E. Thesis / Dissertations

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    Nonequilibrium Phase Transition in Ferromagnetic Model Systems
    Acharyya, Muktish
    In this thesis, I have mainly discussed the dynamical responses and behaviours of a ferromagnetic system under different kinds of magnetic field variations that are varied in time as well as in space, especially in the form of propagating magnetic waves and standing magnetic wave using Monte-Carlo simulation. These magnetic field waves cause the ferromagnet to undergo nonequilibrium phase transition; depending on the temperature, amplitude and wavelength of the magnetic field and the strength of anisotropy. In an Ising ferromagnet driven by standing magnetic field wave the high temperature phase is found to be quite different from that observed when propagating magnetic wave was passing through the Ising ferromagnet. Dynamical phases having similar attributes are formed in Blume-Capel (S = 1) ferromagnet when placed under these kinds of waves. However, in BC ferromagnet the strength of anisotropy affects the transition temperature as well as the morphological structure of the ferromagnetic spins. The studies regarding general characteristics of spin-S Ising ferromagnet excited by magnetic field waves revealed that the nature of dynamic phase transition is similar to the earlier studies but the transition temperature is found to decrease towards a limiting value with increase in the value of S. The values of critical exponents of spin - 1/2 Ising ferromagnet driven by propagating magnetic field waves are found to be very close to those obtained in Onsager’s solution for equilibrium ferro-para phase transition. This indicates that the nonequilibrium phase transition in an Ising ferromagnet driven by propagating magnetic wave belongs to the same Universality Class of equilibrium Ising ferromagnet.
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    Stratigraphy and Nature of uranium mineralization from Precambrian Basement Granitoid -Srisailam Formation contact around Chitrial area, Cuddapah Basin, Telangana
    Ghosh, Gautam; Bose, Sankar
    The biotite rich granitoid rocks exposed around Chitrial village varies in character from a porphyritic to massive granite to gneiss or mylonite with characteristic foliations defined by alternate quartzo-feldspathic and biotite rich layers in the latter units. It is intruded by ca. 1.9-1.8 Ga age mafic dyke sets and is overlain by Mesoproterozoic Srisailam Formation rocks of the Cuddapah Supergroup represented by an arenaceous gritty or pebbly sandstone interspersed with thin shale and siltstone horizons. The granitoid locally becomes uranium-rich near its contact with the overlying Srisailam Formation rocks. The present work encompasses stratigraphic, petrological, geochemical and geochronological analyses of the granitoids and accompanying supracrustals with special emphasis on nature and localization of uranium mineralization. Major element geochemical data characterize the granitoid rocks as monzogranites and alkali feldspar granite and the cover rocks as quartz arenites. The trace and rare earth element data were used to identify the protolith history of the granitoid rocks as well as about the nature of provenance of the cover sediments. The geochemical data further provide clues regarding probable tectonic and geodynamic setting of these rocks. A marked enrichment in U, Th and REE (particularly LREE) content of the granitoids has been noted. The overall REE pattern suggests a similar source for all the granitoid types. Several tectonic discrimination diagrams suggest a volcanic arc tectonic setting for these rocks. The recycled mature quartzose cover rocks show distinctly similar geochemical characteristics as the granitoids suggesting a granitoid/felsic source of mature continental provenance. REE patterns of the basement granite and the cover sandstone show similar variation which represents that the derivation of the sediments could be from the underlying basement granite. Recent exploration programme by Atomic Minerals Directorate for Exploration and Research (AMDER) has led to the discovery of a number of potential radioactive mineralized zones in the northwestern part of the Cuddapah basin such as around the Chitrial area. Uranium bearing minerals are intimately associated with sulphide rich minerals within the basement granitoids of the area. There is ample evidence of hydrothermal activity straddling across the unconformity surface which includes- (1) development of fracture filling veins of various dimensions comprising quartz, quartz-epidote, quartz-chlorite or pyrite, (2) hydrothermal alteration of granitoids adjacent to these veins resulting in chloritization and sericitization and (3) epigenetic uranium mineralization in micro-fractures and inter-granular spaces within granitoids. Evidence of uranium mineralization within the cover rocks is comparatively less. In the uraniferous zones in granitoid and overlying quartzite, pitchblende and coffinite are the main uranium phases occurring in micro-fractures and inter-granular spaces of host rock, often in association with pyrite. Depending upon micro-textural data, the paragenetic history of the mineralization has been divided into seven stages in the present study. U-Pb zircon radiometric dating of the basement granitoids reveals that the main tectonothermal event took place in Chitrial area between ca. 2535 Ma and 2519 Ma. Granitoid samples including the grey massive variety, pink granite, granite gneiss, foliated granite and alkali feldspar granite show emplacement ages of 2525±20 Ma, 2519±12 Ma, 2524±18 Ma, 2514±22 Ma and 2524±20 Ma respectively. Hence, it can be concluded that major tectonothermal event affected these rocks of the study area around 2535 to 2514 Ma. Probability density plot of weighted mean ages for the sample CT206 (granite gneiss) shows a strong peak at ca. 2465 Ma while the sample CT207 (foliated granite) shows another strong peak at ca. 2455 Ma which may be related to a second phase of tectonothermal event. U-Pb zircon detrital age of the cover rocks of the Chitrial area gives major cluster ages at ca. 2468 and 2488 Ma that may be correlated with this second tectonothermal event. From these rocks, diagnostic detrital zircons show age peaks at ca. 2520 Ma, 3000 Ma and 3200 Ma, which correspond to the established emplacement ages of the basement granitoid plutons in the Eastern Dharwar Craton. Younger dates are discordant with a lower intercept ages of near 200 Ma in the Wetherill concordia. Older zircon cores with spot data ranging from 2636±28 Ma to 3200±7 Ma are interpreted as grains inherited from the crustal source region or from the wall-rock of the granite intrusion. From the detrital zircon data, it can be inferred that source of the sediments is proximal. EPMA chemical dates of uraninites from the drill core sample 226B shows that the area underwent several episodes of hydrothermal activity, which have left their imprints on the isotope systematics of uraninite. Thus the younger ages furnished by U-Pb zircon radiometric dating of uranium rich in-situ zircon grains of the granite drill core sample (289Av) shows a group age of 172 Ma, possibly related to the much younger tectonothermal event. From this study, it is concluded that the Chitrial granitoids are ‘S’ type in character and formed by intracrustal melting of the deeply buried clastic sediments and subsequent incubational heating. It also implies crustal recycling could be the likely mechanism for granite magmatism during ca. 2535-2514 Ma. Uranium mineralization in the granite was influenced by increased fracture volume in the rocks and was controlled by oxygen fugacity in the ore-bearing hydrothermal fluid. This mineralization is related with the later stage fracture reactivation of the Eastern Dharwar Craton during a major younger tectonic activity.
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    Synthesis and Characterization of Polymer Grafted Carbon Nano Particles
    Chatterjee, Dhruba Prosad
    The present thesis entitled “Synthesis and Characterization of Polymer Grafted Carbon Nano Particles” deals with the synthesis and characterization of controlled and covalently grafted nanostructured carbon material-g-polyaniline nano composites. A thorough analysis of their structure, morphology and electrochemical properties are presented. The work is carried out at the Department of Chemistry, Presidency University, Kolkata 700073 India, under the supervision of Dr. Dhruba Prosad Chatterjee. The thesis comprises of five chapters. Chapter 1 deals with a brief introduction of carbon nano particles; their classification, synthesis, their composites with different polymers and their application in electronics, biomedical, energy application. Due to their high surface area and porosity, carbon nano materials are capable of showing electrochemical double layer capacitance (EDLC), whereas conducting polymers like polyaniline, polythiophene and polypyrrole show pseudocapacitance. Achieving their best of synergistic effect via covalent bonding hence, improvement in electrochemical properties is the main focus of my research. Chapter 2 describes controlled polymerization of aniline on spherical carbon nano dots (CND) obtained from oxidation followed by size separation from cheap raw material like candle soot, resulting in distinguishable morphology between controlled and uncontrolled product with much improved electrochemical property of the former. Chapter 3 illustrates the synthesis of covalently attached graphene oxide-g-polyaniline nano composites having hierarchical nano structuring of one dimensional (1D) polyaniline nano cylinders over two dimensional (2D) graphene oxide surfaces along with formation of unique microflower or ‘sea urchin’ like highly porous three dimensional (3D) microstructures resulting in superior electrochemical properties than non covalent product. Chapter 4 investigates synthesis of covalently attached GO-g-PANI chiral nanocomposites seeded by oligomeric aniline attached GO sheets, which shows better electrochemical properties compared to non covalently attached composite with much inferior degree of PANI chain chirality. A summary of the research work along with the future prospects obtained from this thesis are presented in Chapter 5.
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    Tbx20 function in Proepicardial organ (PEO) & epicardium derived cell differentiation and Asporin /PLAP-1 function in aortic valve calcification
    Chakraborty, Santanu
    Nowadays, the problem of cardiovascular diseases is a major burden and a leading causes of morbidity and mortality in humans, globally. A proper understanding of the cellular and molecular mechanisms of heart failure has just started to provide better medical care and patient management. It has now become increasingly clear that cardiomyocyte proliferation, cardiac progenitor cell induction, development and differentiation of several cardiac cell lineages and cardiac extracellular matrix (ECM) remodeling are the dynamic processes, critical for injured myocardial repair. Proepicardial organ (PEO) is an extra cardiac villous protrusion at the venous pole of vertebrate embryonic heart that forms epicardium migrating onto the myocardium. PEO-derived epicardium and epicardium derived cells or EPDCs contribute several cardiac cell lineages including smooth muscle cells (SMs), fibroblasts, endothelial cells and cardiomyocytes (CMs). But in the developing heart, detailed gene expression pattern of several lineage specific markers within PEO progenitor cells and its epicardial derivatives are relatively unknown. Cardiomyocyte differentiation from proepicardial organ (PEO) and embryonic epicardium (eEpi) derived cells or EPDCs in developing heart, emerges a wide interest in purview of cardiac repair and regenerative medicine. Embryonic epicardium (eEpi) originates from the precursor PEO and EPDCs and contributes to several cardiac cell types including smooth muscle cells, fibroblasts, endothelial cells and also cardiomyocytes (CMs) during cardiogenesis. Using avian explant culture system, our data have yielded differential expression of several marker genes in PEO versus epicardial cells. Next, to explore the role of Wnt/β-catenin signaling in PEO and EPDCs, avian E5 epicardial cells were treated with lithium chloride (LiCl), recombinant Wnt3a (rhWnt3a) protein and Xav939. Addition of LiCl and rhWnt3a have inhibited glycogen synthase kinase 3β, stabilizing β-catenin and reversely, addition of Xav939 have inhibited Wnt/ β-catenin signaling in avian explant cultures. Interestingly avian epicardial explant cultures, treated with LiCl and rhWnt3a, show increased mRNA expression of Tbx20 concomitant with induced expression of CM lineage markers and Xav939 treated epicardial explant cultures show decreased expression Tbx20 and CM markers. In addition, Wnt signaling activation also increases the number of proliferating and sarcomeric myosin (Mf20) positive cells in eEpi explant culture. Together, these data suggest, eEpi cells as a source for CM differentiation and Wnt signaling mediator, β-catenin might play an important role in CM differentiation from eEpicells in culture. Overall, aim1of this thesis suggests the importance of Tbx20 viii | P a g e and β-catenin in regulation of CM lineage differentiation from EPDCs. Therefore, our studies will further provide a mechanistic insight into the PEO based therapies for CM support improving therapeutic and regenerative approaches following adult cardiac injury. Likewise, valvular diseases, importantly calcific aortic valve diseases (CAVDs) are also projecting serious concerns throughout the world. CAVDs account for 25% of all types of cardiac disease, causing significant number of morbidity and mortality among patients with cardiac abnormalities. Aortic valve mineralization and calcification are the key events of adult calcific aortic valve disease manifestation and functional insufficiency. Due to heavy mineralization and calcification, adult aortic valvular cusps show disorganized and dispersed stratification concomitant with deposition of calcific nodules with severely compromised adult valve function. Interestingly, shared gene regulatory pathways are identified between bone forming cells and heart valve cells during development. Asporin, a small leucine rich proteoglycan, acts to inhibit mineralization in periodontal ligament cells and is also detected in normal murine adult aortic valve leaflets with unknown function. Therefore, to understand the Asporin function in aortic cusp mineralization and calcification, adult avian aortic valvular interstitial cell culture system is established and osteogenesis has been induced in these cells successfully. Upon induction of osteogenesis, reduced expression of Asporin mRNA and increased expression of bone and osteogenesis markers are detected compared to cells maintained without osteogenic induction. Importantly, treatment with human recombinant Asporin protein reduces the mineralization level in osteogenic media induced aortic valvular interstitial cells with the concomitant decreased level of Wnt/β-catenin signaling. Overall, all these data are highly indicative that Asporin might be a novel bio-molecular target to treat patients of calcific aortic valve disease over current cusp replacement surgery. Thus, studies of two aims in cardiovascular research area will enrich and reveal new insights which will enhance the ongoing as well as future investigations in cardiac therapeutic field
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