Global Navigation Satellite Systems (GNSS) are vital tools for accurate navigation and timing for both civil and military use. Due to the low power of the GNSS signals, these systems are sensitive to interference attacks. For wideband GNSS jamming, adaptive antenna arrays are commonly used to suppress interference.  This thesis focuses on how distortions induced by adaptive antenna arrays can affect the performance of a GNSS receiver and how prone different beamforming algorithms are to suffer from such distortions. To investigate this, simulations in software have been performed for static scenarios with two different beamforming algorithms and four different antenna arrays. The results show that the method for interference suppression that uses constraints in direction and frequency achieves a higher signal-to-interference-plus-noise ratio, more stable acquisition over the hemisphere, and less fluctuating code delay error than the method that only minimizes the power of the output signal.

Manufacturing induced shape distortions is a common problem for composite materials. Due to the non-isotropic nature of carbon fibre reinforced polymers (CFRP) unavoidable deformations occur during part production. During fabrication of polymer composites, the material obtains its final shape at elevated temperatures. The curing process involves a transition from the liquid state to the solid, glassy state, allowing bonding between fibres and matrix. As the material cools the mismatch in thermal expansion coefficients and cure shrinkage obtained during the matrix polymerization leads to residual stresses on the mechanical level within composite part. There is a great interest from the aircraft and automotive industries, to increase the ability to understand development of shape distortions and residual stresses during the cure, since these deformations often lead to dissatisfaction of tolerances and it is essential to predict the deformations beforehand in order to compensate time and cost.  In this context, a study of residual stresses during the curing process of thermosetting resin composites is presented. A methodology is proposed for predicting the formation and development of manufacturing- induced residual stresses. The present project reports on a comprehensive experimental study on the dependency of different short curing cycles on the build-up of residual stresses in a carbon fibre/fast-curing epoxy system and evaluate of post-curing methods through induction heating and oven post-curing with unidirectional [904] and unsymmetrical [9020] laminates. It includes characterization in thermo-elastic properties and degree-of-cure of the material by Thermal bending test, thermal expansion test, mechanical tensile test and Differential Scanning Calorimetry (DSC) in non-post-cured and post-cured laminates. The results showed slight variation in the thermal properties and not effect in the mechanical properties at different cure and post-curing conditions. Analytical data by Laminate Analysis program validated the experimental thermo-elastic data with analytical simulations. In addition, it is shown improvements in the temperature distributions in the post-curing by induction heating with different experimental set-ups, however, oven post-curing showed a more systematic system, higher heat efficient a low cure temperature, with more consistent mechanisms of shape distortions and residual stresses compared to induction heating. These findings are relevant for the future development of prediction methods for process induced deformations of Fast Curing Epoxy Resins (FCER).

В работе обсуждается проблема дефиниции критического мышления, описывается структура критического мышления. Также обсуждаются различные виды когнитивных ошибок, выделяются 11 основных разновидностей. Представлен дизайн методики «Опросник когнитивных искажений». / The paper discusses the problem of defining critical thinking, describes the structure of critical thinking. Various types of cognitive errors are also discussed, and 11 major varieties are highlighted. The design of the “Cognitive distortion questionnaire” technique is presented.

Many distributed energy resource (DER) systems are remotely located and are often interfaced at low or medium voltage levels through power electronics converters such as voltage-sourced converters (VSC). Therefore, a weak-grid situation is encountered where the voltage and frequency at the point of DER coupling can experience fluctuations. A power converter designed to operate in normal and strong grid conditions may not perform satisfactorily during such weak and distorted grid conditions. Hence, considering the full dynamics of the system during weak-grid conditions in the design of converter control is indispensable to ensure the stability of the DER and the grid. For instance, the phase-locked loop (PLL) has been identified as a critical component of the VSC controller that can compromise the DER performance during weak-grid conditions. This dissertation investigates and enhances the performances of inverters connected to weak and polluted grids. It primarily presents a novel approach of enhancing the inverter current controller by including the PLL state variables among the entire system state and use them to optimally generate the control input for the VSC. This mitigates the loop interactions between the PLL and other control loops resulting in a mitigation of the oscillations that could cause system instabilities. The procedure is accomplished using the recently developed linear model of the enhanced PLL (EPLL) for single-phase applications and using a model of the three-phase PLL developed in this dissertation. Extensive simulation and experimental results are presented to evaluate and validate the proposed control approaches. Full practical models of all system components are considered for simulation studies. The experimental tests are done on a practical inverter connected to the utility grid. Significant improvement of the inverter performance in weak-grid conditions is confirmed. This dissertation offers a systematic way of integrating and designing the PLL and controller in a VSC to achieve a robust performance in weak-grid conditions.

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<p> This thesis presents a study of diagnostics of pulsed laser systems. Two simple and cost effective devices are constructed that measure common spatio-temporal distortions. The first is a spectrally-resolved knife-edge (SRKE) for spatially and spectrally resolving a laser beam, which enables spatio-temporal distortions to be measured. The second is an interferometric autocorrelation taken with a 2-photon diode. A lens is used to focus light from the entire cross section of the beam onto the diode. By scanning the diode through the focus, the effects of pulse-front-tilt on focused beam pulse durations can be measured. These techniques are compared with current theoretical models, and with each other, to establish their reliability and practicality, as well as the reliability of the commercial techniques. SRKE is found to be highly sensitive to spatial and angular dispersion, and also able to measure the frequency gradient, although not as precisely. Interferometric autocorrelation is only able to resolve effects on duration. It can detect the presence of significant spatio-temporal distortion, but several scans must be taken as a function of distance from the lens, through the focus.</p> <p> A commercially built GRENOUILLE was also tested on pulses compressed with a hollow-capillary-prism pulse compressor. Compression of 800 nm, 50 fs pulses to less than 19 fs was achieved with an overall transmission efficiency of 33%. With further work, efficiency could be increased, and pulse duration decreased.</p> / Thesis / Master of Science (MSc)