• Refine Query
  • Source
  • Publication year
  • to
  • Language
  • 90
  • 71
  • 55
  • 17
  • 13
  • 6
  • 5
  • 4
  • 3
  • 2
  • 1
  • 1
  • 1
  • 1
  • 1
  • Tagged with
  • 316
  • 316
  • 76
  • 67
  • 58
  • 57
  • 56
  • 32
  • 27
  • 25
  • 17
  • 17
  • 16
  • 14
  • 14
  • 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.
161

Mediální reflexe negativní předvolební kampaně do PSČR v letech 2002,2006 a 2010 / Media reflection of negative parliamentary election campaign in 2002,2006 and 2010

Pistulková, Petra January 2011 (has links)
Diploma thesis focuses on media reflection of negative Czech parliamentary election campaign in 2002, 2006 and 2010. The main goal of this thesis is to find out, whether media did reflect at the time the use of negative political marketing by Czech political parties in the way Czech political scientists describe it. Theoretical part explains the principles of political marketing and characterises parliamentary election campaign in 2002, 2006 and 2010. Empirical part gathers results of quantitative content analysis that were made for each pre- election period 13 weeks before elections in Hospodářské noviny, Lidové noviny and Mladá fronta DNES. The results of quantitative analysis did not confirm the hypothesis that those researched newspapers would in the period of 13 weeks before election reflect higher use of negative political marketing.
162

Mediální obraz Vietnamu v tištěných médiích / Media image of Vietnam in printed media

Hantonová, Barbora January 2013 (has links)
This diploma thesis concentrates on the media coverage of Vietnam in 2012, particularly in four Czech newspapers. Applying qualitative and quantitative method, it analyzes 358 articles, which appeared throughout the selected newspapers in 2012. This paper is divided into two parts, a theoretical and a practical one. The theoretical part describes Vietnam in the 20th century, the history of Czech-Vietnamese relations as well as the main media concepts that help to create a media image. The practical part of the quantitative method answers the research questions, which have been put forward at the beginning of the research. The data, such as the frequency of the topic during the year, topics that are usually connected with Vietnam, occurrence of the word Vietnam in headline and the amount of articles in which Vietnam is the main topic will be depicted using graphs and tables. The results of the qualitative analysis will then show, which characteristics are attributed to Vietnam in Czech daily press.
163

Srovnání ukazatelů týmového herního výkonu mezi družstvem USA a družstvy jeho soupeřů na olympijských hrách v basketbale mužů 2012 a proti výkonu USA na mistrovství světa 2010 / Comparison of indicators of the team game performance between the U.S. team and teams of its rivals at Men's Basketball at the Olympic Games 2012 and against the performance of the U.S. at World Championship 2010

Rédli, Tomáš January 2013 (has links)
Title of thesis: Comparison of indicators of the team game performance between the U.S. team and teams of its rivals at Men's Basketball at the Olympic Games 2012 and against the performance of the U.S. at World Championship 2010. Aim of thesis: The main goal of the thesis was to find out the difference between the U.S. team game performance and its rivals after the confrontation and comparsion of the indicators written down. Another point was to detect how the USA performance at the Olympic Games 2012 resembled to or differed from its performance at the World Championship 2010. This comparsion signifies some specific tendency in conception of the american elite man' s basketball. Methods of thesis: The main approach of the thesis was the quantitative analysis of video recordings of all matches between the U.S. team and its rivals at the Olympic Games 2012. From the video recordings we registered the characteristic of the match by the method of observation and subsequently we compared the achieved values in terms of the teams involved. In the next part the achieved values of the indicators of the USA at the Olympic Games 2012 were compared to the values of the World Championship 2010. Results of thesis: According to the thesis it was found that the U.S. team at the Olympic Games 2012 provided high...
164

Mediální reprezentace utváření komunální politiky (na příkladu sporu o grantování pražských divadel v letech 2007 až 2008) / Mediarepresentation of forming local policy

Švubová, Jana January 2013 (has links)
The diploma thesis on the "Media representation of forming of local policy (on the example of the financing of the Prague theatres)" suggests that mass media contribute to the forming of local policy by selective reporting of the politics. This fact is illustrated on the example of forming grant policy of the capital city of Prague. The analysed media are the daily papers MF Dnes, Lidové noviny, Právo and the televisions TV Nova and Česká televize in 2007 and 2008. The theoretical part of the diploma thesis introduces the relation between mass media and reality, the effects of media and the factors influencing forming of the news content. The political communication is discussed; this phenomenon is introduced together with the personalisation of politics and the mediatisation. Furthermore the paper deals with the agenda- setting theory and its relation to framing theory and the theory of news values. Then the development of the dispute is given, the most important moments are emphasized. The research part of the diploma thesis includes results of the quantitative content analysis. The aim of this research was to discover the media image of the dispute and to confirm or to disprove the hypothesis (i.e. the mass media were not impartial). The qualitative frame analysis shows the ways the dispute was...
165

Analýza měsíčníku Roš chodeš (1990-2015) / Analysis of the Monthly Magazine Roš chodeš (1990-2015)

Bronec, Jakub January 2016 (has links)
The aim of this diploma thesis Analysis of Rosh chodesh (1990-2015) is to analyze the Jewish monthly magazine Rosh chodesh in the specific period of 1990-2015, and make a comparison with another Jewish magazine Maskil. The theoretical part provides general information about the Jewish media and life in the First Czechoslovak Republic, the Second World War and the Communist era. The practical part of my thesis brings the detailed description of the journal's history, purpose, graphic design, columns, journalist committee, authors, distribution and the way of financing. Quantitative analysis of the Rosh chodesh and Maskil gives an insight into the development of both periodicals during 2005-2015 in comparison with the previously conducted research. The changes in the composition, structure and the editing system are captured. More than 1 504 coding units were the subject to detailed analysis. Moreover, there is also the general research dealing with the Czech Jewish Media and selected international media together with a concise content analysis
166

Avaliação quantitativa automática de volumes e densidades pulmonares em TCAR de pacientes com esclerose sistêmica antes e após transplante de medula óssea / Automatic quantification of pulmonary volumes and densities in HRCT of patients with systemic sclerosis before and after bone marrow transplantation

Almeida, Fabrício Arantes de 08 February 2019 (has links)
O objetivo deste estudo foi avaliar as medidas de volume e densidade pulmonar em exames de tomografia computadorizada de alta resolução (TCAR) de tórax de pacientes com esclerose sistêmica (ES), antes e após o transplante de medula óssea (TMO). As medidas foram comparadas com a avaliação funcional e resposta ao tratamento. Este foi um estudo retrospectivo observacional. A avaliação clínica e tomográfica foi realizada antes, após 6 e 18 meses do TMO, dos pacientes com ES que realizaram o procedimento entre 2011 e 2017. A análise quantitativa da TCAR foi feita utilizando programa totalmente automatizado (Yacta), capaz de obter o volume pulmonar, a densidade pulmonar média e os percentis de atenuação (P10, P40, P50, P80 e P90). Os dados clínicos, incluindo o resultado das espirometrias, foram obtidos dos prontuários eletrônicos dos pacientes. A capacidade vital forçada (CVF) aos 18 meses foi utilizada para classificar os pacientes em grupo \"melhor resposta\" (aumento >= 10% dos valores da CVF) ou \"resposta estável\" (redução, estabilidade ou aumento < 10% na CVF). Nenhum paciente apresentou redução da CVF > 10% pós-TMO. Foram incluídos 33 pacientes, com alteração tomográfica ou da função pulmonar antes da realização do TMO. O grupo \"melhor resposta\" foi composto por 15 pacientes (45,4%, 4 homens, idade média de 32,1 anos), enquanto o grupo \"resposta estável\" por 18 pacientes (54,6%, 4 homens, idade média de 37,5 anos). A análise quantitativa das TCAR não demonstrou diferença significativa entre os grupos na fase pré-TMO. No grupo \"melhor resposta\" houve redução significativa da densidade pulmonar média e dos valores dos percentis de densidade após o TMO, destacando-se os percentis 80 e 90. No grupo \"resposta estável\" não houve alteração significativa pós-TMO nos valores de volumes e densidades pulmonares. Concluímos que a análise quantitativa automática da TCAR de pacientes com ES foi capaz de identificar redução significativa da densidadepulmonar nos pacientes com melhora significativa da função pulmonar. Inferimos que, além dos volumes e densidades médias, podem ser utilizados também os percentis de densidade como parâmetro no acompanhamento da doença intersticial. Esta ferramenta pode representar um biomarcador na avaliação de tratamento da doença intersticial pulmonar na ES, complementando as provas de função pulmonar. / The purpose of this study was to evaluate pulmonary volume and density measurements in high resolution computed tomography (HRCT) scans of patients with systemic sclerosis (SSc) before and after bone marrow transplantation (BMT). Measurements were compared with functional assessment and response to treatment. This was a retrospective observational study. Clinical and tomographic evaluation of patients was performed before, after 6 and 18 months of BMT, for patients submitted to the procedure between 2011 and 2017. The quantitative analysis of HRCT scans was performed using a fully automated program (Yacta), capable of obtaining lung volume, density and attenuation percentiles (P10, P40, P50, P80 and P90). Clinical data, including the results of spirometry, were obtained from patients\' electronic records. Forced vital capacity (FVC) at 18 months was used to classify patients into \"best response\" group (>= 10% increase in FVC values) or \"stable response\" (reduction, stability or FVC increase < 10%). No patient had FVC reduction > 10% after BMT. Thirty-three patients were included, with tomographic or pulmonary function alterations before the BMT. The \"best response\" group consisted of 15 patients (45.4%, 4 men, mean age 32.1 years), while the \"stable response\" group comprised 18 patients (54.6%, 4 men, mean age of 37.5 years). Quantitative analysis of HRCT did not show a significant difference between the groups in the pre-BMT evaluation. In the \"best response\" group there was a significant reduction in mean lung density and density percentile values after BMT, with emphasis on the 80th and 90th percentiles. In the \"stable response\" group there was no significant post-BMT change in lung volumes and pulmonary densities. We conclude that the quantitative automatic HRCT analysis of patients with ES identified a significant reduction in pulmonary density in patients with improved pulmonary function. We speculate that, in addition to the mean volumes and densities, density percentiles may also be used as a parameter in the follow-up ofpatients with interstitial lung disease. This tool may represent a biomarker in the evaluation of interstitial lung disease treatment in patients with SSc, complementing pulmonary function tests.
167

Learner mobility in Johannesburg-Soweto, South Africa : dimensions and determinants.

De Kadt, Julia Ruth 07 March 2012 (has links)
Many South African school children are known to travel fairly long distances to school each day, in pursuit of the best possible educational opportunities in a schooling system that is known to vary greatly in quality. This thesis documents the dimensions and determinants of the daily, education-related travel of primary school aged children in Johannesburg-Soweto, South Africa. It uses data on a sample of 1428 children drawn from the Birth to Twenty cohort study to provide the first population-based data on the extent of learner mobility in contemporary urban South Africa. Learner mobility is measured in three different ways: firstly by the straight line distance between a child‘s home and his or her school; secondly by whether the child‘s school falls into the same geographical area as his or her home; and thirdly by whether the child attends his or her nearest, grade-appropriate school. The thesis provides clear evidence for extensive mobility using all three of these approaches to measurement. Over 25% of children were found to be travelling more than 5km each way to school and back on a daily basis. Almost 60% of children attended a school outside of the Census 2001 Sub-Place (roughly equivalent to a suburb) in which they lived, and fewer than 20% of children attended the grade-appropriate school nearest to their home. Counter to expectations, these figures were fairly stable over time, suggesting that educational mobility does not increase substantially as children age or transition to high school. Mobile children attended significantly more well-resourced and well-performing schools than their non-mobile peers, and the quality of schools attended increased with distance travelled. This substantiates the assumption that children and families make use of educational mobility to improve the quality of education that they are able to access. The analyses presented in the thesis suggest that two distinct patterns of mobility, with different determinants, are in use in the Johannesburg-Soweto area. The first relates primarily to travel from townships to historically advantaged schools in suburban Johannesburg, and typically requires substantial economic investment and extensive parental involvement. The second form of mobility operates at a more local level, and relates to children and families making choices between a number of relatively local schools. This form of mobility is less resource intensive. Children engaging in the first form of mobility were more likely to attend a particularly advantaged school, and to have a well-educated mother. By contrast, children engaged in the second form of mobility were more likely to live in a disadvantaged area, and come from households with moderate SES levels. iv The findings of this thesis provide important insights into the nature of school choice in South Africa, which have implications for educational policy, and the understanding of the nature of urban poverty as experienced by South African children. They also contribute to the international school choice literature, by providing novel information about the implications of relatively unregulated school choice for educational inequality and segregation in the South African context.
168

Analyse quantitative des paramètres issus de l'IRM cardiaque / Quantitative analysis in cardiac magnetic resonance imaging and prognosis

Bière, Loïc 04 May 2015 (has links)
L'IRM cardiaque est un examen non invasif qui permet aujourd’hui de proposer une analyse multiparamétrique alliant notamment fonction, caractérisation tissulaire, perfusion, et appréciation de la fibrose. Cependant afin d'uniformiser ces analyses il convient de favoriser une interprétation objective des images obtenues passant par une étape de quantification de l'information. Nous avons suivi une cohorte de 195 patients ayant présenté un premier infarctus du myocarde avec sus décalage du segment ST et ayant bénéficié d'une revascularisation coronaire en phase aigüe avec succès. Des IRM ont été réalisées au cours de leur hospitalisation puis à 3 mois. Ont été investigués de façon quantitative les volumes ventriculaires, le stress pariétal systolique, la taille d'infarctus, la taille d'obstruction microvasculaire et la taille de l'épanchement péricardique. Une cohorte de 42 patients présentant une cardiomyopathie hypertrophique a également été étudiée par ECG et IRM. Nous avons débuté par une validation clinique comparative des méthodes de quantification semi-automatique de la taille d'infarctus. L’obtention du seuil par la méthode FWHM permet de mesurer la taille d’infarctus initial la mieux corrélée aux volumes ventriculaires à 3 mois. Nous avons également confronté et souligné les relations entre l’ECG et le phénotype des cardiomyopathies hypertrophiques documenté par IRM cardiaque. Nous montrons qu’il n’existe pas de critère ECG corrélé à la présence de fibrose myocardique dans cette pathologie ; à l’inverse la présence d’une onde q semble en relation avec la géométrie cardiaque tel qu’un rapport de la paroi septale sur latérale élevé. Nous avons également montré que les composantes de la déformation myocardique étaient altérées selon le degré de fibrose myocardique dans le post-infarctus. Nous montrons une altération plus marquée en cas d’obstruction microvasculaire et un caractère prédictif du strain longitudinal global pour la taille d’infarctus à 3 mois. Nos analyses soulignent l'intérêt d'une approche multiparamétrique pour préciser les déterminants d'une part de l'insuffisance cardiaque, d'autre part de la constitution d'un épanchement péricardique post-infarctus. Alors que la taille d’infarctus initiale est le meilleur marqueur de risque de développer un épisode d’insuffisance cardiaque pendant l’hospitalisation, c’est le stress pariétal systolique qui est le mieux relié aux épisodes d’insuffisance cardiaque après la sortie. Enfin, un épanchement péricardique était retrouvé chez 58.5% des patients avec une moyenne de 31.6±24.0 ml. Les paramètres associés en analyse multivariée étaient la taille d’infarctus, la présence d’une obstruction microvasculaire et le stress pariétal systolique. L’ensemble de nos résultats montre l’intérêt d’une approche quantitative et multiparamétrique de l’IRM cardiaque. Ses potentielles applications sont nombreuses dans le domaine de la recherche aussi bien descriptive que prospective et randomisée. / The various aspect of cardiac function may now be investigated non-invasively by cardiac imaging. Cardiac magnetic resonance (CMR) allows to study multiple parameters in one time, including function, perfusion, tissular characteristics and fibrosis. There is a need to propose adequate and objective criteria for CMR analysis, which may be warranted by a quantitative analysis. We prospectively followed 195 patients with a first ST elevation myocardial infarction and successful revascularisation. CMR were performed at baseline and 3 months. We analysed ventricular volumes, systolic wall stress, infarct size, microvascular obstruction, and pericardial effusion extent. A cohort of 42 patients with hypertrophic cardiomyopathy were also studied. We demonstrated the clinical interest for semi-automated analysis of late gadolinium enhancement imaging. The use of the FWHM algorithm appeared strongly related to left ventricular volumes at 3 months. Then we depicted the lack of relationships between electrocardiograms and fibrosis in patients with hypertrophic cardiomyopathy. The presence of q waves appeared to be related to cardiac phenotype, namely higher septal to posterior ratios. We showed the impairment of myocardial deformations in regard of myocardial fibrosis following a myocardial infarction. We found a much depressed deformation in case of microvascular obstruction and an interest for longitudinal global strain for the prediction of infarct size at 3 months. We also studied the determinants of post-infarction heart failure on one part, pericardial effusion on the other, by the use of a CMR multiparametric approach. Infarct size and systolic wall stress were the best markers of in-hospital and post-discharge heart failure, respectively. A pericardial effusion was found in 58.5% of the patients with a mean size of 31.6±24.0 ml. The determinants by multivariate analysis were infarct size, microvascular obstruction and systolic wall stress. Our results highlighted the interest for a quantitative and multiparametric approach of CMR. Further applications are expected in both descriptive and randomized studies.
169

Reparação óssea sobre superfícies de titânio usinadas ou tratadas por óxido de titânio com exerto autógeno em bloco coberto por membrana reabsorvível / Healing of bone on machined or grit-blasted titanium surfaces with autogenous block graft covered with resorbable membrane

Hespanhol, Andre Micheletti 14 September 2009 (has links)
Este estudo avaliou, quantitativamente, o osso regenerado após técnica de regeneração óssea guiada, utilizando osso autógeno em bloco e membrana de colágeno e descreveu seu processo de reparação ao redor de superfícies de implantes usinadas ou tratadas por jato de óxido de titânio em períodos de até 150 dias. Foram utilizados 60 ratos machos Wistar, divididos em 2 grupos: um recebeu implantes com superfície usinada (U) e o outro recebeu implantes com superfície tratada por jato de óxido de titânio (T). Uma trefina foi utilizada para a remoção do enxerto ósseo em bloco da calvária do animal. O enxerto foi fixado próximo ao ângulo da mandíbula do rato, na cortical vestibular, com o uso do implante. O conjunto foi coberto por membrana de colágeno. A ortotanásia foi realizada em 0, 14, 21, 45 e 150 dias. Foi realizado processamento histológico para material nãodescalcificado, e um corte no longo eixo do implante foi obtido para cada espécime. Foram realizadas análises qualitativa e quantitativa. Os dados foram analisados estatisticamente, em um nível de significância de 5%, pelos testes de Kruskal-Wallis e de Dunn. Os resultados relativos aos períodos de observação mostraram que a média do tamanho do defeito inicial foi de DO-U = 604,13 m e DO-T = 585,90 m (p=0,720) e que a média de espessura inicial do leito foi de EL-U = 257,29 m e ELT = 243,57 m (p=0,07); houve uma redução da espessura do enxerto no período de 150 dias para o grupo T em relação ao grupo U (EE-T = 338,25 m; EE-U = 407,71m) (p=0,003), não havendo outras diferenças significativas entre os grupos. Notou-se a presença de osso regenerado, vestibularmente ao enxerto, a partir de 21 dias, com uma nítida tendência ao aumento de sua espessura até o período de 150 dias, onde notamos um aumento da espessura óssea total de cerca de 4,6 (T) e 4,8 (U) vezes a espessura original da mandíbula, com valores de ETTO U = 1254,40 m e ETTO T = 1141,85 m (p=0,48). / This study quantitatively analyzed the regenerated bone after guided bone regeneration technique using autogenous block graft with resorbable membrane and described its pattern around machined titanium or oxide grit-blasted titanium surfaces in periods of up to 150 days. Sixty male, adult, Wistar rats were randomly assigned to one of two groups: machined titanium surface (U) or oxide grit-blasted titanium surface (T). A block graft was harvested from the rat calvarium with a trephine, laid and stabilized on the external cortex near the angle of the mandible with implants. A collagen membrane was adapted to completely cover the bone graft in both groups. The animals were euthanized at 0, 14, 21, 45 and 150 days after surgery. Nondecalcified histological sections were processed for each specimen and one section on the long axis of the implant was obtained. Qualitative and quantitative analysis were carried out. Statistical analyses were carried out with a significance level of 5% and used Kruskal-Wallis and Dunn tests. Results showed that the mean bone defect was DO-U = 604,13 m and DO-T = 585,90 m (p=0,720), and the mean mandible bone width was EL U = 257,29 m and EL-T = 243,57 m at zero hour. The mean graft width was reduced after 150 days for the T group as compared to group U (EET = 338,25 m and EE-U = 407,71 m) (p=0,003). No other significant differences between groups were observed. Regenerated bone was observed buccal to the bone graft after 21 days increasing in width after 150 days. The final mean mandible bone width after 150 days (ETTO-U = 1254,40 m and ETTO-T = 1141,85 m) achieved 4,8 (U) and 4,6 (T) times the original mandible width (p=0,48).
170

Aplicação da difração de raios-X e método de Rietveld no estudo de Cimento Portland / Application of X-ray diffraction and Rietveld method in Portland Cement study

Gobbo, Luciano de Andrade 19 June 2009 (has links)
O projeto desenvolvido enfocou a aplicação da difração de raios-X e método de Rietveld (DRX-Rietveld) na caracterização e quantificação do Cimento Portland, constituindo-se em contribuição pioneira sobre o tema em âmbito nacional. Foram estudadas amostras de pozolanas naturais e artificiais, subprodutos industriais de grande disponibilidade na indústria nacional, tais como escórias de alto-forno provenientes das siderúrgicas e cinzas volantes das termelétricas. Adicionalmente, foram estudadas amostras dos componentes utilizados para composição de cimentos laboratoriais, tais como clínqueres, calcários e fosfogesso, e por fim, cimento Portland com adições, preparados em laboratório. Também foram realizados ensaios para acompanhamento da hidratação do cimento Portland com uso da difração de raios-X e método de Rietveld. O cimento Portland é o material composto de clínquer, gesso e eventuais adições, tais como calcário, pozolanas e escórias. O clínquer de cimento Portland é o material sinterizado e peletizado, resultante da calcinação de uma mistura adequada de calcário e argila e, eventualmente, de componentes corretivos. O método de Rietveld, foi introduzido por Hugo Rietveld em 1969, tendo em base a simulação de todo o perfil difratométrico a partir de parâmetros estruturais das fases constituintes, permitindo refinar parâmetros de natureza instrumental e cristalográfica. A comparação do difratograma calculado com o observado e redução das diferenças através do método de mínimos quadrados permitem a obtenção de resultados quantitativos. Para desenvolvimento do projeto foram utilizadas técnicas analíticas tradicionais como apoio à difração de raios-X, tais como a microscopia óptica de luz transmitida, microscopia eletrônica de varredura (MEV-EDS), fluorescência de raios-X (FRX) e o calorímetro de condução. DRX-Rietveld apresentou-se como uma técnica de quantificação de elevada reprodutibilidade com vantagens de cunho técnico e logístico. As condições instrumentais e de coleta de difratogramas foram avaliadas, onde se verificou que a condição adequada para a obtenção de resultados de proporções de fases coerentes e em tempo reduzido pode ser obtida com coletas realizadas em 20s/passo, levando desta forma 10 minutos para sua realização, quando considerado o uso de detetores sensíveis a posição. Fendas divergentes automáticas e fixas testadas apresentaram resultados muito similares, validando a técnica nas diferentes condições. A redução no tempo de análise constitui um fator importante da técnica visando atender os interesses da indústria do cimento. A técnica estudada se mostrou adequada para a quantificação de componentes do cimento Portland tais como o calcário, materiais pozolânicos e escórias de alto-forno, e principalmente cimentos com estas adições. Com DRX-Rietveld foi possível avaliar as proporções das fases do clínquer, calcário e gipsita, e com a utilização de um padrão interno, a técnica possibilitou a quantificação de compostos com fase amorfa, o que é de grande importância para a correlação com as propriedades físico-mecânicas destes materiais. Resultados das proporções de calcário na quantificação dos cimentos apresentaram elevada correlação com as proporções dosadas em sua composição (R2=0,96-0,99), o que também foi observado com relação às proporções de fosfogesso dosadas (R2=0,99-1,0). Boas correlações também foram obtidas entre as proporções de cinzas volante e escória adicionadas nas amostras e os valores obtidos por DRX-Rietveld (R2=0,97-0,99 para cinza volante; R2=0,97 para escória). Ensaios DRX aplicados à uma pasta de cimento Portland mostraram-se adequados para o estudo quantitativo de cimentos hidratados e também para o acompanhamento das reações de hidratação. A técnica possibilitou a quantificação dos compostos hidratados como etringita, portlandita e C-S-H, o que foi aferido através de ensaios para determinação de calor de hidratação, mostrando resultados de refinamento confiáveis. / The project has focused on the application of X-ray diffraction and Rietveld method (XRD-Rietveld) on the characterization and quantification of Portland cement, and represents a pioneer scientific contribution on the theme in Brazil. Natural and artificial pozzolans, and also industrial byproducts that are highly available in the Brazilian industry were studied, as the blast furnace slags from steel works and fly ash from power stations. Furthermore components of laboratorial cements were studied, as clinker, limestone, gypsum, and finally the Portland cement with additions, prepared in laboratory. Hydration studies to follow the reactions in a cement paste were also performed using XRD-Rietveld. The Portland cement is composed by clinker, gypsum and fillers, as limestone, pozzolan and slags. Portland cement clinker is the sintered and pelletized product from calcination of an adequate mix of limestone and clay and minor corrective materials. The Rietveld method was introduced by Hugo Rietveld in 1969 and is based on the simulation of the whole diffraction spectrum from the components structural data, allowing for refining instrumental and crystallographic parameters. Quantitative values are obtained by comparing the calculated and actual diffractograms and minimizing differences mathematically through a least squares method. To develop the project several analytical traditional techniques were used with XRD: optical microscopy, electronic microscopic (SEM), X-ray fluorescence (XRF) and calorimeter. XRD-Rietveld presented as a high reproducibility technique with technical and logistics advantages. The evaluation of the instrumental conditions showed that to obtain a good quantitative result in reduced time were with a scan with 20s/step, a 10 minutes scan, possible with position sensitive detectors. Automatic (ADS) and fixed divergent slits (FDS) were tested, validating the technique in both conditions. The reduction in the time of analysis is very important to follow the cement industry interests on quality control. The technique was considered adequate to be applied on the quantification of Portland cement components such as limestone, pozzolanic materials and blast-furnace slags. With XRD-Rietveld, was possible to evaluate the clinker phases, limestone and gypsum, and using an internal standard, the technique lead to the quantification of compounds with amorphous phases, that is very important to correlate with the physic- mechanical properties of these materials. Results of limestone proportions in the quantification of cements presents a high correlation with the proportions added in the cement composition (R2=0,96-0,99), what was also observed in the case of gypsum added (R2=0,99-1,0). Good correlations were also obtained between the fly ash and slags proportions in the samples and XRD-Rietveld obtained values (R2=0,97-0,99 to fly ash; R2=0,97 to slag). XRD experiments applied to Portland cement paste were adequate to the quantitative analysis of hydrated cements and also to follow the hydration reactions. The technique permitted the quantification of hydration compounds such as ettringite, portlandite and C-S-H, that was confirmed using the calorimeter, showing good refinement results.

Page generated in 0.1668 seconds