No description available.

L’imbibition est d’une importance fondamentale dans de nombreuses applications technologiques et intervient par ailleurs dans de nombreux phénomènes naturels (industrie textile, industrie pharmaceutique, érosion des sols ….). Malgré l’importance de ce phénomène, la description et la modélisation des mécanismes d’imbibition sont encore sujettes à discussion dans la littérature, en particulier, la prédiction des cinétiques d’imbibition à partir de la connaissance de la topographie du milieu poreux. L’objectif de ce travail de thèse a été de relier les cinétiques d’imbibition à la structure du milieu poreux imbibé. Pour cela, nous avons étudié l’imbibition capillaire (ou spontanée) en suivant une démarche expérimentale dans laquelle nous avons utilisé des substrats poreux modèles dont nous contrôlons le volume et la structure de pores. La configuration d’imbibition choisie dans ce travail est celle d’une goutte sessile (ou posée).Ces travaux ont permis de mettre en œuvre une technique de construction de pastilles macroscopiques, autosupportées et cohésives, par assemblage de microbilles de polymère. Ces systèmes modèles ont été utilisés pour étudier les cinétiques d’imbibition capillaire de liquides dans des supports tridimensionnels à structure de pores complexe en fonction de la taille des microbilles constituant la pastille poreuse, de la reconstruction thermique, de la perméabilité pour une structure poreuse bicouches et de la force capillaire. Ces études ont permis entre autres de mettre en évidence des régimes cinétiques et des transitions d’imbibition inattendues dans ces systèmes (régimes visqueux et inertiel). / Imbibition is of fundamental importance in many technological applications, and is also involved in many natural phenomena (textile industry, pharmaceutical industry, soil erosion ....). Despite the importance of this phenomenon, the description and modelling of imbibition mechanisms are still subject to discussion in the literature, in particular, the prediction of the kinetics of imbibition from the knowledge of the morphology of the porous medium.The aim of this thesis was to relate the imbibition kinetics with the structure of a model porous medium. For this, we studied the capillary imbibition (or spontaneous) following an experimental approach in which we used a model porous substrate with both a controlled porous volume and pore structure. The experimental configuration for studying this imbibition was that of a sessile drop. In this work we developed a technique for the fabrication of self-supported and cohesive macroscopic pellets of polymer microbeads. These model porous systems have been characterized for their internal structure and used to study the capillary imbibition kinetics as a function of i) the size of the microbeads, ii) the temperature of the thermal annealing, iii) the permeability in the case of bilayered porous structures and iv) the capillary force (concentration of ethanol in water, nature of the liquid). This approach allowed observing and discussing unexpected imbibition regimes and transitions (inertial and viscous regimes).

Face à l'intérêt grandissant pour les forêts mélangées, des d'outils et des modèles adaptés à leur gestion sont nécessaires. L'objectif de cette thèse est de montrer comment la construction et la comparaison de modèles ayant différents niveaux de détail peuvent nous aider à choisir le niveau le plus approprié pour modéliser la croissance d'un peuplement mélangé dans un contexte d'application donné. A partir de données récoltées dans des peuplements mélangés chêne sessile (Quercus petraea L.) pin sylvestre (Pinus sylvestris L.), nous avons construit une famille de modèles à différents niveaux de détail : un modèle arbre indépendant des distances (MAID), un modèle arbre dépendant des distances (MADD), trois modèles peuplement et un modèle intermédiaire entre le MAID et le MADD utilisant des distributions de voisinage. Pour que la comparaison de ces modèles soit pertinente, nous avons assuré une cohérence entre les modèles en utilisant plusieurs approches. Ces modèles nous ont permis d'acquérir des connaissances sur la croissance et la dynamique de ces forêts en particulier sur les interactions spatiales et temporelles entre le chêne et le pin. Ainsi le MAID a permis de montrer qu'il peut y avoir des phénomènes de compensation de croissance entre les deux espèces. Le MADD a permis de montrer que dans ces peuplements la compétition intraspécifique est supérieure à la compétition interspécifique. Un modèle peuplement obtenu à partir du MADD a permis d'étudier l'influence du taux de mélange sur la production. Pour évaluer la qualité prédictive des modèles, nous avons utilisé un jeu de données indépendant obtenu en partageant nos données avant la construction des modèles. Nous avons ainsi montré que le MAID était plus performant que le MADD pour prédire les accroissements individuels. Les modèles ont aussi été comparés sur des exemples d'applications mettant en œuvre des simulations à court ou moyen terme. La démarche proposée présente un intérêt aussi bien pour la compréhension du phénomène étudié que pour sa modélisation dans un but prédictif. En regroupant l'ensemble des résultats acquis, ce travail nous a permis d'apprécier la pertinence d'un type de modèle en fonction du contexte d'utilisation. Cette démarche très générale pourrait être appliquée à la modélisation d'autres processus comme la mortalité ou la régénération.

Le thème de l'évolution historique de la productivité forestière est abordé pour les deux grands feuillus sociaux du territoire, hêtre commun (Fagus sylvatica L.) et chêne sessile (Quercus petraea Liebl.), conduits en futaie régulière et pure, en forêt domaniale, avec un objectif de description et quantification du phénomène à l'échelle du peuplement. L'analyse privilégie la croissance en hauteur dominante, indicateur classique de la productivité forestière. Elle repose sur la comparaison d'accroissements reconstitués de façon rétrospective (analyses de tiges) de deux générations de peuplements, associés en couples pour assurer un contrôle efficace des conditions de fertilité. L'évolution de la vitesse de croissance est estimée par une modélisation statistique des accroissements, qui prend en compte l'effet du stade de développement des peuplements et les différences de fertilité entre couples. Le diagnostic a été régionalisé, conduisant à échantillonner les hêtraies dans 2 secteurs (Normandie/Picardie et Lorraine/Alsace) et les chênaies dans 4 secteurs (Normandie, val de Loire, plaine d'Allier, Lorraine/Alsace). Une analyse complémentaire de la croissance radiale dominante (lectures de cernes) et de la densité du bois (microdensitométrie aux rayons X) à 1,30 m a été réalisée dans les hêtraies du Nord-Est. Les conditions trophiques et climatiques des peuplements ont été caractérisées. <br />L'augmentation de la vitesse de croissance en hauteur dominante a un caractère général sur le territoire, structuré selon un gradient longitudinal. Pour chaque essence, elle est plus marquée dans le Nord-Est, tandis qu'elle reste faible ou récente dans le Nord-Ouest. L'essentiel de l'évolution a été acquis dans la seconde moitié du siècle. La progression est ponctuée de crises d'origine climatique, communes ou spécifiques, dont la plus marquée est celle de la décennie 1940. Défavorable au hêtre, la décennie 1990 a été bénéfique au chêne, et explique que l'évolution constatée pour cette essence culmine en fin de siècle à un niveau bien supérieur à celui du hêtre. L'augmentation séculaire est comprise pour les extrêmes entre +20% et +100%, et atteint dans le Nord-Est un niveau commun aux deux essences de +50-60% en excluant la période récente. Dans ce secteur, les évolutions de croissance radiale et en hauteur du hêtre sont similaires. La densité du bois est restée stable. En conséquence, la productivité en biomasse a pu suivre l'évolution estimée sur la hauteur dominante. L'analyse des relations croissance - facteur du milieu permet d'aborder la causalité des changements de productivité, et suggère un déterminisme multifactoriel. Le climat aurait eu jusqu'alors des conséquences essentiellement conjoncturelles. Des effets saisonniers opposés sur la croissance sont de plus possibles. Le caractère récent des évolutions constatées, leur organisation spatiale, conjugués à une sensibilité des essences aux conditions trophiques, font ressortir le rôle clé possible des dépôts atmosphériques azotés dans la réponse aux changements de l'environnement.

The present work was initiated to investigate the surface- and interfacial phenomena for iron and slag/iron systems. The aim was to understand the mechanism of the effect of surface active elements on surface and interfacial properties. In the present work, the adsorption of oxygen and sulfur on iron surface as well as adatom surface movements were studied based on the ab initio method. BCC iron melting phenomena and sulfur diffusion in molten iron were investigated by Monte Carlo simulations. The impact of oxygen potential on interfacial mass transfer was carried out by X-ray sessile drop method. Firstly, the structural, electronic and magnetic properties as well as thermodynamic stability were studied by Density functional theory (DFT). The hollow site was found to be the most stable adsorption site both for oxygen and sulfur adsorbed on iron (100) surface, which is in agreement with the experiment. The relaxation geometries and difference charge density of the different adsorption systems were calculated to analyze the interaction and bonding properties between Fe and O/S. It can be found that the charge redistribution was related to the geometry relaxation. In addition, the sulfur coverage is considered from a quarter of one monolayer (1ML) to a full monolayer. It was found that the work function and its change Δφ increased with S coverage, in very good agreement with experiment. Due to a recent discussion regarding the influence of charge transfer on Δφ, it is shown in the present work that the increase in Δφ can be explained by the increasing surface dipole moment as a function of S coverage. S strongly interacts with the surface Fe layer and decreases the surface magnetic moment as the S coverage increases. Secondly, a two dimensional (2D) gas model based on density functional calculations combined with thermodynamics and statistical physics, was proposed to simulate the movement of the surface active elements, viz. oxygen and sulfur atoms on the Fe(100) surface. The average velocity of oxygen and sulfur atoms was found to be related to the vibration frequencies and energy barrier in the final expression developed. The calculated results were based on the density function and thermodynamics &amp; statistical physics theories. In addition, this 2D gas model can be used to simulate and give an atomic view of the complex interfacial phenomena in the steelmaking refining process. A distance dependent atomistic Monte Carlo model was developed for studying the iron melting phenomenon as well as effect of sulfur on molten iron surface. The effect of boundary conditions on the melting process of an ensemble of bcc iron atoms has been investigated using a Lennard-Jones distance dependent pair potential. The stability of melting process was energetically and spatially analyzed under fixed wall and free surface conditions and the effects of short and long-range interactions were discussed. The role of boundary conditions was significantly reduced when long-range interactions were used in the simulation. This model was further developed for investigating the effect of sulfur on molten iron surface. A combination of fixed wall and free surface boundary condition was found to well-represent the molten bath configuration while considering the second nearest neighbor interactions. Calculations concerning the diffusion of sulfur on molten surface were carried out as a function of temperature and sulfur concentration. Our results show that sulfur atoms tended to diffuse away from the surface into the liquid bulk and the diffusion rate increased by increasing temperature. Finally, impact of oxygen potential on sulfur mass transfer at slag/metal interface, was carried out by X-ray sessile drop method. The movement of sulfur at the slag/metal interface was monitored in dynamic mode at temperature 1873 K under non-equilibrium conditions. The experiments were carried out with pure iron and CaO-SiO2-Al2O3-FeO slag (alumina saturated at the experimental temperature) contained in alumina crucibles with well-controlled partial pressures of oxygen and sulfur. As the partial pressure of oxygen increased, it was found that interfacial velocity as well as the oscillation amplitude increased. The thermo-physical and thermo-chemical properties of slag were also found to influence interfacial velocity. / QC 20101123

The present thesis deals with two-phase electrohydrodynamic simulations of bubble and droplet dynamics under externally applied electric fields. We used the Coupled Level-Set and Volume-of-fluid method (CLSVOF) and two different electrohydrody-namic formulations to study the process of bubble and drop formation from orifices and needles, the interactions of two conducting drops immersed in a dielectric medium, and the oscillations of sessile drops under two different ways of applying external elec-tric field. For the process of bubble formation in dielectric liquids due to the injection of air from submerged orifices and needles, we show that a non-uniform electric field pro-duces smaller bubbles while a uniform electric field changes only the bubble shape. We further explain the reason behind the bubble volume reduction under a non-uniform electric field. We show that the distribution of the electric stresses on the bubble inter-face is such that very high electric stresses act on the bubble base due to a non-uniform electric field. This causes a premature neck formation and bubble detachment lead-ing to the formation of smaller bubbles. We also observe that the non-uniform elec-tric stresses pull the bubble interface contact line inside the needle. With oscillatory electric fields, we show that a further reduction in bubble sizes is possible, but only at certain electric field oscillation frequencies. At other frequencies, bubbles bigger than those under a constant electric field of strength equal to the amplitude of the AC electric field, are produced. We further study the bubble oscillation modes under an oscillatory electric field. We implemented a Volume-of-fluid method based charge advection scheme which is charge conservative and non-diffusive. With the help of this scheme, we were able to simulate the electrohydrodynamic interactions of conducting-dielectric fluid pairs. For two conducting drops inside a dielectric fluid, we observe that they fail to coalesce when the strength of the applied electric field is beyond a critical value. We observe that the non-coalescence between the two drops occur due to the charge transfer upon drop-drop contact. The electric forces which initially bring the two drops closer, switch direction upon charge transfer and pull the drops away from each other. The factors governing the non-coalescence are the electric conductivity of the drop’s liquid which governs the time scale of charge transfer relative to the capillary time scale and the magnitude of the electric forces relative to the capillary and the viscous forces. Similar observations are recorded for the interactions of a charged conducting drop with an interface between a dielectric fluid and a conducting fluid which is the same as the drop’s liquid. For the case of a pendant conducting drop attached to a capillary and without any influx of liquid from the capillary, we observed that the drop undergoes oscillations at lower values of electric potential when subjected to a step change in the applied electric potential. At higher values of electric potential, we observed the phenomenon of cone-jet formation which results due to the accumulation of the electric charges and thus the electric forces at the drop tip. For the formation of a pendant conducting drops from a charged capillary due to liquid injection, we observed that the drops are elongated in presence of an electric field. This happens because the free charge which appears at the drop tip is attracted towards the grounded electrode. This also leads to the formation of elongated liquid threads which connect the drop to the capillary during drop detachment. We plotted the variation of total electric charge inside the drops with respect to time and found the charge increases steeply as the drop becomes elongated and moves towards the grounded electrode. For sessile drop oscillations under an alternating electric field, two different modes of operations are studied. In the so called ‘Contact mode’ case, the droplet is placed on a dielectric coated grounded electrode and the charged needle electrode remains in direct contact with the drop as it oscillates. In the ‘Non-contact mode’ case, the drop is placed directly on the grounded electrode and electric potential is applied to a needle electrode which now remains far from the drop. We show that the drop oscillations in the contact mode are caused by concentration of electric forces near the three phase contact line where the electric charge accumulates because of the repulsion from the needle. For the non-contact mode, we observe that the electric charge is attracted by the needle towards the drop apex resulting in a concentration of the electric forces in that region. So the drop oscillates due to the electric forces acting on a region near the drop tip. We also present the variation of the total electric charge inside the drop with respect to time for the two cases studied.

Experimental vibration analysis of mechanical structures is a well established field.Plenty of literature exists on macro scale structures in the fields of civil, mechanical and aerospace engineering, but the study of vibrations of micro scale structures such as MEMS, liquid droplets, and biological cells is relatively new. For such structures, the amplitudes of vibration are typically in nanometeror sub-nanometer range and the frequencies are in KHz to MHz range depending upon the dimensions of the structure. In our study, we use a scanningLaser Doppler Vibrometer (LDV) to measure the vibrations of micro-scale objects such as MEMS structures, micro droplets and cells. The vibrometercan capture frequency response up to 24 MHz withpicometer displacement resolution. First, we present the study of dynamics of a 2-D micromechanical structure—a MEMSelectrothermal actuator. The structure is realized using SOI MUMPs process from MEMSCAP. The fabricated device is tested for its dynamic performance characteristics using the LDV. In our experiments, we could capture up to 50 out-of-plane modes of vibration—an unprecedented capture—with a single excitation. Subsequent FEM based numerical simulations confirmed that the captured modes were indeed what the experiments indicated, and the measured frequencies werefound to be within 5% of theoretically predicted. Next, we study the dynamics of a 3-D micro droplet and show how the substrate adhesion modulates the natural frequency of the droplet. Adhesion properties of droplets are decided by the degree of wettability that is generally measured by the contact angle between the substrate and the droplet. In this work, we were able to capture 14 modes of vibration of a mercury droplet on different substrates and measure the correspondingfrequencies experimentally. We verify these frequencies with analytical calculations and find that all the measured frequencies are within 6% of theoretically predicted values. We also show that considering any two pairs of natural frequencies, we can calculate the surface tension and the contact angle, thus providing a new method for measuring adhesion of a droplet on an unknown surface. Lastly, we present a study of vibrations of biological cells.Our first study is that of single muscle fibers taken from drosophila.Muscle fibers with different pathological conditions were held in two structural configurations—asa fixed-fixed beam and a cantilever beam—and their vibration signatures analysed.We found that there was significant reduction in natural frequency of diseased fibers. Among the diseased fibers, we could confidently classify the myopathies into nemaline and cardiac types based on the natural frequency of single fibers. We have noticed that the elastic modulus of the muscle which decides the natural frequency is dictated by the myosin expression levels. Our last example isa study of the vibration signatures of cancer cells. Here we measure the natural frequencies of normal and certain cancerous cells, and show that we can distinguish the two based on their natural frequencies. We find that the natural frequency of cancerous cells is approximately half of that of normal cells. Within the cancerous cells, we are able to distinguished epithelial cancer cells and mesenchymal cancer cells based on their natural frequency values. For Epithelial cells,we activate the signaling pathways to induce EMT and notice the reduction in the natural frequency. This mechanical assay based on vibration response corroborates results from the biochemical assays such as Western blots and PCR, thus opening a new technique of mechano-diagnostics.

This work deals with the metal surface wetting problems of molten lead-free solder and monitoring of ongoing processes at the inter-phase interface using the method of evaluation of the height of the molten solder deducted from the video sequences. The work is aimed at evaluating the metal surface wettability, wetting angle determined. Wettability of the metal surface is compared for different types of surface treatments and for different ages of the measured samples. Measurement is performed at the improved workplace, is used to evaluate the newly derived formula for calculating the wetting angle and created program for automatic evaluation of Picture is used to.

Serratierte Läsionen im Kolorektum stellen eine Problemzone für Kliniker und Pathologen dar; dies liegt zum einen an der noch nicht allgemein bekannten Nomenklatur, zum anderen an dem noch nicht abschließend geklärten Progressionsrisiko der verschiedenen serratierten Polypen. Mittlerweile gilt als akzeptiert, dass neben der klassischen Adenom-Karzinom-Sequenz ein alternativer serratierter und ein sogenannter gemischter Karzinogeneseweg existiert; diese Karzinogenesewege sind in Bezug auf die präinvasiven Vorstufen, die molekularen Pfade und die Prognose der Karzinome heterogen. Bei den serratierten Adenokarzinomen lassen sich ein Niedrigrisiko-Subtyp (Häufigkeit <20%, mit meist proximaler Lokalisation, dem sessilen serratierten Adenom als Vorläuferläsion, BRAF-Mutation, hoher Mikrosatelliteninstabilität, CpG-Methylierung/hMLH1-Ausfall und einer 5-Jahres-Überlebensrate von >70%) sowie ein Hochrisiko-Subtyp (Häufigkeit >80%, mit meist distaler Lokalisation, dem traditionellen serratierten Adenom als Vorläuferläsion, KRAS-Mutation, niedriger Mikrosatelliteninstabilität/mikrosatellitenstabil, CpG-Methylierung/ p53-Akkumulation und einer 5-Jahres-Überlebens-Rate von <30%) unterscheiden. Eine molekular pathologische Bestimmung des Mikrosatellitenstatus und einer BRAF-oder KRAS-Mutation in Verbindung mit einer hMLH1-und p53-Immunhistochemie lässt eine bessere Unterscheidung dieser beiden Typen zu und wird klinisch zunehmend relevant. / Serrated Lesions of the Colorectum – a Pathological or a Pathologist’s Problem? The classification and treatment of serrated lesions in the lower gastrointestinal tract remains a difficult task for clinicians and surgical pathologists; on the one hand, due to the inconsistent nomenclature of serrated lesions in the lower gastrointestinal tract and, on the other hand, due to the poor understanding of the underlying mechanisms and risk factors for progression of these lesions. It is widely accepted that in addition to the classic adenoma-carcinoma sequence a recently discovered serrated or mixed pathway is important in colorectal carcinogenesis. These two pathways are heterogeneous with regard to precursor lesions, molecular mechanisms and prognosis. Depending on their molecular signature, serrated colorectal adenocarcinomas, for instance, can be subdivided into a low-risk (frequency <20%, often with proximal location, the sessile serrated adenoma as a precursor lesion, BRAF mutation, high microsatellite instability, CpG methylation/hMLH1 loss and a 5-year survival rate of >70%) and a high-risk subtype (frequency >80%, often with distal location, the traditional serrated adenoma as a precursor lesion, KRAS mutation, low microsatellite instability/microsatellite stable, CpG methylation/ p53 accumulation and a 5-year survival rate of <30%). The evaluation of the microsatellite status as well as the detection of BRAF or KRAS mutations together with immunohistochemistry for hMLH1 and p53 will allow a discrimination between these two subtypes and will become increasingly important in the future. / Dieser Beitrag ist mit Zustimmung des Rechteinhabers aufgrund einer (DFG-geförderten) Allianz- bzw. Nationallizenz frei zugänglich.

Macroinvertebrates constitute the backbone of megafaunal communities in benthic ecosystems around the globe. Many macroinvertebrates have vital roles in benthic ecosystems, ranging from enhancing habitat complexity to providing staple food sources for other organisms. Regardless of how familiar macroinvertebrates are to the general public, very few studies have attempted to describe benthic macroinvertebrate assemblages across large spatial scale in the continental shelf waters of the Pacific Northwest. This study describes different subtidal macroinvertebrate assemblages off Washington and Oregon based on species-substrata associations and the key species that distinguish one assemblage from another. Two data sets were used for this study: underwater footage collected by the submersible Delta during 1993-1995 geological surveys, and footage collected by the remotely operated vehicle (ROV) Hammerhead during macroinvertebrate surveys in late summer 2011. Footages from these surveys were used to document species-substrata associations and distinguish different assemblages based on species composition similarities and dissimilarities. In addition, I determined if a specific group of invertebrates, Asteroids (Echinodermata), were useful in explaining different assemblage patterns, after all other environmental parameters were taken into account. Findings of this study can be used not only to shed light on the structure of macroinvertebrate communities in the Pacific Northwest, but also as baseline data for future research on the direct and indirect effects of potential offshore installations on macroinvertebrate communities across the continental shelf waters. / Graduation date: 2012