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Lattice Strain in Li+ -Doped NIR-Upconverting Crystals: A Bridge between Photoluminescence Intensity and Local Disorder
No full textExplaining the intensification of upconversion luminescence (UCL) from single phase NIR-upconverting (UC) crystal due to non-lanthanide dopant insertion appears challenging in absence of proper mechanistic investigation. This PhD thesis aimed to extend and complement the existing hypothesis of symmetry distortion of UC lattice due to non-lanthanide dopant (Li+) insertion through experimental evidence. Through extensive synchrotron-based X-ray probing, an attempt has been made to understand the variations in the structural attributes of UC crystals generated through non-lanthanide ion (Li+) doping. The context and the significance of this dissertation have been presented in the first chapter as Introduction. First, the Li+ ion was doped in a hexagonal NaYF4 host system containing Yb3+ as a sensitizer with different activator ions (Ho3+, Er3+, Tm3+), and the change in UCL intensity of green and blue emission and other structural parameters were analyzed. While the details are included in the third chapter of this thesis (Crystal Growth and Design, 2020, 20, 468−478 DOI: 10.1021/acs.cgd.9b01426, CrystEnggComm, 2021, 23, 8631–8640 DOI: 10.1039/D1CE01253C), the overall methodology and general characterization techniques have been included in the second chapter. Next, the same study was performed on white light-emitting hexagonal Yb3+/NaYF4 host using a combination of Er3+ and Tm3+ activator ions. The method of thermal decomposition was adopted to synthesize Li+ doped WEN UC crystals. Detailed characterization of these materials was performed using synchrotron X-ray diffraction analysis (SXRD), XAFS, TEM, FESEM, XPS, etc. The details are included in the fourth chapter of this thesis. (The Journal of Physical Chemistry C, 2021, 125, 21211−21222, DOI: 10.1021/acs.jpcc.1c06480). 2 Further, in the fifth chapter, the comparative study was verified on a completely different host system, which is cubic Gd2O3 having Yb3+ as sensitizer and Ho3+ as the activator ion. All the crystalline systems were subjected to synchrotron X-ray diffraction (SXRD)-based in-depth structural analysis. In all three studies, the UCL intensity behavior was found to follow a specific trend. However, no morphological or structural lattice parameters appeared successful to explain the intensity behavior. Next in the sixth chapter, the lattice strain, which often reflects structural intricacy at the local level is conventionally assessed using Williamson-Hall (WH) plot derived from XRD data. The study of crystal lattice strain using the Williamson Hall method on the obtained SXRD data revealed a unique correlation between the variation of UCL intensity and that of lattice strain
Finally, high energy X-ray scattering experiments using Pair Distribution Function Analysis on the selected samples from hexagonal NaYF4 host system and cubic Gd2O3 host system were performed. Concerned analysis showed that the corresponding lattice strain behavior that shared a proportional relationship with the associated UCL intensity was actually linked with the Li+-induced respective local disorders at the atomic scale. The findings reported herein are expected to open up a fresh perspective in further understanding the physics of upconversion host lattices
Application of Metaheuristic Techniques for the Prediction and Optimization of Blast Induced Ground Vibration
No full textMining is considered to be the primary industry. The industrial and technological infrastructure of the modern world is one way or another dependent upon this sector. With the advancement of many alternate exploitation technologies and methods, blasting is an inseparable part of mining ever since its first implementation though it has many disadvantages. Despite its ease of use and being economic it adversely affects the surrounding structures and environment. A major challenging parameter is to reduce the ground vibration induced from blasting so as to minimize the damage to the surrounding structures and environment. Therefore, the blasting parameters need to be optimized in order to reduce the ground vibration. Before the optimization, a correlating objective function has to be established so as to ensure the most accurate prediction model. Although there have been many implementations of ordinary backpropagation networks for prediction of peak particle velocity (PPV), still not a single one can be recommended because of their underwhelming accuracy. Therefore, many of the hybrid neural networks have been implemented in this study and compared with existing ordinary neural networks, regression methods and also various empirical predictors. The best performing networks are coalesced to create an ensemble network and used in the final prediction to compensate for the biases of a single neural network. The ensemble network using firefly algorithm based artificial neural network (FA-ANN), grey wolf optimization (GWO-ANN) and teaching and learning based optimization (TLBO-ANN) is used as the objective function for the optimization of the blasting parameters. The firefly algorithm has been used for optimization of the blasting parameters and it resulted in a considerable reduction in the ground vibration. The ensemble network is also used to create a graphical user interface (GUI) for the end user to easily predict and display the prediction when the input parameters are given. Another GUI has been built for the optimization which displays the optimized parameters from the given upper and lower bounds of input parameters. This GUIs can help the field technicians to estimate the PPV and optimize their blast design to minimize the ground vibration before conducting the blasting
Path Optimization and Control of Robotic Agents Using Hybrid Artificial Intelligence Techniques in Various Terrains
No full textSince the last decade, autonomous robots have been the centre of attraction among robotics researchers by virtue of increasing demand in every sector of human intervention. Sectors such as automation industries, planetary exploration, and military exercises finds appropriate applications. Therefore, an autonomous robot is required, that could travel intelligently in any unknown environment. In view of the above, many researchers have proposed their work on mobile robots by focusing on path planning and obstacle avoidance as major part of the problem statement. However, these aspects plays an important role in the navigational control of robots. Keeping above aspects in mind, path optimization, time optimization, avoidance of local minima trapping, and precise motion of robots are also considered as multi-objectives of smart navigation in the current research. To address these multi-objective problems of robot navigation, hybrid artificial intelligence controllers such as Sine Cosine-Ant colony optimization technique (AC-ACO), Fuzzy-Whale optimization algorithm (Fuzzy-WOA), Intelligent water drops-Genetic algorithm (IWD-GA), Fuzzy- Marine predators optimization algorithm (Fuzzy-MPO) and Modified Flow direction optimization-Firefly algorithm (MFDA-FA) are designed and developed in this research. The controllers proposed here are implemented on multi robotic systems to solve current research objectives in static and dynamic terrains. Through these techniques, the robot maps the terrains with the help of sensors and actuators, and utilizes the controller's instructions for optimal navigation. Simulation works are performed on MATLAB and WEBOTS software platforms, while real-time experiments are conducted on the laboratory platform. Further, these techniques are compared with previously published algorithms to authenticate the effectiveness of proposed approaches. Remarkable improvements are observed in navigational parameters during comparison. In future, these techniques may be implemented on any autonomous robot for precise movement and operations
Novel Iron-based Hybrid Nanoadsorbents for Removal of Arsenic from Aqueous Stream
No full textContamination of water by highly noxious arsenic (As) species is a severe environmental threat that threatens human life negatively by causing adverse health complications. Nowadays, various advanced techniques such as adsorption, membrane filtration, capacitive deionization, ion exchange, etc. are developed by different researchers to obtain As-free drinking water. Adsorption of As species by iron-based nano-adsorbents is regarded as the most promising one. The high affinity of iron-based nano-materials toward As species is mainly due to their specific properties such as improved reactivity, biocompatibility, high stability, greater charge density, multi-functionality, and dispersibility nature. However, pristine iron-based nano-materials possess certain limitations. This includes the irreversible accumulation of individual nanoparticles (NPs), which may hinder their effectiveness in sorption. Therefore, the fabrication of iron-based functional nanohybrids is highly essential, which improves their stability, dispersibility, and performance. Other distinctive properties of well-dispersed functional nanohybrids are that they can be directly implemented for the in-situ elimination of As from contaminated water. In light of the foregoing concerns, the key objective of this doctoral dissertation is to investigate the synthesis, physicochemical characteristics, and applicability of various iron-based hybrid nanostructures for As adsorption. Here, we have successfully synthesized various iron-based hybrid and functional architectures such as α-Fe2O3 decorated hydroxyl functionalized porous graphitic carbon nitride (P-gCN-OH/α-Fe2O3) binary nanohybrid, L-Cysteine functionalized mesoporous magnetite (Fe3O4@Cy) nanosphere, maghemite & graphene oxide (GO) embedded polyacrylonitrile (PAN) electrospun nanofibers matrix (PAN/GO/γ-Fe2O3), and magnetite & amine-functionalized gCN embedded PAN nanofibers matrix (PAN/gCN-NH2/Fe3O4) by suitable synthetic approach. All the synthesized materials have been characterized by various instrumental characterization techniques such as X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR), Field emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM), Vibrating-sample magnetometry (VSM), Raman, Brunauer-Emmett-Teller (BET), Thermogravimetric analysis (TGA), Universal testing instrument (UTI), Contact angle (CA), Zeta potential (η), and X-ray photoelectron spectroscopy (XPS), etc. to investigate their physicochemical characteristics. XRD and other characterization results indicate the presence of α-Fe2O3, Fe3O4, γ-Fe2O3, and Fe3O4, phases of the iron-oxide in P-gCN-OH/α-Fe2O3, Fe3O4@Cy, PAN/GO/γ-Fe2O3, and PAN/gCN-NH2/Fe3O4, respectively. FESEM and TEM results signify the formation of ultrafine spherical α-Fe2O3, γ-Fe2O3, and Fe3O4 NPs in the respective adsorbent system. UTI provides the enhanced mechanical behavior of the PAN/GO/γ-Fe2O3 and PAN/gCN-NH2/Fe3O4 nanofibers matrix with greater elastic modulus and tensile strength. From the Batch adsorption experiment, it is clear that pH is an important variable for the adsorption of As. Therefore, adsorption of As(III) occurs nearly at neutral conditions as it exists as non-ionic species under pH 2-9, while As(V) adsorption occurs at lower pH as it exists in anionic form, which facilitates the strong electrostatic attraction between positively charged adsorbent surface and negatively charged As(V). Also, the kinetics, isotherm, and thermodynamics investigation provides insight into the adsorption mechanism. The maximum adsorption capacity of P-gCN-OH/α-Fe2O3, Fe3O4@Cy, and PAN/gCN-NH2/Fe3O4 towards As(III) adsorption were found to be 22.22, 20.0, and 32.26 mg/g respectively from the Langmuir isotherm plot. Also, the maximum adsorption capacity of P-gCN-OH/α-Fe2O3, Fe3O4@Cy, PAN/GO/γ-Fe2O3, and PAN/gCN-NH2/Fe3O4 towards As(V) were found to be 27.8, 34.0, 36.1, and 33.22 mg/g respectively. From the effect of the co-ion study, it is clear that in all the cases phosphate (PO43-) is a good competitor for As adsorption, as P and As are present in the same group of the periodic table. All the adsorbents possess good regeneration ability with retention of their applicability. The proposed mechanism by XPS analysis revealed that the adsorption of As on the adsorbent surface follows a physio-chemical process. Based on the overall investigation it is demonstrated that the addition of various supporting materials such as gCN, GO, PAN, or subsequent functionalization of iron-based materials improves their stability and adsorption efficiency as compared to the pristine one. In the future study, we will apply these nanostructures to analyze real water samples and design an engineering prototype for industrial and domestic water filtration
Development of Nickel-Based Hybrid Metal Oxide Nanocomposite Electrodes for Advanced Electrochemical Supercapacitor and Electric Field Emission Application
No full textThis thesis work preferentially motivates us to investigate intriguing electrochemical energy storage performance of some innovative nickel based hybrid metal oxides nanocomposite which have been rarely studied so far. Besides, some other nickel based transition metal oxide compounds have been publicized first time their potential field emission response for future application. Various dynamic synthesis protocols i.e. co-precipitation, sol-gel, and ultra-sonication have been adopted to prepare hierarchical surface morphology which can boost up electrochemical and FE performances. The enhanced properties of the assynthesized nanoparticles and their composites have been explained in terms of synthesis techniques, surface morphology, electrode and electrolytic properties, and process control. The aforementioned work has been described systematically in six different chapters as follows: Chapter I accentuates a brief introduction to electrochemical supercapacitors and their classification, components and materials, performance & testing, theoretical model of field emission and FE parameters, and their applications etc. Additionally, the theory of DFT and important parameters (i.e. work function, quantum capacitance) related to our experiment has been discussed briefly. The motivation, literature survey, and objective of our nanomaterials used for performance testing have been disclosed. Chapter II provides a detailed description of the synthesis protocols used to synthesize our chosen compounds and their carbon-based composites have been illustrated schematically. The basic theory of experimental techniques used for the structural, morphological, electrochemical, and FE characterization of as-prepared samples was also demonstrated with a diagram. Chapter III deals with the primary characterization results (i.e. XRD, Raman, FTIR, FESEM, TEM, EDS, BET etc.) with electrochemical response of two compounds core@shell NiCo2O4@MnO2 and NiMnO3/NiMn2O4 nano-cotton and their performences further upgraded with inclusion of MWCNT. The electrochemical response (CV, GCD) was observed at different scan rates and current densities using glassy carbon as the working electrode and 3 M KOH as an electrolytic solution. High specific capacitance 824 Fg-1 and 869 Fg-1 was observed for core@shell and nano-cotton and its value further upgraded 1048 Fg-1 and 1037 Fg-1 due to incorporation of MWCNT respectively. Good cyclic stability between ~82.6%-93% was examined over 5000 cycles for all compounds and EIS spectrum before and after testing was inspected. Chapter IV represents the primary experimental results of three nickel based transition metal oxide (NiMn2O4, NiCr2O4, and NiO [CdO]2) with unique nano morphology, high phase purity, balanced stoichiometry, and exclusive surface morphology for FE characterization. The field emission features including current density (J) electric field (E), FN plots, long stability were studied over long period and field enhancement factor (β) 3381, 2074, and 1854 were determined. The DFT calculation was also performed to calculate work function (Ф) using the supercell approach for the calculation of field enhancement factor (β). Chapter V covers the structural, electrochemical, field emission, and in-depth DFT study of two other productive compounds La2NiO4 and NiGa2O4 and further compared with La2NiO4/CNT and NiGa2O4/r-GO respectively. Preceding primary characterization was carried out to confirm their crystal symmetry, elemental indication, and hierarchical porous morphology. The electrochemical and field emission response was examined and compared. Good specific capacitance 426 Fg 1 and 643 Fg-1 was discovered for La2NiO4/CNT and NiGa2O4/r GO in 1M KOH electrolytic solution and Ni foam as a working electrode with capacitance retention 93% and 99.1% over 5000 cycles. Besides, improved field enhancement factor 4144 and 4429 was estimated for their CNT and r-GO based composite FE electrodes. The DFT study reveals exciting features related to charge transfer due to orbital interaction, enhanced electronic states near Fermi level for their carbonous composites leading to enhanced conductivity, increased mobility of electrolytic ions in the open space of CNT or r GO. The lower work function and higher quantum capacitance support the improved charge storage performance and field emission response. Chapter VI concludes the work carried out in the thesis with their future scope. The electrochemical performance and field emission characteristics of all compounds have been compared and discussed best outputs from our research with merits and demerits
Development of a Generic Microscopic Cellular Automata Model on Traffic Flow
Get PDFEfficient design of traffic facilities catering to the safe movement of vehicular traffic can be achieved only by understanding the traffic stream properties in a comprehensive manner. In this thesis work, an attempt is made to closely observe traffic stream characteristics for various situations. Traffic stream properties is an outcome of human decision during driving. As human decisionmaking process is a complex phenomenon, understanding the stream characteristics using field experiments is a difficult task. To avoid this difficulty computer simulation of a model which is a powerful tool can be used to understand the traffic stream characteristics. In this thesis, an attempt\ is made to develop a microscopic simulation model using cellular automata (CA), which can simulate traffic stream of various densities, involving various road geometries, traffic composition involving homogeneous as well as heterogeneous traffic and movement characteristics of vehicles with and without lane discipline. The proposed model is a discrete microscopic model that describes movement of individual vehicle on a discrete representation of flow space and time. The flow space is divided into various square cells and time is divided into discrete time steps. Static and dynamic obstacles occupy flow space. Static obstacles refer to roadside vending, on street parking etc. whereas dynamic obstacles refer to other moving vehicles. Depending upon the type and position of the obstacle, the test vehicle takes decision about its course of action i.e., change in speed and change in steering angle at every time step. In order to complete the decision process every vehicle is assigned a pivot point (i.e., front right corner of every vehicle). It is with the reference to the pivot point every decision about the vehicle is taken i.e., calculation of speed, calculation of steering angle, updated position of the vehicle etc. A vehicle taking decision about changing its steering angle, first checks the relative speed (i.e. difference in speed between leading vehicle and following vehicle) and the space availability at its sides either to the right or to the left. The position of the pivot point of the following vehicle with respect to the position of the pivot point of the leading vehicle decides the steering angle change either to the left or to the right. Various microscopic and macroscopic studies were performed using the proposed model. Microscopic properties were studied for single lane traffic stream where the car following characteristics of the drivers was stressed. It may be noted that in case of single lane traffic stream study, the lateral movement of vehicles were absent. Microscopic studies include study of stability properties, time headway distribution and speed distribution. Macroscopic properties include relationship between speed flow-density for road widths starting from single lane to multi-lane and traffic composition with homogeneous and heterogeneous traffic. The proposed model takes into account the gap between the vehicles during motion as well as at static condition. Concept of buffer space has been proposed which takes care about the spacing between the vehicles. As in real life scenario, the gap between vehicles increase with increase in speed and is the least when at rest, the proposed model is capable of capturing the phenomena very well. Microscopic properties are also obtained from the proposed model which are an integral part of any microscopic traffic flow model. Collected field data (speed, flow and density) was used for calibration and validation of the proposed model. Parameters representing the gap between the vehicles during motion as well as at static condition (C1 and C2 respectively) are used for calibration. The values of C1 and C2 are changed iteratively until the square sum of errors (SSE) between the trendlines of distance headway - speed plots for simulated and field condition becomes the least. Statistical tests were performed to validate the model using the distance headway and speed data for simulated and observed data. Regression analysis for simulated distance headway versus field distance headway and simulated speed versus field speed has been done. The results obtained from regression analysis indicates the simulated data and observed data are matching well
Enol ester: A Versatile Synthetic Equivalent for Isocoumarin and Chromone Synthesis
No full textOxygen counterpart of enamide, called as “Enol ester”, is abundant in various biological active natural products, and hence considered as an important structural motif with immense attention. Enol esters also involved in different reactions such as cycloadditions, Aldol reactions, Mannich type reactions, and asymmetric hydrogenation reactions to afford synthetically useful products. Considering the versatile applications of enol esters, several methods have been appeared in the literature for their synthesis. On the other hand, synthetic applications of enol esters in oxygen-containing heterocycle synthesis is relatively less literature precedent. Therefore, a work has been initiated to employ the enol ester as an important structural scaffold to assemble biologically potent oxygen-containing heterocycles. The present thesis entitled “Enol ester: A Versatile Synthetic Equivalent for Isocoumarin and Chromone Synthesis” involves the base-mediated synthesis of enol esters from the reaction of aromatic carboxylic acid and propiolic esters as well as 1,3-dicarbonyl compounds, and the utilization of the so formed enol esters in flavonoid synthesis. Additionally, silver-catalyst was exploited for the first time in the formation of Csp2−Csp3 bond to assemble isocoumarin and chromone motif under mild reaction conditions
Synthesis and Characterizations of Organometallic Lead Halide Perovskite Single Crystals for Photovoltaic Applications
No full textSolar energy is a clean source of energy that can help to fulfill the increasing global energy demand. Among light-harvesting devices, perovskite solar cells (PSCs) have been a focus of interest among next-generation photovoltaic (PV) technologies due to their incredible conversion efficiency (certified PCE of ~25.2%) along with their lower cost and ease of fabrication. However, many transport barriers and defect trap states at the interfaces and grain boundaries have negative effects on PSCs. It decreases their efficiency and stability and increases the hysteresis effect. From the literature survey, the above drawbacks can be minimized by controlling the morphology, grain boundary, grain size, charge recombination, and density of defect states in the perovskite layer by different surface passivation. However, the growth of high-quality single-crystal (SC) perovskite films is a great strategy for the fabrication of defect-free PSCs with photovoltaic parameters close to the theoretical limit, which resulted in high efficiency and superior stability of the device. Thus, considering the potential improvement in terms of stability and performance of PSCs using single-crystalline perovskite absorbing layer and different passivation layers, this work focuses on synthesizing perovskite single crystals and passivation layer for photovoltaic applications. Methylammonium lead iodide (MAPbI3) is the most commonly used photo absorber in PSCs. We have chosen MAPbI3 perovskite single crystal in the present work and modified them with guanidinium (GUA) cation and bromide halides. Following single crystals (SCs) were synthesized via inverse temperature crystallization (ITC) synthesis root. 1. MAPbI3 and Methylammonium lead bromide (MAPbBr3) SCs 2. GUAxMA1-xPbI3 SCs 3. MAPb(I1-x Brx)3 SCs (x = 0.04, 0.08, 0.12 and 0.16) However, a water-resistive lead sulfate layer is used as a surface passivator for improving the stability against moisture. XRD patterns of grounded crystals showed a single perovskite phase. There is no grain boundary (from SEM microstructure study). Temperature stability of the MAPbI3 SCs ware examined by temperature depended XRD patterns. From the detailed bias- and temperature-dependent studies, we found that the low-frequency capacitance values are influenced by ion density and mobility. Consequently, single-crystalline MAPbI3 depicts an activation energy of ~0.53–0.54 eV with an exceptionally low electronic trap density of ~0.96 × 1010 cm–3. The small substitution of Methylammonium (MA) with guanidinium (GUA) decreases the activation energy for iodide ion migration in comparison to pristine MAPbI3 SCs. The presence of large GUA cations in the 3D perovskite structure induces lattice enlargement, which perturbs the atomic interactions within the perovskite lattice. Consequently, the GUAxMA1−xPbI3 crystal exhibits a higher degree of hysteresis during current-voltage (J–V) measurements than the single crystalline MAPbI3 counterpart. It is found that I/Br alloying structure effectively slows down the degradation of MAPbI3 SCs over time. Single-phase cubic structure was obtained from XRD study when a certain amount of Br (x=0.12) incorporated in MAPbI3 SCs, leading to a tetragonal to the cubic phase transition. We find that the smaller Br atoms decrease the lattice spacing of the MAPbI3 SCs, which restricts the ion migrations and increases the activation energy, leading to improve stability of MAPbI3 SCs. The calculated activation energy of ~0.34±0.007 and ~0.51±0.008 eV is associated with the tetragonal and cubic phases of MAPbI3 SCs. A clear tetragonal-cubic phase transition of the MAPbI3 SCs was noticed in the 50-55 oC temperature range. On the other hand, tetragonal-cubic phase transition temperatures are decreasing with Br inclusion, and the most crucial benefits in terms of phase stability are found for MAPb(I0.88Br0.12)3 SCs. We fabricated MAPb(I1-x Brx)3 SCs based photodetectors (PDs) and studied their response and stability. The best values reached for MAPb(I0.88Br0.12)3 SC PDs under white light with an intensity of ~0.5 mW cm-2, and the values of responsivity and specific detectivity are ~2.049 mA/W and ~15.19 × 1010 jones, respectively. More importantly, the photocurrent of MAPb(I0.88Br0.12)3 SCs based photodetectors (PDs) decrease by only ~54% without encapsulation, while the photoresponse of MAPbI3 PDs is reduced by ~81% after 365 days. Additionally, the responsivity of PDs with 12% Br doping is decreased by only ~15.4% compared to a ~37.5 % reduction for pure MAPbI3 SC-based planar PDs after 10 days of continuous operation. We studied the role of lead sulfate (PbSO4) as an effective passivator in MAPbI3 and MAPbBr3 SCs. Using impedance spectroscopy, we evaluated the ion migration and electrical properties of lead sulfate-passivated MAPbI3 and MAPbBr3 SCs. We found that the low-frequency impedance response that is assigned to the ionic motion in the MAPbBr3 and SCs is strongly affected by the inorganic PbSO4 surface treatment. The activation energy corresponding to the ion migration of MAPbBr3 and MAPbI3 SC increased from ~0.28 to ~0.36 eV and ~0.54 and ~0.59 eV after PbSO4 surface treatment, respectively. The temperature-dependent I–V hysteresis of the MAPbBr3 SCs upon PbSO4 passivation was also measured. We found that such PbSO4 surface treatment stabilizes the crystal surface and improves the hysteresis properties of the crystals at elevated temperatures
Development and Evaluation of Hot and Warm Sand-Sulphur-Bitumen Paving Mixes
No full textThe economic growth of a country leads to urban expansion and infrastructure development importantly in pavements, which eventually increases the demand for stone aggregates. The uncontrolled extraction of construction aggregates has resulted in severe depletion of existing natural stone reserves. Keeping this issue in mind, the use of locally available and waste materials as a substitute for stone aggregates, particularly in road construction has become a major research interest. Contemporarily, sand is available abundantly in some places, such as in coastal deltaic plains, beaches and desert areas. Hence, researches involving utilisation of sand as an alternative to coarse aggregates are worth taking up. In this direction, few studies reported sand-bitumen mix to be weak and unstable (low stability and high air void content), and hence unsuitable for pavement construction. However, the properties of sand-bitumen mix could be improved with inclusion of sulphur which is a by-product of coal processing, and petroleum and gas refining processes. When Sulphur is added as third material along with sand and bitumen, the mix is typically termed as sand-sulphur-bitumen (SSB) mix. This research work addresses the development and evaluation of SSB mixes in order to utilise locally available sand as an alternative to coarse aggregates for paving purposes. This study basically investigates two types of mixes namely, hot and warm SSB mixes. For preparation of hot mixes, VG 30 bitumen was used whereas for warm mixes, VG 30 bitumen was modified with sasobit so as to facilitate mixing and compaction at lower temperature. First of all, a suitable mixing method was developed to prepare SSB mixes that involved selection of critical mixing parameters such as mixing sequence, mixing temperature, mixing time and compaction effort. Concurrently, gaseous emissions were monitored to assess the potential hazards due to toxic gases released during mix preparation. Next, the effects of varying proportions of constituents such as sand, sulphur and bitumen were considered to determine the optimum mix compositions based on Marshall properties. Further, crusher dust in varying concentrations and/or various types of fillers such as fly ash, stone dust and cement were considered for the mix, and the Marshall properties were studied to determine the best proportions of ingredients. In addition to Marshall properties, the selected mixes were evaluated in terms of other performance characteristics such as indirect tensile strength, moisture susceptibility, resilient modulus, fatigue performance and rutting characteristics. Furthermore, an attempt was made to study the internal structure of SSB mixes with the help of effective and quick non-destructive 3D (three-dimensional) high resolution technology namely X-Ray micro computed tomography coupled with digital image analysis techniques. Various air void (AV) parameters such as volume, size and shape of voids, connected air void content, and tortuosity of compacted specimens were assessed to describe the geometric and topological properties of voids. The impacts of variation in the mix constituents on AV parameters were examined to understand their effects on void structure and their properties. Additionally, probabilistic analysis was performed to model the void size distributions in SSB mix specimens. The permeability of SSB mixes was also measured using an asphalt permeameter and correlation analysis was performed to establish the relationships between permeability and AV parameters. In addition, predictive models for permeability were developed based on the fundamental mix properties. Experimental results revealed that for hot SSB mixes, the optimum mixing sequence included mixing of VG 30 bitumen with sand-molten sulphur blend at 145°C, whereas for warm SSB mixes the mixing sequence involving mixing of molten sulphur with sand-modified binder at 125°C produced the best results. The gaseous emission analysis showed that the concentration levels of various harmful emissions near the place for SSB mix preparation (in the laboratory) were found to be much below the prescribed limits specified in different standards for hot SSB mixes. The emissions were found to be much less for warm SSB mixes. With regard to mix composition, the concentrations of sand and sulphur by weight of mix were found to be 85% and10% respectively for both hot and warm SSB mixes. Substantial improvements in Marshall properties were noticed with the replacement of sand by 30% crusher dust. For all filler types, optimal filler content was found to be 5% by weight of aggregate. For each mix type, bitumen contents of 4.5 and 5% by weight of each mix were chosen based on the Marshall test results. The SSB mixes with selected mix compositions were found to exhibit satisfactory performance characteristics. The microstructural characterisation of SSB mixes revealed that the mix constituents, mainly incorporation of crusher dust, had significant impacts on the AV parameters. A two-parameter loglogistic distribution and a four-parameter stable distribution were found to be the best fit models for void size distribution of hot and warm mixes respectively. Further, permeability of SSB mixes had significant correlations with the geometric and topological void properties. Despite having high air void content, the SSB mixes exhibited a high degree of impermeability which is attributed to the less connectivity of air voids and higher tortuosity of the mixes. Predictive models developed using neighbourhood component analysis (NCA) regression approach for prediction of permeability was found to be accurate (R2 = 0.99) for both hot and warm SSB mixes. Furthermore, the life cycle cost analysis of typical SSB mixes revealed that there is a substantial economic benefit as compared with conventional bituminous mixes. In summary, the SSB mixes exhibited essential performance characteristics as required for a normal bituminous pavement. Overall, this study showed an effective way to use SSB mixes as a bituminous layer with complete exclusion of conventional coarse aggregates which are scarce in some locations
Cash Holdings; Financing Decisions; and Firm Value: Evidence from India
No full textFinancing decisions are key to the success of corporates and, cash holdings and debt structure have emerged as reliable financing choices for managers. Although the traditional financial structure revolved around debt-equity decisions, lately cash holdings have emerged as a fundamental financial policy. Both policies are integral to firm’s financial structure and combined they provide firms with a financial flexibility that enables managers to maximize firm value. However, regardless of the recent development of cash holdings among corporates, limited literature exists that explains the characteristics of cash holdings and its role in the valuation aspect of firms. Further, the interrelationship between cash holdings and debt financing structure is missing in recent developments that needs to be explained. In this thesis, we have mainly explored four interrelated empirical studies that relate cash holdings, debt structure, and firm value in the Indian context. While each empirical chapter addresses a specific objective, together, the findings provide the framework of the thesis regarding the firm’s financing choices and the role of cash holdings in aiding managers in handling internal liquidity and risk management. The study undertakes listed manufacturing firms of India for the time period of 2008 to 2021. The first empirical study investigates the factors determining cash holdings with special impetus on debt structure. The findings not only support the classical theories of cash holdings but also bring forth the important determinants explained in light of the theories. The results find evidence of the pecking order theory, trade-off theory, and agency theory in explaining the financial factors that affect cash holding decisions. Besides, the thesis also examines the relationship between debt financing choices and cash holdings. A negative linkage is observed between debt-asset ratio and cash levels. However, debt-cash implications is more attributed to bank debts since borrowings from non-bank sources have a positive effect on cash holdings. The second study explores the impact of macroeconomic indicators on cash holding decisions. Firms are inclined to regulate their financial policies by considering economic risks, and cash holdings serve as reliable sources of financing. Hence, economic indicators are important to gauge the cash holding decisions. The findings indicate that economic risks exhibit a significant effect on cash holdings. The study undertakes three indicators that are relevant to businesses and measures economic uncertainty. The study report that fluctuations in the inflation rate and the exchange rate
exhibit inverse impact on cash holdings. Although, a positive influence is witnessed between interest rates and cash holdings. Later chapters develop on the interrelationships among firm value, cash holdings, and debt structure. The fourth chapter attempts to relate firm value and cash holdings under non-linear conditions and risk management prospects. From the precautionary motive, the study explores the risk aversion and shielding effect of cash during financial distress. The study first documents a positive drive of cash holdigs on firm value. However, the relationship is not static and excess cash devalues the firm. Hence, the study claims that an inverse U-shaped relationship exists between firm value and cash holdings. Further, the study models different scenarios that mark financial crises and economic failures and investigate the role of cash holdings as a risk-hedging instrument. Specifically, the study undertakes the liquidity risks, the great financial recession, and the recent pandemic induced economic crisis to mark different circumstances that led to economic and financial turmoil. The study reports that the cash-value linkage strengthens during recessions. The study also estimates that despite the crisis, the non-linear association is still valid between cash reserves and company’s value. The last empirical chapter ascertains the role of debt financing in determining firm value under heterogeneous beliefs. Specifically, the study investigates the relationship between debt diversification, debt ownership, and firm value. While the classical literature has investigated the relationship between debt and firm value confined to homogeneous debt construction, the objective of the study is to investigate the role of accessing debts from various debt instruments available to firms. The study classifies debt structure as broadly borrowings from either banks or non-bank debt instruments. On the contrary, debt diversification measures the number of independent debt sources from which firms have availed loans. Moreover, the study estimates the relationship for different proxies of measuring firm value, which are ROA, Tobin’s Q, and PE ratio. Debt diversification is found to have a negative and significant impact on firm value for all the measures adopted in the model. The debt asset ratio also reports a negative effect on firm value. However, when constituents of debt are considered, the study finds variations in impact of debt structure on firm value.. While bank debt has a significant positive impact on firm value, non-bank debt borrowings do not exhibit a significant effect on firm value. The empirical findings of the thesis document novel contributions to the existing research. From an academic forefront, the thesis documents the factors influencing the cash holding decisions of firms and validates the appropriateness of various theories in explaining cash holdings. Further, the study explores the relationship between debt structure and cash holdings and explains that debt structure has a lot of consideration in the actual analysis of cash holdings rather than assuming debt as homogeneous. Moreover, the thesis document the impact of changing dynamics of macroeconomic indicators on corporate cash holdings and mark the addition of economic risks as key to cash holding decisions. The thesis also documents the paradigm shift in the role of cash holdings as a mere financing instrument for a firm’s activities to risk management capabilities. From a risk management perspective, the thesis documents the risk hedging prospects of cash holdings regarding their ability to sustain the exposure of the risk and minimize defaults. While the literature has documented the precautionary motive to hold cash, the findings of the thesis contribute to how exactly cash holdings can hedge firms from financial exposures. The thesis also contributes to the recent developments regarding an optimal cash level by exploring the non-linear association between cash holding and firm value. Lastly, the thesis explores the relationship between debt financing and firm value under the context of debt diversification and debt ownership. The thesis establishes the significance of debt structure under heterogeneous beliefs to substantiate how a firm’s reliance on debt financing has gradually incorporated various debt instruments apart from bank borrowings