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V P N Nampoori; Litty, Irimpan; Dann, V J; Krishnan, B; Deepthy, A; Radhakrishnan, P (Laser Physics, 2008)[+][-]
Abstract: Light-scattering experiments gained prominence as potential applications of quantum optics, nonlinear optics, and photon localization. The possibility of the realization of lasing action in random media has created much interest in the study of the coherent structure of the backscattered light from disordered media. Backscattering (BS) studies are carried out to analyze the possibilities of photon localization in colloidal silica. The scattering enhancement is best associated with the density of the scatterers. The width of the BS cone and, hence, the mean-free path is related to the concentration of the medium. The dependence of the photon wavelength on the possible characteristics of the scattering is presented. URI: http://dyuthi.cusat.ac.in/xmlui/purl/2041 Files in this item: 1
Files Size Backscattering of laser light...pdf (179.0Kb) -
Jinesh, Mathew; Mahesh, V V; Radhakrishnan, P (International Frequency Sensor Association, August , 2008)[+][-]
Abstract: The design and fabrication of fiber based ammonia sensors employing Bromothymol blue and Chitosan as sensing elements are presented in this paper. In the presence of ammonia gas the absorption of Bromothymol blue changes while in the case of Chitosan the refractive index changes which in turn modulates the intensity of light propagating through a fiber. URI: http://dyuthi.cusat.ac.in/xmlui/purl/2042 Files in this item: 1
Files Size Comparative performance of two...pdf (162.7Kb) -
Litty, Irimpan; Ambika, D; Kumar, V; V P N Nampoori; Radhakrishnan, P (American Institute of Physics, 2008)[+][-]
Abstract: The annealing effect on the spectral and nonlinear optical NLO characteristics of ZnO thin films deposited on quartz substrates by sol-gel process is investigated. As the annealing temperature increases from 300–1050 °C, there is a decrease in the band gap, which indicates the changes of the interface of ZnO. ZnO is reported to show two emission bands, an ultraviolet UV emission band and another in the green region. The intensity of the UV peak remains the same while the intensity of the visible peak increases with increase in annealing temperature. The role of oxygen in ZnO thin films during the annealing process is important to the change in optical properties. The mechanism of the luminescence suggests that UV luminescence of ZnO thin films is related to the transition from conduction band edge to valence band, and green luminescence is caused by the transition from deep donor level to valence band due to oxygen vacancies. The NLO response of these samples is studied using nanosecond laser pulses at off-resonance wavelengths. The nonlinear absorption coefficient increases from 2.9 ×10−6 to 1.0 ×10−4 m/W when the annealing temperature is increased from 300 to 1050 °C, mainly due to the enhancement of interfacial state and exciton oscillator strength. The third order optical susceptibility x(3) increases with increase in annealing temperature (T) within the range of our investigations. In the weak confinement regime, T2.4 dependence of x(3) is obtained for ZnO thin films. The role of annealing temperature on the optical limiting response is also studied. URI: http://dyuthi.cusat.ac.in/xmlui/purl/2043 Files in this item: 1
Files Size Effect of annealing on the spectral...pdf (755.1Kb) -
Josephkunju, Paul C; Dr. Sreejith, P S (Cochin University of Science & Technology, September , 2008)[+][-]
Abstract: The thesis presented here unveils an experimental study of the hydrodynamic characteristics of swirling fluidized bed viz. pressure drop across the distributor and the bed, minimum fluidizing velocity, bed behaviour and angle of air injection. In swirling fluidized bed the air is admitted to the bed at an angle 'Ѳ' to the horizontal. The vertical component of the velocity v sin Ѳ causes fluidization and the horizontal component v cos Ѳ contributes to swirl motion of the bed material.The study was conducted using spherical particles having sizes 3.2 mm, 5.5 mm & 7.4 mm as the bed materials. Each of these particles was made from high density polyethylene, nylon and acetal having relative densities of 0.93, 1.05 and 1.47 respectively.The experiments were conducted using conidour type distributors having four rows of slits. Altogether four distributors having angles of air injection (Φ)- 0°, 5°, 10° & 15° were designed and fabricated for the study. The total number of slits in each distributor was 144. The area of opening was 6220 mm2 making the percentage area of opening to 9.17. But the percentage useful area of opening of the distributor was 96.The experiments on the variation of distributor pressure drop with superficial velocity revealed that the distributor pressure drop decreases with angle of air injection. Investigations related to bed hydrodynamics were conducted using 2.5 kg of bed material. The bed pressure drop measurements were made along the radial direction of the distributor at distances of 60 mm, 90 mm, 120 mm & 150 mm from the centre of the distributor. It was noticed that after attaining minimum fluidizing velocity, the bed pressure drop increases along the radial direction of the distributor. But at a radial distance of 90 mm from the distributor centre, after attaining minimum fluidizing velocity the bed pressure drop remains almost constant. It was also observed that the bed pressure drop varies inversely with particle size as well as particle density.An attempt was made to determine the effect of various parameters on minimum fluidizing velocity. It was noticed that the minimum fluidizing velocity varies directly with angle of air injection (Φ), particle size and particle density.The study on the bed behaviour showed that the superficial velocity required for initiating various bed phenomena (such as swirl motion and separation of particles from the cone at the centre) increase with increase in particle size as well as particle density. It was also observed that the particle size and particle density directly influence the superficial velocity required for various regimes of bed behaviour such as linear variation of bed pressure drop, constant bed pressure drop and sudden increase or decrease in bed pressure drop.Experiments were also performed to study the effect of angle of air injection (Φ). It was noticed that the bed pressure drop decreases with angle of air injection. It was also noticed that the angle of air injection directly influence the superficial velocity required for initiating various bed phenomena as well as the various regimes of bed behaviour. Description: Division of Mechanical Engineering, Cochin University of Science and Technology URI: http://dyuthi.cusat.ac.in/purl/2626 Files in this item: 1
Files Size Dyuthi-T0705.pdf (9.679Mb) -
Bijoy, S Nandan (The university of Waikato, November 4, 2008)[+][-]
Abstract: Soth west coast of india is blessed with a series of wetland systems popularly referred to as backwaters covering a total area of 46128.94 ha. these backwaters are internationallyrenowed for their aesthetic and scientific values including being a repository for several species fish and shell fishes. this is more significant in thatthre wetlands( Vembanad, Sasthamcotta & Ashtamudi) have recently been designated as Ramsar sites og international importance.Thirty major backwaters forming the crux of the coastal wetlands from an abodefor over 200 residentry and migratory fish and shellfish species. the fishing activities in these water bodies provide the livilihoodto about 200,000 fishers and also provide full time employment to over 50,000 fishermen. this paper describes the changes on the environmental and biodiversity status of selected wetlands, during 1994-2005 period. the pH was generally near neutral to alkaline in range. the salinity values indicated mixohaline condition ranging from 5.20-32.38 ppt in the 12 wetlands. the productivity values were generally low in mostof the wetlands during the study, where the gross production varied from 0.22gC/m3/ day in Kadinamkulam to 1.10gC/m3/day in the kayamkulam. the diversity of plankton and benthos was more during the pre monsoon compared to the monsoon and post monsoon periods in most of the wetlands.the diversity of plankton and benthos was more during the premonsoon compared to the monsoon and post monsoon periods in most of the wetlands.the average fish yield per ha.varied from 246kg in valapattanam to 2747kg in azhikode wetland. Retting of coconut husk in most of the wetlands led to acidic pH conditions with anoxia resulting in the production of high amounts of sulphide, coupled with high carbon dioxide values leading to drastic reduction in the incidence and abundance of plankton, benthic fauna and the fishery resources.The major fish species recorded from the investigation were Etroplus argentimaculatus, Mystus sp., tachysurus sp. and Hemiraamphus sp. . The majority of these back waters are highly stressed, especially during the pre monsoon period when the retting activity at its peak. The study has clearly reflected that a more restrained and cautions approach is needed to manage and preserve the unique backwater ecosystems of south west india. URI: http://hdl.handle.net/purl/1892 Files in this item: 1
Files Size Bijoy S Nandan,.pdf (916.1Kb) -
Sanjay, Gopinath; Sugunan, S (Springer Netherlands, 2008)[+][-]
Abstract: Three enzymes, α-amylase, glucoamylase and invertase, were immobilized on acid activated montmorillonite K 10 via two independent techniques, adsorption and covalent binding. The immobilized enzymes were characterized by XRD, N2 adsorption measurements and 27Al MAS-NMR spectroscopy. The XRD patterns showed that all enzymes were intercalated into the clay inter-layer space. The entire protein backbone was situated at the periphery of the clay matrix. Intercalation occurred through the side chains of the amino acid residues. A decrease in surface area and pore volume upon immobilization supported this observation. The extent of intercalation was greater for the covalently bound systems. NMR data showed that tetrahedral Al species were involved during enzyme adsorption whereas octahedral Al was involved during covalent binding. The immobilized enzymes demonstrated enhanced storage stability. While the free enzymes lost all activity within a period of 10 days, the immobilized forms retained appreciable activity even after 30 days of storage. Reusability also improved upon immobilization. Here again, covalently bound enzymes exhibited better characteristics than their adsorbed counterparts. The immobilized enzymes could be successfully used continuously in the packed bed reactor for about 96 hours without much loss in activity. Immobilized glucoamylase demonstrated the best results. URI: http://dyuthi.cusat.ac.in/purl/2264 Files in this item: 1
Files Size Dyuthi-P00057.pdf (233.7Kb) -
Sreekumar, Krishnapillai; Rajesh Krishnan, G (Eur. J. Org. Chem, August , 2008)[+][-]
Abstract: This paper describes the first use of polystyrene-supported poly(amidoamine) (PAMAM) dendrimers as heterogeneous basic organocatalysts for carbon–carbon bond formation. Polystyrene-supported PAMAM dendrimers of first, second and third generations have been used as reusable base catalysts in Knoevenagel condensations of carbonyl compounds with active methylene compounds. The reactions proceed in short periods of time and with 100% selectivity. This novel catalyst eliminates the use of aromatic and halogenated solvents, as well as complex purification processes. The catalysts can be recycled ten times. URI: http://dyuthi.cusat.ac.in/xmlui/purl/1966 Files in this item: 1
Files Size First Exaple of Organocatalysis....pdf (135.4Kb) -
V P N Nampoori; Litty, Irimpan; Radhakrishnan, P (Journal of Applied Physics, American Institute of Physics,, 2008)[+][-]
Abstract: In this article, we present the spectral and nonlinear optical properties of ZnO–CdS nanocomposites prepared by colloidal chemical synthesis. The optical band gap (Eg) of the material is tunable between 2.62 and 3.84 eV. The emission peaks of ZnO–CdS nanocomposites change from 385 to 520 nm almost in proportion to changes in Eg. It is possible to obtain a desired luminescence color from UV to green by simply adjusting the composition. The nonlinear optical response of these samples is studied by using nanosecond laser pulses from a tunable laser at the excitonic resonance and off-resonance wavelengths. The nonlinear response is wavelength dependent, and switching from saturable absorption (SA) to reverse SA (RSA) has been observed for samples as the excitation wavelength changes from the excitonic resonance to off-resonance wavelengths. Such a changeover in the sign of the nonlinearity of ZnO–CdS nanocomposites is related to the interplay of exciton bleach and optical limiting mechanisms. The ZnO–CdS nanocomposites show self-defocusing nonlinearity and good nonlinear absorption behavior at off-resonant wavelengths. The nonlinear refractive index and the nonlinear absorption increase with increasing CdS volume fraction at 532 nm. The observed nonlinear absorption is attributed to two photon absorption followed by weak free carrier absorption. The enhancement of the third-order nonlinearity in the composites can be attributed to the concentration of exciton oscillator strength. This study is important in identifying the spectral range and composition over which the nonlinear material acts as a RSA based optical limiter. ZnO–CdS is a potential nanocomposite material for the tunable light emission and for the development of nonlinear optical devices with a relatively small limiting threshold. URI: http://dyuthi.cusat.ac.in/xmlui/purl/2047 Files in this item: 1
Files Size Spectral and nonlinear optical...pdf (360.4Kb) -
Samuel Varghese, K; Dr. Nampoori, V P N; Dr. Girijavallabhan, C P (Cochin University of Science and Technology, December , 2008)[+][-]
Abstract: This Thesis deals with the fabrication and characterization of novel all-fiber components for access networks. All fiber components offer distinctive advantages due to low forward and backward losses, epoxy free optical path and high power handling. A novel fabrication method for monolithic 1x4 couplers, which are vital components in distributed passive optical networks, is realized. The fabrication method differs from conventional structures with a symmetric coupling profile and hence offers ultra wideband performance and easy process control. New structure for 1x4 couplers, by fusing five fibers is proposed to achieve high uniformity, which gives equivalent uniformity performance to 1x4 planar lightwave splitters, isolation in fused fiber WDM is improved with integration of long period gratings. Packaging techniques of fused couplers are analyzed for long term stability. Description: International School of Photonics, Cochin University of Science and Technology URI: http://dyuthi.cusat.ac.in/xmlui/purl/1917 Files in this item: 1
Files Size Dyuthi-T0408.pdf (2.489Mb) -
Sunil K Narayanankutty; George,K E; Thomas Kurian (Department of Polymer Science and Rubber Technology, Indian Rubber Institute, September 25, 2008)
[+][-]URI: http://dyuthi.cusat.ac.in/purl/943 Files in this item: 13
Files Size Abstract.pdf (284.1Kb) APT08.html (7.304Kb) committee.html (9.967Kb) department.html (5.966Kb) Full paper PDF.pdf (4.265Mb) Invited Talks-list.htm (26.31Kb) Logo.jpg (169.4Kb) Oral abstracts edited. 1pdf.pdf (1.189Mb) Oral full paper PDF. 2 pdf.pdf (16.41Mb) Oral Presentations.htm (54.33Kb) pOSTER ABSTRACTS EDITED 1.pdf (470.6Kb) poster full paper PDF.pdf (5.219Mb) Poster presentations.htm (54.19Kb)
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