variable that is conjugate with respect to entropy. By splitting up entropy production into one of the system and one of the medium, it is shown that for systems with a genuine equilibrium state the FDT of the NESS differs from its equilibrium form by an additive term involving total entropy production. A related variant of the FDT not requiring explicit knowledge of the stationary state is particularly useful for coupled Langevin systems. The a priori surprising freedom apparently involved in different forms of the FDT in a NESS is clarified.

Gravitaxis of asymmetric self-propelled colloidal particles

Abstract: Gravitaxis describes the ability of microorganisms to adjust their swimming motion on the gravitational field, yet its mechanism remains unclear. Here, the authors show that an asymmetric shape of colloidal particles is alone sufficient to induce gravitactic motion in the absence of density inhomogeneity.

Lattice-Boltzmann and finite-difference simulations for the permeability for three-dimensional porous media.

Abstract: Numerical micropermeametry is performed on three-dimensional porous samples having a linear size of approximately 3 mm and a resolution of 75 microm One of the samples is a microtomographic image of Fontainebleau sandstone Two of the samples are stochastic reconstructions with the same porosity, specific surface area, and two-point correlation function as the Fontainebleau sample The fourth sample is a physical model that mimics the processes of sedimentation, compaction, and diagenesis of Fontainebleau sandstone The permeabilities of these samples are determined by numerically solving at low Reynolds numbers the appropriate Stokes equations in the pore spaces of the samples The physical diagenesis model appears to reproduce the permeability of the real sandstone sample quite accurately, while the permeabilities of the stochastic reconstructions deviate from the latter by at least an order of magnitude This finding confirms earlier qualitative predictions based on local porosity theory Two numerical algorithms were used in these simulations One is based on the lattice-Boltzmann method, and the other on conventional finite-difference techniques The accuracy of these two methods is discussed and compared, also with experiment