Application of a Reynolds stress turbulence model to the compressible shear layer

Theoretically based turbulence models have had success in predicting many features of incompressible, free shear layers. However, attempts to extend these models to the high-speed, compressible shear layer have been less effective. In the present work, the compressible shear layer was studied with a second-order turbulence closure, which initially used only variable density extensions of incompressible models for the Reynolds stress transport equation and the dissipation rate transport equation. The quasi-incompressible closure was unsuccessful; the predicted effect of the convective Mach number on the shear layer growth rate was significantly smaller than that observed in experiments. Having thus confirmed that compressibility effects have to be explicitly considered, a new model for the compressible dissipation was introduced into the closure. This model is based on a low Mach number, asymptotic analysis of the Navier-Stokes equations, and on direct numerical simulation of compressible, isotropic turbulence. The use of the new model for the compressible dissipation led to good agreement of the computed growth rates with the experimental data. Both the computations and the experiments indicate a dramatic reduction in the growth rate when the convective Mach number is increased. Experimental data on the normalized maximum turbulence intensities and shear stress also show a reduction with increasing Mach number

Cosmology of the Next-to-Minimal Supersymmetric Standard Model

We discuss the domain wall problem in the Next-to-Minimal Supersymmetric Standard Model, with particular attention to the usual solution of explicit breaking of the discrete symmetry by non-renormalisable operators. This ``solution'' leads to a contradiction between the requirements of cosmology and those of avoiding the destabilisation of the hierarchy.Comment: 6 pages LaTeX, needs sprocl.sty (included at end) Talk presented by P.L. White at Valencia 9

"Papillonotus tricarinatus" sp. nov. from India (Acarina: Oribatida: Oppiidae)

Es descriu una nova espècie d'oribàtid, Papillonotus tricarinatus sp. nov., de sòls de Tripura, Índia. Aquest gènere es citat per primera vegada per a l'Índia

Radiative seesaw in left-right symmetric model

There are some radiative origins for the neutrino masses in the conventional left-right symmetric models with the usual bi-doublet and triplet Higgs scalars. These radiative contributions could dominate over the tree-level seesaw and could explain the observed neutrino masses.Comment: 5 pages, 3 figures. Revised version with minor change. Accepted by PR

Cornwall-Jackiw-Tomboulis effective potential for canonical noncommutative field theories

We apply the Cornwall-Jackiw-Tomboulis (CJT) formalism to the scalar $\lambda \phi^{4}$ theory in canonical-noncommutative spacetime. We construct the CJT effective potential and the gap equation for general values of the noncommutative parameter $\theta_{\mu\nu}$. We observe that under the hypothesis of translational invariance, which is assumed in the effective potential construction, differently from the commutative case ($\theta_{\mu\nu}= 0$), the renormalizability of the gap equation is incompatible with the renormalizability of the effective potential. We argue that our result, is consistent with previous studies suggesting that a uniform ordered phase would be inconsistent with the infrared structure of canonical noncommutative theories.Comment: 15 pages, LaTe

Formulation and evaluation of matrix microspheres for simultaneous delivery of salbutamol sulphate and theophylline

Purpose: The objective of this study was to formulate and evaluate a matrix microsphere system for simultaneous delivery of two anti-asthmatic drugs Salbutamol sulphate and Theophylline which are often indicated for the management of asthma, their frequent dosing may reduce compliance, thus making a prolonged release formulation necessary. Ethylcellulose was used as a retardant polymer and its compatibility with the drugs and the drug-drug compatibility were established through IR, XRD and DSC studies. Method: Microspheres were prepared by emulsion solvent evaporation using acetone/light liquid paraffin system. Tween 80 was used as the dispersing agent and cyclohexane was added to harden the microspheres. The prepared microspheres were characterized for their micromeritic properties and drug loading, as well as by infrared spectroscopy (IR), differential scanning calorimetry (DSC), x-ray powder diffractometry (XRD) and scanning electron microscopy (SEM). The in vitro release studies were performed in pH 7.4, phosphate buffer. Result: The prepared microspheres were white, free flowing and spherical in shape. The drug-loaded microspheres showed 67-91% of entrapment and release was extended upto 6 to 8 h. The infrared spectra, differential scanning calorimetry thermographs and XRD spectra all showed the stable character of both the drugs in the drug-loaded microspheres and revealed the absence of drug-polymer interactions. Scanning electron microscopy study revealed that the microspheres were spherical and porous in nature. Conclusion: The matrix microspheres have a potential for the prolongation and simultaneous delivery of the anti asthmatic drugs (salbutamol and theophylline). Keywords: Matrix microspheres, Salbutamol sulphate, Theophylline, Ethylcellulose, Emulsion solvent evaporation technique. Tropical Journal of Pharmaceutical Research Vol. 7 (2) 2008: pp. 995-100

The Complex Time WKB Approximation And Particle Production

The complex time WKB (CWKB) approximation has been an effective technique to understand particle production in curved as well as in flat spacetime. Earlier we obtained the standard results on particle production in time dependent gauge in various curved spacetime. In the present work we generalize the technique of CWKB to the equivalent problems in space dependent gauge. Using CWKB, we first obtain the gauge invariant result for particle production in Minkowski spacetime in strong electric field. We then carry out particle production in de-Sitter spacetime in space dependent gauge and obtain the same result that we obtained earlier in time dependent gauge. The results obtained for de-Sitter spacetime has a obvious extension to particle production in black hole spacetime. It is found that the origin of Planckian spectrum is due to repeated reflections between the turning points. As mentioned earlier, it is now explicitly shown that particle production is accompanied by rotation of currents.Comment: 12 pages, Revte