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51.
Abstract This paper describes the first stage of an experiment aiming to evaluate the potential and limitations of MIVIS data for mapping the degradational state of soils in a sub‐scene of a southern Apennines study area (Italy). After radiometric rectification of the image data and the collection of a field/laboratory spectral library, linear spectral mixture modelling (SMA) was used to decompose image spectra into fractions of spectrally distinct mixing components. Spectral endmember selection was based upon a principal component analysis (PCA) applied to a set of soil spectra, collected from the spectral library. The resulting abundance estimates (fractions) trough SMA were then analysed to identify soil conditions and to obtain an improved measure of dry and green vegetation cover. A map of soil conditions and dry‐green vegetation abundance, based upon MIVIS data was then derived from normalised fractions of soil‐vegetation endmembers obtained from SMA. 相似文献
52.
L. Bohlen A.W. Dale S. Sommer T. Mosch C. Hensen A. Noffke F. Scholz K. Wallmann 《Geochimica et cosmochimica acta》2011,75(20):6094-7276
Benthic nitrogen (N) cycling was investigated at six stations along a transect traversing the Peruvian oxygen minimum zone (OMZ) at 11°S. An extensive dataset including porewater concentration profiles and in situ benthic fluxes of nitrate (NO3−), nitrite (NO2−) and ammonium (NH4+) was used to constrain a 1-D reaction-transport model designed to simulate and interpret the measured data at each station. Simulated rates of nitrification, denitrification, anammox and dissimilatory nitrate reduction to ammonium (DNRA) by filamentous large sulfur bacteria (e.g. Beggiatoa and Thioploca) were highly variable throughout the OMZ yet clear trends were discernible. On the shelf and upper slope (80-260 m water depth) where extensive areas of bacterial mats were present, DNRA dominated total N turnover (?2.9 mmol N m−2 d−1) and accounted for ?65% of NO3− + NO2− uptake by the sediments from the bottom water. Nonetheless, these sediments did not represent a major sink for dissolved inorganic nitrogen (DIN = NO3− + NO2− + NH4+) since DNRA reduces NO3− and, potentially NO2−, to NH4+. Consequently, the shelf and upper slope sediments were recycling sites for DIN due to relatively low rates of denitrification and high rates of ammonium release from DNRA and ammonification of organic matter. This finding contrasts with the current opinion that sediments underlying OMZs are a strong sink for DIN. Only at greater water depths (300-1000 m) did the sediments become a net sink for DIN. Here, denitrification was the major process (?2 mmol N m−2 d−1) and removed 55-73% of NO3− and NO2− taken up by the sediments, with DNRA and anammox accounting for the remaining fraction. Anammox was of minor importance on the shelf and upper slope yet contributed up to 62% to total N2 production at the 1000 m station. The results indicate that the partitioning of oxidized N (NO3−, NO2−) into DNRA or denitrification is a key factor determining the role of marine sediments as DIN sinks or recycling sites. Consequently, high measured benthic uptake rates of oxidized N within OMZs do not necessarily indicate a loss of fixed N from the marine environment. 相似文献
53.
The effects of deformation on radiogenic argon (40Ar∗) retentivity in mica are described from high pressure experiments performed on rock samples of peraluminous granite containing euhedral muscovite and biotite. Cylindrical cores, ∼15 mm in length and 6.25 mm in diameter, were drilled from granite collected from the South Armorican Massif in northwestern France, loaded into gold capsules, and weld-sealed in the presence of excess water. The samples were deformed at a pressure of 10 kb and a temperature of 600 °C over a period 29 of hours within a solid medium assembly in a Griggs-type triaxial hydraulic deformation apparatus. Overall shortening in the experiments was approximately 10%. Transmitted light and secondary and backscattered electron imaging of the deformed granite samples reveals evidence of induced defects and for significant physical grain size reduction by kinking, cracking, and grain segmentation of the micas.Infrared (IR) laser (CO2) heating of individual 1.5-2.5 mm diameter grains of muscovite and biotite separated from the undeformed granite yield well-defined 40Ar/39Ar plateau ages of 311 ± 2 Ma (2σ). Identical experiments on single grains separated from the experimentally deformed granite yield results indicating 40Ar∗ loss of 0-35% in muscovite and 2-3% 40Ar∗ loss in biotite. Intragrain in situ ultraviolet (UV) laser ablation 40Ar/39Ar ages (±4-10%, 1σ) of deformed muscovites range from 309 ± 13 to 264 ± 7 Ma, consistent with 0-16% 40Ar∗ loss relative to the undeformed muscovite. The in situ UV laser ablation 40Ar/39Ar ages of deformed biotite vary from 301 to 217 Ma, consistent with up to 32% 40Ar∗ loss. No spatial correlation is observed between in situ40Ar/39Ar age and position within individual grains. Using available argon diffusion data for muscovite the observed 40Ar∗ loss in the experimentally treated muscovite can be utilized to predict average 40Ar∗ diffusion dimensions. Maximum 40Ar/39Ar ages obtained by UV laser ablation overlap those of the undeformed muscovite, indicating argon loss of <1% and an average effective grain radius for 40Ar∗ diffusion ?700 μm. The UV laser ablation and IR laser incremental 40Ar/39Ar ages indicating 40Ar∗ loss of 16% and 35%, respectively, are consistent with an average diffusion radius ?100 μm. These results support a hypothesis of grain-scale 40Ar∗ diffusion distances in undeformed mica and a heterogeneous mechanical reduction in the intragrain effective diffusion length scale for 40Ar∗ in deformed mica. Reduction in the effective diffusion length scale in naturally deformed samples occurs most probably through production of mesoscopic and submicroscopic defects such as, e.g., stacking faults. A network of interconnected defects, continuously forming and annealing during dynamic deformation likely plays an important role in controlling both 40Ar∗ retention and intragrain distribution in deformed mica. Intragrain 40Ar/39Ar ages, when combined with estimates of diffusion kinetics and distances, may provide a means of establishing thermochronological histories from individual micas. 相似文献
54.
Guneshwar Thangjam Vishnu Reddy Lucille Le Corre Andreas Nathues Holger Sierks Harald Hiesinger Jian‐Yang Li Juan A. Sanchez Christopher T. Russell Robert Gaskell Carol Raymond 《Meteoritics & planetary science》2013,48(11):2199-2210
The surface composition of Vesta, the most massive intact basaltic object in the asteroid belt, is interesting because it provides us with an insight into magmatic differentiation of planetesimals that eventually coalesced to form the terrestrial planets. The distribution of lithologic and compositional units on the surface of Vesta provides important constraints on its petrologic evolution, impact history, and its relationship with vestoids and howardite‐eucrite‐diogenite (HED) meteorites. Using color parameters (band tilt and band curvature) originally developed for analyzing lunar data, we have identified and mapped HED terrains on Vesta in Dawn Framing Camera (FC) color data. The average color spectrum of Vesta is identical to that of howardite regions, suggesting an extensive mixing of surface regolith due to impact gardening over the course of solar system history. Our results confirm the hemispherical dichotomy (east‐west and north‐south) in albedo/color/composition that has been observed by earlier studies. The presence of diogenite‐rich material in the southern hemisphere suggests that it was excavated during the formation of the Rheasilvia and Veneneia basins. Our lithologic mapping of HED regions provides direct evidence for magmatic evolution of Vesta with diogenite units in Rheasilvia forming the lower crust of a differentiated object. 相似文献
55.
by Ralf Köber Götz Hornbruch Carsten Leven Lars Tischer Jochen Großmann Peter Dietrich Holger Weiß Andreas Dahmke 《Ground water》2009,47(4):536-546
Most established methods to characterize aquifer structure and hydraulic conductivities of hydrostratigraphical units are not capable of delivering sufficient information in the spatial resolution that is desired for sophisticated numerical contaminant transport modeling and adapted remediation design. With hydraulic investigation methods based on the direct-push (DP) technology such as DP slug tests, DP injection logging, and the hydraulic profiling tool, it is possible to rapidly delineate hydrogeological structures and estimate their hydraulic conductivity in shallow unconsolidated aquifers without the need for wells. A combined application of these tools was used for the investigation of a contaminated German refinery site and for the setup of hydraulic aquifer models. The quality of DP investigation and the models was evaluated by comparisons of tracer transport simulations using these models and measured breakthroughs of two natural gradient tracer tests. Model scenarios considering the information of all tools together showed good reproduction of the measured breakthroughs, indicating the suitability of the approach and a minor impact of potential technical limitations. Using the DP slug tests alone yielded significantly higher deviations for the determined hydraulic conductivities compared to considering two or three of the tools. Realistic aquifer models developed on basis of such combined DP investigation approaches can help optimize remediation concepts or identify flow regimes for aquifers with a complex structure. 相似文献
56.
Gómez-Herrero Raúl RodrÍguez-FrÍas M. Dolores del Peral Luis Sequeiros Juan Müller-Mellin Reinhold Kunow Horst Sierks Holger 《Solar physics》2000,194(2):405-413
An analysis of the hydrogen and helium isotopic composition from EPHIN data, during the quiet-time period from January 1 to June 1, 1996, is presented. An isotopic discrimination and background rejection have been applied and relationships between the abundances of 2H/1H, 3He/4He, and 4He/1H have been calculated. The energy spectra in the 4–50 MeV nucl–1 range have been obtained and the contribution of the different spectral components have been analysed in this energy range. We conclude that the main contribution to the 4He spectrum is of anomalous origin, while the proton and 3He spectra have contributions mainly from particles of solar origin at low energies and from the galactic cosmic radiation modulated by the heliosphere at high energies. The deuterium spectrum is mainly of galactic origin. 相似文献
57.
Holger Siebert Manfred Wendisch Thomas Conrath Ulrich Teichmann Jost Heintzenberg 《Boundary-Layer Meteorology》2003,106(3):461-482
A new scientific payload is introduced for fine-scale measurements of meteorological (wind vector, static air temperature, humidity, and air pressure) and microphysical (aerosol particles and cloud droplets) properties, suspended below a tethered balloon. The high resolution sensors and the tethered balloon are described. Measurements in a lifted fog layer from a first field campaign are presented.The detailed investigation of the fog/haze and the temperature inversion layer demonstrates the damping influence of the fog on temperature fluctuations, while thewind fluctuations are significantly decreased by theevolving temperature inversion, whichwas about 30 m above the fog layer.From spectral analysis the noise floors of the high-resolution sensors are determined to10-6 kg m-3 for the LWC (liquid water content) and 4 mK for the fast temperature sensor (UFT-B). The correlation betweentemperature and LWC structures in shallow haze layers is investigated. The release of latent heat and the corresponding warming in the haze of about 0.1 K could be quantified. 相似文献
58.
The HUS-Ulysses team has prepared an instrument aboard the ULYSSES spacecraft consisting of 2 CsI detectors and 2 Si surface barrier detectors for measuring X-rays in the range 5–200 keV up to 8 ms resolution. The prime objectives are the study of solar flares and of cosmic gamma-ray bursts. The ULYSSES mission will leave the ecliptic during the next solar cycle. The solar data can be used in conjunction with other experiments to measure the directivity of the emission and for correlative studies. The cosmic gamma-ray burst data will improve source localizations, allowing sensitive searches for counterparts. The energy range and the 4 field of view is well suited to the detection of the soft gamma-ray repeaters.Paper presented at the 11th European Regional Astronomical Meetings of the IAU on New Windows to the Universe, held 3–8 July, 1989, Tenerife, Canary Islands, Spain 相似文献
59.
A space-time discontinuous Galerkin finite element method is proposed and applied to a convection-dominant single-phase flow
problem in porous media. The numerical scheme is based on a coupled space-time finite element discretization allowing for
discontinuous approximations in space and in time. The continuities on the element interfaces are weakly enforced by the flux
treatments, so that no extra penalty factor has to be determined. The resulting space-time formulation possesses the advantage
of capturing the steep concentration front with sharp gradients efficiently. The stability and reliability of the proposed
approach is demonstrated by numerical experiments.
The author is grateful to the DFG (German Science Foundation—Deutsche Forschungsgemeinschaft) for the financial support under
the grant number Di 430/4-2. 相似文献
60.