We present an investigation of the magnetic field geometries and inhomogeneous distribution of chemical elements in the atmospheres of peculiar A and B stars. Our study combines high-quality spectroscopic and spectropolarimetric stellar observations with the development and application of novel techniques for theoretical interpretation of the shapes and variability of stellar line profiles. In particular, we extend the method of Doppler imaging to the analysis of spectra in the four Stokes parameters, making it possible to derive detailed and reliable stellar magnetic maps simultaneously with the imaging chemical inhomogeneities. The magnetic Doppler imaging is applied to study of magnetic topologies and distributions of chemical elements in the peculiar stars α2 CVn and 53 Cam. We found that the magnetic field geometry of 53 Cam is considerably more complex than a low-order multipolar topology, commonly assumed for magnetic A and B stars. Our Doppler imaging analysis also led to a discovery and study of spots of enhanced mercury abundance in the atmosphere of α And, a star where the presence of a global magnetic field is unlikely. The ESO 3.6-m telescope is used to collect unique, very high spectral- and time-resolution observations of rapidly oscillating peculiar A (roAp) stars and to reveal line profile variations due to stellar pulsations. We present a detailed characterization of the spectroscopic pulsational behaviour and demonstrate a remarkable diversity of pulsations in different spectral lines. The outstanding variability of the lines of rare-earth elements is used to study propagation of pulsation waves through the stellar atmospheres and identify pulsation modes. This analysis led to a discovery of a non-axisymmetric character of pulsations in roAp stars. Our study of chemical stratification in the atmosphere of the roAp star γ Equ provides a compelling evidence for significant variation of the chemical composition with depth. We find a combined effect of extreme chemical anomalies and a growth of pulsation amplitude in the outermost atmospheric layers to be the most likely origin of the high-amplitude pulsational variations of the lines of rare-earth elements. Observations of cool magnetic CP stars are obtained with the ESO Very Large Telescope and are used for empirical investigation of the anomalies in the atmospheric temperature structure. We show that the core-wing anomaly of the hydrogen Balmer lines observed in some cool CP stars can be attributed to a hot layer at an intermediate atmospheric depth.

This thesis is based on work done in two different experimental projects. The first project, the Tau RICH, is a previously proposed τ-neutrino appearance experiment for the CERN neutrino beam at the Gran Sasso laboratory in Italy. The proposed experimental concept is based on the use of focusing RICH detectors with liquid radiator (C6F14). Simulations made with a Geant4 code show that in the proposed experimental set-up, Cherenkov light from delta electrons will constitute a severe background that in practice would render the experiment unfeasible. The second project, ATLAS, is a general purpose detector at the CERN 14 TeV proton-proton collider LHC which will start operation in 2007. To make the reconstruction and selection of the events in ATLAS more accurate, complete and up-to-date information on the interaction of the produced particles with the detector is needed. A service program code, the Material Integration Service (MIS), has been developed which makes use of the detector descriptions already available in a Geant4 code and which uses a novel algorithm, based on line integrals evaluated within small volume elements that build up the detector. This code is demonstrated to constitute a practically useful tool of satisfactory performance and accuracy. The charged Higgs boson production in the gluon-bottom quark mode, gb → tH±, followed by charged Higgs decays into a chargino and a neutralino, is studied for a specific choice of values for the Minimal Supersymmetric Standard Model (MSSM) parameters. It is shown, using a Monte Carlo code to simulate the ATLAS detector and the assumed MSSM physics model, that for an integrated luminosity of 300 fb-1, in the intermediate region 4 < tanβ < 10 where H± decays to SM particles cannot be used for H± discovery, charged Higgs decays to non-SM particles can be used for Higgs discovery at the 5 σ significance level.

Separated flows about single and multi-element airfoils are featured in many scenarios of practical interest, including: stall of fixed wing aircraft, dynamic stall of rotorcraft blades, and stall of compressor and turbine elements within jet engines. In each case, static and/or dynamic stall can lead to losses in performance. More importantly, modeling and analysis tools for stalled flows are relatively poorly evolved and designs must completely avoid stall due to a lack of understanding. The underlying argument is that advancements are necessary to facilitate understanding of and applications involving static and dynamic stall. The state-of-the-art in modeling stall involves numerical solutions to the governing equations of fluids. These tools often either lack fidelity or are prohibitively expensive. Ever-increasing computational power will likely lead to increased application of numerical solutions. The focus of this thesis is improvements in numerical modeling of stall, the need of which arises from poorly evolved analysis tools and the spread of numerical approaches. Technical barriers have included ensuring unsteady flow field and vorticity reproduction, transition modeling, non-linear effects such as viscosity, and convergence of predictions. Contributions to static and dynamic stall analysis have been been made. A hybrid Reynolds-Averaged Navier-Stokes/Large-Eddy-Simulation turbulence technique was demonstrated to predict the unsteadiness and acoustics within a cavity with accuracy approaching Large-Eddy-Simulation. Practices to model separated flows were developed and applied to stalled airfoils. Convergence was characterized to allow computational resources to be focused only as needed. Techniques were established for estimation of integrated coefficients, onset of stall, and reattachment from unconverged data. Separation and stall onset were governed by turbulent transport, while the location of reattachment depended on the mean flow. Application of these methodologies to oscillating flapped airfoils revealed flow through the gap was dominated by the flap angle for low angles of attack. Lag between the aerodynamic response and input flap scheduling was associated with increased oscillation frequency and airfoil/flap gap size. Massively separated flow structures were also examined.

No description available.

Delaying stall is always an attractive option in the aerospace industry. The major benefit of delaying stall is increased lift during takeoff and landings as well as during high angle of attack situations. Devices, such as fluidic oscillators, can be integrated into wing flaps to help delay the occurrence of stall by adding energized air to the airflow on the upper surface of the wing flap. The energized air from the oscillator allows the airflow to remain attached to the upper surface of the wing flap. The fluidic oscillator being integrated in this thesis is an active flow control device (AFC). One common method for integrating any device into a wing flap is to remove a section of the flap and mechanically secure the device. A current trend in the aerospace industry is the increased use of fiber-reinforced composites to replace traditional metal components on aircraft. The traditional methods of device integration cause additional complications when applied to composite components as compared to metal components. This thesis proposes an alternative method for integration of the AFC devices, which occurs before the fabrication of wing flaps is completed and they are attached to the aircraft wing. Seven design concepts are created to reduce the complications from using current methods of integration on composite wing flaps. The concepts are based on four design requirements: aerodynamics, manufacturing, maintenance, and structure. Four of the design concepts created are external designs, which place the AFC on the exterior surface of the wing flap in two types of grooved channels. The other three designs place the AFC inside the wing flap skin and are categorized as internal designs. In order for the air exiting the AFC to reach the upper surface of the wing flap, slots are created in the wing flap skin for the internal designs. Within each of the seven design concepts two design variants are created based on foam or ribbed core types. Prototypes were created for all of the external design AFC devices and the side inserted AFC and retaining pieces. Wing flap prototypes were created for the rounded groove straight AFC design, the semi-circular groove with straight AFC, and the side inserted AFC designs. The wing flaps were created using the VARTM process with a vertical layup for the external designs. The rounded groove and semi-circular groove prototypes each went through three generations of prototypes until an acceptable wing flap was created. The side inserted design utilized the lessons learned through each generation of the external design prototypes eliminating the need for multiple generations. The lessons learned through the prototyping process helped refine the designs and determine the ease of manufacturing to be used in the design evaluation. The evaluation of the designs is based on the four design requirements stated above. The assessment of the designs uses two levels of evaluation matrices to determine the most fitting design concept. As a result of the evaluation, all four of the external designs and one of the internal designs are eliminated. The two remaining internal designs' foam core and ribbed variants are compared to establish the final design selection. The vertically inserted AFC foam core design is the most fitting design concept for the integration of an AFC device into a composite wing flap.

No description available.

The aim of this study is to simulate the unsteady flow around rotating or oscillating airfoils. This will help to understand the rotor aerodynamics, which is essential in turbines and propellers. In this study, a pre-existing Euler solver with finite volume method that is developed in the Mechanical Engineering Department of Middle East Technical University (METU) is improved. This structured pre-existing code was developed for 2-D internal flows with Lax-Wendroff scheme. The improvement consist of firstly, the generalization of the code to external flow / secondly, implementation of first order Roe&rsquo / s flux splitting scheme and lastly, the implementation of rotation with the help of Arbitrary Lagrangian Eulerian (ALE) method. For the verification of steady and unsteady results of the code, the experimental and computational results from literature are utilized. For steady conditions, subsonic and transonic cases are investigated with different angle of attacks. For the verification of unsteady results of the code, oscillating airfoil case is used. The flow is assumed as inviscid, unsteady, adiabatic and two dimensional. The gravity is neglected and the air is taken as ideal gas. The developed code is run on computers housed in METU Mechanical Engineering Department Computational Fluid Dynamics High Performance Computing (CFD-HPC) Laboratory.

[Truncated abstract] This thesis is split into two parts. In part one; A 50 K dual mode oscillator, the aim of the project was to build a 50 K precision oscillator with frequency stability on the order of 1014 from 1 to 100 seconds. A dual-mode temperature compensation technique was used that relied on a turning point in the frequency-temperature relationship of the difference frequency between two orthogonal whispering gallery modes in a single sapphire crystal. A cylindrical sapphire loaded copper cavity resonator was designed, modelled and built with a turning point in the difference frequency between an E-mode and H-mode pair at approximately 52.5 K . . . The frequencies and Q-factors of whispering spherical modes in the 3-12 GHz range in the fused silica resonator are measured at 6, 77 and 300 K and the Q-factor is used to determine the loss tangent at these temperatures. The frequency and Q-factor temperature dependence of the TM2,1,2 whispering gallery mode at 5.18 GHZ is used to characterise the loss tangent and relative permittivity of the fused silica from 4-300 K. Below 22 K the frequency-temperature dependence of the resonator was found to be consistent with the combined effects of the thermal properties of the dielectric and the influence of an unknown paramagnetic impurity, with a spin resonance frequency at about 138 ± 31 GHz. Below 8 K the loss tangent exhibited a 9th order power law temperature dependence, which may be explained by Raman scattering of Phonons from the paramagnetic impurity ions. A spherical Bragg reflector resonator made from multiple concentric dielectric layers loaded in a spherical cavity that enables confinement of field in the centre of the resonator is described. A set of simultaneous equations is derived that allow the calculation of the required dimensions and resonance frequency for such a resonator and the solution is confirmed using finite element analysis. A spherical Bragg reflector resonator is constructed using Teflon and free-space as the dielectric materials. A Q-factor of 22,000 at 13.87 GHz was measured and found to compare well with the design values.

Made available in DSpace on 2016-06-02T20:28:27Z (GMT). No. of bitstreams: 1 4698.pdf: 604113 bytes, checksum: 033e879a6c06b9c3ad1884a3611729fe (MD5) Previous issue date: 2012-08-10 / Universidade Federal de Sao Carlos / We study the behavior, as t ∞, of the energy for the solutions of the Cauchy problem for some strictly hyperbolic linear second order equations with coeficients very rapidly oscillating. / Nós estudamos o comportamento da energia, para t ∞, das soluções do problema de Cauchy para algumas equações estritamente hiperbólicas de segunda ordem com coeficientes que oscilam rapidamente.

Conselho Nacional de Desenvolvimento Científico e Tecnológico / This work presents the design and analysis of an electronic system with universal input to supply a fluorescent lamp. The system includes a self-oscillating electronic ballast and an additional circuit which allows keeping the nominal lamp power although a variation of the input voltage. The electronic ballast design comprises some steps: resonant filter design, self-oscillating gate driver design, additional circuit design and stability test. The electronic ballast is represented as a nonlinear control system in order to achieve a feasible design methodology. Moreover, the system must be analyzed considering the describing function method and the extended Nyquist stability criterion. The proposed electronic ballast must maintain the main characteristics of the traditional self-oscillating electronic ballast. Besides that, the additional circuit has a small number of components and it allows the input voltage full range with automatic selection of the switching frequency. The design, simulation and experimental results of the prototype are presented. / Este trabalho apresenta a análise e o projeto de um sistema eletrônico com entrada universal para alimentação de lâmpadas fluorescentes. O sistema é composto por um reator eletrônico auto-oscilante com um circuito adicional, que permite manter a potência da lâmpada no valor nominal independente da tensão de alimentação. O projeto do reator eletrônico é dividido em etapas, que compreendem o projeto do filtro ressonante, do comando auto-oscilante, do circuito adicional e a análise da oscilação auto-sustentada. Para viabilizar uma metodologia de projeto adequada, o reator eletrônico é representado como um sistema de controle. Para análise e projeto são utilizados a função descritiva e o critério de estabilidade estendido de Nyquist. O reator eletrônico mantém as principais características do reator eletrônico auto-oscilante tradicional. Além disso, o circuito adicional possui um número reduzido de componentes, o que permite empregar o reator eletrônico em qualquer rede de alimentação monofásica sem a necessidade de ajuste manual para escolha da tensão de alimentação. São apresentados resultados de simulação e experimentais do protótipo implementado.