The poor representation of cloud processes in general circulation models (GMCs) has been recognized for decades as one of the major sources of uncertainties in weather and climate predictions. Because of the coarse spatial resolution of GCMs, subgrid- scale cloud and convection processes are modelled by parameterization schemes that provide a statistical representation of the subgrid-scale processes in terms of the large- scale, gridbox fields. This thesis focuses on the stochastic multicloud parameterization of Khouider et al. (2010), which is based on the three cloud types (congestus, deep, and stratiform) that are most observed in tropical convective systems. A rigorous parameter estimation model based on the Bayesian paradigm is developed to infer from data a set of seven convective timescales that determine the transition rates from one cloud type to another in the multicloud framework. The Bayesian posterior is given in terms of a costly model likelihood function that must be approximated numerically using high-performance linear algebra routines for parallel distributed computing. The Bayesian procedure is applied to the Giga-LES dataset of Khairout- dinov et al. (2009), a large-eddy simulation of tropical deep convection that covers a physical domain comparable to that of a typical horizontal grid cell in a GCM. The stochastic multicloud model and its deterministic version are then coupled to a zonally iv symmetric atmospheric model to study the meridional Hadley circulation and mon- soon dynamics. The main model is based on the hydrostatic Boussinesq equations on a rotating sphere, and is composed of a deep convective troposphere and a dynamical planetary boundary layer to sustain shallow convection. The resulting equations form a system of nonconservative partial different equations, which is solved numerically using high order non-oscillatory finite volume methods. Results from deterministic and stochastic simulations reveal a mean local Hadley cell structure with some fea- tures of organized convection. In the stochastic case, the Giga-LES parameter regime best captures the Hadley-type circulation and monsoon trough features, compared to a parameter regime used in a different study. / Graduate / mdelachev@gmail.com

abstract: Self-heating degrades the performance of devices in advanced technology nodes. Understanding of self-heating effects is necessary to improve device performance. Heat generation in these devices occurs at nanometer scales but heat transfer is a microscopic phenomena. Hence a multi-scale modeling approach is required to study the self-heating effects. A state of the art Monte Carlo device simulator and the commercially available Giga 3D tool from Silvaco are used in our study to understand the self heating effects. The Monte Carlo device simulator solves the electrical transport and heat generation for nanometer length scales accurately while the Giga 3D tool solves for thermal transport over micrometer length scales. The approach used is to understand the self-heating effects in a test device structure, composed of a heater and a sensor, fabricated and characterized by IMEC. The heater is the Device Under Test(DUT) and the sensor is used as a probe. Therefore, the heater is biased in the saturation region and the sensor is biased in the sub-threshold regime. Both are planar MOSFETs of gate length equal to 22 nm. The simulated I-V characteristics of the sensor match with the experimental behavior at lower applied drain voltages but differ at higher applied biases. The self-heating model assumes that the heat transport within the device follows Energy Balance model which may not be accurate. To properly study heat transport within the device, a state of the art Monte Carlo device simulator is necessary. In this regard, the Phonon Monte Carlo(PMC) simulator is developed. Phonons are treated as quasi particles that carry heat energy. Like electrons, phonons obey a corresponding Boltzmann Transport Equation(BTE) which can be used to study their transport. The direct solution of the BTE for phonons is possible, but it is difficult to incorporate all scattering mechanisms. In the Monte Carlo based solution method, it is easier to incorporate different relevant scattering mechanisms. Although the Monte Carlo method is computationally intensive, it provides good insight into the physical nature of the transport problem. Hence Monte Carlo based techniques are used in the present work for studying phonon transport. Monte Carlo simulations require calculating the scattering rates for different scattering processes. In the present work, scattering rates for three phonon interactions are calculated from different approaches presented in the literature. Optical phonons are also included in the transport problem. Finally, the temperature dependence of thermal conductivity for silicon is calculated in the range from 100K to 900K and is compared to available experimental data. / Dissertation/Thesis / Masters Thesis Electrical Engineering 2016

L'effet de l'espacement interlamellaire sur le comportement sous chargements monotone et cyclique de l'acier perlitique C70 a été étudié. Une démarche expérimentale conjuguant les essais de traction " in-situ " sous DRX et traction " in-situ " sous MEB couplées à une modélisation auto-cohérente a été adoptée. Les essais ont été effectués sur deux microstructures, à deux espacements interlamellaires différents. Il a été montré que l'écoulement plastique de la perlite est contrôlé par celui de la ferrite lequel est gouverné par l'espacement interlamellaire, il en est de même pour les distributions des contraintes résiduelles. La modélisation auto-cohérente met en évidence l'anisotropie élastique à l'échelle des phases et l'effet de l'espacement interlamellaire sur les rigidités et les limites d'écoulement directionnelles. L'analyse microstructurale des mécanismes de déformation montre que la déformation plastique de la perlite est caractérisée par le développement de bandes de cisaillement. Ces bandes sont le siège de l'amorçage des fissures par cisaillement des lamelles de cémentite pour les taux de déformation élevés. L'effet de l'espacement interlamellaire sur le comportement en fatigue giga-cyclique a été étudié par des essais de fatigue sous une fréquence de 20 KHz. Des différences de 30 MPa, pour la perlite à SP= 230 nm et de 50 MPa pour la perlite à SP= 170 nm entre les limites de fatigue conventionnelle (106cycles) et giga-cyclique (109cycles) ont été obtenues. L'effet de l'espacement interlamellaire sur le comportement en fatigue apparait peu significatif comparativement aux caractéristiques mécaniques de traction. Les limites de fatigue giga-cycliques obtenues intègrent l'effet bénéfique des contraintes résiduelles stabilisées ainsi que les effets d'écrouissage induit par l'usinage et par écrouissage cyclique. L'examen des sites d'amorçage, révèle essentiellement un amorçage en surface dans le domaine méga-cyclique et mixte en surface et/ou en sous-couches dans le domaine giga-cyclique. Ces résultats peuvent être interprétés sur la base des effets des propriétés de surface stabilisées et de la microstructure. Le recours à un critère de fatigue de type Goodman permet d'identifier d'une manière qualitative la contribution des différents facteurs d'influence, ci-dessus cités, dans l'amorçage des fissures de fatigue.

L’effet de l’espacement interlamellaire sur le comportement sous chargements monotone et cyclique de l’acier perlitique C70 a été étudié. Une démarche expérimentale conjuguant les essais de traction « in-situ » sous DRX et traction « in-situ » sous MEB couplées à une modélisation auto-cohérente a été adoptée. Les essais ont été effectués sur deux microstructures, à deux espacements interlamellaires différents. Il a été montré que l'écoulement plastique de la perlite est contrôlé par celui de la ferrite lequel est gouverné par l’espacement interlamellaire, il en est de même pour les distributions des contraintes résiduelles. La modélisation auto-cohérente met en évidence l'anisotropie élastique à l'échelle des phases et l'effet de l'espacement interlamellaire sur les rigidités et les limites d'écoulement directionnelles. L'analyse microstructurale des mécanismes de déformation montre que la déformation plastique de la perlite est caractérisée par le développement de bandes de cisaillement. Ces bandes sont le siège de l'amorçage des fissures par cisaillement des lamelles de cémentite pour les taux de déformation élevés. L’effet de l’espacement interlamellaire sur le comportement en fatigue giga-cyclique a été étudié par des essais de fatigue sous une fréquence de 20 KHz. Des différences de 30 MPa, pour la perlite à SP= 230 nm et de 50 MPa pour la perlite à SP= 170 nm entre les limites de fatigue conventionnelle (106cycles) et giga-cyclique (109cycles) ont été obtenues. L’effet de l’espacement interlamellaire sur le comportement en fatigue apparait peu significatif comparativement aux caractéristiques mécaniques de traction. Les limites de fatigue giga-cycliques obtenues intègrent l’effet bénéfique des contraintes résiduelles stabilisées ainsi que les effets d’écrouissage induit par l’usinage et par écrouissage cyclique. L’examen des sites d’amorçage, révèle essentiellement un amorçage en surface dans le domaine méga-cyclique et mixte en surface et/ou en sous-couches dans le domaine giga-cyclique. Ces résultats peuvent être interprétés sur la base des effets des propriétés de surface stabilisées et de la microstructure. Le recours à un critère de fatigue de type Goodman permet d’identifier d’une manière qualitative la contribution des différents facteurs d’influence, ci-dessus cités, dans l’amorçage des fissures de fatigue. / The effect of interlamellar spacing on the monotonic and cyclic behavior of C70 pearltic steel was investigated. Tensile tests under scanning electron microscope and under X-ray diffraction coupled with self-consistent model have been used. Tests have been carried out on two microstructures with different interlamellar spacing. It has been demonstrated that pearlite yielding is controlled by ferrite critical shear stress), which depend on the interlamellar spacing. The pearlite deforms inhomogeneously under tensile loading by localized shearing in intense shear bands. In the large shear bands, parallel cementite plate offsets before fracture and contributes to the occurrence of localized damage. The residual stress in ferrite is higher for the coarse pearlite. Giga-cycle fatigue tests were performed to identify the effect of interlamellar spacing on the fatigue behavior; tests were performed at a frequency of 20 KHz. The difference of the fatigue strength between 106 and 109 cycles is about 30 MPa for coarse pearlite and 50 MPa for fine pearlite. The effect of interlamellar spacing on the mega-cycle and giga-cycle fatigue limit appears not significant compared to the mechanical characteristics. Giga-cycle fatigue limit obtained includes the beneficial effect of stabilized residual stress. It also includes the effect of hardening induced by machining and cyclic hardening. However, any significant effect of interlamellar spacing on the C70 fatigue limits has been shown. SEM examinations shows that failures initiated on surface for the mega-cycle regime and on different sites for the giga-cycle regime. The experimental results can be interpreted based on the effects of stabilized surface properties and microstructure. The use of a fatigue Goodman criterion would identify qualitatively the contribution of different factors, cited above, in the fatigue life.

[pt] Este trabalho de Tese apresenta a pesquisa e desenvolvimento de conexões de ondas guiadas sobre substratos semicondutores (SiGe, GaAs). A integração de circuitos digitais através de guias S-SIWG (Semiconductor Substrate Integrated Waveguide) utilizando formato de modulação QAM é avaliada e destacada. Conexões internas aos chips e entre chips são associadas com o novo padrão Gigabit Ethernet 802.3ba operando na taxa de 100 Gbit/s estendendo-se a aplicações de 0,5 – 1,5 Terahertz. É também apresentada a pesquisa e o desenvolvimento de guias e dispositivos de microondas utilizando substratos de baixo custo e altas perdas (FR-4), substratos cerâmicos de alta constante dielétrica (Er igual a 80) e aplicações em subsistemas híbridos integrados. / [en] This work presents the research, design and development of guided waves connections in semiconductor substrates (SiGe, GaAs). The integration of digital systems using Semiconductor Wave Guides (S-SIWG) with QAM modulation formats are highlighted. Ultra-fast inter-chip and inner-chip connections are associated with the new Gigabit Ethernet IEEE 802.3ba standard at 100Gbit/s extended to (0.5-1.5) Terahertz domain. Additionally fiber glass substrates with high losses (Teflon/FR-4) and high dielectric ceramic substrates (Er equal 80) are also developed to be integrated with microwave devices, analog printed circuits boards and high Speed digital circuits and systems.

M. Tech. (Department of Information and Communication Technology, Faculty of Applied and Computer Sciences), Vaal University of Technology. / Since their emergence in the 1990’s, recommendation systems have transformed the intelligence of both the web and humans. A pool of research papers has been published in various domains of recommendation systems. These include content based, collaborative and hybrid filtering recommendation systems. Recommendation systems suggest items to users and their principal purpose is to increase sales and recommend items that are predicted to be suitable for users. They achieve this through making calculations based on data that is available on the system. In this study, we give evidence that the research on group recommendation systems must look more carefully at the dynamics of group decision-making in order to produce technologies that will be more beneficial for groups based on the individual interests of group members while also striving to maximise satisfaction. The matrix factorization algorithm of collaborative filtering was used to make predictions and three movie recommendation for each and every individual user. The three recommendations were of three highest predicted movies above the pre-set threshold which was three. Thereafter, four virtual groups of varied sizes were formed based on four highest predicted movies of the users in the dataset. Plurality voting strategy was used to achieve this. A publicly available dataset based on Group Recommender Systems Enhanced by Social Elements, constructed by Lara Quijano from the Group of Artificial Intelligence Applications (GIGA), was used for experiments. The developed recommendation system was able to successfully make individual movie recommendations, generate virtual groups, and recommend movies to these respective groups. The system was evaluated for accuracy in making predictions and it was able to achieve 0.7027 MAE and 0.8996 RMSE. This study was able to recommend to virtual groups to enable social network group members to engage in discussions of recommended items. The study encourages members in engaging in similar activities in their respective physical locations and then discuss on social network.