New space-time perspectives on the propagation characteristics of the Black Death epidemic and its relation to bubonic plague     

George Christakos  Ricardo A. Olea 《Stochastic Environmental Research and Risk Assessment (SERRA)》2005,19(5):307-314

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The Río Tinto Basin, Spain: Mineralogy, sedimentary geobiology, and implications for interpretation of outcrop rocks at Meridiani Planum, Mars     

David C. Fernández-Remolar  Richard V. Morris  Ricardo Amils  Andrew H. Knoll 《Earth and Planetary Science Letters》2005,240(1):149-167

Exploration by the NASA rover Opportunity has revealed sulfate- and hematite-rich sedimentary rocks exposed in craters and other surface features of Meridiani Planum, Mars. Modern, Holocene, and Plio-Pleistocene deposits of the Río Tinto, southwestern Spain, provide at least a partial environmental analog to Meridiani Planum rocks, facilitating our understanding of Meridiani mineral precipitation and diagenesis, while informing considerations of martian astrobiology. Oxidation, thought to be biologically mediated, of pyritic ore bodies by groundwaters in the source area of the Río Tinto generates headwaters enriched in sulfuric acid and ferric iron. Seasonal evaporation of river water drives precipitation of hydronium jarosite and schwertmannite, while (Mg,Al,Fe³⁺)-copiapite, coquimbite, gypsum, and other sulfate minerals precipitate nearby as efflorescences where locally variable source waters are brought to the surface by capillary action. During the wet season, hydrolysis of sulfate salts results in the precipitation of nanophase goethite. Holocene and Plio-Pleistocene terraces show increasing goethite crystallinity and then replacement of goethite with hematite through time. Hematite in Meridiani spherules also formed during diagenesis, although whether these replaced precursor goethite or precipitated directly from groundwaters is not known. The retention of jarosite and other soluble sulfate salts suggests that water limited the diagenesis of Meridiani rocks.Diverse prokaryotic and eukaryotic microorganisms inhabit acidic and seasonally dry Río Tinto environments. Organic matter does not persist in Río Tinto sediments, but biosignatures imparted to sedimentary rocks as macroscopic textures of coated microbial streamers, surface blisters formed by biogenic gas, and microfossils preserved as casts and molds in iron oxides help to shape strategies for astrobiological investigation of Meridiani outcrops.  相似文献   

The solubility of calcite — probably containing magnesium — in seawater     

David C. Plath  Kenneth S. Johnson  Ricardo M. Pytkowicz 《Marine Chemistry》1980,10(1):9-29

The apparent solubility product of calcite was measured by saturometry as a function of temperature and salinity. Simplified equations for the carbonic-acid dissociation constants of Mehrbach et al., 1973 (Limnol. Oceanogr., 18: 897–907) have been derived from their experimental data and used to calculate apparent solubility product, K′_sp, K′_sp at 25°C and 35‰ salinity, was found to be K′_sp = 4.70 × 10^?7(mol²kgseawater^?2) An equation was fitted to the experimental data, resulting in pK′_sp = 6.5795 ? 3.7159 × 10⁵(TS) + 0.91056(T/S) ? 22.110(1.0/S)The mean activity coefficients, $\text{γ±}\text{CaCO}{}_3$, were calculated at various temperatures and salinities, using the thermodynamic solubility product of Jacobson and Langmuir, 1974 (Geochim. Cosmochim. Acta, 38: 301–318) and the apparent solubility products quoted in their paper. The change in K′_sp at each salinity, as a function of temperature, was used to calculate the apparent enthalpy of dissociation for calcite, ΔH′, and the extrapolated value of ΔH⁰ was in good agreement with that of Jacobson and Langmuir. Finally, this work was used to calculate saturation profiles for oceanic stations and as a basis for comment of the accuracy of in-situ saturometry, as well as the applicability of in-situ K′_sp pressure corrections.  相似文献   

Secondary fabrics revealed by remanence anisotropy: methodological study and examples from plutonic rocks   总被引：1，自引：0，他引：1  

Ricardo I. F. Trindade  Jean-Luc Bouchez  Olivier Bolle  Anne Nédélec  Anne Peschler  Franck Poitrasson 《Geophysical Journal International》2001,147(2):310-318

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Global economic restructuring and the world of labor in Brazil: the challenges to trade unions and social movements     

Ricardo 《Geoforum》2001,32(4)

The crisis and challenges faced by labor, including the trade unions and social movements have proportions not yet fully understood. The repercussions, owing to globalization, also reached Third World countries, especially intermediate countries that hold important industrial estates such as Brazil, Mexico, Argentina, etc. Brazil is part of an economic, social, political and cultural context which has universal traces of global capitalism, but also possesses singularities. During the last decades, Brazilian trade unions and social movements have either followed a different path. There was a widespread and highly significant strike movement (in the 1980s) with a notable expansion of trade unions organizing salaried sector (teachers, bank workers, public sector workers, etc.); there was also the rise of the Union Congresses such as the CUT-Central Única dos Trabalhadores (Workers Central) and the advance of rural unionism and the Landless Workers' Movement (MST, Movimento dos Trabalhadores Sem Terra) and new urban social movements such as the Homeless Movement. By the end of these decades, we joined in a more significant way the challenges which were presented to the unionism and social movements. These challenges are discuss in this paper.  相似文献   

Heterogeneous deformation and texture development in halite polycrystals: comparison of different modeling approaches and experimental data     

Ricardo A. Lebensohn  Paul R. Dawson  Hartmut M. Kern  Hans-Rudolf Wenk   《Tectonophysics》2003,370(1-4):287-311

Modeling the plastic deformation and texture evolution in halite is challenging due to its high plastic anisotropy at the single crystal level and to the influence this exerts on the heterogeneity of deformation over halite polycrystals. Three different assumptions for averaging the single crystal responses over the polycrystal were used: a Taylor hypothesis, a self-consistent viscoplastic model, and a finite element methodology. The three modeling approaches employ the same single crystal relations, but construct the polycrystal response differently. The results are compared with experimental data for extension at two temperatures: 20 and 100 °C. These comparisons provide new insights of how the interplay of compatibility and local equilibrium affects the overall plastic behavior and the texture development in highly anisotropic polycrystalline materials. Neither formulation is able to completely simulate the texture development of halite polycrystals while, at the same time, giving sound predictions of microstructural evolution. Results obtained using the finite element methodology are promising, although they point to the need for greater resolution of the individual crystals to capture the full impact of deformation heterogeneities.  相似文献   

Ordovician collision of the Argentine Precordillera with Gondwana, independent of Laurentian Taconic orogeny     

Willliam A. Thomas  Ricardo A. Astini  Germn Bayona 《Tectonophysics》2002,345(1-4)

The Argentine Precordillera, a rifted fragment of Laurentian crust and sedimentary cover, collided with Gondwana in Middle Ordovician time; the time of collision (Ocloyic orogeny) is similar to that of the Taconic orogeny of eastern Laurentia. Three hypotheses have been proposed to explain Ordovician docking of the Precordillera with western Gondwana: (A) the Precordillera microcontinent was rifted from Laurentia in Cambrian time and, following solitary drift, collided with Gondwana, independent of the Laurentian Taconic orogeny; (B) a continent–continent collision of Laurentia with Gondwana, producing a continuous Taconic–Ocloyic orogenic belt, was followed by rifting that left the Precordillera attached to Gondwana; and (C) the Precordillera at the tip of a distal plateau on greatly stretched Laurentian crust collided with Gondwana and subsequently separated from Laurentia.Contrasts in several aspects of Taconic and Ocloyic orogenic history provide for discrimination between the microcontinent and continent–continent-collision hypotheses. Stratigraphic gradients and lithologic assemblages within the synorogenic clastic wedges are incompatible with a single continuous orogenic belt, which, in palinspastic location, places the thin, fine-grained southern fringe of the Taconic clastic wedge adjacent to the thickest and coarsest part of the Ocloyic clastic wedge. Separate temporal and spatial distribution patterns of volcanic ash (bentonite) beds in Laurentia and the Precordillera indicate originally separate dispersal systems. Late Ordovician Hirnantian Gondwanan glacial deposits in the Precordillera indicate substantial latitudinal separation from Laurentia. Post-collision faults with large vertical separation in the Precordillera have no coeval counterparts on the Laurentian foreland. These contrasts indicate originally separate (not initially continuous, and subsequently dismembered) orogenic belts, favoring the microcontinent hypothesis and eliminating the continent–continent-collision hypothesis.Initial Taconic tectonic loading near the southern corner of the Alabama promontory of Laurentia and the lack of post-Taconic extension there are inconsistent with the tectonic history required by the plateau hypothesis, but are consistent with the tectonic history required by the microcontinent hypothesis. Paleobiogeography, distribution of bentonite beds, and the Hirnantian glacial deposits, all indicate wide separation (Iapetus Ocean) between the Precordillera and southern Laurentia at the time of the Ocloyic and Taconic orogenies, further favoring the microcontinent hypothesis.  相似文献   

Dispersal and germination ofProsopis flexuosa(Fabaceae) seeds by desert mammals in Argentina     

Claudia M Campos  Ricardo A Ojeda 《Journal of Arid Environments》1997,35(4):707-714

The ‘algarrobo’Prosopis flexuosais an important food resource in the Monte Desert of Argentina. Native, domestic, and exotic mammals consume the fruit of this legume and disperse the seed through faeces. In the present study we analyse the effect that different dispersal agents (cattle, horse, European wild boar, rodents, gray fox) have on seed damage, viability, and germination. Cattle increase germination at the expense of reduced viability, whereas horses maintain viability but do not contribute to a prompt germination response. Among native mammals, the gray fox maintains seed viability without increasing germination, whereas rodents affect seed viability but enhance germination rates. The European wild boar, however, damages all of the seeds it consumes.  相似文献   

Compensating for estimation smoothing in kriging   总被引：2，自引：0，他引：2  

Ricardo A. Olea  Vera Pawlowsky 《Mathematical Geology》1996,28(4):407-417

Smoothing is a characteristic inherent to all minimum mean-square-error spatial estimators such as kriging. Cross-validation can be used to detect and model such smoothing. Inversion of the model produces a new estimator—compensated kriging. A numerical comparison based on an exhaustive permeability sampling of a 4-ft² slab of Berea Sandstone shows that the estimation surface generated by compensated kriging has properties intermediate between those generated by ordinary kriging and stochastic realizations resulting from simulated annealing and sequential Gaussian simulation. The frequency distribution is well reproduced by the compensated kriging surface, which also approximates the experimental semivariogram well—better than ordinary kriging, but not as well as stochastic realizations. Compensated kriging produces surfaces that are more accurate than stochastic realizations, but not as accurate as ordinary kriging.  相似文献   

Provenance and tectonic implications of Orán Group foreland basin sediments,Río Iruya canyon,NW Argentina (23° S)          下载免费PDF全文

William H. Amidon  Lisa V. Luna  G. Burch Fisher  Douglas W. Burbank  Andrew R. C. Kylander‐Clark  Ricardo Alonso 《Basin Research》2017,29(Z1):96-112

Foreland basins are important recorders of tectonic and climatic processes in evolving mountain ranges. The Río Iruya canyon of NW Argentina (23° S) exposes ca. 7500 m of Orán Group foreland basin sediments, spanning over 8 Myr of near continuous deposition in the Central Andes. This study presents a record of sedimentary provenance for the Iruya Section in the context of a revised stratigraphic chronology. We use U‐Pb zircon ages from six interbedded ash layers and new magnetostratigraphy to constrain depositional ages in the section between 1.94 and 6.49 Ma, giving an average sedimentation rate of 0.93 ± 0.02 (2σ) km Myr^?1. We then pair U‐Pb detrital zircon dating with quartz trace‐element analysis to track changes in sedimentary provenance from ca. 7.6 to 1.8 Ma. Results suggest that from ca. 7.6 to ca. 6.3 Ma, the Iruya watershed did not tap the Salta Group or Neogene volcanics that are currently exposed in the eastern Cordillera and Puna margin. One explanation is that a long‐lived topographic barrier separated the eastern Puna from the foreland for much of the mid‐late Miocene, and that the arrival of Jurassic‐Neogene zircons records regional tectonic reactivation at ca. 6.3 Ma. A second major provenance shift at ca. 4 Ma is marked by changes in the zircon and quartz populations, which appear to be derived from a restricted source region in Proterozoic‐Ordovician meta‐sediments. Considered in conjunction with the onset of coarse conglomerate deposition, we attribute this shift to accelerated uplift of the Santa Victoria range, which currently defines the catchment's western limit. A third shift at ca. 2.3 Ma records an apparent disconnection of the Iruya with the eastern Puna, perhaps due to defeat of the proto Rio‐Iruya by the rising Santa Victoria range. This study is one of the first applications of quartz trace‐element provenance analysis, which we show to be an effective complement to U‐Pb detrital zircon dating when appropriate statistical methods are applied.  相似文献