Os polímeros conjugados luminescentes são materiais com grande potencial tecnológico, mas apesar de estudados desde a década de 80, algumas de suas propriedades óticas ainda não foram totalmente entendidas. Por exemplo, ainda persistem dúvidas quanto à natureza das suas excitações primárias. Nesse sentido foi feito um estudo da fotoluminescência do poli[2-metoxy-5-(2-etil-hexiloxi)-1,4-fenileno vinileno] (MEH-PPV), polímero semicondutor luminescente cujas propriedades ópticas já foram muito investigadas. Além da banda de absorção principal na região visível do espectro, ele possui três bandas no ultravioleta. O objetivo deste trabalho é investigar a fotoluminescência do MEH-PPV quando excitado na região do ultravioleta. Após fotoexcitação no ultravioleta, observou-se apenas a fotoluminescência usual no visível. A intensidade da emissão depende fortemente da energia de excitação, da temperatura e da estrutura morfológica do sistema polimérico, determinada pelo método de preparação das amostras. Os resultados indicam que os estados excitados no ultravioleta relaxam rapidamente de forma não-radiativa até os estados de menor energia, de onde então ocorre a luminescência. Entretanto, a eficiência da fotoluminescência excitada no ultravioleta é consideravelmente reduzida, indicando que a excitação a altas energias abre novos canais de relaxação não-radiativos. / Luminescent semiconducting polymers are technological promising materials, but although studied since the 80’s some of their optical properties have not yet been fully understood. For instance, the nature of their primary excitations is still on debate. Therefore we proposed to study the photoluminescence following photoexcitation in the ultraviolet of the polymer poly(2-methoxy-5-(2-ethyl-hexyloxy)-1,4-phenylene vinylene) (MEH-PPV). It is a semiconducting luminescent polymer with a main absorption band in the visible part of the spectrum, but with three other absorption bands in the ultraviolet. After ultraviolet photoexcitation it was observed only the usual visible photoluminescence. The intensity of photoluminescence depends strongly on temperature, excitation wavelength and morphological structure of the polymer, determined by the method of sample preparation. The results show that by ultraviolet excitation the excited states relax rapidly non-radiatively to the lower energy states, from where luminescence results. However, the photoluminescence efficiency with ultraviolet photoexcitation is considerably reduced, implying that the highly excited states in the polymer have more non-radiative relaxation channels available.

Made available in DSpace on 2014-06-12T18:05:21Z (GMT). No. of bitstreams: 2 arquivo2577_1.pdf: 1425861 bytes, checksum: 6b478a5b001cb3d32788925e389ba3b6 (MD5) license.txt: 1748 bytes, checksum: 8a4605be74aa9ea9d79846c1fba20a33 (MD5) Previous issue date: 2009 / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / O desenvolvimento do processo de reforma do metano com dióxido de carbono abordado na presente pesquisa recorre à ação do catalisador de níquel suportado em alumina, disposto em reator de leito fixo com membrana seletiva para hidrogênio associada. Atividade e estabilidade do sistema de níquel (50mg), foram avaliadas através de contato catalisador com uma mistura gasosa de composição em razões molares de alimentação CH4/CO2/Ar (10%/40%/50%), a uma vazão total fixa de 100 cm3/min, operando-se na faixa de temperatura de 1.023 K e 1.073 K, sob pressão de 1,0 bar. A reação de Boudouard (C+CO2→2CO) foi utilizada como base para a regeneração do catalisador de níquel, sob coqueamento, tendo-se observado retomadas de níveis de conversão do metano e de produção de hidrogênio. Operações em reator de membrana, na linha de desenvolvimento do processo, com 2 g de catalisador de níquel (3,31% em massa suportado em alumina), utilizaram uma mistura de reagentes em razões molares CH4/CO2/Ar (40,50%/14,00%/45,50%), com uma vazão total de 110 cm3/min , aplicando-se as temperaturas de 773 K, 823 K e 873 K, sob pressão de 1,0 bar. O processo de reforma seca do metano com dióxido de carbono foi operado em reator de leito fixo de membrana com permeação de hidrogênio, evidenciando uma importante conversão do metano com um rendimento em hidrogênio elevado. A 873 K, sob 1,0 bar de pressão, converteu-se neste sistema 35% de metano rendendo 47% de hidrogênio, significando aumentos de conversão em cerca de 83 % e de rendimento em hidrogênio de mais de 100%, em relação às operações em leito fixo sem permeação. Modelagem e simulações foram elaboradas a partir da cinética já ajustada, permitindo simulações retratando perfis de concentração dos reagentes (CH4 + CO2) e produtos (H2 + CO) com e sem permeação do hidrogênio através da membrana Pd-Ag, destacando-se os efeitos da temperatura

Abastract The thesis called Analysis of The 5+2 Days Weekly Magazine between 2012 and 2013 in its empiric part looks into the contents structure, its preferred topics and ratios of stories and cases from the defined parametres point of view throughout the period beginning the foundation of the magazine to the parliamentary elections held in October 2013. The analysis deals with the issue of presentation of the Agrofert holding as the magazine is its part and Andrej Babiš from his position of an owner and chairman of a political movement ANO he led to the snap parliamentary elections in 2013. The analysis examines if the fact that its owner is an enterpreneur, owner of one of the bigest Czech companies and a high-ranking politician has any impact on the contents of the magazine. The method used to analyse the contents is quantitative contents analysis. In its theoretical part the paper deals with basic social roles and functions of the media, concepts of free speech and independence of the media. This part of the thesis sees these concepts mainly from the ownership of the media point of view and the ownership's impact on their contents and function. The theoretical part also presents a review of the Czech media environment development after 2008 from the change of the ownership point of view.

The academic challenges faced by pregnant and nursing students in Zimbabwe do not seem to attract the attention of scholars. This study focused on the educational challenges faced by pregnant and nursing adult learners at Morgenster Teachers‟ College, a tertiary education institution. Participants‟ perceptions of the academic challenges they faced were established through the use of a qualitative methodology in which the semi-structured interview was the dominant data collection method. Non-participant observation and document analysis were employed to complement the dominant method. The findings indicated that the academic challenges faced by mothering adult learners are related to physical problems, social relationships, inadequate financial resources and administrative problems. The study revealed that such students develop strategies to alleviate some of the educational challenges they face. In view of the findings, recommendations are made to improve the learning environment of mothering students and for further research to address the problem. / M. Ed. (Adult Education) / Educational Studies

The academic challenges faced by pregnant and nursing students in Zimbabwe do not seem to attract the attention of scholars. This study focused on the educational challenges faced by pregnant and nursing adult learners at Morgenster Teachers‟ College, a tertiary education institution. Participants‟ perceptions of the academic challenges they faced were established through the use of a qualitative methodology in which the semi-structured interview was the dominant data collection method. Non-participant observation and document analysis were employed to complement the dominant method. The findings indicated that the academic challenges faced by mothering adult learners are related to physical problems, social relationships, inadequate financial resources and administrative problems. The study revealed that such students develop strategies to alleviate some of the educational challenges they face. In view of the findings, recommendations are made to improve the learning environment of mothering students and for further research to address the problem. / M. Ed. (Adult Education) / Educational Studies

DEd (Curriculum Studies) / Department of Curriculum Studies / The study examined challenges that confront lecturers and student teachers at colleges of primary teacher education in Zimbabwe in the use of action research as a teaching and learning strategy. The study focused on lecturer competency, personal dispositions of students towards mastery of action research skills and institutional challenges. The mixed methods research design was used in this study. A combination of the two research approaches exhibits complementary strengths and non-overlapping weaknesses of the techniques, methods and processes involved. Purposive sampling technique was employed to choose one principal and 9 heads of departments while simple random sampling was used to select 140 student teachers. Qualitative data was generated through interviews, observation and documentary analysis. A survey was administered to obtain quantitative data. Thematic analysis was employed to analyse narrative data. Statistical Package for Social Sciences (SPSS) version 24 was used for statistical information. It was established that student teachers have limited practical experience in action research prior to proceeding on teaching practice as well as weak communication skills to support its conduct. The study recommends that lecturers should cater for the characteristics and experiences of student teachers when planning and delivering lectures in order to improve their acquisition of action research skills.