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Research aimed at improving spacecraft attitude estimation using stand-alone star trackers has focused upon the measurement of star image on CMOS APS array. The precision and speed of the star identification process from the image of stars is the critical issue. An algorithm for star pattern identification, using a star catalog, the database with information about individual stars, and a set of derived catalogs to provide information regarding the attributes of star pairs, is presented. A star pair is designated with the inter-star angular displacement and the scaled difference between their corresponding visual magnitudes. This algorithm is developed for general lost-in-space conditions and further extended for normal mode of operation to track the stars in the field of view.

Minimization of car vibrations has been a topic of research over the years and many control strategies have been developed. Therefore, there needs to be a method for active vibration control in cars. This paper presents two methods for designing the controller for a quarter car model which would help in minimizing car vibrations and increasing passenger comfort subjected to road disturbances. The methodologies used are H-infinity and H-2 optimal control. The main aim of this article is to design a controller to control the response of a quarter car model to various road inputs. This is a non-linear model with 2 degrees of freedom. It is linearized and modelled as a disturbance rejection (regulatory) problem wherein the effect of disturbances are minimised. Different weighing functions have been considered to take the impact of road disturbances into account. The results are compared with the Proportional Integral Derivative (PID) controller designed using the same system parameters and performance specifications. The behaviour of the open loop and closed loop system is observed by examining the impulse and frequency responses in MATLAB. A detailed discussion is done with the choice of weighing functions. It is found that the disturbance rejection techniques suggested in this paper help in improving the system response

This paper aims at determining the fundamental frequency of square perforated plate with square perforation pattern of square holes. Rayleigh’s method is used for the solution of this problem. Non homogeneity in Young’s modulus and density at the perforation is expressed by using greatest integer function i.e. floor function. Boundary condition considered is clamped on all edges. Perforated plate is considered as plate with uniformly distributed mass and holes are considered as non homogeneous patches. The deflected surface of the plate is approximated by a function which satisfies the boundary conditions. Finite Element Method (FEM) modal analysis is carried out to validate the results of the proposed approach.

Torque transmitted from rim to the shaft through the arms of the pulley is analyzed in this paper. Dynamic and vibration response of the arm of the pulley of a belt drive is studied by transferring the system to equivalent spring, mass and damper system. The number of arms present in the load zone is assumed to take charge of the load zone angle equally as they appear in the load zone. Hence, the arms are subjected to stepped load wave. The arm is considered as a tapered cantilever beam fixed at the hub and stepped loading at the rim end. Response of this equivalent system is studied by varying equivalent damping coefficient from 0 to 5·0. This investigation aims at getting a cursory idea of the maximum stress due to vibration.The natural frequency of equivalent system is compared with that of tapered cantilever beam to check its accuracy.

The effect of 2 mol % of P2O5 or TiO2 on the crystallization of yttrium-iron-garnet (YIG) in Na2O-SiO2-Y2O3-Fe2O3 glass ceramics has been investigated by X-ray and Mössbauer spectroscopic studies. These studies indicate that the glass ceramics containing P2O5 are more favourable for the crystallization of YIG. Analysis of the results suggest that an optimum growth temperature for crystallization of the YIG phase is 800° C in the sample with P2O5 as the nucleating agent. The sample heat-treated at the growth temperature for 40 h is not as favourable for crystallization of the YIG phase as the sample which is given a two-stage heat-treatment.

Mössbauer spectroscopic studies have been performed on glass ceramics in which barium and strontium hexaferrites have been crystallized as a major magnetic phase. The crystallization process of the different magnetic phases has been studied by suitable heat treatments of the initial glass compositions 35BaO-40B2O3-25Fe2O2, 35SrO-40B2O3-25Fe2O3 and 47SrO-28B2O3-25Fe2O3. The nucleation and growth times have been varied and Mössbauer spectra of differently heat-treated samples analysed to determine the optimum composition and heat treatment required for the good growth of the hexagonal ferrites BaM and SrM.

Mössbauer, EPR and magnetization experiments have been carried out on the glass composition Na2O-SiO2-Fe2O2-Y2O3 in which yttrium iron garnet (YIG) can be precipitated by suitable heat-treatment. The measurements have been carried out on the as-quenched sample as well as samples heat-treated for 4 h at 400, 500, 600, 650, 700, 750, 810 and 850‡ C. Mössbauer spectra from the as-quenched sample as well as the first six samples showed a quadrupole splitting while the last two samples, as well as the sample heat-treated (i) by a two-stage process at 600‡ C and then at 750‡ C for 4 h each, and (ii) at 700‡ C for 40 h, showed a hyperfine as well as quadrupole splitting. The behaviour of the isomer shift (IS) and quadrupole splitting (dE) with the heat-treatment temperature show significant changes at the glass transition and crystallization temperatures. The Mössbauer data have been found consistent with optical and electron micrographs which show a large variation in particle size of the precipitated magnetic phase. This has been further correlated with EPR and magnetization data.

The system Y3-xGdxFe5O12(x = 0, 0.5 and 3.0) synthesized through an amorphous citrate gel process has been investigated by Mössbauer and EPR spectroscopy. These studies delineate the co-ordination, symmetry, valence and relaxation phenomena which in turn give information on the growth of garnet and other phases in the above system. Furthermore these studies help in finding the optimum growth conditions for the garnet phase.

The peak value of the Comptonp rofile, J(0), is equal to 1/2 〈p-1〉, the moment of the electron momentum distribution. It has been experimentally observed by Weiss (1973) and by Manninen and Paakkari (1974) that for 3d transition metals the values of J(0) are roughly constant. We have calculated the Compton profiles J(q) for the 3d transition metals Sc, Ti, V, Cr, Fe, Co, Ni and Cu for different outer electron configurations 3dn-x 4sx (with x = 0·75, 1·00, 1·25, 1·50, 1·75 and 2·00) using a renormalized-free-atom model. Our calculations also show that J(0) is roughly constant for the 3d transition metals for each configuration. Tables of theoretical Compton profiles for these metals for different configurations are given.

Positron lifetime spectroscopy has been applied to study the temperature dependence of free-volume properties in a solvent-free polymer–salt complex polyethylene oxide (PEO) doped with ammonium iodide (NH4I, with $NH^{+}_{4}/EO$ ≈ 0.076) in the temperature range of 298–353 K. The observed lifetime spectra were resolved into three components and the longest lifetime, τ3, was associated with the pick-off annihilation of ortho-positronium (o-Ps) trapped by the free volume. The lifetime component, τ3, and its intensity, I3, both showed a significant variation with temperature, which followed a different course in the heating and cooling cycle. Changes in the temperature coefficient of τ3 and I3 were observed at T ≈ 328 K, the melting point of the sample. This behaviour is correlated to the temperature variation of the electrical conductivity. © 1998 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 36: 969–976, 1998

Phase-precipitation studies have been performed on samples of the metallic glasses Fe79B16Si5 and Fe78B13Si9, heated in the range 300–475 °C for various times (1–16 h) using 57Fe Mössbauer transmission spectroscopy and X-ray diffraction methods. These measurements have helped in identifying the temperature ranges and annealing durations in which the amorphous structure of these metallic glasses is retained. The results revealed that the thermal stability increases as boron is replaced by silicon in the Fe-B-Si metallic glasses and that these alloys remain amorphous below 450 °C. The various phases precipitated above this temperature were identified as a-Fe, a-(Fe, Si), Fe3B, and Fe2B. The direction of magnetization in the two metallic glasses appears to change upon annealing.