446 research outputs found
General properties of response functions of nonequilibrium steady states
We derive general properties, which hold for both quantum and classical
systems, of response functions of nonequilibrium steady states. We clarify
differences from those of equilibrium states. In particular, sum rules and
asymptotic behaviors are derived, and their implications are discussed. Since
almost no assumptions are made, our results are applicable to diverse physical
systems. We also demonstrate our results by a molecular dynamics simulation of
a many-body interacting system.Comment: After publication of this paper, several typos were found, which have
been fixed in the erratum (J. Phys. Soc. Jpn., 80 (2011) 128001). All the
corrections have been made in this updated arXive version. 13 pages with 3
figure
Sum rule for response function in nonequilibrium Langevin systems
We derive general properties of the linear response functions of
nonequilibrium steady states in Langevin systems. These correspond to extension
of the results which were recently found in Hamiltonian systems [A. Shimizu and
T. Yuge, J. Phys. Soc. Jpn. {\bf 79}, 013002 (2010)]. We discuss one of the
properties, the sum rule for the response function, in particular detail. We
show that the sum rule for the response function of the velocity holds in the
underdamped case, whereas it is violated in the overdamped case. This implies
that the overdamped Langevin models should be used with great care. We also
investigate the relation of the sum rule to an equality on the energy
dissipation in nonequilibrium Langevin systems, which was derived by Harada and
Sasa.Comment: 8 page
Indications of Universal Excess Fluctuations in Nonequilibrium Systems
The fluctuation in electric current in nonequilibrium steady states is
investigated by molecular dynamics simulation of macroscopically uniform
conductors. At low frequencies, appropriate decomposition of the spectral
intensity of current into thermal and excess fluctuations provides a simple
picture of excess fluctuations behaving as shot noise. This indicates that the
fluctuation-dissipation relation may be violated in a universal manner by the
appearance of shot noise for a wide range of systems with particle or momentum
transport.Comment: 4 pages, 4 figures; title changed, major revision; to appear in J.
Phys. Soc. Jp
Universal Properties of Nonlinear Response Functions of Nonequilibrium Steady States
We derive universal properties of nonlinear response functions of
nonequilibrium steady states. In particular, sum rules and asymptotic behaviors
are derived. Their consequences are illustrated for nonlinear optical materials
and nonlinear electrical conductors.Comment: 10 pages, 1 figure; added a few sentences and references to explain
detail
Long-Time Behavior of Velocity Autocorrelation Function for Interacting Particles in a Two-Dimensional Disordered System
The long-time behavior of the velocity autocorrelation function (VACF) is
investigated by the molecular dynamics simulation of a two-dimensional system
which has both a many-body interaction and a random potential. With
strengthening the random potential by increasing the density of impurities, a
crossover behavior of the VACF is observed from a positive tail, which is
proportional to t^{-1}, to a negative tail, proportional to -t^{-2}. The latter
tail exists even when the density of particles is the same order as the density
of impurities. The behavior of the VACF in a nonequilibrium steady state is
also studied. In the linear response regime the behavior is similar to that in
the equilibrium state, whereas it changes drastically in the nonlinear response
regime.Comment: 12 pages, 5 figure
Long-time Low-latency Quantum Memory by Dynamical Decoupling
Quantum memory is a central component for quantum information processing
devices, and will be required to provide high-fidelity storage of arbitrary
states, long storage times and small access latencies. Despite growing interest
in applying physical-layer error-suppression strategies to boost fidelities, it
has not previously been possible to meet such competing demands with a single
approach. Here we use an experimentally validated theoretical framework to
identify periodic repetition of a high-order dynamical decoupling sequence as a
systematic strategy to meet these challenges. We provide analytic
bounds-validated by numerical calculations-on the characteristics of the
relevant control sequences and show that a "stroboscopic saturation" of
coherence, or coherence plateau, can be engineered, even in the presence of
experimental imperfection. This permits high-fidelity storage for times that
can be exceptionally long, meaning that our device-independent results should
prove instrumental in producing practically useful quantum technologies.Comment: abstract and authors list fixe
Optimization of a frame structure subjected to a plastic deformation
An optimization method for a frame structure subjected to a plastic deformation is proposed in this paper. The method is based on the generalized layout optimization method proposed by Bendsøe and Kikuchi in 1988, where the solid-cavity composite material is distributed in the admissible domain and the cavity size is determined so that it becomes large in the area where the strain energy is small. Elasto-plastic analysis based on the homogenization method is carried out to obtain the nonlinear average stress-strain relations of a porous material first. Then the optimization algorithm of a frame structure is derived by taking plastification into account. Finally in order to demonstrate the effectiveness of the present algorithm, several numerical examples are illustrated.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/46071/1/158_2005_Article_BF01742592.pd
Anomalous Heat Conduction in Three-Dimensional Nonlinear Lattices
Heat conduction in three-dimenisional nonlinear lattice models is studied
using nonequilibrium molecular dynamics simulations. We employ the FPU model,
in which there exists a nonlinearity in the interaction of biquadratic form. It
is confirmed that the thermal conductivity, the ratio of the energy flux to the
temperature gradient, diverges in systems up to 128x128x256 lattice sites. This
size corresponds to nanoscopic to mesoscopic scales of several tens of
nanometers. From these results, we conjecture that the energy transport in
insulators with perfect crystalline order exhibits anomalous behavior. The
effects of lattice structure, random impurities, and natural length in
interactions are also examined. We find that face-centered cubic (fcc) lattices
display stronger divergence than simple cubic lattices. When impurity sites of
infinitely large mass, which are hence fixed, are randomly distributed, such
divergence vanishes.Comment: 10pages, 10 figures, Fig. 1 is replaced and some minor corrections
were mad
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