| Abstract: | Cosmology deals with the studies on the structure and evolution of the universe. The model of the universe formulated by Friedmann, Lemaitre, Robertson andWalker known as the standard model (FLRW model) of the universe, which is based on the Einstein's theory of gravity, turned out to be the accepted model because of the various observational supports. The major observational supports to this model are the explanation for the Hubble's law, primordial nucleosynthesis, microwave back ground radiation etc. Recent observations on Type Ia supernovae by teams led by S Perlmutter, Brian P Schmidt and Adam G Riess led to the discovery that the present universe is expanding in an accelerated manner. The exotic form of matter which causes the acceleration is termed as dark energy which produce negative pressure. Understanding the nature and evolution of dark energy is a challenge for the cosmologists. In addition to the evidences from supernovae, the anisotropy in CMBR spectra, large scale structures and Baryon acoustic oscillations are also supporting the discovery. To explain dark energy, various theoretical models have been proposed. One such model is the CDM model, in which the universe is assumed to be composed of dark energy and dark matter. In this model, Einstein's cosmological constant is considered as dark energy. It has a constant equation of state; ! = p = 1: The model predicts the values of cosmological parameters such as the Hubble parameter, transition redshift and present deceleration parameter, having a very good agreement with the observational constraints. But this model has two major aws, which are: 1. Cosmological constant problem:- Theoretically predicted value of dark energy density as the vacuum constant is, 1074GeV 4; while the observed value is 1047GeV 4: The predicted value is greater than the observed value by 120 orders of magnitude. This discrepancy between the theoretical and observational values is known as the cosmological constant problem. 2. Cosmological coincidence problem:- Energy densities of dark energy and dark matter are found to be of the same order even though their evolutionary nature are di erent. This is known as the coincidence problem which is not explained by the CDM model. These led to the proposals of dynamical dark energy models by considering that the equation of state parameter is evolving with the expanding universe. Scalar models of dark energy such as Quintessence, K-essence, Phantom model, Chaplygin gas model and holographicdark energy model are examples of dynamic dark energy models. Holographic dark energy model is based on the holographic principle developed by Susskind and 't Hooft. The principle says that the degrees of freedom of a system resides on its surface rather than in its volume. The total energy inside a region of size L must not exceed the mass of a black hole of the same size. The holographic dark energy density can then be formulated as, = 3c2M2 plL2 (1) where 3c2 is a numerical constant, M2 pl = 8 G is the reduced Planck mass. Possible choices for L; the IR cut-o , are Hubble horizon, particle horizon and event horizon. The choices for the IR cut-o whether it be Hubble horizon or particle horizon will not support an accelerating universe, while the third choice, the event horizon, violates causality. Another alternative for the IR cut-o is the Ricci scalar, which was rst introduced by Gao et al. Later modi ed holographic Ricci dark energy was proposed by Granda and Oliveros. In the present thesis, the modi ed Ricci dark energy is studied by considering its interaction with the dark matter present in the universe. Owing to the lack of knowledge about the microscopic origin of such an interaction, phenomenological interaction forms of nongravitational nature is assumed. |
| URI: | http://dyuthi.cusat.ac.in/purl/5163 |
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| Dyuthi-T2197.pdf | (2.575Mb) |
| Abstract: | the thesis entitled “STUDIES ON DEVELOPING A FACILE ROUTE FOR THE SYNTHESIS OF HIGHLY SUBSTITUTED QUINOLINE AND INDOLE DERIVATIVES” portrays our attempt to revisit the mechanism of 1,3- dipolar additions with a view to establishing whether it follows a concerted pathway or a stepwise reaction sequence through the formation of a zwitterionic intermediate, which will definitely contribute to the better use of this technique. Furthermore, we propose to develop novel routes for the synthesis of quinoline and indole derivatives with predefined substitution pattern. The thesis is devided into four chapters |
| Description: | Department of Applied Chemistry, Cochin University of Science and Technology |
| URI: | http://dyuthi.cusat.ac.in/purl/3745 |
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| Dyuthi-T1708.pdf | (4.224Mb) |
| URI: | http://dyuthi.cusat.ac.in/purl/5280 |
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| Dyuthi T-2316.pdf | (7.804Mb) |
| URI: | http://dyuthi.cusat.ac.in/purl/5317 |
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| Dyuthi T-2353.pdf | (10.52Mb) |
| URI: | http://dyuthi.cusat.ac.in/xmlui/purl/1982 |
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| Dyuthi-T0460.pdf | (7.131Mb) |
| Abstract: | The objective of the present work is to study the effect of rare-earth (RE) doping on the superconducting properties of (Bi,Pb)-2212 system and to develop novel superconductors in the system with improved properties, especially, the self- and in-field critical current densities so as to use them for practical applications. This dissertation describes a range of findings in Bi-based superconductor using the cationic substitution of rare earth (RE) elements. Most of the experiments reported here take advantage of the difference in the valency and ionic radii of dopant and doping site. |
| URI: | http://dyuthi.cusat.ac.in/purl/2799 |
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| Dyuthi-T0820.pdf | (7.962Mb) |
| Abstract: | The subject of electroluminescence has currently acquired great importance because of its potential applications in display systems of a wide variety. A large number of scientists working in commercial, governmental as well as academic institutions all over the world are at present engaged in the intense effort to develop new and efficient phosphor materials and electroluminescent devices. This thesis presents the work carried out by the author in this field during the past few years. The studies discussed in this thesis are mostly confined to the development of some new phosphor materials, their uses in powder and thin film electroluminescent devices and to their electrical and spectral characteristics. Care has been taken to bring' out the physics involved in all the above aspects of the phenomenon |
| Description: | Department of physics, Cochin University of Science And Technology |
| URI: | http://dyuthi.cusat.ac.in/purl/3301 |
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| Dyuthi-T1277.pdf | (15.64Mb) |
| URI: | http://dyuthi.cusat.ac.in/purl/1099 |
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| Muraleedharan Pillai S 1984.pdf | (653.4Kb) |
| Abstract: | The thesis mainly discussed the isolation and identification of a probiotic Lactobacillus plantarum, fermentative production of exopolysaccharide by the strain, its purification, structural characterisation and possible applications in food industry and therapeutics. The studies on the probiotic characterization explored the tolerance of the isolated LAB cultures to acid, bile, phenol, salt and mucin binding. These are some of the key factors that could satisfy the criteria for probiotic strains . The important factors required for a high EPS production in submerged fermentation was investigated with a collection of statistical and mathematical approach. Chapter 5 of the thesis explains the structural elucidation of EPS employing spectroscopic and chromatographic techniques. The studies helped in the exploration of the hetero-polysaccharide sequence from L. plantarum MTCC 9510. The thesis also explored the bioactivities of EPS from L. plantarum. As majority of chemical compounds identified as anti-cancerous are toxic to normal cells, the discovery and identification of new safe drugs has become an important goal of research in the biomedical sciences. The thesis has explored the anti-oxidant, anti-tumour and immunomodulating properties of EPS purified from Lactobacillus plantarum. The presence of (1, 3) linkages and its molecular weight presented the EPS with anti-oxidant, anti-tumour and immunomodulating properties under in vitro conditions. |
| Description: | Division of Biotechnology,National Institute for Interdisciplinary science and Technology, Thiruvananthapuram |
| URI: | http://dyuthi.cusat.ac.in/purl/3044 |
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| Dyuthi-T1018.pdf | (5.206Mb) |
| URI: | http://dyuthi.cusat.ac.in/purl/1681 |
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| Dyuthi-T0025.pdf | (3.372Mb) |
| Abstract: | The thesis deals with detailed theoretical analysis of fluxon dynamics in single and in coupled Josephson junctions of different geometries under various internal and external conditions. The main objective of the present work is to investigate the properties of narrow Long Josephson junctions (LJJs) and to discuss the intriguing physics. In this thesis, Josephson junctions of three types of geometries, viz, rectangular, semiannular and quarter annular geometries in single and coupled format are studied to implement various fluxon based devices. Studies presented in this thesis reveal that mulistacked junctions are extremely useful in the fabrication of various super conducting electronic devices. The stability of the dynamical mode and therefore the operational stability of the proposed devices depend on parameters such as coupling strength, external magnetic fields, damping parameters etc. Stacked junctions offer a promising way to construct high-TC superconducting electronic components. Exploring the complex dynamics of fluxons in coupled junctions is a challenging and important task for the future experimental and theoretical investigations |
| URI: | http://dyuthi.cusat.ac.in/purl/1004 |
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| Dyuthi-T0026.pdf | (6.739Mb) |
| Abstract: | FPS is a more general form of synchronization. Hyperchaotic systems possessing more than one positive Lypaunov exponent exhibit highly complex behaviour and are more suitable for some applications like secure communications. In this thesis we report studies of FPS and MFPS of a few chaotic and hyperchaotic systems. When all the parameters of the system are known we show that active nonlinear control method can be efectively used to obtain FPS. Adaptive nonlinear control and OPCL control method are employed for obtaining FPS and MFPS when some or all parameters of the system are uncertain. A secure communication scheme based on MFPS is also proposed in theory. All our theoretical calculations are verified by numerical simulations. |
| Description: | Department of Physics, Cochin University of Science and Technology |
| URI: | http://dyuthi.cusat.ac.in/purl/2140 |
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| Dyuthi-T0503.pdf | (6.063Mb) |
| Abstract: | In this thesis an attempt to develop the properties of basic concepts in fuzzy graphs such as fuzzy bridges, fuzzy cutnodes, fuzzy trees and blocks in fuzzy graphs have been made. The notion of complement of a fuzzy graph is modified and some of its properties are studied. Since the notion of complement has just been initiated, several properties of G and G available for crisp graphs can be studied for fuzzy graphs also. Mainly focused on fuzzy trees defined by Rosenfeld in [10] , several other types of fuzzy trees are defined depending on the acyclicity level of a fuzzy graph. It is observed that there are selfcentered fuzzy trees. Some operations on fuzzy graphs and prove that complement of the union two fuzzy graphs is the join of their complements and complement of the join of two fuzzy graphs is union of their complements. The study of fuzzy graphs made in this thesis is far from being complete. The wide ranging applications of graph theory and the interdisciplinary nature of fuzzy set theory, if properly blended together could pave a way for a substantial growth of fuzzy graph theory. |
| URI: | http://dyuthi.cusat.ac.in/purl/43 |
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| Dyuthi-T0027.pdf | (2.557Mb) |
| Abstract: | The doctoral thesis focuses on the Studies on fuzzy Matroids and related topics.Since the publication of the classical paper on fuzzy sets by L. A. Zadeh in 1965.the theory of fuzzy mathematics has gained more and more recognition from many researchers in a wide range of scientific fields. Among various branches of pure and applied mathematics, convexity was one of the areas where the notion of fuzzy set was applied. Many researchers have been involved in extending the notion of abstract convexity to the broader framework of fuzzy setting. As a result, a number of concepts have been formulated and explored. However. many concepts are yet to be fuzzified. The main objective of this thesis was to extend some basic concepts and results in convexity theory to the fuzzy setting. The concept like matroids, independent structures. classical convex invariants like Helly number, Caratheodoty number, Radon number and Exchange number form an important area of study in crisp convexity theory. In this thesis, we try to generalize some of these concepts to the fuzzy setting. Finally, we have defined different types of fuzzy matroids derived from vector spaces and discussed some of their properties. |
| Description: | Department of Mathematics, Cochin University of Science and Technology |
| URI: | http://dyuthi.cusat.ac.in/purl/3119 |
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| Dyuthi-T1093.pdf | (1.804Mb) |
| URI: | http://dyuthi.cusat.ac.in/purl/1670 |
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| Dyuthi-T0028.pdf | (2.745Mb) |
| Abstract: | In classical field theory, the ordinary potential V is an energy density for that state in which the field assumes the value ¢. In quantum field theory, the effective potential is the expectation value of the energy density for which the expectation value of the field is ¢o. As a result, if V has several local minima, it is only the absolute minimum that corresponds to the true ground state of the theory. Perturbation theory remains to this day the main analytical tool in the study of Quantum Field Theory. However, since perturbation theory is unable to uncover the whole rich structure of Quantum Field Theory, it is desirable to have some method which, on one hand, must go beyond both perturbation theory and classical approximation in the points where these fail, and at that time, be sufficiently simple that analytical calculations could be performed in its framework During the last decade a nonperturbative variational method called Gaussian effective potential, has been discussed widely together with several applications. This concept was described as a means of formalizing our intuitive understanding of zero-point fluctuation effects in quantum mechanics in a way that carries over directly to field theory. |
| Description: | Department of Physics, Cochin University of Science and Technology |
| URI: | http://dyuthi.cusat.ac.in/purl/3405 |
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| Dyuthi-T1382.pdf | (2.275Mb) |
| Abstract: | Beta-glucosidases are critical enzymes in biomass hydrolysis process and is important in creating highly efficient enzyme cocktails for the bio-ethanol industry. Among the two strategies proposed for overcoming the glucose inhibition of commercial cellulases, one is to use heavy dose of BGL in the enzyme blends and the second is to do simultaneous saccharification and fermentation where glucose is converted to alcohol as soon as it is being generated. While the former needs extremely high quantities of enzyme, the latter is inefficient since the conditions for hydrolysis and fermentation are different. This makes the process technically challenging and also in this case, the alcohol generation is lesser, making its recovery difficult. A third option is to use glucose tolerant β-glucosidases which can work at elevated glucose concentrations. However, there are very few reports on such enzymes from microbial sources especially filamentous fungi which can be cultivated on cheap biomass as raw material. There has been very less number of studies directed at this, though there is every possibility that filamentous fungi that are efficient degraders of biomass may harbor such enzymes. The study therefore aimed at isolating a fungus capable of secreting glucose tolerant β- glucosidase enzyme. Production, characterization of β-glucosidases and application of BGL for bioethanol production were attempted. |
| Description: | Biotechnology Division National Institute for Interdisciplinary Science & Technology –CSIR Thiruvananthapuram |
| URI: | http://dyuthi.cusat.ac.in/purl/3756 |
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| Dyuthi-T1718.pdf | (11.62Mb) |
| Abstract: | This study on halocin production by Natrinema sp.BTSH10 indicate the prospects for intensive research which could lead to discovery of novel halocins which could have far reaching impact in biopharmaceutical industry particularly as anticancer drug. It is also anticipated that further research on this halocin could lead towards development of novel anticancer drug and new era in pharmaceutical biotechnology. There is no doubt that haloarchaea from saltern ponds have immense potential to return novel and valuable drugs and bioactive substances. |
| Description: | Microbial Technology Laboratory Department of Biotechnology Cochin University of Science and Technology |
| URI: | http://dyuthi.cusat.ac.in/purl/3738 |
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| Dyuthi-T1702.pdf | (8.837Mb) |
| Abstract: | In the present study, radio frequency plasma polymerization technique is used to prepare thin films of polyaniline, polypyrrole, poly N-methyl pyrrole and polythiophene. The thermal characterization of these films is carried out using transverse probe beam deflection method. Electrical conductivity and band gaps are also determined. The effect of iodine doping on electrical conductivity and the rate of heat diffusion is explored.Bulk samples of poyaniline and polypyrrole in powder form are synthesized by chemical route. Open photoacoustic cell configuration is employed for the thermal characterization of these samples. The effect of acid doping on heat diffusion in these bulk samples of polyaniline is also investigated. The variation of electrical conductivity of doped polyaniline and polypyrrole with temperature is also studied for drawing conclusion on the nature of conduction in these samples. In order to improve the processability of polyaniline and polypyrrole, these polymers are incorporated into a host matrix of poly vinyl chloride. Measurements of thermal diffusivity and electrical conductivity of these samples are carried out to investigate the variation of these quantities as a function of the content of polyvinyl chloride. |
| Description: | Department of Physics, Cochin University of Science and Technology |
| URI: | http://dyuthi.cusat.ac.in/purl/2573 |
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| Dyuthi-T0702.pdf | (5.178Mb) |
| Abstract: | The thesis deals with the study of super conducting properties of layered cuprates within the frame work of a modified Lawrence-Doniach (LD) model. The thesis is organized in seven chapters. Chapter I is a survey of the phenomena and theories of conventional superconductivity which can serve as a springboard for launching the study of the new class of oxide superconductors and it also includes a chronological description of the efforts made to overcome the temperature barrier. Chapter II deals with the structure and properties of the copper oxide superconductors and also the experimental constraints on the theories of high te:::nperature superconductivity. A modified Lawrence-Doniach type of phenomenological model which forms the basis of the presnt study is also discussed. In chapter III~ the temperature dependence of the upper critical field both parallel and perpendicular to the layers is determined and the results are compared with d.c. magnetization measurements on different superconducting compoilllds. The temperature and angular dependence of the lower critical field both parallel and perpendicular to the layers is also discussed. Chapters IV, V and VI deal with thermal fluctuation effects on superconducting properties. Fluctuation specific heat is studied in chapter IV. Paraconductivity both parallel and perpendicular to the layers is discussed in chapter V. Fluctuation diamagnetism is dealt with in chapter VI. Dimensional cross over in the fluctuation regime of all these quantities is also discussed. Chapter VII gives a summary of the results and the conclusions arrived at. |
| Description: | Department of Physics, Cochin University of Science and Technology |
| URI: | http://dyuthi.cusat.ac.in/purl/3815 |
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| Dyuthi-T1746.pdf | (17.56Mb) |
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