Lakshminath Bezbaroa Central Library Digital Repository
Welcome to the Institutional Digital Repository of Lakshminath Bezbaroa Central Library.
- This digital archive comprised of the Institutes' intellectual output.
- It manages, preserves & makes available the academic works of faculty and research scholars.
- It is established to facilitate deposit of digital content of scholarly or heritage nature.
- Allowing academics & their departments to share & preserve contents in a managed environment.
Communities in DSpace
Select a community to browse its collections.
Recent Submissions
Aspects of Some Physical Processes Around Compact Objects in Theories of Gravity
(2025) Devi, Saraswati
Although Einstein's theory of general relativity (GR) is regarded as one of the most successful theories for comprehending gravity both from an experimental as well as from theoretical perspective, numerous pathologies are known to exist in the theory. A number of alternatives to GR are proposed with a hope to remove such pathologies and to also provide hint about the regimes of spacetimes where physics is not clearly understood at present. Such alternatives are expected to reduce to GR as a low energy effective theory. The Universe provides us with a number of platforms where different theories of gravity can be put to test to check their validity. Among them, black holes (BH) provide a perfect test bed to explore and understand different physical processes as well as different theories of gravity. Other compact objects like naked singularities (NS), wormholes, etc. are also further helpful in carrying out the above investigations. The progress in the observational arena both in the gravitational and electromagnetic channel via the gravitational wave detectors and event horizon telescope (EHT) have provided indirect and direct ways to probe the Universe and has further pushed the frontiers of research in alternative theories and compact objects. The present thesis is aligned with this area and tries to focus in brief to the study of some aspects of the physical processes like shadows, quasinormal modes, superradiance and stability of solutions in two different types of alternative theories of gravity: the novel four dimensional Einstein-Gauss-Bonnet (EGB) gravity and the Loop Quantum Gravity. The former one contains higher order curvature corrections in the action in addition to the Einstein-Hilbert term, while the later was developed with a view to circumvent the loopholes of GR such as singularity by incorporating quantum corrections that gives the spacetime the notion of discreteness thereby rendering the spacetime regular. The QNMs and greybody factors of 4D-EGB BH have been studied by the perturbation technique using test scalar, electromagnetic and Dirac fields. The parameter of the 4D-EGB theory modifies these quantities, thereby providing us with an opportunity to check for these modifications in the observed data and comment on the nature of the compact object or the theory of gravity. The NS solution in this theory has also been explored and its stability was checked. Since it acts as a BH mimicker for various reasons, the thesis discusses the distinguishable features exhibited by the NS in the form of echoes in the time evolution of the test fields against which the response of the background has been studied. Such spacetimes were found to be unstable, thereby respecting the Cosmic censorship conjecture and restricting the parameter space of the Gauss-Bonnet coupling constant. On the other hand in order to understand the implications of quantum parameters on some astrophysical processes, the thesis discussed the shadows and superradiance in a quantum corrected BH in the domain of LQG and found that even if the effects are, at present, not within the domain of any observational techniques, interesting physical insights could still be found to take place at the scale of Planckian regimes, which might help in understanding the primordial BHs. The studies discussed in the thesis are important in understanding the nature of effects due to modifications in the theories of gravity, thereby providing a window to understand the nature of the background spacetime and check for distinctive observational features, if any.
Experimental Investigation on Condensation Heat Transfer Coefficient and Frictional Pressure Drop of Refrigerant R1234yf on Brazed Plate Fin Compact Heat Exchanger Surfaces
(2025) Kemprai, Partha Pratim
Compact heat exchanger an improved heat transfer equipment, is being widely used in many industrial applications such as automobiles, aerospace, cryogenic, electronic cooling, oil and gas sectors. Among the various types of compact heat exchangers, brazed plate fin types are mostly preferred due to their compactness, higher effectiveness, reduced space and weight. Brazed plate fin compact heat exchangers generally use plain fins, serrated, perforated, wavy and louvered fins that offer large fin density. The single-phase heat transfer characteristics study in compact heat exchangers are more available when compared to the phase change heat transfer applications. However, there exists an extensive application of phase change heat transfer mechanisms in compact heat exchanger due to their better performance. There are many studies available using refrigerant R134a in literature. But the condensation study of low GWP refrigerant R1234yf is found to be limited in compact heat exchangers design and the works available are mostly for tubes, channels, mini-channels and micro-fins. Literature survey also indicates that the work on condensation heat transfer of refrigerant R1234yf inside brazed plate fin compact heat exchangers with serrated and wavy fin surfaces are not available.
Probabilistic Machine Learning Approach Towards Diagnostic and Prognostic of Degrading Engineering Systems
(2025) Ojha, Shivam
Damage detection and prognosis are critical to managing degrading systems in the engineering infrastructure. The damage detection relying on sensor data and prognosis on historical failure data, usually both are treated separately. However, a holistic approach is needed to capture degradation at initial stages and prognosis. When implementing a machine learning framework for remaining useful life (RUL) estimation, two primary scenarios emerge: (1) utilizing a complete run-to-failure dataset for training, and (2) relying on a partial dataset. The latter presents significant challenges due to the necessity for extrapolation. Furthermore, limited research has explored extending damage detection results to RUL estimation by modeling the underlying degradation process using a surrogate measure. Moreover, few studies extend damage detection results to remaining useful life (RUL) estimation by modeling the underlying degradation process using a surrogate measure. An integrated probabilistic machine learning framework that systematically undertakes diagnosis, prognosis, and RUL estimation is lacking in the literature. Additionally, parameters for the surrogate degradation model used for prognosis are often estimated using conjugate gradient methods, which often fall into local minima. These surrogate models also ignore general population trends.
(A) New Strain Gage Technique for the Accurate Determination of Mode-I Notch Stress Intensity Factors of Sharp V-Notches
(2025) Paul, Pranjol
Notch stress intensity factor (NSIF) of a sharp V-notch is a vital parameter in notch fracture mechanics whose limiting value is frequently used in assessing the fracture of V-notched components. The accuracy of NSIFs acts as a regulatory aspect for appropriately making use of principles of linear elastic fracture mechanics in predicting and preventing aforesaid failures.
Anthracene and Aminothiazole Based Organo-Cations Guiding Ionic-Cocrystals, Hydrates of Pyridinedicarboxylic Acids and Selected Metal Complexes
(2025) Singh, Abhay Pratap
The research presented in this thesis is based on the synthesis, structural characterization, and self-assemblies of salts, ionic-cocrystals and hydrates. Series of 2,6- and 3,5-pyridinedicarboxylate ionic-cocrystals were investigated to show newness in their compositions by complete or partial deprotonations. Different multi-component cocrystals with novel photoluminescence properties are demonstrated in the thesis. Multiple numbers of hydrates from different anionic cobalt(II), copper(II), and zinc(II) pyridinedicarboxylate complexes possessing anthracene-based organo-cations and their interconversions are depicted. The contribution highlights diverse non-covalent assemblies formed through weak interactions such as hydrogen bonds, halogen bonds, π-stacking, and chelate-chelate interactions. The study was extended to zinc(II) pyridinedicarboxylate complexes containing sulfathiazolium cations to demonstrate variations in the bioavailability of a drug molecule derived from the same components in each case but with different compositions. This thesis has opened scopes for newer avenues to explore assemblies of ionic-cocrystals as well as solvated metal complexes to observe new properties and transformations among the ionic forms within an assembly by stimuli such as concentration gradient or additives.