IV. Bücher- und Zeitschriftenschau

Ohne Zusammenfassung     

Bücher- und Zeitschriftenschau

Ohne Zusammenfassung     

Imaging of the Structure and Evolution of the Coma Morphology of Comet Hale–Bopp (C/1995 O1)

Imaging of coma morphology of Comet Hale-Bopp from pre-perihelion through perihelion to post-perihelion is presented. Broad band images from 1996 and late 1997 show nearly radial jets streaking out from the nucleus. During both 1996 and late 1997, the brightest jets are approximately in a northern/northeastern direction. The slight curvature present in these radial jets is consistent with radiation pressure effects. Narrow band images around perihelion show two distinctive pictures of the CN and the continuum coma morphology. Spirals are clearly seen in the CN images but not in the continuum where structure is confined to the sunward side. The CN structure is consistent with continuous outgassing of the source of CN from the nucleus during both day and night. This revised version was published online in July 2006 with corrections to the Cover Date.     

The role of hydrogeological setting in two Canadian peatlands investigated through 2D steady-state groundwater flow modelling

This study investigated how hydrogeological setting influences aquifer–peatland connections in slope and basin peatlands. Steady-state groundwater flow was simulated using Modflow on 2D transects for an esker slope peatland and for a basin peatland in southern Quebec (Canada). Simulations investigated how hydraulic heads and groundwater flow exported toward runoff from the peatland can be influenced by recharge, hydraulic properties, and heterogeneity. The slope peatland model was strongly dominated by horizontal flow from the esker. This suggests that slope peatlands are dependent on the hydrogeological conditions of the adjacent aquifer reservoir, but are resilient to hydrological changes. The basin peatland produced groundwater outflow to the surface aquifer. Lateral and vertical peat heterogeneity due to peat decomposition or compaction were identified as having a significant influence on fluxes. These results suggest that basin peatlands are more dependent on recharge conditions, and could be more susceptible to land use and climate changes.     

P-T stability of the lazulite-scorzalite solid-solution series

Summary The stability of members of the lazulite-scorzalite solid-solution series, (Mg,Fe)Al₂ (OH)₂(PO₄)₂, was investigated as a function of T (505 to 675 °C), P (0.1 to 0.3 GPa) and Fe/Mg ratio in hydrothermal synthesis experiments. The oxygen fugacity was controlled by means of the Ni/NiO buffer. It was found that starting from end-member lazulite the stability of the solid-solution members strongly decreases with increasing content of scorzalite component. At 0.2 GPa pure lazulite decomposes at about 660 °C whereas at the same pressure a solid-solution with 80% of lazulite component is only stable up to 590 °C under the oxygen fugacity of the Ni/NiO buffer. The members of the lazulite-scorzalite solid-solution series with limiting composition coexist with an Fe-richer member of the (Mg,Fe)Al(PO₄)O series and berlinite. The mixing behaviour of both the lazulite-scorzalite and the (Mg,Fe)Al(PO₄)O solid-solution series disregarding small amounts of Fe³⁺ is interpreted in terms of a model on the basis of a simple mixture for the lazulite-scorzalite system and of an ideal mixture for the (Mg,Fe)Al(PO₄)O series. With this model the interaction parameter which expresses the non-ideality of the lazulite-scorzalite solid-solution series amounts to . Zusammenfassung P-T Stabilit?t von Lazulith-Scorzalith Mischkristallen Die Stabilit?t der Glieder der Lazulith-Scorzalith Mischkristallreihe, (Mg, Fe)Al₂(OH)₂(PO₄)₂ wurde als Funktion der Temperatur (505 bis 675 °C), des Druckes (0.1 bis 0.3 GPa) und des Fe/Mg-Verh?ltnisses in hydrothermalen Syntheseversuchen untersucht. Die Sauerstoffugazit?t wurde mittels eines Ni/NiO-Puffer kontrolliert. Es konnte festgestellt werden, da? ausgehend vom Lazulith-Endglied die Stabilit?t der Mischkristalle mit zunehmendem Scorzalith-Gehalt stark abnimmt. Reiner Lazulith, MgAl₂(OH)₂(PO₄)₂ zerf?llt unter 0.2 GPa bei 660 °C, w?hrend ein Mischkristall mit 80 mol% Gehalt an Lazulith-Komponente nur bis 590 °C unter der Sauerstoffugazit?t des Ni/NiO-Puffers stabil ist. Hierbei koexistieren die Lazulith-Scorzalith Mischkristalle mit Grenzzusammensetzung mit eisenreicheren Mischphasen des Systems (Mg,Fe)Al(PO₄)₂O und Berlinit. Das Mischungsverhalten sowohl der Lazulith-Scorzalith- als auch der (Mg,Fe)Al(PO₄)₂O-Reihe wurde mit Hilfe eines quantitativen Modelles auf der Basis einer symmetrischen Mischung für Lazulith-Scorzalith und einer idealen Mischung für das System (Mg,Fe)Al(PO₄)₂O interpretiert. Mit Hilfe dieses Modelles wurde der Wechelwirkungsparameter , der die Nichtidealit?t der Lazulith-Scorzalith Mischreihe ausdrückt zu bestimmt. Received August 26, 1998; revised version accepted July 30, 1999     

Predicting river water temperatures using stochastic models: case study of the Moisie River (Québec,Canada)

Successful applications of stochastic models for simulating and predicting daily stream temperature have been reported in the literature. These stochastic models have been generally tested on small rivers and have used only air temperature as an exogenous variable. This study investigates the stochastic modelling of daily mean stream water temperatures on the Moisie River, a relatively large unregulated river located in Québec, Canada. The objective of the study is to compare different stochastic approaches previously used on small streams to relate mean daily water temperatures to air temperatures and streamflow indices. Various stochastic approaches are used to model the water temperature residuals, representing short‐term variations, which were obtained by subtracting the seasonal components from water temperature time‐series. The first three models, a multiple regression, a second‐order autoregressive model, and a Box and Jenkins model, used only lagged air temperature residuals as exogenous variables. The root‐mean‐square error (RMSE) for these models varied between 0·53 and 1·70 °C and the second‐order autoregressive model provided the best results. A statistical methodology using best subsets regression is proposed to model the combined effect of discharge and air temperature on stream temperatures. Various streamflow indices were considered as additional independent variables, and models with different number of variables were tested. The results indicated that the best model included relative change in flow as the most important streamflow index. The RMSE for this model was of the order of 0·51 °C, which shows a small improvement over the first three models that did not include streamflow indices. The ridge regression was applied to this model to alleviate the potential statistical inadequacies associated with multicollinearity. The amplitude and sign of the ridge regression coefficients seem to be more in agreement with prior expectations (e.g. positive correlation between water temperature residuals of different lags) and make more physical sense. Copyright © 2006 John Wiley & Sons, Ltd.     

Yttrium geochemistry applied to petrogenesis utilizing calcium-yttrium relationships in minerals and rocks

A survey of Y data from all sources shows that Y behaves systematically in igneous, metamorphic and sedimentary rock series, due to its incorporation in a predictable and uniform manner in Ca minerals. Compared with average calc-alkali basalt melts, plagioclase, kaersutite, augitic clinopyroxene and calcite have low Y for their CaO contents; whereas hornblende, garnet, orthopyroxene, apatite, sphene, zircon and most K, Na rich minerals other than plagioclase have high Y for their Ca contents. In sedimentary processes, Ca/Y becomes lower in shales and sandstones, but higher in limestones than their source. In metamorphic processes Y appears to be inert. In all igneous series for which Y data has been assembled Ca/Y falls as Ca falls. These series can be classified into three categories: (i) a standard calc-alkali trend, used as a reference (ii) J-type trends which become progressively impoverished in Y as Ca falls when compared with the standard trend, and (iii) L-trends which become progressively enriched in Y as Ca falls when compared with the standard trend. Despite little knowledge of partition coefficients, the J-type trends appear to have a significant component of hornblende control in their fractionation processes, whereas plagioclase and augitic clinopyroxene dominate the L-type trend. Alternative names for these series might therefore be the standard series, the hornblendic and the pyroxenic series respectively. Modern ocean floor basalts appear to be significantly richer in Y than modern calc-alkali basalts, and these in turn may be richer in Y than their Archaean counterparts.     

PROBLEMS IN THE DEFINITION AND MEASUREMENT OF STREAM LENGTH

Although stream length is a fundamental property of fluvially eroded landscapes, methods of obtaining this basic measure vary; therefore, data compiled from several sources are often not comparable. Not only are measurement methods inconsistent, but there is no standaid definition of stream length itself. Most measurements are taken directly from maps where accuracy may be questionable, and air photos have proven more reliable than topographic maps. Obtaining reliable stream-length data from published sources is perhaps the most perplexing problem of all. In investigations of stream length, therefore, it is imperative that data sources, measurement techniques, and methodology be clearly defined so that results may be studied in a meaningful context.