Les convertisseurs électroniques de puissance sont voués à fonctionner sous des conditions applicatives de plus en plus sévères tout en respectant les impératifs d’efficacité énergétique et de fiabilité. Or, les besoins industriels tendent vers un plus haut niveau d’intégration fonctionnelle tout en améliorant le rapport qualité-prix. Dès lors, la solution utilisée pour le report des puces semi-conductrices est le siège de densités de courant importantes et d’un flux thermique élevé. La présence de défauts dans cette couche d’interconnexion peut conduire à la dégradation de ses performances et au vieillissement prématuré du composant. L’objectif de nos recherches est d’évaluer la pertinence d’une méthodologie basée sur la confrontation de simulations numériques et de campagnes expérimentales. L’objectif est d’améliorer la compréhension du comportement électrothermique en régime de conduction d’un transistor MOSFET en présence d’un void dans sa brasure. Dans cette manuscrite, nous présenterons la construction d’un modèle intégrant le couplage électrothermique de la partie active qui sera confronté à la réponse de résultats expérimentaux. Puis, une étude numérique basée sur la théorie des plans fractionnaires, qui minimise le nombre de simulations, sera exploitée afin de quantifier l’impact de la taille et de la position du défaut sur la réponse électrothermique du composant et de ses liaisons électriques. Les détails de la mise en place d’une étude expérimentale analogue permettront de mettre en perspective la complémentarité de cette approche. / Power converters nowadays are required to function under harsh conditions in meeting energy efficiency and reliability requirement. Whereas, industrial specifications tend toward a higher level of power integration in respect to the cost constraint. As a result, the die attach is one of the key elements in power module packaging because of high current densities and high heat flow which are transported through. Void formation in the die attach may lead to performance degradation and premature aging of the component. This study introduces a methodology based on the comparison of numerical simulations and experimental campaigns. The obtained results help to improve our understanding on the electro-thermal behaviour of MOSFETs with solder voids. In this thesis, we depict a finite element model in which electro-thermal coupling of a MOSFET active layer is taken in to account. Simulation results will be correlated to the experimental responses. Later on, a parametric numerical study based on the response surface method (RSM) which minimizes the number of simulations and future tests will be exploited to quantify the impact of void position and size on several selective performance criteria. A future serial experimental study in respect to the same RSM design is expected in prospect, in order to fulfil the complementarity for this approach.

No description available.

We consider two applications of control charts in health care. The first involves the comparison of four methods designed to detect an increase in the incidence rate of a rare health event, such as a congenital malformation. A number of methods have been proposed: among these are the Sets method, two modifications of the Sets method, and the CUSUM method based on the Poisson distribution. Many of the previously published comparisons of these methods used unrealistic assumptions or ignored implicit assumptions which led to misleading conclusions. We consider the situation where data are observed as a sequence of Bernoulli trials and propose the Bernoulli CUSUM chart as a desirable method for the surveillance of rare health events. We compare the steady-state average run length performance of the Sets methods and its modifications to the Bernoulli CUSUM chart under a wide variety of circumstances. Except in a very few instances we find that the Bernoulli CUSUM chart performs better than the Sets method and its modifications for the extensive number of cases considered. The second application area involves monitoring clinical outcomes, which requires accounting for the fact that each patient has a different risk of death prior to undergoing a health care procedure. We propose a risk-adjusted survival time CUSUM chart (RAST CUSUM) for monitoring clinical outcomes where the primary endpoint is a continuous, time-to-event variable that is right censored. Risk adjustment is accomplished using accelerated failure time regression models. We compare the average run length performance of the RAST CUSUM chart to the risk-adjusted Bernoulli CUSUM chart, using data from cardiac surgeries to motivate the details of the comparison. The comparisons show that the RAST CUSUM chart is more efficient at detecting deterioration in the quality of a clinical procedure than the risk-adjusted Bernoulli CUSUM chart, especially when the fraction of censored observations is not too high. We address details regarding the implementation of a prospective monitoring scheme using the RAST CUSUM chart. / Ph. D.

We examine the effect of lane preference on a quasi one-dimensional three-state driven lattice gas, consisting of holes and positive and negative particles, and periodic boundary conditions in the longitudinal direction. Particles move via particle-hole and, with a lesser rate, particle-particle exchanges; the species are driven in opposite directions along the lattice, each preferring one of the lanes with a given probability, <I>p</I>. The model can be interpreted as traffic flow on a two-lane beltway, with fast cars preferring the left lane and slow cars preferring the right, viewed in a comoving frame. In steady-sate, the system typically exhibits a macroscopic cluster containing a majority of the particles. At very high values of <I>p</I>, a first order transition takes the system to a spatially disordered state. Using Monte Carlo simulations to analyze the system, we find that the size of the cluster increases with lane preference. We also observe a region of negative response, where increasing the lane preference <I>decreases</I> the number of particles in their favored lane, against all expectations. In addition, simulations show an intriguing sequence of density profiles for the two species. We apply mean-field theory, continuity equations, and symmetries to derive relationships between observables to make a number of predictions verified by the Monte Carlo data. / Master of Science

The calibration of modern internal combustion engines requires ever improving measurement data quality such that they comply with increasingly stringent emissions legislation. This study establishes methodology and a software tool to improve the quality of steady-state emissions measurements from engine dynamometer tests. Literature shows state of the art instrumentation are necessary to monitor the cycle-by-cycle variations that significantly alter emissions measurements. Test methodologies that consider emissions formation mechanisms invariably focus on thermal transients and preconditioning of internal surfaces. This work sought data quality improvements using three principle approaches. An adapted steady-state identifier to more reliably indicate when the test conditions reached steady-state; engine preconditioning to reduce the influence of the prior day’s operating conditions on the measurements; and test point ordering to reduce measurement deviation. Selection of an improved steady-state indicator was identified using correlations in test data. It was shown by repeating forty steady-state test points that a more robust steady-state indicator has the potential to reduce the measurement deviation of particulate number by 6%, unburned hydrocarbons by 24%, carbon monoxide by 10% and oxides of nitrogen by 29%. The variation of emissions measurements from those normally observed at a repeat baseline test point were significantly influenced by varying the preconditioning power. Preconditioning at the baseline operating condition converged emissions measurements with the mean of those typically observed. Changing the sequence of steady-state test points caused significant differences in the measured engine performance. Examining the causes of measurement deviation allowed an optimised test point sequencing method to be developed. A 30% reduction in measurement deviation of a targeted engine response (particulate number emissions) was obtained using the developed test methodology. This was achieved by selecting an appropriate steady-state indicator and sequencing test points. The benefits of preconditioning were deemed short-lived and impractical to apply in every-day engine testing although the principles were considered when developing the sequencing methodology.

No description available.

Shallow foundations are widely used in different types of soils for supporting the loads from the lightly loaded superstructures of various civil infrastructures both on level and sloping ground. Design of shallow foundations in geotechnical engineering practice is widely based on the principles of saturated soil mechanics because they are relatively simple. However, the soil near the ground surface (i.e., vadose zone) in which the shallow foundations are typically placed is in an unsaturated state. The water content variation in unsaturated soils is influenced by hydrological events such as the snow melt, rainfall infiltration, evaporation, and the plant transpiration. Due to this reason, the hydro-mechanical properties (i.e., coefficient of permeability, shear strength and volume change) of unsaturated soils are sensitive to the variation in soil suction associated with water content changes. These properties in turn have a significant impact on the bearing capacity and settlement behavior of the shallow foundations. Therefore, it is rational to investigate shallow foundations’ behavior extending the principles of unsaturated soil mechanics. During the last two decades, there has been a significant interest towards investigating shallow foundations based on unsaturated soil mechanics. Laboratory, field, and model studies highlight that matric suction variation in unsaturated soils has a significant influence on the bearing capacity and settlement behavior of shallow foundations. However, the focus of most of the presently available studies in the literature consider mostly vertical loading conditions on level soil ground. There are limited studies related to the design of shallow foundations on sloping ground and subjected to inclined and eccentric loading conditions. Also, there are only few studies that consider the effect of the steady state and transient flow conditions on the foundation bearing capacity evaluation. Therefore, one of the key objectives of this thesis is directed toward developing rational tools for investigating shallow foundations considering the steady state and transient flow conditions associated with water infiltration and evaporation in unsaturated soils. Comprehensive investigation studies are undertaken to interpret the influence of the steady state and transient flow conditions on the shallow foundations related to: (i) bearing capacity on the sloping ground in different types of soils including expansive soils, and (ii) bearing capacity under the inclined and eccentric loading conditions with homogeneous soil properties and considering spatial variation of soil properties. Succinct details related to investigated studies are summarized below: (1) An analytical method is proposed for quantifying the bearing capacity of the shallow foundations on unsaturated soil slopes considering different rainfall infiltration conditions. The proposed method is a novel tool for considering the simultaneous influence of several parameters that include the flow rates, the infiltration duration, the foundation set-back distance and the ground water table depth on the foundation bearing capacity. (2) Another analytical method is proposed for evaluating the foundation bearing capacity under inclined and eccentric loading considering both the steady state and transient flow conditions. Semi-empirical equations are proposed for describing the failure envelops in vertical and horizontal (V - H) loading space and in the vertical and moment (V - M) loading space. These equations are capable to describe the variation of failure envelops considering the influence of the groundwater table depth variation, internal friction angles, surface flux boundary conditions and different infiltration durations. (3) The influence of infiltration on the combined performance of both the foundation and the slope in cracked expansive soils is evaluated with the aid of a numerical technique. A semi-empirical model that describes the elastic modulus and the matric suction is implemented into the numerical model. Bimodal soil water characteristic curve is used as a tool for understanding the influence of surface cracks in the numerical study in a simplified manner. The influence of the rainfall intensity, rainfall duration, foundation setback distance and foundation loading on the combined performance of foundation and slope were investigated. Results combined with some suggestions for rational design procedures are presented that can be useful for geotechnical engineers in practice applications. (4) Numerical analyses are conducted for shallow foundations under vertical and combined loading subjected to different flow conditions. A numerical code procedure is exclusively developed as a part of this study to: (i) consider the variation of soil properties along with the matric suction fluctuations in the commercial software ABAQUS with the aid of a user developed subroutine USDFLD; (ii) incorporate the spatial variability of soil properties into the finite element model. Comparisons are provided between the numerical study and other methods such as the experimental investigations, the analytical methods, and the semi-empirical equations for bearing capacity failure envelopes. In addition, comparisons are also made between the failure envelopes and the failure mechanisms contour using the model considering soil spatial variability and homogeneous soil properties. The proposed methods in this thesis are simple to use for evaluating bearing capacity of shallow foundations that are subjected to steady state and transient state flow conditions considering two scenarios: (i) foundation on sloping ground (ii) foundation under inclined and eccentric loading. The results from the above studies reveal that it is the relationship between the soil permeability and the rainfall characteristics that mainly control the water infiltration rates. The soil suction and the effective degree of saturation are influenced by the water infiltration rates and have a significant impact on the foundation as well as the slope behavior. More importantly, the investigations undertaken in this thesis contribute towards addressing the research gaps related to the behavior of foundations in unsaturated soils. Various scenarios considered in this thesis include the influence of unsaturated flow have not been considered earlier in the literature. The results of the studies summarized in this thesis are expected to be useful for practicing geotechnical engineers in the optimal design of shallow foundations extending the principles of unsaturated soil mechanics for various soils. Moreover, the proposed methods can be used for interpreting the foundation behavior for their entire life span service. In addition, these methods can be employed to rationally explain the field-measured data and can also be used in the forensics analyses of failed slopes and shallow foundations.

No description available.

No description available.

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