7,131 research outputs found
Atomistic-continuum multiscale modelling of magnetisation dynamics at non-zero temperature
In this article, a few problems related to multiscale modelling of magnetic
materials at finite temperatures and possible ways of solving these problems
are discussed. The discussion is mainly centred around two established
multiscale concepts: the partitioned domain and the upscaling-based
methodologies. The major challenge for both multiscale methods is to capture
the correct value of magnetisation length accurately, which is affected by a
random temperature-dependent force. Moreover, general limitations of these
multiscale techniques in application to spin systems are discussed.Comment: 30 page
Dynamical mechanisms leading to equilibration in two-component gases
Demonstrating how microscopic dynamics cause large systems to approach
thermal equilibrium remains an elusive, longstanding, and actively-pursued goal
of statistical mechanics. We identify here a dynamical mechanism for
thermalization in a general class of two-component dynamical Lorentz gases, and
prove that each component, even when maintained in a non-equilibrium state
itself, can drive the other to a thermal state with a well-defined effective
temperature.Comment: 5 pages, 5 figure
Bell's theorem as a signature of nonlocality: a classical counterexample
For a system composed of two particles Bell's theorem asserts that averages
of physical quantities determined from local variables must conform to a family
of inequalities. In this work we show that a classical model containing a local
probabilistic interaction in the measurement process can lead to a violation of
the Bell inequalities. We first introduce two-particle phase-space
distributions in classical mechanics constructed to be the analogs of quantum
mechanical angular momentum eigenstates. These distributions are then employed
in four schemes characterized by different types of detectors measuring the
angular momenta. When the model includes an interaction between the detector
and the measured particle leading to ensemble dependencies, the relevant Bell
inequalities are violated if total angular momentum is required to be
conserved. The violation is explained by identifying assumptions made in the
derivation of Bell's theorem that are not fulfilled by the model. These
assumptions will be argued to be too restrictive to see in the violation of the
Bell inequalities a faithful signature of nonlocality.Comment: Extended manuscript. Significant change
Bell's theorem as a signature of nonlocality: a classical counterexample
For a system composed of two particles Bell's theorem asserts that averages
of physical quantities determined from local variables must conform to a family
of inequalities. In this work we show that a classical model containing a local
probabilistic interaction in the measurement process can lead to a violation of
the Bell inequalities. We first introduce two-particle phase-space
distributions in classical mechanics constructed to be the analogs of quantum
mechanical angular momentum eigenstates. These distributions are then employed
in four schemes characterized by different types of detectors measuring the
angular momenta. When the model includes an interaction between the detector
and the measured particle leading to ensemble dependencies, the relevant Bell
inequalities are violated if total angular momentum is required to be
conserved. The violation is explained by identifying assumptions made in the
derivation of Bell's theorem that are not fulfilled by the model. These
assumptions will be argued to be too restrictive to see in the violation of the
Bell inequalities a faithful signature of nonlocality.Comment: Extended manuscript. Significant change
Spatially Resolved Thermodynamic Integration: An Efficient Method to Compute Chemical Potentials of Dense Fluids
Many popular methods for the calculation of chemical potentials rely on the
insertion of test particles into the target system. In the case of liquids and
liquid mixtures, this procedure increases in difficulty upon increasing density
or concentration, and the use of sophisticated enhanced sampling techniques
becomes inevitable. In this work we propose an alternative strategy, spatially
resolved thermodynamic integration, or SPARTIAN for short. Here, molecules are
described with atomistic resolution in a simulation subregion, and as ideal gas
particles in a larger reservoir. All molecules are free to diffuse between
subdomains adapting their resolution on the fly. To enforce a uniform density
profile across the simulation box, a single-molecule external potential is
computed, applied, and identified with the difference in chemical potential
between the two resolutions. Since the reservoir is represented as an ideal gas
bath, this difference exactly amounts to the excess chemical potential of the
target system. The present approach surpasses the high density/concentration
limitation of particle insertion methods because the ideal gas molecules
entering the target system region spontaneously adapt to the local environment.
The ideal gas representation contributes negligibly to the computational cost
of the simulation, thus allowing one to make use of large reservoirs at minimal
expenses. The method has been validated by computing excess chemical potentials
for pure Lennard-Jones liquids and mixtures, SPC and SPC/E liquid water, and
aqueous solutions of sodium chloride. The reported results well reproduce
literature data for these systems
Integrability and Disorder in Mesoscopic Systems: Application to Orbital Magnetism
We present a semiclassical theory of weak disorder effects in small
structures and apply it to the magnetic response of non-interacting electrons
confined in integrable geometries. We discuss the various averaging procedures
describing different experimental situations in terms of one- and two-particle
Green functions. We demonstrate that the anomalously large zero-field
susceptibility characteristic of clean integrable structures is only weakly
suppressed by disorder. This damping depends on the ratio of the typical size
of the structure with the two characteristic length scales describing the
disorder (elastic mean-free-path and correlation length of the potential) in a
power-law form for the experimentally relevant parameter region. We establish
the comparison with the available experimental data and we extend the study of
the interplay between disorder and integrability to finite magnetic fields.Comment: 38 pages, Latex, 7 Postscript figures, 1 table, to appear in Jour.
Math. Physics 199
Strongly magnetized classical plasma models
Discrete particle processes in the presence of a strong external magnetic field were investigated. These processes include equations of state and other equilibrium thermodynamic relations, thermal relaxation phenomena, transport properties, and microscopic statistical fluctuations in such quantities as the electric field and the charge density. Results from the equilibrium statistical mechanics of two-dimensional plasmas are discussed, along with nonequilibrium statistical mechanics of the electrostatic guiding-center plasma (a two-dimensional plasma model)
Drude Weight for the Lieb-Liniger Bose Gas
Based on the method of hydrodynamic projections we derive a concise formula
for the Drude weight of the repulsive Lieb-Liniger -Bose gas. Our
formula contains only quantities which are obtainable from the thermodynamic
Bethe ansatz. The Drude weight is an infinite-dimensional matrix, or bilinear
functional: it is bilinear in the currents, and each current may refer to a
general linear combination of the conserved charges of the model. As a
by-product we obtain the dynamical two-point correlation functions involving
charge and current densities at small wavelengths and long times, and in
addition the scaled covariance matrix of charge transfer. We expect that our
formulas extend to other integrable quantum models.Comment: 23 pages. v2: improved discussion, typos corrected, references added.
v3: 26 pages, further improved discussion, references adde
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