In the present work, two phase reacting flow in a single cavity Trapped Vortex Combustor (TVC) is studied at atmospheric conditions. KIVA-3V, numerical program for simulating three dimensional compressible reacting flows with sprays using Lagrangian-Drop Eulerian-fluid procedure is used. The stochastic discrete droplet model is used for simulating the liquid spray. In each computational cell, it is assumed that the volume occupied by the liquid phase is very small. But this assumption of very low liquid volume fraction in a computational cell is violated in the region close to the injection nozzle. This introduces grid dependence in predictions of liquid phase in the region close to the nozzle in droplet collision algorithm, and in momentum coupling between the liquid and the gas phase. Improvements are identified to reduce grid dependence of these algorithms and corresponding changes are made in the standard KIVA-3V models. Pressure swirl injector which produces hollow cone spray is used in the current study along with kerosene as the liquid fuel. Modifications needed for modelling pressure swirl atomiser are implemented. The Taylor Analogy Breakup (TAB) model, the standard model for predicting secondary breakup is improved with modifications required for low pressure injectors. The pressure swirl injector model along with the improvements is validated using experimental data for kerosene spray from the literature. Simulations of two phase reacting flow in a single cavity TVC are performed and the temperature distribution within the combustor is studied. In order to identify an optimum configuration with liquid fuel combustion, the following parameters related to fuel and air such as cavity fuel injection location, cavity air injection location, Sauter Mean Diameter (SMD) of injected fuel droplets, velocity of the fuel injected are studied in detail in order to understand the effect of these parameters on combustion characteristics of a single cavity TVC.

Cold, trapped atomic ions have enabled the investigation of fundamental physics and generated a rich field of applications. Foremost among these is quantum computation which has recently driven the development of the sophisticated, scalable surface-electrode trap. Despite the many advantages of surface-electrode traps, the typically smaller ion-electrode distance, d, in these traps results in an increased ion heating rate that is proportional to d^(-4) and a decreased trap well-depth that is proportional to d^(-2). These shortcomings can be simultaneously addressed by installing the trap into a cryogenic environment. With this in mind, a closed-cycle, cryogenic ion trapping apparatus that maintains excellent vacuum, is highly modular, has increased optical access, and uses a simple vibration isolation system has been developed. Single ions are trapped and used to characterize system properties such as the motion of the vibration isolation stage. In order to compare this system to a similar room temperature apparatus, the ion trapping lifetime and heating rate are determined. A single ion also serves as a sensitive electric field probe that is used to measure and compensate stray electric fields across the trap. Due to the long dark ion lifetimes in this system, it is well-suited to probing the stability of small, linear ion crystals. Linear ion crystals of arbitrary length are built in an automated fashion using transport waveforms and the scaling of dark lifetime with ion number for N <= 6 is investigated. These data are then used to consider the relevance of various loss channels.

This thesis aims at revealing the fundamental guiding and coupling properties of nonreciprocal electromagnetic surface waves on magneto-optical or gyromagnetic media and designing novel applications based on the properties. We introduce the background in the first chapter. We then describe the concept of nonreciprocity and the main calculation method in the second chapter. In the third chapter, we show that one-way waves can be sustained at the edge of a gyromagnetic photonic crystal slab under an external magnetic field. We also investigate the coupling between two parallel one-way waveguides. We reveal the condition for effective co-directional and contra-directional coupling. We also notice that the contra-directional coupling is related to the concept of a “trapped rainbow”. In the fourth chapter, we address the concept of a “trapped rainbow”. It aims at trapping different frequency components of the electromagnetic wave packet at different positions in space permanently. In previous structures, the entire incident wave is reflected due to the strong contra-directional coupling between forward and backward modes. To overcome this difficulty, we show that utilizing nonreciprocal waveguides under a tapered external magnetic field can achieve a truly “trapped rainbow” effect at microwave frequencies. We observe hot spots and relatively long duration times around critical positions through simulations and find that such a trapping effect is robust against disorders. Lastly, in the fifth chapter, we study the one-way waves in a surface magnetoplasmon cavity. We find that the external magnetic field can separate the clockwise and anti-clockwise cavity modes into two totally different frequency ranges. This offers us more choices, both in the frequency ranges and in the one-way directions, for realizing one-way components. We also show the waveguide-cavity coupling by designing a circulator, which establishes the foundation for potential applications. / <p>QC 20160816</p><p></p>

Neste trabalho apresentamos a construção de uma armadilha de dipolo com laser de CO2 que envolveu a utilização de novas e modernas tecnologias nunca utilizadas pelo nosso grupo até então. Podemos destacar a construção de uma nova câmara de aprisionamento com grande acesso óptico, getters como fonte de átomos e um laser de CO2 de alta potência e sua óptica. Demonstramos o aprisionamento de átomos de 85Rb em uma armadilha magnética e magneto-óptica e analisamos sua dinâmica, obtendo resultados das taxas de perdas provocadas por colisões entre átomos aprisionados e átomos quentes provenientes do vapor de fundo e do getter. Este entendimento será importante na implementação da técnica totalmente óptica de aprisionamento simultâneo de átomos de Rb e moléculas de Rb2. / In this work we present the construction of an optical dipole trap using a CO2 laser, which involves the use of news and modern technologies never utilized by our group up to now. We have builded a new trap chamber with large optical access, used atomic dispensers as an atomic source and a high power CO2 laser and its optical components. We have demonstrated trapping and cooling of 85 Rb in a magneto-optical trap as well as and magnetic trap. By analyze its dynamic, we have obtained results on the collisional loss rates between trapped atoms imprisoned and hot atoms originating from the background gas. This understanding will be important in the implementation of the technical one entirely optical trap for Rb atoms as well as Rb2 molecules.

O presente trabalho procura investigar alguns dos processos colisionais de átomos de Rydberg ultrafrios. Utilizando uma armadilha magneto-óptica (MOT), foi possível aprisionar átomos de 85Rb, um elemento alcalino metálico, numa região da ordem de lmn a temperaturas da ordem de poucas centenas de ?K, regime chamado de \"ultrafrio\" na literatura. Os átomos de 85Rb são então excitados para estados de alto número quântico principal, também chamados de estados de Rydberg, através de um laser pulsado. Nesses estados, os átomos apresentam propriedades exageradas devido ao tamanho da órbita do elétron de valência, sendo uma delas os potenciais de longo-alcance. Em nossos experimentos, após a excitação, são detectados átomos em estados vizinhos ao originalmente excitado, evidenciando a existência de transições. Como esses estados são muito próximos em energia, a presença de potenciais de longo alcance pode fazer a energia de um par de átomos de Rydberg no seu estado inicial ficar ressonante com a energia do mesmo par numa combinação de outros estados, tornando então possível transições para esses estados. Nosso estudo visa quantificar de certa forma essas observações, assim como estimar a importância do movimento desses átomos nas transições observadas. / This dissertation seeks to address some of the characteristics of collisional processes in ultracold Rydberg atoms. With a Maqneto-Optical Trap (MOT), we trapped a sample of 85Rb, an alkaline metal element, in a region of about lmm at a temperature of a few hundreds of ?K, known in the literature as the \"ultracold\" regime. The 85Rb atoms are then excited to high principal quantum number states, also known as Rydberg states, with a pulsed laser. In these states, the atoms present exaggerated properties due to the large valence electron orbit, such as long-range potentials in our experiments, after excitation, we have detected atoms in neighboring states to the originally excited state, an evidence of atomic transitions. Since these states have similar energy, the presence of long-range potentials can make the energy of a pair of atoms in the initial state be resonant with the energy of the same pair in a combination of different states, making it possible to have transitions to these nearby states. Our work tries to quantify these observations, as well as to gauge the role of atomic movement in these transitions.

The work presented in this thesis studies acoustic perturbations in slowly varying pipes. The slow variation is introduced in the form of a small parameter ${\epsilon}$ and through this in turn gives rise to a slow axial scale $X$ such that $X = {\epsilon}x$ where $x$ is the normal axial coordinate. This allows an asymptotic approach and the WKB method is used to solve the subsequent mathematical problems. The first deals with the existence of a trapped mode in a hard-walled pipe of varying radius conveying fluid. For the derived leading order propagating mode solution, its amplitude becomes singular at transition points $X_{t}$ and $X_{t'}$ where $X_{t} > 0$ and $X_{t'} < 0$ and thus is unable to propagate past these points. Because of the break down in the solution, this leads to the theory that in the neighbourhood of these points there exists a boundary layer in which the original assumption about having slow variation does not hold. By first seeking the thickness of the layer, valid solutions can then be derived and then matched to the outer solutions in order to produce a uniform solution which holds for the entire axial domain. Once this is achieved, it is then used to derive trapped mode solutions. In this case, the theory used is that of two single turning points which are then combined to obtain the full solution. It is illustrated through consideration of examples and the dependence on ${\epsilon}$ is also shown through various plots. This problem will be considered for a symmetric and asymmetric duct and for differing duct parameters. Problems may arise when the two turning points lie close together and so we seek to improve on the method used by deriving a solution to trapped modes encompassing both turning points, which will be proposed together with some illustrations in order to justify its use and reliability. Next, the case of mode propagations on a thin elastic shell of varying radius conveying fluid is studied. The acoustic solutions of a straight shell in vacuo are first briefly reviewed and then built up by the addition of radius variation and the presence of a stationary fluid. The work presented first outlines the analysis for wave propagation in a slowly-varying thin elastic shell in vacuo. It is found that the shell and the fluid terms are coupled through the fluid pressure term, which is added to the equation governing the radial shell displacements since the pressure is assumed to affect radial motion only. Once the newly corrected equation for the radial shell displacements has been obtained, together with the axial and azimuthal displacements equations, this new system of governing equations is then separated into leading order ${\epsilon}^{0}$ and first order ${\epsilon}^{1}$ systems. In order to simplify the calculations, only the zeroth azimuthal order $m = 0$ will be studied here. With this simplification, a notable result is that the solutions of the torsional motion is decoupled from the axial and radial solutions. Once the dispersion equation is extracted from the leading order system, it can be seen that the axial and radial solutions are in fact coupled. The solution to the in vacuo with varying radius problem is first briefly presented and it is then followed by the solution to the fluid inclusion problem with varying radius, which makes up the main part of this section. The solution is studied for various frequencies and at various points along the shell. In addition, the axial and radial components of the first three modes are examined along with their amplitudes and energy distributions. Finally, mean flow is added and the same analysis is carried out, paying particular attention to the differences which arise in comparison to the stationary flow case.

The world demand for energy is estimated to increase by up to 70% from 2016 to 2040. To meet this demand in a sustainable way, the power density of electric motors and generators can be increased by using superconducting materials. In particular, trapped field superconducting magnets, where the field is generated by a circulating persistent current in the sample, can create magnetic fields an order of magnitude higher than possible using conventional ferromagnets, thus increasing the power density of motors and generators. This is of great interest where added weight comes at a premium, such as for naval propulsion motors, wind generators and motors/generators for future electric aircraft. This work investigates the suitability of stacked tape layers of second generation high temperature superconductors (HTS), such as YBa2Cu3O7-x (YBCO) for trapped field applications. The present limits for trapped field magnitude have been determined, which provide a basis for the optimization of pulsed field magnetization techniques for in-situ magnetization in motors and generators. Trapped fields were increased by optimising the magnetic pulse sequence, using thermally conductive material to reduce temperature rise during pulse and changing the duration of the magnetic field pulse. Finite element method computer modelling was used to model and predict the behaviour of the trapped field magnets made of HTS tape with good agreement to experiment for both field cooling and pulsed field magnetisation. The models rely on critical current data for the HTS tape and its dependence on magnetic field and temperature. For this reason, a critical current testing facility was developed and constructed as a part of this work capable of measuring critical current up to 900 A, magnetic field of 1.5 T and down to temperatures of ~10 K in forced and dynamically controlled helium vapour flow. Lastly, first steps into scaling up by pulse magnetising an array of HTS tape stacks were made, allowing for larger overall trapped flux values. Such an array exhibits geometry, similar to what is going to be used in a functional motor prototype being developed in our research group (Applied Superconductivity and Cryoscience Group, ASCG). The work done culminated in the highest trapped field achieved to date using both field cooling (13.4 T between two stacks) and pulsed field magnetization (2.1 T above a single stack), for this type of trapped field magnet.

Neste trabalho, estudamos as subvariedades das formas espaciais pseudo-Riemannianas M^n_v(c) com vetor curvatura média de tipo luz, chamadas marginalmente aprisionadas, explorando as relações desta condição (motivada pela Física) com várias outras hipóteses de caráter geométrico, como lambda-isotropia, presença de nulidade relativa e invariância por um certo grupo de transformações de Lorentz. Em particular, apresentamos vários resultados de classificação e rigidez de superfícies marginalmente aprisionadas nos espaços de Lorentz-Minkowski L^4, de Sitter S^4_1 e anti-de Sitter H^4_1 nestes contextos, adaptando e generalizando resultados de alguns artigos. / In this work, we study the submanifolds of pseudo-Riemannian space forms M^n_v(c) with lightlike mean curvature vector, called marginally trapped, exploring the relations of this condition (motivated by Physics) with several other assumptions of geometric character, such as \\lambda-isotropy, presence of relative nullity and invariance by a certain group of Lorentz transformations. In particular, we prove several ridigity and classification results for marginally trapped surfaces in Lorentz-Minkowski space L^4, de Sitter space S^4_1 and anti-de Sitter space H^4_1 in these settings, adapting and generalizing results from several papers.

Neste trabalho, estudamos as subvariedades das formas espaciais pseudo-Riemannianas M^n_v(c) com vetor curvatura média de tipo luz, chamadas marginalmente aprisionadas, explorando as relações desta condição (motivada pela Física) com várias outras hipóteses de caráter geométrico, como lambda-isotropia, presença de nulidade relativa e invariância por um certo grupo de transformações de Lorentz. Em particular, apresentamos vários resultados de classificação e rigidez de superfícies marginalmente aprisionadas nos espaços de Lorentz-Minkowski L^4, de Sitter S^4_1 e anti-de Sitter H^4_1 nestes contextos, adaptando e generalizando resultados de alguns artigos. / In this work, we study the submanifolds of pseudo-Riemannian space forms M^n_v(c) with lightlike mean curvature vector, called marginally trapped, exploring the relations of this condition (motivated by Physics) with several other assumptions of geometric character, such as \\lambda-isotropy, presence of relative nullity and invariance by a certain group of Lorentz transformations. In particular, we prove several ridigity and classification results for marginally trapped surfaces in Lorentz-Minkowski space L^4, de Sitter space S^4_1 and anti-de Sitter space H^4_1 in these settings, adapting and generalizing results from several papers.

Neste trabalho apresentamos a construção de uma armadilha de dipolo com laser de CO2 que envolveu a utilização de novas e modernas tecnologias nunca utilizadas pelo nosso grupo até então. Podemos destacar a construção de uma nova câmara de aprisionamento com grande acesso óptico, getters como fonte de átomos e um laser de CO2 de alta potência e sua óptica. Demonstramos o aprisionamento de átomos de 85Rb em uma armadilha magnética e magneto-óptica e analisamos sua dinâmica, obtendo resultados das taxas de perdas provocadas por colisões entre átomos aprisionados e átomos quentes provenientes do vapor de fundo e do getter. Este entendimento será importante na implementação da técnica totalmente óptica de aprisionamento simultâneo de átomos de Rb e moléculas de Rb2. / In this work we present the construction of an optical dipole trap using a CO2 laser, which involves the use of news and modern technologies never utilized by our group up to now. We have builded a new trap chamber with large optical access, used atomic dispensers as an atomic source and a high power CO2 laser and its optical components. We have demonstrated trapping and cooling of 85 Rb in a magneto-optical trap as well as and magnetic trap. By analyze its dynamic, we have obtained results on the collisional loss rates between trapped atoms imprisoned and hot atoms originating from the background gas. This understanding will be important in the implementation of the technical one entirely optical trap for Rb atoms as well as Rb2 molecules.