In this thesis, we develop a physical understanding of the effects of viscosity and geometry on the dynamics of interfacial flows in drops and bubbles. We first consider the coalescence of pairs of conical water droplets surrounded by air. Droplet pairs can form cones under the influence of an electric field and have been observed to coalesce or recoil depending on the angle of this cone. With high resolution numerical simulations we show the coalescence and non-coalescence of these drop pairs is negligibly affected by the electric field and can be understood through a purely hydrodynamic process. The coalescence and recoil dynamics are shown to be self similar, demonstrating that for these conical droplet pairs viscosity has a negligible effect on the observed behavior. We generalize this result to the coalescence and recoil of droplets with different cone angles, and focus on droplets coalescing with a liquid bath and flat substrate. From the simulations of these droplets with different cone angles, an equivalent angle is found that describes the coalescence and recoil behavior for all water cones of any cone angle. While viscosity is found to negligibly affect the coalescence of conical water drops, it plays a key role in regulating the coalescence process of bursting gas bubbles. When these gas bubbles burst, a narrow liquid jet is formed that can break up into tiny liquid jet drops. Through consideration of the effects of viscosity, we show that these jet drops can be over an order of magnitude smaller than previously thought. Here, viscosity plays a key role in balancing surface tension and inertial forces and determining the size of the jet drops. Finally, we investigate the drainage of surfactant free, ultra-viscous bubbles where surface tension serves only to set the initial shape of the bubble. We use interferometry to find the thickness profiles of draining bubble films up to the point the of rupture. A theoretical film drainage model considering the balance of viscous and gravitational stresses is developed and numerically computed. The numerical results are found to be consistent with the experimentally obtained thickness profiles. In this work we provide insight into the role of viscosity in the outlined interfacial flows. The results of this thesis will advance the understanding of drop production in clouds, the marine climate, and the degassing of glass melts.

Developing chemical bonding models in clusters is one of the most challenging tasks of modern theoretical chemistry. There are two reasons for this. The first one is that clusters are relatively new objects in chemistry and have been extensively studied since the middle of the 20th century. The second reason is that clusters require high-level quantum-chemical calculations; while for many classical molecules their geometry and properties can be reasonably predicted by simpler methods. The aim of this dissertation was to study doped clusters and explain their chemical bonding. The research was focused on three classes of compounds: aluminum clusters doped with one nitrogen atom, planar compounds with hypercoordinate central atom, partially mixed carbon-boron clusters, and transition metal clusters. The geometry of the two latter classes of compounds was explained using the concept of aromaticity, previously developed in our group.

No description available.

A physically motivated Internal State Variable (ISV) constitutive model is extended to account for shear influenced void evolution for predicting damage behavior in ductile solids. The revised ISV model is calibrated for an aluminum 7085-T711 alloy using a series of microstructure and mechanical property quantification experiments. The calibrated ISV model for the aluminum alloy is implemented in an implicit finite-element code (Abaqus) to simulate the deformation of notch Bridgman tension specimens at a variety of stress states and temperatures. The model revisions and calibrated aluminum ISV model are validated through successful prediction of mechanical and microstructure evolution for structures subjected to a variety of complex stress state conditions. The extended ISV model framework is used to study shear influenced plasticity and damage mechanisms resulting from ballistic impact of metals. A Rolled Homogeneous Armor (RHA) steel alloy is selected for the impact model due to wide availability of documented penetration characteristics and ballistic performance data of RHA steel. Finite Element Analysis (FEA) simulations of ballistic impact of rolled homogeneous armor (RHA) steel projectiles against RHA steel plates are performed using a calibrated ISV constitutive model for RHA steel. An FEA simulation based parametric study is performed to assess the effect of a variety of microstructure and mechanical properties on the ballistic performance of RHA steel targets. FEA simulations are used to predict a transition in ballistic perforation mechanisms for high hardness steel alloys by accounting for variations in microstructure properties qualitatively documented in the literature.

No description available.

No description available.

No description available.

No description available.

Acetylcholinesterase (AChE) terminates cholinergic neurotransmission by catalyzing the hydrolysis of the neurotransmitter acetylcholine (ACh). Inhibition of AChE has proven an effective treatment for the memory loss exhibited by early stage Alzheimer's disease (AD) patients; four AChE inhibitors (AChEI) have been approved by the FDA for this purpose. The first AChEI approved for the palliative treatment of AD-related memory loss was 9-amino-1,2,3,4-tetrahydroacridine (tacrine). Inhibition of AChE may present either therapeutic or toxic effects depending upon the dose administered. With the goal of discovering safe and effective pesticides to control the population of Anopheles gambiae, a malaria-transmitting mosquito indigenous to Sub-Saharan Africa, the reoptimization of the tacrine pharmacophore was undertaken. Because the optimized drug would necessarily be a poor inhibitor for human AChE (hAChE), initial ligand design focused on modification to tacrine known to negatively impact the inhibition potency for hAChE. Ultimately, an AChEI was discovered, which exhibited micromolar inhibition of Anopheles gambiae AChE (AgAChE) and essentially no potency for hAChE. Two units of this lead compound were tethered through an alkyl chain to yield a nanomolar inhibitor of AgAChE that was more than 1,100-fold selective for the mosquito enzyme over hAChE. Dimerization of an active inhibitor is an effective strategy to increase the potency and selectivity of AChEI, and many examples of tacrine hetero- and homodimers complexed to AChE can be found in the RCSB Protein Data Bank (PDB). The bond formed between the exocyclic amine moiety and the heterocyclic ring system of tacrine is analogous to an amide bond when tacrine is protonated. Therefore, the rotational profile of protonated N-alkyltacrine should exhibit a conformational profile in which dihedral angles significantly out of the plane formed by the ring system are associated with high energies relative to those when the dihedral angles are nearly coplanar with the ring system. The barrier of rotation (ΔG^‡) produced by this phenomenon in two tacrine derivatives and two quinoline derivatives was experimentally determined using dynamic 1H NMR. These values were compared to density functional theory (DFT) derived values for the same phenomenon. Furthermore, since the ΔG^‡ proved to be impossible to experimentally determine for the optimal model compound for the active site portion of tacrine dimers, N-methyltacrine, the DFT method employed for modeling the ΔG^‡ of the tacrine and quinoline analogs was used to computationally derive the entire rotational conformation diagram of N-methyltacrine. The calculated values were then used to comment on the relative energies of adopting certain conformations found in the X-ray crystal structures of dimer/AChE complexes. / Ph. D.

Cette thèse est consacrée à l'étude de systèmes subissant des coagulations et fragmentations successives. Dans le cas déterministe, on travaille avec des solutions mesures de l'équation de coagulation - multifragmentation. On étudie aussi la contrepartie stochastique de ces systèmes : les processus de coalescence - multifragmentation qui sont des processus de Markov à sauts. Dans un premier temps, on étudie le phénomène de coagulation seul. D'un côté, l'équation de Smoluchowski est une équation intégro-différentielle déterministe. D'un autre côté, on considère le processus stochastique connu sous le nom de Marcus-Lushnikov qui peut être regardé comme une approximation de la solution de l'équation de Smoluchowski. Nous étudions la vitesse de convergence par rapport à la distance de type Wassertein $d_{lambda}$ entre les mesures lorsque le nombre de particules tend vers l'infini. Notre étude est basée sur l'homogénéité du noyau de coagulation $K$.On complémente les calculs pour obtenir un résultat qui peut être interprété comme une généralisation de la Loi des Grands Nombres. Des conditions générales et suffisantes sur des mesures discrètes et continues $mu_0$ sont données pour qu'une suite de mesures $mu_0^n$ à support compact existe. On a donc trouvé un taux de convergence satisfaisant du processus Marcus-Lushnikov vers la solution de l'équation de Smoluchowski par rapport à la distance de type Wassertein $d_{lambda}$ égale à $1/sqrt{n}$.Dans un deuxième temps on présente les résultats des simulations ayant pour objectif de vérifier numériquement le taux de convergence déduit précédemment pour les noyaux de coagulation qui y sont étudiés. Finalement, on considère un modèle prenant en compte aussi un phénomène de fragmentation où un nombre infini de fragments à chaque dislocation est permis. Dans la première partie on considère le cas déterministe, dans la deuxième partie on étudie un processus stochastique qui peut être interprété comme la version macroscopique de ce modèle. D'abord, on considère l'équation intégro-partielle différentielle de coagulation - multifragmentation qui décrit l'évolution en temps de la concentration $mu_t(x)$ de particules de masse $x>0$. Le noyau de coagulation $K$ est supposé satisfaire une propriété de $lambda$-homogénéité pour $lambdain(0,1]$, le noyau de fragmentation $F$ est supposé borné et la mesure $beta$ sur l'ensemble de ratios est conservative. Lorsque le moment d'ordre $lambda$ de la condition initial $mu_0$ est fini, on est capable de montrer existence et unicité d'une solution mesure de l'équation de coagulation - multifragmentation. Ensuite, on considère la version stochastique de cette équation, le processus de coalescence - fragmentation est un processus de Markov càdlàg avec espace d'états l'ensemble de suites ordonnées et est défini par un générateur infinitésimal donné. On a utilisé une représentation Poissonienne de ce processus et la distance $delta_{lambda}$ entre deux processus. Grâce à cette méthode on est capable de construire une version finie de ce processus et de coupler deux processus démarrant d'états initiaux différents. Lorsque l'état initial possède un moment d'ordre $lambda$ fini, on prouve existence et unicité de ces processus comme la limite de suites de processus finis. Tout comme dans le cas déterministe, le noyau de coagulation $K$ est supposé satisfaire une propriété d'homogénéité. Les hypothèses concernant la mesure $beta$ sont exactement les mêmes. D'un autre côté, le noyau de fragmentation $F$ est supposé borné sur tout compact dans $(0,infty)$. Ce résultat est meilleur que celui du cas déterministe, cette amélioration est due à la propriété intrinsèque de masse totale non-explosive que possède un système avec un moment fini d'ordre $lambda$ / This thesis is devoted to the study of systems of particles undergoing successive coagulations and fragmentations. In the deterministic case, we deal with measure-valued solutions of the coagulation - multifragmentation equation. We also study, on the other hand, its stochastic counterpart: coalescence - multifragmentation Markov processes. A first chapter is devoted to the presentation of the mathematical tools used in this thesis and to the discussion on some topics treated in the following chapters. n Chapter 1 we only take into account coagulation phenomena. We consider the Smoluchowski equation (which is deterministic) and the Marcus-Lushnikov process (the stochastic version) which can be seen as an approximation of the Smoluchowski equation. We derive a satisfying rate of convergence of the Marcus-Lushnikov process toward the solution to Smoluchowski's coagulation equation. The result applies to a class of homogeneous-like coagulation kernels with homogeneity degree ranging in $(-infty,1]$. It relies on the use of the Wasserstein-type distance $d_{lambda}$, which has shown to be particularly well-adapted to coalescence phenomena. It was introduced and used in preceding works. In Chapter 2 we perform some simulations in order to confirm numerically the rate of convergence deduced in Chapter ref{Chapter1} for the kernels studied in this chapter.medskip Finally, in Chapter 3 we add a fragmentation phenomena and consider a coagulation multiple-fragmentation equation, which describes the concentration $c_t(x)$ of particles of mass $x in (0,infty)$ at the instant $t geq 0$. We study the existence and uniqueness of measured-valued solutions to this equation for homogeneous-like kernels of homogeneity parameter $lambda in (0,1]$ and bounded fragmentation kernels, although a possibly infinite number of fragments is considered. We also study a stochastic counterpart of this equation where a similar result is shown. We prove existence of such a process for a larger set of fragmentation kernels, namely we relax the boundedness hypothesis. In both cases, the initial state has a finite $lambda$-moment