Showing papers by "Indian Institute of Technology Bombay published in 1994"
TL;DR: In this article, the authors reported the discovery of bulk superconductivity at rather high (g10 K) values in samples having nominal compositions (i.e., they had nickel in large proportions) and showed that these materials are distinct superconductors.
Abstract: We report here our discovery of bulk superconductivity at rather high ${\mathit{T}}_{\mathit{c}}$ in samples having nominal compositions ${\mathrm{YNi}}_{4}$${\mathrm{BO}}_{0.2}$ (${\mathit{T}}_{\mathit{c}}$\ensuremath{\approxeq}12.5 K) and ${\mathrm{YNi}}_{2}$${\mathrm{B}}_{3}$${\mathrm{O}}_{0.2}$ (${\mathit{T}}_{\mathit{c}}$\ensuremath{\approxeq}13.5 K). While ${\mathrm{YNi}}_{4}$${\mathrm{BC}}_{0.2}$ seems to be a single phase material, ${\mathrm{YNi}}_{2}$${\mathrm{B}}_{3}$${\mathrm{C}}_{0.2}$ is a multiphase system. Our experimental results show that the two materials are distinct superconductors. Discovery of superconductivity in these materials is of significance since not only is their ${\mathit{T}}_{\mathit{c}}$ high (g10 K) but they also have nickel in large proportions. No nickel-based ternary superconductor was previously known.
535 citations
TL;DR: High quality pseudorandom pattern generators built around rule 90 and 150 programmable cellular automata with a rule selector has been proposed as running key generators in stream ciphers, both the schemes provide better security against different types of attacks.
Abstract: This paper deals with the theory and application of Cellular Automata (CA) for a class of block ciphers and stream ciphers. Based on CA state transitions certain fundamental transformations are defined which are block ciphering functions of the proposed enciphering scheme, These fundamental transformations are found to generate the simple (alternating) group of even permutations which in turn is a subgroup of the permutation group, These functions are implemented with a class of programmable cellular automata (PCA) built around rules 51, 153, and 195. Further, high quality pseudorandom pattern generators built around rule 90 and 150 programmable cellular automata with a rule selector (i.e., combining function) has been proposed as running key generators in stream ciphers, Both the schemes provide better security against different types of attacks. With a simple, regular, modular and cascadable structure of CA, hardware implementation of such schemes idealy suit VLSI implementation. >
381 citations
TL;DR: The thermodynamics of binding of concanavalin A with a series of linear and branched chain oligosaccharides including certain N-linked complex type and oligomannose type carbohydrates and a fraction of quail ovalbumin containing Man7 and Man8 oligomANNose chains have been determined using titration microcalorimetry.
Abstract: The thermodynamics of binding of concanavalin A (Con A) with a series of linear and branched chain oligosaccharides including certain N-linked complex type and oligomannose type carbohydrates and a fraction of quail ovalbumin containing Man7 and Man8 oligomannose chains have been determined using titration microcalorimetry. Methyl3,6-di-O-(alpha-D-mannopyranosyl)-alpha-D-mannopyranoside, a branch chain trisaccharide moiety found in all N-linked carbohydrates which possesses approximately 60-fold higher affinity than methyl alpha-D-mannopyranoside, exhibited a change in enthalpy of binding (delta H) of -14.4 kcal mol-1 as compared to -8.2 kcal mol-1 for the monosaccharide. This demonstrates that Con A possesses an extended binding site for the trimannoside. However, a biantennary complex type carbohydrate with terminal beta (1,2)-GlcNAc residues which binds with 3-fold higher affinity than the trimannoside possesses a delta H of only -10.6 kcal mol-1. A plot of -delta H versus -T delta S for the carbohydrates in the present study showed positive deviations in -T delta S for the complex type carbohydrate, as well as alpha (1,2)-di- and trimannosyl oligosaccharides which are part of the structures of oligomannose type carbohydrates. The relative favorable changes in binding entropies of these compounds are attributed to the presence of multiple internal and terminal residues in each molecule which can independently bind to the monosaccharide binding site of the lectin. The delta H values for the complex type carbohydrate and the alpha (1,2) mannose oligosaccharides were also approximately -2.5 kcal mol-1 greater than that of methyl alpha-D-mannopyranoside, indicating some extended binding site interactions.(ABSTRACT TRUNCATED AT 250 WORDS)
262 citations
01 Jun 1994
TL;DR: This contribution investigates local differential techniques for estimating optical flow and its derivatives based on the brightness change constraint by using the tensor calculus representation and builds the Taylor expansion of the gray-value derivatives as well as of the optical flow in a spatiotemporal neighborhood.
Abstract: This contribution investigates local differential techniques for estimating optical flow and its derivatives based on the brightness change constraint. By using the tensor calculus representation we build the Taylor expansion of the gray-value derivatives as well as of the optical flow in a spatiotemporal neighborhood. Such a formulation simplifies a unifying framework for all existing local differential approaches and allows to derive new systems of equations to estimate the optical flow and its derivatives. We also tested various optical flow estimation approaches on real image sequences recorded by a calibrated camera fixed on the arm of a robot. By moving the arm of the robot along a precisely defined trajectory we can determine the true displacement rate of scene surface elements projected into the image plane and compare it quantitatively with the results of different optical flow estimators.
237 citations
TL;DR: In this article, a theoretical model was developed to predict the density and temperature variation with time for rigid polyurethane foam formation, where the physical blowing agent (R-11) evaporation process was assumed to be heat generation-controlled and the carbon dioxide generation process was controlled by the rate of the water-isocyanate reaction.
Abstract: Polyurethane foam formation involves both polymerization and expansion processes. The dynamics of the water and R-11 blown foams depend on the rates of chemical and physical blowing processes, along with the rate of viscosity increase of the reacting mixture. Experiments were carried out to study the dynamics of free rising, water and R-11 blown rigid polyurethane foams. The density and temperature change during the foam formation were monitored. A theoretical model was developed to predict the density and temperature variation with time. In the model, the physical blowing agent (R-11) evaporation process is assumed to be heat generation–controlled and the carbon dioxide generation process to be controlled by the rate of the water-isocyanate reaction. The kinetic parameters of the reactions of isocyanate with polyol and water were obtained separately and were asssumed to be independent of each other. The water-isocyanate reaction appears to follow first-order kinetics with respect to concentration of water. The theoretical predictions of the model show good agreement with the experimental data for density variation with time. The model predictions for temperature rise also match experimental data, except at the later stages of foaming when it is found to be slower than the experimental measurements. However, this deviation does not affect the dynamics of density change since it occurs after the completion of the expansion process.
76 citations
TL;DR: In this paper, the Tiri river sediments were analyzed for Pb, Zn, Cu, Cd, Fe, Mn, Ca and Mg to recognize the extent of contamination and the geochemical process of dispersion.
75 citations
TL;DR: In this paper, the continuous precipitation of calcium carbonate is studied with on-line particle size distribution evaluation and in-situ video visualization and morphological characterizations of collected samples using differential scanning calorimetry (DSC), X-ray diffraction (XRD), scanning electron microscopy (SEM), and cryo-SEM were also performed.
Abstract: The continuous precipitation of calcium carbonate is studied here with on-line particle size distribution evaluation and in-situ video visualization. Morphological characterizations of collected samples using differential scanning calorimetry (DSC), X-ray diffraction (XRD), scanning electron microscopy (SEM), and cryo-SEM were also performed. It is found that in a scaled reactor the nucleation is homogeneous and predominantly of vaterite which transforms to calcite within the reactor itself, and subsequently outside the reactor during sample collection and drying. In an unsealed reactor the precipitation is predominantly heterogeneous with both vaterite and calcite being nucleated. The heterogeneously nucleated material is morphologically more perfect and is therefore slower to transform and has a lower growth rate. As a result of the transformation of vaterite, conventional characterizations such as DSC, XRD, and SEM, involving sample collection, filtration, and drying, at room temperature are unreliable. More meaningful determinations are available from cryo-SEM studies of rapidly frozen samples in which the transformation and subsequent nucleation is arrested.
75 citations
TL;DR: In this article, a simple C0 isoparametric finite element formulation based on a higher-order displacement model for the analysis of symmetric and unsymmetric, composite, and sandwich laminates subjected to a thermal gradient across the thickness is presented.
Abstract: A simple C0 isoparametric finite element formulation based on a higher-order displacement model for the analysis of symmetric and unsymmetric, composite, and sandwich laminates subjected to a thermal gradient across the thickness is presented. The displacement model accounts for the nonlinear distribution of in-plane displacement components through the plate thickness, and the theory requires no shear correction coefficients. The nine-noded quadratic Lagrangian two-dimensional element is used with five and nine degrees of freedom per node. The accuracy of the formulation is verified by analyzing sample problems available in literature. Numerical results are presented in nondimensional form for symmetric, antisymmetric, and cross-ply laminates, both thick and thin.
65 citations
TL;DR: In this paper, the authors developed theoretical models to predict the temperature and density change with time and spatial variation of temperature in the foam due to heat losses, by considering the foaming dynamics to be either heat generation controlled or heat and mass transfer controlled.
Abstract: The dynamics of R-11 blown polyurethane foam formation depend on the rates of viscosity increase of the reacting mixture and R-11 evaporation, and both are controlled by the polymerization process. Detailed experiments were carried out to study the dynamics of foaming and the measurements made included the cream and rise times, the density change of the expanding foam with time, and the temperature rise during reaction. Dynamic temperature measurements at different points in the foaming mixture were also made to study the spatial variation of the temperature in the foam. The experimental results showed the rate of foaming, the final density, and the maximum temperature decreased with increasing R-11 concentration. The heat losses from the foam were also found to be significant towards the later stages of foaming when density was low. Theoretical models were developed to predict the temperature and density change with time and spatial variation of temperature in the foam due to heat losses, by considering the foaming dynamics to be either heat generation controlled or heat and mass transfer controlled. In the former, the foam was assumed to be a pseudohomogeneous phase and the approach was similar to that of Rojas, et al. (5). New features accounted for in the model were dilution of the reactant concentration due to the presence of liquid blowing agent and heat loss from the foam due to radiation. While excellent agreement between theoretical predictions and experimental results was obtained for temperature variation with time at different locations in the foam, the model gave a much sharper reduction in density with time as compared to the experimental data. In the second model, the rate of foaming was assumed to be controlled by the rate of heat and mass transfer to a single bubble in the foam. Assuming a film model for heat and mass transfer, the theoretical predictions for both temperature and density were found to be in very good agreement with experimental data.
61 citations
TL;DR: In this paper, it was shown that the structural and electrical properties of CdO films are primarily influenced by the chamber pressure and the substrate temperature, whereas the oxygen percentage in the chamber has comparatively less influence on film properties.
61 citations
TL;DR: In this article, the effect of the geocell configuration on the bearing capacity and the failure settlement of a two-layer system was investigated. But the results were limited to the case of marine clay overlain by a sand layer.
TL;DR: A generalized theory of bit vector data flow analysis is presented which explains the known results in unidirectional and bidirectional data flows and provides a deeper insight into the process of data flowAnalysis.
Abstract: The classical theory of data flow analysis, which has its roots in unidirectional flows, is inadequate to characterize bidirectional data flow problems. We present a generalized theory of bit vector data flow analysis which explains the known results in unidirectional and bidirectional data flows and provides a deeper insight into the process of data flow analysis. Based on the theory, we develop a worklist-based generic algorithm which is uniformly applicable to unidirectional and bidirectional data flow problems. It is simple, versatile, and easy to adapt for a specific problem. We show that the theory and the algorithm are applicable to all bounded monotone data flow problems which possess the property of the separability of solution.The theory yields valuable information about the complexity of data flow analysis. We show that the complexity of worklist-based iterative analysis is the same for unidirectional and bidirectional problems. We also define a measure of the complexity of round-robin iterative analysis. This measure, called width, is uniformly applicable to unidirectional and bidirectional problems and provides a tighter bound for unidirectional problems than the traditional measure of depth. Other applications include explanation of isolated results in efficient solution techniques and motivation of new techniques for bidirectional flows. In particular, we discuss edge splitting and edge placement and develop a feasibility criterion for decomposition of a bidirectional flow into a sequence of unidirectional flows.
TL;DR: An algorithm for learning decision trees for classification and prediction is described which converts real-valued attributes into intervals using statistical considerations, and some applications are described, especially the task of predicting the high water level in a mountain river.
Abstract: An algorithm for learning decision trees for classification and prediction is described which converts real-valued attributes into intervals using statistical considerations. The trees are automatically pruned with the help of a threshold for the estimated class probabilities in an interval. By means of this threshold the user can control the complexity of the tree, i.e. the degree of approximation of class regions in feature space. Costs can be included in the learning phase if a cost matrix is given. In this case class dependent thresholds are used. Some applications are described, especially the task of predicting the high water level in a mountain river.
TL;DR: A grammar to represent a nontrivial subset of more complex driving activities on a highway is formulated and can be investigated not only at thelevel of control algorithms, but simultaneously at the level of natural language descriptions.
Abstract: This contribution is based on two previously published approaches one of which automatically extracts vehicle trajectories from image sequences of traffic scenes and associates these trajectories with motion verbs. The second approach exploits machine vision in order to maneuver autonomous road vehicles. The combination of these two approaches provides a link from the evaluation of video signals via an abstract representation at the level of natural language concepts to actuator devices in automatic closed loop control of road vehicles. Building on implemented representations for elementary motion verbs and for elementary road vehicle maneuvers, a grammar to represent a nontrivial subset of more complex driving activities on a highway is formulated. Driving on a highway can thereby be investigated not only at the level of control algorithms, but simultaneously at the level of natural language descriptions.
TL;DR: In this article, a failure criterion based on thickness gradients that develop during biaxial stretching was proposed to predict limit strain. But this criterion can be used under a wide range of forming conditions, including infinite-length defects and finite compact defects.
02 May 1994
TL;DR: Dropping the assumption that the partial derivatives of the gray value distribution are independent from each other affects the estimation procedure and offers the possibility to replace heuristic tests for the local detection of discontinuities in optical flow fields by well known stochastic tests.
Abstract: While estimating both components of optical flow based on the postulated validity of the Optical Flow Constraint Equation (OFCE), it has been tacitly assumed so far that the partial derivatives of the gray value distribution — which are required for this approach at the pixel positions involved — are independent from each other. [Nagel 94] has shown in a theoretical investigation how dropping this assumption affects the estimation procedure. The advantage of such a more rigorous approach consists in the possibility to replace heuristic tests for the local detection of discontinuities in optical flow fields by well known stochastic tests. First results from various experiments with this new approach are presented and discussed.
TL;DR: The calculated single particle spectrum for odd mass systems using relativistic mean field theory and the RMF reproduces the spin-orbit splittings quite well, despite the fact that the RMf incorporates leftover correlations only phenomenologically through the choice of effective Lagrangian parameters rather than incorporating them explicitly.
Abstract: The calculated single particle spectrum for odd mass systems using relativistic mean field (RMF) theory are analyzed. Assuming these states for nuclei having one particle (hole) in addition to the conventional doubly magic core, of pure single particle (hole) character, the spin-orbit splittings are calculated. The effect of time reversal breaking which exists for these odd A systems seems to cancel while taking the difference between the single particle energies. Therefore one can solve the RMF equations with time reversal invariance and obtain a reasonable estimate of the spin-orbit splittings. The RMF reproduces the spin-orbit splittings quite well. The agreement between the theory and the experiment is impressive in view of the fact that the RMF incorporates leftover correlations only phenomenologically through the choice of effective Lagrangian parameters rather than incorporating them explicitly.
TL;DR: In this article, the effect of manganese on the alkali promoted iron catalysts towards hydrocarbon synthesis was studied, and it was shown that using a catalyst containing about 20 mol-% Mn and 0.5% K, at 673 K, 3kg/cm2 pressure, WHS V = 800 h−1 and H2/CO = 1, it was possible to obtain good carbon monoxide coversion with 70-80% lower alkenes without formation of excess methane and carbon dioxide.
Abstract: Unsupported Fe-Mn-K catalysts prepared earlier by incorporating potassium in-situ during coprecipitation of iron- and manganese oxides have been found to exhibit good catalytic activity and high alkene selectivity in the C2-C4 range, during syngas conversion. The effect of manganese on the alkali promoted iron catalysts towards hydrocarbon synthesis was studied here. Manganese in moderate amount promotes catalytic activity as well as selectivity of lower alkenes. Using a catalyst containing about 20 mol-% Mn and 0.5% K, at 673 K, 3kg/cm2 pressure, WHS V = 800 h−1 and H2/CO = 1, it was possible to obtain good carbon monoxide coversion with 70–80% lower alkenes without formation of excess methane and carbon dioxide.
TL;DR: It was found that U.S. EPA source profiles are not suitable for such regions in India and site-specific source profiles should be used in the application of chemical mass balance for source apportionment.
Abstract: Aerosol samples collected within an industrial region of Bombay were analyzed for elemental concentrations using inductively coupled plasma emission spectroscopy, ultraviolet/visible spectrophotometry and X-ray fluorescence spectroscopy. Nineteen elements were selected as tracers of identified sources of aerosol in the region. The U.S. EPA chemical mass balance model was employed for source apportionment. Seven major source types were identified and the performance of the model was evaluated at different sampling locations. Model results were unsatisfactory at highly polluted sites in the study regions. It was found that U.S. EPA source profiles are not suitable for such regions in India and site-specific source profiles should be used in the application of chemical mass balance for source apportionment.
TL;DR: In this paper, the electron-doped Nd 2-x Ce x CuO y superconducting system in the range 0.120⩽ x ⩽0.190 with Δx = 0.005 was investigated.
Abstract: We report a refined phase diagram for the electron-doped Nd 2- x Ce x CuO y superconducting system in the range 0.120⩽ x ⩽0.190 with Δx =0.005. It is found that the highest T c ( ϱ =0) ∼17 K is confined to the very narrow range 0.145⩽ x ⩽0.150; a T conset ∼ 24 K with sharp superconducting transition is also observed. An attempt is made to understand the T c dependence on the variation of the oxygen content ( y ) in the Nd 2- x Ce x CuO y system.
TL;DR: In this article, a mixed culture biofilm consisting of Nitrifiers and Thiosphaera pantotropha (a heterotrophic nitrifier and aerobic denitrifier) was acclimated to 1386 mg l−1 of TKN and 400 mg l −1 of nitrate nitrogen.
Abstract: Simultaneous nitrification\aerobic denitrification studies of a high strength synthetic nitrogenous fertilizer wastewater in a single stage were carried out using a rotating biological contactor (RBC). Mixed culture biofilm consisting of Nitrifiers and Thiosphaera pantotropha (a heterotrophic nitrifier and aerobic denitrifier) was acclimated to 1386 mg l‐1 of TKN & 400 mg l‐1 of nitrate nitrogen. The effect of different nitrogen loadings and hydraulic retention times (HRTs) on percentage removal of TKN and nitrate nitrogen simultaneously, was investigated. A maximum TKN removal of 95.6 percent could be achieved at a nitrogen loading of 9.36 gN m‐2 d‐1 and HRT of 2 days. The results showed that the process is zero order with respect to nitrogen removal. The HRT studied were in the range of 0.5–3 days. The corresponding percentage TKN removal ranged from 43.9–93.7. Nitrate removal of 97–98% could also be achieved simultaneously. Nitrite accumulated significantly throughout these studies. Nitrogen l...
TL;DR: In this article, Fe(III)-saccharide complexes of d-glucose and d-fructose have been synthesized from methanol using stoichiometric quantities of sodium salts of the corresponding saccharides.
Abstract: Fe(III)-saccharide complexes of d-glucose and d-fructose have been synthesized from methanol using stoichiometric quantities of sodium salts of the corresponding saccharides. Both the compounds were isolated in the solid state and characterized by various analytical, spectroscopic, magnetic and cyclic voltammetric methods. Both the complexes were found to be stable, in solution, in the pH range 2.5–12.0.
TL;DR: A distributed model for estimation of transmission losses described in this article represents an attempt to develop a procedure for practical applications and is shown to produce reasonable estimates, and requires a minimum of observed data for calibration.
TL;DR: In this paper, the effect of replacing nickel with palladium has been examined in the Y-Ni-B-C system, where the d- electrons are carriers of superconductivity in these materials.
TL;DR: A token based mutual exclusion algorithm which is k-resilient in that it can tolerate up to k site/link failures and which uses many features of the token based algorithm by Raymond and inherits many of its advantages.
TL;DR: In this paper, an MST (mesosphere/stratosphere/troposphere) radar is currently under installation at Gadanki, a low latitude station in India, and preliminary observations conducted on the detection of the tropopause.
TL;DR: In this paper, the effect of the ions in healing and strengthening the existing oxide film of the aluminium alloy was found to increase in the following order: cadmium(II) < sulphate < molybdate < nitrate < Ce(III).
TL;DR: In this article, three regression equations were developed for relating transmission loss to channel characteristics for an arid region in north-west India, and two equations utilizing log-transformed data are a better predictor of transmission losses.
TL;DR: In this paper, magnetization studies on the quaternary intermetallic superconductor YNi2B2C have been carried out, and they have observed magnetic history effects that establish its response as consistent with that of a conventional hard type-II super-conductor.
Abstract: We present magnetization studies on the quaternary intermetallic superconductor YNi2B2C. We have observed magnetic history effects that establish its response as consistent with that of a conventional hard type-II superconductor, and we also report irreversibility line measurements.
TL;DR: A stochastic model is developed to analyse the two-stage transfer-line production system and explicit analytical expressions for some of the transient state characteristics have been obtained using the state-space method and regeneration point technique.
Abstract: This paper provides a complete framework to consider manufacturing, inspection and rework activities in two-stage transfer-line production systems. The purpose of this paper is to analyse some of the transient state characteristics of a two-stage production system subject to an initial buffer of infinite capacity, inspection at both the inter- and end-stages and rework. The first stage of the system is never starved and the second stage is never blocked. A stochastic model is developed to analyse the system and explicit analytical expressions for some of the system characteristics have been obtained using the state-space method and regeneration point technique. All the random variables involved in the analysis are assumed to be arbitrary (general). Numerical illustrations have also been presented for some particular cases.