Stability conditions for a pipeline polling scheme in satellite communications

This paper considers the unknown stability conditions of a pipeline polling scheme proposed for satellite communications. This scheme is modelled as a cyclic-service system with limited service and reservation. The walk times and the maximum number of services to be performed during each polling are dependent on the queue lengths of the stations. The main result is the derivation of the necessary and sufficient stability conditions of the system. Our approach is to map the multi-dimensional stability problem into many 1-dimensional stability problems through the concept of the least stable queue. The least stable queue is one that will become unstablefirst when the system load increases in some parameter region. The stability of the least stable queue thus implies stability of the system. The stability region for the whole system is then the union of the queue stability regions of all the least stable queues that are obtained through dominant systems and Loynes' theorem. We also propose a computable sufficient condition that is tighter than the existing result and present some numerical results.     

Power spectrum of density fluctuations in a finite reactive-diffusive system: resistance fluctuation spectroscopy

The measurement in thermal equilibrium of the vacancy contribution to the residual resistivity of metals has posed certain difficulties. The recent experiment of Celasco and co-workers represents a new, powerful approach to this problem, via the measurement of the power spectrum of the voltage noise generated by resistivity fluctuations. The latter originate in vacancy number fluctuations. We develop a theory for the power spectrum, incorporating three basic features. Vacancies can be annihilated in the material and they diffuse. Grain boundaries act as sources and sinks for vacancies. Both annihilation (a form of reaction) and diffusion are noisy processes. We therefore set up and solve a reactive-diffusive stochastic equation for the instantaneous density, with appropriatefinite boundary conditions. Assuming for simplicity that the grains are spherical, the power spectrum is evaluated exactly, in closed form. A detailed comparison with experiment is made. The physical origins of different time scales in the problem and the consequent frequency regimes in the power spectrum are analysed. Recognising the very general applicability of our theory, we also mention possible applications to other problems.     

The theorem of hohenberg and kohn for subdomains of a quantum system

The theorem of Hohenberg and Kohn is extended to subdomains of a bounded quantum system. It is shown that the ground state particle density of an arbitrary subdomain uniquely determines the ground state properties of this subdomain, of any other subdomain, and of the total domain of the system.     

The influence of distortions and other effects on theD(d,t)H reaction

The differential cross section for the reactionD(d, t)H has been calculated in the distorted wave Born approximation including finite range effects. All 6 interactions between the 4 nucleons are explicitly evaluated. It has been found that the interactions neglected by earlier work are significant. Distortions are necessary to reproduce the minimum at 37.5° observed at an incident energy of 25.3 MeV in the cross section. The absolute cross section at 14.3° is predicted by theory to be 23.5 mb/sr as against the experimental 16.4 mb/sr. Better agreement with experiment at backward angles may be obtained with the use of an expanded deuteron and the inclusion ofd-state effects.     

Parallelizing of macro-scale pseudo-particle modeling for particle-fluid systems

Particle methods such as SPH (smoothed particlehydrodynamics)[1,2], DEM (distinct-element model)[3],DPD (dissipative particle dynamics)[4— and pseudo- 6]particle modeling (PPM)[7,8] are getting more and morepopular as numerical methods in material science andfluid dynamics, due to their flexibility in simulatingcomplicated phenomena like fluid-solid coupling,multi-phase flow and large deformation and rupture insolid materials. However, a comm…