Combined addition of nano diamond and nano SiO2, an effective method to improve the in-field critical current density of MgB2 superconductor

MgB₂ bulk samples added with nano SiO₂ and/or nano diamond were prepared by powder-in-sealed-tube (PIST) method and the effects of addition on structural and superconducting properties were studied. X-ray diffraction (XRD) analysis revealed that the addition caused systematic reduction in ‘a’ lattice parameter due to the substitution of C atoms at B sites and the strain caused by reacted intragrain nano particles of Mg₂Si as evinced by transmission electron microscope image. Scanning electron microscopy images showed distinct microstructural variations with SiO₂/diamond addition. It was evident from DC magnetization measurements that the in-field critical current density [J_C(H)] of doped samples did not fall drastically like the undoped sample. Among the doped samples the J_C(H) of co-doped samples were significantly higher and the best co-doped sample yielded a J_C, an order of magnitude more than the undoped one at 5 K and 8 T.     

Determination of interface state density of PtSi/strained-Si1-xGex/Si Schottky diodes

PtSi/p-strained-Si_1-xGe_x (x=0.19 and x=0.29) Schottky barrier diodes have been fabricated and characterized for the determination of barrier height, ideality factor and the interface state density distribution with energy. Diodes having an epitaxial layer thickness of 20 and 52 nm were modeled with emphasis on comparison with experiment. To achieve better agreement with experimental data, an interfacial layer and associated series resistance were included in the model. The capacitance–voltage (C–V) technique has been used for the determination of the energy distribution of interface state density. The interface state density distribution for the Si_0.81Ge_0.19 and Si_0.71Ge_0.29 diodes is found to decrease with increasing energy from the valence band edge.     

Simulation and experimental study of interharmonic performance of a Cycloconverter-FedSynchronous motor drive

High-power synchronous motor drives are usually fed from naturally commutated cycloconverters. The output voltage of the cycloconverter contains interharmonics/subharmonics which affect the power quality and restrict the allowable frequency range. Further, a practical circulating current-free cycloconverter usually gives rise to stator current discontinuities. The present paper deals with a simulation method to study the performance of a cycloconverter-fed synchronous motor drive in the presence of interharmonics/subharmonics taking into account the discontinuities in the output current as well as the effect of ripple in the output current on the input current of the cycloconverter. Interharmonics in output phase voltage, output phase current, input supply current, and the field current are estimated and verified with experimental results on a laboratory prototype. The significant oscillating torque components due to these interharmonics are identified in a typical case. The simulation results are useful in power quality studies for such drives and in devising methods for suppression of these interharmonics/subharmonics.     

Diffraction of shear waves by a rigid strip in a medium of monoclinic type

Summary The paper discusses the two dimensional problem of diffraction of shear waves by a rigid strip in an infinite medium of monoclinic type. This problem is reduced to a system of dual integral equations of which the solution provides the diffracted field. The method of steepest descent has been used in the determination of the diffracted fields at a large distance from the strip. Diffraction pattern for displacement and stress field have been computed and the effect of anisotropy is distinctly marked.With 6 Figures     

Study of microstructure in vanadium-palladium alloys by X-ray diffraction technique

Present study considers microstructural characterization of vanadium-based palladium (V-Pd) alloys, which are widely used in marine environment due to their high corrosion resistance. The X-ray diffraction line profile analysis (XRDLPA) have been used to assess the microstructure in body centred cubic (bcc) V-Pd alloys having four different nominal compositions in wt.%. X-ray diffraction line broadening analysis on V-Pd alloys has been performed by using different methods like the Warren-Averbach, double-Voigt and Rietveld methods. Finally microstructural defect parameters such as domain size (D), r.m.s. microstrain 〈ɛ ²〉^1/2, twin fault (β′), spacing fault (αɛ) and deformation stacking fault (α) were evaluated in these alloys by Fourier line shape analysis using Rietveld method in which the X-ray diffraction profiles of these alloys were described by the pseudo-Voigt function to fit the experimental data. From analysis it has been observed that twin fault, β′, and the spacing fault, αɛ, are totally absent in these bcc alloy systems because the twin fault, β′, has been observed to be either negative or very small (within experimental error limit) for these alloy systems and the spacing fault, αɛ, appears to be negative. This analysis also revealed that the deformation stacking fault, α, is significantly present in this alloy system and increases with Pd content.     

Feed horn coupled bolometer arrays for SPIRE - design, simulations, and measurements

In this paper, we present the design, modeling, and measurements of feed horn coupled large bolometer arrays being developed for the Herschel Space Observatory's Spectral and Photometric Imaging REceiver (SPIRE) instrument. SPIRE has five arrays of feed horn coupled silicon-nitride micromesh "spider-web" bolometers in two instruments, a three-band photometer, and a two-band Fourier transform spectrometer, each covering the 430-GHz-1.5-THz band. The optical coupling efficiency, bandwidth, and crosstalk between adjacent pixels of the arrays were investigated with numerical electromagnetic-field simulators, and prototype arrays were measured extensively in a test facility. The measured results were found to be in good agreement with simulation predictions, and the simulation results were used as a benchmark for the design goals of the instrument.     

Allocation of unit start-up costs using Cooperative game theory

This paper discusses a three-part generation offer strategy that enables generators to put in unbundled variable operating costs and fixed start-up/no-load costs. We then propose methods based on cost sharing axioms to allocate fixed start-up/no-load costs among electricity consumers/load/retailers that take into account equity and rationality considerations. We focus on the single period cost allocation first. We apply three well-known game theoretic axioms: the core, the nucleolus, and the Shapley value. We discuss the relative merits and demerits of each criterion and also explore certain theoretical conditions for the existence of the core and the Shapley value lying inside the core. Finally, the multiperiod start-up cost allocation problem is studied. Allocations based on individual periods vis-a/spl grave/-vis composite allocation for all periods are compared and contrasted. Numerical examples are used to illustrate all theoretical concepts.     

A single-reset-integrator-based implementation ofline-current-shaping controller for high-power-factor operation offlyback rectifier

The objective of this paper is to present a simple yet accurate implementation of a resistor-emulator-type line-current-shaping controller for high-power-factor operation of a flyback rectifier. The important feature is that input voltage sensing is not required. In the circuit realization of the controller, no multiplier is used. Current shaping is performed directly on the input filter inductor current. The modulator uses only one reset integrator for the generation of duty ratio. The analysis presented in this paper shows the effect of input filter capacitance on discontinuous conduction mode of operation of the flyback inductor. Design equations for selection of the input filter components are derived. A low-frequency small-signal model of the rectifier is developed and verified by measurement up to 1 kHz. The performance of the controller is first tested by the SABER circuit simulator package. Then, a 100-W 110-V AC input 50-V DC output single-phase flyback rectifier prototype is built for experimental verification     

Modulation of agonist and antagonist interactions in serotonin 1A receptors by alcohols

The serotonin type IA (5-HT1A) receptors are members of a superfamily of seven transmembrane domain receptors that couple to GTP binding regulatory proteins (G-proteins). Serotonergic signalling has been shown to play an important role in alcohol tolerance and dependence. We have studied the effects of alcohols on ligand (agonist and antagonist) binding to bovine hippocampal 5-HT1A receptor in native as well as solubilized membranes. Our results show that alcohols inhibit the specific binding of the agonist OH-DPAT and the antagonist p-MPPF to 5-HT1A receptors in a concentration-dependent manner.