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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.

Four-Dimensional Passive Velocity Tomography of a Longwall Panel

Luxbacher, Kramer Davis 13 January 2006 (has links)
Velocity tomography is a noninvasive technology that can be used to determine rock mass response to ore removal. Velocity tomography is accomplished by propagating seismic waves through a rock mass to measure velocity distribution of the rock mass. Tomograms are created by mapping this velocity distribution. From the velocity distribution relative stress in the rock mass can be inferred, and this velocity distribution can be mapped at specific time intervals. Velocity tomography is an appropriate technology for the study of rockbursts. Rockbursts are events that occur in underground mines as a result of excessive strain energy being stored in a rock mass and sometimes culminating in violent failure of the rock. Rockbursts often involve inundation of broken rock into open areas of the mine. They pose a considerable risk to miners and can hinder production substantially. The rock mass under investigation in this research is the strata surrounding an underground coal mine in the western United States, utilizing longwall mining. The mine has experienced rockbursts. Seismic data were collected over a nineteen day period, from July 20th, 1997 to August 7th, 1997, although only eighteen days were recorded. Instrumentation consistsed of sixteen receivers, mounted on the surface, approximately 1,200 feet above the longwall panel of interest. The system recorded and located microseismic events, and utilized them as seismic sources. The data were analyzed and input into a commercial program that uses an algorithm known as simultaneous iterative reconstruction technique to generate tomograms. Eighteen tomograms were generated, one for each day of the study. The tomograms consistently display a high velocity area along the longwall tailgate that redistributes with face advance. Numerical modeling and mine experience confirm that the longwall tailgate is subject to high stress. Additionally, microseismic events are correlated with the velocity tomograms. Velocity tomography proves to be an effective method for the study of stress redistribution and rockburst phenomena at underground longwall coal mines, because it generates images that are consistent with prior information about the stress state at the mine and with numerical models of the stress in the mine. / Master of Science

Energy Redistribution with Controllable Binary State Latch Element

Chu, Chiang-Kai 12 July 2017 (has links)
An application of binary state latch device with proper real-time control algorithm for energy redistribution application is introduced in this thesis. Unlike traditional tuned vibration absorber, the latch device can be viewed as variable semi-active dampers such as magnetorheological (MR) and piezoelectric friction dampers. The distinct difference between other semi-active dampers and our latch device is that other semi-active dampers can provide continuous resistance according to the amount of input current, however, the binary latch device can only provide two different values of resistance - either the maximum or no resistance at all. This property brings the latch possibly having higher maximum and minimum ratio of resistance than MR dampers. As for the operating structure, the mechanism of latch element is nearly the same as the piezoelectric friction dampers which the resistance force is provided according to the normal force acting on two rough plates. Nonetheless, because of the characteristic of the binary states output of the latch element, this make it very different from the ordinary variable dampers. Since it is either being turned on or turned off, a novel control law is required for shifting energy. Also, because of the simplicity of the binary states output, it is very accessible to implement the controller on Field Programmable Gate Array (FPGA). With this accessibility, it is promising to apply plenty of latch elements in the same time for large scale application, such as multi-agent networks. In this thesis, an energy-based analytic solution is proposed to illustrate the universal latch-off condition. And a latch-on condition under ideal situations is discussed. At the end, a control law under nonideal condition is being suggested for real-time periodically excited system. We found that energy redistribution is achievable by using the proper control law under fairly broad conditions. / Master of Science

Voluntary contributions to a public good and endowments redistribution : An experimental study / Contributions volontaires à un bien public et redistribution des revenus : Une étude expérimentale

Rouaix, Agathe 05 July 2012 (has links)
Les inégalités de revenu affectent-elles la fourniture des biens publics ? Warr a établi en1983 un théorème de neutralité : sous certaines conditions, une redistribution marginale des revenus entre agents n'affecte pas la quantité de bien public fournie par leurs contributions volontaires. Les généralisations de ce résultat par Bergstrom et al. (1986), ont permis de mieux comprendre ce phénomène : les redistributions neutres sont de " faible "amplitude de sorte que les agents dont le revenu a été amputé ont toujours la possibilité de maintenir leur dépense en biens privés, et les ajustements des contributions individuelles laissent inchangée la contribution agrégée au bien public. Itaya et al. (1997) se sont intéressés aux conséquences d'une redistribution non neutre sur le bien-être. Dans les deux premiers chapitres de cette thèse nous testons ces prédictions en laboratoire grâce à un jeu de bien public avec utilités quadratiques. Le premier chapitre considère une redistribution de " faible " amplitude qui ne devrait pas entrainer une modification de la quantité de bien public. En revanche dans le chapitre 2, la redistribution est d'une amplitude telle qu'elle affecte la quantité de bien public fournie et le bien-être de la société. Bien que nous retrouvions en laboratoire certaines prédictions théoriques, notamment au niveau de la modification ou non de la quantité de bien public produit et du bien-être, les prédictions concernant les comportements et les gains individuels sont rarement vérifiées. En particulier, nous observons que, suite à la modification de leur revenu, certains joueurs réduisent ou augmentent moins leur contribution que la théorie ne le prédit et que les agents pauvres sur-contribuent. Il semble enfin que l'émergence d'inégalités n'affecte pas de la même façon les comportements que lorsque ces inégalités préexistent et donc que le sens de la redistribution, selon qu'elle crée ou diminue les inégalités, importe. Dans le chapitre 3, nous étudions plus précisément une redistribution créatrice d'inégalités dans un jeu de bien public linéaire et nous regardons si les hommes et les femmes réagissent de la même façon à ce changement et quelles conséquences cela entraine sur la quantité de bien public fournie. Nous montrons que lorsque les femmes bénéficient de la redistribution,la quantité de bien public produit diminue. Il apparait aussi que les comportements sont modifiés lorsque les sujets connaissent le genre de ceux qui se sont enrichis. / Do income inequalities affect the provision of public goods? Warr established in 1983 a theorem of neutrality : under some conditions, a marginal redistribution of endowments among agents does not affect the amount of public good provided by their voluntary contributions. Generalizations of this result by Bergstrom et al. (1986), helped to better understand this phenomenon: neutral redistributions are those of "low" amplitude, so that agents whose income decreases can maintain their consumption of private goods, and adjustments of individual contributions leave unchanged the aggregate contribution to the public good. Itaya et al. (1997) have focused on the consequences of a non-neutral redistribution on welfare. In the first two chapters of this thesis we test these predictions in the laboratory using a public good game with quadratic utility functions. The first chapter considers a redistribution of a "low" amplitude that should not modify the amount of public good supplied. However in Chapter 2, we run a redistribution of a "high" magnitude so that it affects the amount of public good provided and the social welfare. Although some theoretical predictions are found in the laboratory, such as the modification or not of the amount of public good and of the welfare, predictions on individual behaviors and payoffs are rarely verified. In particular, we note that following a modification of their endowment, some subjects decrease or increase their contribution less than theory predicts and that poor agents over-contribute. It further appears that the emergence of inequalities does not affect behaviors in the same way than when these inequalities preexist and thus that the direction of the redistribution, depending on whether it creates or decreases inequalities, matters. In Chapter 3 we study more precisely a redistribution that creates inequalities in a linear public good game and we test wether men and women respond similarly to the modification of their endowment and what are the consequences on the supply of the public good. We show that when women become rich, the quantity of public good provided decreases. It also appears that behaviors are modified when the rich gender is common knowledge.

Etude et simulation de la siliciuration du cobalt en couches ultraminces pour la microélectronique : cinétique de formation, contraintes, texture et redistribution des dopants

Delattre, Roger 26 April 2013 (has links)
Ce travail de thèse consiste en l'étude des mécanismes de formation de CoSi2 par diffraction X in-situ et son intégration dans un simulateur commercial TCAD (Technology Computer Aided Design). Nous avons observé que la formation du CoSi2 est contrôlée par la germination dans les premiers instants de la réaction où les germes croissent latéralement jusqu'à leur coalescence. Cette dernière marque la modification du mécanisme de croissance qui est alors contrôlée par la diffusion. En fin de réaction, la source de CoSi s'épuise en formant des îlots en surface du CoSi2 et ralentit sa vitesse de formation. Nos études ont permis d'établir des cinétiques de croissance pour ces différents régimes. Nous avons également montré que pour l'épaisseur la plus fine de notre étude, la croissance de CoSi2 n'est contrôlée que par celle des germes. La cinétique de formation de CoSi2 a été étudiée en fonction du dopage du substrat.L'évolution des contraintes des films de CoSi2 est également analysée. Ce dernier croit en compression.Nous avons développé un modèle TCAD en deux dimensions permettant de réaliser la croissance séquentielle des siliciures de cobalt et de reproduire avec un bon accord les cinétiques de croissances de CoSi2.Les redistributions de l'arsenic, du phosphore et du bore aux interfaces CoSi/Si et CoSi2/Si sont également analysées en prévision de la simulation électrique de composants siliciurés.Dans ce travail nous apportons une meilleure compréhension des mécanismes de croissance du CoSi2. Nous proposons un outil de simulation prédictif pour la formation des siliciures de cobalt qui apporte donc une aide à l'optimisation du procédé SALICIDE (Self Aligned siLICIDE). / The aim of this thesis is to study the growth of CoSi2 thin films using in-situ x-ray diffraction and to model it in a commercial TCAD (Technology Computer Aided Design) simulator.. We observed that the first instant of the reaction is limited by nucleation where the CoSi2 nuclei laterally grow until their coalescence. Then, the homogeneous CoSi2 layer grows by a diffusion limited mechanism. At the end of the reaction, the CoSi source run out and decrease the CoSi2 formation rate. Kinetics of these growth behaviors has been quantified. We also observed that the thinnest CoSi2 layer of our study only the CoSi2 nuclei growth take place.Influence of dopants on the CoSi2 kinetics of formation has also been studied. Arsenic decreases the CoSi2 rate of formation. However Boron does not impact the growth of CoSi2.During CoSi2 growth, stress is monitored using x-ray diffraction showing that cobalt disilicide forms in compression.From these experimental results, we developed a TCAD model in one dimension in order to simulate the sequential growth of cobalt silicides. Kinetics of formation of CoSi2 is also in good agreement with our results.The application in two dimensions of this model reproduces the morphology of 2D silicided structures as the lack of silicide under the spacers.Redistributions of Arsenic, Boron and Phosphorus are also studied in expectation of the electrical simulation of silicided components.In this word we provide a better comprehension of the growth of cobalt disilicide used in the silicidation process. We also provide a simulation tool for the silicide formation in order to help the optimization of the SALICIDE (Self Aligned siLICIDE) process.

Le rôle de la psychologie dans les dynamiques de la production, des inégalités et de la redistribution / The role of psychology in the dynamics of production, redistribution and inequalities

Ghosn, Sandra 22 September 2014 (has links)
L’objectif de cette thèse est de mettre en avant le rôle de la psychologie dans les fluctuations de la production, de la redistribution et des inégalités. Notre travail s’articule autour de deux axes : i) l’importance de la psychologie à l’égard des inégalités dans la détermination des croyances des agents concernant le rôle de l’effort ii) l’impact de ces croyances sur les dynamiques des grandeurs économiques. L’objectif du premier chapitre est de présenter une revue de littérature sur la relation entre croyances et faits économiques. Au second chapitre, nous développons un modèle théorique, dans lequel nous introduisons une composante psychologique immuable dans les croyances des agents. Nous aboutissons à une explication d’ordre psychologique des disparités entre pays de la volatilité de la TFP, de la production, de la redistribution et des inégalités. Dans le troisième chapitre, nous vérifions, économétriquement, les implications du modèle. / The objective of this doctoral thesis is to put forth the role of psychology in the fluctuations of production, redistribution and inequalities. Our work is centered on two axes : i) the importance of psychology with regards to inequalities in determining individual beliefs about the role of effort ii) the impact of beliefs on the dynamics of economic aggregates. The objective of the first chapter is to provide a literature review on the relationship between beliefs and economic events. In the second chapter, we develop a theoretical model, in which we introduce an unchanging psychological component in individual beliefs. We end at an explanation, of a psychological nature, for cross-country disparities in TFP, production, redistribution and inequalities volatilities. In the third chapter, we provide an empirical verification of the model implications.

Trois essais sur l'équité d'accès à l'éducation en Afrique subsaharienne / Three essays on the equity of access to education in sub-saharan Africa

Delesalle, Esther 16 February 2018 (has links)
Si de nombreux efforts ont été déployés pour améliorer l’accès à l’éducation en Afrique subsaharienne, la proportion d’enfants qui interrompent leur scolarité avant la fin du cycle primaire reste encore très élevée. Pour tenter de répondre à ce défi majeur, cette thèse se propose d’examiner les déterminants de la demande d’éducation dans un environnement rural exposé à de nombreux risques. Le premier chapitre s’intéresse à la place essentielle, et pourtant peu étudiée, que tiennent les coûts d’opportunité du temps des enfants dans les choix éducatifs. Il s’avère dans ce cas nécessaire d’estimer la productivité du travail des enfants afin d’identifier les coûts susceptibles de compromettre leur scolarisation. Afin de mieux appréhender les choix en matière d’éducation, le deuxième chapitre dresse quant à lui une estimation des bénéfices de l’éducation dans un contexte agricole qui se distingue à la fois par un accès limité aux nouvelles technologies et par la prédominance d’exploitations familiales de petites tailles. Enfin, le troisième chapitre interroge les effets des chocs de productivité sur les décisions de scolarisation et sur les performances scolaires des enfants. Deux critères retiennent notre attention, l'âge auquel les enfants sont confrontés à ces chocs et leur intensité. Ce sujet nous semble d’autant plus pertinent que la fréquence de ces chocs ne cesse aujourd’hui d’augmenter. À travers ces trois chapitres centrés sur la Tanzanie rurale, cette thèse offre ainsi un aperçu du rôle des politiques publiques dans la protection et le développement de l’éducation. / Despite numerous investments that have been made to increase access to education in sub-Saharan Africa, a noteworthy share of children drop out of school prior to completing primary education. To address this issue, this thesis examines the factors that drive education decisions in a rural risky environment. The first chapter focuses on one of the core determinant of education investment that has been under-explored, the opportunity costs of education. To identify these costs that can significantly hinder education, we determine children's productivity on the farm and provide an estimate range of the value of one day of child labor. In order to better understand education decisions in rural sub-Saharan Africa, the second chapter assesses the different benefits of education in rural Tanzania, where family farm is the dominant structure in agriculture and where the technology level is low. Finally, the third chapter investigates whether productivity shocks are detrimental to educational achievement and children’s cognitive skills by considering two particular aspects, the age at which shocks occur, and the length of shocks. This subject is all the more relevant today when the number of productivity shocks is growing. Throughout these three chapters which focus on rural Tanzania, this thesis provides some insight into the role of public policies in protecting and promoting education.

Essais sur la réforme des retraites , son impact sur la croissance et ses effets redistributifs.

Gonand, Frédéric 22 February 2007 (has links) (PDF)
Cette thèse analyse empiriquement les effets macroéconomiques de différentes réformes des retraites par répartition et leurs conséquences redistributives. Dans un modèle d'équilibre général avec générations imbriquées, le critère de l'effet sur la croissance permet d'écarter le choix d'une hausse des cotisations sociales comme levier exclusif de la réforme. Cependant il ne permet pas de départager, notamment en France, des scénarios aussi différents qu'une hausse de l'âge effectif de départ en retraite liée à l'espérance de vie ou une baisse du taux de remplacement avec âge de la retraite inchangé, qui permettraient chacun de soutenir le taux de croissance annuel moyen futur du PIB par tête d'environ 0.2% par rapport au scénario d'augmentation des prélèvements obligatoires. La prise en compte des conséquences redistributives devient décisive pour le choix de la réforme. Un gel de l'âge de la retraite alimente un conflit intergénérationnel entre actifs alors qu'une augmentation de cet âge répartit le coût en bien-être de la réforme plus également entre les actifs. Un planificateur utilitariste avec aversion modérée à l'inégalité intergénérationnelle privilégie ainsi l'âge effectif de la retraite comme principal levier d'une réforme. Les réformes avec hausse de l'âge de la retraite modèrent aussi les effets de redistribution selon le niveau de revenu par rapport aux réformes avec âge de la retraite inchangé. Enfin, la prise en compte des effets des réformes sur le bien-être des bas revenus (carrières incomplètes, éligibles au minimum vieillesse) peut infléchir le choix du paramètre d'ajustement (taux de cotisations sociales ou de remplacement) accompagnant une hausse de l'âge de la retraite. Au total, cette thèse incite à privilégier, en France, une hausse de l'âge de la retraite d'un peu plus d'une année par décennie, accompagnée d'un repli contenu du taux de remplacement moyen de 0.5 point de pourcentage par an sur les vingt prochaines années.

Privatisation as a tenet of GEAR and its socio-economic impact on the poor in the Western Cape with specific reference to the township of Khayelitsha

Domingos, Joao Mateus January 2007 (has links)
ABSTRACT The purpose and objectives of this research project was to understand and assess the progress or failure of privatisation in the South African context and to critically investigate the effects and factors, which influence privatisation. Chapter one dealt with background information to the research. Chapter two dealt with privatisation as a worldwide trend in many countries. It analysed privatisation since its inception in Africa, and South Africa in particular. Furthermore it assesses the impact of privatisation socially and economically. Chapter three dealt with the research methodologies used, while chapter four presents the data chapter five concludes the study and make recommendations. An in-depth literature review was conducted to investigate the macro-economic policy of GEAR and the socio-economic impacts of privatisation on the Khayelitsha communities were investigated to attain this aim the research utilised four questions. The researcher employed, qualitative and quantitative research methodology. Two types of data analysis were used namely structural and interpretational. These techniques were advantageous for the study because they explored the feelings of those who are at the receiving end of government policies and business. It also explored how different people react to unemployment and privatisation by getting responses from the respondents in their own words. The result of the data analysis revealed that privatisation is not creating jobs as expected. The research revealed the financial inability of people to afford basic services. The Khayelitsha community prefer services rendered by government instead of private sector. The findings of the statistical analysis were supporting and responding to research questions; it furthermore, indicated the respondent dissatisfaction with government’s privatisation objectives. The researcher concludes that it is necessary to take into account that government in principle has the interests of the citizens at heart. However its macro-economic policy is not having the desired results. Therefore, the researcher recommends that government policies be revised. In turn, efficient, effective and affordable services will be ensured.

Flexural Redistribution in Ultra-High Performance Concrete Lab Specimens

Moallem, Mohammad Reza 30 July 2010 (has links)
No description available.

The political origins of support for redistribution : Argentina and Peru in comparative perspective

Camacho Solis, Luis Antonio Antonio 25 February 2013 (has links)
Why do some individuals endorse public policies aimed at reducing income inequality while others oppose them? Why is there widespread support for such policies in certain countries, but not in others? This dissertation advances scholarship toward a general theory of support for redistribution by analyzing variation in redistributive attitudes within and across two developing democracies, Argentina and Peru. Support for redistribution is higher in the former country. It examines existing theories based on interests and group identity, explanations whose predictions have been almost exclusively evaluated in the context of advanced industrial democracies. It also introduces and assesses a belief-based explanation that focuses on inequality frames, simplified mental models of the issue of inequality comprised of individuals’ beliefs about the causes of economic outcomes, about the extent to which society provides equal opportunities, and about the nature of wealth accumulation. This dissertation argues that these theories are complementary and identifies the contextual factors that condition the extent to which the considerations emphasized by these accounts inform redistributive attitudes. Interests and group identity are salient in contexts where individuals have access to material and informational resources that make them more cognizant of their position along economic and ethnic cleavages. In contrast, inequality frames inform redistributive attitudes regardless of context because of their inside-the-head nature. This study shows that the relative dominance of redistributive beliefs in Argentina and self-reliance beliefs in Peru help explain why support for redistribution is higher in the former country. Finally, this dissertation develops a politico-historical explanation for why and how these frames became relatively dominant. This account argues that individuals’ inequality frames are relatively stable during times of normal politics, but malleable during certain critical political junctures brought about by major events like mass political incorporation or economic crises. During such times, individuals are particularly receptive to elite cues and messages that are transmitted not only via rhetoric but also via public policies. Redistributive beliefs become dominant wherever political actors whose discourse features elements consistent with the redistributive frame are able to implement successful comprehensive social policies. The self-reliance frame becomes dominant in countries where this combination of rhetoric and policies does not take place during a critical juncture. / text

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