Realization of an n-channel GaAs/AlGaAs bistable transistor(BISFET)

The first realization of a novel heterostructure device, the bistable field-effect transistor (BISFET), is reported. The device uses an n-channel GaAs/AlGaAs inversion channel structure. It contains a positive feedback loop between the gate and source terminals, which is activated above a gate voltage of 1.7 V. This leads to abrupt transitions between high- and low-current states as the drain voltage is changed, with a switching ratio of 1.5. The transitions are accompanied by sharp changes in gate current as the feedback loop turns on and off. These transitions, referred to as switch up and switch down, form a large hysteresis loop in the drain characteristics. Hysteresis as large as 3.7 V is observed, making the device strongly bistable     

Shape, wear & mechanical properties of spray formed hypoeutectic Al-Si alloys

Manufacturing process through spray forming leads to give near-net-shape and fine grain microstructure. In this process Si particles, which are not distributed uniformly in conventional casting process, are distributed uniformly throughout the casting. In the present study disc shape spray form castings were made of Al-6.91Si and Al-10.1Si alloys, and then their shape, wear and mechanical properties were studied. The shape of the deposit was observed to be the most uniform at 30o inclination angle of the substrate. The hardness and tensile strength value of spray formed alloys shows the increment in the mechanical property in contrast to as cast alloys. The wearing properties of Al-10.1Si alloy were found to be better than that of the Al-6.91Si alloy.     

Effect of CaCl2 on the hydration of tricalcium silicate

The hydration of tricalcium silicate has been studied at 30° C in the presence and absence of 2 wt % CaCl₂ with a water∶solid ratio of 0.8. Free lime determinations, X-ray diffraction analysis, thermal analysis, infra-red spectroscopy, scanning electron microscopy and zeta potential measurements were used for hydration studies. The results indicate that the accelerating action of CaCl₂ is due to higher diffusivity of chloride ions.     

Josephson effects and dc SQUID behaviour in break junction of Y-Ba-Cu-O at 77 K

Break junctions of Y-Ba-Cu-O superconductor were realized by creating fresh crack in the bar shape bulk samples mounted in a specially designed probe kept in the liquid nitrogen bath. While the bulk sample was kept static, a sharp tip of a shaft was moved downward from the outside of the dewar in order to break the sample. It was possible to change the critical current of the break junctions by adjusting pressure on the tip of the shaft. The effects of magnetic field and microwave power on the I-V characteristic of the junction were studied. The junction was found to show periodic V-B behaviour and the microwave-induced Shapiro steps were clearly observed at 77 K. The flux noise spectrum of the junction was also studied.     

Thermal boundary layer of a micropolar fluid jet impinging normally on a flat plate

Summary The heat transfer is studied in the boundary layer formed on a flat plate by the impingement of an incompressible micropolar fluid jet. The thermal boundary layer equations are obtained after writing the governing equations for the steady two-dimensional flow of an incompressible micropolar fluid in cartesian co-ordinate system. The solution for the energy equation inside the boundary layer is obtained as a polynomial in terms of the distance from the stagnation point. The temperature of the plate and the temperature outside the boundary layer are assumed to be constant. The temperature distribution and the dimensionless heat transfer coefficient are presented graphically for various values of the material parameters which arise due to the micropolar property of the fluid. These results have been compared with the corresponding results for a Newtonian fluid.

---

Thermische Grenzschicht eines mikropolaren Flüssigkeitsstrahles, der senkrecht auf eine ebene Platte auftrifft

Zusammenfassung Der Wärmeübergang in der Grenzschicht einer ebenen Platte, zufolge des Auftreffens eines inkompressiblen, mikropolaren Flüssigkeitsstrahles wird untersucht. Die thermischen Grenzschichtgleichungen werden aus den Grundgleichungen für die stationäre zweidimensionale Strömung einer inkompressiblen, mikropolaren Flüssigkeit in kartesischen Koordinaten erhalten. Die Lösung der Energiegleichung innerhalb der Grenzschicht wird als Polynom in Termen des Abstandes zum Staupunkt angegeben. Die Temperatur der Platte, sowie die Temperatur außerhalb der Grenzschicht werden als konstant vorausgesetzt. Die Temperaturverteilung und der dimensionslose Wärmeübergangskoeffizient sind graphisch für verschiedene Werte der Materialparameter, zufolge der mikropolaren Eigenschaften der Flüssigkeit, dargestellt. Diese Ergebnisse wurden mit den entsprechenden Ergebnissen für Newtonsche Flüssigkeiten verglichen.

---

---

With 6 Figures     

Microstructural features associated with spray atomization and deposition of Al-Mn-Cr-Si alloy

An inert gas atomization process was employed in production of rapidly solidified powders as well as disc-shape preform by spray deposition of an Al₇₅Mn₁₀Cr₅Si₁₀ alloy. Microstructural features of atomized powders and spray deposited preforms were evaluated by scanning and transmission electron microscopy and X-ray diffractometry techniques. Solidification structure of powders revealed cellular and dendritic morphology, depending on their size. The interdendritic regions consisted of second phase particles. In contrast the spray formed alloy exhibited microstructural homogeneity with distribution of ultra-fine second phase particles of intermetallic compound. The structure of second phase intermetallics was identified as a cubic -Al(Mn,Cr)Si, in both the atomized powders and the spray-deposits. The formation of cubic phase is discussed as rational approximant structure of an icosahedral quasicrystal.     

Fabrication of SiGe optical waveguides using VLSI processingtechniques

The fabrication of rib waveguides in SiGe using the local oxidation of silicon (LOCOS) was investigated. Samples consisted of strained Si_.97Ge_.03 or Si_.94Ge_.06 waveguiding layers with silicon cladding layers. The structural stability of these strained layers during thermal cycling up to 1050°C was examined using X-ray rocking curve analysis, scanning electron microscopy, and Nomarski microscopy of etched samples. Since single SiGe layers sufficiently thick to support optical waveguiding are typically above the equilibrium critical thickness, dislocation formation during high-temperature processing is unavoidable. This work concentrated on minimizing these dislocations. It was found that the dislocation density induced by the processing can be minimized by using a strain-compensating mask layer as a barrier to oxidation. For a specified thermal oxide layer thickness, higher oxidation temperatures were found to minimize the dislocation density relative to oxidation at temperatures closer to the metastable limit. Furthermore, the large birefringence found in all strained-layer SiGe waveguides is significantly reduced after LOGOS processing. These effects were used to fabricate the first reported optical waveguides and photonic devices in SiGe using standard VLSI-type processing. The device is a 1.3/1.55-μm duplexer with wavelength isolation of roughly 10 dB     

Predictive modeling of die filling of the pharmaceutical granules using the flexible neural tree

In this work, a computational intelligence (CI) technique named flexible neural tree (FNT) was developed to predict die filling performance of pharmaceutical granules and to identify significant die filling process variables. FNT resembles feedforward neural network, which creates a tree-like structure by using genetic programming. To improve accuracy, FNT parameters were optimized by using differential evolution algorithm. The performance of the FNT-based CI model was evaluated and compared with other CI techniques: multilayer perceptron, Gaussian process regression, and reduced error pruning tree. The accuracy of the CI model was evaluated experimentally using die filling as a case study. The die filling experiments were performed using a model shoe system and three different grades of microcrystalline cellulose (MCC) powders (MCC PH 101, MCC PH 102, and MCC DG). The feed powders were roll-compacted and milled into granules. The granules were then sieved into samples of various size classes. The mass of granules deposited into the die at different shoe speeds was measured. From these experiments, a dataset consisting true density, mean diameter (d50), granule size, and shoe speed as the inputs and the deposited mass as the output was generated. Cross-validation (CV) methods such as 10FCV and 5x2FCV were applied to develop and to validate the predictive models. It was found that the FNT-based CI model (for both CV methods) performed much better than other CI models. Additionally, it was observed that process variables such as the granule size and the shoe speed had a higher impact on the predictability than that of the powder property such as d50. Furthermore, validation of model prediction with experimental data showed that the die filling behavior of coarse granules could be better predicted than that of fine granules.

     

A comparative investigation of bio waste filler (wood apple‐coconut) reinforced polymer composites

During the last century natural fibers are used as reinforcement in polymer composite has been continuously growing in the composite industry. This polymer matrix composite has wide range of application in hostile environment where it is exposed to external attacks such as solid particle erosion. The mechanical properties of different polymer composites are also most important characteristics. An attempt has been made to compare the mechanical and tribological properties of the both biowaste wood apple and coconut shell particulate polymer matrix composite. The results show that maximum flexural strength is obtained 78.19 MPa for wood apple shell and 68.25 MPa for coconut shell at 15 wt% filler content. The wood apple particulate composite shows best erosion and mechanical properties than coconut particulate composite. POLYM. COMPOS., 35:180–185, 2014. © 2013 Society of Plastics Engineers