Polarimetric NIR reflectance measurements of regolith simulants at zero phase angle

Polarimetric reflectance measurements have been made at a wavelength of for a suite of predominantly lunar regolith simulants in support of development efforts for the BepiColombo Laser Altimeter (BELA). Measurements were made using an instrument at the University of Bern, Switzerland, that has been modified to accommodate photometric characterizations of laboratory samples down to 0^° phase angle (g) with linearly polarized illumination and a linearly polarized receiver. The data reveal opposition surges that are dominated by polarization state-conserving reflectance terms for all samples. Relative strengths of the trans-state reflectance terms are lowest for the darkest samples, suggesting that multiple scattering is responsible for state conversions. Normal albedo measurements of the lunar simulants range from 0.13 to 0.22 at zero illumination angle (i=0^°). The total reflectance of the regolith simulants at g=0^° were found to decrease with increasing i, which is inconsistent with predictions of reflectance models for Mercury. However, the g=0^° reflectance remains higher at i>0^° than would be expected for a gray Lambert surface that is scaled to the g=i=0^° reflectance value. Polarization ratios for reflectance under polarized illumination but unconstrained emission show that the samples scatter light in the in-plane polarization state more efficiently than in the transverse state at g=0^° and i>0^°. The opposite is true for g>0^° polarization ratios, which indicate that transverse polarized illumination scatters more efficiently at high g. The polarization effect appears to correlate with the sample's characteristic grain size, but the statistical basis of this trend is weak. The implications of these measurements upon the performance of the BELA instrument are discussed.     

The triple multimineral barrier for hazardous waste encapsulation

According to the present state of science and technology, the ultimate disposal of critical substances such as chemotoxic wastes, metal slurries, radioactive substances, etc., as well as houshold waste, necessitates enclosure within a multi-barrier system. The geology of the disposal site plays an important role. The site itself defines the geological barrier which has to fulfill at least two requirements: namely low permeability and retention, respectively retardation qualities. These can be achieved to a certain degree either by clay minerals, zeolites or an artificial product such as active coal. In order to increase the imperviousness and retardation potentials of e.g. clayey geological barriers, technical barriers have to be added. One of them and the most important is the mineralogic barrier. It consists of clay dominated layers and according to the multimineral barrier concept the different layers have to meet different functions.     

Astron observations of the Rapid Burster MXB 1730-335 and constraints on burster parameters from spectra of trailing bursts

We report on eight X-ray bursts detected by ASTRON from the Rapid Burster (RB) on 13 and 28 April and 16 August, 1983. Six of them (trailing bursts), with durations of 1.5–2 min, rise times of 5–10 s and intervals of 1–1.5 hours, exhibit spectral softening during the burst decay and may be related to the type I bursts. Two of the bursts (triangle bursts) observed on 28 April at interval of 28 min with much longer rise times (30–50 s) and longer durations (3 min), do not show distinct spectral softening. Persistent flux from RB on 16 August was estimated asF _p(2.0–2.4)×10^–9 erg cm^–2 s^–1. Spectral evolution of two trailing bursts was investigated by fitting their spectra in consecutive time intervals with the blackbody (BB), isothermal scattering photosphere (SP) and thermal bremsstrahlung (TB) models. Around the burst maxima the SP model fits the data best whereas in the burst tails the TB model is generally better. The BB model is worse than at least one of the two others. Interpretation of the burst spectra in terms of the BB radiation leads to improbably small neutron star mass and radius (M<0.86M ,R _NS<5 km) if the peak luminosity does not exceed the Eddington limit. Interpretation of the spectra around the burst maxima (3–15 s from the burst onset) in terms of an isothermal SP yields reasonable constraints onM,R _NS, and distanceD. For instance, for the hydrogen photosphere we obtainedM=(1.0–2.1)M R _NS=(7.1–16.4) km ifD=11 kpc. If one postulatesM=1.4M , thenD=(8.5–13) kpc for hydrogen photosphere; if, besides,D=11 kpc, thenR _NS=(8.1–13.3) km. It follows also from the SP-interpretation that the photosphere radius may increase up to 20–30 km in maxima of the trailing bursts when the luminosity becomes close to the Eddington luminosity.     

Three-dimensional model and late stage warping of the Plattengneis Shear Zone in the Eastern Alps

The Plattengneis shear zone is a 250–600 m thick, flat lying, Cretaceous, eclogite facies, mylonitic shear zone, with north-over-south transport direction, that is exposed over almost 1000 km² in the Koralpe region along the eastern margin of the Alps. Although the shear zone is one of the largest in the Alps, its role in the Eoalpine metamorphic evolution and the subsequent exhumation of the region, remain enigmatic and its large-scale geometry is not well understood. The outcrop pattern suggests that the shear zone is made up of a single sheet that is folded into a series of open syn- and antiforms with wavelengths of about 10 km. Eclogite bodies occur above, within and below the shear zone and there is no metamorphic grade change across the shear zone. In the south, the fold axes strike east–west and plunge shallowly to the east. In the north, the fold axes are oriented in north–south direction and form a dome shaped structure of the shear zone. Total shortening during this late stage warping event was of the order of 5%. Indirect evidence constrains this folding event to have occurred between 80 and 50 Ma and the fold geometry implies that the final exhumation in the Koralpe occurred somewhat later than further north. Interestingly, the shear zone appears to strike out of the topography in the south and dip into the topography in the north, so that north of the shear zone only hanging-wall rocks are exposed and south of it only foot-wall rocks. Possibilities for the geometric relationship of the Plattengneis shear zone with the surrounding south dipping detachments are discussed.     

Morphological analysis of the drainage system in the Eastern Alps

We study the morphology of the major rivers draining the Eastern Alps to test whether the active tectonics of this part of the orogen is reflected in the shape of channel profiles of the river network. In our approach we compare channel profiles measured from digital elevation models with numerically modelled channel profiles using a stream power approach. It is shown that regions of high stream power coincide largely with regions of highest topography and largest uplift rates, while the forelands and the Pannonian Basin are characterised by a significantly lower stream power. From stream power modelling we conclude that there is young uplift at the very east of the Eastern Alps, in the Bohemian Massif and in the Pohorje Range. The impact of the Pleistocene glaciations is explored by comparing properties of rivers that drain in proximal and distal positions relative to the ice sheet during the last glacial maximum. Our analysis shows that most knick points, wind gaps and other non-equilibrium features of catchments covered by ice during the last glaciations (Salzach, Enns) can be correlated with glacial processes. In contrast the ice free catchments of the Mur and Drava are characterized by channels in morphological equilibrium at the first approximation and are showing only weak evidence of the strong tectonic activity within these catchments. Finally, the channel profiles of the Adige and the divide between the upper Rhine and Danube catchments differ significantly from the other catchments. We relate this to the fact that the Adige and the Rhine respond to different base levels from the remainder of the Eastern Alps: The Adige may preserve a record from the Messininan base level change and the Rhine is subject to the base level lowering in the Rhine Graben.     

Diatom assemblages from Costa Rican lakes: an initial ecological assessment

We compared the distributions of 59 diatom species in surface sediments of 25 Costa Rican lakes with 21 environmental variables using canonical correspondence analysis (CCA). The distribution of taxa was related to the chemical and physical characteristics of the lakes. The most influential chemical variables were cation concentrations (especially magnesium) and related variables such as water hardness, pH, and temperature. Lake area and lake depth were among the most important physical variables.A number of taxa were identified as potential environmental indicators. The diatoms Brachysira serians var. brachysira and Frustulia rhomboides seem to be associated with low values of alkalinity, hardness, Ca, Mg, and SiO2. Cymbella minuta var. silesiaca is associated with low to moderate values of alkalinity, hardness, Ca, and Mg. Nitzschia cf. amphibia may be an indicator of moderate-to-high concentrations of Mg. Pinnularia braunii var. amphicephala seems to prefer low values of hardness, Ca, Mg, and SiO2.In many closed lakes, these environmental variables (Mg/Ca/hardness/alkalinity) increase with effective evaporation. Consequently, these diatoms may be indirectly tracking P:E ratios. Results from this initial, small data set indicate the potential of diatoms for inferring lake paleochemistry, and perhaps P:E ratios, in Costa Rica.     

Die wirkliche Solarkonstante

Zusammenfassung Die Solarkonstante 2.4 wird begründet.

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Summary The true solar constant 2.4 is proved.

     

Cladocora caespitosa bioconstructions in the Columbretes Islands Marine Reserve (Spain,NW Mediterranean): distribution,size structure and growth

Today, living banks of the coral Cladocora caespitosa appear to be restricted to a few Mediterranean locations and are threatened by the escalating impacts affecting coastal areas. In this study the exceptional occurrence of the Mediterranean coral C. caespitosa in the Columbretes Islands Marine Reserve (NW Mediterranean, Spain) is characterised in terms of spatial distribution, cover area, colony size and growth rates. The coral colonies form beds and banks in rocky bottoms within a semi‐enclosed bay that offers both hydrodynamic protection and high water exchange. The spatial distribution of the C. caespitosa colonies, from 5 to 27 m depth, is highly aggregated, depending on sea‐floor morphology and showing up to 80% of substrate coverage. The annual corallite growth rates obtained through the alizarin red staining method and x‐ray image analysis are similar, and range between 2.55 ± 0.79 mm and 2.54 ± 0.81 mm, respectively. The exceptional nature of these bioconstructions is due to their cumulative cover area, which is comparable in size to the largest C. caespitosa bioconstructions described to date in Mljet National Park (Croatia, Adriatic Sea).