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991.
The amino acid and hydrocarbon contents of the Paris meteorite: Insights into the most primitive CM chondrite 下载免费PDF全文
Zita Martins Paola Modica Brigitte Zanda Louis Le Sergeant d'Hendecourt 《Meteoritics & planetary science》2015,50(5):926-943
The Paris meteorite is one of the most primitive carbonaceous chondrites. It is reported to be the least aqueously altered CM chondrite, and to have experienced only weak thermal metamorphism. We have analyzed for the first time the amino acid and hydrocarbon contents of this pristine meteorite by gas chromatography–mass spectrometry (GC–MS). When plotting the relative amino acids abundances of several CM chondrites according to the increasing hydrothermal scale (petrologic subtypes), from the CM2.7/2.8 Paris to the CM2.0 MET 01070, Paris has the lowest relative abundance of β‐alanine/glycine (0.15), which fits with the relative abundances of β‐alanine/glycine increasing with increasing aqueous alteration for CM chondrites. These results confirm the influence of aqueous alteration on the amino acid abundances and distribution. The amino acid analysis shows that the isovaline detected in this meteorite is racemic (d /l = 0.99 ± 0.08; l ‐enantiomer excess = 0.35 ± 0.5%; corrected d /l = 1.03; corrected l ‐enantiomer excess = ?1.4 ± 2.6%). The identified hydrocarbons show that Paris has n‐alkanes ranging from C16 to C25 and 3‐ to 5‐ring nonalkylated polycyclic aromatic hydrocarbons (PAHs). The lack of alkylated PAHs in Paris seems to be also related to this low degree of aqueous alteration on its parent body. The extraterrestrial hydrocarbon content, suggested by the absence of any biomarker, may well have a presolar origin. The chemistry of the Paris meteorite may thus be closely related to the early stages of the solar nebula with a contribution from interstellar (molecular cloud) precursors. 相似文献
992.
In order to derive the distribution of olivine and pyroxene in Crater Copernicus,we compute two band ratios(950/750 and 2 000/1 500 nm) ,percent content of elements(Al%,Ca%,Mg%,FeO%) and maturity(Is/FeO) based on Clementine UVVIS and NIR image data.The central peaks of Copernicus,which are known to be olivine-rich or pyroxene-rich,are chosen as ground truth and ROIs used to derive the distribution of olivine and pyroxene with a decision tree and spectral angle mapper(SAM) .Additionally,we compared previous ... 相似文献
993.
E. M. Blanter J.-L. Le Mouél M. G. Shnirman V. Courtillot 《Doklady Earth Sciences》2011,440(1):1316-1319
This paper describes seasonal peculiarities of modern climate warming in the European region. It is shown that warming scenarios
considerably differ in cold and warm periods of the year. The warming is accompanied with growth and considerable change in
the phase of the yearly cycle in solarity data. A strong half-year cycle is recognized in seasonal variation of long-term
trends over the last few years. Peculiarities of climate change in Europe and the increased influence of the tropics are discussed
in view of the results obtained. 相似文献
994.
995.
Joel C. Le Baron Stefan W. Grab Kathleen Kuman 《Journal of African Earth Sciences》2011,59(4-5):384-394
The Hackthorne 1 site (southern Tuli Basin, South Africa) is situated on a sand-covered plateau adjacent to the Limpopo River Valley. Although the site is well known for its Stone Age archaeology, the past environmental contexts (particularly sedimentological/geomorphological) are not well known. We examine the Hackthorne sand grain surface textures, so as to provide some insight on the site specific and regional depositional history. Quartz sands at Hackthorne were collected from surface sands and from underlying weathered calcrete. SEM analysis was performed on sand grains, through which several mechanical and chemical microtextures were identified. Microtextures typical of fluvial environments were found only on grains derived from the plateau calcrete host sediment, whilst the surface sands exhibited only textures associated with aeolian environments. The results indicate that the calcrete host sediment is composed of alluvium, and that the surface sands mantling the Hackthorne Plateau are not deflated from the alluvial deposits in the Limpopo Valley, but may rather be derived from distant aeolian sources. The deposition of aeolian sands is consistent with OSL dates which place sand deposition, or remobilization, at 23 and 15 kya, periods in southern Africa associated with increased aridity. 相似文献
996.
F. J. Cerino Córdova Ph.D. A. M. García León Ph.D. R. B. Garcia Reyes Ph.D. M. T. Garza González Ph.D. E. Soto Regalado Ph.D. M. N. Sánchez González Ph D. I. Quezada López 《International Journal of Environmental Science and Technology》2011,8(4):695-704
A central composite face-centered design was used to study and to optimize lead biosorption from aqueous solution on Aspergillus terreus biomass. Four factors such as stirring speed, temperature, solution pH and biomass dose at different levels were studied.The hierarchical quadratic model were established by adding replicates at the central point and axial points to the initial full factorial design (24). The percentage removal of lead was affected by biomass dose, pH, and interactions between pH and biomass dose, pH and stirring speed, pH and temperature. The hierarchical quadratic model described adequately the response surface based on the adjusted determination coefficient (R2 Adj= 0.97) and the adequate precision ratio (42.21). According to this model, the optimal conditions to remove lead completely from aqueous solutions (at initial lead concentration of 50 mg/L and solutions of 100 mL) with Aspergillus terreus were at pH 5.2, 50 °C, stirring speed of 102/min and a biomass dose of 139 mg.The response surface methodology can be used to determine the optimal conditions for metal adsorption on several adsorbents. In addition, results reported in this research demonstrated the feasibility of employing A. terreus as biosorbent for lead removal. 相似文献
997.
Shavkat Rakhmatullaev Antoine Marache Frédéric Huneau Philippe Le Coustumer Masharif Bakiev Mikael Motelica-Heino 《Environmental Earth Sciences》2011,63(3):447-460
The paper presents the results of a new geostatistical approach to generate bathymetric surface models from point measurement
converted into continuous contour surfaces of reservoir bottoms in Uzbekistan. Sedimentation of reservoirs raises engineering,
environmental and economical issues for the communities around the world in areas affected by a strong water deficit. Because
of Uzbekistan’s arid climatic conditions, and uneven spatial and temporal water resources distribution, responsive and innovative
water availability assessment surveys of all major water reservoirs are required. Bathymetric surveying is a traditional method
that is carried out for the estimation of reservoir volumes and surface areas of the corresponding reservoir stages in order
to assess the water availability. Volume and surface area differences derived from multiple surveys of a reservoir provide
storage loss estimates over time due to sedimentation. However, two main factors, such as intensive field data measurement
and post data-processing, often limit the frequency of these surveys. Alternatively, innovative depth measurement technologies
coupled with contouring and surface mapping programs provide automated reservoir volume and surface area calculations. This
significantly reduces time, workload and financial burdens for reservoir sedimentation projects. This research proposes the
use of geostatistical approach to assess the reservoir sedimentation in the Akdarya reservoir of Uzbekistan. The geostatistical
approach includes (semi-) variogram analysis and interpolation (kriging and simulations—turning bands) techniques predicting
values at unsampled locations for generating digital bathymetric surface models of reservoir bottom conditions in order to
calculate the volume and surface area at a given water elevation. The simulation enables to have range of reservoir volumes
and surface areas with the same probability, in comparison to the kriging and traditional methods. This gives a real estimation
of the resource availability for water operators to manage natural resources and hydraulic infrastructure in a sustainable
manner. 相似文献
998.
999.
Mathieu?Le?CozEmail author Pierre?Genthon Pierre?M.?Adler 《Mathematical Geosciences》2011,43(7):861-878
Multiple-point statistics are used to model facies heterogeneities in the vadose zone of the Komadugu-Yobe River valley (southeastern
Niger) which is presently submitted to an undergoing intensive agricultural development; therefore, increasing quantitative
and qualitative pressures are exerted on groundwater resources. The sand–clay heterogeneities are analyzed by means of a Landsat
image acquired during a high flow period over a 160 km stretch in the downstream part of the valley and a set of 50 boreholes
drilled near the town of Diffa (4 km×4 km area). The horizontal variograms of heterogeneities are characterized by a noticeably
constant length scale of 380 m and clayey objects are shown to be randomly distributed in space according to a Poisson process.
A set of two-dimensional vertical images is built based on a Boolean procedure and the Snesim algorithm is used to simulate
synthetic three-dimensional media. When the vertical correlation length is fitted, the three-dimensional model satisfactorily
reproduces the second order statistics of heterogeneities and the specific facies patterns. 相似文献
1000.