Entity

Time filter

Source Type


Pereira G.R.,Federal University of Rio de Janeiro | Rocha H.S.,Federal University of Rio de Janeiro | Calza C.,Federal University of Rio de Janeiro | Anjos M.J.,State University of Rio de Janeiro | And 4 more authors.
X-Ray Spectrometry | Year: 2011

An X-ray transmission microtomography (CT) system combined with an X-ray fluorescence microtomography (XRFμCT) system was implemented in the Brazilian Synchrotron Light Laboratory (LNLS), Campinas, Brazil. The aim of this work was to determine the elemental distribution in biological samples (breast, prostate and lung samples) in order to verify the concentration of some elements correlated with characteristics and pathology of each tissue observed by the transmission CT. The experiments were performed at the X-ray fluorescence beamline (D09B-XRF) of the Brazilian Synchrotron Light Laboratory, Campinas, Brazil. A quasi-monochromatic beam produced by a multilayer monochromator was used as an incident beam. The sample was placed on a high-precision goniometer and translation stages that allow rotating as well as translating it perpendicularly to the beam. The fluorescence photons were collected with an energy dispersive HPGe detector placed at 90° to the incident beam, while transmitted photons were detected with a fast Na(Tl) scintillation counter placed behind the sample on the beam path. The CT images were reconstructed using a filtered-back projection algorithm and the XRFμCT images were reconstructed using a filtered-back projection algorithm with absorption corrections. The 3D images were reconstructed using the 3D-DOCTOR software. Results from the 3D visualization showed that the distribution of iron, copper and zinc is different and heterogeneous from the analyzed samples. © 2011 John Wiley & Sons, Ltd.. Source


Duncan Keppie J.,National Autonomous University of Mexico | Fraser Keppie D.,Nova Energy
Geoscience Canada | Year: 2014

Current Ediacaran–Cambrian, paleo-geographic reconstructions place Aval-onia, Carolinia and Ganderia (Greater Avalonia) at high paleolatitudes off northwestern Gondwana (NW Africa and/or Amazonia), and locate NW Gondwana at either high or low paleo-latitudes. All of these reconstructions are incompatible with 550 Ma Avalon-ian paleomagnetic data, which indicate a paleolatitude of 20–30ºS for Greater Avalonia and oriented with the present-day southeast margin on the northwest side. Ediacaran, Cambrian and Early Ordovician fauna in Avalonia are mainly endemic, which suggests that Greater Avalonia was an island micro-continent. Except for the degree of Ediacaran deformation, the Neopro-terozoic geological records of mildly deformed Greater Avalonia and the intensely deformed Bolshezemel block in the Timanian orogen into eastern Baltica raise the possibility that they were originally along strike from one another, passing from an island micro-continent to an arc-continent collision-al zone, respectively. Such a location and orientation is consistent with: (i) Ediacaran (580–550 Ma) ridge-trench collision leading to transform motion along the backarc basin; (ii) the reversed, ocean-to-continent polarity of the Ediacaran cratonic island arc recorded in Greater Avalonia; (iii) derivation of 1–2 Ga and 760–590 Ma detrital zircon grains in Greater Avalo-nia from Baltica and the Bolshezemel block (NE Timanides); and (iv) the similarity of 840–1760 Ma TDM model ages from detrital zircon in pre-Uralian–Timanian and Nd model ages from Greater Avalonia. During the Cambrian, Greater Avalonia rotated 150º counterclockwise ending up off northwestern Gondwana by the beginning of the Ordovician, after which it migrated orthogonally across Iapetus to amalgamate with eastern Laurentia by the Late Ordovician–Early Silurian. © 2014 GAC/AGC® Source


Two end-member models have been invoked to accommodate the Mesozoic dispersal of the supercontinent Pangaea. In one end-member, the opening of the Atlantic Ocean is inferred to have been balanced by the closure of the Panthalassan Ocean related to subduction off the western margins of the Americas. In the other end-member model, the opening of the Atlantic Ocean is accommodated by the closure of the paleo-Tethys and Tethys oceans linked to subduction off the southern margins of Eurasia. Here, I re-evaluate global plate circulation data compiled for the middle Mesozoic Era. The present evaluation confirms that closure of the paleo-Tethys and Tethys oceans compensated for the early opening of the central Atlantic and proto-Caribbean oceans. This result implies that the tectonic evolution of the North American Cordillera was independent from the processes governing Pangaea breakup in the Jurassic and Early Cretaceous Periods. As well, the opening Atlantic and closing Tethys realm must have been tectonically connected through the Mediterranean region in terms of a transform fault or point yet to be factored into geological interpretations. Tight geometric and kinematic correlations evident between the opening Atlantic and closing Tethyan domains can be demonstrated, which are most readily explained if the forces causing Pangaea breakup were transmitted from the Tethyan domain into the Atlantic domain, and not vice versa. Thus, slab sinking-based forces produced during the evolution of the Tethyan subduction zones are hypothesized to have controlled the early Atlantic breakup of Pangaea. © 2015 Geological Society of America. Source


Torres Silva Dos Santos A.,Federal University of Rio Grande do Norte | Torres Silva Dos Santos A.,Nova Energy | Santos E Silva C.M.,Federal University of Rio Grande do Norte
The Scientific World Journal | Year: 2013

Wind speed analyses are currently being employed in several fields, especially in wind power generation. In this study, we used wind speed data from records of Universal Fuess anemographs at an altitude of 10 m from 47 weather stations of the National Institute of Meteorology (Instituto Nacional de Meteorologia-INMET) from January 1986 to December 2011. The objective of the study was to investigate climatological aspects and wind speed trends. To this end, the following methods were used: filling of missing data, descriptive statistical calculations, boxplots, cluster analysis, and trend analysis using the Mann-Kendall statistical method. The seasonal variability of the average wind speeds of each group presented higher values for winter and spring and lower values in the summer and fall. The groups G1, G2, and G5 showed higher annual averages in the interannual variability of wind speeds. These observed peaks were attributed to the El Niño and La Niña events, which change the behavior of global wind circulation and influence wind speeds over the region. Trend analysis showed more significant negative values for the G3, G4, and G5 groups for all seasons of the year and in the annual average for the period under study. © 2013 Alexandre Torres Silva dos Santos and Cláudio Moisés Santos e Silva. Source


Keppie F.,Nova Energy
Geological Society Special Publication | Year: 2016

Mechanisms that can explain the Mesozoic motion of Pangaea in a palaeomagnetic mantle reference frame may also be able to explain its breakup. Calculations indicate that Pangaea moved along a non-rigid path in the mantle frame between the late Triassic and early Jurassic. The breakup of Pangaea may have happened as a response to this non-rigid motion. Tectonic forces applied to the margins of Pangaea as a consequence of subduction at its peripheries can explain both the motion and deformation of Pangaea with a single mechanism. In contrast, mantle forces applied to the base of Pangaea appear to be inconsistent with the kinematic constraints and do not explain the change in supercontinent motion that accompanied the breakup event. Top-down plate tectonics are inferred to have caused the breakup of Pangaea. Strong coupling between the mantle and lithosphere may not have been the case during the Phanerozoic eon when the Pangaean supercontinent formed and subsequently dispersed. Gold Open Access: This article is published under the terms of the CC-BY 3.0 license. © 2016 The Geological Society of London. Source

Discover hidden collaborations