Showing papers by "Indian Institute of Technology Madras published in 1992"
TL;DR: A method of spectrum estimation using group delay functions is proposed that exploits the additive property of the Fourier transform (FT) phase to extract spectral information of the signal in the presence of noise.
Abstract: A method of spectrum estimation using group delay functions is proposed. This method exploits the additive property of the Fourier transform (FT) phase to extract spectral information of the signal in the presence of noise. The phase is generally featureless due to random polarity and wrappings, but the group delay function can be processed to derive significant information such as peaks in the spectral envelope. In the resulting spectral estimates obtained the resolution properties of the periodogram estimate are preserved while the variance is reduced. Variance caused by the sidelobe leakage due to windows and additive noise are significantly reduced even in the spectral estimate obtained using a single realization of the observation peak. Resolution is primarily dictated by the size of the data window. The method works even for high noise levels. The results of this procedure are demonstrated through two illustrative examples: estimation of sinusoids in noise and estimation of the narrowband autoregressive process in noise. >
136 citations
TL;DR: In this article, three heuristic algorithms for flow shop scheduling with the objective of minimizing total flowtime are presented, and the proposed algorithms are found to give consistently near-optimal solutions and fare better than the existing methods.
115 citations
TL;DR: An algorithm based on simulated annealing is presented to solve the machine-component grouping problem for the design of cells in a manufacturing system and it is found that it fares better for large problems.
97 citations
TL;DR: In this paper, a one-dimensional mathematical model for heat and mass transfer in metal hydride beds of annular cylindrical configuration is presented in dimensionless form, covering a wide range of alloys and operating conditions.
87 citations
TL;DR: Mixed metal oxides are more advantageous and are better catalytic materials than simple oxides because of the crystal structure can accomodate various metal ions and can stabilize unusual and mixed valence states of active metal ion; appropriate formulation of these oxides leads to easy tailoring of many desirable properties such as valence state of transition metal ion, distance between active sites, binding energy, diffusion of oxygen in the lattice, magnetic and conducting properties of the solid.
Abstract: Mixed metal oxides crystalizing in a perovskite-related structure have long been of interest to solid state chemists and physicists because of their technologically important physical properties. The ready availability of a family of isomorphic solids with controllable physical properties makes these oxides suitable for basic research in catalysis. These mixed metal oxides are more advantageous and are better catalytic materials than simple oxides because: (i) the crystal structure can accomodate various metal ions and can stabilize unusual and mixed valence states of active metal ion; (ii) appropriate formulation of these oxides leads to easy tailoring of many desirable properties such as valence state of transition metal ion, distance between active sites, binding energy, diffusion of oxygen in the lattice, magnetic and conducting properties of the solid; (iii) the catalytic activity can be correlated to solid state properties since many of their solid state properties are thoroughly understood...
73 citations
TL;DR: In this paper, a computerized method for the whole-field determination of isoclinic and isochromatic parameters in a stressed photoelastic model is presented The intensity data obtained from the fringe pattern at three analyzer positions (0, 45, and 90 degrees) in a plane polariscope, are used for the computations.
Abstract: A new computerized method for the whole-field determination of isoclinic and isochromatic parameters in a stressed photoelastic model is presented The intensity data obtained from the fringe pattern at three analyzer positions (0, 45, and 90 degrees) in a plane polariscope, are used for the computations The relationships between the intensity values and the photoelastic parameters are derived using Stokes representation of polarized light The experiments were carried out using a computer-based image-processing system The accuracy achieved is assessed by comparing the theoretical and measured values Accuracies of within ±3 degrees for isoclinics and ±005 fringe for isochromatics are shown to be possible
60 citations
TL;DR: In this article, Fan's best approximation theorem was extended to a class of factorizable multifunctions, which has been of great importance in nonlinear analysis, game theory, and minimax theorems.
Abstract: A well-known Ky Fan's best approximation theorem which has been of great importance in nonlinear analysis, game theory, and minimax theorems is extended to a class of factorizable multifunctions.
57 citations
TL;DR: In this paper, a branch-and-bound algorithm for obraining a permutation schedule for the multi-stage flowshop with parallel processors is presented, with a view to achieving the practical objective of minimizing total flowtime.
57 citations
TL;DR: This paper presents a branch-and-bound algorithms for scheduling in the flowshop with parallel processors and relaxes the assumption that every stage has a single processor.
49 citations
TL;DR: This article presents a branching algorithm with effective dominance rules to obtain the optimal schedule for replacements to minimize the total cost for a given planning period.
Abstract: The problem of imperfect preventive maintenance (pm) and replacement schedule for a system which works below a specified failure rate is studied. For a given planning period, the optimal schedule for replacements to minimize the total cost is obtained. This article presents a branching algorithm with effective dominance rules to obtain the optimal schedule. Numerical illustration and computational experience are also presented.
48 citations
TL;DR: A new and simple technique for the determination of the focal length of positive lenses and concave spherical surfaces by Talbot interferometry is described and it is shown that high measurement accuracy can be achieved with this technique.
Abstract: A new and simple technique for the determination of the focal length of positive lenses and concave spherical surfaces by Talbot interferometry is described. Results of measurements are presented. We show that high measurement accuracy can be achieved with this technique.
TL;DR: In this article, the wave transmission and reflection by a partially immersed rigid vertical barrier was studied in detail in deep water conditions by measuring the transmitted and reflected wave histories, and the experimental investigations were carried out for a wide range of wave steepness, at different depths of immersion of the barrier in a wave flume 0.3 m wide, 10 m long and in a constant water depth of 0.8 m at Ocean Engineering Centre, Indian Institute of Technology, Madras, India.
TL;DR: In this article, a Petri net model is used to construct the reachability graphs used in flexibility measurement, and the contribution of each factor to the value of a given type of flexibility is estimated using the analytic hierarchy process (AHP).
Abstract: This paper develops an analytical approach to quantifying manufacturing system flexibility (MSF). Measures of flexibility, namely, producibility, processivity, transferability and introducibility are developed based on a state-transition formalism, the reachability graph. The uncertainty in system operating conditions is specified in terms of certain disturbing factors, external and internal to the system, which impinge on system performance. The contribution of each factor to the value of a given type of flexibility is estimated using the analytic hierarchy process (AHP). The individual flexibility measures are thus combined to give a measure of MSF under a given operating environment. A Petri net model is used to construct the reachability graphs used in flexibility measurement. Uses of the proposed measures at the design and operational analysis stages of FMS are presented
TL;DR: In this paper, the wave transmission and reflection characteristics of a rigidly fixed surface and submerged horizontal plate were investigated experimentally in detail for a wide range of incident wave steepnesses and for different depths of submerge of the plate in deep water conditions in regular water wave fields.
TL;DR: In this paper, a wide variety of sub-mospheric flames are observed for the propellants with additives. But the results of the experiments were limited by the low-pressure deflagration limit is reduced by the addition of Fe2O3, copper chromite catalyst, LiF, and CaCO3.
Abstract: Fe2O3, copper chromite catalyst (CC), LiF, and CaCO3 are the four burning rate modifying additives considered in this study. A wide variety of subatmospheric flames are observed for the propellants with additives. Under subatmospheric pressures a dark zone is present; this zone becomes thicker at lower pressure and with finer ammonium perchlorate (AP) particles. A smoldering surface without a gas-phase flame is noted for the additive Fe2O3. From the smoke deposits, obtained from the subatmospheric burning of propellants with burning rate enhancers, it is shown that the breakdown of heavy fuel molecules is better with finer AP particles. The low-pressure deflagration limit is reduced by the addition of Fe2O3 or CC and increased by the addition of LiF or CaCO3. In the presence of LiF or CaCO3, above certain additive concentration levels, reduction in AP particle size is found to depress the burning rate further. LiF, below certain concentration levels, acts as a burning rate enhancer up to a certain pressure and as a depressant thereafter. The type of additive influences the pressure at which the shape of burning AP surface changes from convex to concave and also the pressure at which the AP surface recesses relative to the mean surface.
TL;DR: A neural network model, viz., the Hopfield net model, is used to develop a Design Retrieval System, which has been verified with test cases on rotational as well as non-rotational parts.
TL;DR: The most suitable conditions for protoplasting were as follows: age of the organism in slant, 3 days; mycelium age, 20 h; volume of lytic enzymes, 190 ml;Mycelial weight (dry equivalent), 1.66 g; time of contact with lytic enzyme, 2 h; temperature of protoplasts, 30°C; phosphate buffer, 25 m m , pH 6.5; KCl as osmotic stabilizer, 0.7 m
TL;DR: A city‐pair model for the demand for domestic air travel has been developed based on the air travel in 40 city pairs in India and was used to predict futu...
Abstract: Forecasting of air travel demand using demand models enables better planning for infrastructure development for air transportation. Modeling for air travel demand is the process of relating a vector of socioeconomic variables and a vector of transport system variables to the demand for air travel. In microanalysis of air travel demand, when models are stratified by origin and destination, the resulting models are called city‐pair models. In this study, a city‐pair model for the demand for domestic air travel has been developed based on the air travel in 40 city pairs in India. The model was calibrated with aggregate cross‐sectional data using multiple linear regression analysis. The model has been validated by two different procedures: the cross‐validation technique and a backward prediction method to know the statistical and logical validity of the model for use in travel demand forecasting. As an illustration of the usefulness of the model in travel demand forecasting, the model was used to predict futu...
TL;DR: The dc Kerr constant and the pretransitional temperature of a polar nematic liquid crystal 4-(trans-4'-4'-n-pentylcyclohexy)-benzonitrile (PCH-5).
Abstract: In this paper we report the dc Kerr constant and the pretransitional temperature of a polar nematic liquid crystal 4-(trans-4'-4'-n-pentylcyclohexy)-benzonitrile (PCH-5). The observed second-order pretransitional temperature ${\mathit{T}}^{\mathrm{*}}$ from our measurements is found to be 1.2 \ifmmode^\circ\else\textdegree\fi{}C below the first-order nematic to isotropic transition temperature. The dependence of the Kerr constant on (T-${\mathit{T}}^{\mathrm{*}}$${)}^{\mathrm{\ensuremath{-}}1}$ is found to be in good agreement with the predictions of the Landau--de Gennes model. The highest value of the Kerr constant observed at 632.8 nm is found to be 9.737\ifmmode\times\else\texttimes\fi{}${10}^{\mathrm{\ensuremath{-}}11}$ m ${\mathrm{V}}^{\mathrm{\ensuremath{-}}2}$, corresponding to a temperature of 55.3 \ifmmode^\circ\else\textdegree\fi{}C.
TL;DR: In this paper, a receding core model is proposed for the drying kinetics and compared with the experimental data for batch and continuous fluidized bed drying of granular cellular materials.
TL;DR: In this article, the authors carried out catalytic decomposition of N2O on oxides having dalofossite structure CuMO2; (M=Al, Cr or Fe) at 50 and 200 torr initial pressure in the temperature range 380-480 °C.
Abstract: Catalytic decomposition of N2O has been carried out on oxides having dalofossite structure CuMO2; (M=Al, Cr or Fe) at 50 and 200 torr initial pressure of N2O in the temperature range 380–480 °C. CuFeO2 showed higher activity while CuCrO2 showed low conversion in the temperature range studied. The variation in activity has been explained based on the presence of mixed valence copper and the concentration of copper on the surface as evinced from X-ray photoelectron spectroscopy.
TL;DR: In this article, a cost model and a branching algorithm are proposed to determine the number of preventive maintenance interventions to be performed between each replacement and the number such replacements during the planning period to minimize the expected total cost.
TL;DR: A simple method for measuring the radius of curvature by using Talbot interferometry in a noncollimated light beam and can also be used to determine the focal length of the collimating lens employed in the setup.
Abstract: We describe a simple method for measuring the radius of curvature by using Talbot interferometry in a noncollimated light beam. This scheme can also be used to determine the focal length of the collimating lens employed in the setup. Results of the measurements are presented. A discussion of achievable accuracies and the proper choice of parameters is included.
TL;DR: In this paper, the suitability of different theories used for vibration studies has been investigated, viz. Love's first approximation shell theory, an improved theory with shear deformation and rotatory inertia, and a shell theory with thickness normal strain and shear deformations.
TL;DR: The constitutive flow behavior of a metal matrix composite (MMC) with 2124 aluminum containing 20 vol pct silicon carbide particulates under hot-working conditions in the temperature range of 300 °C to 550 °C and strain-rate range of 0.001 to 1 s-1 has been studied using hot compression testing.
Abstract: The constitutive flow behavior of a metal matrix composite (MMC) with 2124 aluminum containing 20 vol pct silicon carbide particulates under hot-working conditions in the temperature range of 300 °C to 550 °C and strain-rate range of 0.001 to 1 s-1 has been studied using hot compression testing. Processing maps depicting the variation of the efficiency of power dissipation given by [2m/(m + 1)] (wherem is the strain-rate sensitivity of flow stress) with temperature and strain rate have been established for the MMC as well as for the matrix material. The maps have been interpreted on the basis of the Dynamic Materials Model (DMM). [3] The MMC exhibited a domain of superplasticity in the temperature range of 450 °C to 550 °C and at strain rates less than 0.1 s-1. At 500 °C and 1 s-1 strain rate, the MMC undergoes dynamic recrystallization (DRX), resulting in a reconstitution of microstructure. In comparison with the map for the matrix material, the DRX domain occurred at a strain rate higher by three orders of magnitude. At temperatures lower than 400 °C, the MMC exhibited dynamic recovery, while at 550 °C and 1 s-1, cracking occurred at the prior particle boundaries (representing surfaces of the initial powder particles). The optimum temperature and strain-rate combination for billet conditioning of the MMC is 500 °C and 1 s-1, while secondary metalworking may be done in the super- plasticity domain. The MMC undergoes microstructural instability at temperatures lower than 400 °C and strain rates higher than 0.1 s-1.
TL;DR: In this paper, the effect of aging on the microstructural stability of Alloy D9 was studied as a function of the amount of cold work and the Larson-Miller parameter.
TL;DR: In this article, the authors measured the volumetric mass transfer coefficient in a down flow jet loop reactor with Newtonian and non-Newtonian systems, and found that volumeetric mass transferred coefficient increase in gas and liquid flow rates, and nozzle diameter.
TL;DR: In this article, the dynamic Jahn-Teller distortion in single crystals of CuII doped magnesium Tutton's salt, MgK2(SO4)2·6H2O was studied by EPR spectroscopy.
TL;DR: In this paper, the axisymmetric and non-symmetric vibrations of spherical shells are analyzed using the thick shell theory and a semi-analytical method is used to reduce the dimension of the problem.
TL;DR: In this paper, a model based on the Marciniak-Kuczynski (M-K) hypothesis was proposed for predicting the formability of sheet metals. But the model only takes into account a single mode of strain localization and it has not yet led to accurate predictions.