771 research outputs found
Oscillating elastic defects: competition and frustration
We consider a dynamical generalization of the Eshelby problem: the strain
profile due to an inclusion or "defect" in an isotropic elastic medium. We show
that the higher the oscillation frequency of the defect, the more localized is
the strain field around the defect. We then demonstrate that the qualitative
nature of the interaction between two defects is strongly dependent on
separation, frequency and direction, changing from "ferromagnetic" to
"antiferromagnetic" like behavior. We generalize to a finite density of defects
and show that the interactions in assemblies of defects can be mapped to XY
spin-like models, and describe implications for frustration and
frequency-driven pattern transitions.Comment: 4 pages, 5 figure
Domain Wall and Periodic Solutions of Coupled phi4 Models in an External Field
Coupled double well (phi4) one-dimensional potentials abound in both
condensed matter physics and field theory. Here we provide an exhaustive set of
exact periodic solutions of a coupled model in an external field in
terms of elliptic functions (domain wall arrays) and obtain single domain wall
solutions in specific limits. We also calculate the energy and interaction
between solitons for various solutions. Both topological and nontopological
(e.g. some pulse-like solutions in the presence of a conjugate field) domain
walls are obtained. We relate some of these solutions to the recently observed
magnetic domain walls in certain multiferroic materials and also in the field
theory context wherever possible. Discrete analogs of these coupled models,
relevant for structural transitions on a lattice, are also considered.Comment: 35 pages, no figures (J. Math. Phys. 2006
Generalized stacking fault energetics and dislocation properties: compact vs. spread unit dislocation structures in TiAl and CuAu
We present a general scheme for analyzing the structure and mobility of
dislocations based on solutions of the Peierls-Nabarro model with a two
component displacement field and restoring forces determined from the ab-initio
generalized stacking fault energetics (ie., the so-called -surface).
The approach is used to investigate dislocations in L1 TiAl and CuAu;
predicted differences in the unit dislocation properties are explicitly related
with features of the -surface geometry. A unified description of
compact, spread and split dislocation cores is provided with an important
characteristic "dissociation path" revealed by this highly tractable scheme.Comment: 7 two columns pages, 2 eps figures. Phys. Rev. B. accepted November
199
Numerical study of domain coarsening in anisotropic stripe patterns
We study the coarsening of two-dimensional smectic polycrystals characterized
by grains of oblique stripes with only two possible orientations. For this
purpose, an anisotropic Swift-Hohenberg equation is solved. For quenches close
enough to the onset of stripe formation, the average domain size increases with
time as . Further from onset, anisotropic pinning forces similar to
Peierls stresses in solid crystals slow down defects, and growth becomes
anisotropic. In a wide range of quench depths, dislocation arrays remain mobile
and dislocation density roughly decays as , while chevron boundaries
are totally pinned. We discuss some agreements and disagreements found with
recent experimental results on the coarsening of anisotropic electroconvection
patterns.Comment: 8 pages, 11 figures. Phys. Rev E, to appea
Evolution of a Network of Vortex Loops in HeII. Exact Solution of the "Rate Equation"
Evolution of a network of vortex loops in HeII due to the fusion and
breakdown of vortex loops is studied. We perform investigation on the base of
the ''rate equation'' for the distribution function of number of loops
of length proposed by Copeland with coauthors. By using the special ansatz
in the ''collision'' integral we have found the exact power-like solution of
''kinetic equation'' in stationary case. That solution is the famous
equilibrium distribution obtained earlier in
numerical calculations. Our result, however, is not equilibrium, but on the
contrary, it describes the state with two mutual fluxes of the length (or
energy) in space of the vortex loop sizes. Analyzing this solution we drew
several results on the structure and dynamics of the vortex tangle in the
superfluid turbulent helium. In particular, we obtained that the mean radius of
the curvature is of order of interline space. We also obtain that the decay of
the vortex tangle obeys the Vinen equation, obtained earlier
phenomenologically. We evaluate also the full rate of reconnection events.
PACS-number 67.40Comment: 4 pages, submitted to PR
Shear-melting of a hexagonal columnar crystal by proliferation of dislocations
A hexagonal columnar crystal undergoes a shear-melting transition above a
critical shear rate or stress. We combine the analysis of the shear-thinning
regime below the melting with that of synchrotron X-ray scattering data under
shear and propose the melting to be due to a proliferation of dislocations,
whose density is determined by both techniques to vary as a power law of the
shear rate with a 2/3 exponent, as expected for a creep model of crystalline
solids. Moreover, our data suggest the existence under shear of a line hexatic
phase, between the columnar crystal and the liquid phase
Predicting dislocation climb: Classical modeling versus atomistic simulations
The classical modeling of dislocation climb based on a continuous description
of vacancy diffusion is compared to recent atomistic simulations of dislocation
climb in body-centered cubic iron under vacancy supersaturation [Phys. Rev.
Lett. 105 095501 (2010)]. A quantitative agreement is obtained, showing the
ability of the classical approach to describe dislocation climb. The analytical
model is then used to extrapolate dislocation climb velocities to lower
dislocation densities, in the range corresponding to experiments. This allows
testing of the validity of the pure climb creep model proposed by Kabir et al.
[Phys. Rev. Lett. 105 095501 (2010)]
The quantum smectic as a dislocation Higgs phase
The theory describing quantum-smectics in 2+1 dimensions, based on
topological quantum melting is presented. This is governed by a dislocation
condensate characterized by an ordering of Burger's vector and this `dual shear
superconductor' manifests itself in the form of a novel spectrum of phonon-like
modes.Comment: 5 pages, 3 figures; minor changes in the tex
Fluctuations and scaling in creep deformation
The spatial fluctuations of deformation are studied in creep in the Andrade's
power-law and the logarithmic phases, using paper samples. Measurements by the
Digital Image Correlation technique show that the relative strength of the
strain rate fluctuations increases with time, in both creep regimes. In the
Andrade creep phase characterized by a power law decay of the strain rate
, with , the fluctuations obey
, with . The local
deformation follows a data collapse appropriate for an absorbing
state/depinning transition. Similar behavior is found in a crystal plasticity
model, with a jamming or yielding phase transition
Diffusion-controlled phase growth on dislocations
We treat the problem of diffusion of solute atoms around screw dislocations.
In particular, we express and solve the diffusion equation, in radial symmetry,
in an elastic field of a screw dislocation subject to the flux conservation
boundary condition at the interface of a new phase. We consider an incoherent
second-phase precipitate growing under the action of the stress field of a
screw dislocation. The second-phase growth rate as a function of the
supersaturation and a strain energy parameter is evaluated in spatial
dimensions d=2 and d=3. Our calculations show that an increase in the amplitude
of dislocation force, e.g. the magnitude of the Burgers vector, enhances the
second-phase growth in an alloy. Moreover, a relationship linking the
supersaturation to the precipitate size in the presence of the elastic field of
dislocation is calculated.Comment: 10 pages, 4 figures, a revised version of the paper presented in
MS&T'08, October 5-9, 2008, Pittsburg
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