Sensitivity oftls and minimum norm methods ofdoa estimation to errors due to either finite data or sensor gain and phase perturbations

In thedoa (direction of arrival) estimation problem, we encounter either finite data or insufficient knowledge in array characterisation or both. It is therefore important to study how the subspace-based methods perform under these conditions. In this paper, we first consider the finite data case and establish two results: (i) the total least-squares approach to the linear prediction method (which we refer to astls-flp method) is equivalent to the minimum norm (min. norm), method and (ii) thetls-fblp method yields a 3 dB lower mean-square error (mse) in thedoa estimates as compared to thetls-flp method. Next, we consider the asymptotic performance of the min. norm method in the presence of sensor gain and phase perturbations, and derive the expressions for themse in thedoa estimates assuming an uniform linear array. For the special case of a single source, we also obtain a simple and explicit expression for themse which, when compared with the corresponding result for themusic algorithm, shows that the min. norm method is more sensitive than themusic when the number of sensors exceeds 2. Computer simulations are included to support the theoretical predictions. This work is supported in part by the Electronics and Radar Development Establishment, Bangalore.     

Analysis of subspace-based direction of arrival estimation methods

In this paper, a general framework for the analysis of eigen-based subspace methods is developed. It is shown that a two-step procedure can be effectively used to analyse subspace methods under fairly general conditions. The first step relates the errors in the covariance matrix to errors in the subspaces, and the second step relates error in the subspaces to the errors in the direction of arrival (doa) estimates. Combining these two steps along with the statistics of the data, expressions for the mean squared error in thedoa estimate are derived. The potential of the approach is demonstrated by analysing two subspace methods,music and the minimum-norm method. This work was supported by the USarmy Research Office under Grant No.daal-03-90-g-0095.     

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.     

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.     

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.     

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.     

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.     

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.     

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.     

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.     

Parametric study of the electrical to thermal power conversion in an inductively coupledrf plasma torch

An inductively coupled (ic) radio-frequency (rf) stabilized argon plasma was generated in a quartz tube using a 7 MHzrf generator. The electrical and thermal powers were measured and the efficiency of energy conversion was computed. The results indicate that for a constant power input, there is an optimum argon flow rate for which maximum energy conversion efficiency occurs.     

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.     

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.     

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.     

Measurement of Specific Fracture Energy and Surface Tension of Brittle Materials in Powder Form

Studies of the influence of specimen geometry and size–effect on the K _R –curves and the related fracture parameters were carried out by the authors (Kumar and Barai 2008b). The present paper is a supplementary contribution and reports interesting results related to the effect of the loading condition and size–effect studies on the K _R –curves associated with the cohesive stress distribution for complete fracture process, the double–K fracture parameters, the CTOD–curves and the process zone length using two different loading conditions (i.e., three–point bending test and four–point bending test). The laboratory size specimen with initial–notch length/depth ratios 0.3 and 0.5 are considered in the work. The load–crack opening displacement curves for these loading conditions are obtained using well known version of fictitious crack model.     

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.     

Utilising high throughput technologies for the determination of the reaction network of the <Emphasis Type="SmallCaps">l</Emphasis>-proline catalysed aldol reaction

The objective of this work is to facilitate the determination of a reliable reaction network for the l-proline catalysed aldol reaction using high throughput technologies (HTT). The availability of reliable reaction network is fundamental to predictive kinetic modelling including scale up, replacing a batch process with a continuous one, optimisation, thermal safety, process simulation, etc. The extent to which HTT experiments may be used to provide the necessary quantitative understanding of both physical and chemical phenomena of the system studied is assessed through a four stage development programme. For this particular system it is shown that, in conjunction with appropriate experimental designs, meaningful data streams for mechanistic/kinetic studies can be generated. The experimental data allowed a reaction network for the l-proline catalysed aldol reaction to be proposed and verified through a kinetic modelling exercise.

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.     

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.     

Optimization design of the split doublet using the shape factors of the third-order aberrations for a thick lens

Abstract

An improved optimization method is presented for doublet design using the shape factor of the third-order aberrations of a thick lens to compensate high-order aberrations. This method can effectively evaluate a minimal area of aberration curves bounded by the ray-fan diagram. For the proposed optimization program, taking the RMS value of the spot diagram to be less than the diffraction limited value of the point spread function (PSF) as the evaluated criterion is suggested. The design specifications for the optimized doublet are F/3.333 and semi-field angle of 1°, within the visible spectral range. Two design examples of the doublet, one a glass lens and the other a plastic lens, are presented. The results show well-designed doublets when compared with Kingslake's design.