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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.
41

Modelos longitudinais de grupos múltiplos multiníveis na teoria da resposta ao item: métodos de estimação e seleção estrutural sob uma perspectiva bayesiana / Longitudinal multiple groups multilevel models in the item response theory : estimation methods and structural selection under a bayesian perspective

Caio Lucidius Naberezny Azevedo 11 March 2008 (has links)
No presente trabalho propomos uma estrutura bayesiana, através de um esquema de dados aumentados, para analisar modelos longitudinais com grupos mútiplos (MLGMTRI) na Teoria da Resposta ao Item (TRI). Tal estrutura consiste na tríade : modelagem, métodos de estimação e métodos de diagnóstico para a classe de MLGMTRI. Na parte de modelagem, explorou-se as estruturas multivariada e multinível, com o intuito de representar a hierarquia existente em dados longitudinais com grupos múltiplos. Esta abordagem permite considerar várias classes de submodelos como: modelos de grupos múltiplos e modelos longitudinais de um único grupo. Estudamos alguns aspectos positivos e negativos de cada uma das supracitadas abordagens. A modelagem multivariada permite representar de forma direta estruturas de dependência, além de possibilitar que várias delas sejam facilmente incorporadas no processo de estimação. Isso permite considerar, por exemplo, uma matriz não estruturada e assim, obter indícios da forma mais apropriada para a estrutura de dependência. Por outro lado, a modelagem multinível propicia uma interpretação mais direta, obtenção de condicionais completas univariadas, fácil inclusão de informações adicionais, incorporação de fontes de dependência intra e entre unidades amostrais, dentre outras. Com relação aos métodos de estimação, desenvolvemos um procedimento baseado nas simulações de Monte Carlo via cadeias de Markov (MCMC). Mostramos que as distribuições condicionais completas possuem forma analítica conhecida e, além disso, são fáceis de se amostrar. Tal abordagem, apesar de demandar grande esforço computacional, contorna diversos problemas encontrados em outros procedimentos como: limitação no número de grupos envolvidos, quantidade de condições de avaliação, escolha de estruturas de dependência, assimetria dos traços latentes, imputação de dados, dentre outras. Além disso, através da metodologia MCMC, desenvolvemos uma estrutura de seleção de matrizes de covariâncias, através de um esquema de Monte Carlo via Cadeias de Markov de Saltos Reversíveis (RJMCMC). Estudos de simulação indicam que o modelo, o método de estimação e o método de seleção produzem resultados bastante satisfatórios. Também, robustez à escolha de prioris e valores iniciais foi observada. Os métodos de estimação desenvolvidos podem ser estendidos para diversas situações de interesse de um modo bem direto. Algumas das técnicas de diagnóstico estudadas permitem avaliar a qualidade do ajuste do modelo de um modo global. Outras medidas fornecem indícios de violação de suposições específicas, como ausência de normalidade para os traços latentes. Tal metodologia fornece meios concretos de se avaliar a qualidade do instrumento de medida (prova, questionário etc). Finalmente, a análise de um conjunto de dados real, utilizando-se alguns dos modelos abordados no presente trabalho, ilustra o potencial da tríade desenvolvida além de indicar um ganho na utilização dos modelos longitudinais da TRI na análise de ensaios educacionais com medidas repetidas em deterimento a suposição de independência. / In this work we proposed a bayesian framework, by using an augmented data scheme, to analyze longitudinal multiple groups models (LMGMIRT) in the Item Response Theory (IRT). Such framework consists in the following set : modelling, estimation methods and diagnostic tools to the LMGMIRT. Concerning the modelling, we exploited multivariate and multilevel structures in order to represent the hierarchical nature of the longitudinal multiple groupos model. This approach allows to consider several submodels such that: multiple groups and longitudinal one group models. We studied some positive and negative aspects of both above mentioned approches. The multivariate modelling allows to represent, in a straightforward way, many dependence structures. Furthermore it possibilities that many of them can be easily considered in the estimation process. This allows, for example, to consider an unstructured covariance matrix and, then, it allows to obtain information about the most appropritate dependece structure. On the other hand, the multilevel modelling permits to obtain: more straightforward interpretations of the model, the construction of univariate full conditional distributions, an easy way to include auxiliary information, the incorporation of within and between subjects (groups) sources of variability, among others. Concerning the estimation methods, we developed a procedure based on Monte Carlo Markov Chain (MCMC) simulation. We showed that the full conditional distributions are known and easy to sample from. Even though such approach demands a considerable amount of time it circumvents many problems such that: limitation in the number of groups that can be considered, the limitation in the number of instants of observation, the choice of covariance matrices, latent trait asymmetry, data imputation, among others. Furthermore, within the MCMC metodology, we developed a procedure to select covariance matrices, by using the so called Reversible Jump MCMC (RJMCMC). Simulation studies show that the model, the estimation method and the model selection procedure produce reasonable results. Also, the studies indicate that the developed metodology presents robustness concerning prior choice and different initial values choice. It is possible to extent the developed estimation methods to other situations in a straightforward way. Some diagnostics techniques that were studied allow to assess the model fit, in a global sense. Others techniques give directions toward the departing from some specific assumptions as the latent trait normality. Such methodology also provides ways to assess the quality of the test or questionaire used to measure the latent traits. Finally, by analyzing a real data set, using some of the models that were developed, it was possible to verify the potential of the methodology considered in this work. Furthermore, the results of this analysis indicate advantages in using longitudinal IRT models to model educational repeated measurement data instead of to assume independence.
42

Μοντελοποίηση, έλεγχος και διάγνωση σφαλμάτων κινητήριου συστήματος αποτελούμενου από δύο ασύγχρονες μηχανές με κοινό φορτίο κλίβανο τσιμεντοβιομηχανίας

Μπογιατζίδης, Ιωάννης 02 March 2015 (has links)
Το κεφάλαιο 1 αποτελεί εισαγωγή του αναγνώστη σε θέματα που αφορούν τα ηλεκτρικά κινητήρια συστήματα. Αρχικά πραγματοποιείται μια σύντομη ιστορική αναδρομή και περιγραφή της εξέλιξης αυτών, ενώ στη συνέχεια παρουσιάζονται οι θεματικές ενότητες που αποτελούν τη συμβολή της παρούσας διατριβής όπως ο έλεγχος των κινητήριων συστημάτων και η διάγνωση σφαλμάτων σε αυτά. Τέλος, υπογραμμίζονται οι στόχοι που ορίστηκαν και εκπληρώνονται στο πλαίσιο της εργασίας αυτής. Στο κεφάλαιο 2 γίνεται μια γενική περιγραφή των σταδίων παραγωγής τσιμέντου, παρουσιάζεται η χαρακτηριστική ροπής-στροφών του κλιβάνου με βάση τη διαθέσιμη βιβλιογραφία, αναλύονται λεπτομερώς οι τοπολογίες συστημάτων μετάδοσης που εγκαθίστανται σε κλιβάνους μικρής και μεγάλης παραγωγικής δύναμης, αναδεικνύονται οι προδιαγραφές που υφίστανται κατά την επιλογή των ηλεκτρικών κινητήριων μηχανών και τέλος τονίζονται οι απαιτήσεις του ελέγχου των κινητήριων μηχανών, έτσι όπως τίθενται από τη βιομηχανία τσιμέντου. Στο κεφάλαιο 3 περιγράφεται το μαθηματικό μοντέλο που αναπτύχθηκε και χρησιμοποιήθηκε για την προσομοίωση της λειτουργίας του συστήματος και το οποίο απαρτίζεται από τα επιμέρους μοντέλα του κλιβάνου, του συστήματος μετάδοσης της κίνησης, των τριφασικών ασύγχρονων μηχανών, των ηλεκτρονικών μετατροπέων ισχύος καθώς και του ελέγχου των κινητήριων μηχανών. Στο κεφάλαιο 4 περιγράφονται τα υποσυστήματα του υπό κλίμακα συστήματος με σκοπό την εξομοίωση, που κατασκευάστηκε στο εργαστήριο με στόχο την επαλήθευση των αποτελεσμάτων της προσομοίωσης στον ηλεκτρονικό υπολογιστή. Στο κεφάλαιο 5 γίνεται λεπτομερής αναφορά στις υφιστάμενες τεχνικές ελέγχου των τριφασικών ασύγχρονων μηχανών και στις εφαρμογές αυτών σε μονά και διπλά κινητήρια συστήματα. Στη συνέχεια πραγματοποιείται σύγκριση δύο εκ των επικρατέστερων μεθόδων ελέγχου διπλών κινητήριων συστημάτων και παρουσιάζονται ενδεχόμενες δυσλειτουργίες αυτών λαμβάνοντας υπόψη τα αποτελέσματα που προέκυψαν από την προσομοίωση του συστήματος και τα οποία πιστοποιούνται μέσω της πειραματικής διαδικασίας αλλά και της διαθέσιμης βιβλιογραφίας. Στη συνέχεια προτείνεται ένας καινοτόμος υβριδικός έλεγχος που, όπως αποδεικνύεται μέσω προσομοίωσης αλλά και πειραματικών αποτελεσμάτων, αντιμετωπίζει αποτελεσματικά τις προαναφερθείσες δυσλειτουργίες οδηγώντας σε ομαλή λειτουργία του συστήματος. Στο κεφάλαιο 6 προτείνεται, αντί των υφιστάμενων μεθόδων που περιλαμβάνουν την εγκατάσταση επιταχυνσιομέτρων, τη χρήση ακουστικών σημάτων και άλλων παρόμοιων μεθόδων, η χρήση της ηλεκτρικής κινητήριας μηχανής (τριφασικής ασύγχρονης μηχανής στην προκειμένη περίπτωση) ως αισθητήριο μέσο για τη διάγνωση μηχανολογικών σφαλμάτων στις οδοντώσεις γραναζιών. Συγκεκριμένα, εξετάζεται η επίδραση των εν λόγω σφαλμάτων στο φάσμα συχνοτήτων του φασικού ρεύματος και της ηλεκτρομαγνητικής ροπής της τριφασικής ασύγχρονης μηχανής, αποδεικνύεται η δυνατότητα διάγνωσης του σφάλματος ανιχνεύοντας την ύπαρξη πολλαπλών αρμονικών στο φάσμα τόσο του φασικού ρεύματος όσο και της ηλεκτρομαγνητικής ροπής. Στο κεφάλαιο 7 γίνεται μια εκτίμηση σε ό,τι αφορά τη συμβολή της διδακτορικής διατριβής, το κεφάλαιο 8 περιλαμβάνει μία ανά κεφάλαιο περίληψη της παρούσας διατριβής ενώ το κεφάλαιο 9 περιέχει τη διαθέσιμη βιβλιογραφία που χρησιμοποιήθηκε στην παρούσα εργασία κατά τη σειρά αναφοράς της στο κείμενο. / This thesis deals with the modeling, the control and the diagnosis of mechanical faults in a dual ac drive with common mechanical load. Chapter 1 constitutes an introduction of the reader to the electrical drive systems. Initially, a short historical retrospection of these systems is realized, while afterwards the thematic units that constitute the contributions of the present thesis, which can be summarized as the control of a dual cement kiln drive and the diagnosis of mechanical gear faults using the ac motor as a sensor, are presented. In chapter 2 the specifications and the operational characteristics of the kiln drive system are presented based on the industrial requirements and the existing references. Particularly the torque – speed characteristic load curve of the kiln, the advantages of upgrading the dc drives with ac ones, the parameters which determine the decision of installing a single or a dual transmission system and the need of uninterrupted operation of the kiln drive are underlined. In addition the step by step development of a simulating model of the under study system in the Matlab/Simulink environment is presented in chapter 3. Particularly the equations of motion for the kiln and the transmission system, the dynamic model equations of the asynchronous motor, the power electronics converters and the control strategy based on the Direct Torque Control have been incorporated in the Matlab/Simulink environment through which a theoretical investigation is realized. Moreover, the design and the development of an under scale laboratory simulating system of the kiln drive has been realized and the characteristics of the design specifications of the laboratory system are presented in chapter 4. Using the theoretical model developed in the Matlab/Simulink environment and the laboratory simulating system, a comparison of the existing control methods used for the electric drive systems (speed control and torque control) is being presented (chapter 5), focusing at specific malfunctions which can be caused by the application of these controls at a dual cement kiln drive. Taking into account these malfunctions, a novel hybrid control method is being presented whose operation is based on the application of a parallel-hybrid speed and torque control, simultaneously at both electric motors. In this way an equal load distribution can be achieved, obviating at the same the appearance of mechanical malfunctions. In chapter 6, the fault diagnosis of electromechanical drives is referenced, focusing on the identification of mechanical faults appeared in the pinion/girth gear coupling using the ac motor as a sensor. The proposed diagnostic method is based on the detection of multiples of the defective frequency at both phase current and electromagnetic torque frequency spectrum. The effectiveness of the proposed method is verified using experimental results from the laboratory simulating system, operating as a single drive. Finally, chapter 7, 8 and 9 include an estimation of the thesis contribution, a summary and the reference part respectively.
43

Výchova dítěte s autismem v ústavní péči / Education of autistic children in social care institutions

Stárková, Blanka January 2011 (has links)
Graduation thesis deal about education children with autism in social care institutions. First part describes pervasive evolutionary disorders, it's etiology, clinical picture, diagnosis of autism and typical triads of disorder. This thesis also deals with institutions care, it's history and present situation in education care. Final part is research of social care institutions which take care persons with autism. Goal of the research is mapped situation education care for people with autism in social care institutions. Research methods are questionnaire, interview, content analysis. Research is complemented by case studies.
44

Stavební průzkum a hodnocení stavu konstrukce / Building survey and evaluating the state of construction

Štěpánek, Jakub January 2018 (has links)
This diploma thesis is focused on building survey and evaluating the state of existing constructions. Process of evaluating the state of existing constructions and selected diagnostic methods are described in the theoretical part. The practical part is dealing with performed structural and technical survey of two industrial structures including evaluation of the strength of concrete and verification of the reinforcement. The final part includes assessment of both of the evaluated structures.
45

Diagnostika točivých elektrických strojů / Diagnostics of rotating electric machines

Soukup, Patrik January 2018 (has links)
The thesis Diagnostics of rotating electric machines deals with the theory of diagnostics of rotating machines, focusing especially on the diagnosis of asynchronous motors of high power. Due to the importance of maintaining the trouble-free condition of these machines with regard to serviceability, the importance of their diagnosis is growing. Due to inappropriate working conditions or for many other reasons, different types of malfunctions may occur in the machine. The list and the way of occurrence of possible failures are included and explained in this thesis. With the growing age of the machine, it is important to check the insulation status through insulation testing. These tests are performed in the practical part of the thesis and the results are presented. In the case of asynchronous machines, each anomaly leaves a signature in the form of an electrical, magnetic or vibrational signal. These signals are analyzed and evaluated using a specific measuring equipment with the intention of deciding on the current state of the machine. Motor current signature analysis (MCSA) is considered to be the main diagnostic method of asynchronous machines in this thesis. This method is described in detail in this paper and is being applied in electrical engineering.
46

Vlastnosti kapalin na bázi organických esterů / Properties of liquids based on organic esters

Toulová, Jana January 2012 (has links)
This master's thesis deals with the electrical insulation fluids used in electronics industry. The analysis of the current state of research and innovations in modern, biodegradable fluids in terms of their use as diagnostics. It is described by the physical nature of polarization and conductivity mechanisms, which are applied in liquids. It was compiled automated workstation for monitoring components of the complex permittivity over a wide temperature range. In the experimental part we analyzed the behavior of liquids selected alternative based on natural esters when exposed to an alternating electric field at various temperatures. Evaluated results are compared with values for conventional mineral oil.
47

Využití mikroskopu k diagnostice struktury materiálu a poruch u el. zařízení / Using the Microscope for diagnostics of Structure of Materials and Fault El. Equipment

Cvak, Jan January 2015 (has links)
The goal of this thesis is to describe the possibility of using a microscope for documentation defects and innovation of electrical machines. I used an electron microscope to document carbon brushes and nanomaterials for possible upgrade of the sliding contact. Use microscopes gives us detailed information about the structure of materials, at the largest stress of the electrical machine. Based on the collected data can be further analyzed and innovation of the carbon brush.
48

Průzkum a hodnocení stavu dřevěné konstrukce / Survey and evaluation of wooden construction

Křivánková, Soňa January 2014 (has links)
This work is focused on compilation of general diagnostic methods used for diagnostic of wooden structures specifically listed wooden roof truss of church st. Bartholomew in Ivan. The main impulse of diagnosis was extensive damage and attack of truss and effort on rehabilitation and construction of the entire building of the church with an emphasis on preserving historical values. Diagnosis of truss was based on the research used sense and instrumental methods. In the first step, identify all dimensions of the individual elements of the structure was determined, the type truss system was intended. Follow-up survey was focused on determining the extent and causes of damage. In design of the rehabilitation process emphasis is placed on structural rehabilitation provided by follow-up processes, such as preventive chemical protection.
49

Standardizace a harmonizace znalecké metodiky pro potřeby Forenzní ekotechniky: les a dřeviny / STANDARDISATION AND HARMONISATION OF EXPERT VALUATION METHODOLOGY FOR THE NEEDS OF FORENSIC ECOTECHNIQUE: FOREST AND TREES

Holušová, Kateřina January 2012 (has links)
In the presented thesis is an overview of the current state solved the problem, specifying the inclusion of Forensic Ecotechnique: forest and trees into the forensic sciences in the world and its description as part of special methods of forensic engineering. The results focus on the design of standardized and harmonized processes according to the type of expert opinions. As another of the key results of the work are designed functional biometric parameters for evaluating trees in the functional diagnosis of Methods of contact flora assessment (“CFA”). Application of some methods of measurement and selected functional biometric parameters are listed in the examples in the measurement of selected forest stands of beech in the National Nature Reserve Voděradské bučiny and in Chřiby hills. As a general supplement usable in Forensic ecotechnique: forest and trees are given the limits for functional diagnostics. In another series of work includes a discussion on the proposed standards and the measurement results. The work is concluded by summarizing the results and the benefits.
50

Hodnocení stavebně technického stavu objektu / Evaluation of technical conditions of the object

Majtánová, Romana Viktória January 2016 (has links)
This work deals with construction material research office building with eighteen floors to the street Šumavská 35 in Brno with ground plan dimensions of about 25 x 25 m. The structure consists of a reinforced concrete substructure and floors of steel frame. The scope of the survey will determine the quality of concrete in vertical supporting columns at level 1. PP structures using cores and subsequent laboratory testing. Another task will be to verify the status of moorings steel perimeter columns to the building of reinforced concrete pillars at the boundary of 1st basement and 1st floor.

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