22,695 research outputs found
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'oribà tid, 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 theory in canonical-noncommutative spacetime. We construct the CJT
effective potential and the gap equation for general values of the
noncommutative parameter . We observe that under the
hypothesis of translational invariance, which is assumed in the effective
potential construction, differently from the commutative case
(), 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
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