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Kesterite CZTS Quantum Dot Based Photovoltaic cells: From the Prospective of Material Characterization and Photovoltaic Performance
No full textIncreasing worldwide clean energy crisis calls urgently for the development of harvesting the renewable solar energy through photovoltaic device. Thin film photovoltaic cells (TFPVCs) belong to the second generation, where the absorber layer attracts the attention of research community due to large versatility in deposition, low-cost device design and easy fabrication process. In contrast to well-known absorber materials such as CdTe, CIGS, Copper-based Multinary I2–II–IV–VI4 quaternary chalcogenide Cu2ZnSnS4also known as CZTS has developed as one of the promising candidates for the absorber layer of photovoltaic cell (PVC) due to its non - toxic nature, cost effective and earth abundance. As a direct p-type semiconductor CZTS offers the advantage of tuneable band gap ~ 1.45–1.65 eV favourably matches with solar spectrum having a high absorption coefficient of 104 cm-1. Effective and promising efficiency improvement of kesterite CZTS photovoltaic cell draws the attention of scientific community for its further development. Inclusiveness of all required materials for thin film photovoltaic cell, specifically absorber material has a major responsibility to establish its futuristic evolutionary footprint. The highest achieved power conversion efficiency (PCE) is at 12.6%, considerably lower than the Schokley-Quassier limit i.e., 32.4% for single a junction CZTS photovoltaic cell device. Therefore, a consistent effort has been focused to develop highly efficient earth abundant, non-toxic, and most importantly cost-effective kesterite CZTS photovoltaic device. To track the unexploited UV photons, CZTS quantum dots (QDs) are highly fascinated due to their wide band gap range, band gap tunability results from quantum confinement, multiple exciton generation (MEG) capability, size dependent photoluminescence, hot electron injection and possibility of solution processed device fabrication.The demonstration of charge carrier multiplication phenomenon in QDs unwraps the possibility to obtain higher quantum efficiency.All the comprehensive and strategic attempts motivate us to fabricate size controlled kesterite CZTS QDs photovoltaic device to use the unexploited UV photons. Dynamic versatility of CZTS QDs structure is the new exploration towards energy harvesting applications. Still, now there are no reports on the application of kesterite CZTS QDs in photovoltaic device and no proper device performance study. Promoting p-type semiconducting quaternary chalcogenide kesterite CZTS QDs as promising absorber; the aim is to synthesize and characterize size controlled CZTS QDs and to estimate their performance in photovoltaic device. To produce high quality, monodisperse CZTS QDs, we followed a very simple, non-toxic solvothermal approach. A regular photovoltaic device with the configuration of Mo/CZTS/CdS/ZnO/Al has been fabricated without post sulphurization, where instead of CZTS thin films; synthesized CZTS QDs were applied as absorber. This PV device resulted open circuit voltage (Voc) of 0.67 V and 15.8 mA/cm2 short circuit current density (Jsc) along with fill factor (FF) of 56.2%, PCE of 5.94%. The stability of fabricated photovoltaic device was investigated over keeping the device in inert atmosphere for long 60 days. However, the high performance has not yet been achieved, motivated the scientific community to study various aspects of kesterite intensively. The short carrier lifetime, poor carrier mobility, truncated charge transference and assortment are the hitches for improved photovoltaic performance. Several used efforts for improving performance mostly stem from the point that semiconducting QDs have enormous surface defects result in substantial charge carrier recombination and consequently in Voc deficit. Most likely Voc arises from non-optimal band alignment of absorber and buffer. Recently, an III-VI n-type semiconductor Indium sulphide (In2S3) has emerged as the replacement of Cd supported by few experimental works. To show the feasibility of In2S3, ZnS, ZnO buffer layers with CZTS QDs absorber, the photovoltaic devices were fabricated and studied. Our results show that alternative buffers (In2S3/ZnS/ZnO) can effectively boost the Voc. Photovoltaic devices with the structure of Mo/CZTS QDs/ In2S3, ZnS, ZnO/ZnO/Al and the fabricated devices achieved efficiency of 5.76%, 4.92% and 4.46% respectively. However, the PCE of fabricated photovoltaic devices with alternative non-toxic and non-carcinogenic buffer does not improve up to our expectations. Moreover, Anion/cation substitution inside CZTS structure facilitates to improve PCE of photovoltaic cell through the enhancement in Voc. Here, in this work we have studied two systems CZTSe and AZTS and used as absorber in the replacement of CZTS QDs in the photovoltaic device fabrication procedure. CZTSe QDs were used successfully in the active layer of a photovoltaic device with the structure of Mo/CZTSe QDs/CdS/ZnO/Al and the fabricated device achieved PCE of 6.23%. The as synthesized AZTS QDs were used successfully in the active layer of a photovoltaic device with the structure of Mo/AZTS QDs/CdS/ZnO/Al and the fabricated device achieved PCE of 6.28%. Their anchoring platform to improve the photo generated charge carrier collection is an alternative promising approach for high performance device without deteriorating their properties. Carbon nano structured materials like reduced graphene oxide (rGO), multi-walled carbon nanotubes (MWCNTs) and few layer graphene sheet (FLGS) are eminent ultrafast charge transporters. Hence, improvement in the charge transfer behaviour has been carried out by incorporating rGO or MWCNTs or FLGS. The active area PCE has seen to be enhanced by adding rGO or MWCNTs or FLGS. CZTS QDs-rGO absorber-based device showed 6.25% PCE and CZTS QDs-MWCNTs showed further enhanced PCE of 6.77% and CZTS QDs-FLGS showed further enhanced PCE of 7.64% due to the establishment of conducting network in active layer which facilitates fast charge carrier transfer process.The stability of fabricated photovoltaic device was investigated over keeping the device in inert atmosphere for long 60 days. Our study can help to provide a practical approach of a low cost, scalable fabrication of CZTS QDs based photovoltaic devices
Development of Hydroxyapatite Coated Titanium Alloy with Improved Corrosion Resistance and Biocompatibility for Bone Implant
No full textThe ability of a material to carry out its intended task by extending desirable functionalities after a medical intervention being performed without getting rejected by the host is known as biocompatibility. The basic criteria for a material to be considered as an implant material is its biocompatibility (cytocompatibility, hemocompatibility, non-immunogenicity), higher fatigue and shear strength, and corrosion resistance. Usually, metallic biomaterials possess appreciable mechanical strength and are nontoxic, but they suffer from inherent shortcomings such as bioinertness and corrosive wear. These problems can be dealt by adopting various surface modification techniques to alter their surface topography. Hydroxyapatite (HAP) is one of such popular coating materials for metallic implants. However, the most undesirable problem with HAP coatings is their lower adhesion to the implant. The resistance to bending, chipping and delamination during the medical procedure and post operative activities are also serious concerns associated with the HAP based coatings. In the present study, the surface morphology of implant grade Ti6Al4V alloy sheets was successfully altered by applying bioactive hydroxyapatite (HAP) coating. This was attempted mainly because HAP possesses the closest structural analogy to human bone and allows chemical functionalization for tailoring its properties. The coating was achieved by two approaches namely, biomimetic mineralization and microwave irradiation. The microwave irradiation process also yielded cationic doped HAP coating by incorporating Niobium (Nb) as dopants in HAP. Three major input parameters viz. irradiation power (W), doping % of Nb and time of exposure (min) were considered for the experimental runs and targeted biological responses such as hemolysis %, clotting time and protein adsorption from blood plasma were optimized using Grey-Taguchi analysis. The sample coated with this optimal factor setting was further used for other assays. Additionally, an attempt was made to co-dope the HAP with Strontium (Sr) along with Nb via microwave irradiation and these samples were also assessed for their physical and biological properties. The surface characterizations revealed that both approaches yielded homogeneous surfaces free from flaws. However, it could be observed that the morphology of the HAP particles altered after the cationic doping in case of microwave assisted coating. The characteristic peaks of HAP could be confirmed in the crystallographic studies performed on the coated samples. After performing various assays, it was observed that both the treatments rendered higher hardness to the substrate, but an insignificant increase of surface roughness was present. However, the wettability of the Ti6Al4V sheet was considerably increased after the coating was applied which could facilitate better host-implant interaction. Potentiodynamic polarization studies revealed that the barrier action offered by the HAP coating had significantly reduced electrochemical corrosion in the form of ionic dissolution. The treated samples showed lesser hemolysis as compared to untreated sample and did not induce clotting of the blood, making them more hemocompatible. The protein adsorption capacity was enhanced by the application of coating, which also significantly enhanced biocompatibility. Reduced cytotoxicity was also evident from cell culture assay and the treated surface also prevented bacterial growth. The cell viability post doping found to have increased by more than 30%. Moreover, there was no evidence of cytotoxic effect of either Sr or Nb on human cells as confirmed from the cell viability assay. The co-doping found to help cell proliferation. So, it can be concluded that the incorporation of metallic ions like Sr and Nb in HAP coating can protect the implant surface from the body fluid-induced wearing as well as bacterial infection and thus, prolong its life. Therefore, microwave-assisted coating can be considered as a one-step solution for simultaneous synthesis and deposition of reinforced HAP coating on metallic implants
Mathematical Analysis of Some Boundary Layer Flows
No full textThe research presented in this thesis focuses on the analysis of some boundary layer flows. This work is divided into three parts, each corresponding to a different flow scenario. The first part regards the mathematical formulation of the boundary layer equations for two- or three-dimensional flow, which are the highly nonlinear partial differential equations (PDEs) of parabolic type. Moreover, the PDEs are converted into nonlinear ordinary differential equations (ODEs) using suitable similarity variables. It is worth recommending that the ODE boundary value problems (BVPs) governing these flow are intrinsic nonlinear, which becomes difficult to find an analytical solution than numerical results. The reduced boundary value problem is then analyzed in the subsequent parts of this thesis to understand the flow behaviours. Previous works were mainly focused on numerical simulations, and several conjectures regarding the existence and the behaviour of the solutions are discussed from the computational results. The ambition of this work is to review these conjectures mathematically. The second and major part contains the existence of a solution to the BVPs for the entire appropriate the physical parameters values. Uniqueness results are also presented for some (but not all) values of the parameters. It is to be mentioned here that the solutions are concave or convex for different parameter values, and in some cases, the differences in proofs and results may be significant. Both the cases are discussed thoroughly. Moreover, the last part contains the numerical results of the governing BVPs. The numerical results elucidate through table and graphs. In the limiting cases, the results are in great agreement with previously reported solutions in the literature. To demonstrate detail physical aspects of the flow domain, the velocity profiles and streamlines are presented graphically for governing parameters, and the results are discussed in detail
Morbidity Patterns, Burden, and Healthcare Utilisation of Major Non-communicable Diseases in India
No full textThe escalating burden of non-communicable diseases (NCDs) is presently being experienced by all countries across the globe. However, the disproportionate concentration of this burden is well documented in the case of low- and middle-income countries, which contribute 77% to the total deaths because of NCDs, out of which 86% are premature deaths. The adverse impact of NCDs is a growing concern for developing countries, particularly India, where public spending on NCDs is relatively scant, and people have limited resources to accommodate their healthcare needs. As per the estimation by World Health Organisation (WHO), in the year 2018, NCDs account for 63% of all deaths, out of which 27% of the deaths are from cardiovascular disease (CVD), 9% from cancer, 3% from diabetes, and 11% from chronic respiratory disease in India. Nevertheless, there is a dearth of research providing a comprehensive assessment of the economic impact of NCDs on both households and the overall economy within the Indian context. The present study aims to address this gap by quantifying the impact of NCDs on households through the assessment of out-of-pocket expenditure (OOPE), catastrophic health expenditure (CHE), and impoverishment effect. In addition, the study also highlights the coping mechanism of households to finance health expenditures. A significant contribution of this study is the realm of equity in healthcare utilisation associated with NCDs. Besides, the study also estimates the macroeconomic burden of NCDs in terms of Gross Domestic Product (GDP) loss in India. The study uses secondary data from the National Sample Survey Office, the World Bank, and the Institute of Health Metric and Evaluation. For empirical analysis, the study has used logistic regression, generalised ordered logit model (gologit), multinomial logit model, and generalised linear model. In addition, it has used concentration curves, the Wagstaff decomposition method, and horizontal and vertical inequity index to analyse inequity. The present study also incorporates insights from economic theories, including the epidemiological transition theory, Grossman's model of demand for health capital, and Andersen's behavioural model of healthcare utilisation. The results show that during the past three decades, the years of life lost due to premature death (YLL) and the years of life lived with disability (YLD) for each of the four NCDs under consideration have increased consistently. Among all the NCDs, cancer and CVD causes more losses due to premature death than disability, whereas diabetes and Chronic Respiratory Diseases (CRD) cause greater losses due to disability than premature death. The economic loss in terms of GDP shows that in 2019, CVD accounted for a loss of 3445 billion rupees for India, the highest among all other NCDs. Similarly, the burden of NCDs on households shows that 59% of rural households are reporting OOPE share in excess of 10% of their total expenditure, whereas it is 49% of urban households for availing treatment of NCDs. The expenditure incurred on doctor’s fees and bed charges are troublesome for households with NCDs treated in private hospitals. The result from vertical inequity shows that the poorest quintile is paying a higher proportion of their total consumption expenditure for NCDs hospitalisation than the richest quintile, indicating that the payment for NCDs is regressive in nature. The result of the gologit model shows that household size, cooking fuel, and region significantly affect CHE at the 40% threshold level. Similarly, the level of poverty due to healthcare payments is higher among Muslims, SC/ST, rural residents, the poorest quintile, more than 7 family members in a household, and casual labourers. The result of inequity in healthcare utilisation shows a significantly pro-rich pattern. The findings of this study could help the policy maker to tackle the burden of NCDs in India by ensuring affordable, equitable, and universal care for all the population, especially for socioeconomically disadvantaged populations
Investigation Into Mechanical And Tribological Behaviour Of Natural Fiber Reinforced Polymer Nanocomposite
No full textMaterial advancement along with environmental sustainability creates a quest among researchers for finding a suitable replacement of conventional materials as well as hazardous synthetic fibers. In this way, the most promising invention is the concept of polymer composites with bio fiber reinforcement. Natural fiber composites are a popular choice in the development of green materials as they possess high specific strength and low density, whilst being cost-effective, low energy consumption, environment friendly, and abundantly available. Despite the growing research and environmental sustainability of natural fibers, there utilization is limited to low end applications due to its comparatively much lower strength than synthetic fibers. Moreover, these fibers also suffer due to poor adhesiveness, higher hydrophilicity and lesser compatibility with polymer matrices. Hence, the use of natural fiber alone cannot fulfill the required strength and stiffness of the composites for high strength structural applications. These drawbacks of Natural Fiber Polymer Composites (NFPC) can be overcome by the concept of hybridization with synthetic fibers. The concept of hybridization enhances the use of sustainable natural fibers along with substantial reduction of hazardous and costly synthetic fibers. Additionally, partial replacement of synthetic fiber with suitable natural fiber also reduces the weight and cost of hybrid polymeric composite considerably with marginal or no loss of strength. Present scientific development of advanced materials creates a quest in between materials designer to discover such materials that possess superior structural along with distinct novel properties. Recently, nano-based polymer composites gained much importance because a small amount of nanoparticle reinforcement has ability to significant enhancement of the mechanical, thermal and physical properties of the polymer composites. Further, reinforcement of inorganic nanoparticles, like CNT, alumina and silica etc., into polymer matrix has been proved its efficiency to improve mechanical and tribological properties. Among various ceramic nano fillers, zirconia based three mol% yttria stabilized tetragonal zirconia polycrystal (3Y-TZP) nanoparticle is possessed a distinct vital properties. The crucial properties of 3Y-TZP nanoparticles are high transformation toughness, high melting point temperature, high strength, corrosion resistant, chemical stability, low thermal conductivity and excellent electrical insulation properties. 3Y-TZP particulates are widely used in high strength and wear resistant applications in enamels and dental restorations. Moreover,these particulates are also used in the field of refractory materials, thermal barriers and insulations. Further, very few literatures are available on zirconia based nano and micro particles as a filler application in polymeric composites for evaluation of mechanical properties. However, no literatures are found for such high strength and wear resistant 3Y-TZP nanoparticles for the filler applications in polymer composite to analyze their effect on mechanical and tribological properties. There are many sustainable natural fibers available on the earth in abundance. Most of it comes from forest, local habitat and agriculture. In which, Abaca (Musa textilis) is one of the strongest natural fiber among various existing bio-fibers whose potential in the field of tribological applications has not been explored till present date. Also their effect on hybridization with synthetic fiber like glass and 3Y-TZP nanoparticles on mechanical and tribological applications are not being investigated. Abaca plant is abundantly produced in humid subtropical regions of Philippines, Costa Rica, and Ecuador. This plant is also playing a crucial part in ecological aspects by avoiding the soil erosion and increasing the water logging capacity. The fiber quality of this plant could be recognized by its existing applications in the field of rope, twins, bank notes, rugs, mats, household construction, cordage industries and textile industries. These versatile applications have proved their worth as a structural material with reasonably good mechanical properties. A natural fiber used for reinforcement purposes should have possess the cellulose, hemicellulose and lignin with other constituents like carbon that make lighter in weight with high strength. The abaca fiber consists of 43.8% carbon, 63.7% cellulose, 18.55% hemicellulose and 15.1% lignin that conforms the utilization of this fiber as a reinforcement in polymer based composite structures. Against these background, the present work has been concentrated to established the following objectives: To evaluate the effect of hybridization and stacking sequence on the mechanical and tribological properties of developed composites. Synthesis of 3Y-TZP nanoparticles by suitable synthesis route in bulk along with economical aspects for filler applications in polymer hybrid composites. To study the favorable mechanical properties of developed hybrid and nanocomposites. An experimental investigation on abrasive and erosive wear analysis for developed hybrid and nanocomposites for tribological applications. For filler applications, 3Y-TZP nanoparticles are synthesized by different drying route and sintering temperatures under cost effective co-precipitation method. It is found that oven dry synthesis route at sintering temperature of 900° C is suitable for production of nanoparticles in bulk for filler applications in polymer composites. In this work, an attempt has been made to develop the abaca/glass hybrid composites by hand lay-up method with utilization of heat gun to minimizes the void content. The effect of hybridization and stacking sequences are evaluated for finding the optimum mechanical and tribological properties. Further, the effect of different doses of 3Y-TZP nanoparticles are analyzed on hybrid composite that have possesses the optimum mechanical and tribological properties. In the present investigation, it is found that hybridization of fiber and further nanoparticle reinforcement significantly enhances the mechanical and tribological properties. It is observed that GAAG (A and G represents abaca and glass fiber sequences respectively) composite showing the maximum tensile and impact strength while AGAG composite possesses the maximum flexural and inter laminar shear strength among various developed hybrid composites. It is also observed that with increase in nanoparticle amount from 1 to 3 wt.% enhances the mechanical strength. Further increase in nano amount up to 5 wt.% lead to decrease the strength. To study the tribological potential of developed hybrid and nanocomposites, abrasive and erosive wear experiments have been performed as per ASTM standards. It is found that AGGA hybrid composite showing the maximum wear resistant in both abrasive and erosive wear analysis. Further, AGGA3% nanocomposite possesses the maximum wear resistance followed by AGGA5% and AGGA1% nanocomposites. The influence of impingement angles on erosion rate established the semi ductile and semi brittle erosive wear behaviour of developed composites according to impact velocities. Further, morphological analyses are performed on SEM machine to observe the cause of failure due to fracture during mechanical tests and worn out surfaces during tribological investigations
Studies On Modelling For Diffusion-Mass Transfer In Solid Oxide Fuel Cell
No full textThe diffusion-mass transfer in Solid Oxide Fuel Cell (SOFC) is a complex phenomenon. A lot of experimental work and modeling work have been conducted over the years to understand and design efficient electrodes in SOFC to facilitate faster diffusion. An accurate model can help in predicting the best physical properties required for the construction of an efficient electrode in a short time. A comparative analysis on different mathematical models available in literature was conducted to assess their viability and accuracy under operating conditions of SOFC. The physical parameters such as porosity and tortuosity factor were used as fitting parameters to validate the modelling results with the experimental data. A binary fuel system with H2- H2O and a ternary fuel system with H2-H2O-Ar were used to validate the modelling results. The study concludes the pressure gradient to be an important factor when the pore radius value goes below 0.6 μm and current density goes above 0.5 A/cm2. The modified Binary Friction model (MBFM) was found to produce the better match with the experimental data under most of the conditions considered in the study. The Dusty Gas modified Friction model (DGMFM) was found to be a good approximation to the Dusty Gas model (DGM) for binary system. Considering advantages of the MBFM and to suit the needs of commercial CFD software, it is desirable to uncouple the mass transport flux equations and re-formulate the MBFM. Thus, the MBFM is rearranged and a model with uncoupled expressions for mass flux is formulated with reasonable assumptions. The new model is tested for Solid Oxide Fuel Cell (SOFC) cermet anode running on two, three and multi component fuel systems using electrochemical modelling. It’s predicting capability is compared with existing conventional models such as the DGM and MBFM for a wide range of structural and operating parameters. The results obtained imply that the new model is capable of predicting in the similar manner as the MBFM for 90% of the parametric conditions applied in the study
Detection of Ocean Eddies using Deep Convolutional Neural Networks
No full textThe ocean eddies are circular water currents with a lifetime of 10 to 100 days and radial scales of 25 to 250 kilometers. Eddies are important for mixing and moving heat, salt, and biogeochemical tracers across the world’s seas. Additionally, eddies have been found to affect marine ecosystems as well as nearby near-surface winds, clouds, rainfall, and moderate the effects of climate change. The cyclonic and anti-cyclonic eddies correspond to negative and positive sea surface height anomalies. As a result, satellite-measured sea surface height images provide information on the eddy character-istics. Data from altimeters that measure sea surface height are utilized in mesoscale eddy detection. These statistics accurately portray the level of sea surface height. Un-derstanding ocean eddies is crucial for research on marine biological ecosystems and climate change. However, manual monitoring of eddies is not feasible. Therefore, the development of automatic techniques is essential, for the detection of ocean eddies. The current automatic eddy detection approaches suffer from unreliable predictions and high computational complexity. Hence, in this dissertation, the problem of automatic detec-tion of eddies from sea surface height images using deep convolutional neural networks is addressed. Here, different supervised learning methods are proposed for the detection of ocean eddies using altimeter data. The developed architectures outperform the ex-isting techniques. At first, a deep convolutional neural network approach based on an attention mechanism is proposed to detect and classify ocean eddies and enhance model performance. The feature representation is further improved by appending the input data and the data produced from the attention method. The different sizes and shapes of eddies make automatic eddy segmentation challenging. U-Net makes a dense prediction to solve this problem. However, the network architecture is very intricate. In this thesis, a dilated convolution based U-Net is developed for the detection of ocean eddies using sea surface height data. This technique decreases architectural complexity without sac-rificing performance. Further, a new residual path is also proposed to cascade encoder outputs with the decoder. The residual path replaces the conventional skip connection between the encoder and decoder modules. Second, due to cascaded convolutions and nonlinearities, spatial details usually get lost in high-level feature maps. This makes reducing false detections for small objects with a lot of shape diversity difficult. This problem is addressed by using the attention mechanism to choose pertinent spatial data from low-level feature maps and passed to the decoder. A VGG16-based U-Net with an attention mechanism which is referred to as modified U-Net or MU-Net is proposed to address this issue. The proposed attention modules are merged with the base network VGG16 to enhance feature representations of ocean eddies. Third, the existing auto-matic eddy detection approaches suffer from high model and computational complexity and have poor multi-scale context fusion. A novel architecture is proposed to tackle the challenging task of extracting objects of varied sizes from remote-sensing images. An attention mechanism is designed to obtain the eddies class context information. A series pyramid pooling module is proposed to aggregate the global context data. To improve the effectiveness of both class context and global context of feature maps and to boost model performance, a feature enhancement approach is proposed. Finally, a dual en-coder and decoder-based architecture is proposed for eddies detection. Since encoded information lacks semantic information, they hinder the segmentation performance. To address this issue, a novel attention module that accumulates semantic data while sup-pressing irrelevant data is proposed. Further, a novel tracking algorithm is proposed to track anti-cyclone and cyclone eddies. The key characters like eddy coordinates and their contours which provide oceanographic representations of an eddy movement are effectively captured. In an experimental analysis of two datasets containing 4383 and 5480 SSH images, the findings of the experiments indicate that the proposed techniques consistently outperformed the current eddy detection approaches
Numerical Solutions and their Convergence Analysis for Fractional Differential and Integro- Differential Equations Involving Weak Singularities
No full textAn important aspect of fractional calculus is the study of fractional order integrals and derivatives and their applications. In the past few decades, the study on fractional differential equations (FDEs) and fractional order integro-differential equations (IDEs) has gained immense interest among many researchers due to its practical implementation in several fields of science and engineering. This helps in modeling many physical problems in control theory, cryptography, neural networks, fluid mechanics, financial market, viscoelasticity, electrodynamics, and bioengineering, etc. The analytical approximations of the FDEs and fractional order IDEs are not straightforward as the fractional differential operators are non-local defined by an integral over the entire region whereas the integer order derivatives are defined on a small neighbourhood of the given point. Further, given smooth data in the governing equation involving fractional order derivatives may not guarantee the smooth solution of the problem. Due to this uncertain behaviour, finding a solution for an FDE and fractional order IDE is not an easy task and there is need for semi-analytical/numerical methods. The major objective of the present thesis is to analyze FDEs as well as fractional IDEs in order to develop time-efficient, accurate, and computationally effective numerical methods such as the L1 scheme, the Adomian decomposition method, the homotopy perturbation method, and the modified Laplace decomposition method, etc., for solving them along with their stability and convergence analysis. This thesis is designed into two parts. The first part is devoted for the numerical simulation of differential equations (IVPs & IBVPs) involving fractional order derivatives, whereas the second part of the thesis shows the reliability of the present approach applying on fractional order IDEs as well as fractional order partial integro-differential equations (PIDEs) of Volterra type, Fredholm type and also of mixed Volterra-Fredholm type. Further, the thesis consists of a total of eleven chapters, out of which Chapter 1 describes the basic preliminaries about fractional calculus, which contains several definitions of fractional order derivatives including their various properties along with the objective and motivation to work on various fractional order models. Chapter 2 considers a one-term Riemann-Liouville fractional IVP for which a fully discrete finite difference scheme is constructed using L1 discretization on uniform mesh. Further, this scheme is applied to a more general multi-term fractional IVP in order to show its applicability in solving the fractional models. Then, in Chapter 3, we develop the idea and introduce the L1 discretization on a rectangular domain in order to solve a time fractional IBVP of mixed convection-diffusion-reaction type for which the L1 discretization is applied on a uniform mesh. Next, in Chapter 4, a time fractional Black-Scholes European option pricing model is considered in which the L1 discretization is introduced on a graded mesh in order to increase the order of accuracy. Chapter 5 presents the numerical solution of a time-space fractional Poisson’s equation by using the homotopy perturbation method. Then, Chapter 6 demonstrates the numerical investigation of a multi-term time fractional nonlinear KdV equation. A modified Laplace decomposition method is used to find an analytical approximate solution. The obtained results are compared with some existing methods. In case of fractional order IDEs, first we consider a fractional IVP with a Volterra integral operator in Chapter 7, where the L1 discretization is applied to approximate the fractional operator and a repeated quadrature rule is used to discretize the integral term. Then, in Chapter 8, we extend the present idea for solving a fractional order PIDE and the method is reconstructed on a nonuniform mesh to solve a more general multi-term time fractional PIDE. Next, Chapter 9 comprises the numerical simulation of a time fractional Black-Scholes model under jump-diffusion, where the model is converted into a time fractional PIDE with a Fredholm integral operator. Finally, a class of multi-term time fractional PIDEs of mixed Volterra-Fredholm type is considered in Chapter 10, where the Adomian decomposition method is applied for numerical convergence. At last, Chapter 11 highlights the concluding remarks obtained from various consequences of the works reported in this thesis followed by a few possible future directions of the present works. Several tests are performed on numerous extensive examples in numerical results and discussion section of each chapters to show the efficiency and accuracy of the proposed methods. Further, several comparison results are presented in terms of tables and figures in order to show the reliability of the present approach
Evodiamine Resensitizes Cisplatin Resistance by Targeting SOX9-β-Catenin Axis in Non-Small Cell Lung Cancer
No full textNatural dietary alkaloid evodiamine has demonstrated anticancer properties. Here, the mechanistic role of evodiamine in cell proliferation and migration in non-small cell lung cancer (NSCLC) was investigated. In A549 and NCI-H522 cells, evodiamine reduces cell viability by inducing apoptotic cell death. It induces cell death by elevating reactive oxygen species (ROS) levels resulted in the depletion of mitochondrial membrane potential. In contrast, the pre-treatment of ROS scavenger, N-acetyl cysteine, attenuates cell death effect of evodiamine. Furthermore, it caused DNA damage and arrested the cell cycle in A549 and NCI-H522 cells at the G2/M phase. Evodiamine also suppressed tumorigenicity significantly by inhibiting tumorsphere formation. However, treatment of evodiamine regulated the expression of cancer stem cell markers CD44 and CD133 and epithelial to mesenchymal transition (EMT) markers E-cadherin, ZO-1, N-cadherin, and Vimentin. Additionally, current study has revealed that evodiamine targets the SOX9–β-catenin axis by reducing SOX9 and β-catenin expression. SOX9 has been also linked to drug resistance in a variety of cancers. Therefore, the role of SOX9 and its regulatory component β-catenin in cisplatin-resistant NSCLC was investigated. SOX9 and β-catenin expression was found to be higher in cisplatin-resistant A549 (A549CR) and NCI-H522 (NCI-H522CR) than in parental A549 and NCI-H522. SOX9 knockdown decreased cell proliferation, colony formation and cell migration in A549CR and NCI-H522CR. As expected, apoptotic cell death was significantly increased in siSOX9 transfected A549CR and NCI-H522CR cells treated with cisplatin compared to control cells. Additionally, silencing of SOX9 reverses resistance to cisplatin by regulating β-catenin. Existing NSCLC patients treated with cisplatin shows resistance. As a result, a new agent capable of sensitizing cisplatin-resistant NSCLC cells to cisplatin is desperately needed. Previously it was demonstrated that evodiamine can limit the growth of NSCLC. Therefore, this study examines the mechanism behind evodiamine's ability to reverse resistance to cisplatin. Results show that evodiamine promotes cisplatin induced cytotoxicity by boosting intracellular ROS production in A549CR and NCI-H522CR cells. Mechanistically, it was found that evodiamine resensitizes cisplatin-resistant NSCLC cells by inhibiting EMT markers and SOX9 and β-catenin expression. Combination of evodiamine and cisplatin may be a therapeutic regimen for overcoming cisplatin resistance in NSCLC
Microscopic Investigation Of Conformational Stability Of Proteins In Amino Acid Solutions And The Properties Of Solvent Around It
No full textTo perform biological functions and avoid unwanted immunological reactions, protein’s threedimensional folded native forms needed to be preserved. Under harsh environmental conditions, a protein may undergo loosening of secondary segments and attend a denatured state. The use of additives in the aqueous solution of protein is a common practice to preserve the native-like structure. The prime objective of this thesis has been to explore the effects of different amino acids as additives on regulating the conformational and solvation properties of protein at ambient and in thermally stressed conditions. To fulfill the objectives, extensive atomistic molecular dynamics (MD) simulations with two proteins, insulin monomer, and ubiquitin, were carried out with amino acid solutions. The thesis consists of six chapters. In Chapter 1, a brief discussion has been enlisted on the current status of knowledge and recent development in this area, along with the methodologies adopted in this thesis. In Chapter 2, the comparative efficiency of three basic amino acids, arginine, histidine, and lysine, on regulating the conformational flexibilities of insulin monomer at ambient conditions was investigated. The study revealed that the relative more loss of configurational entropy of insulin in arginine solution than in the pure water and other two amino acid solutions was due to the presence of motionally bound, less entropic hydration water around insulin in arginine solution than in histidine/lysine solution. This instigated choosing arginine as one of the most promising preservative additives (osmolyte) among the three at ambient temperature. As a result, in Chapter 3 influence of arginine concentrations in modulating insulin conformations at ambient and elevated temperatures was studied thoroughly by conventional MD and replica-exchange molecular dynamics (REMD) approaches. To identify the physical origin of the arginine concentration dependent differential stability of insulin in solution, a detailed investigation on insulin-water and insulin-arginine interactions was carried out in Chapter 4. The study showed that the exclusion of arginine from the protein surface increases the local structuration of water around it. The favourable formation of a sluggish water-arginine mixed solvation layer at a higher arginine concentration of 2 M helps to maintain the structural rigidity of the protein. Further, it has been observed that arginine stabilizes the protein through several aromatic interactions; cation-pi/anion-pi, as well as hydrogen-bonded interactions. Motivated by this, the relative effects of aromatic amino acids, phenylalanine, tyrosine, and tryptophan solutions, on insulin’s conformational properties were studied in Chapter 5. The calculations revealed that while tryptophan was prone to interact with the protein through cation-pi interactions, phenylalanine and tyrosine preferred pi-pi stacking. In Chapter 6, the preserving efficacy of the 2 M arginine solution has been tested by considering another model protein, ubiquitin. Such a study would facilitate establishing the general idea about the preservation efficiency of this solution. In this work, the conformational stability of the secondary structural segments of ubiquitin at ambient and elevated temperatures was studied through combined MD and REMD techniques. This chapter unfolds the detailed story of the structural transitions of ubiquitin and the reason behind the restricted hydrogen-bond dynamics of protein-water and protein-arginine solutions that primarily helped to conserve protein’s native folded form firmly