Le but du travail de cette thèse est d'optimiser le procédé de mise en forme par tréfilage en utilisant une approche expérimentale, une modélisation analytique et une simulation numérique par éléments finis. Cette étude consiste à analyser les mécanismes de déformation et d'endommagement, mis en jeu par ce processus, qui constitue un problème multi physique complexe. Cette complexité se traduit par l'influence de nombreux paramètres intrinsèques et extrinsèques sur les propriétés de tréfilabilité des matériaux. Une analyse paramétrique du procédé de tréfilage a montré que différents paramètres ainsi que leurs interactions mutuelles, ont des effets significatifs sur la contrainte de tréfilage durant le processus de déformation plastique, en prenant en compte la géométrie de l'outil et le taux d'écrouissage. Les effets de la température dans la filière et de la vitesse de déformation sur le coefficient de frottement, à l'interface fil-filière, ont été pris en considération dans les formulations analytiques. La simulation numérique du tréfilage d'un fil en cuivre a été réalisée en se basant sur une modélisation utilisant une loi de comportement élastoviscoplastique du matériau, validée par des résultats expérimentaux. Les problèmes de contact, les effets thermomécaniques ont été pris en compte dans cette phase de calculs. Un modèle d'endommagement découplé, basé sur un critère énergétique, est utilisé pour prédire la localisation et la forme des défauts dans les fils soumis à des conditions critiques de tréfilage. Les résultats sont validés à partir des données expérimentales et des observations microscopiques de! l'endommagement dans la partie centrale du fil et de l'usure des filières. / The aim of this thesis work is to optimize the process of forming by wiredrawing, using an experimental approach, an analytical modeling and a numerical simulation by finite elements. This study is to analyze the mechanisms of deformation and damage, being involved in this process, which is a multi complex physical problem. This complexity is reflected by the influence of many intrinsic and extrinsic parameters on the properties of materials drawability. A parametric analysis of the drawing process has shown that different parameters and their mutual interactions have significant effects on the drawing stress during the plastic deformation process, taking into account the tool geometry and the hardening of the drawn material. The effects of temperature in the die and the strain rate on the coefficient of friction at the interface wire-die have been taken into account in the analytical formulations. The numerical simulation of a copper wiredrawing was done based on modeling using a behavior law for material taking account the hardening and the strain rate dependence, and validated by experimental results. Contact problems, the thermo mechanical effects were taken into account in these calculations. A coupled damage model based on an energy criterion is used to predict the location and the shape of defects in a wire deformed by critical conditions of drawing. The results have validated using experimental data and microscopie observations of damage in the central part of the wire and the die wear.

In this thesis, the c-axis-oriented AlN films were deposited on piezoelectric substrates, lithium niobate (LiNbO3), ST-Quartz, and non-piezoelectric substrate, silicon (Si), by reactive rf magnetron sputtering. AlN films were deposited with the nitrogen concentration (N2/Ar+N2) of 20¡ã80%, the chamber pressure of 1¡ã15mTorr, the rf power of 200¡ã450W, the deposition time of 1~3 hours and the substrate temperature of 100¡ã400¢J. The correlation between growth parameters and piezoelectric coefficients will be investigated by XRD¡Bd33 and K2 analysis in this study. The experimental results showed that the values of d33 become larger as the intensity of X-ray is stronger. It can also be concluded that the smaller the FWHM of (002) XRD peak is, the larger the value of d33 is. With various sputtering parameters, the K2 values exhibit diversely. The multilayer structures of AlN/LiNbO3 and AlN/ST-Quartz both make lower values of K2. In general, by combining the higher K2 and d33 values of LiNbO3 and ST-Quartz with high wave velocity of AlN, the high-frequency with high performance SAW devices can be obtained.

In this paper, the slipping friction is considered in the problem of a progressive wave of real fluids propagating over a permeable bottom. In the interface of soil and fluid, the ¡§no-slip¡¨ condition is relaxed and a sliding friction coefficient is introduced. Thus, the slipping effect and the permeability of bottom on the velocity near the seabed can be studied. The results indicate that the joint effect of slipping friction and permeability is crucial. The overshooting phenomena also can be explained by this joint effect.

Research indicates a warming global climate leads to change in the spatial and temporal characteristics of precipitation. Although precipitation is inherently variable through time and space, for some water-sensitive stakeholders, the evenness with which precipitation is distributed through a time interval rivals the importance of total precipitation amount and frequency within that period. This study uses a relatively new approach of analyzing inequity in the temporal distribution of precipitation to examine the recent historical record of precipitation across the United States. The Gini coefficient (GC), which has been commonly used in the field of economics to measure wealth distribution, was used here to assess inequity in the temporal distribution of daily precipitation through seasonal and annual timeframes. Additionally, the Lorenz asymmetry coefficient (LAC) was used to assess the magnitude of daily precipitation events (light, heavy) associated with inequity in the temporal distribution of precipitation. The concept of using these two metrics together to quantify changes in the character with which precipitation occurs across a time interval has yet to be documented for areas within the United States. Therefore, this study expands upon previous research of long-term hydroclimatic change and variability by illustrating the combined ability of these two relatively under-utilized metrics, the GC and the LAC, to enhance quantification of recent change in the characteristics of the temporal distribution of daily precipitation across the United States. The first element of the research presented here is demonstration of the utility of the GC and LAC metrics using data from the physically diverse mid-Atlantic sub-region of the United States. This research used station-level daily precipitation data to compute historic time series of intra-annual and intra-seasonal precipitation amount, precipitation frequency, GC, LAC, variance (V), and interquartile range (IQR). The results of this portion of the research show that when compared to other simpler measures of characterizing variability (i.e., V and IQR), the GC is relatively robust to both the number of days with precipitation and the total precipitation received in a temporal increment (i.e., season or year). The research expanded in scale to the continental United States, requiring data integration to a regional level to facilitate data analysis and physical understanding. The analysis used gridded seasonal means (1981 – 2010) of four precipitation characteristics: precipitation amount, precipitation frequency, GC, and LAC to delineate regions of homogenous precipitation characteristics. To accomplish this, a multi-step regionalization technique was employed. Specifically, the historic seasonal means were subjected to a Principal Components Analysis (PCA), and the resulting component scores were subjected to several cluster analysis techniques. The average linkage clustering technique produced the most logical clustering solution, indicating that 15 regions of homogenous precipitation exist within the contiguous United States. It is argued that the regions better serve hydroclimatic analyses than the nine climate regions designated by the United States National Centers for Environmental Information (NCEI). The third element of the research integrates the first two research elements in study of recent United States hydroclimate variability and change. For the 15 United States hydroclimate regions, regionally averaged water year time series (1949 – 2018) of precipitation amount, precipitation frequency, GC, and LAC were computed using in-situ precipitation data gathered from the NCEI's Global Historical Climatology Network (GHCN)-Daily database. The time series of all precipitation characteristics for each region were then subjected to the nonparametric Mann-Kendall trend test to assess the significance of each trend, and the Sen's slope estimator was used to quantify the magnitude of the trend. Time series that characterize two key atmospheric characteristics, total column water vapor and static stability, were also computed for each region. For most of the 15 study regions, water year total precipitation and precipitation frequency increased through the latter half of the 20th century. The largest magnitude of change in water year total precipitation and precipitation frequency occurred in the time series of regions located within the eastern and northern portions of the contiguous United States. Results also show that inequity in the temporal distribution of water year precipitation increased through the 70-year study period for most of the 15 study regions. Combined, these results indicate that days with light and heavy precipitation are becoming more prevalent at the expense of days with moderate precipitation. Furthermore, variability in the time series of some precipitation characteristics for several regions coincide with variability in the atmospheric variables that characterize total column water vapor and static stability, however the dominant driver of hydroclimatic change across the contiguous United States remains elusive. / Doctor of Philosophy / Research indicates a warming global climate leads to change in the spatial and temporal characteristics of precipitation. These changes could adversely affect some water-sensitive stakeholders who are concerned not only with the amount of precipitation received over time, but also with the manner in which the precipitation is distributed through time – all at once, or spread evenly. The Gini coefficient (GC), which has been commonly used in the field of economics to measure wealth distribution, was used here to assess inequity in the temporal distribution of daily precipitation through seasonal and annual timeframes. Additionally, the Lorenz asymmetry coefficient (LAC) was used to assess the magnitude of daily precipitation events (light, heavy) that were primarily responsible for inequity in the distribution of daily precipitation amounts through each time interval. The research presented here used gridded seasonal means (1981 – 2010) of four precipitation characteristics: precipitation amount, precipitation frequency, GC, and LAC to delineate regions of homogenous precipitation characteristics. Through this process, 15 hydroclimatic regions were delineated within the contiguous United States. Regionally averaged annual time series (1949 – 2018) of precipitation amount, precipitation frequency, GC, and LAC were computed for each region using station-level precipitation. The time series of each precipitation characteristic, and for each region were then examined for statistical trends through the 70-year study period. Regional time series which characterize two key atmospheric characteristics, total column water vapor and static stability, were also computed for each region. For most of the 15 study regions, water year total precipitation and precipitation frequency increased through the latter half of the 20th century. The largest magnitude of change in water year total precipitation and precipitation frequency occurred in the time series of regions located within the eastern and northern portions of the contiguous United States. Results also show that precipitation became less evenly distributed across the water year through the 70-year study period for most of the 15 study regions. Combined, these results indicate that days with light and heavy precipitation are becoming more prevalent at the expense of days with moderate precipitation. Furthermore, variability in the time series of some precipitation characteristics for several regions coincide with variability in the atmospheric variables that characterize total column water vapor and static stability, however the dominant driver of hydroclimatic change across the contiguous United States remains elusive.

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The well known binomial coefficient is the building block of Pascal’s triangle. We explore the relationship between functions of the binomial coefficient and Pascal’s triangle, providing proofs of connections between Catalan numbers, determinants, non-intersecting paths, and Baxter permutations.

Les paramètres de résistance au cisaillement des sols saturés sont souvent utilisés pour les analyses de stabilité de pentes. Dans les couches de sol situées au-dessus de la nappe, les pressions interstitielles de leau sont négatives et leffet de la succion est généralement négligé. Cette hypothèse est-elle raisonnable lorsque la majeure partie de la surface de glissement est au-dessus du niveau de la nappe? Notre travail tient compte des développements récents dans les procédures expérimentales et les approches théoriques. Ces recherches mettent en évidence certains aspects du comportement d'un sol non saturé et les effets de la succion sur la stabilité des pentes. Dans la partie expérimentale de ce travail, nous avons testé un limon d'Awans, un matériau naturel représentatif des sols de la région de Hesbaye (Belgique). Nous l'avons d'abord étudié en conditions saturées afin davoir un état de référence. Ensuite, des essais oedométriques et triaxiaux à succion ou à teneur en eau contrôlée ainsi que les essais de mesure de succion nous ont permis de mettre en évidence certains comportements hydromécaniques du matériau en conditions non saturées. Des essais oedométriques à succion contrôlée par la méthode osmotique ont montré que la succion rend le matériau plus rigide et accroît sa surface de plasticité. L'évaluation de la résistance au cisaillement a été faite de deux manières. D'une part en réalisant des essais triaxiaux à surpression d'air, une méthode assez complexe et qui dure longtemps. D'autre part, des essais triaxiaux non consolidés et non drainés UU qui sont nettement plus simples et plus rapides à réaliser, mais moins précis. D'une façon générale, les deux méthodes ont montré que la succion favorise le drainage du sol. Cet état s'accompagne d'une augmentation de la résistance au cisaillement du matériau via la "cohésion capillaire". Dans la partie numérique de ce travail, nous avons étudié deux cas d'étude afin de montrer l'effet de la succion sur la stabilité des pentes. Pour cela, nous avons développé des outils numériques qui offrent la possibilité de prendre en compte la succion. Pour le calcul de la stabilité, nous avons utilisé la méthode appelée "c-ø réduction" du code éléments finis LAGAMINE et nous l'avons comparée aux méthodes de calcul classiques. Les applications ont montré que la prise en compte de la succion dans le calcul de stabilité des pentes conduit à une augmentation du coefficient de sécurité.

Abtract In this thesis, our purpose is to improve the refractive index models for direct-gap semiconductors. For refractive index spectrum of direct-gap compound semiconductors, most experimental data is available only bellow the bandgap absorption edge. For used in the optimum design of eltro-optic devices, such as waveguide, electro-absorption modulator and Mach-Zehnder interferometer. We have to utilize a little experimental data to extend refractive index spectrum to near and just above the band-gap edge. We have known that square of refractive index ( ) is dielectric constant ( ), so we decompose the dielectric constant ( ) into the part of band-to-band absorption and another part of single-oscillator high energy absorption. For the part of band-to-band absorption, we added broadening parameter ( ) and used Kramers-Kronig relation to transform the absorption coefficient into dielectric constant. For another part of single-oscillator high energy background absorption, we first cut the absorption part form experimental data and then use Sellmeier¡¦s equation to fit the residue data. Finally, recombine all equations and extend refractive index spectrum to near and just above the band-gap edge. We successfully built whole model and confirm our model with GaAs. The calculation result on GaAs shows an excellent agreement with the reported experimental data. Furthermore, We apply our model to direct-gap binary¡Bternary and quaternary compounded materials and extend our model to near and just above the band-gap edge very well.

The structures constructed on unsaturated soils are damaged by the movement of the soil underneath. The movement is basically due to the flow of moisture in and out of the soil. This change in moisture also affects the strength of the soil, thus resulting in failure of slopes of embankments constructed with these soils. Therefore, it is very important to study the diffusion properties of unsaturated soils. Study of the diffusion properties requires the determination of the diffusion coefficient (/). In this thesis improvements in the drying test, originally proposed by Mitchell (1979), have been discussed. The study also involves defining the evaporation coefficient (he) which has been ill-defined in previous research work. The flow through unsaturated soils is non-linear but due to the complexity involved it has been simplified to a linear problem. The nonlinear behavior has been studied during this research. Therefore, certain refinements have been applied in the determination of the diffusion coefficient. The laboratory procedure followed involves measuring the soil suction along the length of the sample and at different times using thermocouple psychrometers. The evaluation of the evaporation coefficient (he) has been made an integral part of the procedure. The diffusion coefficient is determined using the curve fitting procedure of Aubeny and Lytton, 2003.