1,652 research outputs found
Random Field and Random Anisotropy Effects in Defect-Free Three-Dimensional XY Models
Monte Carlo simulations have been used to study a vortex-free XY ferromagnet
with a random field or a random anisotropy on simple cubic lattices. In the
random field case, which can be related to a charge-density wave pinned by
random point defects, it is found that long-range order is destroyed even for
weak randomness. In the random anisotropy case, which can be related to a
randomly pinned spin-density wave, the long-range order is not destroyed and
the correlation length is finite. In both cases there are many local minima of
the free energy separated by high entropy barriers. Our results for the random
field case are consistent with the existence of a Bragg glass phase of the type
discussed by Emig, Bogner and Nattermann.Comment: 10 pages, including 2 figures, extensively revise
Temperature separation under compression of moderately-coupled plasma
In moderately-coupled plasmas, a significant fraction of the internal energy
resides in electric fields. As these plasmas are heated or compressed, the
shifting partition of energy between particles and fields leads to surprising
effects, particularly when ions and electrons have different temperatures. In
this work, quasi-equations of state (quasi-EOS) are derived for two-temperature
moderately-coupled plasma in a thermodynamic framework and expressed in a
simple form. These quasi-EOS readily yield expressions for correlation heating,
in which heating of the electrons causes a rapid increase in ion temperature
even in the absence of collisional energy exchange between species. It is also
shown that, remarkably, compression of moderately-coupled plasma drives a
temperature difference between electrons and ions, even when the species start
at equal temperature. These additional channels for ion heating may be relevant
in designing ignition schemes for inertial confinement fusion (ICF)
Topological Defects in the Random-Field XY Model and the Pinned Vortex Lattice to Vortex Glass Transition in Type-II Superconductors
As a simplified model of randomly pinned vortex lattices or charge-density
waves, we study the random-field XY model on square () and simple cubic
() lattices. We verify in Monte Carlo simulations, that the average
spacing between topological defects (vortices) diverges more strongly than the
Imry-Ma pinning length as the random field strength, , is reduced. We
suggest that for the simulation data are consistent with a topological
phase transition at a nonzero critical field, , to a pinned phase that is
defect-free at large length-scales. We also discuss the connection between the
possible existence of this phase transition in the random-field XY model and
the magnetic field driven transition from pinned vortex lattice to vortex glass
in weakly disordered type-II superconductors.Comment: LATEX file; 5 Postscript figures are available from [email protected]
Vlasov equation and collisionless hydrodynamics adapted to curved spacetime
The modification of the Vlasov equation, in its standard form describing a
charged particle distribution in the six-dimensional phase space, is derived
explicitly within a formal Hamiltonian approach for arbitrarily curved
spacetime. The equation accounts simultaneously for the Lorentz force and the
effects of general relativity, with the latter appearing as the gravity force
and an additional force due to the extrinsic curvature of spatial
hypersurfaces. For an arbitrary spatial metric, the equations of collisionless
hydrodynamics are also obtained in the usual three-vector form
Implicit Communication and Enforcement of Corporate Disclosure Regulation
This study examines the challenge of implicit communication -- qualitative statements, tone, and non-verbal cues -- to the effectiveness of enforcing corporate disclosure regulation. We use a Regulation Fair Disclosure (Reg FD) setting, given that the SEC adopted the regulation recognizing that managers can convey non-public information privately not just through explicit quantitative disclosures but also through implicit communication. In a high-profile enforcement action, however, the court focused on a literal examination of the manager’s language rather than his positive spin to conclude that the SEC had been “too demanding” in examining the manager’s statements and that its enforcement policy was “overly aggressive.” We provide empirical evidence suggesting that selective disclosure from managers to financial analysts increased significantly after the court’s ruling. We also report survey responses from 60 securities lawyers with Reg FD expertise which support the proposition that this increase in disclosure is more likely due to an increase in implicit communication than in explicit communication or any other reason. Our results highlight the challenges associated with enforcing corporate disclosure regulation in the context of implicit communication
Nonlinear dispersion of stationary waves in collisionless plasmas
A nonlinear dispersion of a general stationary wave in collisionless plasma
is obtained in a non-differential form from a single-particle
oscillation-center Hamiltonian. For electrostatic oscillations in nonmagnetized
plasma, considered as a paradigmatic example, the linear dielectric function is
generalized, and the trapped particle contribution to the wave frequency shift
is found analytically as a function of the wave amplitude .
Smooth distributions yield , as usual. However,
beam-like distributions of trapped electrons result in different power laws, or
even a logarithmic nonlinearity, which are derived as asymptotic limits of the
same dispersion relation
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