3,507 research outputs found
Liquid phase epitaxy of GaAlAs on GaAs substrates with fine surface corrugations
Liquid phase epitaxy of GaAlAs was performed on GaAs fine surface corrugations. By optimizing the growth conditions, GaAlAs layers were grown successfully with only minimal meltback
Cosmological Constraints on a Dynamical Electron Mass
Motivated by recent astrophysical observations of quasar absorption systems,
we formulate a simple theory where the electron to proton mass ratio is allowed to vary in space-time. In such a minimal theory only
the electron mass varies, with and kept constant. We find
that changes in will be driven by the electronic energy density after
the electron mass threshold is crossed. Particle production in this scenario is
negligible. The cosmological constraints imposed by recent astronomical
observations are very weak, due to the low mass density in electrons. Unlike in
similar theories for spacetime variation of the fine structure constant, the
observational constraints on variations in imposed by the weak
equivalence principle are much more stringent constraints than those from
quasar spectra. Any time-variation in the electron-proton mass ratio must be
less than one part in since redshifts This is more than
one thousand times smaller than current spectroscopic sensitivities can
achieve. Astronomically observable variations in the electron-proton must
therefore arise directly from effects induced by varying fine structure
'constant' or by processes associated with internal proton structure. We also
place a new upper bound of on any large-scale spatial
variation of that is compatible with the isotropy of the microwave
background radiation.Comment: New bounds from weak equivalence principle experiments added,
conclusions modifie
Numerical investigation of friction in inflaton equations of motion
The equation of motion for the expectation value of a scalar quantum field
does not have the local form that is commonly assumed in studies of
inflationary cosmology. We have recently argued that the true, temporally
non-local equation of motion does not possess a time-derivative expansion and
that the conversion of inflaton energy into particles is not, in principle,
described by the friction term estimated from linear response theory. Here, we
use numerical methods to investigate whether this obstacle to deriving a local
equation of motion is purely formal, or of some quantitative importance. Using
a simple scalar-field model, we find that, although the non-equilibrium
evolution can exhibit significant damping, this damping is not well described
by the local equation of motion obtained from linear response theory. It is
possible that linear response theory does not apply to the situation we study
only because thermalization turns out to be slow, but we argue that that the
large discrepancies we observe indicate a failure of the local approximation at
a more fundamental level.Comment: 13 pages, 7 figure
The asymptotic quasi-stationary states of the two-dimensional magnetically confined plasma and of the planetary atmosphere
We derive the differential equation governing the asymptotic quasi-stationary
states of the two dimensional plasma immersed in a strong confining magnetic
field and of the planetary atmosphere. These two systems are related by the
property that there is an intrinsic constant length: the Larmor radius and
respectively the Rossby radius and a condensate of the vorticity field in the
unperturbed state related to the cyclotronic gyration and respectively to the
Coriolis frequency. Although the closest physical model is the
Charney-Hasegawa-Mima (CHM) equation, our model is more general and is related
to the system consisting of a discrete set of point-like vortices interacting
in plane by a short range potential. A field-theoretical formalism is developed
for describing the continuous version of this system. The action functional can
be written in the Bogomolnyi form (emphasizing the role of Self-Duality of the
asymptotic states) but the minimum energy is no more topological and the
asymptotic structures appear to be non-stationary, which is a major difference
with respect to traditional topological vortex solutions. Versions of this
field theory are discussed and we find arguments in favor of a particular form
of the equation. We comment upon the significant difference between the CHM
fluid/plasma and the Euler fluid and respectively the Abelian-Higgs vortex
models.Comment: Latex 126 pages, 7 eps figures included. Discussion on various forms
of the equatio
Implementation of Drug and Alcohol Testing in the Unionized Workplace
Society has long been troubled by illegal drug and alcohol abuse
Scaling Relations for Collision-less Dark Matter Turbulence
Many scaling relations are observed for self-gravitating systems in the
universe. We explore the consistent understanding of them from a simple
principle based on the proposal that the collision-less dark matter fluid terns
into a turbulent state, i.e. dark turbulence, after crossing the caustic
surface in the non-linear stage. The dark turbulence will not eddy dominant
reflecting the collision-less property. After deriving Kolmogorov scaling laws
from Navier-Stokes equation by the method similar to the one for Smoluchowski
coagulation equation, we apply this to several observations such as the
scale-dependent velocity dispersion, mass-luminosity ratio, magnetic fields,
and mass-angular momentum relation, power spectrum of density fluctuations.
They all point the concordant value for the constant energy flow per mass: , which may be understood as the speed of the hierarchical
coalescence process in the cosmic structure formation.Comment: 26 pages, 6 figure
Thiol density dependent classical potential for methyl-thiol on a Au(111) surface
A new classical potential for methyl-thiol on a Au(111) surface has been
developed using density functional theory electronic structure calculations.
Energy surfaces between methyl-thiol and a gold surface were investigated in
terms of symmetry sites and thiol density. Geometrical optimization was
employed over all the configurations while minimum energy and thiol height were
determined. Finally, a new interatomic potential has been generated as a
function of thiol density, and applications to coarse-grained simulations are
presented
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