| Abstract: | The work presented in the thesis is centered around two important types of cathode materials, the spinel structured LixMn204 (x =0.8to1.2) and the phospho -oIivine structured LiMP04 (M=Fe and Ni). The spinel system LixMn204, especially LiMn204 corresponding to x= 1 has been extensively investigated to understand its structural electrical and electrochemical properties and to analyse its suitability as a cathode material in rechargeable lithium batteries. However there is no reported work on the thermal and optical properties of this important cathode material. Thermal diffusivity is an important parameter as far as the operation of a rechargeable battery is concerned. In LixMn204, the electronic structure and phenomenon of Jahn-Teller distortion have already been established theoretically and experimentally. Part of the present work is an attempt to use the non-destructive technique (NDT) of photoacoustic spectroscopy to investigate the nature of the various electronic transitions and to unravel the mechanisms leading to the phenomenon of J.T distortion in LixMn204.The phospho-olivines LiMP04 (M=Fe, Ni, Mn, Co etc) are the newly identified, prospective cathode materials offering extremely high stability, quite high theoretical specific capacity, very good cycIability and long life. Inspite of all these advantages, most of the phospho - olivines especially LiFeP04 and LiNiP04 show poor electronic conductivity compared to LixMn204, leading to low rate capacity and energy density. In the present work attempts have been made to improve the electronic conductivity of LiFeP04 and LiNiP04 by adding different weight percentage MWNT .It is expected that the addition of MWNT will enhance the electronic conductivity of LiFeP04 and LiNiP04 with out causing any significant structural distortions, which is important in the working of the lithium ion battery. |
| Description: | Department of Physics, Cochin University of Science and Technology |
| URI: | http://dyuthi.cusat.ac.in/purl/2523 |
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| Dyuthi-T0682.pdf | (14.52Mb) |
| Abstract: | The main objective of the of present study are to study the intraseasonal variability of LLJ and its relation with convective heating of the atmosphere, to establish whether LLJ splits into two branches over the Arabian sea as widely believed, the role of horizonatal wind shear of LLJ in the episodes of intense rainfall events observed over the west coast of India, to perform atmospheric modeling work to test whether small (meso) scale vortices form during intense rainfall events along the west coast; and to study the relation between LLJ and monsoon depression genesis. The results of a study on the evolution of Low Level Jetstream (LLJ) prior to the formation of monsoon depressions are presented. A synoptic model of the temporal evolution of monsoon depression has been produced. There is a systematic temporal evolution of the field of deep convection strength and position of the LLJ axis leading to the genesis of monsoon depression. One of the significant outcomes of the present thesis is that the LLJ plays an important role in the intraseasonal and the interannual variability of Indian monsoon activity. Convection and rainfall are dependent mainly on the cyclonic vorticity in the boundary layer associated with LLJ. Monsoon depression genesis and the episodes of very heavy rainfall along the west coast of India are closely related to the cyclonic shear of the LLJ in the boundary layer and the associated deep convection. Case studies by a mesoscale numerical model (MM5) have shown that the heavy rainfall episodes along the west coast of India are associated with generation of mesoscale cyclonic vortices in the boundary layer. |
| URI: | http://dyuthi.cusat.ac.in/purl/64 |
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| Dyuthi-T0178.pdf | (7.850Mb) |
| Synopsis.pdf | (65.70Kb) |
| Abstract: | This thesis has focused on the synthesis and analysis of some important phosphors (nano, bulk and thin film) for display applications. ACTFEL device with SrS:Cu as active layer was also fabricated.Three bulk phosphors: SrS:Cu,CI; SrS:Dy,Cl; and SrS:Dy,Cu,Cl were synthesized and their structural, optical and electrical properties were investigated. Special emphasis was given to, the analysis of the role of defects and charge compensating centers, on the structural changes of the host and hence the luminance. A new model describing the sensitizing behaviour of Cu in SrS:Dy,Cu,Cl two component phosphor was introduced. It was also found that addition of NH4CI as flux in SrS:Cu caused tremendous improvement in the structural and luminescence properties.A novel technique for ACTFEL phosphor deposition at low temperature was introduced. Polycrystalline films of SrS:Cu,F were synthesized at low temperature by concomitant evaporation of host and dopant by electron beam evaporation and thermal evaporatin methods.Copper doped strontium sulphide nanophosphor was synthesized for the first time. Improvement in the luminescence properties was observed in the nanophosphor with respect to it' s bulk counterpart. |
| Description: | Department of Physics, Cochin University of Science and Technology |
| URI: | http://dyuthi.cusat.ac.in/purl/2513 |
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| Dyuthi-T0672.pdf | (7.469Mb) |
| URI: | http://dyuthi.cusat.ac.in/purl/5505 |
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| Dyuthi T-2547.pdf | (10.00Mb) |
| URI: | http://dyuthi.cusat.ac.in/purl/5508 |
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| Dyuthi T-2550.pdf | (5.535Mb) |
| Abstract: | Thermoelectric materials are revisited for various applications including power generation. The direct conversion of temperature differences into electric voltage and vice versa is known as thermoelectric effect. Possible applications of thermoelectric materials are in eco-friendly refrigeration, electric power generation from waste heat, infrared sensors, temperature controlled-seats and portable picnic coolers. Thermoelectric materials are also extensively researched upon as an alternative to compression based refrigeration. This utilizes the principle of Peltier cooling. The performance characteristic of a thermoelectric material, termed as figure of merit (ZT) is a function of several transport coefficients such as electrical conductivity (σ), thermal conductivity (κ) and Seebeck coefficient of the material (S). ZT is expressed asκσTZTS2=, where T is the temperature in degree absolute. A large value of Seebeck coefficient, high electrical conductivity and low thermal conductivity are necessary to realize a high performance thermoelectric material. The best known thermoelectric materials are phonon-glass electron – crystal (PGEC) system where the phonons are scattered within the unit cell by the rattling structure and electrons are scattered less as in crystals to obtain a high electrical conductivity. A survey of literature reveals that correlated semiconductors and Kondo insulators containing rare earth or transition metal ions are found to be potential thermoelectric materials. The structural magnetic and charge transport properties in manganese oxides having the general formula of RE1−xAExMnO3 (RE = rare earth, AE= Ca, Sr, Ba) are solely determined by the mixed valence (3+/4+) state of Mn ions. In strongly correlated electron systems, magnetism and charge transport properties are strongly correlated. Within the area of strongly correlated electron systems the study of manganese oxides, widely known as manganites exhibit unique magneto electric transport properties, is an active area of research.Strongly correlated systems like perovskite manganites, characterized by their narrow localized band and hoping conduction, were found to be good candidates for thermoelectric applications. Manganites represent a highly correlated electron system and exhibit a variety of phenomena such as charge, orbital and magnetic ordering, colossal magneto resistance and Jahn-Teller effect. The strong inter-dependence between the magnetic order parameters and the transport coefficients in manganites has generated much research interest in the thermoelectric properties of manganites. Here, large thermal motion or rattling of rare earth atoms with localized magnetic moments is believed to be responsible for low thermal conductivity of these compounds. The 4f levels in these compounds, lying near the Fermi energy, create large density of states at the Fermi level and hence they are likely to exhibit a fairly large value of Seebeck coefficient. |
| URI: | http://dyuthi.cusat.ac.in/purl/5068 |
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| Dyuthi-T 2132.pdf | (6.138Mb) |
| URI: | http://dyuthi.cusat.ac.in/purl/1662 |
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| Dyuthi-T0198.pdf | (1.136Mb) |
| Abstract: | The current study is aimed at the development of a theoretical simulation tool based on Discrete Element Method (DEM) to 'interpret granular dynamics of solid bed in the cross section of the horizontal rotating cylinder at the microscopic level and subsequently apply this model to establish the transition behaviour, mixing and segregation.The simulation of the granular motion developed in this work is based on solving Newton's equation of motion for each particle in the granular bed subjected to the collisional forces, external forces and boundary forces. At every instant of time, the forces are tracked and the positions velocities and accelarations of each partcle is The software code for this simulation is written in VISUAL FORTRAN 90 After checking the validity of the code with special tests, it is used to investigate the transition behaviour of granular solids motion in the cross section of a rotating cylinder for various rotational speeds and fill fraction.This work is hence directed towards a theoretical investigation based on Discrete Element Method (DEM) of the motion of granular solids in the radial direction of the horizontal cylinder to elucidate the relationship between the operating parameters of the rotating cylinder geometry and physical properties ofthe granular solid.The operating parameters of the rotating cylinder include the various rotational velocities of the cylinder and volumetric fill. The physical properties of the granular solids include particle sizes, densities, stiffness coefficients, and coefficient of friction Further the work highlights the fundamental basis for the important phenomena of the system namely; (i) the different modes of solids motion observed in a transverse crosssection of the rotating cylinder for various rotational speeds, (ii) the radial mixing of the granular solid in terms of active layer depth (iii) rate coefficient of mixing as well as the transition behaviour in terms of the bed turnover time and rotational speed and (iv) the segregation mechanisms resulting from differences in the size and density of particles.The transition behaviour involving its six different modes of motion of the granular solid bed is quantified in terms of Froude number and the results obtained are validated with experimental and theoretical results reported in the literature The transition from slumping to rolling mode is quantified using the bed turnover time and a linear relationship is established between the bed turn over time and the inverse of the rotational speed of the cylinder as predicted by Davidson et al. [2000]. The effect of the rotational speed, fill fraction and coefficient of friction on the dynamic angle of repose are presented and discussed. The variation of active layer depth with respect to fill fraction and rotational speed have been investigated. The results obtained through simulation are compared with the experimental results reported by Van Puyvelde et. at. [2000] and Ding et at. [2002].The theoretical model has been further extended, to study the rmxmg and segregation in the transverse direction for different particle sizes and their size ratios. The effect of fill fraction and rotational speed on the transverse mixing behaviour is presented in the form of a mixing index and mixing kinetics curve. The segregation pattern obtained by the simulation of the granular solid bed with respect to the rotational speed of the cylinder is presented both in graphical and numerical forms. The segregation behaviour of the granular solid bed with respect to particle size, density and volume fraction of particle size has been investigated. Several important macro parameters characterising segregation such as mixing index, percolation index and segregation index have been derived from the simulation tool based on first principles developed in this work. |
| URI: | http://dyuthi.cusat.ac.in/purl/2381 |
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| Dyuthi-T0653.pdf | (5.339Mb) |
| Abstract: | One can do research in pointfree topology in two ways. The rst is the contravariant way where research is done in the category Frm but the ultimate objective is to obtain results in Loc. The other way is the covariant way to carry out research in the category Loc itself directly. According to Johnstone [23], \frame theory is lattice theory applied to topology whereas locale theory is topology itself". The most part of this thesis is written according to the rst view. In this thesis, we make an attempt to study about 1. the frame counterparts of maximal compactness, minimal Hausdor - ness and reversibility, 2. the automorphism groups of a nite frame and its relation with the subgroups of the permutation group on the generator set of the frame |
| Description: | Department of Mathematics Cochin University of Science and Technology |
| URI: | http://dyuthi.cusat.ac.in/purl/4746 |
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| Dyuthi-T1844.pdf | (460.2Kb) |
| URI: | http://dyuthi.cusat.ac.in/purl/1014 |
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| RAVEENDRAN NAIR B 1988.pdf | (259.7Kb) |
| Abstract: | The incidence of diabetes is rapidly increasing and by 2030 an expected 592 million individuals are projected to be affected (WHO report). Hyperglycaemic condition is recognized as the causal link between diabetes and its complications. The chronic hyperglycemia resulting from diabetes brings about a rise in oxidative stress due to overproduction of reactive oxygen species (ROS) as a result of glucose auto oxidation and protein glycosylation. Generation of ROS leads to oxidative damage of the structural components (such as lipids, DNA and proteins) of cells and potentiate diabetes related complications. Oxidative insult in cells is also created by the impairment in functioning of endogenous antioxidant enzymes because of their non enzymatic glycosylation and oxidation. The prolonged exposure of oxidative stress may cause insulin resistance by triggering an alteration in cellular redox balance. Several lines of evidence suggest that oxidative stress occurs in diabetes and could have a role in the development of insulin resistance. The cause and cellular mechanism responsible for this abnormality is not fully understand despite of intense investigative efforts. However it is unknown whether it is the cause or consequence of diabetes. Despite strong experimental evidence indicating that oxidative stress may determine the onset and progression of late-diabetic complications, controversy exists between the cause and associative relationship between oxidative stress and diabetes mellitus. Disruption of glucose homeostasis is a characteristic feature of Non-insulin dependent diabetes mellitus (NIDDM) and is associated with some complications including cardiovascular disease and renal failure. Glucose transport, the rate limiting step in glucose metabolism, can be activated in peripheral tissues by two distinct pathways. One stimulated by insulin through IRS-1/PI3K, Preface Page 2 the other by muscle contraction/exercise through the activation of AMPK. Both pathways also increase the phosphorylation and activity of MAPK family components of which p38 MAPK participates in the full activation of GLUT4.Insulin exerts its biological effect upon binding with the insulin receptor (IR) thereby activating the downstream signaling that lead to enhanced glucose uptake. In skeletal muscle, it potentiates glucose transport through PI3K mediated or non-PI3K mediated pathways. Alterations or defects in its signal transduction pathway was found in diabetic patients associated with decreased levels of IRb, IRS-1, and PI3K. In the insulin signaling, PI3K is a key molecule and inhibition of PI3K completely abolish insulin stimulated uptake. Akt or Pkb is an important downstream target of insulin stimulated glucose transport and metabolism.Impairment in fuel metabolism occurs in obesity, and this impairment is a leading pathogenic factor in type 2 diabetes. The insulin resistance associated with type 2 diabetes is most profound at the level of skeletal muscle as this is the primary site of glucose and fatty acid utilization. Therefore, an understanding of how to activate AMPK in skeletal muscle would offer significant pharmacologic benefits in the treatment of type 2 diabetes. Metformin and the thiazolidinedione drugs exert the effects via activation of AMPK. Activation of AMPK occurs in response to exercise, an activity known to have significant benefit for type 2 diabetics. AMPK serves as sensor of energy status whose activity is triggered in response to changes in nutritional status in order to modulate tissue-specific metabolic pathways |
| URI: | http://dyuthi.cusat.ac.in/purl/5151 |
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| Dyuthi-T2185.pdf | (9.806Mb) |
| URI: | http://dyuthi.cusat.ac.in/purl/5083 |
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| Dyuthi-T 2146.pdf | (10.28Mb) |
| URI: | http://dyuthi.cusat.ac.in/purl/5122 |
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| Dyuthi-T 2187.pdf | (6.440Mb) |
| Abstract: | A critical survey of the fruits and vegetable markets of the towns and cities in South India reveals that banana fruit stalk wastes share a dominant proportion among the solid wastes generated. In the light of the review of literature presented in the foregoing section, few reports are available on the utilisation of banana waste for the production of alcoholic beverages, biogas, and single cell protein. However, it is not yet tried for the production of industrial enzymes. Moreover, preliminary fermentation studies conducted under uncontrolled conditions revealed that banana fruit stalk could be aptly utilised as solid substrate? for the industrial production of microbial amylases and cellulases at a cheaper cost. Therefore, it was proposed to conduct a detailed study towards the development of a suitable fermentation process for the production of industrial enzymes using banana fruit stalk wastes, which is rich in carbohydrate, as solid substrate, employing bacteria, under SSF. |
| Description: | Department of Biotechnology, Cochin University of Science & Technology, |
| URI: | http://dyuthi.cusat.ac.in/purl/3362 |
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| Dyuthi-T1339.pdf | (3.715Mb) |
| URI: | http://dyuthi.cusat.ac.in/purl/1739 |
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| Dyuthi-T0202.pdf | (2.099Mb) |
| URI: | http://dyuthi.cusat.ac.in/xmlui/purl/2021 |
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| Dyuthi-T0432.pdf | (2.889Mb) |
| Abstract: | there has been much research on analyzing various forms of competing risks data. Nevertheless, there are several occasions in survival studies, where the existing models and methodologies are inadequate for the analysis competing risks data. ldentifiabilty problem and various types of and censoring induce more complications in the analysis of competing risks data than in classical survival analysis. Parametric models are not adequate for the analysis of competing risks data since the assumptions about the underlying lifetime distributions may not hold well. Motivated by this, in the present study. we develop some new inference procedures, which are completely distribution free for the analysis of competing risks data. |
| Description: | Department of Statistics, Cochin University of Science and Technology |
| URI: | http://dyuthi.cusat.ac.in/purl/3810 |
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| Dyuthi-T1741.pdf | (1.808Mb) |
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