Showing papers by "Indian Institute of Science published in 1987"

Plastics technology handbook

Abstract: Characteristics of polymers fabrication processes plastics properties and testing industrial polymers polymers in special uses recycling of polymers trends in polymer applications appendices - trade names for some industrial polymers, index of trade names manufacturers and suppliers of metal deactivators, index of trade names, manufacturers and suppliers of light stabilizers, index of trade names and suppliers of flame retardants, index of trade names and suppliers of foaming agents, harmonic motion of a Maxwell model, formulations of flame-retarded selected thermoplastics, formulations of selected rubber compounds, formulations of selected PVC compounds, formulations of polyurethane foams, commercial polymer blends and alloys, conversion of units, typical properties of polymers used for moulding and extrusion, typical properties of cross-linked rubber compounds, typical properties of representative textile fibres.

Gaussian-Wigner distributions in quantum mechanics and optics

Abstract: Gaussian kernels representing operators on the Hilbert space scrH=L2(openRn) are studied. Necessary and sufficient conditions on such a kernel in order that the corresponding operator be positive semidefinite, corresponding to a density matrix (cross-spectral density) in quantum mechanics (optics), are derived. The Wigner distribution method is shown to be a convenient framework for characterizing Gaussian kernels and their unitary evolution under Sp(2n,openR) action. The nontrivial role played by a phase term in the kernel is brought out. The entire analysis is presented in a form which is directly applicable to n-dimensional oscillator systems in quantum mechanics and to Gaussian Schell-model partially coherent fields in optics.

Learning automata with changing number of actions

Abstract: A reinforcement scheme that is based on the linear reward-inaction updating algorithm is presented for a learning automaton whose action set changes from instant to instant. A learning automaton using the algorithm is shown to be both absolutely expedient and e-optimal. The simulation results verify the e-optimality of the algorithm. The results can be extended to the design of general nonlinear absolutely expedient learning algorithms.

Identification of the phase responsible for high-temperature superconductivity in $Y-Ba-Cu$ oxides

Abstract: The discovery of La–Ba(Sr)–Cu oxides of K2NiF4 structure exhibiting superconductivity in the 30–40 K region was reported early this year1. The recent announcement of superconductivity above the temperature of liquid nitrogen in Y–Ba–Cu oxides2 has belied all expectations. Unfortunately, all the Y–Ba–Cu oxide compositions exhibiting this remarkable feature were biphasic or multiphasic. We have studied various compositions of the Y3–xBa3+xCu6O14 and now report the isolation of the pure oxide phase responsible for high Tc superconductivity. This oxide has the composition Y0.33Ba0.67CuO2.33±δ, with an oxygen defect perovskite structure. The pure oxide shows the onset of superconductivity at 120 K, attaining zero resistance at 87 K. It also exhibits the highest Meissner effect of all the high-Tc oxide superconductors.

Photoemission study of YBa2Cu3O7 through the superconducting transition: Evidence for oxygen dimerization.

Abstract: Photoemission spectra of $\mathrm{Y}{\mathrm{Ba}}_{2}{\mathrm{Cu}}_{3}{\mathrm{O}}_{7\ensuremath{-}\ensuremath{\delta}}$ in the normal and superconducting states provide direct evidence for dimerization of oxygen below ${T}_{c}$. ${\mathrm{Cu}}^{2+}$ is found to reduce to ${\mathrm{Cu}}^{1+}$ concomitantly. These changes may be of vital importance to the mechanism of high-temperature superconductivity.

A Methodology for Knowledge Acquisition and Reasoning in Failure Analysis of Systems

Abstract: The problem of modeling knowledge about the fault behavior of a system and utilizing this model for reasoning about and diagnosing failures is addressed. A solution that merges graph and fault-tree-based failure analysis with rule-oriented reasoning is presented. Failure analysis is divided into two phases, a failure source location phase and a failure cause identification phase. Each phase consists of a failure model and a process that operates on it. The failure models for the first and second phases are based on lesel-structured fault propagation digraphs and augmented fault trees, respectively. The augmented fault tree (AFT) is a conceptual structure that encodes probabilistic, temporal, and heuristic information in addition to the causal aspects of failures modeled by conventional fault trees. The two models are combined to form a novel hierarchical failure knowledge representation scheme. Upper levels of this hierarchy are made up of the fault propagation digraphs. Each level represents a view of the system under a particular granularity, and the granularity increases with levels. This feature permits control over the resolution of fault diagnosis. The lowest level consists of a set of cause-consequence knowledge bases containing production rules. These production rules are derived from augmented fault trees and represent the cause-effect relations among failure events that lead to the corresponding subsystem's failure. A knowledge acquisition procedure to generate these failure models and failure analysis processes that operate on them are described. The methodology proposed is inherently parallel as the processes may operate on different levels independently.

Sporotrichum thermophile Growth, Cellulose Degradation, and Cellulase Activity.

Abstract: The activity of components of the extracellular cellulase system of the thermophilic fungus Sporotrichum thermophile showed appreciable differences between strains; ..beta..-glucosidase was the most variable component. Although its endoglucanase and exoglucanase activities were markedly lower, S. thermophile degraded cellulose faster than Trichoderma reesei. The production of ..beta..-glucosidase lagged behind that of endoglucanase and exoglucanase. The latter activities were produced during active growth. When growth was inhibited by cycloheximide treatment, the hydrolysis of cellulose was lower than in the control in spite of the presence of both endoglucanase and exoglucanase activities in the culture medium. Degradation of cellulose was a growth-associated process, with cellulase preparations hydrolyzing cellulose only to a limited extent. The growth rate and cell density of S. thermophile were similar in media containing cellulose or glucose. A distinctive feature of fungal development in media incorporating cellulose or lactose (inducers of cellulase activity) was the rapid differentiation of reproductive units and autolysis of hyphal cells to liberate propagules which were capable of renewing growth immediately.

Coloured Petri net models for automated manufacturing systems

Abstract: In this paper, we propose an approach, using Coloured Petri Nets (CPN) for modelling flexible manufacturing systems. We illustrate our methodology for a Flexible Manufacturing Cell (FMC) with three machines and three robots. We also consider the analysis of the FMC for deadlocks using the invariant analysis of CPNs.

Diversity: Cultural and biological.

Abstract: Early human populations utilized a wide range of biological resources in a tremendous diversity of environments. As a result, they possessed high levels of cultural diversity dependent on and supportive of high levels of biological diversity. This pattern changed drastically with technological innovations enabling certain human groups to break down territorial barriers and to usurp resources of other groups. The dominant groups have gone on to exhaust a whole range of resources, depleting both biological and cultural diversity. Traditions of resource conservation can, however, re-emerge when the dominant cultures spread over the entire area and the innovations diffuse to other human groups. This could change once again as genetically engineered organisms become an economically viable proposition with the accruing advantages concentrated in the hands of a few human groups: a further drastic reduction in biological and cultural diversity may ensue.

Novel solid solution precursor method for the preparation of ultrafine Ni-Zn ferrites

Abstract: Ultrafine Ni-Zn ferrites, $Ni_xZn_{1-x}Fe_20_4$, have been prepared by the thermal decomposition/combustion of novel solid solution precursors of the type, $(N_2H_5)_3Ni_xZn_{1-x}Fe_2(N_2H_3COO)_9.3H_20$ where x = 0.2 to 0.8. The novelty of the precursors being their low temperature, exothermic, gas producing self-sustained decomposition. Fine particle nature of the ferrites has been indicated by X-ray powder diffraction, transmission electron microscopy and surface area measurements. Fine particle Ni-Zn ferrites sinter at $1000^0C$, 24 h to achieve almost 99% theoretical density.

Evolution of cooperation by reciprocation within structured demes

Abstract: The iterative two-person Prisoners’ Dilemma game has been generalised to theN-person case. The evolution of cooperation is explored by matching the Tit For Tat (TFT) strategy (Axelrod and Hamilton 1981) against the selfish strategy. Extension of TFT toN-person situations yields a graded set of strategies from the softest TFT, which continues cooperation even if only one of the opponents reciprocates it, to the hardest, which would do so only when all the remaining opponents cooperate. The hardest TFT can go to fixation against the selfish strategy provided it crosses a threshold frequencypc. All the other TFT are invadable by the selfish (D) or the pure defector strategy, while none can invadeD. Yet, provided a thresholdpc is crossed, they can coexist stably withD. AsN, the size of the group increases, the threshold pc also increases, indicating that the evolution of cooperation is more difficult for larger groups. Under certain conditions, only the soft TFT can coexist stably against the selfish strategyD, while the harder ones cannot. An interesting possibility of a complete takeover of the selfish population by successive invasions by harder and harder TFT strategies is also presented.

Learning Optimal Discriminant Functions through a Cooperative Game of Automata

Abstract: The problem of learning correct decision rules to minimize the probability of misclassification is a long-standing problem of supervised learning in pattern recognition. The problem of learning such optimal discriminant functions is considered for the class of problems where the statistical properties of the pattern classes are completely unknown. The problem is posed as a game with common payoff played by a team of mutually cooperating learning automata. This essentially results in a probabilistic search through the space of classifiers. The approach is inherently capable of learning discriminant functions that are nonlinear in their parameters also. A learning algorithm is presented for the team and convergence is established. It is proved that the team can obtain the optimal classifier to an arbitrary approximation. Simulation results with a few examples are presented where the team learns the optimal classifier.

On the short-range order in Al-Mn quasicrystals during low-temperature ageing

Abstract: We report the evolution of diffuse intensity during the low-temperature ageing of Al-Mn quasicrystals This is taken as evidence of short-range order in the icosahedral phase prior to its decomposition The implication of these diffuse intensities is discussed