Radiation pressure and dust particle dynamics

The dynamics of small dust grains orbiting a planet are investigated when solar radiation pressure forces are added to the planet's gravitational central field. In the first part a set of differential equations is derived in a reference frame linked to the solar motion. The complete solution of these equations is given for particles lying in the planet's orbital plane, and we show that the orbital eccentricity may undergo considerable variation. At the same time the pericenter longitude librates or circulates according to initial conditions. With this result we establish a criterion for any orbiting particle (because of its highly eccentric orbit) to collide with its planet's atmosphere. The case of inclined orbit is studied through a numerical integration and allows us to draw conclusions related to the stability of the orbital plane. All solutions are periodic, with the period being independent of the initial conditions. This last point permits us to investigate the different time scales involved in that problem. Finally, the Poynting-Robertson drag is included, along with the radial radiation pressure forces, and the secular trend is considered. A coupling effect between the two components is ascertained, yielding a systematic behavior in the eccentricity and thus in the pericenter distance. Our solutions generalize the results of S. J. Peale (1966, J. Geophys. Res.71, 911–933) and J. A. Burns, P. Lamy, and S. Soter (1979, Icarus40, 1–48) by allowing eccentricities to be large (of order 1) and inclinations to be nonzero and by considering Poynting-Robertson drag.     

51 Peg and Upsilon and: Confirmation of the Planet Hypothesis

Earth, Moon, and Planets -     

Laboratory sulfurisation of the marine microalga Nannochloropsis salina

To understand more fully the mode of preservation of organic matter in marine sediments, laboratory sulfurisation of intact cells of the cultured microalga Nannochloropsis salina was performed using inorganic polysulfides in seawater at 50°C. Solvent extractable and non-extractable materials were analysed by GC–MS and Py–GC–MS, respectively, to study the incorporation of sulfur into the microalgal organic matter. No GC-amenable sulfur-containing compounds were found in the extracts apart from some minor thiophenes with a phytanyl carbon skeleton. The residue after extraction and hydrolysis contained abundant macromolecular sulfur-containing moieties as revealed by the presence of dominant C₂₈–C₃₂ thiols, thiophenes, thianes and thiolanes in the flash pyrolysates. These products are thought to be formed from moieties derived from sulfurisation of C₂₈–C₃₂ diols and alkenols, characteristic lipids of N. salina. C₁–C₂ alkylated thiophenes were also found in the pyrolysates and probably result from moieties formed upon sulfurisation of carbohydrates. The highly resistant biomacromolecule (algaenan) synthesised by N. salina remains unaffected by sulfurisation. The non-hydrolysable residue isolated from the sulfurised N. salina thus comprises algaenan and (poly)sulfide-bound long alkyl chains. The sulfurisation experiments show that both selective preservation of algaenans and lipid and carbohydrate “vulcanisation” can be involved in the preservation of algal organic matter in marine environments.     

Scale effects in the determination of rock mass strength and deformability

SummaryScale Effects in the Determination of Rock Mass Strength and Deformability An extensive literature search was conducted, to investigate the effect of the scale of testing on the measurement of strength and stiffness of rock masses. The results are presented for bearing capacity tests, compression tests, and several types of deformability tests.Field strength values are generally several times smaller than laboratory values. Field moduli generally appear to be between 20 per cent to 60 per cent of laboratory measured moduli.All strength and deformability results reviewed point to the great need for more field tests. Specific suggestions are given.

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ZusammenfassungMastabeffekte bei der Bestimmung mechanischer Eigenschaften von Fels Ein eingehendes Literaturstudium wurde durchgeführt, um den Maßstabeffekt auf die Festigkeits- und Verformbarkeitsmessungen im Fels zu untersuchen. Es werden Resultate von Plattendruckversuchen, Druckversuchen und mehreren Verformungsversuchen aufgeführt. Die in-situ gemessene Festigkeit ist im allgemeinen ein Bruchteil derjenigen, die bei Laborversuchen festgestellt wird. Die Verformbarkeiten in-situ betragen meistens 20 bis 60 Prozent der im Labor erhaltenen Werte. Alle Resultate zeigen, daß mehr In-situ-Versuche notwendig sind. Der Autor macht dazu einige Vorschläge.

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RésuméL'effet d'échelle dans les mesures de propriétés mécaniques des massifs rocheux. On a fait une recherche bibliographique détaillée, pour étudier l'effet d'échelle sur les mesures de résistance et de déformabilité des masses rocheuses. On présente des résultats concernant les essais de résistance à la plaque, les essais de compression, et plusieurs types d'essais de déformabilité en place.Les résistances mesurées in-situ sont généralement une fraction de celles mesurées au laboratoire. Les déformabilités mesurées en place sont généralement entre 20 et 60 pour cent des valeurs au laboratoire.Tous les résultats que l'on a examiné indiquent la nécessité d'effectuer plus d'essais en place. L'auteur offre un certain nombre de suggestions.

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With 22 Figures     

Monitoring de la Pollution Atmosphérique au-dessus d'un Site Urbain par mesures Lidar

We have used a ruby Lidar to study the space and time variations of atmospheric aerosols on a horizontal level above a town site. It has allowed us to locate the main sources of industrial pollution and to evaluate the amplitude of retrodiffusion signals due to the town activity.We have demonstrated the influence of the winds whose speed is higher than 3 m/s. We have observed that at any particular place in the town the ratio Am/Amo varied from 1 to 14, this radio characterizing the concentration in pollutants above a place in the town (Am is the amplitude of the retrodiffusion Lidar signal, Amo is the echo lidar amplitude characterizing the average noise of the urban site).     

Evolution de la structure de la couche limite planetaire sur des sites oceaniques et continentaux

We have studied the evolution of the planetary boundary layer using both oceanic and continental stations. This has been possible through the analysis of twice-daily temperature radiosondes at three different oceanic stations (Point A; Point K; and Azores) and also at three continental stations (Berlin, Trappes and Madrid) all situated in the Northern Hemisphere. We have studied the annual evolution of mixing layers and of temperature inversion levels; an annual evolution presenting a minimum in winter and a maximum in summer has been observed in the continental stations; the oceanic stations present a lesser variation and in the opposite sense. As for the elevated inversion layers, their maximum frequency can be observed in summer at the oceanic stations and in winter at the continental stations. We have shown that considering the studied stations, both the level and the frequency of the elevated inversion layers are similar at 00 h and at 12 h; such a result is important because these layers regulate the intensity of the exchanges between the ground and the free atmosphere. Using the equivalent coefficient, we have determined the annual variation of the vertical exchanges between the surface and different altitudes. At the continental stations, the vertical exchanges are more important in summer than they are in winter; the opposite behaviour occurs at the oceanic stations.     

Annual survey of water vapor behavior from the OMEGA mapping spectrometer onboard Mars Express

We present here the annual behavior of atmospheric water vapor on Mars, as observed by the OMEGA spectrometer on board Mars Express during its first martian year. We consider all the different features of the cycle of water vapor: temporal evolution, both at a seasonal and at a diurnal scale; longitudinal distribution; and the vertical profile, through the variations in the saturation height. We put our results into the context of the current knowledge on the water cycle through a systematic comparison with the already published datasets. The seasonal behavior is in very good agreement with past and simultaneous retrievals both qualitatively and quantitatively, within the uncertainties. The average water vapor abundance during the year is ∼10 pr. μm, with an imbalance between northern and southern hemisphere, in favor of the first. The maximum of activity, up to 60 pr. μm, occurs at high northern latitudes during local summer and shows the dominance of the northern polar cap within the driving processes of the water cycle. A corresponding maximum at southern polar latitudes during the local summer is present, but less structured and intense. It reaches ∼25 pr. μm at its peak. Global circulation has some influence in shaping the water cycle, but it is less prominent than the results from previous instruments suggest. No significant correlation between water vapor column density and local hour is detected. We can constrain the amount of water vapor exchanged between the surface and the atmosphere to few pr. μm. This is consistent with recent results by OMEGA and PFS-LW. The action of the regolith layer on the global water cycle seems to be minor, but it cannot be precisely constrained. The distribution of water vapor on the planet, after removing the topography, shows the already known two-maxima system, over Tharsis and Arabia Terra. However, the Arabia Terra increase is quite fragmented compared with previous observations. A deep zone of minimum separates the two regions. The saturation height of water vapor is mainly governed by the variations of insolation during the year. It is confined within 5-15 km from the surface at aphelion, while in the perihelion season it stretches up to 55 km of altitude.     

Solubility of manganotantalite, zircon and hafnon in highly fluxed peralkaline to peraluminous pegmatitic melts

The behavior of tantalum and zirconium in pegmatitic systems has been investigated through the determination of Ta and Zr solubilities at manganotantalite and zircon saturation from dissolution and crystallization experiments in hydrous, Li-, F-, P- and B-bearing pegmatitic melts. The pegmatitic melts are synthetic and enriched in flux elements: 0.7–1.3 wt% Li₂O, 2–5.5 wt% F, 2.8–4 wt% P₂O₅ and 0–2.8 wt% B₂O₃, and their aluminum saturation index ranges from peralkaline to peraluminous (ASI_Li = Al/[Na + K + Li] = 0.8 to 1.3) with various K/Na ratios. Dissolution and crystallization experiments were conducted at temperatures varying between 700 and 1,150°C, at 200 MPa and nearly water-saturated conditions. For dissolution experiments, pure synthetic, end member manganotantalite and zircon were used in order to avoid problems with slow solid-state kinetics, but additional experiments using natural manganotantalite and zircon of relatively pure composition (i.e., close to end member composition) displayed similar solubility results. Zircon and manganotantalite solubilities considerably increase from peraluminous to peralkaline compositions, and are more sensitive to changes in temperature or ASI of the melt than to flux content. A model relating the enthalpy of dissolution of manganotantalite to the ASI_Li of the melt is proposed: ∆H _diss (kJ/mol) = 304 × ASI_Li − 176 in the peralkaline field, and ∆H _diss (kJ/mol) = −111 × ASI_Li + 245 in the peraluminous field. The solubility data reveal a small but detectable competitivity between Zr and Ta in the melt, i.e., lower amounts of Zr are incorporated in a Ta-bearing melt compared to a Ta-free melt under the same conditions. A similar behavior is observed for Hf and Ta. The competitivity between Zr (or Hf) and Ta increases from peraluminous to peralkaline compositions, and suggests that Ta is preferentially bonded to non-bridging oxygens (NBOs) with Al as first-neighbors, whereas Zr is preferentially bonded to NBOs formed by excess alkalies. As a consequence Zr/Ta ratios, when buffered by zircon and manganotantalite simultaneously, are higher in peralkaline melts than in peraluminous melts.