850 research outputs found

    A temperate former West Antarctic ice sheet suggested by an extensive zone of bed channels

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    Several recent studies predict that the West Antarctic Ice Sheet will become increasingly unstable under warmer conditions. Insights on such change can be assisted through investigations of the subglacial landscape, which contains imprints of former ice-sheet behavior. Here, we present radio-echo sounding data and satellite imagery revealing a series of ancient large sub-parallel subglacial bed channels preserved in the region between the Möller and Foundation Ice Streams, West Antarctica. We suggest that these newly recognized channels were formed by significant meltwater routed along the icesheet bed. The volume of water required is likely substantial and can most easily be explained by water generated at the ice surface. The Greenland Ice Sheet today exemplifies how significant seasonal surface melt can be transferred to the bed via englacial routing. For West Antarctica, the Pliocene (2.6–5.3 Ma) represents the most recent sustained period when temperatures could have been high enough to generate surface melt comparable to that of present-day Greenland. We propose, therefore, that a temperate ice sheet covered this location during Pliocene warm periods

    Resiliencia y metas académicas en estudiantes de secundaria de una institución pública de Trujillo

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    La investigación tuvo como objetivo principal establecer la relación que existe entre la resiliencia y las metas académicas en estudiantes de secundaria de una Institución Pública de Trujillo. El diseño de investigación fue no experimental, descriptivo correlacional; se trabajó con una muestra de 262 estudiantes de tercer, cuarto y quinto de secundaria de una Institución Pública de Trujillo. Los instrumentos que se utilizaron fueron: Escala de Resiliencia elaborado por Wagnild y Young, en la versión peruana elaborada por Novella en el año 2002 y adaptaba en Trujillo por Nunja en el año 2016, y el Cuestionario de Metas Académicas (C.M.A.) elaborado, por Hayamizu y Weiner en 1991, siendo traducida por Núñez y González en 1994, así también fue adaptada en la ciudad de Trujillo para esta investigación. Los resultados reflejaron que existe relación entre resiliencia y las metas académicas con una intensidad baja (Pearson= 253**; Spearman= 286**) a un 99% de significancia

    Understanding the Interdependence of Penetration Depth and Deformation on Nanoindentation of Nanoporous Silver

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    International audienceA silver-based nanoporous material was produced by dealloying (selective chemical etching) of an Ag 38.75 Cu 38.75 Si 22.5 crystalline alloy. Composed of connected ligaments, this material was imaged using a scanning electron microscope (SEM) and focused ion-beam (FIB) scanning electron microscope tomography. Its mechanical behavior was evaluated using nanoindentation and found to be heterogeneous, with density variation over a length scale of a few tens of nanometers, similar to the indent size. This technique proved relevant to the investigation of a material's mechanical strength, as well as to how its behavior related to the material's microstructure. The hardness is recorded as a function of the indent depth and a phenomenological description based on strain gradient and densification kinetic was proposed to describe the resultant depth dependence

    Antarctic ice sheet fertilises the Southern Ocean

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    Open access journalSouthern Ocean (SO) marine primary productivity (PP) is strongly influenced by the availability of iron in surface waters, which is thought to exert a significant control upon atmospheric CO2 concentrations on glacial/interglacial timescales. The zone bordering the Antarctic Ice Sheet exhibits high PP and seasonal plankton blooms in response to light and variations in iron availability. The sources of iron stimulating elevated SO PP are in debate. Established contributors include dust, coastal sediments/upwelling, icebergs and sea ice. Subglacial meltwater exported at the ice margin is a more recent suggestion, arising from intense iron cycling beneath the ice sheet. Icebergs and subglacial meltwater may supply a large amount of bioavailable iron to the SO, estimated in this study at 0.07-0.2 Tg yr-1. Here we apply the MIT global ocean model (Follows et al., 2007) to determine the potential impact of this level of iron export from the ice sheet upon SO PP. The export of iron from the ice sheet raises modelled SO PP by up to 40%, and provides one plausible explanation for seasonally very high in situ measurements of PP in the near-coastal zone. The impact on SO PP is greatest in coastal regions, which are also areas of high measured marine PP. These results suggest that the export of Antarctic runoff and icebergs may have an important impact on SO PP and should be included in future biogeochemical modelling.Philip Leverhulme PrizeLeverhulme Research FellowshipLeverhulme TrustRoyal Society Fellowship7th European Community Framework Programme - Marie Curie Intra European FellowshipNatural Environment Research Council (NERC

    Diseño y desarrollo de un sistema portable de proximidad para invidentes que permite el uso de ambas manos

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    El presente trabajo de investigación tiene por objetivo diseñar y desarrollar un sistema portable de proximidad para invidentes que permite el uso de ambas manos, utilizando sensores de distancia por ultrasonido y un sistema de aviso por vibración, los cuales permiten a las personas invidentes alertar ante los obstáculos que existan en su desplazamiento. Adicionalmente, en este trabajo de investigación se muestra de forma general el modelamiento de las distintas variables asociadas a los elementos empleados en la construcción así mismo la implementación y construcción del prototipo como el desarrollo del hardware y software del prototipo. También se incluye simulaciones y pruebas de funcionamiento del sistema electrónico cuya implementación será un gorro visera, por última parte se tienen las conclusión y recomendaciones obtenidas tras el desarrollo del prototipo electrónico.Trabajo de investigaciónCampus Lima Centr

    Ancient pre-glacial erosion surfaces preserved beneath the West Antarctic Ice Sheet

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    Open access journalpresent ice-penetrating radar evidence for ancient (pre-glacial) and extensive erosion surfaces preserved beneath the upstream Institute and Möller ice streams, West Antarctica. Radar data reveal a smooth, laterally continuous, gently sloping topographic block, comprising two surfaces separated by a distinct break in slope. The erosion surfaces are preserved in this location due to the collective action of the Pirrit and Martin–Nash hills on ice sheet flow, resulting in a region of slow flowing, cold-based ice downstream of these major topographic barriers. Our analysis reveals that smooth, flat subglacial topography does not always correspond to regions of either present or former fast ice flow, as has previously been assumed. We discuss the potential origins of the erosion surfaces. Erosion rates across the surfaces are currently low, precluding formation via present-day glacial erosion. We suggest that fluvial or marine processes are most likely to have resulted in the formation of these surfaces, but we acknowledge that distinguishing between these processes with certainty requires further data.Natural Environment Research Council (NERC
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