El mineral estudiado corresponde a la Mina Koricolqui S.A.C. ubicada en la provincia de Otuzco, departamento de La Libertad. La caracterización de la muestra se realizó en el microscopio óptico polarizado de la Escuela Académico - Profesional de Ingeniería Geológica de la UNMSM. Observamos la presencia de esfalerita, calcopirita, pirita, electrum, marcasita, arsenopirita, goetita, calcosita, tetraedrita y gangas, siendo las leyes de la muestra de cabeza de 6.63 gr. de Au /TM y 11.22 oz. de Ag /TM. La primera prueba de flotación convencional de la muestra se realizó a una granulometría de 55% -200 mallas, cuyo balance metalúrgico global nos indica una recuperación de Au igual 56.85% y Ag igual 44.71%. En vista de que los resultados obtenidos no fueron muy satisfactorios y teniendo en cuenta el estudio microscópico de las especies mineralizadas, se realizó una etapa de preconcentración al mineral utilizando el concentrador centrífugo Falcon previo a la etapa de flotación a una granulometría de 55% -200 mallas, y se obtuvo una recuperación de Au igual 42.68% y Ag igual a 30.08%. En la etapa de Flotación del relave del concentrador centrífugo Falcon, los resultados nos muestran una recuperación de Au igual a 24.57% y Ag igual a 28.19%. Finalmente, la recuperación total del proceso Concentrador centrífugo Falcon más Flotación del relave Falcon es de Au igual 67.25% y Ag igual a 58.27%. Es aquí donde se observó que con la etapa de preconcentración las recuperaciones en Au y Ag se incrementaron en 10.40% y 13.56% respectivamente. En la segunda prueba de Flotación Convencional del mineral inicial, realizado con una granulometría de 66% -200 mallas, los resultados nos indican una recuperación de Au igual a 62.63% y Ag igual a 49.36%.

Diss.--Philosophische Fakultät--Universität zu Köln, 1995. / Bibliogr. p. 351-366.

Tesis doctoral--Facultad de ciencias históricas--Universität Hamburg, 1997. / Bibliogr. p. 206-220. Index. 2000 d'après la notice du catalogage à la source.

En aquest treball s’ha estudiat la quimisorció d’una sèrie d’àtoms (H, N, i O), i molècules (CO i O2) sobre la superfície 100 de coure mitjançant un model de clúster, i utilitzant pseudopotencials no empírics. Es proposa un nou mètode de tractament de l’entorn (embedding) per als models de clúster metàl•lics. El propòsit de la nova metodologia és la de disminuir els artefactes de clúster, en la mesura que sigui possible, que apareixen en les petites agrupacions metàl•liques. Per tal de minimitzar els efectes de contorn s’ha utilitzat un potencial basat en el projector de Phillips-Kleiman, com un terme addicional del potencial de core dels àtoms metàl•lics i s’ha optimitzat amb la finalitat d’aconseguir la electro-neutralitat de tots els àtoms metàl•lics del clúster aïllat, com si formés part d’un bulk infinit. La metodologia presentada condueix a una millora en la caracterització de propietats, en especial l’energia de quimisorció en clústers de grandària relativament petita, amb una millor descripció de la densitat electrònica en l’entorn del centre actiu.

El objetivo general del presente Trabajo de Tesis fue la preparación y caracterización de superficies sólidas modificadas con nanopartículas de plata con potenciales aplicaciones en Biomedicina. Para esto se optimizó el método de síntesis de nanopartículas de plata (NPs Ag) recubiertas con citrato, obteniendo NPs Ag monodispersas de 6 ± 2 nm de diámetro recubiertas con citrato y estables en medios acuosos. Asimismo, se estudió la inmovilización de estas NPs Ag sobre superficies de Ti/TiO<SUB>2</SUB>, encontrándose que las mismas se adsorben espontáneamente sobre dichas superficies como resultado de la inmersión del sustrato en la dispersión acuosa de NPs. Se analizó el efecto antimicrobiano de estas NPs Ag sobre bacterias Gram (-) (Pseudomonas aeruginosa) y bacterias Gram (+) (Staphylococcus aureus), tanto en dispersión como inmovilizadas sobre los sustratos antes mencionados. Asimismo, se estudió la citotoxicidad de las NPs Ag sobre células osteoblásticas. La caracterización de los sistemas se realizó por diferentes técnicas fisicoquímicas: microscopía de fuerzas atómicas (AFM), microscopía electrónica de transmisión (TEM), microscopía óptica de epifluorescencia, espectroscopías de UV- visible y de fotoelectrones de rayos X (XPS) y medidas de absorción atómica. Los resultados permiten concluir que las NPs Ag preparadas poseen una alta capacidad bactericida, ya que se produce una mortandad del 99,9% con sólo pequeñas dosis de las mismas. Los estudios realizados con células osteoblásticas permitieron concluir que la concentración mínima de Ag total presente en las NPs Ag necesaria para erradicar ambas bacterias ensayadas no genera efectos citotóxicos en dichas células. En cuanto a los sustratos de Ti/TiO<SUB>2</SUB> modificados con NPs Ag, éstos demostraron ser eficaces para inhibir la formación de biofilms de ambas bacterias (Pseudomona aeruginosa y Staphylococcus aureus). Asimismo, se halló que el efecto bactericida producido por las NPs Ag adsorbidas es similar al causado por un sustrato de Ag masivo, indicando que muy pequeñas dosis de plata adsorbidas sobre la superficie son suficientes para producir este efecto. El agregado de levofloxacina (un antibiótico de amplio espectro) a los sustratos de Ti/TiO<SUB>2</SUB> modificados con NPs Ag produjo un efecto sinérgico en el caso de Staphylococcus aureus, mientras que para Pseudomona aeruginosa sólo se encontró efecto aditivo. El uso de un antibiótico podría constituir una estrategia adicional para potenciar el efecto bactericida de las superficies modificadas con NPs Ag. Finalmente, se debe destacar la importancia de los resultados de este trabajo en relación a los materiales implantables. El método desarrollado para modificar las superficies de titanio, un material ampliamente utilizado en implantes, biocompatible y con una alta resistencia a la corrosión, es rápido, sencillo y de bajo costo, pudiendo implementarse en cualquier entorno clínico y sin la necesidad de contar para ello con personal altamente capacitado.

This thesis aims to contribute to current discussions on citizenship and transnationalism by analyzing the circumstances of Paraguayan, Bolivian and Peruvian immigrants in Argentina. More precisely, I examine the impact that state-promoted criminalizing discourses had on the lives of these immigrants in La Plata city in the late 1990s. On the one hand, their access to public services and resources was importantly constrained, submerging many into increasingly pauperized conditions. On the other hand, new distinctions were created within these nationally defined groups as a result of discursive and residential strategies deployed by many of these immigrants.

This is a study of the early colonial period of the Río de la Plata from first contact in 1516 to the emergence of a predominantly mestizo population in Asunción by 1580. The central focus of the study is the period from 1537, when Spaniards founded Asunción in the territories of the Guaraní-speaking Carios, until the establishment of the encomienda, a colonial labour system, in 1556. Through a close reading of archival documents and chronicles, the study presents a narrative history of the transcultural dynamics of Spanish-Guaraní relations, including the convergence of kinship and alliances, cacique and conquistador rivalries, competing spiritual beliefs of shamanism and Catholicism, and the role of castaways, lenguas (interpreters) indigenous women, priests, and mestizos as intermediaries. How these transcultural dynamics were dominated by indigenous norms until 1556, and how they shaped the cultural, social, and spiritual dimensions of mestizaje (racial mixing) are analysed. The study covers key moments in the conquest and early colonial period. These include Sebastián Caboto’s exploration of the Río de la Plata from 1527 to 1529; Pedro de Mendoza’s armada to the Río de la Plata in 1535 that led to the founding of Asunción in 1537 and the first governorship of Domingo Martínez de Irala from 1539 to 1542; the rule of Asunción by Álvar Núñez Cabeza de Vaca as adelantado from 1542 to 1544; and Domingo Martínez de Irala’s second governorship of the region from 1544 to 1556. An in-depth examination of the establishment of the encomienda is undertaken to consider how cultural identification, social status, and ethnic distinctions were reconfigured between the Cario and other Guaraní-speaking groups, the Spanish, and mestizos after 1556. The study concludes with an analysis of the Oberá Rebellion of 1579-80 as an example of how kinship and warrior norms, Christianity, and shamanistic practices converged in indigenous resistance to colonial rule.

This is a study of the early colonial period of the Río de la Plata from first contact in 1516 to the emergence of a predominantly mestizo population in Asunción by 1580. The central focus of the study is the period from 1537, when Spaniards founded Asunción in the territories of the Guaraní-speaking Carios, until the establishment of the encomienda, a colonial labour system, in 1556. Through a close reading of archival documents and chronicles, the study presents a narrative history of the transcultural dynamics of Spanish-Guaraní relations, including the convergence of kinship and alliances, cacique and conquistador rivalries, competing spiritual beliefs of shamanism and Catholicism, and the role of castaways, lenguas (interpreters) indigenous women, priests, and mestizos as intermediaries. How these transcultural dynamics were dominated by indigenous norms until 1556, and how they shaped the cultural, social, and spiritual dimensions of mestizaje (racial mixing) are analysed. The study covers key moments in the conquest and early colonial period. These include Sebastián Caboto’s exploration of the Río de la Plata from 1527 to 1529; Pedro de Mendoza’s armada to the Río de la Plata in 1535 that led to the founding of Asunción in 1537 and the first governorship of Domingo Martínez de Irala from 1539 to 1542; the rule of Asunción by Álvar Núñez Cabeza de Vaca as adelantado from 1542 to 1544; and Domingo Martínez de Irala’s second governorship of the region from 1544 to 1556. An in-depth examination of the establishment of the encomienda is undertaken to consider how cultural identification, social status, and ethnic distinctions were reconfigured between the Cario and other Guaraní-speaking groups, the Spanish, and mestizos after 1556. The study concludes with an analysis of the Oberá Rebellion of 1579-80 as an example of how kinship and warrior norms, Christianity, and shamanistic practices converged in indigenous resistance to colonial rule.

Incidental mortality in fisheries, especially gillnets, is one of the most important causes of decline of many species of cetaceans around the globe. Local populations of franciscana, Pontoporia blainvillei, and Hector�s dolphins, Cephalorhynchus hectori, have been subject to high levels of mortality in gillnets for several decades. This is due to a combination of extensive overlap in distribution of these coastal dolphins and large numbers of fishing nets. Stage-specific population dynamic models (without environmental stochasticity) suggest that both species have a low potential for population growth of approximately 0.2% (95% CI: -3.7% to 4.2%) to 3.4% (95% CI: 1.6% to 6.4%) for franciscana and 0.85% (95% CI: -1.0% to 2.6%) for Hector�s dolphins. Although the two species have similar population growth rates, they result from different life history strategies. Franciscana has a relatively low adult survival rate (0.86; SD = 0.016) which is compensated by a relatively high reproductive potential. The latter is a combination of early reproduction and high fecundity. Hector�s dolphin has a low reproductive potential, which is a combination of late reproduction and low fecundity, which is probably compensated by a relatively high adult survival rate (0.92; SD = 0.02) Apparent differences in growth rate among franciscana populations are possibly due to a combination of varying population-specific reproductive potential and, in some populations, inaccuracy in parameter estimates. Inaccuracy in estimating natural survival rates is also a cause for the low growth rate of Hector�s dolphins. The estimated low population growth rates of these species are insufficient to compensate for current levels of fishing-related mortality in some local populations, especially when environmental and/or demographic stochasticity is considered. Under these circumstances Banks Peninsula population would have a negative mean population growth rate of 0.54% (95% CI: -2.2% to 0.9%) and would decrease below its initial size in approximately 74% of the simulations. Stochasticity alone would decrease considerably the probability of the Banks Peninsula population to grow and recover from past and current high bycatch levels. Effects of stochasticity were also high for one of the franciscana stocks (i.e. stock from Franciscana Management Area II). In other areas (e.g. West Coast of the South Island; franciscana stock from FMA I) fishing effort and bycatch mortality rate seem not to be impeding population growth. Even in a stochastic environment and under current levels of fishing effort, the West Coast population and the franciscana stock from FMA I would grow at a positive rate of 0.32% (95% CI: -1.2% to 1.8%) and 3.1% (95% CI: 2.2 to 7.2%), respectively. Parameter uncertainty does not change the conclusion that immediate and extreme limitations on fishing practice and effort are necessary to increase the chances of recovery for some local populations/stocks. Fishing effort in New Zealand is regulated by a quota system. The quota system, the low number of fishing boats and the relatively low overlap between fishing nets and dolphins are probably the reasons for the positive population growth of Hector�s dolphins from the West Coast of the South Island. On the other hand, not even the Marine Mammal Sanctuary is sufficient to avoid negative mean population growth rate of Hector�s dolphins under current levels of fishing effort off Banks Peninsula. In Brazil, Uruguay and Argentina, where franciscana occurs, gillnet fisheries are not regulated. In some areas, faced with a declining fish stocks, fishermen have increased fishing effort to compensate for reduced catches, and the bycatch of franciscana has increased as a consequence. Strategies aiming at the conservation of these two species are likely to benefit other components of the ecosystem. Especially in the case of franciscana, reducing fishing effort is likely to promote the recovery of depleted fish stocks.

Publicación a texto completo no autorizada por el autor / Desarrolla una nueva ruta de síntesis del complejo polimérico sacarinato plata (I), [Ag(sac)]n, y la síntesis del complejo 2-(2-piridil)bencimidazol sacarinato plata(I), [Ag(pbi)(sac)]. La caracterización de ambos compuestos se realiza a través de los métodos de amperometría, análisis elemental, análisis por XPS, espectroscopía de IR, UV-Visible, 1H-RMN y 13C-RMN. / Tesis