Experimental investigation of turbulent processes in a complex terrain

In the present paper the first results of the international KOPEX-86 experiment are presented. The experiment took place at the Kopisty Atmospheric Observatory of the Institute of Physics of the Atmosphere in Prague as part of a special project of the Commission of the Academy of Sciences in Planetary Geophysics (KAPG) in June and July 1986. Using 4 ultrasonic anemometers at 4 levels up to 80 m, Doppler-SODAR and wind-, temperature- and radiation balance gradients from 2 to 80 m, a complex investigation of the atmospheric boundary layer in an industrial area was made. The authors present the first results of

The supergene origin of ruthenian hexaferrum in Ni‐laterites

For two decades, the nature of Fe‐rich, oxygen‐bearing, Ru–Os compounds found in the supergene environment has been debated. Ru–Os–Fe‐oxides and nano‐intergrowths of ruthenium with magnetite have been proposed. We applied FE‐SEM, EMPA, μ‐Raman spectroscopy and synchrotron tts‐μXRD to Ru–Os–Fe compounds recovered from Ni‐laterites from the Dominican Republic. The results demonstrate that a significant portion of Fe exists in a common structure with the Ru–Os alloy, that is, ruthenian hexaferrum. This mineral occurs both as nanoparticles and as micrometric patches within a matrix of Fe‐oxide(s). Our data suggest that supergene ruthenian hexaferrum with a (Ru_0.4(Os,Ir)_0.1Fe_0.5)_?1.0 stoichiometry represents the most advanced weathering product of primary laurite within Ni‐laterites from the Dominican Republic.     

Low-resolution spectra of the Io plasma torus 2 days after the Ulysses encounter

Low-resolution spectra of the Io plasma torus have been obtained on 10 and 11 February 1992 (2 days after the Ulysses encounter) using the 2 m telescope of the Bulgarian National Observatory. The spectra show the forbidden line emissions of S⁺ (λλ 6716, 6731 Å) and S²⁺ (λ 6312 Å). Measured intensities are compared with a Voyager-type model. The intensity distribution of [SII] is found to deviate from the model predictions which indicates a change in the torus at the Ulysses encounter when compared with the Voyager epoch. A corotating structure was observed, both in [SII] and [SIII], at λ_III = 170°, showing that the torus was not azimuthally symmetric. The λ 6716/λ 6731 and λ 6731/ λ 6312 line ratios indicate a higher electron density at the time of the Ulysses observations. Additionally, the shift of the torus caused by the dawn-dusk electric field could be observed. Peak intensities in [SII] were found at 5.66 ± 0.02 R_J on the West ansa and 5.91 ± 0.04 R_J on the East.     

Pre‐drill Groundwater Geochemistry in the Karoo Basin,South Africa

Enhanced production of unconventional hydrocarbons in the United States has driven interest in natural gas development globally, but simultaneously raised concerns regarding water quantity and quality impacts associated with hydrocarbon extraction. We conducted a pre‐development assessment of groundwater geochemistry in the critically water‐restricted Karoo Basin, South Africa. Twenty‐two springs and groundwater samples were analyzed for major dissolved ions, trace elements, water stable isotopes, strontium and boron isotopes, hydrocarbons and helium composition. The data revealed three end‐members: a deep, saline groundwater with a sodium‐chloride composition, an old, deep freshwater with a sodium‐bicarbonate‐chloride composition and a shallow, calcium‐bicarbonate freshwater. In a few cases, we identified direct mixing of the deep saline water and shallow groundwater. Stable water isotopes indicate that the shallow groundwater was controlled by evaporation in arid conditions, while the saline waters were diluted by apparently fossil meteoric water originated under wetter climatic conditions. These geochemical and isotopic data, in combination with elevated helium levels, suggest that exogenous fluids are the source of the saline groundwater and originated from remnant seawater prior to dilution by old meteoric water combined with further modification by water‐rock interactions. Samples with elevated methane concentrations (>14 ccSTP/kg) were strongly associated with the sodium‐chloride water located near dolerite intrusions, which likely provide a preferential pathway for vertical migration of deeply sourced hydrocarbon‐rich saline waters to the surface. This pre‐drill evaluation indicates that the natural migration of methane‐ and salt‐rich waters provides a source of geogenic contamination to shallow aquifers prior to shale gas development in the Karoo Basin.     

New Methodology to Characterize Shear Behavior of Joints by Combination of Direct Shear Box Testing and Numerical Simulations

A new procedure is presented, which combines big shear box tests on rocks and corresponding numerical simulations with explicit consideration of joint roughness to get deeper insight into the shear behavior of rock joints. The procedure consists of three parts: (1) constant normal load- or CNS-shear box tests with registration of shear- and normal-components of stress and displacements and deduction of basis rock mechanical parameters; (2) high resolution 3D-scanning of joint surface to deduce joint topography; and (3) set-up, run and evaluation of 3-dimensional numerical model with explicit duplication of joint roughness as back-analysis of shear box tests. The numerical back-analysis provides deeper insight into the joint behavior at the micro-scale. Several parameters can be deduced, like micro-slope angle distribution, aperture size distribution, local normal stress distribution and detailed analysis of dilation in relation to shear direction. The potential of the new procedure is illustrated exemplary by shear box tests on slate.     

Analysing Debris-Flow Impact Models, Based on a Small Scale Modelling Approach

The objective of this study is to analyse adaptable debris-flow impact models, which are very important for mitigation measurements and buildings using their sphere of influence. For this reason, 16 debris-flow experiments, on a small-scale modelling approach, were performed. Impact forces were measured with a force plate panel, consisting of 24 aluminium devices, coaxially mounted with resistance strain gauges. Flow velocities, flow heights as well as horizontal impact forces were sampled with a frequency of 2.4 kHz. Sub datasets of sampled raw force data were defined by applying an average median filter, a low-pass filter routine. Further, estimated peak pressure values as well as empirical coefficients of hydraulic impact models were compared, and the influence of signal processing is discussed.     

Contaminants in sediments from the central Gulf of Mexico

Surface sediment samples at 89 locations and 300-cm cores from 43 sites in the Mississippi Sound were examined for evidence of pollutant impact upon this coastal environment. Chemical variables determined were total organic carbon, Kjeldahl nitrogen, phenols, and hydrocarbons. Values of these pollutant indicators were about the same or lower in Gulf of Mexico samples compared to Missippi Sound sediments and considerably lower than those from rivers and bays emptying into the sound, indicating limited impact from sites of pollutant sources into the sound. Concentrations of sedimentary pollutants peaked in the Pascagoula River where levels of total organic carbon (TOC), Kjeldahl nitrogen (TKN), phenols, and hydrocarbons exceeded sound values by one to three orders of magnitude. Analysis of cores shows pollutant intrusion to sediment strata predating industrial development. The level of pollution varies from site to site but fortunately is only serious at localized sites within the sound.     

Semi-automated extraction of digital objective prism spectra

We describe a method for the extraction of spectra from high-dispersion objective prism plates. Our method is a catalogue-driven plate solution approach, making use of the right ascension and declination coordinates for the target objects. In contrast to existing methods of photographic plate reduction, we digitize the entire plate and extract spectra off-line. This approach has the advantages that it can be applied to CCD objective prism images and spectra can be re-extracted (or additional spectra extracted) without having to re-scan the plate. After a brief initial interactive period, the subsequent reduction procedure is completely automatic, resulting in fully reduced, wavelength-justified spectra. We also discuss a method of removing stellar continua using a combination of non-linear filtering algorithms.   The method described is used to extract over 12 000 spectra from a set of 92 objective prism plates. These spectra are used in an associated project to develop automated spectral classifiers based on neural networks.