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81.
AbstractGully erosion is considered to be one of the most important soil erosion processes in Mediterranean marly environments, but its actual contribution to total soil loss is still under discussion. The objectives of this paper are: (a) to acquire the distributed value of erosion rate in a permanent gully developed on a marly substratum in a Mediterranean environment; and (b) to quantify the key factors responsible for the spatial and temporal differences in erosion rates observed within the gully. A permanent gully located in Cap Bon (northeastern Tunisia) has been intensively and regularly monitored over a 7-year period with electronic survey equipment (total station) to give five field topographic surveys, as well as hydrological measurements at the gully outlet. The net soil loss for the 7-year period comprised a denudation of 51 m3 of sediment on the gully bank slopes, which corresponds to a mean soil loss of 61 m3 ha?1 year?1 or 6.1 mm year?1. Denudation was observed on bed units with a slope gradient greater than 20%, while the remainder showed deposition. By confirming the factors involved in gully evolution, and by refining the statistical link between factors and erosion rates within the gully, the results provide important information to predict gully erosion rates in Mediterranean marly environments.Editor Z.W. Kundzewicz; Associate editor G. MahéCitation El Khalili, A., Raclot, D., Habaieb, H., and Lamachère, J.M., 2013. Factors and processes of permanent gully evolution in a Mediterranean marly environment (Cape Bon, Tunisia). Hydrological Sciences Journal, 58 (7), 1519–1531. 相似文献
82.
Origin of EL3 chondrites: Evidence for variable C/O ratios during their course of formation—A state of the art scrutiny 下载免费PDF全文
A. El Goresy Y. Lin M. Miyahara A. Gannoun M. Boyet E. Ohtani P. Gillet M. Trieloff A. Simionovici L. Feng L. Lemelle 《Meteoritics & planetary science》2017,52(5):781-806
Mineral inventories of enstatite chondrites; (EH and EL) are strictly dictated by combined parameters mainly very low dual oxygen (fO2) and sulfur (fS2) fugacities. They are best preserved in the Almahata Sitta MS‐17, MS‐177 fragments, and the ALHA 77295 and MAC 88136 Antarctic meteorites. These conditions induce a stark change of the geochemical behavior of nominally lithophile elements to chalcophile or even siderophile and changes in the elemental partitioning thus leading to formation of unusual mineral assemblages with high abundance of exotic sulfide species and enrichment in the metallic alloys, for example, silicides and phosphides. Origin and mode of formation of these exotic chondrites, and their parental source regions could be best scrutinized by multitask research experiments of the most primitive members covering mineralogical, petrological, cosmochemical, and indispensably short‐lived isotopic chronology. The magnitude of temperature and pressure prevailed during their formation in their source regions could eventually be reasonably estimated: pre‐ and postaccretionary could eventually be deduced. The dual low fugacities are regulated by the carbon to oxygen ratios estimated to be >0.83 and <1.03. These parameters not only induce unusual geochemical behavior of the elements inverting many nominally lithophile elements to chalcophile or even siderophile or anthracophile. Structure and mineral inventories in EL3 and EH3 chondrites are fundamentally different. Yet EH3 and EL3 members store crucial information relevant to eventual source regions and importantly possible variation in C/O ratio in the course of their evolution. EL3 and EH3 chondrites contain trichotomous lithologies (1) chondrules and their fragments, (2) polygonal enstatite‐dominated objects, and (3) multiphase metal‐rich nodules. Mineralogical and cosmochemical inventories of lithologies in the same EL3 indicate not only similarities (REE inventory and anomalies in oldhamite) but also distinct differences (sinoite‐enstatite‐graphite relationship). Oldhamite in chondrules and polygonal fragments in EL3 depict negative Eu anomaly attesting a common cosmochemical source. Metal‐dominated nodules in both EL3 and EH3 are conglomerates of metal clasts and sulfide fragments in EH3 and concentrically zoned C‐bearing metal micropebbles (≥25 μm ≤50 μm) in EL3 thus manifesting a frozen in unique primordial accretionary metal texture and composition. Sinoite‐enstatite‐diopside‐graphite textures reveal a nucleation and growth strongly suggestive of fluctuating C/O ratio during their nucleation and growth in the source regions. Mineral inventories, sulfide phase relations, sinoite‐enstatite‐graphite intergrowth, carbon and nitrogen isotopic compositions of graphite, spatial nitrogen abundance in graphite in metal nodules, and last but not least 129I/129Xe and 53Mn/53Cr systematics negate any previously suggested melting episode, pre‐accretionary or dynamic, in parental asteroids. 相似文献
83.
The authors presented indoor practice experiments of parameters affect on foaming and foam stability. Experiments were carried out and special equipments were used to determine foaming and foam stability; tests were tabulated and charted. The effects of chemical and physical parameters on foaming and foam stability have been conducted. 相似文献
84.
The contraction of an interstellar cloud is followed. The results indicates that there are shock waves appear during contraction. In order to study the effect of shock waves, two models have been studied. The post-shock temperature for the two models are, respectively, 3006 K and 2984 K. The density increases by more than three orders of magnitude. The gas is generally cooled by atoms, molecules, and grains. The dominant cooling process changes according to the chemical composition and the temperature of the gas. The thermal equilibrium depends on the existing physical conditions. 相似文献
85.
Our observations with the 6-m telescope revealed six new magnetic chemically peculiar (CP) stars among objects with large depressions in the continuum: HDE 293764, BD+17°3622, HD 169887, HDE 231054, HDE 338226, and HDE 343872. The presence of a magnetic field is suspected in several other CP stars. The maximum longitudinal field component B e exceeds 1.5 kG for all six stars; in HDE 293764 and HDE 343872, it reaches 3.8 kG. For each object, we present our magnetic-field measurements and published data on previous studies. The method of searching for magnetic stars based on an analysis of spectrophotometry shows its efficiency. 相似文献
86.
Abdullah Gamil M. S. El Aal Ahmed Abd Radwan Ahmed E. Qadri Talha Aly Nevin 《Acta Geotechnica》2023,18(1):105-125
Acta Geotechnica - One of the most important geotechnical parameters in studying the engineering behavior of a rock mass is slake durability. The major goal of this research is to test how a series... 相似文献
87.
Geotectonics - The monitoring of network measures, such as degree centrality, betweenness centrality, and clustering coefficient is performed, aiming to identify the periods that the earthquake... 相似文献
88.
Hassan M. El Shaer 《寒旱区科学》2015,7(1):0016-0022
Environmental degradation resulting from current climate changes, including prolonged drought, land degradation, desertification, and loss of biodiversity, is presenting enormous challenges to achieve ... 相似文献
89.
Hassan M. El Shaer 《寒旱区科学》2015,7(1):0007-0015
The Middle East and North Africa (MENA) region is characterized by high population growth, degraded and fragile nat-ural ecosystems, and a limited amount of arable lands. It is one of the most water-sc... 相似文献
90.
Sedimentology,three‐dimensional geobody reconstruction and carbon dioxide origin of Pleistocene travertine deposits in the Ballık area (south‐west Turkey) 下载免费PDF全文