Comparative phylogeography of African rain forest trees: A review of genetic signatures of vegetation history in the Guineo-Congolian region

The biogeographic history of the African rain forests has been contentious. Phylogeography, the study of the geographic distribution of genetic lineages within species, can highlight the signatures of historical events affecting the demography and distribution of species (i.e. population fragmentation or size changes, range expansion/contraction) and, thereby, the ecosystems they belong to. The accumulation of recent data for African rain forests now enables a first biogeographic synthesis for the region. In this review, we explain which phylogeographic patterns are expected under different scenarios of past demographic change, and we give an overview of the patterns detected in African rain forest trees to discuss whether they support alternative hypotheses regarding the history of the African rain forest cover. The major genetic discontinuities in the region support the role of refugia during climatic oscillations, though not necessarily following the classically proposed scenarios. We identify in particular a genetic split between the North and the South of the Lower Guinean region. Finally we provide some perspectives for future study.     

Reaction rims of orthopyroxene and plagioclase around chrome spinels in olivine from Skye and Rhum (NW Scotland)

Reaction between chrome spinel and its supernatant magma due to changes in magmatic composition or temperature is well known; its effects can be observed in these rocks. However, evidence of solid-solid reaction between chrome spinels and enclosing olivine is also present, in the form of relict diffusion profiles in some of the olivines, and an orthopyroxene reaction product rimming the spinel. In addition, the Rhum specimens contain rims of plagioclase resulting from solid-liquid reaction around chrome spinels within the margins of olivine. Detailed microprobe traverses and analysis of reaction products have been made in an attempt to determine the equations for these reactions.     

Cordieritite and Leucogranite Formation during Emplacement of Highly Peraluminous Magma: the El Pilon Granite Complex (Sierras Pampeanas, Argentina)

Cordieritites and highly peraluminous granites within the ElPilón granite complex, Sierras Pampeanas, Argentina,were emplaced during a medium-P, high-T metamorphic event duringthe initial decompression of a Cambrian orogen along the southwesternmargin of Gondwana. Very fresh orbicular and massive cordierititebodies with up to 90% cordieritite are genetically associatedwith a cordierite monzogranite pluton and a larger body of porphyriticgranodiorite. The petrogenesis of this association has beenstudied using petrographical, mineralogical, thermobarometric,geochemical, geochronological and isotope methods. The graniticmagmas were formed by anatexis of mid-crustal metamorphic rocksformed earlier in the Pampean orogeny. The cordieritites appearat the top of feeder conduits that connected the source regionlocated at     

3d transition metal L-edge X-ray absorption studies of the dichalcogenides of Fe, Co and Ni

The X-ray absorption spectra of the transition metal L_3,2-edges of the dichalcogenides FeS₂ (pyrite), FeSe₂, FeTe₂, CoS₂, CoSe₂, CoTe₂, NiS₂, NiSe₂ and NiTe₂ have been studied. These spectra are compared with theoretical simulations make using the atomic multiplet approach assuming on octahedral site for the metal atoms. The Ni spectra can be closely simulated using this approach but the Fe and Co spectra show less good fits to the experimental data. The reasons for this and its implications for the use of L-edge spectra in the study of such minerals are discussed in terms of the covalency and the ground states of the compounds; these results indicate the mixing of the ground states increases in the order Ni<Co<Fe.     

Weathering of ilmenite from Chavara deposit and its comparison with Manavalakurichi placer ilmenite,southwestern India

The magnetic fractions of ilmenite from the beach placer deposit of Chavara, southwest India have been studied for mineralogical and chemical composition to assess the range of their physical and chemical variations with weathering. Chavara deposit represents a highly weathered and relatively homogenous concentration. Significant variation in composition has been documented with alteration. The most magnetic of the fractions of ilmenite, separated at 0.15 Å, and with a susceptibility of 3.2 × 10^?6 m³ kg^?1, indicates the presence of haematite–ilmenite intergrowth. An iron-poor, titanium-rich component of the ilmenite ore has been identified from among the magnetic fractions of the Chavara ilmenite albeit with an undesirably high Nb₂O₅ (0.28%), Cr₂O₃ (0.23%) and Th (149 ppm) contents. The ilmenite from Chavara is compared with that from the nearby Manavalakurichi deposit of similar geological setting and provenance. The lower ferrous iron oxide (2.32–14.22%) and higher TiO₂ (56.31–66.45%) contents highlight the advanced state of alteration of Chavara. This is also evidenced by the relatively higher Fe³⁺/Fe²⁺ ratio compared to Manavalakurichi ilmenite. In fact, the ilmenite has significantly been converted to pseudorutile/leucoxene.     

Influence of rotational darkening on ultraviolet interstellar extinction

Der Einfluß der Rotationsverdunklung schnell rotierender Sterne wird einer Neudiskussion unterzogen. Dafür werden filterphotometrische Helligkeiten vom Satelliten ANS herangezogen. Von schwach verfärbten B Sternen (E(B - V) 0.1 mag) wurden die Helligkeiten vom Einfluß der interstellaren Extinktion befreit. Die Verleilung der Sterne im Rotationsgeschwindigkeits-Farbenindex-Diagramm weist eine Streuung auf, die den Betrag der photometrischen Fehler übersteigt. Die Lage der Sterne im Rotationsgeschwindigkeits-Farbenindex-Diagramm befindet sich in qualitativer Übereinstimmung mit entsprechenden theoretischen Resultaten. Bei der Diskussion von individuell abweichenden Verläufen der interstellaren Extinktion vom durchschnittlichen Extinktionsgesetz sollte der Einfluß der Rotationsverdunklung als eine mögliche Quelle für die Abweichungen in Betracht gezogen und geprüft werden.     

Evidence for downflow following a coronal transient?

On 11 September 1973 a peculiar prominence was observed. The prominence displayed strong ( 50km s^–1) systematic motions toward and away from the observer. The unusual spectrographic appearance of the prominence might have been due to downflowing material lifted into the corona during an earlier coronal transient.The National Center for Atmospheric Research is sponsored by the National Science Foundation.Operated by the Association of Universities for Research in Astronomy, Inc., under contract with the National Science Foundation.     

AN ANALYTICAL SCHEME FOR CHONDRITIC METEORITES

A chemical scheme is reported for the analysis of chondritic materials and results are presented for the Cocklebiddy meteorite. Analytical problems associated with chondrite inhomogeneity including phase leaching selectivity and the completeness of individual phase attack are considered. Data obtained by this method can be used to classify chondrites according to the accepted weight and molar ratio methods (Van Schmus and Wood, 1967: Wasson, 1974) The analytical scheme uses selective leaching techniques to determine, in each sample, the chemical composition of metallic, sulphide and silicate phases. Elemental concentrations are obtained by atomic absorption spectrometry, flame photometry, spectrophotometry or titration techniques, and the total sample average compositions are determined on fully oxidised specimens by XRF     

Solar wind induction in Mercury: Constraints on the formation of a magnetosphere

The discovery of Mercury's magnetosphere by Mariner 10 was surprising since the conventional view of regenerative planetary dynamos had been that the spin requirement would likely have been in excess of the observed spin rate of Mercury. Also internal fluid motions were not expected to be sufficiently large. This paper explores the alternative model of the formation of Mercury's magnetosphere via electromagnetic induction forced by the solar wind. It is shown, however, that the constraints are so severe as to limit severely the applicability of such a model. Although induction is easily observed on the Moon, the modification of the magnetic boundary condition associated with a plasma magnetosphere on Mercury rules out its formation via induction except for interplanetary driving fields which are decreasing in amplitude. That model is explored but retains the difficulty that induced magnetospheres tend to be of small radial and temporal extent compared to that inferred by Ness et al. for Mercury.