Degradation of carbon disulphide (CS2) in soils and groundwater from a CS2-contaminated site

This study is the first investigation of biodegradation of carbon disulphide (CS₂) in soil that provides estimates of degradation rates and identifies intermediate degradation products and carbon isotope signatures of degradation. Microcosm studies were undertaken under anaerobic conditions using soil and groundwater recovered from CS₂-contaminated sites. Proposed degradation mechanisms were validated using equilibrium speciation modelling of concentrations and carbon isotope ratios. A first-order degradation rate constant of 1.25 × 10^?2 h^?1 was obtained for biological degradation with soil. Carbonyl sulphide (COS) and hydrogen sulphide (H₂S) were found to be intermediates of degradation, but did not accumulate in vials. A ¹³C/¹²C enrichment factor of ?7.5 ± 0.8 ‰ was obtained for degradation within microcosms with both soil and groundwater whereas a ¹³C/¹²C enrichment factor of ?23.0 ± 2.1 ‰ was obtained for degradation with site groundwater alone. It can be concluded that biological degradation of both CS₂-contaminated soil and groundwater is likely to occur in the field suggesting that natural attenuation may be an appropriate remedial tool at some sites. The presence of biodegradation by-products including COS and H₂S indicates that biodegradation of CS₂ is occurring and stable carbon isotopes are a promising tool to quantify CS₂ degradation.     

The influence of particle adhesion on the stability of agglomerates in Saturn's rings

In planetary rings, binary collisions and mutual gravity are the predominant particle interactions. Based on a viscoelastic contact model we implement the concept of static adhesion. We discuss the collision dynamics and obtain a threshold velocity for restitution or agglomeration to occur. The latter takes place within a range of a few cm s⁻¹ for icy grains at low temperatures. The stability of such two-body agglomerates bound by adhesion and gravity in a tidal environment is discussed and applied to the saturnian system. A maximal agglomerate size for a given orbit location is obtained. In this way we are able to resolve the borderline of the zone where agglomerates can exist as a function of the agglomerate size and thus gain an alternative to the classical Roche limit. An increasing ring grain size with distance to Saturn as observed by the VIMS-experiment on board the Cassini spacecraft can be found by our estimates and implications for the saturnian system will be addressed.     

Chaotic motions of prometheus and pandora

Recent HST images of the saturnian satellites Prometheus and Pandora show that their longitudes deviate from predictions of ephemerides based on Voyager images. Currently Prometheus is lagging and Pandora leading these predictions by somewhat more than 20°. We show that these discrepancies are fully accounted for by gravitational interactions between the two satellites. These peak every 24.8 days at conjunctions and excite chaotic perturbations. The Lyapunov exponent for the Prometheus-Pandora system is of order 0.3 year⁻¹ for satellite masses based on a nominal density of 0.63 g cm⁻³. Interactions are strongest when the orbits come closest together. This happens at intervals of 6.2 years when their apses are antialigned. In this context, we note the sudden changes of opposite signs in the mean motions of Prometheus and Pandora at the end of 2000 occurred around the time their apsidal lines were antialigned.     

Does the Milky Way launch a large-scale wind?

The ROSAT All-Sky Survey revealed soft X-ray emission on kiloparsec scales towards the Galactic center. Separately, it has also been observed that the cosmic ray intensity (measured via γ-ray emission) rises only very slowly towards the center of the Galaxy, counter to expectations based on the greater number of cosmic ray sources there. A thermal and cosmic-ray driven wind could potentially explain both of these observations. We find that a cosmic-ray and thermally driven wind fits the X-ray observations well; in fact, a wind fits significantly better than an earlier-proposed static-polytrope gas model.     

Magnetic changes observed in the formation of two filaments in a complex active region: TRACE and MSDP observations

This paper is focused on the formation of two filaments in a complex center of decaying active regions (AR 8329 and AR 8326), located in the northern hemisphere. The observations were obtained in Hα by the Multi-channel Subtractive Double Pass spectrograph (MSDP mounted on the German telescope VTT in Tenerife) and EUV lines with TRACE (Transition Region And Corona Explorer). High Doppler shifts are found to be related to the ends of filament segments where canceling magnetic fields are also located (as seen on magnetograms from Big Bear Solar Observatory). At these locations, velocities along the line of sight, derived by using a cloud model method reach −20 km s⁻¹, the segments of filaments merge and frequently a time-related sub-flare is observed by TRACE. The chirality of the filament segments has been determined by different methods: the segments of dextral chirality join together and form a long dextral filament, and a single filament of sinistral chirality forms end to end with the dextral filament but does not merge with it. Assuming a model of twisted flux tube for filament material, we suggest that the dextral filament has negative helicity and a relationship between its formation and the close by sunspot with the same sign of helicity.