No description available.

Enhancing the quality of services in the distribution system is an important topic for power system research. It is imperative to employ precise network modeling and effective simulation tools, and a good system model is the key. This dissertation starts with modifying the building algorithms of Y-admittance and Z-impedance matrices. The Y-matrix will be built according to phase sequences. With the facts that the line self-impedance is significantly greater than the mutual-coupling terms and the existence of a high r/x ratio in distribution, two decoupled load flow methods (Phase-Decoupled¡BPD and Sub-Phase-Decoupled¡BSPD) with Current Injection Model(CIM) were developed. A new Z-matrix building algorithm was also developed in this dissertation. It decomposed the traditional Z into two sub-matrices, the upper and lower triangular matrices respectively. The matrices represent the relationships between the branch current and the bus injection current, and between the bus voltage and the branch current. Enhancing the quality of services will be effectively achieved by a proper capacitor placement technique. This dissertation develops a linear relationships of voltage changes versus the capacitor compensation, the branch current changes versus the capacitor compensation, and loss reductions versus the capacitor compensation. For loss reduction, a linear optimization function was defined to solve the capacitor placement problem. Tests have shown that the proposed methods were suitable for applications to an unbalance distribution system.

No / Due to high penetration of single-phase Photovoltaic (PV) cells into low voltage (LV) distribution networks, several impacts such as voltage unbalance, voltage rise, power losses, reverse power flow arise which leads to operational constraints violation in the network. In this paper, a time series Three Phase Optimal Power Flow (TPOPF) method is proposed to minimize the voltage unbalance in LV distribution networks with high penetration of residential PVs. TPOPF problem is formulated using the current injection method in which the PVs are modelled via a time-varying PV power profile with active and reactive power control. The proposed method is validated on a real LV distribution feeder. The results show that the reactive power management of the PVs helps mitigate the voltage unbalance significantly. Moreover, the voltage unbalance index reduced significantly compared to the case without voltage unbalance minimisation. / Innovate UK GCRF Energy Catalyst Pi-CREST project under Grant number 41358; British Academy GCRF COMPENSE project under Grant GCRFNGR3\1541; Mut’ah University, Jordan

Estimation of the total mission life of a spacecraft is an important issue for the communication satellite industries. For accurate determination of the remaining mission life of the satellite it is essential to estimate the amount of propellant present in the propellant tank of the spacecraft at various stages of its mission life. Because the annual revenue incurred from a typical communication satellite operating at its full capacity is on the order of millions of dollars, premature removal of spacecraft from their orbits results in heavy losses. Various techniques such as the bo okkeeping method, the gas law method, numerical modeling techniques, and use of capacitive sensors have been employed in the past for accurate determination of the amount of propellant present in a spacecraft. First half of the thesis is concerned with sensitivity analysis of the various propellant gauging techniques, that is, estimating the e ects of the uncertainty in the instruments employed in the propellant gauging system on the onboard propellant estimation. This sensitivity analysis is done for three existing propellant gauging techniques – gas injection method, book-keeping method and the propellant tank heating method. A comparative study of the precision with which the onboard propellant is estimated by the three techniques is done and the primary source of uncertainty for all the three techniques is identified. It is illustrated that all the three methods — the gas injection method, the book-keeping method and the propellant tank heating method — are inherently indirect methods of propellant gauging, as a consequence of which, the precision with which the three techniques estimate the residual propellant decreases towards the end of mission life of the spacecraft. The second half of the thesis explores the possibility of using a new propellant tank configuration, consisting of a truncated cone centrally mounted within a spherical propellant tank, to measure the amount of liquid propellant present within the tank. The liquid propellant present within the propellant tank orients itself in a geometry, by virtue of its dominant surface tension force in zero-g condition, which minimizes its total surface energy. Study reveals that the amount of liquid propellant present in the tank can thus be estimated by measuring the height of the propellant meniscus within the central cone. It is also observed that, unlike gas law metho d, bookkeeping method or the propellant tank heating metho d, where the precision of the estimated propellant fill-fraction decreases towards the end-of-life of the spacecraft, for the proposed new configuration the precision increases.

Estimation of the total mission life of a spacecraft is an important issue for the communication satellite industries. For accurate determination of the remaining mission life of the satellite it is essential to estimate the amount of propellant present in the propellant tank of the spacecraft at various stages of its mission life. Because the annual revenue incurred from a typical commu-nication satellite operating at its full capacity is on the order of millions of dollars, premature removal of spacecraft from their orbits results in heavy losses. Various techniques such as the bookkeeping method, the gas law method, numerical modeling techniques, and use of capacitive sensors have been employed in the past for accurate determination of the amount of propellant present in a spacecraft. First half of the thesis is concerned with sensitivity analysis of the various propellant gauging techniques, that is, estimating the effects of the uncertainty in the instruments employed in the propellant gauging system on the onboard propellant estimation. This sensitivity analysis is done for three existing propellant gauging techniques – gas injection method, book-keeping method and the propellant tank heating method. A comparative study of the precision with which the onboard propellant is estimated by the three techniques is done and the primary source of uncertainty for all the three techniques is identified. It is illustrated that all the three methods — the gas injection method, the book-keeping method and the propellant tank heating method — are inherently indirect methods of propellant gauging, as a consequence of which, the precision with which the three techniques estimate the residual propellant decreases towards the end of mission life of the spacecraft. The second half of the thesis explores the possibility of using a new propellant tank configuration, consisting of a truncated cone centrally mounted within a spherical propellant tank, to measure the amount of liquid propellant present within the tank. The liquid propellant present within the propellant tank orients itself in a geometry, by virtue of its dominant surface tension force in zero-g condition, which minimizes its total surface energy. Study reveals that the amount of liquid propellant present in the tank can thus be estimated by measuring the height of the propellant meniscus within the central cone. It is also observed that, unlike gas law method, bookkeeping method or the propellant tank heating method, where the precision of the estimated propellant fill-fraction decreases towards the end-of-life of the spacecraft, for the proposed new configuration the precision increases.

No description available.

This thesis addresses the syntheses towards high quality CdSe and CdTe nanoparticles. Therefore, thermodynamic and kinetic aspects of the hot injection method are investigated. By means of the introduction of a thermodynamically less favored nuclei species the nucleation event of CdSe quantum dot synthesis is affected. Utilizing highly reactive tin or lithium silylamides, primarily formed SnSe or Li2Se nuclei undergo a cation exchange to the demanded CdSe particles. The further growth proceeds without the incorporation of the so called quasi-seed species. In this manner, the mechanism of the cation exchange-mediated nucleation is proven and optimized with respect to the required amount of the quasi-seed species. Furthermore, this protocol is applied to up-scaling attempts to reduce the efforts for optimization to a minimum. Following this, a successful laboratory batch up-scaling is achieved by increasing flask size as well as precursor concentrations by factors of 2 and 10, respectively. A further possibility to thermodynamically influence the hot injection synthesis is the activation of the precursor species. By altering the injection pathway, as compared to the standard synthesis, the precursor species are differently coordinated and hence possess different thermodynamic stabilities. Investigations on the system of CdTe quantum dots lead to the result of a cation activation by the use of the thermodynamically less stable carboxylate ligands instead of phosphonates. Additionally, anion activation is suggested due to a kind of aging of the phosphine ligands via their oxidation by phosphonic acids. Furthermore, it is found that the ratio of Cd-to-Te strongly influences the formation of so called magic-sized clusters. Following the results, the smallest detectable species is determined as a cluster species with a size of 1.8 nm. The role of the magic-sized clusters is not fully resolved, but the initial growth is assumed to occur via monomer deposition onto or the fusion of the observed clusters. On the other hand, cluster dissolution is thermodynamically forced by the decreasing monomer concentration and can simply be explained by the process of Ostwald ripening via the creation of a smaller cluster species. Mechanistically this is explained by the formation of configurational deviations from the ideal closed-shell structure. Finally the inorganic coating of the core quantum dots in investigated. Therefore, homoepitaxial coating is employed to overcome the limit in particle size by introducing additional monomer supply. As a result, following the classical crystallization theory, defined injections of precursor material during the diffusion limited growth regime allow a fine tuning of the final particle size. Nevertheless, homoepitaxial coating inevitably leads to photoluminescence quenching, whereas heteroepitaxial growth usually improves the optical quality. By means of a type I structure, CdSe/CdS/ZnS, the successive ion layer adsoption and reaction mechanism is discussed. Furthermore, alloy structures of CdSe/ZnSe with a radially gradated intermediate shell of CdZnSe are achieved by postsynthetic high temperature treatments. This annealing induces internal diffusion processes and allows exactly adjusting the emission wavelength due to defined shrinkage of the initial core size during the alloying process.

Submitted by Renata Lopes (renatasil82@gmail.com) on 2016-02-11T10:15:45Z No. of bitstreams: 1 marciodecarvalhofilho.pdf: 1308253 bytes, checksum: ce4bec8646b462983e485a5bcad4f5c1 (MD5) / Approved for entry into archive by Adriana Oliveira (adriana.oliveira@ufjf.edu.br) on 2016-02-26T11:53:11Z (GMT) No. of bitstreams: 1 marciodecarvalhofilho.pdf: 1308253 bytes, checksum: ce4bec8646b462983e485a5bcad4f5c1 (MD5) / Made available in DSpace on 2016-02-26T11:53:11Z (GMT). No. of bitstreams: 1 marciodecarvalhofilho.pdf: 1308253 bytes, checksum: ce4bec8646b462983e485a5bcad4f5c1 (MD5) Previous issue date: 2014-08-13 / CAPES - Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / Neste trabalho desenvolveu-se uma ferramenta para análise de falhas, sendo os modelos de diversos equipamentos do sistema elétrico considerados de forma detalhada, permitindo a análise multifásica do sistema, representando-o da maneira mais generalizada e realista possível. A metodologia desenvolvida para análise de falhas baseia-se no método de injeção de correntes a n condutores em coordenadas retangulares, onde utiliza-se o método de Newton-Raphson no processo de solução e todas as grandezas são definidas diretamente em coordenadas de fase. A modelagem de todo o sistema elétrico é realizada baseando-se em elementos que compõem as estruturas dos equipamentos em seus modelos, sendo que estes elementos podem estar conectados das mais diversas maneiras. As próprias condições de curto-circuito são modeladas por meio de elementos, conectados em diferentes configurações. Também a inclusão dos controles é feita de forma otimizada. Com a modelagem considerada, o sistema a ser solucionado é o estritamente necessário, e, portanto, a metodologia apresenta-se bastante eficiente. A metodologia também se mostra bastante flexível, pois é capaz de representar equipamentos com qualquer número de condutores nas mais diversas configurações, permitindo representar desequilíbrios, acoplamentos mútuos, sistemas de aterramento e cabos neutros explicitamente, e permitindo modelar diversos tipos de falhas, dentre outras características. Desta forma, a metodologia possibilita análises bastante completas, sendo que a representação do sistema pode ser feita com o nível de detalhe que for possível e desejável em cada situação. A ferramenta desenvolvida é bastante abrangente sendo capaz de simular sistemas equilibrados ou desequilibrados, radiais ou reticulados, diversos tipos de falhas (como curtos-circuitos em derivação, interno e simultâneo, ou abertura série), podendo ser aplicada em sistemas de transmissão, subtransmissão, distribuição, e industriais, inclusive de grande porte. / In this work a tool for fault analysis was developed, and models of many electrical systems equipment were considered in detail, allowing the analysis of multiphase systems by representing it in a more general and realistic way possible. The methodology developed for fault analysis is based on the current injection method in rectangular coordinates, where the Newton-Raphson method is used in the solution process and all quantities are defined directly in phase coordinates. The modeling of the entire electrical system is made based on elements which assemble the structures of equipment in their models, and these elements can be connected in various ways. Even the short circuit conditions are modeled by elements connected in different configurations. Also the inclusion of controls is done optimally. With the considered modeling the system to be solved is the strictly necessary, and therefore, the method shows to be efficient. The methodology is also very flexible because it is able to represent equipments with any number of conductors in many different configurations, allowing the representation of imbalances, mutual couplings, groundings and neutral cables explicitly, and allowing to model various types of faults, among other features. Therefore, the methodology allows fairly complete analysis, and the representation of the system can be made with the level of detail that is possible and desirable in every situation. The tool developed is quite ample being able to simulate balanced or unbalanced, radial or meshed systems, various types of failures (such as shunt short circuits, internal faults, simultaneous fault, and series opening), it can be applied to the transmission, subtransmission, distribution and industrial systems, including large scale systems.

This thesis addresses the syntheses towards high quality CdSe and CdTe nanoparticles. Therefore, thermodynamic and kinetic aspects of the hot injection method are investigated. By means of the introduction of a thermodynamically less favored nuclei species the nucleation event of CdSe quantum dot synthesis is affected. Utilizing highly reactive tin or lithium silylamides, primarily formed SnSe or Li2Se nuclei undergo a cation exchange to the demanded CdSe particles. The further growth proceeds without the incorporation of the so called quasi-seed species. In this manner, the mechanism of the cation exchange-mediated nucleation is proven and optimized with respect to the required amount of the quasi-seed species. Furthermore, this protocol is applied to up-scaling attempts to reduce the efforts for optimization to a minimum. Following this, a successful laboratory batch up-scaling is achieved by increasing flask size as well as precursor concentrations by factors of 2 and 10, respectively. A further possibility to thermodynamically influence the hot injection synthesis is the activation of the precursor species. By altering the injection pathway, as compared to the standard synthesis, the precursor species are differently coordinated and hence possess different thermodynamic stabilities. Investigations on the system of CdTe quantum dots lead to the result of a cation activation by the use of the thermodynamically less stable carboxylate ligands instead of phosphonates. Additionally, anion activation is suggested due to a kind of aging of the phosphine ligands via their oxidation by phosphonic acids. Furthermore, it is found that the ratio of Cd-to-Te strongly influences the formation of so called magic-sized clusters. Following the results, the smallest detectable species is determined as a cluster species with a size of 1.8 nm. The role of the magic-sized clusters is not fully resolved, but the initial growth is assumed to occur via monomer deposition onto or the fusion of the observed clusters. On the other hand, cluster dissolution is thermodynamically forced by the decreasing monomer concentration and can simply be explained by the process of Ostwald ripening via the creation of a smaller cluster species. Mechanistically this is explained by the formation of configurational deviations from the ideal closed-shell structure. Finally the inorganic coating of the core quantum dots in investigated. Therefore, homoepitaxial coating is employed to overcome the limit in particle size by introducing additional monomer supply. As a result, following the classical crystallization theory, defined injections of precursor material during the diffusion limited growth regime allow a fine tuning of the final particle size. Nevertheless, homoepitaxial coating inevitably leads to photoluminescence quenching, whereas heteroepitaxial growth usually improves the optical quality. By means of a type I structure, CdSe/CdS/ZnS, the successive ion layer adsoption and reaction mechanism is discussed. Furthermore, alloy structures of CdSe/ZnSe with a radially gradated intermediate shell of CdZnSe are achieved by postsynthetic high temperature treatments. This annealing induces internal diffusion processes and allows exactly adjusting the emission wavelength due to defined shrinkage of the initial core size during the alloying process.

Este trabalho baseia-se no estudo e aplicação da Análise Estatística de Energia (SEA). Tal técnica é amplamente empregada nos estudos de vibrações em altas freqüências, dominadas por altas densidades modais e oferecendo toda a solução para o modelo em termos de parâmetros estatísticos. Aplica-se SEA tanto a modelos teóricos e numéricos quanto a modelos experimentais. Qualquer uma das duas abordagens descrita anteriormente tem como objetivo a obtenção dos parâmetros SEA, conhecidos por fator de perda por dissipação interna, fator de perda por acoplamento e densidade modal. Para o estudo e aplicação experimental da técnica SEA utiliza-se o Método de Injeção de Potência, sendo este aplicado a estruturas acopladas do tipo viga, numa configuração em T e estruturas acopladas do tipo placa que formam uma caixa. O estudo numérico e analítico também faz parte deste trabalho, tendo como base o desenvolvimento de uma formulação para vigas relativamente espessas, mostrando a influência geométrica na transmissão da vibração entre subsistemas. Comparações também são feitas entre os resultados obtidos experimentalmente na caixa e na viga T com os obtidos analiticamente e computacionalmente e em ambos os casos estes apresentaram uma boa correlação. Por fim, uma estrutura composta por uma cavidade acústica é estudada e um aparato o para injeção de potência é construído com base no estudo em altas freqüências. / This work is based in the study and application of the Statistical Energy Analysis (SEA), which is applied to high frequencies vibrations characterized by high modal densities and the solution, is given in statistical terms. This analysis is used in numerical, analytical and experimental models and the principal objective is the estimative of the SEA parameters, known by damping loss factors, coupling loss factors and modal densities. The experimental model is based on the Power Injection Method (PIM), and this was applied in coupled structures, like beam type, that was coupled in a T-beam configuration and the other type of coupling was studied in a box type structure. An analytical model was developed in this thesis, it was based on the Timoshenko beam formulation and the possible geometrical effects were studied. The results obtained as experimentally as numerically or analytically were compared and showed a good agreement. Finally, an acoustic cavity was studied and a new display was constructed to inject power in the cavity and a high frequency study was performed.