Effect of variation of load resistance on amplifier characteristics of complementary composite transistors. II

A configuration has been proposed by which an ideally infinite input impedance can be realized at all frequencies. The advantage of this configuration is that both positive and negative capacitive reactance can be realized just be controlling the gain of the amplifier, the realized capacitance being independent of frequency.     

Compact solid state radio frequency amplifiers in kW regime for particle accelerator subsystems

Radio frequency and Microwave (RFM) infrastructure test facility is under development at RRCAT for evaluating and powering, subsystems of particle accelerator. As a part of this facility, design of 20–30 kW UHF solid state power amplifiers is in progress. For this work, design procedure has been formulated for the development of solid state amplifier modules, radial combiner, divider and directional coupler; with specifications suited to RFM power system for particle accelerator. Methodology has been demonstrated by developing two different compact amplifiers with power output of 2 kW each, operating at 352 MHz and 505.8 MHz, respectively. This paper describes underlying design principles and indigenous development of these amplifiers, consisting of 270–300 W amplifier modules, 8-way 2 kW radial combiner/divider and directional couplers. Design methodology for power combiner has been extended by physically realizing higher power (4 kW) 16-way power combiner and 2-way combiner (8 kW) for higher power (8 kW) amplifier configuration planned. Simple design, indigenous technology, high efficiency and ease of fabrication, are the main features of this design.     

LOCAL OPTIMAL COORDINATION BASED ADAPTIVE COORDINATION

ABSTRACT

This paper presents the development of an adaptive coordination scheme for the coordination of directional overcurrent relays for large interconnected power systems, using the concept of local optimal coordination under the changed system conditions. In response to a structural change or an operational change in the power system, the developed adaptive local optimal coordination algorithm automatically identifies the local disturbed region and re-coordinates only the settings of the relays which fall inside this identified local region in an on-line manner. The scheme developed is applied to the IEEE 57-bus test power transmission system. The results are validated through a full system coordination study and the usefulness of the reported algorithm is demonstrated.     

Locating the detonation point of China's first nuclear explosive test on 16 October 1964

On 23 May 1995, the U.S. Government released a declassified image acquired by the satellite-based KH-4A camera that showed the surface scarring from China's first nuclear explosive test on 16 October 1964. The sub-scene showed the surface effects from the test with respect to the surrounding natural features. The detonation point was located by visually matching the lithological and terrain features shown in the KH-4A sub-scene with the same features shown in a Large Format Camera (LFC) ortho-image. The geographic coordinates of the 16 October 1964 test were then measured directly from the LFC ortho-image: 40·8152 ± 0-0005° N, 89·7925 ± 0·0005° E. The successful effort to locate the 16 October 1964 detonation point demonstrated the value of using declassified images with commercial images acquired by satellite-based sensors. Research on other geographic areas could also lead to the discovery of new information through the synthesis of these two sources of imagery.     

Two unit cold standby system with correlated failures and repairs

A two unit cold standby system with correlated failure and repair processes is studied. Such a system has not been studied so far in the context of reliability. We obtain the reliability characteristics of interest to system designers such as the mean time to system failure, pointwise and steady state availablity of the system, expected up time and down time of the system in a finite interval, etc. In fact the joint distribution of failure and repair times is taken as bivariate exponential. Earlier results with independent failure and repair times are verified.     

Stability and weighted sensitivity analysis of robust controller for heat exchanger

This study presents a parametric system identification approach to estimate the dynamics of a chemical plant from experimental data and develops a robust PID controller for the plant. Parametric system identification of the heat exchanger system has been carried out using experimental data and prediction error method. The estimated model of the heat exchanger system is a time-delay model and a robust PID controller for the time-delayed model has been designed considering weighted sensitivity criteria. The mathematical background of parametric system identification, stability analysis, and ${{\rm H}_\infty }$ weighted sensitivity analysis have been provided in this paper. A graphical plot has been provided to determine the stability region in the $( {{K_{\rm p}},{K_{\rm i}}} )$, $( {{K_{\rm p}},{K_{\rm d}}} )$ and $( {{K_{\rm i}},{K_{\rm d}}} )$ plane. The stability region is a locus dependent on parameters of the controller and frequency, in the parameter plane.     

An investigation in InGaO<Subscript>3</Subscript>(ZnO)<Subscript>m</Subscript> pellets as cause of variability in thin film transistor characteristics

Indium–gallium–zinc oxide (IGZO) is a novel amorphous oxide semiconductor, which recently has received much attention for thin film transistors (TFTs) in flat panel displays. Published literature reports significant variations in the properties of thin films and TFTs prepared from IGZO even though the reported process conditions are similar. We demonstrate that these differences could arise from the method for preparation of targets from which the films are made. Accordingly, we also propose simple and appropriate conditions, specifically using much lower sintering temperatures and thus avoiding use of sealed Pt tubes for preparation of IGZO targets in composition range, InGaO₃(ZnO) _m , with 1 ≤ m ≤ 5. These target materials are suitable in physical vapour deposition processes such as pulsed laser deposition and sputtering. In developing the process for sintering, the phase analysis of the target pellets was carried out using X-ray diffraction (XRD). The chemical compositions of the phases are also confirmed with inductively coupled plasma optical emission spectrometry (ICP-OES) and energy dispersive X-ray (EDX) techniques. We also demonstrate successful deposition of amorphous IGZO thin films by pulse laser deposition using the targets prepared by the proposed sintering process. Finally, we demonstrate that unmonitored method of making pellets for films deposition is a cause of variability associated in published literature on IGZO TFTs.     

A BRIEF HISTORY OF THE BEGINNING OF THE FINITE ELEMENT METHOD

This paper presents summaries of the works of several authors associated with the invention of the analysis technique now referred to as the finite element method. It stresses the notion of first development from which subsequent ideas evolved and gives what is believed to be an accurate record of the historical sequence of published papers in the international literature.     

INNOVATIVE NETWORKING CONCEPTS TESTED ON THE ADVANCED COMMUNICATIONS TECHNOLOGY SATELLITE

This paper describes a program of experiments conducted over the advanced communications technology satellite (ACTS) and the associated T1-VSAT (very small aperture terminal). The experiments were motivated by the commercial potential of low-cost receive-only satellite terminals that can operate in a hybrid network environment, and by the desire to demonstrate frame relay technology over satellite networks. The first experiment tested highly adaptive methods of satellite bandwidth allocation in an integrated voice–data service environment. The second involved comparison of forward error correction (FEC) and automatic-repeat-request (ARQ) methods of error control for satellite communication with emphasis on the advantage that a hybrid architecture provides, especially in the case of multicasts. Finally, the third experiment demonstrated hybrid access to databases and compared the performance of internetworking protocols for interconnecting local area networks (LANs) via satellite. A custom unit termed frame relay access switch (FRACS) was developed by COMSAT Laboratories for these experiments; the preparation and conduct of these experiments involved a total of 20 people from the University of Maryland, the University of Colorado and COMSAT Laboratories, from late 1992 until 1995.