Ce travail de thèse a pour objet la mise en oeuvre d'une méthode de calcul des états liés dans les structures à multipuits quantiques. Il participe ainsi à l'amélioration des outils de simulation permettant d'optimiser les composants avant leur réalisation. Nous présentons le modèle physique utilisé ainsi que les différentes méthodes couramment employées pour le calcul de ces états. Une comparaison avec le calcul par éléments finis du premier ordre montre un avantage majeur de notre approche dans des cas limites usuels comme le couplage de deux puits identiques ou le calcul des bandes de valence d'un puits quantique large, ainsi qu'en terme de rapidité. La finalité de ce calcul est l'évaluation du gain matériau, élément de base de la simulation des composants. Ce nouveau module vient compléter le simulateur BCBV dont nous rappelons les principaux modèles tels que celui de dérive-diffusion et du couplage électrique-optique en semi-classique. Cependant, la présence de zones quantiques peut nécessiter une approche par la matrice de densité pour rendre compte, de manière plus précise, des phénomènes de transport. Pour finir, nous tentons de comparer les résultats de la simulation du gain avec des mesures effectuées à partir de lasers de type Fabry-Pérot.

<p>Fixed-collision correlated sampling for Monte Carlo (MC) simulations is a method which can be used in order to shorten the simulation time for brachytherapy treatment planning in a 3D patient geometry. The increased efficiency compared to conventional MC simulation is measured by efficiency gain. However, a previous study showed that, in some cases, PDFs (probability density functions) of estimates of the efficiency gain, simulated using resampling and other MC methods, were multimodal with values below 1. This means that the method was less effective than conventional sampling for these cases. The aims of this thesis were to trace the causes of the multimodal distributions and to propose techniques to mitigate the problem caused by photons with high statistical weights.Two simulation environments were used for the study case, a homogeneous and a heterogeneous environment. The homogenous environment consisted of a water sphere with the radius 100mm. For the heterogeneous environment a cylindrical block of tungsten alloy (diameter 15 mm, height 2.5 mm) was placed in the water sphere. The sphere was divided into an array of cubic voxels of size 2.5 mm x 2.5 mm x 2.5 mm for dose calculations. A photon source was positioned in the middle of the water sphere and emitted photons with the energy 400 keV.It was found that the low values and multimodal PDFs for the efficiency gain estimates originated from photons depositing high values of energy in some voxels in the heterogeneous environment. The high energy deposits were due to extremely high statistical weights of photons interacting repeatedly in the highly attenuating tungsten cylinder. When photon histories contributing to the rare events of high energy deposits (outliers) were removed, the PDFs became uni-modal and efficiency gain increased. However, removing outliers will cause results to be biased calling for other techniques to handle the problem with high statistical weights.One way to resolve the problem in the current implementation of the fixed-collision correlated sampling scheme in PTRAN (the MC code used) could be to split photons with high statistical weights into several photons with the same sum weight as the initial photon. The splitting of photons will result in more time consuming simulations in areas with high attenuation coefficients, which may not be the areas of interest. This could be resolved by using Russian roulette, eliminating some of the photons with high statistical weight in such areas.Fixed-collision correlated sampling for Monte Carlo (MC) simulations is a method which can be used in order to shorten the simulation time for brachytherapy treatment planning in a 3D patient geometry. The increased efficiency compared to conventional MC simulation is measured by efficiency gain. However, a previous study showed that, in some cases, PDFs (probability density functions) of estimates of the efficiency gain, simulated using resampling and other MC methods, were multimodal with values below 1. This means that the method was less effective than conventional sampling for these cases. The aims of this thesis were to trace the causes of the multimodal distributions and to propose techniques to mitigate the problem caused by photons with high statistical weights.Two simulation environments were used for the study case, a homogeneous and a heterogeneous environment. The homogenous environment consisted of a water sphere with the radius 100mm. For the heterogeneous environment a cylindrical block of tungsten alloy (diameter 15 mm, height 2.5 mm) was placed in the water sphere. The sphere was divided into an array of cubic voxels of size 2.5 mm x 2.5 mm x 2.5 mm for dose calculations. A photon source was positioned in the middle of the water sphere and emitted photons with the energy 400 keV.It was found that the low values and multimodal PDFs for the efficiency gain estimates originated from photons depositing high values of energy in some voxels in the heterogeneous environment. The high energy deposits were due to extremely high statistical weights of photons interacting repeatedly in the highly attenuating tungsten cylinder. When photon histories contributing to the rare events of high energy deposits (outliers) were removed, the PDFs became uni-modal and efficiency gain increased. However, removing outliers will cause results to be biased calling for other techniques to handle the problem with high statistical weights.One way to resolve the problem in the current implementation of the fixed-collision correlated sampling scheme in PTRAN (the MC code used) could be to split photons with high statistical weights into several photons with the same sum weight as the initial photon. The splitting of photons will result in more time consuming simulations in areas with high attenuation coefficients, which may not be the areas of interest. This could be resolved by using Russian roulette, eliminating some of the photons with high statistical weight in such areas.</p>

<p>An analog-to-digital converter (ADC) is a link between the analog and digital domains and plays a vital role in modern mixed signal processing systems. There are several architectures, for example flash ADCs, pipeline ADCs, sigma delta ADCs,successive approximation (SAR) ADCs and time interleaved ADCs. Among the various architectures, the pipeline ADC offers a favorable trade-off between speed,power consumption, resolution, and design effort. The commonly used applications of pipeline ADCs include high quality video systems, radio base stations,Ethernet, cable modems and high performance digital communication systems.Unfortunately, static errors like comparators offset errors, capacitors mismatch errors and gain errors degrade the performance of the pipeline ADC. Hence, there is need for accuracy enhancement techniques. The conventional way to overcome these mentioned errors is to calibrate the pipeline ADC after fabrication, the so-called post fabrication calibration techniques. But environmental changes like temperature and device aging necessitates the recalibration after regular intervals of time, resulting in a loss of time and money. A lot of effort can be saved if the digital outputs of the pipeline ADC can be used for the estimation and correctionof these errors, further classified as foreground and background techniques. In this thesis work, an algorithm is proposed that can estimate 10% inter stage gain errors in pipeline ADC without any need for a special calibration signal. The efficiency of the proposed algorithm is investigated on an 8-bit pipeline ADC architecture.The first seven stages are implemented using the 1.5-bit/stage architecture whilethe last stage is a one-bit flash ADC. The ADC and error correction algorithms simulated in Matlab and the signal to noise and distortion ratio (SNDR) is calculated to evaluate its efficiency.</p>

<p>This thesis focuses on the widely acknowledged so-called brain drain controversy. More concretely on developments in the traditional brain drain literature towards a new shift, claiming the brain gain effect, as an alternative to the brain drain effect, that emigration may bring to a source country. The research investigates not only the obvious direct loss effects – the so called brain drain – but also the possibility of more subtle indirect beneficial effects.</p>

Recent years have seen a growing interest in a new kind of periodic structures called ``metamaterials'. These new artificial materials exhibit many new appealing properties, not found in nature, and open many new possibilities in the domain of antenna design. This thesis describes efficient numerical tools and methods for the analysis of infinite and finite periodic structures. A numerical simulation code based on the Method of Moments has been developed for the study of both large phased arrays and periodic metamaterials made of metal and/or dielectrics. It is shown how fast infinite-array simulations can be used in a first instance to approximately describe the fields radiated by large antenna arrays or compute transmission and reflection properties of metamaterials. These infinite-array simulations rely on efficient computation schemes of the doubly periodic Green’s function and of its gradient. A technique based on eigenmode analysis is also described, that allows to efficiently compute the dispersion curves of periodic structures. Accounting for the finiteness of real structures is possible in good approximation thanks to a finite-by-infinite array approach. Moreover, the excitation of large finite periodic structures by a single (non periodic) source can be studied by using a combination of the Array Scanning Method with a windowing technique. All these techniques were validated numerically on several examples and it is finally shown how they can be combined to design high gain antennas, based on metamaterial superstrates excited by a slotted waveguide. The proposed design method relies on the separation of the whole structure in two different problems. An interior problem is used to optimize the input impedance of the antenna, while the radiation pattern can be optimized in the exterior problem.

Genetic gain studies in the past have been used to evaluate the historical improvement of different traits and give insight into what magnitudes of gain might be possible in the future. Additionally, they have been carried out to defend the role of genetics during periods of stagnant or decreasing yield trends. This study was conducted over a 2-year period (2003 and 2004) and included nine current or obsolete cotton (Gossypium hirsutum L.) cultivars grown in 5 plant densities designed to evaluate varying levels of interplant competition. Plant densities were single plant culture with plants spaced 3m x 3m, 2m x 2m, 1m x 1m, 1m x 0.3m, and two commercial populations with plants spaced 1m x 0.1m. Results were analyzed for each trait to determine whether genetic gains are interrelated with tolerance to interplant competition or strictly under genetic control. The rates of genetic gain for lint yield were highest in the 1m x 0.1m, 1m x 0.3m, and 1m x 1m treatment with slopes of 8.7, 8.2, and 7.1 kg ha-1 yr-1 respectively. The slopes were each significantly smaller in the 2m x 2m and 3m x 3m spaced populations with gains of 3.6 and 1.5 kg ha-1 yr-1 respectively, implying that for lint yield, genetic gains have been made for tolerance to interplant competition. Similarly, modern maize hybrids only out perform obsolete hybrids at higher plant densities. Genetic gain for lint yield, fiber length, fiber strength, and fiber micronaire made in the context of tolerance to interplant competition is due in large part to the excellent performance of Deltapine 491 (2002) at higher plant populations.

With increased demand for bandwidth-hungry applications such as video-on-demand, wavelength-division-multiplexing passive optical network (WDM-PON) has become a strong contender in overcoming the last mile bottle neck. However, the wide-scale deployment of WDM-PONs has been delayed mainly due to the high cost of wavelength-specific optical components. To realize cost-effective WDM-PONs, various wavelength-independent, so called colorless architectures, have been developed so that all the subscribers can have identical optical network units (ONUs). In such WDM-PONs, however, single-fiber bidirectional transmission results in degradation of system performance caused by interference between the signals and backreflections. This thesis investigates the impact of backreflections on single-fiber bidirectional WDM-PONs. A WDM-PON with various optical line terminals (OLTs) and colorless ONU configurations is presented. The dependence of the power penalty, caused by backreflections, on a variety of parameters is investigated. This includes parameters such as the source linewidths, receiver bandwidth, transmission line loss (TLL), ONU gain, chirp effect at the ONU and optical return loss (ORL), in various WDM-PON configurations. The WDM-PON with continuous wave (CW) seed light and remodulation schemes are both presented and studied experimentally. The impacts of the backreflections on the single-fiber bidirectional WDM-PON with various OLT and ONU configurations are compared and analyzed accordingly.

Introduction: Using an animal model, we examined weight gain in rats exposed to olanzapine, as well as whether increased weight was associated with food intake, visceral fat and/or locomotion. Methods: Sprague-Dawley rats were chronically treated with olanzapine while being offered diets including standard chow, a high fat (60% fat) diet, and a high fat/high carbohydrate (42% fat; 42.7% carbohydrate) diet. Body weight, food intake, visceral fat and locomotor activity were measured. Results: Our findings related to weight gain are in line with other reports indicating that while olanzapine-induced weight gain can be observed, it does not mirror what is observed in humans on two levels: (i) it is not of the same magnitude, and (ii) it is more gender specific i.e., females greater than males. Conclusions: These data confirm that chronic treatment with olanzapine has varying effects on weight gain, food intake, visceral fat and locomotor activity.

The European emission standard is an EU directive which describes what emission limits car manufactures are required to meet. In order to meet these requirements car manufacturers use different techniques and components. In a modern diesel automobile a Diesel Particulate Filter (DPF) is used to gather soot from the exhausts. As soot accumulates in the DPF, the back pressure increases and the capability to hold more soot decreases. Therefore the DPF continuously needs to get rid of the stored soot. The soot is removed through a process called regeneration. In order to optimize when to perform regeneration, it is vital to know the amount of soot in the filter. A method for estimating the soot mass in a DPF using a radio frequency-based sensor has been developed. The sensor that has been studied is the Accusolve soot sensor from General Electric. A parameter study has been performed to evaluate the parameters that affects the sensor’s output. Parameters that have been studied include positioning of the sensor, temperature in the DPF, flow rate through the DPF and distribution of soot in the DPF. Different models for estimation of soot mass in the DPF has been developed and analyzed. An uncertainty caused by removing the coaxial cable connectors when weighing the DPF has been identified and methods for minimizing this uncertainty has been presented. Results show that the sensor output is sensitive to temperature, soot distribution and position, and also show some sensitivity to the flow rate. An ARX model, with only one state, is proposed to estimate the soot mass in the DPF, since it gives the best prediction of soot mass and showed good resistance to bias errors and noise in all the input signals.

Introduction: Using an animal model, we examined weight gain in rats exposed to olanzapine, as well as whether increased weight was associated with food intake, visceral fat and/or locomotion. Methods: Sprague-Dawley rats were chronically treated with olanzapine while being offered diets including standard chow, a high fat (60% fat) diet, and a high fat/high carbohydrate (42% fat; 42.7% carbohydrate) diet. Body weight, food intake, visceral fat and locomotor activity were measured. Results: Our findings related to weight gain are in line with other reports indicating that while olanzapine-induced weight gain can be observed, it does not mirror what is observed in humans on two levels: (i) it is not of the same magnitude, and (ii) it is more gender specific i.e., females greater than males. Conclusions: These data confirm that chronic treatment with olanzapine has varying effects on weight gain, food intake, visceral fat and locomotor activity.