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1
Mhanna, Elissa. "Beyond gradients : zero-order approaches to optimization and learning in multi-agent environments". Electronic Thesis or Diss., université Paris-Saclay, 2024. http://www.theses.fr/2024UPASG123.
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L'essor des dispositifs connectés et des données qu'ils génèrent a stimulé le développement d'applications à grande échelle. Ces dispositifs forment des réseaux distribués avec un traitement de données décentralisé. À mesure que leur nombre augmente, des défis comme la surcharge de communication et les coûts computationnels se présentent, nécessitant des méthodes d'optimisation adaptées à des contraintes de ressources strictes, surtout lorsque les dérivées sont coûteuses ou indisponibles. Cette thèse se concentre sur les méthodes d'optimisation sans dérivées, qui sont idéales quand les dérivées des fonctions sont inaccessibles. Ces méthodes estiment les gradients à partir des évaluations de fonction, ce qui les rend adaptées à l'apprentissage distribué et fédéré, où les dispositifs collaborent pour résoudre des tâches d'optimisation avec peu d'informations et des données bruitées. Dans le premier chapitre, nous traitons de l'optimisation distribuée sans dérivées pour des fonctions fortement convexes sur plusieurs agents. Nous proposons un algorithme distribué de descente de gradient projete sans dérivées, qui utilise des estimations de gradient à un point, où la fonction est interrogée une seule fois par réalisation stochastique, et les évaluations sont bruitées. Ce chapitre démontre la convergence presque sûre de l'algorithme et fournit des bornes théoriques sur le taux de convergence. Avec des pas constants, l'algorithme atteint un taux de convergence linéaire. C'est la première fois que ce taux est établi pour des estimations de gradient à un point (voire même pour des estimations de gradient à deux points) pour des fonctions stochastiques. Nous analysons aussi les effets des pas décroissants, établissant un taux de convergence correspondant aux méthodes centralisées sans dérivées. Le deuxième chapitre se penche sur les défis de l'apprentissage fédéré qui est limité par le coût élevé de la transmission de données sur des réseaux à bande passante restreinte. Pour y répondre, nous proposons un nouvel algorithme qui réduit la surcharge de communication en utilisant des estimations de gradient à un point. Les dispositifs transmettent des valeurs scalaires plutôt que de grands vecteurs de gradient, réduisant ainsi la quantité de données envoyées. L'algorithme intègre aussi directement les perturbations des communications sans fil dans l'optimisation, éliminant le besoin de connaître explicitement l'état du canal. C'est la première approche à inclure les propriétés du canal sans fil dans un algorithme d'apprentissage, le rendant résilient aux problèmes de communication réels. Nous prouvons la convergence presque sûre de cette méthode dans des environnements non convexes et validons son efficacité à travers des expériences. Le dernier chapitre étend l'algorithme précédent au cas des estimations de gradient à deux points. Contrairement aux estimations à un point, les estimations à deux points interrogent la fonction deux fois, fournissant une approximation plus précise du gradient et améliorant le taux de convergence. Cette méthode conserve l'efficacité de communication des estimations à un point, avec uniquement des valeurs scalaires transmises, et assouplit l'hypothèse de bornitude de la fonction objective. Nous prouvons des taux de convergence linéaires pour des fonctions fortement convexes et lisses. Pour les problèmes non convexes, nous montrons une amélioration notable du taux de convergence, en particulier pour les fonctions dominées par le gradient K, atteignant également un taux linéaire. Nous fournissons aussi des résultats montrant l'efficacité de communication par rapport à d'autres techniques d'apprentissage fédéréThe rise of connected devices and the data they produce has driven the development of large-scale applications. These devices form distributed networks with decentralized data processing. As the number of devices grows, challenges like communication overhead and computational costs increase, requiring optimization methods that work under strict resource constraints, especially where derivatives are unavailable or costly. This thesis focuses on zero-order (ZO) optimization methods are ideal for scenarios where explicit function derivatives are inaccessible. ZO methods estimate gradients based only on function evaluations, making them highly suitable for distributed and federated learning environments where devices collaborate to solve global optimization tasks with limited information and noisy data. In the first chapter, we address distributed ZO optimization for strongly convex functions across multiple agents in a network. We propose a distributed zero-order projected gradient descent algorithm that uses one-point gradient estimates, where the function is queried only once per stochastic realization, and noisy function evaluations estimate the gradient. The chapter establishes the almost sure convergence of the algorithm and derives theoretical upper bounds on the convergence rate. With constant step sizes, the algorithm achieves a linear convergence rate. This is the first time this rate has been established for one-point (and even two-point) gradient estimates. We also analyze the effects of diminishing step sizes, establishing a convergence rate that matches centralized ZO methods' lower bounds. The second chapter addresses the challenges of federated learning (FL) which is often hindered by the communication bottleneck—the high cost of transmitting large amounts of data over limited-bandwidth networks. To address this, we propose a novel zero-order federated learning (ZOFL) algorithm that reduces communication overhead using one-point gradient estimates. Devices transmit scalar values instead of large gradient vectors, lowering the data sent over the network. Moreover, the algorithm incorporates wireless communication disturbances directly into the optimization process, eliminating the need for explicit knowledge of the channel state. This approach is the first to integrate wireless channel properties into a learning algorithm, making it resilient to real-world communication issues. We prove the almost sure convergence of this method in nonconvex optimization settings, establish its convergence rate, and validate its effectiveness through experiments. In the final chapter, we extend the ZOFL algorithm to include two-point gradient estimates. Unlike one-point estimates, which rely on a single function evaluation, two-point estimates query the function twice, providing a more accurate gradient approximation and enhancing the convergence rate. This method maintains the communication efficiency of one-point estimates, where only scalar values are transmitted, and relaxes the assumption that the objective function must be bounded. The chapter demonstrates that the proposed two-point ZO method achieves linear convergence rates for strongly convex and smooth objective functions. For nonconvex problems, the method shows improved convergence speed, particularly when the objective function is smooth and K-gradient-dominated, where a linear rate is also achieved. We also analyze the impact of constant versus diminishing step sizes and provide numerical results showing the method's communication efficiency compared to other federated learning techniques
2
Calvez, Vincent. "Modèles et analyses mathématiques pour les mouvements collectifs de cellules". Phd thesis, Université Pierre et Marie Curie - Paris VI, 2007. http://tel.archives-ouvertes.fr/tel-00255811.
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Cette thèse est consacrée à certains modèles mathématiques décrivant le mouvement d'une population de cellules, qui interagissent via un signal chimique. L'accent est mis sur le modèle parabolique de Patlak-Keller-Segel, et dans une moindre mesure, sur le modèle cinétique d'Othmer-Dunbar-Alt.Dans une première partie nous étudions plusieurs variantes du modèle PKS classique, incluant notamment une diffusion non-linéaire des cellules, ou bien une loi de diffusion chimique à noyau de Green logarithmique. Puis nous montrons l'existence globale pour une masse sous-critique du modèle PKS classique dans tout l'espace $\mathbb{R}^2$.
On complexifie ensuite le modèle de base en ajoutant un intermédiaire chimique réactionnel, ce qui modifie l'homogénéité du système. Enfin les conditions d'existence globale pour le modèle cinétique ODA avec effets délocalisants sont affaiblies par rapport aux travaux précédents.
Dans une deuxième partie nous appliquons le modèle phénoménologique de PKS, et son principe de masse critique, à un processus d'auto-organisation remarquable dans le cerveau: la sclérose concentrique de Baló. Un couplage adéquat entre un front de propagation et une instabilité de PKS décrit raisonnablement les motifs en anneaux de la maladie.
La troisième partie adopte le point de vue du transport optimal de masse pour analyser le modèle de PKS unidimensionnel modifié auparavant (afin de partager les caractéristiques de PKS 2D). Bien que la fonctionnelle d'énergie ne soit pas convexe par déplacement, nous démontrons la convergence vers un unique état d'équilibre, lorsqu'il existe. Ces nouvelles idées sont mises en oeuvre numériquement~: un flot gradient discret pour la distance de Wasserstein est analysé, puis simulé en dimension un d'espace.
Plusieurs annexes viennent compléter ce travail, dont une annexe qui regroupe tous les aspects numériques de la thèse.
3
Swapp, David. "Estimation of visual textural gradient using Gabor functions". Thesis, University of Strathclyde, 1996. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.320238.
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Yang, Junjun. "Seafloor Topography Estimation from Gravity Gradients". The Ohio State University, 2017. http://rave.ohiolink.edu/etdc/view?acc_num=osu1512048462472145.
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Shahnaz, Sabina. "Gas flux estimation from surface gas concentrations". Thesis, Georgia Institute of Technology, 2016. http://hdl.handle.net/1853/55073.
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A gradient-independent model of gas fluxes was formulated and tested. The
model is built on the relationship between gas flux and the time history of surface gas
concentration, known as half-order derivative (HOD), when the transport of the gas in the
boundary layer is described by a diffusion equation. The eddy-diffusivity of gas is
parameterized based on the similarity theory of boundary layer turbulence combined with
the MEP model of surface heat fluxes. Test of the new model using in-situ data of CO2
concentration and fluxes at several locations with diverse vegetation cover, geographic
and climatic conditions confirms its usefulness and potential for monitoring and
modeling greenhouse gases. The proposed model may also be used for estimating other
GHGS fluxes such as methane (CH4) and Water vapor flux. This proof-of-concept study
justifies the proposed model as a practical solution for monitoring and modeling global
GHGS budget over remote areas and oceans where ground observations of GHGS fluxes
are limited or non-existent. One focus of the on-going research is to investigate its
application to producing regional and global distributions of carbon fluxes for identifying
sinks and sources of carbon and re-evaluating the regional and global carbon budget at
monthly and annual time scales.
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Lee, Choon. "Interframe image coding with three-dimensional gradient motion estimation". Diss., This resource online, 1990. http://scholar.lib.vt.edu/theses/available/etd-08252008-162144/.
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Miyoshi, Naoto. "Studies on Gradient Estimation for Stationary Single-Server Queues". Kyoto University, 1997. http://hdl.handle.net/2433/202289.
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Kyoto University (京都大学)0048
新制・課程博士
博士(工学)
甲第6839号
工博第1590号
新制||工||1063(附属図書館)
15926
UT51-97-H223
京都大学大学院工学研究科応用システム科学専攻
(主査)教授 長谷川 利治, 教授 沖野 教郎, 教授 茨木 俊秀
学位規則第4条第1項該当
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Zotov, Alexander. "Models of disparity gradient estimation in the visual cortex". Birmingham, Ala. : University of Alabama at Birmingham, 2007. https://www.mhsl.uab.edu/dt/2008r/zotov.pdf.
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Mehrparvar, Arash. "ATTITUDE ESTIMATION FOR A GRAVITY GRADIENT MOMENTUM BIASED NANOSATELLITE". DigitalCommons@CalPoly, 2013. https://digitalcommons.calpoly.edu/theses/1097.
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Attitude determination and estimation algorithms are developed and implemented in simulation for the Exocube satellite currently under development by PolySat at Cal Poly. A mission requirement of ±5˚ of attitude knowledge has been flowed down from the NASA Goddard developed payload, and this requirement is to be met with a basic sensor suite and the appropriate algorithms. The algorithms selected in this work are TRIAD and an Extended Kalman Filter, both of which are placed in a simulation structure along with models for orbit propagation, spacecraft kinematics and dynamics, and sensor and reference vector models. Errors inherent from sensors, orbit position knowledge, and reference vector generation are modeled as well. Simulations are then run for anticipated dynamic states of Exocube while varying parameters for the spacecraft, attitude algorithms, and level of error. The nominal case shows steady state convergence to within 1˚ of attitude knowledge, with sensor errors set to 3.5˚ and reference vector errors set to 2˚. The algorithms employed have their functionality confirmed with the use of STK, and the simulations have been structured to be used as tools to help evaluate attitude knowledge capabilities for the Exocube mission and future PolySat missions.
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Castillo, Anthony. "Contribution à l'étude de l'endommagement de matériaux composites par estimation des termes sources et des diffusivités thermiques". Thesis, Aix-Marseille, 2017. http://www.theses.fr/2017AIXM0592/document.
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Ce travail porte sur la détection de l’endommagement de matériaux composites. Une première partie concerne l’élaboration de méthodes permettant d’estimer les termes sources de chaleur d’un matériau sollicité mécaniquement. Lors de ce processus, un ensemble de défauts mécaniques mènent à des productions de chaleur. La détection des sources peut permettre la détection de ces défauts. Deux principales méthodes sont présentées : une méthode dite « directe » basée sur une discrétisation du champ de température mesuré et une méthode « itérative » basée sur la méthode du gradient conjugué. A ces méthodes sont couplées des techniques de filtrages des données comme la SVD. Les équations sont résolues par différences finies sous leur forme linéaire. Des modifications sont apportées à l’algorithme itératif pour améliorer sa convergence ainsi que les résultats. Les problématiques envisagées font partie des problèmes inverses en thermique. L’objectif de la première partie est de trouver un lien entre l’apparition de macro-fissure et la localisation de termes sources de chaleur au sein d’un matériau composite. La seconde partie consiste à élaborer des méthodes d’estimation des diffusivités thermiques directionnelles. Les méthodes reposent sur une modélisation du transfert de chaleur à l’aide des quadripôles thermiques. Les estimations de paramètres sont réalisées sur des zones ciblées à risque sur un matériau déjà endommagé. Le but est de faire le lien entre un endommagement mécanique connu diffus et une dégradation des propriétés thermiques. Ce manuscrit est présenté en deux parties : une partie de validation des méthodes. Une partie expérimentale où sont analysés les compositesThis work deals with the damage detection of composite materials. These materials are used in the aeronautics industry. The first part concerns the development of methods to estimate the heat sources terms of a stressed material. During this process, a set of mechanical defects leads to heat productions. The sources detection can conduct to the detection of these defects. Two main methods are presented: a "direct" method based on a discretization of the measured temperature field and an "iterative" method based on the conjugate gradient method. These methods are coupled with data filtering techniques such as SVD. In order to optimize computation time, equations are solved by finite differences in their linear form. Modifications are also made for the iterative algorithm to improve its convergence as well as the results of the estimation. These problems are considered as thermal inverse problems. The main objective of the first part is to find an experimental link between the appearance of a macro fissure and the localization of a heat source term within a composite material. The second part consists in the elaboration of methods for estimating thermal directional diffusivities. The methods are based on a modeling of heat transfer using thermal quadrupoles. Parameter estimations are made on targeted "risked" areas on a material, which is already damaged but not under stress. The aim is to link a known mechanical damage, which is called "diffuse" to thermal properties degradation in the main directions. This manuscript is presented in two parts: a validation part of the methods, and an experimental part in which composites are analyzed
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Lacinová, Veronika. "Odhady diskrétního rozložení pravděpodobnosti a bootstrap". Doctoral thesis, Vysoké učení technické v Brně. Fakulta strojního inženýrství, 2015. http://www.nusl.cz/ntk/nusl-234260.
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Doctoral thesis is focused on the unconventional methods of the discrete probability estimation of categorical quantity from its observed values. The gradient of quasinorm and so-called line estimation were emlopyed for these estimations. Bootstrap method was used for the improvement of accuracy. Theoretical results for selected quasinorms were illustrated on specific examples.
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Giacomini, Matteo. "Quantitative a posteriori error estimators in Finite Element-based shape optimization". Thesis, Université Paris-Saclay (ComUE), 2016. http://www.theses.fr/2016SACLX070/document.
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Les méthodes d’optimisation de forme basées sur le gradient reposent sur le calcul de la dérivée de forme. Dans beaucoup d’applications, la fonctionnelle coût dépend de la solution d’une EDP. Il s’en suit qu’elle ne peut être résolue exactement et que seule une approximation de celle-ci peut être calculée, par exemple par la méthode des éléments finis. Il en est de même pour la dérivée de forme. Ainsi, les méthodes de gradient en optimisation de forme - basées sur des approximations du gradient - ne garantissent pas a priori que la direction calculée à chaque itération soit effectivement une direction de descente pour la fonctionnelle coût. Cette thèse est consacrée à la construction d’une procédure de certification de la direction de descente dans des algorithmes de gradient en optimisation de forme grâce à des estimations a posteriori de l’erreur introduite par l’approximation de la dérivée de forme par la méthode des éléments finis. On présente une procédure pour estimer l’erreur dans une Quantité d’Intérêt et on obtient une borne supérieure certifiée et explicitement calculable. L’Algorithme de Descente Certifiée (CDA) pour l’optimisation de forme identifie une véritable direction de descente à chaque itération et permet d’établir un critère d’arrêt fiable basé sur la norme de la dérivée de forme. Deux applications principales sont abordées dans la thèse. Premièrement, on considère le problème scalaire d’identification de forme en tomographie d’impédance électrique et on étudie différentes estimations d’erreur. Une première approche est basée sur le principe de l’énergie complémentaire et nécessite la résolution de problèmes globaux additionnels. Afin de réduire le coût de calcul de la procédure de certification, une estimation qui dépend seulement de quantités locales est dérivée par la reconstruction des flux équilibrés. Après avoir validé les estimations de l’erreur pour un cas bidimensionnel, des résultats numériques sont présentés pour tester les méthodes discutées. Une deuxième application est centrée sur le problème vectoriel de la conception optimale des structures élastiques. Dans ce cadre figure, on calcule l’expression volumique de la dérivée de forme de la compliance à partir de la formulation primale en déplacements et de la formulation duale mixte pour l’équation de l’élasticité linéaire. Quelques résultats numériques préliminaires pour la minimisation de la compliance sous une contrainte de volume en 2D sont obtenus à l’aide de l’Algorithme de Variation de Frontière et une estimation a posteriori de l’erreur de la dérivée de forme basée sur le principe de l’énergie complémentaire est calculéeGradient-based shape optimization strategies rely on the computation of the so-called shape gradient. In many applications, the objective functional depends both on the shape of the domain and on the solution of a PDE which can only be solved approximately (e.g. via the Finite Element Method). Hence, the direction computed using the discretized shape gradient may not be a genuine descent direction for the objective functional. This Ph.D. thesis is devoted to the construction of a certification procedure to validate the descent direction in gradient-based shape optimization methods using a posteriori estimators of the error due to the Finite Element approximation of the shape gradient.By means of a goal-oriented procedure, we derive a fully computable certified upper bound of the aforementioned error. The resulting Certified Descent Algorithm (CDA) for shape optimization is able to identify a genuine descent direction at each iteration and features a reliable stopping criterion basedon the norm of the shape gradient.Two main applications are tackled in the thesis. First, we consider the scalar inverse identification problem of Electrical Impedance Tomography and we investigate several a posteriori estimators. A first procedure is inspired by the complementary energy principle and involves the solution of additionalglobal problems. In order to reduce the computational cost of the certification step, an estimator which depends solely on local quantities is derived via an equilibrated fluxes approach. The estimators are validated for a two-dimensional case and some numerical simulations are presented to test the discussed methods. A second application focuses on the vectorial problem of optimal design of elastic structures. Within this framework, we derive the volumetric expression of the shape gradient of the compliance using both H 1 -based and dual mixed variational formulations of the linear elasticity equation. Some preliminary numerical tests are performed to minimize the compliance under a volume constraint in 2D using the Boundary Variation Algorithm and an a posteriori estimator of the error in the shape gradient is obtained via the complementary energy principle
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Siow, Bernard, Ivana Drobnjak, Andrada Ianus, Isabel N. Christie, Mark F. Lythgoe e Daniel C. Alexander. "Axon radius estimation with Oscillating Gradient Spin Echo (OGSE) diffusion MRI". Diffusion fundamentals 18 (2013) 1, S. 1-6, 2013. https://ul.qucosa.de/id/qucosa%3A13707.
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The estimation of axon radius provides insights into brain function [1] and could provide progression and classification biomarkers for a number of white matter diseases [2-4]. A recent in silico study [5] has shown that optimised gradient waveforms (GEN) and oscillating gradient waveform spin echo (OGSE) have increased sensitivity to small axon radius compared to pulsed gradient spin echo (PGSE) diffusion MR sequences. In a follow-up study [6], experiments with glass capillaries show the practical feasibility of GEN sequences and verify improved pore-size estimates. Here, we compare PGSE with sine, sine with arbitrary phase, and square wave OGSE (SNOGSE, SPOGSE, SWOGSE, respectively) for axon radius mapping in the corpus callosum of a rat, ex-vivo. Our results suggest improvements in pore size estimates from OGSE over PGSE, with greatest improvement from SWOGSE, supporting theoretical results from [5] and other studies [7-9].
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Siow, Bernard, Ivana Drobnjak, Andrada Ianus, Isabel N. Christie, Mark F. Lythgoe e Daniel C. Alexander. "Axon radius estimation with Oscillating Gradient Spin Echo (OGSE) diffusion MRI". Universitätsbibliothek Leipzig, 2015. http://nbn-resolving.de/urn:nbn:de:bsz:15-qucosa-184163.
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The estimation of axon radius provides insights into brain function [1] and could provide progression and classification biomarkers for a number of white matter diseases [2-4]. A recent in silico study [5] has shown that optimised gradient waveforms (GEN) and oscillating gradient waveform spin echo (OGSE) have increased sensitivity to small axon radius compared to pulsed gradient spin echo (PGSE) diffusion MR sequences. In a follow-up study [6], experiments with glass capillaries show the practical feasibility of GEN sequences and verify improved pore-size estimates. Here, we compare PGSE with sine, sine with arbitrary phase, and square wave OGSE (SNOGSE, SPOGSE, SWOGSE, respectively) for axon radius mapping in the corpus callosum of a rat, ex-vivo. Our results suggest improvements in pore size estimates from OGSE over PGSE, with greatest improvement from SWOGSE, supporting theoretical results from [5] and other studies [7-9].
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Nwagbara, Anuri Nwadimma Chiamaka. "Contribution for heat flow density estimation in the Meso-Cenozoic basins of Portugal". Master's thesis, Universidade de Évora, 2021. http://hdl.handle.net/10174/30091.
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The evolution of temperature in sedimentary basins is a fundamental tool for the evaluation and exploration of hydrocarbons, for the evaluation of geothermal potential, for paleogeographic reconstruction, for carbon sequestration and for the hydrogeological evaluation of a given region. Estimates of heat flow density (HFD) on the surface in the Portuguese Meso Cenozoic basins are difficult to obtain. The small number of HFD estimates in the Meso Cenozoic basins is a consequence of the high drilling costs for determining HFD and strict drilling regulation measures. Most of the temperature data available for estimating HFD is obtained in oil exploration holes; however, the temperature data obtained from them are subject to high uncertainty. Twelve oil exploration holes carried out in Portugal, with temperature records, were considered in this work; only one hole was rejected because they did not present the minimum quality requirements for HFD estimation. The values of thermal conductivity of the rock formations traversed by the various holes were assumed since there are no laboratory determinations for those geological formations. Bottom temperatures (BHT) have been corrected with Zetaware software that uses the Horner method and produces results with acceptable uncertainties. Only three sedimentary basins (Lusitanian, Porto, Alentejo) were identified and possessing a regional HFD estimates ranging from 61 to 174 mWm-2. The average geothermal gradient and average HFD estimates of the Lusitanian basin were found to be 33 ℃ km-1 and 113 mWm-2, Porto (24 ℃ km-1, 78 mWm-2) and Alentejo (21 ℃ km-1, 61 mWm-2) respectively. Compared to previous geothermal and HFD values, the new estimates obtained had a fair correspondence with a high regional sedimentary HFD estimates. Nevertheless, a heat flow density map was generated and an attempt to geothermally characterize the Portuguese Meso Cenozoic basins is made; RESUMO:
CONTRIBUIÇÃO PARA A ESTIMATIVA DA DENSIDADE DO FLUXO DE CALOR NAS BACIAS MESO CENOZÓICAS DE PORTUGAL
A evolução da temperatura nas bacias sedimentares é uma ferramenta fundamental para a avaliação e exploração de hidrocarbonetos, para a avaliação do potencial geotérmico, para a reconstrução paleogeográfica, para o sequestro de carbono e para a avaliação hidrogeológica de uma determinada região. Estimativas da densidade do fluxo de calor (DFC) na superfície das bacias Meso Cenozóicas Portuguesas são difíceis de obter. O pequeno número de estimativas de DFC nas bacias Meso Cenozóicas é uma consequência dos elevados custos de perfuração para a determinação do DFC e de medidas rigorosas de regulação da perfuração. A maioria dos dados de temperatura disponíveis para estimar o DFC é obtida em furos de prospeção de petróleo; no entanto, os dados de temperatura neles obtidos estão sujeitos a uma elevada incerteza. Neste trabalho foram considerados doze furos de prospeção de petróleo realizados em Portugal com registos de temperatura; apenas um furo foi rejeitado por não apresentar os requisitos mínimos de qualidade para a estimativa do DFC. Assumiram-se os valores de condutividade térmica das formações rochosas atravessadas pelos diversos furos uma vez que não existem determinações laboratoriais para essas formações geológicas. As temperaturas de fundo de furo (BHT) foram corrigidas com o software Zetaware que utiliza o método de Horner e produz resultados com incertezas aceitáveis. Apenas foram identificadas três bacias sedimentares (Lusitanianas, do Porto, do Alentejo) e com uma estimativa regional de DFC que varia entre 61 e 174 mWm-2. Verificou-se que o gradiente geotérmico médio e a DFC média na bacia Lusitaniana são, respectivamente, 33 ℃km-1 e 113 mWm-2 Porto (24 ℃ km-1, 78 mWm-2) e Alentejo (21 ℃ km-1, 61 mWm-2) respectivamente. Em comparação com valores geotérmicos e de DFC anteriores, as novas estimativas obtidas correspondem a uma DFC sedimentar regional elevada. Foi desenhado um mapa da densidade de fluxo de calor e é feita uma tentativa de caracterizar geotermicamente as bacias Meso Cenozóicas Portuguesas.
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Valstad, Bård Arve. "Parameter Estimation and Control of a Dual Gradient Managed Pressure Drilling System". Thesis, Norwegian University of Science and Technology, Department of Engineering Cybernetics, 2009. http://urn.kb.se/resolve?urn=urn:nbn:no:ntnu:diva-9025.
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The increasing demand for oil and gas in the world, and the fact that most of the easily accessible reservoirs are in production or already abandoned, result in a need to develop new resources. These may be new reservoirs that have previously been considered uneconomical or impossible to develop, or extended operation of existing fields. Developing smaller reservoirs, means that more wells have to be drilled per barrel, which gives both more and eventually greater challenges as more and more wells are drilled because the wells has to be drilled further and into more difficult formations. Mature fields are drained, which leads to lowering of reservoir pressure and therefore tighter pressure margins for drilling. Because of the challenges with deep water drilling and depleted reservoirs, there is a need to precisely control the pressure profile in the well during drilling in such formations. Some of the parameters that are needed to control the well precisely are not easily obtained during drilling, and an estimation of these will therefore be crucial to be able to use a model to control the well. The transmission of measurements from a well is also often either delayed or absent during periods of drilling, which will cause problems for the control of the well. It is therefore required that an estimation scheme is able to estimate the pressure in the well for the time interval between the updates of the measurements from the well. The conventional method for transmitting measurements from the bottom of the well is by mud pulse telemetry which is pressure waves transmitted through the drilling mud. These measurements will be delayed, so accurate real-time measurements will never be available. To estimate the bottom hole pressure, a extended kalman filter was evaluated. This filter is based on a simple mathematical model derived for the drilling process. The states in the filter is height of mud in the riser, mud weight and different friction factors for the well. The filter is tested when the measurements are continuous available, with delayed update of the bottom hole measurement, and for cases where one of the measurements are absent. A simple controller to control the bottom hole pressure is implemented to control the pressure for reference tracking and during a simulated pipe connection. During simulations, it was not possible to achieve convergence for the friction factor for normal flows, and this led to errors in the other states. The friction factor would only converge to its true value during very high flows during the nominal testing, which led to the other states also achieving their correct values. The problem in estimating the friction factor applied to all different forms for friction parameters. The kalman filter was tested against an artificial well simulated in WeMod, and gave decent estimates of the bottom hole pressure except for at low flows.
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Ades, Michel. "Topics in stochastic systems, cumulative renewal processes, stochastic control and gradient estimation". Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1997. http://www.collectionscanada.ca/obj/s4/f2/dsk3/ftp04/nq44336.pdf.
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Levine, N. D. "Superconvergent estimation of the gradient from linear finite element approximations on triangular elements". Thesis, University of Reading, 1985. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.353472.
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Mangan, S. J. "Development of an intelligent road gradient estimation method using vehicle CAN bus data". Thesis, University of Liverpool, 2003. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.406640.
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Lawrence, Joseph Scott. "Use of Phase and Amplitude Gradient Estimation for Acoustic Source Characterization and Localization". BYU ScholarsArchive, 2018. https://scholarsarchive.byu.edu/etd/6969.
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Energy-based acoustic quantities provide vital information about acoustic fields and the characterization of acoustic sources. Recently, the phase and amplitude gradient estimator (PAGE) method has been developed to reduce error and extend bandwidth of energy-based quantity estimates. To inform uses and applications of the method, analytical and experimental characterizations of the method are presented. Analytical PAGE method bias errors are compared with those of traditional estimation for two- and three-microphone one-dimensional probes. For a monopole field when phase unwrapping is possible, zero bias error is achieved for active intensity using three-microphone PAGE and for specific acoustic impedance using two-microphone PAGE. A method for higher-order estimation in reactive fields is developed, and it is shown that a higher-order traditional method outperforms higher-order PAGE for reactive intensity in a standing wave field. Extending the applications of PAGE, the unwrapped phase gradient is used to develop a method for directional sensing with improved bandwidth and arbitrary array response.
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Genest, Laurent. "Optimisation de forme par gradient en dynamique rapide". Thesis, Lyon, 2016. http://www.theses.fr/2016LYSEC022/document.
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Afin de faire face aux nouveaux challenges de l’industrie automobile, les ingénieurs souhaitent appliquer des méthodes d’optimisation à chaque étape du processus de conception. En élargissant l’espace de conception aux paramètres de forme, en augmentant leur nombre et en étendant les plages de variation, de nouveaux verrous sont apparus. C’est le cas de la résistance aux chocs. Avec les temps de calcul long, la non-linéarité, l’instabilité et la dispersion numérique de ce problème de dynamique rapide, la méthode usuellement employée, l’optimisation par plan d’expériences et surfaces de réponse, devient trop coûteuse pour être utilisée industriellement. Se pose alors la problématique suivante : Comment faire de l’optimisation de forme en dynamique rapide avec un nombre élevé de paramètres ?. Pour y répondre, les méthodes d’optimisation par gradient s’avèrent être les plus judicieuses. Le nombre de paramètres a une influence réduite sur le coût de l’optimisation. Elles permettent donc l’optimisation de problèmes ayant de nombreux paramètres. Cependant, les méthodes classiques de calcul du gradient sont peu pertinentes en dynamique rapide : le coût en nombre de simulations et le bruit empêchent l’utilisation des différences finies et le calcul du gradient en dérivant les équations de dynamique rapide n’est pas encore disponible et serait très intrusif vis-à-vis des logiciels. Au lieu de déterminer le gradient, au sens classique du terme, des problèmes de crash, nous avons cherché à l’estimer. L’Equivalent Static Loads Method est une méthode permettant l’optimisation à moindre coût basée sur la construction d’un problème statique linéaire équivalent au problème de dynamique rapide. En utilisant la dérivée du problème équivalent comme estimation du gradient, il nous a été possible d’optimiser des problèmes de dynamique rapide ayant des épaisseurs comme variables d’optimisation. De plus, si l’on construit les équations du problème équivalent avec la matrice de rigidité sécante, l’approximation du gradient n’en est que meilleure. De cette manière, il est aussi possible d’estimer le gradient par rapport à la position des nœuds du modèle de calcul. Comme il est plus courant de travailler avec des paramètres CAO, il faut déterminer la dérivée de la position des nœuds par rapport à ces paramètres. Nous pouvons le faire de manière analytique si nous utilisons une surface paramétrique pour définir la forme et ses points de contrôle comme variables d’optimisation. Grâce à l’estimation du gradient et à ce lien entre nœuds et paramètres de forme, l’optimisation de forme avec un nombre important de paramètres est désormais possible à moindre coût. La méthode a été développée pour deux familles de critères issues du crash automobile. La première est liée au déplacement d’un nœud, objectif important lorsqu’il faut préserver l’intégrité de l’habitacle du véhicule. La seconde est liée à l’énergie de déformation. Elle permet d’assurer un bon comportement de la structure lors du chocIn order to face their new industrial challenges, automotive constructors wish to apply optimization methods in every step of the design process. By including shape parameters in the design space, increasing their number and their variation range, new problematics appeared. It is the case of crashworthiness. With the high computational time, the nonlinearity, the instability and the numerical dispersion of this rapid dynamics problem, metamodeling techniques become to heavy for the standardization of those optimization methods. We face this problematic: ”How can we carry out shape optimization in rapid dynamics with a high number of parameters ?”. Gradient methods are the most likely to solve this problematic. Because the number of parameters has a reduced effect on the optimization cost, they allow optimization with a high number of parameters. However, conventional methods used to calculate gradients are ineffective: the computation cost and the numerical noise prevent the use of finite differences and the calculation of a gradient by deriving the rapid dynamics equations is not currently available and would be really intrusive towards the software. Instead of determining the real gradient, we decided to estimate it. The Equivalent Static Loads Method is an optimization method based on the construction of a linear static problem equivalent to the rapid dynamic problem. By using the sensitivity of the equivalent problem as the estimated gradient, we have optimized rapid dynamic problems with thickness parameters. It is also possible to approximate the derivative with respect to the position of the nodes of the CAE model. But it is more common to use CAD parameters in shape optimization studies. So it is needed to have the sensitivity of the nodes position with these CAD parameters. It is possible to obtain it analytically by using parametric surface for the shape and its poles as parameters. With this link between nodes and CAD parameters, we can do shape optimization studies with a large number of parameters and this with a low optimization cost. The method has been developed for two kinds of crashworthiness objective functions. The first family of criterions is linked to a nodal displacement. This category contains objectives like the minimization of the intrusion inside the passenger compartment. The second one is linked to the absorbed energy. It is used to ensure a good behavior of the structure during the crash
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Santos, Jailson França dos. "Análise dos erros na estimação de gradientes em malhas de Voronoi". Universidade do Estado do Rio de Janeiro, 2013. http://www.bdtd.uerj.br/tde_busca/arquivo.php?codArquivo=4876.
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Coordenação de Aperfeiçoamento de Pessoal de Nível SuperiorEste trabalho apresenta um estudo teórico e numérico sobre os erros que ocorrem nos cálculos de gradientes em malhas não estruturadas constituídas pelo diagrama de Voronoi, malhas estas, formadas também pela triangulação de Delaunay. As malhas adotadas, no trabalho, foram as malhas cartesianas e as malhas triangulares, esta última é gerada pela divisão de um quadrado em dois ou quatro triângulos iguais. Para tal análise, adotamos a escolha de três metodologias distintas para o cálculo dos gradientes: método de Green Gauss, método do Mínimo Resíduo Quadrático e método da Média do Gradiente Projetado Corrigido. O texto se baseia em dois enfoques principais: mostrar que as equações de erros dadas pelos gradientes podem ser semelhantes, porém com sinais opostos, para pontos de cálculos em volumes vizinhos e que a ordem do erro das equações analíticas pode ser melhorada em malhas uniformes quando comparada as não uniformes, nos casos unidimensionais, e quando analisada na face de tais volumes vizinhos nos casos bidimensionais.
This work presents a theoretical and numerical study on the errors that occur in the calculation of gradients on unstructured meshes Voronoi type, these meshes, also formed by Delaunay triangulation. The meshes adopted in the work were cartesian and triangular meshes, the latter is formed by dividing a square in two or four equal triangles. For this analysis, we adopt the choice of three different methodologies for the calculation of gradients: Green Gauss method, weighted least-squares method and mean value of the projected gradients method. The text is based on two main approaches: to show that the equations of errors given by the gradients may be similar, but with opposite signs, for calculation point in opposite volumes. And show that the order of the error of the analytical equations can be improved in uniform mesh when compared to not uniform, the one-dimensional case, and when viewed from the opposite face of such volumes for the two-dimensional case.
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Smith, Leanna Marie. "Fast Corn Grading System Verification and Modification". OpenSIUC, 2012. https://opensiuc.lib.siu.edu/theses/795.
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A fast corn grading system can replace the traditional method in unofficial corn grading locations. The initial design of the system proved that it can classify corn kernels with a high success rate. This study tested the robustness of the system against samples from different locations with different moisture contents. The experimental results were compared with the official grading results for 3 out of the 6 samples. This study also tested the limitations of the segmentation algorithm. The results showed that 60 to 70 kernels in a 100 cm2 could be correctly segmented in a relatively short running time. Classification accuracy would improve with modifications to the system, including increased training samples of damaged kernels, uniform illumination, color calibration, and improved weight approximation of the kernels.
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Baidoo-Williams, Henry Ernest. "Novel techniques for estimation and tracking of radioactive sources". Diss., University of Iowa, 2014. https://ir.uiowa.edu/etd/1539.
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Radioactive source signal measurements are Poisson distributed due to the underlying radiation process. This fact, coupled with the ubiquitous normally occurring radioactive materials (NORM), makes it challenging to localize or track a radioactive source or target accurately. This leads to the necessity to either use highly accurate sensors to minimize measurement noise or many less accurate sensors whose measurements are averaged to minimize the noise. The cost associated with highly accurate sensors places a bound on the number that can realistically be deployed. Similarly, the degree of inaccuracy in cheap sensors also places a lower bound on the number of sensors needed to achieve realistic estimates of location or trajectory of a radioactive source in order to achieve reasonable error margins.
We first consider the use of the smallest number of highly accurate sensors to localize radioactive sources. The novel ideas and algorithms we develop use no more than the minimum number of sensors required by triangulation based algorithms but avoid all the pitfalls manifest with triangulation based algorithms such as multiple local minima and slow convergence rate from algorithm reinitialization. Under the general assumption that we have a priori knowledge of the statistics of the intensity of the source, we show that if the source or target is known to be in one open half plane, then N sensors are enough to guarantee a unique solution, N being the dimension of the search space. If the assumptions are tightened such that the source or target lies in the open convex hull of the sensors, then N+1 sensors are required. Suppose we do not have knowledge of the statistics of the intensity of the source, we show that N+1 sensors is still the minimum number of sensors required to guarantee a unique solution if the source is in the open convex hull of the sensors.
Second, we present tracking of a radioactive source using cheap low sensitivity binary proximity sensors under some general assumptions. Suppose a source or target moves in a straight line, and suppose we have a priori knowledge of the radiation intensity of the source, we show that three binary sensors and their binary measurements depicting the presence or absence of a source within their nominal sensing range suffices to localize the linear trajectory. If we do not have knowledge of the intensity of the source or target, then a minimum of four sensors suffices to localize the trajectory of the source.
Finally we present some fundamental limits on the estimation accuracy of a stationary radioactive source using ideal mobile measurement sensors and provide a robust algorithm which achieves the estimation accuracy bounds asymptotically as the expected radiation count increases.
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Jia, Zhen. "Image Registration and Image Completion: Similarity and Estimation Error Optimization". University of Cincinnati / OhioLINK, 2014. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1406821875.
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Cengiz, Acarturk. "Gradient Characteristics Of The Unaccusative/unergative Distinction In Turkish: An Experimental Investigation". Master's thesis, METU, 2005. http://etd.lib.metu.edu.tr/upload/12605912/index.pdf.
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This thesis investigates the gradient behaviour of monadic intransitive verb classes in Turkish, under an aspectual classification of the unaccusative/unergative verb types, namely The Split Intransitivity Hierarchy. This Hierarchy claims that intransitive verb types are subject to gradient acceptability in certain syntactic constructions. The methods used in judgment elicitation studies in psychophysics, such as the magnitude estimation technique have recently been adapted to be used in capturing gradient linguistic data. Also, the practical benefits of the Internet directed researchers to design and conduct web-based experiments for linguistic data elicitation. Research on Human Computer Interaction offers suggestions for the design of more usable user interfaces. Considering these developments, in this thesis, a web based experiment interface has been designed as an extension to the magnitude estimation technique to elicit acceptability judgments on two syntactic constructions, i.e. the -mIS participle (the unaccusative diagnostic) and impersonal passivization (the unergative diagnostic) for different verb types on the Split Intransitivity Hierarchy. The experiment was conducted on the Internet.
The results show that in the two diagnostics, the verb types receive categorical or indeterminate acceptability judgments, which allows us to specify the core or peripheral status of the verbs. Within the classes we have examined, change of state verbs constitute the core unaccusative verbs, and controlled (motional and non-motional) process verbs constitute the core unergative verbs. Stative verbs and uncontrolled process verbs are peripheral unaccusatives and unergatives, respectively. Change of location verbs (with an animate subject) are close to the unergative end.
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Beiki, Majid. "New Techniques for Estimation of Source Parameters : Applications to Airborne Gravity and Pseudo-Gravity Gradient Tensors". Doctoral thesis, Uppsala universitet, Geofysik, 2011. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-143015.
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Gravity gradient tensor (GGT) data contains the second derivatives of the Earth’s gravitational potential in three orthogonal directions. GGT data can be measured either using land, airborne, marine or space platforms. In the last two decades, the applications of GGT data in hydrocarbon exploration, mineral exploration and structural geology have increased considerably. This work focuses on developing new interpretation techniques for GGT data as well as pseudo-gravity gradient tensor (PGGT) derived from measured magnetic field. The applications of developed methods are demonstrated on a GGT data set from the Vredefort impact structure, South Africa and a magnetic data set from the Särna area, west central Sweden. The eigenvectors of the symmetric GGT can be used to estimate the position of the causative body as well as its strike direction. For a given measurement point, the eigenvector corresponding to the maximum eigenvalue points approximately toward the center of mass of the source body. For quasi 2D structures, the strike direction of the source can be estimated from the direction of the eigenvectors corresponding to the smallest eigenvalues. The same properties of GGT are valid for the pseudo-gravity gradient tensor (PGGT) derived from magnetic field data assuming that the magnetization direction is known. The analytic signal concept is applied to GGT data in three dimensions. Three analytic signal functions are introduced along x-, y- and z-directions which are called directional analytic signals. The directional analytic signals are homogenous and satisfy Euler’s homogeneity equation. Euler deconvolution of directional analytic signals can be used to locate causative bodies. The structural index of the gravity field is automatically identified from solving three Euler equations derived from the GGT for a set of data points located within a square window with adjustable size. For 2D causative bodies with geometry striking in the y-direction, the measured gxz and gzz components of GGT can be jointly inverted for estimating the parameters of infinite dike and geological contact models. Once the strike direction of 2D causative body is estimated, the measured components can be transformed into the strike coordinate system. The GGT data within a set of square windows for both infinite dike and geological contact models are deconvolved and the best model is chosen based on the smallest data fit error.Felaktigt tryckt som Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology 730
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Strydom, Willem Jacobus. "Recovery based error estimation for the Method of Moments". Thesis, Stellenbosch : Stellenbosch University, 2015. http://hdl.handle.net/10019.1/96881.
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Thesis (MEng)--Stellenbosch University, 2015.ENGLISH ABSTRACT: The Method of Moments (MoM) is routinely used for the numerical solution of electromagnetic surface integral equations. Solution errors are inherent to any numerical computational method, and error estimators can be effectively employed to reduce and control these errors. In this thesis, gradient recovery techniques of the Finite Element Method (FEM) are formulated within the MoM context, in order to recover a higher-order charge of a Rao-Wilton-Glisson (RWG) MoM solution. Furthermore, a new recovery procedure, based specifically on the properties of the RWG basis functions, is introduced by the author. These recovered charge distributions are used for a posteriori error estimation of the charge. It was found that the newly proposed charge recovery method has the highest accuracy of the considered recovery methods, and is the most suited for applications within recovery based error estimation. In addition to charge recovery, the possibility of recovery procedures for the MoM solution current are also investigated. A technique is explored whereby a recovered charge is used to find a higher-order divergent current representation. Two newly developed methods for the subsequent recovery of the solenoidal current component, as contained in the RWG solution current, are also introduced by the author. A posteriori error estimation of the MoM current is accomplished through the use of the recovered current distributions. A mixed second-order recovered current, based on a vector recovery procedure, was found to produce the most accurate results. The error estimation techniques developed in this thesis could be incorporated into an adaptive solver scheme to optimise the solution accuracy relative to the computational cost.
AFRIKAANSE OPSOMMING: Die Moment Metode (MoM) vind algemene toepassing in die numeriese oplossing van elektromagnetiese oppervlak integraalvergelykings. Numeriese foute is inherent tot die prosedure: foutberamingstegnieke is dus nodig om die betrokke foute te analiseer en te reduseer. Gradiënt verhalingstegnieke van die Eindige Element Metode word in hierdie tesis in die MoM konteks geformuleer. Hierdie tegnieke word ingespan om die oppervlaklading van 'n Rao-Wilton-Glisson (RWG) MoM oplossing na 'n verbeterde hoër-orde voorstelling te neem. Verder is 'n nuwe lading verhalingstegniek deur die outeur voorgestel wat spesifiek op die eienskappe van die RWG basis funksies gebaseer is. Die verhaalde ladingsverspreidings is geïmplementeer in a posteriori fout beraming van die lading. Die nuut voorgestelde tegniek het die akkuraatste resultate gelewer, uit die groep verhalingstegnieke wat ondersoek is. Addisioneel tot ladingsverhaling, is die moontlikheid van MoM-stroom verhalingstegnieke ook ondersoek. 'n Metode vir die verhaling van 'n hoër-orde divergente stroom komponent, gebaseer op die verhaalde lading, is geïmplementeer. Verder is twee nuwe metodes vir die verhaling van die solenodiale komponent van die RWG stroom deur die outeur voorgestel. A posteriori foutberaming van die MoM-stroom is met behulp van die verhaalde stroom verspreidings gerealiseer, en daar is gevind dat 'n gemengde tweede-orde verhaalde stroom, gebaseer op 'n vektor metode, die beste resultate lewer. Die foutberamingstegnieke wat in hierdie tesis ondersoek is, kan in 'n aanpasbare skema opgeneem word om die akkuraatheid van 'n numeriese oplossing, relatief tot die berekeningskoste, te optimeer.
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Pavlik, Stacey C. "Estimating the Impact of House Sparrows on Eastern Bluebird Reproductive Success Across an Urban Gradient". Youngstown State University / OhioLINK, 2012. http://rave.ohiolink.edu/etdc/view?acc_num=ysu1364373664.
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Bang, Bohyun. "Inverse estimation of horizontal pressure gradients and vertical eddy viscosity profiles in shallow waters". W&M ScholarWorks, 1994. https://scholarworks.wm.edu/etd/1539616559.
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A least-squares inverse method was devised to estimate horizontal pressure gradients and vertical eddy-viscosity profiles simultaneously, from current profiles. The method was designed mostly for observations of deterministic or near-deterministic wave currents. Tidal-current observations were chosen for the present study. The inverse system was constructed from a linearized momentum equation. The viscosity was modeled with a time-constant and harmonic function in time, but without its vertical structure predefined. The least-squares problem was solved with the singular value decomposition, by taking current harmonic profiles as input. at first, the method was tested with current profiles simulated by a numerical model employing the mixing-length theory for vertical eddy viscosity. Analyses were done on fourteen sets of real measurements at 6 stations in Chesapeake Bay and one of its tributaries. Thirteen were from current-meter moorings, and one was from a bottom-mounted acoustic Doppler current profiler. It turned out that the proposed method performed well enough to diagnose a linearized dynamic balance which involved a friction term with time-constant, but depth-dependent eddy viscosity. Eddy-viscosity profiles appeared to have linear-exponential structure. The apparent maximum varied significantly in season, implying some stratification effect. Using the primary results, values of drag coefficient (&C\sb{lcub}d{rcub}&) and depth-average TKE production were deduced. Results of &C\sb{lcub}d{rcub}& indicated some seasonal variation of bottom roughness. Depth-average TKE production in the lower bay appeared to be &{lcub}\sim{rcub}&8 times higher than in the mid- or upper bay. The production in the upper part of the York River appeared to be 3&{lcub}\sim{rcub}&4 times higher than the lower part. Among them, the upper part of the York River appeared to have the highest production. The approach will be a good tool for the analysis of ADCP measurements in field, due to the simplicity, yet the diagnostic power. The application, however, is limited mostly to deterministic current measurements. The approach is not appropriate to strongly advective flows. Even for weakly advective flows, it is incapable of determining the oscillatory part of the viscosity successfully, due to truncated nonlinear-advective terms.
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Meftahi, Houcine. "Études théoriques et numériques de quelques problèmes inverses". Thesis, Lille 1, 2009. http://www.theses.fr/2009LIL10090/document.
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Le travail de la thèse concerne l'étude de quelques problèmes inverses par différents approches mathématiques. Dans la première partie, nous considérons le problème inverse géométrique consistant à retrouver une fissure ou cavité(s) inconnue à partir de mesures sur le bord d'un domaine plan. Nous traitons ce problème par des techniques d'approximation rationnelle et méromorphe dans le plan complexe. Nous étudions un autre problème inverse consistant à estimer l'aire d'une cavité. Nous donnons une majoration explicite de l'aire de la cavité. Cette majoration est basée sur une estimation de croissance dans l'espace de Hardy-Sobolev de la couronne. Nous appliquons également cette estimation pour donner la vitesse de comvergence d'un schéma d'ïnterpolation d'une fonction de l'espace de Hardy-Sobolev de la couronne. Dans la deuxième partie, nous considérons d'abord le problème inverse d'identification des paramètres de Lamé en élasticité linéaire. Nous transformons ce problème en un problème de minimisation et nous exhibons quelques exemples numériques. Nous considérons également le problème inverse d'identification d'une inclusion correspondant à une discontinuité de la conductivité. Nous utilisons la méthode du gradient topologique pour une première approximation et ensuite la méthode du gradient classique pour identifier plus précisément celles-ci. Enfin, nous étudions un problème inverse d'identification d'une inclusion en élasticité linéaire. Nous utilisons le gradient de forme pour retrouver numériquement des inclusions elliptiquesThis work concerns the study of some inverse problems by different mathematical approaches. ln the first part, we consider the geometrical inverse problem. related to the identification of an unknown crack or inclusion(s) by boundary measurements. We treat this problem by technique of rational and meromorphic approximation in the complex plane. We study another inverse problem, namely estimating the area of a cavity. We derivive an explicit upper bound on the area of the cavity. We also aplly this estimation, to find an upper bound on the rate of convergence of a recovery interpolation schema in the Hardy-Sobolev space of an annulus. ln the second part. we first consider the inverse problem of recovering the Lamé parameters in linear elasticity from boundary measurements. we perform numerical experiments. We also consider the inverse problem or identification of an inclusion corresponding to a discontinuity of the conductivity. We use the method of the topological gradient to obtain a first estimate on the location of one or several inclusions and then, we use the method of the classical gradient to identify more precisely these. Finally. in the context of shape optimization, we study the inverse problem of identification of an inclusion in linear elasticity. We calculate the shape gradient of a functional of Kohn-Vogelius type, minmax of a lagrangian with respect to the parameter of deformation. We use this gradient to numerically flnd elliptic inclusions
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Yu, Jia. "Distributed parameter and state estimation for wireless sensor networks". Thesis, University of Edinburgh, 2017. http://hdl.handle.net/1842/28929.
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The research in distributed algorithms is linked with the developments of statistical inference in wireless sensor networks (WSNs) applications. Typically, distributed approaches process the collected signals from networked sensor nodes. That is to say, the sensors receive local observations and transmit information between each other. Each sensor is capable of combining the collected information with its own observations to improve performance. In this thesis, we propose novel distributed methods for the inference applications using wireless sensor networks. In particular, the efficient algorithms which are not computationally intensive are investigated. Moreover, we present a number of novel algorithms for processing asynchronous network events and robust state estimation. In the first part of the thesis, a distributed adaptive algorithm based on the component-wise EM method for decentralized sensor networks is investigated. The distributed component-wise Expectation-Maximization (EM) algorithm has been designed for application in a Gaussian density estimation. The proposed algorithm operates a component-wise EM procedure for local parameter estimation and exploit an incremental strategy for network updating, which can provide an improved convergence rate. Numerical simulation results have illustrated the advantages of the proposed distributed component-wise EM algorithm for both well-separated and overlapped mixture densities. The distributed component-wise EM algorithm can outperform other EM-based distributed algorithms in estimating overlapping Gaussian mixtures. In the second part of the thesis, a diffusion based EM gradient algorithm for density estimation in asynchronous wireless sensor networks has been proposed. Specifically, based on the asynchronous adapt-then-combine diffusion strategy, a distributed EM gradient algorithm that can deal with asynchronous network events has been considered. The Bernoulli model has been exploited to approximate the asynchronous behaviour of the network. Compared with existing distributed EM based estimation methods using a consensus strategy, the proposed algorithm can provide more accurate estimates in the presence of asynchronous networks uncertainties, such as random link failures, random data arrival times, and turning on or off sensor nodes for energy conservation. Simulation experiments have been demonstrated that the proposed algorithm significantly outperforms the consensus based strategies in terms of Mean-Square- Deviation (MSD) performance in an asynchronous network setting. Finally, the challenge of distributed state estimation in power systems which requires low complexity and high stability in the presence of bad data for a large scale network is addressed. A gossip based quasi-Newton algorithm has been proposed for solving the power system state estimation problem. In particular, we have applied the quasi-Newton method for distributed state estimation under the gossip protocol. The proposed algorithm exploits the Broyden- Fletcher-Goldfarb-Shanno (BFGS) formula to approximate the Hessian matrix, thus avoiding the computation of inverse Hessian matrices for each control area. The simulation results for IEEE 14 bus system and a large scale 4200 bus system have shown that the distributed quasi-Newton scheme outperforms existing algorithms in terms of Mean-Square-Error (MSE) performance with bad data.
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Roshani, Pedram. "The Effect of Temperature on the SWCC and Estimation of the SWCC from Moisture Profile under a Controlled Thermal Gradient". Thèse, Université d'Ottawa / University of Ottawa, 2014. http://hdl.handle.net/10393/31072.
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In many situations, the upper layers of soil above the ground water table are in a state of unsaturated condition. Although unsaturated soils are found throughout the world, they are predominant in arid or semi-arid regions. In these areas, the soil water characteristic curve (SWCC) which relates the water content to the matric suction could be used as key tool to implement the mechanics of unsaturated soils into the designs of geotechnical structures such as dams, embankments, pavements, canals, and foundations.
Several experimental techniques are available for determining the SWCC in a laboratory environment. However, these experimental techniques are expensive, time consuming typically requiring days or weeks, depending on the soil type, and demanding intricate testing equipment. Due to these reasons, there has been a growing interest to find other means for estimating SWCC and encourage the adoption of unsaturated soils mechanics in geotechnical engineering practice.
Several methods exist to indirectly estimate the SWCC from basic soil properties. Some may include statistical estimation of the water content at selected matric suction values, correlation of soil properties with the fitting parameters of an analytical equation that represents the SWCC, estimation of the SWCC using a physics-based conceptual model, and artificial intelligence methods such as neural networks or genetic programming.
However, many studies have shown that environmental effects such as temperature, soil structure, initial water content, void ratio, stress history, compaction method, etc. can also affect the SWCC. This means that the estimation SWCC from set of conditions may not reliably predict the SWCC in other conditions. Due to this reason, it is crucial for engineers involved with unsaturated soils to take into account all the factors that influence the SWCC.
The two key objectives of the present thesis are the development of a method based on first principles, using the capillary rise theory, to predict the variation of the SWCC as a function of temperature, as well as developing a technique for the prediction of the fixed parameters of a well-known function representing the SWCC based on basic soil properties together with the moisture profile of a soil column subjected to a known temperature gradient.
A rational approach using capillary rise theory and the effect of temperature on surface tension and liquid density is developed to study the relation between temperature and the parameters of the Fredlund and Xing (1994) equation. Several tests, using a Tempe cell submerged in a controlled temperature bath, were performed to determine the SWCC of two coarse-grained soils at different temperatures. A good comparison between the predicted SWCC at different temperatures using the proposed model and the measured values from the Tempe cell test results is achieved.
Within the scope of this thesis, a separate testing program was undertaken to indirectly estimate the SWCC of the same two coarse-grained soils from the measurement of their steady state soil-moisture profile while subjected to a fixed temperature differences. The water potential equation in the liquid and vapor phases is used to analyses the steady state flow conditions in the unsaturated soil. A good comparison is obtained for the SWCC estimated using this technique with the SWCC measured used a Tempe cell submerged in a controlled temperature bath.
The results of this study indicate that knowledge of the moisture content of a soil specimen under a constant thermal gradient and basic soil properties can be used to estimate the SWCC of the soil at the desired temperature.
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Hagos, Tesfamichael Marikos. "Estimation of phases for compliant motion : Auto-regressive HMM, multi-class logistic regression, Learning from Demonstration (LfD), Gradient descent optimization". Thesis, Luleå tekniska universitet, Rymdteknik, 2017. http://urn.kb.se/resolve?urn=urn:nbn:se:ltu:diva-65613.
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Keller, Frank. "Gradience in grammar : experimental and computational aspects of degrees of grammaticality". Thesis, University of Edinburgh, 2001. http://hdl.handle.net/1842/744.
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This thesis deals with gradience in grammar, i.e., with the fact that some linguistic structures are not fully acceptable or unacceptable, but receive gradient linguistic judgments. The importance of gradient data for linguistic theory has been recognized at least since Chomsky's Logical Structure of Linguistic Theory. However, systematic empirical studies of gradience are largely absent, and none of the major theoretical frameworks is designed to account for gradient data. The present thesis addresses both questions. In the experimental part of the thesis (Chapters 3-5), we present a set of magnitude estimation experiments investigating gradience in grammar. The experiments deal with unaccusativity/unergativity, extraction, binding, word order, and gapping. They cover all major modules of syntactic theory, and draw on data from three languages (English, German, and Greek). In the theoretical part of thesis (Chapters 6 and 7), we use these experimental results to motivate a model of gradience in grammar. This model is a variant of Optimality Theory, and explains gradience in terms of the competition of ranked, violable linguistic constraints. The experimental studies in this thesis deliver two main results. First, they demonstrate that an experimental investigation of gradient phenomena can advance linguistic theory by uncovering acceptability distinctions that have gone unnoticed in the theoretical literature. An experimental approach can also settle data disputes that result from the informal data collection techniques typically employed in theoretical linguistics, which are not well-suited to investigate the behavior of gradient linguistic data. Second, we identify a set of general properties of gradient data that seem to be valid for a wide range of syntactic phenomena and across languages. (a) Linguistic constraints are ranked, in the sense that some constraint violations lead to a greater degree of unacceptability than others. (b) Constraint violations are cumulative, i.e., the degree of unacceptability of a structure increases with the number of constraints it violates. (c) Two constraint types can be distinguished experimentally: soft constraints lead to mild unacceptability when violated, while hard constraint violations trigger serious unacceptability. (d) The hard/soft distinction can be diagnosed by testing for effects from the linguistic context; context effects only occur for soft constraints; hard constraints are immune to contextual variation. (e) The soft/hard distinction is crosslinguistically stable. In the theoretical part of the thesis, we develop a model of gradient grammaticality that borrows central concepts from Optimality Theory, a competition-based grammatical framework. We propose an extension, Linear Optimality Theory, motivated by our experimental results on constraint ranking and the cumulativity of violations. The core assumption of our model is that the relative grammaticality of a structure is determined by the weighted sum of the violations it incurs. We show that the parameters of the model (the constraint weights), can be estimated using the least square method, a standard model fitting algorithm. Furthermore, we prove that standard Optimality Theory is a special case of Linear Optimality Theory. To test the validity of Linear Optimality Theory, we use it to model data from the experimental part of the thesis, including data on extraction, gapping, and word order. For all data sets, a high model fit is obtained and it is demonstrated that the model's predictions generalize to unseen data. On a theoretical level, our modeling results show that certain properties of gradient data (the hard/soft distinction, context effects, and crosslinguistic effects) do not have to be stipulated, but follow from core assumptions of Linear Optimality Theory.
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Silva, Antonio Kelson Vieira da. "Estimativas gradiente para autofunções do V-Laplaciano e métricas m-quasi-Einstein generalizadas compactas com bordo". reponame:Repositório Institucional da UFC, 2015. http://www.repositorio.ufc.br/handle/riufc/22559.
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SILVA, A. K. V. Estimativas gradiente para autofunções do V-Laplaciano e métricas m-quasi-Einstein generalizadas compactas com bordo. 2017. 40 f. Tese (Doutorado em Matemática) – Centro de Ciências, Universidade Federal do Ceará, Fortaleza, 2017.Submitted by Andrea Dantas (pgmat@mat.ufc.br) on 2017-04-18T14:49:03Z No. of bitstreams: 1 2015_tese_akvsilva.pdf: 322426 bytes, checksum: d6abc5541598409191f635ad25e1f501 (MD5)
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The main of this work was to study properties of Riemannian when subjected to conditions on Bakry-Émery-Ricci tensor. Essentially we study two cases. In the first case, motivated by the work of Barros and Ribeiro Jr. (2014), He, Petersen and Wylie (2012) and Miao and Tam (2011), was introduced generalized m-quasi-Einstein metrics compact with boundary, where we get a result that classify these metrics; more specifically, assuming that gradient field of the exponential of potential function is a conformal vector field, we obtain that this must be a geodesic ball in a simply connected space form. That we get some results that implies when these are trivial metrics. In the second case, we work the Bakry-Émery-Ricci tensor bounded bellow, initially in a compact Riemannian, with or without boundary, and later on balls in complete Riemannian. With this study, we obtain gradient estimates for eigenfunctions of V-Laplacian operator, that generalize results of (Li, 2005) and (Li, 2015). Finally, as consequence theses results, we show an Harnack’s inequality.
Este trabalho tem como principal objetivo estudar propriedades de variedades Riemannianas quando submetidas a condições sobre tensores de Ricci-Bakry-Émery. Essencialmente estudamos dois casos. No primeiro caso, motivados pelos trabalhos de Barros e Ribeiro Jr (2014), He, Petersen e Wylie (2012) e por Miao e Tam (2011), introduzimos métricas m-quasi-Einstein generalizadas compactas com bordo, donde obtemos um resultado que garante uma classificação para estas métricas; mais precisamente, assumindo que o gradiente da exponencial da função potencial é um campo conforme, obtemos que aquela deve ser uma bola geodésica de uma forma espacial simplesmente conexa. Disso, obtemos alguns resultados em que garantimos quando estas métricas são triviais. No segundo caso, trabalhos o tensor de Ricci-Bakry-Émery limitado por baixo, inicialmente, em variedades Riemannianas compactas, com bordo ou sem bordo, e posteriormente, sobre bolas em variedades Riemannianas completas. Com esse estudo, obtivemos estimativas do gradiente para autofunções do operador V-Laplaciano, generalizando resultados de (Li, 2005) e (Li, 2015). Finalmente, como consequências desses resultados, exibimos uma desigualdade de Harnack.
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Leblond, Timothée. "Calcul de gradient sur des paramètres CAO pour l’optimisation de forme". Thesis, Université Paris-Saclay (ComUE), 2017. http://www.theses.fr/2017SACLC017/document.
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Dans ce manuscrit, nous présentons une méthode d’optimisation de forme qui se base sur des paramètres géométriques comme des longueurs, des angles, etc. Nous nous appuyons sur des techniques d’optimisation basées sur un gradient. La sensibilité de la fonction objectif par rapport à la position des noeuds du maillage nous est fournie par un solveur adjoint que l’on considère comme une boîte noire. Afin d’optimiser par rapport aux paramètres CAO, nous nous concentrons sur l’évaluation de la sensibilité de la position des noeuds par rapport à ces paramètres. Ainsi, nous proposons deux approches par différences finies. La première méthode s’appuie sur une projection harmonique afin de comparer dans un même espace le maillage initial et celui obtenu suite à la variation d’un paramètre CAO. Les développements présentés dans ce manuscrit permettent d’étendre l’application aux formes ayant plusieurs frontières comme les collecteurs d’échappement. Nous avons développé une méthode d’interpolation adaptée à cette comparaison. L’ensemble du processus a été automatisé et nous en montrons l’entière efficacité sur des applications industrielles en aérodynamique interne. La deuxième méthode se base directement sur les géométries CAO pour évaluer cette sensibilité. Nous utilisons la définition intrinsèque des patches dans l’espace paramétrique (u;v) pour effectuer cette comparaison. Grâce à l’utilisation des coordonnées exactes en tout point de la surface fournies par la CAO, nous évitons d’avoir recours à une interpolation afin d’avoir la meilleure précision de calcul possible. Cependant, contrairement à la première méthode, elle requiert d’identifier les correspondances entre les patches d’une forme à l’autre. Une application sur un cas académique a été faite en aérodynamique externe. La pertinence de la première méthode a été démontrée sur des cas représentatifs et multiobjectifs, ce qui permettrait de faciliter son déploiement et son utilisation dans un cadre industriel. Quant à la deuxième méthode, nous avons montré son fort potentiel. Cependant, des développements supplémentaires seraient nécessaires pour une application plus poussée. Du fait qu’elles sont indépendantes des solveurs mécaniques et du nombre de paramètres, ces méthodes réduisent considérablement les temps de développement des produits, notamment en permettant l’optimisation multiphysique en grande dimensionIn this manuscript, we present a shape optimization method based on CAD parameters such as lengths, angles, etc. We rely on gradient-based optimization techniques. The sensitivity of the objective function, with respect to the mesh nodes position, is provided by an adjoint solver considered here as a black box. To optimize with respect to CAD parameters, we focus on computing the sensitivity of the nodes positions with respect to these parameters. Thus, we propose two approaches based on finite differences. The first method uses a harmonic projection to compare in the same space the initial mesh and the one obtained after a change of the set of CAD parameters. The developments presented in this manuscript open up new doors like the application to shapes with multiple borders such as exhaust manifolds. We also developed an interpolation method suitable for this comparison. The entire process is automated, and we demonstrate the entire effectiveness on internal aerodynamics industrial applications. The second method is directly based on the CAD geometries to assess this sensitivity. To perform this comparison, we use the intrinsic definition of the patches in the parametric space (u;v). Through the use of the exact coordinates at any point on the surface provided by the CAD, we avoid using an interpolation to get the best calculation accuracy possible. However, unlike the first method, it requires to identify the correspondence between patches from one shape to another. An application on an external aerodynamics academic case was made. The relevance of the first method is demonstrated on a representative multi-objective case, which facilitate its deployment use in an industrial environment. Regarding the second method, we showed its great potential. However, further developments are needed to handle more advanced cases. Because they are independent of the mechanical solver and the number of parameters, these methods significantly reduce product development time, particularly by allowing large and multiphysics optimization
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Koppanooru, Sampat Kumar Reddy. "Estimating Thermal Conductivity and Volumetric Specific Heat of a Functionally Graded Material using Photothermal Radiometry". Thesis, University of North Texas, 2017. https://digital.library.unt.edu/ark:/67531/metadc1062896/.
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Functionally graded materials (FGMs) are inhomogeneous materials in which the material properties vary with respect to space. Research has been done by scientific community in developing techniques like photothermal radiometry (PTR) to measure the thermal conductivity and volumetric heat capacity of FGMs. One of the problems involved in the technique is to solve the inverse problem, i.e., estimating the thermal properties after the frequency scan has been obtained. The present work involves finding the unknown thermal conductivity and volumetric heat capacity of the FGMs by using finite volume method. By taking the flux entering the sample as periodic and solving the discretized 1-D thermal wave field equation at a frequency domain, one can obtain the complex temperatures at the surface of the sample for each frequency. These complex temperatures when solved for a range of frequencies gives the phase vs frequency scan which can then be compared to original frequency scan obtained from the PTR experiment by using a residual function. Brute force and gradient descent optimization methods have been implemented to estimate the unknown thermal conductivity and volumetric specific heat of the FGMs through minimization of the residual function. In general, the spatial composition profile of the FGMs can be approximated by using a smooth curve. Three functional forms namely Arctangent curve, Hermite curve, and Bezier curve are used in approximating the thermal conductivity and volumetric heat capacity distributions in the FGMs. The use of Hermite and Bezier curves gives the flexibility to control the slope of the curve i.e. the thermal property distribution along the thickness of the sample. Two-layered samples with constant thermal properties and three layered samples in which one of the layer has varying thermal properties with respect to thickness are considered. The program is written in Fortran and several test runs are performed. Results obtained are close to the original thermal property values with some deviation based on the stopping criteria used in the gradient descent algorithm. Calculating the gradients at each iteration takes considerable amount of time and if these gradient values are already available, the problem can be solved at a faster rate. One of the methods is extending automatic differentiation to complex numbers and calculating the gradient values ahead; this is left for future work.
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Freitas, Ana Carla Almeida de. "Estimativas para o estoque de carbono do solo ao longo de um gradiente topográfico na Amazônia Central". Instituto Nacional de Pesquisas da Amazônia, 2013. http://bdtd.inpa.gov.br/handle/tede/2340.
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Conselho Nacional de Pesquisa e Desenvolvimento Científico e Tecnológico - CNPq
The growing concern with the increasing concentrations of greenhouse gases in the atmosphere and the resulting global warming has led the scientific community to question the role of soils as a source or sink of carbon. Due to the importance of estimates of carbon stocks in the soil and need for methods, reliable and capable of auditing, to estimate soil carbon stocks, this study aimed to understand how the system sampling influence on the estimates as sampling effort required for the determination of carbon stock and from this suggest equations for estimating the carbon stock in the soil depth. The study was conducted at the Experimental Station of Tropical Forestry of the National Institute for Amazon Research in Manaus region. Was collected from 90 sampling units distributed systematically in 40 hectares of primary forest, at 0-5, 5-10,10-20, 20- 30, 30-40, 40-50, 50-75 and 75 - 100 cm. Granulometry or texture analysis and soil density, quantification of carbon in the soil and subsequent calculation of carbon stock in the soil. The statistic used was ANOVA and post hoc Tukey analysis correlation and simple linear regression. The texture along the topographic gradient was very sandy loam plateau until the shoal. There was a decrease in carbon content with increasing depth and the opposite occurred that the soil density increased with depth. The plateau had the highest carbon content and low bulk density, while the shoal with the lowest carbon content and soil density. The plateau has a carbon stock of 98.14 ± 4.05 Mg C.ha-1, on the slope the stock was 92.64 ± 9.02 Mg C.ha-1, in the shallows stock was 65.52 ± 11.46 Mg C.ha-1 and considering the total area of the carbon stock was 92.75 ± 4.40 MgC.ha-1. It was observed that in areas of high topoghraphy variability, with different contours and soil types, systematic sampling was more efficient, with a lower sampling effort, contrasting with that observed in the stratified sampling suggests that a greater sampling effort, which can more difficult and expensive to collect. The equations for estimating the carbon stock in depth were adjusted for total area, without stratification and noted the need to collect in the lower layers when you want to know the stock at depth. The sampling plan for collecting soil in Central Amazonia, is suggested based on a systematic sampling, collecting in the 0-20 cm or 0- 40 cm, since these layers were highly correlated with the uncertainty and lower layers below and provided the best fit of equations to estimate the carbon stock in depth.
A crescente preocupação com o aumento das concentrações de gases do efeito estufa na atmosfera e o consequente aquecimento global, levou a comunidade científica a se questionar sobre o papel dos solos como fonte ou sumidouro de carbono. Devido à importância das estimativas do estoque de carbono no solo e a necessidade de dispor de métodos, confiáveis e passíveis de auditagem, para estimar os estoques de carbono do solo, este trabalho teve o objetivo de testar como o sistema de amostragem influencia nas estimativas assim como o esforço amostral necessário para determinação do estoque de carbono e a partir disso sugerir equações para estimar o estoque de carbono no solo em profundidade. O trabalho foi desenvolvido na Estação Experimental de Manejo Florestal do Instituto Nacional de Pesquisas da Amazônia, na região de Manaus. Coletou-se 90 unidades amostrais distribuídas de forma sistemática em 40 ha de floresta primária, nas profundidades de 0-5, 5-10,10-20, 20-30, 30-40, 40-50, 50-75 e 75-100 cm. Realizou-se análise granulométrica e densidade do solo, quantificação do teor de carbono no solo e posterior cálculo do estoque de carbono do solo. A estatística utilizada foi ANOVA e teste post hoc de Tukey, análises de correlação e regressão linear simples. A textura, ao longo do gradiente topográfico, foi de muito argilosa no platô até arenosa no baixio. Houve uma redução no teor de carbono com o aumento da profundidade e o contrario ocorreu para a densidade que aumentou com a profundidade. O platô apresentou o maior teor de carbono e a menor densidade do solo, enquanto que o baixio apresentou o menor teor de carbono e a maior densidade do solo. O platô possui um estoque de carbono de 98,14±4,05 MgC.ha-1, na vertente o estoque foi de 92,64±9,02 MgC.ha-1, no baixio o estoque foi de 65,52±11,46 MgC.ha-1 e considerando a área total o estoque de carbono foi de 92,75±4,40 MgC.ha-1. Observou-se que em áreas de alta variabilidade, com diferentes relevos e tipos de solo, a amostragem sistemática mostrou-se mais eficiente, apresentando um menor esforço amostral, contrastando com o observado na amostragem estratificada que sugere um maior esforço amostral, o que pode dificultar e encarecer a coleta. As equações para estimar o estoque de carbono em profundidade foram ajustadas para área total, sem estratificações e observou-se a necessidade de coletar em camadas inferiores quando se deseja conhecer o estoque em profundidade. O plano amostral, para coleta de solo na Amazônia Central, está baseado em uma amostragem sistemática, coletando-se na camada 0-20 cm ou 0-40 cm, uma vez que essas camadas apresentaram altas correlações e menores incertezas com as camadas mais inferiores e proporcionaram os melhores ajustes de equações para estimar o estoque de carbono em profundidade.
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Liu, Peng. "Joint Estimation and Calibration for Motion Sensor". Thesis, KTH, Skolan för elektroteknik och datavetenskap (EECS), 2020. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-286839.
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In the thesis, a calibration method for positions of each accelerometer in an Inertial Sensor Array (IMU) sensor array is designed and implemented. In order to model the motion of the sensor array in the real world, we build up a state space model. Based on the model we use, the problem is to estimate the parameters within the state space model. In this thesis, this problem is solved using Maximum Likelihood (ML) framework and two methods are implemented and analyzed. One is based on Expectation Maximization (EM) and the other is to optimize the cost function directly using Gradient Descent (GD). In the EM algorithm, an ill-conditioned problem exists in the M step, which degrades the performance of the algorithm especially when the initial error is small, and the final Mean Square Error (MSE) curve will diverge in this case. The EM algorithm with enough data samples works well when the initial error is large. In the Gradient Descent method, a reformulation of the problem avoids the ill-conditioned problem. After the parameter estimation part, we analyze the MSE curve of these parameters through the Monte Carlo Simulation. The final MSE curves show that the Gradient Descent based method is more robust in handling the numerical issues of the parameter estimation. The Gradient Descent method is also robust to noise level based on the simulation result.I denna rapport utvecklas och implementeras en kalibreringsmethod för att skatta positionen för en grupp av accelerometrar placerade i en så kallad IMU sensor array. För att beskriva rörelsen för hela sensorgruppen, härleds en dynamisk tillståndsmodell. Problemställningen är då att skatta parametrarna i tillståndsmodellen. Detta löses med hjälp av Maximum Likelihood-metoden (ML) där två stycken algoritmer implementeras och analyseras. En baseras på Expectation Maximization (EM) och i den andra optimeras kostnadsfunktionen direkt med gradientsökning. I EM-algoritmen uppstår ett illa konditionerat delproblem i M-steget, vilket försämrar algoritmens prestanda, speciellt när det initiala felet är litet. Den resulterande MSE-kurvan kommer att avvika i detta fall. Däremot fungerar EM-algoritmen väl när antalet datasampel är tillräckligt och det initiala felet är större. I gradientsökningsmetoden undviks konditioneringsproblemen med hjälp av en omformulering. Slutligen analyseras medelkvadratfelet (MSE) för parameterskattningarna med hjälp av Monte Carlo-simulering. De resulterande MSE-kurvorna visar att gradientsökningsmetoden är mer robust mot numeriska problem, speciellt när det initiala felet är litet. Simuleringarna visar även att gradientsökning är robust mot brus.
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Hoffmann, Júlio Cury. "Avaliação de métodos para estimativas de dissimilaridade em gradientes ecológicos com alta diversidade beta". Universidade Federal de Goiás, 2018. http://repositorio.bc.ufg.br/tede/handle/tede/8649.
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Coordenação de Aperfeiçoamento de Pessoal de Nível Superior - CAPES
There are several problems on the analysis of biological communities with sparse data, resulting from gradients with high beta diversity. I used four strategies to solve this problem (Beals smoothing, Swan, Shortest Path and Extended Dissimilarity). I randomly removed from 1% to 50% of the individuals in empirical and simulated matrices. I then performed PCoA and nMDS ordinations and used Procrustes correlation of the original two dimensional ordination with the ordination obtained using the degraded matrices. For the simulated data set, I also correlated the ordenation in two dimensions with the coordinates of the samples in the two-dimensional simulated gradients. Finally, I analyzed how robustness to degradation, quantified as Procrustean correlation, was related to the matrix properties. Different from the expected, in the comparison of the degraded and original ordinations, the uncorrected data with a traditional dissimilarity index (Bray-Curtis) produced higher fit than the four methods evaluated. In relation to the coordinates of the simulated two-dimensional gradients, the evaluated methods were slightly better than the raw data. Overall, the simulated data were more robust to the degradation than the empirical ones and the data of abundance were more robust than matrices of presence and absence. Matrices with small proportion of zeros were more robust to degradation. I conclude that the correction methods evaluated distorted the pattern on the original data. Also, data with low beta diversity (few zeros) are robust to degradation and sufficient to reconstruct the original gradient.
Existem vários problemas nas análises de comunidades em Ecologia decorrentes da grande quantidade de zeros na matriz de espécies por locais (dados esparsos), principalmente em situações em que a diversidade beta é alta. Usando quatro estratégias para resolver estes problemas (Beals, Swan, Menor Caminho e Dissimilaridade estendida) retirei aleatoriamente de 1 ate 50 % dos indivíduos de matrizes empíricas e simuladas (degradação das matizes). Realizei ordenações PCoA e nMDS e, com correlações de Procrustes, relacionei a ordenação original em duas dimensões com a ordenação obtida pelas matrizes degradadas. Com dados simulados relacionei a ordenação em duas dimensões também com as coordenadas das amostras no gradiente bidimensional simulado. Além disso, analisei como a robustez à degradação, medida como correlação Procrustes, está relacionada às características da matriz. Diferente do esperado, na comparação das ordenações de matrizes degradadas com a ordenação da matriz original, os dados utilizados sem correções e com índice de dissimilaridade tradicional (Bray-Curtis) tiveram maior ajuste que os quatro métodos avaliados. Em relação às coordenadas, os métodos aplicados tiveram desempenho um pouco melhor do que os dados sem correções quando a diversidade beta foi maior. Em geral, os dados simulados foram mais robustos à degradação que os empíricos e os dados de abundância foram mais robustos que de presença e ausência. Matrizes com menor proporção de zeros foram mais robustas à degradação. Concluo que os métodos de correção distorceram o padrão dos dados originais. Ainda, dados com baixa diversidade beta (poucos zeros na matrix) são robustos à degradação e são suficientes para reconstruir o gradiente original.
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LASRI, ABDELLAH. "Estimation du gradient pour les équations aux dérivées partielles paraboliques non linéaires et les équations différentielles stochastiques rétrogrades par la méthode de Bernstein". Tours, 1995. http://www.theses.fr/1995TOUR4015.
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Cette thèse s'organise autour de deux thèmes. Le premier concerne les solutions de viscosité continues d'EDP paraboliques non linéaires gérées par un hamiltonien H. Le second se rapporte aux solutions de carré intégrables d'EDS rétrogrades engendrées par un générateur F. Notre but, dans les deux cas, est d'obtenir des estimations de la solution sous certaines propriétés intrinsèques par rapport aux fonctions H et F. Pour cela, nous avons utilisé l'approche dite version faible de la méthode de Bernstein introduite par G. Barles. Les propriétés en question sont appelées conditions de structure. Dans la première partie, nous avons établi une généralisation de cette approche au cas des EDP paraboliques. Ainsi, nous avons obtenu, sous certaines conditions de structure par rapport à H, un résultat de régularité lipschitzienne en x des solutions de viscosité continues. Concernant le comportement de telles solutions par rapport au temps, nous avons établi un résultat de type effets régularisants quand H satisfait certaines hypothèses de croissance. Dans la deuxième partie, nous avons obtenu des estimations à priori des solutions de carré intégrables d'EDSR linéaires ou les coefficients vérifient une certaine condition de structure. Nous avons étendu ce résultat au cas paramètre (resp. Markovien) pour obtenir un résultat de régularité lipschitzienne par rapport à (resp. X) quand F satisfait certaines conditions de structure. Par des techniques similaires, nous avons établi un résultat d'unicité pour les solutions de carré intégrables d'EDSR
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Acosta, Alvaro. "Estimating diurnal patterns of water uptake by roots from detailed measurement of soil moisture and soil temperature gradients". Thesis, University of Reading, 2000. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.269928.
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Younes, Laurent. "Problèmes d'estimation paramétrique pour des champs de Gibbs Markoviens : applications au traitement d'images". Paris 11, 1988. http://www.theses.fr/1988PA112269.
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Nous nous intéressons à l’estimation paramétrique par maximum de vraisemblance pour des champs de Gibbs markoviens. Apres une introduction composée d'une part d'une discussion heuristique de l'analyse statistique des images aboutissant à une modélisation par champs aléatoires. Et d'autre part d'un rappel de différentes techniques d'estimation paramétrique existant dans la littérature, nous consacrons un chapitre au rappel de quelques résultats reliés aux champs de Gibbs, et à leur étude statistique: nous introduisons la notion de potentiel, ainsi que les définitions qui s’y rattachent, puis nous rappelons des conditions d'existence et d'unicité de champs de Gibbs associés à un potentiel. Nous présentons ensuite te un algorithme de gradient stochastique permettant la maximisation de la vraisemblance. Il utilise l'échantillonneur de Gibbs qui est une méthode itérative de simulation de champs markoviens. Des propriétés relatives à l'ergodicité de cet échantillonneur sont alors données. En fin de chapitre, nous rappelons des résultats de Métivier et Priouret sur les algorithmes stochastiques du type de celui que nous utilisons, qui permettent de mesurer la (tendance à la) convergence de telles procédures. Le chapitre 4 est consacré à l'étude plus précise de la convergence de l’algorithme. A réseau fixé, tout d'abord nous étudions le cas de modèle exponentiel, et nous démontrons un résultat de convergence presque sûre de l'algorithme. Nous étudions ensuite les modèles plus généraux en nous intéressant en particulier aux problèmes d’estimation basée sur de observations imparfaites (ou bruitées). Dans le chapitre 5, nous étudions le comportement asymptotique de l'estimateur de maximum de vraisemblance proprement dit, prouvant un résultat de consistance et de normalité asyptotique. Enfin, nous donnons quelques remarques pratiques sur l'algorithme d'estimation, suivies de résultats expérimentaux, composés d'une part de simulations et d'autre part de traitements appliqués à de vraies imagesWe study parameter estimation by maximum of likelihood for Gibbs Markov Random Fields. We begin by a heuristic discussion about statistical analysis of pictures, to obtain a modelization by random fields, and by a summary of various parameter estimation technics that exist. Then, we recall some results related to Gibbs Fields, and to their statistical analysis we introduce the notion of potential, and recall existence and uniqueness conditions for an associated Gibbs field. Ln the next chapter, we present a stochastic gradient algorithm in order to maximize the Likelihood. It uses the Gibbs sampler, which is an iterative method for Markov field simulation. We give properties related to the ergodicity of this sampler. Finaly we recall some results of Métivier and Priouret about stochastic gradient algorithms, such as the one we use that allow measurement of the (trend for) convergence for this kind of procedures. Ln chapter 4, we make a precise study of the convergence of the algorithm. First, with fixed lattice, we deal with the case of exponential models and show almost sure convergence of the algorithm. We study then more general models, and especialy problems related to imperfect (or noisy) observa tions. Ln chapter 5, we study the asymptotic behaviour of the maximum of likelihood estimator, and prove consistency, and asymptotic normality. Eventualy we give some practical remarks on the estimation algorithm, followed by some experiments
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Ögren, Petter. "Formations and Obstacle Avoidance in Mobile Robot Control". Doctoral thesis, KTH, Mathematics, 2003. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-3555.
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This thesis consists of four independent papers concerningthe control of mobile robots in the context of obstacleavoidance and formation keeping.
The first paper describes a new theoreticallyv erifiableapproach to obstacle avoidance. It merges the ideas of twoprevious methods, with complementaryprop erties, byusing acombined control Lyapunov function (CLF) and model predictivecontrol (MPC) framework.
The second paper investigates the problem of moving a fixedformation of vehicles through a partiallykno wn environmentwith obstacles. Using an input to state (ISS) formulation theconcept of configuration space obstacles is generalized toleader follower formations. This generalization then makes itpossible to convert the problem into a standard single vehicleobstacle avoidance problem, such as the one considered in thefirst paper. The properties of goal convergence and safetyth uscarries over to the formation obstacle avoidance case.
In the third paper, coordination along trajectories of anonhomogenuos set of vehicles is considered. Byusing a controlLyapunov function approach, properties such as boundedformation error and finite completion time is shown.
Finally, the fourth paper applies a generalized version ofthe control in the third paper to translate,rotate and expanda formation. It is furthermore shown how a partial decouplingof formation keeping and formation mission can be achieved. Theapproach is then applied to a scenario of underwater vehiclesclimbing gradients in search for specific thermal/biologicalregions of interest. The sensor data fusion problem fordifferent formation configurations is investigated and anoptimal formation geometryis proposed.
Keywords:Mobile Robots, Robot Control, ObstacleAvoidance, Multirobot System, Formation Control, NavigationFunction, Lyapunov Function, Model Predictive Control, RecedingHorizon Control, Gradient Climbing, Gradient Estimation.
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Bonifacio, Henry F. "Estimating particulate emission rates from large beef cattle feedlots". Diss., Kansas State University, 2013. http://hdl.handle.net/2097/15530.
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Doctor of PhilosophyDepartment of Biological and Agricultural Engineering
Ronaldo G. Maghirang
Emission of particulate matter (PM) and various gases from open-lot beef cattle feedlots is becoming a concern because of the adverse effects on human health and the environment; however, scientific information on feedlot emissions is limited. This research was conducted to estimate emission rates of PM[subscript]10 from large cattle feedlots. Specific objectives were to: (1) determine feedlot PM[subscript]10 emission rates by reverse dispersion modeling using AERMOD; (2) compare AERMOD and WindTrax in terms of their predicted concentrations and back-calculated PM[subscript]10 emission rates; (3) examine the sensitivity of both AERMOD and WindTrax to changes in meteorological parameters, source location, and receptor location; (4) determine feedlot PM[subscript]10 emission rates using the flux-gradient technique; and (5) compare AERMOD and computational fluid dynamics (CFD) in simulating particulate dispersion from an area source. PM[subscript]10 emission rates from two cattle feedlots in Kansas were determined by reverse dispersion modeling with AERMOD using PM[subscript]10 concentration and meteorological measurements over a 2-yr period. PM[subscript]10 emission rates for these feedlots varied seasonally, with overall medians of 1.60 and 1.10 g /m[superscript]2 -day. Warm and prolonged dry periods had significantly higher PM emissions compared to cold periods. Results also showed that the PM[subscript]10 emissions had a diurnal trend; highest PM[subscript]10 emission rates were observed during the afternoon and early evening periods. Using particulate concentration and meteorological measurements from a third cattle feedlot, PM[subscript]10 emission rates were back-calculated with AERMOD and WindTrax. Higher PM[subscript]10 emission rates were calculated by AERMOD, but their resulting PM[subscript]10 emission rates were highly linear (R[superscript]2 > 0.88). As such, development of conversion factors between these two models is feasible. AERMOD and WindTrax were also compared based on their sensitivity to changes in meteorological parameters and source locations. In general, AERMOD calculated lower concentrations than WindTrax; however, the two models responded similarly to changes in wind speed, surface roughness, atmospheric stability, and source and receptor locations. The flux-gradient technique also estimated PM[subscript]10 emission rates at the third cattle feedlot. Analyses of PM[subscript]10 emission rates and meteorological parameters indicated that PM[subscript]10 emissions at the feedlot were influenced by friction velocity, sensible heat flux, temperature, and surface roughness. Based on pen surface water content measurements, a water content of at least 20% (wet basis) significantly lowered PM[subscript]10 emissions at the feedlot. The dispersion of particulate from a simulated feedlot pen was predicted using CFD turbulence model ([kappa]-[epsilon] model) and AERMOD. Compared to CFD, AERMOD responded differently to wind speed setting, and was not able to provide detailed vertical concentration profiles such that the vertical concentration gradients at the first few meters from the ground were negligible. This demonstrates some limitations of AERMOD in simulating dispersion for area sources such as cattle feedlots and suggests the need to further evaluate its performance for area source modeling.
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Greenberg, Neil Louis. "Estimation of diastolic intraventricular pressure gradients using color Doppler M-mode echocardiographic spatiotemporal velocity distributions and the one dimensional Euler equation /". The Ohio State University, 1997. http://rave.ohiolink.edu/etdc/view?acc_num=osu1487944660931866.
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Kirchner, William. "Anthropomimetic Control Synthesis: Adaptive Vehicle Traction Control". Diss., Virginia Tech, 2012. http://hdl.handle.net/10919/26620.
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Human expert drivers have the unique ability to build complex perceptive models using correlated sensory inputs and outputs. In the case of longitudinal vehicle traction, this work will show a direct correlation in longitudinal acceleration to throttle input in a controlled laboratory environment. In fact, human experts have the ability to control a vehicle at or near the performance limits, with respect to vehicle traction, without direct knowledge of the vehicle states; speed, slip or tractive force. Traditional algorithms such as PID, full state feedback, and even sliding mode control have been very successful at handling low level tasks where the physics of the dynamic system are known and stationary. The ability to learn and adapt to changing environmental conditions, as well as develop perceptive models based on stimulus-response data, provides expert human drivers with significant advantages. When it comes to bandwidth, accuracy, and repeatability, automatic control systems have clear advantages over humans; however, most high performance control systems lack many of the unique abilities of a human expert. The underlying motivation for this work is that there are advantages to framing the traction control problem in a manner that more closely resembles how a human expert drives a vehicle. The fundamental idea is the belief that humans have a unique ability to adapt to uncertain environments that are both temporal and spatially varying. In this work, a novel approach to traction control is developed using an anthropomimetic control synthesis strategy. The proposed anthropomimetic traction control algorithm operates on the same correlated input signals that a human expert driver would in order to maximize traction. A gradient ascent approach is at the heart of the proposed anthropomimetic control algorithm, and a real-time implementation is described using linear operator techniques, even though the tire-ground interface is highly non-linear. Performance of the proposed anthropomimetic traction control algorithm is demonstrated using both a longitudinal traction case study and a combined mode traction case study, in which longitudinal and lateral accelerations are maximized simultaneously. The approach presented in this research should be considered as a first step in the development of a truly anthropomimetic solution, where an advanced control algorithm has been designed to be responsive to the same limited input signals that a human expert would rely on, with the objective of maximizing traction. This work establishes the foundation for a general framework for an anthropomimetic control algorithm that is capable of learning and adapting to an uncertain, time varying environment. The algorithms developed in this work are well suited for efficient real time control in ground vehicles in a variety of applications from a driver assist technology to fully autonomous applications.Ph. D.
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Gaspar, Jonathan. "Fluxmétrie et caractérisation thermiques instationnaires des dépôts des composants face au plasma du Tokamak JET par techniques inverses". Thesis, Aix-Marseille, 2013. http://www.theses.fr/2013AIXM4739/document.
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Ces travaux portent sur la résolution successive de deux problèmes inverses en transferts thermiques : l'estimation de la densité de flux en surface d'un matériau puis de la conductivité thermique équivalente d'une couche déposée en surface de ce matériau. Le modèle direct est bidimensionnel orthotrope (géométrie réelle d'un matériau composite), instationnaire, non-linéaire et ses équations sont résolues par éléments finis. Les matériaux étudiés sont les composants face au plasma (tuiles composite carbone-carbone) dans le Tokamak JET. La densité de flux recherchée varie avec une dimension spatiale et avec le temps. La conductivité du dépôt de surface varie spatialement et peut également varier au cours du temps pendant l'expérience (toutes les autres propriétés thermophysiques dépendent de la température). Les deux problèmes inverses sont résolus à l'aide de l'algorithme des gradients conjugués associé à la méthode de l'état adjoint pour le calcul exact du gradient. La donnée expérimentale utilisée pour la résolution du premier problème inverse (estimation de flux surfacique) est le thermogramme fourni par un thermocouple enfoui. Le second problème inverse utilise, lui, les variations spatio-temporelles de la température de surface du dépôt inconnu (thermographie infrarouge) pour identifier sa conductivité. Des calculs de confiance associée aux grandeurs identifiées sont réalisés avec la démarche Monte Carlo. Les méthodes mises au point pendant ces travaux aident à comprendre la dynamique de l'interaction plasma-paroi ainsi que la cinétique de formation des dépôts de carbone sur les composants et aideront au design des composants des machines futures (WEST, ITER)This work deals with the successive resolution of two inverse heat transfer problems: the estimation of surface heat flux on a material and equivalent thermal conductivity of a surface layer on that material. The direct formulation is bidimensional, orthotropic (real geometry of a composite material), unsteady, non-linear and solved by finite elements. The studied materials are plasma facing components (carbon-carbon composite tiles) from Tokamak JET. The searched heat flux density varies with time and one dimension in space. The surface layers conductivity varies spatially and can vary with time during the experiment (the other thermophysical properties are temperature dependent). The two inverse problems are solved by the conjugate gradient method with the adjoint state method for the exact gradient calculation. The experimental data used for the first inverse problem resolution (surface heat flux estimation) is the thermogram provided by an embedded thermocouple. The second inverse problem uses the space and time variations of the surface temperature of the unknown surface layer (infrared thermography) for the conductivity identification. The confidence calculations associated to the estimated values are done by the Monte Carlo approach. The method developed during this thesis helps to the understanding of the plasma-wall interaction dynamic, as well as the kinetic of the surface carbon layer formation on the plasma facing components, and will be helpful to the design of the components of the future machines (WEST, ITER)
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Authesserre, Jean-baptiste. "Alignement paramétrique d’images : proposition d’un formalisme unifié et prise en compte du bruit pour le suivi d’objets". Thesis, Bordeaux 1, 2010. http://www.theses.fr/2010BOR14136/document.
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L’alignement d’images paramétrique a de nombreuses applications pour la réalité augmentée, la compression vidéo ou encore le suivi d’objets. Dans cette thèse, nous nous intéressons notamment aux techniques de recalage d’images (template matching) reposant sur l’optimisation locale d’une fonctionnelle d’erreur. Ces approches ont conduit ces dernières années à de nombreux algorithmes efficaces pour le suivi d’objets. Cependant, les performances de ces algorithmes ont été peu étudiées lorsque les images sont dégradées par un bruit important comme c’est le cas, par exemple, pour des captures réalisées dans des conditions de faible luminosité. Dans cette thèse, nous proposons un nouveau formalisme, appelé formalisme bidirectionnel, qui unifie plusieurs approches de l’état de l’art. Ce formalisme est utilisé dans un premier temps pour porter un éclairage nouveau sur un grand nombre d’approches de la littérature et en particulier sur l’algorithme ESM (Efficient Second-order Minimization). Nous proposons ensuite une étude théorique approfondie de l’influence du bruit sur le processus d’alignement. Cette étude conduit à la définition de deux nouvelles familles d’algorithmes, les approches ACL (Asymmetric Composition on Lie Groups) et BCL (Bidirectional Composition on Lie Groups) qui permettent d’améliorer les performances en présence de niveaux de bruit asymétriques (Rapport Signal sur Bruit différent dans les images). L’ensemble des approches introduites sont validées sur des données synthétiques et sur des données réelles capturées dans des conditions de faible luminositéParametric image alignment is a fundamental task of many vision applications such as object tracking, image mosaicking, video compression and augmented reality. To recover the motion parameters, direct image alignment works by optimizing a pixel-based difference measure between a moving image and a fixed-image called template. In the last decade, many efficient algorithms have been proposed for parametric object tracking. However, those approaches have not been evaluated for aligning images of low SNR (Signal to Noise ratio) such as images captured in low-light conditions. In this thesis, we propose a new formulation of image alignment called Bidirectional Framework for unifying existing state of the art algorithms. First, this framework allows us to produce new insights on existing approaches and in particular on the ESM (Efficient Second-order Minimization) algorithm. Subsequently, we provide a theoretical analysis of image noise on the alignment process. This yields the definition of two new approaches : the ACL (Asymmetric Composition on Lie Groups) algorithm and the BCL (Bidirectional Composition on Lie Groups) algorithm, which outperform existing approaches in presence of images of different SNR. Finally, experiments on synthetic and real images captured under low-light conditions allow to evaluate the new and existing approaches under various noise conditions