13,334 research outputs found
Effect of ion hydration on the first-order transition in the sequential wetting of hexane on brine
In recent experiments, a sequence of changes in the wetting state (`wetting
transitions') has been observed upon increasing the temperature in systems
consisting of pentane on pure water and of hexane on brine. This sequence of
two transitions is brought about by an interplay of short-range and long-range
interactions between substrate and adsorbate. In this work, we argue that the
short-range interaction (contact energy) between hexane and pure water remains
unchanged due to the formation of a depletion layer (a thin `layer' of pure
water which is completely devoid of ions) at the surface of the electrolyte and
that the presence of the salt manifests itself only in a modification of the
long-range interaction between substrate and adsorbate. In a five-layer
calculation considering brine, water, the first layer of adsorbed hexane
molecules, liquid hexane, and vapor, we determine the new long-range
interaction of brine with the adsorbate {\em across} the water `layer'.
According to the recent theory of the excess surface tension of an electrolyte
by Levin and Flores-Mena, this water `layer' is of constant, i.e.\
salt-concentration independent, thickness , with being the
hydrodynamic radius of the ions in water. Our results are in good agreement
with the experimental ones.Comment: 27 pages, 2 tables, 4 figure
Spatial Resonator Solitons
Spatial solitons can exist in various kinds of nonlinear optical resonators
with and without amplification. In the past years different types of these
localized structures such as vortices, bright, dark solitons and phase solitons
have been experimentally shown to exist. Many links appear to exist to fields
different from optics, such as fluids, phase transitions or particle physics.
These spatial resonator solitons are bistable and due to their mobility suggest
schemes of information processing not possible with the fixed bistable elements
forming the basic ingredient of traditional electronic processing. The recent
demonstration of existence and manipulation of spatial solitons in emiconductor
microresonators represents a step in the direction of such optical parallel
processing applications. We review pattern formation and solitons in a general
context, show some proof of principle soliton experiments on slow systems, and
describe in more detail the experiments on semiconductor resonator solitons
which are aimed at applications.Comment: 15 pages, 32 figure
The twist-2 Compton operator and its hidden Wandzura-Wilczek and Callan-Gross relations
Power corrections for virtual Compton scattering at leading twist are
etermined at operator level. From the complete off-cone representation of the
twist-2 Compton operator integral representations for the trace, antisymmetric
and symmetric part of that operator are derived. The operator valued invariant
functions are written in terms of iterated operators and may lead to
interrelations. For matrix elements they go over into relations for generalized
parton distributions. -- Reducing to the s-channel relevant part one gets
operator pre-forms of the Wandzura-Wilczek and the (target mass corrected)
Callan-Gross relations whose structure is exactly the same as known from the
case of deep inelastic scattering; taking non-forward matrix elements one
reproduces earlier results [B. Geyer, D. Robaschik and J. Eilers, Nucl. Phys. B
704 (2005) 279] for the absorptive part of the virtual Compton amplitude. --
All these relations, obtained without any approximation or using equations of
motion, are determined solely by the twist-2 structure of the underlying
operator and, therefore, are purely of geometric origin.Comment: 13 pages, Latex 2e, Introduction shortend, Section Prerequisites
added, more obvious formulations used, some formulas rewritten as well as
added, conclusions extended, references added. Final version as appearing in
PR
Scaling and data collapse for the mean exit time of asset prices
We study theoretical and empirical aspects of the mean exit time of financial
time series. The theoretical modeling is done within the framework of
continuous time random walk. We empirically verify that the mean exit time
follows a quadratic scaling law and it has associated a pre-factor which is
specific to the analyzed stock. We perform a series of statistical tests to
determine which kind of correlation are responsible for this specificity. The
main contribution is associated with the autocorrelation property of stock
returns. We introduce and solve analytically both a two-state and a three-state
Markov chain models. The analytical results obtained with the two-state Markov
chain model allows us to obtain a data collapse of the 20 measured MET profiles
in a single master curve.Comment: REVTeX 4, 11 pages, 8 figures, 1 table, submitted for publicatio
Dissipation in Compressible MHD Turbulence
We report results of a three dimensional, high resolution (up to 512^3)
numerical investigation of supersonic compressible magnetohydrodynamic
turbulence. We consider both forced and decaying turbulence. The model
parameters are appropriate to conditions found in Galactic molecular clouds. We
find that the dissipation time of turbulence is of order the flow crossing time
or smaller, even in the presence of strong magnetic fields. About half the
dissipation occurs in shocks. Weak magnetic fields are amplified and tangled by
the turbulence, while strong fields remain well ordered.Comment: 5 pages, 3 Postscript figures, LaTeX, accepted by Ap.J.Let
Influences of an impurity on the transport properties of one-dimensional antisymmetric spin filter
The influences of an impurity on the spin and the charge transport of
one-dimensional antisymmetric spin filter are investigated using bosonization
and Keldysh formulation and the results are highlighted against those of
spinful Luttinger liquids. Due to the dependence of the electron spin
orientation on wave number the spin transport is not affected by the impurity,
while the charge transport is essentially identical with that of spinless
one-dimensional Luttinger liquid.Comment: 7 pages, 2 figures. To appear in Physical Review
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