86 research outputs found
Dynamical effects of subducting ridges: Insights from 3-D laboratory models
We model the subduction of buoyant ridges and plateaus to study their effect
on slab dynamics. Oceanic ridges parallel to the trench have a stronger effect
on the process of subduction because they simultaneously affect a longer trench
segment. Large buoyant slab segments sink more slowly into the asthenosphere,
and their subduction result in a diminution of the velocity of subduction of
the plate. We observe a steeping of the slab below those buoyant anomalies,
resulting in smaller radius of curvature of the slab, that augments the energy
dissipated in folding the plate and further diminishes the velocity of
subduction. When the 3D geometry of a buoyant plateau is modelled, the dip of
the slab above the plateau decreases, as a result of the larger velocity of
subduction of the dense "normal" oceanic plate on both sides of the plateau.
Such a perturbation of the dip of the slab maintains long time after the
plateau has been entirely incorporated into the subduction zone. We compare
experiments with the present-day subduction zone below South America.
Experiments suggest that a modest ridge perpendicular to the trench such as the
present-day Juan Fernandez ridge is not buoyant enough to modify the slab
geometry. Already subducted buoyant anomalies within the oceanic plate, in
contrast, may be responsible for some aspects of the present-day geometry of
the Nazca slab at depth
Agricultura ou pastagem? Papel das coberturas pedológicas na diferenciação e na transformação de sistemas agrårios pioneiros no Brasil.
O objetivo deste estudo Ă© mostrar como a natureza da cobertura pedolĂłgica orienta as modalidades de manejo agrĂcola desde o inĂcio do processo de desmatamento. Numa zona de dinĂąmica antiga do ParanĂĄ, Ă© mostrado como os agricultores, aproximadamente 40 anos apĂłs terem destruĂdo completamente a floresta, foram obrigados a remodelar totalmente a paisagem para a construção de estruturas anti-erosivas, e como o controle da erosĂŁo, nĂŁo sendo eficiente, os obrigou a mudar seus sistemas de cultura de acordo com os solos explorados, optando tambĂ©m pela associação agricultura/pastagem. Paralelamente, observa-se o mesmo processo em curso numa zona de dinĂąmica atual da AmazĂŽnia. Esses dois exemplos fornecem elementos para projetar formas racionais de manejo para a AmazĂŽnia, considerando as caracterĂsticas do agricultor e dos solos, antes do seu total desmatamento
A propĂłsito da periodicidade climato-hidrolĂłgica que vem provocando grandes crises em Santa Catarina
The SuperCam Instrument Suite on the Mars 2020 Rover: Science Objectives and Mast-Unit Description
On the NASA 2020 rover mission to Jezero crater, the remote determination of the texture, mineralogy and chemistry of rocks is essential to quickly and thoroughly characterize an area and to optimize the selection of samples for return to Earth. As part of the Perseverance payload, SuperCam is a suite of five techniques that provide critical and complementary observations via Laser-Induced Breakdown Spectroscopy (LIBS), Time-Resolved Raman and Luminescence (TRR/L), visible and near-infrared spectroscopy (VISIR), high-resolution color imaging (RMI), and acoustic recording (MIC). SuperCam operates at remote distances, primarily 2-7 m, while providing data at sub-mm to mm scales. We report on SuperCam's science objectives in the context of the Mars 2020 mission goals and ways the different techniques can address these questions. The instrument is made up of three separate subsystems: the Mast Unit is designed and built in France; the Body Unit is provided by the United States; the calibration target holder is contributed by Spain, and the targets themselves by the entire science team. This publication focuses on the design, development, and tests of the Mast Unit; companion papers describe the other units. The goal of this work is to provide an understanding of the technical choices made, the constraints that were imposed, and ultimately the validated performance of the flight model as it leaves Earth, and it will serve as the foundation for Mars operations and future processing of the data.In France was provided by the Centre National d'Etudes Spatiales (CNES). Human resources were provided in part by the Centre National de la Recherche Scientifique (CNRS) and universities. Funding was provided in the US by NASA's Mars Exploration Program. Some funding of data analyses at Los Alamos National Laboratory (LANL) was provided by laboratory-directed research and development funds
Spatial distribution of pollen grains and spores in surface sediments of Guanabara Bay, Rio de Janeiro, Brazil
Failure processes and gravity-flow transformation revealed by high-resolution AUV swath bathymetry on the Nice continental slope (Ligurian Sea)
International audienceThe continental slope offshore Nice is a natural laboratory to investigate submarine landslides and gravity-flow processes. Using EM300 bathymetry data (spatial resolution of 25 m), about 250 scars with volume less than 8 Ă 108 m3 were identified. The AUV bathymetric data (spatial resolution of 2 m) revealed a greater number of scar-related failures with two main morphologies: some scars are affected by retrogressive processes of erosion, suggesting failures were triggered a long time ago, while other scars exhibit no evidence of post-failure erosion, suggesting they could have been triggered recently. Downslope from the scars, there are scattered blocks, on average 5-m high and 40-m wide, and well-developed asymmetrical waves, on average 2-m high and 20-m in wavelength. Such evolution could be evidence for the transformation of the remobilized deposits into cohesive flows then turbulent flows. Such transformation took place over a distance of less than 6-8 km
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