Eta carinae nebulosities in 1963

The purpose of this note is to give further information regarding the positions of some condensations around Carinae in 1963, an epoch not yet considered in the literature. The new information is unable to confirm the deceleration hypothesis of theeir motion.     

Study of the influence of katabatic flows on the Antarctic circulation using GCM simulations

Summary A one dimensional analytical model of katabatic wind over the Antarctica has been developed. This parametric model is derived from the bulk two-layer model of Ball including the surface friction and taking into account the Earth's rotation and the geostrophic wind in the upper layer.This model is validated using the data set (70 soundings) collected during IAGO experiment at D47 (67°24S, 138°43E, altitude 1 564m), 110 km inland from the coast of Adélie Land.The parameteric model is then introduced into a GCM which is a spectral global version of the operational numerical weather prediction model used by the French weather service. The most significant effect of the parameterization is a 50 m increase of the geopotential height over the South Pole. The surface temperature at the South Pole increases (2°C) reducing the pole-midlatitude thermal gradient. The westerly circulation at 50° S is slowed down (4m/s at 850 hPa), and the surface pressure at the South Pole increases (4hPa). These results, consistent with an increase of katabatic winds, would however be improved by a better coupling between the parameterization and the GCM boundary layer.With 8 Figures     

A Monte Carlo investigation of Jovian perturbations on short-period comet orbits

We present statistical distributions of Jovian perturbations on short-period comet orbits resulting from accurate numerical integrations. Our sample of 60, 000 cometary orbits with low inclinations and random orientations is characterized by perihelia between 0 and 7 AU and aphelia between 4 and 13 AU. The perturbations considered are those experienced because of Jupiter's gravitation per orbital revolution by the comets. Regularization and accurate step-length control in the numerical integration gives statistical results appreciably different from those computed by Rickman and Vaghi (1978). Their use of a crude method of integration led to erroneous results for close encounters. Strong asymmetries of the $\text{δ(}\text{1}\text{a}\text{)}$ distributions, in particular for the extreme tails, are observed for perihelion- or aphelion-tangent orbits. These orbits are also shown to experience the strongest energy perturbations on the average. Some results concerning the perturbations of Tisserand parameters are indicated. The perturbation distributions for the angular elements are described and discussed. The role of the minimum distance from Jupiter as an indicator of perturbations is investigated.     

Interstellar clouds and the formation of stars

Part I gives a survey of the drastic revision of cosmic plasma physics which is precipitated by the exploration of the magnetosphere throughin situ measurements. The pseudo-plasma formalism, which until now has almost completely dominated theoretical astrophysics, must be replaced by an experimentally based approach involving the introduction of a number of neglected plasma phenomena, such as electric double layers, critical velocity, and pinch effect. The general belief that star light is the main ionizer is shown to be doubtful; hydromagnetic conversion of gravitational and kinetic energy may often be much more important.In Part II the revised plasma physics is applied to dark clouds and star formation. Magnetic fields do not necessarily counteract the contraction of a cloud; they may just as well pinch the cloud. Magnetic compression may be the main mechanism for forming interstellar clouds and keeping them together.Part III treats the formation of stars in a dusty cosmic plasma cloud. Star formation is due to an instability, but it is very unlikely that it has anything to do with the Jeans instability. A reasonable mechanism is that the sedimentation of dust (including solid bodies of different size) is triggering off a gravitationally assisted accretion. A stellesimal accretion analogous to the planetesimal accretion leads to the formation of a star surrounded by a very low density hollow in the cloud. Matter falling in from the cloud towards the star is the raw material for the formation of planets and satellites.The study of the evolution of a dark cloud leads to a scenario of planet formation which is reconcilable with the results obtained from studies based on solar system data. This means that the new approach to cosmical plasma physics discussed in Part I logically leads to a consistent picture of the evolution of dark clouds and the formation of solar systems.     

The behavior of trace elements during schwertmannite precipitation and subsequent transformation into goethite and jarosite

Schwertmannite is a ubiquitous mineral formed from acid rock drainage (ARD), and plays a major role in controlling the water chemistry of many acid streams. The formation of schwertmannite was investigated in the acid discharge of the Monte Romero abandoned mine (Iberian Pyrite Belt, SW, Spain). Schwertmannite precipitated from supersaturated solutions mainly owing to the oxidation of Fe(II) to Fe(III) and transformed with time into goethite and jarosite. In a few hours, schwertmannite precipitation removed more than half of the arsenic load from solution, whereas the concentration of divalent trace metals (Zn, Cu, Pb, Cd, Ni, and Co) remained almost unchanged. In the laboratory, natural schwertmannite was kept in contact with its coexisting acid water in a flask with a solid-liquid mass ratio of 1:5 for 353 days. During this time, the pH of the solution dropped from 3.07 to 1.74 and the concentrations of sulfate and Fe increased. During the first 164 days, schwertmannite transformed into goethite plus H₃O-jarosite but, subsequently, goethite was the only mineral to form. Some of the trace elements, such as Al, Cu, Pb, and As were depleted in solution during the first stage as schwertmannite transformed into goethite plus H₃O-jarosite. On the contrary, the transformation of schwertmannite to goethite (with no jarosite) during the second stage released Al, Cu, and As to the solution. Despite the variation in their concentrations in solution, approximately 80% of the total Al and Cu inventories and more than 99% As and Pb remained in the solid phase throughout the entire aging process.     

Natural attenuation and bioremediation of Prestige fuel oil along the Atlantic coast of Galicia (Spain)

Heavy fuel oil spilled from the oil tanker Prestige in November 2002 affected hundreds of km of Spanish shoreline. We carried out a two year study at two highly contaminated sites in order to monitor natural attenuation of the residues coating shore rocks and to test the effectiveness of bioremediation with an oleophilic fertilizer (S200). The methodology included an innovative approach for oil load calculation (based on image analysis techniques), the analysis of the fate of hydrocarbons by means of chemical biomarkers and different microbiological techniques for isolating and examining hydrocarbon degraders.Considerable hydrocarbon depletion from shorelines (≈100% for light-medium linear alkanes and ≈35% for aromatics such as pyrene) was observed within the first months after the spill. However, this natural attenuation effect dramatically slowed down in the following year, although partial enhancement (especially for the aromatic fraction) was attained as a result of the application of S200 to stimulate indigenous microorganisms. In addition, one of the main outcomes of this work concerns the remarkable hydrocarbon depletion achieved at points where fresh water flowed through the shore rocks. The study of samples collected where this natural attenuation phenomenon took place made it possible to isolate heterotrophic bacteria and fungi that are likely to cooperate with cyanobacteria in hydrocarbon biodegradation. The overall results strongly advocate the implementation of new bioremediation approaches, including alternatives such as the use of natural fresh water to irrigate polluted areas.     

Modeling nonlinear seagrass clonal growth: Assessing the efficiency of space occupation across the seagrass flora

The clonal growth of 9 seagrass species was modeled using a simulation model based on observed clonal growth rules (i.e., spacer length, rhizome elongation rates, branching rates, branching angle) and shoot mortality rates for seagrass species. The results of the model confirmed the occurrence of complex, nonlinear growth of seagrass clones derived from internal dynamics of space occupation. The modeled clones progressed from a diffuse-limited aggregation (DLA), dendritic growth, identified with a guerrilla strategy of space occupation, to a compact (Eden) growth, comparable to the phalanx strategy of space occupation, once internal recolonization of gaps, left by dead shoots within the clone, begins. The time at which seagrass clones shifted from diffuse limited to compact growth was predictable from the branching angle and frequency of the species and varied from 1 yr to several decades among species. As a consequence the growth behavior and the apparent growth strategy of the species changes with the development of the clones. The results of the model demonstrate that the emergent complexity of seagrass clonal growth is contained within the simple set of growth rules that can be used to represent clonal growth.     

Mais comment s'écoule donc un glacier ? Aperçu historique

Ice and snow have often helped physicists understand the world. On the contrary it has taken them a very long time to understand the flow of the glaciers. Naturalists only began to take an interest in glaciers at the beginning of the 19th century during the last phase of glacier advances. When the glacier flow from the upslope direction became obvious, it was then necessary to understand how it flowed. It was only in 1840, the year of the Antarctica ice sheet discovery by Dumont d'Urville, that two books laid the basis for the future field of glaciology: one by Agassiz on the ice age and glaciers, the other one by canon Rendu on glacier theory. During the 19th century, ice flow theories, adopted by most of the leading scientists, were based on melting/refreezing processes. Even though the word ‘fluid’ was first used in 1773 to describe ice, more the 130 years would have to go by before the laws of fluid mechanics were applied to ice. Even now, the parameter of Glen's law, which is used by glaciologists to model ice deformation, can take a very wide range of values, so that no unique ice flow law has yet been defined. To cite this article: F. Rémy, L. Testut, C. R. Geoscience 338 (2006).     

Les failles récentes des Grands-Moulins (Savoie) : un Sackung (tassement gravitaire) majeur dans les Alpes françaises

In Savoy, the Grands-Moulins recent fault scarps, previously interpreted as seismic fault ruptures, are in fact part of a major Sackung (deep seated gravitational spreading) of the French Alps (9 km long). We mapped more than 60 sackung scarps, some of them reaching 1330 m long and 30 m high. These antislope scarps stop the active screes and offset relict Dryassic rock glaciers by 16 m. We present geomorphologic observations attesting for their gravitational origin. This Sackung is primarily due to glacial debuttressing, while seismic shaking could be a triggering mechanism. To cite this article: J.-C. Hippolyte et al., C. R. Geoscience 338 (2006).