Showing papers by "Indian Institute of Technology Kharagpur published in 1998"
TL;DR: This is the first considerable improvement on this bound after its early solution approximately 27 years ago and applies to improve the current bounds on the combinatorial complexities of k -levels in the arrangement of line segments, convex polygons in the union of n lines, parametric minimum spanning trees, and parametric matroids in general.
Abstract: We prove an O(n(k+1)1/3) upper bound for planar k -sets. This is the first considerable improvement on this bound after its early solution approximately 27 years ago. Our proof technique also applies to improve the current bounds on the combinatorial complexities of k -levels in the arrangement of line segments, k convex polygons in the union of n lines, parametric minimum spanning trees, and parametric matroids in general. 26 June, 1998 Editors-in-Chief: la href=../edboard.html#chiefslJacob E. Goodman, Richard Pollackl/al 19n3p373.pdf yes no no yes
277 citations
TL;DR: In this article, a method of predicting the local bifurcation structure through the construction of a normal form is applied to many power electronic circuits as well as other piecewise smooth systems.
Abstract: Interesting bifurcation phenomena are observed for the current feedback-controlled buck converter. We demonstrate that most of these bifurcations can be categorized as "border-collision bifurcations." A method of predicting the local bifurcation structure through the construction of a normal form is applied. This method applies to many power electronic circuits as well as other piecewise smooth systems.
243 citations
TL;DR: In this article, a nonlinear model in the form of a mapping from one point of observation to the next has been derived, which has a closed form even when the parasitic elements are included.
Abstract: The occurrence of nonlinear phenomena like subharmonics and chaos in power electronic circuits has been reported recently. In this paper, the authors investigate these phenomena in the current-mode-controlled boost power converter. A nonlinear model in the form of a mapping from one point of observation to the next has been derived. The map has a closed form even when the parasitic elements are included. The bifurcation behavior of the boost power converter has been investigated with the help of this discrete model.
197 citations
TL;DR: A birds eye view of the continuous-time related aspects of the greater field of system identification is presented and some recent developments in the identification of linear systems and nonlinear systems are outlined.
148 citations
TL;DR: In this article, the authors have shown that nitrogen when applied in the form of ammonium sulfate was more lethal than urea, and the number of phytoplankton species, which are fish food, was also less when chemical fertilizers were used as a nitrogen source.
147 citations
TL;DR: In the present paper, the authors define F-open sets,F-closed sets, F-adherent points, F -limit points, and F-isolated points to make some characterizations of fuzzy metric spaces.
144 citations
TL;DR: In this article, the Kalina cycle has been analyzed thermodynamically for which a general code has been developed for the calculation of thermodynamic properties of the mixture of NH3-H2O mixture.
139 citations
TL;DR: In this article, the results of the directional solidification (DS) experiments on particle engulfment and pushing by solidifying interfaces (PEP), conducted on the space shuttle Columbia during the Life and Microgravity Science (LMS) Mission, are reported.
Abstract: Results of the directional solidification (DS) experiments on particle engulfment and pushing by solidifying interfaces (PEP), conducted on the space shuttle Columbia during the Life and Microgravity Science (LMS) Mission, are reported. Two pure aluminum (99.999 pct) 9 mm cylindrical rods, loaded with about 2 vol pct 500µm-diameter zirconia particles, were melted and resolidified in the microgravity (µg) environment of the shuttle. One sample was processed at a stepwise increased solidification velocity and the other at a stepwise decreased velocity. It was found that a pushing/engulfment transition (PET) occurred in the velocity range of 0.5 to 1 µm/s. This is smaller than the ground PET velocity of 1.9 to 2.4 µm/s. This demonstrates that natural convection increases the critical velocity. A previously proposed analytical model for PEP was further developed. A major effort to identify and produce data for the surface energy of various interfaces required for calculation was undertaken. The predicted critical velocity for PET was 0.775 µm/s.
117 citations
TL;DR: In this paper, the conductivity of fiber-rubber composites is measured against the loading of conductive carbon fiber to check the percolation limit for each system, and the applicability of different theoretical models to predict the modulus and conductivities of these composites has been tested.
107 citations
TL;DR: In this paper, Nanocrystalline lead zirconate titanate (PZT) powders, with a Zr:Ti ratio of 60:40, have been prepared from a solution of triethanolamine (TEA) and Ti4+, Zr4+, and Pb2+ ions.
Abstract: Nanocrystalline lead zirconate titanate (PZT) powders, with a Zr:Ti ratio of 60:40, have been prepared from a solution of triethanolamine (TEA) and Ti4+, Zr4+, and Pb2+ ions. The metal ions were in solution through complex formation with TEA. The soluble metal-ion–TEA complex formed the precursor material when it was completely dehydrated. Heat treatment of the precursor at 450°C resulted in single-phase PZT powders. The precursor and the heat-treated powders have been characterized by using thermal analysis and X-ray diffractometry (XRD) studies. The average particle size, as measured from X-ray line broadening and transmission electron microscopy studies, was ∼20 nm. PZT powders modified with 3 mol% of lanthanum (PLZT) also were prepared through this route and were investigated via XRD studies. The dielectric constants of the PZT and PLZT powders were 12475 and 11262, and their corresponding Curie temperatures were 362° and 315°C, respectively.
94 citations
TL;DR: In this article, the transient vibration response of a cracked rotor passing through its critical speed is analyzed, as an attempt for crack detection and monitoring, and effects of different factors such as crack depth, unbalance eccentricity with phase and acceleration influencing vibration are investigated.
TL;DR: In this article, the softness and the polarizability of the ground (1S) and several excited electronic states (1P, 1D, 1F) of various helium isoelectronic systems (He, Li, Be2+, B3+, B4+, C4+) were calculated.
Abstract: Global reactivity parameters like the softness and the polarizability and local reactivity parameters like the Fukui function and the local hardness have been calculated for the ground (1S) and several excited electronic states (1P, 1D, 1F) of various helium isoelectronic systems (He, Li+, Be2+, B3+, C4+). Only the lowest energy state of a given symmetry is chosen because of the validity of the excited state density functional theory exclusively for this type of states. The softness varies linearly with the cube root of the polarizability for both the ground and the excited states. It has been demonstrated for the first time for the systems studied that a system is harder and less polarizable in its ground state than in any of its excited states. Radial distributions of the charge density, the Fukui function, and the local hardness exhibit characteristic shell structures in both the ground and the excited states.
TL;DR: In this paper, a thermoplastic polyurethane was prepared from cardanol, a renewable resource and a waste of the cashew industry by double vacuum distillation, which was characterized by 1H-NMR, FTIR, and UV spectroscopy.
Abstract: A novel thermoplastic polyurethane was prepared from cardanol, a renewable resource and a waste of the cashew industry. Cardanol was recovered from cashew nut shell liquid (CNSL) by double vacuum distillation. It was characterized by CHN analysis and IR, 1H-NMR, and 13C-NMR spectroscopy techniques. Cardanol is a meta-substituted long chain phenol. The long aliphatic chain unit substituent was found to be a monoene. The monomer, 4-[(4-hydroxy-2-pentadecenylphenyl)diazenyl]phenol was prepared from cardanol. It was a dihydroxy compound as characterized by CHN analyzer, UV, and 1H-NMR spectroscopy. The polyurethane was synthesized from this dihydroxy compound by the treatment with 4,4′-diphenylmethane diisocyanate (MDI) in dimethylformamide (DMF) solvent at 80–90°C under nitrogen atmosphere. The polymer was characterized by 1H-NMR, FTIR, and UV spectroscopy. The elemental analysis was done for determining the percentage content of C, H, and N, and the intrinsic viscosity [η] of polymer showed 1.85 dL/gm. Thermogravimetric investigations (TGA) of the cardanol, the dihydroxy compound, and the polyurethane were performed to study their decomposition. The semicrystalline nature of the PU was confirmed by differential scanning calorimetry (DSC) and dynamic mechanical thermal analyzer (DMTA). The wide-angle X-ray diffraction (WAXS) study of PU shew a broad amorphous halo indicative of absence of crystallinity in the polymer, which has been explained as due to strong hydrogen bonding in the hard phase. PU may possibly be useful as a telecommunication and as a nonlinear optical material. © 1998 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 36: 391–400, 1998
TL;DR: Gold complex, HAuCl(4) has been transformed into pink-coloured stable gold sol having lambda(max) at 523 nm at room temperature in aqueous Triton X-100 (TX-100) upon photoirradiation.
TL;DR: A parallel implementation of the Differential Box Counting technique is reported, and the accuracy and computational complexity of the parallel implementation are discussed.
01 Jan 1998
TL;DR: In this article, the transient vibration response of a cracked rotor passing through its critical speed is analyzed, considering a simple Laval rotor with a transverse crack, assuming that the vibrations remain small in comparison to the sag of the rotor under its own weight.
Abstract: In the present study a simple Laval rotor with a transverse crack is considered. The analysis assumes that the vibrations remain small in comparison to the sag of the rotor under its own weight. If a cracked shaft rotates slowly under the load of its own weight, then the crack will open and close once per revolution. i.e. it breathes. Considering a simple hinge model which is a very good model for small cracks with the breathing action of crack, the transient vibration response of a cracked rotor passing through its critical speed is analysed. as an attempt for crack detection and monitoring. Effects of different factors such as crack depth. unbalance eccentricity with phase and acceleration influencing vibration are investigated.
TL;DR: In this article, the authors attempt to interpret the experimentally observed nonideal Al-pSi Schottky diode I-V and C-V characteristics, and derive expressions for the capacitance-voltage relationship at low frequency and high frequency.
Abstract: In this study we attempt to interpret the experimentally observed nonideal Al–pSi Schottky diode I – V and C – V characteristics. The expressions for the capacitance–voltage relationship at low frequency and high frequency are derived considering two non idealities, namely interface states and series resistance. After extracting the diode parameters from the I – V and C – V characteristics, theoretical plots for the high frequency and low frequency capacitance are obtained using the expressions derived. A comparison of the latter with available experimental plots reveals that the expressions for the low frequency and high frequency capacitance derived here are simpler, more accurate and closer to experimental results than those used in the past. The variation of interface state density with the applied bias voltage is obtained from the low frequency and high frequency C – V plots by using the capacitance technique. To examine the validity of the present approach, the value of density of interface states is compared with that obtained by the multifrequency admittance method. It is observed that there is good agreement between the results obtained by both methods.
TL;DR: In this article, a simply supported symmetric cross-ply (0°/90°/0°) graphite-epoxy composite plate covered with piezoelectric material polyvinylidene fluoride (PVDF) is presented.
TL;DR: In this article, the thermal degradation behavior of thermoplastic elastomeric blends of nylon-6 and an acrylate rubber (ACM) has been studied by non-isothermal thermogravimetry.
TL;DR: In this article, the pushing/engulfment transition for two different metal/particle systems were determined by X-ray transmission microscopy (XTM) and optical metallography after processing.
Abstract: Directional solidification experiments have been carried out to determine the pushing/engulfment transition for two different metal/particle systems. The systems chosen were aluminum/zirconia particles and zinc/zirconia particles. Pure metals (99.999 pct A1 and 99.95 pct Zn) and spherical particles (500 µm in diameter) were used. The particles were nonreactive with the matrices within the temperature range of interest. The experiments were conducted so as to ensure a planar solid/liquid (SL) interface during solidification. Particle location before and after processing was evaluated by X-ray transmission microscopy (XTM) for the Al/ZrO2 samples. All samples were characterized by optical metallography after processing. A clear methodology for the experiment evaluation was developed to unambiguously interpret the occurrence of the pushing/engulfment transition (PET). It was found that the critical velocity for engulfment ranges from 1.9 to 2.4 µm/s for Al/ZrO2 and from 1.9 to 2.9 µm/s for Zn/ZrO2.
TL;DR: Optically active strontium substituted barium titanate (Ba x Sr 1− x TiO 3 ) thin films have been prepared on p-silicon and glass (Corning 7059) substrates by RF magnetron sputtering in a flowing Ar/O 2 atmosphere as discussed by the authors.
TL;DR: In this article, the surface active properties of the culture filtrates of Micrococcus are described in terms of surface tension, emulsification and foamability using carbon sources.
TL;DR: In this article, the authors present two methods for controlling chaos particularly suitable for switching circuits and demonstrate the results of numerical investigation and experimental implementation with reference to the duty cycle controlled buck converter.
Abstract: It has been demonstrated previously that DC-DC buck and boost converters with current or voltage feedback exhibit chaos for significantly large ranges of parameter values. In this paper, we present two methods for controlling chaos particularly suitable for switching circuits. The results of numerical investigation and experimental implementation are presented with reference to the duty cycle controlled buck converter.
TL;DR: In this paper, a grafting of trimethylol propane triacrylate (TMPTA) onto EPDM has been carried out over a wide range of irradiation doses (0-200 kGy) using a fixed concentration (10%) of TMPTA.
TL;DR: In this article, the percolation limit for the attainment of high conductivity is found to be relatively less for silicone rubber based composites compared to EPDM or NBR-based composites reported earlier.
Abstract: Electrically conductive silicone rubber composites have been prepared through incorporation of conductive acetylene black and short carbon fibre (SCF). The percolation limit for the attainment of high conductivity is found to be relatively less for silicone rubber based composites compared to EPDM or NBR based composites reported earlier. Percolation limit is found to be lower for SCF-filled systems (7.5 phr) compared to black-filled ones (14 phr). Both black- and SCF-filled systems exhibit an increase in resistivity with the increase in temperature (PCT effect). This PCT effect may be explained in terms of differences in the thermal expansion between the rubber matrix and the conductive filler. However, resistivity-versus-temperature plots are not identical during the heating-cooling cycle, leading to some hysteresis and electrical set. The current-voltage relationship is linear (Ohmic in nature) at room temperature but becomes non-linear (non-Ohmic) at elevated temperatures. The resistivity of these composites is measured under different conditions such as on applying pressure and being subjected to different mechanical stress and strain over the specimens. An effort has been made to correlate the effect of different parameters on electrical resistivity with the change in the conductive network structure under different conditions.
Elektrisch leitende Silikonkautschuk-Verbundwerkstoffe wurden durch Fullen mit leitfahigem Acetylenrus bzw. kurzen Kohlenstoffasern (SCF) hergestellt. Die Perkolationsgrenze fur das Erreichen einer hohen Leitfahigkeit liegt bei Silikonkautschuk-Verbundwerkstoffen relativ niedrig im Vergleich zu den bereits beschriebenen Verbundwerkstoffen auf EPDM- oder NBR-Basis. Die Perkolationsgrenze ist bei den SCF-gefullten (7.5 phr) Systemen niedriger als bei den mit Rus (14 phr) gefullten. Sowohl die rusgefullten als auch die SCF-gefullten Systeme zeigen eine Erhohung des spezifischen Widerstands mit der Temperatur (PCT-Effekt). Dieser PCT-Effekt kann mit dem unterschiedlichen thermischen Ausdehnungsverhalten von Kautschukmatrix und Fullstoff erklart werden. Die Temperatur/Widerstands-Meskurven bleiben jedoch wahrend eines Heiz-Kuhl-Durchgangs nicht gleich, was sich in Hysteresekurven und Differenzen zwischen Anfangs- und Endwert des spezifischen Widerstands zeigt. Die Beziehung zwischen Strom und Spannung ist bei Raumtemperatur linear (Ohmsches Gesetz), weicht jedoch bei hoheren Temperaturen vom linearen Verhalten ab. Der spezifische Widerstand dieser Verbundwerkstoffe wurde unter verschiedenen Bedingunn untersucht, unter Druck oder bei unterschiedlichen Spannungs- oder Dehnungszustanden der Probekorper. Ein Zusammenhang zwischen der Wirkung der verschiedenen Parameter auf den elektrischen Widerstand und der Strukturanderung des leitfahigen Netzwerks unter verschiedenen Bedingungen wurde untersucht.
TL;DR: In this article, electrical properties of different pre-strained samples derived from EPDM, 50 50 NBR/EPDM blend and NBR rubbers, were measured.
Abstract: Conductivity of conductive rubber composites changes significantly when subjected to mechanical stress and strain. Electrical properties of different pre-strained samples derived from EPDM, 50 50 NBR/EPDM blend and NBR rubbers, were measured. It was found that electrical resistivity of strained samples depends on strain amplitude (% elongation), frequency of stress-strain cycle, and also number of stress-strain cycles. Samples were strained in three different instruments: an Instron UTM; a Monsanto fatigue to failure tester; and a Goodrich flexometer. Under different conditions, electrical properties of strained and unstrained (original) samples were measured. It was found that there is similarity in the change of modulus and electrical resistivity against degree of strain and frequency of strain for different samples. The results of different experiments have been discussed in light of breakdown and formation of the carbon black-rubber structure.
TL;DR: An order-level inventory model is developed by assuming that the demand rate is stock-dependent and two separate warehouses are used and a sensitivity analysis is carried out by taking a numerical example.
Abstract: An order-level inventory model is developed by assuming that the demand rate is stock-dependent and two separate warehouses are used When the stock level exceeds the capacity of the own warehouse (OW), a rented warehouse (RW) is used The stock is transferred periodically in bulk from RW to OW and there is an associated transportation cost No shortages are allowed An algorithm is developed to obtain the optimal solution of the model To study the effects of changes in the system parameters on the decision variables, a sensitivity analysis is carried out by taking a numerical example
TL;DR: Production of extracellular alkaline protease by a locally isolated fungal species, Rhizopus oryzae, under solid state fermentation was optimized and the maximum enzyme activity under the optimum conditions of temperature, humidity, and spore count was 341 unit/g wheat bran.
Abstract: Production of extracellular alkaline protease by a locally isolated fungal species, Rhizopus oryzae, under solid state fermentation was optimized. The maximum enzyme activity under the optimum conditions of temperature (32 °C), relative humidity (90%–95%), spore count (∼2 × 105/g wheat bran), moisture content of solid substrate (140%) adjusted suitably with salt solution (M-9) of pH 5.5 was 341 unit/g wheat bran.
TL;DR: The polycrystalline samples of Ba 5 RTi 3 Nb 7 O 30 (R = Dy, Sm ) complex tungsten-bronze-type compounds were prepared using a high-temperature solid-state reaction technique as discussed by the authors.
TL;DR: Graft copolymers of polyacrylamide with starch, amylose, and amylopectin have been synthesized using ceric-ion-induced redox initiation technique as mentioned in this paper.
Abstract: Graft copolymers of polyacrylamide with starch, amylose, and amylopectin have been synthesized using ceric-ion-induced redox initiation technique. The polymers were characterized using different instrumental techniques like thermal, XRD, SEM, IR, NMR, and elemental analysis. The results indicated that there is a substantial amount of grafting with minimum formation of homopolyacrylamide. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 70: 1795–1810, 1998