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91.
92.
There are a number of techniques for estimating the amount of weathering a clast has undergone. These usually have the objective of establishing an ordinal chronology of geomorphological surfaces, or investigation of site-specific conditions affecting weathering rates. Three such techniques are applied to a dated sequence of alluvial fan segments in southern Tunisia. Two of these techniques depend on measuring surface roughness (the micro-roughness meter and a displacement approach) and one uses the structural weakening of the rock fabric (Schmidt hammer). The micro-roughness meter enables calculation of standard deviation of surface height variation, root mean square roughness and surface autocorrelation function. Of these techniques, Schmidt hammer rebound values, standard deviation, root mean square roughness and the displacement technique show systematic changes on the three fan segments which are statistically significant at the 0·05 level. However, the amount of variance in all datasets is very large, indicating the need for caution in application of these techniques for relative dating. © 1998 John Wiley & Sons, Ltd. 相似文献
93.
Elias Symeonakis Rogerio Bonifaçio Nick Drake 《International Journal of Applied Earth Observation and Geoinformation》2009
Interpolated rain-gauge data were compared to Meteosat-based precipitation estimates for sub-Saharan Africa. Validation was carried out using a dataset from a very dense gauge network in South Africa, on a point-to-pixel (PO–PI) as well as on a pixel-to-pixel (PI–PI) basis. Error criteria computed at the gauged pixels indicate that overall the interpolated estimates perform similarly to the satellite-based data: they provide good estimates of lower but underestimate larger precipitation amounts. It is concluded that the satellite estimates are more fitted for the operational modelling of processes such as surface runoff and soil erosion, especially in the developing areas where resources are scarce. 相似文献
94.
The combination of low pH and high concentrations of nitrate and radionuclides in the subsurface is representative of many sites within the U.S. nuclear weapons complex managed by the Department of Energy (DOE), including the DOE’s Environmental Remediation Sciences Program Field Research Center (ORFRC), in Oak Ridge, Tennessee. In order to provide a further understanding of the coupled microbiological and geochemical processes limiting radionuclide bioremediation, we determined the rates and pathways of terminal-electron accepting processes (TEAPs) in microcosm experiments using close to in situ conditions with ORFRC subsurface materials. At the in situ pH range of 4-5, carbon substrate utilization and TEAP rates were diminished, such that nitrate was not depleted and metal reduction was prevented. Upon biostimulation by pH neutralization and carbon substrate addition, TEAPs were stimulated to rates that rival those measured in organic-rich surficial sediments of aquatic environments, and extremely high nitrate concentrations (0.4-0.5 M) were not found to be toxic to microbial metabolism. Metal reduction under neutral pH conditions started once nitrate was depleted to low levels in response to biostimulation. Acidity controlled not only the rates but also the pathways of microbial activity. Denitrification predominated in sediments originating from neutral pH zones, while dissimilatory nitrate reduction to ammonium occurred in neutralized acidic microcosms amended with glucose. Electron donors were determined to stimulate microbial metabolism leading to metal reduction in the following order: glucose > ethanol > lactate > hydrogen. In microcosms of neutralized acidic sediments, 80-90% of C equivalents were recovered as fermentation products, mainly as acetate. Due to the stress imposed by low pH on microbial metabolism, our results indicate that the TEAPs of acidic subsurface sediment are inherently different from those of neutral pH environments and neutralization will be necessary to achieve sufficient metabolic rates for radionuclide remediation. 相似文献
95.
This paper explores the influence of a fluorine-rich granite on fluoride concentration in a small boreal catchment in northern
Europe. The materials include stream water and shallow groundwater sampled in spatial and temporal dimensions, and analytical
data on fluoride and a number of ancillary variables. Fluoride increased strongly towards the lower reaches of the catchment—at
the stream outlet the concentrations were up to 4.2 mg L−1 and 1.6–4.7 times higher than upstream. Additionally, fluoride concentrations were particularly high in groundwater and small
surface-water bodies (including quarries) above or in direct contact with the granite and showed a strong inverse correlation
with water discharge in the stream. Taken together, these data and patterns pin-point the granite intrusion as the ultimate
source, explaining the abundance and distribution of dissolved fluoride within the catchment. The granite most likely deliver
fluoride to the stream by three mechanisms: (1) weathering of the fine fraction of glacial deposits, derived from the granite
and associated fluorine-rich greisen alterations, (2) large relative input of baseflow, partially originating in the granite
and greisen, into the lower reaches during low flow in particular, and (3) water-conducting fractures or fracture zones running
through the fluorine-rich granite and greisen. 相似文献
96.
Biological soil crust development and its topsoil properties in the process of dune stabilization, Inner Mongolia, China 总被引:4,自引:0,他引:4
This study was undertaken at Horqin Sand Land, Inner Mongolia, Northern China. Field samples of biological soil crusts (BSCs)
and underlying topsoil (0–5 cm under BSC) were taken in areas of different dune stabilization stages, and their physicochemical
properties were analyzed, including particle size distribution, bulk density, organic matter, nitrogen, phosphorus, electrical
conductivity (EC), pH, and CaCO3 content. The results revealed that semi-mobile dunes, semi-fixed dunes and fixed dunes had developed a physical crust, algae
crust and moss crust, respectively. The thickness, hardness, water content, fine fraction and nutrient contents of BSCs were
gradually increasing along the dune stabilization gradient. Meanwhile, BSC establishment and development enhanced the bulk
density, silt and clay content, and nutrients of the topsoil under it, in an increasing tend from semi-mobile dune to fixed
dune. Organic matter concentrations and other nutrients in the 0–5 cm topsoil layer under BSCs were significantly higher compared
to unconsolidated soil (control). Moreover, there were strong significant positive correlations between topsoil and BSCs’
organic matter, total nitrogen, available nitrogen, available phosphorus, CaCO3, and <0.05 mm particle content, suggesting that BSCs have an influence on some of the properties of the underlying topsoil. 相似文献
97.
N. Polosukhina A. Shavrina N. Drake D. Kudryavtsev M. Smirnova 《Bulletin of the Crimean Astrophysical Observatory》2010,106(1):57-62
New spectral observations of chemically peculiar (CP) magnetic stars were obtained using an NES echelle spectrometer with a BTA telescope in the Special Astrophysical Observatory (Russian Academy of Sciences). Several stars were shown to have anomalous Li abundances. Testing and monitoring the stars with Doppler shifts Vsini > 10 km/s indicated that the lithium 6708 Å line was variable in the spectra of some roaAP-CP stars. To distinguish variable features in the spectra, the dispersogram technique was used. The most peculiar among the stars studied is HD 12098. The strong and variable lithium 6708 Å line was detected in the spectrum of this star. The star has been shown to have greatly different lithium abundances in two rotation phases corresponding to opposite surface areas. As mentioned earlier, a similar behavior of the Li blend was found in the spectra of HD 83368 and HD 60435 which have lithium spots on their surface. Spectral observations of slowly rotating CP stars with the Doppler shifts Vsini < 10 km/s revealed the strong and nonvariable lithium 6708 Å line in the spectra of these stars. Quantitative spectral analysis using the Li I 6708 Å resonance doublet and the Li I 6103 Å line shows the lithium abundance, as determined by the 6103 Å line, to be somewhat greater than that determined by the 6708 Å line. A higher ratio of 6Li/7Li amounting to ~0.3–0.5 was found in these stars. 6Li production is assumed to be due to spallation reactions on the surface of magnetic CP stars; this isotope ratio remained in strong magnetic fields. 相似文献
98.
A. S. Moskvitin T. A. Fatkhullin V. V. Sokolov V. N. Komarova A. J. Drake R. Roy D. Yu. Tsvetkov 《Astrophysical Bulletin》2010,65(3):230-237
This paper describes the aims, objectives and first results of the observational program for the study of distant core-collapse
supernovae (SNe) with redshifts z ≲ 0.3. This work is done within the framework of an international cooperation program on the SNe monitoring at the 6-m BTA
telescope of the Special Astrophysical Observatory of the Russian Academy of Sciences, and other telescopes. We study both
the early phases of events (SN type determination, redshift estimation, and a search for manifestations of a wind envelope),
and the nebular phase (the effects of explosion asymmetry). The SNe, associated with cosmic gamma-ray bursts are of particular
interest. An interpretation of our observational data along with the data obtained on other telescopes is used to test the
existing theoretical models of both the SN explosion, and the surrounding circumstellar medium. In 2009 we observed 30 objects;
the spectra were obtained for 12 of them. We determined the types, phases after maximum, and redshifts for five SNe (SN 2009db,
SN 2009dy, SN 2009dw, SN 2009ew, SN 2009ji). Based on the obtained photometric data a discovery of two more SNe was confirmed
(SN 2009bx and SN 2009cb). A study of two type II supernovae in the nebular phase (SN 2008gz and SN 2008in) is finalized,
four more objects (SN 2008iy, SN 2009ay, SN 2009bw, SN 2009de) are currently monitored. 相似文献
99.
M. J. Grosskopf R. P. Drake C. C. Kuranz A. R. Miles J. F. Hansen T. Plewa N. Hearn D. Arnett J. C. Wheeler 《Astrophysics and Space Science》2009,322(1-4):57-63
The National Ignition Facility (NIF) will soon provide experiments with far more than ten times the energy than has been previously available on laser facilities. In the context of supernova-relevant hydrodynamics, this will enable experiments in which hydrodynamic instabilities develop from multiple, coupled interfaces in a diverging explosion. This paper discusses the design of such blast-wave-driven explosions in which the relative masses of the layers are scaled to those within the star. It reports scaling simulations with CALE to model the global dynamics of such an experiment. CALE is a hybrid, Arbitrary Lagrangian-Eulerian code. The simulations probed the instability growth and multi-interface interactions in mass-scaled systems using different materials. The simulations assist in the target design process and in developing an experiment that can be diagnosed. 相似文献
100.
C. Michaut E. Falize C. Cavet S. Bouquet M. Koenig T. Vinci A. Reighard R. P. Drake 《Astrophysics and Space Science》2009,322(1-4):77-84
Radiative shocks (RS) occur in astrophysical systems and in high-energy density laboratory experiments. Aided by three dimensionless parameters, we propose a classification of RS into four types, integrating previous work that has focused independently on optical depth and on Mach number. Specific terms, such as a cooling function, a radiative flux, or radiative energy and pressure must be added to the Euler equations in order to model these various kinds of shocks. We examine how these terms correspond to the radiative classification regimes. In astrophysics, observed RS arise generally in optically thin material. Thus, radiation escapes without interaction with the surrounding gas, except perhaps to ionize it, and the energy loss in such shocks can be modeled by a cooling function Λ. In this case only the post-shock region is structured by the radiation cooling. We found the analytical solution for hydrodynamic equations including Λ∝ ρ ε P ζ x θ for arbitrary values of ε, ζ, θ. This is a completely new result. An application of this calculation for the accretion shock in cataclysmic variables of polar type is given in astrophysical terms. We also draw a parallel between RS experiments performed using the LULI2000 laser facility, in France and the Omega laser Facility, in USA. RS developed in these laboratories are more or less optically thick. These high-Mach number RS present a radiative precursor. 相似文献