Early angiosperm diversification: evidence from southern South America     

Sergio Archangelsky  Viviana Barreda  Mauro G. Passalia  Maria Gandolfo  Mercedes Prámparo  Edgardo Romero  Rubén Cúneo  Alba Zamuner  Ari Iglesias  Magdalena Llorens  Gabriela G. Puebla  Mirta Quattrocchio  Wolfgang Volkheimer 《Cretaceous Research》2009,30(5):1073-1082

In this report, we analyze the angiosperm fossil record (micro- and megafossil) from the central and southern basins of Argentina, southern South America, deposited between the late Barremian (128.3 Ma) to the end of the Coniacian (85.8 Ma). Based on this analysis, three major stages in the evolution of the angiosperms in the southernmost region of South America are established as follows: the late Barremian–Aptian, the latest Aptian-earliest Albian, and the middle Albian- Coniacian. The comparison between our fossil data set and those from Australia, North America, Asia and Europe suggest that the evolution and diversification of the angiosperms at mid and high latitudes in both hemispheres occurred roughly synchronously.  相似文献   

Determination of the spinel group end-members based on electron microprobe analyses     

Gabriela R. Ferracutti  M. Florencia Gargiulo  M. Luján Ganuza  Ernesto A. Bjerg  Silvia M. Castro 《Mineralogy and Petrology》2015,109(2):153-160

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Sensitivity of near-surface Tropical Instability Waves to submonthly wind forcing in the tropical Atlantic     

Gabriela Athi  Frdric Marin  Anne-Marie Treguier  Bernard Bourls  Catherine Guiavarc&#x;h 《Ocean Modelling》2009,30(4):241-255

This study demonstrates the sensitivity of the near-surface properties in the tropical Atlantic Ocean to the high-frequency of the winds in numerical simulations. At intra-seasonal timescales (2–50 days), two distinct period ranges dominate the variability in the upper ocean: periods between 2 and 20 days, which are essentially wind-forced and periods between 20 and 50 days, due mostly to Tropical Instability Waves (TIWs). Using a numerical model forced by different wind fields, it is shown that the characteristics of the intra-seasonal variability in the ocean surface mixed-layer are strongly dependent on the wind forcing. Submonthly winds are shown to force large variability in the upper ocean that can strikingly decrease the amplitude of the TIWs in the mixed-layer and their imprint on the horizontal distribution of sea surface temperatures. Wind products containing too much energy at submonthly periods thus prevent wind-forced simulations from reproducing a realistic surface signature of TIWs, when compared to satellite observations of sea surface temperature. In addition, submonthly wind variability may be responsible for part of the observed interannual variability of the TIW signature in the temperature. The impact of submonthly winds is strongest in the mixed-layer: beneath the mixed-layer, all simulations show similar characteristics of the TIWs.  相似文献   

Net Primary Productivity of <Emphasis Type="Italic">Spartina densiflora</Emphasis> Brong in an SW Atlantic Coastal Salt Marsh     

Gabriela González Trilla  Silvia De Marco  Jorge Marcovecchio  Ricardo Vicari  Patricia Kandus 《Estuaries and Coasts》2010,33(4):953-962

Coastal marshes are known as organic matter producers. The goal of this work is to study tiller demography, standing biomass, and net aerial primary productivity (NAPP) in a Spartina densiflora coastal wetland, using a method applied to permanent sample plots located at two sites differing in topographic location, a regularly flooded zone [relative low marsh (LM)] and an irregularly flooded one [relative high marsh (HM)]. Measurements were made every 2 months during the 2005–2007 period. The annual NAPP was estimated to be 2,599?±?705 gDW m^?2?year^?1 for the HM and 2,181?±?605 gDW m^?2?year^?1 and 602?±?154 gDW m^?2?year^?1 for the first and second period of the LM populations, respectively, showing a seasonal pattern reaching maximum values in summer. The reduced NAPP values of the LM sites in the second year was associated with an extremely high precipitation period related to the 2007–2008 El Niño event.  相似文献   

Synchrotron-based X-ray study of iron oxide transformations in terraces from the Tinto-Odiel river system: Influence on arsenic mobility     

Rafael Pérez-López  Maria P. Asta  Gabriela Román-Ross  José Miguel Nieto  Carles Ayora  Rémi Tucoulou 《Chemical Geology》2011,280(3-4):336-343

Simultaneous analysis of micro-X-ray diffraction (μ-XRD) and micro-X-ray fluorescence (μ-XRF) based on synchrotron light sources, and electron microprobe (EMP) analyses, were performed on iron terrace samples taken from Tinto-Odiel river system from the Iberian Pyrite Belt (IBP, SW Iberian Peninsula). Iron terraces are formed during the oxidation and precipitation of dissolved iron along the riverbeds impacted by acid mine drainage (AMD). This paper includes the study of actively-forming current terraces and fossil terraces isolated from the stream courses due to the river migration over time. The results of the study of current terrace samples from AMD-affected streams of two IPB abandoned mines (Tinto Santa Rosa and Cueva de la Mora) showed that fresh precipitates at the surface are composed primarily of metastable schwertmannite, which is gradually transformed at depth over short-time scales into goethite. Sediments of ancient terraces are composed mainly of goethite, which most likely originated from the re-crystallization of a precursor schwertmannite. However, at century-time scale, goethite partially re-crystallizes to hematite due to diagenetic processes. The transformation rate of goethite into hematite is negatively correlated with grain size and the crystallinity of goethite. Moreover, this transformation is accompanied by an increase in grain size and a decrease in surface area of hematite, and a concomitant decrease in arsenic trapped in the solid. This increase in the arsenic mobility during the diagenetic maturation should be considered in the development of conceptual and analytical models describing long-term fate, transport and bioavailability of arsenic in environmental systems.  相似文献   

A Comparative Analysis of Traveling Salesman Solutions from Geographic Information Systems     

Kevin M. Curtin  Gabriela Voicu  Matthew T. Rice  Anthony Stefanidis 《Transactions in GIS》2014,18(2):286-301

The Traveling Salesman Problem is one of the most prominent problems in combinatorial optimization, and is regularly employed in a wide variety of applications. The objective of this article is to demonstrate the extent of sub‐optimality produced by Traveling Salesman solution procedures implemented in the context of Geographic Information Systems and to discuss the consequences that such solutions have for practice. Toward that end, an analysis is made of Traveling Salesman solutions from implementations in four Geographic Information System packages. These implementations are tested against the optimal solution for a range of problem sizes. Computational results are presented in the context of a school bus routing application. This analysis concludes that no Traveling Salesman implementation in GIS is likely to find the optimal solution when problems exceed 10 stops. In contrast, optimal solutions can be generated with desktop linear programming software for up to 25 cities. Moreover, one GIS implementation consistently found solutions that were closer to optimal than its competitors. This research strongly suggests that for applications with fewer than 25 stops, the use of an optimal solution procedure is advised, and that GIS implementations can benefit from the integration of more robust optimization techniques.  相似文献   

Rms-flux relation in the optical fast variability data of BL Lacertae object S5 0716+714     

Gabriela Raluca Mocanu  Bulcsú Sándor 《Astrophysics and Space Science》2012,342(1):147-153

The possibility that BL Lac S5 0716+714 exhibits a linear root mean square (rms)-flux relation in its IntraDay Variability (IDV) is analysed. The results may be used as an argument in the existing debate regarding the source of optical IDV in Active Galactic Nuclei. 63 time series in different optical bands were used. A linear rms-flux relation at a confidence level higher than 65 % was recovered for less than 8 % of the cases. We were able to check if the magnitude is log-normally distributed for eight timeseries and found, with a confidence ≥95 %, that this is not the case.  相似文献   

Atmospheric circulation associated with extreme generalized frosts persistence in central-southern South America   总被引：1，自引：1，他引：0  

Gabriela V. Müller  Guillermo J. Berri 《Climate Dynamics》2012,38(5-6):837-857

Generalized frosts (GF) in central-southern South America have a strong impact due to their spatial extension, and they are especially important when they become persistent. This paper aims at identifying the atmospheric circulation features that determine the extreme GF persistence, i.e. very persistent and without persistence, and the differences between them, during the 1961–1990 winters. Since the GF without persistence group outnumbers the other one, two subgroups are composed with events selected from winters with maximum and minimum frequency of GF occurrence, respectively. Additionally, the individual event of July 1988 within the very persistent GF group is analyzed due to its exceptional persistence. GF persistence is mainly conditioned by two large-scale dynamic factors. One is the Rossby wave train propagation across the Pacific Ocean, and the other one is the location with respect to the continent and the magnitude of the confluence in the jet entrance region in subtropical latitudes. A predominantly meridional Rossby wave train propagation with a confluence region to the west of the continent prior to the event favors GF with intermediate (null) persistence depending on the greater (lesser) jet acceleration. This is conditioned by the magnitude of the confluence, which, in turn, depends on the disposition of the wave train propagation pattern. Instead, an essentially zonal propagation with a confluence region to the east of the continent favors the GF persistence for several days, yet if there is no confluence the event does not persist. The greatest persistence of an event combines the confluence/diffluence of the jet entrance/exit region, which depends on the disposition with respect to the continent of the zonally propagating Rossby wave trains.  相似文献   

Quantifying the role of sandy–silty sediments in generating slope failures during earthquakes: example from the Algerian margin     

Gabriela Dan  Nabil Sultan  Bruno Savoye  Jacques Deverchere  Karim Yelles 《International Journal of Earth Sciences》2009,98(4):769-789

The Algerian margin is a seismically active region, where during the last century, several large magnitude earthquakes took place. This study combines geotechnical and sedimentological data with numerical modelling to quantitatively assess the present-day slope stability of the Algerian margin. Geotechnical laboratory tests, such as cyclic triaxial tests, oedometric tests and vane shear tests were carried out on sediment cores collected on the study area. The liquefaction potential of a sediment column located about 30 km from the Boumerdès earthquake epicentre of 21st May 2003 was evaluated theoretically for an earthquake of M _w  = 6.8. We show that thin sand and silt beds such as those described on recovered sediment cores are the main cause of sediment deformation and liquefaction during earthquakes. Numerical calculations showed that the slope failure may occur during an earthquake characterised by a PGA in excess of 0.1g, and also that, under a PGA of 0.2g liquefaction could be triggered in shallow silty–sandy deposits. Moreover, comparison of the predicted slope failure with failure geometries inferred from seafloor morphology showed that earthquakes and subsequent mass movements could explain the present-day morphology of the study area.  相似文献   

Neotectonic activity at the eastern border of the Pannonian Depression and its seismic implications     

Gabriela Polonic 《Tectonophysics》1985,117(1-2)

Based on geological and geophysical data, characteristics of neotectonic activity of the eastern border of the Pannonian Depression are presented.As a result of differential tectonic movements during the Neogene-Quaternary, separate morphostructural units are subjected to subsidence and uplifting, along active faults.The local seismic activity is related, mainly, to the movements along the borders of grabens, as well as at the contact between different crustal blocks.  相似文献