Compressibility effects on fluid entrainment by turbulent mixing layers

Compressibility effects on fluid entrainment by supersonic turbulent mixing layer

Why medical students choose not to carry out an intercalated BSc : a questionnaire study.

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IMPACTS OF THE NORTHEAST INTERSTATE DAIRY COMPACT ON SUPPLY, RETAIL PRICES AND THE WIC PROGRAM: AN INTRODUCTION

Demand and Price Analysis, Food Security and Poverty,

Coexpression of rat P2X2 and P2X6 subunits in Xenopus oocytes.

Transcripts for P2X(2) and P2X(6) subunits are present in rat CNS and frequently colocalize in the same brainstem nuclei. When rat P2X(2) (rP2X(2)) and rat P2X(6) (rP2X(6)) receptors were expressed individually in Xenopus oocytes and studied under voltage-clamp conditions, only homomeric rP2X(2) receptors were fully functional and gave rise to large inward currents (2-3 microA) to extracellular ATP. Coexpression of rP2X(2) and rP2X(6) subunits in Xenopus oocytes resulted in a heteromeric rP2X(2/6) receptor, which showed a significantly different phenotype from the wild-type rP2X(2) receptor. Differences included reduction in agonist potencies and, in some cases (e.g., Ap(4)A), significant loss of agonist activity. ATP-evoked inward currents were biphasic at the heteromeric rP2X(2/6) receptor, particularly when Zn(2+) ions were present or extracellular pH was lowered. The pH range was narrower for H(+) enhancement of ATP responses at the heteromeric rP2X(2/6) receptor. Also, H(+) ions inhibited ATP responses at low pH levels (<pH 6.3). The pH-dependent blocking activity of suramin was changed at this heteromeric receptor, although the potentiating effect of Zn(2+) on ATP responses was unchanged. Thus, the rP2X(2/6) receptor is a functionally modified P2X(2)-like receptor with a distinct pattern of pH modulation of ATP activation and suramin blockade. Although homomeric P2X(6) receptors function poorly, the P2X(6) subunit can contribute to functional heteromeric P2X channels and may influence the phenotype of native P2X receptors in those cells in which it is expressed

Constraints on small-scale cosmological perturbations from gamma-ray searches for dark matter

Events like inflation or phase transitions can produce large density perturbations on very small scales in the early Universe. Probes of small scales are therefore useful for e.g. discriminating between inflationary models. Until recently, the only such constraint came from non-observation of primordial black holes (PBHs), associated with the largest perturbations. Moderate-amplitude perturbations can collapse shortly after matter-radiation equality to form ultracompact minihalos (UCMHs) of dark matter, in far greater abundance than PBHs. If dark matter self-annihilates, UCMHs become excellent targets for indirect detection. Here we discuss the gamma-ray fluxes expected from UCMHs, the prospects of observing them with gamma-ray telescopes, and limits upon the primordial power spectrum derived from their non-observation by the Fermi Large Area Space Telescope.Comment: 4 pages, 3 figures. To appear in J Phys Conf Series (Proceedings of TAUP 2011, Munich

On the evolution of tachyonic perturbations at super-Hubble scales

In the slow-roll inflationary scenario, the amplitude of the curvature perturbations approaches a constant value soon after the modes leave the Hubble radius. However, relatively recently, it was shown that the amplitude of the curvature perturbations induced by the canonical scalar field can grow at super-Hubble scales if there is either a transition to fast roll inflation or if inflation is interrupted for some period of time. In this work, we extend the earlier analysis to the case of a non-canonical scalar field described by the Dirac-Born-Infeld action. With the help of a specific example, we show that the amplitude of the tachyonic perturbations can be enhanced or suppressed at super-Hubble scales if there is a transition from slow roll to fast roll inflation. We also illustrate as to how the growth of the entropy perturbations during the fast roll regime proves to be responsible for the change in the amplitude of the curvature perturbations at super-Hubble scales. Furthermore, following the earlier analysis for the canonical scalar field, we show that the power spectrum evaluated in the long wavelength approximation matches the exact power spectrum obtained numerically very well. Finally, we briefly comment on an application of this phenomenon.Comment: v1: 15 pages, 4 figures; v2: 16 pages, 5 figures, power spectrum included, discussion in section 5 enlarged, references added; v3: 17 pages, 5 figures, enhancement AS WELL AS suppression of modes at super-Hubble scales pointed out, title changed, discussions enlarged, references added, to appear in JCA

Stirring of Sea‐Ice Meltwater Enhances Submesoscale Fronts in the Southern Ocean

In the sea‐ice‐impacted Southern Ocean, the spring sea‐ice melt and its impact on physical processes set the rate of surface water mass modification. These modified waters will eventually subduct near the polar front and enter the global overturning circulation. Submesoscale processes modulate the stratification of the mixed layer (ML) and ML properties. Sparse observations in polar regions mean that the role of submesoscale motions in the exchange of properties across the base of the ML is not well understood. The goal of this study is to determine the interplay between sea‐ice melt, surface boundary layer forcing, and submesoscale flows in setting properties of the surface ML in the Antarctic marginal ice zone. High‐resolution observations suggest that fine‐scale lateral fronts arise from either/both mesoscale and submesoscale stirring of sea‐ice meltwater anomalies. The strong salinity‐driven stratification at the base of the ML confines these fronts to the upper ocean, limiting submesoscale vertical fluxes across the ML base. This strong stratification prevents the local subduction of modified waters by submesoscale flows, suggesting that the subduction site that links to the global overturning circulation does not correspond with the location of sea‐ice melt. However, surface‐enhanced fronts increase the potential for Ekman‐driven cross‐frontal flow to modulate the stability of the ML and ML properties. The parameterization of submesoscale processes in coupled‐climate models, particularly those contributing to the Ekman buoyancy flux, may improve the representation of ML heat and freshwater transport in the ice‐impacted Southern Ocean during summer