Lakshminath Bezbaroa Central Library Digital Repository
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Recent Submissions
Cobalt(II) and Manganese(II) Nitrosyl Complexes as Potential HNO/NOˉ Donor
(2024) Saha, Shankhadeep
This dissertation addresses our attempt to understand the potential of Co(II) and Mn(II) nitrosyl complexes as nitroxyl (HNO/NOˉ) donors. A series of nitrosyl complexes were synthesized by varying the ligand framework (from electron deficient to electron rich) with a central metal ion (e.g. Co2+ and Mn2+). The ability of these metal-nitrosyl complexes to act as HNO/NOˉ donors under different reaction conditions was discussed in chapters 2 to 5. The potential of cobalt-nitrosyl complexes as nitroxyl donors was extensively discussed in chapters 2 to 4, whereas chapter 5 addresses the manganese-nitrosyl complex, which led to some significant observations. For instance, in chapter 2, the nitroxyl releasing ability of a {Co(NO)}8 complex in presence of anionic sixth ligands like BF4ˉ and DTCˉ was observed, which is the first example of such kind of reaction. Chapter 3 describes our in detailed findings of the reaction between a {Co(NO)}8 complex and DTCˉ anion, which also leads to the NOˉ donation. In chapter 4, a neutral imidazole ligand mediated NOˉ release from a highly electron rich {Co(NO)}8
complex was studied. All of these sixth ligand mediated nitroxyl release from cobalt-nitrosyl complexes
are found to be concomitant in nature. The kinetic inertness of low-spin d6 cobalt-centre of {Co(NO)}8 complexes makes the release of HNO very difficult. Our recent findings on the methodology for HNO/NOˉ release from {Co(NO)}8 complexes will contribute significantly to the existing knowledge of nitroxyl donation from cobalt-nitrosyl complexes.
Process Development for Microalgal Cultivation System Towards Enhancement of CO2 Fixation and Biochemical Production Efficiency
(2024) Chauhan, Deepesh Singh
Microalgae present a promising avenue for CO₂ sequestration and biofuel production due to their rapid growth and high lipid content. However, their commercial viability faces challenges, such as low CO₂ capture efficiency, sensitivity to environmental stresses, and high water and nutrient demands. This thesis aims to overcome these challenges by focusing on strain selection, optimizing cultivation conditions, ensuring CO₂ utilization stability, achieving high biomass productivity, cost-effective harvesting, and water reuse strategies.
Exploration of Novel approaches for offline writer identification using handwritten words
(2024) Kumar, Vineet
This thesis presents innovative approaches for offline handwritten word image author identification, leveraging various deep learning techniques. The first work employs feature maps from pre-trained CNN layers to capture writer-specific characteristics. Key-point regions are first detected using the SIFT algorithm across different abstractions like characters and their combinations. These regions are processed through a CNN, producing feature maps that are then represented using a modified HOG feature descriptor. A unique contribution lies in extracting additional cues from these feature maps through a saliency measure derived using Sparse Principal Component Analysis (SPCA). The saliency scores are integrated with HOG features to create customized descriptors, which are then classified using SVMs to determine the identity of the writer.
Numerical and Experimental Investigations of Nonlinear Dynamics and Heat Transfer Deterioration in Supercritical Natural Circulation Loop
(2024) Srivastava, Tanuj
The natural circulation loop (NCL) efficiently transfers energy from a high-temperature source to a low-temperature sink without direct contact. The key driving force in natural circulation systems is buoyancy, caused by density differences. Single-phase NCLs face limitations from saturation temperature and low flow rates, while two-phase loops risk dry-out and complex flow regimes. Supercritical fluids offer an alternative, combining the benefits of both single- and two-phase systems. The concept of a supercritical natural circulation loop (sNCL) is important for Generation-IV nuclear reactors. This thesis evaluates sNCLs using CO2 through both numerical and experimental methods. Numerical studies analyze the steady-state and transient behavior of sNCL, using 3D simulations for steady-state and 2D/1D models for transient cases. Buoyancy and friction forces determine system behavior. As heating power increases, buoyancy dominates, leading to a rise in flow rate and heat transfer. However, friction eventually takes over, reducing flow rate and leading to flow-induced heat transfer deterioration (FiHTD). This phenomenon, which can be delayed but not avoided, is key to ensuring safe operation. Based on fluid temperature, four heat transfer zones were identified: low power, enhanced heat transfer, transition, and deteriorated heat transfer. 3D simulations using ANSYS Fluent confirmed the boundary of safe operation, with data fitting a power-law curve. Changes in friction factor along the heater section also signal the onset of FiHTD. The dissertation further explores static and dynamic instability in sNCL. Steady-state circulation shows a sharp decline, consistent with previous analyses, and exhibits Ledinegg instability at intermediate power levels. Both static and dynamic instabilities were identified, with results aligning across simulations. Under varying heat input, sinusoidal heating caused chaotic oscillations, while ramp heating remained stable due to gradual buoyancy generation. A 2D model explored startup transients, revealing the complex behavior of sNCL near the pseudocritical point. The system's bulk motion is influenced by phenomena like the piston effect, Rayleigh-Taylor instability, and adiabatic heating, which create hot fluid packets that drive system dynamics. Flow reversals and chaotic behavior result from intermittent fluid packet generation and disappearance. Experiments using CO2 examined the effects of sink temperature, pressure, tilt angle, and heating power for FiHTD. Flow rate peaked before declining, with the highest rates in vertical loops. No instability was observed under the test conditions, but the mass flow trends closely matched the simulations.
Novel aspects of radiation pressure in hybrid quantum systems
(2024) Das, Sanket
The study of radiation pressure involves a wave's average force on a surface or a particle. This force arises from the transfer of linear momentum when the wave interacts with the surface or particle. The application of radiation pressure ranges from the universe's development to modern laser applications, such as optical tweezers and cavity optomechanics. In cavity optomechanics, when a laser is reflected from a surface, it generates various types of elastic waves that travel through the object but are generally delicate. In simple terms, light can cause
a slight movement within the material, and it is observed in whispering-gallery-mode resonators and optomechanical crystals with photonic and phononic modes. The force of radiation pressure leads to various physical phenomena stemming from semi-classical lightmatter interactions, one of which is the mechanical analog of electromagnetically induced transparency (EIT). In EIT, an initially opaque three-level atomic medium becomes transparent due to applying strong control and weak probe fields. The destructive interference between
two excitation pathways creates a narrow transparency window, resulting in anomalous dispersion and slow light effects. An optomechanical system with a single cavity mode and an acoustic mode closely resembles an atomic three-level system when a strong drive field and a weak probe field are present. This setup allows for the observation of an effect analogous to EIT.