Showing papers by "Cochin University of Science and Technology published in 1991"
TL;DR: In this article, a polycrystalline stoichiometric Bi 2 S 3 thin films are prepared by reactive evaporation at substrate temperatures ranging from 423 to 473 K. A band gap of 1.38 eV is obtained from electrical and optical studies.
41 citations
TL;DR: In this paper, the failure rates of the Pearson family of distributions were characterized in terms of failure rates, and theorems were proved which generalize some previously published results concerning the gamma and negative binomial distributions.
Abstract: The Pearson family of distributions is characterized in terms of the failure rates. Analogous results when failure time is discrete are presented. Theorems are proved which generalize some previously published results concerning the gamma and negative binomial distributions. >
39 citations
TL;DR: In this article, the authors used sequential extraction to characterize the various forms of cadmium, copper, lead and zinc in the sediments of Cochin estuary, southwest India, a typical positive tropical estuary.
28 citations
24 Jun 1991
TL;DR: In this article, the authors present the results of a detailed experimental investigation exploring the possibility of improving the impedance bandwidth of a printed dipole antenna, which can give considerable enhancement of impedance bandwidth without adversely affecting the efficiency of the antenna.
Abstract: The authors present the results of a detailed experimental investigation exploring the possibility of improving the impedance bandwidth of a printed dipole antenna. This configuration can give considerable enhancement of impedance bandwidth without adversely affecting the efficiency of the antenna. Specifically, the new microstrip version of the FMDA (flared microstrip dipole antenna) has a bandwidth twice that of a conventional dipole antenna. This enhancement in the bandwidth is not accompanied by any losses. It is noted that this compact broadband microstrip dipole is a substitute for conventional dipoles in phased-array antennas for terrestrial applications. >
26 citations
Journal Article•
TL;DR: Results suggested that at extreme conditions each individual factor had an independent influence on the growth of bacteria.
Abstract: Effect of environmental factors such as temperature,pH and sodium chloride concentrations, individually and at various combinations, on the growth and survival of spoilage bacteria was studied in flesh broth and Zobells broth. Eight isolates, belonging to three different genera namely, Pseudomonas , Vibrio and Acinetobacter , harvested from spoiled Penaeus indicus were stored at 5,15,30,35 and 50°C, pH 2,4,6,8,10 and 12 and sodium chloride concentrations of 0,1,3,6,10 and 15%. Optimum growth for all the isolates was found to vary from 15 to 45°C and pH from 5-10. The growth pattern of all the isolates, in rcsponse to various sodium chloride concentrations was not similar in flesh broth and Zobells broth. Optimum sodium chloride concentration was found to vary from 1 to 6%. Influence of more than one environmental factor on the growth of spoilage bacteria was tested at various levels in flesh media by maintaining one of the factors constant and altering the other two. Results suggested that at extreme conditions each individual factor had an independent influence on the growth of bacteria.
26 citations
TL;DR: This work considers the stability properties of spatial and temporal periodic orbits of one-dimensional coupled-map lattices of the block-circulant form to reduce the problem of stability of spatially periodic orbits to the smaller orbits corresponding to the building blocks of spatial periodicity.
Abstract: We consider the stability properties of spatial and temporal periodic orbits of one-dimensional coupled-map lattices. The stability matrices for them are of the block-circulant form. This helps us to reduce the problem of stability of spatially periodic orbits to the smaller orbits corresponding to the building blocks of spatial periodicity, enabling us to obtain the conditions for stability in terms of those for smaller orbits.
23 citations
TL;DR: In this paper, Toluene 2,4 diisocyanate (TDI) was used as the coupling agent for combining both types of segments and water absorption capability of these block copolymers was determined.
Abstract: Segmented block copolymers were prepared from hydroxyl-terminated liquid natural rubber (HTNR) and poly(ethylene oxide) (PEO). Toluene 2,4 diisocyanate (TDI) was used as the coupling agent for combining both types of segments. Keeping the molecular weight of HTNR constant, a series of materials were prepared using PEO with varying molecular weights. Their thermal and mechanical properties were evaluated. With increasing the PEO content, the properties vary from soft to rigid elastomers and rubber-toughened plastics. This variation in properties is caused by the changes in the sample morphology, which depends on the relative fractions of the hard and soft segments. Water absorption capability of these block copolymers was determined. Hydrogels with water content approximately up to 80% were obtained.
21 citations
TL;DR: In this article, the sorptional behavior of an organophosphorus pesticide, Malathion, has been investigated by an experiment designed to assess the effects of variations in pesticide concentrations as well as of environmental influences on sediment samples from a tropical estuary.
20 citations
TL;DR: In this article, the limits of electron transfer from the oxide surface to the acceptor in electron affinity were reported and the electron acceptors with electron affinity from 1.26 to 2.84 eV on two metal oxides have been studied.
Abstract: Adsorption of electron acceptors with electron affinity from 1.26 to 2.84 eV on two metal oxides have been studied. The limits of electron transfer from the oxide surface to the acceptor in electron affinity are reported.
19 citations
TL;DR: In this article, the general formula for the Co(II), Ni(II) and Cu(II)-clusters of l-(2'-hydroxybenzyl)-2-(2"-hydroxy-phenyl) benzimidazole (L) has been characterized.
16 citations
TL;DR: In this paper, the design and development of an L-band printed dipole antenna, optimized for wide-band applications near first resonance, is reported, achieving more than 48% impedance bandwidth (VSWR 2:1), without degrading its overall radiation efficiency.
Abstract: The design and development of an L-band printed dipole antenna, optimized for wide-band applications near first resonance, is reported. This design has achieved more than 48% impedance bandwidth (VSWR 2:1), without degrading its overall radiation efficiency.
TL;DR: Antioxidants were attached to hydroxyterminated liquid natural rubber by modified Friedel-crafts alkylation reaction using anhydrous zinc chloride as catalyst as mentioned in this paper, and the rubber bound antioxidants were found to be less volatile and less extractable compared to conventional antioxidants.
Abstract: Antioxidants were attached to hydroxy-terminated liquid natural rubber by modified Friedel-Crafts alkylation reaction using anhydrous zinc chloride as catalyst. The rubber bound antioxidants were found to be less volatile and less extractable compared to conventional antioxidants. The bound antioxidants were tried both in latex compounds and dry rubber compounds. The vulcanizates showed improved ageing resistance compared to vulcanizates based on conventional antioxidants.
Antioxidantien wurden in einer modifizierten Friedel-Crafts-Reaktion mit wasserfreiem Zinkchlorid als Katalysator an Flussig-Naturkautschuk mit Hydroxy-Endgruppen gebunden. Die immobilisierten Antioxidantien waren weniger fluchtig und extrahierbar als konventionelle Antioxidantien. Sie wurden sowohl einem Latex als auch trockenem Kautschuk zugesetzt; die daraus hergestellten Vulkanisate zeigten eine bessere Alterungsbestandigkeit als Vulkanisate mit konventionellen Antioxidantien.
TL;DR: In this paper, the dielectric properties of electron beam evaporated Sm 2 O 3 films have been investigated in the frequency range from 1 kHz to 1 MHz at various temperatures (300 K-453 K).
TL;DR: In this article, the authors used a piezoelectric transducer to detect photoacoustic signals generated in solids due to interaction with pulsed laser beam to determine the ablation threshold.
Abstract: The acoustic signals generated in solids due to interaction with pulsed laser beam is used to determine the ablation threshold of bulk polymer samples of teflon (polytetrafluoroethylene) and nylon under the irradiation from a Q-switched Nd:YAG laser at 1.06µm wavelength. A suitably designed piezoelectric transducer is employed for the detection of photoacoustic (PA) signals generated in this process. It has been observed that an abrupt increase in the amplitude of the PA signal occurs at the ablation threshold. Also there exist distinct values for the threshold corresponding to different mechanisms operative in producing damages like surface morphology, bond breaking and melting processes at different laser energy densities.
TL;DR: In this article, reaction of Aromatic and Aralkyl ketoximes with iodobenzene dichloride leads to the formation of corresponding ketones in good yields in a single pot reaction.
TL;DR: In this article, two cases of forced harmonic oscillators with time-dependent mass for which exact propagators can be evaluated are presented, and normalized solutions of the corresponding Schrodinger equations are arrived at.
Abstract: Two cases of forced harmonic oscillators with time dependent mass for which exact propagators can be evaluated are presented. From the exact propagators, normalized solutions of the corresponding Schrodinger equations are arrived at. Time-dependent invariants are also found.
TL;DR: A review of the present knowledge about the origin of blue-green window in the attenuation spectrum of ocean waters is presented in this paper, where various physical mechanisms which contribute to the formation of the w-indow are dealt separately and discussed.
Abstract: A review of the present knowledge about the origin of blue-green window in the attenuation spectrum of ocean waters is presented. The various physical mechanisms which contribute to the formation of the w-indow are dealt separately and discussed. The typical values of attenuation coefficient arising out of the various processes are compiled to obtain the total beam attenuation coefficient. These values are then compared with measured values of attenuation coefficient for ocean waters collected from Arabian sea and Bay of Bengal. The region of minimum attenuation in pure particle-free sea water is found to be at 450 to 500 nm. It is sbown that in the presence of suspended 'particlesand chlorophyll, the window shifts to longer wavelength side. Some suggestions for future work in this area are also given in the concluding section.
TL;DR: In this article, the multiplication of dislocations and dislocation density of bismuth telluride was studied by using chemical etching, and spiral structures due to Frank-Read sources were observed on the basal plane.
Abstract: Stoichiometric crystals of bismuth telluride have been grown from the melt by the horizontal zone levelling technique. The multiplication of dislocations and dislocation density was studied by using chemical etching. Dislocation spirals and loops due to Frank-Read sources have been observed on the basal plane.
TL;DR: In this article, the photoacoustic technique has been used for the determination of the glass transition temperature T g and the thermal diffusivity α in several glasses belonging to the As-Sb-Se system.
Abstract: The photoacoustic (PA) technique has been used for the determination of the glass-transition temperature T g and the thermal diffusivity α in several glasses belonging th the As-Sb-Se system. The compositional dependence of T g and α are reported for AsxSb5Se95-x, AsxSb10Se90-x, AsxSb15Se85-x and AsxSb20Se80-x glasses. The results are discussed on the basis of a chemically ordered network model and a threshold for rigidity corresponding to an average coordination number of 2.4.
Journal Article•
TL;DR: The maturation and spawning of Gerres filamentosus Cuvier in the Cochin estuary was studied from January to December 1980 and it is inferred that they may spawn in three successive batches within the same prolonged spawning season itself.
Abstract: The maturation and spawning of Gerres filamentosus Cuvier in the Cochin estuary was studied from January to December 1980. The spawning season extends from October to February. Relatively high Gondosomatic index values were observed from October to February. The fully ripe ovary is characterised with three batches of matured eggs which are not sharply differentiated among themselves and hence it is inferred that they may spawn in three successive batches within the same prolonged spawning season itself. Size at first maturity of males and females were respectively 117 and 118 mm SL. The sex ratio was significantly different in January, March, June and November andthe mean ratio of males to females were 1:11.39. Fecundity of the species varied from 64,278 to 3,87,576 eggs.
TL;DR: In this paper, an ellipsometric technique is used for this study and the effective medium theory which is utilized to interpret the results is based on the difference in reaction rate in the grains as well as grain boundaries during chemiplating.
Abstract: Irregularities at the interface in CuxS/CdS thin films can be controlled by annealing CdS film prior to chemiplating. The interlayer formed on CdS films annealed at 200°C is comparatively smooth. In CdS films annealed at higher temperatures, the interlayer is rather thick and the CdS intrusions into this layer are thin. An ellipsometric technique is used for this study and the effective medium theory which is utilized to interpret the results is based on the difference in reaction rate in the grains as well as grain boundaries during chemiplating.
TL;DR: In this article, it was shown that the grown crystals had an fcc structure with lattice constant a = 18.471 A, and the possible mechanism for the growth of hollow needles has been suggested on the basis of morphological studies.
TL;DR: In this article, an inventory system with unit demand, varying ordering levels and random lead times is considered, and the ordering quantity will be such as to bring back the inventory level to S at the ordering epoch.
Abstract: An inventory system with unit demand, varying ordering levels and random lead times is considered in this paper. Ordering level is determined by the number of demands during last lead time. The ordering quantity will be such as to bring back the inventory level to S at the ordering epoch. No backlog is permitted. The time dependent probability distribution of the inventory level is obtained. Correlation between the number of demands during a lead time and the length of the next inventory dry period is obtained and it is illustrated by an example.
TL;DR: In this paper, a high density polyethylene grade is blended with two selected grades of linear low density polymethylene and the mechanical and rheological properties of the blends are evaluated over the entire composition range.
Abstract: A high density polyethylene grade is blended with two selected grades of linear low density polyethylene and the mechanical and rheological properties of the blends are evaluated over the entire composition range. The blends show sufficient compatibility in the solid phase and in the melt and hence they can be advantageously used to capitalize on their useful properties.
Die rheologischen und mechanischen Eigenschaften von Blends aus PE-HD und zwei verschiedenen PE-LLD-Typen wurden im gesamten Mischungsbereich gemessen. Die Polymeren sind im festen Zustand und in der Schmelze ausreichend vertraglich, so das ihre vorteilhaften Eigenschaften genutzt werden konnen.
TL;DR: In this article, Noether's second theorem is adapted to the generalized hydromechanical variational principle and a particular group of transformations is characterized and is shown to be closely connected with the generalized Helmholtz theorems.
TL;DR: In this paper, an indigenous isolate Bacillus R-8 was found to produce thermostable β-amylase, achieving the maximum production of 100 units per ml in the maltose medium and also in the alkaline conditions of fermentation.
Abstract: An indigenous isolate Bacillus R–8 was found to produce thermostable β-amylase. The enzyme yield was highest during the stationary phase of the culture. Maximum production of 100 units per ml was achieved in the maltose medium and also in the alkaline conditions of fermentation. It has been observed that the rate of enzyme formation was highest (2.8 units/g of cells/h) with glucose under neutral conditions. The variations in the fermentation parameters which have resulted in the significant difference in terms of total enzyme production and the rate of enzyme formation have been discussed.
Synthese von warmebestandiger Alpha-Amylase mittels Bacillus-Isolat R–8.
Es wurde ein einheimisches Isolat aus Bacillus R–8 zur Gewinnung von warmebestandiger β-Amylase gefunden. Die Enzymausbeute war am hochsten wahrend der stationaren Phase der Kultur. Die maximale Produktion von 100 Einheiten je ml wurde im Maltose-Medium erreicht sowie unter alkalischen Bedingungen bei der Fermentation. Es wurde beobachtet, das die Geschwindigkeit der Enzymbildung (2,8 Einheiten/g Zellen/h) mit Glucose unter neutralen Bedingungen am hochsten war. Die Variationen der Fermentationsparameter, die in merklichen Unterschieden der Gesamt-Enzymproduktion resultierten, und die Geschwindigkeit der Enzymbildung werden diskutiert.
TL;DR: In this paper, the effect of laser induced two-photon photoemission optogalvanic (TPPOG) effect from tungsten electrode in a discharge cell using 564 nm radiation obtained from a pulsed dye laser is described.
Abstract: Observation of laser induced two-photon photoemission optogalvanic (TPPOG) effect from tungsten electrode in a discharge cell using 564 nm radiation obtained from a pulsed dye laser is described. The magnitude of the POG signal is studied as a function of laser energy under various discharge parameters. Competition between one-photon and two-photon processes has been observed when nitrogen gas is used in the discharge cell.
Journal Article•
TL;DR: In this article, the Tertiary sequence is overlain by carbonaceous clay, china clay, and laterite, and the Duricrust layer is found interbedded within the carbonaceous clays, showing abnormal geochemical anomalies.
Abstract: The Tertiary sequence begins with fossiliferous marl and is overlain by carbonaceous clay, china clay and laterite. The thin (3 cm thick), hard, compact duricrust layer, which is found interbedded within the carbonaceous clays, shows abnormal geochemical anomalies. Major elements such as Fe, Mn and Ca and the trace element Co show about 2-3 fold and 1-2 fold increase respectively in the duricrust than the upper and lower sections. However, the content of Na, K, Ni, Cu and organic carbon show an opposite trend. Cd does not show any marked variation along the profile. The CaCO 3 content is remarkably high in the duricrust and marl than the other layers. Fe and Mn contents are much higher in the laterite than china clay, other parameters do not show much variation. The high content of Fe, Mn, Ca and CaCO 3 and low Ni/Co ratio and organic carbon content in the duricrust layer indicate an oxidizing environmental condition which existed at the time of the formation of this layer, while the converse trend of these parameters in the carbonaceous clays indicate the prevalence of a reducing condition.