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101.
Anderson José Maraschin Ana Maria Mizusaki Horst Zwingmann André Weissheimer de Borba Gesiane Fraga Sbrissa 《Journal of South American Earth Sciences》2010,29(2):400-411
Several analytical studies performed on alluvial-eolian sandstones of the Early Paleozoic Guaritas Allogroup (Camaquã Basin, southern Brazil) indicate illite to be abundant, showing different morphologies as authigenic grain rims and pore-bridging filaments. Authigenic illite separates of variable grain sizes from distinct stratigraphic intervals of the Guaritas Allogroup yielded 40K–40Ar ages from 521.7 ± 10.3 to 473.7 ± 9.4 Ma. These ages, interpreted to record the timing of illite authigenesis, are coincident with the age of emplacement of the Rodeio Velho andesites (470 ± 19 Ma). Moreover, field structures suggest interaction between hot, andesite lava flows and wet, poorly consolidated sediments of the Pedra Pintada Alloformation (lower strata of the Guaritas Allogroup). This set of data indicates that the Rodeio Velho volcanism could have been responsible for a widespread remobilization of interstitial fluids and consequent authigenic illite precipitation in the sandstones of the Guaritas Allogroup. 相似文献
102.
Peter Gege Jochen Fries Peter Haschberger Paul Schtz Horst Schwarzer Peter Strobl Birgit Suhr Gerd Ulbrich Willem Jan Vreeling 《ISPRS Journal of Photogrammetry and Remote Sensing》2009,64(4):387-397
A new facility designed to perform calibration measurements of airborne imaging spectrometers was established at the German Aerospace Center (DLR) in Oberpfaffenhofen. This Calibration Home Base (CHB) is optimized to characterize radiometrically, spectrally, and geometrically the APEX (Airborne Prism Experiment) imaging spectrometer, which is currently being developed under the authority of the European Space Agency (ESA). It however can be used for other optical sensors as well. Computer control of major laboratory equipment allows automation of time consuming measurements. In APEX configuration (wavelength range: 380 to 2500 nm, instantaneous field of view: 0.48 mrad, field of view: ±14) spectral measurements can be performed to a wavelength uncertainty of ±0.15 nm, geometric measurements at increments of 0.0017 mrad across track and 0.0076 mrad along track, and radiometric measurements to an uncertainty of ±3% relative to national standard. The CHB can be adapted to similar sensors (including those with thermal infrared detectors) by exchanging the monochromator’s lamp, the gratings and the filters, and by adjusting the distance between the sensor and folding mirror. 相似文献
103.
The gas transport through non-volatile random porous media is investigated numerically. We extend our previous research of the transport of molecules inside the uppermost layer of a cometary surface (
[Skorov and Rickman, 1995] and [Skorov et al., 2001]). We assess the validity of the simplified capillary model and its assumptions to simulate the gas flux trough the porous dust mantle as it has been applied in cometary physics. A microphysical computational model for molecular transport in random porous media formed by packed spheres is presented. The main transport characteristics such as the mean free path distribution and the permeability are calculated for a wide range of model parameters and compared with those obtained by more idealized models. The focus in this comparison is on limitations inherent in the capillary model. Finally a practical way is suggested to adjust the algebraic Clausing formula taking into consideration the nonlinear dependence of permeability on layer porosity. The retrieved dependence allows us to accurately calculate the permeability of layers whose thickness and porosity vary in the range of values expected for the near-surface regions of a cometary nucleus. 相似文献
104.
Horst G. Brandes 《Ocean Engineering》2011,38(7):835-848
Geotechnical properties from a series of deep-sea sites in the North Atlantic and North Pacific oceans are examined to evaluate overall trends and to compare with similar fine-grained soils found on land. The study areas encompass a range of sedimentary environments dominated by combinations of turbidite and pelagic deposits. Carbonate content in excess of 20% is seen to result in a decrease in liquid limit and compressibility. Vertical profiles of geotechnical properties in the North Pacific show broader changes in down-core geotechnical properties compared to the North Atlantic and reflect the effects of long-term climatic changes and seafloor spreading. Sediments in the North Atlantic indicate significant differences depending on location, which is attributed to variability in turbidite deposition, water depth, distance from sediment sources, and the effects of bottom currents. Compared to equivalent fine-grained soils on land, deep-sea sediments are generally softer, more compressible and have higher friction angles at comparable Atterberg limits. Deeper and older sediments in the North Pacific are characterized by unusually large plastic limits, which are attributed to the presence of volcanic fractions. Empirical relationships for compression index and friction angle are discussed for sediments from both oceans. 相似文献
105.
Skorov Yuri V. Keller Horst U. Jorda Laurent Davidsson Bjørn J. R. 《Earth, Moon, and Planets》2002,90(1-4):293-303
In this work, we continue revising the theoretical basis ofnumerical models describing the transport of matter andenergy inside
a porous dust-ice mixture at low temperature. Amodel of a light-absorbing near-surface layer of a comet nucleus isinvestigated.
Gas transport is considered simultaneously with thesolution of the general heat transfer equation. Thequasi-stationary temperature
distribution and the H2O massflux and sublimation rate are computed for a nucleus model ofcomet 19P/Borrelly at the Deep Space 1 (DS1) encounter.
Theenergy is deposited in a layer of about 20 particle radii: Thiscorresponds to a solid-state greenhouse effect. The surfacetemperature
of the layer-absorbing model as well as the gasproduction rate are significantly smaller than the ones in thesurface-absorbing
model. An active fraction of 40–50% would berequired to explain the observed water production rate ofP/Borrelly with our layer-absorption
model at the time of the DS1encounter. 相似文献
106.
107.
108.
Observations from the Horizontal Array Turbulence Study (HATS) field program are used to examine the attenuation of measured
scalar fluxes caused by spatial separation between the vertical velocity and scalar sensors. The HATS data show that flux
attenuation for streamwise, crosswind, and vertical sensor displacements are each a function of a dimensionless, stability-dependent
parameter n
m
multiplied by the ratio of sensor displacement to measurement height. The scalar flux decays more rapidly with crosswind
displacements than for streamwise displacements and decays more rapidly for stable stratification than for unstable stratification.
The cospectral flux attenuation model of Kristensen et al. agrees well with the HATS data for streamwise sensor displacements,
although it is necessary to include a neglected quadrature spectrum term to explain the observation that flux attenuation
is often less with the scalar sensor downwind of the anemometer than for the opposite configuration. A simpler exponential
decay model provides good estimates for crosswind sensor displacements, as well as for streamwise sensor displacements with
stable stratification. A model similar to that of Lee and Black correctly predicts flux attenuation for a combination of streamwise
and crosswind displacements, i.e. as a function of wind direction relative to the sensor displacement. The HATS data for vertical
sensor displacements extend the near-neutral results of Kristensen et al. to diabatic stratification and confirm their finding
that flux attenuation is less with the scalar sensor located below the anemometer than if the scalar sensor is displaced an
equal distance either horizontally or above the anemometer. 相似文献
109.
Babatunde Anifowose Damian M. Lawler Dan van der Horst Lee Chapman 《Applied geography (Sevenoaks, England)》2012,32(2):636-651
In countries with insufficient investments in infrastructure and weak environmental governance, oil leakage from pipelines often occurs as a result of poor management and maintenance. Nigeria has its share of such incidents, but also, it suffers a large number of deliberate attacks (‘interdictions’) on oil pipelines. Often these attacks are accompanied by oil theft, carried out by well-equipped professionals and/or at a smaller scale by opportunistic local residents. The causes of these attacks, and the extent of subsequent damage to local communities and the environment, are obscured by a complex web of stakeholders, claims and actions. Any efforts to mitigate the negative impacts of interdiction on the environment and people require a better understanding of its spatiotemporal pattern of occurrence. This article presents a first quantitative and regional exploration of the problem of oil pipeline interdiction in Nigeria. It illustrates geographic patterns through choroplethic and bivariate GIS (Geographical Information Systems) map overlays. We examine interdiction statistics, identify spatiotemporal patterns and discuss correlations with socioeconomic factors. Findings include: (a) strong negative correlation between pipeline interdiction and poverty; and (b) statistically and non-statistically significant mean differences in the pattern of interdiction occurrence amongst the five geographic regions. Finally, we highlight the need for much better data collection and reporting for the mitigation of the negative socio-environmental impacts of interdiction incidences. 相似文献
110.
Jens Gröger Jennifer Franke Kay Hamer Horst D. Schulz 《Geostandards and Geoanalytical Research》2009,33(1):17-27
Chromium-reducible sulfur (CRS) distillations are intended to recover only reduced inorganic sulfur compounds (RIS) including elemental sulfur. However, the quantitative recovery of elemental sulfur is not ensured in common CRS-distillations. The new method presented here was designed to remedy this deficiency. An increase in ethanol concentration assured the quantitative recovery of elemental sulfur in various forms and, in addition, all other RIS-compounds were quantitatively recovered. Furthermore, the selectivity of the procedure was improved by an additional filtration step to eliminate zinc particles from the Cr(II)-solution. Thus, the recovery of sulfates and organic sulfur compounds was significantly decreased by a factor of up to 35, depending on the compound analysed. Exhaustive testing with a variety of pure phases, rock and soil samples demonstrated the precision and accuracy of the new method. The new protocol eliminated the constraints of previous procedures. The improved distillation efficiency for elemental sulfur ensured the quantitative recovery of all RIS-compounds in a single-step distillation. 相似文献