Ce travail porte sur l’étude des phénomènes induits par implantation d’hydrogène et/ou d’hélium dans le silicium monocristallin. Le cloquage et l’exfoliation dus à la coimplantation d’hélium et d’hydrogène ont été étudiés en fonction des paramètres d’implantation (énergie, fluence, courant, rapport H/He) et des conditions de recuit. Un comportement de type fenêtre à été observé dont le maximum de surface exfoliée dépend uniquement de la fluence. Deux mécanismes d’exfoliation liés aux régimes de fluence ont été identifiés et discutés. D’autre part, la microstructure des échantillons a été étudié par MET, et les déformations ont été mesurées par diffraction des Rayons X. Un modèle décrivant la distribution des contraintes dans le substrat implanté a été proposé. Le phénomène de delamination des substrats qui apparaît pour des conditions particulières d’implantation a également été étudié, comparé aux phénomènes de cloquage et exfoliation, et expliqué en utilisant des concepts de la mécanique de la fracture. Enfin, l’interaction élastique entre précipités d’He et d’H a été étudiée pour des profils d’implantation superposés et décalés. Dans ce dernier cas, nous avons montré que le champ de contraintes générées par les plaquettes d’hélium en surpression pouvait être utilisé comme source locale de contraintes pour contrôler la formation et la croissance de plaquettes d’hydrogène. Afin d’interpréter nos résultats expérimentaux, nous avons développé un modèle basé sur l’interaction élastique pour la nucléation des précipités dans un solide semi-infini. / The present work relates an investigation of H2 + and He+ coimplanted (001)-Si substrates. The phenomena of blistering and exfoliation were studied by SEM as a function of the implantation parameters (energy, fluence, current and H/He ration) and annealing protocol. A window behavior as function of the implanted fluence was observed and two distinct fluence dependents mechanisms of exfoliation were indentified and discussed. The microstructure of the implanted samples was studied using TEM and related to ballistic effects and stress-strain dependent interactions. The strain was measured using DRX and a model to describe the stress-strain distribution into the implanted layer is developed. A new phenomenon of delamination of thin layer from implanted Si substrates was observed to emerge from particular implantation conditions. The behavior was studied and explained using fracture mechanics concepts and contrasted to blistering/exfoliation processes. Finally, the elastic interaction between He and H plate-like precipitates giving rise to arranged nanostructure was demonstrated and studied using TEM. An elasticity based model was developed to understand the behavior. The result set the basis for further developments of nanostructures within a crystalline matrix by manipulating preferential orientations of precipitates in nanometric scale.

Ce travail porte sur l’étude des phénomènes induits par implantation d’hydrogène et/ou d’hélium dans le silicium monocristallin. Le cloquage et l’exfoliation dus à la coimplantation d’hélium et d’hydrogène ont été étudiés en fonction des paramètres d’implantation (énergie, fluence, courant, rapport H/He) et des conditions de recuit. Un comportement de type fenêtre à été observé dont le maximum de surface exfoliée dépend uniquement de la fluence. Deux mécanismes d’exfoliation liés aux régimes de fluence ont été identifiés et discutés. D’autre part, la microstructure des échantillons a été étudié par MET, et les déformations ont été mesurées par diffraction des Rayons X. Un modèle décrivant la distribution des contraintes dans le substrat implanté a été proposé. Le phénomène de delamination des substrats qui apparaît pour des conditions particulières d’implantation a également été étudié, comparé aux phénomènes de cloquage et exfoliation, et expliqué en utilisant des concepts de la mécanique de la fracture. Enfin, l’interaction élastique entre précipités d’He et d’H a été étudiée pour des profils d’implantation superposés et décalés. Dans ce dernier cas, nous avons montré que le champ de contraintes générées par les plaquettes d’hélium en surpression pouvait être utilisé comme source locale de contraintes pour contrôler la formation et la croissance de plaquettes d’hydrogène. Afin d’interpréter nos résultats expérimentaux, nous avons développé un modèle basé sur l’interaction élastique pour la nucléation des précipités dans un solide semi-infini. / The present work relates an investigation of H2 + and He+ coimplanted (001)-Si substrates. The phenomena of blistering and exfoliation were studied by SEM as a function of the implantation parameters (energy, fluence, current and H/He ration) and annealing protocol. A window behavior as function of the implanted fluence was observed and two distinct fluence dependents mechanisms of exfoliation were indentified and discussed. The microstructure of the implanted samples was studied using TEM and related to ballistic effects and stress-strain dependent interactions. The strain was measured using DRX and a model to describe the stress-strain distribution into the implanted layer is developed. A new phenomenon of delamination of thin layer from implanted Si substrates was observed to emerge from particular implantation conditions. The behavior was studied and explained using fracture mechanics concepts and contrasted to blistering/exfoliation processes. Finally, the elastic interaction between He and H plate-like precipitates giving rise to arranged nanostructure was demonstrated and studied using TEM. An elasticity based model was developed to understand the behavior. The result set the basis for further developments of nanostructures within a crystalline matrix by manipulating preferential orientations of precipitates in nanometric scale.

LOPES, Marcos Oliveira. Formas de (R) existir cinema: o cinema como acontecimento no corpo em Álbum de Família e em CC5 hendrix-war. 2015. 139f. – Dissertação (Mestrado) – Universidade Federal do Ceará, Programa de Pós-graduação em Comunicação Social, Fortaleza (CE), 2015. / Submitted by Márcia Araújo (marcia_m_bezerra@yahoo.com.br) on 2016-03-29T22:52:38Z No. of bitstreams: 1 2015_dis_molopes.pdf: 2098559 bytes, checksum: eeb006dde123ff07cb5c7c0785528775 (MD5) / Approved for entry into archive by Márcia Araújo(marcia_m_bezerra@yahoo.com.br) on 2016-03-29T22:58:45Z (GMT) No. of bitstreams: 1 2015_dis_molopes.pdf: 2098559 bytes, checksum: eeb006dde123ff07cb5c7c0785528775 (MD5) / Made available in DSpace on 2016-03-29T22:58:45Z (GMT). No. of bitstreams: 1 2015_dis_molopes.pdf: 2098559 bytes, checksum: eeb006dde123ff07cb5c7c0785528775 (MD5) Previous issue date: 2015 / Formas de (r) existir cinema: o cinema como acontecimento no corpo em “Álbum de família” e em “CC5 hendrix-war”; existe como uma conversa-texto em forma de pesquisa acadêmica que dialoga sobre as possibilidades de existência de cinemas em situações-cinemas experimentadas em duas proposições poéticas a partir da imersão do corpo em espaços/objetos interativos. O trabalho CC5 hendrix-war realizado em parceria entres os artistas Hélio Oiticica e Neville de Almeida, bem como o trabalho Álbum de família de minha autoria, são aqui problematizados como situações-cinemas como efeito de acontecimentos no corpo a partir da ação de um corpo-dançante. A questão que este trabalho apresenta diz da possibilidade de existência de cinema a partir de um corpo que dança no momento em que dança. Assim, a ideia de um livro-cinema que experimentado com um corpo-dançante faz existir uma situação-cinema em Álbum de Família introduz a conversa e tenciona em suas particularidades as capacidades de um conjunto de fotografias poderem ser experimentadas como cinema. Dialogo com os conceitos de situação-cinema (PARENTE, 2009), Transcinemas (MACIEL, 2009), estética do desaparecimento (FURTADO, 2010) e acontecimento (DELEUZE, 2007). O segundo momento desse dialogo trata da possibilidade de existência de cinema a partir a observação sobre os quasi-cinemas de Hélio Oiticica e Neville de almeida. Assim, o conceito de duração é problematizado no sentido de compreender mais atentamente como se efetivam as propostas poéticas em Oiticica/Neville no que se refere as suas experimentações poéticas com o cinema. Aqui, dialogo com os conceitos de quasi-cinema (OITICICA/NEVILLE, 1973), duração (BERGSON, 1999), Linha de fuga (PELBART,2007), e cartografia(DELEUZE &GUATTARI, 2010). A terceira parte do trabalho trata da possibilidade de existência de cinema em CC5 hendrix-war na medida da ação de um corpo que dança. Dialogo com os conceitos de dança (NIETZSCHE, 2002), corpo-dançante (GADELHA, 2010), movimento dançado (GIL, 2006) e agenciamento (DELEUZE, 1998). Nos termos de Deleuze e Guattari a cartografia pretendida no ínterim dessa conversa visa acompanhar um processo, e não representar um objeto. A cartografia como um modo de existência para essa conversa cria seus próprios movimentos, seus próprios desvios. É um projeto que pede passagem, que fala que incorpora sentimentos, que afeta e que é afetado pelos processos pelos quais se efetiva. O que proponho como maneira de fazer pesquisa é uma espécie de mapa do presente que demarca um conjunto de fragmentos, em eterno movimento de produção. Assim, no contexto do plano traçado aqui é pertinente reafirmar que o cinema como acontecimento no corpo nas situações-cinemas aqui problematizadas (r)existe, ou seja, o cinema existe e também resisti em “Álbum de família” e em “CC5 hendrix-war” a partir de um corpo que dança no momento em que dança.

Tese (doutorado)—Universidade de Brasília, Intituto de Ciências Sociais, Departamento de Sociologia, 2011. / Submitted by Luciana Pontes Lemos (lucianalemos@bce.unb.br) on 2012-02-17T13:24:17Z No. of bitstreams: 1 2011_MarcioHagihara.pdf: 1632170 bytes, checksum: f9d4f234a0eceb58d29c6d58b65975e1 (MD5) / Rejected by Guimaraes Jacqueline(jacqueline.guimaraes@bce.unb.br), reason: Luciana, Por favor, proteger o arquivo. Grata, Jacqueline on 2012-02-17T13:52:13Z (GMT) / Submitted by Luciana Pontes Lemos (lucianalemos@bce.unb.br) on 2012-02-17T13:55:13Z No. of bitstreams: 1 2011_MarcioHagihara.pdf: 1632170 bytes, checksum: f9d4f234a0eceb58d29c6d58b65975e1 (MD5) / Approved for entry into archive by Guimaraes Jacqueline(jacqueline.guimaraes@bce.unb.br) on 2012-02-17T14:10:53Z (GMT) No. of bitstreams: 1 2011_MarcioHagihara.pdf: 1632170 bytes, checksum: f9d4f234a0eceb58d29c6d58b65975e1 (MD5) / Made available in DSpace on 2012-02-17T14:10:53Z (GMT). No. of bitstreams: 1 2011_MarcioHagihara.pdf: 1632170 bytes, checksum: f9d4f234a0eceb58d29c6d58b65975e1 (MD5) / O advento das instalações e de obras que visam à interação com o público, criando ambientes que envolvem percepções sinestésicas, estão presentes nas mais célebres bienais e exposições de arte pelo mundo. A arquitetura e a arte brasileiras contribuíram bastante para a mudança espacial da obra de arte. O modernismo brasileiro forjou o discurso de ampliação dos princípios das artes plásticas para a construção da cultura nacional. A dimensão construtiva das artes plásticas refletiuse na ampliação da criação plástica dos singelos quadros de cavalete burgueses para os murais sociais de Portinari e para a nacional e monumental arquitetura do Grupo Carioca. Oscar Niemeyer e Lucio Costa projetaram a pretensão máxima de ampliação de escala da obra de arte: Brasília. Frustrada a utopia, irrompe o Movimento Neoconcreto, cuja crítica infligiu-se contra a arquitetura, o espaço clássico e o conceito de cultura nacional, por meio da quebra da tradicional associação simbólica entre arte e cultura. A ligação entre a arquitetura e o Movimento Neoconcreto só faz sentido se ligada à análise iconográfica, pois o exame do discurso escrito – que é uma das obsessões de nossa cultura pela palavra – é insuficiente para estabelecer tal ligação. Entre maquetes e instalações labirínticas de Hélio Oiticica, observa-se a crítica visual da coerência espacial imposta pela política cultural das elites brasileiras. Mais do que isso, a arte brasileira deu sua contribuição, modificando a configuração espacial da obra de arte. Foi preciso destruir a última grande regra da arte, através da morte do Plano. ___________________________________________________________________________________ ABSTRACT / The advent of installations and artworks that aims interaction with the public by creating environments that involve synesthesic perceptions are present in the most famous biennial art exhibition around the world. Brazilian art and architecture contributed enough for the change of the spatial notions of work of art. Brazilian modernism created a speech which aimed to extend the principles of art for the construction of national culture. The constructive dimension of art reflected on an expansion: from the creation of single plastic easel paintings of bourgeois, to the social murals of Portinari, and to the national and monumental architecture of Carioca School. Oscar Niemeyer and Lucio Costa projected the intention of extending the maximum scale of the work of art: Brasilia. The utopia was over, and then the Neo-concrete Movement breaks with its criticism against the architecture, classical space and the concept of national culture, destroying the traditional symbolic association between art and culture. The connection between architecture and Neo-concrete Movement only makes sense if it is related to the iconographic analysis, because the examination of written speech – which is one of the obsessions of our culture – is not enough to establish such connection. Between Helio Oiticica’s models and neo-concretist labyrinthine installations, there is the criticism against visual spatial coherence imposed by the cultural policy of the Brazilian elites. More than this, the Brazilian arts contributed with the changing of the spatial scope of work of art. It was necessary to destroy the last great rule of the art, through the death of the Plan. ___________________________________________________________________________________ RESUMÉ / L'avènement de l’installation et d’ oeuvre d’art qui visant à l'interaction avec le public à travers de la création des environnements qui impliquent des perceptions synèsthesique sont présentes dans la plus célèbre exposition biennale d'art dans le monde. L'art et l'architecture brésilienne ont contribué suffisamment à la transformation spatiale de l'oeuvre d'art. Le modernisme brésilien a établi un discours de vulgarisation des principes de l'art pour la construction de la culture nationale. La dimension constructive de l'art reflète dans l'expansion d’oeuvres d’art plastiques: de la peintures de chevalet de bourgeois, à travers les peintures murales de Portinari et jusqu’à social et national monumentale l'architecture d’École Carioca. Oscar Niemeyer et Lucio Costa ont conçu l'intention d'étendre la maximale l'échelle de l'oeuvre d'art: Brasília. Frustré l'utopie, le Mouvement Neo-concrète a provoqué des critiques contre l'architecture, l'espace classique et le concept de la culture nationale, a travès de la rupture de la traditionnelle association symbolique entre l'art et culture. Le lien entre l'architecture et le Mouvement Neo-concrète n'a de sens que si liées à l'analyse iconographique, parce que l'examen du discours écrit – qui est l'une des obsessions de notre culture, le mot – est insuffisante pour établir tel lien. Entre les labyrinthiques et rhizomateuses maquettes et installations de Hélio Oiticica, il y a une critique de la cohérence dans l'espace visuelle imposée par la politique culturelle de l'élite brésilienne. Plus que cela, l'art brésilien donnait sa contribution, la modification de la notion spaciale de l’oeuvre d'art. Il faut détruire la dernière grand règle de l’art, à travers de la mort du Plan.

Many scholars have considered Cuban American artist Ana Mendieta to be a translator of Afro-Cuban culture. In her 2019 monograph on the artist, for example, Genevieve Hyacinthe writes: “brownness made Mendieta a powerful translator of Black Atlantic forms into contemporary art language because she was not, and could never be, part of the dominant white culture.” Mendieta also announced herself as a translator (and inheritor) of Siboney and Taino cultures. Her gallery notes that to celebrate her return to Cuba’s “maternal breast” as an adult, the artist titled the rock carvings she made there with “names of zemis, or Taíno spirits, such as Bacayu for ‘Light of Day.’” I argue that alongside her claims on Taino cultural heritage we might consider her actual ancestry and claims on Indigenous women in the art of Cuban settlers before her. My dissertation considers Mendieta as a translator not of Taino myths or Black cultural practices but of ethnological texts and nationalistic folklore which catalogued and caricatured Black and Indigenous cultures. “Bacayu,” for example, is not a Taino “zemi” but rather a word she culled from a glossary of Black and Indigenous terms: a performance of knowledge over Indigenous cultures rather than a Taino cultural product. It hails from a lecherous story written by a Havana dentist about the death of an “Indian doncella.” Each chapter considers her translations of such pieces, focusing in particular on her translation choices which I suggest are motivated by her feminist and anti-imperial politics. My first chapter considers the influence of ethnographic studies on Abakuá and particularly the writings of Fernando Ortiz in her Iowa campus performances which reference crime scenes and “sacrificial” initiation ceremonies. Rather than offering unmediated access to Black religious practices, I suggest she is performing an abased view of Abakuá as seen through the (exterminationist) lens of Ortiz’s scholarship from his criminological ethnography, Los negros brujos (1906), to his less punitive but still highly fetishizing account of Abakuá in “La ‘tragedia’ de los ñáñigos” (1950). I don’t believe Mendieta translates this work to oppress Black people. Rather as a bodywork artist composing a militant, corporal language of feminist critique, she aims the violence of cultural translation toward her chauvinistic art school cohort. The second chapter considers her literary translation of “La Venus Negra, based on a Cuban legend,” which was composed by Adrián del Valle, Ortiz’s secretary at La Sociedad Económica de los Amigos del País for which he collated Cuba’s first public library among other projects. The original legend can be contextualized by del Valle’s broader stewardship of Cuban letters: he penned “La Venus Negra” for a collection celebrating the Centenary of Cienfuegos from the family notes of a prominent cienfueguero, Pedro Modesto. Examining the tacky national showcase in which the legend originally appears, I consider the ways Mendieta repositions la Venus Negra as a display of her own “will to continue being Other.” In particular, her translation imposes a “Siboney” ancestry on la Venus Negra and dispenses with the conditions which determine the protagonist’s muteness (in the original, la Venus Negra is a nude Black woman who is captured and displaced from her island hideout by criollo enslavers). In Mendieta’s translation la Venus is not muted Black protest incarnate but becomes an anti-colonial symbol. Mendieta publishes the piece in the feminist magazine Heresies, illustrating the legend with a silhouette of her own body from her Silueta Series. Again, I don’t think Mendieta poses as a Ciboney woman or absents Black women in a gesture of ill will toward Black and Indigenous people. Rather, she does so as an anti-imperial strategy consistent with Fidel Castro’s cadre, as her unavowed translation of Roberto Fernández Retamar’s “Calibán” into her “Dialectics of Isolation: An Exhibition of Third World Women Artists of the United States” curatorial statement indicates. In the essay, Retamar, a white Cuban scholar, aligns the revolution with Black and Indigenous Cuba by “reclaiming” the caricature Caliban, which, as Coco Fusco writes, Shakespeare himself had based on an “Indian” exhibited in London. In the third chapter, I consider Mendieta’s Esculturas Rupestres, not as tributes to Taino spirits but as monuments of settler longing for mutilated Indigenous women. The legend I mentioned in the introductory paragraph, “Bacayu,” for example, is settler fanfiction about a daughter of a “cacique” whose death portends the coming of the white man and includes a lengthy description of the dead woman’s body. I also point toward the misnamings of Black women which appear within this rock series (Black Venus, Mother) which are often overlooked by scholars who ask us to read the work as Taino myth. Finally, building on these themes, I suggest a comparison to the work of Brazilian artist Hélio Oiticica: emphasizing the similarities in their “cannibalistic” approaches to translation. Although differently aligned politically (leftist, anarchist), Oiticica’s family, like Mendieta’s, were culturally and politically prominent settlers; and, like Mendieta, Oiticica is often read as a translator of Black Atlantic culture. Further both artists engaged in the caricaturing of Indigenous “American” cultures. In New York, Oiticica translated Oswald de Andrade’s “Manifesto Antropófago” (1928) to contextualize his work and the work of his friends. Artists in Brazil had adapted de Andrade’s manifesto into a translation program “cannibalizing” European and North American cultures, a practice they misidentified as Tupi as de Andrade had. Comparing Mendieta and Oiticica as translators reveals shared patterns of Latin American vanguards employing caricatures of Black and Indigenous cultures in anti-imperial performances. These caricatures and their resemblance to caricatures in the U.S. also point to older (and enduring) transnational networks of white nationalism in the Americas.

This study takes up the phrase ‘the skin of all’ as a means to explore the tension between the singular and the collective, and between union and estrangement. I examine aesthetic, symbolic, and theoretical attempts at unification amidst various forms of difference and the political imperatives and implications attached to this aim. The goal is to analyze how such attempts were related to the development of artistic institutions and discourses as well as to broader sociopolitical conditions within and beyond Brazil’s dictatorship era (1964-1985). This dissertation reflects on the reemergence of the discourse of antropofagia throughout the sixties and seventies in Brazil, a concept first developed in the 1920s as an explicit rejection of the privileged position of European culture and the assertion of a unified Brazilian national identity forged from its colonial histories and the co-presence of indigenous, African, and European identities. I emphasize that antropofagia has functioned as a counterhegemonic proposition reliant on the appropriation of marginal racial positions and their integration into a larger national framework, while still acknowledging the productive potentials that antropofagia’s collapsing of boundaries facilitates. My project challenges simplified narratives of harmonic exchange, embracing contradiction and the tensions of privilege, access, and power. Examining primary sources, contemporaneous writings and present-day scholarship, this project interrogates the mythos, life, and after-life of Pape and Oiticica’s performance and participatory works and analyzes these alongside both artist’s media-based practices. Analyzing the broader aims and implications of Lygia Pape and Hélio Oiticica’s engagement with Black and indigenous cultures, I unpack the ways their works irresolutely engage with race in the Brazilian context and how a primitivistic essentialism has been central to these works and their reception.

O objetivo deste trabalho e a determinação dos coeficientes de viscosidade de cisalhamento e condutividade térmica de gases ideais quânticos. No cálculo dos coeficientes de transporte foram considerados dois aspectos: uma estatística quântica com seções transversais quânticas e uma estatística quântica com seções transversais quânticas. No primeiro caso, e utilizado um método alternativo para a determinação das aproximações sucessivas (ate a quinta ordem) para os coeficientes de transporte dos gases Helio 4, Helio 3, para-hidrogênio e orto-hidrogênio. No caso de estatística quântica desenvolvida uma teoria com base no método dos momentos de Grad e na equação de Uehling- Uhlenbeck, com a finalidade de determinar as express6es algébricas para os coeficientes de transporte. Esta teoria e baseada em 13 momentos, de densidade, velocidade, tensor pressão e fluxo de calor. Do conhecimento da função de distribuição em termos dos momentos, as equações constitutivas são determinadas e os coeficientes de transporte seguem de um método iterativo semelhante ao procedimento Maxwelliano. / The aim of this work is the determination of the coefficients of shear viscosity and thermal conductivity of quantum ideal gases. In the calculation of the transport coefficients two aspects have been taken into account: a classical statistical with quantum cross-sections and a quantum statistical with quantum cross-sections. In the first case, an alternative method is used for the determination of the successive approximations (up to the fifth order) to the transport coefficients of the gases helium 4, helium 3, para-hydrogen, ortho-hidrogen. In the case of quantum statistical a theory based on method of moments of Grad and on the Uehling-Uhlenbeck equation is developed in order to determine the algebraic expressions to the transport coefficients. This theory is based on 13 moments of density, velocity, pressure tensor and heat flux. From the knowledge of the distribution function the constitutive equations are determinate and the transport coefficients follow from an iterative method akin to the 11axwellian procedure.

O objetivo deste trabalho e a determinação dos coeficientes de viscosidade de cisalhamento e condutividade térmica de gases ideais quânticos. No cálculo dos coeficientes de transporte foram considerados dois aspectos: uma estatística quântica com seções transversais quânticas e uma estatística quântica com seções transversais quânticas. No primeiro caso, e utilizado um método alternativo para a determinação das aproximações sucessivas (ate a quinta ordem) para os coeficientes de transporte dos gases Helio 4, Helio 3, para-hidrogênio e orto-hidrogênio. No caso de estatística quântica desenvolvida uma teoria com base no método dos momentos de Grad e na equação de Uehling- Uhlenbeck, com a finalidade de determinar as express6es algébricas para os coeficientes de transporte. Esta teoria e baseada em 13 momentos, de densidade, velocidade, tensor pressão e fluxo de calor. Do conhecimento da função de distribuição em termos dos momentos, as equações constitutivas são determinadas e os coeficientes de transporte seguem de um método iterativo semelhante ao procedimento Maxwelliano. / The aim of this work is the determination of the coefficients of shear viscosity and thermal conductivity of quantum ideal gases. In the calculation of the transport coefficients two aspects have been taken into account: a classical statistical with quantum cross-sections and a quantum statistical with quantum cross-sections. In the first case, an alternative method is used for the determination of the successive approximations (up to the fifth order) to the transport coefficients of the gases helium 4, helium 3, para-hydrogen, ortho-hidrogen. In the case of quantum statistical a theory based on method of moments of Grad and on the Uehling-Uhlenbeck equation is developed in order to determine the algebraic expressions to the transport coefficients. This theory is based on 13 moments of density, velocity, pressure tensor and heat flux. From the knowledge of the distribution function the constitutive equations are determinate and the transport coefficients follow from an iterative method akin to the 11axwellian procedure.

A formação de camadas de cargas elétricas na superfície de Hélio liquido e em filmes de H´leio sobre um substrato está bem estabelecida tanto teórica quanto experimentalmente. Não existia, porém, até o presente, um cálculo auto-consistente para essas camadas de cargas, pois no regime de baixas densidades eletrônicas, estes sistemas podem ser tratados como o problema de 1-elétron. Em nosso trabalho incluímos os efeitos de muitos corpos usando a aproximação de Hartree-Fock e, via cálculos auto-consistentes, mostramos que estes efeitos tornam-se relevantes para densidades a partir de 108 e/cm2 para elétrons sobre Hélio e 103 e/ cm2 para elétrons sobre filme de Hélio. Calculamos também a mobilidade desses elétrons, em superfície de Hélio, incluindo dois mecanismos diferentes de espalhamento; as interações elétron-ripplons e elétrons-átomos de vapor. Usando nossos cálculos auto-consistentes obtivemos resultados que melhores concordam com dados experimentais para a mobilidade, em regimes de altas densidades eletrônicas / The formation of electric charged layers outside liquid Helium and outside films are well understood experimentally as well as theoretically. But, until today, there was not a self-consistent calculation for these electronic layers because, at low densities, these system can be treated as a one-electron problem. In this work we have included the many-body effects using the Hartree-Fock approximations and, via self-consistent calculations, we pointed out that these effects are relevants for densities above 108 e/cm2 for liquid Helium and 103 e/ cm2 for Helium films. We also have calculated the electronic mobility due to different scattering mechanisms: electron-ripplon and electron-vapour interactions. Using our self-consistents calculations we have obtained results that fit very well the experimental data, at high densities

Made available in DSpace on 2015-03-04T18:51:11Z (GMT). No. of bitstreams: 1 tese_erasmo_digital.pdf: 2003361 bytes, checksum: 220a10261604ff1d47174ccfbcec41a9 (MD5) Previous issue date: 2009-04-03 / Coordenacao de Aperfeicoamento de Pessoal de Nivel Superior / The element helium, found mainly in natural gas reserves, condenses at temperature of 4.2K, and is the unique known substance that remains in liquid to absolute zero. In the liquid phase, the helium presents still another phase change in 2.19K, where passes of common liquid to superfluous liquid, with almost zero viscosity. These properties give the helium important applications. One of the major applications is as a coolant in superconductors, such as in the particle accelerator LHC, which is being built in the French border with Switzerland, in magnetic resonance devices, artificial satellites, etc.. In this paper, we present two mathematical models for heat transfer in liquid helium. The first model, considering only macroscopic movements, is derived based on constitutive laws of Fourier and Gorter-Mellink. The second model, based on techniques of Fremond, includes microscopic movements and can be seen as a regularization of the first model. Both models are governed by highly nonlinear differential equations resulting from the nonlinearity of the law of Gorter-Mellink and change of phase. Both models can be considered special cases of the Stefan problem in two phases, with phase one of the heat flux is governed by non-linear equation of the problem known as p-Laplacian, with p = 4/3. We also presented techniques to efficiently solve the problem of p-Laplacian, both for large values of p, p>> 2, and for values of p close to 1, which are major numerical challenges. Are proposed two simple iterative methods, one based on the method of quasi-Newton, with the relaxation term and the other by the Helmholtz decomposition, creating a system of equations whose matrices are constant, which reduces significantly the computational cost. Numerical experiments are conducted to test the efficiency of numerical models proposed and the algorithms developed for solving systems of nonlinear algebraic equations arising from approximations by finite elements. Are also presented results of studies of convergence, showing rates of optimal or near optimal convergence, comparable to that of interpolates. For the problem with phase change, due to the discontinuity of the gradient of temperature on the interface separating the two phases of liquid helium, the rate of convergence is not optimal. Using adaptive mesh, it is also great rates to the problem with change of phase. Using experimental data found in literature, for the parameters of thermal conductivity, density and specific heat, temperature dependent, are also presented for validation testing of the model and examples of possible applications. In tests for validating the model, compared to the numerical solution of the mathematical model with experimental results for the temperature found in literature. / O elemento hélio, encontrado principalmente em reservas de gás natural, entra em condensação à temperatura de 4,2K, e é a única substância conhecida que permanece no estado líquido até o zero absoluto. Na fase liquida, o hélio apresenta ainda, em K, outra mudança de fase, onde passa de líquido comum à superfluido, com viscosidade praticamente nula. Estas propriedades conferem ao hélio importantes aplicações. Uma hdas principais aplicações é como agente refrigerante em supercondutores, como por exemplo, no acelerador de partículas LHC, que está sendo construído na fronteira da França com a Suíça, em aparelhos de ressonância magnética, satélites artificiais, etc. Neste trabalho, são apresentados dois modelos matemáticos para a transferência de calor no hélio líquido. O primeiro modelo, considerando apenas movimentos macroscópicos, é derivado com base nas leis constitutivas de Fourier e de Gorter-Mellink. O segundo modelo, baseado nas técnicas de Fremond, inclui movimentos microscópicos e pode ser visto como uma regularização do primeiro modelo. Os dois modelos são governados por equações diferenciais fortemente não lineares resultantes da não linearidade da lei de Gorter-Mellink e da mudança de fase. Ambos os modelos podem ser considerados casos particulares do problema de Stefan de duas fases, sendo que em uma das fases o fluxo de calor é governado pela equação não-linear do problema conhecido como p-laplaciano, com p=4/3. São também apresentadas técnicas para resolver de forma eficiente o problema do p-laplaciano, tanto para valores grandes de p, p>>2, quanto para valores de p próximos à 1, que constituem importantes desafios numéricos. Para tanto são propostos dois métodos iterativos simples, um baseado no método de quase-Newton, com termo de relaxação e, outro através da decomposição de Helmholtz, gerando um sistema de equações cujas matrizes são constantes, o que diminui significativamente o custo computacional. Experimentos numéricos são realizados para testar a eficiência dos modelos numéricos propostos bem como dos algoritmos desenvolvidos para resolver os sistemas de equações algébricas não lineares resultantes das aproximações por elementos finitos. São apresentados resultados de estudos de convergência, mostrando taxas de convergência ótimas ou quase ótimas, comparáveis às das interpolantes. Para o problema com mudança de fase, devido à descontinuidade do gradiente da temperatura sobre a interface que separa as duas fases do hélio líquido, as taxas de convergência não são ótimas. Usando malhas adaptativas, consegue-se taxas ótimas também para o problema com mudança de fase. Usando dados experimentais, encontrados na literatura, para os parâmetros de condutividade térmica, densidade e calor específico, dependentes da temperatura, são também apresentados testes de validação do modelo e exemplos de possíveis aplicações. Nos testes de validação do modelo, compara-se a solução numérica do modelo matemático com resultados experimentais para a temperatura, encontrados na literatura.