Monte Carlo calculation of velocity-field characteristics in II-VI compound semiconductors

The velocity field characteristics of II–VI compound semiconductors at 77K have been obtained by the Monte Carlo simulation technique. The results agree with the available experimental data and with those obtained by solving the Boltzmann Transport Equation analytically. The simulation technique is described in detail and various aspects regarding the convergence of the simulation are discussed. The carrier distribution function has also been obtained from the simulation. The effects of the various simulation parameters, as well as those of the ionized impurity concentration, on the mobility values for the different semiconductors are discussed and results are presented.     

Elemental micro-segregation characteristic of fiber laser welded Hastelloy C-276 sheet

The elemental micro-segregation characteristic within the weld zone for ytterbium fiber laser welded Hastelloy C-276 sheet was investigated. The analysis of segregation ratio and equilibrium distribution coefficient of elements, determined through EDS data, indicate the reduction in micro-segregation of elements compared with the previous reported literatures for laser welded Hastelloy C-276. High melting efficiency of ytterbium fiber laser, reduction in the amount of linear heat input, and high cooling rate of the mushy zone lead to the reduction in micro-segregation. The melting efficiency of ytterbium fiber laser for welding of Hastelloy C-276 of 64% is higher than that (48%) of conventional welding methods. High melting efficiency leads to the reduction in the linear heat input required for welding. Hence, in the present investigation, the same was found to substantially reduce as compared to the previous reported literature. The cooling rate from liquidus temperature to solidus temperature at the weld centerline was found to be in the order of 10³ °C/s. Cellular dendritic substructure that constituted for lower micro-segregation was formed at the weld centerline.     

Microprocessor based simulation and digital logic model of gate turn-off thyristor

A digital logic model of a gate turn-off thyristor is developed considering the turn-on and turn-off mechanisms of the device. A commonly used R-C-D snubber circuit is also included in the proposed model. Relations between different delay times, e.g. storage time, Tall time, turn-off time and tail time, become apparent from the model. The model is simulated with the help of a microprocessor to establish the validity of the proposal.     

A new formulation of operation allocation problem in flexible manufacturing systems: mathematical modelling and computational experience

This paper extends the formulation of the operation allocation problem to include the important planning aspects of refixturing and limited tool availability. A 0–1 integer programming formulation is proposed with two objective functions and a set of realistic constraints. The computational behavior of the solution is discussed and a number of observations prompted by the solution methodology have been made.     

Pyrolysis of petroleum asphaltenes from different geological origins and use of methylnaphthalenes and methylphenanthrenes as maturity indicators for asphaltenes

Asphaltenes separated from two different crude oils from upper Assam, India, having different geological origins, viz. DK (eocene) and JN (oligocene–miocene) were pyrolysed at 600 °C and the products were analysed by gas chromatography–mass spectrometry (GC/MS) especially for the generated alkylnaphthalenes and alkylphenanthrenes. Both the asphaltenes produce aliphatic as well as aromatic compound classes. Alkylnaphthalenes and alkylphenanthrenes were identified by using reference chromatograms and literature data and the distributions used to assess thermal maturity of the asphaltenes. The ratios of β -substituted to α -substituted isomers of both alkylnaphthalenes and alkylphenanthrenes revealed higher maturity of the JN asphaltenes than the DK asphaltenes. For both the asphaltenes, the abundance of 1-methylphenanthrene dominates over that of 9-methylphenanthrene showing the terrestrial nature of the organic matter.     

MASS TRANSFER AUGMENTATION DUE TO WALL SLIP IN HAEMODIALYSERS†

The inadequacy of the current theories to accurately predict the haemodialyser performance is shown to be a result of the effective slip at the membrane surface. This slip phenomenon, manifested by the Fahraeus-Lindqvist effect is peculiar to (heterogeneous) blood flow. Literature data have been analyzed to substantiate the slip hypothesis proposed in this work. Both the theoretical analysis and the experimental observations indicate that slip enhances haemodialyser performance. Some design considerations have been provided, which will account for the beneficial effect of wall slip in practical haemodialyser operations.     

Performance analysis of ASR system in hybrid DNN-HMM framework using a PWL euclidean activation function

Automatic Speech Recognition (ASR) is the process of mapping an acoustic speech signal into a human readable text format. Traditional systems exploit the Acoustic Component of ASR using the Gaussian Mixture Model- Hidden Markov Model (GMM-HMM) approach.Deep NeuralNetwork (DNN) opens up new possibilities to overcome the shortcomings of conventional statistical algorithms. Recent studies modeled the acoustic component of ASR system using DNN in the so called hybrid DNN-HMM approach. In the context of activation functions used to model the non-linearity in DNN, Rectified Linear Units (ReLU) and maxout units are mostly used in ASR systems. This paper concentrates on the acoustic component of a hybrid DNN-HMM system by proposing an efficient activation function for the DNN network. Inspired by previous works, euclidean norm activation function is proposed to model the non-linearity of the DNN network. Such non-linearity is shown to belong to the family of Piecewise Linear (PWL) functions having distinct features. These functions can capture deep hierarchical features of the pattern. The relevance of the proposal is examined in depth both theoretically and experimentally. The performance of the developed ASR system is evaluated in terms of Phone Error Rate (PER) using TIMIT database. Experimental results achieve a relative increase in performance by using the proposed function over conventional activation functions.     

Sensitivity analysis in fractional programming—the tolerance approach

Sensitivity analysis in fractional programming using a tolerance approach is studied. This approach yields a maximum tolerance percentage within which the cost vectors and the elements of a column or a row of the coefficient matrix are accurate to within that percentage of their estimated values while retaining the same set of basic variables in an optimal solution.     

Effect of fuzzification on the plosive cognition system

Fuzzy algorithms provide a simpler and more powerful approach than statistical decision methods for describing non-ideal (fuzzy) environments in which there exists no precise boundary between the categories due to inherent vagueness rather than randomness. This paper attempts to demonstrate the effectiveness of such an algorithm when applied to the computer recognition of patterns of biological origin such as Telugu unaspirated plosives in initial position of large number of utterances in CVC context. A multieategorizer is described in which the fuzzy processor embodies a fuzzy property extractor and a similarity matrix generator. A provision fur controlling fuzziness in property sets had been made by keeping two parameters. ‘exponential’ and ‘denominational’ fuzzifiers, in the components of property matrices ; their effect on recognition score is also studied.

Machines’ performances are explained by plotting curves and through confusion matrices when transition, duration and slope of transition from the point of transient release of stop closure to the steady state of only first two formants were used as input features. Voiced stops are differentiated more easily than unvoiced stops, with the maximum overall recognition score ranging from 60% for dentals to 85% for bilabials. The fuzzy hedge ‘ slightly ’ when applied to property sets reduces the confusion from that of the hedge ‘ very ’ and consecutive utilizations of the operations ‘CONT’, ‘ OIL’ and ‘INT’ resulted in a wide variation of about 20 to 25% in the recognition score. Such a variation is found to be insignificant beyond an optimum value of the exponential fuzzifier’.