1,660 research outputs found
The axisymmetric antidynamo theorem revisited
The axisymmetric kinematic dynamo problem is reconsidered and a number of
open questions are answered. Apart from axisymmetry and smoothness of data and
solution we deal with this problem under quite general conditions, i.e. we
assume a compressible fluid of variable (in space and time) conductivity moving
in an arbitrary (axisymmetric) domain. We prove unconditional, pointwise and
exponential decay of magnetic field and electric current to zero. The decay
rate of the external (meridional) magnetic field can become very small
(compared to free decay) for special flow fields and large magnetic Reynolds
numbers. We give an example of that. On the other hand, we show for fluids with
weak variation of mass density and conductivity that the meridional and
azimuthal decay rates do not drop significantly below those of free decay.Comment: Revised version, 28 pages, 1 figur
Realistic, Extensible DNS and mDNS Models for INET/OMNeT++
The domain name system (DNS) is one of the core services in today's network
structures. In local and ad-hoc networks DNS is often enhanced or replaced by
mDNS. As of yet, no simulation models for DNS and mDNS have been developed for
INET/OMNeT++. We introduce DNS and mDNS simulation models for OMNeT++, which
allow researchers to easily prototype and evaluate extensions for these
protocols. In addition, we present models for our own experimental extensions,
namely Stateless DNS and Privacy-Enhanced mDNS, that are based on the
aforementioned models. Using our models we were able to further improve the
efficiency of our protocol extensions.Comment: Published in: A. F\"orster, C. Minkenberg, G. R. Herrera, M. Kirsche
(Eds.), Proc. of the 2nd OMNeT++ Community Summit, IBM Research - Zurich,
Switzerland, September 3-4, 201
An Annular Plate Model in Arbitrary-Lagrangian-Eulerian Description for the DLR FlexibleBodies Library
The bending deformation of rotating annular plates and the associated vibration behaviour is important in engineering applications which range from automotive or railway brake systems to discs that form essential components in turbomachinery.
In order to extend the capabilities of the DLR FlexibleBodies library for such use cases, a new Modelica class has been implemented which is based on the analytical description of an annular Kirchhoff plate. In addition the so-called Arbitray Langrangian-Eulerian (ALE) representation has been adopted so that rotating and non-rotating external loads may be applied conventiently to rotating plates.
Besides these particularities the new class AnnularPlate completely corresponds to the concept of FlexibleBodies library with the two already available model classes Beam and ModalBody.
This paper gives an overview on the theoretical background of the new class AnnularPlate, explains the usage and presents application examples
Differently Shaped Hard Body Colloids in Confinement: From passive to active particles
We review recent progress in the theoretical description of anisotropic hard
colloidal particles. The shapes considered range from rods and dumbbells to
rounded cubes, polyhedra and to biaxial particles with arbitrary shape. Our
focus is on both static and dynamical density functional theory and on computer
simulations. We describe recent results for the structure, dynamics and phase
behaviour in the bulk and in various confining geometries, e.g. established by
two parallel walls which reduce the dimensionality of the system to two
dimensions. We also include recent theoretical modelling for active particles,
which are autonomously driven by some intrinsic motor, and highlight their
fascinating nonequilibrium dynamics and collective behaviour.Comment: 15 pages, 6 figures, EPJ ST (accepted
Fundamentals of electro-mechanically coupled cohesive zone formulations for electrical conductors
Motivated by the influence of (micro-)cracks on the effective electrical properties of material systems and components, this contribution deals with fundamental developments on electro-mechanically coupled cohesive zone formulations for electrical conductors. For the quasi-stationary problems considered, Maxwell’s equations of electromagnetism reduce to the continuity equation for the electric current and to Faraday’s law of induction, for which non-standard jump conditions at the interface are derived. In addition, electrical interface contributions to the balance equation of energy are discussed and the restrictions posed by the dissipation inequality are studied. Together with well-established cohesive zone formulations for purely mechanical problems, the present developments provide the basis to study the influence of mechanically-induced interface damage processes on effective electrical properties of conductors. This is further illustrated by a study of representative boundary value problems based on a multi-field finite element implementation
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