Protection and Switching-Aid Networks for Transistor Bridge Inverters

The present trend in the industry is towards the use of power transistors in the development of efficient Pulsewidth Modulated (PWM) inverters, because of their operation at high frequency, simplicity of turn-off, and low commutation losses compared to the technology using thyristors. But the protection of power transistors, minimization of switching power loss, and design of base drive circuit are very important for a reliable operation of the system. The requirements, analysis, and a simplified procedure for calculation of the switching-aid network components are presented. The transistor is protected against short circuit using a modified autoregulated and autoprotection drive circuit. The experimental results show that the switching power loss and voltage stress in the device can be reduced by suitable choice of the switching-aid network component values.     

Process Development Aspects of Aluminium-Titanium Master Alioys

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Physical properties of fcc lanthanum under pressure

We report here a theoretical calculation of band strucure and superconductivity in the fcc phase of lanthanum under pressure. The effect of pressure on the band structure is obtained by means of the linear muffintin orbital method. McMillan's formula is used to calculate the superconducting transition temperature (T _c). It is found that the value ofT _c increases continuously up to 17.8 GPa and then begins to decrease. The change in the slope ofT _c is attributed to the appearance of a new piece of Fermi surface. The calculated values ofT _c are compared with the available experimental data.     

Regression Model for Daily Maximum Stream Temperature

An empirical model is developed to predict daily maximum stream temperatures for the summer period. The model is created using a stepwise linear regression procedure to select significant predictors. The predictive model includes a prediction confidence interval to quantify the uncertainty. The methodology is applied to the Truckee River in California and Nevada. The stepwise procedure selects daily maximum air temperature and average daily flow as the variables to predict maximum daily stream temperature at Reno, Nev. The model is shown to work in a predictive mode by validation using three years of historical data. Using the uncertainty quantification, the amount of required additional flow to meet a target stream temperature with a desired level of confidence is determined.     

A recursive algorithm for maximum likelihood-based identificationof blur from multiple observations

A maximum likelihood-based method is proposed for blur identification from multiple observations of a scene. When the relations among the blurring functions are known, the estimate of blur obtained using the proposed method is very good. Since direct computation of the likelihood function becomes difficult as the number of images increases, we propose an algorithm to compute the likelihood function recursively.     

Site-specific photobiotinylation of immunoglobulins, fragments and light chain dimers

Mesophasic proliposomal system for levonorgestrel was developed and evaluated both in vitro and in vivo. The vesicles were mostly unilamellar, however, few vesicles were multilamellar which budded off spontaneously upon hydration. The release of drug from this system adhered to zero order kinetics. The effect of alcohols and volatile oils on transdermal flux was investigated. The flux was found to be the highest for alcohol, and followed by that for lemon oil. The in vivo studies indicate the requirement for a loading dose, since, a significant lag phase was observed before the therapeutic levels were reached. This system was, however, superior to the PEG-based ointment system which was employed as the control formulation. The results demonstrate the potential of proliposomal system for efficacious transdermal delivery of hydrophobic drugs.     

Space-Variant Approaches to Recovery of Depth from Defocused Images

The recovery of depth from defocused images involves calculating the depth of various points in a scene by modeling the effect that the focal parameters of the camera have on images acquired with a small depth of field. In the approach to depth from defocus (DFD), previous methods assume the depth to be constant over fairly large local regions and estimate the depth through inverse filtering by considering the system to be shift-invariant over those local regions. But a subimage when analyzed in isolation introduces errors in the estimate of the depth. In this paper, we propose two new approaches for estimating the depth from defocused images. The first approach proposed here models the DFD system as a block shift-variant one and incorporates the interaction of blur among neighboring subimages in an attempt to improve the estimate of the depth. The second approach looks at the depth from defocus problem in the space-frequency representation framework. In particular, the complex spectrogram and the Wigner distribution are shown to be likely candidates for recovering the depth from defocused images. The performances of the proposed methods are tested on both synthetic and real images. The proposed methods yield good results and the quality of the estimates obtained using these methods is compared with the existing method.     

A Comparative Evaluation of Air-Jet Sieve for Particle Size Analysis of Pharmaceutical Powders

The performance of the air-jet sieve (AJS), for the particle size analysis of pharmaceutical powder, was evaluated and compared with the conventional sieve shaker (ESS). Two grades of acetaminophen (APAP) were used as test pharmaceutical powders. The particle size analysis by the AJS was simple, reproducible, efficient and accurate. The problematic powder, possessing excessive electrostatic charges and ranging in mean diameter from 17 nm to 800 nm (beyond the scope of ESS) could be evaluated accurately by AJS. The analysis time required by AJS was relatively less than that required by ESS. The accuracy of the determination by AJS was not affected by the sample size. Both the speed of rotation (vibrations and/or shaking) and the total time of sifting affected the results of the determination by ESS. The particle size value of APAP-special determined by ESS and AJS were 680.0 ± 0.14 nm and 40.0 ± 0.32 respectively, whereas the value assigned by the manufacturer was below 74 nm (-200 mesh). The precision of either method for particle size analysis of powder possessing excessive electrostatic charge was improved by the use of carbon black as an anti-static agent.     

Starch urea formaldehyde matrix encapsulation of solid agrochemicals. II. Release mechanism and release modeling

Based on experimental observation, a mechanism is proposed to describe the release of carbofuran from a starch-UF matrix. A simple mathematical model is developed to describe the diffusion-controlled release of a solid insecticide from a porous starch-UF matrix undergoing both volume and surface erosions. The model is tested with the release data collected for different matrices and with different pH values of the environmental liquid. The comparison between the model predictions and data is found to be reasonably good. The model describes the release process at different pH values by accounting for the influence of pH on the erosion rates.