Compressible magnetohydrodynamic boundary layer swirling nozzle and diffuser flows with a magnetic field

The flow, heat and mass transfer problem for boundary layer swirling flow of a laminar steady compressible electrically conducting gas with variable properties through a conical nozzle and a diffuser with an applied magnetic field has been studied. The partial differential equations governing the flow have been solved numerically using an implicit finite-difference scheme after they have been transformed into dimensionless form using the modified Lees transformation. The results indicate that the skin friction and heat transfer strongly depend on the magnetic field, mass transfer and variation of the density-viscosity product across the boundary layer. However, the effect of the variation of the density-viscosity product is more pronounced in the case of a nozzle than in the case of a diffuser. It has been found that large swirl is required to produce strong effect on the skin friction and heat transfer. Separationless flow along the entire length of the diffuser can be obtained by applying appropriate amount of suction. The results are found to be in good agreement with those of the local nonsimilarity method, but they differ quite significantly from those of the local similarity method.

Unsteady Incompressible Three-Dimensional Asymmetric Stagnation-Point Boundary Layers

The unsteady laminar incompressible boundary-layer flow near the three-dimensional asymmetric stagnation point has been studied under the assumptions that the free-stream velocity, wall temperature, and surface mass transfer vary arbitrarily with time. The partial differential equations governing the flow have been solved numerically using an implicit finite-difference scheme. It is found that in contrast with the symmetric flow, the maximum heat transfer occurs away from the stagnation point due to the decrease in the boundary-layer thickness. The effect of the variation of the wall temperature with time on heat transfer is strong. The skin friction and heat transfer due to asymmetric flow only are comparatively less affected by the mass transfer as compared to those of symmetric flow.

An annotated checklist of amphibian of India with some insights into the patterns of species discoveries, distribution and endemism

An annotated checklist of 284 species of amphibians of India accommodated under 50 genera and 14 families is provided. Synonyms, English names, type localities, deposition of type specimens, type specimen availability and distributional records in India and outside India are provided for all the species. Among the 284 species of amphibians from India, 132 are endemic to Western Ghats; 29 to Northeastern India; and 5 to Andaman Nicobar islands. Species discovery patterns from the various biogeographic zones in India are discussed in detail. Cumulative discovery pattern with special reference to the genera Fejervarya (17 species), Nyctibatrachus (16 species), Indirana (10 species), Micrixalus (11 species), Philautus (46 species) and Gegeneophis (10 species) are also discussed.

Studies on boundary lubrication properties of oxidised coconut and soy bean oils

Vegetable oils are a potential source of base oils for biodegradable lubricants, with limited oxidative stability. This study focuses on the effect of long-term ageing and the influence of oxidation products on the boundary lubrication performance of coconut and soy bean oils, by subjecting them to accelerated ageing in a dark oven at elevated temperature. The samples were collected at regular intervals and analysed for the changes in viscosity, percentage of free fatty acid and peroxide number compared to fresh oil samples. The boundary lubrication properties of these samples were evaluated using a four-ball tester. Increased wear observed with aged oil samples was linked to the destruction of triglyceride structure and formation of peroxides. The difference in the wear properties of soy bean oil to coconut oil was accounted by its high content of unsaturated fatty acids and its susceptibility to undergo oxidation. It was concluded that the coconut oil can perform as a better lubricant and has got a better storage life compared to soy bean oil.

Determination of skin friction in strong pressure-gradient equilibrium and near-equilibrium turbulent boundary layers

The conventional Clauser-chart method for determination of local skin friction in zero or weak pressure-gradient turbulent boundary layer flows fails entirely in strong pressure-gradient situations. This failure occurs due to the large departure of the mean velocity profile from the universal logarithmic law upon which the conventional Clauser-chart method is based. It is possible to extend this method,even for strong pressure-gradient situations involving equilibrium or near-equilibrium turbulent boundary layers by making use of the so-called non-universal logarithmic laws. These non-universal log laws depend on the local strength of the pressure gradient and may be regarded as perturbations of the universal log law.The present paper shows that the modified Clauser-chart method, so developed, yields quit satisfactory results in terms of estimation of local skin friction in strongly accelerated or retarded equilibrium and near-equilibrium turbulent boundary layers that are not very close to relaminarization or separation.

Mitochondrial and nuclear markers suggest Hanuman langur (Primates: Colobinae) polyphyly: Implications for their species status

Recent molecular studies on langurs of the Indian subcontinent suggest that the widely-distributed and morphologically variable Hanuman langurs (Semnopithecus entellus) are polyphyletic with respect to Nilgiri and urple-faced langurs. To further investigate this scenario, we have analyzed additional sequences of mitochondrial cytochrome b as well as nuclear protamine P1 genes from these species. The results confirm Hanuman langur polyphyly in the mitochondrial tree and the nuclear markers suggest that the Hanuman langurs share protamine P1 alleles with Nilgiri and purple-faced langurs. We recommend provisional splitting of the so-called Hanuman langurs into three species such that the taxonomy is consistent with their evolutionary relationships.

Azospirillum lipoferum tRNAs: Fractionation and identification of tRNA species and the nucleotide sequence of tRNA(Asn) (QUU)

Transfer RNAs of Azospirillum lipoferum were separated by two- dimensional gel electrophoresis and identified by aminoacylation. Thirty-six tRNA spots were resolved by this technique and twenty-six tRNA species have been identified. There are five tRNAs for Leu, four for Val, three for Pro, two each for Arg, Ile, Lys and Tyr, and one each for Ala, Asp, His, Phe, Ser and Thr. The tRNA(Asn) (QUU) was purified and its nucleotide sequence was determined. The A. lipoferum tRNA(Asn) (QUU) is 92% similar to B. subtilis tRNA(Asn) gene and two hypermodified nucleosides, queuosine (Q) and N-(9-beta-D Ribofuranosylpurine-6-YL) carbamoyl)-threonine (t(6)A) are present in this tRNA.

The effect of closed boundary conditions on a stationary dynamo

One of two boundary conditions generally assumed in solutions of the dynamo equation is related to the disappearance of the azimuthal field at the boundary. Parker (1984) points out that for the realization of this condition the field must escape freely through the surface. Escape requires that the field be detached from the gas in which it is embedded. In the case of the sun, this can be accomplished only through reconnection in the tenuous gas above the visible surface. Parker concludes that the observed magnetic activity on the solar surface permits at most three percent of the emerging flux to escape. He arrives at the conclusion that, instead of B(phi) = 0, the partial derivative of B(phi) to r is equal to zero. The present investigation is concerned with the effect of changing the boundary condition according to Parker's conclusion. Implications for the solar convection zone are discussed.

Boundary-layer effects on internal flow choking in dual-thrust solid rocket motors

Theoretical studies have been carried out to examine internal flow choking in the inert simulators of a dual-thrust motor. Using a two-dimensional k-omega turbulence model, detailed parametric studies have been carried out to examine aerodynamic choking and the existence of a fluid throat at the transition region during the startup transient of dual-thrust motors. This code solves standard k-omega turbulence equations with shear flow corrections using a coupled second-order-implicit unsteady formulation. In the numerical study, a fully implicit finite volume scheme of the compressible, Reynolds-averaged, Navier-Stokes equations is employed. It was observed that, at the subsonic inflow conditions, there is a possibility of the occurrence of internal flow choking in dual-thrust motors due to the formation of a fluid throat at the beginning of the transition region induced by area blockage caused by boundary-layer-displacement thickness. It has been observed that a 55% increase in the upstream port area of the dual-thrust motor contributes to a 25% reduction in blockage factor at the transition region, which could negate the internal How choking and supplement with an early choking of the dual-thrust motor nozzle. If the height of the upstream port relative to the motor length is too small, the developing boundary layers from either side of the port can interact, leading to a choked,flow. On the other hand, if the developing boundary layers are far enough apart, then choking does not occur. The blockage factor is greater in magnitude for the choked case than for the unchoked case. More tangible explanations are presented in this paper for the boundary-layer blockage and the internal flow choking in dual-thrust motors, which hitherto has been unexplored.

Why do birds participate in mixed-species foraging flocks? A large-scale synthesis

Mixed-species flocks of foraging birds have been documented from terrestrial habitats all over the world and are thought to form for either improved feeding efficiency or better protection from predators. Two kinds of flock participants are recognized: those that join other species ('followers') and are therefore likely to be the recipients of the benefits of flock participation and those that are joined ('leaders'). Through comparative analyses, using a large sample of flocks from around the world, we show that (1) 'followers' tend to be smaller, more insectivorous, and feed in higher strata than matched species that participate in flocks to a lesser extent and (2) 'leaders' tend to be cooperative breeders more often than matched species that are not known to lead flocks. Furthermore, meta-analyses of published results from across the world showed that bird species in terrestrial mixed-species flocks increase foraging rates and reduce vigilance compared to when they are solitary or in conspecific groups. Moreover, the increase in foraging rates is seen only with flock followers and not flock leaders. These findings suggest a role for predation in the evolution of mixed-species flocking. Species that are vulnerable to predation follow species whose vigilance they can exploit. By doing so, they are able to reduce their own vigilance and forage at higher rates. (C) 2009 The Association for the Study of Animal Behaviour. Published by Elsevier Ltd. All rights reserved.

Energy identities in water wave theory for free-surface boundary condition with higher-order derivatives

A modified form of Green's integral theorem is employed to derive the energy identity in any water wave diffraction problem in a single-layer fluid for free-surface boundary condition with higher-order derivatives. For a two-layer fluid with free-surface boundary condition involving higher-order derivatives, two forms of energy identities involving transmission and reflection coefficients for any wave diffraction problem are also derived here by the same method. Based on this modified Green's theorem, hydrodynamic relations such as the energy-conservation principle and modified Haskind–Hanaoka relation are derived for radiation and diffraction problems in a single as well as two-layer fluid.

Grain boundary sliding during diffusion and dislocation creep in a Mg-0.7 pct Al alloy

Early studies on grain boundary sliding (GBS) in Mg alloys have suggested frequently that the contribution of GBS to creep is high even under conditions corresponding to dislocation creep. The role of creep strain and grain size in influencing the experimental measurements has not been clearly identified. Grain boundary sliding measurements were conducted in detail over experimental conditions corresponding to diffusion creep as well as dislocation creep in a single-phase Mg-0.7 wt pet Al alloy. The results indicated clearly that the GBS contribution to creep was Very high during,, diffusion creep at low stresses (similar to 75 pct) and substantially reduced during dislocation creep at high stresses (similar to 15 pct). These measurements were consistent with the observation of significant intragranular slip band activity observed in most grains at high stresses and very little slip band activity at low stresses. The experimental measurements and analysis indicated also that the GBS contribution to creep was high during the initial stages of creep and decreased to a steady-state value at large strains.

Evolution of isolated streamwise vortices in the late stages of boundary layer transition

Experiments were conducted with two, smooth hills, lying well within the boundary layer over a flat plate mounted in a wind tunnel. One hill was shallow, with peak height 1.5 mm and width 50 mm; the other, steep, 3 mm high and 30 mm wide. Since the hills occupied one-half of the tunnel span, streamwise vorticity formed near the hills' edge. At a freestream speed of 3.5 m/s, streaks formed with inflectional wall-normal and spanwise velocity profiles but without effecting transition. Transition, observed at 7.5 m/s, took different routes with the two hills. With the steep hill, streamwise velocity signals exhibited the passage of a wave packet which intensified before breakdown to turbulence. With the shallow hill there was a broad range of frequencies present immediately downstream of the hill. These fluctuations grew continuously and transition occurred within a shorter distance. Since the size of the streamwise vorticity generated at the hill edge is of the order of the hill height, the shallow hill generates vorticity closer to the wall and supports an earlier transition, whereas the steep hill creates a thicker vortex and associated streaks which exhibit oscillations due to their own instability as an additional precursor stage before transition.

Quantitative photoacoustic tomography from boundary pressure measurements: noniterative recovery of optical absorption coefficient from the reconstructed absorbed energy map

We describe a noniterative method for recovering optical absorption coefficient distribution from the absorbed energy map reconstructed using simulated and noisy boundary pressure measurements. The source reconstruction problem is first solved for the absorbed energy map corresponding to single- and multiple-source illuminations from the side of the imaging plane. It is shown that the absorbed energy map and the absorption coefficient distribution, recovered from the single-source illumination with a large variation in photon flux distribution, have signal-to-noise ratios comparable to those of the reconstructed parameters from a more uniform photon density distribution corresponding to multiple-source illuminations. The absorbed energy map is input as absorption coefficient times photon flux in the time-independent diffusion equation (DE) governing photon transport to recover the photon flux in a single step. The recovered photon flux is used to compute the optical absorption coefficient distribution from the absorbed energy map. In the absence of experimental data, we obtain the boundary measurements through Monte Carlo simulations, and we attempt to address the possible limitations of the DE model in the overall reconstruction procedure.

Psychoacoustic sampling as a reliable, non-invasive method to monitor orthopteran species diversity in tropical forests

We evaluated trained listener-based acoustic sampling as a reliable and non-invasive method for rapid assessment of ensiferan species diversity in tropical evergreen forests. This was done by evaluating the reliability of identification of species and numbers of calling individuals using psychoacoustic experiments in the laboratory and by comparing psychoacoustic sampling in the field with ambient noise recordings made at the same time. The reliability of correct species identification by the trained listener was 100% for 16 out of 20 species tested in the laboratory. The reliability of identifying the numbers of individuals correctly was 100% for 13 out of 20 species. The human listener performed slightly better than the instrument in detecting low frequency and broadband calls in the field, whereas the recorder detected high frequency calls with greater probability. To address the problem of pseudoreplication during spot sampling in the field, we monitored the movement of calling individuals using focal animal sampling. The average distance moved by calling individuals for 17 out of 20 species was less than 1.5 m in half an hour. We suggest that trained listener-based sampling is preferable for crickets and low frequency katydids, whereas broadband recorders are preferable for katydid species with high frequency calls for accurate estimation of ensiferan species richness and relative abundance in an area.