10,107 research outputs found

### Pion Charge Exchange on Deuterium

We investigate quantum corrections to a classical intranuclear cascade
simulation of pion single charge exchange on the deuteron. In order to separate
various effects the orders of scattering need to be distinguished and, to that
end, we develop signals for each order of scattering corresponding to
quasi-free conditions. Quantum corrections are evaluated for double scattering
and are found to be large. Global agreement with the data is good.Comment: 30 pages, 12 figure

### Comment on: Failure of the Work-Hamiltonian Connection for Free-Energy Calculations [Phys Rev Lett 100, 020601 (2008), arXiv:0704.0761]

We comment on a Letter by Vilar and Rubi [arXiv:0704.0761].Comment: one page, including one figure; to appear in Phys Rev Let

### Anisotropic imbibition on surfaces patterned with polygonal posts

We present and interpret lattice Boltzmann simulations of thick films
spreading on surfaces patterned with polygonal posts. We show that the
mechanism of pinning and depinning differs with the direction of advance, and
demonstrate that this leads to anisotropic spreading within a certain range of
material contact angles.Comment: DSFD Proceedings 201

### Information-theoretic determination of ponderomotive forces

From the equilibrium condition $\delta S=0$ applied to an isolated
thermodynamic system of electrically charged particles and the fundamental
equation of thermodynamics ($dU = T dS-(\mathbf{f}\cdot d\mathbf{r})$) subject
to a new procedure, it is obtained the Lorentz's force together with
non-inertial terms of mechanical nature. Other well known ponderomotive forces,
like the Stern-Gerlach's force and a force term related to the Einstein-de
Haas's effect are also obtained. In addition, a new force term appears,
possibly related to a change in weight when a system of charged particles is
accelerated.Comment: 10 page

### Convex Functions and Spacetime Geometry

Convexity and convex functions play an important role in theoretical physics.
To initiate a study of the possible uses of convex functions in General
Relativity, we discuss the consequences of a spacetime $(M,g_{\mu \nu})$ or an
initial data set $(\Sigma, h_{ij}, K_{ij})$ admitting a suitably defined convex
function. We show how the existence of a convex function on a spacetime places
restrictions on the properties of the spacetime geometry.Comment: 26 pages, latex, 7 figures, improved version. some claims removed,
references adde

### The Gibbs free energy of homogeneous nucleation: from atomistic nuclei to the planar limit

In this paper we discuss how the information contained in atomistic
simulations of homogeneous nucleation should be used when fitting the
parameters in macroscopic nucleation models. We show how the number of solid
and liquid atoms in such simulations can be determined unambiguously by using a
Gibbs dividing surface and how the free energy as a function of the number of
solid atoms in the nucleus can thus be extracted. We then show that the
parameters of a model based on classical nucleation theory can be fit using the
information contained in these free-energy profiles but that the parameters in
such models are highly correlated. This correlation is unfortunate as it
ensures that small errors in the computed free energy surface can give rise to
large errors in the extrapolated properties of the fitted model. To resolve
this problem we thus propose a method for fitting macroscopic nucleation models
that uses simulations of planar interfaces and simulations of three-dimensional
nuclei in tandem. We show that when the parameters of the macroscopic model are
fitted in this way the numerical errors for the final fitted model are smaller
and that the extrapolated predictions for large nuclei are thus more reliable

### Estimation of Kalman filter model parameters from an ensemble of tests

A methodology for estimating initial mean and covariance parameters in a Kalman filter model from an ensemble of nonidentical tests is presented. In addition, the problem of estimating time constants and process noise levels is addressed. Practical problems such as developing and validating inertial instrument error models from laboratory test data or developing error models of individual phases of a test are generally considered

### Pion double charge exchange on 4He

The doubly differential cross sections for the $^4$He$(\pi^+,\pi^-) 4p$
reaction were calculated using both a two-nucleon sequential single charge
exchange model and an intranuclear cascade code. Final state interactions
between the two final protons which were the initial neutrons were included in
both methods. At incident pion energies of 240 and 270 MeV the low-energy peak
observed experimentally in the energy spectrum of the final pions can be
understood only if the contribution of pion production is included. The
calculated cross sections are compared with data.Comment: 25 pages, 9 figure

### Generalized Phase Rules

For a multi-component system, general formulas are derived for the dimension
of a coexisting region in the phase diagram in various state spaces.Comment: In the revised manuscript, physical meanings of D's are explained by
adding three figures. 10 pages, 3 figure

### Description of the fluctuating colloid-polymer interface

To describe the full spectrum of surface fluctuations of the interface
between phase-separated colloid-polymer mixtures from low scattering vector q
(classical capillary wave theory) to high q (bulk-like fluctuations), one must
take account of the interface's bending rigidity. We find that the bending
rigidity is negative and that on approach to the critical point it vanishes
proportionally to the interfacial tension. Both features are in agreement with
Monte Carlo simulations.Comment: 5 pages, 3 figures, 1 table. Accepted for publication in Phys. Rev.
Let

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