Showing papers by "Cochin University of Science and Technology published in 2001"
TL;DR: In this article, the intrinsic acidity among the ferrites was found to decrease in the order: cobalt>nickel>copper, whereas the strong acid sites were left unaffected.
Abstract: Ferrospinels of nickel, cobalt and copper and their sulphated analogues were prepared by the room temperature coprecipitation route to yield samples with high surface areas. The intrinsic acidity among the ferrites was found to decrease in the order: cobalt>nickel>copper. Sulphation caused an increase in the number of weak and medium strong acid sites, whereas the strong acid sites were left unaffected. Electron donor studies revealed that copper ferrite has both the highest proportion of strong sites and the lowest proportion of weak basic sites. All the ferrite samples proved to be good catalysts for the benzoylation of toluene with benzoyl chloride, copper and cobalt ferrites being much more active than nickel ferrite. The catalytic activity for benzoylation was not much influenced by sulphation, but it increased remarkably with calcination temperature of the catalyst. Surface Lewis acid sites, provided by the octahedral cations on the spinel surface, are suggested to be responsible for the catalytic activity for the benzoylation reaction.
216 citations
TL;DR: Flocculation is faster at higher concentrations of kaolinite and the flocs are large and settle rapidly, and flocculation efficiency is very sensitive to pH, and reaches a maximum at pH 7.5.
211 citations
TL;DR: In this article, the fabrication and characterization of a fiber optic pH sensor based on evanescent wave absorption is presented, where the unclad portion of a multi-mode optical fiber is coated with a pH sensitive dye, which is immobilized by the sol-gel route.
Abstract: The fabrication and characterization of a fibre optic pH sensor based on evanescent wave absorption is presented. The unclad portion of a multi-mode optical fibre is coated with a pH sensitive dye, which is immobilized by the sol-gel route. The sensitivity of the device has been found to increase when multiple sol-gel coatings are used as the sensing region. The dynamic range and the temporal response of the sensor are investigated for two different dyes, namely bromocresol purple and bromocresol green. The performance of the device is evaluated in terms of the results obtained during actual measurements.
75 citations
TL;DR: The sensor described here is sensitive enough to detect concentrations as low as nanomoles per liter of a chemical species, with a dynamic range of more than 6 orders of magnitude.
Abstract: We propose and demonstrate the possibility of using a permanently microbent bare optical fiber for detecting chemical species. Two detection schemes, viz., a bright-field detection scheme (for the core modes), and a dark-field detection scheme (for the cladding modes) have been employed to produce a fiber-optic sensor. The sensor described here is sensitive enough to detect concentrations as low as nanomoles per liter of a chemical species, with a dynamic range of more than 6 orders of magnitude.
70 citations
TL;DR: In this article, the inter phase conversion of Cu 2− x Se and Cu 3 Se 2 thin films prepared using the chemical bath deposition (CBD) technique is found to be cyclic.
68 citations
TL;DR: The results indicate that parameters, like the concentration of the dye solution, aggregate formation and excited state absorption, affect the absolute values of the fluorescence yield significantly.
Abstract: A dual-beam transient thermal-lens technique was employed for the determination of absolute fluorescence quantum-yield measurements of Rhodamine B laser dye in different solvents. We investigated the effect of excitation on the absolute fluorescence quantum yield of Rhodamine B. 514 nm radiation from an argon ion laser was used as a cw excitation source and 532 nm pulses from a Q-switched Nd:YAG laser were used as a pulsed excitation source. The fluorescence quantum-yield values were found to be strongly influenced by environmental effects as well as the transient nature of the excitation beam. Our results also indicate that parameters, like the concentration of the dye solution, aggregate formation and excited state absorption, affect the absolute values of the fluorescence yield significantly.
68 citations
TL;DR: In this article, solid solution phases between the aeschynite and the euxenite groups are characterized by X-ray diffraction and microwave methods, and the results indicate the possibility of tailoring the dielectric properties by varying the composition of the solid solution phase.
65 citations
TL;DR: In this article, the authors examined the cross spectral correlation between gravity and bathymetry along 21 profiles across the Eastern Continental Margin of India (ECMI) and 16 profile across the conjugate East Antarctica Margin using both ship and satellite-derived gravity data.
65 citations
TL;DR: In this article, the authors performed time resolved emission spectroscopic measurements on a plasma plume generated by pulsed laser ablation of carbon in helium ambient atmosphere and found that the emission features of C2 species were significantly influenced by the ambient helium atmosphere.
50 citations
TL;DR: In this article, simple equations are proposed to predetermine the magnetic and dielectric properties of rubber ferrite composites containing various mixed ferrites, and the results are correlated.
Abstract: Rubber ferrite composites containing various mixed ferrites were prepared for different compositions and various loadings. The magnetic and dielectric properties of the fillers as well as the ferrite filled matrixes were evaluated separately. The results are correlated. Simple equations are proposed to predetermine the magnetic and dielectric properties. The validity of these equations is verified and they are found to be in good agreement. These equations are useful in tailoring the magnetic and dielectric properties of these composites with predetermined properties.
45 citations
TL;DR: The synergistic activity of binary accelerator systems in rubber vulcanization is well known as discussed by the authors, and it is suggested that thiourea and its derivatives are important secondary accelerators in this context, which can effectively prevent prevulcanization and produce a vulcanizate with superior mechanical properties compared to those of a stock cured with a single accelerator.
Abstract: The synergistic activity of binary accelerator systems in rubber vulcanization is well known. Binary accelerator systems are being widely used in industry and are becoming increasingly popular because of the fact that such mixed systems can effectively prevent prevulcanization, permit the vulcanization to be carried out at a lower temperature in a shorter time, and produce a vulcanizate with superior mechanical properties compared to those of a stock cured with a single accelerator. Thiourea and its derivatives are important secondary accelerators in this context. It is suggested that thiourea containing binary accelerator systems cause rubber vulcanization to proceed by a nucleophilic reaction mechanism. In the present study 1-phenyl-5-ortho, -meta, and -para-tolyl derivatives of 2,4-dithiobiurets, which are more nucleophilic than thiourea and vary in their nucleophilic reactivity, are used as secondary accelerators along with 2-morpholinothiobenzothiazole in the vulcanization of natural rubber. The results show an appreciable reduction in the cure time for the mixes containing the dithiobiurets compared to the reference mix. These results are indicative of a nucleophilic reaction mechanism in the vulcanization reaction under consideration. These vulcanizates also demonstrate comparatively better tensile properties and good retention of these properties after aging. An attempt is also made to correlate the variation in physical properties to chemical crosslink formation in the various vulcanizates. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 90: 3173–3182, 2003
TL;DR: In this paper, the magnetic properties of the rubber filler and the ferrite loaded rubber ferrite composites (RFCs) were evaluated and compared, and the validity of these equations were checked and correlated with the experimental data.
Abstract: Polycrystalline single phasic mixed ferrites belonging to the series Ni1−xZnxFe2O4 for various values of x have been prepared by conventional ceramic techniques. Pre-characterized nickel zinc ferrites were then incorporated into a natural rubber matrix according to a specific recipe for various loadings. The processability and cure parameters were then determined. The magnetic properties of the ceramic filler as well as the ferrite loaded rubber ferrite composites (RFC) were evaluated and compared. A general equation for predicting the magnetic properties was also formulated. The validity of these equations were then checked and correlated with the experimental data. The coercivity of the RFCs almost resemble that of the ceramic component in the RFC. Percolation threshold is not reached for a maximum loading of 120 phr (parts per hundred rubber by weight) of the filler. These studies indicate that flexible magnets can be made with appropriate magnetic properties namely saturation magnetisation (Ms) and magnetic field strength (Hc) by a judicious choice of x and a corresponding loading. These studies also suggest that there is no possible interaction between the filler and the matrix at least at the macroscopic level. The formulated equation will aid in synthesizing RFCs with predetermined magnetic properties.
TL;DR: In this article, high crystalline, ultra fine TiO2 (anatase) having high surface area has been prepared by thermal hydrolysis of titanyl sulphate solution and characterized using B.E.T surface area measurements, XRD and chemical analysis.
TL;DR: Bismuth Selenide single crystals have been grown by the vertical normal freezing technique and confirmation of the compound formation and the lattice parameters are calculated from the X-ray diffractogram as discussed by the authors.
TL;DR: In this paper, the authors reported the data obtained on an attempt at the utilisation of the oily sludge, which is a dumped waste of petroleum refineries, which was used in the preparation of bituminous paints.
Abstract: This paper reports the data obtained on an attempt at the utilisation of the oily sludge, which is a dumped waste of petroleum refineries. Growing public concern over the health and environmental implications of these wastes has forced the regulatory agencies to make it mandatory for these industries to undertake the disposal of these wastes in an effective and environmentally safe manner. In the present work, the above sludge after purification was subjected to vacuum distillation to recover approximately 17% of lighter oils. The residue was subjected to heat treatment at 225°C for 2.5 h with ‘2.5% w/w AlCl 3 ’ to obtain industrial bitumen 90/15 grade (Industrial bitumen are of different types depending on the softening point–penetration relationship. The first figure 90 represents the softening point while the second figure 15, represents the penetration. Both penetration and softening points are a measure of consistency for bitumen). The usefulness of the above industrial bitumen was tried in the preparation of bituminous paints. All three formulations investigated were found to be homogeneous showing no separation of solvent. There was no coagulation of the asphalt base nor settling or packing in the container. These samples were found to meet the requirements of drying time, consistency, finish, stripping, flexibility and adhesion, keeping properties, etc. It was also seen that the heat resistance of these bituminous paints can be increased considerably by including cashew nut shell liquid–formaldehyde resin in the formulation. Cashew nut shell liquid (CNSL) is a cheap by-product of the cashew industry, and its utilisation can also help to reduce production costs of bituminous paints. This study also showed that incorporation of chlorinated rubber in the formulation would enhance the acid resistance considerably without affecting heat resistance and other desirable properties. This method of using sludge as bituminous paints can be a simple, eco-friendly and useful means of disposal in petroleum refining industries.
TL;DR: This is the first report of a cell culture system from the ovarian tissues of African catfish, and the cell cultures can be maintained for 12–15 days without fluid change between the passages.
TL;DR: In this paper, it was shown that for each k ≥ 1, the spectral approximation of selfadjoint linear operators converges to the corresponding approximation numbers asn→∞.
Abstract: LetA be a bounded linear operator onsome infinite-dimensional separable Hilbert spaceH and letA
n be the orthogonal compression ofA to the span of the firstn elements of an orthonormal basis ofH. We show that, for eachk≥1, the approximation numberss
k(An) converge to the corresponding approximation numbers
k(A) asn→∞. This observation implies almost at once some well known results on the spectral approximation of bounded selfadjoint operators. For example, it allows us to identify the limits of all upper and lower eigenvalues ofA
n in the case whereA is selfadjoint. These limits give us all points of the spectrum of a selfadjoint operator which lie outside the convex hull of the essential spectrum. Moreover, it follows that the spectrum of a selfadjoint operatorA with a connected essential spectrum can be completely recovered from the eigenvalues ofA
n asn goes to infinity.
TL;DR: In this article, the integrability condition of NLS equation is arrived from the linear eigenvalue problem and is studied by using the Painleve singularity structure analysis.
Abstract: Nonlinear Schrodinger (NLS) equation which governs the propagation of single field in the fibre medium with pulse chirping and gain (loss) is considered. The integrability condition of NLS equation is arrived from the linear eigenvalue problem and is studied by using the Painleve singularity structure analysis. From the Lax pair, soliton solution is constructed by using the Darboux–Backlund transformation technique. From the results, we show that the soliton is alive, i.e., pulse area is conserved with the inclusion of damping and pulse chirping effects.
TL;DR: In this article, the authors studied a k-out-of-n reliability system in which a single unreliable server maintains n identical components and the failure times of the components are assumed to follow an exponential distribution.
Abstract: In this paper we study a k-out-of-n reliability system in which a single unreliable server maintains n identical components. The reliability system is studied under the (N, T) policy. An idle server takes a vacation for a random amount of time T and then attends to any failed component waiting in line upon completion of the vacation. The vacationing server is recalled instantaneously upon the failure of the N th component. The failure times of the components are assumed to follow an exponential distribution. The server is subject to failure with failure times exponentially distributed. Repair times of the component, fixing times of the server, and vacationing times of the server are assumed to be of phase type. Using matrix-analytic methods we perform steady state analysis of this model. Time spent by a failed component in service, total time in the repair facility, vacation time of the server, non-vacation time of the server, and time until failure of the system are all shown to be of phase type. Several performance measures are evaluated. Illustrative numerical examples are presented.
TL;DR: In this paper, a dual-band, dual-polarized microstrip antenna for terrestrial and satellite communications is presented. But the antenna is not suitable for satellite communications, and its performance is not as good as a standard rectangular patch antenna.
Abstract: A new compact dual-band, dual-polarized microstrip an- tenna is presented. 7'iris antenna resonates at two frequencies with different polarizations: a linearly polarized one for terrestrial communica- tion, and a circularly polarized one for satellite mobile communication. This antenna also provides an area reduction of 70% compared to a standard rectangular patch antenna . © 2001 John Wiley & Sons, Inc. Microwave Opt Technol Lett 29: 315-317, 2001.
Journal Article•
TL;DR: Increased IL-18 production in chronic CD lesions is shown and epithelial cells and macrophages are identified as IL- 18-producing cells and these results are in accordance with a putative role of matureIL-18 in the pathogenesis of CD.
Abstract: A local increase of interleukin-18 (IL-18) expression has been recently demonstrated in Crohn's disease (CD), suggesting a role for mature IL-18 (cleaved by ICE protease) in the induction of proinflammatory cytokines and Th1 polarization observed in CD lesions. The aim of this study was to investigate IL-18 modulation and its potential immune consequences in CD lesions. We showed increased IL-18 production in chronic CD lesions and identified epithelial cells and macrophages as IL-18-producing cells. A twofold increase in ICE alpha, beta, and/or gamma mRNA that encodes for the complete mature peptide was required for ICE activity, and a marked increase in IL-18R-positive immune cells was observed in chronic lesions compared to uninvolved areas or normal control samples. Chronic lesions also displayed intense transcription of IL-18-induced cytokines, IFN-gamma, IL-1beta, TNF-alpha, and IL-8. By contrast, when neither IL-18 nor ICE mRNAs were enhanced (early asymptomatic CD lesions), IL-18-induced cytokines were not up-regulated. These results are in accordance with a putative role of mature IL-18 in the pathogenesis of CD.
TL;DR: The results suggest that GABA(A) receptor act as an inhibitory signal for hepatic cell proliferation and enhanced the transforming growth factor beta1 (TGFbeta1) mediated DNA synthesis suppression in primary hepatocyte cultures.
TL;DR: In this article, a polymer-bound p-phenylenediamine was chemically attached to low molecular weight chlo- rinated paraffin wax and used as an antioxidant in natural rubber vulcanizates.
Abstract: p-Phenylenediamine was chemically attached to low molecular weight chlo- rinated paraffin wax. The polymer-bound p-phenylenediamine was characterized by vapor-phase osmometry (VPO), proton magnetic resonance spectroscopy ('H-NMR), infrared spectroscopy (IR), and thermogravimetric analysis (TGA). The efficiency and permanence of the polymer-bound p-phenylenediamine as an antioxidant was com- pared with a conventional amine-type antioxidant in natural rubber vulcanizates. The vulcanizates showed improved aging resistance in comparison to vulcanizates contain- ing a conventional antioxidant. The presence of liquid polymer-bound p-phenylenedi- amine also reduces the amount of the plasticizer required for compounding. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 81: 2183-2189, 2001
Journal Article•
TL;DR: The autolytic activity was significantly higher in small fish in all the three species and the total biochemical composition of freshwater major carps in relation to size was evaluated.
Abstract: Total biochemical composition of freshwater major carps, Labeo rohita -(rohu); Catla catla (catla); Cirrhinus mrigala (mrigal), in relation to size was evaluated. The water soluble nitrogen iraction constituted about 21% of the total nitrogen. Salt soluble fraction constituted 55 - 60% of the total nitrogen. Non-protein nitrogen represented 12% of the total nitrogen in all the cases except mrigal of small size (9.36%). The insoluble connective tissue contributed to 2-3 per cent of total nitrogen. The monounsaturated fatty acids (MUFA) formed 31-39% of the total fatty acids and 60-68% of the MUFA in freshwater carps was C18:l. The essential amino acids contributed to 41 to 51% of the total amino acids in freshwater major carps. Aromatic amino acid content was slightly higher compared to marine fishes while the proportion of proline was less. Variations in composition in relation to size are discussed. The autolytic activity was significantly higher in small fish in all the three species
TL;DR: In this article, the synthesis and characterization of a new series of chiral poly(ester-amide)s were reported, which were prepared by the simple reaction of diacid chlorides with biphenolic azo chromophores and optically active dihydroxy compound (isosorbide) in dimethyl acetamide at 100°C.
Abstract: The synthesis and characterization of a new series of chiral poly(ester-amide)s are reported. They were prepared by the simple reaction of diacid chlorides with biphenolic azo chromophores and optically active dihydroxy compound (isosorbide) in dimethyl acetamide at 100 °C. The polymers containing isosorbide units were optically active. The polymers showed Tg between 100 and 190 °C and were stable up to 400 °C. These poly(ester-amide)s showed a positive solvatochromism in UV–visible absorption spectra. Second harmonic generation activities were measured by the powder method.
© 2001 Society of Chemical Industry
TL;DR: The optimal D -value is examined by bringing in costs such as the cost of system being down, the server activation cost, and several other measures of performance by computing the optimal D value which maximizes a suitably defined cost function.
Journal Article•
TL;DR: It is inferred from the present study that the antioxidant defenses and the in vivo metabolism of the surfactants are key factors in deciding the Surfactant toxicity.
Abstract: Exposure to anionic (sodium dodecyl sulfate, SDS), cationic (cetyl trimethyl ammonium bromide CTAB) and non ionic (Triton X-100) surfactants at a sub lethal concentration of 1 ppm resulted in severe oxidative stress in the hepatic, renal and cardiac tissues of fresh water adapted Oreochromis mossambicus. Hepatic catalase showed significant increase (P Triton > SDS. Thus it may be inferred from the present study that the antioxidant defenses and the in vivo metabolism of the surfactants are key factors in deciding the surfactant toxicity.
TL;DR: Magnetic nanocomposites containing iron oxide particles embedded in a polymer matrix have been synthesized using the method of ion exchange and the results have been analyzed and explained in this paper, where some of the unique properties of these materials find application in information storage, color imaging, ferrofluids and magnetic refrigeration.
Abstract: Magnetic nanocomposites containing iron oxide particles embedded in a polymer matrix have been synthesized using the method of ion exchange. They have been characterized by using low temperature and room temperature magnetic measurements and Mossbauer spectroscopy. The iron content in these samples has also been determined. The results have been analysed and explained. The physical and chemical properties of these nanocomposite materials are different from those of the bulk. Some of the unique properties of these materials find application in information storage, color imaging, ferrofluids and magnetic refrigeration.
TL;DR: In this article, a photopyroelectric measurement of the thermal parameters of glycine phosphite (GPI) single crystals across the ferroelectric phase transition temperature has been carried out.
TL;DR: It is shown that a class of tailed shift chaotic maps can be designed with substantial negative dependence, both linear and non‐linear, and that extended Perron–Frobenius theory gives their dependence structure.
Abstract: Summary. It is shown that a class of tailed shift chaotic maps can be designed with substantial negative dependence, both linear and non-linear, and that extended Perron-Frobenius theory gives their dependence structure. Using a simplified chaos-based communication system, it is shown that chaotic spreading sequences with low kurtosis and negative non-linear mean-centred quadratic autocorrelations can improve bit-received accuracy. This quadratic form of non-linear dependence is investigated and shown to be statistically sensible.