Showing papers by "Indian Institute of Technology Guwahati published in 2004"
17 May 2004
TL;DR: This paper proposes a new hierarchical monothetic clustering algorithm to build a topic hierarchy for a collection of search results retrieved in response to a query that progressively identifies topics in a way that maximizes the coverage while maintaining distinctiveness of the topics.
Abstract: Organizing Web search results into a hierarchy of topics and sub-topics facilitates browsing the collection and locating results of interest. In this paper, we propose a new hierarchical monothetic clustering algorithm to build a topic hierarchy for a collection of search results retrieved in response to a query. At every level of the hierarchy, the new algorithm progressively identifies topics in a way that maximizes the coverage while maintaining distinctiveness of the topics. We refer the proposed algorithm to as DisCover. Evaluating the quality of a topic hierarchy is a non-trivial task, the ultimate test being user judgment. We use several objective measures such as coverage and reach time for an empirical comparison of the proposed algorithm with two other monothetic clustering algorithms to demonstrate its superiority. Even though our algorithm is slightly more computationally intensive than one of the algorithms, it generates better hierarchies. Our user studies also show that the proposed algorithm is superior to the other algorithms as a summarizing and browsing tool.
224 citations
TL;DR: Oxidation of alcohols to aldehydes and ketones has been studied in high yields using atmospheric oxygen and a catalytic amount of V2O5 in toluene under heating.
179 citations
TL;DR: In this paper, the numerical approximation of Navier-Stokes equations in a domain with moving boundaries using the arbitrary Lagrangian-Eulerian (ALE) method is presented.
109 citations
TL;DR: Oxidation of alcohols to aldehydes and ketones has been studied in high yields using molecular oxygen and a catalytic amount of 1 in toluene under stirring to find reactions that are faster than secondary alcohols and can be recycled without loss of activity.
108 citations
TL;DR: Amines are efficiently acylated by both cyclic and acyclic anhydrides by dissolving them in an aqueous medium with the help of a surfactant, sodium dodecyl sulfate (SDS) as discussed by the authors.
102 citations
TL;DR: In this article, eigenvalue analysis is carried out using Lanczos algorithm in an adaptive h-version finite element environment in order to control the discretization error for accurate evaluation of modal parameters.
101 citations
TL;DR: An iterative non-overlapping domain decomposition method for singularly perturbed two-point boundary-value problems for second-order ordinary differential equations (DEs) is suggested.
Abstract: A class of singularly perturbed two-point boundary-value problems (BVPs) for second-order ordinary differential equations (DEs) is considered here. In order to obtain numerical solution to these problems, an iterative non-overlapping domain decomposition method is suggested. The BVPs are independent in each subdomain and one can use parallel computers to solve these BVPs. One of the characteristics of the method is that the number of processors available is a free parameter of the method. Practical experiments on a Silicon Graphics Origin 200, with 4 MIPS R10000 processors have been performed, showing the reliability and performance of the proposed parallel schemes. Error estimates for the solution and numerical examples are provided.
96 citations
TL;DR: Polyaniline supported vanadium complex 1 catalyzes efficiently the oxidation of alcohols to aldehydes and ketones in high yields under molecular oxygen in toluene at ca. 100°C as discussed by the authors.
88 citations
TL;DR: In this paper, a higher order compact finite difference solution procedure has been proposed for the steady two-dimensional convection-diffusion equation on non-uniform orthogonal Cartesian grids involving no transformation from the physical space to the computational space.
Abstract: A higher order compact (HOC) finite difference solution procedure has been proposed for the steady two-dimensional (2D) convection–diffusion equation on non-uniform orthogonal Cartesian grids involving no transformation from the physical space to the computational space. Effectiveness of the method is seen from the fact that for the first time, an HOC algorithm on non-uniform grid has been extended to the Navier–Stokes (N–S) equations. Apart from avoiding usual computational complexities associated with conventional transformation techniques, the method produces very accurate solutions for difficult test cases. Besides including the good features of ordinary HOC schemes, the method has the advantage of better scale resolution with smaller number of grid points, with resultant saving of memory and CPU time. Gain in time however may not be proportional to the decrease in the number of grid points as grid non-uniformity imparts asymmetry to some of the associated matrices which otherwise would have been symmetric. The solution procedure is also highly robust as it computes complex flows such as that in the lid-driven square cavity at high Reynolds numbers (Re), for which no HOC results have so far been seen. Copyright © 2004 John Wiley & Sons, Ltd.
83 citations
TL;DR: In this paper, a single pot synthesis of polyaniline nanoparticles and aniline composite nanoparticles was performed in a micellar medium using sodium dodecyl sulfate as the micelles.
Abstract: In this paper, we report a single pot synthesis of polyaniline nanoparticles and Au nanoparticle−polyaniline composite nanoparticles using vapor phase introduction of aniline monomer. The synthesis was carried out in a micellar medium using sodium dodecyl sulfate as the micelles. Also, H2O2 was used both to reduce HAuCl4 to Au nanoparticles and to polymerize aniline in the same pot. The particles were synthesized in the form of aqueous dispersion with particle sizes of about 100 nm. UV−visible absorption spectra indicated the formation of emeraldine salt form in both the PANI and the composite particles. FTIR spectra showed the formation of identical polymer in both the systems. Transmission electron microscopic investigation was carried out to measure particle sizes for both the cases. X-ray diffraction measurements showed the presence of Au in the composite in addition to indicating the formation of polyaniline with low crystalline phase in both the cases. Also, the electrical conductivity of the compos...
83 citations
TL;DR: The encapsulation was completely reversible and the dissolved polyaniline as well as the composite could be recovered by replacement with molecular iodine, and the polymer particles could also replace molecular iodine from starch-iodine complex.
Abstract: In this paper we report a new method of solubilization of polyaniline and polyaniline-Au-nanoparticle composite by encapsulating nanometer-size particles in starch The solubilization was carried out in the presence of ultrasonic waves We also report that the encapsulation was completely reversible and the dissolved polyaniline as well as the composite could be recovered by replacement with molecular iodine In addition, the polymer particles could also replace molecular iodine from starch-iodine complex UV-Visible and Fourier transform infrared (FTIR) spectroscopic measurements established the reversible nature of encapsulation Transmission electron microscopic measurements showed that the sizes of the particles encapsulated in starch were on the order of 10-20 nm for both polyaniline and Au-nanoparticle-polyaniline composite particles X-ray diffraction evidenced the presence ofAu-nanoparticles in the starch-polyaniline-Au-nanoparticle composite Finally, we also mention here that the dissolved polyaniline could also be recovered as a precipitate by enzyme (diastage) hydrolysis of the polyaniline encapsulating starch
TL;DR: The starch-stabilized nanoparticles could be precipitated from the solution by a starch digesting enzyme which also binds with the particles resulting in its precipitation and the change in shape from spherical to triangular to hexagonal particles with increasing initial HAuC14 concentration was revealed.
Abstract: We report the synthesis ofAu nanoparticles, with tunable longitudinal plasmon band and shape selectivity, mediated by starch in the presence of ultrasonic waves. The synthesis was carried out by reduction of HAuCl4, at various concentrations, using H2O2 as the reducing agent. When the reactions were carried out in the absence of ultrasonic waves, there was no occurrence of the longitudinal resonance band, while the transverse plasmon resonance band shifted toward a higher wavelength. Transmission electron microscopic measurements revealed an increase in particle sizes with increasing higher initial HAuCl4 concentration. On the other hand, in the presence of ultrasonic waves, as the initial concentration of HAuCl4 was increased, while the transverse plasmon resonance band remained the same, the longitudinal plasmon resonance band increasingly shifted toward a higher wavelength. Transmission electron microscopic measurements revealed the change in shape from spherical to triangular to hexagonal particles with increasing initial HAuC14 concentration. We also report that the starch-stabilized nanoparticles could be precipitated from the solution by a starch digesting enzyme which also binds with the particles resulting in its precipitation.
TL;DR: In this paper, the authors used a back-propagation neural network to identify the behavior of the undamaged structure as well as of the structure with various possible damaged states.
Abstract: Damage to structures may occur as a result of normal operations, accidents, deterioration or severe natural events such as earthquakes and storms. Most often the extent and location of damage may be determined through visual inspection. However, in some cases this may not be feasible. The basic strategy applied in this study is to train a neural network to recognize the behaviour of the undamaged structure as well as of the structure with various possible damaged states. When this trained network is subjected to the measured response, it should be able to detect any existing damage. This idea is applied on a simple cantilever beam. Strain and displacement are used as possible candidates for damage identification by a back-propagation neural network. The superiority of strain over displacement for identification of damage has been observed in this study
TL;DR: In this paper, Ghosh and Juvekar studied the rest time of air bubbles at flat air-water and water-organic interfaces and found that the relative rest time is determined by the strength of the interfacial repulsive force and the magnitude of surface diffusivity of the surfactant molecules.
Abstract: The rest time of air bubbles at flat air–water and water–organic interfaces is studied in the present work. Effects of cationic and anionic surfactants, alcohol, salts and bubble-size on rest time are investigated. Wide distributions in rest times are observed in all the systems, which establishes the stochastic nature of the process. The stochastic model of Ghosh and Juvekar (2002; Chem Eng Res Des 80: 715–728) is used to fit the bubble rest time distributions. The results show that the magnitude of the rest time is determined by the strength of the interfacial repulsive force and the magnitude of surface diffusivity of the surfactant molecules. Entanglement of surfactants by hydrophobic interaction is believed to be a major factor behind the high rest time in many of the systems studied, apart from the repulsive electrostatic double layer, hydration and steric forces. The nature of the repulsion differs from system to system depending on the type of the adsorbed species. The work provides further support to the viewpoint (Ghosh and Juvekar, 2002) that the hydrodynamic drainage of the thin liquid film trapped between the bubble and the flat interface is complete once the bubble comes to a rest on the interface and the lubrication force plays a negligible role in supporting the weight of the bubble.
TL;DR: In this paper, temperature variation of DC electrical resistivity and magneto-resistivity have been measured on mono-valent, Ag-doped La 1− x Ag x MnO 3 compounds for x = 0.05-0.30.
Abstract: Temperature variation of DC electrical resistivity and magneto-resistivity have been measured on mono-valent, Ag- doped La 1− x Ag x MnO 3 compounds for x =0.05–0.30. All these samples exhibit metal–insulator transitions and the transition temperature increases with applied field. The resistivity data in the metallic region, i.e. below the transition temperature could be fitted to the empirical relation ρ = ρ 0 + ρ 1 T n . The value of exponent n , mostly varies from n =3 for zero field case to n =2 for 50 kOe field. The electrical transport in zero field is controlled by strong spin fluctuations scattering and in the presence of high magnetic field, it is mostly due to electron–electron scattering. The applied magnetic fields are found to suppress the scattering due to spin fluctuations. The resistivity data in the semiconducting region, i.e. above the transition temperature could be fitted to Mott variable range hopping model. The applied magnetic fields tend to delocalize the charge carriers in the semiconducting region and thereby decrease in hopping energy and increase in density of states has been observed. Colossal magneto-resistivity have been observed in all the above samples and the maximum value is found to be 73% for x =0.15 sample for 50 kOe field.
TL;DR: In this article, a 2D rectangular porous radiant burner is modeled as a spatially dependent heat generation zone, where the solid phase is assumed to be absorbing, emitting and scattering, while the gas phase is considered transparent to radiation.
Abstract: This paper deals with the heat transfer analysis of a 2-D rectangular porous radiant burner. Combustion in the porous medium is modelled as a spatially dependent heat generation zone. The gas and the solid phases are considered in non-local thermal equilibrium, and separate energy equations are used for the two phases. The solid phase is assumed to be absorbing, emitting and scattering, while the gas phase is considered transparent to radiation. The radiative part of the energy equation is solved using the collapsed dimension method. The alternating direction implicit scheme is used to solve the transient 2-D energy equations. Effects of various parameters on the performance of the burner are studied.
TL;DR: In this article, a general identification algorithm has been developed to estimate crack flexibility coefficients and the crack depth based on the force-response information, which is extended to overcome practical limitations of measuring number of degrees of freedom (dofs).
TL;DR: A wide variety of carbonyl compounds can be converted smoothly to the corresponding acetals on treatment with alcohols or diols and triethyl orthoformate in the presence of a catalytic amount of (bromodimethylsulfonium bromide) at room temperature.
TL;DR: It is demonstrated the workability of a TDDVR based novel quantum-classical approach, for simulating scattering processes on a quasi-Jahn-Teller model and excellent agreement betweenTDDVR and DVR results is obtained in both the representations.
Abstract: We demonstrate the workability of a TDDVR based [J. Chem. Phys. 118, 5302 (2003)], novel quantum-classical approach, for simulating scattering processes on a quasi-Jahn–Teller model [J. Chem. Phys. 105, 9141 (1996)] surface. The formulation introduces a set of DVR grid points defined by the Hermite part of the basis set in each dimension and allows the movement of grid points around the central trajectory. With enough trajectories (grid points), the method converges to the exact quantum formulation whereas with only one grid point, we recover the conventional molecular dynamics approach. The time-dependent Schrodinger equation and classical equations of motion are solved self-consistently and electronic transitions are allowed anywhere in the configuration space among any number of coupled states. Quantum-classical calculations are performed on diabatic surfaces (two and three) to reveal the effects of symmetry on inelastic and reactive state-to-state transition probabilities, along with calculations on an adiabatic surface with ordinary Born–Oppenheimer approximation. Excellent agreement between TDDVR and DVR results is obtained in both the representations.
TL;DR: In this paper, various alcohols and phenols can be smoothly converted to the corresponding THP ethers using 20% CuSO4·5H2O under mild reaction conditions at room temperature.
TL;DR: In this article, the authors presented a study conducted for the selection of optimal GA parameters to be adopted for backcalculation of pavement layer moduli, the parameters have been selected on the basis of the level of accuracy desired and the corresponding computational effort.
Abstract: In the context of pavement evaluation, backcalculation is the process of estimation of elastic properties of pavement layers using measured structural responses. A number of backcalculation programs are available for estimating effective pavement layer moduli from surface deflections. Different optimization techniques have been used in the development of these backcalculation models. Genetic algorithm (GA) has been used successfully in the recent past for backcalculation of pavement layer moduli. Selection of appropriate GA parameters is important for the efficient performance of the GA-based algorithm. However, there are no general guidelines available at present for the selection of GA parameters. This paper presents a study conducted for the selection of optimal GA parameters to be adopted for backcalculation of pavement layer moduli. The parameters have been selected on the basis of the level of accuracy desired and the corresponding computational effort (CE). The performance of the GA-based program w...
TL;DR: In this article, the various types and synthetic strategies for the production of siloxanes are described, with the emphasis being on their structural aspects, and a description is given of the various synthetic methods for the synthesis of organic compounds with silicon-oxygen bonds.
Abstract: This review describes the various types and synthetic strategies for the production of siloxanes. A description is given of the various synthetic methods for the production of organic compounds with silicon–oxygen bonds. The different types of siloxane are described, with the emphasis being on their structural aspects. Copyright © 2004 John Wiley & Sons, Ltd.
TL;DR: In this paper, the facile catalytic oxidation of sulfides to sulfoxides has been achieved with VO(acac)2 supported on titania using tert-butyl hydroperoxide (TBHP) as an oxidant in dichloromethane in quantitative yields at room temperature.
Abstract: The facile catalytic oxidation of sulfides to sulfoxides has been achieved with VO(acac)2 supported on titania using tert-butyl hydroperoxide (TBHP) as an oxidant in dichloromethane in quantitative yields at room temperature. The catalyst is reusable and tested for five cycles without significant loss of activity and selectivity.
TL;DR: In this article, the acetalization of aldehydes has been studied with methanol, ethanol, and 2-propanol using CoCl2 in high yields under reflux conditions.
27 Jun 2004
TL;DR: A novel and simple technique for the detection, and subsequent de-noising, of these ocular artifacts using Haar wavelets of high orders and has the advantage of being highly artifact selective.
Abstract: The electroencephalogram (EEG) is a biological signal that represents the electrical activity of the brain. A commonly encountered problem in clinical practice during EEG recording is 'blanking' of the EEG signal due to blinking of the user's eyes. Eye-blinks and movements of the eyeballs produce electrical signals that are collectively known as ocular artifacts and these are 10-100 times stronger than the EEG signal which is being recorded. The effective filtering of these ocular artifacts is extremely difficult because their frequency spread (1-50 Hz) overlaps with that of the EEG. Another major drawback of existing frequency based de-noising techniques is that they require continuous recording of electrooculargram (EOG) signals as well. Recently, a stationary wavelet transform (SWT) of the corrupted EEG signal has been used to de-noise it. We present a novel and simple technique for the detection, and subsequent de-noising, of these ocular artifacts using Haar wavelets of high orders. A comprehensive error analysis has been carried out, in both the time domain based artifact detection and the frequency domain based SWT de-noising of EEG. This procedure also has the advantage of being highly artifact selective, and so we have applied it to detect and de-noise epileptic EEG signals.
TL;DR: The Bayesian regularization technique used for training the network for pulse radar detection results in superior performance in terms of signal-to-sidelobe ratio compared to the Backpropagation algorithm.
TL;DR: The phonon sideband spectrum associated with the excitation transition 7F0−5D2 is used to analyze the electron–phonon coupling and nonradiative deexcitiation of the rare earth ions in the glass host.
Abstract: Silica glass samples containing CdSe/Eu3+ ions were prepared by sol-gel route. Size distribution and optical band gap of the nanoparticles were calculated from absorption spectrum. It is observed that the presence of CdSe nanocrystallites enhances the fluorescence of europium in silica glass. The phonon sideband spectrum associated with the excitation transition 7F0−5D2 is used to analyze the electron–phonon coupling and nonradiative deexcitiation of the rare earth ions in the glass host. The observed fluorescence enhancement is discussed on the basis of phonon assisted energy transfer from electron-hole recombination of the CdSe nanocrystallites to the rare earth ion and multiphonon relaxation.
TL;DR: In this article, a study on temper rolling process has been carried out using rigid-plastic finite element method to predict the roll force and roll torque and to study the deformation field of the rolled sheet.
19 Jun 2004
TL;DR: This paper compares the relative performance of FUSS with the well known tournament selection scheme on a range of problems and concludes that FUSS biases selection towards sparsely populated fitness levels.
Abstract: In evolutionary algorithms a critical parameter that must be tuned is that of selection pressure. If it is set too low then the rate of convergence towards the optimum is likely to be slow. Alternatively if the selection pressure is set too high the system is likely to become stuck in a local optimum due to a loss of diversity in the population. The recent fitness uniform selection scheme (FUSS) is a conceptually simple but somewhat radical approach to addressing this problem - rather than biasing the selection towards higher fitness, FUSS biases selection towards sparsely populated fitness levels. In this paper, we compare the relative performance of FUSS with the well known tournament selection scheme on a range of problems.
TL;DR: PdCl2 can catalyze the acetylation of primary and secondary alcohols with vinyl acetate as mentioned in this paper, which is selective and mild with high yields, but it is not suitable for the synthesis of tertiary alcohols.