Comparative sensitivity of harbour and grey seals to several environmental contaminants using in vitro exposure

In this study, we investigated the effects of cadmium chloride (CdCl₂), mercury chloride (HgCl₂), methylmercury chloride (CH₃HgCl), and PCBs on lymphocyte proliferation in phocids. PBMCs isolated from harbour and grey seals were exposed in vitro to varying concentrations of contaminants. A reduction of viability occurred when cells were exposed to 10⁻⁴ M HgCl₂ or CH₃HgCl or to 50 ppm of Aroclor 1254. In both grey and harbour seals, T-lymphocyte proliferation was suppressed when their cells were incubated with 5 × 10⁻⁵ M CdCl₂ or 10⁻⁴ M HgCl₂. An inhibition of proliferation occurred with CH₃HgCl from 10⁻⁶ M in grey seals and from 10⁻⁵ M in harbour seals. In grey seals, Aroclor 1254 reduced lymphocyte proliferation at 15 ppm. In both harbour and grey seals, CH₃HgCl was ten times more immunotoxic that HgCl₂. From IC₅₀, chemicals were ranked in terms of toxicity as followed: CH₃HgCl > CdCl₂ > HgCl₂ > Aroclor 1254.     

Algorithms for Stellar Perturbation Computations on Oort Cloud Comets

We investigate different approximate methods of computing the perturbations on the orbits of Oort cloud comets caused by passing stars, by checking them against an accurate numerical integration using Everhart’s RA15 code. The scenario under study is the one relevant for long-term simulations of the cloud’s response to a predefined set of stellar passages. Our sample of stellar encounters simulates those experienced by the Solar System currently, but extrapolated over a time of 10¹⁰ years. We measure the errors of perihelion distance perturbations for high-eccentricity orbits introduced by several estimators – including the classical impulse approximation and Dybczyński’s (1994, Celest. Mech. Dynam. Astron. 58, 1330–1338) method – and we study how they depend on the encounter parameters (approach distance and relative velocity). We introduce a sequential variant of Dybczyński’s approach, cutting the encounter into several steps whereby the heliocentric motion of the comet is taken into account. For the scenario at hand this is found to offer an efficient means to obtain accurate results for practically any domain of the parameter space.     

On the modelling of stationary planetary waves

The structure of the atmospheric stationary planetary waves is obtained by means of the quasi‐geostrophic linear model developed by Matsuno (1 970). To show the influence of the upper boundary condition on the structure of the waves, the latter is computed using a rigid top and a radiation condition. The modifications to the wave structure obtained when the upper boundary is lowered from a height of 65 km to 42.5 km, 32.5 km, and 22.5 km are examined. The effects of varying the vertical grid increment are studied through a comparison of the wave structures obtained with 6, 12, and 24 levels between 5 and 65 km.     

Secular Dynamics of Asteroids in the Inner Solar System

In the last three years we have carried out numerical and semi-analytical studies on the secular dynamical mechanisms in the region (semimajor axis a < 2 AU) where the NEA orbits evolve. Our numerical integrations (over a time span of a few Myr) have shown that: (i) the linear secular resonances with both the inner and the outer planets may play an important role in the dynamical evolution of NEAs; (ii) the apsidal secular resonance with Mars could provide an important dynamical transport mechanism by which asteroids in the Mars-crossing region eventually achieve Earth-crossing orbits; (iii) in this region, due to the interaction with the terrestrial planets, the Kozai resonance can occur at small inclinations, with the argument of perihelion ω librating around 0° or 180°, providing a temporary protection mechanism against close approaches to the planets. The location of the linear secular resonances in this zone has also been obtained by an automatic procedure using a semi-numerical method valid for all values of the inclinations and eccentricities of the small bodies, and also in the case of libration of the argument of perihelion. A map of the secular resonances in the (a, i) plane shows — in agreement with the numerical integrations — that all the resonances with the terrestrial and giant planets are present, and also that some of them overlap. Thus the way is now open to fully take into account secular resonances in modelling the dynamical evolution of NEAs. This revised version was published online in July 2006 with corrections to the Cover Date.     

The mechanism of mine-collapse deduced from seismic observations

On May 2, 1993 more than 200 seismic events from an underground mine in Tyrol/Austria were recorded with short-period seismometers of a local seismic network which was introduced in the late 1980s to monitor the tectonic seismicity in Tyrol in greater detail. The cause of this series of mining-associated events has become the subject of intensive investigations — as it was associated with a subsidence affecting an area of 10.000 m². Underground observations revealed a number of discontinuities along which the rock mass was able to move. Seismic recordings of the close-by seismic stations revealed two types of mechanisms: One mechanism seems to be associated with pure block-sliding along several discontinuities, while other signals indicate additional collapse. The consideration and combination of several seismological principles made possible the construction of a model of the mine collapse.     

The Chemical Evolution of the Universe on its Smallest Scales: Dust in Stars,Disks and Planets

D15 Dust and gas in the inner accretion disk around the Herbig star MWC 147 resolved with infrared spectro‐interferometry D21 The effective temperature of OGLE‐TR‐10 – The Balmer α line D29 Metal Injection into the Intracluster Medium D30 Eigenmodes of circumstellar dust shells D40 Numerical Modelling Approach of Circumstellar Dust Shells Around Pulsating AGB Stars Aiming at Multi Time Scale Processes D45 UV radiation induced CO molecule formation patterns in low density PDRs D46 IR properties of calcite and dolomite at low temperatures D47 Observations and Models of Dusty Giants – Past and Present D51 A multi‐method approach to the outer layers of AGB stars D53 On the convective energy transport in M‐type brown dwarf atmospheres D70 Structure and Dust Composition of the TW Hya Disc D75 Chemical Abundances in the Carina Dwarf Spheroidal Galaxy D76 Kinematic and chemical constraints on the formation of M31's inner halo structures D77 IR band profiles of silicate and oxide dust obtained by laboratory measurements of free‐flying particles D98 Dust particle growth in protoplanetary disks D134 Comparative study of dust cloud modelling for substellar atmospheres D137 Photometric study of neglected binary DV Psc D154 Quantitative Spectroscopy of Deneb D160 Hot subluminous Ostars from the SDSS D166 Simultaneous Observations of Solar Ca II H and Ca II 8662 lines and Numerical Simulation of these lines D182 Present‐day carbon abundances in the solar vicinity D189 Detection of a giant planet around a pulsating extreme horizontal branch star: the oldest known planet? D200 Confirmation of a very young binary brown dwarf candidate with disk in Chamaeleon D208 Galaxy ages and metallicities in the cluster A1314 D217 Charge‐dipole induced dust gelation – fastening the process of dust growth in protoplanetary disks D246 Protoplanetary Disk Structure and Evolution     

Long-term effects of the Galactic tide on cometary dynamics

We introduce a model for integrating the effects of Galactic tides on Oort cloud comets, which involves two procedures, according to the values of the osculating semi-major axis a and eccentricity e. Ten simulations of the dynamics of 10⁶ comets over 5 Gyr are performed using this model. We thus investigate the long-term effects of the Galactic tide with and without a radial component, the effects of the local density of the Galactic disk, and those of the Oort constants. Most of the results may be understood in terms of the integrability or non-integrability of the system. For an integrable system, which occurs for moderate semi-major axes with or without radial component, the dynamics is explained by periodic variation of the cometary perihelion, inducing the depletion of the outer region of the Oort cloud, a constant flux from the inner region after 500 Myr, and the quick formation of a reservoir of comets with argument of perihelion near 26.6°. When the system is non-integrable, the efficiency of the tide in reducing the cometary perihelion distance is enhanced both by replenishing the Oort cloud domain from which comets are sent toward the planetary system, and by reducing the minimal value that the perihelion distance may reach. No effects of varying the Oort constants were observed, showing that the flat rotation curve is a satisfactory approximation in Oort cloud dynamics.     

Meteorites from the asteroid 6 Hebe

We have numerically integrated the orbits of 18 fictitious fragments ejected from the asteroid 6 Hebe, an S-type object about 200km across which is located very close to theg=g ₆ (orv ₆) secular resonance at a semimajor axis of 2.425AU and a (proper) inclination of 15° .0. A realistic ejection velocity distribution, with most fragments escaping at relative speeds of a few hundredsm/s, has been assumed. In four cases we have found that the resonance pumps up the orbital eccentricity of the fragments to values >0.6, which result into Earth-crossing, within a time span of 1Myr; subsequent close encounters with the Earth cause strongly chaotic orbital evolution. The closest Earth and Mars encounters recorded in our integration occur at miss distances of a few thousandths ofAU, implying collision lifetimes <10⁹ yr. Some other fragments affected by the secular resonance become Mars-crossers but not Earth-crossers over the integration time span. Two bodies are injected into the 3 : 1 mean motion resonance with Jupiter, and also display macroscopically chaotic behaviour leading to Earth-crossing. 6 Hebe is the first asteroid for which a realistic collisional/dynamical evolutionroute to generate meteorites has been fully demonstrated. It may be the parent body of one of the ordinary chondrite classes.