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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
101

Estudo de um atuador planar de indução

Baggio Filho, Nolvi Francisco January 2012 (has links)
O presente trabalho trata do estudo, análise, construção e teste de uma nova configuração para um atuador planar. O dispositivo, que apresenta uma movimentação sobre o plano com dois graus de liberdade a partir de um único dispositivo de tração, é formado por um carro, também chamado de primário, que apresenta dois enrolamentos trifásicos independentes, ortogonais entre si, montados em um núcleo ranhurado de material compósito magneticamente macio de grão isolado; e por um estator, também chamado de secundário, formado por uma chapa de alumínio plana montada sobre um núcleo ferromagnético igualmente plano, formando a área de trabalho ou de movimentação do primário. Através de um acionamento trifásico, os enrolamentos produzem campos magnéticos viajantes, fazendo com que correntes elétricas induzidas apareçam nos materiais eletricamente condutores do secundário. A interação entre os campos magnéticos e as correntes induzidas proporciona o aparecimento de uma força planar de propulsão na direção do campo magnético viajante, responsável pelo deslocamento do primário sobre a área de trabalho, definida pelo secundário. O atuador apresenta uma distribuição espacial da densidade de fluxo magnético em toda a sua estrutura. Este trabalho preocupa-se em analisar analítica, numérica e experimentalmente os fenômenos eletromagnéticos envolvidos, tanto em regime estático como dinâmico. O emprego de duas configurações para o secundário, utilizados separadamente, é investigado: no caso 1 é montado um núcleo de material ferromagnético sobre o qual é colocada uma chapa de alumínio; já no caso 2, é retirado o alumínio do conjunto, mantendo-se o mesmo material ferromagnético, a saber, aço maciço 1020. Uma análise estática e dinâmica, a partir do método dos elementos finitos tornou possível a verificação da densidade de fluxo magnético no entreferro e da distribuição da densidade de corrente elétrica induzidas nos materiais do secundário em função da excitação trifásica dos enrolamentos do primário, bem como a obtenção dos seus efeitos sobre a força planar de propulsão, considerando as duas configurações propostas para o estator. Além disso, pode-se comparar esses resultados, direta ou indiretamente, como os resultados analíticos e experimentais obtidos. Esses resultados apontam que existem diferenças significativas na utilização das duas configurações, indicando que o caso 1, quando utilizado de maneira adequada no sistema, produz uma melhor resposta de força em função da excitação elétrica. / The present work presents the study, analysis, implementation and test of a new type of planar actuator, the induction planar actuator with orthogonal windings. The device, which presents movement over the plan with two degrees of freedom from a unique traction device, is formed by a car, also called primary, which presents two three-phase independent winding, orthogonal among each other, assembled on a slotted core made of grain insulated soft magnetic composite material and by a stator, also called secondary, formed by an aluminum plate assembled over a plan ferromagnetic core equally plan, forming a work area or of primary movement. Through the three-phase operation drive, the windings produce traveling magnetic fields, having the electric induced current to appear at the electrically conductor materials of the secondary. The interaction between the magnetic fields and the induced currents provides the appearance of a planar traction force towards the traveling magnetic field, responsible for the displacement of the primary over the work area, defined by the secondary. The actuator presents magnetic flow density spatial distribution in all its structure. This paper is concerned about analyzing analytically, numerically and experimentally the phenomena involved as in steady as dynamic state. The employment of two settings to the secondary used separately is argued: in case 1 a ferromagnetic core is assembled over which is placed an aluminum plate; in case 2 the aluminum is taken off the setting, maintaining the same ferromagnetic material (steel 1020). Dynamic and statics analysis, from the finite elements method, made the verification of the magnetic flux density possible in the air gap and the distribution of the electric current density induced on the material of the secondary due to the three-phase excitation of the winding of the primary, as well as the obtainment of its effects over the planar traction force, regarding the two settings proposed for the stator. Besides, it’s possible to compare these results, direct or indirectly as analytical and experimental results obtained. These results point the there are meaningful differences at both settings, indicating that case 1, when used adequately in the system, produces better force response due to the electric excitation.
102

Metodologia de análise e caracterização de materiais compósitos magnéticos macios aplicados em atuador planar de indução

Mota Neto, João January 2015 (has links)
O trabalho apresenta o desenvolvimento de uma metodologia denominada modelo de núcleo reduzido, aplicada para avaliar o desempenho de máquinas elétricas no que tange a geometria e materiais empregados na fabricação do núcleo completo. Para fins de validação da metodologia utiliza-se um Atuador Planar de Indução Trifásico com dois graus de liberdade, comparando os resultados numéricos e experimentais. Através desta metodologia, pode-se realizar a análise dos fenômenos eletromagnéticos ocorridos no núcleo completo por meio da avaliação de seu modelo reduzido, composto neste caso por 33% do núcleo completo empregado no Atuador Planar de Indução Trifásico. A comprovação da metodologia do modelo de núcleo reduzido ocorreu através da fabricação de uma bancada de testes, composta por uma célula de carga para realizar aquisição da força de propulsão planar, interface de potência e os núcleos reduzidos com seguintes materiais ferromagnéticos: compósitos SMC 1P Somaloy 500®, Ferro resinado e Aço ABNT 1020. Com auxilio da estrutura de testes, validou-se o modelo numérico dos três núcleos reduzidos quanto a força de propulsão planar. Na análise dos dados experimentais e numéricos, o material Ferro resinado apresentou a diferença 14% referente a força de propulsão planar, sendo a maior diferença entre os materiais estudados. Com a convergência dos resultados experimental e numéricos, realiza-se a comparação numérica entre os núcleos reduzidos e completos utilizando-se os três materiais ferromagnéticos. A análise numérica do núcleo reduzido com o material SMC 1P Somaloy 500® apresentou o fator de relação médio da força de propulsão planar de 2,65 em relação ao núcleo completo. O núcleo completo com Aço ABNT 1020 resultou no consumo médio de 56,7Watts para gerar a força de propulsão planar de 1 Newton. Dessa forma, proporciona-se uma ferramenta de maior rapidez para fabricação e avaliação do desempenho de materiais ferromagnéticos utilizados no núcleo completo da máquina elétrica. / This paper presents the development of a methodology denominated low core model applied to evaluate the performance of electrical machines with respect to geometry and materials used in manufacturing of the complete core. For validation purposes of the methodology is used a Planar Three-phase Induction Actuator with two degrees of freedom, comparing the experimental and numerical results. Through this methodology, it is possible to perform the analysis of electromagnetic phenomena occurring in the complete core based evaluation of the reduced model, made in this case with 33% of the full core employed in the Planar Three-phase Induction Actuator. The verification of the reduced core model methodology occurred through the manufacture of a testing bench, which is composed of a load cell to realize the acquisition of the planar propulsion force, potency interface and reduced cores with the following ferromagnetic materials: SMC 1P Somaloy 500® composites, resinated Iron and Steel ABNT 1020. With the help of the test structure, it was validated the numerical model of the three reduced cores regarding to the planar propulsion force. In the analysis of experimental and numerical data, the resinated Iron material showed a 14% difference concerning the strength of the planar propulsion, which is the biggest difference between the materials studied. With the convergence of the experimental and numerical results, a numerical comparison is performed between the reduced and complete cores using the three ferromagnetic materials. The numerical analysis of the reduced core with the SMC 1P Somaloy 500® material showed the average ratio of the planar factor propulsive force of 2.65 when compared with the complete core. The complete core with ABNT 1020 Steel resulted in an average consumption of 56.7 Watts to generate a planar propulsive force of 1 Newton. Thus, it is provided a faster tool for manufacturing and evaluation of ferromagnetic materials performance used in the complete core of the electric machine.
103

Estudo de um atuador planar de indução

Baggio Filho, Nolvi Francisco January 2012 (has links)
O presente trabalho trata do estudo, análise, construção e teste de uma nova configuração para um atuador planar. O dispositivo, que apresenta uma movimentação sobre o plano com dois graus de liberdade a partir de um único dispositivo de tração, é formado por um carro, também chamado de primário, que apresenta dois enrolamentos trifásicos independentes, ortogonais entre si, montados em um núcleo ranhurado de material compósito magneticamente macio de grão isolado; e por um estator, também chamado de secundário, formado por uma chapa de alumínio plana montada sobre um núcleo ferromagnético igualmente plano, formando a área de trabalho ou de movimentação do primário. Através de um acionamento trifásico, os enrolamentos produzem campos magnéticos viajantes, fazendo com que correntes elétricas induzidas apareçam nos materiais eletricamente condutores do secundário. A interação entre os campos magnéticos e as correntes induzidas proporciona o aparecimento de uma força planar de propulsão na direção do campo magnético viajante, responsável pelo deslocamento do primário sobre a área de trabalho, definida pelo secundário. O atuador apresenta uma distribuição espacial da densidade de fluxo magnético em toda a sua estrutura. Este trabalho preocupa-se em analisar analítica, numérica e experimentalmente os fenômenos eletromagnéticos envolvidos, tanto em regime estático como dinâmico. O emprego de duas configurações para o secundário, utilizados separadamente, é investigado: no caso 1 é montado um núcleo de material ferromagnético sobre o qual é colocada uma chapa de alumínio; já no caso 2, é retirado o alumínio do conjunto, mantendo-se o mesmo material ferromagnético, a saber, aço maciço 1020. Uma análise estática e dinâmica, a partir do método dos elementos finitos tornou possível a verificação da densidade de fluxo magnético no entreferro e da distribuição da densidade de corrente elétrica induzidas nos materiais do secundário em função da excitação trifásica dos enrolamentos do primário, bem como a obtenção dos seus efeitos sobre a força planar de propulsão, considerando as duas configurações propostas para o estator. Além disso, pode-se comparar esses resultados, direta ou indiretamente, como os resultados analíticos e experimentais obtidos. Esses resultados apontam que existem diferenças significativas na utilização das duas configurações, indicando que o caso 1, quando utilizado de maneira adequada no sistema, produz uma melhor resposta de força em função da excitação elétrica. / The present work presents the study, analysis, implementation and test of a new type of planar actuator, the induction planar actuator with orthogonal windings. The device, which presents movement over the plan with two degrees of freedom from a unique traction device, is formed by a car, also called primary, which presents two three-phase independent winding, orthogonal among each other, assembled on a slotted core made of grain insulated soft magnetic composite material and by a stator, also called secondary, formed by an aluminum plate assembled over a plan ferromagnetic core equally plan, forming a work area or of primary movement. Through the three-phase operation drive, the windings produce traveling magnetic fields, having the electric induced current to appear at the electrically conductor materials of the secondary. The interaction between the magnetic fields and the induced currents provides the appearance of a planar traction force towards the traveling magnetic field, responsible for the displacement of the primary over the work area, defined by the secondary. The actuator presents magnetic flow density spatial distribution in all its structure. This paper is concerned about analyzing analytically, numerically and experimentally the phenomena involved as in steady as dynamic state. The employment of two settings to the secondary used separately is argued: in case 1 a ferromagnetic core is assembled over which is placed an aluminum plate; in case 2 the aluminum is taken off the setting, maintaining the same ferromagnetic material (steel 1020). Dynamic and statics analysis, from the finite elements method, made the verification of the magnetic flux density possible in the air gap and the distribution of the electric current density induced on the material of the secondary due to the three-phase excitation of the winding of the primary, as well as the obtainment of its effects over the planar traction force, regarding the two settings proposed for the stator. Besides, it’s possible to compare these results, direct or indirectly as analytical and experimental results obtained. These results point the there are meaningful differences at both settings, indicating that case 1, when used adequately in the system, produces better force response due to the electric excitation.
104

Diffusion and perfusion MRI and applications in cerebral ischaemia

Calamante, Fernando January 2000 (has links)
No description available.
105

Conformal Maps, Bergman Spaces, and Random Growth Models

Sola, Alan January 2010 (has links)
This thesis consists of an introduction and five research papers on topics related to conformal mapping, the Loewner equation and its applications, and Bergman-type spaces of holomorphic functions. The first two papers are devoted to the study of integral means of derivatives of conformal mappings. In Paper I, we present improved upper estimates of the universal means spectrum of conformal mappingsof the unit disk. These estimates rely on inequalities  obtained by Hedenmalm and Shimorin using Bergman space techniques, and on computer calculations. Paper II is a survey of recent results on the universal means spectrum, with particular emphasis on Bergman spacetechniques.Paper III concerns Bergman-type spaces of holomorphic functions in subsets of $\textbf{C}^d$ and their reproducing kernel functions. By expanding the norm of a function in a Bergman space along the zero variety of a polynomial, we obtain a series expansion of reproducing kernel functions in terms of kernels associated with lower-dimensionalspaces of holomorphic functions. We show how this general approach can be used to explicitly compute kernel functions for certain weighted Bergman and Bargmann-Fock spaces defined in domains in $\textbf{C}^2$.The last two papers contribute to the theory of Loewner chains and theirapplications in the analysis of planar random growth model defined in terms of compositions of conformal maps.In Paper IV, we study Loewner chains generated by unimodular L\'evy processes.We first establish the existence of a capacity scaling limit for the associated growing hulls in terms of whole-plane Loewner chains driven by a time-reversed process. We then analyze the properties of Loewner chains associated with a class of two-parameter compound Poisson processes, and we describe the dependence of the geometric properties of the hulls on the parameters of the driving process. In Paper V, we consider a variation of the Hastings-Levitov growth model, with anisotropic growth. We again establish results concerning scaling limits, when the number of compositions increases and the basic conformal mappings tends to the identity. We show that the resulting limit sets can be associated with solutions to the Loewner equation.We also prove that, in the limit, the evolution of harmonic measure on the boundary is deterministic and is determined by the flow associated with an ordinary differential equation, and we give a description of the fluctuations around this deterministic limit flow. / <p>QC 20100414</p>
106

High Frequency (MHz) Resonant Converters using GaN HEMTs and Novel Planar Transformer Technology

Kotte, Hari Babu January 2013 (has links)
The increased power consumption and power density demands of modern technologies have increased the technical requirements of DC/DC and AC/DC power supplies. In this regard, the primary objective of the power supply researcher/engineer is to build energy efficient, high power density converters by reducing the losses and increasing the switching frequency of converters respectively. Operating the converter circuits at higher switching frequencies reduces the size of the passive components such as transformers, inductors, and capacitors, which results in a compact size, weight, and increased power density of the converter. Therefore, the thesis work is focussed on the design, analysis and evaluation of isolated converters operating in the 1 - 5MHz frequency region with the assistance of the latest semi conductor devices, both coreless and core based planar power transformers designed in Mid Sweden University and which are suitable for consumer applications of varying power levels ranging from 1 – 60W. In high frequency converter circuits, since the MOSFET gate driver plays a prominent role, different commercially available MOSFET gate drivers were evaluated in the frequency range of 1 - 5MHz in terms of gate drive power consumption, rise/fall times and electromagnetic interference (EMI) and a suitable driver was proposed. Initially, the research was focused on the design and evaluation of a quasi resonant flyback converter using a multilayered coreless PCB step down transformer in the frequency range of 2.7 – 4MHz up to the power level of 10W. The energy efficiency of this converter is found to be 72 - 84% under zero voltage switching conditions (ZVS). In order to further improve the energy efficiency of the converter in the MHz frequency region, the new material device GaN HEMT was considered. The comparisons were made on a quasi resonant flyback DC-DC converter using both the Si and GaN technology and it was found that an energy efficiency improvement of 8 – 10% was obtained with the GaN device in the frequency range of 3.2 – 5MHz. In order to minimize the gate drive power consumption, switching losses and to increase the frequency of the converter in some applications such as laptop adapters, set top box (STB) etc., a cascode flyback converter using a low voltage GaN HEMT and a high voltage Si MOSFET was designed and evaluated using a multi-layered coreless PCB transformer in the MHz frequency region. Both the simulation and experimental results have shown that, with the assistance of the cascode flyback converter, the switching speeds of the converter can be increased with the benefit of obtaining a significant improvement in the energy efficiency as compared to that for the single switch flyback converter. In order to further maximize the utilization of the transformer, to reduce the voltage stress on MOSFETs and to obtain the maximum power density from the converter circuit, double ended topologies were considered. Due to the lack of high voltage high side gate drivers in the MHz frequency region, a gate drive circuitry utilizing the multi-layered coreless PCB signal transformer was designed and evaluated in both a half-bridge and series resonant converter (SRC). It was found that the gate drive power consumption using this transformer was around 0.66W for the frequency range of 1.5 - v 3.75 MHz. In addition, by using this gate drive circuitry, the maximum energy efficiency of the SRC using multilayered coreless PCB power transformer was found to be 86.5% with an output power of 36.5W in the switching frequency range of 2 – 3MHz. In order to further enhance the energy efficiency of the converter to more than 90%, investigations were carried out by using the multiresonant converter topology (LCC and LLC), novel hybrid core high frequency planar power transformer and the GaN HEMTs. The simulated and experimental results of the designed LCC resonant converter show that it is feasible to obtain higher energy efficiency isolated DC/DC converters in the MHz frequency region. The peak energy efficiency of the LCC converter at 3.5MHz is reported to be 92% using synchronous rectification. Different modulation techniques were implemented to regulate the converter for both line and load variations using a digital controller. In order to realize an AC/DC converter suitable for a laptop adapter application, consideration was given to the low line of the universal input voltage range due to the GaN switch limitation. The energy efficiency of the regulated converter operating in the frequency range of 2.8 – 3.5MHz is reported to be more than 90% with a load power of 45W and an output voltage of 22V dc. In order to determine an efficient power processing method on the secondary side of the converter, a comparison was made between diode rectification and synchronous rectification and optimal rectification was proposed for the converters operating in the MHz frequency range for a given power transfer application. In order to maintain high energy efficiency for a wide load range and to maintain the narrow switching frequency range for the given input voltage specifications, the LLC resonant converter has been designed and evaluated for the adapter application. From the observed results, the energy efficiency of the LLC resonant converter is maintained at a high level for a wide load range as compared to that for the LCC resonant converter. Investigations were also carried out on isolated class E resonant DC-DC converter with the assistance of GaN HEMT and a high performance planar power transformer at the switching frequency of 5MHz. The simulated energy efficiency of the converter for the output power level of 16W is obtained as 88.5% which makes it feasible to utilize the designed isolated converter for various applications that require light weight and low profile converters. In conclusion, the research in this dissertation has addressed various issues related to high frequency isolated converters and has proposed solution by designing highly energy efficient converters to meet the current industrial trends by using coreless and core based planar transformer technologies along with the assistance of GaN HEMTs. With the provided solution, in the near future, it is feasible to realize low profile, high power density DC/DC and AC/DC converters operating in MHz frequency region suitable for various applications. / High Frequency Switch Mode Power Supplies
107

A Multi-Dimensional Width-Bounded Geometric Separator and its Applications to Protein Folding

Oprisan, Sorinel 20 May 2005 (has links)
We used a divide-and-conquer algorithm to recursively solve the two-dimensional problem of protein folding of an HP sequence with the maximum number of H-H contacts. We derived both lower and upper bounds for the algorithmic complexity by using the newly introduced concept of multi-directional width-bounded geometric separator. We proved that for a grid graph G with n grid points P, there exists a balanced separator A subseteq P$ such that A has less than or equal to 1.02074 sqrt{n} points, and G-A has two disconnected subgraphs with less than or equal to {2over 3}n nodes on each subgraph. We also derive a 0.7555sqrt {n} lower bound for our balanced separator. Based on our multidirectional width-bounded geometric separator, we found that there is an O(n^{5.563sqrt{n}}) time algorithm for the 2D protein folding problem in the HP model. We also extended the upper bound results to rectangular and triangular lattices.
108

Geração e otimização de trajetórias de um manipulador robótico utilizando algoritmos genéticos /

Nunes, Luiz Eduardo Nicolini do Patrocínio. January 2007 (has links)
Resumo: Este trabalho trata da geração e otimização de trajetórias de um manipulador robótico planar (2D) de três graus de liberdade, num ambiente livre de obstáculos. Visto que a cinemática inversa de braços robóticos é um problema complexo que, em geral, geram múltiplas soluções, otimizam-se, aqui, estas soluções através de algoritmos genéticos (AGs). A função de avaliação do AG tem caráter multi-objetivo, de forma a minimizar os deslocamentos angulares e obter de forma precisa a posição da garra, usando funções desenvolvidas para o ambiente Matlab, tais como, GAOT e PLANMANT, devido a sua facilidade de programação e geração de gráficos. A seguir, foram obtidos resultados através de programa desenvolvido em linguagem C, utilizando a biblioteca GAUL, e tem-se avaliado o desempenho computacional de processamento. E finalmente, para a validação experimental deste estudo, tem-se implementado este procedimento em um manipulador robótico Robix RCS-6 de configuração similar ao modelo simulado. Os resultados mostram que o método implementado é eficiente, computacionalmente rápido e viável em aplicações reais. / Abstract: This work treats of the generation and optimization of trajectories for a planar robotic manipulator (2D) of three degrees of freedom, in free environment obstacles. Since the inverse kinematics of robotic arms are a complex problem that, generally, generate multiple solutions, here are optimized these solutions through genetic algorithms (AGs). The evaluation function of the AG has multi-objective character which minimize the angular displacements and the positional errors, being used functions developed for the Matlab environment, such as, GAOT and PLANMANT, due its compliance of programming and graphics generation. Immediately, results were obtained through program developed in language C, using the GAUL library. The computational processing performance has been evaluated. And finally, for the experimental validation of this study, has been implemented this procedure in a robotic manipulator Robix RCS-6 of similar configuration to the simulated model. The results show that the implemented method is efficient, and computationally fast and viable in real applications. KEYWORDS: Robotic manipulator, Optimal trajectory, Inverse kinematics, Genetic algorithm. / Orientador: Victor Orlando Gamarra Rosado / Coorientador: Francisco José Grandinetti / Banca: Mauro Pedro Peres / Banca: Luiz Octavio Mattos dos Reis / Banca: José Rui Camargo / Banca: Carlos Alberto Chavez / Doutor
109

Efeitos da dinâmica da nanopartícula catalisadora e controle da direção de crescimento de nanofios semicondutores / Effects of the catalyst nanoparticle dynamics and control of the growth direction of semiconductor nanowires

Zavarize, Mariana, 1990- 28 July 2017 (has links)
Orientador: Mônica Alonso Cotta / Dissertação (mestrado) - Universidade Estadual de Campinas, Instituto de Física Gleb Wataghin / Made available in DSpace on 2018-09-02T10:59:50Z (GMT). No. of bitstreams: 1 Nica_MarianaZavarize_M.pdf: 75724631 bytes, checksum: 1480ea9eb35b1740d4b908e32d13c9c4 (MD5) Previous issue date: 2017 / Resumo: Neste trabalho, estudamos o crescimento de nanofios planares de InP pelo mecanismo Vapor-Líquido-Sólido (VLS), com o objetivo de entender a dinâmica da nanopartícula metálica catalisadora durante o processo. Para isso utilizamos substratos de GaAs (111)A e o sistema de Epitaxia de Feixe Químico (CBE). O óxido nativo não foi totalmente removido termicamente antes do crescimento, com o objetivo de manter o nanofio isolado eletricamente do substrato. Como um dos objetivos do trabalho, estudamos a possibilidade de controle da direção de crescimento do nanofio planar através de diferentes tratamentos de superfície, e de modo independente da cristalografia do substrato utilizado. As amostras processadas e/ou crescidas foram caracterizadas por técnicas de microscopia eletrônica (varredura e transmissão) e microscopia de força atômica. Investigamos inicialmente como a camada de óxido influencia as direções de crescimento dos nanofios planares no substrato não tratado. Posteriormente, processamos padrões de linhas com rugosidade ligeiramente diferente da mostrada pelo substrato, utilizando técnicas como Litografia por Feixe de Elétrons (EBL), Corrosão por Feixe de Íons Focalizados (FIB) e Ataque por Íons Reativos (RIE). Os padrões gravados eram compostos por linhas perpendiculares com várias micra de comprimento e larguras de dezenas de nm. Observamos que existe uma relação direta do diâmetro do nanofio com a orientação que este assume ao chegar à região onde se encontra a linha (se segue alinhado à linha ou se a ignora; ou se muda sua orientação). Nossos resultados podem ser explicados pelas diferentes energias de superfície presentes no problema, que afetam a dinâmica da nanopartícula catalisadora. Nosso trabalho também mostra que é possível obter maior controle da orientação espacial do nanofio planar crescido, controlando o processamento da superfície e o diâmetro da nanopartícula / Abstract: In this work, we studied the growth of InP planar nanowires by the vapor-liquid-solid (VLS) mechanism, in order to understand the metallic catalyst nanoparticle dynamics during this process. In our studies, we used GaAs (111)A substrates and the Chemical Beam Epitaxy (CBE) system. The native oxide layer was not completely thermally desorbed, in order to keep the nanowire electrically isolated from the substrate. As one of the goals of this work, we study the possibility to control nanowire growth direction via different surface treatments, independently of the substrate crystallography. Our processed and/or grown samples were characterized by electron (scanning and transmission) and atomic force microscopy. We first investigated how the oxide layer influences the growth directions of planar nanowires on unprocessed substrates. Subsequently, patterns of lines with roughness slightly different from those shown by the substrate were patterned using techniques such as Electron-beam Lithography (EBL), Focused Ion-beam Corrosion (FIB) and Reactive Ion Etching (RIE). These patterns were composed of perpendicular lines with several micra in length and tens of nanometers wide. We observed that there is a direct relation between the nanowire diameter and the orientation that the nanowire assumes when it reaches the region where the line is located (if the nanowire aligns with the line or ignores it, or if its orientation changes). Our results can be explained by the different surface energies present in the problem, which affect the dynamics of the catalytic nanoparticle. Our work also shows that it is possible to obtain better control of the spatial orientation of the grown planar nanowire, by controlling the surface processing and the nanoparticle diameter / Mestrado / Física / Mestra em Física / 132655/2015-2 / CNPQ
110

Estudo do potencial de interação elétron-elétron no contexto da Teoria de Maxwell-Chern-Simonsproca com violação de Lorentz / STUDY OF POTENTIAL OF INTERACTION ELECTRON-ELECTRON IN THE CONTEXT OF THE THEORY OF MAXWELL - CHERN - SIMONSPROCA WITH BREACH OF LORENTZ

Tavares, Márcio da Silva 03 October 2006 (has links)
Submitted by Rosivalda Pereira (mrs.pereira@ufma.br) on 2017-06-02T21:18:29Z No. of bitstreams: 1 MarcioSilvaTavares.pdf: 635099 bytes, checksum: e3591020bd7da5c3ab47652f130bc48e (MD5) / Made available in DSpace on 2017-06-02T21:18:29Z (GMT). No. of bitstreams: 1 MarcioSilvaTavares.pdf: 635099 bytes, checksum: e3591020bd7da5c3ab47652f130bc48e (MD5) Previous issue date: 2006-10-03 / Fundação de Amparo à Pesquisa e ao Desenvolvimento Científico e Tecnológico do Maranhão (FAPEMA) / This work is initiated with the presentation of an overview on the main theoretical models of planar electrodynamics (QED3), which are studied for their classical solutions. This is done by obtaining the equations of wave, which provide their solutions to the fields and potential. As a result, makes up the youngest of the potential for interaction and e-e- and in the context of models of planar Maxwell-Chern-Simons (MCS) and Maxwell-Chern-Simons-Proc (MCS-proc), which is conducted within the regime of validity of the Born approximation, where the potential for interaction is given by the Fourier transform of the amplitude of spreading Möller (calculated to tree level, the scheme not relativístico). In the meantime, there is the prospect of investigating the infuência a Lorentz word rapist on the interaction of electron-electron. As a theoretical tool to carry out such research, takes up the planar version of the model-Maxwell-Carrol Field-Jackiw, coupled to the sector of Dirac. Following the procedure already established, the potential of electron-electron interaction is obtained for the case of a background of type-time, vµ = (v0,→0 ): This potential for having a logarithmic type of asymptotic behavior is not appropriate to represent physical interactions in (1 +2) dimensions. As end of this research work, is addressing this issue in the context of the model plane Proc of MCS-in violation of Lorentz (originated from the reduction of the dimensional model of Higgs-abelian of Maxwell-Carroll-Field-Jackiw). It is supplementing this model with the industry to properly Dirac coupled with the field of gauge (Aµ) And climbing (φ), and using the same procedures for calculating already adopted, are the words of the potential interaction of electron-electron, it is completely armored. This potential exhibits a region of pit, which leads to attraction, which may be relevant in an attempt to explain the formation of electron-electron pairs in the context of this theoretical model. / Este trabalho é iniciado com a apresentação de um overview sobre os principais modelos teóricos da eletrodinâmica planar (QED3); para quais são estudadas as respectivas soluções clássicas. Isto é feito através da obtenção das equações de onda, que fornecem as respectivas soluções para os campos e potenciais. Na sequência, efetua-se o cálculo do potencial de interação e-e- no contexto dos modelos planares de Maxwell-Chern-Simons (MCS) e Maxwell-Chern-Simons-Proca (MCS-Proca), o que é realizado dentro do regime de validade da aproximação de Born, onde o potencial de interação é dado pela transformada de Fourier da amplitude de espalhamento Möller (calculada a tree level, no regime não relativístico). Nesse ínterim, levanta-se a perspectiva de investigar a infuência de um termo violador de Lorentz sobre a interação elétron-elétron. Como ferramental teórico para realizar tal investigação, adota-se a versão planar do modelo de Maxwell-Carrol- Field-Jackiw, acoplado ao setor de Dirac. Seguindo o procedimento já estabelecido, o potencial de interação elétron-elétron é obtido para o caso de um background do tipo-tempo,vµ = (v0,→0 ):Tal potencial, por ter um comportamento assintótico do tipo logarítmico, não é adequado para representar interações físicas em (1+2) dimensões. Como investigação final desse trabalho, aborda-se esta mesma questão no contexto do modelo planar de MCS-Proca com violação de Lorentz (originado da redução dimensional do modelo de Higgs-Abeliano de Maxwell-Carrol-Field-Jackiw). Suplementando-se tal modelo com o setor de Dirac devidamente acoplado com o campo de gauge (Aµ) e escalar (φ), e usando os mesmos procedimentos de cálculo já adotados, obtém-se a expressão do potencial de interação elétron-elétron, que se revela totalmente blindado. Tal potencial exibe uma região de poço, que implica em atratividade, o que pode ser relevante na tentativa de explicar a formação de pares elétron-elétron no contexto deste modelo teórico.

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