Showing papers in "Iete Journal of Research in 1991"
TL;DR: A linguistic recognition system based on approximate reasoning has been described along with its implementation in speech recognition problem and some of the implementation to real life problems have been mentioned.
Abstract: Approximate Reasoning is the process or processes by which a possible imprecise conclusion is deduced from a collection of imprecise premises. Fuzzy logic plays the major role in approximate reasoning. It has the ability to deal with different types of uncertainty.An overview of the different aspects of the theory of approximate reasoning has been provided here based on the existing literature. Suitable illustrations are included, whenever necessary, to make the concept clear. Some of the implementation of the theory to real life problems have been mentioned. Finally, a linguistic recognition system based on approximate reasoning has been described along with its implementation in speech recognition problem.
67 citations
TL;DR: 23 basic and 24 primitive shapes are carefully chosen which when properly concatenated can generate the whole character vocabulary and a new font is proposed where the characters are concatenation of straight lines.
Abstract: This paper deals with the computer generation of characters of various fonts and sizes for the Telugu alphabet. It also deals with the problem of automatic recognition of Telugu printed scripts. Telugu and many other Indian languages scripts have the problem of combined character formation that makes a few hundred shapes to be generated or recognized, although the number of vowel and consonant characters in isolation does not exceed hundred. In this paper, 23 basic and 24 primitive shapes are carefully chosen which when properly concatenated can generate the whole character vocabulary. To generate these shapes, curve drawing based on Bezier and Spline techniques are used. A new font is proposed where the characters are concatenation of straight lines. A grammar to generate the combined characters is also proposed. Next, the recognition of characters is done by shape matching using directed curve tracing method. A concept of T-tuple is introduced for the tracing problem that act on the skeleton of the char...
10 citations
TL;DR: In this article, the basic theory of synchronous machine field orientation is outlined and the difference between 90° spatial orientation of field flux and armature mmf is examined in some detail.
Abstract: Although field orientation in induction machines is only 20 years old, the corresponding concept in synchronous machines dates back almost 60 years to the days of the thyratron tube. After a brief historical review, the basic theory of synchronous machine field orientation is outlined. The difference between 90° spatial orientation of field flux and armature mmf, which always yields a lagging terminal power factor, and other forms of space angle control is examined in some detail. The problems associated with current regulators and flux position sensing are explored and present day techniques are discussed. Applications to high performance servomotors, dc brushless motors, wide speed range drives and high power synchronous motors are considered. A substantial bibliography is included.
8 citations
TL;DR: In this article, a buck-boost converter topology is presented for DC-DC power conversion, which makes power flow in both directions possible, and the possibility of bidirectional power flow is useful for certain applications.
Abstract: A system for DC-DC power conversion based on a buck-boost converter topology is presented which makes power flow in both directions possible. The possibility of bidirectional power flow is useful for certain applications, such as uninterruptable power supplies (UPS) etc. The structure is compared with the well known unidirectional buck-boost converter. Open-loop control is treated based on simulation using duty cycle averaging. The system behaviour of the bidirectional converter is analyzed; a structure diagram is given and the transfer function of the system is derived. The validity of the duty cycle averaging is proven by comparison to a switched model. The controller for the converter is then realized as simple voltage controller, as voltage controller with an inner-loop current controller (cascade control) and with two kinds of state space control. The transfer functions of the different system parts are derived and dimensioning guide-lines for the controller sections are presented. The closed-loop be...
7 citations
TL;DR: In this paper, the authors present the present status of the research efforts in understanding and improving the performance of the CSI-IM drive, particularly with regard to the commutation analysis, frequency range, torque pulsations, stability and control strategies.
Abstract: The current source inverter-fed induction motor (CSI-IM) drive has emerged today as a reliable, rugged and high performance adjustable-speed ac drive. During the last several years, various attempts have been made to obviate its several limitations when compared with the voltage source inverter-fed induction motor drive. This paper reviews the present status of the research efforts in understanding and improving the performance of the CSI-IM drive- particularly with regard to the commutation analysis, frequency range, torque pulsations, stability and control strategies-including microprocessor-based control.
5 citations
TL;DR: In this paper, the characteristics of modern power devices have been discussed and compared from the viewpoint of power electronics applications, such as triac, gate turn-off thyristor (GTO), bipolar power transistor and power MOSFET.
Abstract: Power semiconductor devices are undergoing dynamic evolution in the recent years. Modern power electronics era started by the invention of thyristor (or silicon controlled rectifier) in Bell Telephone Laboratory in 1956, and it was then commercially introduced by General Electric Company in 1958. Since then, we have seen the advent of triac, gate turn-off thyristor (GTO), bipolar power transistor and power MOSFET. The power semiconductors that appeared in the 1980's are insulated gate bipolar transistor (IGBT), static induction transistor (SIT), static induction thyristor (SITH) and MOS-controlled thyristor (MCT). The characteristics of these modern power devices have been discussed and compared from the viewpoint of power electronics applications. For completeness of description, other devices, such as thyristor, triac, GTO, bipolar transistor and power MOSFET have also been briefly reviewed. Finally, the trend of power converters has been discussed.
5 citations
TL;DR: A new computational approach along with the computational results are presented based on the concept of differential geometry for recognition and position determination of partially occluded 2D rigid object and successful extension and implementation of the method for the 3D objects.
Abstract: The most important application area of visual pattern recognition is design and development of a computer visions system wheather for robotics or for industrial inspection, capable of recognising and determining the portion of an object in a scene, particularly so when the objects are occluded. In this paper a new computational approach along with the computational results are presented based on the concept of differential geometry for recognition and position determination of partially occluded 2D rigid object and successful extension and implementation of the method for the 3D objects.For a partially occluded 2D objects in a scene a set of invarient local features are generated initially. Next, based upon matching of local features of the objects in a scene and the models which are considered as cognitive data base, a computer vision scheme is described using AI concept of hypothesis generation and verification of features for the best possible recognition. The method is successfully extended to the rea...
5 citations
TL;DR: To have a comprehensive data base for Hindi language a statistical study of printed-Hindi-text characters using computer is reported to find relative occurrence of different characters, their neighbours and the most-frequent words.
Abstract: To have a comprehensive data base for Hindi language a statistical study of printed-Hindi-text characters using computer is reported. The data-base is needed for the research community in the areas of speech recognition, synthesis, system development and performance evaluation. Frequency of occurrence and frequency information is needed to choose isolated words and sentences. The corpus of this pilot study is of about 51,000 printed characters. A code of English alphabets using English computer keyboard has been used to represent Hindi characters and computer algorithm was developed to find relative occurrence of different characters, their neighbours and the most-frequent words.
4 citations
TL;DR: This paper addresses the problem of synthesizing connected handwritten script from individual characters written in isolation, and shows that connected writing is viewed as a natural evolution from writing tributes to poetry.
Abstract: In this paper, we address the problem of synthesizing connected handwritten script from individual characters written in isolation. Connected writing is viewed as a natural evolution from writing the characters in isolation, characterized by the use of continuous pen-down connecting movement from one character to the next. The problem is one of concatenation of individual character shapes to generate the connected script and consists in synthesizing a so called transition stroke from one character to the next. Particular emphasis is laid on recreating the context effect underlying the pen-down transition stroke and in preserving the continuity of motion and shape in the transition. Under this framework, we propose an approach based on a shape specific splining technique where the transition stroke is generated from the isolated character shapes by a direct application of the Bezier curve formulation, Here, in the concatenation of two characters, the end segments of the characters are considered as the con...
4 citations
TL;DR: In this paper, the authors discuss the different aspects of power electronics, including power semiconductors, the topologies of the converters and inverters, control strategies and furthermore modern computer-aided design and optimization tools.
Abstract: Power electronics seemed for a long period an obsolete area with very few innovations. This period of stagnation is replaced now due to rapid developments in semiconductor technology. This development boosts development in all areas of power electronics, too: the power semiconductors, the topologies of the converters and inverters, the control strategies and furthermore modern computer-aided-design and optimization-tools. This paper will discuss the different aspects.
3 citations
TL;DR: The algorithms for various preprocessing operations and feature extraction together with the approaches for FP matching are discussed and the results are found to be good and can be employed in practical applications.
Abstract: The principle of fingerprint (FP) identification and a Pattern Recognition Model for automatic fingerprint identification is given. The input fingerprint image is subjected to a number of preprocessing operations to improve the quality of the image. Contextual filters suitable for fingerprint image enhancement are developed. Direction based segmentation is used to separate the foreground from the background and noisy areas. The ridge endings and bifurcation points, the minutiae, are the features used for FP identification. The algorithms for various preprocessing operations and feature extraction together with the approaches for FP matching are discussed. These algorithms have been tested for more than 10,000 FP imges of different quality. The results are found to be good and can be employed in practical applications.
TL;DR: This paper introduces this exciting and fast expanding field by reviewing some of the important neural networks of proven performance and detailed explanation and simulation examples are presented for Hopfield net, Hamming net, Bidirectional Associative memory, Temporal Associative Memory and Kohonen's network.
Abstract: Modelled on the cerebral cortex of the human brain, Artificial Neural Networks are presently being applied to solve elusive problems of AI viz, speech and image recognition, computer vision and adaptive control. The neural net topology, interconnections and ‘learning’ algorithms are topics of current research. This paper introduces this exciting and fast expanding field by reviewing some of the important neural networks of proven performance. A detailed explanation and simulation examples are presented for Hopfield net, Hamming net, Bidirectional Associative Memory, Temporal Associative Memory and Kohonen's network. Perceptions and multilayer perceptions are also explained in the light of their class discrimination capabilities. The classical pattern recognition algorithms vis-a-vis their neural network equivalents are also discussed.
TL;DR: In this paper, a recursive least-square estimation algorithm has been developed for finding the coefficients of the Laguerre- polynomial expansion of a signal, when a finite set of polynomials are used to represent the signal.
Abstract: A recursive least-square estimation algorithm has been developed for finding the coefficients of the Laguerre- polynomial expansion of a signal, when a finite set of polynomials are used to represent the signal. We have shown how the same algorithm can be used for both the single and double variable functions. Numerical results are given to illustrate the algorithm.
TL;DR: Features and properties that should be satisfied in the design of medium level pictorial languages implemented for massive parallel machines, with main emphasis given to hierarchical architectures are described.
Abstract: The paper describes features and properties that should be satisfied in the design of medium level pictorial languages implemented for massive parallel machines. An overview of relevant pictorial languages is done. Main emphasis it is given to hierarchical architectures; pyramid machines are an example of such kind of machines. Pictorial data type and a concurrency model are also described. A C-like syntax, for the design of pictorial languages is introduced.
TL;DR: In this article, the effect of reverse saturation current on the high frequency and low frequency of a silicon double-drift region (DDR) operating in the mm-wave range (W-band) was investigated.
Abstract: Computer studies have been carried out on the effect of electron and hole reverse saturation current on the high frequency (i) negative resistance and reactance profiles, (ii) admittance characteristics, and (iii) device quality factor of a silicon double-drift region (DDR) IMPATT operating in the mm-wave range (W-band). The results indicate that the negative resistance peaks in the electron and hole drift layers decrease with increasing reverse saturation current. The total diode negative resistance also decreases appreciably with the increase of either electron or hole reverse saturation current, ie, with decrease in electron or hole current multiplication factors (M & Mp).It has further been observed that in the lower frequency range of the W-band, the device negative conductance decreases with the increase of reverse saturation current, while in the frequency range from 160–210 GHz, the device negative conductance increases with the enhancement of reverse saturation current.An upward frequency shift b...
TL;DR: In this paper, the authors investigated the impedance and dispersion characteristics of shielded, broadside coupled, suspended and inverted slotlines and found that the even mode is less sensitive to variation in the air gap (between the substrates) as compared with that for the odd mode.
Abstract: The impedance and dispersion characteristics of shielded, broadside coupled, suspended and—inverted-slotlines are investigated. Spectral domain formulation is used for the analysis. Numerical results are reported for each of these slotline configurations in two different sizes of shielded enclosures—namely, a standard rectangular waveguide at Ka-band and a square waveguide with twice the height of the Ka-band guide. It is found that in all the cases, the propagation constant of the even mode is less sensitive to variation in the air gap (between the substrates) as compared with that for the odd mode. Furthermore, for small air gaps, the variation in the odd mode propagation constant as a function of air gap is rather small in the case of broadside coupled inverted slotline as compared with that in a corresponding broadside coupled suspended slotline.
TL;DR: In this article, an in-situ rapid isothermal processor was used for chemical cleaning of InP, solid phase epitaxial growth of II-A fluorides and metallization of capacitors.
Abstract: Rapid isothermal processing (RIP) is emerging as a reduced thermal budget processing technique. As compared to a stand alone rapid isothermal annealing unit, the integration of deposition system and rapid isothermal processing units is very attractive for the fabrication of next generation of devices and circuits. We have used an in-situ rapid isothermal processor for the in-situ rapid isothermal chemical cleaning of InP, solid phase epitaxial growth of II-A fluorides and in-situ metallization of InP capacitors. Based on high frequency capacitance-voltage (C-V) measurement of Al-SrF2-InP structure and scanning electron microscopic (SEM) study, improved ohmic contacts were observed in the case where InP surface was in-situ rapid isothermally cleaned before metallization.
TL;DR: In this paper, an over view of various control strategies to implement the principle of field orientation in synchronous motors is presented, and a novel scheme of hysteresis current control with field orientation for a salient pole synchronous motor is illustrated.
Abstract: Field orientation method of speed control has emerged as a powerful tool for ac machines. The dynamic performance of such a drive is comparable to that of a converter fed four quadrant dc drive. An over view of various control strategies to implement the principle of field orientation in synchronous motors is presented. In addition, a novel scheme of hysteresis current control with field orientation for a salient pole synchronous motor is illustrated. In view of the significant reduction in cost and simplification of the circuit complexity of the scheme, it can very well replace the commonly favoured separately excited dc motor drive.
IBM1
TL;DR: In this paper, the authors discuss the recent trends in reactor development, along with underlying principles that are used in their design, and discuss some of the most important aspects of these technologies.
Abstract: Increasing circuit densities on a chip is placing aggressive demands on metallization. In recent years, metal interconnection technology has indeed became a gating factor in realizing high speeds at the circuit level. Stringent process requirements have brought about major changes in the design of process equipment, particularly plasma etchers and chemical vapor deposition systems. Among the noteworthy are the low pressure, single wafer magnetron and “electron cyclotron resonance” reactors, a new breed of thin film deposition systems, down-stream reactors, clustered integrated process systems, and laser processing equipment. This paper discusses these recent trends in reactor development, along with underlying principles that are used in their design.
TL;DR: A comprehensive surrey of Professor Gift Siromoney's contributions in the area of pattern recognition is done, which deals with his pioneering work on syntactic methods to picture generation and description.
Abstract: Professor Gift Siromoney, who was the founder-chairman of the Department of Statistics, Madras Christian College, Madras passed away on March 21, 1988. He was a much-loved teacher and a highly productive research scientist with a wide range of interests in different fields. A comprehensive surrey of his contributions in the area of pattern recognition is done in this paper. The first part deals with his pioneering work on syntactic methods to picture generation and description. The second part surveys innovative computer methods he developed in the areas of character recognition, epigraphy, Kamatic music and Tamil studies.
TL;DR: In this paper, several new techniques to reject dc-link voltage ripple in PWM inverters are examined in detail, where continuous elimination of harmonics is achieved at the inverter output while simultaneously rejecting the voltage ripple.
Abstract: In this paper several new techniques to reject dc-link voltage ripple in PWM inverters are examined in detail. It is demonstrated how continuous elimination of harmonics is achieved at the inverter output while simultaneously rejecting the dc-link voltage ripple. Thus with the proposed techniques it is possible to guarantee high quality inverter output voltage even with substantial low frequency voltage ripple on the dc-link. A thorough modeling of these techniques along with the tradeoffs involved in acquiring the immunity to dc-link ripple is illustrated in detail. Potential applications of these techniques are in fixed and variable frequency inverters for power supplies and ac motor drives which experience voltage ripple in the dc-link such as when fed from a weak ac system which is frequently unbalanced. Suitable design equations along with a digital implementation procedure of the proposed technique is described in detail. Finally, selected results are verified experimentally on a laboratory inverter.
TL;DR: In this paper, a detailed hybrid mode analysis of periodic structures in unilateral and bilateral finlines is presented, which makes use of Floquet's theorem in conjunction with Galerkin's method to find the propagation characteristics.
Abstract: This paper reports a detailed hybrid mode analysis of periodic structures in unilateral and bilateral finlines. The analysis makes use of Floquet's theorem in conjunction with Galerkin's method to find the propagation characteristics of periodic structures. Two types of periodic structures are considered; one consisting of transverse stubs periodically coupled to the main slot of an asymmetric finline in unilateral and bilateral configurations, and the other is formed by placing inductive stubs at periodic intervals along the main slot of unilateral and bilateral finlines.
TL;DR: In this paper, a non-linear circuit model for a Gunn oscillator has been presented based on experimental and simulation results, and the model has been applied to a single-input single-output (SISO) model.
Abstract: Based on experimental and simulation results, a new non-linear circuit model for a Gunn oscillator has been presented.
TL;DR: In this paper, three phase PWM pattern generators that are simple to implement with low cost circuitry, particularly with analog components, are presented, where the current in the built-in load model is forced to follow a reference by means of hysteresis control.
Abstract: Optimized PWM techniques have been developed and used with good results for voltage source inverters. However, implementation frequently requires complex electronic circuits, usually microprocessor-based, that cannot be justified in low cost applications. The paper examines three phase PWM pattern generators that are simple to implement with low cost circuitry, particularly with analog components. These modulation techniques are based on the model reference adaptive (MRA) technique. They exhibit intrinsic constant Volts/Hertz operation, and do not require frequency synchronization and frequency jumping, making them ideal for low cost inverter driven variable speed ac motor drives. The PWM patterns are generated by forcing the current in the built-in load model to follow a reference, by means of hysteresis control, also known as the delta modulation technique, or error triangulation control. Unlike delta modulation, the latter technique exhibits constant switching frequency and has an output voltage spectr...
TL;DR: In this paper, a comparative analysis between a series turned and paralleled tuned induction heating load fed by a transistor voltage source inverter is presented, and the results of the comparison lead to the following conclusions: the voltage source is much more suitable for driving a series tuned load, the variable frequency controlled VSI is not suitable for drive a parallel tuned load; the optimal control method for a parallel-tuned load is DC input voltage control; the variable DC voltage-controlled VSI was optimally utilized at a leading power factor when operating at increasing frequency and power levels.
Abstract: This paper presents a comparative analysis between a series turned and paralleled tuned induction heating load fed by a transistor voltage source inverter. The operation of the two systems are comparatively evaluated on the basis of the following three control schemes: DC input voltage control; Frequency control; and Pulse width modulation control. The results of the comparison lead to the following conclusions: the voltage source inverter is much more suitable for driving a series tuned load; the variable frequency controlled VSI is not suitable for driving a parallel tuned load; the optimal control method for a parallel tuned load is DC input voltage control; the variable DC voltage controlled VSI is optimally utilized at a leading power factor when operating at increasing frequency and power levels.
TL;DR: It is shown how optimised PWM for VSI drives can be generated “on-line” in “real-time” using modified regular-sampling techniques, without resorting to the laborious, time-consuming, main-frame computer minimisation techniques normally associated with these PWM techniques.
Abstract: This paper surveys recent research into the development of new optimal Regular-Sampled PWM techniques for both voltage source inverter (VSI) and current source inverter (CSI) drives.It is shown how optimised PWM for VSI drives can be generated “on-line” in “real-time” using modified regular-sampling techniques, without resorting to the laborious, time-consuming, main-frame computer minimisation techniques normally associated with these PWM techniques. Using these new regular-sampling PWM techniques it is possible to produce a PWM drive performance which closely approximates the optimised PWM performance up to quasi-square wave operation.In addition, a survey of a number of new high pulse number harmonic-elimination, harmonic minimisation, and optimal PWM techniques for CSI drives will be presented which minimise rotor speed ripple and positional error, and provide smoother rotor motion at low speeds.
TL;DR: It is necessary to be able to quantify the whole-body power absorption and its distribution for the various irradiation conditions and to know for humans subjected to irradiation at different frequencies and for realistic exposure conditions.
Abstract: The expanding usage of electromagnetic (EM) radiation has necessitated an understanding of its interaction with humans. Such knowledge is vital in evaluating and establishing radiation safety standards, determining definitive hazard levels, and understanding several of the biological effects that have been reported in the literature. Studies of the effects of EM radiation have used laboratory animals such as rats, rabbits, etc. for the study of biological and/or behavioral effects. For these experiments to have any projected meanings for humans, it is necessary to be able to quantify the whole-body power absorption and its distribution for the various irradiation conditions. It is further necessary that dosimetric information be known for humans subjected to irradiation at different frequencies and for realistic exposure conditions.
TL;DR: In this article, the chemical vapor deposition of tungsten (CVD W) by the reduction of WF6 using Si, silane (SiH4) polysiiane (Si2H6 and Si3H8): SinH2n+2), diborane (B2H 6), phosphine (PH3), and H2.
Abstract: This paper reports on the chemical vapor-deposition of tungsten (CVD W) by the reduction of WF6 using Si, silane (SiH4) polysiiane (Si2H6 and Si3H8: SinH2n+2), diborane (B2H6), phosphine (PH3), and H2. These depositions can be changed from selective to blanket configuration by increasing the deposition temperature. In the selective deposition, deposition rate of tungsten by SiH4 and SinH2n+2 reductions is faster even at low temperature than by H2, B2H6, and PH3 reductions. The deposition rate of tungsten using SiH4 and Si2H6 reductions does not change with temperatures, the only exception is WF6 reduction by H2. Deposition rate decreases with the magnitude of selectivity loss. The deposition temperature decreases with molecular number for SinH2n+2. Tungsten deposition starts at 180 °C for SiH4, 80 °C for Si2H6 and 40 °C for Si3H8. Tungsten deposits selectively in the temperature range from 300 °C to 340 °C using B2H6 and PH3. H2 reduction starts at about 250 °C, similar to Si reduction period. Silicon sub...
TL;DR: In this article, the authors used vector control for the speed control of a 3 phase induction motor, which is smaller, more sturdy, less expensive and does not have the commutator or other rubbing contacts, and is therefore free of associated maintenance requirements and sparking problems.
Abstract: Vector control, also described as field oriented control, is being increasingly used for the speed control of induction motors. This is because, with vector control, it is possible to achieve high dynamic (transient) performance, equalling that of the separately excited DC motor, in variable speed AC drives. Therefore, vector control makes it possible to use, in place of a DC motor, a 3 phase induction motor, which is smaller, mechanically more sturdy, less expensive, and does not have the commutator or other rubbing contacts, and is therefore free of associated maintenance requirements and sparking problems. Vector control, however, requires on-line computation of certain control variables using inputs from sensing elements which continually sense operating motor variables such as motor line currents, motor shaft position or speed. These computed control variables serve as feedback values, which are compared with the appropriate reference values. The errors are continuously corrected by appropriately del...
TL;DR: The use of secondary ion mass spectrometers (SIMS) and Rutherford backscattering spectrometry (RBS) have been critical in the development of very large scale integrated circuits because of their shared ability of determining the distribution of elements in a small localized areas as well as good sensitivity for many of the common do pants used in semiconductor technology as discussed by the authors.
Abstract: The use of secondary ion mass spectrometry (SIMS) and Rutherford backscattering spectrometry (RBS) have been critical in the development of very large scale integrated circuits because of their shared ability of determining the distribution of elements in a small localized areas as well as good sensitivity for many of the common do pants used in semiconductor technology. This review paper will discuss the uses of both SIMS and RBS in contributing towards the development of advanced metallization technology.