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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
11

Micro-estruturas de filmes de petróleo na interface ar-água: efeitos da irradiação luminosa e de agentes tensoativos sobre as propriedades interfaciais / Microstructure of petroleum films at the air-water interface: Effects of the irradiation and surfactant on their interfacial properties

Vieira, Vinicius Curcino Carvalho 15 December 2010 (has links)
Entender o comportamento de filmes de petróleo na interface ar-água é crucial para lidar com derrames de petróleo e reduzir os consecutivos danos ao meio ambiente. Para tanto, filmes de Langmuir preparados com frações de petróleo tem sido normalmente estudados. Entretanto, as propriedades dos filmes preparados a partir de amostras de petróleo bruto podem diferir consideravelmente dos filmes preparados a partir das suas frações individuais. Filmes preparados na interface ar-água de diversas amostras de petróleo com composições distintas foram estudadas usando técnicas espectroscópicas e de superfície incluindo pressão superficial, potencial de superfície, BAM, fluorescência e MEV. Mostramos que petróleo forma um filme de Langmuir não homogêneo na interface ar-água. As isotermas de pressão superficial para os filmes de petróleo exibem as fases gás (G), líquido expandido (LE), líquido condensado (LC) e sólido (S) com quase nenhuma histerese nos ciclos de compressão e descompressão, ao contrário da grande histerese observada em filmes de asfaltenos, maltenos e/ou resinas. A pressão superficial e os dados de microscopia de fluorescência indicam a presença de domínios fluorescentes em equilíbrio com uma fase menos fluorescente do petróleo contendo água estabilizada. Imagens de BAM e fluorescência de filmes LB confirmam a presença dos domínios de água, mesmo em pressões superficiais elevadas, caracterizando inequivocamente a tendência do petróleo em estabilizar sistemas emulsionados. O aumento da quantidade de asfalteno torna o filme mais instável, devido à formação de agregados irreversíveis. Nossos resultados sugerem que é necessário utilizar amostras de petróleo cru ao invés de suas frações, para entender a estrutura e as propriedades de filmes finos de petróleo. Demonstramos que os agentes coletores tensoativos que comprimem uma mancha de óleo sobre a superfície da água por diferença de pressão superficial, não entram no filme de petróleo, mantendo inalterado a estrutura dos domínios. Investigamos também a capacidade de monocamadas dos ácidos graxos saturados C4 a C18 em comprimir e confinar manchas de petróleo bruto brasileiro e seus derivados. A pressão superficial e a velocidade de espalhamento das monocamadas foram determinadas em uma balança de superfície e pelo teste do talco, respectivamente. A compressão e o confinamento das manchas foram estudados em placas de Petri, medindo-se a área das manchas e a espessura das lentes confinadas. Monocamadas de C8 a C12 foram capazes de comprimir manchas de petróleo formando lentes com cerca de 5% de sua área original. Os melhores resultados foram obtidos com as monocamadas de C8 e C12, que confinaram a mancha de petróleo em uma lente com 5 mm de espessura por até 72 horas sem mudanças significativas em sua área. E para finalizar foi estudado a influência da irradiação com fonte de luz artificial em amostras de petróleo com diferentes porcentagens de asfaltenos e volumes espalhados sobre a água. Tais experimentos foram acompanhados de estudos sobre a geração de oxigênio singlete, espectroscopia de fluorescência e de infravermelho. Caracterizamos que as alterações de pressão superficial e encolhimento da mancha são devidos a oxidação por oxigênio singlete que gera novos compostos tensoativos que comprimem a mancha / Understanding the behavior of petroleum films at the air-water interface is crucial for dealing with oil slicks and consecutive reducing the damages to the environment. For this, Langmuir films prepared with oil fractions have often been studied. However, the properties of films prepared from crude oil samples may differ considerably from those of films prepared from its individual fractions. Films prepared in the ar-water interface with several oil samples with different compositions were studied using spectroscopic and surface techniques including surface pressure, surface potential, BAM, fluorescence and SEM. We showed that petroleum forms an inhomogeneous Langmuir film at the air-water interface. The surface pressure isotherms for petroleum films exhibit gas (G), liquid expanded (LE), liquid condensed (LC) and solid (S) phases, with almost no hysteresis in the compression-decompression cycles, unlike the large hysteresis observed in asphaltenes, maltenes and/or resins films. The surface pressure and fluorescence microscopy data indicate the presence of fluorescent areas in balance with a less fluorescent oil containing water stabilized. BAM and LB films microscopy images confirm the presence of water areas, even at high surface pressures, characterizing unequivocally the trend of petroleum to stabilize emulsion systems. The increase in the amount of asphaltene turned the film more unstable. Our results strongly suggest that it is necessary to use crude oil samples instead of its fractions, to understand the structure and properties of oil thin films. We showed that surface collecting agents, which compress an oil slick on the water surface by surface pressure difference, do not mix in the oil film leaving unchanged the structure at the domains. We also examined the ability of monolayers of C4 to C18 saturated fatty acids in compressing and confining slicks of a Brazilian crude oil and its derivates. Surface pressure and monolayer spreading velocity were measured by the surface balance and by the talc test, respectively. The compression and confinement of the oil slicks were studied in Petri dishes, measuring the area of the slick and the thickness of the confined lenses. Monolayers of C8 and C12 were able to compress oil slicks forming lenses with about 5% of its original area. The best results were obtained with C8 and C12 monolayers, which confined oil slick in a lens with 5 mm thick and up to 72 hours without significant changes in the area. And finally we studied the influence of irradiation with artificial light in oil samples with different percentages of asphaltenes and volumes spread on the water. These experiments were accompanied by studies on the generation of singlet oxygen, fluorescence and infrared spectroscopy. We characterized that the changes of surface pressure and shrinkage of the oil slick is due to oxidation by singlet oxygen and generation of new surfactant compounds that compress the oil slick.
12

Pastoralism on the horns of a dilemma : is there a viable future for the Maasai?

Holland, Killian. January 1986 (has links)
No description available.
13

What it means to be a herdsman the practice and image of reindeer husbandry among the Komi of northern Russia /

Habeck, Joachim Otto. January 1900 (has links)
Thesis (Ph. D.)--Cambridge University. / "Max Planck Institute for Social Anthropology"--Cover. Includes bibliographical references (p. [245]-271.
14

The central Asian Arabs of Afghanistan pastoral nomadism in transition /

Barfield, Thomas J. January 1900 (has links)
Originally presented as the author's thesis (Ph. D.--Harvard, 1980) / Includes index. Bibliography: p. 171-175.
15

The central Asian Arabs of Afghanistan pastoral nomadism in transition /

Barfield, Thomas J. January 1900 (has links)
Originally presented as the author's thesis (Ph. D.--Harvard, 1980) / Includes index. Bibliography: p. 171-175.
16

Micro-estruturas de filmes de petróleo na interface ar-água: efeitos da irradiação luminosa e de agentes tensoativos sobre as propriedades interfaciais / Microstructure of petroleum films at the air-water interface: Effects of the irradiation and surfactant on their interfacial properties

Vinicius Curcino Carvalho Vieira 15 December 2010 (has links)
Entender o comportamento de filmes de petróleo na interface ar-água é crucial para lidar com derrames de petróleo e reduzir os consecutivos danos ao meio ambiente. Para tanto, filmes de Langmuir preparados com frações de petróleo tem sido normalmente estudados. Entretanto, as propriedades dos filmes preparados a partir de amostras de petróleo bruto podem diferir consideravelmente dos filmes preparados a partir das suas frações individuais. Filmes preparados na interface ar-água de diversas amostras de petróleo com composições distintas foram estudadas usando técnicas espectroscópicas e de superfície incluindo pressão superficial, potencial de superfície, BAM, fluorescência e MEV. Mostramos que petróleo forma um filme de Langmuir não homogêneo na interface ar-água. As isotermas de pressão superficial para os filmes de petróleo exibem as fases gás (G), líquido expandido (LE), líquido condensado (LC) e sólido (S) com quase nenhuma histerese nos ciclos de compressão e descompressão, ao contrário da grande histerese observada em filmes de asfaltenos, maltenos e/ou resinas. A pressão superficial e os dados de microscopia de fluorescência indicam a presença de domínios fluorescentes em equilíbrio com uma fase menos fluorescente do petróleo contendo água estabilizada. Imagens de BAM e fluorescência de filmes LB confirmam a presença dos domínios de água, mesmo em pressões superficiais elevadas, caracterizando inequivocamente a tendência do petróleo em estabilizar sistemas emulsionados. O aumento da quantidade de asfalteno torna o filme mais instável, devido à formação de agregados irreversíveis. Nossos resultados sugerem que é necessário utilizar amostras de petróleo cru ao invés de suas frações, para entender a estrutura e as propriedades de filmes finos de petróleo. Demonstramos que os agentes coletores tensoativos que comprimem uma mancha de óleo sobre a superfície da água por diferença de pressão superficial, não entram no filme de petróleo, mantendo inalterado a estrutura dos domínios. Investigamos também a capacidade de monocamadas dos ácidos graxos saturados C4 a C18 em comprimir e confinar manchas de petróleo bruto brasileiro e seus derivados. A pressão superficial e a velocidade de espalhamento das monocamadas foram determinadas em uma balança de superfície e pelo teste do talco, respectivamente. A compressão e o confinamento das manchas foram estudados em placas de Petri, medindo-se a área das manchas e a espessura das lentes confinadas. Monocamadas de C8 a C12 foram capazes de comprimir manchas de petróleo formando lentes com cerca de 5% de sua área original. Os melhores resultados foram obtidos com as monocamadas de C8 e C12, que confinaram a mancha de petróleo em uma lente com 5 mm de espessura por até 72 horas sem mudanças significativas em sua área. E para finalizar foi estudado a influência da irradiação com fonte de luz artificial em amostras de petróleo com diferentes porcentagens de asfaltenos e volumes espalhados sobre a água. Tais experimentos foram acompanhados de estudos sobre a geração de oxigênio singlete, espectroscopia de fluorescência e de infravermelho. Caracterizamos que as alterações de pressão superficial e encolhimento da mancha são devidos a oxidação por oxigênio singlete que gera novos compostos tensoativos que comprimem a mancha / Understanding the behavior of petroleum films at the air-water interface is crucial for dealing with oil slicks and consecutive reducing the damages to the environment. For this, Langmuir films prepared with oil fractions have often been studied. However, the properties of films prepared from crude oil samples may differ considerably from those of films prepared from its individual fractions. Films prepared in the ar-water interface with several oil samples with different compositions were studied using spectroscopic and surface techniques including surface pressure, surface potential, BAM, fluorescence and SEM. We showed that petroleum forms an inhomogeneous Langmuir film at the air-water interface. The surface pressure isotherms for petroleum films exhibit gas (G), liquid expanded (LE), liquid condensed (LC) and solid (S) phases, with almost no hysteresis in the compression-decompression cycles, unlike the large hysteresis observed in asphaltenes, maltenes and/or resins films. The surface pressure and fluorescence microscopy data indicate the presence of fluorescent areas in balance with a less fluorescent oil containing water stabilized. BAM and LB films microscopy images confirm the presence of water areas, even at high surface pressures, characterizing unequivocally the trend of petroleum to stabilize emulsion systems. The increase in the amount of asphaltene turned the film more unstable. Our results strongly suggest that it is necessary to use crude oil samples instead of its fractions, to understand the structure and properties of oil thin films. We showed that surface collecting agents, which compress an oil slick on the water surface by surface pressure difference, do not mix in the oil film leaving unchanged the structure at the domains. We also examined the ability of monolayers of C4 to C18 saturated fatty acids in compressing and confining slicks of a Brazilian crude oil and its derivates. Surface pressure and monolayer spreading velocity were measured by the surface balance and by the talc test, respectively. The compression and confinement of the oil slicks were studied in Petri dishes, measuring the area of the slick and the thickness of the confined lenses. Monolayers of C8 and C12 were able to compress oil slicks forming lenses with about 5% of its original area. The best results were obtained with C8 and C12 monolayers, which confined oil slick in a lens with 5 mm thick and up to 72 hours without significant changes in the area. And finally we studied the influence of irradiation with artificial light in oil samples with different percentages of asphaltenes and volumes spread on the water. These experiments were accompanied by studies on the generation of singlet oxygen, fluorescence and infrared spectroscopy. We characterized that the changes of surface pressure and shrinkage of the oil slick is due to oxidation by singlet oxygen and generation of new surfactant compounds that compress the oil slick.
17

Farmer-herder relations in Ghana: interplay of environmental change, conflict, cooperation and social networks

Bukari, Kaderi Noagah 22 September 2016 (has links)
No description available.
18

Rangeland Dynamics and Pastoral Development in the High Andes: The Camelid Herders of Cosapa, Bolivia

Buttolph, Lita P. 01 January 1998 (has links)
Current models of rangeland system dynamics were evaluated in Cosapa, a pastoral community on the Bolivian altiplano. Two specific models were tested: the "equilibrium" model, which assumes biotic interactions dominate rangeland dynamics and lead to system stability , and the "nonequilibrium" model, in which stochastic, abiotic factors control systems such that equilibrium is never attained. A livestock development project (called "Project Alpaca ") working in the community was then assessed in terms of how its assumptions of system dynamics compared with empirical findings. The goal of Project Alpaca was to increase incomes for camelid (i.e., llama and alpaca) herders on the Bolivian altiplano by improving the processing, production, and marketing of alpaca wool. Project implementation was carried out by an indigenous herders' association, with funds provided for construction of a modern alpaca wool processing plant and technical interventions at the farm level. Specific research objectives were to determine which conceptual model of system dynamics (equilibrium or nonequilibrium) best approximated the vegetation and livestock dynamics in Cosapa, and determine the impacts of technical innovations introduced by Project Alpaca . Vegetation dynamics were assessed by comparing plant species composition and production between grazed and ungrazed sites. Pastoral management strategies, livestock population dynamics between 1982 to 1995, and project impacts were assessed using a household survey. Results from the vegetation analyses showed that grazing protection had little impact on plant productivity, but reduced species diversity in wetland areas. The vegetation thus exhibited nonequilibrial characteristics. Regarding livestock dynamics, populations were relatively stable (over 13 years), although mortality was affected by severe drought, suggesting a combination of equilibrial and nonequilibrial interactions . Project Alpaca assumed an equilibrium model by emphasizing system stability and production maximization. The technical interventions showed positive, negative, and neutral associations with animal productivity. Construction of fenced exclosures on communal land has increased conflicts over land tenure rights, and may marginalize poorer households and increase social stratification . Development recommendations include shifting efforts away from intensification interventions that limit movement and flexibility, and strengthening social and economic networks that buffer the impacts of system variability.
19

Rangeland Dynamics and Pastoral Development in the High Andes: The Camelid Herders of Cosapa, Bolivia

Buttolph, Lita P. 01 May 1998 (has links)
Current models of rangeland system dynamics were evaluated in Cosapa, a pastoral community on the Bolivian altiplano. Two specific models were tested: the "equilibrium" model, which assumes biotic interactions dominate rangeland dynamics and lead to system stability , and the "nonequilibrium" model, in which stochastic, abiotic factors control systems such that equilibrium is never attained. A livestock development project (called "Project Alpaca ") working in the community was then assessed in terms of how its assumptions of system dynamics compared with empirical findings. The goal of Project Alpaca was to increase incomes for camelid (i.e., llama and alpaca) herders on the Bolivian altiplano by improving the processing, production, and marketing of alpaca wool. Project implementation was carried out by an indigenous herders' association, with funds provided for construction of a modern alpaca wool processing plant and technical interventions at the farm level. Specific research objectives were to determine which conceptual model of system dynamics (equilibrium or nonequilibrium) best approximated the vegetation and livestock dynamics in Cosapa, and determine the impacts of technical innovations introduced by Project Alpaca . Vegetation dynamics were assessed by comparing plant species composition and production between grazed and ungrazed sites. Pastoral management strategies, livestock population dynamics between 1982 to 1995, and project impacts were assessed using a household survey. Results from the vegetation analyses showed that grazing protection had little impact on plant productivity, but reduced species diversity in wetland areas. The vegetation thus exhibited nonequilibrial characteristics. Regarding livestock dynamics, populations were relatively stable (over 13 years), although mortality was affected by severe drought, suggesting a combination of equilibrial and nonequilibrial interactions . Project Alpaca assumed an equilibrium model by emphasizing system stability and production maximization. The technical interventions showed positive, negative, and neutral associations with animal productivity. Construction of fenced exclosures on communal land has increased conflicts over land tenure rights, and may marginalize poorer households and increase social stratification . Development recommendations include shifting efforts away from intensification interventions that limit movement and flexibility, and strengthening social and economic networks that buffer the impacts of system variability.
20

Pastoralism on the horns of a dilemma : is there a viable future for the Maasai?

Holland, Killian. January 1986 (has links)
No description available.

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