Measurement of capacitances and their loss factors

A method is described for measuring the capacitance values and the loss factors of a pair of capacitors simultaneously. The method uses the principle of oscillators. No standard capacitor is required. The possible errors introduced in the measurements are discussed. Both theoretical and experimental results are provided. The method can be used with any other oscillator circuit that contains only two capacitors     

Growth and properties of Hg1-xCdxTe on GaAs,with x − 0.27

The organometallic vapor phase epitaxy of HgCdTe onto (100)2°-(110) GaAs substrates is described in this paper. A buffer layer of CdTe has been grown prior to the growth of HgCdTe, to take up the large lattice mismatch with the GaAs. Considerations for the thickness of this buffer layer are outlined, and it is shown by quantitative Secondary Ion Mass Spectroscopy that there is negligible diffusion of gallium from the GaAs substrate for the growth conditions described. Hall effect measurements give mobilities comparable to those reported for bulk grown crystals. An extrinsicn-type carrier concentration of 2 × 10¹⁶/cm³ is obtained, and is mainly due to residual impurities in the starting chemicals. The alloy composition has been determined at 298 K by Fourier transform infrared transmission (FTIR) spectrometry; this is found to be extremely uniform over a 15 × 7 mm area, as evidenced by an overlapping of FTIR plots taken over this area. HgCdTe layers have been grown on buffer layers varying in thickness from 0.1 to 1.9μm. It is found that a buffer thickness of about 1.9μm or larger is required to obtain high quality HgCdTe, both in terms of the electrical characteristics (mobility and carrier concentration) and the infrared transmission curves (peak transmission).     

Synthesis of base impurity distributions for improved figure of merit of transistors

This paper deals with the problem of determining the impurity distribution which will improve the minority carrier base transit time and figure of merit of transistors. From the study of a special form of doping distribution which presents a point of inflection in the resulting built-in electric field configuration, it is concluded that the optimum doping distributions derived through variational methods [2–4] do not necessarily offer a unique minimum for base transit time. A new technique called “The Segmentation Technique” is evolved to synthesise base impurity distributions for improved high frequency performance of present-day junction transistors. It is shown that typical impurity distributions presenting retarding field over a small portion of the base and an aiding field over the rest of the base region offer a significant improvement in base transit time and the high frequency figure of merit.     

Case Study on Speed Failure Causes in a Microprocessor

In this article, we identify the underlying speed paths and perform a detailed analysis on the effects of multiple input switching, cross-coupling noise, and localized voltage drop on microprocessor. We employ cycle-wise clock shrinks on a tester combined with a CAD methodology to unintrusively identify and analyze these speed paths. Understanding the causes of speed failures can help designers make better power and performance tradeoffs.     

Extrusion of rate-sensitive materials using a viscoplastic constitutive equation and the finite element method

The flow of a rate sensitive material in a forming process in general and an extrusion process in particular has been analysed by using a constitutive equation in the form where such a material is treated as a viscous, non-Newtonian incompressible fluid flow. The discretized form of the flow equation is obtained using the principle of virtual work and the finite element technique. Velocities and pressures are used as primary variables in the formulation.The method which is presently applied to the axisymmetric steady state extrusion of rate sensitive materials can readily be extended to unsteady problems. The two rate-sensitive materials choosen are an aluminium having a definite yield stress and a Pb-Sn eutectic alloy having no detectable yield limit. The results of the present analysis are compared with available experimental values or with that obtained by other methods and in general good agreement is found to exist.     

Growth and development ofThiobacillus ferrooxidans for engineering applications

A bioprocessing approach for the extraction of base, nuclear and precious metals from refractory and lean grade ores has been reviewed in this paper. Characteristic morphological features ofThiobacillus ferrooxidans, the organism which has been extensively used for biooxidation of sulphide ores have been discussed. Mechanisms of chemoautotrophy and mineral oxidation have been illustrated. The current engineering applications of this microorganism have also been brought out. Various methods for accelerating the growth ofThiobacillus ferrooxidans for faster biooxidation and genetic manipulation for development of desired strains have been outlined.     

Pluronic lecithin organogel of 5-aminosalicylic acid for wound healing

5-Aminosalicylic acid (5-ASA) is an aminosalicylate anti-inflammatory drug, which is also known as mesalazine or mesalamine. Currently employed in treating inflammatory bowel disease, ulcerative colitis, inflamed anus or rectum, and maintain remission in Crohn's disease. Evidence from the researchers highlighted its significant re-epithelization in allergic asthma, aphthous, and gastric ulcerative conditions. The objective of the study was to formulate the pluronic lecithin organogel (PLO) containing 5-ASA and evaluate its wound-healing ability in a full thickness excision wound rat model. The data obtained from in silico docking studies revealed 5-ASA is having an affinity towards the transforming growth factor-beta (TGF-β) specifically towards beta1. Among various formulations prepared (F1 to F8), F1, and F6 have shown a maximum in vitro drug release with optimum pH and viscosity. From MTT assay it was found that selected PLO formulations showed no toxicity and enhanced cell proliferation in HaCaT cell lines. In vivo wound-healing studies in albino Wistar rats has revealed that PLO accelerates wound closure and reepithelization to the statistically significant level on day 3 (p?相似文献   

A simple method to estimate gain-bandwidth product and the secondpole of the operational amplifiers

A method for realizing a sine-wave voltage-controlled oscillator (VCO) with a linear frequency to control voltage characteristics over three decades of frequencies, or more, in one sweep is discussed. The method employed is the conversion of a simple integrated square-wave VCO into a sine-wave VCO by separating the first-harmonic component and providing frequency shifting to achieve the desired output range. The sources of distortion of the output waveform are shown to be higher-order components of the square-wave used and higher-order components produced in the mixer. Possible improvements of the circuit are suggested, including the use of higher-order filters to reduce distortion and the use of a square-wave VCO operating at higher frequencies to provide operation at higher frequencies or over wider sweep ranges     

The role of N,N-dimethylaniline in the formation of titania gel monolith by sol-gel method

19950405 Our investigation on the rheological aspects such as gelling time, specific density, fluidity, viscosity and surface tension of the sol derived from titanium-tetra-isopropoxide (TTIP), water and isopropanol (i-PrOH) has been reviewed in the presence of n,n-dimethylaniline (DMA) as a drying control chemical agent (DCCA). Dry gels derived from DMA stabilized sol were found to be crack free with a larger surface area. The titania gel monolith obtained in the presence of DMA could be processed into rutile at much lower temperatures.