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481.
Uranium minerals from the San Marcos District, Chihuahua, Mexico 总被引:1,自引:0,他引:1
Manuel Reyes-Cortés Luis Fuentes-Cobas Enrique Torres-Moye Hilda Esparza-Ponce María Elena Montero-Cabrera 《Mineralogy and Petrology》2010,99(1-2):121-132
The mineralogy of the two uranium deposits (Victorino and San Marcos I) of Sierra San Marcos, located 30 km northwest of Chihuahua City, Mexico, was studied by optical microscopy, powder X-ray diffraction with Rietveld analysis, scanning electron microscopy with energy dispersive X-ray analysis, inductively coupled plasma spectrometry, and gamma spectrometry. At the San Marcos I deposit, uranophane Ca(UO2)2Si2O7·6(H2O) (the dominant mineral at both deposits) and metatyuyamunite Ca(UO2)(V2O8)·3(H2O) were observed. Uranophane, uraninite (UO2+x), masuyite Pb(UO2)3O3(OH)·3(H2O), and becquerelite Ca(UO2)6O4(OH)6 ·(8H2O) are present at the Victorino deposit. Field observations, coupled with analytical data, suggest the following sequence of mineralization: (1) deposition of uraninite, (2) alteration of uraninite to masuyite, (3) deposition of uranophane, (4) micro-fracturing, (5) calcite deposition in the micro-fractures, and (6) formation of becquerelite. The investigated deposits were formed by high-to low-temperature hydrothermal activity during post-orogenic evolution of Sierra San Marcos. The secondary mineralization occurred through a combination of hydrothermal and supergene alteration events. Becquerelite was formed in situ by reaction of uraninite with geothermal carbonated solutions, which led to almost complete dissolution of the precursor uraninite. The Victorino deposit represents the second known occurrence of becquerelite in Mexico, the other being the uranium deposits at Peña Blanca in Chihuahua State. 相似文献
482.
Manuel Stark Tobias Heckmann Livia Piermattei Fabian Dremel Andreas Kaiser Patrick Machowski Florian Haas Michael Becht 《地球表面变化过程与地形》2021,46(10):2019-2043
Uncrewed aerial systems (UAS), combined with structure-from-motion photogrammetry, has already proven to be very powerful for a wide range of geoscience applications and different types of UAS are used for scientific and commercial purposes. However, the impact of the UAS used on the accuracy of the point clouds derived is not fully understood, especially for the quantitative analysis of geomorphic changes in complex terrain. Therefore, in this study, we aim to quantify the magnitude of systematic and random error in digital elevation models derived from four commonly used UAS (XR6/Sony α6000, Inspire 2/X4s, Phantom 4 Pro+, Mavic Pro) following different flight patterns. The vertical error of each elevation model is evaluated through comparison with 156 GNSS reference points and the normal distribution and spatial correlation of errors are analysed. Differences in mean errors (−0.4 to −1.8 cm) for the XR6, Inspire 2 and Phantom 4 Pro are significant but not relevant for most geomorphological applications. The Mavic Pro shows lower accuracies with mean errors up to 4.3 cm, thus showing a higher influence of random errors. QQ plots revealed a deviation of errors from a normal distribution in almost all data. All UAS data except Mavic Pro exhibit a pure nugget semivariogram, suggesting spatially uncorrelated errors. Compared to the other UAS, the Mavic Pro data show trends (i.e. differences increase with distance across the survey—doming) and the range of semivariances is 10 times greater. The lower accuracy of Mavic Pro can be attributed to the lower GSD at the same flight altitude and most likely, the rolling shutter sensor has an effect on the accuracy of the camera calibration. Overall, our study shows that accuracies depend highly on the chosen data sampling strategy and that the survey design used here is not suitable for calibrating all types of UAS camera equally. 相似文献
483.
Maya García-Comas Manuel López-Puertas Bianca M. Dinelli Alberto Adriani Angioletta Coradini 《Icarus》2011,214(2):571-583
After molecular nitrogen, methane is the most abundant species in Titan’s atmosphere and plays a major role in its energy budget and its chemistry. Methane has strong bands at 3.3 μm emitting mainly at daytime after absorption of solar radiation. This emission is strongly affected by non-local thermodynamic equilibrium (non-LTE) in Titan’s upper atmosphere and, hence, an accurate modeling of the non-LTE populations of the emitting vibrational levels is necessary for its analysis. We present a sophisticated and extensive non-LTE model which considers 22 CH4 levels and takes into account all known excitation mechanisms in which they take part. Solar absorption is the major excitation process controlling the population of the v3-quanta levels above 1000 km whereas the distribution of the vibrational energy within levels of similar energy through collisions with N2 is also of importance below that altitude. CH4-CH4 vibrational exchange of v4-quanta affects their population below 500 km. We found that the ν3 → ground band dominates Titan’s 3.3 μm daytime limb radiance above 750 km whereas the ν3 + ν4 → ν4 band does below that altitude and down to 300 km. The ν3 + ν2 → ν2, the 2ν3 → ν3, and the 13CH4ν3 → ground bands each contribute from 5% to 8% at regions below 800 km. The ν3 + 2ν4 → 2ν4and ν2 + ν3 + ν4 → ν2 + ν4 bands each contribute from 2% to 5% below 650 km. Contributions from other CH4 bands are negligible. We have used the non-LTE model to retrieve the CH4 abundance from 500 to 1100 km in the southern hemisphere from Cassini-VIMS daytime measurements near 3.3 μm. Our retrievals show good agreement with previous measurements and model results, supporting a weak deviation from well mixed values from the lower atmosphere up to 1000 km. 相似文献
484.
A minimum of angular velocity is not found at the equator as suggested by Gilman, but at a latitude of 6° in both hemispheres. 相似文献
485.
Cid Rafael Calvo Manuel Correas Jose M. 《Celestial Mechanics and Dynamical Astronomy》1975,12(2):131-138
Celestial Mechanics and Dynamical Astronomy - In this paper the relation between the Von Zeipel generating functions, in two canonical systems, is considered. Explicit recursive formulae between... 相似文献
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Frédéric Villiéras Laurent J. Michot Frédérique Bardot Manuel Chamerois Céline Eypert-Blaison Michèle François Gilles Gérard Jean-Maurice Cases 《Comptes Rendus Geoscience》2002,334(9):597-609
The precise study of adsorption mechanisms at solid–liquid interfaces requires a good analysis of the surface heterogeneity of the studied solids. For that purpose, molecular probe technique is one of the most powerful, especially at solid–gas interfaces. Indeed, low-pressure gas adsorption coupled to modelling of derivative adsorption isotherms as a function of logarithm of pressure allows to study qualitatively and quantitatively the effect of surface heterogeneity on the energy distribution of adsorption centres. The present review points out the interests of that approach to determine the shape of particles, the presence of high-energy adsorption sites and the surface polarity. Results comparing adsorption at solid–gas and solid–liquid interfaces are also mentioned. To cite this article: F. Villiéras et al., C. R. Geoscience 334 (2002) 597–609. 相似文献
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490.
It has been suggested that lower rates of granivory in South American warm deserts compared to their North American counterparts arose from a reduction of seed reserves in the former owing to the extinction of argyrolagid marsupials. We measured seed reserves in two habitats of the central Monte Desert in an attempt to detect such seed decline, but to no avail. After moderate rainfall, maximum seed standing crops reached 16,000 and 23,000 seeds m−2in shrublands and open forests, respectively. Under the canopy of trees and shrubs there were 19,000 and 37,000 seeds m−2; whereas in exposed areas there werec. 10,000 seeds m−2in both habitats. Seed banks in other South American semi-arid areas showed similar values. Total grass seeds as well as those presumably preferred by ants also seem to be similar in both continents. Hence, granivory in South America, as has been already reported for Australia, is lower than in North America in spite of the great similarity of seed bank sizes. Moreover, argyrolagids were unlikely seed-hoarding granivores, therefore some other reason than argyrolagid extinction should be sought to explain the lack of specialized seed-eating mammals, and the smaller overall seed consumption rates in South American deserts. 相似文献