71,410 research outputs found
Quasicontinuum Models of Interfacial Structure and Deformation
Microscopic models of the interaction between grain boundaries (GBs) and both
dislocations and cracks are of importance in understanding the role of
microstructure in altering the mechanical properties of a material. A recently
developed mixed atomistic and continuum method is extended to examine the
interaction between GBs, dislocations and cracks. These calculations elucidate
plausible microscopic mechanisms for these defect interactions and allow for
the quantitative evaluation of critical parameters such as the stress to
nucleate a dislocation at a step on a GB and the force needed to induce GB
migration.Comment: RevTex, 4 pages, 4 figure
Extended Feynman Formula for the Harmonic Oscillator by the Discrete Time Method
We calculate the Feynman formula for the harmonic oscillator beyond and at
caustics by the discrete formulation of path integral. The extension has been
made by some authors, however, it is not obtained by the method which we
consider the most reliable regularization of path integral. It is shown that
this method leads to the result with, especially at caustics, more rigorous
derivation than previous.Comment: 9 page
Simulation of electron transport in quantum well devices
Double barrier resonant tunneling diodes (DBRTD) have received much attention as possible terahertz devices. Despite impressive experimental results, the specifics of the device physics (i.e., how the electrons propagate through the structure) are only qualitatively understood. Therefore, better transport models are warranted if this technology is to mature. In this paper, the Lattice Wigner function is used to explain the important transport issues associated with DBRTD device behavior
Synchronization of dynamical hypernetworks: dimensionality reduction through simultaneous block-diagonalization of matrices
We present a general framework to study stability of the synchronous solution
for a hypernetwork of coupled dynamical systems. We are able to reduce the
dimensionality of the problem by using simultaneous block-diagonalization of
matrices. We obtain necessary and sufficient conditions for stability of the
synchronous solution in terms of a set of lower-dimensional problems and test
the predictions of our low-dimensional analysis through numerical simulations.
Under certain conditions, this technique may yield a substantial reduction of
the dimensionality of the problem. For example, for a class of dynamical
hypernetworks analyzed in the paper, we discover that arbitrarily large
networks can be reduced to a collection of subsystems of dimensionality no more
than 2. We apply our reduction techique to a number of different examples,
including a class of undirected unweighted hypermotifs of three nodes.Comment: 9 pages, 6 figures, accepted for publication in Phys. Rev.
Dissipationless Anomalous Hall Current in the Ferromagnetic Spinel CuCrSeBr
In a ferromagnet, an applied electric field invariably produces an
anomalous Hall current that flows perpendicular to the plane
defined by and (the magnetization). For decades, the question
whether is dissipationless (independent of the scattering rate),
has been keenly debated without experimental resolution. In the ferromagnetic
spinel CuCrSeBr, the resistivity (at low temperature)
may be increased 1000 fold by varying (Br), without degrading the .
We show that (normalized per carrier, at 5 K) remains unchanged
throughout. In addition to resolving the controversy experimentally, our
finding has strong bearing on the generation and study of spin-Hall currents in
bulk samples.Comment: 7 pages, 6 figure
Magnetized Iron Atmospheres for Neutron Stars
Using a Hartree-Fock formalism, we estimate energy levels and photon cross
sections for atomic iron in magnetic fields B ~ 10^13 G. Computing ionization
equilibrium and normal mode opacities with these data, we construct LTE neutron
star model atmospheres at 5.5 < Log(T_eff) < 6.5 and compute emergent spectra.
We examine the dependence of the emergent spectra on T_eff and B. We also show
the spectral variation with the angle between the magnetic field and the
atmosphere normal and describe the significant limb darkening in the X-ray
band. These results are compared with recent detailed computations of neutron
star H model atmospheres in high fields and with low field Fe and H model
atmospheres constructed from detailed opacities. The large spectral differences
for different surface compositions may be discernible with present X-ray data;
we also note improvements needed to allow comparison of Fe models with high
quality spectra.Comment: 18 pages with 5 eps figures, accepted for publication in ApJ Replaced
due to clerical error only: one more author, no new conten
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