3,389 research outputs found
Conservation and persistence of spin currents and their relation to the Lieb-Schulz-Mattis twist operators
Systems with spin-orbit coupling do not conserve "bare" spin current
. A recent proposal for a conserved spin current [J. Shi {\it
et.al} Phys. Rev. Lett. {\bf 96}, 076604 (2006)] does not flow persistently in
equilibrium. We suggest another conserved spin current that may
flow persistently in equilibrium. We give two arguments for the instability of
persistent current of the form : one based on the equations of motions
and another based on a variational construction using Lieb-Schulz-Mattis twist
operators. In the absence of spin-orbit coupling, the three forms of spin
current coincide.Comment: 5 pages; added references, simplified notation, clearer introductio
Modelling thermomechanical behaviour of Cr-Mo-V steel
This paper presents a mechanism-based approach for modelling the thermomechanical behaviour of a Cr-Mo-V steel. A set of unified viscoplastic constitutive equations were employed to model dislocation density, recrystallisation and grain size during deformation. The evolution of dislocation density accounts for the build-up of dislocations due to plastic strain, the static and dynamic recovery and the effect of recrystallisation. Recrystallisation occurs when a critical dislocation density is reached after an incubation time, and grain size becomes smaller after such event. Gleeble compression tests were used to obtain Stress-strain curves and evaluate the microstructural evolution at different temperature and strain rate, and the material constants for the model were determined from the experimental data. Copyright © 2010 MS&T10®
Evidence for existence of many pure ground states in 3d Spin Glasses
Ground states of 3d EA Ising spin glasses are calculated for sizes up to
using a combination of genetic algorithms and cluster-exact
approximation . The distribution of overlaps is calculated. For
increasing size the width of converges to a nonzero value, indicating
that many pure ground states exist for short range Ising spin glasses.Comment: 4 pages, 3 figures, 2 tables, 16 reference
Dynamic scaling of fronts in the quantum XX chain
The dynamics of the transverse magnetization in the zero-temperature XX chain
is studied with emphasis on fronts emerging from steplike initial magnetization
profiles. The fronts move with fixed velocity and display a staircase like
internal structure whose dynamic scaling is explored both analytically and
numerically. The front region is found to spread with time sub-diffusively with
the height and the width of the staircase steps scaling as t^(-1/3) and t^1/3,
respectively. The areas under the steps are independent of time, thus the
magnetization relaxes in quantized "steps" of spin-flips.Comment: 4 pages, 3 eps figures, RevTe
Thredbo at Thirty: Review of Past Papers and Reflections
Institute of Transport and Logistics Studies. Faculty of Economics and Business. The University of Sydne
Growth Laws for Phase Ordering
We determine the characteristic length scale, , in phase ordering
kinetics for both scalar and vector fields, with either short- or long-range
interactions, and with or without conservation laws. We obtain
consistently by comparing the global rate of energy change to the energy
dissipation from the local evolution of the order parameter. We derive growth
laws for O(n) models, and our results can be applied to other systems with
similar defect structures.Comment: 12 pages, LaTeX, second tr
Generalized Dynamic Scaling for Critical Relaxations
The dynamic relaxation process for the two dimensional Potts model at
criticality starting from an initial state with very high temperature and
arbitrary magnetization is investigated with Monte Carlo methods. The results
show that there exists universal scaling behaviour even in the short-time
regime of the dynamic evolution. In order to describe the dependence of the
scaling behaviour on the initial magnetization, a critical characteristic
function is introduced.Comment: Latex, 8 pages, 3 figures, to appear in Phys. Rev. Let
Numerical study of the transition of the four dimensional Random Field Ising Model
We study numerically the region above the critical temperature of the four
dimensional Random Field Ising Model. Using a cluster dynamic we measure the
connected and disconnected magnetic susceptibility and the connected and
disconnected overlap susceptibility. We use a bimodal distribution of the field
with for all temperatures and a lattice size L=16. Through a
least-square fit we determine the critical exponents and . We find the magnetic susceptibility and the overlap
susceptibility diverge at two different temperatures. This is coherent with the
existence of a glassy phase above . Accordingly with other simulations
we find . In this case we have a scaling theory with
two indipendet critical exponentsComment: 10 pages, 2 figures, Late
Breakdown of Scaling in the Nonequilibrium Critical Dynamics of the Two-Dimensional XY Model
The approach to equilibrium, from a nonequilibrium initial state, in a system
at its critical point is usually described by a scaling theory with a single
growing length scale, , where z is the dynamic exponent
that governs the equilibrium dynamics. We show that, for the 2D XY model, the
rate of approach to equilibrium depends on the initial condition. In
particular, if no free vortices are present in the
initial state, while if free vortices are
present.Comment: 4 pages, 3 figure
Phase separation in an homogeneous shear flow: Morphology, growth laws and dynamic scaling
We investigate numerically the influence of an homogeneous shear flow on the
spinodal decomposition of a binary mixture by solving the Cahn-Hilliard
equation in a two-dimensional geometry. Several aspects of this much studied
problem are clarified. Our numerical data show unambiguously that, in the shear
flow, the domains have on average an elliptic shape. The time evolution of the
three parameters describing this ellipse are obtained for a wide range of shear
rates. For the lowest shear rates investigated, we find the growth laws for the
two principal axis , , while
the mean orientation of the domains with respect to the flow is inversely
proportional to the strain. This implies that when hydrodynamics is neglected a
shear flow does not stop the domain growth process. We investigate also the
possibility of dynamic scaling, and show that only a non trivial form of
scaling holds, as predicted by a recent analytical approach to the case of a
non-conserved order parameter. We show that a simple physical argument may
account for these results.Comment: Version accepted for publication - Physical Review
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