Submitted by Clebson Anjos (clebson.leandro54@gmail.com) on 2016-02-11T20:45:07Z No. of bitstreams: 1 arquivototal.pdf: 2311643 bytes, checksum: 43ddbb48531f37b68376b2f7a5285c70 (MD5) / Made available in DSpace on 2016-02-11T20:45:07Z (GMT). No. of bitstreams: 1 arquivototal.pdf: 2311643 bytes, checksum: 43ddbb48531f37b68376b2f7a5285c70 (MD5) Previous issue date: 2014-07-31 / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior - CAPES / Social network analysis techniques can be used to extract knowledge from the network by analyzing the interactions between its members. In this work we intend to apply echniques of social network analysis on networks formed through scientific collaborations among researchers. Our objective with this study is to analyze if these collaboration connections may have any influence in the evaluation of scientific merit. We will focus our work on two specific scenarios. The first scenario targets the evaluation of individual merit for granting scholarships to researcher and is conducted by CNPQ, the Brazilian Research Council. The second scenario focus on the evaluation of graduate programs in the country and is conducted by CAPES, the governmental body entitled to evaluate and coordinate the graduate education program in Brazil. On both scenarios we will restrict our analysis to the Computer Science area. / Técnicas de análise de redes sociais podem ser utilizadas para extrair conhecimento da rede por meio da análise das interações entre seus membros. Neste trabalho pretendemos aplicar técnicas de análise de redes sociais a redes formadas pela colaborações científicas entres pesquisadores. Pretendemos com isso avaliar se as relações de colaboração entre pesquisadores possuem alguma influência na avaliação do mérito científico. Utilizaremos como estudos de caso o processo de concessão das chamadas bolsas de produtividade em pesquisa do CNPQ e a avaliação dos programas de pós-graduação pela CAPES, ambos focados na área de Ciência da Computação.

Qualitative research based on a half standardized interview with seniors is aimed at identifying the seniors´ perception of the dignity concerning dignity of merit, moral strength and personal identity, and the related values of every human being, also known as Menschenwürde {--} human dignity. The results show the risk of loss or reduction of dignity in old age. The reasons are external and internal. External reasons include the approach of society and individuals to the elderly, (un) availability of social services for seniors and their families and also the social system. Internal reasons involve the change of the inner self, reduction of self-sufficiency, financial provision, degree of independence, evaluation of the past life, the age and gender. In the highest risk of loss of dignity are the very old, individuals dependent on the care of others and women. The research makes us think about creating decent living conditions for the elderly. The issues of supportive background creation and available home care services for the elderly and possibilities of a better support for families caring for dependent and dying elderly persons are also addressed. On an individual level it is necessary to instruct people, who come into contact with the elderly, with risk factors that may decrease dignity of the elderly and to gain skills for assistance to enhance seniors´ dignity by an appropriate and sensible approach. Perception of dignity changes with a social system. Dignity is an important component of the quality of life perception. Attention must be paid to this issue also in the future. With prolonged longevity of an individual and an active participation in community life up to the old age it should be reconsidered since what age an individual is regarded as old. For example, according to the WHO the early old age starts at 60 years of age. This is what young seniors perceive negatively. They do not consider themselves old even when they are 65 years old.

College completion agendas necessarily presume year-to-year student persistence. Institutional efforts to retain admitted students has emerged for a variety of reasons, some intrinsic and others extrinsic. Some of these reasons include (1) financial exigency as institutions strive to retain tuition-paying students or meet prescribed enrollment and retention criteria currently used in performance funding strategies; (2) reputation enhancement as institutions attempt to ascend annual publications such as the U.S. News & World Report which rely on retention rates as one of several indicators used to measure institutional quality; (3) gaining a perceived advantage in admissions, marketing, and fundraising as persistence rates have, for better or worse, become a de facto measure of quality undergraduate programs; and (4) mission fulfillment as institutions, especially public institutions, are tasked with contributing towards broadly cast social goals such as access to education, economic competitiveness, and community development. Knowledge about forces that impact student attrition is critical to the development of preventative strategies that seek to improve student persistence rates. One such environmental force that has an impact on student persistence is financial aid and a student’s ability to pay for their college education. While research examining the impact of financial aid on student persistence has accumulated over the years, little is known about how the loss of certain types of aid, specifically, state-based merit aid, affects students once they enroll in an institution. The majority of studies about financial aid’s impact on student persistence were conducted prior to the establishment of many state-wide merit scholarship programs. Tinto’s (1975, 1986, 1993) interactional theory of student departure serves as the theoretical framework employed in this study. Tinto (1975) states that entering college students bring with them specific background characteristics and initial commitments that influence the student’s social and academic integration at the institution that, in turn, impact subsequent institutional and goal commitments and, ultimately, persistence. This study intends to examine pre- and post-matriculation data gathered through the admissions and financial aid processes to develop predictive models useful in calculating the probabilities associated with Bright Futures scholarship retention, institutional persistence after losing a Bright Futures scholarship award at the conclusion of a student’s first year of enrollment, and a student’s eligibility to recapture a Bright Futures scholarship award in their third year of enrollment. Data was collected passively from institutional databases on 2,418 students meeting the study criteria for inclusion in the model building process. Findings indicate that the models developed throughout the course of this study hold potential for informing institutional retention initiatives among Bright Futures scholarship award recipients.

O estudo analisa, à luz do direito positivo em vigor no Brasil, a possibilidade de emissão de sentenças parciais dentro de um mesmo processo, de modo a solucionar por etapas o objeto litigioso. Procura-se demonstrar que não se trata de novidade absoluta, já convivendo o sistema brasileiro de longa data com situações de fracionamento da resposta judiciária, possibilidade que ficou amplificada com as sucessivas alterações por que passou o Código de Processo Civil Brasileiro. Examinam-se e refutam-se os afirmados obstáculos que impediriam ou contraindicariam o uso da técnica, com a demonstração de ser ela, em verdade, uma imposição do modelo processual constitucional brasileiro. Examinam-se aspectos técnicos ligados ao uso da técnica, verificando-se, principalmente: (i) em quais modalidades de cumulação de pedidos e de sujeitos ela tem cabimento; (ii) se também é possível falar na apreciação por etapas dos diferentes fundamentos da ação e da defesa; (iii) se a emissão de sentença parcial é ato discricionário ou vinculado do juiz; (iv) qual o momento adequado para que o juiz delibere acerca do custo financeiro do processo; (v) se é possível a formação gradual da coisa julgada dentro de um mesmo processo. Por fim, procura-se harmonizar o sistema de recursos ao uso da técnica, fazendo-se rápida menção aos sistemas jurídicos de outros países e ao Projeto do Novo Código de Processo Civil, que contempla o instituto aqui tratado na figura do Julgamento Antecipado Parcial do Mérito. / In the light of positive law in force in Brazil, this study analyses the possibility of partial judgements being given in relation to the same lawsuit, in order to settle litigation in stages. The study seeks to demonstrate that this is not an absolute novelty and that the Brazilian legal system has been accustomed for a long time to situations in which the judicial response is fragmented. This possibility has increased following the successive alterations undergone by the Brazilian Code of Civil Procedure. The obstacles alleged to prevent or counterindicate the use of this technique are examined and refuted, demonstrating that in truth the technique is an imposition of the Brazilian constitutional procedural model. An examination is made of the technical aspects related to the use of the technique, verifying in particular: (i) in which modes of joinder of claims and subjects it is admissible; (ii) if it is also possible for the different grounds for the suit and the defence to be examined in stages; (iii) if the giving of partial judgement is a discretionary or binding act of the judge; (iv) what is the appropriate moment for the judge to decide on the financial cost of the proceedings; (v) if it is possible for res judicata to be gradually formed within the same lawsuit. Finally an attempt is made to harmonize the appeal system with the use of the technique, referring rapidly to the legal systems of other countries and the Bill of Law for the New Code of Civil Procedure, which contemplates the institution dealt with here as Partial Summary Judgement of Merit.

Orientadores: Aparecida Neri de Souza, Selma Borghi Venco / Tese (doutorado) - Universidade Estadual de Campinas, Faculdade de Educação / Made available in DSpace on 2018-08-23T05:19:43Z (GMT). No. of bitstreams: 1 Rigolon_WalkiriaDeOliveira_D.pdf: 5923142 bytes, checksum: 738c26a23afe45f4a2e8085fe8e011ac (MD5) Previous issue date: 2013 / Resumo: Essa pesquisa tem como objetivo compreender as alterações na organização do trabalho de professores alfabetizadores vinculados à Secretaria de Estado da Educação de São Paulo, cuja hipótese centrou-se na perspectiva de que a nova política implementada a partir dos anos 2000 repercutiu diretamente no trabalho docente. Nesse sentido, analisa-se como os professores (em grande maioria mulheres) interagem com a reorganização de sua atividade e com a inserção de novas formas de gerenciamento da educação, aqui compreendidas como efetivas forma de controle, instauradas pelo estabelecimento de metas, pela promoção por mérito, por avaliações externas, pela reorganização curricular, além das ações de intervenção direta em sala de aula. Foram realizadas entrevistas em profundidade com professores que se encontram em atividade e com docentes já aposentados, no interior e na capital paulista, contemplando, também, outros profissionais a exemplo de: professores coordenadores, diretores de escola, supervisores de ensino e assessores da Secretaria da Educação. A análise pautou-se, ainda, em dados estatísticos, em documentos institucionais e oficiais do governo do estado de São Paulo relativos à docência do segmento de ensino em questão. A pesquisa indicou que o trabalho docente nos anos iniciais do Ensino Fundamental tem se deparado com novas demandas e formas de controle que têm aportado crescente precariedade nas relações de trabalho que, concomitantemente passaram a desencadear pressões e tensões até então inéditas neste campo / Abstract:This research, whose hypothesis focused on the perspective that the new policy implemented by the Secretaria de Estado da Educação, from 2000s on, reflected directly into the teaching, aims to understand the changes in the organization of the literacy teachers work linked to it. In this sense, we have analyzed how teachers (most of them women) interact with the reorganization of their activities and with the introduction of new methods of education management, here presented as effective ways of to control, implemented by goals establishment, by promotion through merit, by external evaluations, by curricular organization, besides direct intervention in the classroom. Interviews in deep with teachers still in activity and some already retired, in the countryside and São Paulo city, were performed besides others professionals: teachers under coordination role, school principals, school supervisors and technical advisers. The analysis was also based on statistics dta, institutional and official documents from the State of São Paulo government related to literacy teachers. The research results have indicated that the teachers of the early years of elementary school (fundamental level) have faced new demands and control requirements that have increasingly led to precarious work relationships, which, at the same time, resulted in pressures and tensions not seen before in this area / Doutorado / Ciencias Sociais na Educação / Doutora em Educação

Les performances de reproduction des vaches laitières se sont dégradées parallèlement à l’augmentation de leurs performances de production. L’intense sélection réalisée sur la production laitière est tenue responsable de cela. Chaque étape du processus de reproduction a été affectée : les anomalies de cyclicité ovarienne sont plus fréquentes dans la population actuelle, la durée et l’intensité des chaleurs ont diminué drastiquement, et les échecs de gestation sont plus fréquents. La littérature s’accorde sur le fait que la reproduction est affectée parce que la majeure partie des ressources est investie dans la production laitière. L’objectif de cette thèse de doctorat est d’étudier l’intérêt d’une stratégie de sélection alternative basée sur un fort potentiel génétique de taux butyreux et protéique sur la robustesse des vaches laitières.Les hypothèses testées étaient que par rapport aux vaches à fort potentiel de production laitière, celles à fort potentiel de taux butyreux et protéique (i) exportent moins d’énergie dans le lait et donc préservent leur réserves corporelles, (ii) ont de meilleures aptitudes à se reproduire. Nos résultats montrent que les vaches à fort potentiel de taux butyreux et protéique ont un retour de cyclicité plus précoce, une expression des chaleurs similaire mais plus d’échecs de gestation que celles à fort potentiel de production laitière. Ces résultats intrigants suggèrent que les étapes de la reproduction sont partiellement découplées sur le plan génétique. Sélectionner les vaches laitières sur les taux butyreux et protéique dans le but d’amé / Reproductive performance of dairy cows has been declining while their milk production was improving. The strong genetic selection that was applied on milk production is considered to be responsible for this. Each step of the reproductive process has been impacted: abnormal ovarian activity is more common in the current population, the duration and intensity of oestrus has dramatically decreased and the occurrence of pregnancy failures has increased. The consensus in the literature is that reproduction is impaired because dairy cows are investing most of their resources in milk production. The aim of this Ph.D. thesis is to explore the effect of alternative selection strategies based on milk fat and protein content on robustness of dairy cows. Our hypotheses were that at similar genetic merit for milk solids yield, compared to cows with high genetic merit for milk yield,dairy cows with high genetic merit for fat and protein contents (i) are exporting less energy in milk and are consequently safeguarding their body reserve; (ii) have better reproductive performance (earlier resumption of ovarian activity, more intense oestrus, better ability to ensure pregnancy). Our results suggest that cows selected for production through high fat and protein content instead of high milk yield would resume ovarian activity earlier, have similar oestrus intensity but more pregnancy failures. These intriguing results suggest that the steps of the reproductive process are genetically partly disentangled. Selecting dairy cows for fat and protein content is not a promising way to improve repro

Wideband, wide-scan antenna arrays are a promising candidate for the future wireless networks and as well as an essential part of experimental radio astrophysics. Understanding the underline physics of the element performance in the array environment is paramount to develop and improve the performance of array systems. The focus of this thesis is to develop novel wideband antenna array technologies and develop new theoretical insights of the fundamental limits of antenna arrays. The developed methodologies have also been extended to include a radio astrophysics application for the global 21cm experiment.   Investigating the fundamental antenna array limits and extracting general performance measures can provide a priori estimates for any application of arrays. In this thesis, a general measure for antenna arrays, the array figure of merit is proposed. This measure couples bandwidth, height from the ground plane and reflection coefficient in a bounded quantity. An extension of the array figure of merit that is able to provide matching, bandwidth and directivity/gain limits is also introduced. The soft Vivaldi array is introduced as a novel wideband, wide-scan angle array technology. Periodic structure loading has been utilized to improve the array's performance and mold the electromagnetic wave behavior to our benefit. The soft condition has been utilized in the same manner as the conventional soft-horn antenna at the Vivaldi element. An integrated matching layer in the form of periodic strip loading is introduced. A single polarized soft Vivaldi array prototype has been developed fabricated and measured. The developed finite array has been loaded with a soft condition in the periphery to mitigate edge effects. The results indicated improved cross-polarization and side-lobe levels. A new class of wideband antenna arrays, the Strongly Coupled Asymmetric Dipole Array (SCADA) was also proposed in this thesis. Exploiting asymmetry in the array element introduces an additional degree of freedom that improves bandwidth and scanning performance. A novel methodology for terminating finite arrays is also proposed. The theory and an experimental antenna array is presented with good agreement between measured and simulated results. An effort to integrate a vertical wide angle matching layer was also addressed and a prototype array with this concept is presented. In the last part of this thesis, a methodology for the detection of the global cosmological 21cm signal from the Epoch of Reionization (EoR) is developed. The main sources of errors in this experiment, the foregrounds and the antenna chromaticity are evaluated. A new algorithmic methodology for extracting the global EoR signal is proposed. The method is based on piecewise polynomial fitting and has successfully been applied and evaluated. An antenna array that is based on the methodologies described in this thesis has been developed and evaluated with the proposed algorithm. / Bredbandiga gruppantenner med stor utstyrningsvinkel är en av de lovande kandidaterna för nästa generations trådlösa kommunikationsnätverk samt en väsentlig del av experimentell radioastrofysik. Att förstå de bakomliggande fysikaliska principerna hos gruppantennens element är avgörande för att kunna utveckla och förbättra prestandan hos ett gruppantennsystem. Denna avhandling är fokuserad på att utveckla nya bredbandstekniker samt nya teoretiska insikter om de grundläggande gränserna för gruppantenner. De här utvecklade metoderna har förutom kommunikationstillämpningar också tillämpats på en radioastrofysik tillämpning i det globala 21cm experimentet. Att undersöka de fundamentala gränserna för gruppantenner och att utröna allmängiltiga mått på deras prestandaegenskaper kan möjliggöra a priori uppskattningar om gruppantenns tillämpbarhet för dess planerade användning. I den här avhandlingen föreslås ett allmänt kvalitetsmått på gruppantenner: gruppantennkvaliten. Detta mått kopplar samman främst bandbredd, reflektionskoefficienten med antennens tjocklek över ett jordplanet. En utvidgning av begreppet gruppantennkvaliten, presenters också i avhandlingen det kopplar samman bandbredd, matchning med antennens direktivitet/förstärkningsfaktor. En Vivaldi-gruppantenn med mjuka ytor introduceras här som en ny sorts bredbandig gruppantenn med stor utstyrningsvinkel. I antennen har en periodisk belastning inkluderats för att förbättra dess egenskaper, och för att forma antennens elektromagnetiska utstrålning till vår fördel. Den mjuka ytan på elementet har används på ett liknande sätt som det välkända korrigerade Vivaldihornets design, och har integrerats direkt i elementets design. Den här utvecklade ändliga gruppantennen har också en mjuk yta på dess yttre delar för att minska kanteffekternas påverkan av antennprestandan. Resultaten indikerade både förbättrad korspolarisations och lägre sidlobsnivåer hos antennen. En ny klass av bredbandiga gruppantenner har utvecklas i denna avhandling, den kallas en Starkt Kopplad Asymmetrisk Dipol-gruppAntennen - SCADA. Genom att utnyttja geometrisk asymmetri i antennelementet introduceras ytterligare en frihetsgrad som möjliggör förbättrad bandbredd och utstyrning. Vidare presenteras här en ny metod för impedansterminering av ändliga gruppantenner. Både SCADA-teorin samt dess verifiering i forma av en experimentell gruppantenn presenteras här. Teori, simulering och experiment visar god överenskommelse, vilket validerar idéerna. En prototyp av ett matchande skikt som stöder stor utstyrbarhet har integrerats med gruppantennprototypen och presenteras i avhandlingen. I den sista delen av avhandling utvecklas också en metod för detektering av den globala kosmologiska 21 cm-signalen från universums rejoniseringsepok - EoR. Huvudkällorna för mätfel i detta experiment utvärderas, de är antennens kromaticiteten och förgrundsstrålningen. En ny algoritmbaserad metod för att extrahera den globala EoR-signalen föreslås. Metoden är baserad på anpassning med multipla polynom och har med framgång tillämpats och utvärderats. En gruppantenn som baseras på de metoder som beskrivs i avhandling har också föreslagits och dess prestanda har utvärderats med den föreslagna metoden. / <p>QC 20171121</p>

This thesis introduces, for the first time, a novel 4-bit, metal-oxide-metal (MOM) digital capacitor switching array (MOMDCSA) which has been implemented into a wideband CMOS voltage controlled oscillator (VCO) for 5 GHz WiMAX/WLAN applications. The proposed MOMDCSA is added both in series and parallel to nMOS varactors. For further gain linearity, a wider tuning range and minor phase noise variations, this varactor bank is connected in parallel to four nMOS varactor pairs, each of which is biased at a different voltage. Thus, VCO tuning gain reduces and optimal phase noise variation is obtained across a wide range of frequencies. Based on this premise, a wideband VCO is achieved with low phase noise variation of less than 4.7 dBc/Hz. The proposed VCO has been designed using UMC 130 nm CMOS technology. It operates from 3.45 GHz to 6.23 GHz, with a phase noise of -133.80 dBc/Hz at a 1 MHz offset, a figure of merit (FoM) of -203.5 dBc/Hz. A novel microstrip low-phase noise oscillator is based on a left-handed (LH) metamaterial bandpass filter which is embedded in the feedback loop of the oscillator. The oscillator is designed at a complex quality factor Qsc peak frequency, to achieve excellent phase noise performance. At a centre frequency of 2.05 GHz, the reported oscillator demonstrates, experimentally, a phase noise of -126.7 dBc/Hz at a 100 kHz frequency offset and a FoM of -207.2 dBc/Hz at a 1 MHz frequency offset. The increasing demands have been placed on the electromagnetic compatibility performance of VCO devices is crucial. Therefore, this thesis extends the potential of highly flexible and conductive graphene laminate to the application of electromagnetic interference (EMI) shielding. Graphene nanoflake-based conductive ink is printed on paper, and then it is compressed to form graphene laminate with a conductivity of 0.43×105 S/m. Shielding effectiveness is experimentally measured at above 32 dB as being between 12GHz and 18GHz, even though the thickness of the graphene laminate is only 7.7µm. This result demonstrates that graphene has great potential for offering lightweight, low-cost, flexible and environmentally friendly shielding materials which can be extended to offering required shielding from electromagnetic interference (EMI), not only for VCO phase noise optimisation, but also for sensitive electronic devices.

Orientador: Ronei Jesus Poppi / Tese (doutorado) - Universidade Estadual de Campinas, Instituto de Química / Made available in DSpace on 2018-08-26T13:27:08Z (GMT). No. of bitstreams: 1 Souza_AndreMarcelode_D.pdf: 34076641 bytes, checksum: 9b864adff6bf9857ffe47d6b6afee68a (MD5) Previous issue date: 2015 / Resumo: As pesquisas atuais apontam que a espectroscopia no infravermelho próximo (NIR) é a técnica alternativa mais promissora para a determinação de carbono orgânico do solo (SOC) nos laboratórios de todo o mundo em substituição total ou parcial aos métodos tradicionais de via úmida. Considerado este fato, foi desenvolvido e validado um método para a determinação de SOC por espectroscopia NIR, visando seu empregado como método de rotina em laboratórios de análise de solos do Brasil. Para este fim, foram construídos modelos de calibração multivariada a partir de um número expressivo de amostras de solos (1490 amostras, 2.980 espectros) que englobam a variabilidade de solos brasileiros. Estes modelos foram validados através da submissão dos valores previstos das concentrações de matéria orgânica do solo (SOM) ao Programa de Análise de Qualidade de Laboratórios de Fertilidade (PAQLF). As questões envolvendo a transferência de calibração entre múltiplos instrumentos também foram abordadas e a regressão por vetores de suporte (SVR) foi avaliada como alternativa à regressão em mínimos quadrados parciais (PLS). Os resultados alcançados comprovaram de maneira contundente a robustez do método proposto e indicaram que o mesmo pode substitui o método de via úmida, superando seu desempenho em alguns casos. No estudo de transferência de calibração, foi demonstrado que quando dois ou mais espectrofotômetros NIR são empregados na aquisição dos dados, recomenda-se que ambos sejam de mesma configuração. Porém, quando instrumentos diferentes foram envolvidos, o método de atualização do modelo através da matriz aumentada apresentou resultados satisfatórios em relação aos demais métodos avaliados. Existem, no entanto, pelo menos dois gargalos da implementação da espectroscopia NIR em análises de rotina: (1) o elevado custo dos instrumentos em relação ao orçamento dos laboratórios de análise de solos no Brasil; e (2) a necessidade do emprego da quimiometria na etapa de modelagem dos dados. Ambas as questões podem ser solucionadas com políticas de subsídios para compra de instrumentos e intensivos treinamentos em quimiometria e espectroscopia NIR, que podem ser oferecidos pela Empresa Brasileira de Pesquisa Agropecuária e por instituições de ensino superior do Brasil / Abstract: Current research indicates that near infrared spectroscopy (NIR) is the most promising alternative technique for the determination of soil organic carbon (SOC) in laboratories around the world in total or partial replacement traditional wet chemistry methods. Considering this fact, in this research it was developed and validated a method for determination of SOC by NIR spectroscopy, aiming its use in soils laboratories in Brazil as a routine analysis method. To this end, multivariate calibration models were constructed from a large number of soil samples (samples 1490, 2980 spectra) covering the variability of brazilian soils. These models were validated by the submission of the predicted concentrations of soil organic matter (SOM) in the Quality Program of Analysis of Fertility Laboratories (PAQLF). Issues involving the calibration transfer among several instruments were discussed and the support vector regression (SVR) was evaluated as an alternative to PLS. The results proved in a conclusive way the robustness of the proposed method and indicated that it can replace the wet chemistry method, outperforming it in some cases. Some general recommendations that can be drawn from this work are: when two or more NIR spectrophotometers are involved, it is recommended purchase or apply those of same configuration because the transfer methods evaluated generate better models when compared to those of different configuration. However, when different instruments are involved, the method of model updating through the augmented matrix showed satisfactory results when compared to other methods evaluated. There are at least two bottlenecks of the implementation of the NIR spectroscopy method in routine analysis of soil laboratories: (1) the cost of NIR spectroscopy instruments and their maintenance are considered high in relation to the budget of the laboratories of soil analysis in Brazil and (2) the spectral data treatment, which requires the use of chemometrics. Both aspects that hinder the implantation of NIR spectroscopy as a routine method can be solved, with a policy of subsidies to purchase equipment and intensive training in chemometrics that can be offered by Brazilian Corporation of Agricultural Research (Embrapa) and also by brazilian teaching institutions / Doutorado / Quimica Analitica / Doutor em Ciências

La thermoélectricité est considérée comme une source prometteuse de l'énergie puisqu'elle est capable de convertir directement la chaleur en électricité. Ceci permet de récupérer la chaleur dissipée sans causer de la pollution. Cependant, les options applicatives à grande échelle sont encore en restriction en raison du faible rendement de conversion thermoélectrique. Par conséquent, de nombreux travaux de recherche sont consacrés à l'amélioration de la performance thermoélectrique de différents matériaux, qui est caractérisée par la figure de mérite ZT. Un ZT favorable comprend simultanément un coefficient Seebeck satisfaisant, une conductivité électrique élevée et une faible conductivité thermique. Rechercher un matériau approprié avec une meilleure performance thermoélectrique est l'objectif de nos analyses. Avec les techniques de dopage, différents éléments peuvent être ajoutés dans des semi-conducteurs à différentes concentrations. La densité de charge pourrait ainsi être modifiée pour améliorer les propriétés thermoélectriques. En raison des obstacles liés à la synthèse des matériaux, des simulations numériques basées sur différentes méthodes, telles que la théorie fonctionnelle de la densité (DFT), la dynamique moléculaire (DM), sont ensuite mises en oeuvre pour estimer l'approche d'amélioration la plus prometteuse. Au cours de cette thèse, les propriétés thermoélectriques de plusieurs matériaux sont étudiées pour des applications dans différentes situations, à savoir CsSnI₃ comme un candidat potentiel avec sa haute conductivité électrique, ZnO comme un matériau thermoélectrique transparent, Bi₂Te₃ comme un traditionnel matériau avec d'autres améliorations et la cellulose comme futur semi- conducteur organique. Comme la DFT ne concerne que les propriétés des électrons (coefficient de Seebeck, conductivité électrique, conductivité thermique due aux électrons), la conductivité thermique du réseau n'est pas incluse ici. Par conséquent, DFT avec des déplacements finis et DM sont utilisés comme méthodes complémentaires pour établir la conductivité thermique due aux phonons. De cette façon, cette thèse est divisée en deux parties. Dans la première partie, des contextes théoriques de DFT sont introduits à partir de l'équation de Schrödinger. Les résultats des simulations DFT classiques sont présentés par la suite. En utilisant des positions atomiques issues de mesures expérimentales, nous avons lancé la relaxation de la structure cristalline pour assurer que chaque atome dans le système est à sa position d'équilibre. Les structures de bande d'énergie électronique sont également calculées pour valider les configurations de calcul (énergie de coupure, conditions de convergence, etc.). Une cartographie complète des valeurs propres dans l'espace réciproque est faite et les propriétés thermoélectriques sont calculées en résolvant les équations de transport de Boltzmann. Dans la deuxième partie, les théories de base des phonons sont mentionnées, suivies des introductions des méthodes en DFT avec des déplacements finis et en DM. Nous avons mis en oeuvre des simulations DM pour étudier l'influence du dopage à l'aluminium sur la conductivité thermique du réseau pour ZnO. Nous avons également utilisé la méthode en DFT avec des déplacements finis pour étudier la variation de la conductivité thermique de l'alliage Bi₂Te₃₋ₓSeₓ. / Thermoelectricity is considered a promising source of energy since it is able to directly convert heat into electricity. This makes it possible to recover dissipated heat without causing pollution. However, large-scale applicative options are still under restriction because of the dim thermoelectric conversion yield. Therefore, numerous research works are dedicated to improving thermoelectric performance of different materials, which is characterized by the dimensionless figure of merit ZT. A favorable ZT includes simultaneously a satisfying Seebeck coefficient, a high electrical conductivity and a low thermal conductivity. To seek a suitable material with a better thermoelectric performance is the objective of our analyses. With doping technics, different elements can be added into semi-conductors within different concentrations. The charge density could be thus modified in order to change thermoelectric properties. Due to hurdles related to materials synthesis, numerical simulations based on different methods, such as density functional theory (DFT), molecular dynamics (MD), are then implemented to estimate the most promising improvement approach. During this thesis, thermoelectric properties of several materials are investigated for applications in different situations, i.e. CsSnI₃ as a potential candidate with its high electronic conductivity, ZnO as a transparent thermoelectric material, Bi₂Te₃ as a traditional material with further improvements and cellulose as future organic semi-conductor. As DFT concerns only properties of electrons (Seebeck coefficient, electric conductivity, thermal conductivity due to electrons), lattice thermal conductivity is not included herein. Therefore, DFT with finite displacement and MD are used as a complementary method to establish thermal conductivity due to phonons. In this way, this thesis is divided into two parts. In the first part, theoretical backgrounds of DFT are introduced starting with Schrödinger equation. Results of classical DFT simulations are presented afterwards. By using atomic positions from experimental measurements, we launched crystal structure relaxation to ensure that every atom in the system is at its equilibrium position. Electronic band structures are also calculated to validate calculation configurations (cutoff energy, convergence conditions, etc.). A full mapping of Eigenvalues in reciprocal space is realized and thermoelectric properties are calculated by solving Boltzmann transport equations. In the second part, basic theories of phonons are mentioned, followed by introductions of DFT with finite displacements and MD methods. We implemented MD simulations to study the influence of aluminum doping on lattice thermal conductivity for ZnO. We also used DFT with finite displacements method to study lattice thermal conductivity variation of Bi₂Te₃₋ₓSeₓ alloy.