A new circuit is proposed that uses an RC-CR filter in a feedback configuration to achieve a wideband precision quadrature phase shift with constant amplitude response. Such a circuit can be used to perform image rejection in a low IF receiver using the Hartley method. Simulation results show that the circuit can achieve an average image rejection ratio of 50 dB over a 16 MHz bandwidth. The feedback loop enables the circuit to maintain high accuracy over process and temperature.

Wind energy is a field with a large number of uncertainties. The random nature of the weather conditions, including wind speed, wind direction, and turbulence intensity, influences the energy output and the structural safety of a wind farm, making its performance fluctuate and difficult to predict. The uncertainties presented in the energy output and structure lifetime lead to increased investment risk. There are possibilities to reduce the risk associated with these uncertainties by optimizing the design of the farm or the wind turbine, with respect to the stochastic parameters. The goal of this project is to improve the wind farm optimization problem by providing accurate and computationally efficient annual energy production (AEP) estimates, which is a uncertainty quantification that is required in every optimization step. Uncertainty quantification has been recognized as a challenge in the wind energy industry, as the chaotic nature of the weather condition complicates the prediction of energy production. High-fidelity wind farm models usually employ advanced models like Large Eddy Simulation or Reynolds averaged Navier-Stokes equation for better accuracy. However, the prolonged computation time of these high-fidelity models make the traditional uncertainty quantification approach like the Monte-Carlo simulation or other integration techniques infeasible for larger wind farms.  To overcome this limitation, the report proposes the use of generalized polynomial chaos expansion (PCE) to characterize the AEP as a function of wind speed and wind direction. PCE is a technique that approximates a random variable using a series of orthogonal polynomials, the polynomials are chosen based on the target distribution. This report explains how a surrogate model of the AEP can be constructed using PCE, which can be used in optimization or model analysis. The objective of the thesis work is to minimize the number of model evaluations required for obtaining an accurate energy response surface. Different ideas of non-intrusive PCE are implemented and explored in this project. The report demonstrates that, the multi-element polynomial chaos fitted by point collocation, with a dependent polynomial basis, is not only able to make accurate and stable (with respect to the placement of the measurements) energy predictions, but also produces realistic energy response surface. / Vindkraft är en bransch med många osäkerheter, där väderförhållandena påverkar energiproduktionen och strukturens livslängd. Denna osäkerhet ökar investeringsrisken, men kan minskas genom optimering av vindkraftverkets design med hänsyn till de stokastiska parametrarna. Syftet med denna rapport är att förbättra optimeringsproblemet för vindkraftverk genom att ge noggranna och effektiva årliga energiproduktionsberäkningar (AEP), vilket krävs vid varje optimeringssteg. I rapporten används polynomial chaos expansion (PCE) för att approximera AEP och minska antalet nödvändiga modellutvärderingar. Resultaten visar att PCE är en effektiv metod för att göra energiprognoser.

The first part of my thesis is concerned with estimation for longitudinal data using generalized semi-parametric mixed models and multilevel generalized linear mixed models for a binary response. Likelihood based inferences are hindered by the lack of a closed form representation. Consequently, various integration approaches have been proposed. We propose a spherical radial integration based approach that takes advantage of the hierarchical structure of the data, which we call the 2 SR method. Compared to Pinheiro and Chao's multilevel Adaptive Gaussian quadrature, our proposed method has an improved time complexity with the number of functional evaluations scaling linearly in the number of subjects and in the dimension of random effects per level. Simulation studies show that our approach has similar to better accuracy compared to Gauss Hermite Quadrature (GHQ) and has better accuracy compared to PQL especially in the variance components. The second part of my thesis is concerned with identifying differentially expressed gene pathways/gene sets. We propose a logistic kernel machine to model the gene pathway effect with a binary response. Kernel machines were chosen since they account for gene interactions and clinical covariates. Furthermore, we established a connection between our logistic kernel machine with GLMMs allowing us to use ideas from the GLMM literature. For estimation and testing, we adopted Clarkson's spherical radial approach to perform the high dimensional integrations. For estimation, our performance in simulation studies is comparable to better than Bayesian approaches at a much lower computational cost. As for testing of the genetic pathway effect, our REML likelihood ratio test has increased power compared to a score test for simulated non-linear pathways. Additionally, our approach has three main advantages over previous methodologies: 1) our testing approach is self-contained rather than competitive, 2) our kernel machine approach can model complex pathway effects and gene-gene interactions, and 3) we test for the pathway effect adjusting for clinical covariates. Motivation for our work is the analysis of an Acute Lymphocytic Leukemia data set where we test for the genetic pathway effect and provide confidence intervals for the fixed effects.

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Wireless body area networks (WBANs) have tremendous potential to benefit from wireless communication technology and are expected to make sweeping changes in the future human health care and medical fields. While the prospects for WBAN products are high, meeting required device performance with a meager amount of power consumption poses significant design challenges. In order to address these issues, IEEE has recently developed a draft of IEEE 802.15.6 standard dedicated to low bit-rate short-range wireless communications on, in, or around the human body. Commercially available SoC (System-on-Chip) devices targeted for WBAN applications typically embed proprietary wireless transceivers. However, those devices usually do not meet the quality of service (QoS), low power, and/or noninterference necessary for WBAN applications, nor meet the IEEE standard specifications. This dissertation presents a design of low-power RF front-end conforming to the IEEE standard in Medical Communication Service (MICS) band of 402-405 MHz. First, we investigated IEEE 802.15.6 PHY specifications for narrow band WBAN applications. System performance analysis and simulation for an AWGN (additive white Gaussian noise) channel was conducted to obtain the BER (bit error rate) and the PER (packet error rate) as the figure of merit. Based on the system performance study, the link budget was derived as a groundwork for our RF front-end design. Next, we examined candidate RF front-end architectures suitable for MICS applications. Based on our study, we proposed to adopt a direct conversion transmitter and a low-IF receiver architecture for the RF front-end. An asynchronous wake-up receiver was also proposed, which is composed of a carrier sensing circuit and a serial code detector. Third, we proposed and implemented low-power building blocks of the proposed RF front-end. Two quadrature signal generation techniques were proposed and implemented for generation of quadrature frequency sources. The two quadrature voltage controlled oscillators (QVCOs) were designed using our proposed current-reuse VCO with two damping resistors. A stacked LNA and a down-conversion mixer were proposed for low supply and low power operation for the receiver front-end. A driver amplifier and an up-conversion mixer for the transmitter front-end were implemented. The proposed driver amplifier uses cascaded PMOS transistors to minimize the Miller effect and enhance the input/output isolation. The up-conversion mixer is based on a Gilbert cell with resistive loads. Simulation results and performance comparisons for each designed building block are presented. Finally, we present a case study on a direct VCO modulation transmitter and a super-regenerative receiver, which can also be suitable for an MICS transceiver. Several crucial building blocks including a digitally-controlled oscillator (DCO) and quench signal generators are proposed and implemented with a small number of external components. / Ph. D.

The probability density function (PDF) approach is a powerful technique for large eddy simulation (LES) based modeling of turbulent reacting flows. In this approach, the joint-PDF of all reacting scalars is estimated by solving a PDF transport equation, thus providing detailed information about small-scale correlations between these quantities. The objective of this work is to further develop the LES/PDF approach for studying flame stabilization in supersonic combustors, and for soot modeling in turbulent flames. Supersonic combustors are characterized by strong shock-turbulence interactions which preclude the application of conventional Lagrangian stochastic methods for solving the PDF transport equation. A viable alternative is provided by quadrature based methods which are deterministic and Eulerian. In this work, it is first demonstrated that the numerical errors associated with LES require special care in the development of PDF solution algorithms. The direct quadrature method of moments (DQMOM) is one quadrature-based approach developed for supersonic combustion modeling. This approach is shown to generate inconsistent evolution of the scalar moments. Further, gradient-based source terms that appear in the DQMOM transport equations are severely underpredicted in LES leading to artificial mixing of fuel and oxidizer. To overcome these numerical issues, a new approach called semi-discrete quadrature method of moments (SeQMOM) is formulated. The performance of the new technique is compared with the DQMOM approach in canonical flow configurations as well as a three-dimensional supersonic cavity stabilized flame configuration. The SeQMOM approach is shown to predict subfilter statistics accurately compared to the DQMOM approach. For soot modeling in turbulent flows, an LES/PDF approach is integrated with detailed models for soot formation and growth. The PDF approach directly evolves the joint statistics of the gas-phase scalars and a set of moments of the soot number density function. This LES/PDF approach is then used to simulate a turbulent natural gas flame. A Lagrangian method formulated in cylindrical coordinates solves the high dimensional PDF transport equation and is coupled to an Eulerian LES solver. The LES/PDF simulations show that soot formation is highly intermittent and is always restricted to the fuel-rich region of the flow. The PDF of soot moments has a wide spread leading to a large subfilter variance. Further, the conditional statistics of soot moments conditioned on mixture fraction and reaction progress variable show strong correlation between the gas phase composition and soot moments. / text

Cette thèse porte sur l'approximation des équations aux dérivées partielles, en particulier l'équation de diffusion en tomographie optique. Elle peut se présenter en deux parties essentielles. Dans la première partie on discute le problème direct alors que le problème inverse est abordé dans la seconde partie. Pour le problème direct, on suppose que les paramètres optiques et les fonctions sources sont donnés. On résout alors le problème de diffusion dans un domaine où la densité du flux lumineux est considérée comme une fonction inconnue à approcher numériquement. Le plus souvent, pour reconstruire le signal numérique dans ce genre de problème, une discrétisation dans le temps est nécessaire. Nous avons proposé d'utiliser la transformée de Fourier et son inverse afin d'éviter une telle discrétisation. Les techniques que nous avons utilisées sont la quadrature de Gauss-Hermite ainsi que la méthode de Galerkin basée sur les B-splines ou les B-splines tensorielles ainsi que sur les fonctions radiales. Les B-splines sont utilisées en dimension un alors que les B-splines tensorielles sont utilisées lorsque le domaine est rectangulaire avec un maillage uniforme. Lorsque le domaine n'est plus rectangulaire, nous avons proposé de remplacer la base des B-splines tensorielles par les fonctions à base radiale construites à partir d'un nuage de points dispersés dans le domaine. Du point de vue théorique, nous avons étudié l'existence, l'unicité et la régularité de la solution puis nous avons proposé quelques résultats sur l'estimation de l'erreur dans les espaces de type Sobolev ainsi que sur la convergence de la méthode. Dans la seconde partie de notre travail, nous nous sommes intéressés au problème inverse. Il s'agit d'un problème inverse non-linéaire dont la non-linéarité est liée aux paramètres optiques. On suppose qu'on dispose des mesures du flux lumineux aux bords du domaine étudié et des fonctions sources. On veut alors résoudre le problème inverse de façon à simuler numériquement l'indice de réfraction ainsi que les coefficients de diffusion et d'absorption. Du point de vue théorique, nous avons discuté certains résultats tels que la continuité et la dérivabilité, au sens de Fréchet, de l'opérateur mesurant le flux lumineux reçu aux bords. Nous avons établi les propriétés lipschitzienne de la dérivée de Fréchet en fonction des paramètres optiques. Du point de vue numérique nous nous somme intéressés au problème discret dans la base des B-splines et la base des fonctions radiales. En suite, nous avons abordé la résolution du problème inverse non-linéaire par la méthode de Newton-Gauss.

The increase in capacity demand along with the advancement in digital signal processing (DSP) have recently revived the interest in coherent optical communications and led to its commercialization. However, design and development of robust DSP algorithms for example for carrier phase recovery (CPR) becomes complex as we opt for high order modulation formats such as 16QAM and beyond. Further, electrical-domain dispersion compensation (EDC), while providing many advantages, makes the system more susceptible to laser frequency noise (FN). For instance, in coherent optical links with post-reception EDC, while the transmitter frequency noise causes only phase impairment, the local oscillator (LO) FN in these systems results in a noise enhancement in both amplitude and phase. This noise is commonly known as equalization enhanced phase noise (EEPN). It results in asymmetric requirements for transmitter laser and LO laser. Further, the system design in the presence of lasers with non-white frequency noise becomes increasingly challenging for increased capacity-distance product. The main contributions of this thesis are, firstly, an experimentally validated theory of coherent optical links with lasers having general non-white frequency noise spectrum and corresponding system/laser design criteria and mitigation technique. Secondly, low complexity and high phase noise tolerant CPR for high order modulation formats. The general theory propounded in this thesis elucidates the origin of the laser frequency noise induced noise enhancement in coherent optical links with different DSP configurations. The thesis establishes the existence of multiple frequency noise regimes and shows that each regime results in different set of impairments. The influence of the impairments due to some regimes can ideally be reduced by optimizing the corresponding mitigation algorithms, while other regimes cause irretrievable impairments. Experimentally validated theoretical boundaries of these regimes and corresponding criteria applicable to system/laser design are provided. Further, an EEPN mitigation method and its two possible implementations are proposed and discussed. The thesis also demonstrates an intrinsic limitation of the conventional Blind Phase Search (BPS) algorithm due to angular quantization and provides methods to overcome it. Finally, this thesis proposes and demonstrates single stage and multi-stage carrier phase recovery algorithms for compensation of phase impairments due to the two lasers for higher order circular and square modulations. The proposed methods outperform the state of art algorithms both in performance and in complexity. / <p>QC 20170516</p> / European project ICONE gr. #608099