Slotted waveguide array (SWGA) antennas find application in systems which require planarity, low profile, high power handling capabilities such as radars. In this thesis, a planar, low sidelobe, phased array antenna, capable of electronically beam scanning in E-plane is designed, manufactured and measured. In the design, slot characterization is done with HFSS and by measurements, and mutual coupling between slots are calculated analytically. A MATLAB code is developed for the synthesis of the SWGA antenna. Grating lobe problem in the scanning array, which is caused by the slot positions, is solved using baffles on the array. A high power feeding section for the planar array, having an amplitude tapering to get low sidelobes is also designed using a corrugated E-plane sectoral horn. The power divider is designed analytically, and simulated and optimized with HFSS.

An axisymmetric, Navier-Stokes finite volume flow solver, which uses Harten, Lax and van Leer (HLL) and Harten, Lax and van Leer&ndash / Contact (HLLC) upwind flux differencing scheme for spatial and uses Runge-Kutta explicit multi-stage time stepping scheme for temporal discretization on unstructured meshe is developed. Developed solver can solve the compressible axisymmetric flow. The spatial accuracy of the solver can be first or second order accurate. Second order accuracy is achieved by piecewise linear reconstruction. Gradients of flow variables required for piecewise linear reconstruction are calculated by Green-Gauss theorem. Baldwin-Lomax turbulent model is used to compute the turbulent viscosity. Approximate Riemann solver of HLL and HLLC implemented in solver are validated by solving a cylindrical explosion case. Also the solver&rsquo / s capability of solving unstructured, multi-zone domain is investigated by this problem. First and second order results of solver are compared by solving the flow over a circular bump. Axisymmetric flow in solid propellant rocket motor is solved in order to validate the axisymmetric feature of solver. Laminar flow over flat plate is solved for viscous terms validation. Turbulent model is studied in the flow over flat plate and flow with mass injection test cases.

Nachrichtentechnische Systeme werden stets durch unvermeidbare zufällige Störungen beeinflußt. Neben anderen Komponenten sind davon besonders Oszillatoren betroffen. Die durch die Störungen verursachten zufälligen Schwankungen in der Oszillatorausgabe können als Amplituden- und Phasenabweichungen modelliert werden. Dabei zeigt sich, daß vor allem zufällige Phasenfluktuationen von Bedeutung sind. Zufällige Phasenfluktuationen können unter Verwendung stochastischer Prozesse zweiter Ordnung mit kurzem oder langem Gedächtnis modelliert werden. Inhalt der Dissertation ist die Herleitung eines Verfahrens zur Simulation zufälliger Phasenfluktuationen von Oszillatoren mit kurzem Gedächtnis unter Berücksichtigung von Datenblattangaben.

La perception visuelle du mouvement est essentielle à l’exécution de déplacements sécuritaires ainsi qu’à l’interaction efficace avec notre environnement. C’est pourquoi il est nécessaire de comprendre la nature des mécanismes responsables de l’analyse de l’information sur le mouvement, ainsi que l’effet du vieillissement sur la réponse de ces mécanismes. Deux études seront présentées. La première avait pour but l’analyse des mécanismes responsables de la perception du mouvement de rotation fractale, nouveau stimulus introduit par Benton, O’Brien & Curran (2007). Ce type de stimulus a été créé afin d’isoler les mécanismes sensibles à la forme. Plusieurs auteurs ont suggéré que les mécanismes sensibles au mouvement de deuxième ordre utiliseraient les indices de position afin d’extraire l’information sur le mouvement (Seiffert & Cavanagh, 1998). Ainsi, la présente étude visait à déterminer si la rotation fractale est analysée par de tels mécanismes. Les résultats obtenus suggèrent que les mécanismes sensibles à la rotation fractale seraient basés sur l’orientation; tandis que ceux sensibles à la rotation de premier ordre, basés sur l’énergie. De plus, une certaine dissociation des mécanismes responsables du traitement de la rotation fractale et de premier ordre serait présente. La deuxième étude avait pour but, quant à elle, d’établir l’effet du vieillissement sur l’intégration du mouvement de premier et deuxième ordre. Les résultats indiquent que les mécanismes sensibles au mouvement de deuxième ordre seraient davantage affectés, comparativement à ceux de premier ordre. Ainsi, les fonctions visuelles requérant une intégration corticale de plus haut niveau seraient davantage affectées par l’effet du vieillissement. / Motion perception ensures the execution of safe navigation, as well as efficient interaction with the environment. As such, it is essential to understand the nature of mechanisms ensuring motion perception, as well as effects of aging on their response. Two studies will be presented. The first aimed at identifying the nature of mechanisms responsible for the perception of fractal rotation, a novel stimulus introduced by Benton et al. (2007). This stimulus has been created to isolate form sensitive mechanisms. Several authors have suggested that second-order motion sensitive mechanisms use position cues to extract motion (Seiffert & Cavanagh, 1998). Hence, the following study aimed at determining whether fractal rotation is analyzed by such mechanisms or not. Results suggest fractal rotation sensitive mechanisms use orientation changes, whereas first-order sensitive mechanisms use energy. Moreover, dissociation between first-order and fractal rotation mechanisms has been observed. The second study aimed at establishing the effect of aging on first- and second-order motion integration. Results indicate second-order sensitive mechanisms would be more affected by aging, than first-order mechanisms. Accordingly, visual functions requiring higher order cortical integration are more likely to be more affected by aging.

During its mission, a launch vehicle is subject to broadband, severe, aeroacoustic and structure-borne excitations of various provenances, which can endanger the survivability of the payload and the vehicles electronic equipment, and consequently the success of the mission. Aerospace structures are generally characterized by the use of exotic composite materials of various configurations and thicknesses, as well as by their extensively complex geometries and connections between different subsystems. It is therefore of crucial importance for the modern aerospace industry, the development of analytical and numerical tools that can accurately predict the vibroacoustic response of large, composite structures of various geometries and subject to a combination of aeroacoustic excitations. Recently, a lot of research has been conducted on the modelling of wave propagation characteristics within composite structures. In this study, the Wave Finite Element Method (WFEM) is used in order to predict the wave dispersion characteristics within orthotropic composite structures of various geometries, namely flat panels, singly curved panels, doubly curved panels and cylindrical shells. These characteristics are initially used for predicting the modal density and the coupling loss factor of the structures connected to the acoustic medium. Subsequently the broad-band Transmission Loss (TL) of the modelled structures within a Statistical Energy Analysis (SEA) wave-context approach is calculated. Mainly due to the extensive geometric complexity of structures, the use of Finite Element(FE) modelling within the aerospace industry is frequently inevitable. The use of such models is limited mainly because of the large computation time demanded even for calculations in the low frequency range. During the last years, a lot of researchers focus on the model reduction of large FE models, in order to make their application feasible. In this study, the Second Order ARnoldi (SOAR) reduction approach is adopted, in order to minimize the computation time for a fully coupled composite structural-acoustic system, while at the same time retaining a satisfactory accuracy of the prediction in a broadband sense. The system is modelled under various aeroacoustic excitations, namely a diffused acoustic field and a Turbulent Boundary Layer (TBL) excitation. Experimental validation of the developed tools is conducted on a set of orthotropic sandwich composite structures. Initially, the wave propagation characteristics of a flat panel are measured and the experimental results are compared to the WFEM predictions. The later are used in order to formulate an Equivalent Single Layer (ESL) approach for the modelling of the spatial response of the panel within a dynamic stiffness matrix approach. The effect of the temperature of the structure as well as of the acoustic medium on the vibroacoustic response of the system is examined and analyzed. Subsequently, a model of the SYLDA structure, also made of an orthotropic sandwich material, is tested mainly in order to investigate the coupling nature between its various subsystems. The developed ESL modelling is used for an efficient calculation of the response of the structure in the lower frequency range, while for higher frequencies a hybrid WFEM/FEM formulation for modelling discontinuous structures is used.

This thesis examines second-order optical nonlinear wave mixing processes in domain-disordered quasi-phase matching waveguides and evaluates their potential use in compact, monolithically integrated wavelength conversion devices. The devices are based on a GaAs/AlGaAs superlattice-core waveguide structure with an improved design over previous generations. Quantum-well intermixing by ion-implantation is used to create the quasi-phase matching gratings in which the nonlinear susceptibility is periodically suppressed. Photoluminescence experiments showed a large band gap energy blue shift around 70 nm after intermixing. Measured two-photon absorption coefficients showed a significant polarization dependence and suppression of up to 80% after intermixing. Similar polarization dependencies and suppression were observed in three-photon absorption and nonlinear refraction. Advanced modeling of second-harmonic generation showed reductions of over 50% in efficiency due to linear losses alone. Self-phase modulation was found to be the dominant parasitic nonlinear effect on the conversion efficiency, with reductions of over 60%. Simulations of group velocity mismatch showed modest reductions in efficiency of less than 10%. Experiments on second-harmonic generation showed improvements in efficiency over previous generations due to low linear loss and improved intermixing. The improvements permitted demonstration of continuous wave second-harmonic generation for the first time in such structures with output power exceeding 1 µW. Also, Type-II phase matching was demonstrated for the first time. Saturation was observed as the power was increased, which, as predicted, was the result of self-phase modulation when using 2 ps pulses. By using 20 ps pulses instead, saturation effects were avoided. Thermo-optically induced bistability was observed in continuous wave experiments. Difference frequency generation was demonstrated with wavelengths from the optical C-band being converted to the L- and U-bands with continuous waves. Conversion for Type-I phase matching was demonstrated over 20 nm with signal and idler wavelengths being separated by over 100 nm. Type-II phase matched conversion was also observed. Using the experimental data for analysis, self-pumped conversion devices were found to require external amplification to reach practical output powers. Threshold pump powers for optical parametric oscillators were calculated to be impractically large. Proposed improvements to the device design are predicted to allow more practical operation of integrated conversion devices based on quasi-phase matching superlattice waveguides.

In this thesis, new design concepts for arch bridges using ultra high-performance fibre-reinforced concrete are developed for spans of 50 to 400 m. These concepts are light-weight and efficient, and thus have the potential to significantly reduce the cost of construction. Lightness is achieved by the thinning of structural components and the efficient use of precompression in the arch, rather than by the decrease of bending stiffness. Using the advanced properties of the material, the design concepts were shown to reduce the consumption of concrete in arch bridges by more than 50% relative to arches built using conventional concrete technology. In addition to span length, other design parameters including span-to-rise ratio and deck-stiffening were considered, resulting in a total of seventy-two design concepts. Other important contributions made in this thesis include: (1) the development of a simple analytical model that describes the transition of shallow arches between pure arch behaviour and pure beam behaviour, (2) a comprehensive comparative study of 58 existing concrete arch bridges that characterizes the current state-of-the-art and serves as a valuable reference design tool, and (3) the development and experimental validation of general and simplified methods for calculating the capacity of slender ultra high-performance fibre-reinforced concrete members under compression and bending. The research presented in this thesis provides a means for designers to take full advantage of the high compressive and tensile strengths of the concrete and hence to exploit the economic potential offered by the material.

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Cette thèse traite des équations différentielles stochastiques rétrogrades réfléchies du second ordre dans une filtration générale . Nous avons traité tout d'abord la réflexion à une barrière inférieure puis nous avons étendu le résultat dans le cas d'une barrière supérieure. Notre contribution consiste à démontrer l'existence et l'unicité de la solution de ces équations dans le cadre d'une filtration générale sous des hypothèses faibles. Nous remplaçons la régularité uniforme par la régularité de type Borel. Le principe de programmation dynamique pour le problème de contrôle stochastique robuste est donc démontré sous les hypothèses faibles c'est à dire sans régularité sur le générateur, la condition terminal et la barrière. Dans le cadre des Équations Différentielles Stochastiques Rétrogrades (EDSRs ) standard, les problèmes de réflexions à barrières inférieures et supérieures sont symétriques. Par contre dans le cadre des EDSRs de second ordre, cette symétrie n'est plus valable à cause des la non linéarité de l'espérance sous laquelle est définie notre problème de contrôle stochastique robuste non dominé. Ensuite nous un schéma d'approximation numérique d'une classe d'EDSR de second ordre réfléchies. En particulier nous montrons la convergence de schéma et nous testons numériquement les résultats obtenus. / This thesis deals with the second-order reflected backward stochastic differential equations (2RBSDEs) in general filtration. In the first part , we consider the reflection with a lower obstacle and then extended the result in the case of an upper obstacle . Our main contribution consists in demonstrating the existence and the uniqueness of the solution of these equations defined in the general filtration under weak assumptions. We replace the uniform regularity by the Borel regularity(through analytic measurability). The dynamic programming principle for the robust stochastic control problem is thus demonstrated under weak assumptions, that is to say without regularity on the generator, the terminal condition and the obstacle. In the standard Backward Stochastic Differential Equations (BSDEs) framework, there is a symmetry between lower and upper obstacles reflection problem. On the contrary, in the context of second order BSDEs, this symmetry is no longer satisfy because of the nonlinearity of the expectation under which our robust stochastic non-dominated stochastic control problem is defined. In the second part , we get a numerical approximation scheme of a class of second-order reflected BSDEs. In particular we show the convergence of our scheme and we test numerically the results.

A need for a South African leadership-unit performance structural model, created from the performance index and second-order factor structure of the Leadership Behaviour Inventory was established. This study focuses on the creation of such a second-order factor structure. Theron and Spangenberg (2005) identified three plausible models and highlighted two for further analysis. Theoretical scrutiny supported the two proposed models. The two-factor model was created from the multifactor leadership questionnaire's transformational and transactional second-order factors (Avolio, Bass & Jung, 1999) and the three-factor model comprised the general leadership, management behaviour and supervisory leadership second-order factors of House (1995). Factor analysis, exploratory factor analysis and confirmatory factor analysis were conducted on the proposed models. Results indicated average-fitting models. The five-factor model proposed by Theron and Spangenberg (2005) comparatively has an improved fit and is viewed as the most plausible model for the creation of the leadership-unit performance structural model. / Psychology / M.A. (Psychology)