Investigation And Modeling of Dip-Coating Process for Dispersions

Dip coating of liquid film deposition on cylindrical substrates is studied using mathematical modeling, numerical simulation and experimental investigation. A mathematical model based on the Landau-Levich approach for dip coating has been developed using the Ellis constitutive equation, for cylindrical geometries, to analyze the effects on the coating thickness of the substrate radius and hydrodynamic behavior for a non-Newtonian fluid. The influence of the viscosity at low shear rates near the surface of the withdrawal film is included in the Ellis model and coating thickness results for Ellis, power law and Newtonian models are compared with experimental data. Good agreement for the measured and predicted coating thickness was obtained with the Ellis model. Dip coating process is numerically simulated to understand the effects of the proximity of the coating bath wall to the substrate. The free surface position is determined by the volume of fluid technique applying Carreau, power law and Newtonian constitutive models in a three dimensional system, including density, viscosity and surface tension effects. Numerical calculations have been performed in an open source CFD software package of OpenFOAM. Numerical outcomes are validated with experimental data over a range of withdrawal velocities up to 6 , capillary range and a dimensionless range of distance, 4 to 60 for bath radius to the substrate radius being withdrawn. Finally, dip coating of dispersions is examined with particle distribution in the free-surface concentrated suspensions studied by developing a numerical algorithm in a computational fluid dynamic platform based on the particle diffusion-flux model. The numerical predictions are for finite length cylinder being pulled out of a concentrated suspension bath in the unsteady condition. The initial rigid particle volume fraction of 0.1-0.4 and the withdrawal velocity varies in the range of 0.05-0.15 and capillary number range of . Simulation results are compared against experimental data with good agreement in the predicted coating thickness

Random Utility Theory for Social Choice

Random utility theory models an agent's preferences on alternatives by drawing a real-valued score on each alternative (typically independently) from a parameterized distribution, and then ranking the alternatives according to scores. A special case that has received significant attention is the Plackett-Luce model, for which fast inference methods for maximum likelihood estimators are available. This paper develops conditions on general random utility models that enable fast inference within a Bayesian framework through MC-EM, providing concave loglikelihood functions and bounded sets of global maxima solutions. Results on both real-world and simulated data provide support for the scalability of the approach and capability for model selection among general random utility models including Plackett-Luce.Engineering and Applied Science

L’enseignement des langues étrangères a l’université Cadi ayyad – Marrakech : de l’enseignement présentiel a l’apprentissage en ligne

L'émergence de l'enseignement en ligne remonte à 1982 lorsque le Western Behavioural Sciences Institute de Californie a utilisé la technique de conférence par ordinateur pour présenter un programme d'enseignement à distance. Depuis lors, les universités et les instituts d’enseignement supérieur du monde entier utilisent l'apprentissage en ligne comme une méthode complémentaire à l'apprentissage présentiel. Cependant, avec la propagation de la pandémie de Covid-19, l'apprentissage en ligne est devenu une alternative inévitable. A cet égard, notre raisonnement, derrière la conduite de ce travail, est d’aborder comment les langues étrangères sont enseignées à l’université Cadi Ayyad- Marrakech (UCA) en donnant un aperçu sur le passage de l’enseignement présentiel à l’enseignement en ligne (à distance). Pour ce faire, nous avons commencé par l’importance des langues étrangères dans un pays multiculturel et plurilingue comme le Maroc. Ensuite, nous avons découvert les pédagogies, les défis, et les programmes adoptés par les professeurs universitaires à UCA. Finalement, le dernier axe a été consacré à l’enseignement à distance dans la même université, en parlant des difficultés que les professeurs et les étudiants ont éprouvées dans le processus enseignement apprentissage sans oublier les solutions approuvées

Computational studies of molybdenum oxide clusters and environmental corrosion of iron and zinc

This dissertation describes two creative activities. The first is a computational study of molybdenum oxide clusters and the other is an experimental study of the corrosion of metals. The first effort covers three topics. First, the UV-Vis spectra for molybdenum oxide clusters were simulated utilizing Time-Dependent Density-Functional Theory (TD-DFT) calculations. The effects on the spectra due to changes in the cluster size and the variation of the formal charge of the molybdenum were investigated. Specifically, the location and transition intensity of a charge transfer transition between the molybdenum atoms were identified.The second computational topic explored the adsorption and dissociation of dimethyl peroxide on the (100) surface of molybdenum trioxide and the hydrogen molybdenum bronze using Density-Functional Theory (DFT) calculations. It was found that dimethyl peroxide adsorbs molecularly on the oxide and bronze surfaces. However, the decomposition can occur only on the bronze surface through an O-O bond cleavage pathway. The final computational topic examined the equilibrium between a molybdenum monomer and a mixed valence dimer complex with gluconic acid. UV-Vis spectroscopy was used to measure the concentration of the dimer and monomer as a function of time and temperature. For this data, the activation energy for the dimer dissociation and the Gibbs free energy of the equilibrium could be calculated. To complement the experimental results, the UV-Vis spectra for complexes were simulated using TD-DFT calculations. The results are in agreement with the experimental assumption that the equilibrium is between a mixed valence dimer and two monomers.The second effort is the experimental study of metal corrosion using a new method for corrosion evaluation based on thin wires. This effort covers two topics. The first topic was the corrosion of small iron wires in sodium chloride solutions, which may lead to a rapid technique to measure the efficiency of corrosion inhibitors. The second topic was the corrosion of mild steel and the galvanic corrosion of zinc wires in two types of soils. These results were used to develop a wireless corrosion sensor for underground structures

Revisiting Random Utility Models

This thesis explores extensions of Random Utility Models (RUMs), providing more flexible models and adopting a computational perspective. This includes building new models and understanding their properties such as identifiability and the log concavity of their likelihood functions as well as the development of estimation algorithms.Engineering and Applied Science

Generalized Method-of-Moments for Rank Aggregation

In this paper we propose a class of efficient Generalized Method-of-Moments(GMM) algorithms for computing parameters of the Plackett-Luce model, where the data consists of full rankings over alternatives. Our technique is based on breaking the full rankings into pairwise comparisons, and then computing parameters that satisfy a set of generalized moment conditions. We identify conditions for the output of GMM to be unique, and identify a general class of consistent and inconsistent breakings. We then show by theory and experiments that our algorithms run significantly faster than the classical Minorize-Maximization (MM) algorithm, while achieving competitive statistical efficiency.Engineering and Applied SciencesStatistic

Generalized Random Utility Models with Multiple Types

We propose a model for demand estimation in multi-agent, differentiated product settings and present an estimation algorithm that uses reversible jump MCMC techniques to classify agents' types. Our model extends the popular setup in Berry, Levinsohn and Pakes (1995) to allow for the data-driven classification of agents' types using agent-level data. We focus on applications involving data on agents' ranking over alternatives, and present theoretical conditions that establish the identifiability of the model and uni-modality of the likelihood/posterior. Results on both real and simulated data provide support for the scalability of our approach.EconomicsEngineering and Applied SciencesMathematic