The appearance of Mars from 1907 to 1971: Graphic synthesis of photographs from the I.A.U. center at Meudon

Using selected high quality plates collected at the I.A.U. Planetary Data Center in Meudon (Paris), the author has drawn 32 Mercator charts of the planet Mars for every opposition from 1907 to 1971. This graphic synthesis of albedo distribution may be used in the study of major surface changes over the years.     

Structural features of some group-silicates with chains of octahedra

Summary The existence of chains of octahedra with tetrahedra as lateral appendixes in some Group-silicates is emphasized. These chains can be considered as building blocks; the different ways of juxta-posing the blocks offer a possibility of schematizing the structure of minerals (lawsonite, ilvaite, epidote, pumpellyite, perrierite, chevkinite), of explaining their twins and polymorphisms.

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Zusammenfassung Auf die Existenz von Oktaederketien mit Tetraedern als Seitenzusätzen in einigen Gruppensilikaten wird hingewiesen. Diese Ketten können als Bauteile betrachtet werden: beim Zusammensetzen dieser Bauteile kann man verschiedene Kristallstrukturen von Mineralien (Lawsonit, IIvait, Epidot, Pumpellyit. Perrierit, Tscheffkinit) darstellen, ihre Zwillingsbildung und einige Polymorphie-Typen erklären.

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Riassunto Si prende in considerazione l'esistenza di catene di ottaedri con tetraedri come appendici laterali in alcuni sorosilicati. Queste catene possono essere considerate come elementi costruttivi: unendo tra di loro in vario modo questi elementi costruttivi si possono schematizzare le strutture di diversi minerali (lawsonite, ilvaite, epidoto, pumpellyite, perrierite, chevkinite), si possono spiegare le loro geminazioni, e certi tipi di polimorfismo.

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With 9 Figures     

Climate control on stacked paleosols in the Pleistocene of the Po Basin (northern Italy)

Paleosols are recurrent features in alluvial successions and provide information about past sedimentary dynamics and climate change. Through sedimentological analysis on six sediment cores, the mud-dominated succession beneath the medieval ‘Two Towers’ of Bologna was investigated down to 100 m depth. A succession of weakly developed paleosols (Inceptisols) was identified. Four paleosols (P1, P2, P3 and PH) were radiocarbon-dated to 40–10 cal ka bp . Organic matter and CaCO₃ determinations indicate low groundwater levels during soil development, which spanned periods < 5 ka. The development and burial of soils, which occurred synchronously in the Bologna region and in other sectors of the Po Plain, are interpreted to reflect climatic and eustatic variations. Climatic oscillations, at the scale of the Bond cycles, controlled soil development and burial during Marine Isotope Stage (MIS) 3 (P1 and P2). Rapid sea-level oscillations probably induced soil development at the MIS 3/2 transition (P3) and favored burial of PH after 10 ka bp . Weakly developed paleosols in alluvial successions can provide clues to millennial-scale climatic and environmental variations. In particular, the paleosol-bearing succession of the Po Plain represents an unprecedent record of environmental changes across the Late Pleistocene (MIS 3 and 2) in the Mediterranean region.     

An accurate time integration method for simplified overland flow models

An accurate time integration method for the diffusion-wave and kinematic-wave approximated models for the overland flow is proposed. The discretization of the first- and second-order spatial derivatives in the basic equation is obtained by using the second-order Lax–Wendroff and the three-point centred finite difference schemes, respectively. For the solution in time, the system of ordinary differential equations, obtained by the linearization of the celerity and of the hydraulic diffusivity by Taylor series expansions, is integrated analytically. The stability and the numerical dissipation and dispersion are investigated by the Fourier analysis. A proper Courant number, and the corresponding time step for the numerical simulations can be established. In addition, the proposed diffusion-wave and kinematic-wave models are straightforwardly extended to the two-dimensional flow. Test cases for both one- and two-dimensional problems, compare the solutions of the diffusion-wave and kinematic-wave models with analytical solutions, with experimental results and with numerical solutions obtained by the Saint–Venant equations. These simulations show that the proposed numerical–analytical models accurately predict the overland flow for several situations, in particular for unsteady rainfall rate and for spatial variations of the surface roughness.     

Evaluation of surface sediment contamination by polycyclic aromatic hydrocarbons in the "Saco do Laranjal" - (Patos Lagoon, Brazil)

This paper evaluates the concentration of Polyaromatic hydrocarbons - PAHs in the Estuarine area of the Patos Lagoon, more precisely in a local named "Saco do Laranjal" in Pelotas City (southern Brazil). The samples were collected in May 2008. The concentrations of 16 US-EPA priority polycyclic aromatic hydrocarbons (PAHs) were determined by gas chromatography with a mass spectrometry detector (GC/MS). The sum of PAHs concentration ranged from 7.3 to 92.8μgkg(-1) in dry weight. The positive correlation (Pearson test) between the total organic material (TOM) and the total PAH concentration (0.98) suggests that TOM plays an important role in controlling the PAHs levels in the sediments. According to the observed ratios of individual PAHs, the contamination in the studied area is originated, predominantly pyrolytic sources. The values found are considered under normal levels and indicates a not impacted area.     

X-ray observations of gamma-ray burst sources

We report on preliminary results of EXOSAT observations of three gamma-ray burst error boxes. No source was detected down to a limit of 10^–10 erg cm^–2s^–1, assuming a black-body spectrum for the burst counterpart. Results are interpreted in the framework of current theoretical models.Paper presented at the 11th European Regional Astronomical Meetings of the IAU on New Windows to the Universe, held 3–8 July, 1989, Tenerife, Canary Islands, Spain.