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Design of Low-power Analog Front-end ASIC for ECG Acquisition System
No full textProviding quality treatment to every section of people along with the traditional health care system is a challenge for today’s world. Regular monitoring of the patient’s vital signs is essential in order to diagnose the health conditions to provide appropriate treatment. Among several vitals, Electrocardiogram (ECG) is one of the most important bio-potentials, which is routinely monitored and recorded in modern clinical practice. In traditional health care, patients are connected to a bulky and mains-powered instrument, which reduces their mobility and creates discomfort. This limits the acquisition time, prevents continuous monitoring, and affects the diagnosis of the illness. Therefore, there is a growing demand for low-power, small-size, ambulatory and wearable bio-potential acquisition systems. These systems must perform signal acquisition, extraction, analysis, and wireless transmission, if required, of the bio-potentials with reduced power consumption, and robust operation under the presence of signal artifacts. In general, the portable system consists of a front-end analog signal acquisition system and a back end digital signal processing unit. The analog front-end (AFE) mainly contains Instrumentation Amplifier (IA), Filter and Programmable Gain Amplifier (PGA). As the bio-potentials are low frequency and low amplitude signal and skin-electrodes are used to sense the signal, the key requirements of the system are high CMRR, high input impedance, low noise, low power consumption, and ability to reduce differential electrode offset (DEO) as well as internal offset. In this work, an analog front-end Application Specific Integrated Circuit (ASIC) is designed to acquire the ECG signal for a bio-potential acquisition system. In this work, four chopper-stabilized AC-coupled current feedback instrumentation amplifiers (CFIA) are designed, which effectively reduce the input DC electrode offset. In addition to IA blocks, two configurations of waveform generators (WFG) to generate square wave and clock signals are also presented. In the design of the AFE readout, WFG-2 generates the required clock signal. Along with the acquisition of the ECG signal, this work also includes a feature extraction channel, which provides the band power of the QRS complex to assist the DSP in further processing in the digital domain. Finally, all proposed and supporting blocks are integrated and simulated using the Spectre simulator in a Cadence Virtuoso environment. In all proposed blocks, the IAs are designed in UMC 180 nm technology, and their performance is compared with the previously reported CFIAs. Simulation results show that the proposed IA configurations achieve maximum offset reduction range of 120 mV, highest CMRR of 133 dB and consumes lowest power of 4.1 μW. On the other hand, the waveform generators are fabricated and tested. The measured results show frequency tuning range up to 960 kHz and 600 kHz for WFG-1 and WFG-2 respectively, whereas the amplitude tuning range for both the WFG varies from 0.45 V to 1.15
Nonlinear Thermomechanical Characteristics of Damaged Smart (Bonded with Shape Memory Alloy Fibre) Layered Composite Structural Panel Theoretical Analysis and Experimental Verification
No full textA novel nonlinear mathematical framework has been developed to compute damaged layered structural responses under combined loading (thermal and mechanical) conditions. The physical composite structural model is derived using higher-order kinematics, including the full-scale geometrical distortion via Green’s strain in the Lagrangian frame. Further, the model uses the marching technique to numerically introduce shape memory alloy (SMA) fibre properties to enhance structural stiffness due to damage and elevated environment. The system responses are obtained numerically using an in-house customized computer code (MATLAB platform) utilizing the mathematical model associated with isoparametric finite element steps, including the solution techniques, i.e., the direct iterative method (nonlinear solution) and Newmark’s integration technique. Initially, the numerical solution consistency and accuracies are verified with the published benchmark solutions (numerical/analytical/experimental) and a few experimental data obtained from the lab-scale experimentation (static, frequency, and dynamic values for damaged layered structure with and without SMA). The numerical prediction efficacies are also verified through a machine-learning model to show the independence of the proposed model variables and the corresponding assumptions. Using the currently derived MATLAB code, the linear and nonlinear static deflection, eigenvalue, dynamic responses, and buckling and/or post-buckling cases. The influence of volume fractions, pre-strain values, and thermal environments on smart material alloy fibre properties is assessed using the numerical model, demonstrating substantial enhancements in composite performance. The study indicates that incorporating SMAs in laminated composites significantly enhances static and dynamic responses, and the improvements range from 40 to 65% and 15 to 58%, respectively. The SMA volume fraction increases from (Vf = 0% to 24%). Similarly, natural frequency values also show an improvement of 4% to 8% when SMA volume fractions increase (Vf =10% to 20%). In damaged laminated plates, SMAs mitigate losses, resulting in notable enhancements of up to 5% to 18% across static, dynamic, and frequency characteristics. It highlights SMAs effectiveness in restoring and reinforcing damaged structures. Additionally, the inclusion of machine learning models within the present analysis utilizing the data set generated using the proposed mathematical model also reflects the desired accuracies in terms of the existence of damage and size of damage. Out of all models of machine learning models, the random forest classifier is capable of predicting the values accurately. Finally, the study explores influential input parameters affecting structural stiffness and design aspects, offering recommendations for future functional materials and composite structure applications
Similarity Analysis of a Class of Non Newtonian Boundary Layer Flows
No full textIn the field of fluid mechanics, despite its well-established foundations, numerous physical phenomena still need to be more adequately understood. One of these is the boundary layer flow of non-Newtonian fluids. Almost all the fluids used in the industries are non-Newtonian, and most of the flows can be numerically modelled by a flow past a stretching/shrinking sheet, flow near a stagnation point, and magnetohydrodynamics flow over a porous shrinking sheet. The present research aims to understand better the behaviour of different non-Newtonian fluids in the laminar boundary layer flow on the aforementioned geometries. The non-Newtonian fluid models are not only important because of their technological significance but also in view of the interesting mathematical features presented by the partial differential equations (PDEs) governing the flows. Lie group analysis is utilized to transform the governing partial differential equations into ordinary differential equations (ODEs), enabling a more simplified mathematical approach and facilitating deeper insights into the physical behaviour of the system. The primary goal of this thesis is to derive suitable similarity variables of the system of PDEs in order to obtain certain classes of group invariant solutions. The self-similar equations are solved numerically. It is interesting to observe that some of these self-similar equations admit dual solutions while others have a unique solution. Our secondary goal is to perform linear temporal stability analysis to determine whether the numerical solutions are physically acceptable and reliable. For dual solutions, linear temporal stability analysis revealed that the upper (first) branch solutions are stable and practically reliable, while the lower (second) branch solutions are unstable. Moreover, in the case of a unique solution, the stability analysis helps us to validate the obtained numerical solution. The stability analysis of these obtained solutions is determined by a sign of the smallest eigenvalue, where the positive or negative sign of the smallest eigenvalue leads to a stable or unstable solution, respectively. Effective numerical schemes have been used to determine the smallest eigenvalue. The effects of various material and flow parameters on the skin friction coefficient, Nusselt number, Sherwood number, shear stresses, velocity, temperature profiles, and boundary and thermal layer thicknesses are shown through graphs and tabular forms
Balancing Energy Poverty and Climate Change: Perspectives from the Developing Countries of Asia and Africa
No full textThe connection between climate change and energy poverty primarily emphasizes the interplay among human development, energy usage and environmental sustainability. In this thesis, we have explored the connections between energy poverty and climate change by emphasizing the common roots, synergies and trade-offs between policies targeted to achieve the twin goals of energy poverty alleviation and climate change mitigation. By adopting an integrated and multidimensional approach that considers the needs of communities and the environment, it is possible to reconcile the dilemma of energy poverty and climate change. The key lies in finding sustainable solutions that provide reliable energy access while reducing greenhouse gas emissions and promoting social well-being. Energy poverty and climate change are two sides of the same coin, intertwined in cause and consequence. Tackling these issues through sustainable energy solutions provides a unique opportunity, not just for the environment but also for human development and equity. The review of existing literature reveals that, there is a lack of sufficient cross-country studies, that simultaneously addresses the dual challenges of energy poverty and climate change. Even though some recent studies acknowledge different aspects of energy poverty and climate change in the developing countries, they often fail to acknowledge the link between energy poverty alleviation and climate change mitigation policies. The current study bridges this gap in the literature by investigating four primary objectives. First of all, we investigate the role of governance and renewable energy in energy poverty alleviation and decarbonisation. Second, we examine the effects of government decentralisation, financial development and climate change mitigation policies on clean energy transition. Third, we estimate the energy efficiency scores for different economic sectors (Agriculture, Industry and Services) and examine the effectiveness of energy efficiency on greenhouse gas emission, by considering the threshold effects of energy poverty and economic growth. And finally, we investigate the effects of different types of cooking fuel usage and fuel switching behaviour on indoor air pollution and indoor pollution attributable mortality rates. The current research draws a comparative analysis between the Asian and the African developing countries in several aspects related to energy poverty and climate change mitigation policies. Such comparative study provides a novel approach in addressing the common problems and solutions specific to these regions, which together comprise of the World’s largest share of the energy poor population. Comparative analyses provide a relative scale for measuring the progress and shortcomings of one area of study in terms of the other. Even though many earlier studies have compared the energy and development problems in two or more countries, there are no such studies yet, that compare the energy poor countries of Africa and Asia for a closer look into the similarities and differences of their problems, and investigate whether they can learn from each other’s best practices. The second important contribution of this research is the development of a conceptual framework that helps in identifying the synergies and trade-offs between the energy poverty alleviation and the climate change mitigation policies. In this context, special emphasis is placed in Chapter-2 on the role of governance and renewable energy. Identifying the synergies help in targeted policies to find optimum solution, whereas by identifying the trade-offs, policymakers can decide their priorities and decide on how much they are willing to sacrifice one goal for the other, if necessary. The third contribution of this thesis is the construction of an Energy Transition Index for the developing countries, based on the framework of Hu et al. (2022), who framed this index for the OECD countries. Moreover, by investigating the effects of environmental policy through the channels of financial development, decentralisation and economic openness, Chapter-3 contributes to the energy and climate literature for the developing countries. A fourth contribution is the estimation of sectoral Total Factor Energy Efficiency Scores for the developing countries considered in this study. Further, although there are many studies which have examined the effects of energy efficiency on Greenhouse gas (GHG) emission, there are no studies which have performed threshold regression to study the impact of sectoral energy efficiency on GHG emission, by considering economic growth and energy poverty as the threshold variables. Finally, the current research estimates a fuel-switching index to capture the switching of fuels from traditional coal or biomass to modern electricity or natural gas cooking fuel. Moreover, most studies on cooking fuel poverty have been conducted at the household level, and there is a lack of cross-country studies to understand the impact of cooking-fuel poverty on indoor air pollutants and mortality rates. The current study provides a holistic approach by incorporating the different aspects related to energy poverty and climate change, and offers policy recommendations to reconcile the dual goals of energy poverty alleviation and climate change mitigation in the developing countries of Asia and Africa
Investigation of Potential piRNA-mediated Regulation of Oncogenicity and Chemoresistance Imparted by FDFT1 in the pathophysiology of Tongue Squamous Cell Carcinoma
No full textPiwi-interacting RNAs (piRNAs) are key regulators of biological processes that mediate gene regulations at various levels. The abnormal expression of piRNAs is involved in pathophysiological diseases, such as cancer. However, its role in tongue squamous cell carcinoma (TSCC), a highly malignant carcinoma originating from tongue squamous epithelium, has not yet been elucidated. Therefore, in the current thesis, we first investigated the presence of PIWILs and piRNAs in TSCC cell lines and found that 407 piRNAs are dysregulated. Among these, we found only 46 piRNAs target 158 differentially expressed genes, of which only 5 genes are enriched in TSCC significantly. Then, we validated the reciprocal expression pattern among the target–piRNA pairs through qRT-PCR, from which we selected FDFT1, the only upregulated target that could be a potential oncogene. To decode mechanistic insights into the functions of FDFT1, we executed several molecular biology assays in SCC-9 and H357 TSCC cell lines in vitro. We overexpressed FDFT1 in TSCC cells and found an increase in viability, proliferation, migration, and ROS generation, indicating its oncogenic nature. We found overexpression of piR-39980, a key regulator in various cancers, and downregulated in TSCC inhibit FDFT1 as its target, which was confirmed from the luciferase reporter assay. To explore the effect of piR-39980 in TSCC, we overexpressed and silenced it in TSCC. We found that its overexpression could attenuate the oncogenicity of FDFT1 and inhibit cell viability, proliferation, migration, and ROS generation by suppressing the EIF3H/HIF1α axis, inducing hypoxia and causing p53-induced apoptosis and its silencing, showing the reverse. This tumor-suppressive nature of piR-39980 and the oncogenic nature of FDFT1 encouraged us to study whether these modulate the chemosensitivity of Doxorubicin in TSCC, an obstinate issue in chemotherapy. Interestingly, we found piR-39980 increases the sensitivity of Doxorubicin in TSCC cells by increasing its accumulation synergistically by deregulation of FDFT1, CYPOR, and EIF3H/HIF1α axis. In summary, these findings build the possibility of piR-39980 as a novel RNA-based therapeutic agent and FDFT1 as a therapeutic target to treat TSCC and overcome chemoresistance, which needs further investigation
Image Forensics: Towards Effective Techniques for Image Authentication in Compressed Domain
No full textNowadays, most images are tampered with in a lossy compressed scenario that can spread fake information on social media. On the other hand, image forensics forms an important sub-domain in detection of such image tampering, and it has various applications: surveillance, copyright protection, journalism, biomedical imaging, etc. Towards this, the research reported in this thesis primarily resides in image forensic analysis in the compressed domain. Further, the thesis examines the issues of manipulation detection, parameter estimation, and manipulation operator chain classification, which are some of the most crucial forensic applications. Therefore, this work is driven by manipulation detection and further move on to parameter estimation, which is relatively less established. In addition, another unsolved issue that required investigation was operator chain classification in JPEG compressed images. The preliminary contribution of this thesis deals with the manipulation detection problem, which is split into sub-problems of manipulation detection and its parameter classification. Manipulation detection focuses on separating altered images from unaltered ones, while parameter classification focuses on further classifying by which factor the doctored image is altered. Towards this, conventional Bartlett and Welch power spectral density (PSD)s are utilized to characterise the compressed domain discrete cosine transform (DCT) histogram. The first approach, Bartlett PSD of the DCT histogram and one-dimensional (1D) convolutional neural network (CNN) are proposed for manipulation detection and its parameter estimation. In contrast, the second approach proposes a Welch periodogram for quality factor estimation of re-compressed images. Both techniques performed well in all experiments using DCT coefficient histograms retrieved from altered and unaltered compressed images, while the Barlett method slightly outperformed the other. When the doctored input images were noisy, however, the performance of the PSD degraded, highlighting the need to investigate more sophisticated approaches capable of mitigating compression noise. To overcome this, the second contribution made an attempt to propose a new approach to the manipulation detection problem by utilizing a CNN-based denoiser to extract the noise residuals. Initially, a CNN-based denoiser with ten convolutional layers without pooling layers is used to capture correlation patterns of neighbouring pixels, which could suppress the blocking artefacts (BAR) and enhance the clues separately. Further, these residuals are fed to the feature conceptual extraction and classification stage to detect manipulation by eliminating the blocking artefacts. In addition, these noise residuals are also utilized for estimating scaling factors, which gives promising results, particularly for detecting downscaling scenarios. However, the proposed deep CNN fails to detect multiple manipulations. Hence, a generalized manipulation detection scheme has to be investigated. The latter part of the thesis shifted towards exploring the multiple manipulation detection problem, which consisted of different manipulations (JPEG-manipulation-JPEG) in most real-time applications. This premise led to exploring two frameworks (MDRNet and MPeRNet) to detect and estimate multiple manipulations by extracting noise residuals using residual blocks. In both frameworks, noise residual extraction stage significantly extracts manipulation traces by expanding the front-end detector that can exploit noise residuals by suppressing the image content. In addition, MDRNet and MPeRNet effectively detect multiple manipulations and estimate the parameters with shortcut connections from noise residuals. However, DCT residuals are not utilized in the above frameworks, which impacts the performance of manipulation operator chain detection under compressed scenarios. The last part of the thesis mainly concentrated on under-explored manipulation operator chain classification problem, which entails recognizing complex manipulations like Gaussian blurring and resampling. According to inferences taken from prior methods, the feature analysis could be enhanced if a representation scheme for the manipulation under compression were investigated rather than the uncompressed scenario. To achieve this, two approaches with multi-streams, such as manipulation-based and compression-based feature maps, are used to describe the tampered information of the doctored images. In the first approach, the spatial and noise streams are concatenated to obtain spatial features, and 25 DCT stream residuals pass through residual blocks to get frequency domain features. In the other approach, two streams, noise residual extraction (NRE) and compression feature extraction (CFE), are utilized to extract features of a doctored image. Finally, these feature maps are concatenated in both approaches and given to the classification stage to identify the operator chains. Both approaches are proposed for JPEG-resistant image operator chain detection using ResNet as a backbone and achieve better results against JPEG compression. Also, the proposed techniques outperform the state-of-the-art methods reported in the literature
Invariant Solutions using Symmetry Analysis with Conservation Laws for Various Nonlinear Partial Differential Equations Appearing in Physical Problems
No full textThis thesis is dedicated to presenting a wide range of applications of continuous symmetry groups and conservation laws to the physically important system of partial differential equations. Lie symmetry analysis has been successfully implemented for obtaining exact analytic solutions, such as similarity solutions, fundamental solutions, wave-traveling solutions, series solutions, and soliton solutions of various partial differential equations. The main idea of the Lie group method is to utilize the invariance property of partial differential equations to obtain similarity reductions and group-invariant solutions. The invariance property is the most effective tool to find the symmetries of a differential equation because it enables us to reduce the number of independent variables by one. With the aid of this analysis, the system of partial differential equations has been reduced to a new system of ordinary differential equations, which brings an analytical solution to the main system. Infinitesimal generators, commutator tables, and group-invariant solutions have been carried out using the Lie symmetry approach. Also, a geometric approach to finding the symmetries of a system of partial differential equations has been talked about, in which Harrison and Estrabrook’s differential forms are used to construct the infinitesimal generators. However, there are an infinite number of possibilities for the linear combination of these symmetries, so to categorize the class of invariant solutions corresponding to these symmetries, an optimal system of subalgebra has been constructed using Olver’s standard approach. To broaden the range of symmetries of the system and therefore the family of solutions, nonlocal symmetries are introduced, in which the infinitesimals of the transformation must be dependent on the integration of local dependent variables. After that, the global behavior of dependent variables can be reflected by a nonlocal symmetry. An important part of the symmetry structure of a partial differential equation is information about its conservation laws. Knowledge of conservation laws for a partial differential equation provides insight into conserved physical quantities and can be used in the development of stable numerical methods. Therefore, in this work, conservation laws corresponding to the symmetries have been established by utilizing the fundamental approaches, namely, the direct approach, multiplier approach, and Ibragimov’s approach
Development of Prolinol-derived Organocatalysts and Their Application to Organocatalytic Michael Addition Reactions
No full textChapter 1. A concise overview of prolinol ether catalyzed Michael addition of aldehydes to β-nitrostyrenes This chapter gives a bird’s eye view of the advent of organocatalysis along with its applications and modes of activation. It is a summary of prolinol ether catalyzed Michael addition reactions of unsubstituted aldehydes with β-nitroalkenes from the beginning of the 20th century. The content discusses the evolution of catalysts to the optimizations of reaction conditions to achieve enantiomerically pure Michael adducts. Also the effects of reactant and catalyst structures on the reactivity of the reaction conditions; along with the role of resting intermediates has been discussed in detail. Chapter 2. Efforts towards Michael addition of isobutyraldehyde to β-methyl-β- Nitrostyrenes This chapter describes the attempt towards racemic Michael addition reaction of isobutyraldehyde with branched nitrostyrenes. The reactions yield the Michael adduct in part but mostly undergo an undesired reverse reaction due to nucleophilic attack of pyrrolidine on the nitrostyrene. A detailed discussion reasoning for the poor forward reaction and the kinetics of the reverse hydrolysis of the nitrostyrene has been documented. Chapter 3. Unmediated Access to organocatalysts: chemoselective O- functionalization of (S)-prolinol In this chapter, the chemoselective synthesis of compact prolinol-derived organocatalysts has been documented which have been synthesized through a single-step chemoselective O functionalization of prolinol. Prolinol ether catalysts are reputed as universal catalysts owing to the wide spectrum of reactions they catalyze. Synthesis of these organocatalysts from prolinol mostly follows a three-step synthetic sequence of NH protection, O- functionalization, and N-deprotection. However, this protocol provides a two-step reduction in the synthetic route as opposed to former protocols, which makes it a more sustainable approach. Effectively seven Hayashi-Jørgensen type organocatalysts, having varied functional groups i.e. ethers, esters, and carbonates have been synthesized, with good to excellent conversions including four newly reported catalysts. These catalysts prove to be applicable as suitable green catalysts in asymmetric organocatalytic reactions. Chapter 4. Mechanistic investigation into the chemoselective mono-boc functionalization of (S)-prolinol In the course of synthesizing these organocatalysts, the varying selectivity obtained, prompted us to revisit the base-mediated functionalization. Consequently, an elaborate investigation into the overlooked sensitivity of the reaction conditions to the highly utilized protocol, Boc-functionalization of prolinol has been reported. Failing to imitate former protocols, a mechanistic investigation was initiated which revealed the rudimentary steps could be governed by a) a suitable base to recognize the differently acidic sites of prolinol (NH/OH), for the formation of the conjugate base (N-/O-), which then reacts to the electrophile, and b) the difference in nucleophilicity of these conjugate basic sites. This chapter documents how the functionalization of prolinol could be controlled for the exclusive synthesis of either N or O-functionalized derivatives by regulating the reaction conditions. Chapter 5. Michael addition of propanal to β-nitrostyrenes via synthesized Organocatalysts In this chapter, the utility of the synthesized prolinol derived organocatalysts in the Michael addition reaction of propanal with differently substituted β-nitrostyrenes has been discussed. The effect of the catalyst substitution on the reactivity of the reactions is studied along with the varying reactivity while using different electrophiles (in this case nitrostyrene). Chapter 6. Conclusion and Future Scope In the last chapter, the present work's overall summary and future scopes have been described
Analysis of non-Fourier Heat Transfer Behavior of Cylindrical Shaped Living Tissue During Laser Based Photo Thermal Therapy
No full textThe application of lasers in the medical field has increased drastically in recent decades. One such field is laser-based photothermal therapy for cancer treatment. The study of laser-tissue interaction is essential to reduce the thermal damage of nearby healthy tissue and enhance the efficacy of photothermal therapy. The present work is mainly concerned with the thermal response of cylindrical-shaped laser-irradiated living tissue embedded with optical inhomogeneity. The phenomena of light propagation through the cylindrical-shaped living tissue have been mathematically modeled using the transient radiative transfer equation. This equation has been solved using the modified discrete ordinate method to obtain the intensity field in the living tissue irradiated by a short-pulsed laser. The laser energy absorbed by the living tissue behaves like a source term in the bio-heat transfer equation. Researchers have experimentally found that the Fourier heat conduction model predicts inaccurate results in the case of biological tissue. So, they modified the Fouier heat conduction model by considering the relaxation time associated with heat flux and temperature gradient, known as the non-Fourier heat conduction model. In the present study, the non-Fourier modelbased bio-heat transfer equation has been numerically solved using the finite volume method to determine the temperature distribution inside the living tissue irradiated by a short-pulsed laser. The two different types of optical inhomogeneity, such as absorption inhomogeneity (mimics malignant cells) and scattering inhomogeneity (mimics benign cells), are considered in the current study. The inhomogeneity's optical and thermophysical properties may be the same/different from the homogeneous living tissue, making the problem a conjugate heat transfer problem. This conjugate heat transfer problem is solved using the harmonic mean technique. The present results have been verified with the results from the literature, and good agreement was found between them. Then, the independent study is performed to select the optimum grid size, control angle size, and time step. A comparative analysis of results (temperature distribution) between the traditional Fourier and non-Fourier (dual phase lag, hyperbolic) models has been performed. The effect of different parameters like relaxation times corresponding to the temperature gradient and heat flux, metabolic heat generation, and blood perfusion on the resultant temperature distribution inside the axisymmetric living tissue exposed to short-pulsed laser has been discussed. Subsequently, the effect of inhomogeneity's optical properties on the temperature distribution is investigated. A comparative study is performed between the same and different thermophysical properties of inhomogeneity from the living tissue. Although the non-Fourier heat conduction model-based bio-heat transfer equation has been widely utilized to determine the temperature distribution, it is essential to carry out the second law analysis to investigate any unphysical behavior. In this context, the equilibrium entropy production rates have been calculated based on the hypothesis of classical irreversible thermodynamics, which may have negative values and violate the second law of thermodynamics. So, the entropy production rate based on classical irreversible thermodynamics is modified using the extended irreversible thermodynamics hypothesis in the present study, and its solution gives the nonequilibrium entropy production rate. A comparative analysis of the entropy production rate corresponding to the Fourier and non-Fourier models was performed. The values of equilibrium and nonequilibrium entropy production rate for the Fourier model are found to be positive. In contrast, the equilibrium entropy production rate is negative for non-Fourier heat conduction and does not satisfy the second law of thermodynamics. On the other hand, the nonequilibrium entropy production rate is always a positive value for Fourier and non-Fourier models and satisfies thermodynamics second law. It has been investigated how thermal relaxation times affect the temperature field and entropy production rates in tissue subjected to laser light. The thermal relaxation parameters associated with the non-Fourier heat conduction model significantly affect the heat transfer process in the laser-irradiated living tissue. Hence, a part of the present work also comprises the numerical solution of the inverse heat transfer problem to estimate the thermal relaxation parameters corresponding to the non- Fourier model-based heat transfer in laser-irradiated living tissue. The inverse heat transfer problem solution has been obtained using the Levenberg–Marquardt algorithm. The direct problem is the non-Fourier heat conduction model-based bio-heat transfer equation in combination with the transient radiative transfer equation. The analytical solution of the non-Fourier heat conduction model-based bio-heat transfer equation is obtained using the finite integral transform technique. The computer code developed for estimating unknown thermal relaxation parameters using the Levenberg–Marquardt algorithm has been tested using data from the literature. The influence of sensor position on the sensitivity of the inverse heat transfer problem solution has been discussed. The impact of the total transient readings and the measurement error on estimating the unknown parameters have been investigated. The present study's findings can significantly contribute to various parameter estimation problems where the conventional methods for direct parameter measurements are impossible or very difficult. The work reported in the present thesis holds its importance in understanding the non-Fourier heat transfer behavior of living tissue during laser-based photo-thermal therapy, which may help to improve its efficacy
Inorganic Porous Framework Based Hybrid Materials for Effective Energy and Environment Applications
No full textIn recent years, the global warming potential (GWP) triggered from the production of greenhouse gases (GHG) has been a significant concern for climate disasters and rising temperatures in the environment. An additional 30-40% of total GHG emissions (carbon dioxide, methane, ozone, nitrous oxide, hydrofluorocarbons, and chlorofluorocarbons) are caused by industrial and residential buildings in developed countries. The rise in the temperature of the earth's surface compelled research scientists and academicians to develop more efficient thermal insulation with higher energy efficiency for green buildings to save energy consumption. With increased space exploration missions in developed countries and heavy-duty construction industries, the demand for high-performance thermal and acoustic insulators tends to increase in efficiency in aerospace structures, spacesuits, industrial buildings, and space satellites. Conventional insulators (glass fiber, mineral wool, gypsum board, extruded polystyrene) have more significant potential in the market share due to their high performance per unit cost. Owing to the low thermal conductivity, the hydrophobic characteristics, non-decomposable nature, and toxicity of such synthetic materials minimize heat gain or loss in green energy buildings. A facile and cost-effective modified sol-gel synthesis is employed to synthesize flexible silica - cellulose hybrid aerogels (SCHA) using recycled cellulose fibers (RCF) of three-dimensional cellular skeletons, Kymene cross-linker, Tetraethylorthosilicate (TEOS) and methyltrimethoxy -silane as filler through simple freeze-drying. The effect of cellulose fiber concentrations, silica concentration, and ambient temperature on the thermal, acoustic, and oil adsorption characteristics was quantified comprehensively. The experiments considered a range of RCF weight fractions from 1 to 4 wt.% with a crosslinker and TEOS as silica precursors. The resultant SCHA aerogels were modified by a sialylation agent with surface hydroxyl groups to achieve superhydrophobic behavior and well impregnation of silica nanoparticles in the 3D cellulose structure. A variety of hierarchical nanoporous silica aerogels with diversified particle distributions were also synthesized from well-dispersed silica sols from traditional sol-gel method trailed by ambient pressure drying (APD), supercritical drying (SCD) and Freeze drying (FD) to check the shape and size of silica nanoparticles. Among the different particle sizes of aerogels, the silica aerogel with 0.4M TEOS/MTMS surface modification and supercritical drying attains 11.61 ± 2.96 nm constituent part with well slender size particle dissemination, elevated temperature confrontation, and lower thermal conductivity. In association with the outmoded two-step acid-base dilution of silica sols, the well-diffused form with surface alteration also delivers a minimum thermal conductivity of 0.01865 W/mK with greater thermal resistance. In addition, the drying shrinkage can be minimized by face modification by proper sialylation with TMCS. The concentrations of well- diffused silica sol were adjusted to achieve higher surface area, low density, large pore size and structure, and temperature resilience by controlling the reaction rate of sol-gel process. The resilient skeleton structure developed from the assembly of tiny particles can efficiently restrict the glutinous heat dissipation between aerogel networks without collapsing a porous network up to a higher temperature of 900°C. However, this network retains a similar pattern up to 1000°C with only 32% volume contraction after 2hr of heat treatments. At an elevated temperature of 1100-1200°C, the viscid heat flow between nanoparticles and the porous network cannot be meritoriously suppressed and starts to collapse after a shorter duration. However, the fabrication cost in FD was effective compared to SCD and provided a comparative tiny particle size with heat-resistant characteristics. Subsequently, the average thermal conductivity of hybrid aerogels was also estimated at a magnitude of 0.038-0.032 W/m K. An enhancement in the thermal conductivity is noted with an increase in wt.% of cellulose to the silica aerogel. At a temperature of about 40-50ºC, thermal degradability improved (as concluded from Thermogravimetry Analysis), with a minimum weight loss observed in hybrid aerogel over cellulose aerogel. A comparatively high sound absorption coefficient of 0.453- 0.628 at low frequency (1500 Hz) and 0.86-0.94 at high frequency (3600 Hz) was achieved with an average thickness of 8mm compared to cellulose aerogel. The compressive Young's modulus of hybrid aerogels was also augmented by 94.12% in comparison with pure silica aerogels due to the impregnation of cellulose network. The resultant SCHAs yield a stable superhydrophobic nature (water contact angle (WCA) of 163.4º±2.5, 160º±1.2, 168º±1.5) with the help of the sialylation process by a functional group modification for 1,2 and 4 wt.% of RCF in hybrid aerogel. Using nanofibers enables the aerogel to possess a highly remarkable undeviating pore size distribution, super elasticity, and compressibility characteristics. At the same time, the inclusion of silica nanoparticles improved its oleophilic performance. Compared with non-biodegradable, low adsorption commercial polypropylene foam, the HRCS aerogel provides an excellent oil adsorption capacity within a data range of 31.67-48.25 g.g-1 with 94% retention capacity and recyclable up to 10 number of cycles for various 1wt.% of RCF concentration. An optimized parameter of 1wt.% of cellulose concentration, 6 ml of Kymene, and 15 ml of TEOS achieves a higher oil adsorption capacity of 44.845 g/g. Moreover, the experimental values of 48.89 g/g of oil adsorption were observed with one wt.% of cellulose concentration, 9 ml of Kymene, and 14 ml of TEOS, respectively. An adsorption kinetics model and isotherm study were also done for suitable oil adsorption on hybrid aerogel. In a comparative analysis, the pseudo-second-order model is more authenticated for oil adsorption kinetics than the pseudo-first-order model. This auspicious feature of SCHA aerogel can be used as an alternative to hostile polymer-based oil absorbents due to its extraordinary oleophilic capacities. Subsequently, phase change composite materials with uniform 3D high thermal conductive shape stabilised aerogel are a potential solution for improving thermophysical properties and enhanced latent heat capacity applicable in thermal management. In this aspect, different weight percentages (25, 30, 35, and 40 wt.%) of graphene oxide (GO) and GO-Ferrous oxide (GO-Fe3O4) samples were synthesised by dispersing individual additives in a solvent followed by crosslinking and freeze drying for augmenting the heat transfer capacity and photothermal conversion of the solar thermal energy storage (TES). These samples were uniformly dispersed in a eutectic mixture (1:1) of paraffin wax (PW) and polyethylene glycol (PEG-6000), resulting in the development of a graphene oxide–Ferrous oxide aerogel (GOFA) composite. The controllable porous structure and hydrogen interactions with the external layer of GO and long- chain PCM benefitted in the good impregnation of PCM and compatibility impregnated into the composite. A higher mass fraction of GOFA-30-based PCM composite unveiled a comparatively higher phase change enthalpy of 119.64 J/g in melting phase and 119.85 J/g in the solidification phase with 98.73% energy conversion efficiency. In contrast to pure eutectic PCM (0.2593 W/mK), the thermal conductivity of GOFA composite is superior and provides a thermal conductivity of 1.7034-2.5156 W/mK for GOFA-25, GOFA-30, GOFA-35, and GOFA-40 PCM composite. The enhancement of thermal conductivity is ascribed to the increased heat conduction pathway facilitated by the conductive GO arrangement. The utilisation of spatially constrained eutectic phase change material (PCM) assembly resulted in the development of GOFA-PCM, which exhibited enhanced thermal conductivity, chemical and physical stability, and thermal consistency across 300 melting-solidification cycles. Benefitting from the thermal conduction path, the GOFA-based PCM also exhibits an excellent heat absorption capacity of 2320-4000 kJ in a shell and tube heat exchanger under a constant water flow rate of 1-2 LPM for quick response. The thermal responsiveness of GOFA-PCM composite samples is superior to that of eutectic PCM without any compromise in thermal performance. With a higher thermal storage capacity and higher heat transfer property, thermally reliable GOFA composites exhibited tremendous application potential in photothermal and thermal energy storage applications