Showing papers by "Indian Institute of Science published in 2002"
TL;DR: Combustion synthesis has emerged as a facile and economically viable technique for the preparation of advanced ceramics, catalysts and nanomaterials as discussed by the authors, and recent innovations in the combustion and processing parameters have resulted in a better understanding of combustion phenomena and control of microstructure and property of the products.
Abstract: Combustion synthesis has emerged as a facile and economically viable technique for the preparation of advanced ceramics, catalysts and nanomaterials. Recent innovations in the combustion and processing parameters have resulted in a better understanding of combustion phenomena and control of microstructure and property of the products.
767 citations
TL;DR: The hydrodynamic equations for suspensions of self-propelled particles (SPPs) with spontaneous orientational order are constructed, and a number of striking, testable predictions are made.
Abstract: Fish, birds, and swimming cells [1–3] are frequently found to move coherently in large groups [4–9] through the fluid medium they inhabit. Can general principles, like those used so successfully for ordered phases at equilibrium [10], reveal the laws governing the long-wavelength dynamics and fluctuations of these striking and ubiquitous examples of liquid-crystalline [11] order in suspensions of self-propelled particles (SPPs)? Although we know of no physics experiments on ordered SPP suspensions, Gruler [12] has studied ordered phases of living cells on a solid substrate, and finds ‘‘living liquid-crystalline’’ [13] phases corresponding to two distinct types of cells: apolar, that is, elongated but head-tail symmetric, and polar, distinguishing front from rear. The ordered phases formed by polar SPPs have a nonzero macroscopic drift velocity v 0 . Those formed by apolar SPPs have a macroscopic axis ^ n of
753 citations
TL;DR: In this article, the authors used an Oceanic General Circulation Model (OGCM) to simulate these currents and estimate their transports, and a 11/2-layer reduced-gravity model to investigate the processes that force them.
655 citations
20 Aug 2002
TL;DR: This work presents a scheme, based on probabilistic distortion of user data, that can simultaneously provide a high degree of privacy to the user and retain a high level of accuracy in the mining results.
Abstract: Data mining services require accurate input data for their results to be meaningful, but privacy concerns may influence users to provide spurious information. We investigate here, with respect to mining association rules, whether users can be encouraged to provide correct information by ensuring that the mining process cannot, with any reasonable degree of certainty, violate their privacy. We present a scheme, based on probabilistic distortion of user data, that can simultaneously provide a high degree of privacy to the user and retain a high level of accuracy in the mining results. The performance of the scheme is validated against representative real and synthetic datasets.
518 citations
TL;DR: In this article, a wind energy conversion system (WECS) using a grid-connected wound rotor induction machine controlled from the rotor side is compared with both fixed speed and variable speed systems using cage rotor induction machines.
Abstract: In this paper, a wind energy conversion system (WECS) using a grid-connected wound rotor induction machine controlled from the rotor side is compared with both fixed speed and variable speed systems using a cage rotor induction machine. The comparison is done on, the basis of: (1) major hardware components required; (2) operating region; and (3) energy output due to a defined wind function using the characteristics of a practical wind turbine. Although a fixed speed system is more simple and reliable, it severely limits the energy output of a wind turbine. In case of variable speed systems, comparison shows that using a wound rotor induction machine of similar rating can significantly enhance energy capture. This comes about due to the ability to operate with rated torque even at supersynchronous speeds; power is then generated out of the rotor as well as the stator. Moreover, with rotor side control, the voltage rating of the power devices and DC bus capacitor bank is reduced. The size of the line side inductor also decreased. Results are presented to show the substantial advantages of the doubly fed system.
477 citations
TL;DR: In this article, a method of tracking the peak power in a wind energy conversion system (WECS) is proposed, which is independent of the turbine parameters and air density.
Abstract: In this paper, a method of tracking the peak power in a wind energy conversion system (WECS) is proposed, which is independent of the turbine parameters and air density. The algorithm searches for the peak power by varying the speed in the desired direction. The generator is operated in the speed control mode with the speed reference being dynamically modified in accordance with the magnitude and direction of change of active power. The peak power points in the P-/spl omega/ curve correspond to dP/d/spl omega/=0. This fact is made use of in the optimum point search algorithm. The generator considered is a wound rotor induction machine whose stator is connected directly to the grid and the rotor is fed through back-to-back pulse-width-modulation (PWM) converters. Stator flux-oriented vector control is applied to control the active and reactive current loops independently. The turbine characteristics are generated by a DC motor fed from a commercial DC drive. All of the control loops are executed by a single-chip digital signal processor (DSP) controller TMS320F240. Experimental results show that the performance of the control algorithm compares well with the conventional torque control method.
475 citations
01 Dec 2002
TL;DR: An attempt has been made to bring together the main ideas involved in a unified framework of learning automata and provide pointers to relevant references.
Abstract: Automata models of learning systems introduced in the 1960s were popularized as learning automata (LA) in a survey paper by Narendra and Thathachar (1974). Since then, there have been many fundamental advances in the theory as well as applications of these learning models. In the past few years, the structure of LA, has been modified in several directions to suit different applications. Concepts such as parameterized learning automata (PLA), generalized learning,automata (GLA), and continuous action-set learning automata (CALA) have been proposed, analyzed, and applied to solve many significant learning problems. Furthermore, groups of LA forming teams and feedforward networks have been shown to converge to desired solutions under appropriate learning algorithms. Modules of LA have been used for parallel operation with consequent increase in speed of convergence. All of these concepts and results are relatively new and are scattered in technical literature. An attempt has been made in this paper to bring together the main ideas involved in a unified framework and provide pointers to relevant references.
379 citations
TL;DR: In this paper, the authors show that the possibility of encountering opposite trends in the responses of these indices to assemblages that differ in only a single component of diversity has not been sufficiently acknowledged.
370 citations
Proceedings Article•
01 Jan 2002TL;DR: A new algorithm suitable for matching discrete objects such as strings and trees in linear time is presented, thus obviating dynamic programming with quadratic time complexity and improvement on the currently available algorithms makes string kernels a viable alternative for the practitioner.
Abstract: In this paper we present a new algorithm suitable for matching discrete objects such as strings and trees in linear time, thus obviating dynamic programming with quadratic time complexity. Furthermore, prediction cost in many cases can be reduced to linear cost in the length of the sequence to be classified, regardless of the number of support vectors. This improvement on the currently available algorithms makes string kernels a viable alternative for the practitioner.
354 citations
TL;DR: In this paper, a color composite image from the Indian Remote Sensing Satellite (IRS) 1D LISS III was used for vegetation mapping and a GIS-based forest fire risk model was found to be in strong agreement with actual fire-affected sites.
352 citations
TL;DR: The lifetime of the hydrogen bond between a PHG and a water molecule is found to be much longer than that between any two water molecules, and is likely to be a general feature of hydrophilic surfaces of organized assemblies.
Abstract: The dynamics of hydrogen bonds among water molecules themselves and with the polar head groups (PHG) at a micellar surface have been investigated by long molecular dynamics simulations. The lifetime of the hydrogen bond between a PHG and a water molecule is found to be much longer than that between any two water molecules, and is likely to be a general feature of hydrophilic surfaces of organized assemblies. Analyses of individual water trajectories suggest that water molecules can remain bound to the micellar surface for more than 100 ps. The activation energy for such a transition from the bound to a free state for the water molecules is estimated to be about 3.5 kcal/mol.
TL;DR: It is shown that for one-dimensional fluids the thermal conductivity generically diverges with system size L as L(1/3), as a result of momentum conservation.
Abstract: We show that for one-dimensional fluids the thermal conductivity generically diverges with system size L as L(1/3), as a result of momentum conservation. Our results are consistent with the largest-scale numerical studies of two-component hard-particle systems. We suggest explanations for the apparent disagreement with studies on Fermi-Pasta-Ulam chains.
TL;DR: In this article, the authors investigated the catalytic properties of 1 at. % Pd/CeO2 by X-ray diffraction (XRD), Xray photoelectron spectroscopy (XPS), and extended Xray absorption fine structure (EXAFS).
Abstract: Pd/CeO2 (1 at. %) prepared by the solution-combustion method shows a higher catalytic activity for CO oxidation and NO reduction than Pd metal, PdO, and Pd dispersed over CeO2 by the conventional method. To understand the higher catalytic properties, the structure of 1 at. % Pd/CeO2 catalyst material has been investigated by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and extended X-ray absorption fine structure (EXAFS) spectroscopy. The diffraction lines corresponding to Pd or PdO are not observed in the high-resolution XRD pattern of 1 at. % Pd/CeO2. The structure of 1 at. % Pd/CeO2 could be refined for the composition of Ce0.99Pd0.01O1.90 in the fluorite structure with 5% oxide ion vacancy. Pd(3d) peaks in the XPS in I at. % Pd/CeO2 are shifted by 3 eV indicating that Pd is in a highly ionic +2 state. EXAFS studies show the average coordination number of 3 around Pd2+ ion in the first shell of 1 at. % Pd/CeO2 at a distance of 2.02 Angstrom, instead of 4 as in PdO. The second shell at 2.72 Angstrom is due to Pd-Pd correlation which is larger than 2.69 Angstrom in PdO. The third shell at 3.31 Angstrom having 7 coordination is absent either in Pd metal or PdO, which can be attributed to -Pd2+-Ce4+- correlation. Thus, 1 at. % Pd/CeO2 forms the Ce1-xPdxO2-delta type of solid solution having -Pd2+-O-2-Ce4+- kinds of linkages.
07 Aug 2002
TL;DR: Performance evaluations over a variety of XML documents and user queries indicate that XGrind simultaneously delivers improved query processing times and reasonable compression ratios.
Abstract: XML documents are extremely verbose since the "schema" is repeated for every "record" in the document. While a variety of compressors are available to address this problem, they are not designed to support direct querying of the compressed document, a useful feature from a database perspective. In this paper, we propose a new compression tool, called XGrind, that directly supports queries in the compressed domain. A special feature of XGrind is that the compressed document retains the structure of the original document, permitting reuse of the standard XML techniques for processing the compressed document. Performance evaluations over a variety of XML documents and user queries indicate that XGrind simultaneously delivers improved query processing times and reasonable compression ratios.
TL;DR: In this article, the authors used time series of temperature and salinity in the upper ocean, measured at 17degrees30'N, 89degreesE in the northern Bay of Bengal, from 27 July to 6 August 1999 captured an event of upper layer freshening.
Abstract: Time series of temperature and salinity in the upper ocean,measured at 17degrees30'N, 89degreesE in the northern Bay of Bengal,from 27 July to 6 August 1999 captured an event of upper layer freshening. Initially, the upper layer that is homogeneous in both temperature and salinity was about 30 m deep. Subsequently, the arrival of a freshwater plume caused the depth of the mixed layer to decrease to about 10 m and the salinity in the surface layer by about 4 psu. The plume led to the formation of a new halocline and hence a barrier layer within the upper 30 m of the water column. The ensuing ocean-atmosphere interaction was restricted to the new thinner mixed layer. The cooling that was restricted to the mixed layer led to an inversion in temperature amounting to 0.5degreesC just below the mixed layer. The source of the plume is traced to freshwater from river discharge and rainfall that was advected by Ekman flow as a 15 m thick layer. This study suggests that wind-driven circulation is crucial in determining the path of freshwater in the Bay of Bengal. The fresh water affects the sea surface temperature and ocean-atmosphere coupling through the dependence of the depth of the mixed layer on salinity.
TL;DR: In this article, the structure and chemical environment of Cu in Cu/CeO2 catalysts synthesized by the solution combustion method have been investigated by X-ray diffraction (XRD), transmission electron microscopy (TEM), electron paramagnetic resonance (EPR) spectroscopy, Xray photoelectron spectroscope (XPS), cyclic voltammetry (CV), and extended Xray fine structure (EXAFS).
Abstract: The structure and chemical environment of Cu in Cu/CeO2 catalysts synthesized by the solution combustion method have been investigated by X-ray diffraction (XRD), transmission electron microscopy (TEM), electron paramagnetic resonance (EPR) spectroscopy, X-ray photoelectron spectroscopy (XPS), cyclic voltammetry (CV), and extended X-ray fine structure (EXAFS) spectroscopy. High-resolution XRD studies of 3 and 5 atom % Cu/CeO2 do not show CuO lines in their respective patterns. The structure could be refined for the composition Ce1-xCuxO2-δ (x = 0.03 and 0.05; δ ∼ 0.13 and 0.16) in the fluorite structure with 5−8% oxide ion vacancy. High-resolution TEM did not show CuO particles in 5 atom % Cu/CeO2. EPR as well as XPS studies confirm the presence of Cu2+ species in the CeO2 matrix. Redox potentials of Cu species in the CeO2 matrix are lower than those in CuO. EXAFS investigations of these catalysts show an average coordination number of 3 around the Cu2+ ion in the first shell at a distance of 1.96 A, indi...
TL;DR: A dynamo model with the correct latitudinal distribution of sunspots is presented and it is demonstrated that this requires a meridional flow of material that penetrates deeper than hitherto believed, into the stable layers below the convection zone.
Abstract: Sunspots, dark magnetic regions occurring at low latitudes on the Sun's surface, are tracers of the magnetic field generated by the dynamo mechanism. Recent solar dynamo models, which use the helioseismically determined solar rotation, indicate that sunspots should form at high latitudes, contrary to observations. We present a dynamo model with the correct latitudinal distribution of sunspots and demonstrate that this requires a meridional flow of material that penetrates deeper than hitherto believed, into the stable layers below the convection zone. Such a deep material flow may have important implications for turbulent convection and elemental abundance in the Sun and similar stars.
TL;DR: Structural comparisons of models of homologous proteins allowed several factors responsible for enhanced thermostability to be identified and several statistically significant, specific amino acid substitutions that occur going from mesophiles to thermophiles are identified.
Abstract: Understanding the molecular basis for the enhanced stability of proteins from thermophiles has been hindered by a lack of structural data for homologous pairs of proteins from thermophiles and mesophiles. To overcome this difficulty, complete genome sequences from 9 thermophilic and 21 mesophilic bacterial genomes were aligned with protein sequences with known structures from the protein data bank. Sequences with high homology to proteins with known structures were chosen for further analysis. High quality models of these chosen sequences were obtained using homology modeling. The current study is based on a data set of models of 900 mesophilic and 300 thermophilic protein single chains and also includes 178 templates of known structure. Structural comparisons of models of homologous proteins allowed several factors responsible for enhanced thermostability to be identified. Several statistically signficant, specific amino acid substitutions that occur going from mesophiles to thermophiles are identified. Most of these are at solvent-exposed sites. Salt bridges occur significantly more often in thermophiles. The additional salt bridges in thermophiles are almost exclusively in solvent-exposed regions, and 35% are in the same element of secondary structure. Helices in thermophiles are stabilized by intrahelical salt bridges and by an increase in negative charge at the N-terminus. There is an approximate decrease of 1% in the overall loop content and a corresponding increase in helical content in thermophiles. Previously overlooked cation-\pi interactions, estimated to be twice as strong as ion-pairs, are significantly enriched in thermophiles. At buried sites, statistically significant hydrophobic amino acid substitutions are typically consistent with decreased side chain conformational entropy.
TL;DR: In this article, the spectral optical depths, black carbon mass concentration (Mb), total (Mt) and size segregated aerosol mass concentrations over an urban continental location, Bangalore (13° N, 77°E, 960 m msl), in India.
Abstract: [1] During a comprehensive aerosol field campaign, simultaneous measurements were made of aerosol spectral optical depths, black carbon mass concentration (Mb), total (Mt) and size segregated aerosol mass concentrations over an urban continental location, Bangalore (13° N, 77°E, 960 m msl), in India. Large amounts of BC were observed; both in absolute terms and fraction of total mass (∼11%) and sub-micron mass (∼23%) implying a significantly low single scatter albedo. The aerosol visible optical depth (τp) was in the range 0.24 to 0.45. Estimated surface forcing is as high as −23 W m−2 and top of the atmosphere (TOA) forcing is +5 W m−2 during relatively cleaner periods (τp ∼ 0.24). The net atmospheric absorption translates to an atmospheric heating of ∼0.8 K day−1 for cleaner periods and ∼1.5 K day−1 for less cleaner periods (τp ∼ 0.45). Our observations raise several issues, which may have impacts to regional climate and monsoon.
TL;DR: In this paper, the authors review recent reports of solvothermal or hydrothermal procedures for the preparation of isolated nanoparticles of some important oxide and chalcogenide materials.
Abstract: We review recent reports of solvothermal or hydrothermal procedures for the preparation of isolated nanoparticles of some important oxide and chalcogenide materials. The synthetic procedures listed here have the advantages of being relatively inexpensive in terms of the solvents used, arguably green (when water is the solvent) and amenable to scale-up. Handling or processing under inert conditions are rarely called for. We include descriptions of work involving the preparation of capped quantum dots using solvothermal techniques as well as microwave-hydrothermal routes and flow-hydrothermal routes that allow continuous and rapid processing of nanoparticulate materials.
TL;DR: Some of the recently reported hybrid systems based on steroid, carbohydrate, C60-fullerene platforms, amongst others, mainly crafted with the object of enhancement of the therapeutical spectrum, will be discussed.
Abstract: Hybrid systems are constructs of different molecular entities, natural or unnatural, to generate functional molecules in which the characteristics of various components are modulated, amplified or give rise to entirely new properties. These hybrids can be designed from carefully selected components either through domain integration of key structural/ functional features or via straightforward covalent linkages. Some of the recently reported hybrid systems based on steroid, carbohydrate, C60-fullerene platforms, amongst others, mainly crafted with the object of enhancement of the therapeutical spectrum, will be discussed.
TL;DR: This review deals with a brief account of relevant graphs and graph theoretic concepts and the structural and biological information derived from protein structures using these methods.
Abstract: The sequence and structure of a large body of proteins are becoming increasingly available. It is desirable to explore mathematical tools for ecient extraction of information from such sources. The principles of graph theory, which was earlier applied in elds such as electrical engineering and computer networks are now being adopted to investigate protein structure, folding, stability, function and dynamics. This review deals with a brief account of relevant graphs and graph theoretic concepts. The concepts of protein graph construction are discussed. The manner in which graphs are analyzed and parameters relevant to protein structure are extracted, are explained. The structural and biological information derived from protein structures using these methods is presented.
TL;DR: In this article, the authors formulated the automatic generation control (AGC) problem as a stochastic multistage decision problem and used reinforcement learning (RL) to obtain an AGC controller.
TL;DR: In this article, two strategies for the generation of molecular complexity in a resource-effective manner were explored, one involving multicomponent reactions and the other involving reactions leading to multiple carbon-carbon bond formation through tandem processes.
TL;DR: In this article, the authors examined the evolution of dipole mode (DM) events in the Indian Ocean using an ocean model that is driven by the NCEP fluxes for the period 1975-1998.
Abstract: The evolution of the dipole mode (DM) events in the Indian Ocean is examined using an ocean model that is driven by the NCEP fluxes for the period 1975-1998. The positive DM events during 1997, 1994 and 1982 and negative DM events during 1996 and 1984-1985 are captured by the model and it reproduces both the surface and subsurface features associated with these events. In its positive phase, the DM is characterized by warmer than normal SST in the western Indian Ocean and cooler than normal SST in the eastern Indian Ocean. The DM events are accompanied by easterly wind anomalies along the equatorial Indian Ocean and upwelling-favorable alongshore wind anomalies along the coast of Sumatra. The Wyrtki jets are weak during positive DM events, and the thermocline is shallower than normal in the eastern Indian Ocean and deeper in the west. This anomaly pattern reverses during negative DM events.
During the positive phase of the DM easterly wind anomalies excite an upwelling equatorial Kelvin wave. This Kelvin wave reflects from the eastern boundary as an upwelling Rossby wave which propagates westward across the equatorial Indian Ocean. The anomalies in the eastern Indian Ocean weaken after the Rossby wave passes. A similar process excites a downwelling Rossby wave during the negative phase. This Rossby wave is much weaker but wind forcing in the central equatorial Indian Ocean amplifies the downwelling and increases its westward phase speed. This Rossby wave initiates the deepening of the thermocline in the western Indian Ocean during the following positive phase of the DM. Rossby wave generated in the southern tropical Indian Ocean by Ekman pumping contributes to this warming. Concurrently, the temperature equation of the model shows upwelling and downwelling to be the most important mechanism during both positive events of 1994 and 1997. (C) 2002 Elsevier Science Ltd. All rights reserved.
TL;DR: In this paper, the impact toughness of a bulk La-based metallic glass due to isothermal and isochronal annealing below the T-g was investigated, and it was shown that the fracture toughness decreases with increasing annaling time or temperature, accompanied by a change in fracture morphology.
TL;DR: In this paper, the authors proposed two measures, one global and the other local, for the minimization of vibrations of structures subjected to periodic loading, which can bring about a reduction in the vibration level by moving the natural frequencies which contribute most significantly to the measures away from the driving frequencies.
19 May 2002
TL;DR: The crucial new idea underlying the first three results above is that of confirming matches by convolving vectors obtained by coding characters in the alphabet with non-boolean entries; in contrast, almost all previous pattern matching algorithms consider only boolean codes for the alphabet.
Abstract: (MATH) This paper obtains the following results on pattern matching problems in which the text has length n and the pattern has length mAn O(nlog m) time deterministic algorithm for the String Matching with Wildcards problems, even when the alphabet is large.An O(klog2 m) time Las Vegas algorithm for the Sparse String Matching with Wildcards problem, where k«n is the number of non-zeros in the text. We also give Las Vegas algorithms for the higher dimensional version of this problem.As an application of the above, an O(nlog2 m) time Las Vegas algorithm for the Subset Matching and Tree Pattern Matching problems, and a Las Vegas algorithm for the Geometric Pattern Matching problem.Finally, an O(nlog2 m) time deterministic algorithm for Subset Matching and Tree Pattern Matching..The crucial new idea underlying the first three results above is that of confirming matches by convolving vectors obtained by coding characters in the alphabet with non-boolean (i.e., rational or even complex) entries; in contrast, almost all previous pattern matching algorithms consider only boolean codes for the alphabet. The crucial new idea underlying the fourth result is a simpler method of shifting characters which ensures that each character occurs as a singleton in some shift.
25 Oct 2002-Materials Science and Engineering A-structural Materials Properties Microstructure and Processing
TL;DR: In this paper, the authors studied the characteristics of hot deformation of a beta titanium alloy Ti-10V-4.5Fe-1.5Al by upset forging in the temperature range 650-900 °C and strain rate range $0.001-100 s^{-1}.
Abstract: The characteristics of hot deformation of a beta titanium alloy Ti–10V–4.5Fe–1.5Al have been studied by upset forging in the temperature range 650–900 °C and strain rate range $0.001–100 s^{-1}$. The true stress–true strain curves at 650 °C show continuous flow softening at strain rates above $0.1 s^{-1}$ whereas at lower strain rates, the flow stress attains a steady-state. At temperatures higher than about 750 °C, there is a distinct peak in the flow stress in the early stages of deformation followed by a steady-state at higher strains. The variation of flow stress with temperature and strain rate follows the standard kinetic rate equation at strain rates lower than about $0.1 s^{-1}$ and the apparent activation energy is estimated to be about $180\hspace{mm} kJ \hspace{2mm} mol^{-1}$. The processing map exhibited a domain in the temperature range 750–900 °C with a peak efficiency of about 48% occurring at 850 °C and $0.01 \hspace{2mm}s^{-1}$. On the basis of the microstructural features, the variation of grain size with temperature and the tensile ductility variations, the domain is interpreted to represent a process of dynamic recrystallisation (DRX). The workability is optimum under peak DRX conditions and the grain size in the DRX domain is linearly dependent on the Zener–Hollomon parameter. At strain rates higher than $10 \hspace{2mm} s^{-1}$ and in a wide temperature range, the material exhibits flow instabilities, which are manifested as flow localisation.
08 Jul 2002
TL;DR: This paper gives a new iterative algorithm for kernel logistic regression based on the solution of a dual problem using ideas similar to those of the Sequential Minimal Optimization algorithm for Support Vector Machines.
Abstract: This paper gives a new iterative algorithm for kernel logistic regression. It is based on the solution of a dual problem using ideas similar to those of the Sequential Minimal Optimization algorithm for Support Vector Machines. Asymptotic convergence of the algorithm is proved. Computational experiments show that the algorithm is robust and fast. The algorithmic ideas can also be used to give a fast dual algorithm for solving the optimization problem arising in the inner loop of Gaussian Process classifiers.