Interesting aspects of the analysis of resistivity in Li irradiated Bi-2212

Differently heat treated and 55 MeV Li³⁺ beam irradiated Bi₂Sr₂Ca₁Cu₂O_8+δ (Bi-2212) high temperature superconductors have been studied from the analysis of resistivity in the normal state as well as near the superconducting transition. For all the unirradiated and irradiated samples the so-called linear temperature dependence of the normal state resistivity, in a wide temperature range, can well be understood within the variable range hopping (VRH) conduction scenario. Near and above the bulk superconducting transition, the fluctuation enhanced conductivity (paraconductivity) analysis shows a noteworthy modification of the conduction process due to radiation induced defects.     

Wear characteristics of ceramic cutting tools in machining steel

Some ceramic materials such as Al₂O₃ which have a high compressive strength, hardness and chemical stability came into use industrially in the middle of this century as powder metallurgy produced indexable cutting tool inserts. These early ceramic tools were inherently weak in tension, impact and dynamic loading owing to their low tensile strength, toughness and transverse rupture strength; because of this their application was limited to medium productivity operations and work materials of softer grades. However, the technology of ceramic cutting tools has made great strides in the last few years through substantial improvements in their strength, toughness and wear resistivity. These modern ceramic tools have found wide and economic applications in high production machining of both cast iron and steels.In this paper the constructional characteristics of some modern ceramic tools and their wear behaviour and overall performances in machining mild steel at both low and high speeds are presented. The comparative results obtained are reported and discussed.     

Effect of inversion on barrier height in a metal-SiO2-Si tunnel system

The effect of strong inversion in a metal-SiO₂-p-Si system has been studied. It is seen that the plot of barrier height versus metal work function of the system becomes nonlinear when the metal work function is lowered below a critical value. These values of critical work function are calculated and analysed for different values of doping and oxide charge.     

Electro-magneto-thermo-visco-elastic Plane Waves in Rotating Media with Thermal Relaxation

A study is made of the propagation of plane electro-magneto-thermo-visco-elastic harmonic waves in an unbounded isotropic conducting visco-elastic medium of Kelvin–Voigt type permeated by a primary uniform magnetic field when the entire medium rotates with a uniform angular velocity. The thermal relaxation time of heat conduction, the electric displacement current, the coupling between heat flow density and current density, and that between the temperature gradient and the electric current are included in the analysis. A more general dispersion relation is obtained to determine the effects of rotation, thermal relaxation time, visco-elastic parameters, and the external magnetic field on the phase velocity of the waves. Perturbation techniques are used to study the influence of small magneto-elastic and thermo-elastic couplings on the phase velocity of the waves. Cases of low and high frequencies are also analyzed to determine the effect of rotation, visco-elastic parameters, thermo elastic and magneto-elastic coupling, as well as thermal relaxation time of heat conduction on the waves.     

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.     

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     

A generalized approach to steady-state analysis of a current-sourceinverter with induction motor load including commutation overlap

A generalized state-space approach is presented for the steady-state commutation analysis of an autosequential commuted current-source inverter-fed induction motor drive covering all possible modes of operation using a digital computer. The analysis adopts the basic per-phase equivalent circuit for the induction motor model, includes the effect of DC link filter impedance and the variation of back EMF during the commutation interval, and extends the inverter model to cover the complex commutation overlap mode occurring during high frequency operation. A digital computer program is evolved, to identify automatically the relevant sets of equations applicable to a particular mode from a generalized set of equations and to solve them