Color mixing in high-energy hadron collisions

The color mixing of mesons propagating in a nucleus is studied with the help of a color-octet Pomeron partner present in the two-gluon model of the Pomeron. For a simple model with four meson-nucleon channels, color mixings are found to be absent for pointlike mesons and very small for small mesons. These results seem to validate the absorption model with two independent color components used in recent analyses of the nuclear absorption of $J/\psi$ mesons produced in nuclear reactions.Comment: 3 journal-style page

Color-Octet Fraction in J/Psi Production and Absorption

The cross section between a $c \bar c$ pair and a nucleon is small and sensitive to the $c - \bar c$ separation if the pair is in a color-singlet state, but very large and insensitive to the separation if it is in a color-octet state. We use this property in an absorption model involving both color components to deduce the color structure of $c \bar c$ pairs produced in $p(B)A \to \psi X$ reactions. Our analysis shows that the NA3, NA38 and E772 data are not inconsistent with the theoretical picture that color-octet and color-singlet precursors are produced in roughly equal proportions if the produced color-singlet precursors are pointlike and transparent. However, if the color-singlet precursors are not transparent but have a cross section of a few mb, these data do show a definite preference for a larger fraction of color-singlet precursors. In either case, the color-octet fraction increases with $x_F$, approaching unity as $x_F$ becomes large.Comment: 9 pages, updated to include new result

Numerical simulation of compressible flow through cascade of profiles

We deal with the numerical simulation of flow through a steam turbine. The system of the compressible Navier-Stokes equations accompanied by the state equation of perfect gas are numerically solved. We propose a new approach for the numerical solution of the Navier-Stokes equations, where the inviscid part is discretized by the finite volume method and the viscous part by the finite element method. To capture precisely the position of shock waves, the suitable mesh refinement method has to be applied. Therefore the anisotropic mesh adaptation technique equipped with some suitable modification for viscous compressible flow is used. The suitable application of the mentioned numerical adaptive method allows us to obtain sufficiently precise results without much requirement on CPU-time and computer memory

A numerical study of a particular non-conservative hyperbolic problem

Abstract We study the ability of several numerical schemes to solve a non-conservative hyperbolic system arising from a flow simulation of solid-liquid-gas slurries with the so-called virtual mass effect. Two classes of numerical schemes are used: some Roetype finite volume schemes, which are based on the resolution of linearized Riemann problems, and some centered schemes with an additional artificial diffusion, such as the classical Rusanov scheme. For flow regimes of interest (steady as well as unsteady flows), several schemes do not achieve the computational process. Indeed, for such flows, the system has at least one eigenvalue having a small magnitude in the interior of the computational domain and this a possible reason for the failure of some upwind schemes using the resolution of a linearized Riemann problem. Such a failure does not appear with, for instance, the Rusanov scheme which is well known for its robustness. Furthermore, since the system is nonconservative, it is not clear what a weak solution is, when the solution is discontinuous (at least, one needs to have the nonconservative equivalent of the Rankine-Hugoniot jump conditions) and we show that the approximate solution given by different numerical schemes converges towards different "weak solutions"

On discontinuous Galerkin methods for nonlinear convection-diffusion problems and compressible flow

summary:The paper is concerned with the discontinuous Galerkin finite element method for the numerical solution of nonlinear conservation laws and nonlinear convection-diffusion problems with emphasis on applications to the simulation of compressible flows. We discuss two versions of this method: (a) Finite volume discontinuous Galerkin method, which is a generalization of the combined finite volume—finite element method. Its advantage is the use of only one mesh (in contrast to the combined finite volume—finite element schemes). However, it is of the first order only. (b) Pure discontinuous Galerkin finite element method of higher order combined with a technique avoiding spurious oscillations in the vicinity of shock waves