Control of properties during the growth of a large number of (Y,Sm)3(Ga,Fe)5O12 films from the same melt

For the growth of a large number of (Y, Sm)₃(Ga, Fe)₅O₁₂ films from the same melt, we describe the drift and methods to control the drift in film properties, so that the films are suitable for making magnetic bubble memory devices. The melt was based on PbO-B₂O₃ flux. The film thickness h and the characteristic length l were kept at around 5.4 μm and 0.54 μm respectively. The desired h was achieved by adjusting the growth time. The desired values for l were achieved by adjusting the growth temperature and by periodically adding small amounts of Ga₂O₃. The lattice constant was kept within the specified limits by periodic additions of Y₂O₃. Using these techniques we were able to grow more than a hundred films, out of which ～ 85% were acceptable for device fabrication. Based on the deduced values for the composition of our films, we have calculated the melt depletion resulting from the growth of a single film. We find that the experimentally determined additions of Ga₂O₃ and Y₂O₃ that gave us good control over film properties are almost equal to the calculated depletions for these two oxides.     

Breakdown and capacitance properties of hyperabrupt epitaxial Schottky barrier diodes

An analysis of the breakdown and capacitance properties of punch-through hyperabrupt epitaxial Schottky barrier diodes has been carried out. Results are given for the dependence of breakdown voltage of such a device on surface concentration and epitaxial layer thickness. Design curves are given for epitaxial hyperabrupt schottky varactor diodes. The design procedure yields an optimal impurity profile in which just-punch-through occurs at the highest voltage of operation. This gives a maximum dynamic range of operation still keeping the series resistance to a minimum. A corrected boundary condition to determine the profile constants associated with an n/n⁺ (high/low) junction is also given.     

Collocation method using artificial viscosity for solving stiff singularly perturbed turning point problem having twin boundary layers

A numerical scheme is proposed to solve singularly perturbed two-point boundary value problems with a turning point exhibiting twin boundary layers. The scheme comprises a B-spline collocation method on a uniform mesh, which leads to a tridiagonal linear system. Asymptotic bounds are established for the derivative of the analytical solution of a turning point problem. The analysis is done on a uniform mesh, which permits its extension to the case of adaptive meshes which may be used to improve the solution. The design of an artificial viscosity parameter is confirmed to be a crucial ingredient for simulating the solution of the problem. Some relevant numerical examples are also illustrated to verify computationally the theoretical aspects.     

Affinity-based screening of combinatorial libraries using automated, serial-column chromatography

We have developed an automated serial chromatographic technique for screening a library of compounds based upon their relative affinity for a target molecule. A "target" column containing the immobilized target molecule is set in tandem with a reversed-phase column. A combinatorial peptide library is injected onto the target column. The target-bound peptides are eluted from the first column and transferred automatically to the reversed-phase column. The target-specific peptide peaks from the reversed-phase column are identified and sequenced. Using a monoclonal antibody (3E-7) against beta-endorphin as a target, we selected a single peptide with sequence YGGFL from approximately 5800 peptides present in a combinatorial library. We demonstrated the applicability of the technology towards selection of peptides with predetermined affinity for bacterial lipopolysaccharide (LPS, endotoxin). We expect that this technology will have broad applications for high throughout screening of chemical libraries or natural product extracts.     

Reverse osmotic properties of the membranes prepared from the polycondensate of 2,5-pyridinedicarboxylic acid chloride and malonyl dihydrazide

Summary The membrane performance of the polycondensates derived from 2,5-pyridinedicarboxylic acid chloride and malonyl dihydrazide was studied in reverse osmosis. It depended on drying time, and the kind and amount of a cross-linking agent and an inorganic additive. The membrane strength generally exceeded that of a cellulose acetate membrane. The rejection difference between transition and alkali metal salts was discussed in terms of complexation and the molecular size of the additive. A potential application was suggested for the separation between the two metals through the membrane of a large rejection difference.     

Synthesis, Densification, and Phase Evolution Studies of Al2O3–Al2TiO5–TiO2 Nanocomposites and Measurement of Their Electrical Properties

Alumina–aluminum titanate–titania (Al₂O₃–Al₂TiO₅–TiO₂) nanocomposites were synthesized using alkoxide precursor solutions. Thermal analysis provided information on phase evolution from the as-synthesized gel with an increase in temperature. Calcination at 700°C led to the formation of an Al₂O₃–TiO₂ nanocomposite, while at a higher temperature (1300°C) an Al₂O₃–Al₂TiO₅–TiO₂ nanocomposite was formed. The nanocomposites were uniaxially compacted and sintered in a pressureless environment in air to study the densification behavior, grain growth, and phase evolution. The effects of nanosize particles on the crystal structure and densification of the nanocomposite have been discussed. The sintered nanocomposite structures were also characterized for dielectric properties.     

Thermotropic mesomorphic polyesters. I. Copolyesters of terephthalic acid,hydroquinone, and flexible diols

A new series of copolyesters has been synthesized by low-temperature solution polycondensation of terephthaloyl dichloride hydroquinone and flexible diols such as 1,2-propane diol, 1,4-butanediol, diethylene glycol, (cis) 1,4-cyclohexanediol and (cis + trans) 1,4-bis(hydroxymethyl) cyclohexane. The copolyesters are all insoluble and display thermotropic mesophases at relatively lower transitions than other commercially important systems. The transition temperatures, the crystallinity, and thermal characterization are reported.     

Deterministic and stochastic analyses of fracture processes in a brittle microstructure system

Variations in constituent properties, phase morphology, and phase distribution cause deformation and failure at the microstructural level to be inherently stochastic. This paper focuses on the stochasticity of fracture processes that arises as a result of measurement uncertainties in the properties of the constituents in the heterogeneous microstructures of an Al₂O₃/TiB₂ ceramic composite system. Basic postulate here is that for a microstructure local material properties vary around their macroscopically measured value with the macroscopically measured value being the mean of the variation. A micromechanical cohesive finite element framework with explicit resolution of arbitrary fracture patterns and arbitrary microstructural morphologies is used in the analyses carried out in this paper. The randomness in the constituent properties at any given point in the microstructure is specified relative to the local mean values of the corresponding properties. A deterministic analysis and a stochastic analysis are carried out simultaneously. The combination of determinism and stochasticity is achieved by integrating a perturbation analysis of the influence of stochastic property variations around their mean values and a deterministic analysis for the microstructure with the mean values of the constituent properties. Calculations are carried out for actual and idealized microstructures of the Al₂O₃/TiB₂ material system. Calculations focus on analyzing the fracture response variation with varying levels of variation of material properties for a particular microstructural morphology as well as on analyzing the variations in fracture response with variations in microstructural morphology. It is observed that microstructural morphology is intricately linked to the variations in fracture response when material properties have stochastic origin. A microstructure less prone to fracture shows higher variations in fracture response when compared to the one which offers least resistance to the crack propagation. In addition, for a particular microstructural morphology, the levels of variations in the crack surface area generated and the variations in the energy release rate are of the same order as the levels of variations in constituent properties. The observations support the conclusion that a material designer needs to make conservative estimates for a material’s performance if its microstructural construction imparts uncertainty to local material properties.     

Breakage of Automotive Spring Washer During Twist Test: A Metallurgical Analysis

A washer is a thin plate with a hole that is normally used to distribute the load of a threaded fastener, such as a screw or nut. The washer used in automotive engine component is of split or spring lock washer. A ring split at one point and bent into helical shape. The benefit of spring lock washers lies in the trapezoidal shape of the washer. When compressed to loads near proof strength of the bolt, it will twist and flatten. This reduces the spring rate of the bolted joint which allows it to maintain more force under the same vibration levels. This prevents from loosening. The steel washer is one of the critical safety components for automobile engine, and its failure may cause severe safety issue. Before subjecting to manufacturing, the washer undergoes different process lines (wire rod → drawing → annealing → pickling → flattening → spring washer → single spring washer). After manufacturing of washer, toughness test is done to find out the metallurgical soundness and surface quality of the washer. In this toughness test the washer in a vice with the split ends free and straight above the vice jaws, a 90° segment of the free end is gripped with a wrench and bent. Washers should withstand twist test through a 90° angle without signs of fracture. The present paper highlights premature failure of automotive washer which failed during twist test. From the analysis, it has been observed that the distribution of spheroidized carbide is more uniform in good samples than that of rejected samples. Hardness profile variation was observed between good and bad spring samples. Overall investigation does not indicate any problem related to supplied wire rod material quality as no wire breakage problem observed. Inhomogeneous annealed structure in flat wire seems to result into variation in washer performance during twist test.