Ceramic foams are versatile materials with properties like chemical inertness, thermal shock resistance, and high-temperature stability. However, their relatively high cost of realisation has been one of the bottleneck in their wide adoption. With the advent of ceramic precursors, especially the low-cost class like siloxanes and borosiloxanes, new opportunities evolve in developing cost-effective ceramic foams from these precursors. The thesis explores some innovative methods to realize SiBOC ceramic foams with methylvinylborosiloxane as a precursor. The techniques utilized include using melamine foam as scaffolds, urea crystals as sacrificial templates, carbon fiber embedding through natural cotton fibers, and aluminosilicate wool as preform. These foams exhibit low density, tunable porosity, and oxidation resistance up to 1300°C, and have the potential for use in thermal protection applications, including re-entry vehicles.

Nickel nanoparticles (NPs) have garnered considerable interest due to their distinct magnetic, chemical, physical and electrochemical properties.

Nickel based nanomaterials with notable electrochemical redox activity, has gained attention as a highly promising electrode material. It offers several advantages, including its affordability, well defined electrochemical behaviour, and the potential for improved performance through various preparation techniques thereby making its application as an electrochemical sensor. The thesis focuses on synthesis of nickel-based nanomaterials and exploring their applications in electrochemical sensing. The synthesized materials include nickel hydroxide nanosheets, nickel hydroxide-molybdenum sulphide nanocomposites, nickel dodecanethiol protected clusters and nickel α-lipoic acid protected clusters. The synthesized materials show 2D and 0D structures. A thorough analysis of the morphology and electrochemical properties of these substances has been conducted, showcasing their utility as electrochemical sensors for identifying biological, environmental, and industrially significant analyte molecules. These materials can be used for real sample analysis and thereby fabricating a device can also be considered as future perspectives.

Mullite ceramics are widely recognized for their superior thermal stability, good creep resistance, low thermal conductivity and resistance to oxidation in high-temperature oxygen-rich environments. This thesis investigates a polymer-derived ceramic approach aimed at overcoming the limitations of traditional oxide composite manufacturing by enabling low-temperature, pressureless sintering while preserving the integrity of reinforcement materials. In this context, aluminosiloxane and zirconoaluminosiloxane precursors were synthesized for mullite and zirconia-mullite ceramics, and thoroughly characterized. Ceramic conversion studies demonstrated that these precursors can form stable ceramic phases at temperatures as low as 900°C, making them suitable for oxide-ceramic matrix composites (OCMCs). Fibrous alumina-reinforced composites derived from these precursors exhibited exceptional thermal and mechanical performance, including the ability to withstand hypersonic heat flux without damage. Additionally, cellular ceramics produced from these precursors formed open-cell structures with low thermal conductivity, critical for thermal protection applications. The influence of ceramic residue on the density, strength, and thermal properties was also explored. The results underscore the potential of these ceramics in advanced aerospace applications, particularly for thermal protection systems in hypersonic vehicles.

Over the last decade, advancements in the electronics sector have raised the bar for EMI shielding requirements. To meet this demand, recent research has focused on developing shielding materials that can give the same level of EMI SE value while eliminating all of the disadvantages of traditionally employed metallic shields. However, there is a significant gap between laboratory-level preparation and industrial applications. In this thesis work, we tried to fill this gap and have suggested simple strategies for preparing water-proof, lightweight, thin, and flexible shielding materials with high- performance EMI shielding in X, Ku, and K-band. Here, carbon nanofibers (CNF) were produced from electrospun PAN by carbonization at 900°C. The obtained CNF mats have inherent nitrogen doping with graphitic structure and 1-D fibrous, porous, and layer-by- layer structure which make them capable of absorbing EM waves. In the first approach, CNF was coated with poly(3,4-ethylenedioxythiophene): polystyrene sulfonate (PEDOT: PSS) with the assistance of polyvinylpyrrolidone (PVP) to improve the EMI shielding properties. Then, we explored different types of fillers such as inorganic semiconductor tellurium nanoparticles (NPs), Semiconductor metal oxide Nb2O5 NPs, conducting perovskite metal oxide La0.85Sr0.15CoO3 NPs, BaTiO3 NPs, and carbon black NPs, incorporated with CNF to improve the electric conductivity as well as EMI shielding properties. The flexible and hydrophobic polydimethylsiloxane (PDMS) composite of these samples have potential applications in flexible electronic devices as shielding materials for next-generation applications. PDMS allows us to design any type of complex structure, which make it suitable shielding materials for practical applications in different forms such as enclosure, gasket, coating over electronic circuits, and wrapping the electronic components.

The realization of a highly developed society with zero-carbon emissions and advanced electrified transportation demands the emergence of batteries delivering superior energy density and charge storage capability. The search of electrochemists to find materials that can outperform Li-ion batteries led to the research on Li-S batteries (LSBs), which are energy-dense, high-capacity energy storage systems. Nonetheless, the widespread development of lithium-sulfur batteries is held back because of some serious concerns. This thesis focuses on developing multifunctional nanostructures as electrode materials to overcome the challenges faced by Li-S batteries (LSBs) and improve the specific capacity. The work introduces a nanostructured graphene-lithium cobalt vanadate-based cathode for LSBs, which delivers excellent capacity with long-term cyclability. Further, studies based on metal sulfide-carbon nanotube-modified separators for LSBs revealed superior electrochemical output with negligible self-discharge. An aqueous processable polymer blend-based cathode binder, which demonstrates better capacity retention and coulombic efficiency over long-term cycling. We envision that this research could provide an effective platform for the emergence of high-performance Li–S batteries.

A cavitating venturi is a passive device that uses hydrodynamic cavitating flow to anchor the mass flow rate. The inter-phase interactions impart inherent cavity oscillations in the venturi operation, presenting challenges in understanding its flow behaviour and developing reliable numerical models. Cavitating venturis are passive devices with no moving parts. This unique feature makes the device an excellent flow rate controller in various industrial applications. Systematic experiments conducted as a part of the project experimentally characterised the nature and dynamics of the cavitation zone in planar cavitating venturi. Predictability limits of the existing two-dimensional models have been assessed using scaling studies in axisymmetric and planar venturis. A simple one-dimensional model has been constituted to aid in the design and sizing of cavitating venturis. An App has been developed based on this model to aid the venturi sizing. The beta version on this App is being evaluated by LPSC, ISRO with the data available from their cavitating venturis in the fuel feed control lines of rocket engines.

Scientific missions to Lagrangian points have the potential to enhance the understanding of the universe and to accelerate the exploration of space. A typical mission design to an orbit around the Lagrangian points from the Earth involves two steps. In the first step, an orbit with prescribed geometrical characteristics is designed and in the second step, an optimal transfer trajectory to the orbit from an Earth parking orbit is designed. In the conventional approach to generate the preliminary design, the model of Circular Restricted Three Body Problem (CRTBP) framework is adopted utilizing differential correction (DC) and the transfer trajectory design using manifold theory. In this research, the preliminary design of orbits and transfer to them from the Earth are proposed to be executed under the framework of Elliptic Restricted Three Body Problem (ERTBP) utilizing an evolutionary optimization technique called Differential Evolution (DE). Various periodic orbits and quasi-periodic orbits in the Sun-Earth-spacecraft and Earth-Moon-spacecraft restricted three body systems and transfer trajectories to them from the Earth are generated without leveraging the manifold theory. For the transfer trajectory design in the Earth-Moon system, the proposed two-impulse methodology avoids the bridge segment and generates optimal trajectories with significantly lower flight durations compared to the manifold theory. The preliminary numerical designs are extended to high fidelity ephemeris models. In the ephemeris model, the generated quasi-halo orbits in the Sun-Earth system do not need any theoretical design maneuvers for about five years. For the mission design in the Sun-Earth system, it is substantively concluded that preliminary design using the ERTBP framework does not provide significant advantages over the CRTBP framework due to the near-circular nature of the Earth’s orbit around the Sun. The differential evolution technique is found to be very versatile in solving Lagrangian point mission design problems and avoids many complexities associated with the differential correction based technique. However, the DE based schemes are found to be computationally more intensive. The outcomes of this research can provide valuable methodologies and insights that can significantly enhance the effectiveness of future Lagrangian point missions, thus paving the way for further exploration and scientific discoveries in space.

This thesis aims to investigate AGC in a conventional regulated power system and a deregulated power system with the integration of Solar PV, Battery Energy Storage System (BESS), Super magnetic Energy Storage (SMES) and Static Synchronous Compensator (STATCOM). The linear time invariant models of Solar PV, BESS, SMES and STATCOM have been implemented in a two area power system for improving transient stability of the system. The average switching models of the active and reactive power devices have been presented to highlight the output current and power dynamics of the devices. With the availability of the active and reactive power compensation devices, the study extends to the optimal location and sizing of the devices which has not been attempted so far.

 Nacre, bone, spider silk, and antlers are some examples of biological composites that exhibit a great combination of mechanical properties such as high strength, stiffness, and toughness when compared to that of their constituents using which they are made up of. This has inspired many researchers to investigate bio-inspired composites to explore the possibilities of making synthetic composites with superior mechanical properties using relatively weaker constituents. There are many reasons behind the achievement of a biological composite’s superior mechanical properties, which range from the selection of constituents to its final arrangement. The basic structure of the above-mentioned biological composites is a kind of brick-and-mortar structure in which platelets with a defined configuration are dispersed in a pool of matrix. Here, the parameters significantly influencing the final mechanical properties are Young’s moduli ratio of platelet to the matrix, the platelet aspect ratio, and the arrangement of platelets, especially the hierarchy. The present study focuses on two staggering types found in nature, regular and stairwise, and conducts a failure analysis on one-hierarchical composites with these configurations. The inclusion of the first failure in the analysis is found to contribute to composite toughness significantly. Case studies using industry materials and recent research works support these findings. Analytical models are formulated for predicting the properties of non-self-similar two hierarchical composites, demonstrating good agreement with finite element analysis results. The generalized model aids in simplifying the design process, providing initial estimations of mechanical properties for hierarchical composites before full-scale fabrication and offering practical insights for future material design.

Despite a large number of studies made using both observations and models, due to the inability to disentangle the meterological effects from the aerosol impacts in cloud radiative forcing and poor parameterization in the numerical simulations, the interaction mechanisms between aerosols and clouds remain among the most un certain processes in the prediction of the global climate system

Due to the increased use of cube- and nano-satellites, the demand for micro-propulsion systems has grown, necessitating the optimization of micronozzle design and efficiency. Research on the flow characteristics of micronozzles is currently centered around micro-thruster applications, with the primary objective of achieving uniformity in the flow structure to ensure optimal thruster performance. Conversely, the secondary application involves gas mixture separation, requiring a highly non-uniform species distribution in the flowing mixture. The flow through micronozzles can encompass multiple scales, including continuum, slip, transition, and rarefied gas regions due to their smaller dimensions. The current research commences with numerical studies related to the thruster applications of micronozzles, utilizing classical N-S with a linear slip model, DSMC method, and a hybrid N-S/DSMC based on the continuum breakdown concept. The impact of geometric factors such as the divergence half-angle, throat depth, and expansion ratio is thoroughly analyzed for planar micronozzles, along with considerations of wall temperature conditions. The work also explores the effects of micronozzle geometry and flow parameters on the aerodynamic species separation within a planar nozzle, incorporating linear, bell, and trumpet divergent sections under the presence of carrier gas and back pressure conditions. Subsequently, these studies are extended to include a curved nozzle. The results of this research are anticipated to contribute to the development of improved designs for micronozzles utilized in satellite propulsion and aerodynamic separation processes.

This thesis aims to quantitatively analyse the effects of solar wind-magnetosphere-ionosphere (SW-M-I) coupling on the near -Earth space environment and enhance the current understanding of both large and small-scale coupling processes and mechanisms in the SW-M-I system during extreme transient events of supersubstorm and geomagnetic storms.At the first,robust quantitative analyses with regard to the LI-point and network of magnetometer and radars are included in comparative assessments and investigations of different coupling functions and the most significant parameters known to define the SW-M-I coupling. The in situ observations from the MMS, cluster, and THEMIS missions are additionally used to investigate the ion and electron scale coupling during the geomagnetic storm of 31 December 2015.

Perchlorate contamination in water due to industrial and space activities remains a serious problem as it seriously affects the function of thyroid glands. Various methods are being explored for the removal of perchlorate from the contaminated water. Among them, adsorption is a simple and cost-effective technique. The development of efficient adsorbent materials is the key to the success of the adsorption method of perchlorate removal. This thesis explores the synthesis of magnetically functionalized novel adsorbent materials from bio-waste such as eggshell and watermelon rind. Synthesis of N-doped activated carbon and Metal-Organic- Framework (MOF) based adsorbents are also explored. The perchlorate adsorption efficiency, adsorption mechanism, adsorption isotherm models, and adsorption kinetics are studied with the developed adsorbents. The regeneration of the spent adsorbents using suitable regents is also demonstrated for their reuse. The high perchlorate adsorption capacity of some of the adsorbents demonstrates their potential for practical applications.

Processing of powders to ceramic components uses a large number of interim additives such as solvents, binders, plasticizers, dispersants, lubricants, and coagulating agents. The majority of these processing additives are synthetically prepared from petroleum-based chemicals. Sustainable development necessitates the replacement of these synthetically prepared additives with naturally renewable materials. The thesis explores the use of natural rubber latex as a binder, gelling agent, and pore stabilizer for the preparation of dense and porous alumina ceramics. Powder pressing, tape casting, slip casting, and freeze-gel casting processes have been established for the preparation of dense and porous alumina ceramics using natural rubber latex binder for the first time.

Transitional flows with an unsteady inflow play a vital role in a broad range of applications, including biological fluid transport to space applications. In such cases, the thickness of the boundary layer formed over the solid surface varies in both space and time, causing a high level of complexity in the path of vortical structures formed from the shear/boundary layer. Also, time and space-dependent shear stress exerted by the fluid, separation, and associated instability phenomena are to be better understood. In this work, direct numerical simulations (DNS) are performed to study the stability of vortical flow structures associated with an unsteady boundary layer under an adverse pressure gradient condition. A trapezoidal pulse of mean velocity, consisting of the acceleration phase from rest followed by the constant velocity phase and deceleration phase to rest, is imposed at the inlet of the computational domain. The impact of the spatial and temporal components on the evolution patterns of the shear-layer and three-dimensional instabilities are examined in detail. By employing dynamic mode decomposition, some key features of the transitional flow and their time dynamics are extracted.

Black hole X-ray binaries (BH-XRBs) are gravitationally bound associations of a compact object (black hole) and a normal star. The compact object can `accrete' matter from the companion star forming an accretion disk which releases tremendous energy, predominantly in X-rays. The stages of sudden bursts of X-ray activity in these systems are commonly known as 'outbursts'. The present thesis endeavours to comprehend the accretion process underlying the exceptionally bright outbursts observed in the two galactic BH-XRB sources: MAXI J1820+070 and 4U 1543-47. The investigation utilizes a wideband spectro-temporal analysis, employing multi-instrument X-ray data. The findings of this study propose the presence of a complex corona geometry (extending both radially and vertically) for MAXI J1820+070 during the 2018 outburst. Additionally, our research reveals a remarkably strong and dynamic absorption feature between 8-11 keV in the 4U 1543-47 spectra. This detection represents the first occurrence of its kind in X-ray binaries. We hypothesize that this feature arises due to the absorption of accretion disk photons by a highly ionized, relativistic disk wind, which attains speeds up to 30% of the speed of light.

N-Dodecane plays a crucial role in surrogate fuels for gasoline and jet fuels. Selecting the right surrogate fuel combination depends on the properties of its individual components. Precise reaction mechanisms are essential to predicting combustion characteristics, including laminar burning velocity and ignition delay times. Unfortunately, data for n-dodecane-air, oxy-n-dodecane with diluents like N2, CO2, H2O, and n-dodecane-H2-air are scarce in the literature. This study aims to bridge this gap. It measured unstretched laminar burning velocity under various conditions using a new cuboidal combustion chamber with optical access and a dedicated heating system. The study used the partial pressure method to prepare combustible mixtures, an electrical spark-ignition system for ignition, and high-speed shadowgraph imaging for flame propagation. A non-linear stretch extrapolation scheme determined unstretched flame speed, and the validation process compared the results with existing data. Finally, simulations using CHEMKIN provided insights into the unstretched laminar burning velocity.

Protostellar jets are fossil records of the accretion history of protostars. Studying these jets opens up an indirect window of knowledge into the evolutionary stages and activities of the protostar, the direct study of which is difficult due to its highly embedded nature. The research highlights a theoretical and observational study of protostellar jets in radio and near-infrared wavelengths, respectively. The first part of the thesis describes a numerical model for radio jets from protostars, having simplistic geometry, which has been developed for the first time to explain the presence of thermal free-free and non-thermal synchrotron emission in these jets. The model has been successfully employed to estimate relevant physical and micro-physical parameters of protostellar jets for which observational data is available. The second part of the thesis covers a near-infrared investigation aimed at exploring the partially ionized and molecular regions of a massive protostellar jet, HH80-81, by utilizing molecular H2 and [FeII] emission lines as shock tracers. This is the first time detection of these emission lines towards the HH80-81 jet and following this, a qualitative and quantitative analysis of the jet has been carried out, enabling the identification of the nature of shocks and estimation of relevant physical parameters of the protostar and its jet.

The work is on Dynamic Compressed Sensing (DCS) system for efficient acquisition and recovery of sparse and compressible time-varying signals. DCS has three key components to be addressed: Estimation of the Sparsity level, indices of those sparse basis functions and their amplitudes. Sparsity Order Estimation (SOE) algorithms based on both Bernoulli/Gaussian sensing matrices and optimal tracking algorithms such as the Kalman filter and Viterbi Algorithm were developed. The developed algorithms resulted in reducing the complexity of CS methods by 25-30 % taking them closer to practical realization.

The work presented in this thesis is a theoretical and numerical investigation of the spin- dynamics in two recently demonstrated experiments involving long periods of RF irradiation on the quadrupolar nuclei channel, the 1 H - 14N double cross polarization (double CP) under fast MAS experiment by Carnevale et al. and the 1H - 35Cl TRAPDOR-HMQC experiment of Hung et al. Creation and evolution of various coherences generated in these proton-detected experiments are explored. To analyse the rich and complex spin dynamics due to the interference between the large time-dependent quadrupolar interaction and the radio-frequency (RF) field, an exact effective Hamiltonian is constructed numerically using the matrix logarithm approach. Structure of the effective Hamiltonian is connected with transfer amplitudes to various coherences, the output signal, etc. and, when possible, features of the spin dynamics are derived theoretically. The analysis also provides insight on the efficiency of these experiments under different experimental conditions.