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  • 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.
91

Vliv antidiabeticky působících látek na vývoj inzulínové rezistence a neurodegenerativních změn v myších modelech diabetu 2. typu / Impact of antidiabetic substances to development of insulin resistance and neurodegenerative changes in mouse models of type 2 diabetes

Mikulášková, Barbora January 2014 (has links)
Numerous epidemiological and experimental studies have shown that patients suffering from metabolic disorders such as type 2 diabetes mellitus (TDM2), insulin resistance or obesity are at a higher risk of cognitive functions impairment and developing Alzheimer's disease (AD). Impairment of insulin signalling in the brain could contribute to two pathological changes which leads to AD development that include insoluble senile plaques and neurofibrillary tangles, containing an abnormally hyperphosphorylated tau protein (Tau). This work is focused on investigating of insulin signaling in hippocampi in the brains of mice models of insulin resistence, impact of disturbed insulin signaling on hyperphosphorylation of Tau, and possible benefical efect of insulin sensitizing agents on insulin signaling and Tau phosphorylation in the hippocampi of diabetic mice. The first, we examined insulin signaling and phosphorylation of Tau in hippocampi in two mouse models of TDM2 - lipodystrofic A-ZIP F-1 mice and monosodium glutamate obese mice (MSG mice). We did not observe any changes in insulin signaling and Tau phosphorylation in hippocampi of A-ZIP F-1 mice compared to controls. In the hippocampi of MSG mice there was attenuated phosphorylation of kinases of insulin signalling including Ser9 of glycogen synthase...
92

Vyhodnocení protismykových vlastností povrchů vozovek na rampách dálničních křižovatek / Evaluation of Motorway Intersection Ramps Surface Skid Resistance

Kachtík, Jiří January 2012 (has links)
The aim of the master´s thesis is to evaluate the current measurement of skid resistance road surface properties of selected interchanges. Assess their development depending on the type, speed and number of vehicles, type of asphalt wearing course, directional and height ratios ramps of motorway intersections.
93

Role fúzního proteinu ETV6-RUNX1 v citlivosti leukemických buněk na L-asparaginázu / The role of ETV6-RUNX1 fusion protein in the sensitivity of leukemic cells to L-asparaginase

Staněk, Petr January 2018 (has links)
Translocation t(12;21) with the presence of the fusion gene ETV6-RUNX1 (TEL-AML1) is the most common chromosomal aberration found in acute lymphoblastic leukemia in childhood. The occurrence of the ETV6-RUNX1 is associated with excellent prognosis and high sensitivity to the treatment with the enzyme L-asparaginase (ASNase). Resistance to the drug aggravates the outlook of the patient and increases the risk of treatment failure, therefore, the CLIP working group has been for a long time involved in the identification of the mechanism of action of ASNase and the origin of the resistance to it. This thesis follows previous findings of the group and is devoted to the analysis of the importance of ETV6-RUNX1 and signalization and metabolic changes accompanying shifts in the L-asparaginase resistance. In the first part of the thesis, the knockout clones with stable increased resistance to ASNase have been established thanks to the CRISPR/Cas9 system, which created frameshift in the fusion gene. The accomplishment in this regard and removal of the fusion protein was confirmed on the level of DNA, mRNA a protein expression. The presence of other significant chromosomal aberrations affection the sensitivity to ASNase was ruled out by the means of SNP analysis. In the second part of the project, the signalization...
94

Proteomic Investigation of Endocrine Therapy Resistance in Breast Cancer Investigating the Molecular Mechanisms for SERM Resistant Cell Lines Using SILAC-Based Proteomic Approach

Al-Kabariti, Aya Y. January 2022 (has links)
Introduction: Breast cancer is the second highest cause of cancer mortality in women worldwide. Hormonal therapy is considered one of the most effective therapies and is used against luminal-type malignancies. However, 40-50% of tumour cells can develop resistance, thereby limiting the success in breast cancer treatment. In this study, mechanisms of resistance were investigated using a novel multi-stable isotope labelled amino acids (SILAC) proteomics approach in phenotype-specific breast cancer cell lines resistant to endocrine treatment. Method: In vitro chemo-sensitivity (IC50) was determined for MCF7, T47D, MDA-MB-231, MDA-MB-468, MDA-MB-453, BT-20 and MCF-10A breast cell lines using four endocrine-based therapeutic agents (Tamoxifen, 4-Hydroxytamoxifen OHT, Raloxifene, Anastrozole) to select viable strains for resistance studies. MCF7 (luminal-type A) and MDA-MB-231 (triple negative breast cancer, TNBC) were selected and initially subject to OHT or raloxifene exposure with gradual increments for 10 months. WT cells were grown in the absence of drug in parallel as passage controls. Resistant cell lines were assessed by MTT and IF for comparison with parental cell lines. Resistant cell lines, along with the passage control and a SILAC control, were grown in “light” SILAC medium together with WT strains cultured in “heavy” SILAC medium. Proteins were extracted, concentrations determined and analysed by SDS PAGE for quality control. An aliquot of each “light” cell line (resistant, passage control or SILAC control) was combined with an equal amount of “heavy” WT, trypsin digested and analysed by nano-HPLC Orbitrap Fusion mass spectrometry (2D-LC MS/MS). Proteins were identified by database searching using MascotTM. Relative changes (resistant/WT ratio) in protein levels were determined and bioinformatics tools (STRING and UniProt) used to explore significantly changed pathways associated with resistance. Western blotting was used to verify selected target proteins. Results: Four consistently resistant sublines were generated MCF7 OHT Res (2.00-fold more resistant), MCF7 Ralx Res (2.00-fold), MDA-MB-231 OHT Res (1.90-fold change) and MDA-MB-231 Ralx Res (2.00-fold), in addition to two high passage controls. ER expression by IF was decreased in MCF7 OHT Res compared to the WT and MCF7 Ralx Res, whereas CD44 was increased. Proteomic analysis revealed 2247 and 2880 total proteins in MCF7 OHT Res and MCF7 Ralx Res whilst 3471 and 3495 total proteins were identified in MDA-MB-231 OHT Res and MDA-MB-231 Ralx Res, respectively. Bioinformatics tools identified significantly changed pathways included apoptosis, cytoskeleton, cell motility and redox cell homeostasis. Components of the MAPK-signalling cascade were consistently found to be upregulated in resistant cell lines. MAPK1 (ERK2), previously associated with tamoxifen resistance was increased in MDA-MB-231 Ralx Res cell lines by 4.45-fold and confirmed by Western blotting. Sorcin, which contributes to calcium homeostasis and is also linked to multidrug resistance was increased 4.11- and 2.35-fold in MCF7 OHT Res and Ralx Res sub cell lines, respectively. Some results, such as those for c-Jun, were inconsistent between proteomic analysis and Western blotting and require further investigation. Conclusion: The unique resistant cell lines generated here, as well the MCF7 OHT resistant line, provided novel data that give insights into the biological pathways involved in mechanisms of endocrine drug resistance in breast cancer. Proteomics analysis provided extensive data on common functionality and pathways across the resistant cell lines independent of phenotype or SERM. Overall, the results provided interesting targets for re-sensitising resistant breast cancer and the potential to investigate novel combination therapies in the future. / Al-Ahliyya Amman University scholaships
95

[pt] UMA CARTOGRAFIA DOS RESTOS / [fr] UNE CARTOGRAPHIE DES DÉBRIS

NAYARA MARFIM GILABERTE BEZERRA 24 April 2020 (has links)
[pt] Esta tese, como um exercício crítico de leitura e escrita, gira em torno da noção de resto e de outras palavras que com ela se relacionam, partindo das figuras do catador e do trapeiro para refletir sobre o processo criativo como ato que aproxima artistas e pesquisadores daqueles que trabalham com o que é descartado, rejeitado e esquecido. Para tanto, apresento uma coleção de fragmentos que versam sobre o gesto de catar a partir da obra da escritora Carolina Maria de Jesus, derivando incialmente do seu conhecido Quarto de despejo para debruçar-me sobre o livro Diário de Bitita. A ênfase na obra em questão, na qual a autora narra cenas de sua infância, parte do mote benjaminiano de acolhimento das sobras e restos das narrativas oficiais, para que, tal como as crianças, possamos fazer história através do lixo da história. O lugar da infância que o Diário nos convida a visitar aproxima ainda a atividade de catadora dos devires criança e trapeira e motiva o diálogo com outros artistas e teóricos para uma conversa sobre resto e resistência, literatura e excremento, lixo e memória. Entre um e outro texto, como respiros, fragmentos inventados ao longo do caminhar da pesquisa são também costurados ao trabalho. Esses textos variam em forma e conteúdo e apresentam lampejos de memória, notas sobre o processo de pesquisa, atravessamentos do momento político que estamos vivendo e invenções biográficas. Compondo um modo crítico-ficcional de pensar a criação artística pela recolha de objetos, memórias e pensamentos, esse movimento pretende, por fim, interrogar-se também sobre o próprio fazer acadêmico, expandindo as noções de catação e coleção para um movimento de observar, escolher e recolher constitutivo do processo de pesquisa. / [fr] Cette thèse, comme un exercice critique de lecture et écriture, porte sur la notion de débris et d autres mots dérivés, partant de la figure du ramasseur de déchets et du chiffonier afin de réflechir sur le processus créatif comme un acte qui rapproche les artistes et les chercheurs de ceux qui travaillent avec ce qui est laissé de côté, rejeté et oublié. Pour cela, je présente une collection de fragments qui abordent le geste de ramasser les déchets à partir de l oeuvre de l écrivain Carolina Maria de Jesus, dérivés initialement de son célèbre Le dépotoir (Quarto de despejo) pour me pencher ensuite sur le livre Journal de Bitita (Diário de Bitita). L emphase dans l oeuvre en question, où l auteur raconte des scènes de son enfance, a comme déclencheur benjaminien la réception de débris des récits officiels afin que, comme les enfants, on puisse faire histoire en se servant des déchets de l histoire. La place de l enfance que le Journal nous présente lie l activité de ramasseur avec le devenir des enfants chiffoniers et encourage le dialogue avec d autres artistes et théoriciens pour une conversation sur débris et résistence, littérature et excrément, déchets et mémoire. Entre un texte et l autre, comme des pauses, des fragments créés au long du parcours de la recherche sont aussi associés au travail. Ces textes varient en forme et contenu et présentent des bribes de mémoire, des notes sur le travail de recherche, croisements du moment politique que l on vit et des inventions biographiques. Suivant un modèle critique-fictionnel de penser la création artistique par le ramassage d objets, mémoires et pensées, ce mouvement a pour but de s interroger aussi sur le faire académique, menant les notions de ramassage de déchets et de collecte vers un mouvement consistant à observer, sélectionner et ramasser constitutif du travail de recherche.
96

[en] BUILDING SHALOM SALAM: AN ANALYSIS OF THE ROLE OF THE JOINT NONVIOLENCE BETWEEN PALESTINIANS AND ISRAELIS AND OF THE CRIATIVITY OF THE PEACEMAKER SUBJECT / [pt] CONSTRUINDO SHALOM/SALAM: UMA ANÁLISE SOBRE O PAPEL DA NÃO VIOLÊNCIA CONJUNTA ENTRE PALESTINOS E ISRAELENSES E DA CRIATIVIDADE DO SUJEITO PACIFICADOR

CARLA ALBALA HABIF 07 May 2024 (has links)
[pt] Esta tese busca compreender o papel da resistência não violenta conjunta entre israelenses e palestinos. Vivendo territorialmente muito próximos e inseridos em um ciclo de violência complexo e de longa data, estes grupos têm suas experiências de vida usualmente pautadas em uma lógica de inimizade profunda e enraizada há gerações, uma vez que ambos existem e se relacionam através da dinâmica da ocupação militar israelense na Palestina. Esta realidade resulta em uma relação permeada por experiências de violência reais vividas pelos dois grupos, comumente associadas ao outro, resultando em muito medo, raiva e preconceito entre as partes. Nas últimas duas décadas, o conflito entre Israel e Palestina vem experienciando uma intensificação ainda maior e constante da violência. Simultaneamente, no entanto, movimentos de resistência não violentos de atuação conjunta entre palestinos e israelenses vêm crescendo na região. Buscando compreender o papel da não violência neste contexto de aprofundamento da violência, a tese em questão pesquisou dois movimentos de resistência não violenta de atuação conjunta - o Combatants for Peace e o Parents Circle Families Forum - acompanhando de forma remota e analisando suas atividades, projetos, depoimentos de seus ativistas, relatórios e outras documentações. Ao longo do processo, foi compreendido que a não violência conjunta entre israelenses e palestinos dá origem a um novo sujeito resistente, que na pesquisa é referido como sujeito pacificador. Compreendendo este contexto complexo no qual estão inseridos, o trabalho analisou a criatividade desenvolvida pelo sujeito pacificador para que um movimento conjunto possa existir, se desenvolver e, inclusive, se expandir, em um sistema que não é favorável à sua existência ou sobrevivência. Através da discussão conceitual dos termos violência, resistência e resistência não violenta e da análise nas fontes, a tese argumenta que o papel da não violência conjunta entre israelenses e palestinos no contexto de constante intensificação da violência tem sido o de produzir uma imaginação moral - como pensada por John Paul Lederach - que cria modelos de reconciliação e parceria, e abre espaço para a visualização de um futuro de paz possível entre Israel e Palestina. / [en] The goal of this thesis is to understand the role of joint non-violent resistance between Israelis and Palestinians. Living territorially very close and inserted in a complex and long-standing cycle of violence, these groups have their life experiences usually based on a logic of deep enmity rooted for generations, since both exist and relate to each other through the dynamics of the israeli military occupation in Palestine. This reality results in a relationship permeated by real experiences of violence lived by both groups, commonly associated with the other, resulting in a lot of fear, anger and prejudice between the parties. In the last two decades, the conflict between Israel and Palestine has experienced an even greater and constant intensification of violence. Simultaneously, however, joint non-violent resistance movements between Palestinians and Israelis have been growing in the region. Seeking to understand the role of non-violence in this context of deepening violence, the thesis researched two joint non-violent resistance movements - Combatants for Peace and the Parents Circle Families Forum - remotely monitoring and analyzing their activities, projects, statements from its activists, reports and other documentation. Throughout the process, it was understood that joint non-resistance between Israelis and Palestinians gives rise to a new resistant subject, who in the research is referred to as the peacemaking subject. Understanding this complex context in which they are inserted, the work analyzed the creativity developed by the peacemaking subject so that a joint movement can exist, develop and even expand, in a system that is not favorable to its existence or survival. Through conceptual debate of the terms violence, resistance and non-violent resistance and analysis of sources, the thesis argues that the role of joint non-violence between Israelis and Palestinians in the context of constant intensification of violence has been to produce a moral imagination - as reflected by John Paul Lederach - which creates models of reconciliation and partnership, and opens space for the visualization of a possible future of peace between Israel and Palestine.
97

Akce Robotka / Robotka's case

Skořepová, Michaela January 2014 (has links)
(in English): This thesis deals with post-war fate of Josef Robotka the member of the second and third resistence and people who cooperated with him. It cannot be mentioned his activities during the Second World War in the Council of three but the key issue will be the engagement after 1945. I would describe his disenchantment with communist ideas while on Vorošilov military academy in Moscow, subsequently forced to return to Czechoslovakia and post-February intelligence cooperation with CIC. I will also try to bring the role of public authorities in the arrest, detention and trial. In the next section I would like to map the entire arrest of Robotka group, their imprisonment and trial. The following chapters will deal with Robotka's execution and the role of wives and close relatives of convicted persons. The work is based mainly on archival research, supplemented by memories of Vlasta Nováčková Jakubová who is Robotka's niece and close collaborator. Main question is how big the importance of the information that the group sent abroad was and what significance should they have in case of possible conflict.
98

Efeito de diferentes modelos de envelhecimento na resistência de união em dentina decídua hígida e cariada / Different degradations models to evaluate bond strength in sound and caries primary dentin

Calvo, Ana Flávia Bissoto 04 March 2015 (has links)
A resistência de união (RU) dos materiais deve ser avaliada após a degradação da interface adesiva, tentando simular um processo que ocorre naturalmente ao longo do tempo na cavidade bucal. O presente estudo avaliou a degradação da interface adesiva em diferentes materiais utilizando o modelo de envelhecimento in vitro e in situ em dentina hígida e cariada. Noventa segundos molares decíduos hígidos e sem defeitos de esmalte, foram aleatoriamente divididos em dois grupos de acordo com o substrato a ser testado (hígido e com lesão de cárie induzida). A seguir, cada um dos grupos foi subdividido aleatoriamente de acordo com o material restaurador (n=15): resina composta associada ao sistema adesivo - RC, cimento de ionômero de vidro modificado por resina - CIVMR e cimento de ionômero de vidro de alta viscosidade - CIVAV. A superfície da dentina foi preparada e com o auxílio de cânulas de polietileno, foram confeccionados os espécimes com os materiais restauradores. Partes de um mesmo dente foram submetidas a cada envelhecimento: in vitro (24 horas e 6 meses) - armazenados em água destilada à 37°C; e in situ (uso de dispositivo intraoral palatino por voluntários em uma fase experimental de 7 dias). Os espécimes foram submetidos ao teste de microcisalhamento (MPa) para avaliação da RU, seguido de análise do padrão de fratura em estereomicroscópio (400X). Os dados foram submetidos a análise de variância de medidas repetidas seguida pelo teste de Bonferroni (? = 5%). De forma geral, o armazenamento por seis meses em água degradou o grupo CIVMR em dentina hígida (<0,001) e RC em dentina cariada (p=0,007), para os outros materiais não houve diferença estatística (p=1,00). O modelo in situ influenciou negativamente os valores de RU nos grupos RC e CIVMR (p<0,001) no substrato hígido e na RC (p<0,001), CIVMR (p=0,001) e CIVAV p=0,020) no substrato cariado. Concluí-se que no modelo in vitro, seis meses em água destilada não foram suficientes para degradar a interface de união dos materiais avaliados e o modelo in situ é uma metodologia rápida que pode ser utilizada para avaliar a degradação da interface de união de materiais restauradores em dentina cariada de dentes decíduo. / Materials bond strength (BS) should be evaluated after degradation of the adhesive interface, simulating the intra-oral enviroment. This study assessed the degradation of the bonding interface of differents materials using in vitro and in situ models of aging in sound and caries - affected primary dentin. Ninety sound second primary molars without enamel defects were randomly assigned into two groups (sound and induced carious) according to the substrate to be tested. Then each group was subdivided according to the restorative material (n=15): composite resin associated with the adhesive system - CR, resin-modified glass ionomer cement - RMGIC or high-viscous glass ionomer cement- HVGIC. Dentin surface was prepared and with the aid of polyethylene tubes specimens of each restorative materials were prepared. Parts of a same tooth were subjected to in vitro and in situ models of aging. For in vitro model, the specimens were stored in distilled water at 37°C during 24 hours per 6 months; and for in situ model an intraoral palatal device was confectioned and used by volunteers in an experimental phase for 7 days. Specimens were submitted to microshear test (MPa) for BS evaluation and then stereomicroscopy (400X) analys of failure mode. Data were analyzed by repeated measures ANOVA for followed by Bonferroni test (? = 5%). In general, the storage for six months in distilled water degraded the RMGIC group in sound dentin (<0.001) and RC group in caries-affect dentin substrate (p = 0.007), for the others materials there was no statistical difference (p = 1.00). The in situ model, adversely, influenced the BS in RC and RMGIC groups (p <0.001) in sound substrate, and in RC (p <0.001), RMGIC (p = 0.001) and HVGIC (p = 0.020) in caries-affected dentin. We can concluded that in in vitro model, using six months distilled water, was not sufficient to degrade the bonded interface of the evaluated materials and in situ model is a faster method to evaluate degradation of the adhesion interface of restorative materials in cariesaffected dentin.
99

Diversidade genética de isolados polispóricos de Crinipellis perniciosa (Stahel) Singer / Genetic diversity of polisporics isolates of Crinipellis perniciosa (Stahel) Singer

Ferreira, Luiz Fernando Romanholo 11 July 2005 (has links)
A diversidade genética de Crinipellis perniciosa foi avaliada quanto à capacidade adaptativa de diferentes genótipos à dispersão geográfica e à associação preferencial ou diferencial com hospedeiros. Isolados polispóricos de C. perniciosa provenientes de diferentes Estados brasileiros (AM, RO, MG, BA, SP, MT e PA) e diferentes hospedeiros (Theobroma cacao L., Solanum cernuum, Solanum paniculatum, Solanum grandiflorum L., Solanum e lianas), foram analisados pelas técnicas de compatibilidade somática (SCG - Somatic Compatibility Group), através de reações de compatibilidade e/ou incompatibilidade, o uso de gel de eletroforese de proteínas totais, velocidade de crescimento, ELISA e Western Blot. Os diversos isolados foram agrupados com base em conjuntos de dados sobre suas características genéticas, identificando-se agrupamentos de acordo com a dispersão geográfica e hospedeiros de onde foram isolados. Foram construídos dois dendogramas pelo teste de compatibilidade permitindo classificar os isolados em três grupos: i)grupo formado pelos isolados de Rondônia e Pará e ii) grupo formado pelos isolados de Rondônia, Pará e Amazonas e o iii) grupo formado pelo isolado de Mato Grosso; o segundo teste separou os isolados em dois grandes grupos: i) grupo formado pelos isolados da Bahia, Minas Gerais, São Paulo, Mato Grosso e Rondônia e ii) grupo formado pelo isolado do Pará. O dendograma criado pelo perfil protéico permitiu agrupar os isolados em três grupos, de acordo com o hospedeiro e região de origem: (1) grupo formado pelo isolado de Theobroma cacao de Ouro Preto D’Oeste; (2) grupo constituído pelos isolados de Theobroma cacao da Bahia e os diversos isolados de Solanaceae do Estado de Minas Gerais, Bahia e São Paulo e grupo (3) formado pelo isolado de Lianas (cipós). De forma geral, conclui-se que há ampla diversidade genética entre os isolados de C. perniciosa provenientes das diferentes regiões brasileiras e em relação aos hospedeiros, comprovando-se haver elevada capacidade adaptativa caracterizada pela prevalência em ambientes diversos e pela disseminação a longas distâncias geográficas. Há também indicativos de que a velocidade de crescimento do fungo pode ser um dos fatores importantes para assegurar a colonização, já que é correlacionada com a dispersão geográfica, e também, para a seleção de biótipos patogênicos e para a variabilidade genética do fungo. / The genetic diversity of Crinipellis perniciosa was evaluated how much to the capacity of adaptation of different genotypes to the geographic dispersion and the preferential or distinguishing association with hosts. Polisporics isolated of C. perniciosa proceeding from different Brazilian States (AM, RO, MG, BA, SP, MT e PA) and different hosts (Theobroma cacao L., Solanum cernuum, Solanum paniculatum, Solanum grandiflorum L., Solanum and lianas), had been analyzed by the techniques of somatic compatibility (SCG - Somatic Compatibility Group), through reactions of compatibility and/or incompatibility, the gel use of proteins electrophoresis, speed of growth, ELISA and Western Blot. Diverse the isolated ones had been grouped on the basis of different data on its genetic characteristics, identifying to groupings in accordance with the geographic dispersion and hosts of where they had been isolated. Two dendrogramas for the compatibility test had been constructed allowing to classify the isolated ones in three groups: i)group formed by isolated of Rondônia and Pará and ii) group formed for the isolated ones of Rondônia, Pará and Amazonas and iii) group formed for the isolated one of Mato Grosso; as the test separated the isolated ones in two great groups: i) group formed for isolated of the Bahia, the Minas Gerais, São Paulo, Mato Grosso and Rondônia and ii) group formed for the isolated one of Pará. The dendrograma created by the protein profile allowed to group the isolated ones in three groups, in accordance with the host and region of origin: (1) group formed for isolated of Theobroma cacao of Ouro Preto D'Oeste; (2) group consisting of isolated of Theobroma cacao of the Bahia and diverse the isolated ones of Solanaceae of the State of Minas Gerais, Bahia and São Paulo and group (3) formed by the isolated one of Liana. Of general form, it is concluded that it has ample genetic diversity enters the isolated ones of C. perniciosa proceeding from the different Brazilian regions and in relation to the hosts, proving to have high capacity of adaptation characterized by the prevalence in diverse environments and the dissemination the long geographic distances. It has also indicative of that the growth speed can be one of the factors important to assure the correlated settling since with the geographic dispersion, favors new biotypes, important factor for the genetic variability of fungus.
100

Estudo da resistência à corrosão das ligas de alumínio 2024-T3 e 7475-T651 soldadas por fricção e mistura (FSW) / Study of the corrosion resistance of aluminium alloys 2024-T3 and 7475-T651 welded by friction stir welding (FSW)

Bugarin, Aline de Fátima Santos 09 June 2017 (has links)
O processo de soldagem por fricção e mistura (FSW) tem despertado grande interesse nos últimos anos e tornou-se uma alternativa para unir materiais de baixa soldabilidade, como as ligas de alumínio das séries 2XXX e 7XXX, as quais são empregadas na estrutura das aeronaves, por possuírem elevada relação resistência/peso. O processo FSW, todavia, causa mudanças microestruturais nos materiais soldados, particularmente na zona misturada (ZM) e nas zonas termicamente (ZTA) ou termomecanicamente (ZTMA) afetadas. Estas mudanças geralmente interferem no desempenho frente à corrosão das ligas soldadas. No presente estudo, a resistência à corrosão das ligas de alumínio 2024-T3 e 7475-T761, unidas pelo processo FSW foi investigada em solução 10 mM de NaCl. Ensaios de visualização em gel ágar-ágar e de imersão associados a técnicas microscópicas foram realizados para investigar o efeito do acoplamento galvânico na corrosão das diferentes regiões da junta soldada. Os resultados do ensaio de visualização em gel mostraram que, quando acopladas, a liga 2024 atua como cátodo e a 7475 como ânodo. Os ensaios de imersão revelaram acoplamento galvânico entre as ligas na zona misturada (ZM). A região mais afetada pela corrosão foi a ZTMA da liga 7475, com corrosão intergranular desde as primeiras horas de imersão. A influência do processo de soldagem na resistência à corrosão das duas ligas de alumínio foi investigada por ensaios eletroquímicos. Os ensaios eletroquímicos adotados foram medidas de potencial de circuito aberto (PCA) em função do tempo de exposição ao meio corrosivo, espectroscopia de impedância eletroquímica (EIE) e curvas de polarização potenciodinâmica. Os ensaios de polarização mostraram elevada atividade eletroquímica na zona de mistura indicada pelos altos valores de densidade de corrente em comparação com as demais zonas testadas. Os resultados de EIE globais mostraram que nas primeiras horas de exposição ao eletrólito o processo de corrosão foi predominantemente controlado pela liga 7475; todavia, com o tempo de exposição ao eletrólito, a corrosão passou a ser controlada pela liga 2024. / Friction stir welding (FSW) has roused great interest in recent years and it is now an alternative for joining materials of low weldability, such as the aluminum alloys of the 2XXX and 7XXX series, used in the aircrafts structure due to their high strength /weight ratio. However, FSW causes material microstructural changes, mainly in the stir zone (SZ), the heat affected zone (HAZ) or thermomechanically (TMAZ) affected zones of the materials welded. These generally interfere with the corrosive performance of the welded joint. In the present study, the corrosion resistance of the 2024-T3 and 7475-T761aluminum alloys, joined by FSW was investigated in 10 mM NaCl electrolyte. Agar-agar gel and immersion tests associated with microscopic techniques were performed to investigate the effect of galvanic coupling between the welded materials. Results from this test showed that, when galvanically coupled, the 2024 alloy acts as cathode and the 7475 as anode. Immersion tests revealed galvanic coupling between the alloys in the SZ. The zone most susceptible to corrosion was the TMAZ of the 7475. Intergranular corrosion was observed in this zone since the first hours of immersion. The influence of the welding process on the corrosion resistance of the alloys was also evaluated by electrochemical tests. The electrochemical tests adopted were open circuit potential measurements (OCP) as a function of time of exposure to the electrolyte, electrochemical impedance spectroscopy (EIS) and potentiodynamic polarization curves. The polarization tests showed high electrochemical activity in the stir zone indicated by the high current densities measured comparatively to the other tested zones. The global EIS results indicated that in the first few hours of exposure to the electrolyte the corrosion process was predominantly controlled by the 7475 alloy; however, with time of exposure to the electrolyte, the corrosion was controlled by alloy 2024.

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