Ceres’ spectral link to carbonaceous chondrites—Analysis of the dark background materials

Ceres’ surface has commonly been linked with carbonaceous chondrites (CCs) by ground‐based telescopic observations, because of its low albedo, flat to red‐sloped spectra in the visible and near‐infrared (VIS/NIR) wavelength region, and the absence of distinct absorption bands, though no currently known meteorites provide complete spectral matches to Ceres. Spatially resolved data of the Dawn Framing Camera (FC) reveal a generally dark surface covered with bright spots exhibiting reflectance values several times higher than Ceres’ background. In this work, we investigated FC data from High Altitude Mapping Orbit (HAMO) and Ceres eXtended Juling (CXJ) orbit (~140 m/pixel) for global spectral variations. We found that the cerean surface mainly differs by spectral slope over the whole FC wavelength region (0.4–1.0 μm). Areas exhibiting slopes ?1 constitute only ~3% of the cerean surface and mainly occur in the bright material in and around young craters, whereas slopes ≥?10% μm^?1 occur on more than 90% of the cerean surface; the latter being denoted as Ceres’ background material in this work. FC and Visible and Infrared Spectrometer (VIR) spectra of this background material were compared to the suite of CCs spectrally investigated so far regarding their VIS/NIR region and 2.7 μm absorption, as well as their reflectance at 0.653 μm. This resulted in a good match to heated CI Ivuna (heated to 200–300 °C) and a better match for CM1 meteorites, especially Moapa Valley. This possibly indicates that the alteration of CM2 to CM1 took place on Ceres.     

Magnetic reconnection in plasmas

A review of the present status of the theory of magnetic reconnection is given. In strongly collisional plasmas reconnection proceeds via resistive current sheets, i.e. quasi-stationary macroscopic Sweet-Parker sheets at intermediate values of the magnetic Reynolds numberR _m , or mirco-current sheets in MHD turbulence, which develops at highR _m . In hot, dilute plasmas the reconnection dynamics is dominated by nondissipative effects, mainly the Hall term and electron inertia. Reconnection rates are found to depend only on the ion mass, being independent of the electron inertia and the residual dissipation coefficients. Small-scale whistler turbulence is readily excited giving rise to an anomalous electron viscosity. Hence reconnection may be much more rapid than predicted by conventional resistive theory.     

Detection of the first X-ray selected large AGN group

We have examined the spatial distribution of 856 AGN detected by the ROSAT All-Sky Survey (RASS) using a direct search for structures with the minimal spanning tree. The AGNs were compiled from an area of ∼7000 deg², in which optical identifications of RASS sources were made with the help of the digitized objective prism plates of the Hamburg Quasar Survey (HQS). Redshifts were taken from the literature or from own follow-up observations. The sample probes the spatial distribution at low redshifts, because the redshift distribution peaks at z ∼0.1. The application of the minimal spanning tree led to a 1.8 σ discovery of an AGN group with seven members in a volume V ∼140×75×75  h ⁻³ Mpc³ in the Pisces constellation. With a mean redshift z =0.27 this group is only the third discovered group at redshifts z <0.5. The RASS offers excellent possibilities to study large-scale structure with AGNs at low redshifts, once these redshifts are determined.     

`Isotopically strange xenon' in meteoritic nanodiamonds: implantation by stellar winds?

It is argued that the cycling of the atomic nuclei of`isotopically strange xenon' through carbon stars and its implantation intometeoritic nanodiamonds by low-energy stellar wind ions of such starslessens several difficulties of earlier theories. The isotopically strangexenon might be an abundant galactic constituent today, or have been suchduring the presolar past.     

Paleoindication of acidification in Kleiner Arbersee (Federal Republic of Germany,Bavarian Forest) by chydorids,chrysophytes, and diatoms

In a sediment core of Lake Kleiner Arbersee, located in the Bavarian Forest on gneiss bedrock and with spodosolic soils in the catchment, acidification was reconstructed using assemblages of chydorids, scaled chrysophytes, and diatoms as paleoindicators. All paleoindicators demonstrated acidification of Kleiner Arbersee. There were marked differences, however, in the extent of the indicated acidification: In lower layers, where scaled chrysophytes and chydorids clearly indicate beginning acidification, pH-decline inferred by diatoms lies within the standard deviation, and is statistically not significant until the 7 cm layer. We conclude that mallomonadaceans reflect the acidification of the water body and strongly respond to the lowest seasonal pH, as their indicated rate of acidification is higher than that of diatoms, which appear to more closely indicate the pH of the sediment/water interface, especially when the pH of the water column has dropped below ca. 5.5. Chydorids may additionally be influenced by proton release of dense Sphagnum-stands, which cover the littoral of Kleiner Arbersee completely.We dedicate this paper to Prof. Dipl.-Ing. L. Strobel, who encouraged new perspectives in limnological water management, on the occasion of his 65^th anniversary.     

Electromagnetic solutions of higher-dimensional gravity

The variation of spectral index _1.4 ⁵ with luminosity (P _1.4) was investigated for Fanaroff and Riley type II galaxies and also for type I and type I/II galaxies. To reduce the effect of the redshift dependence of luminosity, samples which did not have widely different median redshifts were used and the data was binned into redshift ranges.By a comparison of the median spectral indices in different redshift bins for FRII galaxies, no dependence of spectral index was formed on redshift. However, an increase in spectral index with increasing luminosity was found. The results for FRI and FRI/II galaxies were similar to those for the FRII galaxies.     

The impact of exceptional events on erosion,bedload transport and channel stability in a step‐pool channel

Sediment transport in the Erlenbach, a small stream with step‐pool morphology in the canton of Schwyz, Switzerland, has been monitored for more than 20 years. During this time three exceptional events (events with high sediment yield and long return times that have a large effect on channel morphology) have impacted the stream and partly or completely rearranged the existing step‐pool morphology. In the aftermath of the events, sediment transport rates at a given discharge and total sediment yield remained elevated for about a year or longer. For the last event, dated on the 20 June 2007, observations of boulder mobility and step destruction were used to interpret channel stability. Boulders with median diameters of up to 135 cm and estimated weights of more than 2·5 tons have moved during the 2007 event. Using hydraulic observations and shear stress calculations boulders up to 65 cm in diameter were predicted to have been fully mobile in peak conditions, even if form resistance and increased critical stresses needed for the initiation of motion in steep streams were taken into account. For two of the events, estimated peak shear stresses at the bed exceeded 1000 Pa, calculated both from observations of the flow hydraulics and from boulder mobility. This suggests that highly energetic flows occur relatively frequently in small, steep streams and that large boulders can be transported by fluvial processes in such streams. The observations have potential significance for hazard risk mitigation, stream engineering and restoration. Copyright © 2009 John Wiley & Sons, Ltd.     

Chemical and geochemical studies of Lake Biel

The mixing and transport processes in Lake Biel have been studied using the heat and excess Rn-222 as natural tracers. The mixing parameters were established in terms of coefficients of eddy diffusion in a two-dimensional box model. To account for observed transient Rn-222 distribution, transport by advection had to be included in the model calculations. Part I: Peter W. Santschi and Paul W. Schindler: A mass balance for Lake Biel and its implications for the rates of erosion of the drainage area. Schweiz. Z. Hydrol.39, 182–200 (1977).