No description available.

No description available.

Orientador: Jose Sanches Mantovani / Resumo: Neste trabalho propõem-se metodologias para realizar o planejamento de sistemas de distribuição de energia elétrica de média tensão (MT), baixa tensão (BT) e o planejamento integrado de sistemas de média e baixa tensão (MT/BT). Nos modelos de funções objetivos considerados minimizam-se os custos associados à construção, expansão, operação e confiabilidade das redes de MT, BT e MT/BT, considerando a presença de geradores distribuídos e variáveis de natureza estocástica. A geração distribuída presente no planejamento de sistemas de distribuição é avaliada através de metodologias de geração de cenários e análise de risco. Como método de busca de soluções para o problema de planejamento dos sistemas de distribuição é proposta a meta-heurística de busca em vizinhança variável GVNS (General Variable Neighborhood Search). A meta-heurística GVNS trabalha com uma série de estruturas de vizinhanças que permitem explorar o espaço de busca de forma eficiente através dos critérios de diversificação e intensificação, aumentando a probabilidade de obter soluções que não sejam ótimos locais. No planejamento integrado MT/BT, as soluções obtidas são analisadas através de um fluxo de potência integrado entre as redes de MT e BT, considerando as relações de conexão dos transformadores entre estes sistemas. Os algoritmos propostos relacionados ao planejamento de sistemas MT, BT e MT/BT são implementados em linguagem de programação C++ e testado em diferentes sistemas testes de MT (54 barras e 182... (Resumo completo, clicar acesso eletrônico abaixo) / Doutor

Submitted by DIOGO RUPOLO null (rupolo.diogo@gmail.com) on 2017-09-08T14:50:14Z No. of bitstreams: 1 Tese Final Diogo Rupolo.pdf: 4125842 bytes, checksum: 60d451cc4d13afb90cca7e443d7436b1 (MD5) / Approved for entry into archive by Monique Sasaki (sayumi_sasaki@hotmail.com) on 2017-09-11T20:51:49Z (GMT) No. of bitstreams: 1 rupolo_d_dr_ilha.pdf: 4125842 bytes, checksum: 60d451cc4d13afb90cca7e443d7436b1 (MD5) / Made available in DSpace on 2017-09-11T20:51:49Z (GMT). No. of bitstreams: 1 rupolo_d_dr_ilha.pdf: 4125842 bytes, checksum: 60d451cc4d13afb90cca7e443d7436b1 (MD5) Previous issue date: 2017-08-18 / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) / Neste trabalho propõem-se metodologias para realizar o planejamento de sistemas de distribuição de energia elétrica de média tensão (MT), baixa tensão (BT) e o planejamento integrado de sistemas de média e baixa tensão (MT/BT). Nos modelos de funções objetivos considerados minimizam-se os custos associados à construção, expansão, operação e confiabilidade das redes de MT, BT e MT/BT, considerando a presença de geradores distribuídos e variáveis de natureza estocástica. A geração distribuída presente no planejamento de sistemas de distribuição é avaliada através de metodologias de geração de cenários e análise de risco. Como método de busca de soluções para o problema de planejamento dos sistemas de distribuição é proposta a meta-heurística de busca em vizinhança variável GVNS (General Variable Neighborhood Search). A meta-heurística GVNS trabalha com uma série de estruturas de vizinhanças que permitem explorar o espaço de busca de forma eficiente através dos critérios de diversificação e intensificação, aumentando a probabilidade de obter soluções que não sejam ótimos locais. No planejamento integrado MT/BT, as soluções obtidas são analisadas através de um fluxo de potência integrado entre as redes de MT e BT, considerando as relações de conexão dos transformadores entre estes sistemas. Os algoritmos propostos relacionados ao planejamento de sistemas MT, BT e MT/BT são implementados em linguagem de programação C++ e testado em diferentes sistemas testes de MT (54 barras e 182 barras), BT (76 barras) e MT/BT (172 e 412 barras), sob diferentes cenários operacionais. / This work proposes methodologies for the planning of medium voltage (MV), low voltage (LV), and integrated planning of medium and low voltage (MV/LV) systems. In the objective function models are considered the costs associated with the construction, expansion, operation and reliability of MV, LV and integrated MV/LV networks. Distributed generators and stochastic variables are also considered in the models. The distributed generation present in the planning of distribution systems is evaluated through methodologies of scenario generation and risk analysis. As a method of finding solutions to the problem of distribution system planning, the GVNS metaheuristic (General Variable Neighborhood Search) is proposed. The metaheuristic GVNS works with a series of neighborhood structures that allow to explore the search space efficiently through diversification and intensification criteria, increasing the probability of obtaining solutions that are not local optimum. In integrated MV/LV planning, the solutions obtained are analyzed through an integrated power flow between the MV and LV networks, considering the connection ratios of the transformers between these systems. The proposed algorithms related to the planning of MV, LV and integrated MV/LV systems are implemented in C ++ programming language and tested in different distribution systems, MV (54 and 182 bus), LV (76 bus) and MV/LV (172 and 412 bus), under different operating scenarios.

Commercialisées depuis 1996, les plantes génétiquement modifiées produisant une toxine insecticide (toxine Cry) dérivée de Bacillus thuringiensis et appelées plantes Bt ciblent certains Lépidoptères ou Coléoptères ravageurs. Au fil des ans, les surfaces cultivées en plantes Bt sont de plus en plus importantes et contrôlent de larges populations d'insectes. Pour limiter le risque de développement de populations résistantes, une stratégie agricole appelée 'Haute Dose / Zone Refuge' est actuellement recommandée aux Etats-Unis par l'Environmental Protection Agency. Cette stratégie préventive nécessite la plantation d'une 'zone refuge' composée de plantes non-Bt utilisables par le ravageur ciblé et plantée à proximité de la 'zone Bt' qui synthétise une haute dose de toxine Cry. <p><p>Mon projet de recherche s’inscrit dans le cadre de l’évaluation de l'efficacité de cette stratégie et s’articule en deux phases :une phase expérimentale et une phase théorique. La première se concentre sur la caractérisation en laboratoire de l'impact des toxines Cry sur la biologie d'un ravageur. Cette phase constitue un support au volet théorique :la mise au point d’un modèle mathématique évaluant l'efficacité de la stratégie HD/R. L'originalité de ce projet repose entre autre sur l'interactivité entre ces deux volets.<p><p>Volet expérimental. Impact des toxines Cry sur la biologie de Plodia interpunctella. Nous évaluons séparément l'impact d'une gamme de concentrations de deux toxines Cry (CryXX et CryYY) sur une série de paramètres comportementaux et biologiques d'un insecte commun des denrées stockées: Plodia interpunctella (Hübner) (Lepidoptera :Pyralidae). Ces paramètres sont sélectionnés car leur variation pourrait avoir un impact sur l'efficacité de la stratégie HD/R dans le contrôle de la résistance. Il est donc pertinent de les quantifier pour intégrer dans le modèle des ordres de grandeur réalistes et générer des résultats qui ne sont pas uniquement basés sur des spéculations théoriques.<p><p>Volet théorique A. Efficacité de la stratégie HD/R pour des plantes Bt synthétisant une ou deux toxines simultanément. La stratégie 'HD/R' a été développée pour prévenir la résistance envers les plantes Bt synthétisant une seule toxine. Or, depuis 2003, de nouvelles variétés de coton Bt synthétisant simultanément deux toxines Cry sont commercialisées (BollgardII® et WidestrikeTM). Nous évaluons, grâce au modèle que nous avons développé, l'efficacité de cette stratégie lors d'une utilisation exclusive de plantes Bt synthétisant une ou deux toxines.<p><p>Volet théorique B. Impact du ralentissement du développement des insectes sur les plantes Bt sur l'efficacité de la stratégie HD/R. Le volet expérimental met en évidence un allongement de la durée du développement des larves se nourrissant sur une diète contaminée en toxine Cry. Ce ralentissement induit une séparation temporelle entre l'émergence des adultes de la zone Bt et de la zone refuge et perturbe une hypothèse principale de la stratégie HD/R: le croisement aléatoire entre adultes, indépendamment du génotype et de la zone d'origine. Dans ce troisième chapitre, nous étudions l'impact de la perturbation du croisement aléatoire sur l'efficacité de la stratégie HD/R. Nous testons également deux options pour optimiser la stratégie en cas d'asynchronie: l'utilisation de plantes Bt synthétisant une faible concentration en toxine (atténuant le décalage entre l'émergence des adultes) ou l'augmentation de la taille de la zone refuge (favorisant la survie des individus porteurs d'allèle de sensibilité et donc optimisant la dilution de la résistance à la génération suivante). <p><p>Ce travail s'intègre dans une problématique actuelle et utilise des outils de biologie théorique (théories de la dynamique et de la génétique des populations) ainsi que le développement d'un modèle mathématique. Il apporte des éléments de réponse et de réflexion sur l'optimisation de la gestion de la résistance des insectes mais c'est aussi une illustration de la complémentarité entre la biologie expérimentale et théorique.<p><p><p>/<p><p>On the market since 1996, genetically modified plants synthesizing an insecticidal toxin (Cry toxin) stemmed from Bacillus thuringiensis, called Bt plants, target several insect pests (Lepidoptera or Coleoptera). Bt crops cover increasingly larger areas and control important pest populations The Insect Resistance Management Strategy (IRM) strategy currently recommended in the U.S.A. to limit the development of resistant populations is the High Dose / Refuge zone (HD/R) strategy. This pre-emptive strategy requires a refuge zone composed by non-Bt plants, usable by the target insect and in close proximity of the Bt zone synthesizing a high toxin concentration.<p><p>My research project contributes to the effectiveness assessment of this HD/R strategy. It is structured on two main parts: an experimental, and a theoretical section. The first part characterizes the impact of Cry toxins on the biology of an insect pest. It is the basis of the theoretical part: the implementation of a mathematical model, which evaluates the effectiveness of the HD/R strategy.<p>The originality of this project is based on the interactivity of these two components.<p><p>Experimental section. Impact of the Cry toxins on the biology of Plodia interpunctella. We assess the impact of a range of concentrations of two Cry toxins (CryXX et CryYY) on several behavioural and biological parameters of a common pest of stored products: Plodia interpunctella (Hübner) (Lepidoptera :Pyralidae). These parameters are selected because their variation could influence the effectiveness of a HD/R strategy. So, it is important to quantify these parameters so that realistic values can be integrated in our model. The results of the model are thus not based on theoretical assumptions alone.<p> <p>Theoretical section A. Effectiveness of a HD/R strategy with Bt plants synthesizing one or two toxins. Initially, the HD/R strategy has been developed to limit the resistance towards Bt plants synthesizing one toxin. However, since 2003, new Bt cotton varieties synthesize two toxins simultaneously (BollgardII® et WidestrikeTM). We assess, with our model, the effectiveness of this strategy for Bt plants synthesizing one or two toxins.<p><p>Theoretical section B. Impact of the slowing down of the insect development reared on Bt plants on the effectiveness of the HD/R strategy. The experimental part demonstrates that larvae reared on a Bt diet have a protracted development duration. The consequence of this is a temporal separation between adult emergence in the two zones (Bt zone and refuge zone). This could affect the main assumption of the HD/R strategy, i. e. random mating independently of the genotype and of the native zone. In this third chapter, we study the impact of random mating disruption on the effectiveness of a HD/R strategy. We test two options to optimise the strategy in case of asynchrony: the use of Bt plants synthesizing a lower toxin concentration (limiting emergence asynchrony) or increasing the refuge zone size (favouring the survival of insect carrying one or two susceptible allele and thus optimising the dilution of resistance at the next generation). <p><p>This work is applied to a current issue. It uses some of the tools of theoretical biology (theories of population dynamics and population genetics) and develops a mathematical model. It provides some responses and some elements of thought about insect resistance management. It is also an illustration of the complementarity between experimental and theoretical biology.<p> / Doctorat en Sciences / info:eu-repo/semantics/nonPublished

The main objective of my dissertation is to analyze and compare the socio-ecological implications of the adoption of genetically modified (GM) seeds and alternative agroecological farming methods for farming communities in Alberta, Canada and Andhra Pradesh, India localities situated in contrasting geopolitical, socio-cultural, and structural-institutional contexts in the global economy. For this research, the adoption of GM canola in Alberta and GM cotton in Andhra Pradesh are used as comparative case studies to explore the qualitative impact of agricultural biotechnology on farming communities. Many studies have examined the potential impact of GM crops, but few have looked beyond economic cost-benefit analysis. In this dissertation, I examine social and cultural aspects of farmer decision-making in the adoption of the new seed technology, farmer receptivity to new cropping methods, knowledge translation between laboratory and farmer, and the impact of global knowledge-based technology on local knowledge systems, socio-cultural practices, the nature-society relationship, and gender relations. I use a global ethnography methodology and draw on a series of field interviews with farmers to provide sociological insight into how global processes of the Gene Revolution impact different farming communities in different localities in the world-economy. In this dissertation I argue that the debate about the new agricultural technologies (e.g. GM seeds), the environment and agrarian crises should not be narrowed to the question of new technologies per se. Rather it should be understood from an agrarian political ecology perspective articulating political economy (neoliberal governance at global, national and provincial levels, and the processes of dispossession of primary agricultural producers from their means and conditions of production), socio-cultural systems (the construction of hegemonic discourse about genetically modified organisms, agricultural deskilling, gender relations), and ecosystems (a process of mastering nature, monoculturization, environmental risks, metabolic rift) in the context of neoliberal globalization. My fieldwork study of the Gene Revolution provides closer, more fine-grained research and analysis of its impacts with sensitivity to local class and status, gender and cultural issues, and the ways in which farmers technology adoption decisions can dramatically alter overall quality of life, local knowledge systems, community development, the sustainability of agriculture and the ecosystem itself.

La génération d'onde THz de grande pureté spectrale par photomélange est une technique très prometteuse afin de réaliser des oscillateurs locaux THz performants. Nous avons donc proposé une approche originale consistant à associer un laser bi-fréquence émettant autour de 1 µm à un photomélangeur de bande interdite compatible. Le choix de cette longueur d'onde permet la réalisation de lasers pompés diodes compacts et peu onéreux ainsi que l'utilisation de photoconducteurs présentant les propriétés électriques requises. <br />Ainsi, nous avons développé 2 lasers bi-fréquence amplifiés utilisant des milieux actifs (KGW et CaF2) dopés Yb dont l'utilisation permet de générer des puissances optiques supérieurs à 1 W ainsi qu'un signal de battement électrique continu de bonne pureté spectrale (<30 kHz).<br />Nous avons ensuite étudié et caractérisé 2 matériaux photoconducteurs compatibles avec une illumination à 1 µm : l'InGaAsN et l'In.23Ga.77As-BT épitaxié à basse température (BT) sur substrat métamorphique et dopé Be. Les propriétés de ces deux matériaux ont été étudiées et comparées avec celles du GaAs-BT.<br />Après avoir modélisé le fonctionnement de photomélangeurs (en prenant en compte la participation des trous) nous avons effectué des expériences de photomélange : nous avons détecté un signal de quelques dizaines de nW dont la fréquence a pu être accordée jusqu'à 2 THz.<br />Enfin, nous avons proposé un nouveau type de photomélangeur guide vertical. Les modélisations ont montré que la puissance THz émise (0,2 mW à 1 THz), l'accordabilité (0-3 THz) et la pureté spectrale du signal généré (< 30 KHz) de cette source devraient en faire une des plus attractive dans cette gamme de fréquence.

No description available.

This project attempts to quantify the integrity of the fixation of total hip arthro- T plasties (THAs) by observing vibration signal features. The aim of this thesis is, therefore, to find the signal differences between firm and loose prosthesis. These difference will be expressed in different transformed domains with the expectation that a certain domain will provide superior results. Once the signal differences have been determined they will be examined for their ability to quantify the looseness. Initially, a new definition of progressive, femoral component loosening was created, based on the application of mechanical fit, involving four general conditions. In order of increasing looseness the conditions (with their equivalent engineering associations) are listed as, firm (adherence), firm (interference), micro-loose (transition) and macro-loose (clearance). These conditions were then used to aid in the development and evaluation of a simple mathematical model based on an ordinary differential equation. Several possible parameters well suited to quantification such as gap displacement, cement/interface stiffness and apparent mass were the identified from the model. In addition, the development of this model provided a solution to the problem of unifying early and late loosening mentioned in the literature by Li et al. in 1995 and 1996. This unification permitted early (micro loose) and late (macro loose) loosening to be quantified, if necessary, with the same parameter. The quantification problem was posed as a detection problem by utilising a varying amplitude input. A set of detection techniques were developed to detect the quantity of a critical value, in this case a force. The detection techniques include deviation measures of the instantaneous frequency of the impulse response of the system (accuracy of 100%), linearity of the systems response to Gaussian input (total accuracy of 97.9% over all realisations) and observed resonant frequency linearity with respect to displacement magnitude (accuracy of 100%). Note, that as these techniques were developed with the model in mind their simulated performance was, therefore, considerably high. This critical value found by the detector was then fed into the model and a quantified output was calculated. The quantification techniques using the critical value approach include, ramped amplitude input resonant analysis (experimental accuracy of 94%) and ramped amplitude input stochastic analysis (experimental accuracy of 90%). These techniques were based on analysing the response of the system in the time-frequency domain and with respect to its short-time statistical moments to a ramping amplitude input force, respectively. In addition, other mechanically sound forms of analysis, were then applied to the output of the nonlinear model with the aim of quantifying the looseness or the integrity of fixation of the THA. The cement/interface stiffness and apparent mass techniques, inspired by the work of Chung et.al. in 1979, attempt to assess the integrity of fixation of the THA by tracking the mechanical behaviour of the components of the THA, using the frequency and magnitude of the raw transducer data. This technique has been developed fron the theory of Chung etal but with a differing perspective and provides accuracies of 82% in experimentation and 71% in simulation for the apparent mass and interface stiffness techniques, respectively. Theses techniques do not quantify all forms of clinical loosening, as clinical loosening can exist in many different forms, but they do quantify mechanical loosening or the mechanical functionality of the femoral component through related parameters that observe reduction in mechanical mass, stiffness and the amount of rattle generated by a select ghap betweent he bone/cement or prosthesis/cement interface. This form of mechanical loosening in currently extremely difficult to detect using radiographs. It is envisaged that a vibration test be used in conjunction with radiographs to provide a more complete picture of the integrity of fixation of the THA.

Ferroelectric ceramics are very promising materials for a variety of piezoelectric applications such as high permittivity dielectrics, piezoelectric sensors, piezoelectric/electrostrictive transducers, actuators, electro-optic devices, etc. Among the commercially viable ferroelectric ceramics, the lead-zircon ate-titivate Pb(Zr1-xTix)O3 (PZT) based ceramics have dominated the market due to their superior piezoelectric and dielectric property along with other advantages like high electromechanical coupling, ease of processing and low cost. However, the toxicity of lead based materials, and its volatility at processing temperatures is a serious health and environmental concern. Several legislations against lead-based products have been passed all over the world in order to encourage identification of alternative lead-free materials for these applications. As a consequence, there has been a remarkable surge in efforts by researchers on identifying lead-free alternatives for piezoelectric applications. A larger emphasis has been placed on perovskite based ceramics since in addition to possessing excellent properties, their relatively simple structure facilitates understanding structure-property relationships which are important for developing novel high performance materials. Na1/2Bi1/2TiO3 (NBT) and its solid solutions are one of the leading classes of perovskite ceramics, which show promising ferroelectric, piezoelectric and dielectric property thereby having the potential to replace PZT based ferroelectrics. The parent compound NBT is ferroelectric with large ferroelectric polarization (~40 C/cm2), promising piezoelectric properties with 0.08% maximum strain and longitudinal piezoelectric coefficient (d33) ~ 80 pC/N. Though NBT was discovered nearly six decades ago, a clear understanding of its structure remained elusive for a long time since different characterization techniques yielded contradicting reports on its structure and nature of phase transformation. However, rapid advances in characterization techniques in recent years have led to uncovering of new results, thereby shedding light on the true structure of NBT. X-ray and neutron diffraction studies in the past have shown that NBT exhibits rhombohedral (R3c) structure at room temperature, which undergoes a gradual transformation into tetragonal (P4bm) structure at ~230oC. However, recent characterization of both single crystal and powder of NBT using high resolution x-ray diffraction showed that the room temperature structure is not purely rhombohedral and the structure can be better modeled with a monoclinic (Cc) structure. In contrast to x-ray and neutron diffraction, electron diffraction studies have shown evidence for the presence of planar disorders, corresponding to in-phase octahedral tilts in the sample which cannot be accounted for by either R3c or Cc structure. In addition, EXAFS, x-ray and neutron total scattering studies, diffuse scattering studies, etc. have shown that the structural parameters obtained from bulk diffraction techniques are significantly different from the local structure of the material. Similar ambiguities have been observed even in NBT based solid solutions like BaTiO3, K1/2Bi1/2TiO3, etc. which show enhanced properties at the morphotropic phase boundary (MPB). A major breakthrough in understanding the structural complexity involved in NBT based solid solutions was achieved when it was found that the structure of the MPB compositions were sensitive to electric field. This led to solving the mystery behind the appearance of cubic-like phase at some of the MPB compositions where the application of electric-field resulted in the transformation of the structure into a co-existence of rhombohedral and tetragonal phases. Observation of an electric-field-induced structural transition at the MPB compositions was expected, because the MPB signifies instability in the system and even a minor external force can significantly influence the system. However, we have found that the structure of even pure NBT is significantly influenced by electric field and the framework of this thesis is based on this particularly important result. The intrinsic tendency of the electric field to affect the structure of NBT is a major factor which needs to be considered when studying similar phase transitions in the MPB compositions of NBT-substituted systems also. This was not taken into account by other research groups, and they assumed that the instability associated with the MPB was the only major factor involved in the electric-field induced transitions. A simple but highly effective strategy of grinding the electrically poled pellet into fine powder and then collecting x-ray diffraction patterns, facilitated elimination of preferred orientation in the sample. Thus, structural analysis by Rietveld refinement was possible even on the poled sample, which has not been carried out by any other groups on any ferroelectric ceramics so far. The initial part of the thesis deals with addressing the structural complexity of pure NBT, wherein the effect of electric field on the bulk structure as well as the local structure was studied in great detail. Later on, similar concepts are used to investigate BaTiO3 and K1/2Bi1/2TiO3 substituted NBT also. The first chapter of the thesis provides a brief introduction to the field of ferroelectrics, perovskite structure and their phase transition. An exposure to concepts like relaxor ferroelectrics, morphotrophic phase boundary, octahedral tilting, etc. has been provided. Then, a detailed overview of the existing literature related to the structure of NBT and its phase transition studies with temperature has been discussed. The details of the experimental procedures, characterization techniques used, and some theory behind these techniques have been provided in chapter 2. The third chapter deals with the room temperature structural characterization of pure NBT using techniques like x-ray diffraction, neutron diffraction, electron diffraction and EXAFS analysis. The results of these structural characterizations are also complemented with first-principles calculation study of the ground state structure of NBT, dielectric and ferroelectric characterization, and ageing studies. While x-ray and neutron diffraction clearly established electric-field induced structural transition from a monoclinic (Cc) to rhombohedral (R3c) structural transition, first principles calculation showed that the monoclinic phase is not stable and hence cannot be the ground state structure of NBT. Also, the possibility of the monoclinic features appearing in the x-ray diffraction solely due to micro structural effects by nano-sized domains was discussed. Comparison of electron diffraction of poled and unpoled samples of NBT showed that the in-phase tilted regions were greatly suppressed in the poled samples. Even HRTEM images showed that the unpoled samples had a very high concentration of strain heterogeneity in them, which was absent in the poled samples. This gave a direct evidence of correlation between observation of monoclinic phase and the presence of in-phase tilted regions in the unpoled samples. It was proposed that the strain caused by these in-phase tilted disorders caused distortion in the original rhombohedral lattice thereby making the structure appear monoclinic. Application of electric field causes the in-phase octahedral tilt disorders to vanish, thereby even the monoclinic features observed in the XRD also disappear. The fourth chapter discusses the consequences of poling on the high temperature phase transition behavior of NBT. We have used temperature dependent x-ray and neutron diffraction, Raman spectroscopy and EXAFS analysis whose results were correlated with the anomalies observed in temperature dependent dielectric and polarization studies. We found that the poled sample shows a sharp anomaly at the depolarization temperature (Td) in all the characterization techniques used, in contrast to a diffuse or negligible effect seen in the unpoled sample. The depolarization temperature was found to be associated with introduction of structural disorder in the sample in the form of in-phase octahedral tilts. This also gave rise to a normal to relaxor ferroelectric transition at Td, and this relaxor behavior persisted even after cooling the sample to room temperature. An intermediate cubiclike phase was observed from x-ray diffraction at around 300C wherein the rhombohedral phase vanishes and the tetragonal phase begins to appear. Even single crystal study of NBT in the past showed sudden disappearance of the domains at 300C, even though they were visible at both above and below this temperature. This effect was called isotropization, and was postulated to arise due to extremely small domains which made the system isotropic. However, our neutron diffraction pattern showed that in-phase tilted superlattice reflections persisted at this temperature which meant that the structure was not truly cubic at this temperature. Further, a neutron diffraction study at higher temperatures showed that the in-phase tilted superlattice reflections persisted even above the cubic phase transition temperature, in corroboration with similar reports from high temperature electron diffraction. Chapter five deals with the BaTiO3 substituted NBT system, which has gained tremendous interest in the last decade as a viable piezoelectric ceramic for commercial applications. Though a large number of groups have already carried out exhaustive studies on this system, most of the work concentrated mainly on the MPB compositions which showed enhanced piezoelectric properties. In this chapter, we highlight some important findings in the pre-MPB and post-MPB compositions. Using room-temperature and high temperature x-ray diffraction, we show that there exists a subtle compositional phase boundary at x = 0.03, which disappears upon poling the sample. While the monoclinic phase in pure NBT becomes cubiclike at this composition, the depolarization temperature (Td) also slightly increases up to this composition and then decreases upon further Ba substitution. Similar studies were also carried out with compositions containing slightly excess bismuth in them (0.1 mol %), whose purpose was to negate the effects of Bi-vaporization during sintering. It was found that while the compositional phase boundary remained essentially unchanged, there was a decrease in Td for all the compositions. It was also realized that the addition of excess bismuth improved the overall piezoelectric property of the system. Studies on higher compositions of Ba in the post-MPB regions further revealed two additional compositional phase boundaries. A criticality in the coercive field and spontaneous tetragonal strain was observed at x = 0.2, which was found to be associated with crossover from a long-period modulated tetragonal phase (for x < 0.2) to a no modulated tetragonal phase (for x > 0.2). Near the BT rich end (x ~ 0.7), the system exhibits a crossover from normal to a diffuse/relaxor ferroelectric transition with increasing Na1/2Bi1/2 substitution. The onset of relaxor state by Na1/2Bi1/2 substitution on the Ba-site, was shown to increase the spontaneous tetragonal strain in the system. This was because of the enhancement in the covalent character of the A-O bond by virtue of the Bi+3 6s2 lone pair effect, and it also led to a sudden increase in the tetragonal-to-cubic transition temperature. This was in contrast to other chemical modifications of BT reported in the past (like Zr, Sn, Sr, etc.) where the relaxor state is accompanied by a weakening of the ferroelectric distortion and a decrease in the critical temperature. Finally, chapter six covers the effect of electric field induced phase transition in K1/2Bi1/2TiO3 substituted NBT. Visual observation showed that while the compositions (x < 0.2) behaved similar to pure NBT, wherein the structure became purely rhombohedral upon poling, the effect of electric field was negligible in the post-MPB compositions (x > 0.2). In addition, the peaks in the annealed samples were considerably overlapping which made identifying the structural transitions at the MPB compositions difficult using Rietveld analysis. However, comparison of the FWHM of the {200}pc peaks of compositions x < 0.2 showed that the FWHM began to increase suddenly for x > 0.15 indicating emergence of the tetragonal phase. Also, all the compositions showed an increase in the {200}pc peak FWHM by 0.03 after poling. The depolarization temperature showed only slight variation in the pre-MPB compositions, but showed a minimum at the MPB compositions. Temperature dependent dielectric studies further showed that for the post-MPB compositions, the system remains relaxor even after poling.