Sobha, Cyrus; Dr.Jose, Babu T(Cochin University of Science & Technology, July , 2008)
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Abstract:
The present study aimed at critically looking at the current practice of the
installation of compacted clay liner using bentonite enhanced sand (BES).
The application of bentonite is currently the most accepted practice for
lining purposes. The ideal bentonite sand combination, which satisfies the liner
requirements is 20% bentonite and 80% sand, was selected as one of the liner
materials for the investigation of development of desiccation cracks. Locally
available sundried marine clay and its combination with bentonite were also
included in the study. The desiccation tests on liner materials were conducted for
wet/dry cycles to simulate the seasonal variations. Digital image processing
techniques were used to measure the crack intensity factor (CIF), a
useful and effective parameter for quantification of desiccation cracking.
The repeatability of the tests could be well established, as the variation in CIF values
of identical samples had a very narrow range of 0 to 2%. The studies on the
development of desiccation cracks showed that the CIF of bentonite enhanced
sand mixture (BES) was 18.09%, 39.75% and 21.22% for the
first, second and third cycles respectively, while it was only 9.83%, 7.52% and
4.58% respectively for sun dried marine clay (SMC). Thus the locally available,
alternate liner material suggested, viz SMC, is far superior to BES, when
subjected to alternate wet/dry cycles. Further, the improvement of these liner materials when amended with randomly distributed fibre reinforcements was also investigated. Three types of
fibres ,namely nylon fibre, polypropylene monofilament and polypropylene fibre
mesh were used for the study of fibre amended BES and SMC.The influence of
these amendments on the properties of the above liner materials is also studied.
The results showed that there is definite improvement in the properties of the liner
materials when it is reinforced with discrete random fibres. The study also proved
that the desiccation cracks could be controlled with the help of fibre
reinforcement.
Description:
School of Engineering, Cochin University of Science and Technology
Litty, Irimpan; Nampoori, V P N; Radhakrishnan, P; Bindu, Krishnan; Deepthy, A(American Institute of Physics, 2008)
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Abstract:
We have investigated the third-order nonlinearity in ZnO nanocolloids with particle sizes in the range 6-18 nm by the z-scan technique. The third-order optical susceptibility χ(3) increases with increasing particle size (R) within the range of our investigations. In the weak confinement regime, an R2 dependence of χ(3) is obtained for ZnO nanocolloids. The optical limiting response is also studied against particle size.
Litty, Irimpan; Deepthy, A; Bindu, Krishnan; Kukreja, L M; Nampoori, V P N; Radhakrishnan, P(Elsevier, 2008)
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Abstract:
In the present work, we report the third order nonlinear optical properties of ZnO thin films deposited using self assembly, sol gel process as well as pulsed laser ablation by z scan technique. ZnO thin films clearly exhibit a negative nonlinear index of refraction at 532 nm and the observed nonlinear refraction is attributed to two photon absorption followed by free carrier absorption. Although the absolute nonlinear values for these films are comparable, there is a change in the sign of the absorptive nonlinearity of the films. The films developed by dip coating and pulsed laser ablation exhibit reverse saturable absorption whereas the self assembled film exhibits saturable absorption. These different nonlinear characteristics in the self assembled films can be mainly attributed to the saturation of linear absorption of the ZnO defect states.
Kailasnath, M; John, P R; Radhakrishnan, P; Nampoori, V P N; Vallabhan, C P G(Elsevier, 2008)
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Abstract:
This study was conducted to identify the concentration dependence of the operating wavelengths and the relative intensities in which a dye
mixture doped polymer optical fibre can operate. A comparative study of the radiative and Forster type energy transfer processes in Coumarin
540:Rhodamine 6G, Coumarin 540:Rhodamine B and Rhodamine 6G:Rhodamine B in methyl methacrylate (MMA) and poly(methyl methacrylate)
(PMMA) was done by fabricating a series of dye mixture doped polymer rods which have two emission peaks with varying relative intensities.
These rods can be used as preforms for the fabrication of polymer optical fibre amplifiers operating in the multi-wavelength regime. The 445 nm
line from an Nd:YAG pumped optical parametric oscillator (OPO) was used as the excitation source for the first two dye pairs and a frequency
doubled Nd:YAG laser emitting at 532 nm was used to excite the Rh 6G:Rh B pair. The fluorescence lifetimes of the donor molecule in pure
form as well as in the mixtures were experimentally measured in both monomer and polymer matrices by time-correlated single photon counting
technique. The energy transfer rate constants and transfer efficiencies were calculated and their dependence on the acceptor concentration was
analysed. It was found that radiative energy transfer mechanisms are more efficient in all the three dye pairs in liquid and solid matrices.
Sajan D, George; Aji A, Anappara; Warrier, P R S; Warrier, K G K; Radhakrishnan, P; Nampoori, V P N; Vallabhan, C P G(Elsevier, September , 2008)
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Abstract:
Laser-induced nondestructive photoacoustic (PA) technique has been employed to determine the thermal diffusivity of nanometal (Ag) dispersed ceramic alumina matrix sintered at different temperatures. The thermal diffusivity values are evaluated by knowing the transition frequency from the amplitude spectrum of PA signal using the one-dimensional heat flow model of Rosencwaig and Gersho. Analysis of the data shows that heat transport and hence the thermal diffusivity value is greatly affected by the influence of incorporation of foreign atom. It is also seen that sintering temperature affects the thermal diffusivity value in a substantial manner. The results are interpreted in terms of variation in porosity and carrier-assisted heat transport mechanism in nanometal dispersed ceramics.
Kailasnath, M; Sreejaya, T S; Rajesh, Kumar; Vallabhan, C P G; Nampoori, V P N; Radhakrishnan, P(Elsevier, 2008)
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Abstract:
Preparation of an appropriate optical-fiber preform is vital for the fabrication of graded-index polymer optical fibers (GIPOF), which are considered to be a good choice for providing inexpensive high bandwidth data links, for local area networks and telecommunication applications. Recent development of the interfacial gel polymerization technique has caused a dramatic reduction in the total attenuation in GIPOF, and this is one of the potential methods to prepare fiber preforms for the fabrication of dye-doped polymer-fiber amplifiers. In this paper, the preparation of a dye-doped graded-index poly(methyl methacrylate) (PMMA) rod by the interfacial gel polymerization method using a PMMA tube is reported. An organic compound of high-refractive index, viz., diphenyl phthalate (DPP), was used to obtain a graded-index distribution, and Rhodamine B (Rh B), was used to dope the PMMA rod. The refractive index profile of the rod was measured using an interferometric technique and the index exponent was estimated. The single pass gain of the rod was measured at a pump wavelength of 532 nm. The extent of doping of the Rh B in the preform was studied by axially exciting a thin slice of the rod with white light and measuring the spatial variation of the fluorescence intensity across the sample.
K G Nair ; P R S Pillai ; Vasudevan,K; Mathew,K T; Mohanan,P; Aanandan,C K(Cochin University of Science and Technology, November 29, 2008)
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Abstract:
In this paper we have investigated the effect of cavity diameter and wall height on resonance and radiation characteristics of a circular microstrip patch antenna. Experiments were conducted using a fabricated prototype placed inside a cylindrical cavity. The results were compared and verified with simulated data obtained using an electromagnetic simulator. About 9.6 to 10.5 dBi peak gain was obtained from measured and simulated data