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251.
Takyi Stephen Appiah Amponsah Owusu Yeboah Ata Senior Mantey Emmanuel 《GeoJournal》2021,86(6):2467-2481
GeoJournal - Slum development has become a major urban planning and management problem due to the challenges they pose to the larger urban environment. Activities of slum dwellers are... 相似文献
252.
253.
Emmanuel J. Gabet 《地球表面变化过程与地形》2000,25(13):1419-1428
It has generally been assumed that diffusive sediment transport on soil‐mantled hillslopes is linearly dependent on hillslope gradient. Fieldwork was done near Santa Barbara, California, to develop a sediment transport equation for bioturbation by the pocket gopher (Thomomys bottae) and to determine whether it supports linear diffusion. The route taken by the sediment is divided into two parts, a subsurface path followed by a surface path. The first is the transport of soil through the burrow to the burrow opening. The second is the discharge of sediment from the burrow opening onto the hillslope surface. The total volumetric sediment flux, as a function of hillslope gradient, is found to be: qs (cm3 cm−1 a−1) = 176(dz/dx)3 − 189(dz/dx)2 + 68(dz/dx) + 34(dz/dx)0·4. This result does not support the use of linear diffusion for hillslopes where gopher bioturbation is the dominant mode of sediment transport. A one‐dimensional hillslope evolution program was used to evolve hillslope profiles according to non‐linear and linear diffusion and to compare them to a typical hillslope. The non‐linear case more closely resembles the actual profile with a convex cap at the divide leading into a straight midslope section. Copyright © 2000 John Wiley & Sons, Ltd. 相似文献
254.
255.
Fulbert Mbowou Ngantche Igor Sébastien Owona Boris Chako Tchamabe Justin Lissom Bruno Lanson Emmanuel Ekodeck Georges 《中国地球化学学报》2020,39(6):830-861
Acta Geochimica - Pozzolans from the Tombel Plain, Bamileke Plateau, and Noun Plain, 3 monogenetic volcanic fields in the central part of the Cameroon Volcanic Line (the Tombel Plain, Bamileke... 相似文献
256.
Emmanuel Jacquet Maxime Piralla Pauline Kersaho Yves Marrocchi 《Meteoritics & planetary science》2021,56(1):13-33
We report microscopic, cathodoluminescence, chemical, and O isotopic measurements of FeO‐poor isolated olivine grains (IOG) in the carbonaceous chondrites Allende (CV3), Northwest Africa 5958 (C2‐ung), Northwest Africa 11086 (CM2‐an), and Allan Hills 77307 (CO3.0). The general petrographic, chemical, and isotopic similarity with bona fide type I chondrules confirms that the IOG derived from them. The concentric CL zoning, reflecting a decrease in refractory elements toward the margins, and frequent rimming by enstatite are taken as evidence of interaction of the IOG with the gas as stand‐alone objects. This indicates that they were splashed out of chondrules when these were still partially molten. CaO‐rich refractory forsterites, which are restricted to ?17O <?4‰ likely escaped equilibration at lower temperatures because of their large size and possibly quicker quenching. The IOG thus bear witness to frequent collisions in the chondrule‐forming regions. 相似文献
257.
Xu Shan Hu Xiangyun Carranza Emmanuel John M. Wang Gongwen 《Natural Resources Research》2020,29(6):3425-3442
Natural Resources Research - Identification of geochemical anomalies from geological background is of great significance in the exploration of complex mineralization systems. For a 2D problem, the... 相似文献
258.
QIAO Shuang-shuang QIN Sheng-wu SUN Jing-bo CHE Wen-chao YAO Jing-yu SU Gang CHEN Yang NNANWUBA Uzodigwe Emmanuel 《山地科学学报》2021,(5):1177-1191
Debris flow susceptibility mapping(DFSM) has been reported in many studies, however, the irrational use of the same conditioning factor system for DFSM in regional-scale has not been thoroughly resolved. In this paper, a region-partitioning method that is based on the topographic characteristics of watershed units was developed with the objective of establishing multiple conditioning factor systems for regional-scale DFSM. First, watershed units were selected as the mapping units and created throughout the entire research area. Four topographical factors, namely, elevation, slope, aspect and relative height difference, were selected as the basis for clustering watershed units. The k-means clustering analysis was used to cluster the watershed units according to their topographic characteristics to partition the study area into several parts. Then, the information gain ratio method was used to filter out superfluous factors to establish conditioning factor systems in each region for the subsequent debris flow susceptibility modeling. Last, a debris flow susceptibility map of the whole study area was acquired by merging the maps from all parts. DFSM of Yongji County in Jilin Province, China was selected as a case study, and the analytical hierarchy process method was used to conduct a comparative analysis to evaluate the performance of the region-partitioning method. The area under curve(AUC) values showed that the partitioning of the study area into two parts improved the prediction rate from 0.812 to 0.916. The results demonstrate that the region-partitioning method on the basis of topographic characteristics of watershed units can realize more reasonable regional-scale DFSM. Hence, the developed region-partitioning method can be used as a guide for regional-scale DFSM to mitigate the imminent debris flow risk. 相似文献
259.
B. Reynard M. Okuno Y. Shimada Y. Syono C. Willaime 《Physics and Chemistry of Minerals》1999,26(6):432-436
Structural modifications induced by shock-wave compression up to 40 GPa in anorthite glass are investigated by Raman spectroscopy.
In the first investigation, densification increases with increasing shock pressure. A maximum densification of 2.2% is obtained
for a shock pressure of 24 GPa. This densification is attributed to a decrease of the average ring size, favoring three-membered
rings. The densification is much lower than in silica glass subject to shock at similar pressures (11%), because the T-O-T
bond angle decrease is impeded in anorthite glass. For higher shock pressures, the decrease of the recovered densification
is attributed to partial annealing of the samples due to high after-shock residual temperatures. The study of the annealing
process of the most densified glass by in-situ high temperature Raman spectroscopy confirms that relaxation of the three-membered
rings occurs above about 900 K.
Received: 21 July 1998 / Revised and accepted: 27 January 1999 相似文献
260.
The production of carbon in the ocean, the so-called primary production, depends on various physicobiological parameters:
the biomass and nutrient amounts in oceans, the salinity and temperature of the water and the light available in the water
column. We focus on the visible spectrum of the solar radiation defined as the Photosynthetically Active Radiation (PAR).
We developed a model (Chamiet al. 1997) to simulate the behavior of the solar beam in the atmosphere and the ocean. We first describe the theoretical basis
of the code and the method we used to solve the radiative transfer equation (RTE): the successive orders of scattering (SO).
The second part deals with a sensitivity study of the PAR just above and below the sea surface for various atmospheric conditions.
In a cloudy sky, we computed a ratio between vector fluxes just above the sea surface and spherical fluxes just beneath the
sea surface. When the optical thickness of the cloud increases this ratio remains constant and around 1.29. This parameter
is convenient to convert vector flux at the sea surface as retrieved from satellite to PAR. Subsequently, we show how solar
radiation as vector flux rather than P A R leads to an underestimate of the primary production up to 40% for extreme cases. 相似文献