Gelman, Jorge. 2005. Rosas, estanciero. Gobierno y expansión ganadera. Buenos Aires: Claves para todos. 96 p.

Fil: Reitano, Emir. Universidad Nacional de La Plata. Facultad de Humanidades y Ciencias de la Educación; Argentina.

Los contextos de descubrimiento y de justificación en la enseñanza de la química

La propuesta de este trabajo se centra en el análisis de la incidencia que los contextos de descubrimiento y de justificación adquieren en la Enseñanza de la Ciencia. Se muestra a través de dos casos paradigmáticos la función que tiene en la enseñanza de la Química la incorporación de estos contextos. Este recurso es valioso tanto para los educadores como para los estudiantes, teniendo en cuenta que algunos científicos podrían convertirse en modelos de los estudiantes en el camino del esfuerzo y el trabajo. Por ello se proponen incluir los contextos de descubrimiento y de justificación en el estudio de la ley de conservación de Antoine Lavoisier y la ley del equilibrio químico de Henry Le Chatelier, no meramente para resaltar su personalidad y rescatar factores históricos, sino como una herramienta didáctica de ayuda en la tarea docente.

Re-apropiación de imaginarios sociales

El presente trabajo es un análisis de las transformaciones en los imaginarios sociales de un colectivo de trabajadores que emprenden el proceso de recuperar y autogestionar la fábrica en la que trabajaron a lo largo de 30 años, tras la amenaza de quedar desocupados. La investigación pone el foco de atención en el análisis de los imaginarios sociales de un grupo de trabajadores, examinados a través de la palabra de los mismos, en torno a los siguientes ejes: la noción de trabajo, los hechos o acontecimientos que permiten la creación colectiva de nuevos imaginarios sociales y la práctica de la autogestión por parte de este colectivo de trabajadores. En el desarrollo del trabajo se realiza en primer lugar la caracterización del repertorio de acción colectiva en cuestión vinculado a la situación económica, política y social de la argentina en las últimas décadas para luego abordar la especificidad de la apropiación de un repertorio de acción colectiva y un proceso de autogestión por parte de un grupo de trabajadores

Diatoms and Silicoflagellates from ODP Hole 114-699A and Site 114-704

The stratigraphic ranges and relative abundances of selected diatoms and silicoflagellates are presented from three Neogene sedimentary sequences from the subantarctic South Atlantic. These data were compiled from Hole 699A in the southwest South Atlantic and Holes 704A and 704B in the southeast South Atlantic. Thirty-five samples were examined from a 67.5-m section of Hole 699A, which is mostly late Miocene or younger in age. A total of 225 samples was examined from the upper 569.1-m lower Miocene to Quaternary section in Holes 704A and 704B. Although the partial census of the Site 704 sequences is only preliminary, it reveals that the Neogene is remarkably complete and serves as a reference for further detailed examination of an important biostratigraphic-magnetostratigraphic reference section for the Neogene record of the Southern Ocean.

Planktonic foraminifera in late Eocene to Pleistocene sediments of ODP Hole 120-747A and 120-749B

Late Eocene to Pleistocene planktonic foraminifers from Leg 120 Holes 747A and 749B on the Kerguelen Plateau were quantitatively analyzed. Microperforate tenuitellid forms dominate the Oligocene to middle Miocene, and 17 species (including the new species Tenuitella jamesi and Tenuitellinata selleyi) are recorded. A lineage zonation of tenuitellid foraminifers is proposed as an alternative scheme for refinement of the Oligocene-Miocene biostratigraphy in high latitudes. Progressive or abrupt alterations in morphological characters within this lineage, producing different morphotypes or species, coincided with prolonged or sudden changes in paleoclimate. These microperforate planktonic foraminifers thus appear to have potential as indicators of cold-water masses and temperature fluctuations in post-Eocene oceans.

Trace-element geochemistry of tholeiitic basalts from DSDP Hole 55-433C

Hole 433C, a multiple re-entry hole drilled in 1862 meters of water on Suiko Seamount in the central Emperor Seamounts, penetrated 387.5 meters of lava flows overlain by 163.0 meters of sediments. The recovered volcanic rocks consist of three flow units (1-3) of alkalic basalt underlain by more than 105 flows or flow lobes (Flow Units 4-67) of tholeiitic basalt. This study reports trace-element, including rare-earth element (REE), data for 25 samples from 24 of the least altered tholeiitic flows. These data are used to evaluate the origin and evolution of tholeiitic basalts from Suiko Seamount and to evaluate changes in the mantle source between the time when Suiko Seamount formed, 64.7 ± 1.1 m.y. ago (see Dalrymple et al., 1980), and the present day. Stearns (1946), Macdonald and Katsura (1964) and Macdonald (1968) have established that chemically distinct lavas erupt during four eruptive stages of development of a Hawaiian volcano. These stages, from initial to final, are shield-building, caldera-filling, post-caldera, and post-erosional. The lavas of the shield-building stage are tholeiitic basalts, which erupt rapidly and in great volume. The shield-building stage is quickly followed by caldera collapse and by the caldera-filling stage, during which the caldera is filled by tholeiitic and alkalic lavas. During the post-caldera stage, a relatively thin veneer of alkalic basalts and associated differentiated lavas are erupted, sometimes accompanied by minor eruptions of tholeiitic lava. After a period of volcanic quiescence and erosion, lavas of the nephelinitic suite, which include both alkalic basalts and strongly SiO2-undersaturated nephelinitic basalts, may erupt from satellite vents during the post-erosional stage. Many Hawaiian volcanoes develop through all four stages; but individual volcanoes have become extinct before the cycle is complete. We interpret the tholeiitic lavas drilled on Suiko Seamount to have erupted during either the shield-building or the caldera-filling stage, and the overlying alkalic flows to have erupted during either the caldera-filling or the post-caldera stage (see Kirkpatrick et al., 1980).