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.

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.

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.

We begin our work by studying the most general class of oscillators, called ‘f-deformed oscillators’ or ‘f-oscillators’. We define the quadrature operator for the f-deformed algebra and hence obtain the deformed quadrature operator eigenstates. We derived a new set of polynomials and derived the deformed oscillator wavefunctions in terms of them. The position probability distribution for three different types of deformations are plotted, and each is compared with the corresponding non-deformed counterpart. The newly obtained quadrature operator eigenstates will be helpful for those who are working in the field of quantum state reconstruction and quantum information processing of deformed states.

The present study focuses on experimental techniques to understand the self-excited oscillation characteristics in low-density round for fully developed and turbulent flow conditions, as well as rectangular jets, and study the effects Reynolds number, momentum thickness, density ratio and aspect ratio on self-excited oscillation. Two global modes exist in low-density round jets. The results confirms that oscillations in low-density round jets are axisymmetric irrespective of S and D/θ, and turbulent jets can exhibit self-excited oscillations for S ≤ 0.53. Studies on rectangular low-density jet reveal that the jet transitions from a stable to a self-excited state through subcritical and supercritical Hopf bifurcation. Only supercritical bifurcations are observed during transition when AR ≥ 12. For lower aspect ratios, the type of Hopf bifurcation is dependent on the density ratio. SPOD analysis of low AR rectangular jets (AR ≤6) show that the spatial structure of the oscillation is a symmetric mode. SPOD analysis reveals that the spatial structure of the oscillation in high AR rectangular jets (AR ≥ 12) consists of three modes: a symmetric mode, a flapping mode in the major dimension and a complex mode similar to the ce2 mode in elliptic jets.

First phase of the research work focuses on dynamic modeling and ascent flight control of a highly unstable and flexible launch vehicle. Stabilizing adaptive PD/PID controllers are developed in MRAC framework using standard quadratic Lyapunov function to control the time varying rigid body dynamics during the atmospheric phase of flight. Further, Lyapunov stability and Barbalat’s Lemma are applied to prove the stability of the time-varying system. In the second phase of the research work proposes projection and barrier Lyapunov based adaptive controllers for the descent phase flight control of a winged re-entry vehicle. A rectangular projection operator is used in the adaptive control design to constrain the adapted gains within a maximum and minimum limit simultaneously.

The current work proposes novel stochastic meshless methods for the analysis of linear and nonlinear problems in structural mechanics which can take care of uncertainties in material property and loading when they appear as random variables or homogeneous random fields. The study suggests an improved response function based stochastic meshless method for the analysis of linear elastic problems. Further, the study also proposes a simple and efficient stochastic meshless method for the analysis of linear eigenvalue problems in structural mechanics. A high dimensional model representation based stochastic meshless technique is proposed in the current study for the analysis of geometric nonlinear problems in solid mechanics. A few numerical examples are solved to validate the proposed method by comparing the results with the direct Monte Carlo simulation or other existing methods. Further, the computational efficiency of the proposed methods is also established.

Defect free machining of Fibre Reinforced Polymer (FRP) Composites, crossing the challenges posed by anisotropic non-homogenous fibre-matrix system, is one of the important material processing requirements with a wide scope in industrial applications. Eccentric Sleeve Grinding (ESG) projected in this research is a unique strategy with progressive-intermittent cutting scheme for achieving minimal damage machined surfaces on FRPs. Progressively varying depth of engagement for active abrasive grains in the cutting zone with an intermittent and periodically repeating cutting pattern, achieved through precisely controlled eccentric rotation of grinding wheel is the key highlight of ESG. Through this step-by-step cutting methodology, significant reduction in average grinding force, surface defects and surface roughness have been achieved on Carbon Fibre Reinforced Polymer (CFRP) composites under varying cutting conditions. The thesis covers the geometric configurations, kinematics, coordination of work feed and wheel rotation to achieve scallop free surfaces during intermittent cutting, theoretical and experimental studies on mechanics and micro-mechanics of ESG, thermal aspects and other miscellaneous findings (theoretical and experimental) on ESG.

A systematic, extensive and in-depth study of channel characteristics for both static and dynamic human body model is reported in this thesis. The work involves design, fabrication and testing of various printed and dielectric antennas with very high gain for the proposed applications. A significant part of the thesis deals with human model which features the critical body segments such as head, shoulder, torso, upper arm, lower arm, thighs and calf for the study of double arm swing activity. Two cross-slot antennas (CSA) are designed and fabricated, for investigation of the double arm swing activity using the newly introduced twelve cylinder body model. The same CSA is used for creeping wave analysis on cylindrical single layered phantom. Simulations are done in CST Microwave studio suite and experiments are carried out using container filled with distilled water as phantom. The work reported in the thesis are published in very high quality journals such as IEEE Antennas and Wireless Propagation Letters, Wiley RFMICAE, Journal of Electronics Materials and so on.

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.

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.

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.

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.

The eco-cultural space Kavu (sacred groves) has been subjected to academic introspection from ecological, anthropological, historical and Folk Culture Studies perspectives. The thesis focuses on the representation of kavu in the popular discourse of Malayalam cinema. The primary objective of this thesis is to determine whether Malayalam films have addressed the heterogeneity of kavu, while considering its diverse systems of worship, caste dynamics, gender equations and ecological diversity.

This study is an earnest attempt to understand the role of mass media in the transition of Adivasis in the Wayanad District of Kerala. It was designed to address certain intriguing questions that emerged in the researcher’s mind, ranging from when the media technologies made inroads into the life of the Adivasi communities, what are the media artefacts that have got diffused, what are the different factors that have influenced the diffusion of mass media among Adivasis and how they have influenced the everyday life.

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.

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.

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.

This dissertation is explored the photonics inter sub band transitions (ISBT) phenomenon in an electronics Gallium Nitride (GaN) high electron mobility transistor (HEMT) device. Conventional photonic devices are operated at cryogenic temperatures to minimize the thermal effect. The reported maximum operating temperature of THz quantum cascade laser (QCL) is in the range of 150-200 K which is too low for general applications. The conduction band tuning through external gate bias makes advantage of HEMT device for room temperature (RT) terahertz applications. The theoretical models for electrically tuneable plasmonic metamaterials assisted ISBT have been developed. Experimental demonstration of electrical tuning of ISBT in a GaN HEMT device at room temperature has not only provided a novel mechanism but also discriminates ISBT from other transitions induced by deep-level traps and defects in the 100 nm GaN HEMT device. It is possible to tune the subband energy level inside triangular quantum well of GaN HEMT by applying gate voltage. The GaN HEMT device responds toward incident terahertz radiation due to inherent advantage of conduction subband tuning through external bias. The presented novel approach for ISBT in GaN HEMT has the potential possibilities in the context of overcome the THz gap in the electromagnetic spectrum at ambient temperature.