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361.
The generalized Pareto distribution has received much popularity as models for extreme events in hydrological sciences. In this note, the important problem of the sum of two independent generalized Pareto random variables is considered. Exact analytical expressions for the probability distribution of the sum are derived and a detailed application to drought data from Nebraska is provided. Copyright © 2007 John Wiley & Sons, Ltd. 相似文献
362.
Marcelo Samuel Berman 《Astrophysics and Space Science》2007,312(3-4):275-278
We discuss astronomical and astrophysical evidence, which we relate to the principle of zero-total energy of the Universe,
that imply several relations among the mass M, the radius R and the angular momentum L of a “large” sphere representing a Machian Universe. By calculating the angular speed, we find a peculiar centripetal acceleration
for the Universe. This is an ubiquituous property that relates one observer to any observable. It turns out that this is exactly
the anomalous acceleration observed on the Pioneers spaceships. We have thus shown that this anomaly is to be considered a
property of the Machian Universe. We discuss several possible arguments against our proposal. 相似文献
363.
John Callahan Frank Hearn Stephen Heron Dennis Schumaker Samuel Swanson 《Journal of Geochemical Exploration》1978,10(1):53-61
A soil geochemical survey for Ni plus magnetic and radiometric surveys were used to outline a small dunite body on Rich Mountain, North Carolina. The dunite body is poorly exposed and is enclosed by garnet-bearing amphibolite of the Ashe Formation. Of the geophysical techniques used, the magnetic survey gives a better definition of the known extent of the body than the radiometric survey. However, the 400-ppm Ni contour from the soil program appears to best define the dunite and suggests that it extends farther to the north and east than was indicated from geologic mapping. Though HF digestion yields higher Ni values than HNO3 + HCl digestion, the patterns are the same. The Mn content of the soil at the Rich Mountain locality probably could also be used to outline the dunite body. 相似文献
364.
Denis Mercier Samuel Étienne Dominique Sellier Marie‐Françoise André 《地球表面变化过程与地形》2009,34(13):1772-1789
This paper evaluates the paraglacial evolution of a sediment‐mantled slope in a polar maritime environment. The intensity of paraglacial processes is estimated through quantification of erosion and dating of field sectors with the help of photographic archives. Gully erosion has been estimated using morphometric parameters and by surveys of vegetation cover. The rapid melting of dead‐ice cores controls gully formation. This leads to slope form modification: gully profile gradients are reduced from a mean of 35° to a mean ranging between 10° and 15°. Profile evolution results from the collapse of glacier lateral moraine. All data (mean slope angle of individual gullies, frequency distribution of slope angles, fractional distance to the apex, gullying index, volume of debris mobilized, vertical erosion rate) tend to increase with increasing deglaciation age and the duration of paraglacial activity. Vegetation colonization is a response to stabilization of the ground surface and the drying up of the ground surface due to dead‐ice melting. The full sequence of paraglacial slope adjustment (gully incision‐stabilization) may occur rapidly at the study site, i.e. within two decades. Finally, a lateral morphogenic sequence is proposed showing the importance of paraglacial processes at the onset of the deglaciation. Copyright © 2009 John Wiley & Sons, Ltd. 相似文献
365.
The goals and objectives of ‘climate stabilization’ feature heavily in contemporary environmental policy and in this paper we trace the factors that have contributed to the rise of this concept and the scientific ideas behind it. In particular, we explore how the stabilization-based discourse has become dominant through developments in climate science, environmental economics and policymaking. That this discourse is tethered to contemporary policy proposals is unsurprising; but that it has remained relatively free of critical scrutiny can be associated with fears of unsettling often-tenuous political processes taking place at multiple scales. Nonetheless, we posit that the fundamental premises behind stabilization targets are badly matched to the actual problem of the intergenerational management of climate change, scientifically and politically, and destined to fail. By extension, we argue that policy proposals for climate stabilization are problematic, infeasible, and hence impede more productive policy action on climate change. There are gains associated with an expansion and reconsideration of the range of possible policy framings of the problem, which are likely to help us to more capably and dynamically achieve goals of decarbonizing and modernizing the energy system, as well as diminishing anthropogenic contributions to climate change. 相似文献
366.
Karst aquifers: can they be protected? 总被引:1,自引:1,他引:0
Panno SV 《Ground water》2006,44(4):494-494
367.
Sarah H. Wallace Samuel Shaw Katherine Morris Joe S. Small Adam J. Fuller Ian T. Burke 《Applied Geochemistry》2012
Strontium-90 is a beta emitting radionuclide produced during nuclear fission, and is a problem contaminant at many nuclear facilities. Transport of 90Sr in groundwaters is primarily controlled by sorption reactions with aquifer sediments. The extent of sorption is controlled by the geochemistry of the groundwater and sediment mineralogy. Here, batch sorption experiments were used to examine the sorption behaviour of 90Sr in sediment–water systems representative of the UK Sellafield nuclear site based on groundwater and contaminant fluid compositions. In experiments with low ionic strength groundwaters (<0.01 mol L−1), pH variation is the main control on sorption. The sorption edge for 90Sr was observed between pH 4 and 6 with maximum sorption occurring (Kd ∼ 103 L kg−1) at pH 6–8. At ionic strengths above 10 mmol L−1, and at pH values between 6 and 8, cation exchange processes reduced 90Sr uptake to the sediment. This exchange process explains the lower 90Sr sorption (Kd ∼ 40 L kg−1) in the presence of artificial Magnox tank liquor (IS = 29 mmol L−1). Strontium K-edge EXAFS spectra collected from sediments incubated with Sr2+ in either HCO3-buffered groundwater or artificial Magnox tank liquor, revealed a coordination environment of ∼9 O atoms at 2.58–2.61 Å after 10 days. This is equivalent to the Sr2+ hydration sphere for the aqueous ion and indicates that Sr occurs primarily in outer sphere sorption complexes. No change was observed in the Sr sorption environment with EXAFS analysis after 365 days incubation. Sequential extractions performed on sediments after 365 days also found that ∼80% of solid associated 90Sr was exchangeable with 1 M MgCl2 in all experiments. These results suggest that over long periods, 90Sr in contaminated sediments will remain primarily in weakly bound surface complexes. Therefore, if groundwater ionic strength increases (e.g. by saline intrusion related to sea level rise or by design during site remediation) then substantial remobilisation of 90Sr is to be expected. 相似文献
368.
Benjamin I. Cook Gordon B. Bonan Samuel Levis Howard E. Epstein 《Climate Dynamics》2008,31(1):107-124
We use a state of the art climate model (CAM3–CLM3) to investigate the sensitivity of surface climate and land surface processes
to treatments of snow thermal conductivity. In the first set of experiments, the thermal conductivity of snow at each grid
cell is set to that of the underlying soil (SC-SOIL), effectively eliminating any insulation effect. This scenario is compared
against a control run (CTRL), where snow thermal conductivity is determined as a prognostic function of snow density. In the
second set of experiments, high (SC-HI) and low (SC-LO) thermal conductivity values for snow are prescribed, based on upper
and lower observed limits. These two scenarios are used to envelop model sensitivity to the range of realistic observed thermal
conductivities. In both sets of experiments, the high conductivity/low insulation cases show increased heat exchange, with
anomalous heat fluxes from the soil to the atmosphere during the winter and from the atmosphere to the soil during the summer. The increase in surface heat exchange leads to soil cooling of up to 20 K in the winter, anomalies that
persist (though damped) into the summer season. The heat exchange also drives an asymmetric seasonal response in near-surface
air temperatures, with boreal winter anomalies of +6 K and boreal summer anomalies of −2 K. On an annual basis there is a
net loss of heat from the soil and increases in ground ice, leading to reductions in infiltration, evapotranspiration, and
photosynthesis. Our results show land surface processes and the surface climate within CAM3–CLM3 are sensitive to the treatment
of snow thermal conductivity. 相似文献
369.
Geochemical fingerprinting is a rapidly expanding discipline in the earth and environmental sciences. It is anchored in the recognition that geological processes leave behind chemical and isotopic patterns in the rock record. Many of these patterns, informally referred to as geochemical fingerprints, differ only in fine detail from each other. For this reason, the approach of fingerprinting requires analytical data of very high precision and accuracy. 相似文献
370.
Hydrogeochemical controls and usability of groundwater in the semi-arid Mayo Tsanaga River Basin: far north province,Cameroon 总被引:2,自引:0,他引:2
Wilson Y. Fantong Hiroshi Satake Samuel N. Ayonghe Festus T. Aka Kazuyoshi Asai 《Environmental Geology》2009,58(6):1281-1293
Deuterium, δ
18O, major ions and dissolved silica in groundwater from semi-arid Mayo-Tsanaga river basin in the Far North Province, Cameroon
were used to trace hydrogeochemical processes that control their concentrations and to explore for usability of the water.
Electrical conductivity ranges from 57–2,581 μs/cm with alternating low and high values along the hydraulic gradient. Waters
from piedmont alluvium show low concentrations in major cations, which peak in Mg within basalt, Na within plain alluvium,
and Ca within basalt and the sandy Limani-Yagoua ridge. The initial dominant groundwater composition is CaHCO3, which did not evolve within the basalt and piedmont alluvium, but evolved to NaHCO3 in the granite and plain alluvium. The main processes controlling the major ions composition include the following: (1) dissolution
of silicates and fluorite; (2) precipitation of fluorite and carbonate; (3) cation exchange of Ca in water for Na in clay;
(4) and anthropogenic activities. The δD and δ
18O ratios vary from −35 to 0.7 and −5.3 to 1.1‰, respectively. The lowest and highest isotope ratios are observed in groundwater
within the downstream sandy Limani-Yagoua ridge and the upstream graintes respectively. Variation in isotope ratios depends
on altitude effect of −0.48‰ per 100 m between 600 and 850 m asl, and on evaporation, which had insignificant effect on the
water salinity. Seventy percent of the groundwater shows poor drinking quality and 90% is suitable for irrigation.
Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users. 相似文献