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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
1

Modeling and Control of Non-contacting Steel Plate Conveyance System

Lin, Sheng-Yang 25 August 2009 (has links)
A non-contacting steel plate conveyance system based on the linear induction motor scheme, which can provide lift and propulsive forces simultaneously, is proposed. It has the features of high power density, direct drive, simple mechanical structure, and being able to reduce the operation noise. A magnetic equivalent circuit method and electromagnetic theory incorporating with 3-D finite element analysis are involved to investigate the static and quasi-dynamic properties and confirm the electrical and mechanical designs. To realize the dynamic behavior and develop the closed-loop control, a proper stationary reference frame transformation of the system voltage equations is also introduced. By considering the practical operational environment, a fuzzy-based control structure integrated with remote optical measurement system has been established and implemented by a DSP-based controller combined with required peripheral circuits. The experimental results show the applicability of such control strategies. With the systematic procedures for design, analysis, and control provided in this dissertation, implementation feasibility of the proposed system can be conveniently demonstrated.
2

Valence sloves v Pražském závislostním korpusu / Valency of Verbs in the Prague Dependency Treebank

Urešová, Zdeňka January 2012 (has links)
Title: Valency of verbs in the Prague Dependency Treebank Author: PhDr. Zdeňka Urešová Department: Institute of Formal and Applied Linguistics MFF UK Supervisor: Prof. PhDr. Eva Hajičová, DrSc. Abstract: This dissertation describes PDT-Vallex, a valency lexicon of Czech verbs, and its relation to the annotation of the Prague Dependency Treebank (PDT). The PDT-Vallex lexicon was created during the an- notation of the PDT and it is a valuable source of verbal valency information available both for linguistic research and for computer- ized natural language processing. In this thesis, we describe not only the structure and design of the lexicon (which is closely related to the notion of valency as developed in the Functional Generative De- scription of language) but also the relation between the PDT-Vallex and the PDT. The explicit and full-coverage linking of the lexicon to the treebank prompted us to pay special attention to diatheses; we propose formal transformation rules for diatheses to handle their surface realization even when the canonical forms of verb arguments as captured in the lexicon do not correspond to the forms of these arguments actually appearing in the corpus.
3

Public memory and political history : news media and collective memory construction after the deaths of former presidents

Patterson, Jeffery Randolph 20 January 2015 (has links)
In recent years, scholars have shown increasing interest in the concept of collective memory for structuring modern social understanding and political dialogue. However, surprisingly few studies have looked at the role that news media play the processes of collective political memory construction, reinterpretation, and change. This study contributes to the literature on collective memory construction, by helping clarify the means by which different news media serve as a site where collective memory is constructed, reinforced, and revised; and, 2) to identify which political actors and institutions act as sources to assert particular memory frames and what media subsidies they offer to influence the memory construction process. Specifically, the study undertook a two-stage longitudinal content analysis of news media to discern the ways former U.S. presidents (i.e., Truman, Johnson, Nixon, Reagan, and Ford) were memorialized in news media coverage at the time of their funerals, and then again in subsequent news media stories through 2012. The content analysis identified dominant news media frames and secondary attribute sub-frames as applied to former U.S. Presidents, and which news media sources and frame advocates are engaged in setting those frames. As a result, the study identified patterns of change and resilience in particular presidential memory frames as represented in news media, and found journalists—beyond other sources and frame advocates—play a significant role in both creating and revising those memories over time. A range of opportunities for further research are discussed. / text
4

Modelování disociační rekombinace lehkých iontů / Modeling the dissociative recombination of light ions

Hvizdoš, Dávid January 2021 (has links)
The purpose of this work and the project under which it was created is to develop, compare and validate several theoretical approaches and computation methods used to calculate the cross sections of dissociative recombination. For the most part it is con- cerned with the indirect dissociative recombination of molecular ions of H+ 2 in the singlet ungerade channels computed with three distinct approaches. First, the fully numerically solvable two-dimensional approach developed at ÚTF MFF UK as a part of my master's thesis. Second, a vibrational frame transformation method based on the work of Chang and Fano [E. S. Chang and U. Fano, Phys. Rev. A 6, 173 (1972)] and then enhanced into a full energy-dependent form by Gao and Greene [H. Gao and C. H. Greene, J. Chem. Phys. 91, 3988 (1989)], [H. Gao and C. H. Greene, Phys. Rev. A 42, 6946 (1990)], fur- ther improved by our own revisions. Third, a two-dimensional R-matrix method based on matching exact 2D solutions from a small interaction region to asymptotic solutions in the non-interacting region. We thoroughly discuss the various advantages and caveats of these methods and, in the later chapters, present our work on employing them for the realistic recombination of HeH+ + e− . Furthermore, we attempt to extend the presented models to the description of the...
5

Evidence for a reference frame transformation of vestibular contributions to voluntary reaching movements

Moreau-Debord, Ian 07 1900 (has links)
Les estimations des mouvements de soi provenant des signaux vestibulaires contribuent à la planification et l’exécution des mouvements volontaires du bras lorsque le corps se déplace. Cependant, comme les senseurs vestibulaires sont fixés à la tête alors que le bras est fixé au corps, les signaux vestibulaires doivent être transformés d’un système de référence centré sur la tête à un système centré sur le corps pour pouvoir contribuer de façon appropriée au contrôle moteur du bras. Le but premier de ce travail était d’étudier l’évidence d’une telle transformation. La stimulation galvanique vestibulaire (SGV) a été utilisée pour activer les afférences vestibulaires et simuler une rotation autour d’un axe naso-occipital fixe pendant que des sujets humains faisaient des mouvements du bras dans le plan horizontal, avec la tête dans différentes orientations. Une transformation des signaux vestibulaires implique que la SVG devrait simuler une rotation autour d’un axe horizontal lorsque la tête est droite et autour d’un axe vertical lorsque la tête est en flexion antérieure. La SGV devrait ainsi perturber les mouvements du bras en fonction de l’orientation de la tête. Nos résultats démontrent que les signaux vestibulaires contribuant aux mouvements d’atteinte sont effectivement transformés en un système de référence centrée sur le corps. Le deuxième but de ce travail était d’explorer les mécanismes utilisant ces signaux vestibulaires transformés. En comparant les effets de la SGV appliquée avant ou pendant les mouvements d’atteinte nous avons montré que les signaux vestibulaires transformés contribuent à des mécanismes de compensation distincts durant la planification des mouvements d’atteinte comparativement à l’exécution. / Vestibular signals provide self-motion estimates that contribute to the planning and execution of voluntary reaching movements during body motion. However, because the vestibular sensors are fixed in the head whereas the arm is fixed to the trunk vestibular signals must be transformed from a head-centered to a body-centered reference frame to contribute appropriately to limb motor control. The first goal of the current work was to investigate the evidence for such a transformation. To do so we used galvanic vestibular stimulation (GVS) to selectively activate vestibular afferents and simulate rotation about a fixed roughly naso-occipital axis as human subjects performed reaching movements with the head in different orientations. If vestibular signals that contribute to reaching are transformed to body-centered coordinates, then with the head upright GVS should simulate mainly tilt about an earth-horizontal axis (roll), whereas with the head pitched forward the same stimulus should simulate rotation about an earth-vertical axis (yaw). We therefore predicted that GVS should perturb horizontal-plane reach trajectories in a head-orientation dependent manner. Our results demonstrate that vestibular signals which contribute to reaching are indeed transformed to a body-centered reference frame. The second goal of this work was to explore the mechanisms that use these transformed vestibular signals. By comparing the effect of GVS applied during versus prior to reaching we also provide evidence that transformed vestibular signals contribute to distinct compensation mechanisms for body motion during reach planning versus execution.
6

Modelagem e controle de conversores fonte de tensão utilizados em sistemas de geração fotovoltaicos conectados à rede elétrica de distribuição

Almeida, Pedro Machado de 29 April 2011 (has links)
Submitted by Renata Lopes (renatasil82@gmail.com) on 2017-04-20T13:39:03Z No. of bitstreams: 1 pedromachadodealmeida.pdf: 13436160 bytes, checksum: 84c66613dade0766ae9ea2bdc8be9f91 (MD5) / Approved for entry into archive by Adriana Oliveira (adriana.oliveira@ufjf.edu.br) on 2017-04-20T14:45:37Z (GMT) No. of bitstreams: 1 pedromachadodealmeida.pdf: 13436160 bytes, checksum: 84c66613dade0766ae9ea2bdc8be9f91 (MD5) / Made available in DSpace on 2017-04-20T14:45:37Z (GMT). No. of bitstreams: 1 pedromachadodealmeida.pdf: 13436160 bytes, checksum: 84c66613dade0766ae9ea2bdc8be9f91 (MD5) Previous issue date: 2011-04-29 / Esta dissertação apresenta uma estratégia de controle para sistemas de geração fotovoltaicos, de único estágio, trifásicos, conectados à rede elétrica de distribuição. São desenvolvidos modelos matemáticos para representar as características dinâmicas dos painéis fotovoltaicos, do conversor fonte de tensão (VSC -“Voltage Source Converter”) e da rede de distribuição. A modelagem do sistema de geração disperso (SGD) é feita no sistema de coordenadas síncrono (dq), fornecendo um sistema de equações diferenciais que pode ser usado para descrever o comportamento dinâmico do sistema quando as tensões da rede estão equilibradas ou desequilibradas. O conversor é controlado no modo de corrente, através da estratégia de modulação vetorial (Space Vector Modulation - SVM). São projetadas duas malhas de controle em cascata para controlar o conversor estático. A malha interna controla a corrente injetada na rede enquanto que a externa controla a tensão no barramento CC do conversor. O controle da tensão CC permite rastrear o ponto de máxima potência do painel PV além de controlar a quantidade de potência ativa injetada na rede CA. Um método ativo de detecção de ilhamento baseado na injeção de corrente de sequência negativa é incorporado ao sistema de controle. Resultados de simulações digitais obtidos com o programa ATP (Alternative Transient Program ) são utilizados para validar os modelos matemáticos e as estratégias de controle. Finalmente, um protótipo experimental de pequena escala é montado em laboratório. Todo o sistema de controle do protótipo experimental foi implementado no DSP TMS320F28212. Os resultados obtidos demonstram o funcionamento do sistema e podem ser usados para validar a estratégia de controle utilizada. / This dissertation presents a control strategy for a single-stage, three-phase, photovoltaic systems to be connected to a distribution network. Mathematical models are developed to represent the dynamic characteristics of the photovoltaic panels, the voltage-source converter (VSC) and the distribution network. The modeling of the dispersed generation system (DGS) is done in the synchronous reference frame (dq), providing a system of differential equations that describes the dynamic behavior of the system when the network voltages are balanced or unbalanced. The converter is controlled in current mode through the space vector modulation (SVM) strategy. Two control loops are designed to control the static converter. The inner loop controls the injected current into the network while the external loop controls the converter DC bus voltage. The DC voltage regulator allows to track the PV maximum power point and to control the active power injected into the AC grid. An active islanding detection method based on negative-sequence current injection is incorporated into the control system. Digital simulations results obtained with Alternative Transients Program (ATP) is used to validate the mathematical models and the control strategies. Finally, a small-scale experimental prototype is implemented in the laboratory. The whole control system of the experimental prototype was programmed in DSP TMS320F2812 of Texas Instruments. The results demonstrate that the operation of the system can be used to validate the applied control strategy.

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