Semiconductor based photoelectrochemical cells for solar energy conversion—An overview

An overview of the semiconductor based photoelectrochemical (pec) cells for solar energy conversion is presented.pec cells are of two types: photoelectrolysis cells and photovoltaic cells. The principles involved, electrode and electrode/electrolyte interface characteristics, experimental methods of investigation and energy conversion efficiency are discussed in detail. Up-to-date data on variouspec cells are also presented and discussed.     

X-ray spectroscopy and local structures in glasses

X-ray spectroscopy which is a combination of two techniques, namely x-ray absorption near edge structure (xanes) and extended x-ray absorption fine structure (EXAFS) analyses, is a unique technique for the study of local structures in glasses. Availability of synchrotron radiation sources has made the technique quite attractive and useful because the photon flux from synchrotrons is very intense and polarized. In this article, a brief summary ofxanes andEXAFS techniques is given along with a few applications to the study of local structures in glasses. Communication No. 323 from Solid State and Structural Chemistry Unit.     

Thermal properties of some α-amino acids in aqueous solutions

The thermal properties (thermal conductivity, thermal diffusivity, and volumetric heat capacity) of aqueous solutions of -amino acids [R-CH(NH₂)COOH]—glycine, dl-alanine, l-valine, and dl-leucine, were measured in the temperature range 20–90C using the hot-wire technique. The results show that the values of the thermal properties depend mainly on the amino acid concentration in the medium, the substituted alkyl group of the substances under investigation, and the temperatures. The mechanism of heat transfer is discussed, and the roles of both radiation and convection are taken into consideration.     

Personal computer-basedcamac system for data acquisition

A single board auxiliarycamac crate controller for a Z80-A based personal computer ZX-spectrum to drive thecamac crate housing multipleadc, tdc, dac and 16 I/O ports has been developed. Thecamac crate controller used in this system is of A2 type which supports multiple auxiliary crate controllers. Acamac exerciser/training software for the use ofcamac commands in process control as well as data acquisition has been developed.     

Inherent safety concepts in nuclear power reactors

Different inherent safety concepts being considered in fast and thermal reactors are presented after outlining the basic goals of nuclear reactor safety, the ‘defence in depth’ philosophy to achieve these goals and the characteristics affecting the safety of liquid metal fast breeder and light water reactors. The inherent safety potential of fast reactors with respect to different sizes and types of fuel is also discussed. Finally, the approach proposed for the Indian Prototype Fast Breeder Reactor (Pfbr), which is in the detailed design stage, is also presented.     

Performance ofesprit in the presence of gain and phase mismatches in sensor doublets

esprit, an acronym for Estimation of Signal Parameters via Rotational Invariance Technique, is a novel method for estimating the Directions of Arrival (doa) of plane waves using an arbitrary array of sensor doublets. However,esprit requires an identical pair of sensors in each doublet, that is the gain and phase characteristics of the sensors in a doublet have to be matched, which may be difficult to ensure in practical situations. In this paper, assuming the sources to be uncorrelated, we analyse the performance ofesprit when the gain and phase characteristics of the sensors in a doublet are not identical. It is shown that the angle estimates are unbiased and expressions are derived for the variance in the estimates ofdoa, when gain and phase mismatches exist in doublets. Computer simulation results are also presented to assert the theoretical predictions.     

A novel method ofrf powder sputtering

A new method ofrf sputtering by which thin films of metals, semiconductors and insulators can be sputtered from their respective powders, has been successfully demonstrated. The films have been characterized for their surface and crystal structure using conventional methods ofsem andtem. All the films are amorphous with a relatively smooth surface topography. The relative merits and demerits of the technique have been briefly discussed.     

Study of a complex water resources system with screening and simulation models

The study describes a sequential iterative modelling process for a complex water resource system. Two types of analytical models are used to find a reasonably small set of possible systems optimal design alternatives for a complex river basin. These models are a linear programming deterministic continuous (lpdc) model and a linear programing deterministic discontinous (lpdd) model. Linear programing has been used with linear approximation of the nonlinear functions. A simulation program has been developed which continues screening on the basis of the information obtained from the linear programing model. The models are developed in the context of analysis of the Narmada river, a large river basin in India, for which in the first instance alternative combinations and capacities of six major dams have to be decided.     

Infrared absorption in spinel ferrites

Their spectra of a number of ferrites, MFe₂O₄, M(Mn, Fe, Co, Ni, Cu and Zn) have been studied at room temperature in the range 200–1000 cm⁻¹. In all the cases the spectrum consists of four bands, two of which have strong absorption while the other two have weak absorption and often appear as shoulders on the main band. However up to 20% of the inverse ferrite, the shoulder in the low energy side appears as a band. In this paper we have analysed the origin of the above bands.     

Chemical amplification — A novel approach to ultratrace analysis

The lowest concentration that can be estimated with 100% error in chemical analysis by instrumental technique is referred to as detection limit. It is equal to the ratio of twice the background signal to the magnitude of analytical signal corresponding to a concentration of unity. Detection limit (dl) could be improved if the analytical signal alone could be selectively amplified without affecting the background. It is shown that this could be achieved by chemical amplification. Atomic amplification of two or three orders of magnitude could be obtained by combining two chemical amplifications in series. It is demonstrated that by using heteropoly acid formation as the first amplification reaction and determining molybdenum in the heteropoly acid by catalyticdc polarographic wave, a detection limit for the hetero atom of less than a ppb can be obtained. It is pointed out that the approach of selectively amplifying analytical signals by tandem chemical amplification reactions makes it possible to perform ultratrace analysis (ppb level) with classical instrumental analytical techniques which havedl at ppm level.     

Thetranair rectangular grid approach to solving the nonlinear full-potential equation about complex configurations

This paper describestranair, a numerical method that uses a rectangular grid to solve the nonlinear full-potential equation about general complex configurations. The grid is locally refined to resolve the high velocity gradients arising from leading edge expansions or shock waves. The grid penetrates the boundary (described by networks of quadrilateral panels) and is generated automatically. Discrete operators are constructed using the finite element method. The system of nonlinear discrete equations is solved iteratively using an orthogonal conjugate gradient method preconditioned by an exterior Poisson solver and a direct sparse solver. The primary emphasis of this work is to provide design engineers with an aerodynamics analysis tool (thetranair code) which is as accurate, reliable, economical, and flexible to use as panel methods. Results obtained by usingtranair to analyse several interesting configurations are presented. This work was supported in part bynasa (Contractnas2-12513) and theirad funds of The Boeing Company.     

Advances in the acoustics of flow ducts and mufflers

This review paper deals with advances made in the last two decades in the acoustics of flow ducts for heating, ventilation and air-conditioning (hvac) systems and engine mufflers. The context, concepts, methods used and results have been highlighted. Frequency-domain one-dimensional analysis of reflective mufflers has been emphasized because of its basic importance and wide application. Finally, problems needing further research have been identified.     

On the mechanism of pairing in thebcs theory

An explanation has been offered for the mechanism of cooper pairing in thebcs theory of superconductivity on the basis of the relativistic Darwin interaction. The theory leads to an expression for critical temperature which depends on a few atomic parameters. Calculated values ofT _c for elements and alloys are in good agreement with experiment.     

Fuzzy medial axis transformation (fmat): Image representation,skeleton extraction and uncertainty management in computer vision

The problem of extraction of medial axis transformation of a gray image with reference to skeletonization, image representation and uncertainty management in a vision system has been addressed. The Fuzzy Medial Axis Transformation (fmat) of a fuzzy setf is a set of fuzzy disks whose sup isf. Unfortunately, specifying thefmat sometimes requires more storage space than specifyingf itself. The present paper describes some techniques to improve the compact representation offmat; thereby making it practically useful to an image for its skeleton extraction and compact representation, for shape analysis and template matching, for representation and retrieval, for uncertainty management in recognition and for creating new images of various poses. The algorithms involve reduction of redundancy infmat, its approximation, and reduction of the searching spaces for its computation. Computational aspects for the convenience of writing an efficient program have been described. Some applications of thefmat have also been mentioned. This work was done while SKP held annrc-nasa Senior Research Associateship at the Lyndon B Johnson Space Center, Houston, Texas.     

Radiation-induced modification of polyurethane with hydroxyethyl methacrylate: blood compatibility

An attempt is made to develop the hydrophilic grafting of polyether urethane urea with hydroxyethyl methacrylate (hema) using⁶⁰Coγ-irradiation for achieving optimum hydrophilic/hydrophobic property needed towards blood compatibility. Contact angle method and platelet adhesion from calf’s blood are used to determine the suitability of these modified surfaces.     

Transistors made in laser recrystallized polysilicon on insulator films

lpcvd polycrystalline silicon films were deposited on thermally oxidized silicon as well as onlpcvd silicon nitride deposited on silicon. Acw argon ion laser was used to recrystallize the polysilicon film into large grains (grain size from 5μm to 40μm). Boron was then implanted and standard N-channel silicon gate process and N-channel metal gate process were carried out to realisemosfets on this material. Channel mobilities upto 450 cm²/V-sec for electrons have been measured. This thin filmmosfet has a four-terminal structure with a top and a bottom gate and the influence of one gate on the drain current due to the other gate has been investigated. Comparison of theI _D v-V _D curves of the devices with physical models was found in good agreement.     

Recent advances in open cycle MHD electrical power generation

The report attempts to summarise the recent developments in the field ofmhd electric power generation and identify the problem areas needing further R and D efforts to achieve commercial acceptance of the process. During the last two decades there has been active interest in the development of this technology. A large volume of literature is available in published form, apart from the unpublished information of commercial value. Judging from this standpoint this report cannot be considered exhaustive. Nevertheless it integrates the scattered information in a condensed volume which would be useful in extrapolating the future trends of development while assessing the present status of the technology. To make this report self-contained and complete, the fundamental principles ofmhd power generation have also been included. Themhd project in India is fully sponsored by the Department of Science and Technology under whose auspices this report has been prepared.     

Applications of scanning transmission electron microscope microanalysis in the study of materials

The dedicatedstem equipped with field emission electron source, affords opportunities for the acquisition of microchemical and microstructural data on a scale approaching the nanometer level. In this presentation, a number of applications of microchemical analysis and microdiffraction to engineering materials will be discussed, with major emphasis on high-strength low-alloy steels, steels for high formability in automotive applications, and aluminium alloys. Some advantages and limitations of the technique are noted, especially for application to analysis of electrochemically prepared thin foils, and to the analysis of extracted particles.     

Elastic properties of As-Sb-Se glasses

Results of measurement of elastic modulii on As-Sb-Se glasses are reported and their composition dependence discussed. The Young’s and the shear modulii lie in the range of 170–210 and 65–80 kb respectively. These values are typical of chalcogenide glasses. For (As, Sb)₄₀Se₆₀ glasses, the modulii increase monotonically with increasing Sb₂Se₃ content. The observed composition dependence of the modulii for the As _x Sb₁₅Se_{85 −x} glasses is examined in terms of the chemically ordered structural units in the glasses.     

Analysis of high temperature gasdynamics in a rectangular channel using a coupled core-boundary layer model

In this paper two-dimensional steady state compressible, turbulent boundary layer equations along with the core are solved for a channel of rectangular cross-section. The behaviour of core velocity, core temperature, pressure profile, friction coefficient and heat flow for different mass flow rates and inlet pressures are analysed for combustion gases. The results are compared with experimental results obtained onzinc (zero induction channel) during the commissioning of themhd plant at Tiruchirapalli. The results match the theoretical predictions quite well.