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Poinot, Christine. "Mécanismes de réactions nucléaires induites par un faisceau de carbone 12 à 20 Mev par nucléon sur cibles moyennes et lourdes." Bordeaux 1, 1985. http://www.theses.fr/1985BOR10635.
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Versavaud, Sophie. "Mise en forme des thermoplastiques chargés de nanotubes de carbone : application à la microinjection de Polyamide 12." Phd thesis, Ecole nationale supérieure d'arts et métiers - ENSAM, 2012. http://pastel.archives-ouvertes.fr/pastel-00866487.
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L'addition de nanotubes de carbone multiparois (MWNT) dans une matrice de polyamide 12 (PA 12), électriquement isolante, permet d'augmenter les propriétés électriques vers un comportement conducteur. Cette modification est influencée par l'arrangement des MWNT en chemins de conduction qui permettent le transfert des charges électriques entre deux électrodes. La conductivité électrique des nanocomposites isotropes atteint une valeur asymptote (~10-2 S.m-1) pour des teneurs supérieures à 1,2% en masse (seuil de percolation électrique). En microinjection, les nanocomposites sont soumis à des taux de cisaillement très élevés (~104 s-1) et des gradients de températures extrêmes, qui conditionnent fortement la microstructure et les propriétés électriques de pièces mises en forme par ce procédé. Cette thèse a eu pour but d'expliquer l'influence de la vitesse de cisaillement (0,02 s-1 - 1 s-1) et la vitesse de refroidissement (3 °C.min-1) sur l'évolution des propriétés électriques du nanocomposite PA12/MWNT. L'analyse de ces propriétés a permis de déduire, à l'état fondu, l'évolution de l'arrangement de MWNT dans cette fenêtre de conditions. Dans les pièces microinjectées, nous constatons une perte complète du comportement conducteur dans la direction normale au plan d'écoulement et une chute de la conductivité dans les directions d'injection et transverse. Ces faits suggèrent alors un arrangement en forme d'agrégats faiblement orientés dans le plan d'écoulement, qui est corroboré par la très large distribution d'orientation déterminée par l'analyse en spectroscopie Raman des pièces micro-injectées. Lors du procédé de microinjection, les agrégats de MWNT seraient alors cassés dans des agrégats plus petits, mais fortement déconnectés les uns des autres, expliquant ainsi la chutedes propriétés électriques mais aussi l'observation d'une microstructure quasi isotrope à l'échelle macro et micro.
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Jammes, Laurent. "Photoproduction de pions neutres au voisinage du seuil sur les noyaux d'hélium-4, de carbone-12 et de calcium-40." Grenoble 2 : ANRT, 1988. http://catalogue.bnf.fr/ark:/12148/cb376144715.
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Jammes, Laurent. "Photoproduction de pions neutres au voisinage du seuil sur les noyaux d'hélium 4, de carbone 12 et de calcium 40." Paris 11, 1988. http://www.theses.fr/1988PA112241.
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Nous présentons les résultats d'une mesure de section efficace totale de photo production de pions neutres sur les noyaux d'hélium 4, de carbone et de calcium, dans le domaine d'énergie de photons allant du seuil de réaction à 180 MeV, ainsi que des données prises à 148 MeV sur les noyaux de lithium 6 et de magnésium. Cette expérience a utilisé le faisceau de photons étiquetés obtenu par annihilation en vol des positrons délivrés par l'accélérateur Linéaire de Saclay (A. L. S. ) sur les électrons atomiques d'une cible d'hydrure de lithium. Le pion neutre est identifié par la détection en coïncidence de ses deux photons de désintégration, dans un ensemble de détecteurs en verre au plomb couvrant un grand angle solide. L'expérience sur l'hélium 4 a nécessité l'étude et la réalisation d'une cible cryogénique d'hélium liquide adaptée à la géométrie de l'installation. Un système de filtre a photons, fonctionnant sur le principe d'un spectromètre à paires, permet une mesure précise du flux incident. La détermination de la section efficace repose sur les analyses conjointes et similaires des événements caractéristiques de la création d'un pion ou d'une paire électron-positron, en coïncidence avec la détection d'un photon d'étiquetage. La simulation du fonctionnement du détecteur de pions neutres par une méthode de type Monte-Carlo, permet le calcul de l'efficacité de détection. Les deux calculs dont nous disposons, qui incluent la distorsion de l'onde du pion dans l'état final, sont tous deux en accord avec les données expérimentales, bien que leurs estimations en onde plane diffèrent notablement. Nous essayons de dégager l'origine de cette coïncidence provenant de l'utilisation, par les auteurs, de diverses simplifications cinématiques et de déterminations différentes du potentiel optique. Enfin, par la comparaison des prédictions d'un modèle simple d'approximation d'impulsion avec les sections efficaces expérimentales, nous déduisons pour chaque noyau, une évaluation de l'effet de l'interaction pion-noyau dans l'état final, relativement au carbone.
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Cachier-Rivault, Hélène. "Approche isotopique du cycle atmospherique du carbone particulaire." Paris 7, 1987. http://www.theses.fr/1987PA077061.
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Etude des emissions naturelles de carbone particulaire et evaluation des perturbations induites par les activites humaines sur le cycle atmospherique du carbone. Travail s'appuyant sur des mesures de concentration et de granulometrie d'aerosol preleve au cours de nombreuses campagnes en milieu continental tempere et tropical ainsi qu'en zone oceanique des deux hemispheres. L'origine et le transport a grande echelle des aerosols sont determines par des mesures de composition isotopique (**(13)c/**(12)c) au spectrometre de masse
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De, Reuse Hilde. "Regulation de l'expression des genes centraux d'un systeme de transport d'hydrates de carbone, le systeme des phosphotransferases dependantes du pep d'escherichia coli k-12." Paris 6, 1990. http://www.theses.fr/1990PA066666.
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Le systeme des phosphotransferases dependantes du pep (dit pts) catalyse simultanement le transport et la phosphorylation (au depens du pep) de plusieurs sources de carbone chez un grand nombre d'especes bacteriennes. Chez e. Coli, ce systeme complexe comprend deux phosphoproteines cytoplasmiques communes a toutes les sources de carbone pts, hpr et enzyme i codees par les genes ptsh et ptsi respectivement. Les autres proteines du pts, des phosphoproteines cytoplasmiques (les eiii) ou des permeases membranaires (les eii), sont specifiques d'une ou de quelques sources de carbone pts. Le transport du glucose fait intervenir l'eiii glucose qui est codee par le gene crr et la permease eii glucose. Une region d'adn portant les genes, ptsh, ptsi et crr d'e. Coli a ete clonee et entierement sequencee. L'expression de ces genes a ete etudiees par deux approches: l'identification des arn-m exprimes dans cette region et des mesures in vivo du niveau d'expression de ces genes par la technique de fusion avec le gene rapporteur lacz. Ces trois genes constituent un operon complexe avec plusieurs modes de transcription. L'expression des genes ptsh, ptsi et crr est soumise a deux controles positifs faisant intervenir: 1) le complexe cap-ampc et 2) une regulation originale dependant du glucose exogene dont nous avons montre qu'elle faisait intervenir un mecanisme de transduction de signal. En amont de l'operon pts, nous avons identifie par les analyses in vivo et in vitro les regions d'adn impliquees dans ces deux regulations transcriptionnelles
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Tatischeff, Vincent. "De la dissociation coulombienne aux observations astronomiques : nouvelles voies d'etude de la reaction de capture alpha radiative sur le carbone 12 dans les etoiles massives." Caen, 1996. http://www.theses.fr/1996CAEN2057.
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La reaction de fusion d'un noyau de carbone 12 avec un noyau d'helium 4 pour former de l'oxygene 16 joue un role essentiel dans la vie des etoiles massives. Malgre plusieurs decennies d'efforts experimentaux, l'incertitude qui subsiste sur la section efficace de cette reaction freine la modelisation stellaire. En etudiant la possibilite de preciser ce taux de reaction au travers d'observations astronomiques, nous avons analyse la recente detection d'un rayonnement gamma caracteristique en provenance des nuages moleculaires d'orion, et montre qu'elle est compatible avec l'hypothese de l'ejection de noyaux de carbone 12 et d'oxygene 16 par une supernova particuliere. Si cette donnee observationnelle peut etre riche d'enseignements sur l'evolution des etoiles massives, elle ne permet pas de se passer d'une determination de la section efficace en laboratoire. Nous avons utilise la methode de la dissociation coulombienne, consistant a mesurer de maniere plus aisee la section efficace de la reaction inverse. Mais dans le cas de la dissociation de l'oxygene 16, il est necessaire de discriminer les composantes e1 et e2, ainsi que les contributions electromagnetique et nucleaire a l'excitation du projectile. Nous avons alors montre theoriquement que la correlation angulaire des fragments alpha et carbone 12 formes par la dissociation de l'oxygene 16 constitue une observable sensible du processus d'excitation. L'experience que nous avons entreprise aupres du spectrometre speg du ganil nous a permis, par l'exemple de l'excitation de l'etat de parite non-naturelle a 12,53 mev de l'oxygene 16, de demontrer la faisabilite experimentale de la methode. Les premiers resultats que nous avons obtenus sur le facteur astrophysique e2 de la capture alpha radiative sont un encouragement certain
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Agrinier, Pierre. "L'evolution de la croute oceanique vue par les rapports isotopiques de l'oxygene, du carbone et de l'hydrogene." Paris 7, 1987. http://www.theses.fr/1987PA077176.
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Nous avons etudie, au moyen des isotopes stables de l'oxygene, du carbone et de l'hydrogene, deux types de roches: la sequence ophiolitique de xigaze. Tibet et les eclogites a carbonates de norvege. Elles peuvent representer 2 etats de la croute oceanique a deux stades extremes de son evolution: 1) l'hydrothermalisme d'une dorsale lente, 2) le metamorphisme de haute pression d'une zone de subduction. Ces travaux et la litterature concernant la croute oceanique, nous permettent de dessiner l'evolution isotopique d'une portion de croute oceanique et d'estimer ses implications sur les echanges globaux manteau-ocean
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Alwan, Raad Aboud. "Analyse des évolutions structurales et du comportement mécanique d'un acier au chrome-nickel-molybdène à très bas carbone du type Z1CNDA 12-09-02, en fonction des traitements thermiques." Paris 11, 1989. http://www.theses.fr/1989PA112002.
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Nous avons étudié le comportement structural d'un alliage inoxydable martensitique de composition : Fe-11,7 Cr-9,2 Ni-1,99 Mo-0,71 A1-0,34 Ti en fonction de différents cycles thermiques appliqués dans l'intervalle des températures comprises entre -160 et 1150°C. La cinétique de la transformation austénitique, ainsi que la fraction volumique d'austénite de réversion conservée à l'ambiante -lors de traitements isochrones ou isothermes- ont été caractérisées en fonction des conditions de traitement. L'étude du comportement de l'alliage au cours de revenus isothermes, a montré que cet alliage se durcit en trois stades, impliquant la formation de précipités différents ou d'amas avant que n'interviennent les phénomènes de survieillissement et la formation de l'austénite de réversion. Finalement, pour obtenir des propriétés mécaniques (Rm et R 0,002) intéressantes ainsi qu'une amélioration de A % et KCV' il s'est révélé souhaitable de procéder à des traitements de revenu à des températures comprises entre 525 et 550°C, pour lesquelles le gain de ductilité et de résilience est obtenu au détriment d'une légère diminution des caractéristiques de résistanceWe have studied the structural behavior of a stainless steel capable of age hardening, with a very low carbon content. The martensitic alloy concerned by this research has the following composition : Fe-11. 7 Cr-9. 2 Ni-1. 99 Mo-0. 71 Al-0. 34Ti. The thermal treatments have been undertaken in the temperature range of -160°C and 1150°C. The kinetics of the austenitic transformation and the volumic fraction of reversed austenite stabilizes at ambient temperature have been caracterized as a function of the treatment conditions (isothermal and/or isochronal). During isothermal tempering three stages of hardening may occure before the overaging phenomenon and the formation of reversed austenite. Finally, interesting mechanical properties (Rm and R0. 002) and the improvement of A % and KCV for this alloy, can be obtained when the tempering is performed in the range of 525-550°C, the increase in ductility and toughness being obtained to the detriment of a small decrease in mechanical proof
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Racicot, Marc-Antoine. "L'effort climatique canadien et le développement durable : l'encadrement réglementaire des mécanismes de tarification du carbone et des autorisations de nouveaux oléoducs." Master's thesis, Université Laval, 2019. http://hdl.handle.net/20.500.11794/36717.
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En ayant pris l’engagement de réduire les émissions de gaz à effet de serre (GES) du Canada de 30% en 2030 par rapport au niveau de 2005, le gouvernement fédéral canadien doit faire face à de nombreux enjeux juridiques pour mettre en oeuvre l’Accord de Paris. De prime abord, il y a une contradiction entre la cible climatique du Canada et les autorisations accordées par le gouvernement fédéral pour aller de l’avant avec des projets pétroliers et gaziers, tels que l’agrandissement du réseau Trans Mountain. De plus, les contestations constitutionnelles qui se profilent à l’horizon ajoutent un risque supplémentaire quant aux chances de succès du Canada d’atteindre son objectif climatique. Le présent mémoire vise donc à effectuer une analyse critique de la stratégie pancanadienne en matière d’atténuation des émissions de gaz à effet de serre, en nous penchant sur les instruments juridiques utilisés. Nous examinerons le Cadre pancanadien sur la croissance propre et les changements climatiques (CPC) et les mesures dont il prévoit l’adoption. Il s’agit dans un premier temps de décrire le contenu de l’Accord de Paris et d’expliquer les mécanismes de mise en oeuvre d’un tel traité dans l’ordre juridique interne du Canada, en insistant sur la prise en compte du partage des compétences constitutionnelles. Une fois cette analyse effectuée, nous dressons un portrait d’ensemble des mesures comprises dans le CPC et l’évaluons selon une grille d’analyse qui permet d’évaluer l’efficacité des mesures climatiques tout en mettant en lumière la façon dont le gouvernement fédéral assume ses différents rôles dans la transition énergétique. En effet, dans sa gestion de la transition, l’État doit en assurer l’intégrité (stabiliser), il doit l’accélérer (impulser), il doit négocier avec les conséquences sociales et politiques de la transition énergétique (amortir) et il doit faire preuve de cohérence (aligner).
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Johnson, Rolfe Bradley. "Crystallization effects of carbon nanotubes in polyamide 12." Thesis, Georgia Institute of Technology, 2010. http://hdl.handle.net/1853/34795.
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Multi-walled carbon nanotubes (MWNTs) are a nanofiller that has desirable multifunctional properties. They have been shown to offer improved mechanical, thermal, and electrical properties in composites. Research has been studying their incorporation into polymer composites. Polyamide 12 is a polyamide of interest that has been manufactured to have lower moisture absorption and higher ductility than other commercial polyamides such as 6 and 6,6 at room temperature.
In these studies, MWNTs have been incorporated into polyamide 12 at different weight loadings and using MWNTs with differing outer diameters. The composites were melt processed and characterized using differential scanning calorimetry (DSC) to understand the effects of MWNTs on the crystallization behavior of polyamide 12. A melt peak splitting behavior was observed in the polyamide 12 and composite samples when the specimens were not allowed to fully anneal.
Total crystallinity in the samples remained the same between the polyamide 12 and composites when the samples were fully annealed. Total crystallinity increased by 1 to 4 percent in the composites over the polyamide 12 when samples were not fully annealed. The addition of MWNTs to the polyamide 12 system increased the amount of crystallization contained in the lower temperature melting peak. An increase in MWNT concentration resulted in an increase in the crystallinity contained in the lower temperature peak. The addition of smaller diameter MWNTs resulted in a further increase in the lower temperature peak when the outer diameter was below a critical size.
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Silva, Silvia Caroline Gomes dos Santos. "Síntese de materiais compósitos micro-mesoporosos visando a captura de CO2." Universidade Federal de Sergipe, 2015. http://ri.ufs.br:8080/xmlui/handle/123456789/3479.
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Coordenação de Aperfeiçoamento de Pessoal de Nível Superiorfactor responsible for climate change worldwide. In recent years, several research are intended to developing new methods and technologies to capture and separation CO2. The use of the adsorption method for separating CO2 is a promising alternative in view of the potential to reduce energy costs by eliminating aqueous solutions and providing capture and regeneration rates adequate. In this context, this paper presents the synthesis of composite type materials ZSM-12 / MCM-41 and ZSM-12 / MCM-48, seeking to combining the properties of the zeolitic material to the structural advantages of mesoporous materials, resulting in obtaining materials with high CO2 adsorption capacity. For this, the materials were synthesized by hydrothermal method and mechanosynthesis. The materials were characterized by XRD, absorption spectroscopy in the infrared, thermal analysis, adsorption-desorption analysis of N2 A 77 K, SEM and TEM. The CO2 adsorption capacity of these materials were investigated by gravimetric analysis. The results obtained from the characterization techniques showed that the synthesis methodology, used for desilication phase of ZSM-12, was efficient in obtaining a composite material with integrated micro and mesoporous phases. On the other hand, the results showed that by mechanosynthesis was possible to obtain materials formed by mixing between the micro and mesoporous phases. Also, comparing the results of adsorption CO2 the obtained composite materials by hydrothermal method with those obtained by mechanosynthesis it was concluded that the adsorption capacity is influenced by crystallinity and amount of the phase ZSM-12. The results showed from adsorption, in general, ZM48-75 samples, ZM41 A/MH R3 and ZM41-50 showed higher adsorption capacity than pure zeolitic and mesoporous materials, respectively. Thus, the composite materials of the type ZSM-12/ZSM-41 and MCM-12/MCM-48 are promising adsorbents for CO2 separation.
O aumento da concentração de dióxido de carbono na atmosfera é apontado como o principal fator responsável pelas mudanças climáticas em escala mundial. Nos últimos anos, várias pesquisas têm por finalidade o desenvolvimento de novos métodos e tecnologias para captura e separação de CO2. A utilização do método de adsorção para separação de CO2 é uma alternativa promissora, tendo em vista o potencial para reduzir os custos energéticos, eliminando soluções aquosas e proporcionando captura e taxa de regeneração adequadas. Nesse contexto, neste trabalho apresenta-se a síntese de materiais compósitos do tipo ZSM-12/MCM-41 e ZSM-12/MCM-48, visando combinar as propriedades do material zeolítico com as vantagens estruturais dos materiais mesoporosos, resultando na obtenção de materiais com elevadas capacidades de adsorção de CO2. Para isto, os materiais foram sintetizados pelo método hidrotérmico e por mecanosíntese. Os materiais obtidos foram caracterizados por DRX, espectroscopia de absorção na região do infravermelho, análise térmica, analise de adsorção-desorção de N2 A 77 K, MEV e TEM. A capacidade de adsorção de CO2 destes materiais foi investigadas através da análise gravimétrica. As técnicas de caracterização mostraram que a metodologia de síntese adotada via dessilicalização da fase ZSM-12 foi satisfatória na obtenção de um material compósito com as fases micro e mesoporosas integradas. Por outro lado, os resultados evidenciaram que através da mecanosíntese foi possível obter materiais formados pela mistura entre as fases micro e mesoporosas. Além disso, comparando-se os resultados de adsorção de CO2 dos materiais compósitos obtidos via método hidrotérmico com os obtidos via mecanosíntese foi possível concluir que a capacidade de adsorção é influenciada pela cristalinidade ou teor da fase ZSM-12. Considerando-se os resultados de adsorção apresentados, de maneira geral, as amostras ZM48-75, ZM41-A/R3-MH e ZM41-50, apresentaram maior capacidade de adsorção que os materiais zeolíticos e mesoporosos puros, respectivamente. Sendo assim, os materiais compósitos do tipo ZSM-12/MCM-41e ZSM-12/MCM-48 são promissores adsorventes para separação de CO2.
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Almeida, Liana Soares. "Síntese e caracterização do ácido 12-tungstofosfórico, H3PW12O40-nH2O, suportado em carbono ativado." reponame:Repositório Institucional da UnB, 2012. http://repositorio.unb.br/handle/10482/10647.
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Os heteropoliácidos de Keggin, de fórmula geral H8-nXnM12O40, onde n é o estado de oxidação do heteroátomo X, podem ser aplicados como catalisares ácidos em diversas reações em âmbito industrial. A fim de demonstrar as vantagens em se aplicar esses heteropoliácidos em reações com solventes polares (ex., esterificação), um catalisador ácido heterogêneo foi sintetizado: o ácido 12-tungstofosfórico (H 3PW12O40·nH2O, ou H3PW) suportado em carbono ativado. O método de preparação envolveu a técnica de impregnação usando como solvente uma solução de ácido clorídrico 0,1 mol L-1 e diferentes concentrações de H3PW (20, 30, 40 e 50% em massa). O catalisador suportado foi calcinado a diferentes temperaturas (200, 300, 400 e 500 ºC) e caracterizado com diversas técnicas físico-químicas. Espectros de FTIR mostraram que as bandas características do H3PW aparecem após a impregnação no carbono ativado, porém quando o catalisador suportado é calcinado acima de 400 ºC as bandas do H3PW (40 e 50%) mostraram-se mais intensas devido à oxidação do carbono. Espectros de RAM-RMN de 31 P demonstraram que o poliânion, antes e depois da calcinação, é retido fortemente na superfície do suporte, pela presença dos sinais típicos entre -14,5 e -13,5 ppm, este último relacionado a amostras com menores graus de hidratação. Resultados de DRX evidenciaram que amostras de concentrações próximas a 20% de H3 PW apresentam elevado grau de dispersão. A cristalinidade aumenta com a concentração do H3PW no suporte e com maiores temperaturas de calcinação, exceto para as amostras contendo 40% que não apresentaram nenhum grau de cristalinidade. As análises de TG/DTG mostraram um aumento da estabilidade térmica dos catalisadores suportados com o teor de H3PW impregnado. Isotermas de adsorção de N2(-196 ºC) indicaram que ao aumentar a temperatura de calcinação há um aumento da área superficial dos catalisadores impregnados devido à liberação de moléculas fisicamente adsorvidas. Contudo, as amostras contendo o teor de 50% H 3PW apresentaram comportamento oposto, provavelmente relacionado a uma melhor distribuição do heteropoliácido suportado e à diminuição de aglomerados catalíticos. Experimentos de calorimetria e adsorção de piridina (Cal-Ad) revelaram que os sítios ácidos dos catalisadores suportados eram mais fracos, mas apresentavam maior dispersão e maior disponibilidade dos que os do H3PW puro. Testes de lixiviação com etanol confirmaram o alto grau de interação com o carbono e apenas nas amostras com teores acima de 40% e temperaturas de calcinação acima de 200 ºC foi detectada lixiviação. ______________________________________________________________________________ ABSTRACT
Keggin heteropolyacids of general formula H 8-nXnM12O40, where n is the oxidation state of heteroatom X, can be applied as acid catalysts in several reactions in industry. In order to demonstrate the advantages of applying these heteropolyacids in reactions with polar solvents (e.g., esterification), a heterogeneous acid catalyst was synthesized: 12-tungstophosphoric acid (H3 PW12O40·nH2O, or H3PW) supported on activated carbon. The preparation method involved the impregnation technique using a solution of hydrochloric acid 0.1 mol L-1 as solvent and different loadings of H3 PW (20, 30, 40 and 50 wt%). The supported catalysts were calcined at different temperatures (200, 300, 400 and 500 ºC) and characterized with several physical-chemistry techniques. FTIR spectra showed that the characteristic bands of H3PW appeared after impregnation on activated carbon, but when the supported catalyst was calcined above 400 °C, the bands of H 3PW (40 and 50%) were more intense due to carbon oxidation. 31P MAS-NMR spectra proved that the polyanion, before and after calcination, was strongly retained on the surface of the support, with typical signals between -14.5 and -13.5 ppm, the later value is related to species with lower degree of hydration. XRD results showed that the samples with loadings close to 20% H3 PW had a high degree of dispersion. The crystallinity of the material increased with the amount of H3PW on the support and with higher calcination temperature, except for the samples with 40%, which had no crystallinity degree. The TG/DTG curves showed a slight increase of thermal stability of the supported catalysts with higher loadings of H3PW. The adsorption isotherms of N2 at -196 ºC indicated that the increase of calcination temperature also increased the surface area of the impregnated catalysts due to the release of physically adsorbed molecules. However, the samples containing 50% H3 PW showed an opposite behavior, probably related to a better distribution of supported heteropolyacid and the decrease of catalytic clusters. Calorimetry and adsorption (Cal-Ad) experiments with pyridine revealed that the acid sites of supported catalysts were weaker, but had a higher dispersion and increased accessibility than pure H3 PW. Leaching tests with ethanol were performed and confirmed the strong degree of interaction with carbon and only the samples with loadings above 40% and calcination above 200 ºC showed detectable leaching.
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CAMPOS, MARIA C. A. "Espalhamento inelastico de eletrons no sup(12) C." reponame:Repositório Institucional do IPEN, 2001. http://repositorio.ipen.br:8080/xmlui/handle/123456789/10947.
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Tese (Doutoramento)
IPEN/T
Instituto de Pesquisas Energeticas e Nucleares - IPEN/CNEN-SP
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Neequaye, Theophilus, George Paa Kwesi Affadu-Danful, and Gregory W. Bishop. "Investigations of Pre and Post treatment protocols in the fabrication of carbon fiber ultramicro- and nanoelectrodes." Digital Commons @ East Tennessee State University, 2018. https://dc.etsu.edu/asrf/2018/schedule/12.
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Ultramicroelectrodes (UMEs) have gained considerable attention over the few past decades due to the important roles they play in electrochemical studies. Electrodes with dimension less than 25 mm can generally be classified as UMEs. These electrodes exhibit enhanced electrochemical properties as their dimensions get smaller hence making nanoelectrode (production of electrodes with limiting dimensions less than 100 nm) a continuing area of interest in research. Nanometer size electrodes have advantages of high sensitivity which enables them to be used in fields such as single particle characterization and single cell analysis, and fast electron and mass transport which permits use for studying short-lived and transient electrochemical reactions such as those involved in neurochemistry. Nanoelectrodes can be fabricated via a few different strategies which include but are not limited to electrochemically etching a thin metal wire down to a cone shape or flame-etching a carbon fiber, and chemical vapor deposition of carbon in nanopipette. This work seeks to employ the use of the laser-assisted pulling method to fabricate carbon fiber electrodes sealed in glass capillary tubes. Effects of various pre- and post- treatment techniques on electrode size and stability are explored.
Key words: Electrodes, Electrochemical, carbon fiber.
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MacKenzie, John Alan. "A study of pion photoproduction on carbon-12 in the delta resonance region." Thesis, University of Edinburgh, 1995. http://hdl.handle.net/1842/1756.
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This thesis describes a study of the 12 C(gamma; pie + n) reaction in the Delta resonance re gion using tagged photons. The experiment was accomplished using the MAMIB c.w. electron accelerator at the Institut f¨ur Kernphysik, Mainz. Bremsstrahlung photons, created when 855 MeV electrons strike a 4 ¯m Nickel radiator, were tagged with a 2 MeV resolution using the Glasgow tagging spectrometer installed in the MAMI A2 experimental hall. The data is presented as triple and (by integrating over the pion energy) double differential cross sections. A comparison is made with Distorted Wave Impulse Approximation (DWIA) predictions generated by the code THREEDEE. It is concluded that more reliable theoretical calculations are required. In particular, a better treatment of the distortion and absorption of the outgoing particles is needed. Initial comparisons with the microscopic theory of Carrasco are attempted and the problems faced in making such a comparison are described and solutions suggested.
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Nchodu, M. R. "Alpha emission from the interactions of 14-200 MeV neutrons on carbon-12." Master's thesis, University of Cape Town, 1994. http://hdl.handle.net/11427/17513.
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Summary in English.Bibliography: pages 89-93.
Cross-sections for the production of alpha particles from the ¹²C(n,α)⁹Begs and ¹²C(n,n')3α reactions were measured for incident neutrons in the energy range 25 to 52 MeV. The measurements were reduced to absolute cross-sections by simultaneously observing deuteron recoils from n-d elastic scattering in the scintillator using D(n,n)D elastic scattering cross-section as a reference standard. Neutron energy was determined by time-of-flight and pulse shape discrimination (PSD) was used to identify and separate alphas and deuterons from other reaction products. The feasibility of distinguishing different mechanisms for the ¹²C(n,n')3α reaction by means of PSD was also investigated.
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Craig, Whitney Richert. "Evaluation of zinc binding groups (ZBGs) as inhibitor building blocks using carbonic anhydrase and the catalytic domain of matrix metalloproteinase 12 (cdMMP-12)." Miami University / OhioLINK, 2017. http://rave.ohiolink.edu/etdc/view?acc_num=miami1500311991462216.
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Gupta, Anju R. "Investigation of neuronal affinity to photoresist derived carbon Study of differentiation and m-RNA expression in PC-12 cells." Link to electronic thesis, 2007. http://www.wpi.edu/Pubs/ETD/Available/etd-050407-142740/.
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Thesis (M.S.) -- Worcester Polytechnic Institute.Keywords: Scanning electron microscope; Cell adhesion; Carbon; Gene expression; Nerve growth factor; nerve regeneration. Includes bibliographical references (leaves 81-87).
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Bledig, Stefan Albert. "Investigation of the genetic regulation affecting carbon flux through phosphoenolpyruvate in Escherichia coli K-12." Thesis, University of Warwick, 1995. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.306975.
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Robson, Joseph Douglas. "Modelling of carbide and Laves phase precipitation in 9-12 wt% chromium steels." Thesis, University of Cambridge, 1997. https://www.repository.cam.ac.uk/handle/1810/224753.
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Bremner, C. A. "High spin resonances in '1'2C+'1'2C scattering." Thesis, University of Oxford, 2000. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.365691.
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Smith, Robin. "Experimental measurements of break-up reactions to study alpha clustering in carbon-12 and beryllium-9." Thesis, University of Birmingham, 2017. http://etheses.bham.ac.uk//id/eprint/7866/.
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Due to the high binding energy of the α-particle, this object can preform in heavier atomic nuclei. This work explores α-clustering in ⁹Be and ¹²C by measuring their nuclear break-up. For ⁹Be, it has been proposed that the two α-particles of the unstable ⁸Be nucleus are bound together by a covalently shared neutron. This thesis reports the observation of a state in ⁹Be at 3.8 MeV through the ⁹Be(⁴He,α)ααn reaction. By comparing its reduced width with that of a potential mirror analogue in ⁹Be, its angular momentum was shown to be J < 7/2. This is consistent with a hitherto unmeasured 3/2⁺ molecular binding configuration state. The ¹²C nucleus is thought to consist of three α-clusters and its famous Hoyle state has been shown to possess an unusually large volume. Due to its low density, this state may behave like a Bose-Einstein condensate, where the fermonic structures of the constituent α-particles are no longer important. By precisely measuring the decay of the Hoyle state into three α-particles, through the ¹²C(⁴He,α)3α reaction, an upper limit for the direct 3α decay branch of 0.047% was obtained. This lies below predictions for the decay of a condensate state, casting doubt on this interpretation.
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Souza, Valdiva Rossato de. "Mensuração contábil dos créditos de carbono no Brasil, China e Índia." Universidade de São Paulo, 2015. http://www.teses.usp.br/teses/disponiveis/12/12136/tde-16062015-105131/.
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A presente pesquisa teve como objetivo identificar a incidência de impactos econômicos no patrimônio das empresas brasileiras, chinesas e indianas provocados pela mensuração e reconhecimento ao valor justo dos ativos provenientes de Reduções Certificadas de Emissões (RCEs) geradas em seus processos produtivos, com a implementação de projetos de Mecanismos de Desenvolvimento Limpo (MDLs), durante o período de 2005 a 2012. Consideraram-se os estímulos oferecidos com as diretrizes do Protocolo de Quioto e a representatividade de implementações de projetos de MDLs da China, da Índia e do Brasil, para apresentar, com base em pesquisas descritiva, analítica e quantitativa, uma proposta de mensuração contábil das RCEs, capaz de evidenciar os fluxos futuros de seus benefícios econômicos, partindo-se do modelo de Ratnatunga, Jones e Balachandran (2011). Para tanto, trabalhou-se com a hipótese de que as RCEs não estão sendo mensuradas ao valor justo enquanto ativo, fato este que tem inviabilizado a evidenciação dos efeitos patrimoniais dos fluxos de caixa futuros. Descreveu-se a teoria da mensuração contábil como suporte ao valor justo; discutiu-se os padrões contábeis existentes nos países mencionados e as principais características que envolvem as adoções das International Financial Reporting Standards (IFRSs) em cada um deles, com foco na mensuração contábil ao valor justo, aceita pelo International Accounting Standards Board (IASB). As orientações contábeis internacionais emanadas para contabilização das RCEs foram apresentadas para analisar o cenário atual de desenvolvimento do tratamento contábil atribuível ao ativo em questão. Assim, detectou-se que a mensuração das RCEs tem sido pouco discutida. Sugeriu-se que com a efetivação do registro dos projetos de MDLs junto ao Conselho Executivo da United Nations Framework Conference on Climate Change (UNFCCC), as RCEs passem a ser reconhecidas ao valor justo e como ativos intangíveis desenvolvidos internamente por parte das entidades hospedeiras dos projetos de MDLs, em contrapartida ao Patrimônio Líquido (PL), até o momento de sua realização. A base para mensuração do valor justo proposta foi os valores de mercados ativos. Em função do lapso temporal que estarão gerando benefícios econômicos, realizou-se projeção financeira sobre as quantidades potenciais constantes estimadas de Reduções Esperadas (REs) para todo o período de desenvolvimento das atividades dos projetos, utilizando-se uma taxa Euribor para desconto de seus valores futuros ao presente. De posse dessas variáveis, os valores justos das REs de 31 projetos de MDLs brasileiros, 379 chineses e 318 indianos, foram projetados sobre o valor do PL de 15 empresas brasileiras, 56 chinesas e 183 indianas componentes da amostra da pesquisa, com apoio do teste estatístico não-paramétrico Wilcoxon. Os resultados da pesquisa forneceram indícios de que a mensuração ao valor justo das RCEs, e seu reconhecimento enquanto ativo intangível, poderia ter representado um impacto positivo no grupo de contas patrimoniais das empresas participantes da pesquisa. Assim, a aplicabilidade empírica da mensuração ao valor justo das RCEs embasada em discussões teóricas já existentes, possibilitou a realização de avaliações desse ativo enquanto item patrimonial capaz de gerar efeitos econômicos positivos no patrimônio das entidades localizadas em países em desenvolvimento, durante a primeira fase do Protocolo de Quioto.This research aimed to identify the incidence of economic impacts on equity of Brazilian, Chinese and Indian companies caused by the measurement and recognition at fair value of the assets from Certified Emission Reductions (CER) generated in their production processes, with the implementation of Clean Development Mechanisms (CDM) projects from 2005 to 2012. It was considered the incentives offered to the guidelines of the Kyoto Protocol and the representativeness of CDM projects implementation of China, India and Brazil, to present, based on descriptive, analytical and quantitative research, a proposal for accounting measurement of CER, able to enhance the future flows of its economic benefits, based on the Ratnatunga, Jones and Balachandran (2011) model. Therefore, it worked with the hypothesis that the CER are not measured at fair value as assets, a fact that has made impossible the disclosure of balance sheet effects of future cash flows. It was described the theory of accounting measurement as support at fair value. It was discussed existing accounting standards in those countries and the main characteristics that involve the adoption of International Financial Reporting Standards (IFRS) in each of them, focusing on accounting measurement at fair value, accepted by the International Accounting Standards Board (IASB). The international accounting guidelines issued for accounting of CER were presented to analyze the current scenario of development of the accounting treatment attributable to the asset. Thus, it was found that the measurement of CERs has been little discussed. It was suggested that with the realization of the registration of CDM projects with the Executive Council of the United Nations Framework Conference on Climate Change (UNFCCC), CER start to be recognized at fair value as intangible assets developed internally by the host entities of CDM projects, in contrast to Equity, until the moment of its realization. The basis for measuring fair value proposition was the values of active markets. Depending on the time gap that will generate economic benefits, a financial projection on potential constants estimated quantities of Expected Reductions (ER) for the whole period of development of project activities was carried out, using a Euribor rate to discount their future values to the present. With these variables, the fair values of ER from 31 Brazilian CDM projects, 379 Chinese and 318 Indians were simulated on the value of equity of 15 Brazilian companies, 56 Chinese and 183 Indian components of the survey sample, with test support statistical non-parametric Wilcoxon. The survey results provided evidence that the fair value measurement of CER, and its recognition as an intangible asset, could have represented a positive impact on the group balance sheet accounts of the participating research companies. Thereby, the empirical applicability of the fair value measurement of CER grounded in existing theoretical discussions, made it possible to carry out assessments of this asset as a heritage item capable of generating positive economic effects on equity of entities located in developing countries, during the first stage of the Kyoto Protocol.
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Gupta, Anju R. "Investigation of Neuronal Affinity to Photoresist Derived Carbon: Study of Diferentiation and m-RNA Expression in PC-12 Cells." Digital WPI, 2007. https://digitalcommons.wpi.edu/etd-theses/713.
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Regenerative medicine holds promises for many neurodegenerative diseases such as Traumatic Brain Injury (TBI), a disorder that occurs when a sudden trauma causes damage to the brain, leading to apoptosis or necrosis of brain neurons. More than 5 million Americans suffer from TBI as a result of inability to regenerate damaged neurons. The aim of this project was to develop a biocompatible and electrically conductive substrate to promote growth and regeneration of neurons and for our long-term goal as a probe to record intracellular and multisite signals from brain. The substrate was fabricated by pyrolyzing a polymeric precursor -SPR 220.7 at temperatures higher than 700 ºC. Human Neuroblastoma cells - SK-N-MC, SY5Y and mouse teratocarcinoma cells P-19 were found to attach and proliferate on photoresist derived carbon film. Growth and differentiation of rat pheochromocytoma cell-PC12 that serves as a model for primary neurons was demonstrated. Initial examination of cell growth and differentiation was done by observing cell shape and size, and measuring the length of neurites after the cells were differentiated by NGF. Further characterization of cells cultured on photoresist derived carbon substrate was achieved by testing mRNA genes- GADPH and Tau. Findings from this investigative work would possibly help to study new approaches to promote neuronal growth and differentiation in damaged brain regions of people with TBI or in patients with other neurodegenerative disorders, such as Alzheimer's disease in regaining memories.
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Athreya, Siddharth Ram. "Processing and characterization of carbon black-filled electrically conductive nylon-12 nanocomposites produced by selective laser sintering." Diss., Georgia Institute of Technology, 2010. http://hdl.handle.net/1853/39508.
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Electrically conductive polymer composites are suitable for use in the manufacture of antistatic products and components for electronic interconnects, fuel cells and electromagnetic shielding. The most widely used processing techniques for producing electrically conductive polymer composites place an inherent constraint on the geometry and architecture of the part that can be fabricated. Hence, this thesis investigates selective laser sintering (SLS), a rapid prototyping technique, to fabricate and characterize electrically conductive nanocomposites of Nylon-12 filled with 4% by weight of carbon black. The objective of the dissertation was to study the effects of the SLS process on the microstructure and properties of the nanocomposite. The effect of laser power and the scan speed on the flexural modulus and part density of the nanocomposite was studied. The set of parameters that yielded the maximum flexural modulus and part density were used to fabricate specimens to study the tensile, impact, rheological and viscoelastic properties. The electrical conductivity of the nanocomposite was also investigated. The thermo-mechanical properties and electrical conductivity of the nanocomposites produced by SLS were compared with those produced by extrusion-injection molding.
The structure and morphology of the SLS-processed and extrusion-injection molded nanocomposites were characterized using gas pycnometry, gel permeation chromatography, differential scanning calorimetry, electron microscopy, polarized light microscopy and x-ray diffraction. Physical models were developed to explain the effects of the processing technique on the structure and properties of the nanocomposites. Finally, a one-dimensional heat transfer model of the SLS process that accounted for sintering-induced densification and thermal degradation of the polymer was implemented in order to study the variation in part density with respect to the energy density of the laser beam.
This dissertation demonstrated that SLS can be successfully used to fabricate electrically conductive polymer nanocomposites with a relatively low percolation threshold. This capability combined with the ability of SLS to fabricate complicated three-dimensional objects without part-specific tooling could open up several new opportunities.
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Sun, Hsueh-Li. "Charge State Dependence of M-Shell X-Ray Production in 67Ho by 2-12 MeV Carbon Ions." Thesis, University of North Texas, 1994. https://digital.library.unt.edu/ark:/67531/metadc278725/.
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The charge state dependence of M-shell x-ray production cross sections of 67HO bombarded by 2-12 MeV carbon ions with and without K-vacancies are reported. The experiment was performed using an NEC 9SDH-2 tandem accelerator at the Ion Beam Modification and Analysis Laboratory of the University of North Texas. The high charge state carbon ions were produced by a post-accelerator stripping gas cell. Ultra-clean holmium targets were used in ion-atom collision to generate M-shell x rays at energies from 1.05 to 1.58 keV. The x-ray measurements were made with a windowless Si(Li) x-ray detector that was calibrated using radiative sources, particle induced x-ray emission (PIXE), and the atomic field bremsstrahlung (AFB) techniques.
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Leask, Peter John. "Probing nuclear molecular analogue states in carbon, boron and beryllium isotopes." Thesis, University of Birmingham, 2000. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.369340.
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Almeida, Liana Soares. "Policondensação catalítica do D,L-ácido lático por meio do ácido 12-tungstofosfórico suportado em carbono, sílica e alumina." reponame:Repositório Institucional da UnB, 2016. http://repositorio.unb.br/handle/10482/20146.
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Tese (doutorado)—Universidade de Brasília, Instituto de Química, Programa de Pós-Graduação em Química, 2016.Submitted by Fernanda Percia França (fernandafranca@bce.unb.br) on 2016-05-03T17:36:10Z No. of bitstreams: 1 2016_LianaSoaresAlmeida_Parcial.pdf: 2359351 bytes, checksum: e93cfeffd7d4692f4d9152ec80260bfa (MD5)
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O poli(ácido lático) (PLA) é um polímero importante devido suas significativas propriedades como a biocompatibilidade e a biodegradabilidade. O H3PW12O40 (H3PW) suportado no carbono ativado (C) em diferentes concentrações foi utilizado na polimerização catalítica do D,L-ácido lático para formar o PLA. Os catalisadores foram caracterizados por diferentes técnicas a fim de confirmar a integridade do ânion de Keggin. A evidência da estrutura foi claramente comprovada através de dados espectroscópicos como FT-IR e de MAS RMN de 31P, os quais exibiram características intrínsecas ao ânion. A presença de microporos e mesoporos foi confirmada por análises de adsorção de nitrogênio a baixa temperatura. A estabilidade da cadeia polimérica foi observada por curvas termogravimétricas (TG) usando a temperatura da velocidade máxima de degradação (TD) a fim de determinar ótimas condições do produto (isto é, temperatura de reação a 180 oC por 15 h; 0,1% m/m de catalisador em relação à massa do D,L-ácido lático; 20% m/m de H3PW no carbono, calcinado a 400 ºC). O melhor catalisador foi reutilizado em mais três ciclos reacionais. O polímero obtido foi caracterizado por cromatografia de permeação em gel (GPC), difração de raios X (DRX), calorimetria exploratória diferencial (DSC), espectroscopia de FT-IR, RMN de 1H e 13C, e rotação óptica específica ([]D25). A massa molar média do polímero foi de 17400 g mol-1. Um isômero esteroespecífico, o poli(L-ácido lático) (PLLA), foi obtido com aproximadamente 70% de seletividade provavelmente por um mecanismo de polimerização catiônica. A superfície do catalisador contendo 20% H3PW/C foi examinada por microscopia eletrônica de varredura (MEV). A análise comparativa do catalisador antes e depois das três reutilizações exibiu boa dispersão das partículas esféricas do H3PW e a presença de resíduos do polímero após o uso do catalisador, o qual pode agir como uma semente cristalina para o crescimento de novas cadeias poliméricas em cada um dos novos ciclos reacionais. Além disso, testes catalíticos utilizando sílica e alumina como suportes para o H3PW12O40 foram realizados. Com o auxílio das técnicas de RMN de 1H e 13C foi possível observar a formação da estrutura polimérica do PLA, a qual foi comprovada por padrões de DRX dos mesmos materiais. Os resultados de rotação óptica específica ([]D25) sugerem que os polímeros obtidos por catálise utilizando alumina pura ou como suporte para o H3PW apresentaram maior teor de caráter L do que aqueles obtidos a partir dos catalisadores análogos com carbono e sílica nas mesmas condições.
Poly(lactic acid) (PLA) is an important polymer because of its significant biocompatibility and biodegradability properties. Supported H3PW12O40 (H3PW) on activated carbon (C) at different loadings was utilized in the catalytic polymerization of D,L-lactic acid to form PLA. The catalysts were characterized by multiple techniques to confirm the integrity of the Keggin anion. The evidence of the structure was clearly proven by FT-IR and 31P MAS NMR spectroscopic data, which showed intrinsic features of the anion. The presence of micropores and mesopores was also confirmed by nitrogen adsorption analysis at low temperature. The stability of the polymer chain was monitored by thermogravimetric analysis (TG) using the temperature of the maximum velocity degradation (TD) to determine the optimal production conditions (i.e., reaction temperature at 180 ºC for 15 h; 0.1 wt.% of catalyst in relation to D,L-lactic acid mass; 20 wt.% loading of H3PW on carbon, calcined at 400 ºC). The obtained polymer was characterized by gel permeation chromatography (GPC), X-ray diffraction (XRD), differential scanning calorimetry (DSC), FT-IR, 1H/13C NMR spectroscopy, and specific optical rotation ([]D25). The average molar mass of the polymer was 17400 g mol-1. A stereo specific isomer, poly(L-lactic acid) (PLLA), was obtained with approximately 70% selectivity, probably by a mechanism of cationic polymerization. The surface of the catalyst with 20wt. % loading of H3PW/C was examined by scanning electron microscopy (SEM). The comparative analysis of the catalyst before and after three reutilizations showed good dispersion of the spherical particles of H3PW and the presence of the polymer after the use of the catalyst, which might act as a crystalline seed for the growth of new chains in each new reaction cycle. Beside this, catalytic tests using silica and alumina as supports for H3PW12O40 were performed. Using 1H and 13C NMR spectroscopy, it was possible to observe the formation of PLA polymeric structure, which was proven by XRD patterns of the same materials. The results of specific optical rotation ([]D25) suggested that catalyzed polymerization using pure alumina or supported H3PW showed L content higher than those obtained from analogous carbon and silica catalysts under the same conditions.
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Paggi, Rodrigo Acácio. "Sinterização seletiva a laser de compósitos com gradiente funcional entre poliamida 12 e nanotubos de carbono aplicáveis no setor aeroespacial." Florianópolis, SC, 2008. http://repositorio.ufsc.br/xmlui/handle/123456789/91882.
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Dissertação (mestrado) - Universidade Federal de Santa Catarina, Centro Tecnológico. Programa de Pós-Graduação em Engenharia MecânicaMade available in DSpace on 2012-10-24T03:30:40Z (GMT). No. of bitstreams: 1 260040.pdf: 26241231 bytes, checksum: 0f22c8ef5cb35d959b17837c3540024e (MD5)
A fabricação rápida de componentes poliméricos é uma alternativa na obtenção de geometrias complexas para as mais variadas aplicações. A tecnologia de fabricação, que compreende a sobreposição de camadas sucessivas de material particulado e sinterização por laser (SLS, Selective Laser Sintering), apresenta enorme potencial de integrar liberdade de forma, com a possibilidade de variação composicional em determinados volumes do componente. Neste contexto, a obtenção de propriedades específicas pode ser alcançada com o emprego de materiais especiais em conjunto com os tradicionalmente utilizados. A adição de nanotubos de carbono (CNTs) ao material particulado, mais especificamente a poliamida, pode dar origem a nanocompósitos com propriedades interessantes para o setor aeroespacial, como: elevada resistência mecânica e propriedades elétricas e térmicas incomuns à maioria dos materiais poliméricos. O objetivo deste trabalho foi a obtenção de peças com gradiente funcional, fabricados pela técnica de Sinterização Seletiva a Laser, a partir de compósitos de Poliamida 12 (PA12) e nanotubos de carbono de múltiplas paredes (MWCNTs). Para a obtenção das propriedades mecânicas otimizadas foram estudadas etapas de tratamento de superfície dos nanotubos, com o objetivo de melhorar sua interação com a matriz. Estudos para obtenção de parâmetros otimizados de processamento foram realizados com compósitos PA12/MWCNTs, com o intuito de aumentar a resistência mecânica em relação à base polimérica. As análises microestruturais e das propriedades mecânicas foram obtidas por ensaios dinâmico-mecânicos e microscópio eletrônico de varredura. Um modelo de componente mecânico exibindo um gradiente de composição foi confeccionado e analisado. Foram obtidos aumentos percentuais em termos de propriedades mecânicas na ordem de 20% com a adição de 1,0% em massa de nanotubos de carbono. A incorporação de 3%p da mesma carga apresentou decréscimo dessas propriedades mecânicas. A fabricação de componentes com gradiente de composição apresentou características interessantes quanto à morfologia e robustez, mostrando as potencialidades deste desenvolvimento para aplicações no setor aeroespacial, principalmente em componentes de satélite. The rapid manufacturing of polymeric parts is an alternative to obtain complex shapes for different applications. Selective laser Sintering (SLS) is a rapid manufacturing technology that presents a great potential to integrate freeform with the possibility of compositional change in the volume of the part through overlapping of successive layers of powder material. In this context, the achievement of specific properties can be obtained with the use of special materials together with common used materials. The addition of carbon nanotubes (CNTs) to the powder material, more specifically the polyamide, can form nanocomposites with interesting properties for aerospace industry, such as: high mechanical strength and unusual thermal and electrical properties for the many kinds of polymeric materials. The main objective of this work it to obtain parts with functional gradient from composites of Polyamide 12 (PA12) and multiple walled carbon nanotubes (MWCNTs), manufactured by the Selective Laser Sintering technique. In order to obtain the desired mechanical properties, it will be necessary steps of surface treatment of the nanotubes with the objective to improve its adhesion properties. Subsequent obtaining the mixture, it will be studied and optimized the processing parameters of the composites during the selective laser sintering process aiming at increase of the mechanical strength compared with the pure matrix material. The microstructural analysis and mechanical properties will be evaluated using dynamical mechanical and scanning electron microscope. A mechanical component consisting on a demonstrative character displaying a gradient of composition was made and analyzed. Percentage increases were achieved in flexural modulus and stress in the order of 20% with the addition of 1.0%wt of carbon nanotubes. The incorporation of 3%wt the same filler has provided decrease of mechanical properties. The manufacture of functionality graded components on the Y axis become possible, presenting interesting features on the morphology and mechanical consistency, showing the potential of this development for applications in the aerospace sector, especially in satellite components.
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Al-Reasi, Hassan Ali. "Tracking mercury biomagnification in fish from the Gulf of Oman using stable isotopes (carbon-13carbon-12 and nitrogen-15nitrogen-14)." Thesis, University of Ottawa (Canada), 2005. http://hdl.handle.net/10393/26836.
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Attempts to use stable isotope carbon (delta13C) and nitrogen (delta15N) ratios to construct trophic positions and track mercury biomagnification in zooplankton and 13 fish species from a coastal food web of the Gulf of Oman illustrated some potential differences in this environment compared to the aquatic ecosystem of the northern hemisphere. Due to the large difference in delta13C values (3.4‰) between zooplankton planktivorous fish species (S. crumenophthalmus, S. longiceps and R. kanagurta), zooplankton would seem to not be the primary diet of these fish species as commonly described in literature.
Total mercury (T-Hg) concentrations of zooplankton were very low (range 0.010 to 0.037 mug·g-1, N = 27) with a mean methyl mercury (MeHg) of 0.001 mug·g-1 (range 1-19%, N = 5). The lowest T-Hg (0.003 mug·g-1) was found in planktivore (S. longiceps) and the highest was 0.760 mug·g -1 in predator shark (R. acutus) with average MeHg for all fish of 72% (range: 33-100%, N = 150). Using 15 N as indicator of trophic position, neither total mercury (T-Hg) nor methyl mercury (MeHg) were found to biomagnify. Regression slopes were 0.08 and 0.05 for T-Hg and MeHg respectively as a function of delta15 N. This indicates that biomagnification was lower in this tropical ocean compared to that found in freshwater and marine ecosystems of the arctic and temperate zones.
Methyl mercury levels in the fish species commonly consumed are low and intake calculations showed that individuals can safely consume fish.
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Junior, Jaime Rissi Passarini. "Estudo interdisciplinar em sedimentos lacustres da região sul do estado de São Paulo. Reconstrução da vegetação e do clima no Quaternário tardio." Universidade de São Paulo, 2009. http://www.teses.usp.br/teses/disponiveis/64/64134/tde-16122009-102402/.
Full textAbstract:
O estudo de um testemunho coletado às margens de uma lagoa situada em meio a vegetação de Mata Atlântica no Parque Estadual Turístico do Alto Ribeira, sul do estado de São Paulo, permitiu a reconstituição da história da vegetação local ao longo dos últimos 2500 anos. Para isso, foram realizadas análises elementares, isotópicas e palinológicas. Também a partir de material retirado deste testemunho procedeu-se a comparação entre dois protocolos de tratamento químico para análises palinológicas do Quaternário. Os protocolos utilizados seguiram as metodologias propostas por Faegri e Iversen, 1989 (Protocolo 2) e por Colinvaux et al., 1999 (Protocolo 1). Foi desenvolvido um método de comparação que envolveu a quantidade de palinomorfos e a quantidade de matéria orgânica amorfa encontrados em 450 pontos escolhidos aleatoriamente em lâminas de ambos os protocolos e também foram levados em consideração o tempo, a praticidade de aplicação em rotina laboratorial, os custos e as quantidades e tipos de resíduos para cada protocolo. Cinco amostras de sedimento foram utilizadas para comparação e o Protocolo 1 apresentou em média 10% menos matéria orgânica amorfa e quase três vezes mais palinomorfos que o Protocolo 2. Os resultados das análises isotópicas e da palinologia mostraram que a vegetação da área em estudo teve uma fisionomia florestal pelo menos desde os últimos 2550 anos. Os valores de \'delta\'13C, em torno de - 29%o, indicaram a presença de plantas C3 em todo o período estudado e registraram um enriquecimento isotópico (-24,9%o) entre aproximadamente 1650 e 1480 anos AP. A análise palinológica apontou para a ocorrência de um clima mais frio que o atual entre 2550 anos AP e 2000 anos AP, com aumento na freqüência de Araucaria e diminuição de Arecaceae. Também foi detectada a ocorrência de um período de clima mais quente e mais úmido entre aproximadamente 1000 anos AP e 680 anos AP, com desaparecimento de Araucaria e aumento de Arecaceae, Weinmannia e de pteridófitas. A maior umidade deste período também é apontada pelos valores de C/N que indicam aumento de influência terrestre no sedimento e pelo aumento de Botryococcus. Em todas as camadas foram encontradas partículas carbonizadas, indicando períodos de ocorrência de paleoincêndios e de abertura florestal provavelmente associados à presença humana na regiãoOne sediment core collected at the margins of a lake surrounded by Atlantic rainforest vegetation at Parque Estadual do Alto Ribeira (PETAR), southern São Paulo state (Brazil), was analyzed, in order to reconstruct the history of the local vegetation over the last 2500 years. Elemental (Total Organic Carbon TOC and Total Organic Nitrogen), isotopic (C and N), pollen analysis and radiocarbon dating were integrated on this work. Also was made a comparison of two protocols for Quaternary pollen chemical treatment. The tested protocols were proposed by Faegri and Iversen, 1989 (Protocol 2) and by Colinvaux et al., 1999 (Protocol 1). The comparison methods developed in this study checked the protocols performance on the quantity of palinomorphs and of organic matter found in 450 random areas of microscope slides of each protocol. The time consuming, laboratory routine, costs and residue production by the protocols were considered for comparison. Five samples were used for comparison and the Protocol 1 showed an average of 10% less organic matter and more palinomorphs than Protocol 2. According to the isotopic and pollen results, the study area vegetation maintained as a forest for the last 2500 years BP. \'delta\'13C values of -29%o indicated the presence of C3 plants during all the sediment study and a isotopic enrichment (- 24,9%o) was observed between 1650 and 1480 yrs BP. Pollen analysis suggested the occurrence of colder climatic conditions between 2550 and 2000 yrs BP and a warmer and humid period was suggested between 1000 and 680 yrs BP. Charcoal particles were found since 2550 yrs BP indicating paleofire probably associated to the human activities
33
Yilmaz, Gokhun. "Effects Of Titanate Coupling Agents On Low Density Polyethylene And Polypropylene Blends And Composites." Master's thesis, METU, 2008. http://etd.lib.metu.edu.tr/upload/12610135/index.pdf.
Full textAbstract:
The objective of this study is to investigate the effects of titanate coupling agents on low density polyethylene (LDPE) and polypropylene (PP) blends and composites in terms of their mechanical and morphological properties. PP and LDPE composites were produced separately in a Brabender internal mixer, and CaCO3 was used as inorganic filler with compositions of 20, 40 and 60 %. PP/LDPE blends were produced in a twin-screw extruder with ratios of 75/25, 50/50 and 25/75. Their composites were prepared with addition of untreated and titanate-treated CaCO3 at 20% filler content.
Titanate coupling agent which is appropriate for LDPE, PP and CaCO3 was used to improve the mechanical properties of the blends and composites. For this purpose, &ldquoLica 12&rdquo
which is a kind of neoalkoxy organotitanate was used. Two forms of Lica 12 were used: powder form (Capow L12) and pellet form (Caps L12). Samples with and without titanate were prepared and then they were injection molded to make specimens for tensile and impact tests. Tensile fracture surfaces of samples were examined by scanning electron microscopy (SEM). Their mechanical and morphological properties were compared with each other to determine the effects of Lica 12. This study showed that Capow L12 improved strain at break and impact strength of PP/CaCO3 composites and PP/LDPE blends containing 75% and 50% PP. The strain at break value of of PP75 composite with 20% titanate-treated filler increased significantly up to 509% which is the highest value among all blends and composites in this study. Capow L12 exhibited its functions in PP matrix much more effectively than in LDPE matrix.
34
Millard, Pierre. "Role of the Csr system in carbon nutrition and in the control of central metabolism in Escherichia coli K-12 MG1655 and Nissle 1917." Thesis, Toulouse, INSA, 2012. http://www.theses.fr/2012ISAT0037/document.
Full textAbstract:
L’implantation d'Escherichia coli dans l’intestin résulte de stratégies adaptatives globales permettant à la bactérie de survivre face aux changements de conditions environnementales. Sur le plan métabolique, la colonisation de l’intestin par E. coli parait associée à la disponibilité de sources de carbone préférentielles glycolytiques, alors que la maintenance et la persistance reposent sur sa capacité à utiliser différents substrats alternatifs (principalement gluconéogéniques) lorsque les substrats préférentiels deviennent limitant. Cette activation des processus gluconéogéniques, qui implique une réorganisation fonctionnelle complète du métabolisme, est associée in situ à de profonds remaniements physiologiques (perte de motilité, formation de biofilms, etc) nécessaires à la persistance d'E. coli dans l’intestin. Ces différents processus sont coordonnés par des réseaux de régulation particulièrement complexes, dont le système Csr (Carbon storage regulator), un des principaux régulateur post-transcriptionnel d'E. coli. Lors de ces travaux, nous avons analysé le rôle du système Csr dans la nutrition carbonée et le contrôle du métabolisme central d'E. coli sur des sources de carbone supportant sa croissance dans l'intestin et représentatives des principales voies de son métabolisme central (glycolyse, voie des pentoses phosphate, voie d'Entner-Doudoroff cycle de Krebs). Cette étude a été réalisée chez deux souches d'E. coli présentant des capacités d'implantation distinctes : la souche de laboratoire K12 MG1655, et la souche Nissle 1917, un excellent colonisateur appartenant au groupe phylogénétique B2. Une analyse détaillée du fonctionnement métabolique par des approches systémiques quantitatives haut-débit (métabolomique et analyse des flux métaboliques par marquage isotopique) a été mise en place. Elle a été exploitée pour caractériser finement le comportement métabolique de souches sauvages et de mutants du système Csr d'E. coli sur différentes sources de carbone, identifier des caractères métaboliques propres à chaque souche, et étendre le rôle du système Csr dans la nutrition carbonée et dans le contrôle du métabolisme central d'E. coli. Nos résultats démontrent que i) Csr favorise l'utilisation d'un large spectre de sources de carbone aussi bien glycolytiques que gluconéogéniques, ii) Csr contrôle un nombre de voies métaboliques plus important que ce que l'on pourrait attendre à partir de ses cibles identifiées, et iii) que le contrôle global exercé par le système Csr sur le fonctionnement du métabolisme central dépend de la source de carbone. Un rôle du système Csr dans le contrôle du métabolisme redox (production de NADH et de NADPH) et énergétique (production d'ATP), non reporté à ce jour, est également démontré. Enfin, nos résultats suggèrent un rôle de Csr dans le contrôle de la balance anabolisme-catabolisme d'E. coli. Ces travaux renforcent le rôle potentiel du système Csr dans l'adaptation d'E. coli face aux changements de conditions environnementalesThe implantation of Escherichia coli in the gut results from global adaptive strategies that allow the bacteria to survive in the changing environment of the intestine. At the metabolic level, recent findings indicate that colonisation is mainly related to the utilization of sugars and sugar derivatives through glycolytic pathways. In contrast, persistence of E. coli in the gut is supported by less favorable substrates, including small organic acids. The use of the latter compounds requires activation of gluconeogenic pathways, and efficient switching between glycolytic and gluconeogenic carbon sources is likely to be a major feature of successful adaptation to life in the intestine. These adaptive processes are controlled by highly sophisticated regulatory networks, such as the Csr (carbon storage regulator) system which is the main post-transcriptional regulator in E. coli. Csr was found to control a broad range of phenotypes allowing E. coli to successfully implant and persist in the gut, such as biofilm formation, motility as well as many functions involved in carbon nutrition, including glycolysis, gluconeogenesis, acetate and glycogen metabolism. Although Csr is likely to play an important role in the adaptation of bacteria to the nutritional context of the host, it is poorly understood sofar. In this work, we investigate the role of the Csr system in the control of E. coli metabolism on physiologically-relevant carbon sources representative of the main glycolytic (Entner-Doudoroff pathway, pentose phosphate pathway, glycolysis) and gluconeogenic pathways of E. coli. This work was carried out on two E. coli strains with distinct implantation capabilities : the K12 MG1655 laboratory strain and the Nissle 1917strain, an efficient colonizer of the gut belonging to the highly competitive B2phylogenetic group. First, we designed a complete methodology (metabolomics and 13C-metabolic flux analysis) for quantitative, system-level investigations of the actual operation of E. coli metabolism. Then, we performed detailed, system-level investigations of wild-type strains and Csr mutants. This work provides valuable information regarding systemic properties of E. coli metabolism, and identifies metabolic specificities of the Nissle 1917strain likely involved in its competitiveness in the gut. The role of Csr appears to be qualitatively and quantitatively the same in both K12 MG1655 and Nissle 1917 strains. We show that i) Csr enhances the utilisation of a broad spectrum of glycolytic and gluconeogenic carbon sources, ii) Csr controls a range of metabolic pathways wider than expected from its known target enzymes, and iii) the actual impact of the Csr system on the central metabolism of E. coli depends on the carbon source. We also demonstrate that Csr controls energy and redox metabolism in E. coli. Csr enhances the production of ATP and of reduced cofactors (NADH and NADPH), and we suggest that it also may control the catabolism-anabolism balance in E. coli. Finally, our results reinforce the potential role of the Csr system in the global adaptation of the bacterium to the gut environment
35
Lee, Sung-Mo. "A performance evaluation of low pressure carbon dioxide discharge test." Link to electronic thesis, 2004. http://www.wpi.edu/Pubs/ETD/Available/etd-0430104-041342/.
Full textAbstract:
Thesis (M.S.)--Worcester Polytechnic Institute.Keywords: Deap-seated fire; flow calculation; maximum percent of agent in pipe; free efflux; carbon dioxide extinguishing system; low pressure; no efflux; surface fire; NFPA 12. Includes bibliographical references (p. 69-70).
36
Powrie, Calum John Young. "A study of the '1'2C(#gamma#,pp) reaction." Thesis, University of Glasgow, 1999. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.301509.
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Fog, Lotte S. "Coherent production of neutral pions on '1'2C and '4'0Ca." Thesis, University of Glasgow, 2001. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.368746.
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Boztosun, Ismail. "Coupled-channels calculations for the scattering of deformed light heavy-ions : a challenge to the standard approach." Thesis, University of Oxford, 2000. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.325373.
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Summers, Neil Christopher. "Beyond the adiabatic model for the elastic scattering of composite nuclei." Thesis, University of Surrey, 2001. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.368376.
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Biggs, Thomas. "Fire Frequency, Nutrient Concentrations and Distributions, and δ13C of Soil Organic Matter and Plants in Southeastern Arizona Grassland." Diss., The University of Arizona, 1997. http://hdl.handle.net/10150/244085.
Full textAbstract:
Over the past century, woody plants and shrubs have increased in abundance at the expense of grasslands in many semiarid regions. The availability and concentrations of nutrients influence the relative success of plants, but the effects of fire frequency on soil nutrients is unknown for semiarid grasslands. On the gunnery ranges of Fort Huachuca in southeastern Arizona, study sites were established to examine the effects of fire frequency on soil biogeochemistry, plant biochemistry, and δ¹³C values in soil organic matter (SOM). The sites were on homogeneous granitic alluvium where wildfire frequency history is known from 1973 to present and no cattle grazing has occurred in recent decades. Subplots represent fire frequencies of no burns, 3 fires per decade, and 5 fires per decade. The "no burn" plot has abundant C₃ Prosopis veleruina (mesquite) trees, whereas the burned plots are open C₄-dominated grasslands with scattered mesquite trees. Prosopis trees have altered SOM pools by the concentration of plant nutrients and the addition of isotopically light shrub litter. Frequent fires have altered the basic geochemistry and nutrient availabilities of the soil, and the changes appear to be significant enough to affect plant growth. Soil pH increases with burning frequency, and TOC, total nitrogen, and plant -available phosphorus show significant increases on the infrequently burned plot. Burning is advantageous for preservation or restoration of grasslands, as total living grass biomass is greater on the two burned plots. Root biomass is significantly lower on the "frequently burned" plot. Concentrations of the key nutrients nitrogen and phosphorus are reduced in plants on the burned sites compared to plants on the unburned site. Fires help re-distribute nutrients but evidence of nutrient concentrations and δ¹³C values are retained in SOM for many decades. Estimates of bulk carbon turnover rates range from 112 to 504 years. Evidence for modern C₃ shrub expansion is found in the shift of SOM δ¹³C values from values characteristic of C₄ grasses to C₃ shrubs in surface soil layers. δ¹³C(SOM) values indicate that the Holocene and Late Pleistocene were dominated by C₄ grasslands, and the pre-Late Pleistocene vegetation was a C₄-grass savanna with abundant C₃ plants.
41
Shawcross, Mark. "Breakup reactions populating cluster states in 28Si and 24Mg." Thesis, University of Surrey, 1999. http://epubs.surrey.ac.uk/843397/.
Full textAbstract:
The 12C+16O breakup of 28Si and the 12C+12C breakup of 24Mg have been studied following the interaction of a 170 MeV 24Mg beam with 7Li, 9Be,12C and 16O target nuclei. The measurements were performed at the Australian National University in Canberra, using the technique of Resonant Particle Spectroscopy. The breakup fragments from the decay of the resonant nuclei were detected in two Gas-Si-CsI telescopes positioned on opposite sides of the beam axis. The data suggest that the same states in 28Si are populated via the 7Li(24Mg, 12C 16O)3H, 9Be(24Mg,12C 16O)5He and 12c(24Mg,12C 16O)8Be reactions. This implies that the cluster decaying states are populated by direct a-transfer. Breakup has been observed from states in 28Si at excitation energies (spins) of (26.15), 28.17 (13-, 29.51, 29.95, 30.45, 30.76, (31.3), 31.65, 31.90, 32.51, 33.14, 33.41, 33.77, 34.45 (12+,14+) and 35.13 MeV. A consistent theoretical interpretation of the 28Si molecular structures has been given, taking into account the predictions of Nilsson-Strutinsky, a-cluster model and two centre shell model calculations. The present results for the 12C(24Mg,12C 12C)12C reaction agree with previous measurements. In addition, new spin assignments have been proposed for several of the breakup states in 24Mg. States have been observed at excitation energies (spins) of 20.54 (2+), 21.07 (4+), 21.88 (4+), 22.33 (4+), 22.90 (6+), 23.80 (6+,(8+)), 24.56 (8+), 25.14 (6+), 25.72, 26.41 (8+) and 27.12 MeV. Evidence for the population of many of these states via the 16O(24Mg,12C 12C)16O reaction has also been observed. However, the data gave no evidence for either the 7Li(24Mg,12C 12C)7Li or 9Be(24Mg,12C 12C)9Be reactions. The presently available information did not allow an unambiguous determination of the reaction mechanism responsible for the population of the 24Mg breakup states. The performance of the Gas-Si-Csl telescopes has been investigated. For multiplicity 2 events in the silicon strip detectors, a crosstalk has been observed between the two active strips. The energy calibration of the silicon strip detectors for penetrating particles has also been found to differ to that for stopped particles. Empirical corrections for both of these effects have been deduced allowing the simultaneous detection and identification of heavy and light ions within a single telescope. These techniques have been extended to the detection of 8Be → alpha+alpha events over a wide range of alpha-particle energies.
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Piela, Christine Marie. "Equatorial Pacific Sediment Deposition during the Early to Middle Miocene: Carbon Cycling and Proxies for Productivity." Thesis, 2010. http://hdl.handle.net/1969.1/ETD-TAMU-2010-12-8194.
Full textAbstract:
The equatorial Pacific is a major region of biological production in the world oceans and an important part of the global carbon cycle. Changes in climate during the Cenozoic (65 Ma to present) have impacted the carbon cycle, and it is important to assess these impacts. This study focuses on the primary productivity of the equatorial Pacific during the early to middle Miocene (24 - 12 Ma) as recorded by Deep Sea Drilling Project (DSDP) Site 574, and investigates the sedimentary components potentially linked to productivity: bio-Ba, bio-SiO₂, Corg, CaCO₃, and uranium, as well as detrital thorium to estimate clay-bound barium. Within this time frame the plate beneath Site 574 traveled northwesterly across the equator and allows a unique opportunity to monitor changes in productivity and the carbon cycle in this region. It is difficult to determine directly primary productivity from the sedimentary record because the preservation of different proxies for this parameter - Corg, bio-CaCO₃, and bio-SiO₂, can be highly variable. The variability has many causes, including nutrient recycling in the water column and the depth of the carbonate compensation depth (CCD), which prevents the preservation and ultimate burial of plankton debris at the seafloor. To interpret the production versus deposition rates during the early and middle Miocene, proxies were used in conjunction with direct measurements of biogenic remains. By determining the concentrations of biogenically produced barium (bio-Ba), which is less affected by degradation, it is evident that the mass of Corg produced was much greater than that preserved in the sediments. We observed higher deposition of bio-Ba and bio- SiO₂ as the site was transported over the equatorial divergence by plate tectonics, as expected. In contrast, CaCO₃, accumulation was low in the divergence region, and coincides with a dissolution event known from other site studies in the equatorial Pacific. The pattern of uranium deposition resembles CaCO₃ and Corg, and average U concentrations suggest that it was primarily deposited as a trace element in the shell material of biogenic carbonate. Corg also resembles CaCO₃ and appears to represent primarily a dissolution signal. Total uranium analysis proved to be a useful proxy for Corg and CaCO₃ preservation, and analysis of detrital thorium (²³²Th) concentration suggests very limited terrigenous clay input. Comparison of the different proxies reveals carbonate preservation events, changes in Corg preservation, and changes in deposition as DSDP Site 574 migrated northwesterly across the equator.
43
Jung, Woodong. "Petrographic, Mineralogic, and Geochemical Studies of Hydrocarbon-derived Authigenic Carbonate Rock from Gas Venting, Seepage, Free Gas, and Gas Hydrate Sites in the Gulf of Mexico and offshore India." Thesis, 2008. http://hdl.handle.net/1969.1/ETD-TAMU-2008-12-133.
Full textAbstract:
Authigenic carbonate rock (ACR) is derived from microbial oxidation of methane, biodegradation of crude oil, and oxidation of sedimentary organic matter. The precipitation of ACR was characterized petrographically, mineralogically, and geochemically. ACR collected from the seafloor in the Gulf of Mexico (GOM) and ACR recovered from drilled cores in the Krishna-Godawari (KG) basin offshore India were used. All study sites are associated with hydrocarbon gas venting, seepage, free gas, or gas hydrate. ACR from the GOM is densely cemented and extremely irregular in shape, whereas ACR from offshore India is generally an oval-shaped smooth nodule and also densely cemented. The dominant mineral in ACR is authigenic calcite.
ACR contains carbon derived from sedimentary organic carbon oxidation that geologically sequesters much fossil carbon. Bulk carbon and oxygen isotopes of ACR were measured. ACR from the GOM is strongly depleted in 13C with ?13C of ?42.5? and enriched in 18O with ?18O of 4.67?. The ?13C of hydrocarbon is typically more depleted in 13C than in the associated ACR. The reason is that authigenic carbonate cements from hydrocarbon oxidation generally enclose skeletal material characterized by normal marine carbonate. Three groups that represent different hydrocarbon sources to ACR were classified in this study: primary carbon sources to ACR from (1) methane plus biodegraded oil, (2) methane, or (3) biodegraded oil. Wide ranges in ?13C (?49.12 to 14.06?) and ?18O ( 1.27 to 14.06?) were observed in ACR from offshore India. In sediments, the ?13C may be affected by differences in the rate of organic carbon oxidation, which generate varying ?13C with depth during methanogenesis. Based on the wide range in ?13C, ACR from offshore India was classified: (1) ?13C may reflect high rates of organic carbon oxidation, (2) ACR may be derived primarily from methane oxidation, and (3) ?13C may reflect low rates of organic carbon oxidation.
?18O values are heavier than those of normal marine carbonates. The ?18O may be caused by reaction with deep-sourced water that was isotopically heavier than ambient seawater. Some samples may reflect heavy ?18O from gas hydrate decomposition, but it would not cause significant heavy oxygen isotopes.
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Jiang, Xiaodong. "Measurement of interference structure functions in quasielastic proton knockout from carbon-12." 1998. https://scholarworks.umass.edu/dissertations/AAI9909174.
Full textAbstract:
A description of the measurement of quasielastic interference structure functions for the nucleus $\sp{12}$C is presented. Longitudinally polarized electrons with an average polarization of 39 $\pm$ 4% and an initial energy of 660.0 MeV were scattered through 33.4 degrees from a graphite target. The scattered electrons were detected with a large magnetic spectrometer in coincidence with the knockout protons which were detected simultaneously by either of two small magnetic spectrometers placed out of the electron scattering plane. The forward-backward asymmetry A$\sb{91}$ and the beam helicity induced asymmetry A$\sbsp{01}{\prime}$ were measured, and the longitudinal-transverse interference structure functions $f\sb{01}$ and $f\sbsp{01}{\prime}$ were extracted for the $\sp{12}$C p-shell knockout reaction at a missing momentum of 115.0 MeV/c and a Q$\sp2$ of 0.13 (GeV/c)$\sp2$. This experiment was the first attempt in a series of $(\vec e,e\sp{\prime}p)$ experiments using multiple out-of-plane spectrometers to detect hadrons in isolating several interference structure functions simultaneously through precise asymmetry and cross section measurements. The equipment for these measurements was installed from 1995 to 1996 at the Bates Linear Accelerator Center in Middleton, Massachusetts, and this experiment was carried out in September of 1996.
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Thakre, Piyush R. "Processing and Characterization of Carbon Nanotubes Reinforced Epoxy Resin Based Multi-scale Multi-functional Composites." 2009. http://hdl.handle.net/1969.1/ETD-TAMU-2009-12-7638.
Full textAbstract:
This research is focused on investigating the effect of carbon nanotubes on
macroscale composite laminate properties, such as, interlaminar shear strength, interlaminar fracture toughness and electrical conductivity along with studying the
micro and nano-scale interactions of carbon nanotubes with epoxy matrix via thermomechanical and electrical characterization of nanocomposites. First an introduction
to the typical advanced composite laminates and multifunctional nanocomposites is
provided followed by a literature review and a summary of recent status on the processing and the characterization work on nanocomposites and composite laminates.
Experimental approach is presented for the development of processing techniques and
appropriate characterization methods for carbon nanotubes reinforced epoxy resin
based multi-functional nanocomposites and carbon fiber reinforced polymer composite laminates modified with carbon nanotubes. The proposed work section is divided
into three sub-sections to describe the processing and the characterization of carbon nanotube reinforced epoxy matrix nanocomposites, woven-carbon fabric epoxy
matrix composite laminates modified with selective placement of nanotubes and unidirectional carbon fiber epoxy matrix composite laminates modified with carbon nanotubes.
Efforts are focused on comparing the effects of functionalized and unfunctionalized carbon nanotubes on the advanced composite laminates. Covalently functionalized carbon nanotubes are used for improved dispersion and fiber-matrix bonding
characteristics and compared with unfunctionalized or pristine carbon nanotubes.
The processing of woven carbon fabric reinforced epoxy matrix composite laminates
is performed using a vacuum assisted resin transfer molding process with selective
placement of carbon nanotubes using a spraying method. The uni-directional carbon
fiber epoxy matrix pre-preg composites are processed using a hot press technique
along with the spraying method for placement of nanotubes. These macroscale laminates are tested using short beam shear and double cantilever beam experiments for
investigating the effect of nanotubes on the interlaminar shear stress and the interlaminar fracture toughness. Fractography is performed using optical microscopy and
scanning electron microscopy to investigate the structure-property relationship. The
micro and nano-scale interactions of carbon nanotubes and epoxy matrix are studied
through the processing of unfunctionalized and functionalized single wall carbon nanotube reinforced epoxy matrix nanocomposites. The multifunctional nature of such
nanocomposites is investigated through thermo-mechanical and electrical characterizations.
46
Wang, Zhaohong. "Study of Acid Response of Qatar Carbonate Rocks." Thesis, 2011. http://hdl.handle.net/1969.1/ETD-TAMU-2011-12-10373.
Full textAbstract:
The Middle East has 62% of the world’s proved conventional oil reserves; more than 70% of these reserves are in carbonate reservoirs. It also has 40% of the world’s proved conventional gas reserves; 90% of these reserves are hold in carbonate reservoirs.
Recently papers published from industry discussed the techniques, planning, and optimization of acid stimulation for Qatar carbonate. To the best of author’s knowledge, no study has focused on the acid reaction to Qatar carbonates. The lack of understanding of Qatar carbonate especially Middle East carbonates and the abundance of Middle East carbonate reservoirs is the main motivation behind this study.
This work is an experimental study to understand the acid response to Qatar rocks in rocks with two types: homogenous carbonate and heterogeneous carbonate. A large portion of this research is to further investigate the impact of centimeter scale heterogeneity on the acid stimulation using Qatar rocks. Qatar carbonates have multi-scale heterogeneities which may cause the impact of the injected acids to differ from homogenous case. Recent published field data indicate a much smaller number of pore volume to breakthrough compared with experimental measurement with homogeneous carbonate and heterogeneity is believed to be one of the contributors of causing the low field measurements.
In this case, acid linear core-flood experiments were conducted with carbonate core samples of different petrophysical properties to study the impact of both separated and connected vugs and channels on pore volume to breakthrough. Computerized tomography was used in characterization of the heterogeneities. One experiment simulated the response of acid to heterogeneous carbonate in downhole condition with drill-in fluid damage.
Homogeneous rock was cored from a well in Qatar. The optimal injection rate was pursued through acid core flood experiments for acid stimulation design and for further reference.
It is been discovered that the optimum injection rate for heterogeneous carbonate exists. For the similar acid flux, the corresponding PVBT for buggy limestone correlates inversely with the fraction of total porosity comprised by vugs. For vuggy carbonates with connected vugs and channels, whether or not formation damage exists, the acid tends to create new pore space nearby to the existing vugs and channels. Different strategies need to be made regarding acid stimulation design with homogeneous carbonate, heterogeneous carbonate with separated vugs and channels and heterogeneous carbonate with connected vugs and channels.
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Tewari, Sanjay. "Regeneration of Carbon Aerogel Exhausted in Water Purification." Thesis, 2011. http://hdl.handle.net/1969.1/ETD-TAMU-2011-12-10562.
Full textAbstract:
Carbon has been used electrochemically in various forms for water treatment and the carbon aerogel is one of them. Carbon Aerogels (CA) are used as electrodes due to their high surface capacity and high electrical conductivity. They are also known as Carbon Nanofoams (CNF). CA electrodes attract oppositely charged ions that are nearby. This concept is known as Capacitive De-Ionization (CDI). The use of CA in CDI for water purification is well documented, but not much work has been done on regeneration of CA electrodes. Once saturated, these electrodes lose their ability to adsorb additional ions and it must be restored by regeneration. If they cannot be regenerated, they would need to be replaced, which would greatly increase the cost of the treatment they are expensive. The goal of this study is to obtain data to define optimal regeneration conditions and to develop predictive capability by examining desorption behavior of adsorbed ions on CA electrodes.
This study focuses on desorption of adsorbed ions and regeneration of CA. Various experiments were conducted to explore the effects on regeneration of CA of shorting of electrodes, change of polarity of electrodes, flow speed of water over CA electrodes, and temperature of regeneration water. The optimal combination of experimental variables was identified and was used for remaining experiments that tested the effect of size, charge and mass of adsorbed ions on regeneration of CA. Also, the effect of thickness of CA and its pore size on regeneration of CA was studied.
Results indicated that application of reverse potential for the first few minutes of the total regeneration time provided the greatest regeneration. Longer application of reverse potential did not result in higher regeneration. The regeneration behavior when no potential applied with and without shorting was as expected. Application of reverse potential with variable temperature or variable flow speed of water over CA surfaces provided results that were different from the ones that were obtained with no potential being applied with or without shorting of electrodes.
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Andreatta, Jeremy R. "Fundamental Studies towards Transistion Metal Catalysis and Application of Chromium Salen Complexes for the Synthesis of Polymers." 2009. http://hdl.handle.net/1969.1/ETD-TAMU-2009-12-7315.
Full textAbstract:
?The body of this work spans both fundamental organometallic chemistry and the
application of previously studied catalyst systems to produce new polymeric materials.
The cone angle of triphenylphosphite was estimated to be 128 degrees by Tolman in the late
70s; however, metal complexes bearing this ligand undergo cis/trans isomerization via a
mechanism indicative of greater steric requirements. X-ray crystallographic studies
coupled with data compiled from the Cambridge Crystallographic Database, were used to
more accurately calculate the steric demand of this wieldy used ligand to be
approximately 140 degrees.
Additionally, in depth kinetic studies of the interaction of furan ligands with
electron deficient manganese and chromium metal centers were performed. Data
collected from timescales ranging from minutes to microseconds was utilized to calculate
the bond dissociation energy of both 2,3-dihydrofuran (DHF) and furan. The aromatic
furan ligand was found to bind to the both metals 7-10 kcal mol-1 weaker than DHF.
Additionally, the more electron rich chromium center was found to bind both ligands ?weaker than the manganese center implying a minimization of the M-L pie -back
bonding interaction. Solution studies coupled with DFT calculations were utilized to
estimate the extent that the furan ligand is dearomatized by approximately 50% upon
interaction with the metal center.
Application-based studies of the separation of polymer catalyst mixtures were
also undertaken. The addition of the 1000 Dalton poly(isobutylene) arms to the salen
ligand in (salen)CrCl complexes yielded a catalyst that could be extracted from the
reaction mixture containing poly(cyclohexene carbonate) via the addition of heptane.
Another approach, not requiring catalyst modification, utilized a secondary amine to
facilitate the purification of the polymer product. The reaction of an amine with CO2 to
form an ionic liquid resulted in the precipitation of the polymer while the catalyst and
byproducts remained in the liquid carbamate phase. Both approaches provided
improvements over the long standing method of precipitating the polymer using
methanol and strong acid.
Lastly, the previous work of the Darensbourg group utilizing (salen)CrCl catalyst
to produce polycarbonates from CO2 and epoxides was employed to synthesized sulfur
rich poly(thiocarbonate)s. The effects of both CS2 loading and temperature on the
copolymerization of CS2 and cyclohexene oxide were studied. Optimal conditions of 1
equivalent of CS2 and 50 degrees C were found to selectively produce the desired polymeric
material. The observation of multiple thiocarbonate as well as carbonate functionalities,
led to a detailed study of the reaction byproducts to gain insight into the
copolymerization process.
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Deshmukh, Sujay. "Characterization of Nanoscale Reinforced Polymer Composites as Active Materials." Thesis, 2010. http://hdl.handle.net/1969.1/ETD-TAMU-2010-12-8990.
Full textAbstract:
Single walled carbon nanotube (SWNT)-based polymer nanocomposites have generated a lot of interest as potential multifunctional materials due to the exceptional physical properties of SWNTs. To date, investigations into the electromechanical response of these materials are limited. Previous studies have shown marginal improvements in the electromechanical response of already electroactive polymers (EAPs) with addition of SWNTs. However, in general, disadvantages of EAPs such as high actuation electric field, low blocked stress and low work capacity remain unaddressed.
This dissertation targets a comprehensive investigation of the electromechanical response of SWNT-based polymer nanocomposites. Specifically, the study focuses on incorporating SWNTs in three polymeric matrices: a non-polar amorphous polyimide (CP2), a polar amorphous polyimide ((-CN) APB-ODPA), and a highly polar semicrystalline polymer (PVDF). In the first step, emergence of an electrostrictive response is discovered in the non-polar polyimide CP2 in the presence of SWNTs. Transverse and longitudinal electrostrictive coefficients are measured to be six orders of magnitude higher than those of known electrostrictive polymers like polyurethane and P(VDF-TrFE) at less than 1/100th of the actuation electric fields.
Next, the effect of the polymer matrix on the electrostrictive response is studied by focusing on the polar (-CN) APB-ODPA. A transverse electrostriction coefficient of 1.5 m2/MV2 is measured for 1 vol percent SWNT- (-CN) APB-ODPA, about twice the value found for 1 vol percent SWNT-CP2. The high value is attributed to higher dipole moment of the (-CN) APB-ODPA molecule and strong non-covalent interaction between the SWNTs and (-CN) APB-ODPA matrix.
Finally, polyvinylidene fluoride (PVDF) matrix is selected as a means to optimize the electrostrictive response, since PVDF demonstrates both a high dipole moment and a strong non-covalent interaction with the SWNTs. SWNT-PVDF nanocomposites fared better than SWNT-CP2 nanocomposites but had comparable response to SWNT-(-CN) APB-ODPA nanocomposites. This was attributed to comparable polarization in both the polar nanocomposite systems. To maximize the SWNT-PVDF response, SWNT-PVDF samples were stretched leading to increase in the total polarization of the nanocomposite samples and decrease in the conductive losses. However, the dielectric constant also decreased after stretching due to disruption of the SWNT network, resulting in a decrease of the electrostrictive response.
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Murali, Shanthi. "Carbon based materials for electrodes in electrochemical double layer capacitors." Thesis, 2012. http://hdl.handle.net/2152/ETD-UT-2012-12-6576.
Full textAbstract:
Electrochemical double layer capacitors (EDLCs, also called supercapacitors or ultracapacitors) are high power density energy storage devices that operate through the separation of charge at the electrochemical interface between an electrode and a supporting electrolyte. Numerous types of carbon materials with high surface area and internal porosity, such as activated carbon, carbon fabrics, nanotubes, and reduced graphene oxide have been studied as electrode materials. Electrolytes such as aqueous alkaline and acid solutions usually give high capacitance, while organic and ionic liquids provide a wider operation voltage.
Graphene, due to its high theoretical surface area of 2630 m2/g, good electrical conductivity, and relatively low density, is being studied as an electrode material in EDLCs. The objective of this dissertation is thus to study effective methods for synthesis
of graphene-based materials, and to investigate their behavior in EDLCs. This work explored microwave assisted synthesis of graphite oxide (‘MEGO’, prepared in less than one minute by irradiation of graphite oxide by microwave). This material was further chemically activated to obtain a unique carbon material, activated microwave exfoliated graphite oxide (‘a-MEGO’) with specific surface areas up to 3100 m2/g. Gas adsorption measurements were used to study the specific surface area and porosity of a set of a-MEGO samples, which were also studied by scanning electron microscopy (SEM) and transmission electron microscopy (TEM) for their structure, and by combustion analysis (i.e., elemental analysis) and X-ray photoelectron spectroscopy (XPS) to understand their elemental composition. Cyclic voltammetry (CV), galvanostatic charge/discharge, and frequency response, tests were done in order to study the performance of these new carbon materials as electrodes in both aqueous and organic electrolytes in a two electrode cell set up.text