Polarization Changes of Radiation through Stimulated Raman Scattering

We study change in the polarization of electromagnetic waves due to the stimulated Raman scattering in a plasma. In this process an electromagnetic wave undergoes coherent scattering off an electron plasma wave. It is found that some of the observed polarization properties such as the rapid temporal variations, sense reversal, rotation of the plane of polarization, and change of nature of polarization in the case of pulsars and quasars could be accounted for through stimulated Raman scattering.

On the dual head-discharge characteristics of a modified chimney weir

This paper is concerned with the dual head-discharge characteristics of a modified chimney weir. It is shown by an optimization procedure that the modified chimney weir having an inward trapezoidal weir over an inverted V-notch can produce discharges proportional to both the logarithm of the head as well as the linear power of the head reckoned independently over two different reference planes, within a prefixed maximum allowable percentage error from the theoretical discharge. A new technique is adopted to optimize the weir parameters, in order to obtain the maximum ranges of measurement under logarithmic, linear as well as combined characteristics. In the case of linear weir it is shown that it is possible to enhance the linearity range of the chimney weir by more than 540% and for a weir with constant indication accuracy by more than 350%. In addition, about 86% of the overall depth of the designed linear weir and over 90% of the logarithmic weir is converted as the corresponding measurable ranges. Experiments with four typical weirs give consistent constant average coefficient of discharge for each weir confirming the theory. The practical application of the weir in minor irrigation, hydraulic and other engineering fields is highlighted.

Autonomous and non-autonomous traits mediate social cooperation in Dictyostelium discoideum

In the trishanku (triA(-)) mutant of the social amoeba Dictyostelium discoideum, aggregates are smaller than usual and the spore mass is located mid-way up the stalk, not at the apex. We have monitored aggregate territory size, spore allocation and fruiting body morphology in chimaeric groups of (quasi-wild-type) Ax2 and triA(-) cells. Developmental canalisation breaks down in chimaeras and leads to an increase in phenotypic variation. A minority of triA(-) cells causes largely Ax2 aggregation streams to break up; the effect is not due to the counting factor. Most chimaeric fruiting bodies resemble those of Ax2 or triA(-). Others are double-deckers with a single stalk and two spore masses, one each at the terminus and midway along the stalk. The relative number of spores belonging to the two genotypes depends both on the mixing ratio and on the fruiting body morphology. In double-deckers formed from 1:1 chimaeras, the upper spore mass has more Ax2 spores, and the lower spore mass more triA(-) spores, than expected. Thus, the traits under study depend partly on the cells' own genotype and partly on the phenotypes, and so genotypes, of other cells: they are both autonomous and non-autonomous. These findings strengthen the parallels between multicellular development and behaviour in social groups. Besides that, they reinforce the point that a trait can be associated with a genotype only in a specified context.

CO adsorption on ionic Pt, Pd and Cu sites in Ce(1-x)M(x)O(2-delta) (M = Pt(2+), Pd(2+), Cu(2+))

Noble metal ion substituted CeO(2) in the form of Ce(0.98)M(0.02)O(2-delta) solid solution (where M = Pt, Pd, Cu) are the new generation catalysts with applications in three-way exhaust catalysis. While adsorption of CO on noble metals ions is well-known, adsorption of CO on noble metal ions has not been studied because creating exclusive ionic sites has been difficult. Using first-principles density functional theory (DFT) we have shown that CO gets adsorbed on the noble metal Pt(2+), Pd(2+), Cu(2+) ionic sites in the respective compounds, and the net energy of the overall system decreases. Adsorption of CO on metal ions is also confirmed by Fourier transform infrared spectroscopy (FTIR).

A Multilevel Inverter Scheme With Dodecagonal Voltage Space Vectors Based on Flying Capacitor Topology for Induction Motor Drives

This paper presents a multilevel inverter topology suitable for the generation of dodecagonal space vectors instead of hexagonal space vectors as in the case of conventional schemes. This feature eliminates all the 6n +/- 1 (n = odd) harmonics from the phase voltages and currents in the entire modulation range with an increase in the linear modulation range. The topology is realized by flying capacitor-based three-level inverters feeding from two ends of an open-end winding induction motor with asymmetric dc links. The flying capacitor voltages are tightly controlled throughout the modulation range using redundant switching states for any load power factor. A simple and fast carrier-based space-vector pulsewidth modulation (PWM) scheme is also proposed for the topology which utilizes only the sampled amplitudes of the reference wave for the PWM timing computation.

Comparative genomics reveals `novel' Fur regulated sRNAs and coding genes in diverse proteobacteria

Ferric uptake regulator (Fur) is a transcriptional regulator controlling the expression of genes involved in iron homeostasis and plays an important role in pathogenesis. Fur-regulated sRNAs/CDSs were found to have upstream Fur Binding Sites (FBS). We have constructed a Positional Weight Matrix from 100 known FBS (19 nt) and tracked the `Orphan' FBSs. Possible Fur regulated sRNAs and CDSs were identified by comparing their genomic locations with the `Orphan' FBSs identified. Thirty-eight `novel' and all known Fur regulated sRNAs in nine proteobacteria were identified. In addition, we identified high scoring FBSs in the promoter regions of the 304 CDSs and 68 of them were involved in siderophore biosynthesis, iron-transporters, two-component system, starch/sugar metabolism, sulphur/methane metabolism, etc. The present study shows that the Fur regulator controls the expression of genes involved in diverse metabolic activities and it is not limited to iron metabolism alone. (C) 2012 Elsevier B.V. All rights reserved.

Hypersensitivity of hypoxia grown Mycobacterium smegmatis to DNA damaging agents: Implications of the DNA repair deficiencies in attenuation of mycobacteria

Mycobacteria are an important group of pathogenic bacteria. We generated a series of DNA repair deficient strains of Mycobacterium smegmatis, a model organism, to understand the importance of various DNA repair proteins (UvrB, Ung, UdgB, MutY and Fpg) in survival of the pathogenic strains. Here, we compared tolerance of the M. smegmatis strains to genotoxic stress (ROS and RNI) under aerobic, hypoxic and recovery conditions of growth by monitoring their survival. We show an increased susceptibility of mycobacteria to genotoxic stress under hypoxia. UvrB deficiency led to high susceptibility of M. smegmatis to the DNA damaging agents. Ung was second in importance in strains with single deficiencies. Interestingly, we observed that while deficiency of UdgB had only a minor impact on the strain's susceptibility, its combination with Ung deficiency resulted in severe consequences on the strain's survival under genotoxic stress suggesting a strong interdependence of different DNA repair pathways in safeguarding genomic integrity. Our observations reinforce the possibility of targeting DNA repair processes in mycobacteria for therapeutic intervention during active growth and latency phase of the pathogen. High susceptibility of the UvrB, or the Ung/UdgB deficient strains to genotoxic stress may be exploited in generation of attenuated strains of mycobacteria. (C) 2013 Elsevier Ireland Ltd. All rights reserved.

Sparsely populated residue conformations in protein structures: Revisiting ``experimental'' Ramachandran maps

The Ramachandran map clearly delineates the regions of accessible conformational (phi-) space for amino acid residues in proteins. Experimental distributions of phi, values in high-resolution protein structures, reveal sparsely populated zones within fully allowed regions and distinct clusters in apparently disallowed regions. Conformational space has been divided into 14 distinct bins. Residues adopting these relatively rare conformations are presented and amino acid propensities for these regions are estimated. Inspection of specific examples in a completely arid, fully allowed region in the top left quadrant establishes that side-chain and backbone interactions may provide the energetic compensation necessary for populating this region of phi- space. Asn, Asp, and His residues showed the highest propensities in this region. The two distinct clusters in the bottom right quadrant which are formally disallowed on strict steric considerations correspond to the gamma turn (C7 axial) conformation (Bin 12) and the i + 1 position of Type II turns (Bin 13). Of the 516 non-Gly residues in Bin 13, 384 occupied the i + 1 position of Type II turns. Further examination of these turn segments revealed a high propensity to occur at the N-terminus of helices and as a tight turn in hairpins. The strand-helix motif with the Type II turn as a connecting element was also found in as many as 57 examples. Proteins 2014; 82:1101-1112. (c) 2013 Wiley Periodicals, Inc.

Electrospun SnSb Crystalline Nanoparticles inside Porous Carbon Fibers as a High Stability and Rate Capability Anode for Rechargeable Batteries

In an electrochemical alloying reaction, the electroactive particles become mechanically unstable owing to large volume changes occurring as a result of high amounts of lithium intake. This is detrimental for long-term battery performance. Herein, a novel synthesis approach to minimize such mechanical instabilities in tin particles is presented. An optimal one-dimensional assembly of crystalline single-phase tin-antimony (SnSb) alloy nanoparticles inside porous carbon fibers (abbreviated SnSb-C) is synthesized for the first time by using the electrospinning technique (employing non-oxide precursors) in combination with a sintering protocol. The ability of antimony to alloy independently with lithium is beneficial as it buffers the unfavorable volume changes occurring during successive alloying/dealloying cycles in Sn. The SnSb-C assembly provides nontortuous (tortuosity coefficient, =1) fast conducting pathways for both electrons and ions. The presence of carbon in SnSb-C completely nullifies the conventional requirement of other carbon forms during cell electrode assembly. The SnSb-C exhibited remarkably high electrochemical lithium stability and high specific capacities over a wide range of currents (0.2-5Ag(-1)). In addition to lithium-ion batteries, it is envisaged that SnSb-C also has potential as a noncarbonaceous anode for other battery chemistries, such as sodium-ion batteries.

降雨坡面径流汇集模型及其在茅坪滑坡中的应用

采用运动波理论,并基于地形对坡面流流向的控制作用,建立了一种能够模拟坡面流集中汇流过程的数值计算模型,该模型得到了人工降雨试验的良好验证.将该模型运用于茅坪滑坡实际情况,得到了茅坪滑坡的表面产流特征,尤其是较好地显示了茅坪滑坡表面的径流汇集路线,可为合理设计茅坪滑坡表面排水工程提供科学依据.