El problema de diagenesis y metamorfismo en el grupo de Bokkeveld de Sud África y las Sierras Australes de la provincia de Buenos Aires

En base a la estratigrafía y tectónica del Grupo de Bokkeveld, suministrado por S0EK0R de Sud Africa, se han ubicado las muestras utilizadas en el presente trabajo. Las muestras de las Sierras Australes, fueron tomadas de los Grupos de Ventana y Pillahuincó, de uno de los perfiles realizados por T. Suero (1967). El estudio Petrográfico de las Rocas de Bokkeveld y S. de la Ventana, muestran una gran similitud y homogeneidad entre ellas. Deben considerarse como rocas Sedimentarias, por la presencia de montmorillonita y de minerales interestratificados de arcillas. Las plagioclasas presentan una composición demasiado básica para incluir las rocas dentro del metamorfismo de bajo rango. Lá presencia de epidoto en las formaciones Bonete y Tunas se considera de origen hidrotermal.The samples used in this study have been selected taking into account the stratigraphy and tectonic of the Bokkeveld Group, submitted by SOEKOR Co. The rocks from the Southern Hills, Buenos Aires, were obtained from Ventana and Pilla- huincd Groups, on the basis of the profile from T. Suero. The petrographic studies of the rocks of Bokkeveld and Ventana Hills, show that there is homogenity and similitude in them. They should be considered as sedimentary rocks, sincje there is montmorillonite and interstratified clay minerals in them. The plagioclases are too basic to include this rocks in the very low range of metamorphism. Epidote, in Bonete and Tunas Formations, should be considered of hydrothermal and not of metamorphic origin

Puzolanas artificiales obtenidas por tratamiento térmico de arcillas de la provincia de Buenos Aires (1ª parte)

Considerando la necesidad creciente de utilizar cementos puzolánicos en hormigones, el LEMIT ha iniciado un estudio para la obtención de puzolanas artificiales, por tratamiento térmico de arcillas provenientes de las formaciones sedimentarias de la Serie de La Tinta en el sistema de Tandilia y de las sierras Australes de la Provincia de Buenos Aires. Para le realización del trabajo, se efectuó un muestreo representativo de arcillas; se procedió luego a su activación a diversas temperaturas. Las muestras así tratadas, se estudiaron por difracción de Rayos X, lo que permitió seguir las transformaciones de la estructura de las arcillas. Finalmente se realizaron ensayos de acuerdo a normas vigentes para este tipo de materiales. Las muestras ensayadas cumplen con los requisitos exigidos en las mismas.The increasing need for the use of pozzolanic cements has induced the LEMIT to start a research for obtaining artificial pozzolans by thermic treatment of clays from sedimentary sequences of the La Tinta Series and Southern Hills of Buenos Aires Province. After a representative sampling, clays were activated at different temperatures and then studied bv X-Ray diffraction to determine transformations of clay structures. Tests were also carried out in accordance with prevailing norms. The results obtained are highly satisfactory, as most treated samples fulfill the specifications of the norms

Estudio mineralógico de algunas calcedonias argentinas

El trabajo se realizó teniendo en cuenta la reacción de este mineral con el cemento portland, la cuál produce efectos perjudiciales en los hormigones. Se comprobó que en ciertos casos la reacción no se produce. Se investigan las causas de tal comportamiento. El material utilizado para el estudio proviene de los ríos Uruguay y Paraná, ya que son las principales fuentes de abastecimiento de agregados del Gran Buenos Aires. Las "calcedonias" estudiadas están compuestas por un agregado fino de cuarzo, calcedonia y ópalo. La proporción relativa de dichos minerales condiciona la reactividad de los mismos.This paper deals with the reaction between chalcedony and Portland cement. This reaction damages the structure of the reinforced concrete, when aggregates of this kind are used for that purpose. In certain cases the concerned reaction do not take place. For that reason a detailed study was carried out to determine the behavior of the materials. The aggregates used for this, study come from Paraná and Uruguay rivers; the sediments of this area supply enough material from the Gran Buenos Aires market. The so call "chalcedony" studies are mainly composed of fine quartz, chalcedony and opal. The relative amounts of these minerals are thought to affect the behavior of the aggregates when they are mixed with portland cement

Emotional and educational accompaniment through dialogic literary gatherings: a volunteer project for families who suffer digital exclusion in the context of COVID-19

In order to improve educational conditions of families lacking digital resources during the home lockdown associated with the COVID-19 crisis, a project of educational and emotional support through books featuring Dialogic Literary Gatherings was carried out, with the name “Books that Bring People Together”. We present the main results of the impact of this activity from the point of view of n = 63 volunteers who participated in it. Using Student’s t-test for related samples, the differences in volunteers’ competencies before (pre-test) and after (post-test) the experience were tested, in order to analyze whether the activity had also exerted an impact on these competencies. Moreover, a correlation analysis was applied between the items for evaluating family participation by the volunteers, volunteer skills, and training, with the aim of testing the relationships between those variables as a result of participation in the experience. Results show that families found that accompaniment improved the quality of life of their children, making them feel loved and accompanied. In addition, the family atmosphere was improved, as did the children’s interest in reading. This mode of training led to greater involvement, motivation, and interest, thereby complying with a transversal axis of the process—community participation

Opinion and community formation in coevolving networks

In human societies opinion formation is mediated by social interactions, consequently taking place on a network of relationships and at the same time influencing the structure of the network and its evolution. To investigate this coevolution of opinions and social interaction structure we develop a dynamic agent-based network model, by taking into account short range interactions like discussions between individuals, long range interactions like a sense for overall mood modulated by the attitudes of individuals, and external field corresponding to outside influence. Moreover, individual biases can be naturally taken into account. In addition the model includes the opinion dependent link-rewiring scheme to describe network topology coevolution with a slower time scale than that of the opinion formation. With this model comprehensive numerical simulations and mean field calculations have been carried out and they show the importance of the separation between fast and slow time scales resulting in the network to organize as well-connected small communities of agents with the same opinion.Comment: 10 pages, 5 figures. New inset for Fig. 1 and references added. Submitted to Physical Review

Satellite-Based Assessment of Grassland Conversion and Related Fire Disturbance in the Kenai Peninsula, Alaska

Spruce beetle-induced (Dendroctonus rufipennis (Kirby)) mortality on the Kenai Peninsula has been hypothesized by local ecologists to result in the conversion of forest to grassland and subsequent increased fire danger. This hypothesis stands in contrast to empirical studies in the continental US which suggested that beetle mortality has only a negligible effect on fire danger. In response, we conducted a study using Landsat data and modeling techniques to map land cover change in the Kenai Peninsula and to integrate change maps with other geospatial data to predictively map fire danger for the same region. We collected Landsat imagery to map land cover change at roughly five-year intervals following a severe, mid-1990s beetle infestation to the present. Land cover classification was performed at each time step and used to quantify grassland encroachment patterns over time. The maps of land cover change along with digital elevation models (DEMs), temperature, and historical fire data were used to map and assess wildfire danger across the study area. Results indicate the highest wildfire danger tended to occur in herbaceous and black spruce land cover types, suggesting that the relationship between spruce beetle damage and wildfire danger in costal Alaskan forested ecosystems differs from the relationship between the two in the forests of the coterminous United States. These change detection analyses and fire danger predictions provide the Kenai National Wildlife Refuge (KENWR) ecologists and other forest managers a better understanding of the extent and magnitude of grassland conversion and subsequent change in fire danger following the 1990s spruce beetle outbreak

Análisis del estado de tensiones en uniones carpinteras de empalme de llave por el método de los elementos finitos

El objeto del presente trabajo es la determinación de la distribución de tensiones en la unión carpintera de empalme de llave mediante el método de los elementos finitos y su comparación con los valores obtenidos mediante la teoría de Resistencia de Materiales. Se analizan las zonas donde se produce concentración de tensiones y se estudia la influencia del refino de la malla sobre los resultados con el fin de determinar el tamaño que proporciona los valores de tensión más ajustados a la teoría. En las zonas donde la concentración de tensiones es menor, distintos tamaños de la malla muestran valores de tensión similares. Los resultados muestran una simetría central de la distribución de isotensiones donde el centro de simetría se corresponde con el centro geométrico de la unión. En las zonas donde se produce concentración de tensiones, los valores de las mismas aumentan considerablemente con el refino de la malla. La comparación de los niveles de tensiones normales obtenidos por el MEF y la teoría clásica muestran diferencias reducidas, excepto en los puntos de concentración de tensiones. The purpose of this study is to determine the stress distribution in the joint carpenter of halved and tabled joint with the finite element method and its comparison with the values obtained using the theory of Strength of Materials. The stress concentration areas where analyzed and the influence of mesh refinement was studied on the results in order to determine the mesh size that provides the stress values more consistent with the theory. In areas where stress concentration is lower, different mesh sizes show similar stress values. The results show a central symmetry of the isobar lines distribution where the centre of symmetry corresponds to the geometric centre of the joint. In areas where stress concentration occurs, the same values increase considerably with the refinement of the mesh. Comparison of normal stress levels obtained by the FEM and the classical theory shows small differences, except at points of stress concentration

Exploring a developing tourism industry: A resource-based view approach.

This exploratory study examines dimensions related to tourism development in the case of Uruguay. Internal and external analyses were conducted to identify key resources to maximise opportunities and minimise threats to the country’s tourism development. The study, which adopts the resource-based view of the firm, is based on the perspectives of key tourism stakeholders. Unstructured, face-to-face interviews were conducted with eight key informants, three representing government institutions, three private, and two public-private. The interviews revealed opportunities in various fronts, primarily consolidating and expanding international markets, and developing additional offerings, including convention/event and heritage tourism to minimise the effects of seasonality. Strong dependence on neighbouring markets, marginal airline connectivity and knowledge of Uruguay internationally were main perceived barriers to further development. The value of employing the resource-based framework in guiding understanding of the themes under investigation was confirmed. Implications emerging from the findings are discussed, and future research directions suggested