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排序方式: 共有428条查询结果,搜索用时 828 毫秒
31.
Isaac Larbi Emmanuel Obuobie Anne Verhoef Stefan Julich Karl-Henz Feger Aymar Yaovi Bossa 《水文科学杂志》2020,65(13):2196-2209
ABSTRACT The need for a detailed investigation of the Vea catchment water balance components cannot be overemphasized due to its accelerated land-cover dynamics and the associated impacts on the hydrological processes. This study assessed the possible consequences of land-use change scenarios (i.e. business as usual, BAU, and afforestation for the year 2025) compared to the 2016 baseline on the Vea catchment’s water balance components using the Soil and Water Assessment Tool (SWAT) model. The data used include daily climate and discharge, soil and land use/land cover maps. The results indicate that the mean annual water yield may increase by 9.1% under the BAU scenario but decrease by 2.7% under the afforestation scenario; actual evapotranspiration would decrease under BAU but increase under afforestation; and groundwater recharge may increase under both scenarios but would be more pronounced under the afforestation scenario. These outcomes highlight the significance of land-cover dynamics in water resource management and planning at the catchment. 相似文献
32.
ABSTRACT White mold of soybeans is one of the most important fungal diseases that affect soybean production in South Dakota. However, there is a lack of information on the spatial characteristics of the disease and relationship with soybean yield. This relationship can be explored with the Normalized Difference Vegetation Index (NDVI) derived from Landsat 8 and a fusion of Landsat 8 and the Moderate Resolution Imaging Spectroradiometer (MODIS) images. This study investigated the patterns of yield in two soybean fields infected with white mold between 2016 and 2017, and estimated yield loss caused by white mold. Results show evidence of clustering in the spatial distribution of yield (Moran’s I = 0.38; p < 0.05 in 2016 and Moran’s I = 0.45; p < 0.05 in 2017) that can be explained by the spatial distribution of white mold in the observed fields. Yield loss caused by white mold was estimated at 36% in 2016 and 56% in 2017 for the worse disease pixels, with the most accurate period for estimating this loss on 21 August and 8 September for 2016 field and 2017 field, respectively. This study shows the potential of free remotely sensed satellite data in estimating yield loss caused by white mold. 相似文献
33.
High-energy proton (E
p > 55 MeV) and electron (E
e > 50 keV) events were observed by University of Iowa experiments on the satellites Explorer 33 and 35. The solar X-ray (2–12 Å) flares associated with the energetic proton events were found to have in general higher peak fluxes, considerably longer decay times (t) and smaller rise to decay time ratios (r) than the X-ray flares associated with the electron events. The most common decay times and rise to decay time ratios are: 80 t 100 min, 0.1 r 0.2 for the proton X-ray flares and t 20 min, 0.3 r 0.7 for the electron ones. 相似文献
34.
Emmanuel J. Gabet 《Estuaries and Coasts》1998,21(4):745-753
Saltmarsh tidal channels have often been recognized as being stable landscape features, despite highly sinous planforms, severely undercut banks, and high rates of bank erosion. In an effort to solve this paradox, a saltmarsh tidal channel in the San Francisco Bay was monitored from March 1995 to March 1996. The short-term rate of bank erosion was measured using erosion pins and found to be 57 ± 10 mm yr?1 on the outside banks of meander bends. In addition, a long-term maximum lateral migration rate of 23 ± 23 mm yr?1 was estimated from aerial photos, producing a dimensionless channel migration rate (defined as the rate of migration divided by channel with), of 0.5% yr?1. The difference in the rates of lateral migration and bank erosion is attributed to the persistence of failed bank material (slump blocks) in the channel. The slump blocks induce sedimentation, protect the banks, and prevent further bank erosion. A published stability analysis method for undercut banks is applied to determine a maximum overhanging width. Using the measured compressive and tensile strengths of rooted bank material, 16.55 ± 1.16 kPa and 2.93 ± 0.71 kPa, respectively, the maximum width of an undercut bank is calculated to be 0.69 m. The average width of slump blocks measured in the field is 0.67 ± 0.25 m. A simple numerical model predicting the rate of lateral migration is derived using the results from the stability analysis and data from sedimentation and erosion pins inserted throughout the channel. This model accurately predicts a rate of 23 ± 3 mm yr?1. 相似文献
35.
Jean Emmanuel Sicart Pierre Ribstein Bernard Francou Bernard Pouyaud Thomas Condom 《Global and Planetary Change》2007,59(1-4):27
A glaciological program has been undertaken since 1991 on Zongo glacier in Bolivia (6000–4850 m asl, 2.4 km2, 16°S). This program involves mass balance measurements, hydrological studies and energy balance investigations. On outer-tropical glaciers, melting and snow accumulation are both maximum in the wet season (austral summer), whereas the dry season (winter) is a period of low ablation. Errors on each term of the glaciological (stakes, snow-pits and integration method of the measurements) and hydrological (precipitation, discharge and runoff coefficient of free ice areas) methods are investigated to estimate the overall accuracy of the mass balance measurements. The hydrological budget is less than the glaciological one (mean difference: 60 cm w.e. per year), but both methods reproduce similar inter-annual variations. Errors in assessment of evaporation or water storage inside the glacier cannot explain the discrepancy. Errors using the glaciological method are large (around ± 40 cm w.e. per year), but no bias can explain the departure from the hydrological balance. Errors on discharge measurements are small and the uncertainty on the runoff coefficient has a minor effect on the mass balance. We concluded that hydrological budgets are too low due to the catch deficiency of rain gauges and absence of precipitation measurements at high altitudes, emphasizing the difficulty to assess snowfall distribution in high mountainous basins. 相似文献
36.
Emmanuel Hinglais 《Experimental Astronomy》2011,30(2-3):85-110
In 2009, the Centre National d??Etudes Spatiales (CNES) carried out an assessment study on a ??Fresnel telescope?? concept based on a two-spacecraftformation flying configuration. This concept uses a binary Fresnel zone plate, and the principle of diffraction focusing, which allows high resolution optical imaging for astrophysics. In addition to CNES, the Laboratoire d??Astrophysique de Toulouse Tarbes (LATT) was deeply involved at two levels: through Research & Technology (R&T) studies to simulate and validate on a test bench the Fresnel concept performance, and through active participation in the CNES team for the optical aspects and to define the astrophysical fields of Fresnel-based space missions. The study was conducted within the technical limitations that resulted from a compromise between the R&T state of the art and the potential scientific domains of interest. The main technical limitations are linked to the size of the primary Fresnel array and to its usable spectral bandwidth. In this framework, the study covers ambitious architectures, correlating the technology readiness of the main critical components with the time-scale and programmatic horizons. The possible scientific topics arise from this range of missions. In this paper, I present a mission launched by a Soyuz, dedicated to astrophysics in the Ultra Violet (UV) band: 120 to 300 nm using a 4-m Fresnel array. It could be competitive in the next fifteen years, whereas a 10-m aperture mission in different bands; UV, visible or Infra Red (IR) (up to 6 ??m) could be achievable in the future. Larger missions, using a primary array larger than 20 m, request technologies not yet available but that will probably be based on new inflatable structures with membranes, as already tested in the USA for other ends. 相似文献
37.
Katharina Marquardt Elena Petrishcheva Rainer Abart Emmanuel Gardés Richard Wirth Ralf Dohmen Hans-Werner Becker Wilhelm Heinrich 《Physics and Chemistry of Minerals》2010,37(10):751-760
In this study, we address volume diffusion of ytterbium in yttrium aluminum garnet (YAG) using thin-film single crystal diffusion
couples. We employ analytical transmission electron microscopy (ATEM) as a tool for combined microstructural and microchemical
analysis and compare the results to Rutherford backscattering (RBS) analysis. Given the high spatial resolution of the method,
we focus on microstructural changes of the thin-film diffusant source during the diffusion anneal. We evaluate the potential
influence of the associated changes in its transport properties on the evolution of concentration profiles in the single crystal
substrate. This approach allows us to test the reliability of determination of volume diffusion coefficients from thin-film
diffusion experiments. We found that for the chosen experimental setting, the influence of thin-film re-crystallization is
small when compared with the experimental uncertainty and good estimates for the volume diffusion coefficients of Yb in YAG
can be obtained using standard assumptions. Both Yb-concentration profiles analyzed with ATEM and with RBS give similar results.
At 1,450°C and 1 bar, we infer log D
Yb (m2/s) values of −19.37 ± 0.07 (TEM) and −19.84 ± 0.02 (RBS). Although the change in thin-film transport properties associated
with successive crystallization during the diffusion anneal does not play a major role for our experimental setup, this effect
cannot generally be ignored. 相似文献
38.
Yves Marrocchi Emmanuel Jacquet Julia Neukampf Johan Villeneuve Michael E. Zolensky 《Meteoritics & planetary science》2023,58(2):195-206
The ungrouped carbonaceous chondrite (CC) Bells has long been considered petrographically similar to CM chondrites based on its matrix abundance and degree of aqueous alteration, but also shows significant isotopic affinities to CR chondrites. Its taxonomic status is thus important for clarifying the relationship of the CRHB (formerly “CR”) clan with other CCs. In this study, we measured the oxygen isotopic compositions of olivines in type I chondrules and isolated olivine grains in Bells. Bells olivines mostly have ∆17O > −4‰, similar to CR chondrites but unlike other CCs that are rich in refractory inclusions, in which chondrules are generally richer in 16O. Therefore, Bells is a CR chondrite (albeit an anomalous one), most similar to the rare, matrix-rich CRs like Al Rais. These chondrites (i) may not necessarily derive from the same primary parent body as mainstream CRs, (ii) bear witness to significant variations of the matrix/chondrule ratio within the CRHB clan, and (iii) may be a good analog for samples retrieved by the space mission OSIRIS-REx. 相似文献
39.
Hadi Shahriari Hojjatollah Ranjbar Mehdi Honarmand Emmanuel John M. Carranza 《Resource Geology》2014,64(4):301-315
The accuracy of classification of the Spectral Angle Mapping (SAM) is warranted by choosing the appropriate threshold angles, which are normally defined by the user. Trial‐and‐error and statistical methods are commonly applied to determine threshold angles. In this paper, we discuss a real value–area (RV–A) technique based on the established concentration–area (C–A) fractal model to determine less biased threshold angles for SAM classification of multispectral images. Short wave infrared (SWIR) bands of the Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) images were used over and around the Sar Cheshmeh porphyry Cu deposit and Seridune porphyry Cu prospect. Reference spectra from the known hydrothermal alteration zones in each study area were chosen for producing respective rule images. Segmentation of each rule image resulted in a RV–A curve. Hydrothermal alteration mapping based on threshold values of each RV–A curve showed that the first break in each curve is practical for selection of optimum threshold angles. The hydrothermal alteration maps of the study areas were evaluated by field and laboratory studies including X–ray diffraction analysis, spectral analysis, and thin section study of rock samples. The accuracy of the SAM classification was evaluated by using an error matrix. Overall accuracies of 80.62% and 75.45% were acquired in the Sar Cheshmeh and Seridune areas, respectively. We also used different threshold angles obtained by some statistical techniques to evaluate the efficiency of the proposed RV–A technique. Threshold angles provided by statistical techniques could not enhance the hydrothermal alteration zones around the known deposits, as good as threshold angles obtained by the RV–A technique. Since no arbitrary parameter is defined by the user in the application of the RV‐A technique, its application prevents introduction of human bias to the selection of optimum threshold angle for SAM classification. 相似文献
40.
Jean Pierre Nguetnkam Fredéric Villiéras Richard Kamga Georges Emmanuel Ekodeck Jacques Yvon 《Chemie der Erde / Geochemistry》2014
Mineralogy, major, trace and rare earth elements of a weathering profile developed on tertiary greenstone belt in the extreme North Cameroon are reported. The aim of which was to investigate mineralogical evolution and element mobilization and redistribution during weathering under dry tropical climate. The weathering profile consists of four main horizons: (1) a spheroidal weathering zone constituted by a corestone–shell complex, (2) a C horizon, (3) a Bw horizon and an Ah horizon. The results indicate that nontronite, a Fe-rich smectite, is the exclusive clay mineral formed in the exfoliated shells and the C horizon. It is associated with kaolinite in the upper horizons. The coexistence of these two clay minerals induced a decrease of CEC and pH which becomes neutral. The weathering index (WI) values reveal that weathering becomes more and more intensive from the corestone up to Bw horizon, which is the most weathered horizon in the weathering profile. Mass balance calculations, using Th as immobile element, indicate that Ti is quite mobile and that Al and Fe are relatively enriched at the bottom and strongly leached at the top of the profile. Alkalis and alkaline earth elements are strong leached through out the profile, except Ca which displays similar trend as Al and Fe. The same goes for LILE (Cs, Sr), TTE (Cr, Co, Ni) and HSFE (Y, Nb, Hf). In opposite, REE are depleted at the bottom and enriched in the upper horizons, with more enrichment for LREE than for HREE. It appears that weathering of greenstone belt causes a fractionation of HREE and induces a concentration of LREEs. Ce and Eu anomalies display opposite behaviour. 相似文献