Showing papers by "Cochin University of Science and Technology published in 1999"

Dielectric properties of rubber ferrite composites containing mixed ferrites

Abstract: Rubber ferrite composites (RFC) are important since they have useful applications as microwave absorbers and flexible magnets. The mouldability of these composites into complex shapes is another advantage. The evaluation of their dielectric and magnetic properties is important in understanding the physical properties of these composites. Pre-characterized nickel zinc ferrites (Ni1-xZnxFe2O4 where 0 x1 in steps of 0.2) prepared by ceramic techniques were incorporated in to a butyl rubber matrix according to a specific recipe to yield RFCs. The dielectric constant of ceramic Ni1-xZnxFe2O4 and the butyl rubber composites incorporated with Ni1-xZnxFe2O4 are studied as a function of frequency, composition, loading and temperature. The observed data indicates that the dependence of the dielectric constant on frequency follows Maxwell-Wagner interfacial polarization. The compositional (zinc content, i.e. x value) dependence shows that the dielectric constant increases initially and reaches a maximum value for the composition corresponding to x = 0.6 and thereafter it decreases. This can be explained on the basis of porosity and alternating current (AC) conductivity. It was also observed that the dielectric constant of the composite material increases with an increase of the volume fraction of the magnetic filler. These observations satisfy some mixture equations, which correlate the dielectric constant of the matrix, filler and the composites. The temperature dependence of the dielectric constant of the ceramic samples as well as the RFCs shows an increase with an increase of temperature at low frequencies. The dielectric constant of the blank butyl rubber was also determined. It was observed that for a blank sample (without filler) the dielectric constant decreases with an increase of temperature. This is due to the decrease in polymer density with increase in temperature. These results suggest that the magnetic and dielectric properties of RFCs can be manipulated by appropriate loading and a judicious choice of the magnetic filler. The modification of these properties will aid in the design of composite materials for microwave absorbers.

Solvent Effect on Absolute Fluorescence Quantum Yield of Rhodamine 6G Determined Using Transient Thermal Lens Technique

Abstract: Dual beam thermal lens technique is successfully employed for the determination of absolute fluorescence quantum yield of rhodamine 6G laser dye in different solvents. A 532 nm radiation from a Q-switched Nd:YAG laser was used for the excitation purpose. The fluorescence quantum yield values are found to be strongly influenced by environmental effects. It has been observed that fluorescence yield is greater for rhodamine 6G in ethylene glycol system than in water or in methanol. Our results also indicate that parameters like concentration of the dye solution, aggregate formation and excited state absorption affect the absolute values of fluorescence yield significantly.

Blends of bisphenol A‐based cyanate ester and bismaleimide: Cure and thermal characteristics

Abstract: A dicyanate ester, namely, 2,2-bis-(4-cyanatophenyl)propane, and a bismaleimide, namely, 2,2-bis[4-(4-maleimido phenoxy)phenyl]propane, possessing closely resembling backbone structures, were cured together to derive bismaleimide–triazine network polymers of varying compositions. The blend manifested a eutectic melting behavior at a 1 : 1 composition with a eutectic melting point of 15°C. The cure characterization of the blends was done by DSC and dynamic mechanical analyses (DMA). The near simultaneous cure of the blend could be transformed to a clear sequential one by catalyzing the dicyanate cure to lower temperature using dibutyl tin dilaurate. The two-stage, independent cure of the components of the blend evidenced in DSC was confirmed by DMA. The cure profile of the bismaleimide component predicted from the kinetic data derived from nonisothermal DSC was found to be in league with the isothermal DMA behavior. Both techniques led to optimization of the cure schedule of the blends. The cured polymers were characterized by FTIR and TGA. The cured blends underwent decomposition in two stages, each corresponding to the polycyanurate and polybismaleimide. Enhancing the bismaleimide component did not alter the initial decomposition temperature, but led to reduced rate of thermal degradation at higher temperature. Interlinking of the two networks and enhancing crosslink density through coreaction of the blend with 4-cyantophenylmaleimide unaffected the initial decomposition properties but was conducive for increasing the char residue significantly. Computation of activation parameters for the thermal decomposition of the polymers confirmed that the first step in the degradation of the blends is caused by the polycyanurate component. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 74: 3365–3375, 1999

An epidemiologic approach to drug prescribing quality assessment: a study in primary care practice in France.

Abstract: Objective To assess drug prescribing by primary care physicians in France for various types of conditions, and to identify patterns and risk factors for poor prescribing quality. Methods The orders (n = 23,080) written for patients with five target diseases (acute nasopharyngitis, acute tonsillitis, essential hypertension, osteoarthrosis, and back and periarticular disorders), by primary care physicians (n = 1,049) were extracted from a nationwide prescription database and analyzed according to 17 quantitative indicators of drug prescribing quality constructed on explicit a priori criteria. Results Ineffective drugs were prescribed in 32% to 88% of orders according to the target disease. Six percent to 40% of orders resulted in drug interactions, age problems, and overdosage. A consistent pattern of associations between indicators was found, which suggests that drug prescribing quality is multidimensional and is composed of at least five dimensions: placebo, novelty, exoticism, misdosage, and interaction. Several factors associated with indicators were also identified, some of them defining groups of patients at risk (women, elderly, and less educated), physicians at risk (women, aged, and isolated), and contexts at risk (patient's home and disease frequently treated by the physician) of poor drug prescribing quality. Conclusions Drug prescribing by French primary care physicians appears nonoptimal, in terms of both risk of iatrogeny and waste of money. This study further documents the complexity and the multidimensionality of drug prescribing quality. It suggests that more attention must be paid to patients' and physicians' risk factors for poor drug prescribing quality if educational programs and regulatory processes are to succeed in promoting safer and more cost-effective practices.

Rubber seed oil: A multipurpose additive in NR and SBR compounds

Abstract: Rubber seed oil was used as a multipurpose ingredient in natural rubber (NR) and styrene butadiene rubber (SBR) compounds. The study shows that the oil, when substituted for conventional plasticiser, imparts excellent mechanical properties to NR and SBR vulcanizates. Further, it also improves aging resistance, reduces cure time, increases abrasion resistance and flex resistance, and reduces blooming. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 72: 487-492, 1999

On Concomitants of Order Statistics from Morgenstern Family

Abstract: In the present paper the distribution theory of concomitants of order statistics from the Morgenstern family of distribution is investigated. An application of the results in providing some quick estimates of the parameters in the Gumbel's bivariate exponential distribution is also discussed.

Selective benzoylation of o-xylene to 3,4-dimethylbenzophenone using various zeolite catalysts

Abstract: The liquid phase benzoylation of o -xylene with benzoyl chloride (BOC) over various zeolite catalysts is studied in a batch reactor at atmospheric pressure and 411 K. The results obtained over different zeolite catalysts are compared with the homogeneous Lewis acid catalyst, AlCl 3 and amorphous silica–alumina. The protonic form of zeolite beta is found to be an efficient catalyst compared to other zeolites in the benzoylation of o -xylene. The conversion of BOC, turnover rate of BOC conversion (TOF) and selectivity for 3,4-dimethylbenzophenone (3,4-DMBP) over zeolite H-beta are found to be 52.8 wt.%, 69.7×10 −5 s −1 mol −1 Al and 94.7 wt.%, respectively, at the following reaction conditions [H-beta to BOC (w/w)=0.28, o -xylene to BOC (molar ratio)=5; 411 K; 1 atm]. The non-shape selective AlCl 3 catalyst produces higher amount of consecutive products (16.2 wt.%) and hence gives lower selectivity for 3,4-DMBP (76.5 wt.%). The acidity and pore structure of H-beta appeared to be responsible for good performance. Increase in reaction time, catalyst concentration, reaction temperature, o -xylene to BOC molar ratio enhances the conversion of BOC, whereas it decreases with the increase in degree of Na-exchange and SiO 2 /Al 2 O 3 molar ratios of H-beta. The zeolite H-beta is recycled three times without the loss of 3,4-DMBP selectivity but with a decline in the catalytic activity of H-beta. Additionally, the benzoylation of m -xylene and p -xylene is also investigated using H-beta. The Friedel–Crafts acylation reaction mechanism involves the formation of an electrophile (C 6 H 5 CO + ) over an acidic zeolite catalyst which attacks the xylene ring resulting in the formation of dimethyl benzophenones.

Studies of nonlinear absorption and aggregation in aqueous solutions of rhodamine 6G using a transient thermal lens technique

Abstract: Dual-beam transient thermal lens studies were carried out in aqueous solutions of rhodamine 6G using 532 nm pulses from a frequency-doubled Nd:YAG laser. The analysis of the observed data showed that the thermal lens method can effectively be utilized to study the nonlinear absorption and aggregation which are taking place in a dye medium.

Reliability of ak-out-of-n system with repair and retrial of failed units

Abstract: We consider ak-out-of-n system with repair. Life times of components are independent exponentially distributed random variables with parameter λ i when the number of working units isi. Failed units are taken for repair to a station, manned by a single server, having no waiting room. The failed units are brought to an orbit, if the server is found to be busy, for retrial. Reliability of the system is computed in the following three situations: (i) Cold system (ii) Warm system and (iii) Hot system. Several other system characteristics are derived.

Extracellular production of L-glutaminase by alkalophilic Beauveria bassiana BTMF S10 isolated from marine sediment

Abstract: Beauveria sp. BTMF S10 isolated from marine sediment produced extracellular L-glutaminase. Maximal L-glutaminase yield (46.9 U/ml) was obtained in a medium supplemented with 1% (w/v) yeast extract and sorbitol, 9% (w/v) sodium chloride and 0.2% (w/v) methionine, initial pH 9.0 and at 27 °C after 108 h. This enzyme was inducible and growth-associated.

Effects of hypertension and its treatment on mental function.

Abstract: This paper addresses the relationship between hypertension and cognitive status and the impact of antihypertensive treatment. Data from cross-sectional and longitudinal studies are reviewed. After adjustment for age and level of education, cognitive function of hypertensive patients is impaired compared with the cognitive status of their nonhypertensive counterparts. The mechanisms underlying hypertension associated cognitive impairment remain to be elucidated. The role of antihypertensive treatment also has to be determined. Some evidence suggests that antihypertensive treatment may prevent dementia in hypertensive patients.

Selective N-monomethylation of aniline over Zn1-xNixFe2O4 (x=0, 0.2, 0.5, 0.8 and 1) type systems

Abstract: The reaction of aniline with methanol was carried out over Zn1−xNixFe2O4 (x=0, 0.2, 0.5, 0.8 and 1) type systems in a fixed-bed down-flow reactor. It was observed that systems possessing low “x” values are highly selective and active for mono N-alkylation of aniline leading to N-methyl aniline. Selectivity for N-methyl aniline over ZnFe2O4 was more than 99% under the optimized reaction conditions. Even at methanol to aniline molar ratio of 2, the yield of N-methyl aniline was nearly 55.5%, whereas its yield exceeded 67% at the molar ratio of 7. The Lewis acid sites of the catalysts are mainly responsible for the good catalytic performance. Cation distribution in the spinel lattice influences their acido-basic properties, and hence, these factors have been considered as helpful to evaluate the activity and stability of the systems.

Enhancement of [m-methoxy 3H]MDL100907 binding to 5HT2A receptors in cerebral cortex and brain stem of streptozotocin induced diabetic rats.

Abstract: 5-Hydroxytryptamine2A (5-HT2A) receptor kinetics was studied in cerebral cortex and brain stem of streptozotocin (STZ) induced diabetic rats. Scatchard analysis with [3H] (±) 2,3dimethoxyphenyl-1-[2-(4-piperidine)-methanol] ([3H]MDL100907) in cerebral cortex showed no significant change in maximal binding (Bmax) in diabetic rats compared to controls. Dissociation constant (Kd) of diabetic rats showed a significant decrease (p < 0.05) in cerebral cortex, which was reversed to normal by insulin treatment. Competition studies of [3H]MDL100907 binding in cerebral cortex with ketanserin showed the appearance of an additional low affinity site for 5-HT2A receptors in diabetic state, which was reversed to control pattern by insulin treatment. In brain stem, scatchard analysis showed a significant increase (p < 0.05) in Bmax accompanied by a significant increase (p < 0.05) in Kd. Competition analysis in brain stem also showed a shift in affinity towards a low affinity State for 5-HT2A receptors. All these parameters were reversed to control level by insulin treatment. These results show that in cerebral cortex there is an increase in affinity of 5-HT2A receptors without any change in its number and in the case of brain stem there is an increase in number of 5HT2A receptors accompanied by a decrease in its affinity during diabetes. Thus, from the results we suggest that the increase in affinity of 5-HT2A receptors in cerebral cortex and upregulation of 5-HT2A receptors in brain stem may lead to altered neuronal function in diabetes.

Mudbank regime off the Kerala coast during monsoon and non-monsoon seasons

Abstract: Field experiments conducted in the nearshore ocean to understand the dynamics of mudbank off Kerala, south-west coast of India, are highlighted Real time monitoring of the nearshore ocean off Purakkad, Kerala was accomplished using pressure transducers for nearshore surface wave measurements, and current sensors for nearshore velocity measurements Comprehensive information on the spatial structure of mudbank was obtained from aerial surveys Extensive data collected on surface waves and currents in the nearshore ocean, indicate that the infra-gravity (IG) waves (leaky modes and trapped edge wave modes), and far infra-gravity (FIG) waves coupled with strong shoreline reflections and undertow play an important role in the dynamics associated with the mudbanks off Kerala during the monsoon season During the non-monsoon season evidence for progressive edge waves in the infragravity frequency band, an energetic gravity wave band and a strong undertow with weak reflections was observed

Interstitial water and hydrochemistry of a mangrove forest and adjoining water system, south west coast of India

Abstract: Eh, pH, salinity, total alkalinity, dissolved O2, NO2 –, PO4 –3, SiO2 and NH4 + of waters from a mangrove forest, an estuary and a creek connecting the mangrove forest and the estuary have been measured. Further, the chemistry of interstitial waters of surficial and core sediments from the mangrove forest have been analyzed for the above parameters, except dissolved oxygen. To understand the flux of nutrients from the mangrove forest to the adjoining estuary, creek waters were monitored during tidal phases. PO4 –3, SiO2 and NH4 + were found to be at elevated levels in mangrove waters whereas NO2 – shows no variation compared to the estuary. Dissolved O2 is low in mangrove waters. PO4 –3, NH4 + and SiO2 are several times higher in interstitial waters than in overlying waters. Several fold enrichment of PO4 –3, NH4 + and, to some extent, SiO2 were measured in creek waters during ebbing relative to flooding, indicating that mangroves act as a perennial source for the above nutrients.

Significance of time scales in nonlinear dynamical analysis of electroencephalogram signals.

Abstract: We propose to show in this paper, that the time series obtained from biological systems such as human brain are invariably nonstationary because of different time scales involved in the dynamical process. This makes the invariant parameters time dependent. We made a global analysis of the EEG data obtained from the eight locations on the skull space and studied simultaneously the dynamical characteristics from various parts of the brain. We have proved that the dynamical parameters are sensitive to the time scales and hence in the study of brain one must identify all relevant time scales involved in the process to get an insight in the working of brain.

Characterization of Lifetime Distributions Using Measure of Uncertainty

Abstract: In the present paper, we characterize exponential, Pareto, Wei bull and beta distributions using the concept of measure of uncertainty defined by Ebrahimi and Pellery (1995). Further, a new measure of uncertainty is introduced and its properties are discussed. Finally, we present a characterization theorem for extreme value distribution by extending the concept into negative set-up.