• Refine Query
  • Source
  • Publication year
  • to
  • Language
  • 1435
  • 1336
  • 530
  • 209
  • 37
  • 30
  • 22
  • 22
  • 18
  • 17
  • 10
  • 9
  • 8
  • 7
  • 5
  • Tagged with
  • 4207
  • 936
  • 624
  • 492
  • 366
  • 300
  • 286
  • 243
  • 237
  • 211
  • 188
  • 188
  • 183
  • 180
  • 175
  • 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.
661

Nano-pipette as nanoparticle analyzer and capillary gated ion transistor

Rudzevich, Yauheni 01 January 2014 (has links)
The ability to precisely count inorganic and organic nanoparticles and to measure their size distribution plays a major role in various applications such as drug delivery, nanoparticles counting, and many others. In this work I present a simple resistive pulse method that allows translocations, counting, and measuring the size and velocity distribution of silica nanoparticles and liposomes with diameters from 50 nm to 250 nm. This technique is based on the Coulter counter technique, but has nanometer size pores. It was found that ionic current drops when nanoparticles enter the nanopore of a pulled micropipette, producing a clear translocation signal. Pulled borosilicate micropipettes with opening 50 ~ 350 nm were used as the detecting instrument. This method provides a direct, fast and cost-effective way to characterize inorganic and organic nanoparticles in a solution. In this work I also introduce a newly developed Capillary Ionic Transistor (CIT). It is presented as a nanodevice which provides control of ionic transport through nanochannel by gate voltage. CIT is Ionic transistor, which employs pulled capillary as nanochannel with a tip diameter smaller than 100 mm. We observed that the gate voltage applied to gate electrode, deposited on the outer wall of a capillary, affect a conductance of nanochannel, due to change of surface charge at the solution/capillary interface. Negative gate voltage corresponds to lower conductivity and positive gate increases conductance of the channel. This effect strongly depends on the size of the channel. In general, at least one dimension of the channel has to be small enough for electrical double layer to overlap.
662

Modélisation théorique et expérimentale du comportement énergétique et environnemental des toitures végétalisées / Experimental and theoretical models for green roofs environmental and energetical characterization

Ouldboukhitine, Salah-Eddine 10 December 2012 (has links)
Les toitures végétalisées ont des répercussions très positives sur la performance énergétique des bâtiments. L’objectif est d’évaluer l’incidence des toitures végétalisées sur la performance énergétique des bâtiments à travers des moyens numériques et expérimentaux. La modélisation du comportement thermo-hydrique des toitures végétalisées permet de quantifier ces effets et contribue à promouvoir cette technique.Cette thématique requiert en premier lieu des compétences en énergétique du bâtiment et de modélisation thermique dynamique, si l’on souhaite établir un modèle représentatif du comportement thermo-hydrique d’un composant de toiture végétalisée. Afin de développer ces différents aspects, un travail préliminaire qui consiste en une étude bibliographique approfondie portant sur les modèles proposés dans la littérature a été entrepris. Sur la base de cette étude bibliographique, un modèle couplé de transfert de chaleur et d’humidité a été développé. Ce modèle est basé sur l’établissement des équations de bilan énergétique sur la surface du feuillage et la surface du sol. Afin d’affiner le modèle développé et d’obtenir de meilleurs résultats numériques, diverses caractérisations expérimentales des matériaux qui entrent dans la composition de la toiture végétalisée ont été effectuées. Une plateforme expérimentale (Climabat, échelle 1/10) a été conçue sur le site de l’Université de La Rochelle dans le but de mesurer l’incidence des toitures végétalisées sur les bâtiments et fournir des données permettant de calibrer et de vérifier le modèle développé. Des comparaisons ont été entreprises entre toiture végétalisée et toiture classique, une différence de température de surface extérieure de 30°C a été notée pendant la période d’été. Les résultats des simulations montrent aussi que la végétalisation des toitures de bâtiment améliore non seulement les conditions de son confort thermique mais aussi sa performance énergétique. Des campagnes de mesures ont été également effectuées sur des bâtiments réels équipés avec des toitures végétalisées. La validation expérimentale du modèle développé a été ensuite entreprise à deux échelles, l’une à échelle réduite (maquette échelle 1:10) sur des bancs d’essais sur le site de l’Université de La Rochelle et une à échelle réelle, sur des pavillons BBC existants où différentes typologies de toitures végétalisées ont été instrumentées. Une fois le modèle développé et sa pertinence vérifiée par comparaison à des mesures expérimentales, il a été couplé à un code de simulation thermique dynamique des bâtiments (TRNSYS). Cela a permis de prédire la performance énergétique et le calcul des besoins de chauffage et de climatisation des bâtiments équipés d'une toiture végétalisée. Les résultats de simulations ont montré que la présence d'une toiture végétalisée permet une réduction des besoins des bâtiments et protège la membrane d’étanchéité de la toiture des températures extrêmes et des grandes fluctuations de température. De plus, il a été constaté que l'effet des toitures végétalisées sur la réduction de la température de l'air intérieur est plus important en été. Aussi, il a été constaté que les besoins de climatisation et de chauffage dépendent fortement du niveau d'isolation de la toiture. Enfin, les simulations réalisées pour différents climats ont montré que la toiture végétalisée est bénéfique pour le climat des pays européens. / Green roofs have a positive effect on the energy performance of buildings, providing a cooling effect in summer, along with a more efficient harnessing of the solar radiation, due to the reflective properties of the foliage. To assess these effects, a thermodynamic model was developed as well as the thermo-physical properties of the green roof components were characterized.The proposed model is based on energy balance equations expressed for foliage and soil media. The influence of the mass transfer on the thermal properties, and evapotranspiration were taken into account. Then, the water balance equation was added into the developed model and numerical simulations were performed. In order to evaluate the temperatures evolution at foliage and soil ground levels.Three of the main physical properties of green roofs were experimentally investigated to determine some of the green roofs’ modeling key parameters. First, the thermo-physical properties of green roofs were characterized by correlating the thermal conductivity of the substrate with the water content for different substrates and maximum water capacities. Next, the moisture storage was characterized using the dynamic vapor sorption technique. Third, themicro-structural properties of green roof substrate were characterized using mercury intrusion porosimetry. In addition to these characterizations, the evapotranspiration term, which is very important in the water balance, was measured.The model was experimentally validated according to a green roof platform (scale 1:10) constructed on the site of the University of La Rochelle. Measurements have also been conducted in a full scale building equipped with green roofs. Once the proposed model validated, it has been coupled to a building thermal code (TRNSYS) to evaluate the impact of green roofs on the energy performance of buildings.The results show that the effect of mass transfer in the subtract was very effective in reducing the model errors. Comparisons were undertaken with a roof slab concrete model; a significant difference in temperature (up to 30 °C) between the outer surfaces of the two roofs was noticed in summer. The heat flux through the roof was also evaluated. The roof passive cooling effect was three times more efficient with the green roof. In the winter, the green roof reduced roof heat losses during cold days; however, it increased these losses during sunny days. With a green roof, the summer indoor air temperature was decreased by 2 °C, and the annual energy demand was reduced by 6% for an oceanic climate such as that of La Rochelle. Finally, the simulations performed for different climates suggest that green roofs are thermally beneficial for hot, temperate, and cold European climates.
663

Caractérisation d'un nouveau matériau et valorisation dans les barrières perméables réactives / Characterisation of a new material and its valorization in a permeable reactive barriers

Zakaria, Khaled 14 December 2012 (has links)
La valorisation des déchets industriels est de nos jour un défit international ayant des intérêts économiques et environnementaux. Dans ce cadre, l’entreprise Solvay travail sur la gestion de ses déchets et plus particulièrement ceux produits de la fabrication du carbonate de sodium « soude ». Ils sont actuellement stockés dans des bassins de décantation. Cependant, des contraintes règlementaires sont récemment apparues limitant ainsi la construction de nouveaux bassins. La valorisation de ces déchets est par conséquent impérative pour l’entreprise. Plusieurs voies de valorisation sont envisageables, notamment le recours à des nouveaux procédés qui permettraient d’en produire de nouveaux matériaux.En effet, un nouveau matériau issu des déchets industriels appelé « Gel d’Apatite » fait l’objet de ce travail de thèse. L’objectif est de caractériser le Gel d’Apatite et de proposer et d’étudier une voie permettant sa valorisation. Ce matériau est constitué principalement d’hydroxyapatite et de l’eau. Il se distingue par un comportement thixotropique et par sa capacité de rétention des métaux lourds. Cette dernière propriété a permis d’envisager sa valorisation dans la dépollution et la protection des nappes phréatiques. La voie étudiée dans ce travail de recherche est la valorisation du Gel d’Apatite dans les Barrières Perméables Réactives « BPR(s)»; technique passive de traitement des eaux souterraines in-situ.La finalité de ces travaux de recherche serait de dresser un cahier de charge du Gel d’Apatite et de définir un mélange conforme au mode de valorisation étudié / The valorization of industrial wastes is nowadays a worldwide challenge that offers several environmental and social interests. In some fields this valorization allows the preservation of natural resources and the releasing of spaces devoted to the wastes storage. Further, it allows developing of new innovative materials and low-cost products. Consequently industries industries have followed these guidelines. A collaborative investigation has been established with Solvay and Ecole Centrale de Lille in order to work on this topic.A new material: hydroxyapatite gel, is thus developed from non-toxic wastes in an industrial research laboratory. This material is composed by hydroxyapatite and water. It is characterized by its capacity to retain heavy metal by ion exchange. This particular characteristic led to consider its valorization in the water pollution control as the permeable reactive barrier (PRB) in particular. In deed, the permeable reactive barrier is a passive technique of in situ groundwater treatment.The results from this study were useful for a better planning of Permeable Reactive Barriers (PRB). The latter requires a high permeability to ensure groundwater flow and a high retention capacity for heavy metals
664

Etude du potentiel des nanotubes de carbone dans la microélectronique de puissance / Study of the potential of the carbon nanotubes in the field of the power microelectronics

Labbaye, Thibault 25 November 2015 (has links)
Le travail présenté dans ce manuscrit de thèse s’inscrit dans le cadre d’une coopération scientifique notamment à travers le projet Région Centre « Connectic » en partenariat avec la société STMicroelectronics de Tours, les laboratoires LMR et CEMHTI. Il concerne les interconnexions des générations futures de circuits intégrés. Par rapport aux technologies d’interconnexion à base d’alliage métallique l’intégration de nanotubes de carbone (NTC) comme connecteur en microélectronique de puissance limiterait les effets d’échauffement dans les empilements de puces grâce à leurs propriétés de transport intéressantes. Les NTC peuvent assurer simultanément une bonne conduction électrique et un maintien mécanique des assemblages de puces. Les objectifs de ce travail étaient d’établir dans un premier temps un procédé reproductible d’élaboration de NTC verticalement alignés sur des substrats de nature multiple, et de réaliser dans un deuxième temps un véhicule test qui permet de caractériser leurs propriétés électrique, thermique et mécanique. Le dispositif expérimental d’élaboration présenté dans cette étude utilise le dépôt de catalyseur (Ni, Fe), la structuration par plasma d’hydrogène simultanément à un recuit thermique, ainsi que la méthode de CVD assistée par plasma radiofréquence d’éthylène et d’hydrogène pour la croissance des NTC. Des conditions optimales reproductibles d’obtention des NTC ont été établies à la suite d’une étude paramétrée utilisant notamment un diagnostic original de suivi in situ par spectroscopie Raman développé en collaboration avec le CEMHTI. Dans le cas d’un tapis de NTC de 10 µm de haut, des performances électrique (⍴ = 10⁻⁵ Ω.m), thermique (λth = 40-60 W.m⁻¹.K⁻¹), et mécanique (E = 480 GPa) comparables aux alliages métalliques ont été établies. Enfin, nous avons été capables d’assembler les substrats de la microélectronique et les NTC par un procédé de thermocompression. / The work presented in this thesis was a scientific cooperation between the society ST Microelectronics in Tours, the laboratories of LMR and CEMHTI within the framework of the project Région Centre “ConnectiC”. The main issue of that project concerns the interconnections for the future generation of integrated circuits. In comparison with the current interconnection technologies on metallic alloys as connectors; the integration of carbon nanotubes (CNT) as connector in power microelectronics would limit effects of overheating in the chip-structure due to their interesting transport properties. CNT can provide at the same time good electrical, thermal conduction characteristics and can be a mechanical support of chip packages. The aims of this work were: firstly, obtain a reproducible growth process of vertically aligned CNT on different kinds of substrate; secondly: to elaborate a test vehicle with CNT interconnects allowing the electrical, thermal and mechanical characterization. The experimental method used herein for synthesis of CNT interconnects combines the catalyst deposition (Ni, Fe), the structuration by both means of hydrogen plasma treatment and thermal annealing, and a RF PECVD method using ethylene and hydrogen for the CNT growth. Optimal reproducible conditions were found using a novel in situ Raman spectroscopy diagnostic developed in collaboration with the CEMHTI. The carpet of CNT (height of 10 µm) produced presents the electrical (⍴ = 10⁻⁵ Ω.m), thermal (λth = 40-60 W.m⁻¹.K⁻¹), and mechanical (E = 480 GPa) performances comparable with the metallic. Finally, by means of thermocompression, we assembled CNT on substrates from the microelectronics.
665

Valorisation durable des laits de chèvre de la région du Nord Liban. Transformation en fromage "Darfiyeh" et établissement de caractéristiques physico-chimiques et microbiologiques en vue de la création d'une appellation d'origine / Substainable valorization of North Lebanon goats's milk. Transformation into Darfiyeh cheese and establishment of physico-chemical and microbiological characteristics in order to create a designation of origin

Serhan, Mireille 13 November 2008 (has links)
Afin de contribuer à la préservation du patrimoine laitier libanais, l'objectif principal de cette étude a été de caractériser le fromage Darfiyeh, une variété traditionnelle fabriquée à partir de lait de chèvre cru et affinée dans une outre en peau de chèvre. Parallèlement à cet objectif, et pour mieux comprendre l'affinage du Darfiyeh, le transfert de composés d’arôme à travers la peau de chèvre a été étudié au moyen d’un dispositif expérimental original. Trois lots indépendants de production de Darfiyeh ont été analysés après 20, 40 et 60 jours d'affinage. Les résultats des analyses physico-chimiques ont montré que le Darfiyeh est un fromage à pâte mi-dure, caractérisé par une protéolyse et une lipolyse modérées. Le 3-méthyl butanal, le 1-phényl éthanol et le 1-octanol contribuent à la fraction aromatique particulière du Darfiyeh. Les analyses microbiologiques ont mis en évidence (Log cfu.g-1 fromage) des lactobacilles mésophiles (7,1-10,4), des bactéries lactiques (BL) thermophiles cocciformes (6,6-8,4) et des lactobacilles thermophiles (5,5-7,2). Afin d'explorer l'écosystème naturel du Darfiyeh, une combinaison d'approches classiques et moléculaires a été appliquée. L'identification classique a révélé des espèces appartenant aux genres Streptococcus, Enterococcus, Lactococcus et Lactobacillus. Les profils de Temporal Temperature Gel Electrophoresis (TTGE) ont révélé des bandes communes avec l'identification classique. Des analyses menées par PCR spécifiques de l'espèce bactérienne ont confirmé la présence of S. thermophilus, E. faecium, E. durans, Lc. lactis subsp. lactis et Lc. lactis subsp. cremoris. La PCR en temps réel a permis la quantification de S. thermophilus et d' E. faecium, avec un seuil de détection respectif de 104 ufc.g-1 de Darfiyeh et une gamme de 107-109 ufc.g-1 de Darfiyeh, respectivement. Pour le transfert d'arômes à travers la peau de chèvre, l'absorption et la perméabilité de trois molécules aromatiques modèles (2-butanone, 2,3-butanedione, 2-butanol) dans un système solution aqueuse/peau de chèvre a été suivi, après 20, 40 et 60 jours d'exposition. Jusqu'à 40 j d'exposition, le transfert des molécules aromatiques était régi par leurs propriétés physico-chimiques et par le temps d'exposition. Après 60 j, le système solution aqueuse/peau s’est traduit par une tendance à la migration des molécules modèles depuis la peau vers la solution simulée de Darfiyeh. Autrement dit, le transfert de ces molécules modèles dans le système simulé paraît s’établir de façon cyclique. Ce travail est une première contribution scientifique et technique au secteur de la valorisation durable de la tradition fromagère libanaise / In order to contribute for the preservation of the Lebanese dairy heritage, the aim of this study was to characterize Darfiyeh cheese, a traditional variety made from raw goats' milk and ripened in goat's skin. Parallel to this objective, and for a better understanding of Darfiyeh ripening, aroma transfer towards goat skin was conducted through an experimental device. Three independent batches of Darfiyeh production were analyzed after 20, 40 and 60 days of ripening. Physico-chemical results showed that Darfiyeh is a semi-hard goat's milk cheese which undergoes a moderate proteolysis and lipolysis. 3-methyl butanal, 1-phenyl ethanol and 1-octanol contribute to the distinctive aromatic fraction of Darfiyeh. As for microbiological results, bacterial counts (Log cfu.g-1 cheese) for mesophilic lactobacilli (7.1-10.4), thermophilic coccal-shaped lactic acid bacteria (LAB) (6.6-8.4) and thermophilic lactobacilli (5.5-7.2) were found. In order to explore Darfiyeh natural ecosystem, a combination of classical and molecular approaches was applied. Classical identification revealed members of the genera Streptococcus, Enterococcus, Lactococcus and Lactobacillus. Temporal Temperature Gel Electrophoresis (TTGE) profiles revealed common bands between the classical identification. Species-specific polymerase chain reactions (PCR) confirmed the presence of S. thermophilus, E. faecium, E. durans, Lc. lactis subsp. lactis and Lc. lactis subsp. cremoris. Real time PCR enabled quantification of S. thermophilus and E. faecium, with a detection threshold of 104 ufc.g-1 of Darfiyeh and a range of 107-109 ufc.g-1 of Darfiyeh, respectively. As for aroma transfer towards goat skin, absorption and permeability of three model aroma molecules (2-butanone, 2,3-butanedione, 2-butanol) in aqueous solution/goat skin system were followed, after 20, 40 and 60 days of exposure. Until 40 days, the transfer of aroma molecules was dependent on their physico-chemical properties and exposure time. After 60 days, the molecules migrate from the skin to the aqueous solution. Therefore, in such a simulated system, aromatic molecules seem to move under a cyclic way. This work is a first scientific and technical contribution to the preservation of traditional Lebanese cheesemaking
666

Effect of nanoparticulate copper, zirconia and graphite: contribution to the friction coefficient and transfer layer formation in dry sliding tests with interfacial media addition. / Efeito do cobre nanoparticulado, zirconia e grafite: contribuição para o coeficiente de atrito e camada de transferência formada em testes pino X disco sem lubrificação com adição de meio interfacial.

Rodrigues, Ana Cecilia Pontes 29 March 2019 (has links)
Copper is present in brake pads in the form of fibres, tough its suppression from pads\' formulations is already a trend compared to the suppression of asbestos in the 1980\'s. As a contribution to this challenging scenario, this work investigated the behaviour of mixture additions containing copper, zirconia, graphite and magnetite in dry sliding tribotests. Pin-on-disc tribotests with interfacial media addition were performed in order to contribute on the mission of understanding how Cu, graphite and ZrO2 particles act on the oxide transfer layer formation on dry sliding conditions. Thus describing some of the tribological properties that a possible replacement for copper in brake pads should mimic. Tests were performed at 23°C in air, 400°C in air and 400°C in N2. Nanoparticulate Cu, ZrO2 and micron-sized graphite were mixed in a Fe3O4 basedmatrix. The ZrO2 particles were incorporated to the mixtures by two mixing methods: manual mixing and high-energy ball milling. This study sought to explain the coefficient of friction (CoF) behaviour of these additions individually, as well as together, by correlating the CoF with comprehensive characterization of the oxide transfer layer. The transfer layer was characterized by means of scanning electron microscopy (SEM), Focused Ion Beam (FIB) and Transmission electron microscopy. Graphite containing mixtures displayed low average CoF values (0.23 to 0.31) due to selective transfer of graphite films to the first bodies\' tribosurfaces. Copper formed agglomerates and patches within the oxide transfer layer that were responsible for raising the CoF values at 23°C and acted as soft copper films at 400°C. The nanoparticulate addition of ZrO2 in the manual mixtures prevented the formation of Cu patches and larger agglomerates, promoting the formation of a smooth and compact oxide tribolayer, though graphite\'s selective transfer was still observed. / O cobre está presente em pastilhas de freio na forma de fibras e sua eliminação das formulações de pastilhas já é comparável aos esforços para a eliminação do amianto dos freios nos anos 1980\'s. Para contribuir nessa missão, esse trabalho investigou o comportamento, em ensaios tribológicos sem lubrificação com adição de misturas de cobre, zircônia, grafite e magnetita. Foram realizados ensaios pino x disco com adição de meio interfacial com o objetivo de contribuir na descrição da atuação do Cu, grafite e partículas de ZrO2 na formação de uma camada de óxido compacta em condições sem lubrificação. De forma a descrever propriedades tribológicas relevantes que um possível substituto do cobre deve mimetizar nas pastilhas de freio. Os ensaios foram realizados a 23°C em ar, 400°C em ar e 400°C em N2. Nanopartículas de Cu, ZrO2 (50 nm) e grafite micrométrico (20 µm) foram misturados em uma base de Fe3O4 nanoparticulado. As partículas de ZrO2 foram incorporadas às misturas, por dois métodos distintos, mistura manual, e moagem de bolas de alta energia. Este estudo procurou explicar os resultados de coeficiente de atrito (CoF) dessas adições, individualmente bem como em conjunto, correlacionando os resultados de coeficiente de atrito à extensa caracterização da camada de transferência. Esta última foi caracterizada por meio de microscopia eletrônica de varredura (SEM), feixe de íons focalizado (FIB) e microscopia eletrônica de transmissão (TEM). As misturas contendo grafite apresentaram os menores valores médios de CoF (0.23 to 0.31) devido à presença de filmes contínuos de grafite na camada de transferência. A adição de cobre formou aglomerados e placas na camada de transferência, que foram responsáveis tanto pelo aumento do CoF a 23°C, e agiram como filmes moles de cobre a 400°C. A adição de ZrO2 em misturas manuais preveniu a formação de aglomerados de Cu, auxiliando na formação de uma camada mais compacta, no entanto, não foi suficiente para prevenir a formação de filmes de grafite.
667

Caracterização microestrutural e mecânica de juntas soldadas a laser em um aço ARBL / Microstructural and mechanical characterization of laser welded joints on a HSLA steel

Ribeiro, Henrique Varella 14 October 2016 (has links)
Os aços de alta resistência e baixa liga (ARBL) são amplamente empregados nas indústrias automotiva, petrolífera e naval por apresentarem boas propriedades mecânicas e boa soldabilidade. A seleção do processo de soldagem utilizado para a fabricação de componentes depende de vários fatores, entre eles a qualidade do cordão de solda e a capacidade de produção, ambas obtidas ao se utilizar a soldagem a laser, processo que vem sendo cada vez mais utilizado nas indústrias. As propriedades dos cordões de solda são afetadas pelo processo de soldagem e pelos parâmetros do processo, e o conhecimento do desempenho mecânico do cordão de solda é essencial para garantir a confiabilidade da união soldada. A caracterização mecânica de cordões de solda é complexa devido aos diversos fatores que podem afetá-lo, como as alterações metalúrgicas, diferentes propriedades mecânicas nas regiões do cordão de solda, presença de descontinuidades, tensão residual e complexo estado de tensão devido à geometria da junta. O presente trabalho obteve uniões entre chapas de aço ARBL pelo processo a laser em duas condições diferentes: com alto aporte térmico e baixo aporte térmico. A utilização de diferentes aportes térmicos gerou cordões de solda com microestruturas distintas, e avaliou-se, deste modo, o comportamento mecânico associando-o à microestrutura gerada. Para a avaliação da microestrutura utilizou-se da microscopia óptica e eletrônica de varredura, e para a caracterização mecânica empregou-se a aferição da dureza, ensaio de tração, ensaio de tenacidade à fratura, avaliada pelo CTOD, e ensaio de propagação da trinca por fadiga. Devido às alterações metalúrgicas causadas pelos diferentes aportes térmicos verificou-se diferente comportamento mecânico entre os cordões de solda em função da microestrutura obtida. / High-strength low-alloy steels (HSLA) are widely used in the automotive and oil industries due to their good mechanical properties and good weldability. The selection of the welding process used to manufacture components depends on several factors, including the quality of the weld bead and the production capacity, both obtained when using laser welding, a process, which is being increasingly used in the industries. The weld beads properties are affected by the welding process and by its parameters, and the knowledge of the weld bead mechanical performance is essential to ensure the reliability of the welded joint. The weld beads mechanical characterization is complex due to various factors that may affect it, such as metallurgical changes, different mechanical properties in the regions of the weld bead, presence of discontinuities, residual stress and complex state of tension due to the geometry of the joint. The present work obtained the joining of HSLA steel sheets by laser process in two different conditions, with high heat input and low heat input. The use of different heat inputs produced weld beads with different microstructures; therefore, the welded joints were evaluated according to their mechanical behavior, relating it with the microstructural generated. For the microstructure evaluation, optical microscopy and scanning electron microscopy were used, and for the mechanical characterization hardness determination, tensile test, fracture toughness test (evaluated by CTOD) and fatigue crack propagation were performed. Due to the metallurgical changes caused by the different heat inputs, a different mechanical behavior was observed between the weld beads as a function of the microstructure obtained.
668

Caracterização funcional e estrutural de uma fosfolipase A2 ácida isolada do veneno de Bothrops pirajai / Functional and structural characterization of acidic phospholipase A2 isolated from Bothrops pirajai snake venom.

Teixeira, Sabrina Schaaf 04 March 2009 (has links)
A caracterização proteômica de venenos de serpentes contribui significativamente para o avanço das Ciências na área Biomédica. Várias destas moléculas, utilizadas como instrumentos de investigação de mecanismos celulares e moleculares, estão envolvidas em diversos processos fisiopatológicos e de intoxicação. No entanto, os venenos de serpentes ainda requerem caracterização funcional e/ou biológica adicionais. As fosfolipases A2s (PLA2s) são enzimas que induzem vários efeitos farmacológicos, e geralmente, correspondem a maior porcentagem do conteúdo protéico dos venenos de serpentes. Desta forma, o isolamento e a caracterização bioquímica, funcional e estrutural de PLA2s poderão gerar informações importantes para o melhor entendimento dos efeitos farmacológicos e de intoxicação ocasionados por estas proteínas. Este trabalho descreve o isolamento e a caracterização bioquímica, enzimática, funcional e estrutural da primeira PLA2 Asp49 ácida, denominada Bpir-I-PLA2, isolada do veneno da serpente Bothrops pirajai, espécie endêmica da região Sul do Estado da Bahia e atualmente, integrante da Lista Nacional das Espécies da Fauna Brasileira Ameaçadas de Extinção. O isolamento da Bpir-I-PLA2 foi realizada através de dois passos cromatográficos, envolvendo inicialmente cromatografia de troca iônica, seguida de HPLC de fase reversa. Quanto submetida à eletroforese em gel de poliacrilamida para proteínas ácidas, Bpir-I-PLA2 apresentou alto grau de homogeneidade. A massa molecular relativa, determinada através de eletroforese em gel de poliacrilamida com agente desnaturante, foi de aproximadamente 28.000 para a forma de dímero e 14.500 para o monômero. A focalização isoelétrica demonstrou uma única banda para a fosfolipase A2, revelando pI aproximado de 4,9. A região N-terminal de Bpir-I-PLA2, seqüenciada através do método de degradação de Edman, apresentou elevada homologia entre outras PLA2s de venenos de serpentes. A composição de amioácidos da proteína corroborou com sua característica ácida, apresentando um elevado conteúdo de aminoácidos carregados negativamente. A enzima apresentou elevada atividade fosfolipásica e induziu edema moderado in vivo. Além disso, Bpir-I-PLA2 foi capaz de inibir a agregação plaquetária e a coagulação do plasma, e também induzir efeito hipotensor in vivo e citotóxico sobre células tumorais, bactérias, fungos e leishmanias. O tratamento da enzima com o reagente brometo de p-bromofenacila neutralizou as atividades enzimática, inibitória sobre a agregação plaquetária, anticoagulante, hipotensora e antitumoral. A moderada atividade edematogênica foi parcialmente inibida. O cDNA contendo 366 bp (BPIR-A) que codifica a proteína Bpir-I-PLA2 foi clonado e a proteína recombinante, expressa. Bpir-I-PLA2 recombinante apresentou a mesma sequência de aminoácidos, estrutura secundária, atividade fosfolipásica e efeito inibitório sobre plaquetas, observados para a proteína nativa Bpir-I-PLA2, sugerindo que a recPLA2 foi eficientemente expressa e purificada. Devido à baixa toxicidade demonstrada, a Bpir-I-PLA2 pode tornar-se uma ferramenta importante nos estudos das desordens da coagulação, como também um potencial modelo para a elaboração de novos fármacos para uso na clínica-médica. / The proteomic characterization of snake venoms significantly contributes to science advance in the biomedical area. Several venom toxins are used as instruments for the investigation of cellular and molecular mechanisms, and are involved in a number of physiopathological and intoxication processes. Nevertheless, snake venoms still require further functional and/or biological characterization. Phospholipases A2 (PLA2s) are enzymes that induce several pharmacological effects and usually correspond to the major percentage of snake venom protein contents. Being so, the isolation and characterization of PLA2s could generate important information for the better understanding of the pharmacological and toxic effects caused by these proteins. This work describes the isolation and biochemical, enzymatic and functional characterization of the first acidic Asp49 PLA2 (named Bpir-I-PLA2) from the venom of Bothrops pirajai snake, an endemic species from the south region of state of Bahia and that nowadays is part of the national list of Brazilian fauna species threatened of extinction. The isolation of Bpir-I-PLA2 was carried out by two chromatographic steps, an ion-exchange chromatography followed by reverse phase HPLC. When submitted to polyacrylamide gel electrophoresis for acidic proteins, Bpir-I-PLA2 showed high homogeneity level. The relative molecular mass, determined by polyacrylamide gel electrophoresis with denaturating agent, was of approximately 28,000 for the dimmer and 14,500 for the monomer. With high phospholipase activity and pharmacological effects, characteristic of acidic isoforms, Bpir-I-PLA2 did not present myotoxic activity and showed to be little edematogenic. However, the enzyme acts inhibiting platelet aggregation, delaying plasma clotting time and inducing hypotension, antitumoral effects, antibacteria, antifungal and parasiticide actions. The treatment of the enzyme with the reagent p-bromofenacil brometo neutralized the enzymatic activities, inhibition of aggregation platelet, anticoagulant, hypotensive and antitumoral. The moderate activity edematogenic was inhibited partially. The cDNA (BPIR-A) that codes the protein Bpir-I-PLA2 was cloned and the protein recombinant, expressed. Bpir-I-PLA2 recombinant presented the same sequence of amino acids, structures secondary, phospholipase activity and inhibitory effects on platelet of the native protein, suggesting that recPLA2 was efficiently express and isolated. Due to its low toxicity, Bpir-I-PLA2 could become an important tool in the study of the disorders of the clotting as well as a potential model for the elaboration of new drugs for use in the clinic-doctor.
669

Avaliação da qualidade da água e do sedimento e ocorrência de cianobactérias potencialmente tóxicas em trecho paulista do Rio Paraíba do Sul / Water and sediment quality assessment and occurrence of potentially toxic cyanobacteria in São Paulo stretch of the Paraíba do Sul River

Queiroz, Lucas Gonçalves 19 June 2015 (has links)
O Rio Paraíba do Sul é considerado um dos mananciais mais importantes da região sudeste, uma vez que está localizado entre as duas maiores capitais brasileiras: São Paulo e Rio de Janeiro. A qualidade das águas deste manancial encontra-se bastante comprometida devido ao desmatamento, mau uso e ocupação do solo em áreas urbanas e rurais, uso de insumos agrícolas e pelo lançamento diário de aproximadamente um bilhão de litros de efluentes domésticos. Esta situação é agravada uma vez que apenas 21% do efluente lançado na Bacia do Rio Paraíba do Sul são tratados. O descarte de efluentes, ricos em nutrientes como fósforo e nitrogênio, pode contribuir diretamente no processo de eutrofização. O objetivo deste trabalho foi avaliar a qualidade da água e do sedimento no trecho paulista do Rio Paraíba do Sul, entre os municípios de Aparecida, Guaratinguetá, Lorena e Cachoeira Paulista, frente às variáveis físicas, químicas, biológicas e ecotoxicológicas, além de determinar a ocorrência de cianobactérias potencialmente tóxicas. Coletas de água e sedimento foram realizadas à jusante e montante de cada município nos meses de agosto/13, novembro/13, fevereiro/14, maio/14 e agosto/14. As variáveis avaliadas foram pH, temperatura, condutividade, turbidez, OD, DBO, DQO, fósforo total, nitrogênio total, série de sólidos, coliformes termotolerantes, clorofila-a e testes de toxicidade utilizando Daphnia similis e Pseudokirchneriella subcapitata para a água. Para o sedimento foram realizadas granulometria, matéria orgânica, fósforo total e testes de toxicidade utilizando D. similis e Chironomus xanthus. Foram calculados Índice de Qualidade das Águas (IQA) e Índice de Estado Trófico (IET) das águas do manancial. Análises estatísticas foram aplicadas: Grupamento de Cluster, Correlação de Spearman e Análise dos Componentes Principais (ACP). Os resultados mostraram que as variáveis OD, fósforo total e coliformes termotolerantes não estão de acordo com o estabelecido pela resolução CONAMA 357/05. Toxicidade aguda e crônica foi determinada nas amostras de água, sobretudo nos períodos chuvosos, novembro/13 e fevereiro/14. Observou-se uma redução ao longo do período avaliado de fósforo total, DBO e sólidos totais na água e fósforo total e matéria orgânica no sedimento. Estes valores podem estar relacionados a implantação de estações de tratamento de esgoto nos municípios de Aparecida e Cachoeira Paulista no final do ano de 2013. O IQA foi classificado como \'Boa\', exceto nos pontos referentes à jusante dos municípios de Aparecida e Guaratinguetá, classificados como \'Regular\'. O IET mostrou que a maioria dos pontos pôde ser classificada como \'Mesotrófico\', exceto pelo ponto referente ao final do trecho, jusante de Cachoeira Paulista, que foi classificado com \'Oligotrófico\'. Os principais gêneros de cianobactérias encontrados foram Borzia sp., Hapalosiphon sp., Johannesbaptistia sp., Leptolyngbya sp., Lyngya sp., Oscillatoria sp., Synechocystis sp. e Phormidium sp. A partir das análises estatísticas observouse que a precipitação pluviométrica obteve grande influência sobre os principais parâmetros avaliados. Além disso, observou-se a influência de parâmetros relacionados ao lançamento de efluentes sobre a qualidade da água. Os resultados sugerem que o Rio Paraíba do Sul demanda maiores ações que promovam a melhoria da qualidade de suas águas, sobretudo quanto ao lançamento de efluentes. / The Paraíba do Sul River is considered one of the most important rivers of the Brazilian Southeast. It is located between the two major Brazilian cities: São Paulo and Rio de Janeiro. The water quality from this source is significantly impaired due to deforestation, misuse and occupation of the soil in urban and rural areas, use of agricultural inputs and the daily release of approximately one billion liters of domestic sewage. This situation is aggravated because only 21% of the effluent released in the basin is treated. The discharge of effluents rich in nutrients such as phosphorus and nitrogen, can contribute directly to the eutrophication process. The aim of this study was to evaluate the water and sediment quality, and determine the occurrence of potentially toxic cyanobacteria in the São Paulo stretch of the Paraíba do Sul River, between the cities of Aparecida, Guaratinguetá, Lorena and Cachoeira Paulista. Water and sediment samples were collected upstream and downstream in each municipality on August/13, November/13, February/14, May/14 and August/14. The variables evaluated were pH, temperature, conductivity, turbidity, DO, BOD, COD, total phosphorus, total nitrogen, solid series, fecal coliforms, chlorophyll-a and toxicity tests using Daphnia similis and Pseudokirchneriella subcapitata in the water. For the sediment, granulometry, organic matter, total phosphorus and toxicity tests were performed using D. similis and Chironomus xanthus. Water Quality Index (WQI) and Trophic State Index (TSI) of the water were calculated. Statistical analyses were applied: Grouping Cluster Analysis, Spearman Correlation and Principal Component Analysis (PCA). The results showed that DO, total phosphorus and fecal coliforms were not in accordance with the CONAMA resolution 357/05. Acute and chronic toxic effect were determined in water samples, during the rainy season, November/13 and February/14. A reduction of total phosphorus, total solids and BOD in the water, and total phosphorus and organic matter in the sediment was observed during this study. These reduced values can be related to implementation of sewage treatment plants in the cities of Aparecida and Cachoeira Paulista at the end of year 2013. The WQI was classified as \'Good\', except at downstream point of the municipalities of Aparecida and Guaratinguetá, classified as \'Regular\'. The TSI has shown that most of the points could be classified as \'mesotrophic\', except for the point downstream of Cachoeira Paulista, classified as \'oligotrophic\'. The main genera of cyanobacteria found were Borzia sp., Hapalosiphon sp., Johannesbaptistia sp., Leptolyngbya sp., Lyngya sp., Oscillatoria sp., Synechocystis sp. and Phormidium sp. From the statistical analysis, it was observed that rainfall had strong influence on the main parameters evaluated. Furthermore, the influence of parameters related to the discharge of effluents on water quality was observed. The results suggest that the Paraíba do Sul River demands more actions to promote the improvement of the quality of its waters, especially regarding the discharge of effluents.
670

Processamento e caracterização da liga 66%Co-28%Cr-6%Mo para implantes / Processing and Characterization of the 66Co-28Cr-6Mo (%weight) alloy for implants

Santos, Luiz Alberto dos 27 February 2012 (has links)
Neste trabalho foram avaliadas as condições de processamento e caracterização da liga 66Co-28Cr-6Mo utilizada em implantes. Cada lingote foi produzido por meio de fusão a arco voltáico, sob atmosfera de argônio em um cadinho de cobre refrigerado à água. Os resultados foram comparados com aqueles de uma barra da liga 66Co-28Cr-6Mo comercial. A temperatura de forjamento a quente da liga é em torno de 1200º C, pois temperaturas menores levam a fraturas do material no decorrer do forjamento. Na análise química realizada na liga 66Co-28Cr-6Mo obteve-se uma concentração de 0,038%C, ou seja, esta concentração encontrada nos lingotes da liga 66Co-28Cr-6Mo produzida estão dentro das especificações da norma ASTM F1537 para a liga com baixo teor de carbono (0,14%C). Os lingotes apresentaram uma microestrutura policristalina, com presença de defeitos volumétricos (poros) possívelmente advindos do processo de solidificação. Foram realizados ensaios de oxidação nas temperaturas de 1200 oC, 1100 oC, 1000 oC e 900 oC por cerca de 30 minutos para avaliar o grau de oxidação da liga de 66Co-28Cr-6Mo em elevadas temperaturas, pois a conformação mecânica da liga é realizada a quente conforme descrito na norma ASTM F1537. O limite de escoamento à tração da liga 66Co-28Cr-6Mo na condição bruta é em média de 750 MPa e o módulo de elasticidade da mesma liga é, aproximadamente de 158 GPa. Notou-se na liga 66Co-28Cr-6Mo comercial uma microestrutura com grãos refinados, proveniente do processo de forjamento a quente. Além disso, observa-se a presença de maclas, porém não se pode afirmar se este defeito é devido à deformação plástica ou tratamento térmico. O limite de escoamento à tração da liga 66Co-28Cr-6Mo comercial foi de 975 MPa e módulo de elasticidade é, de aproximadamente de 203 GPa. A densidade de corrente de corrosão das ligas 66Co-28Cr-6Mo produzida e comercial são respectivamente 1,9x10-7 e 1,5x10-7 Acm-2. Estes valores indicam uma alta resistência à corrosão de ambas as ligas em solução de Ringer. As amostras das ligas 66Co-28Cr-6Mo comercial e produzida apresentaram uma curva de viabilidade celular acima da linha do índice de citotoxicidade (IC50%) = 50%, ou seja, as ligas são consideradas não tóxica. / In this study we evaluated the processing conditions and characterization alloy 28%Cr 66%Co-6%Mo used in implants. Each ingot was produced by through arc melting arcing under argon atmosphere in a water-cooled copper crucible. The results were compared with those of a commercial bar 66Co-28Cr-6Mo alloy. The temperature of hot forging 66Co-28Cr-6Mo alloy should be around 1200 º C because lower temperatures lead to fracture of the material during forging. In the chemical analysis performed on the alloy 66Co-28Cr-6Mo obtained a concentration 0,038 %C. Indeed the alloy 66Co-28Cr-6Mo produced are within the specifications of ASTM F1537 for the alloy with low carbon (0.14% C). The ingots had a polycrystalline microstructure with the presence of volumetric defects (pores) possibly arised from the solidification process. Oxidation tests were carried out at temperatures of 1200 oC, 1100 oC 1000 oC and 900 oC for about 30 minutes to evaluate the degree of oxidation of 66Co-28Cr -6Mo alloy at high temperatures because of the mechanical forming league will be held hot. The tensile yield strength of the 66Co-28Cre-6Mo alloy is provided and gross average of 750 MPa and elasticity of the same alloy is approximately 158 GPa. It was noted in the 66Co-28Cr-6Mo alloy commercial grain microstructure with a refined, from the hot forging process. Moreover, observed the presence of twinned, but one cannot say whether this defect is due to plastic deformation or heat treatment. The tensile yield strength of the 66%Co-28%Cr-6%Mo alloy trade was 975 MPa and modulus of elasticity is of approximately 203 GPa. The corrosion current density of the 66Co-28Cr-6Mo alloys and commercial produced are respectively 1,9.10-7 and 1,5.10-7 Acm-2. These values indicate a high corrosion resistence of both alloys in Ringer\'s solution. Samples of the commercial and produced 66Co-28Cr-6Mo alloys a curve above the cell viability index of citotoxicity (IC50%) = 50% the alloys are considered non-toxic.

Page generated in 0.0534 seconds