Post-mortem wear as indicator of taphonomic processes affecting enamel surfaces of hominin teeth from Laetoli and Olduvai (Tanzania): implications to dietary interpretations

The buccal microwear pattern of premolar and molar teeth has been linked to the composition of the ingested diet in human populations, both extant and fossil. However, numerous enamel surfaces observed for microwear analyses show microscopic damage that can be attributed to post-mortem taphonomic processes, not related to dietary habits. Post-depositional processes may greatly affect enamel surfaces, occasionally hindering dietary reconstructions based on dental microwear patterns. The present study analyses the damage patterns that can be observed on fossil Hominin teeth from the sites of Laetoli and Olduvai (Tanzania) to differentiate between ante-mortem and post-mortem processes. The results obtained show that post-mortem wear can be easily differentiated from ante-mortem abrasion for its distinct effects, mainly consisting of obliteration of enamel features. The frequency of abraded surfaces in the samples studied is considerably high. Despite the great antiquity of the remains studied, patches of well preserved enamel can still be distinguished in a number of teeth. Well preserved enamel surfaces can be discriminated for their polished appearance and the presence of distinct microwear features

Changes in hydrodynamic, structural and geochemical properties in carbonate rock samples due to reactive transport

Reactive transport plays an important role in the development of a wide range of both anthropic and natural processes affecting geological media. To predict the consequences of reactive transport processes on structural and hydrodynamic properties of a porous media at large time and spatial scales, numerical modeling is a powerful tool. Nevertheless, such models, to be realistic, need geochemical, structural and hydrodynamic data inputs representative of the studied reservoir or material. Here, we present an experimental study coupling traditional laboratory measurements and percolation experiments in order to obtain the parameters that define rock heterogeneity, which can be altered during the percolation of a reactive fluid. In order to validate the experimental methodology and identify the role of the initial heterogeneities on the localization of the reactive transport processes, we used three different limestones with different petrophysical characteristics. We tracked the changes of geochemical, structural and hydrodynamic parameters in these samples induced by the percolation of an acid fluid by measuring, before and after the percolation experiment, petrophysical and hydrodynamic properties of the rocks.Peer ReviewedPostprint (published version

El desarrollo de competencias literarias en el nivel medio básico

En este trabajo se presentan un conjunto de reflexiones en torno al papel que juega la literatura en el aprendizaje de una lengua, especialmente en la enseñanza del español en la educación secundaria. Se parte de relacionar la literatura como objeto de estudio con su didáctica. Todas las actividades que se realizan en la sala de clases, que están orientadas por los objetivos del programa de un curso, incluso las de evaluación del aprendizaje, constituyen las estrategias didácticas que el docente desarrolla para provocar cambios en los estudiantes. Estos cambios tienen relación con los logros cognitivos, que consideran no solo el conocimiento que ellos adquieren sino también las actitudes, los afectos y las competencias que desarrollen. Los cambios cognitivos y el desarrollo de competencias de los estudiantes dependerán de ellos en principio, de su voluntad de aprender y luego de los docentes que les ayuden a construir su aprendizaje en forma individual y en contacto con otros, mediante las actividades que realizan

Tooth replication techniques, SEM imaging and microwear analysis in Primates: methodological obstacles

Dental microwear analyses are among the most significant techniques though which a researcher can make dietary and ecological inferences from primate fossil specimens. Hard particles, such as plant phytoliths or silica-base sands, can scratch tooth enamel surfaces during food mastication producing a dietary specific pattern of microwear on the enamel surface. The density, axis length and orientation of microwear features, either striations or pits, are highly informative of dietary habits in both extant and fossil primates. The analysis of tooth enamel surfaces requires the use of scanning electron microscopy (SEM) techniques, because of its high resolution power, including gold-coating of teeth for observation. Problems arise when specimens to be analysed are unique and there is no possibility of a direct observation with an environmental microscope. Negative moulds must then be made and silicone-base components are indicated for high quality replication of enamel surfaces. A positive cast needs to be obtained, and epoxy-base resins are frequently used for their good quality and durability. However, successive silicon and epoxy replications result in the loosing of surface detail and precision. Surface observation errors can also be caused be the SEM technology itself, especially if back-scattered electrons are used instead of secondary electrons for maximizing the topographical information of enamel images. This paper reviews the most commonly used methodological approaches to tooth moulding and casting, comparing SEM micrographs of casts with actual tooth surfaces, and contrasting the reliability of SEM images for dietary interpretation of tooth microwear in both extant and fossil primates

The Minority American Dream in Sandra Cisneros' The House on Mango Street and Celeste Ng's Everything I Never Told You.

Incluso antes de su independencia, el concepto del sueño americano se ha considerado parte de la identidad de los Estados Unidos. El que una persona mediante perseverancia y trabajo duro pueda conseguir cualquier cosa que se proponga siempre ha alimentado las expectativas para mejorar la calidad de vida de sus ciudadanos. Sin embargo, la realidad que muchos estudios revelan es que este ideal no se presenta de forma equitativa ante toda la población estadounidense, lo que puede provocar que el concepto se contradiga a sí mismo. Desde su nacimiento, Estados Unidos ha excluido muchas veces a minorías étnicas en su historia, y con ello, les ha privado de formar parte de la identidad del país; dejándolos al margen para priorizar un canon literario primariamente blanco. Aun así, desde el movimiento por los derechos civiles de los setenta, una gran mayoría de autores pertenecientes a minorías raciales se han rebelado en contra de este aislamiento. Sandra Cisneros y Celeste Ng son dos escritoras que exploran el concepto del sueño americano visto a través de la perspectiva de las minorías a las que pertenecen. Exploran este ideal fundamental de la identidad estadounidense en dos de sus obras más prestigiosas y que este trabajo analiza. Una de las primeras en abordar este tema en los ochenta, visibilizando a los latinos americanos, es Sandra Cisneros a través de su novela The House on Mango Street (1984). Tomando el mismo concepto, pero de una forma más actualizada, Ng presenta en Everything I Never Told You (2014) los problemas de integración y el sueño americano como ideal inalcanzable a través de la experiencia asiática-americana de sus protagonistas.<br /

New evidence and interpretation of subvertical grooves in eandertal teeth from Cueva de Sidrón (Spain) and Figueira Brava (Portugal)

Interproximal tooth wear is caused by tooth-to-tooth rubbing that results in the formation of flat wear surfaces characterized by an intense pattern of enamel pitting caused by prism-plucking. The rate of wear of such surfaces depends on the forces involved in food processing and chewing. In some instances, the interproximal wear facets, mainly of molar teeth, show a number of subvertical grooves with a nearly vertical direction. These grooves are mostly present in Neanderthal teeth, but have also been described in some African fossil teeth and in European Homo heidelbergensis, as well as in several modern hunter-gatherer populations, such as Australian Aborigines. Subvertical grooves have seldom been attributed to taphonomic processes, although most probably they are caused by natural biomechanical processes during mastication of hard objects included in the diet. They have also been associated to acidic dietary habits given their radial disposition and their inter-digitalisation. The present study analyses the subvertical grooves observed in the Neanderthal dentition of Cueva de Sidrón (Spain). Comparisons are made with the similar interproximal grooves pattern observed in the Neanderthal specimen from Figueira Brava (Portugal) and some remains of H. heidelbergensis from Sima de los Huesos (Spain). Other cases have been described for the Neanderthal sites of Genay and Le Fate (France). The results obtained allow discarding a post-mortem origin of these structures, the most probable cause of the subvertical grooves being natural biomechanical chewing processes combined with some dietary habits indicative of hard plant foods ingestion

Cooperative learning on the promotion of oral production

Un mundo competitivo como el de hoy, exige tener unas bases firmes y claras en el idioma Inglés ya que este se ha convertido en una lengua franca que permite a los hablantes comunicarse con otras nacionalidades. Por esta razón es necesario articular en las aulas de clase métodos contemporáneos como trabajo cooperativo que ayude a los estudiantes a hablar inglés. Este proyecto de clase analizó el impacto del trabajo cooperativo, implementando dos métodos: el sabio y resolver problemas en grado primero en la escuela Jorge Eliecer Gaitán, con el fin de ayudar a los estudiantes a desarrollar la parte hablada del inglés. Los resultados evidenciados en la escuela mostraron que los niños y niñas de grado primero tienen dificultades trabajando en grupos y necesitan la presencia del profesor para mantener la disciplina y el uso del inglés.A competitive world as today`s demands good English speaking skills since English has become a lingua franca that facilitates communication among speakers from all over the world. That’s why, it is necessary to articulate in the classroom contemporary approaches like cooperative work to help learners to speak in English. This classroom project analyzed the impact of cooperative work through the implementation of two methods such as: circle the sage and problem solving tasks in first graders at the Jorge Eliecer Gaitan School in order to help them to develop oral English skills. The results showed that at the school first graders had difficulties working in groups and needed the presence of the teacher to maintain discipline and the use of the target language. Also, in order to get learners engaged, the material needed to be creative and meaningful. Modeling constituted the utmost pattern in this project since students could speak. When the educator modeled the language, learners were expected to produce it, and this was evidenced in the fact that students were able to say a few things in English properly

Testing dietary hypotheses of East African hominines using buccal dental microwear data

Abstract There is much debate on the dietary adaptations of the robust hominin lineages during the Pliocene-Pleistocene transition. It has been argued that the shift from C3 to C4 ecosystems in Africa was the main factor responsible for the robust dental and facial anatomical adaptations of Paranthropus taxa, which might be indicative of the consumption of fibrous, abrasive plant foods in open environments. However, occlusal dental microwear data fail to provide evidence of such dietary adaptations and are not consistent with isotopic evidence that supports greater C4 food intake for the robust clades than for the gracile australopithecines. We provide evidence from buccal dental microwear data that supports softer dietary habits than expected for P. aethiopicus and P. boisei based both on masticatory apomorphies and isotopic analyses. On one hand, striation densities on the buccal enamel surfaces of paranthropines teeth are low, resembling those of H. habilis and clearly differing from those observed on H. ergaster, which display higher scratch densities indicative of the consumption of a wide assortment of highly abrasive foodstuffs. Buccal dental microwear patterns are consistent with those previously described for occlusal enamel surfaces, suggesting that Paranthropus consumed much softer diets than previously presumed and thus calling into question a strict interpretation of isotopic evidence. On the other hand, the significantly high buccal scratch densities observed in the H. ergaster specimens are not consistent with a highly specialized, mostly carnivorous diet; instead, they support the consumption of a wide range of highly abrasive food items

Martin Amis's Night Train and the Developement of Female Characters in Detective Fiction.

Este ensayo se centra en los personajes principales de la novela de Martin Amis Night Train (1997), cuyo análisis se enmarca en una explicación de la evolución de los personajes femeninos en la novela de detectives. Hasta el siglo pasado, las mujeres habían ocupado un segundo plano en la ficción, siendo vistas como personajes débiles que no eran cruciales en el desarrollo de la historia. No es de extrañar que la figura tradicional del detective perspicaz sea un hombre que siempre encuentra la solución al misterio. Con el paso del tiempo, la representación de las mujeres en la literatura cambió, con mujeres escritoras que contribuyeron a este cambio de forma significativa y con la publicación de más novelas en las que las mujeres eran las protagonistas. Como explico en la Introducción, esto se aplica también a las novelas de detectives, que a veces siguen y a veces subvierten —especialmente en la ficción postmoderna— las convenciones del género. Mi ensayo presenta la novela Night Train de Amis como una ficción antidetectivesca construida sobre dos protagonistas femeninas fuertes, independientes y complejas, una en el papel de víctima y la otra en el de detective. A continuación, en la parte central del ensayo, se analizan estos dos personajes con vistasa ilustrar la creciente relevancia de la mujer en este tipo de ficción, y en la literatura en general, reflejando así el rol cambiante de las mujeres en la sociedad.<br /