Strengthening of Glasses by Partial Leaching

A technique for strengthening certain alkali borosilicate glasses is described. Porous surface layers of a desired thickness are created on an article, taking advantage of the phase separation and leaching phenomena in such glasses. The semiporous composite is then heated to sinter the high-silica clad about the borosilicate core. On cooling, residual compressive stresses develop within the cladding. The mechanical properties of cylindrical specimens prestressed by this method were characterized by photoelastic measurements and moduius-of-rupture tests. Residual stresses as high as —410 MPa were observed and found to be in reasonable agreement with the form of a previously developed thermal-stress model. The roles played by thermal tempering and stress-relaxation effects are also discussed.     

OPSYN: A CAD BASED EXPERT SYSTEM FOR OPTIMUM STRUCTURAL SYNTHESIS

This paper presents an overview of an expert system, OPSYN, for optimum structural synthesis, with particular emphasis on the significance of the development environment for such systems. The knowledge base for this system includes rules for facilitating finite element modeling, optimum design modeling, and selection of optimization strategies and parameters. The environment for this development is an inference engine with both forward and backward reasoning capabilities, a detailed explanation facility, and an automated knowledge acquisition system with a knowledge base editor facility. The use of a computer aided design (CAD) interface with its significant data structure and graphics capabilities in the knowledge acquisition and knowledge representation process is demonstrated with this expert system.     

THERMOPHYSICAL PROPERTIES OF FRESH AND ROASTED COFFEE POWDERS1

The present work deals with experimental determination of bulk specific heat, bulk thermal conductivity, bulk and true density and moisture content of Columbian and Mexican coffee bean powders. Specific heat was determined by DSC, thermal conductivity by modified Fitch apparatus, density by stereopycnometer and moisture contents by standard vacuum oven method. Specific heat values showed marginal rise over the temperature range (45 to 150C) studied. Thermal conductivity values, determined in the temperature range of 20–60C were not found to have any definite trend with rise in moisture in the experimental range of 4.8 to 9.8% moisture (dry basis). Bulk density of powders varied appreciably (1.298 to 0.882 g.cm^?3), while the change was negligible for true density (1.361 to 1.092 g.cm^?3) with the degree of roasting. Statistical analysis of the data shows the reliability of the experimental determinations. Suitable correlations were developed to determine bulk specific heat and bulk density.     

Some Further Studies on Determination of all the Minimal Prime Implicant Covers of Switching Functions†

A method of determination of all the minimal prime implicant covers of switching functions by utilizing their connected cover term matrices is suggested in the paper. The method presented is an extension of the technique suggested by the authors in a previous paper (Choudhury and Das 1964). When majority of the prime implicants of a switching function will occur in more than two different columns of the cover table, it is shown that the determination of all the minimal prime implicant covers can often be greatly facilitated by initially dividing the cover table into more than two suitable sub-tables.     

System dynamics simulation of Hopfield neural networks

Hopfield networks are a class of neural network models where non-linear graded response neurons organized into networks with effectively symmetric synaptic connections are able to implement interesting algorithms, thereby introducing the concept of information storage in the stable states of dynamical systems. In addition to opening up the possibility of using system dynamics as a vehicle to gain potentially useful insights into the behaviour of such networks, especially in the field or nonelectrical engineering, we study the dynamics of the state-space trajectory as well as time domain evolution of sensitivities of the states with respect to circuit parameters.     

Sliding wear characteristics of solid lubricant coating on titanium alloy surface modified by laser texturing and ternary hard coatings

Titanium alloys are poor in wear resistance and it is not suitable under sliding conditions even with lubrication because of its severe adhesive wear tendency. The surface modifications through texturing and surface coating were used to enhance the surface properties of the titanium alloy substrate. Hard and wear resistant coatings such as TiAlN and AlCrN were applied over textured titanium alloy surfaces with chromium as interlayer. To improve the friction and wear resisting performance of hard coatings further, solid lubricant, molybdenum disulphide (MoS2), was deposited on dimples made over hard coatings. Unidirectional sliding wear tests were performed with pin on disc contact geometry, to evaluate the tribological performance of coated substrates. The tests were performed under three different normal loads for a period of 40 min at sliding velocity of 2 m/s. The tribological behaviours of multi-layer coatings such as coating structure, friction coefficient and specific wear rate were investigated and analyzed. The lower friction coefficient of approximately 0.1 was found at the early sliding stage, which reduces the material transfer and increases the wear life. Although, the friction coefficient increased to high values after MoS₂ coating was partially removed, substrate was still protected against wear by underlying hard composite layer.     

Diffusion-Controlled Redox Kinetics in a Glassmelt

A diffusion model was developed to analyze the rate at which Fe²⁺/Fe³⁺ equilibration occurs in a Ca-Al-borosilicate melt in an air atmosphere at 1260°C. The resulting diffusion coefficient of oxygen determined from the model of 3.7 × 10⁻⁷ cm²/s is in agreement with the range of values reported for other glass-melts at this temperature and with the value determined from the viscosity of the melt using the Eyring model. The results support the general interpretation of the multivalent ion oxidation equilibrium as a diffusion-controlled process. The model thus provides a means to determine the diffusivity of oxygen in glassmelts from the kinetics of the oxidation reaction for a variety of redox ions.     

Energy modelling for the national economy — generalized model based on a physical systems theory approach

This paper presents an approach to the study of the energy related issues of the national economy using physical systems theory concepts for economic and real life systems. The main issues are: the efficiency of various energy conversion and utilization processes in terms of the macro-level technological coefficients; the direct and indirect energy wastes as calculated on the basis of technological coefficients; the effect of energy wastes on the unit cost of energy available to the consumers; the consumption of natural resources based on the final and intermediate demands of various sectors; and the amount of environmental pollution due to energy wastes disposed of to nature. A model is developed for a simplified two-sector national economy which is later extended to a generalized multi-sector model in a branchchord framework. This generalization is a step forward in simplifying the solution methodology for the multi-sector models through substitution, thus avoiding the necessity of drawing a complex system graph or solving large matrices required in the solution methodology.     

Simplification of Switching Functions Involving a very Large Number of ‘Don't Care’ States†

A method of simplification of switching functions involving a very large number of ‘ don't care’ states is suggested in the present paper. First a tabular technique is suggested which generates all the prime implicants starting from the maxterm type expressions of switching functions, avoiding generation of the prime implicants formed of ‘don't care’ states only. The technique presented is simple and iterative. Next it is suggested how the knowledge of the sets of prime implicants thus obtained can be utilized for finding minimal or other irredundant sums of switching functions.