Dihadron fragmentation functions and their evolution arestudied in the process of e+e- annihilation. Under the collinearfactorization approximation and facilitated by the cut-vertex technique,the two hadron inclusive cross section at leading order (LO) is shown tofactorize into a short distance parton cross section and a long distancedihadron fragmentation function. We provide the definition of such adihadron fragmentation function in terms of parton matrix elements andderive its DGLAP evolution equation at leading log. The evolutionequation for the non-singlet quark fragmentation function is solvednumerically with a simple ansatz for the initial condition and resultsare presented for cases of physical interest.

The top quark is currently only observed at the Tevatron, where it is mainly produced in t{bar t} pairs. Due to the very high mass of the top quark compared to the other quarks and the gauge bosons, it is expected to play a special role in electroweak symmetry breaking. Therefore it might be especially sensitive to new physics. Measurements of various production and decay quantities of the top quark could lead to discoveries of physics beyond the standard model. Several such measurements were performed by the CDF collaboration during Run1 of the Tevatron. These measurements and first results from CDF in Run2 are presented.

Over half a century ago, von Neumann and Richtmyer [1] introduced the idea of adding artificial viscosity to the Euler equations in order to help stabilize shock calculations. Their ideas regarding artificial viscosity influenced Smagorinsky [2, 3] in his development of a subgrid-scale model designed to match the Kolmogorov spectrum for atmospheric turbulence (C. E. Leith, private communication). Since that time, numerous artificial viscosity formulations have been proposed for simulating both shocks and turbulence [4, 5, 6, 7, 8, 9, 10]. Over the years however, a rift has developed between shock-capturing (monotonicity-preserving) and turbulence-capturing (large-eddy simulation) methods. Artificial viscosities for shock-capturing typically depend on sound speed, which makes them unsuitable for low Mach number flows. On the other hand, subgrid-scale models, customized for incompressible turbulence, usually fail to capture shocks in a monotonic fashion. The purpose of this paper is to introduce an artificial viscosity suitable for computing shock-turbulence interactions. This is accomplished by extending the model of Cook and Cabot [10] to multi-dimensions.

Layered earth models are well justified by experience, and provide a simple means of studying fairly general behavior of the elastic and poroelastic characteristics of seismic waves in the earth. Thomsen's anisotropy parameters for weak elastic and poroelastic anisotropy are now commonly used in exploration, and can be conveniently expressed in terms of the layer averages of Backus. Since our main interest is usually in the fluids underground, it would be helpful to have a set of general equations relating the Thomsen parameters as directly as possible to the fluid properties. This end can be achieved in a rather straightforward fashion for these layered earth models, and the present paper develops and then discusses these relations. Furthermore, it is found that, although there are five effective shear moduli for any layered VTI medium, one and only one effective shear modulus for the layered system contains all the dependence of pore fluids on the elastic or poroelastic constants that can be observed in vertically polarized shear waves in VTI media. The effects of the pore fluids on this effective shear modulus can be substantial - an increase of shear wave speed on the order of 10% is shown to be possible …