Edwin, Xavier; Dr.Girijavallabhan, C P(Cochin University of Science & Technology, March , 1997)
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Abstract:
The present thesis is centered around the study of electrical and thermal
properties of certain selected photonic materials.We have studied the electrical conduction mechanism in various
phases of certain selected photonic materials and those associated with different phase
transitions occurring in them. A phase transition leaves its own impressions on the key
parameters like electrical conductivity and dielectric constant. However, the activation
energy calculation reveals the dominant factor responsible for conduction process.PA measurements of thermal diffusivity in certain other important photonic
materials are included in the remaining part of the research work presented in this
thesis. PA technique is a promising tool for studying thermal diffusivities of solid
samples in any form. Because of its crucial role and common occurrence in heat flow
problems, the thermal diffusivity determination is often necessary and knowledge of
thermal diffusivity can intum be used to calculate the thermal conductivity. Especially,knowledge of the thermal diffusivity of semiconductors is important due to its relation
to the power dissipation problem in microelectronic and optoelectronic devices which
limits their performances. More than that, the thermal properties, especially those of
thin films are of growing interest in microelectronics and microsystems because of the
heat removal problem involved in highly integrated devices. The prescribed chapter
of the present theis demonstrates how direct measurement of thermal diffusivity can be
carried out in thin films of interest in a simple and elegant manner using PA techniques.
Although results of only representative measurements viz; thermal diffusivity values in
Indium, Aluminium, Silver and CdS thin films are given here, evaluation of this
quantity for any photonic and / electronic material can be carried out using this
technique in a very simple and straight forward manner.
Description:
International School of Photonics,Cochin University of Science and Technology
Sumangala,R; Saseendran Pillai,P R(Cochin University OF Science and Technology, December , 1996)
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Abstract:
The main objective of carrying out this investigation is to develop suitable transducer array systems so that underwater pipeline inspection could be carried out in a much better way, a focused beam and electronic steering can reduce inspection time as well. Better results are obtained by optimizing the array parameters. The spacing between the elements is assumed to be half the wavelength so that the interelement interaction is minimum. For NDT applications these arrays are operated at MHz range. The wavelengths become very small in these frequency ranges. Then the size of the array elements becomes very small, requiring hybrid construction techniques for their fabrication. Transducer elements have been fabricated using PVDF as the active, mild steel as the backing and conducting silver preparation as the bonding materials. The transducer is operated in the (3,3) mode. The construction of a high frequency array is comparatively complicated. The interelement spacing between the transducer elements becomes considerably small when high frequencies are considered. It becomes very difficult to construct the transducer manually. The electrode connections to the elements can produce significant loading effect. The array has to be fabricated using hybrid construction techniques. The active materials has to be deposited on a proper substrate and etching techniques are required to fabricate the array. The annular ring, annular cylindrical or other similar structural forms of arrays may also find applications in the near future in treatments were curved contours of the human body are affected.
Krishnan Nair, P R; Nandakumaran, V M(Cochin University of Science and Technology, October , 1999)
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Abstract:
This thesis is a study of discrete nonlinear systems represented by one dimensional mappings.As one dimensional interative maps represent Poincarre sections of higher dimensional flows,they offer a convenient means to understand the dynamical evolution of many physical systems.It highlighting the basic ideas of deterministic chaos.Qualitative and quantitative measures for the detection and characterization of chaos in nonlinear systems are discussed.Some simple mathematical models exhibiting chaos are presented.The bifurcation scenario and the possible routes to chaos are explained.It present the results of the numerical computational of the Lyapunov exponents (λ) of one dimensional maps.This thesis focuses on the results obtained by our investigations on combinations maps,scaling behaviour of the Lyapunov characteristic exponents of one dimensional maps and the nature of bifurcations in a discontinous logistic map.It gives a review of the major routes to chaos in dissipative systems,namely, Period-doubling ,Intermittency and Crises.This study gives a theoretical understanding of the route to chaos in discontinous systems.A detailed analysis of the dynamics of a discontinous logistic map is carried out, both analytically and numerically ,to understand the route it follows to chaos.The present analysis deals only with the case of the discontinuity parameter applied to the right half of the interval of mapping.A detailed analysis for the n –furcations of various periodicities can be made and a more general theory for the map with discontinuities applied at different positions can be on a similar footing