Liquid-Phase Sintering of TiC-Ni Composites

The sintering of TiC-Ni particle compacts was studied with specific attention to effects of processing conditions. Densification was progressively inhibited with the increasing additions of free carbon to the system. These results are explained on the basis of changes in the eutectic reactions in the system, reduced solubility of TiC in the Ni-rich liquid, and decreased wetting of the solid by the liquid. Presintering hydrogen heat treatment reduced the carbon content of the TiC-Ni compacts and led to reduction in sintering rates and elevated temperatures of liquid-phase formation. Wetting experiments with hydrogen-treated materials showed a time-dependent wetting angle. These results are discussed based on wetting theory and reactions predicted by the equilibrium ternary-phase diagram.     

Physico—chemical modifications of liposome structures through interaction with surfactantsy‡

The liposome-surfactant interaction has been studied in this paper through the disrupting effect caused by surfactant molecules on large unilamellar vesicles prepared by reverse-phase evaporation. This process leads, in the end, to the rupture of such structures and to the solubilization of the phospholipidic components, via mixed surfactant-phospholipid micelle formation. This phenomenon is described by a three-stage model and characterized by two parameters: the highest surfactant/phospholipid ratio that can exist in a vesicle (R_{e sat}) and the lowest surfactant/phospholipid ratio required to keep the lipid and surfactant in the form of mixed micelles (R_{e sat}). These parameters have been determined by spectrophotometry and ³¹P NMR spectroscopy, obtaining results in a good agreement with both techniques. The surfactants tested have been: sodium dodecyl sulfate (SDS), sodium laurylether sulfate (SLES), N-hexadecyl-trimethylammonium bromide (HTAB), octylphenol series (8–20 EO) and alkylbetaines(C-10, C-12 and C-14). Different R_{e sat} and R_{e sol} values have been obtained for each of the surfactants. This has permitted a study of the solubilizing capacity versus the phospholipidic bilayer of the different surfactants as a function of their structure.     

Applications of Variance Reduction Techniques in Construction Simulation

A technique that can be used to reduce the variance of a stochastic simulation output is reviewed. This technique allows the user to reduce the number of simulation runs without sacrificing the level of confidence of the output. This technique entails inducing an artificial correlation between the various runs. The specific technique presented uses common random numbers (CRN). The use of CRN can be applied to the comparison of alternative systems. Using CRN when comparing alternatives insures that the comparison is properly conducted. A sample simulation is presented in order to illustrate these two applications of CRN.     

Environmental ageing effects in a silicon carbide fibre-reinforced glass-ceramic matrix composite

A silicon carbide fibre-reinforced glass-ceramic composite, based upon a BaO–MgO–Al₂O₃–SiO₂ (BMAS) matrix, has been used for a study of microstructural stability (specifically interface stability) after environmental exposure at elevated temperature. Characterization of the as-received material demonstrated the presence of a thin ‘carbon-rich’ interfacial layer between fibre and matrix, as typically observed in glass-ceramic/silicon carbide fibre composite systems. Samples have been subjected to heat-treatments in an oxidizing atmosphere at temperatures between 723 and 1473 K, for up to 500 h. Intermediate-temperature ageing, between 873 and 1073 K, results in strong fibre/matrix bonding, with consequent degradation of strength and composite ‘ductility’. This is due to oxidative removal of the carbon interfacial layer and subsequent oxidation of the fibre surface, forming a silica bridge. Carbon is retained at higher ageing temperatures due to the formation of a protective surface oxide scale at exposed fibre ends. Attempts to pretreat the BMAS composite at high temperature (1273–1473 K), designed to inhibit intermediate-temperature degradation via the formation of silica plugs at exposed fibre ends, has given mixed results due to the high residual porosity content in these materials, allowing paths of ‘easy’ oxygen ingress to be retained.     

Comparison of Rapid Methods for isolation and Enumeration of Clostridium perfringens in Meat

Three strains of Clostridium pefringens, ATCC 12924, ATCC 12917, and ATCC 14809, were inoculated separately into thioglycollate broth and ground beef samples and enumerated by Fung's Double Tube (FDT), Oxyrase Enzyme (OE), Gas Pak Anaerobic System (GPAS), and Anaerobic Petri Dish (APD) methods. Recovery of the three strains by FDT was significantly higher (P < 0.05) than that by the other three methods from both thioglycollate broth and ground beef, with OE second highest. FDT gave better recovery (84%) in less time (8–10 hr) at 42°C compared with the OE method (61%). FDT was also least costly.     

THE NEW PRIVATISM,FEDERALISM, AND THE FUTURE OF URBAN GOVERNANCE: NATIONAL URBAN POLICY IN THE 1980s

Two policies of the Reagan administration threaten the traditional role of cities both as basic elements in the nation's governing structure and as socio-economic communities. The long-standing belief that an important criterion for judging both public and private action is its contribution to the welfare of the city has been abandoned. Under what may be called the New Privatism the existence or creation of any community is now primarily justified by its capacity to serve the locational needs of private firms in a technology-driven national market. To continue Federal development aid to economically declining cities would contribute to inefficiency in the national spatial economy and cannot be justified. The Reagan version of the New Federalism calls for devolving greater power to the state and local levels. For cities, the opposite effect is more likely. The ending or reduction of most federal programs relating to cities and their residents has put many cities in a double bind. They must choose between using scarce local resources to compete with other communities to lure or hold job-generating firms and attempting to meet the needs of large numbers of their citizens who formerly received federal social and welfare aid. Further, much of the national money which is still available for economic development and social needs is now administered by state governments under block grants. States have seldom been responsive to such needs in urban areas. If our assessment of the negative effects of these policies on the viability of cities as governing units is correct, then the question that must be addressed is: what is to replace local government as the primary means for citizens to act collectively below the state level?     

Hydrolytic Stability and Changes in E Vitamers and Oryzanol of Extruded Rice Bran During Storage

Rice bran was extruded at 110, 120, 130, and 140°C with post extrusion holding times of 0, 3, and 6 min and stored at ambient temperatures for 1 yr. Holding time had no effect (p>0.05) on hydrolytic stability whereas 110°C was slightly less effective in maintaining hydrolytic stability. Increased holding times reduced (p<0.05) total vitamin E content. Oryzanol concentration was lower (p<0.05) only after 6 min holding time. Oryzanol was relatively more stable to extrusion temperatures than vitamin E. The highest retentions of total vitamin E and oryzanol were found in raw rice bran during storage. Increased extrusion temperatures reduced the retention of vitamin E and oryzanol during storage.     

Feedback Control of Limit Cycle Amplitudes from A Frequency Domain Approach

In this paper, a problem in feedback control of limit cycle amplitudes is studied. A graphical approach for this bifurcation control problem is developed by means of higher-order harmonic balance approximations for both amplitude and frequency of the system oscillatory outputs. The approach starts with the familiar Hopf bifurcation mechanism, and employs the second, fourth, and sixth-order harmonic balance approximations to generate a sequence of graphical tests for convergence analysis of the system oscillatory outputs. This sequential graphical testing leads to accurate approximations of limit cycles of small amplitudes in the system outputs. Degenerate Hopf bifurcation theory is used to formulate an appropriate control objective of capturing small-amplitude limit cycles, which can avoid reaching unstable equilibria or other undesirable limit sets. A rich cubic planar model is presented for illustration of the proposed control method.     

Heat-Stability of Milk-Clotting Enzymes in Conditions Encountered in Swiss Cheese Making

Chymosin is inactivated in gelled milk at pH 6.50 at 53°C according to a biphasic kinetic. Both phases appear to follow first-order kinetics. The D-value for the first phase is 30 min. In the same medium, the Mucor miehei and Mucor pusillus proteases are much more stable (D_53°C > 100 min) while bovine pepsin, a heat-labile Mucor miehei protease and the Endothia parasitica protease are rapidly inactivated (D_53°C < 10 min). pH appears to be the most important parameter for heat stability. Protein and calcium concentrations affect the resistance to heat treatment. A residual activity of chymosin in Swiss-type curd will be very weak at the most unless the curd is cooked at pH < 6.50.     

Influence of temperature on crystallization of lactose in ice-cream

Sandiness in ice-cream due to lactose crystallization can still be a problem in many circumstances. Lactose crystallization occurs in ice-cream as the unfrozen phase becomes supersaturated. However, the effects of storage temperature and temperature fluctuations on lactose crystallization have not been very well quantified. In this work, an accelerated storage apparatus was used to determine the effects of thermal fluctuations (from ±0.01°C to ±2.0°C), at several mean storage temperatures (from −5.0 to −20.0°C), on the onset of lactose nucleation and subsequent crystal growth in a standard vanilla ice-cream. the induction time for nucleation initially decreased as temperature was lowered (for temperature oscillations of ±1.0°C), until a minimum induction time of 3 h was found between −10.0 and −12.0°C. Further decreases in storage temperature caused the induction time to increase. the induction time for nucleation increased as the extent of temperature fluctuations increased, from 0.01 to 2.0°C, while initial lactose crystal growth rate showed the opposite trend. the initial growth rate increased as temperature decreased between −5.0 and −10.0°C, but then decreased for temperatures below −10.0°C. At −20.0°C lactose crystals grew very slowly. At −10.0°C the rate of growth decreased with increasing amplitude of temperature oscillations.