A vector-parallel scheme for Navier-Stokes computations at multi-gigaflop performance rates

A class of vector-parallel schemes for solution of steady compressible or incompressible viscous flow is developed and performance studies carried out. The algorithms employ an artificial transient treatment that permits rapid integration to a steady state. In the present work a four-stage explicit Runge-Kutta scheme employing variable local step size is utilized for the ODE system integration. The RK-4 scheme is restructured to allow vectorization and enhance concurrency in the calculation for a streamfunction-vorticity formulation of the flow problem. The parameters of the resulting RK scheme can be selected to accelerate convergence of the RK recursion. Four main procedures are considered which permit vector-parallel solution: a Jacobi update, a hybrid of the Jacobi and Gauss-Seidel method, red-black ordering and domain decomposition. Numerical performance studies are conducted with a representative viscous incompressible flow calculation. Results indicate that a scheme involving domain decomposition with a Gauss-Seidel type of update for the RK four-stage scheme is most effective and provides performance in excess of 8 Gflops on the Cray C-90.     

Impurity distribution and electrical characteristics of boron-doped Si1−x Ge x /Si p +/N heterojunction diodes produced using pulsed UV-laser-induced epitaxy and Gas-immersion laser doping

A two-step pulsed UV-laser process which independently controls the metallurgical and electrical junction depth of a Si_1–x Ge _x /Si heterojunction diode has been implemented. Pulsed Laser-Induced Epitaxy (PLIE) combined with Gas-immersion Laser Doping (GILD) are used to fabricate boron-doped heteroepitaxial p ⁺/N Si_1–x Ge _x /Si layers and diodes. Borontrifluoride is used as the gaseous dopant source in the GILD process step. Boron incorporation and activation are investigated as a function of laser energy fluence and the number of laser pulses using SIMS and Halleffect measurements. The dose of incorporated dopant is on the order of 10¹³ cm^–2 per pulse. The B profiles obtained are flat except for a peak at the interface resulting from segregation effects. The B and Ge distributions are compared with shifts in the turn-on voltage of p ⁺/N Si_1–x /Si heterojunction diodes produced by the process. The GILD/PLIE process is spatially selective with the resulting diodes fabricated being quasiplanar. Hole mobilities in the heavily doped Si_1–x Ge _x films are found to be slightly lower than in comparable Si films.Presently at the Oregon Graduate Institute, Beaverton, OR 97006, USA     

Metal nanoparticle production by pulsed laser nanostructuring of thin metal films

The controllable nanostructuring of thin metal films by nanosecond UV laser pulses is introduced as a novel technique for the production of metal nanoparticles supported on a range of different oxide substrates, including indium tin oxide. This processing is performed at low macroscopic temperatures. The physical mechanisms underlying the nanostructuring are discussed and applications for these nanoparticle films, including as catalysts for nanotube/nanowire growth and in surface enhanced Raman spectroscopy measurements, are introduced.     

On the minimization of concave information functionals for unsupervised classification via decision trees

A popular method for unsupervised classification of high-dimensional data via decision trees is characterized as minimizing the empirical estimate of a concave information functional. It is shown that minimization of such functionals under the true distributions leads to perfect classification.     

Absence of vacuum polarisation in fock space

We show that, under plausible hypotheses which are known to be satisfied for certain cases, a charged vacuum cannot occur in the external field problem in quantum electrodynamics.     

Determination of ranitidine and its metabolites in human urine by reversed-phase ion-pair high-performance liquid chromatography

A method using ion-pair high-performance liquid chromatography is presented for determining ranitidine, ranitidine N-oxide, ranitidine S-oxide and desmethyl ranitidine in the urine from four volunteers, given on separate occasions an intravenous and oral dose of 100 mg ranitidine. This method has been used to study the metabolism and pharmacokinetics of ranitidine by man. It was found that the elimination half-life of ranitidine ranged from 110-246 min. The mean renal clearance of ranitidine in these four volunteers was 512 ml/min.     

Principal functions,index theory,geometric measure theory and function algebras

The aim of this paper is twofold: first to provide evidence of a nice relationship between index theory and operator algebras within the framework of geometric measure theory by exhibiting basic examples involving one dimensional singular integral operators; second to expose certain connections that exist involving the principal function associated to an operator having trace class self-commutator and the theory of function algebras.