Electroluminescence from modulation-doped pseudomorphic AlGaAs/InGaAs/GaAs quantum wells

Low-temperature electroluminescence (EL) is observed in n-type modulation-doped AlGaAs/InGaAs/GaAs quantum well samples by applying a positive voltage between the semitransparent Au gate and alloyed Au–Ge Ohmic contacts made on the top surface of the samples. We attribute impact ionization in the InGaAs QW to the observed EL from the samples. A redshift in the EL spectra is observed with increasing gate bias. The observed redshift in the EL spectra is attributed to the band gap renormalization due to many-body effects and quantum-confined Stark effect.

Flow between torsionally oscillating disks rotating about different axes at different speeds

The flow of an incompressible viscous fluid confined between two parallel infinite disks performing torsional oscillations with the same frequency, but rotating about different axes with different speeds has been studied. The solutions are presented for the symmetric and asymmetric first harmonic and steady streaming. The interesting features of the symmetric and asymmetric flow are discussed for the cases of small and large Womersley parameter at different ratios of the rotation speeds. The forces acting on one of the disks are also calculated.

Thermal stresses around circular holes in spherical shells

The thermal stress problem of a circular hole in a spherical shell of uniform thickness is solved by using a continuum approach. The influence of the hole is assumed to be confined to a small region around the opening. The thermal stress problem is converted as usual to an equivalent boundary value problem with forces specified around the cutout. The stresses and displacement are obtained for a linear variation of temperature across the thickness of the shell and presented in graphical form for ready use.

Shape-Dependent Confinement in Ultrasmall Zero-, One-, and Two-Dimensional PbS Nanostructures

Spatial dimensionality affects the degree of confinement when an electron-hole pair is squeezed from one or more dimensions approaching the bulk exciton Bohr radius (alpha(B)) limit. The etectron-hole interaction in zero-dimensional (0D) dots, one-dimensional (1D) rods/wires, and two-dimensional (2D) wells/sheets should be enhanced by the increase in confinement dimensions in the order 0D > 1D > 2D. We report the controlled synthesis of PbS nanomateriats with 0D, 1D, and 2D forms retaining at least one dimension in the strongly confined regime far below alpha(B) (similar to 10 nm for PbS) and provide evidence through varying the exciton-phonon coupling strength that the degree of confinement is systematically weakened by the loss of confinement dimension. Geometry variations show distinguishable far-field optical polarizations, which could find useful applications in polarization-sensitive devices.

Reorientation of Water Inside Carbon Nanorings by Large Angular Jumps

Molecular dynamics simulations of the orientational dynamics of water molecules confined inside narrow carbon nanorings reveal that reorientational relaxation is mediated by large amplitude angular jumps. The distribution of waiting time between jumps peaks at about 60 fs, and has a slowly decaying exponential tail with a timescale of about 440 fs. These time scales are much faster than the mean waiting time between jumps of the water molecules in bulk.

Spectroscopic studies of micro-explosions

NONEL tube finds vast applications in civil and military because of its safe and confined explosion technique. Spectroscopic and chemical analysis of a NONEL tube with an uniform mixture of HMX and Al is reported here. Peak temperature obtained at the open end of the NONEL tube due to the detonation of the explosive has been calculated using Planck’s radiation law. The products of the chemical reaction taking place due to the ignition of HMX + Al are characterized using FTIR spectroscopy.

Semi-Classical Mechanics in Phase Space: A Study of Wigner's Function

We explore the semi-classical structure of the Wigner functions ($\Psi $(q, p)) representing bound energy eigenstates $|\psi \rangle $ for systems with f degrees of freedom. If the classical motion is integrable, the classical limit of $\Psi $ is a delta function on the f-dimensional torus to which classical trajectories corresponding to ($|\psi \rangle $) are confined in the 2f-dimensional phase space. In the semi-classical limit of ($\Psi $ ($\hslash $) small but not zero) the delta function softens to a peak of order ($\hslash ^{-\frac{2}{3}f}$) and the torus develops fringes of a characteristic 'Airy' form. Away from the torus, $\Psi $ can have semi-classical singularities that are not delta functions; these are discussed (in full detail when f = 1) using Thom's theory of catastrophes. Brief consideration is given to problems raised when ($\Psi $) is calculated in a representation based on operators derived from angle coordinates and their conjugate momenta. When the classical motion is non-integrable, the phase space is not filled with tori and existing semi-classical methods fail. We conjecture that (a) For a given value of non-integrability parameter ($\epsilon $), the system passes through three semi-classical regimes as ($\hslash $) diminishes. (b) For states ($|\psi \rangle $) associated with regions in phase space filled with irregular trajectories, ($\Psi $) will be a random function confined near that region of the 'energy shell' explored by these trajectories (this region has more than f dimensions). (c) For ($\epsilon \neq $0, $\hslash $) blurs the infinitely fine classical path structure, in contrast to the integrable case ($\epsilon $ = 0, where $\hslash $ )imposes oscillatory quantum detail on a smooth classical path structure.

Glycodelin A triggers T cell apoptosis through a novel calcium-independent galactose-binding lectin activity

Glycodelin A (GdA) is one of the progesterone inducible endometrial factors that protect the fetal semiallograft from maternal immune rejection. The immumoregulatory effects of GdA are varied, with diverse effects on the fate and function of most immune cell types. Its effects on T cells are particularly relevant as it is capable of regulating T cell activation, differentiation, as well as apoptosis. We have previously reported that GdA triggers mitochondrial stress and apoptosis in activated T cells by a mechanism that is distinct and independent of its effects on T cell activation. In this study we describe the characterization of a cell surface receptor for GdA on T cells. Our results reveal a novel calcium-independent galactose-binding lectin activity of GdA, which is responsible for its apoptogenic function. This discovery adds GdA to a select group of soluble immunoregulatory lectins that operate within the feto-placental compartment, the only other members being the galectin family proteins. We also report for the first time that both CD4(+) and CD8(+) T cell subsets are equally susceptible to inhibition with GdA, mediated by its novel lectin activity. We demonstrate that GdA selectively recognizes complex-type N-linked glycans on T cell surface glycoproteins. and propose that the galectin-1 glycoprotein receptor CD7 maybe a novel target for GdA on T cells. This study, for the first time, links the lectin activity of GdA to its biological function.

Do dholes (Cuon alpinus) live in packs in response to competition with or predation by large cats?

Interactions between carnivores during the defence of kills may be one reason why certain carnivores live in groups. This is especially true of lions, hyaenas and the African wild dog, The dhole or the Asiatic wild dog, primarily a pack living animal, has been observed to regularly interact with both tigers and leopards, Such interactions have taken place over kills and otherwise. In this report, five such interactions are described, It was found that the pack's behaviour of surrounding bushes acid trees on which the cat was confined precluded immediate escape. The presence of sentinels, while the pack was resting, warned the pack of the presence of a big cat and the pack grouped when a big cat appeared, Costs to both individuals within the dhole packs and the cats involved in the encounters were found to be slight, The reasons for such potentially costly encounters could be competition for finite food resources or thwarting predation, Dholes have a significant diet overlap with both leopards and tigers and aggressively encounter with leopards but not with tigers, Differences between diet overlaps may not be the basis behind the differences in aggression, It is more likely that, the small size of leopards and the fact that they predate more often on dholes, cause dhole packs to be more aggressive to leopards than to tigers, The size of carnivore groups may thus pose an advantage during competitive interactions among carnivore species.

Numerical Study of Heat Transfer From Pin-Fin Heat Sink Using Steady and Pulsated Impinging Jets

This paper investigates numerically the heat transfer characteristics of confined slot jet impingement on a pin-fin heat sink. A variety of pin-fin heat sinks is investigated, and the resulting enhancement of heat transfer studied. The distribution of heat transfer coefficient on the top surface of the base plate and that along the fin height are examined. Both steady and pulsated jets are studied. It is observed that for a steady jet impingement on a pin-fin heat sink, the effective heat transfer coefficient increases with fin height, leading to a corresponding decrease in base plate temperature for the same heat flux. In the case of pulsated jets, the influence of pulse frequency and the Reynolds number is examined, and their effect on the effective heat transfer coefficient is studied.

The Out-of-India hypothesis: What do molecules suggest?

The remarkable geological and evolutionary history of peninsular India has generated much interest in the patterns and processes that might have shaped the current distributions of its endemic biota. In this regard the Out of India hypothesis, which proposes that rafting peninsular India carried Gondwanan forms to Asia after the break-up of Gondwana super continent, has gained prominence. Here we have reviewed molecular studies undertaken on a range of taxa of supposedly Gondwanan origin to better understand the Out-of-India scenario. This re-evaluation of published molecular studies indicates that there is mounting evidence supporting Out-of-India scenario for various Asian taxa. Nevertheless, in many studies the evidence is inconclusive due to lack of information on the age of relevant nodes. Studies also indicate that not all Gondwanan forms of peninsular India dispersed out of India. Many of these ancient lineages are confined to peninsular India and therefore are relict Gondwanan lineages. Additionally for some taxa an Into India rather than Out-of-India scenario better explains their current distribution. To identify the Out-of-India component of Asian biota it is imperative that we understand the complex biogeographical history of India. To this end, we propose three oversimplified yet explicit phylogenetic predictions. These predictions can be tested through the use of molecular phylogenetic tools in conjunction with palaeontological and geological data.

Thermoelectric power in ultrathin films, quantum wires and carbon nanotubes under classically large magnetic field: Simplified theory and relative comparison

We study the thermoelectric power under classically large magnetic field (TPM) in ultrathin films (UFs), quantum wires (QWs) of non-linear optical materials on the basis of a newly formulated electron dispersion law considering the anisotropies of the effective electron masses, the spin-orbit splitting constants and the presence of the crystal field splitting within the framework of k.p formalism. The results of quantum confined III-V compounds form the special cases of our generalized analysis. The TPM has also been studied for quantum confined II-VI, stressed materials, bismuth and carbon nanotubes (CNs) on the basis of respective dispersion relations. It is found taking quantum confined CdGeAs2, InAs, InSb, CdS, stressed n-InSb and Bi that the TPM increases with increasing film thickness and decreasing electron statistics exhibiting quantized nature for all types of quantum confinement. The TPM in CNs exhibits oscillatory dependence with increasing carrier concentration and the signature of the entirely different types of quantum systems are evident from the plots. Besides, under certain special conditions, all the results for all the materials gets simplified to the well-known expression of the TPM for non-degenerate materials having parabolic energy bands, leading to the compatibility test. (C) 2009 Elsevier B.V. All rights reserved.

Force-free equilibria of magnetized jets

Force-free equilibrium configurations of magnetic-pressure-dominated magnetized supersonic jets confined by slowly varying external pressure are investigated analytically. For the case where internal dissipation mechanisms are active, the lowest-energy field configuration is found to be the superposition of an axisymmetric mode and a helical mode with a wavelength equal to 5 times the jet radius, and the pressure below which the nonaxisymmetric mode becomes energetically favorable is given as 2700 times the product of the 4th power of the magnetic helicity per unit length and the -6th power of the magnetic flux. A model of the total and polarized emission of such a configuration is developed and applied to the extended well-collimated astronomically resolved jet NGC 6251. The model is shown to reproduce significant features such as transverse oscillations of the ridge line, width oscillations and emission knots, the projected magnetic-field configuration, oscillations of the degree of polarization, and the distribution of the Faraday rotation measure.

High P-T granulite relicts from the Imjingang belt, South Korea:Tectonic significance

This study presents a detailed description on crustal metamorphic signatures of garnet-clinopyroxene-quartz-rutile-bearing high P-T granulites, Samgot unit, Imajingang belt, northwestern Korean Peninsula that formed during Permo-Triassic regional metamorphism related to the amalgamation of East Asian continental fragments. Lenses and blocks of high P-T granulites and garnet-bearing leucosomes occur within mafic metamorphic rocks (mainly amphibolites). The mafic blocks comprise relicts of granoblastic garnet and clinopyroxene with medium-grained quartz and rutile. These relict mineral assemblages are confined to local micro-domains and constitute remnants of peak metamorphism. Plagioclase and amphibole form only as retrograde phases in medium ton coarse-grained moats that rim grain boundaries between relict peak mineral assemblages. This microstructure represents the reaction between garnet, clinopyroxene, quartz and rutile in the presence of melt to form amphibole, plagioclase and titanite with minor biotite. The leucosome domains consist of euhedral garnets within the quartz-K feldspar-plagioclase (granitic) matrix, probably representing peritectic garnet growth along with melting. The rare earth element (REE) composition of minerals also support the peritectic garnet growth with a positive Eu/Eu* (positive Eu anomaly), while the relict garnet shows a slight negative anomaly typical for high-grade granulites. The peak-metamorphic conditions calculated from thermodynamic modeling and compositional isopleths indicate a temperature around c. 900 degrees C at a pressure around c. 20 kbar. The present P-T path indicates a clear multi-stage decompression history with initial decompression and cooling followed by a stage of decompression during hydration possibly during Late Triassic exhumation. The results from this study together with the presence of eclogites from the Hongsung area suggest that the Imjingang area and the western Gyeonggi massif likely resided at crustal levels deeper than those of the eastern and southern part of the Gyeonggi massif. (C) 2009 International Association for Gondwana Research. Published by Elsevier B.V. All rights reserved.

Correlation between conductivity or diffusivity and activation energy in amorphous solids

There exist many investigations of ionic transport in a variety of glasses. These studies exhibit strong correlation between ionic conductivity and activation energy: Typically, it is found that higher conductivity is associated with lower activation energies and vice versa. Although there are explanations for this at a phenomenological level, there is no consistent physical picture to explain the correlation between conductivity and activation energy. We have carried out molecular dynamics simulation as a function of the size of the impurity atom or diffusant (both neutral and charged) in a host amorphous matrix. We find that there is a maximum in self-diffusivity as a function of the size of the impurity atom suggesting that there is an appropriate size for which the diffusivity is maximum. The activation energy is found to be the lowest for this size of the impurity. A similar maximum has been previously found in other condensed phases, such as confined fluids and dense liquids, and has its origin in the levitation effect. The implications of this result for understanding ionic conductivity in glasses are discussed. Our results suggest that there is a relation between microscopic structure of the amorphous solid, diffusivity or conductivity, and activation energy. The nature of this relationship is discussed in terms of the levitation parameter showing that diffusivity is maximum when the size of the neck or doorway radius is comparable with the size of the diffusant. Our computational results here are in excellent agreement with independent experimental results of Nascimento et al. [Braz. J. Phys. 35, 626 (2005)] that structural features of the glass are important in determining the ionic conductivity.