11,432 research outputs found
Measure of combined effects of morphological parameters of inclusions within composite materials via stochastic homogenization to determine effective mechanical properties
In our previous papers we have described efficient and reliable methods of
generation of representative volume elements (RVE) perfectly suitable for
analysis of composite materials via stochastic homogenization.
In this paper we profit from these methods to analyze the influence of the
morphology on the effective mechanical properties of the samples. More
precisely, we study the dependence of main mechanical characteristics of a
composite medium on various parameters of the mixture of inclusions composed of
spheres and cylinders. On top of that we introduce various imperfections to
inclusions and observe the evolution of effective properties related to that.
The main computational approach used throughout the work is the FFT-based
homogenization technique, validated however by comparison with the direct
finite elements method. We give details on the features of the method and the
validation campaign as well.
Keywords: Composite materials, Cylindrical and spherical reinforcements,
Mechanical properties, Stochastic homogenization.Comment: 23 pages, updated figures, version accepted to Composite Structures
201
Unfolding the Sulcus
Sulci are localized furrows on the surface of soft materials that form by a
compression-induced instability. We unfold this instability by breaking its
natural scale and translation invariance, and compute a limiting bifurcation
diagram for sulcfication showing that it is a scale-free, sub-critical {\em
nonlinear} instability. In contrast with classical nucleation, sulcification is
{\em continuous}, occurs in purely elastic continua and is structurally stable
in the limit of vanishing surface energy. During loading, a sulcus nucleates at
a point with an upper critical strain and an essential singularity in the
linearized spectrum. On unloading, it quasi-statically shrinks to a point with
a lower critical strain, explained by breaking of scale symmetry. At
intermediate strains the system is linearly stable but nonlinearly unstable
with {\em no} energy barrier. Simple experiments confirm the existence of these
two critical strains.Comment: Main text with supporting appendix. Revised to agree with published
version. New result in the Supplementary Informatio
Dynamical tunnelling with ultracold atoms in magnetic microtraps
The study of dynamical tunnelling in a periodically driven anharmonic
potential probes the quantum-classical transition via the experimental control
of the effective Planck's constant for the system. In this paper we consider
the prospects for observing dynamical tunnelling with ultracold atoms in
magnetic microtraps on atom chips. We outline the driven anharmonic potentials
that are possible using standard magnetic traps, and find the Floquet spectrum
for one of these as a function of the potential strength, modulation, and
effective Planck's constant. We develop an integrable approximation to the
non-integrable Hamiltonian and find that it can explain the behaviour of the
tunnelling rate as a function of the effective Planck's constant in the regular
region of parameter space. In the chaotic region we compare our results with
the predictions of models that describe chaos-assisted tunnelling. Finally we
examine the practicality of performing these experiments in the laboratory with
Bose-Einstein condensates.Comment: V1: 12 pages, 10 figures. V2: 14 pages, 12 figures, significantly
updated in response to referee report. Some figures are lower quality to
reduce file sizes, please contact submitter for high quality versions. V3:
Introduction rewritten, but mostly unchanged; updated to published versio
Wave packet approach to transport in mesoscopic systems
Wave packets provide a well established and versatile tool for studying
time-dependent effects in molecular physics. Here, we demonstrate the
application of wave packets to mesoscopic nanodevices at low temperatures. The
electronic transport in the devices is expressed in terms of scattering and
transmission coefficients, which are efficiently obtained by solving an initial
value problem (IVP) using the time-dependent Schroedinger equation. The
formulation as an IVP makes non-trivial device topologies accessible and by
tuning the wave packet parameters one can extract the scattering properties for
a large range of energies.Comment: 12 pages, 4 figure
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