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11.
Mantsis Damianos F. Sherwood Steven Dixit Vishal Morrison Hugh Thompson Greg 《Climate Dynamics》2020,54(7):3425-3439
Climate Dynamics - The simulation of Saharan mid tropospheric clouds is investigated with the weather research and forecasting (WRF) regional atmospheric model at convection permitting... 相似文献
12.
Shrubland expansion in the American Southwest 总被引:8,自引:0,他引:8
Sherwood B. Idso 《Climatic change》1992,22(1):85-86
13.
Li-Hung Lin Greg F. Slater Barbara Sherwood Lollar T.C. Onstott 《Geochimica et cosmochimica acta》2005,69(4):893-903
The production rate and isotopic composition of H2 derived from radiolytic reactions in H2O were measured to assess the importance of radiolytic H2 in subsurface environments and to determine whether its isotopic signature can be used as a diagnostic tool. Saline and pure, aerobic and anaerobic water samples with pH values of 4, 7, and 10 were irradiated in sealed vials at room temperature with an artificial γ source, and the H2 abundance in the headspace and its isotopic composition were measured. The H2 concentrations were observed to increase linearly with dosage at a rate of 0.40 ± 0.04 molecules (100 eV)−1 within the dosage range of 900 to 3500 Gray (Gy; Gy = 1 J Kg−1) with no indication of a maximum limit on H2 concentration. At ∼2000 Gy, the H2 concentration varied only by 16% across the experimental range of pH, salinity, and O2. Based upon this measured yield and H2 yields for α and β particles, a radiolytic H2 production rate of 10−9 to 10−4 nM s−1 was estimated for the range of radioactive element concentrations and porosities typical of crustal rocks. The δD of H2 was independent of the dosage, pH (except for pH 4), salinity, and O2 and yielded an αDH2O-H2 of 2.05 ± 0.07 (αDH2O-H2 = (D/H)H2O to (D/H)H2), slightly less than predicted radiolytic models. Although this radiolytic fractionation value is significantly heavier than that of equilibrium isotopic exchange between H2 and H2O, the isotopic exchange rate between H2 and H2O will erase the heavy δD of radiolytic H2 if the age of the groundwater is greater than ∼103 to 104 yr. The millimolar concentrations of H2 observed in the groundwater of several Precambrian Shields are consistent with radiolysis of water that has resided in the subsurface for a few million years. These concentrations are well above those required to support H2-utilizing microorganisms and to inhibit H2-producing, fermentative microorganisms. 相似文献
14.
Geochemical Constraints on the Origin of Volcanic Rocks from the Andean Northern Volcanic Zone, Ecuador 总被引:2,自引:0,他引:2
BRYANT J. A.; YOGODZINSKI G. M.; HALL M. L.; LEWICKI J. L.; BAILEY D. G. 《Journal of Petrology》2006,47(6):1147-1175
Whole-rock geochemical data on basaltic to rhyolitic samplesfrom 12 volcanic centers are used to constrain the role of continentalcrust in the genesis of magmas formed beneath the anomalouslywide subduction-related volcanic arc in Ecuador. Relativelyhomogeneous, mantle-like, isotopic compositions across the arcimply that the parental magmas in Ecuador were produced largelywithin the mantle wedge above the subduction zone and not byextensive melting of crustal rocks similar to those upon whichthe volcanoes were built. Cross-arc changes in 143Nd/144Nd and7/4Pb are interpreted to result from assimilation of geochemicallymature continental crust, especially in the main arc area, 330360km from the trench. Mixing calculations limit the quantity ofassimilated crust to less than 10%. Most andesites and dacitesin Ecuador have adakite-like trace element characteristics (e.g.Y <18 ppm, Yb <2 ppm, La/Yb >20, Sr/Y >40). Availablewhole-rock data do not provide a clear basis for distinguishingbetween slab-melting and deep crustal fractionation models forthe genesis of Ecuador adakites; published data highlightinggeochemical evolution within individual volcanoes, and in magmaticrocks produced throughout Ecuador since the Eocene, appear tosupport the deep fractionation model for the genesis of mostevolved Ecuadoran lavas. A subset of andesites, which displaya combination of high Sr (>900 ppm), Nd >4·1 and7/4Pb <6·0, appear to be the best candidates amongEcuador lavas for slab-melts associated with the subductionof the relatively young, over-thickened, oceanic crust of theCarnegie Ridge. KEY WORDS: andesite; Ecuador; trace elements; isotopes; adakite 相似文献
15.
Brad R. HALL 《国际泥沙研究》1999,(2)
ILOWERGUADALUPERIVER,SANJOSECALIFORNIATheLowerGuadalupeRiverProjectAreadoesnothavetheabilitytoconveytheflowofthe100-yearfloodevent.LocatedbetweentheSanrranciscoBayandDowntownSanJose,theLowerGuadalupeRiverProjectareaissubjecttomanynaturalandman-inducedagentsandnaturalphysicalprocessesthataffectthehydraulicandsedimenttransportcharacteristicsoftheRiver.Themostsignificantagentsandprocessesincludethelocalgeology,regionalseismicity,tidalprocesses,pastsubsidenceintheregion,risings… 相似文献
16.
The estimation of erosion and sediment delivery rates in tropical mountain watersheds is difficult and most of the methods widely used for estimating soil erosion over large areas have serious limitations. The 137Cs approach has potential for quantifying soil erosion because it can provide retrospective estimates of long‐term (since 1963) net sediment redistribution relatively quickly. Despite its great potential, 137Cs has not yet been used in an extensive, reconnaissance level survey of erosion in complex tropical mountain environments. The objective of this study was to examine the applicability of the 137Cs method to estimate erosion on steep tropical agricultural lands (23 to 80% slopes) in the Nizao watershed, a humid, tropical mountain area of the Dominican Republic. In this study we (i) examine the variation of 137Cs in ten reference sites—eight coffee groves and two forested sites—and (ii) estimate erosion from 14 cultivated fields. The soil pool of 137Cs ranged from to 150 to 192 mBq cm−2 on reference sites with minimal erosion. Variability among reference sites was less than expected for such complex mountain terrain. The variability within coffee and forested reference (average CV=28%) sites was similar to the variability found on grassland and forested reference sites in the temperate zone. The estimated annual soil loss from 14 sampled fields ranged from 6 to 61 t ha−1 year−1 with an overall mean of 26 t ha−1 year−1. Overall, the soil erosion estimates found using the 137Cs method were much lower than those often assumed for such steep tropical hillsides. These erosion estimates account for soil loss since 1963 only and it seems likely that soil losses may have been much higher in earlier decades immediately after initial forest clearing earlier in the 20th century. Copyright © 2000 John Wiley & Sons, Ltd. 相似文献
17.
18.
FANGJU WANG G. BRENT HALL SUBARYONO 《International journal of geographical information science》2013,27(3):261-283
Currently used methods for representing geographical information are inadequate because they do not tolerate imprecision. This leads to information loss and inaccuracy in analysis. Such expressive inadequacy is largely due to the underlying membership concept of classical set theory. To improve information processing in GIS research and application, an alternative membership concept is required. In this paper, we explore the inadequacy imposed upon geographical information representation by classical set theory and address the problems of information loss. A fuzzy relational data model is defined which is more representative for geographical information. A GIS database for agricultural land resource management is created by using the data model and a new technique for assessing land suitability is developed. The fuzzy representation largely facilitates data analysis in this GIS. The methods are tested with data from North Java, Indonesia using a vector-based GIS software package, Arc Info, and the analysis results are presented. 相似文献
19.
Microartifact analysis is a worthwhile endeavor in archaeological research. A recurring problem, however, has been the time invested in sample quantification. In this paper we offer an interactive way to quantify microartifact samples using a computer program called MMCOUNT. When the technique is applied during the point counting process, the time required to acquire reliable proportions of material classes can be reduced to approximately 25 minutes per sample, significantly less than usual counting times reported in other studies. 相似文献
20.
A standard table for predicting equilibrium dissolved oxygen concentrations in Salt Lakes dominated by sodium chloride 总被引:3,自引:0,他引:3
J. E. Sherwood F. Stagnitti M. J. Kokkinn W. D. Williams 《International Journal of Salt Lake Research》1992,1(1):1-6
An equation of state was used to prepare a standard table for the solubility of oxygen in sodium chloride sobutions at temperatures
between 0 and 35°C and for concentrations up to saturation (260 ppt). The uncertainty introduced by linear interpolation between
DO values in the table is less than the experimental uncertainty of data which was used to generate the equation of state.
Where pressures differ from 1 atm the DO value from the table can be corrected provided the equilibrium vapour pressure of
the salt solution is known. Where this is not the case an approximate correction (±0.5 per cent) can be used provided atmospheric
pressure is in the range 950 to 1030 mbar.
Predictions made using the standard tables will provide near but probably low (<0.2 mg L−1) estimates of DO in salt lakes where sodium chloride is the dominant electrolyte (>70 per cent by mass). 相似文献