10,107 research outputs found

    Pion Charge Exchange on Deuterium

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    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]

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    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

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    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

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    From the equilibrium condition δS=0\delta S=0 applied to an isolated thermodynamic system of electrically charged particles and the fundamental equation of thermodynamics (dU=TdS(fdr)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

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    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,gμν)(M,g_{\mu \nu}) or an initial data set (Σ,hij,Kij)(\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

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    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

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    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

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    The doubly differential cross sections for the 4^4He(π+,π)4p(\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

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    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

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    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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