2,170 research outputs found
Modeling the behavior of elastic materials with stochastic microstructure
Even in the simple linear elastic range, the material behavior is not deterministic, but ïŹuctuates randomly around some expectation values. The knowledge about this characteristic is obviously trivial from an experimentalistâs point of view. However, it is not considered in the vast majority of material models in which âonlyâ deterministic behavior is taken into account. One very promising approach to the inclusion of stochastic eïŹects in modeling of materials is provided by the Karhunen-Lo`eve expansion. It has been used, for example, in the stochastic ïŹnite element method, where it yields results of the desired kind, but unfortunately at drastically increased numerical costs. This contribution aims to propose a new ansatz that is based on a stochastic series expansion, but at the GauĂ point level. Appropriate energy relaxation allows to derive the distribution of a synthesized stress measure, together with explicit formulas for the expectation and variance. The total procedure only needs negligibly more computation eïŹort than a simple elastic calculation. We also present an outlook on how the original approach in [7] can be applied to inelastic material
Construction of classical superintegrable systems with higher order integrals of motion from ladder operators
We construct integrals of motion for multidimensional classical systems from
ladder operators of one-dimensional systems. This method can be used to obtain
new systems with higher order integrals. We show how these integrals generate a
polynomial Poisson algebra. We consider a one-dimensional system with third
order ladders operators and found a family of superintegrable systems with
higher order integrals of motion. We obtain also the polynomial algebra
generated by these integrals. We calculate numerically the trajectories and
show that all bounded trajectories are closed.Comment: 10 pages, 4 figures, to appear in j.math.phys
Phase Coherence and Superfluid-Insulator Transition in a Disordered Bose-Einstein Condensate
We have studied the effects of a disordered optical potential on the
transport and phase coherence of a Bose-Einstein condensate (BEC) of 7Li atoms.
At moderate disorder strengths (V_D), we observe inhibited transport and
damping of dipole excitations, while in time-of-flight images, random but
reproducible interference patterns are observed. In-situ images reveal that the
appearance of interference is correlated with density modulation, without
complete fragmentation. At higher V_D, the interference contrast diminishes as
the BEC fragments into multiple pieces with little phase coherence.Comment: 4 pages, 5 figures, distortions in figures 1 and 4 have been fixed in
version 3. This paper has been accepted to PR
Full-analytic frequency-domain 1pN-accurate gravitational wave forms from eccentric compact binaries
The article provides ready-to-use 1pN-accurate frequency-domain gravitational
wave forms for eccentric nonspinning compact binaries of arbitrary mass ratio
including the first post-Newtonian (1pN) point particle corrections to the
far-zone gravitational wave amplitude, given in terms of tensor spherical
harmonics. The averaged equations for the decay of the eccentricity and growth
of radial frequency due to radiation reaction are used to provide stationary
phase approximations to the frequency-domain wave forms.Comment: 28 pages, submitted to PR
Experimental investigation of the tire wear process using camera-assisted observation assessed by numerical modeling
This paper presents a novel experimental method to study the abrasion mechanism of car tires. It is based on the detection of microscopic movements associated with material damage (cracking) on the rubber tread. This is referred to as degrading layer relaxation. It correlates with the wear rate and, interestingly, the direction of the pattern's movement is opposite to the lateral forces during cornering. To measure and analyze the microscopic movements, a new camera-based method with feature point matching using video stabilization was developed. Besides extensive experimental investigation, the formation and propagation of microcracks are investigated using a simplified numerical model in which a phase field approach coupled with a viscoelastic constitutive behavior is implemented in a finite element framework
Topological methods for searching barriers and reaction paths
We present a family of algorithms for the fast determination of reaction
paths and barriers in phase space and the computation of the corresponding
rates. The method requires the reaction times be large compared to the
microscopic time, irrespective of the origin - energetic, entropic, cooperative
- of the timescale separation. It lends itself to temperature cycling as in
simulated annealing and to activation-relaxation routines. The dynamics is
ultimately based on supersymmetry methods used years ago to derive Morse
theory. Thus, the formalism automatically incorporates all relevant topological
information.Comment: 4 pages, 4 figures, RevTex
Freezing of Spinodal Decompostion by Irreversible Chemical Growth Reaction
We present a description of the freezing of spinodal decomposition in
systems, which contain simultaneous irreversible chemical reactions, in the
hydrodynamic limit approximation. From own results we conclude, that the
chemical reaction leads to an onset of spinodal decomposition also in the case
of an initial system which is completely miscible and can lead to an extreme
retardation of the dynamics of the spinodal decomposition, with the probability
of a general freezing of this process, which can be experimetally observed in
simultaneous IPN formation.Comment: 10 page
Double Neutron Star Systems and Natal Neutron Star Kicks
We study the four double neutron star systems found in the Galactic disk in
terms of the orbital characteristics of their immediate progenitors and the
natal kicks imparted to neutron stars. Analysis of the effect of the second
supernova explosion on the orbital dynamics, combined with recent results from
simulations of rapid accretion onto neutron stars lead us to conclude that the
observed systems could not have been formed had the explosion been symmetric.
Their formation becomes possible if kicks are imparted to the radio-pulsar
companions at birth. We identify the constraints imposed on the immediate
progenitors of the observed double neutron stars and calculate the ranges
within which their binary characteristics (orbital separations and masses of
the exploding stars) are restricted. We also study the dependence of these
limits on the magnitude of the kick velocity and the time elapsed since the
second explosion. For each of the double neutron stars, we derive a minimum
kick magnitude required for their formation, and for the two systems in close
orbits we find it to exceed 200km/s. Lower limits are also set to the
center-of-mass velocities of double neutron stars, and we find them to be
consistent with the current proper motion observations.Comment: 25 pages, 6 figs (9 parts), 4 tables, AASTeX, Accepted in Ap
Duality and Anholonomy in Quantum Mechanics of 1D Contact Interactions
We study systems with parity invariant contact interactions in one dimension.
The model analyzed is the simplest nontrivial one --- a quantum wire with a
point defect --- and yet is shown to exhibit exotic phenomena, such as strong
vs weak coupling duality and spiral anholonomy in the spectral flow. The
structure underlying these phenomena is SU(2), which arises as accidental
symmetry for a particular class of interactions.Comment: 4 pages ReVTeX with 4 epsf figures. KEK preprint 2000-3. Correction
in Eq.(14
Coalescing binary systems of compact objects: Dynamics of angular momenta
The end state of a coalescing binary of compact objects depends strongly on
the final total mass M and angular momentum J. Since gravitational radiation
emission causes a slow evolution of the binary system through quasi-circular
orbits down to the innermost stable one, in this paper we examine the
corresponding behavior of the ratio J/M^2 which must be less than 1(G/c) or
about 0.7(G/c) for the formation of a black hole or a neutron star
respectively. The results show cases for which, at the end of the inspiral
phase, the conditions for black hole or neutron star formation are not
satisfied. The inclusion of spin effects leads us to a study of precession
equations valid also for the calculation of gravitational waveforms.Comment: 22 pages, AASTeX and 13 figures in PostScrip
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