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41.
Recent improvements in both Infra-red spectroscopy and equilibrator techniqueshave allowed to determine, for the first time, pCO2using simultaneously and continuously both the direct and indirect methods in an estuary where pCO2 values range from 500 to 8500 atm and salinity from 0 to 30. Our results show that both methods are in excellent agreement in the wholeestuary (r2 = 0.999, n = 1075, p < 0.0001). Thus, the NBS (US National Bureau of Standards) scale, although inadequate for seawater samples, is appropriate for estuarine waters and can be applied with confidence to calculate pCO2. 相似文献
42.
43.
The Variscan Belt in western Europe shows an arcuate geometry that is usually named Ibero-Armorican Arc. The nucleus of this arc, known as the Asturian Arc, comprises the Cantabrian Zone which is a foreland fold and thrust belt. The Trubia River area is located in the inflexion zone of the Asturian Arc, which is a strategic structural position for unraveling the geometry and kinematics of the Variscan thrust sheets and related folds. Geological mapping, construction of stratigraphic and structural cross sections, analysis of kinematic indicators, and estimate of shortening for each cross section have been carried out. This area consists of two major antiform-synform pairs related to two imbricate thrust systems. These folds are asymmetric, tight, and their axial traces follow the trend of the Asturian Arc. They have been interpreted as fault-propagation folds. The emplacement directions measured in the Trubia River area change from north to south and converge towards the core of the Asturian Arc. The minimum shortening estimated ranges between 16.4 and 17.6 km, which corresponds to 56.9 and 59.4%. The complex cross-cutting relationships between folds and thrusts suggest that, in general, the different structural units followed a forward-breaking sequence of emplacement, with some breaching and a few out-of-sequence thrusts. The analysis of the transport vectors together with the disposition of the fold axes and post-thrusting faults that deform the thrust stack are evidence of a late deformation event that is partially or totally responsible for the arcuate form of the Asturian Arc. The timing of the Asturian Arc, amount of shortening, and sequence of emplacement of the structures are in accordance with previous regional studies of the Cantabrian Zone. 相似文献
44.
Loreto Donoso Rodrigo Romero Alberto Rondón Emmanuel Fernandez Pedro Oyola Eugenio Sanhueza 《Journal of Atmospheric Chemistry》1996,25(2):201-214
The levels of low molecular weight hydrocarbons were measured at pristine sites and rural locations affected by hydrocarbon emissions from oil and gas producing fields in Venezuela. At the clean sites, lower concentrations of C2 to C6 alkanes were observed, whereas, in comparison with remotes sites, very much higher levels were measured at the polluted sites. Alkenes present relatively high concentrations, with isoprene being the most abundant, all over the study region. The main sources of alkenes are likely to be natural, mainly from vegetation. The levels of alkanes recorded at the clean sites and the alkene levels found everywhere in the region are in agreement with the values reported for other clean sites in the tropics. The increase of ozone production capacity due to the anthropogenic emissions of alkanes from oil and gas fields was estimated. Due to the presence in the atmosphere of important amounts of naturally emitted isoprene, ethene and propene, which makes a substantial contribution to the reactivity of the hydrocarbon mixture, a small increase (<5%) was estimated to occur in the capacity of the ozone production at a regional scale during the rainy season. 相似文献
45.
The proposed existence of magnetic lineations in the Terra Cimmeria and Terra Sirenum regions of Mars was initially explained by Earth-like sea-floor spreading. Here we argue instead that these lineations could have been formed at a convergent plate margin through collision and accretion of terranes. A similar process produced banded magnetic anomalies, similar in geometry and even in size to those in Earth's North American Cordillera. Because only sparse and generally weak anomalies have been detected in the martian northern lowlands, which could constitute an analog to the terrestrial oceanic crust, it is possible that the magnetic field stopped its activity while crustal recycling was still active in Mars. 相似文献
46.
In the first part of this study, results of a computational fluid dynamics simulation over an array of cubes have been validated
against a set of wind-tunnel measurements. In Part II, such numerical results are used to investigate spatially-averaged properties
of the flow and passive tracer dispersion that are of interest for high resolution urban mesoscale modelling (e.g. non resolved
obstacle approaches). The results show that vertical profiles of mean horizontal wind are linear within the canopy and logarithmic
above. The drag coefficient, derived from the numerical results using the classical formula for the drag force, is height
dependent (it decreases with height). However, a modification of the formula is proposed (accounting for subgrid velocity
scales) that makes the drag coefficient constant with height. Results also show that the dispersive fluxes are similar in
magnitude to the turbulent fluxes, and that they play a very important role within the canopy. Vertical profiles of turbulent
length scales (to be used in k–l closure schemes, where k is the turbulent kinetic energy and l a turbulent length scale) are also derived. Finally the distribution of the values around the mean over the reference volumes
are analysed for wind and tracer concentrations. 相似文献
47.
Jos María Viramonte Raúl Alberto Becchio Jos Germn Viramonte Marcio Martins Pimentel Roberto Donato Martino 《Journal of South American Earth Sciences》2007,24(2-4):167-183
New field, petrological, geochemical, and geochronological data (U–Pb and Sm–Nd) for Ordovician rock units in the southeastern Puna, NW Argentina, indicate two lithostratigraphic units at the eastern–northeastern border of salar Centenario: (1) a bimodal volcanosedimentary sequence affected by low- to medium-grade metamorphism, comprising metasediments associated with basic and felsic metavolcanic rocks, dated 485 ± 5 Ma, and (2) a plutonic unit composed of syenogranites to quartz-rich leucogranites with U–Pb zircon ages between 462 ± 7 and 475 ± 5 Ma. Felsic metavolcanic and plutonic rocks are peraluminous and show similar geochemical differentiation trends. They also have similar Sm–Nd isotopic compositions (TDM model ages of 1.54–1.78 Ga; εNd(T) values ranging from −3.2 to −7.5) that suggest a common origin and derivation of the original magmas from older (Meso-Paleoproterozoic?) continental crust. Mafic rocks show εNd(T) ranging from +2.3 to +2.5, indicating a depleted mantle source. The data presented here, combined with those in the literature, suggest Ordovician magmatism mainly recycles preexisting crust with minor additions of juvenile mantle-derived material. 相似文献
48.
Graciela Salinas de Salmuni Inés Velasco Mirta Fresina Alberto L. Flores 《GeoJournal》2007,70(4):273-279
Much of the central-western region of Argentina, where San Juan Province is located, experiences arid to semi-arid climatic
conditions with low average annual rainfall accompanied by substantial evapotranspiration. Consequently, a viable crop industry
depends to a large extent upon irrigation from major river systems. Increasing demand for water in the lower basin of the
San Juan River is emphasizing the need for more accurate estimates of water used for irrigation. Since the water demand for
a particular crop is very closely related to crop area, monitoring the area of crop under irrigation is considered a proxy
for the amount of water used. Landsat 5 imagery for the growing season, field data and aerial photographs were used to evaluate
crop area. 相似文献
49.
Alberto Berretti 《Planetary and Space Science》1998,46(11-12)
We review some results about the analytic structure of Lindstedt series for some complex analytic dynamical systems: in particular, we consider Hamiltonian maps (like the standard map and its generalizations), the semi-standard map and Siegel's problem of the linearization of germs of holomorphic diffeomorphisms of (
,0). The analytic structure of those series can be studied numerically using Padé approximants, and one can show the existence of natural boundaries for real, diophantine values of the rotation number; by complexifying the rotation number, we show how these natural boundaries arise from the accumulation of singularities due to resonances, providing a new intuitive insight into the mechanism of the break-down of invariant KAM curves. Moreover, we study the Lindstedt series at resonances, i.e. for rational values of the rotation number, by suitably rescaling to 0 the value of the perturbative parameter, and a simple analytic structure emerges. Finally, we present some proofs for the simplest models and relate these results to renormalization ideas. 相似文献
50.