8,119 research outputs found
Vibration-induced climbing of drops
We report an experimental study of liquid drops moving against gravity, when
placed on a vertically vibrating inclined plate, which is partially wetted by
the drop. The frequency of vibrations ranges from 30 to 200 Hz, and, above a
threshold in vibration acceleration, drops experience an upward motion. We
attribute this surprising motion to the deformations of the drop, as a
consequence of an up or down symmetry breaking induced by the presence of the
substrate. We relate the direction of motion to contact angle measurements.
This phenomenon can be used to move a drop along an arbitrary path in a plane,
without special surface treatments or localized forcing.Comment: 4 pages, 7 figure
A phenomenological theory giving the full statistics of the position of fluctuating pulled fronts
We propose a phenomenological description for the effect of a weak noise on
the position of a front described by the Fisher-Kolmogorov-Petrovsky-Piscounov
equation or any other travelling wave equation in the same class. Our scenario
is based on four hypotheses on the relevant mechanism for the diffusion of the
front. Our parameter-free analytical predictions for the velocity of the front,
its diffusion constant and higher cumulants of its position agree with
numerical simulations.Comment: 10 pages, 3 figure
An exactly soluble noisy traveling wave equation appearing in the problem of directed polymers in a random medium
We calculate exactly the velocity and diffusion constant of a microscopic
stochastic model of evolving particles which can be described by a noisy
traveling wave equation with a noise of order . Our model can be
viewed as the infinite range limit of a directed polymer in random medium with
sites in the transverse direction. Despite some peculiarities of the
traveling wave equations in the absence of noise, our exact solution allows us
to test the validity of a simple cutoff approximation and to show that, in the
weak noise limit, the position of the front can be completely described by the
effect of the noise on the first particle.Comment: 5 page
An Intrisic Topology for Orthomodular Lattices
We present a general way to define a topology on orthomodular lattices. We
show that in the case of a Hilbert lattice, this topology is equivalent to that
induced by the metrics of the corresponding Hilbert space. Moreover, we show
that in the case of a boolean algebra, the obtained topology is the discrete
one. Thus, our construction provides a general tool for studying orthomodular
lattices but also a way to distinguish classical and quantum logics.Comment: Under submission to the International Journal of Theoretical Physic
Emergence of pulled fronts in fermionic microscopic particle models
We study the emergence and dynamics of pulled fronts described by the
Fisher-Kolmogorov-Petrovsky-Piscounov (FKPP) equation in the microscopic
reaction-diffusion process A + A A$ on the lattice when only a particle is
allowed per site. To this end we identify the parameter that controls the
strength of internal fluctuations in this model, namely, the number of
particles per correlated volume. When internal fluctuations are suppressed, we
explictly see the matching between the deterministic FKPP description and the
microscopic particle model.Comment: 4 pages, 4 figures. Accepted for publication in Phys. Rev. E as a
Rapid Communicatio
Asymptotic Scaling of the Diffusion Coefficient of Fluctuating "Pulled" Fronts
We present a (heuristic) theoretical derivation for the scaling of the
diffusion coefficient for fluctuating ``pulled'' fronts. In agreement
with earlier numerical simulations, we find that as ,
approaches zero as , where is the average number of particles per
correlation volume in the stable phase of the front. This behaviour of
stems from the shape fluctuations at the very tip of the front, and is
independent of the microscopic model.Comment: Some minor algebra corrected, to appear in Rapid Comm., Phys. Rev.
Front Propagation and Diffusion in the A <--> A + A Hard-core Reaction on a Chain
We study front propagation and diffusion in the reaction-diffusion system A
A + A on a lattice. On each lattice site at most one A
particle is allowed at any time. In this paper, we analyze the problem in the
full range of parameter space, keeping the discrete nature of the lattice and
the particles intact. Our analysis of the stochastic dynamics of the foremost
occupied lattice site yields simple expressions for the front speed and the
front diffusion coefficient which are in excellent agreement with simulation
results.Comment: 5 pages, 5 figures, to appear in Phys. Rev.
Deterministic reaction models with power-law forces
We study a one-dimensional particles system, in the overdamped limit, where
nearest particles attract with a force inversely proportional to a power of
their distance and coalesce upon encounter. The detailed shape of the
distribution function for the gap between neighbouring particles serves to
discriminate between different laws of attraction. We develop an exact
Fokker-Planck approach for the infinite hierarchy of distribution functions for
multiple adjacent gaps and solve it exactly, at the mean-field level, where
correlations are ignored. The crucial role of correlations and their effect on
the gap distribution function is explored both numerically and analytically.
Finally, we analyse a random input of particles, which results in a stationary
state where the effect of correlations is largely diminished
Reweighting of the form factors in exclusive B --> X ell nu decays
A form factor reweighting technique has been elaborated to permit relatively
easy comparisons between different form factor models applied to exclusive B
--> X l nu decays. The software tool developped for this purpose is described.
It can be used with any event generator, three of which were used in this work:
ISGW2, PHSP and FLATQ2, a new powerful generator. The software tool allows an
easy and reliable implementation of any form factor model. The tool has been
fully validated with the ISGW2 form factor hypothesis. The results of our
present studies indicate that the combined use of the FLATQ2 generator and the
form factor reweighting tool should play a very important role in future
exclusive |Vub| measurements, with largely reduced errors.Comment: accepted for publication by EPJ
Saturation momentum at fixed and running QCD coupling
A relationship, linking the saturation momentum in the case of fixed and
running QCD coupling, respectively, is derived from the Balitsky-Kovchegov
equation. It relies on the linear instability of the evolution equation in the
dilute regime. The leading orders of the saturation momenta are mapped onto
each other exactly. For subleading terms a qualitative correspondence is
achieved with a relative error going to zero for large rapidities. The
relationship can also be derived for the Balitsky-Kovchegov equation with a
cutoff accounting for low-density effects and is satisfied by the corresponding
isoline functions. Further implications arise for the existence of
travelling-wave solutions in the two situations.Comment: revised version, 6 pages, no figure
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