10,231 research outputs found
Resonance Damping in Ferromagnets and Ferroelectrics
The phenomenological equations of motion for the relaxation of ordered phases
of magnetized and polarized crystal phases can be developed in close analogy
with one another. For the case of magnetized systems, the driving magnetic
field intensity toward relaxation was developed by Gilbert. For the case of
polarized systems, the driving electric field intensity toward relaxation was
developed by Khalatnikov. The transport times for relaxation into thermal
equilibrium can be attributed to viscous sound wave damping via
magnetostriction for the magnetic case and electrostriction for the
polarization case.Comment: 5 pages no figures ReVTeX
Reply to "Comment on `Quenches in quantum many-body systems: One-dimensional Bose-Hubbard model reexamined' ''
In his Comment [see preceding Comment, Phys. Rev. A 82, 037601 (2010)] on the
paper by Roux [Phys. Rev. A 79, 021608(R) (2009)], Rigol argued that the energy
distribution after a quench is not related to standard statistical ensembles
and cannot explain thermalization. The latter is proposed to stem from what he
calls the eigenstate thermalization hypothesis and which boils down to the fact
that simple observables are expected to be smooth functions of the energy. In
this Reply, we show that there is no contradiction or confusion between the
observations and discussions of Roux and the expected thermalization scenario
discussed by Rigol. In addition, we emphasize a few other important aspects, in
particular the definition of temperature and the equivalence of ensemble, which
are much more difficult to show numerically even though we believe they are
essential to the discussion of thermalization. These remarks could be of
interest to people interested in the interpretation of the data obtained on
finite-size systems.Comment: 3 page
Droplet evaporation in one-component fluids: Dynamic van der Waals theory
In a one-component fluid, we investigate evaporation of a small axysymmetric
liquid droplet in the partial wetting condition on a heated wall at . In the dynamic van der Waals theory (Phys. Rev. E {\bf 75}, 036304
(2007)), we take into account the latent heat transport from liquid to gas upon
evaporation. Along the gas-liquid interface, the temperature is nearly equal to
the equilibrium coexisting temperature away from the substrate, but it rises
sharply to the wall temperature close to the substrate. On an isothermal
substrate, evaporation takes place mostly on a narrow interface region near the
contact line in a late stage, which is a characteristic feature in
one-component fluids.Comment: 6 pages, 6 figure
Monte Carlo Simulations of Ultrathin Magnetic Dots
In this work we study the thermodynamic properties of ultrathin ferromagnetic
dots using Monte Carlo simulations. We investigate the vortex density as a
function of the temperature and the vortex structure in monolayer dots with
perpendicular anisotropy and long-range dipole interaction. The interplay
between these two terms in the hamiltonian leads to an interesting behavior of
the thermodynamic quantities as well as the vortex density.Comment: 10 figure
Creation of entangled states in coupled quantum dots via adiabatic rapid passage
Quantum state preparation through external control is fundamental to
established methods in quantum information processing and in studies of
dynamics. In this respect, excitons in semiconductor quantum dots (QDs) are of
particular interest since their coupling to light allows them to be driven into
a specified state using the coherent interaction with a tuned optical field
such as an external laser pulse. We propose a protocol, based on adiabatic
rapid passage, for the creation of entangled states in an ensemble of pairwise
coupled two-level systems, such as an ensemble of QD molecules. We show by
quantitative analysis using realistic parameters for semiconductor QDs that
this method is feasible where other approaches are unavailable. Furthermore,
this scheme can be generically transferred to some other physical systems
including circuit QED, nuclear and electron spins in solid-state environments,
and photonic coupled cavities.Comment: 10 pages, 2 figures. Added reference, minor changes. Discussion,
results and conclusions unchange
Properties of Accretion Shocks in Viscous Flows with Cooling Effects
Low angular momentum accretion flows can have standing and oscillating shock
waves. We study the region of the parameter space in which multiple sonic
points occur in viscous flows in presence of various cooling effects such as
bremsstrahlung and Comptonization. We also quantify the parameter space in
which shocks are steady or oscillating. We find that cooling induces effects
opposite to heating by viscosity even in modifying the topology of the
solutions, though one can never be exactly balanced by the other due to their
dissimilar dependence on dynamic and thermodynamic parameters. We show that
beyond a critical value of cooling, the flow ceases to contain a shock wave.Comment: 18 pages, 12 figures, Accepted for Publication in Int. J. Mod. Phys.
Impact of composite plates: Analysis of stresses and forces
The foreign object damage resistance of composite fan blades was studied. Edge impact stresses in an anisotropic plate were first calculated incorporating a constrained layer damping model. It is shown that a very thin damping layer can dramatically decrease the maximum normal impact stresses. A multilayer model of a composite plate is then presented which allows computation of the interlaminar normal and shear stresses. Results are presented for the stresses due to a line impact load normal to the plane of a composite plate. It is shown that significant interlaminar tensile stresses can develop during impact. A computer code was developed for this problem using the fast Fourier transform. A marker and cell computer code were also used to investigate the hydrodynamic impact of a fluid slug against a wall or turbine blade. Application of fluid modeling of bird impact is reviewed
Relaxation Mechanism for Ordered Magnetic Materials
We have formulated a relaxation mechanism for ferrites and ferromagnetic
metals whereby the coupling between the magnetic motion and lattice is based
purely on continuum arguments concerning magnetostriction. This theoretical
approach contrasts with previous mechanisms based on microscopic formulations
of spin-phonon interactions employing a discrete lattice. Our model explains
for the first time the scaling of the intrinsic FMR linewidth with frequency,
and 1/M temperature dependence and the anisotropic nature of magnetic
relaxation in ordered magnetic materials, where M is the magnetization. Without
introducing adjustable parameters our model is in reasonable quantitative
agreement with experimental measurements of the intrinsic magnetic resonance
linewidths of important class of ordered magnetic materials, insulator or
metals
Stretching An Anisotropic DNA
We present a perturbation theory to find the response of an anisotropic DNA
to the external tension. It is shown that the anisotropy has a nonzero but
small contribution to the force-extension curve of the DNA. Thus an anisotropic
DNA behaves like an isotropic one with an effective bending constant equal to
the harmonic average of its soft and hard bending constants.Comment: 29 pages and 4 figure. To appear in J. Chem. Phy
Limitation of the modulation method to smooth wire guide roughness
It was recently demonstrated that wire guide roughness can be suppressed by
modulating the wire currents so that the atoms experience a time-averaged
potential without roughness. We theoretically study the limitations of this
technique. At low modulation frequency, we show that the longitudinal potential
modulation produces a heating of the cloud and we compute the heating rate. We
also give a quantum derivation of the rough conservative potential associated
with the micro-motion of the atoms. At large modulation frequency, we compute
the loss rate due to non adiabatic spin flip and show it presents resonnances
at multiple modulation frequencies. These studies show that the modulation
technique works for a wide range of experimental parameters. We also give
conditions to realise radio-frequency evaporative cooling in such a modulated
trap.Comment: 11 page
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