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Experimental Investigation of LHR Engine Run on an Antioxidant-Doped Biodiesel-Diesel Blend
No full textBiodiesel is derived from plant oils, animal fat, and algae by the esterification/transesterification process. It can be either used directly or in a blended form with diesel in compression ignition (CI) engines. The important merits of biodiesel when used as an alternate fuel in CI engines are (i) it does not produce SOx emissions, (ii) hydrocarbon (HC), carbon monoxide (CO), and smoke emissions are lower. However, there are a few important technical challenges found with the utilization of biodiesel in CI engines, which include (i) lower engine performance, (ii) higher oxides of nitrogen (NOx) emissions, and (iii) oxidation stability. The brake thermal efficiency (BTE) of the engine is slightly reduced and brake-specific fuel consumption (BSFC) is higher in the biodiesel-fueled diesel engine. This research work is aimed at simultaneously improving efficiency and reducing NOx emissions of a biodiesel-diesel blend run direct injection (DI) diesel engine. For this purpose, a conventional DI diesel engine is made to run in a low heat rejection (LHR) mode to inhibit heat loss to improve the thermal efficiency of the engine. The biodiesel-diesel blend considered in this study is JME20 which contains 20% Jatropha methyl ester (JME) and 80% diesel on a volume basis. On the other hand, an antioxidant is doped in the biodiesel-diesel blend to reduce NOx emissions.
Initially, thermal and structural analyses are carried out considering two different TBC pistons. Thermal barrier coating (TBC) comprising Yttria stabilized zirconia (YSZ), and YSZ + Cerium oxide (CeO2) (85%YSZ+15%CeO2) is applied on an aluminum alloy piston. Three different thicknesses of the topcoat of materials for YSZ and YSZ+CeO2 coating viz. 0.3 mm, 0.6 mm, and 0.9 mm are chosen. SOLIDWORKS software is used to draw pistons and different thicknesses of layers (top coatings). ANSYS software is used for performing structural and thermal analyses on the piston surface. The YSZ+CeO2-coated piston gives better results in thermal and structural analysis when compared to the YSZ-coated piston. Therefore, the YSZ+CeO2-coated piston is used to form an LHR engine for experimental investigations that are further carried out in this research work. Six experimental works are carried out to study the combined effect of running a DI diesel engine run in the LHR mode fueled with an antioxidant-doped JME20. For this purpose, a single cylinder, four-stroke DI developing the power of 4.4 kW at 1500 rpm is converted to LHR mode by coating the piston with YSZ+CeO2. Initially, the engine is run on diesel and JME20 to obtain baseline data. The peak cylinder pressure and heat release rate are increased by 1.8% and 2.2%, respectively, for the YSZ+CeO2-coated piston-fitted engine compared to the uncoated piston-fitted engine run on JME20. The ignition delay and combustion duration are improved by 16.8% and 3.5%, respectively, at full load when compared to the uncoated diesel engines fueled with JME20. BTE increased by about 7%, and BSFC decreased by 5.3% at full load in the LHR engine run on JME20. HC, CO, and smoke opacity are reduced by about 11.5%, 7.2%, and 4.7%, respectively, at full load for the JME20-fueled LHR engine. Nitric oxide (NO) emission is increased by 11.2% at full load for the LHR diesel engine fueled with JME20. The analysis of the experimental results reveals that the engine performance improves and diminishes engine emissions such as HC, CO, and smoke in the LHR diesel engine but increases NO emission due to the high cylinder temperature and availability of oxygen in the test fuel (JME20). Therefore, further experiments are carried out on the use of antioxidants to reduce NO emissions from the test engine. Two synthetic antioxidants, namely N-Isopropyl-N'-phenyl-1, 4-phenylenediamine (IPPD) and N, N'-Diphenyl p-phenylenediamine (DPPD), each taken at four concentrations viz., 500 ppm, 1000 ppm, 1500 ppm, and 2000 ppm are doped with JME20. The mixtures obtained with IPPD are designated as JME20A1, JME20A2, JME20A3, and JME20A4, where A1, A2, A3, and A4 indicate 500, 1000, 1500, and 2000 ppm respectively. Similarly, the mixtures obtained from doping DPPD in JME20 are designated as JME20B1, JME20B2, JME20B3, and JME20B4, where B1, B2, B3, and B4 indicate 500, 1000, 1500, and 2000 ppm respectively. Before examining the fuel mixtures test engine, they are characterized by X-ray diffraction (XRD), Scanning Electron Microscope (SEM), Fourier Transform Infrared Spectroscopy (FTIR), and Energy Dispersive Spectroscopy (EDS) for their oxidant behavior. Further, experiments are conducted in the test LHR engine. Due to the combined effects of micro-explosion and the secondary atomization of IPPD-doped JME20 fuels, HC and CO emissions are reduced by 30.6% and 22.4%, respectively, compared to those of diesel operation at full load. The smoke opacity is reduced by 11.5% at full load condition for JME20 A3 in the LHR engine. NO emission is reduced by 11.7% for JME20A3 at full load condition compared to an uncoated engine. The peak heat release rate (HRR) and the peak cylinder pressure are lesser by about 5.6% and 5.1% for JME20B4 in the coated engine (CE), respectively, at maximum engine load. NO, HC and CO emissions are reduced by 6.5%, 17.4%, and 34.6%, respectively, at full load for the JME20B4 fueled in the LHR diesel engine. The next set of experimental studies used two leaves extracted natural antioxidants doped with JME20 to reduce the NO emission and analyze the engine performance also.
Natural antioxidants are available in various biomass substances, which can be used for improving human health and fuel oxidation stability. Therefore, the next two sets of experiments are carried out using antioxidants derived from two potentially available biomass substances (i) Albizia lebbeck, and (ii) Pongamia pinnata leaves. Albizia lebbeck leaves, and Pongamia pinnata leaves are characterized by XRD, SEM, FTIR, and EDS for their oxidant behavior. Antioxidant obtained from Albizia lebbeck at various concentrations viz., 500, 1000, 1500, and 2000 ppm is doped in JME20, and the blends are designated as AL1, AL2, AL3, and AL4, respectively. Antioxidant from Pongamia pinnata leaves at 500, 1000, 1500, and 2000 ppm is doped in JME20, and the fuel mixtures are designated as PLA1, PLA2, PLA3, and PLA4, respectively. The combustion, performance, and emissions of the test engine run on antioxidant-doped JME20 fuels in the conventional engine operation and LHR mode are evaluated. Results indicate that among the four antioxidants doped-JME20 fuels, JME20AL4 gives better performance and lower exhaust emissions. The cylinder pressure and heat release rate are lesser by about 4.7% and 6.4%, respectively, at full load, for JME20 AL4. The fuel's delay period and combustion duration are improved by about 26.8% and 10.8%, respectively, at maximum load. NO, HC and CO emissions are reduced by about 17.3%, 19.3%, and 44.2%, respectively, for JME20 AL4, at maximum load. Cylinder pressure is reduced by about 5.9% and the heat release rate by 6.9% for JME20 at a concentration of 2000 ppm in the LHR engine. The engine emissions are reduced by 17.5% and 16.3% for HC and smoke, respectively, at maximum load for JME20 PLA4, in the LHR engine. NO emission is decreased by 16% for JME20 with 2000 ppm (JME20 PLA4) at a higher load in the coated engine
Study of Multi-functional Materials Using First-principles Method
No full textThe realization that the electric current through a sequence of thin alternating magnetic and metallic non-magnetic layers is strongly affected depending on the relative orientation of the magnetization gave birth to the new paradigm of electronics, now commonly known as spintronics, based on the manipulation of the spin degree of freedom of the electrons. Spintronics devices consist of a spin injector and a detector, and the efficiency of such a device crucially depends on the effectiveness of the injection and detection of polarized spins. Typically, a ferromagnetic metal is used as a spin injector or detector. However, a ferromagnetic half-metal, which has a band gap for one spin channel while the other spin channel is conducting, is the most suitable material for the spin injection or detection process. There are several theoretical predictions of bulk half-metallic ferromagnets, some of which have also been experimentally verified. However, a common problem seems to be that the half-metallic ferromagnetic states do not always survive at the surfaces, especially on the (001) surface, which is desirable from the point of view of experimental fabrication of the same system or at the interface with other materials. Recently, density functional theory-based first-principles calculations have predicted that the multi-functional perovskite BiFeO3 having spacegroup-R3c becomes a magnetic semiconductor in the presence of ferromagnetic ordering. Motivated by these findings, in this thesis, we have investigated the tetragonal BiFeO3 structure having P4mm space-group symmetry in the presence of ferromagnetic ordering using first-principles methods based on density functional theory. Since the tetragonal phase can exist with a wide range of possible structural parameters, it is expected that it will host much richer electronic properties compared to the R3c phase. In this thesis, we report, for the first time, that this is indeed true. Out of four different possible structural parameters of tetragonal BiFeO3 studied in this thesis, we find that one of the bulk structures is a half-metallic ferromagnet. Interestingly, we find that the (001) surface of the same structure is also a half-metallic ferromagnet, and the half-metallic states are further retained at the interface in certain heterostructure geometry as well
Efficient Re-Embedding Strategies for Virtual Data Centers over Multi-Domain Substrate Networks
No full textNetwork virtualization (NV) has allowed the service providers (SPs) to logically partition the substrate resources into independent executable entities called virtual data center (VDC). Typically a VDC comprises multiple interactive virtual machines (VMs) and virtual links (VLs) reflecting their communication dependencies. NV brings about multiple benefits to the SPs, including complete service isolation, reduced security threats, higher quality-of-services (QoS) satisfaction, and better utilization of substrate resources. However, it also introduces many research challenges, such as scalability, failure tolerance, monitoring, interfacing, security, pricing, and resource management. This thesis focuses on the issue of resource management– specifically, the objective is to develop efficient complete/selective re-embedding strategies for already embedded VDC experiencing demand fluctuations. In this regard, reassigning resources to the VDC comprises two closely related sub-problems, i.e., reassigning server resources to the VMs, also termed VM re-embedding, followed by reassigning substrate paths to VLs, also termed VL re-embedding. Moreover, both the sub-problems are computationally-intensive intractable problems and are proven to be NP-Hard. Firstly, a genetic-meta-heuristic-based framework called GAMap is proposed that addresses the issue of complete re-embedding of VDC over a multi-domain substrate network catering to their dynamic resource demands. GAMap adopts improved crossover and mutation operations to obtain a re-embedding assignment with minimum re-embedding cost. Although GAMap is efficient and reduces the re-embedding cost, it has pitfalls. Firstly, it is time-consuming, computationally expensive, and not scalable. Secondly, the complete re-embedding of VDC may not always be desirable when only a few components experience a surge/drop in demands. Thirdly, re-embedding the VDC with the minimum re-embedding cost at the expense of under-utilizing substrate resources may not be favorable for the SPs. The second contribution presents a model called ReMatch addressing the shortcomings of GAMap. ReMatch adopts a one-to-many matching theory-based re-embedding strategy that generates a stable, efficient, and polynomial-time re-embedding plan. It reassigns solution components (SCs) instead of the entire VDC, where a SC comprises a VM and its attached VLs with at least the VM and/or one of the VLs experiencing a surge/drop in demands. Moreover, ReMatch adopts an analytical hierarchy process (AHP)-based ranking of servers to minimize re-embedding cost and improve utilization of substrate servers. Although ReMatch could generate stable, efficient, and polynomial-time reassignments, it has the following lacunas. Firstly, the agents’ preferences in ReMatch are static, which can often lead to inaccuracies, especially when multiple SCs of a VDC is re-embedded. Secondly, the utility computation in ReMatch is imprecise as it only considers the available resources and the VM re-embedding cost. To deal with the pitfalls of static preferences of ReMatch, the third contribution discusses a framework called CoMap based on a one-to-many matching between VMs and servers with coalition formation at the servers. Dynamic preferences of VMs are computed in CoMap, considering the substrate network’s current state and the allocation of the dependent VMs. Moreover, the utility computation is upgraded to consider the VM demands and the total re-embedding cost of the relocating SC. The former boosts the utilization of the substrate servers, whereas the latter assists in reducing the re-embedding cost
Surface Modification of Ti-6Al-4V Alloy by Depositing MMC Coating with Variant of Matrix Phases through TIG Cladding Method
No full textTi-6Al-4V alloy has numerous applications in the field of aircraft, chemical, marine, and biomedical industries because of its remarkable properties, like, high strength-to-weight ratio, elevated melting temperature, excellent corrosion resistance, and biocompatibility. Nevertheless, its poor wear resistance, restrains its scope of application, when it is working under a wear and friction environment. Depositing a hard and wear resistance coating through Tungsten Inert Gas (TIG) cladding route was found as a suitable approach to enhance the wear resistance of Ti-6Al-4V alloy. TiC as a reinforcement ceramic, widely used in composite coating, and proficiently improve the hardness and wear resistance of a metallic component, even at elevated temperature. Present research emphasized on the development of TiC reinforced hard and wear resistance composite coatings on Ti-6Al-4V alloy, by using a variety of matrix phases through TIG cladding route. Primarily, TiC-Co coating was fabricated on a Ti-6Al-4V alloy plate using TiC/Co powder blend. Co as a matrix phase with TiC reinforcement enhanced the interfacial bonding and accelerated the anti-oxidation and abrasive wear resistance of the composite coating. The effect of processing current, and stand-off-distance (SOD) during TIG cladding on the quality and performance of the coating was also analyzed. It was revealed that the TiC-Co composite coating developed with higher SOD (6 mm) and lower current (120 A) exhibited higher hardness and wear resistance against different counter rotating discs. Further, to increase the microstructural uniformity of the composite coating nano-Y2O3 was added to the precursor powder, and accordingly TiC-Co-Y2O3 cladding was developed on the Ti-6Al 4V alloy by the TIG cladding method. With the addition of nano-Y2O3, the melting efficiency of the precursor augmented, which completely melted the TiC particles and transformed them into elongated dendrites during solidification. The addition of nano-Y2O3 effectively refined the grain structure of the clad material, and improved the micro-hardness, fracture toughness, and ductility of the coating. Almost, a four times reduction in the wear value was recorded for TiC-Co-2%Y2O3 coating as compared to TiC-Co coating. In the succeeding work, TiC reinforced composite coating with NiCoCrFeTi high entropy alloy (HEA) as matrix phase was developed on Ti-6Al-4V alloy. The microstructural analysis of the coating revealed that, along with dendritic TiC, the presence of HEA matrix, augmented the wear resistance of the coating enormously, and shows almost 7.5 times lower wear value as compared to the uncoated Ti-6Al-4V alloy. Through EBSD, XRD, and thermodynamic analysis, the formation of BCC/FCC phases shows the possibility of solid solution/intermetallic in the coating. Additionally, large area TiC-NiCoCrFeTi HEA composite coating was also fabricated through side-by-side deposition of the consecutive clad tracks. A least discrepancy in the thickness and hardness of the coating was witnessed for using 50% overlapping to produce the large area cladding. The corrosion test performed on the TiC-NiCoCrFeTi HEA coating showed its adequate corrosion resistance in 3.5% NaCl solution
Instability and Nonlinear Dynamic Analyses of Convex Bimorph DE Actuator for Soft Fish Robotic Tail
No full textBiomimetic robots are currently experiencing a surge in demand due to their exceptional engineering applications and impressive performance capabilities. The soft fish robot is a novel type of aquatic organism that is constructed using electro-active polymer (EAP) based dielectric elastomer (DE) materials. This unique robot is designed specifically for the purpose of underwater exploration. This type of intelligent/smart actuator can support human interactions or communications with the dynamic environments. These actuators are capable of producing large strains/ mechanical actuation when electric fields are applied. Electrical energy gets converted to mechanical energy during bending actuation of bimorph DE actuator. The present work proposes an anisotropic convex bimorph DE actuator (DEA) to generate the flapping motion in the tail of soft fish robot. The fibers attached in the anisotropic case are oriented in some angles, the convex structure has led to the concept of taper ratio and temperature variation analysis for practical applications is necessary. Therefore, in this present analysis, the fibre angles of the reinforcement, the taper ratios, and the temperatures are varied to study the performance of the system. The instability and nonlinear dynamic responses of the proposed actuator have been studied and analysed by developing the mathematical models. The system is modelled under coupled electro-thermo-mechanical field considering without and with reinforcement of soft fibers in DE layer of such actuator. The equilibrium equations to study the instability have been derived in terms of taper ratios of the convex shaped actuator and the ply angles due to anisotropy at different temperatures. After obtaining the mathematical derivations, numerical solutions of the complex nonlinear equations for critical stretch, nominal electric field, and entropy under different mechanical, electrical, and thermal loads are determined using MATLAB. The observations demonstrated that with growth in nominal stress as well as temperature the peak point of nominal electric field gets enhanced. Results also inferred that with rise in temperature, nominal stress and axial stretch, entropy surges, making the system disordered. After obtaining the range of stability, the dynamic performances of system are studied and analysed. Nonlinear dynamic analyses of the anisotropic convex bimorph DEA are performed to determine bending actuation/flap. Experimentally stress relaxation behaviours of the elastomer at different temperatures are obtained using dynamic mechanical analysis (DMA 8000) to obtain shear moduli (relaxed and unrelaxed) and relaxation time. The thermo-electro-visco-hyperelastic behaviour of such actuators is represented by Gent model of hyperelasticity in conjunction with the new relaxation model of viscoelasticity based on the obtained experimental data. The governing equations of motion are derived based on the Euler Lagrangian principle and solved using MATLAB and Simulink to analyse the nonlinear dynamics of active layer for such actuator. Based on the obtained axial stretch of the active layer, flapping movements of the bimorph DEA have been determined. The effects of the parameters are observed on the time series and frequency responses. The frequency spectrum indicates generation of different frequencies which are linear combination of natural and excitation frequencies. The stretch histories, deflections, phase planes, Poincaré maps along with hysteresis loops and bifurcation diagram are obtained to represent the physical behaviour of nonlinear dynamics. Then from the responses, it is inferred that with a hike in temperature and taper ratio, the stretch and deflection increase. From the phase portraits, the quasi-periodic nature of the system is evident at dominant spike and the hysteresis loop indicates energy dissipation. From the bifurcation diagram, it is observed that subharmonic, harmonic and super harmonic exists in the system’s responses. At low frequency it is found that the stretch histories are chaotic. It is also identified that in isotropic actuator, the stretch obtained is more compared to anisotropic actuator. The proposed work aims to provide guidance for conducting stability and dynamic performance analyses of bimorph actuators, with the ultimate goal of enabling their integration into high performance underwater robots
Molecular Design, Synthesis and Photophysical Investigations of Blue Emitting Fluorophores for Organic Light Emitting Diodes and Sensing
No full textThe current thesis work addresses the potential for utilising new class of unipolar and bipolar blue emissive organic materials in applications for chemosensors and organic light emitting diodes (OLEDs) through molecular engineering and production. In chapter 1, a general overview of the development of the new generation and several molecular design strategies based on blue fluorophores: introduction, literature survey of recent trends and brief objectives of the present thesis work was discussed. The design and production of blue emissive materials based on imidazoles (phenanthroimidazole/diphenylimidazole), as well as their use in blue OLEDs, phosphorescent organic light emitting diodes (PhOLEDs) and chemosensors, were the key topics covered in the introduction. This chapter provided a summary of the thesis‟s principal objective and significance. In chapter 2, a series of luminophores (construction of diphenylimidazole (m-CF3PTPI) groups functionalizing with N1-positions of imidazole moiety) were designed and synthesized for optoelectronics and selective nitroaromatic detection. All the luminophores showed deep blue emission in solution, thin-film and solid phase with reasonable quantum yield as well as good thermal stability (5% weight loss at 258 296○C). From electrochemical analysis as well as theoretical calculations, the HOMO-LUMO energy gaps are found to be good agreement and all of them showed good triplet energy. The luminophores can be explored as host for phosphorescent organic light emitting diodes (PhOLEDs). Furthermore, the m-CF3PTPI derivatives were used as emitters for fluorescent OLEDs and host (m-CF3PTPI-1 and m-CF3PTPI-2) for triplet dopant in PhOLEDs. All the doped devices exhibited near-UV emissions with EL peaks raising ~380395 nm with Commission International deL'Eclairage (CIE) coordinate of (CIEy ~0.09). Of all the devices, m-CF3PTPI-5 (3 wt%) based device displayed maximum EQE (EQEmax) of 2.8%, power efficiency (PEmax) of 0.9 lm/W, current efficiency (CEmax) of 1.3 cd/A, and the brightness of 953 cd/m2. Moreover, the device was further optimized using different host approach. Amongst, SimCP2 displayed the best performance by achieving a high EQEmax of 4.0% that is close to the theoretical limit of fluorescent materials. Furthermore, m-CF3PTPI-1 and m-CF3PTPI-2 possessing triplet energy of 2.67 and 2.63 eV, respectively, were used as host for efficient green (Ir(ppy)3-2.4 eV) PhOLEDs. The m-CF3PTPI-2 based device achieved EQEmax (4.8%), CEmax (17.5 cd/A), PEmax (13.4 lm/W), and maximum brightness (Lmax) of 4695 cd/m2, much higher than that of counterpart m-CF3PTPI-1 based OLED. Taking advantage of the structural functionality, the luminophores were used for the detection of nitro aromatic compounds (including picric acid (PA)). All the luminophores showed good selectivity and high sensitivity towards the PA and the sensing mechanism was carefully investigated by using nuclear magnetic resonance (NMR) spectroscopy and DFT analysis. In chapter-3, as mentioned earlier, the efficient near ultraviolet light-emitting materials are pivotal for organic light emitting devices (OLEDs) because of its long life time, energy saving and for high-quality flat panel displays. In the present investigation, a series of luminophores having electron donating and electron withdrawing group with N1 functionalization were designed which can act as host as well as chemosensors. All TPTI luminophores showing deep blue emission in respective phase (solution, thin-film and solid) with reasonable quantum yield. Electrochemical analysis and theoretical calculations show similar trend for HOMO-LUMO energy gaps calculation and all of them having high triplet energy (2.76-2.91 eV). High triplet energy of the TPTI luminophores are extensively apply for green (Ir(ppy)3 2.4eV) emitting materials. It has been observed that the host TPTI-1 possess the highest efficiency and luminance among all the four hosts in all respects at 15.0 wt% with a maximum power efficacy (PEmax) 24.0 lmW-1, maximum current efficacy (CEmax) 38.2 cdA-1, and maximum external quantum efficiency (EQEmax) 6.8 % with a maximum luminance of 7549 cdm-2 at a turn-on voltage 4.4 V. To have the use of structural functionality, the TPTI luminophores were used for the recognition of nitro aromatic compounds (including picric acid (PA)). All the luminophores showed good selectivity and high catching towards the PA and the sensing mechanism was thoroughly investigated theoretically and experimentally. In chapter-4, a series of N1-functionalized imidazole have been synthesized in very good yield and due to the amphoteric nature it is selectively recognizing the varieties of nitroaromatic compounds. The fluorescence spectra of all luminophores are highly sensitive towards picric acid compared to other nitroaromatics compounds. The fluorescence method is fast response and low cost as well as high selectivity towards other nitroaromatic compounds. Electrochemical analysis were performed and verified by DFT calculations. The electrochemical properties were studied through cyclic voltammetry to calculate the HOMO-LUMO gap and the same confirmed by theoretical study. The stern-volmer quenching
constant and detection limit were found to be 6.68 x 106 M-1 and 446 ppb. The capability of luminophores to recognised PA was estimated by fluorescence, DFT analysis as well as 1H NMR spectroscopies. The potential luminophores were synthesized for the convenient and promising multifunctional sensors for toxic and explosive nitroaromatics analytes. In chapter-5, Phenanthroimidazole (PI) has great proficiency to design efficient near UV deep blue emitting materials due to its bipolarity behavior. The tuning of N1 and C1 Centre of the PI further reveals the improvement of the optical and electronical properties. Thorough investigation is also executed to explore the influence of alkyl chain on the optical and electroluminescence (EL) properties of these emissive materials. The incorporation of alkyl chain in the materials can tune the optical properties, leading to better solid state emission and enhance the photoluminescence quantum yield (PLQY) of thin film ( 74%) as compared to solution ( 65%). The EL spectra also exhibited between 395-420 nm (in the near UV spectral region). Furthermore, boost the device efficiency and color purity, the OLED device is fabricated by doping CBP as host matrix. Selectively, CBP is used as a host because of the similar energy level (HOMO and LUMO) of the synthesized emitters which assist efficient charge trapping. Predominantly, the emitters in OLED device blended with 0.5 wt% concentration, achieved brilliant device efficiency and luminance properties. Among all the synthesized fluorophores, PIPP (0.5 wt%) doped OLED device showed 4.4% of maximum external quantum efficiency (EQEmax), 1202 cd/m2 of highest luminance, 2.2 lm/W of power efficiency (PE), 2.7 cd/A of current efficiency (CE) with Commission International de L‟Eclairage (CIE) coordinates x= 0.17, y= 0.10 (nearer to NTSC standard value). In chapter-6, For full-colour organic light emitting diodes (OLEDs) displays, it is requisite to synthesize new deep blue emitters with high luminous performance. The hybridized local and charge transfer (HLCT) is a remarkable excited state that intermix the local and charge transfer state to assure eminent fluorescence quantum yield. The ambition of this study is to implement a subtle interpretation of photophysical and electroluminescence properties. The density functional theories (DFT) were studied to apprehend more about their geometry and orientations. Herein, two sets of deep blue emitting fluorophores with twisted geometry (Donor-π-Acceptor). In the first set of fluorophores, three blue emissive materials are connected with the triphenylamine (TPA) which act as donor, 9,9 diethylfluorene act as spacer and phenanthroimidazole act as acceptor. The electroluminescence (EL) spectra of the device are very similar to spectra of photoluminescence (PL) in the solution phase. Among all, the best performing 15 wt% MCFBI-fl-TPA based OLED device illustrates a maximum luminance of 3290 cd/m2. The device illustrate 8.2 lmW-1 of power efficiency (PE), 7.9 cdA-1 of current efficiency (CE) and 3.5% of high external quantum efficiency (EQE) with chromaticity coordinates (x, y) of the device are found to be (0.20, 0.23) emits deep blue colour. In the second set of fluorophores, three blue emissive materials are connected with the carbazole (CBZ) which act as donor, 9,9 diethylfluorene act as spacer and phenanthroimidazole act as acceptor. Some degree of overlap of electron cloud between HOMO and LUMO of the fluorophores which results radiative transition rate for this fluorophores to obtain high photoluminescence quantum yield (PLQY) and also favour the locally excited (LE) character. The optical properties show that the peak shows vibrational emission which is located due to the locally excited (LE) character. The PL emission peaking around 418 nm in the DCM solution and 430 nm in solid phase due to the π-π interaction of the fluorophores. The higher quantum yield reveals the coexistence of both LE and CT character in the fluorophores. In chapter 7, deals with the summary and conclusion of the present thesis work. The present thesis works deals with molecular engineering and synthesis of new class of unipolar and bipolar D-π-A) blue organic fluorophores combine with sensing mechanism, with the aim of exploring their potential application in blue OLED. The observations and the conclusions derived from the present investigations are summarized in this chapter
Statistical Inference of Some Life Testing Models under Various Censoring Schemes
No full textIn this dissertation, statistical inferences for the unknown model parameters for various lifetime distributions have been investigated along with different scenarios, including accelerated life testing and competing risks model. Some well-known lifetime models are considered in this purpose. Due to limitations of time, cost, and resources in life-testing experiments, failure times of all experimental units can not be recorded. Thus, different censoring schemes have been suggested as potential responses to such scenarios. In this study, Type I progressive hybrid censoring, adaptive Type II progressive censoring, improved adaptive Type II progressive censoring, unified hybrid censoring, and unified progressive hybrid censoring schemes are considered. In life-testing experiments, a product may fail due to various causes, competing with each other. Such models are dubbed as the competing risks models. It is not always feasible to determine the underlying causes of failure for each experimental unit. In such circumstances, the causes accountable for the failure can only be partially noticed. Further, it is also possible that no failure occurs during the testing of extremely reliable products under ordinary stress circumstances. As a result, many products like this undergo extensive testing at high stress levels in order to see the necessary number of failures in a short period of time. In this study, statistical inferences for unknown model parameters have been obtained under different censoring schemes. Point estimates have been inferred under both classical and Bayesian frameworks. In case of classical estimation, maximum likelihood and maximum product spacing estimation procedures are employed. To compute these estimates some numerical techniques such as Newton’s method, expected maximization, and stochastic expected maximization methods have been adapted. Existence and uniqueness of the maximum likelihood estimates have been studied. The Bayes estimates are derived under symmetric and asymmetric loss functions based on informative and non-informative priors. To obtain the Bayes estimates, Lindley’s approximation method and Markov chain Monte Carlo method have been employed. These samples have been generated by using Gibb’s sampling technique, Metropolis-Hastings algorithm, and importance sampling method. By using the asymptotic normality property of the maximum likelihood estimates, approximate confidence intervals of the unknown model parameters have been constructed from the observed Fisher information matrix. Further bootstrap confidence intervals and highest posterior density credible intervals for the model parameters are derived in the context of comparing interval estimates. An extensive Monte Carlo simulation study has been carried out to compare the performance of proposed estimates. Finally, some real data sets have been analyzed to illustrate the operability and applicability of the proposed methods. Finally, some concluding remarks and future research directions are presented
Development of Anti-Corrosion Coatings for Copper from Electrochemically Exfoliated Few Layered Graphene Nano-Sheets
No full text“Corrosion” is an age-old phenomenon that has crucially affected humanity especially the industrial sector causing substantial economic losses and also compromising safety. In order to counteract this “destructive” force, many mechanisms have been developed out of which “coatings” are a reliable method. Deposition of graphene on copper has found use in electronics, energy storage, and catalysis, among other fields due to the outstanding properties of graphene coupled with copper's strong thermal and electrical conductivity. The current work revolves around the idea of using graphene as a corrosion preventor owing to its exceptional mechanical, electrical, and barrier properties. The concept of electrophoretic deposition has been utilized to coat graphene nanosheets onto copper substrates and the latter has been tested for corrosion preventive behaviour. In present study, few layer graphene nanosheets (FLGNs) were synthesized from pyrolytic graphite by using four different molarities of Na2SO4 (sodium sulphate) aqueous solution in concentrations of 0.5 M, 1.0 M, 1.5 M and 2.0 M via electrochemical exfoliation methodology. FLGNs were also exfoliated from four different acid-based solutions of 1 M concentration (sulphuric, perchloric, nitric and combination of the three). The obtained FLGNs were characterised by XRD spectroscopy, Raman spectroscopy, UV spectroscopy, FTIR spectroscopy, XPS spectroscopy, DLS, SEM, TEM and AFM. X-ray diffraction and Raman is used to investigate structural characteristics and crystal structure arrangement. (002) lattice plane corresponding to basal plane of graphene is identified at around 26° (2θ angle). Raman spectroscopy depicts an increase in disordered value of the FLGNs which may be due to exfoliative activity and surface functionalization. UV, FTIR and XPS confirm the presence of functional groups attached to graphene network which however was not present in large amounts in the case of FLGNs derived from Na2SO4 solutions. Acid based FLGNs on the other hand showed a higher oxygen content pointing out to the presence of hydroxyl and carbonyl groups. The energy transitions occurring with respect to π-π* and n-π* orbitals are detected through the absorbance spectra in UV-visible spectroscopy. A wrinkled, folded sheet type of structure is visible in SEM which appears arranged in a stacked manner. TEM depicts transparent and semi-transparent morphologies which gives idea about the number of layers. AFM supplements the morphological results by giving inputs about the lateral dimensions and approximate number of layers. The obtained FLGNs were dispersed in double distilled water and ultrasonicated for around 3 – 4 hours to get a homogenous solution. This solution is then used for electrophoretic deposition with copper substrates as anode and graphite rod as cathode. The samples are coated through a iterative process consisting of different potentials, time and layers. A set of coatings was made to undergo heat treatment (130°C for 1 hour) to analyse the effects. Methyl violet (surfactant) was dispersed with graphene for creating another set of coatings to view the effects of added environment. The coatings were observed under optical microscope and SEM for morphological characterization along with EDS. SEM micrographs show layer-upon-layer deposition of graphene on copper substrate. The coatings were subjected to scratch tests to determine their adhesion strength and complement the electrochemical measurements. Thereafter, the coatings underwent potentiodynamic polarization and electrochemical impedance spectroscopy tests to assess their corrosion characteristics and coating behaviour. Results from polarisation and impedance testing demonstrated that graphene was an effective corrosion barrier compared to an uncoated substrate. The authors also made an effort to comprehend how the coating's thickness impacts the substrate and the latter's resistance to damage. It was discovered that 2-layer coatings provided the best resistance. In conclusion, graphene's use for corrosion protection seems warranted, however further research is obviously necessary
Dynamic analysis of stiffened Plated Structures Under Moving Forces and Masses
No full textDynamic analysis of structures under moving forces and masses has been one of the most important challenges for engineers during the last few years. The vast application of this time-varying position of forces and masses in many fields of industry has intensified the importance of evaluating the dynamic response of vibrant structures under moving loads. Hence in the present work, the dynamic behavior of rectangular and curved stiffened plated structures are studied. The free vibration and dynamic response analyses of bare and stiffened plates under moving forces and masses are carried out using the finite element method. The stiffened plates depending on their use, accommodate various stiffeners that are placed either concentrically or eccentrically. The stiffener’s orientation in a particular direction is important because of its strength contribution to the plate. Moreover, the stiffener’s size and shape play a crucial role in strengthening the plates keeping the structure’s weight low. All these parameters – stiffener’s disposition, orientation, size, shape, and type contribute productively to the dynamic analysis of the stiffened plates with much significance. Hence, a parametric study for the free vibration characteristics of stiffened plates having various boundary conditions and considering all the above parameters is carried out. The dynamic responses of stiffened plates subjected to moving forces and masses are also investigated using the Newmark integration method. The displacements, velocities and accelerations for each time interval are computed using this approach. The influence of single or multiple moving forces and masses travelling on the plate in a straight or arbitrary path is also reported. An isoparametric quadratic plate bending element with shear deformation is considered to accomplish this task. The plate and stiffener’s stiffness and mass matrices are developed separately and assembled to form the entire structure’s global matrices. A finite element based MATLAB code is established to offer an efficient solution to these analyses. The results are validated with the published ones and the FEAST (Finite Element Analysis of STructures) software solution wherever possible to show the present method’s efficacy. Various numerical examples of unstiffened and stiffened rectangular and curved plates and bridge decks with concentric and eccentric stiffeners for different boundary conditions are presented to show the formulation’s versatility. Some new results obtained by the proposed method are also presented
Stochastic Seismic Response of RC Building and Multi-Span Bridge using Metamodel Approach
No full textVariability in geometry, material qualities, and loads all contribute to the stochasticity of a structure's dynamic response. Stochastic analysis gives a decent representation of the random dynamic responses. Stochastic analysis techniques fall into two broad categories: statistical and non-statistical. Although statistical methods such as Monte Carlo simulation are generally accepted as the gold standard for stochastic analysis, simpler, non statistical alternatives that need less processing resources without sacrificing accuracy are required. High Dimensional Model Representation is a relatively new non-statistical metamodel based methodology that is being compared in this work to traditional response surface methods including Central Composite Design, Box Behnken Design, and Full Factorial Design in the context of a dynamic response analysis. To examine the stochastic reactions, the High Dimensional Model Representation technique is used to the shape of a reinforced concrete frame utilising natural frequencies and nonlinear dynamic analysis. Results for the chosen issues were found to be comparable to those obtained using traditional sampling approaches, but with significantly less computational work required thanks to this technique. The recent earthquakes have shown that bridges, which are essential to transportation networks, are also one of the most susceptible parts of these networks. Bridge damage following an earthquake can hinder rescue attempts and lead to significant financial losses for affected towns. An examination of a bridge's seismic resilience both during and after an earthquake is crucial. While advances in design principles have greatly reduced bridges' seismic vulnerability, the earthquake research community remains deeply concerned about the possibility of damage to the culvert stock. The seismic risk evaluation of bridges makes extensive use of fragility curves. In this analysis, the fragility curves for multi-span bridges are presented, taking into consideration the uncertainties in the bridge's structural and material properties. Modern highways frequently have reinforced concrete box-girder bridges, therefore their seismic safety has been the subject of extensive study. However, the nonlinearity and variability in geometry, material parameters, and loading must be taken into account for a thorough seismic analysis of box-girder bridges. This study introduces a novel nonstatistical metamodel-based approach, high-dimensional model representation, to the generation of metamodels for chosen seismic behavior parameters of a box-girder bridge while accounting for uncertain input variables. Comprehensive finite element analysis is used to assess the seismic responses at the sample locations of the high dimensional model representation. In addition, the derived metamodels are used to construct seismic fragility curves, which is proven to be significantly easier than standard fragility analysis. This method yields conclusions that are consistent with those of two well-known response surface methods (Central Composite Design and Box Behnken Design), but requires vastly less simulations to reach a conclusion. High-dimensional model representation not only greatly simplifies the computing burden of fragility assessments by providing a failure metamodel that incorporates all relevant random variables, but it also gives a far more accurate representation of the underlying system. Direct Monte Carlo simulation is the foundation of the most accurate and robust method of seismic reliability analysis. However, it is difficult to compute since many nonlinear time history studies must be performed. In such cases, a metamodeling strategy using the response surface method can be a useful tool. In order to improve seismic reliability analysis of multi-span bridge piers, this work investigates the benefit of using an adaptive response surface method based on the moving least squares method. Three-dimensional finite element models of bridges are constructed on the OpenSees platform, with accurate representations of the bridge's components like the columns, super structure, bearings, and abutments, allowing for nonlinear time history analysis. High Dimensional Model Representation is a relatively new non-statistical metamodel-based approach that is being evaluated in this study in comparison to traditional response surface methods like Central Composite Design, Box Behnken Design, and Full Factorial Design for use in a dynamic response analysis