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Prediction of threshold conditions and incipient motion is the essential issue for the study of sediment transport. This work compares existing empirical threshold curves proposed for Shields diagram, a method based on the concept of probability of sediment movement, and an empirical method based on movability number. These methods are used to predict the incipient motion conditions for experimental runs taken from various studies. Most of the experimental data, used in this work, have not been used before in derivation of alternative formulations for Shields diagram and other methods. The empirical threshold curves based on the Shields entrainment function was the least successful at predicting the measured incipient motion conditions, while the use of the movability number gives good predictions of critical shear velocity compared with experimental data. 相似文献
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Watershed morphometric analysis of Wadi Baish Dam catchment area using integrated GIS-based approach
The integration of Remote Sensing (RS) and Geographic Information Systems (GIS) constitutes a powerful tool for the evaluation of watershed morphometric parameters. The benefits of this integration include saving time and effort as well as improving the accuracy of the analysis. Moreover, this technique is appropriate for describing the watershed and its streams. In this study, a detailed morphometric analysis of the Wadi Baish catchment area has been performed using the Shuttle Radar Topography Mission (SRTM). The performed morphometric analysis includes linear, areal, and relief aspects. The results of the morphometric analysis reveal that the catchment can be described as of eighth stream order and consists of an area of 4741.07 km2. Additionally, the basin is characterized by a relatively high mean value of bifurcation (4.012), indicative of the scarcity of permeable rocks with high slope in the area. This value of bifurcation ratio is consistent with the high drainage density value of 2.064 km/km2 and confirms the impermeability of the subsurface material and mountainous relief. The hypsometric integral of the catchment is 47.4%, and the erosion integral of the catchment is 52.6%, both were indications of a mature catchment area. 相似文献
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Abstract: The Late Cretaceous Khabr–Marvast tectonized ophiolite is located in the middle part of the Nain–Baft ophiolite belt, at the south-western edge of the central Iranian microcontinent. Although all the volcanic rocks in the study area indicate subduction-related magmatism (e.g. high LILE (large ion lithophile elements) / HFSE (high field strenght elements) ratios and negative anomalies in Nb and Ta), geological and geochemical data clearly distinguish two distinct groups of volcanic rocks in the tectonized association: (1) group 1 is comprised of hyaloclastic breccias, basaltic pillow lavas, and andesite sheet flows. These rocks represent the Nain–Baft oceanic crust; and (2) group 2 is alkaline lavas from the top section of the ophiolite suite. These lavas show shoshonite affinity, but do not support the propensity of ophiolite. 相似文献
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Corey A Cohn Christopher E Pedigo Shavonne N Hylton Sanford R Simon Martin AA Schoonen 《Geochemical transactions》2009,10(1):8-9
Background
Given the importance of highly reactive oxygen species (hROS) as reactants in a wide range of biological, photochemical, and environmental systems there is an interest in detection and quantification of these species. The extreme reactivity of the hROS, which includes hydroxyl radicals, presents an analytical challenge. 3'-(p-Aminophenyl) fluorescein (APF) is a relatively new probe used for measuring hROS. Here, we further evaluate the use of APF as a method for the detection of hydroxyl radicals in particle suspensions. 相似文献6.
Alexander Smirnov Douglas Hausner Richard Laffers Daniel R Strongin Martin AA Schoonen 《Geochemical transactions》2008,9(1):1-20
Experiments with dinitrogen-, nitrite-, nitrate-containing solutions were conducted without headspace in Ti reactors (200°C), borosilicate septum bottles (70°C) and HDPE tubes (22°C) in the presence of Fe and Ni metal, awaruite (Ni80Fe20) and tetrataenite (Ni50Fe50). In general, metals used in this investigation were more reactive than alloys toward all investigated nitrogen species. Nitrite and nitrate were converted to ammonium more rapidly than dinitrogen, and the reduction process had a strong temperature dependence. We concluded from our experimental observations that Hadean submarine hydrothermal systems could have supplied significant quantities of ammonium for reactions that are generally associated with prebiotic synthesis, especially in localized environments. Several natural meteorites (octahedrites) were found to contain up to 22 ppm Ntot. While the oxidation state of N in the octahedrites was not determined, XPS analysis of metals and alloys used in the study shows that N is likely present as nitride (N3-). This observation may have implications toward the Hadean environment, since, terrestrial (e.g., oceanic) ammonium production may have been supplemented by reduced nitrogen delivered by metal-rich meteorites. This notion is based on the fact that nitrogen dissolves into metallic melts. 相似文献
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Corey A Cohn Shawn C Fisher Bruce J Brownawell Martin AA Schoonen 《Geochemical transactions》2010,11(1):2
Cellular exposure to particulate matter with concomitant formation of reactive oxygen species (ROS) and oxidization of biomolecules
may lead to negative health outcomes. Evaluating the particle-induced formation of ROS and the oxidation products from reaction
of ROS with biomolecules is useful for gaining a mechanistic understanding of particle-induced oxidative stress. Aqueous suspensions
of pyrite particles have been shown to form hydroxyl radicals and degrade nucleic acids. Reactions between pyrite-induced
hydroxyl radicals and nucleic acid bases, however, remain to be determined. Here, we compared the oxidation of adenine by
Fenton-generated (i.e., ferrous iron and hydrogen peroxide) hydroxyl radicals to adenine oxidation by hydroxyl radicals generated
in pyrite aqueous suspensions. Results show that adenine oxidizes in the presence of pyrite (without the addition of hydrogen
peroxide) and that the rate of oxidation is dependent on the pyrite loading. Adenine oxidation was prevented by addition of
either catalase or ethanol to the pyrite/adenine suspensions, which implies that hydrogen peroxide and hydroxyl radicals are
causing the adenine oxidation. The adenine oxidation products, 8-oxoadenine and 2-hydroxyadenine, were the same whether hydroxyl
radicals were generated by Fenton or pyrite-initiated reactions. Although nucleic acid bases are unlikely to be directly exposed
to pyrite particles, the formation of ROS in the vicinity of cells may lead to oxidative stress. 相似文献
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Xiang?Zhang Michael?J?Borda Martin?AA?Schoonen Daniel?R?StronginEmail author 《Geochemical transactions》2003,4(1):8
The effect of a diacetylene-containing phospholipid on the oxidation of pyrite, FeS2, was investigated. Earlier work reported by our research group showed that the adsorption of l,2-bis(10,12-tricosadiynoyl)-sn-glycero-3-phosphocholine on pyrite suppressed the extent of its oxidation by about 75% over a specific time period. Results
presented here show that the pre-exposure to UV radiation of this lipid after sorption onto pyrite results in a 90% suppression.
Attenuated total reflection (ATR) Fourier transform infra-red spectroscopy (FTIR) suggests that the UV irradiation of the
lipid does not result in degradation of the adsorbed layer. It is believed that the UV exposure results in the cross-linking
and polymerization of the adsorbed phospholipid into a relatively impermeable barrier that separates the pyrite from the aqueous
phase. The results of this study might have implications for the protection of pyrite from oxidation in the environment. 相似文献
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Greg?K?Druschel Martin?AA?SchoonenEmail author D?Kirk?Nordstrom James?W?Ball Yong?Xu Corey?A?Cohn 《Geochemical transactions》2003,4(1):12
A sampling protocol for the retention, extraction, and analysis of sulfoxyanions in hydrothermal waters has been developed
in the laboratory and tested at Yellowstone National Park and Green Lake, NY. Initial laboratory testing of the anion-exchange
resin Bio-Rad™ AG1-X8 indicated that the resin was well suited for the sampling, preservation, and extraction of sulfate and
thiosulfate. Synthetic solutions containing sulfate and thiosulfate were passed through AG1-X8 resin columns and eluted with
1 and 3 M KCl, respectively. Recovery ranged from 89 to 100%. Comparison of results for water samples collected from five
pools in Yellowstone National Park between on-site IC analysis (U.S. Geological Survey mobile lab) and IC analysis of resin-stored
sample at SUNY-Stony Brook indicates 96 to 100% agreement for three pools (Cinder, Cistern, and an unnamed pool near Cistern)
and 76 and 63% agreement for two pools (Sulfur Dust and Frying Pan). Attempts to extract polythionates from the AG1-X8 resin
were made using HCl solutions, but were unsuccessful. Bio-Rad™ AG2-X8, an anion-exchange resin with weaker binding sites than
the AG1-X8 resin, is better suited for polythionate extraction. Sulfate and thiosulfate extraction with this resin has been
accomplished with KCl solutions of 0.1 and 0.5 M, respectively. Trithionate and tetrathionate can be extracted with 4 M KCl.
Higher polythionates can be extracted with 9 M hydrochloric acid. Polythionate concentrations can then be determined directly
using ion chromatographic methods, and laboratory results indicate recovery of up to 90% for synthetic polythionate solutions
using AG2-X8 resin columns. 相似文献