Investigation of capacitor-excited induction generators and permanent magnet alternators for small scale wind power generation

This paper examines two electric generator options for use in autonomous wind systems producing asynchronous electric power. The first makes use of a capacitor-excited squirrel-cage induction generator feeding a battery bank and an induction motor driven centrifugal pump. The second uses a permanent magnet alternator. Results obtained from field tests and laboratory experiments are included.A model to calculate the wind energy captured by a commercial 5 kW wind turbine, used in the field tests, is presented. This information is then used in a cost benefit analysis based on the present value method.     

On the choice of hexagonal boron nitride for high pressure phase transformation using the catalyst solvent process

The degree of three-dimensional ordering, particle-size distribution and purity of two types of hexagonal boron nitride have been studied with a view to establish any possible correlation between these characteristics with the conversion of hexagonal form to cubic phase at high pressure and high temperature using magnesium as the catalyst solvent. The crystalline phases formed at high pressure and high temperature have been studied and the dependence of degree of graphitization of boron nitride and purity on the cubic boron nitride conversion discussed.     

Properties of conducting zinc oxide films prepared by R.F. Sputtering

An effective method of dopant incorporation in rf sputtered ZnO film is reported. The electrical, optical and structural properties of zinc doped ZnO films are investigated. Electron mobility of∼10 cm² /V-sec and electron concentration of∼10¹⁹ cm⁻³ have been measured at room temperature. X-ray diffraction data obtained on films prepared on Corning 7059 glass show (002) peak, dominating. The high electrical conductivity and transmission makes ZnO films very attractive as a component for heterojunction solar cells.     

The effect of electrode films on the electrical resistance of thin tin films

The variation in resistance of thin films of tin deposited onto glass substrates was studied using pre-deposited gold, silver, aluminum and tin electrodes. The percentage variation in resistance of the tin films was found to be different for the different electrode materials. The structural features of the tin-electrode film junctions were investigated using optical and scanning electron microscopes. The difference between the variations in resistance with time for different electrode films is explained on the basis of interdiffusion, alloy formation and oxidation at the electrode film junctions.     

Experimental 1.5 μm coherent optical fibre transmission systems

The authors consider the design requirements for 1.52 μm coherent optical fibre transmission systems. Some of the essential requirements are: narrow linewidth sources, polarisation stable transmission media, low insertion loss optical mixers and frequency tracking or phase locked local oscillators. Having been successful in reducing the linewidth of semiconductor lasers to less than 30 kHz, by using injection locking techniques, and in fabricating optical mixers with insertion losses of the order of dB, they have been able to experiment with coherent optical fibre transmission systems to assess their practicability. In this paper it will be shown that coherent systems can be operated over long lengths of conventional low loss monomode fibre without any polarisation penalty and give far better performance than direct detection systems.     

Rectified catadioptric stereo sensors

It has been shown elsewhere how mirrors can be used to capture stereo images with a single camera, an approach termed catadioptric stereo. We present novel catadioptric sensors that use mirrors to produce rectified stereo images. The scanline correspondence of these images benefits real-time stereo by avoiding the computational cost and image degradation due to resampling when rectification is performed after image capture. First, we develop a theory which determines the number of mirrors that must be used and the constraints on those mirrors that must be satisfied to obtain rectified stereo images with a single camera. Then, we discuss in detail the use of both one and three mirrors. In addition, we show how the mirrors should be placed in order to minimize sensor size for a given baseline, an important design consideration. In order to understand the feasibility of building these sensors, we analyze rectification errors due to misplacement of the camera with respect to the mirrors     

Development and operation of a high current density high pressure advanced electrolysis cell

This paper deals with the development work in Bhabha Atomic Research Centre, India, on alkaline water electrolysis cells. Indigenous development of an advanced type, high amperage, high pressure electrolyser using porous nickel electrodes for tonnage production of hydrogen is described. Methods of producing porous nickel plaques and other cell components are also presented. Operation and performance characteristics of the cells are reported.     

Polarization-based vision through haze

We present an approach for easily removing the effects of haze from passively acquired images. Our approach is based on the fact that usually the natural illuminating light scattered by atmospheric particles (airlight) is partially polarized. Optical filtering alone cannot remove the haze effects, except in restricted situations. Our method, however, stems from physics-based analysis that works under a wide range of atmospheric and viewing conditions, even if the polarization is low. The approach does not rely on specific scattering models such as Rayleigh scattering and does not rely on the knowledge of illumination directions. It can be used with as few as two images taken through a polarizer at different orientations. As a byproduct, the method yields a range map of the scene, which enables scene rendering as if imaged from different viewpoints. It also yields information about the atmospheric particles. We present experimental results of complete dehazing of outdoor scenes, in far-from-ideal conditions for polarization filtering. We obtain a great improvement of scene contrast and correction of color.     

Clustered blockwise PCA for representing visual data

Principal component analysis (PCA) is extensively used in computer vision and image processing. Since it provides the optimal linear subspace in a least-square sense, it has been used for dimensionality reduction and subspace analysis in various domains. However, its scalability is very limited because of its inherent computational complexity. We introduce a new framework for applying PCA to visual data which takes advantage of the spatio-temporal correlation and localized frequency variations that are typically found in such data. Instead of applying PCA to the whole volume of data (complete set of images), we partition the volume into a set of blocks and apply PCA to each block. Then, we group the subspaces corresponding to the blocks and merge them together. As a result, we not only achieve greater efficiency in the resulting representation of the visual data, but also successfully scale PCA to handle large data sets. We present a thorough analysis of the computational complexity and storage benefits of our approach. We apply our algorithm to several types of videos. We show that, in addition to its storage and speed benefits, the algorithm results in a useful representation of the visual data.