Remplacements isomorphiques par synthèses hydrothermales dans les silicates fluores: Topaze et zunyite

The substituted topaz Al₂GeO₄(OH,F)₂, Al₂(Si_xGe_1-x)O₄(OH,F)₂ and Ga₂GeO₄(OH,F)₂, as well as the substituted zunyite Al₁₃Ge₅O₂₀(OH,F)₁₆F₂Cl have been synthetised. The unit-cell parameters of these artificial minerals, isomorphs of natural compounds, have been determined; the corresponding lists of d_hkl are given. The study by I.R. spectroscopy of these compounds with a total or a partial replacement of Si by Ge in the same way as Ga-Ge topaz suggests the assignment of certain absorption bands to characteristic structural groups. The thermal decomposition of AlSi and AlGe topaz into mullite has been studied.     

Outline of the geology of the Cape Verde Archipelago

The Cape Verde Archipelago, totalling 4033km², lies some 460km WNW from Dakar, West Africa. Topography, relief and geomorphologic development enable the islands to be placed into two major groups, indicative of their respective ages.The islands are overwhelmingly of igneous constitution, with basic volcanics and pyroclastics comprising some 83% of the total area, and sedimentary rocks amounting to some 9%. Volcanics and plutonics are distinctly basic in character, the archipelago representing a soda-alkaline petrographic province, with a petrologic succession similar to that in other Atlantic islands.Rocks perhaps as old as the Mahn, most certainly Neocomian, are present in the island of Maio, and here are found the highest dips and greatest thicknesses of sedimentary rocks. Post-Aptian Cretaceous, Palaeogene and Neogene are only sporadically represented, and indeed it can be questioned wheter any sediments are of these ages.Fogo is an active volcano, last erupting in 1951. The 8 km diameter caldera, at an elevation of 1600 m with an interior cone rising to 2829 m, is thought to have resulted from subsidence of a large cylindrical block, the feeding magma chamber lying at a depth of some 8 km.The archipelago probably dates back some 180 m. y., with an older and younger volcanic episode, the latter probably of late Neogene times.

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Zusammenfassung Der Kapverden-Archipel, insgesamt 4033 km² umfassend, liegt ca. 460 km WNW von Dakar, Westafrika. Nach Topographie, Relief und geomorphologischer Entwicklung lassen sich die Inseln auf zwei größere Gruppen verteilen, die einen Hinweis auf ihr Alter geben.Die Insekt bestehen überwiegend aus Erstarrungsgesteinen. Aus basischen Ergußgesteinen und Tuffen sind gegen 83% der Gesamtfläche aufgebaut, während Sedimentgesteine etwa 9% bedecken. Erguß- und Tiefengesteine sind deutlich basischer Natur; die Inselgruppe bildet eine natron-alkalische petrographische Provinz mit einem Differentiationsverlauf ähnlich dem anderer atlantischer Vulkaninseln.Gesteine, vielleicht des Malms, sicher des Neokoms, finden sich auf der Insel Maio; sie zeigen das steilste Einfallen und die größten Mächtigkeiten unter den Sedimentgesteinen. Kreide jünger als Alb, Paläogen und Neogen sind nur sporadisch vertreten; die Existenz von Sedimenten dieses Alters kann vielleicht überhaupt in Zweifel gezogen werden.Fogo ist ein aktiver Vulkan; der letzte Ausbruch erfolgte 1951. Die in 1600 m Höhe gelegene Caldera mit 8 km Durchmesser, in der sich ein auf 2829 m ansteigender Innenkegel erhebt, wird auf das Einsinken eines großen zylindrischen Blocks zurückgeführt. Der Magmaherd dürfte in einer Tiefe von ca. 8 km liegen.Die Entstehung des Archipels begann wahrscheinlich vor etwa 180 Millionen Jahren. Seine Geschichte weist eine ältere und eine jüngere vulkanische Periode auf, die letztere wahrscheinlich spät-neogenen Alters.

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Résumé L'Archipel du Cap-Vert, qui se monte à 4033 km², se trouve à 460 km ONO de Dakar, l'Afrique Occidentale. La topographie, le relief et un développement géomorphologique nous permet à classer les îles en deux groupes principaux, indiquant leurs âges respectifs.Les îles sont composées principalement des roches ignées. Les roches volcaniques basiques et les roches pyroclastiques comprendent environ 83% de la superficie totale, tandis que les roches sédimentaires n'en causent qu'environ 9%. Les roches volcaniques et les roches plutoniques sont d'un caractère distinctivement basiques, l'archipel représentant une province pétrographique soude-alcaline, avec une suite pétrologique semblable à celle des autres îles atlantiques.Les roches, peut-être aussi vieilles que le Malm, mais certainement de l'âge Néocomien, sont présentes dans l'île de Maio, et ici se trouvent les plus hautes plongées et l'épaisseur maximum des roches sédimentaires. Le Crétacé post-Aptien, le Paléogène et le Néogène ne sont représentés que sporadiquement et même on n'est pas certain s'il y a des sédiments de ces âges.Fogo est un volcan actif, ayant fait sa dernière éruption en 1951. La caldéra, située à une hauteur de 1600 m, avec un diamètre de 8 km, et dans laquelle s'élève un cône intérieur d'une hauteur de 2829 m, est probablement le résultat de l'affaissement d'un grand bloc cylindrique, la chambre magmatique « fournissante » située à une profondeur de 8 km.La naissance de cet archipel remonte probablement à quelques 180 m. a. Son histoire montre une période volcanique ancienne et une période plus récente, celle-ci datant peut-être de l'époque néogène.

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Kapverden, 4033 ², 460 WNW Dakar, . , , . , . ., . 83% ; 9%. . - , . Maio. . , . .Fogo — ; 1951 . , 1600 8 , 2829 , . 8 . 180 . , , , - .

     

A radar survey of M- and X-class asteroids

We observed ten M- and X-class main-belt asteroids with the Arecibo Observatory's S-band (12.6 cm) radar. The X-class asteroids were targeted based on their albedos or other properties which suggested they might be M-class. This work brings the total number of main-belt M-class asteroids observed with radar to 14. We find that three of these asteroids have rotation rates significantly different from what was previously reported. Based on their high radar albedo, we find that only four of the fourteen—16 Psyche, 216 Kleopatra, 758 Mancunia, and 785 Zwetana—are almost certainly metallic. 129 Antigone has a moderately high radar albedo and we suggest it may be a CH/CB/Bencubbinite parent body. Three other asteroids, 97 Klotho, 224 Oceana, and 796 Sarita have radar albedos significantly higher than the average main belt asteroid and we cannot rule out a significant metal content for them. Five of our target asteroids, 16 Psyche, 129 Antigone, 135 Hertha, 758 Mancunia, and 785 Zwetana, show variations in their radar albedo with rotation. We can rule out shape and composition in most cases, leaving variations in thickness, porosity, or surface roughness of the regolith to be the most likely causes. With the exception of 129 Antigone, we find no hydrated M-class asteroids (W-class; Rivkin, A.S., Howell, E.S., Lebofsky, L.A., Clark, B.E., Britt, D.T., 2000. Icarus 145, 351-368) to have high radar albedos.     

Temporospatial dynamics and public health significance of bacterial flora identified on a major leatherback turtle (Dermochelys coriacea) nesting beach in the Southern Caribbean

Grande Riviere beach, on the island of Trinidad, supports the largest nesting population of leatherback turtles in the Caribbean region. Throughout the nesting season, nests are naturally disturbed by newly nesting females, resulting in egg breakage and loss of some nest viability. This environment is ideal for the growth and proliferation of microorganisms. The range of bacterial flora present in beach sand and egg shells was examined, with emphasis on bacteria that may pose a threat to public and animal health. The extent to which the bacterial load and genera on the beach changed throughout the season was also assessed. Twenty‐five genera were identified, with Pseudomonas spp. found to be the most predominant environmental bacteria. Four genera identified possess zoonotic potential, while five additional genera are known to be of public and animal health significance. Distinct shifts in the density and distribution of bacteria were observed along the beach from early to peak nesting season. Shifts were seen across heavily traversed zones, thus highlighting the potential exposure threats posed to beach visitors and animals alike. Further studies aimed at speciating this population of bacteria, as well as isolating potential fungal pathogens may mitigate this threat. Identification of bacterial agents that are specifically pathogenic to leatherback turtles, turtle eggs, hatchlings and those who may interact with these animals will serve to enhance and guide efforts to better conserve this species and protect the health of all who visit this ecologically significant site.     

Comet Machholz (C/2004 Q2): morphological structures in the inner coma and rotation parameters

Extensive observations of comet C/2004 Q2 (Machholz) were carried out between August 2004 and May 2005. The images obtained were used to investigate the comet’s inner coma features at resolutions between 350 and 1500 km/pixel.     

Perceived effects of climate change on profit efficiency among small scale chili pepper marketers in Benue State,Nigeria

GeoJournal - In the determination of the level of efficiency of an enterprise, the role of climate change cannot be overemphasized. However, some scholars are of the view that climate change might...