An independent estimate of the triple-Pomeron coupling

The value of the important triple-Pomeron coupling is estimated by an unorthodox procedure using the known diffractive parton distribution functions. The result is g_{3P}\simeq 0.2g_N, where g_N is the Pomeron-nucleon coupling. This is in excellent agreement with an independent determination, g_{3P}\simeq 0.2g_N, previously obtained by analysing the available data in the triple-Regge region with absorptive effects taken into account.Comment: 7 pages, 5 figure

Upsilon photoproduction at HERA compared to estimates of perturbative QCD

We estimate the cross section for gamma p -> Upsilon p by two independent methods. First, by studying the corrections to the naive leading-order QCD formula and, second, by using parton-hadron duality. The estimates are in good agreement with each other and with the recent measurements of the cross section at HERA.Comment: 9 pages, LaTeX, one figur

Numerical solution of free-boundary problems in fluid mechanics. Part 3. Bubble deformation in an axisymmetric straining flow

We consider the deformation of a bubble in a uniaxial extensional flow for Reynolds numbers in the range 0.1 [less-than-or-eq, slant] R [less-than-or-eq, slant] 100. The computations show that the bubble bursts at a relatively early stage of deformation for R [gt-or-equal, slanted] O(10), never reaching the highly elongated shapes observed and predicted at lower Reynolds numbers. We also compute the deformation of the bubble under the assumption of potential flow, and conclude that the potential-flow solution provides a good approximation to the real flow in this case for R [gt-or-equal, slanted] O(100)

Bubble shapes in steady axisymmetric flows at intermediate Reynolds number

The shape of a gas bubble which rises through a quiescent incompressible, Newtonian fluid at intermediate Reynolds numbers is considered. Exact numerical solutions for the velocity and pressure fields, as well as the bubble shape, are obtained using finite difference techniques and a numerically generated transformation to an orthogonal, boundary-fitted coordinate system. No restriction is placed on the allowable magnitude of deformation

Diffractive rho-meson Leptoproduction on Polarized Nucleon as a Way to Measure the Polarized Gluon Distribution

The amplitude of diffractive $\rho$ (and open quark) leptoproduction on a polarized target is calculated in the leading log approximation of pQCD using the hadron-parton duality hypothesis. The spin-spin asymmetry is expressed in terms of the spin dependent gluon and quark structure functions in the small $x$ region. Therefore the $\gamma^*+p\to \rho +p$ reaction provides a promising tool to study the spin dependent gluon distribution $\Delta G(x,q^2)$.Comment: 13 pages, LaTeX, 2 figure

The extensional viscosity of a dilute suspension of spherical particles at intermediate microscale Reynolds numbers

The extensional viscosity of a dilute suspension of spherical particles (rigid spheres, viscous drops or gas bubbles) is computed for the case when the Reynolds number of the microscale disturbance motion R is not restricted to be small, as in the classical analysis of Einstein and Taylor. However, the present theory is restricted to steady axisymmetric pure straining flow (uniaxial extension). The rate of energy dissipation is expressed using the Bobyleff-Forsythe formula and then conditionally convergent integrals are removed explicitly. The problem is thereby reduced to a determination of the flow around a particle, subject to pure straining at infinity, followed (for rigid particles) by an evaluation of the volume integral of the vorticity squared. In the case of fluid particles, further integrals over the volume and surface of the particle are required. In the present paper, results are obtained numerically for 1 [less-than-or-eq, slant] R [less-than-or-eq, slant] 1000 for a rigid sphere, for a drop whose viscosity is equal to the viscosity of the ambient fluid, and for an inviscid drop (gas bubble). For the last case, limiting results are also obtained for R [rightward arrow] [infinity] using Levich's approach. All of these results show a strain-thickening behaviour which increases with the viscosity of the particle. The possibility of experimental verification of the results, which is complicated by the inapplicability of the approximation of material frame-indifference in this case, is discussed