Made available in DSpace on 2014-12-17T14:55:13Z (GMT). No. of bitstreams: 1 JoemiaLGMM_TESE.pdf: 3140610 bytes, checksum: 8bdf88d29c888d95e74fd24e403e60fc (MD5) Previous issue date: 2013-06-07 / Coordena??o de Aperfei?oamento de Pessoal de N?vel Superior / Ceramic substrates have been investigated by researchers around the world and has achieved a high interest in the scientific community, because they had high dielectric constants and excellent performance in the structures employed. Such ceramics result in miniaturized structures with dimensions well reduced and high radiation efficiency. In this work, we have used a new ceramic material called lead zinc titanate in the form of Zn0,8Pb0,2TiO3, capable of being used as a dielectric substrate in the construction of various structures of antennas. The method used in constructing the ceramic combustion synthesis was Self- Sustained High Temperature (SHS - "Self-Propagating High-Temperature Synthesis") which is defined as a process that uses highly exothermic reactions to produce various materials. Once initiated the reaction area in the reaction mixture, the heat generated is sufficient to become self-sustaining combustion in the form of a wave that propagates converting the reaction mixture into the product of interest. Were analyzed aspects of the formation of the composite Zn0,8Pb0,2TiO3 by SHS powders and characterized. The analysis consisted of determining the parameters of the reaction for the formation of the composite, as the ignition temperature and reaction mechanisms. The production of composite Zn0,8Pb0,2TiO3 by SHS performed in the laboratory, was the result of a total control of combustion temperature and after obtaining the powder began the development of ceramics. The product was obtained in the form of regular, alternating layers of porous ceramics and was obtained by uniaxial pressing. 10 The product was characterized by analysis of dilatometry, X-ray diffraction analysis and scanning electron microscopy. One of the contributions typically defined in this work is the development of a new dielectric material, nevertheless presented previously in the literature. Therefore, the structures of the antennas presented in this work consisted of new dielectric ceramics based Zn0,8Pb0,2TiO3 usually used as dielectric substrate. The materials produced were characterized in the microwave range. These are dielectrics with high relative permittivity and low loss tangent. The Ansoft HFSS, commercial program employee, using the finite element method, and was used for analysis of antennas studied in this work / Substratos cer?micos t?m sido investigados por pesquisadores de todo o mundo e tem despertado um grande interesse na comunidade cient?fica, pelo fato de apresentarem altas constantes diel?tricas e um excelente desempenho nas estruturas empregadas. Tais cer?micas resultam em estruturas miniaturizadas, com dimens?es bem reduzidas e de alta efici?ncia de radia??o. Neste trabalho, utilizou-se um novo material cer?mico, chamado de titanato de zinco chumbo, na forma de Zn0,8Pb0,2TiO3, capaz de ser utilizado como substrato diel?trico na constru??o de diversas estruturas de antenas. O m?todo utilizado na constru??o da cer?mica foi a S?ntese por Combust?o Auto-Sustentada a Alta Temperatura (SHS Self-Propagating High-Temperature Synthesis ) que ? definido como um processo que utiliza rea??es altamente exot?rmicas para produzir os mais diversos materiais. Uma vez iniciada a rea??o numa ?rea da mistura reagente, o calor gerado ? suficiente para tornar a combust?o auto-sustent?vel, na forma de uma onda que se propaga convertendo a mistura reagente no produto de interesse. Foram analisados os aspectos da forma??o do comp?sito Zn0,8Pb0,2TiO3 por SHS e os p?s obtidos, foram caracterizados. A an?lise consistiu na determina??o dos par?metros da rea??o para a forma??o do comp?sito, como a temperatura de igni??o e os mecanismos de rea??o. A produ??o do comp?sito Zn0,8Pb0,2TiO3 por SHS, realizada em laborat?rio, foi resultado de um controle total da temperatura de combust?o e ap?s a obten??o do p? 8 iniciou-se o desenvolvimento das cer?micas. O produto foi obtido na forma de camadas regulares e altern?ncia de porosidades e as cer?micas foram obtidas por prensagem uniaxial. O produto foi caracterizado atrav?s de an?lises de dilatometria, difra??o de raios-X e an?lise de microscopia de varredura eletr?nica. Uma das contribui??es principais deste trabalho foi o desenvolvimento de um novo material diel?trico, n?o obstante apresentado anteriormente na literatura. Portanto, as estruturas das antenas apresentadas neste trabalho foram constitu?das por novas cer?micas diel?tricas ? base de Zn0,8Pb0,2TiO3, geralmente utilizado como substrato diel?trico. Os materiais desenvolvidos foram caracterizados na faixa de micro-ondas. S?o substratos diel?tricos de alta permissividade relativa e baixa tangente de perda. O software comercial empregado, Ansoft HFSS, baseado no m?todo dos elementos finitos, foi utilizado na an?lise das antenas estudadas neste trabalho

I studien undersöks användningen av digital portfolio i bildämnet och hur den digitala portfolion ingår i att synliggöra lärandeprocessen, samt hur den kan skapa en pågående dialog mellan elev och lärare. Vidare undersöks den digitala portfolions roll i elevers delaktighet i bedömningsprocessen. Metoden är kvalitativ och stödjer sig på halvstrukturerade intervjuer med pedogog och elever från högstadiet som använder sig av digital portfolio i bildämnet. Resultatet visar att både pedagog och elever ser möjligheterna med den digitala portfolion vad det gäller synliggörande av elevernas lärprocess i bild. Ett multimodalt arbetssätt är en framgångsfaktor som bidrar både till synligheteten av lärprocess och bedömningsprocess, samt främjar alternativa kommunikationsformer. Hinder i att uppnå en synlighet och delaktighet i lärandeprocessen och bedömningsprocessen kan dels bero på att den digitala portfolion kan betraktas av eleverna som för abstrakt och därmed också negligeras, eller att eleverna inte ser eller har förstått värdet i att dokumentera. Ytterligare en faktor som är nödvändig för att eleverna ska känna sig delaktiga i, bland annat bedömningsprocessen, är att pedagogens feedback måste vara kontinuerlig och effektiv. Ur ett socialkulturellt perspektiv, med fokus på design för lärande, visar sig den digitala portfolion ha stor potential för synlighet och delaktighet i både lär- och bedömningsprocessen. / The study examines the usage of digital portfolio in the art subject and how the digital portfolio is a part of making the learning process visible. It also investigates how it facilitates an ongoing dialogue between student and teacher. In addition, the study aims to investigate the digital portfolio’s roll in making students involved in the assessment proceqss. The method used in the study is qualitative and relies on half structured interviews with a teacher and students from a Swedish högstadie (8th and 9th grade) who use digital portfolio in the art subject. The result indicate that both the teacher and students alike see the possibilities with the digital portfolio concerning visibility of the students’ learning process in the art subject. A factor for success is a multimodal working practice which contributes both to the visibility of the learning process and assessment process, while also encouraging alternative communication channels. Obstacles in accomplishing visibility in the learning and assessment process can be attributed to the students’ perceiving the digital portfolio as too abstract, consequently neglecting it, or that the students do not see the value in documenting. Yet another factor necessary for students to feel involved, especially in the assessment process, is that the teacher’s feedback needs to be continuous and effective. From a sociocultural perspective, with a focus on design for learning, the digital portfolio has proved to have great potential for visibility and participation in both the learning and assessment process.