On the Effective Potential of the Dp- anti Dp system in type II theories

We compute the effective potential of a system composed by a Dp brane and a separated anti-Dp brane at tree level in string theory. We show explicitly that the tachyon condenses and that the scalars which describe transverse fluctuations acquire a VEV proportional to the distance.Comment: latex2e, 1+19 pages Corrected typos. Added criticisms to the previous interpration of the results and a new interpretatio

On steady compressible flows with compact vorticity; the compressible Stuart vortex

Numerical and analytical solutions to the steady compressible Euler equations corresponding to a compressible analogue of the linear Stuart vortex array are presented. These correspond to a homentropic continuation, to finite Mach number, of the Stuart solution describing a linear vortex array in an incompressible fluid. The appropriate partial differential equations describing the flow correspond to the compressible homentropic Euler equations in two dimensions, with a prescribed vorticity–density–streamfunction relationship. In order to construct a well-posed problem for this continuation, it was found, unexpectedly, to be necessary to introduce an eigenvalue into the vorticity–density–streamfunction equation. In the Rayleigh–Janzen expansion of solutions in even powers of the free-stream Mach number M[infty infinity], this eigenvalue is determined by a solvability condition. Accurate numerical solution by both finite-difference and spectral methods are presented for the compressible Stuart vortex, over a range of M[infty infinity], and of a parameter corresponding to a confined mass-flow rate. These also confirm the nonlinear eigenvalue character of the governing equations. All solution branches followed numerically were found to terminate when the maximum local Mach number just exceeded unity. For one such branch we present evidence for the existence of a very small range of M[infty infinity] over which smooth transonic shock-free flow can occur

Remark on a result of D. Dritschel

A hypothesis put forward by D. Dritschel [J. Fluid Mech. 94, 511 (1988)], namely that an isolated symmetrical disturbance on a uniform vortex patch will filament in time proportional to the inverse square of the disturbance amplitude, is subject to independent testing using a nonintrusive numerical method. The hypothesis that the trend is maintained to substantially smaller amplitudes than were originally considered by Dritschel is both supported and verified. The results may be interpreted as providing limited evidence that contour smoothness is maintained in filamentation and that corner formation does not occur up to the time of wave overturning

Comment on `Pressure of Hot QCD at large N_f'

It is argued why quasiparticle models can be useful to describe the thermodynamics of hot QCD excluding, however, the case of a large number of flavors, for which exact results have been calculated by Moore.Comment: 5 pages, 2 figures (version accepted for publication

Scattering quantum random-walk search with errors

We analyze the realization of a quantum-walk search algorithm in a passive, linear optical network. The specific model enables us to consider the effect of realistic sources of noise and losses on the search efficiency. Photon loss uniform in all directions is shown to lead to the rescaling of search time. Deviation from directional uniformity leads to the enhancement of the search efficiency compared to uniform loss with the same average. In certain cases even increasing loss in some of the directions can improve search efficiency. We show that while we approach the classical limit of the general search algorithm by introducing random phase fluctuations, its utility for searching is lost. Using numerical methods, we found that for static phase errors the averaged search efficiency displays a damped oscillatory behaviour that asymptotically tends to a non-zero value.Comment: 10 pages, 10 figures. Two figures added for clarity, also made improvements to the tex

Atmosphere Behavior in Gas-Closed Mouse-Algal Systems: An Experimental and Modelling Study

A dual approach of mathematical modelling and laboratory experimentation aimed at examining the gas exchange characteristics of artificial animal/plant systems closed to the ambient atmosphere was initiated. The development of control techniques and management strategies for maintaining the atmospheric levels of carbon dioxide and oxygen at physiological levels is examined. A mathematical model simulating the atmospheric behavior in these systems was developed and an experimental gas closed system was constructed. These systems are described and preliminary results are presented