Joint IGCP 499/SDS Meeting     

Peter konigshof Eberhard Schidler Volker Wilde Jurga Lazauskiene M.Namik Yalicn 《《幕》》2006,29(2):134-134

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GPS volcano deformation monitoring     

Volker Janssen 《GPS Solutions》2002,6(1-2):128-130

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Cosmic reionization by stellar sources: Population II stars     

Aaron Sokasian  Tom Abel  Lars Hernquist  Volker Springel 《Monthly notices of the Royal Astronomical Society》2003,344(2):607-624

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Rigid unit modes in the molecular dynamics simulation of quartz and the incommensurate phase transition     

Frank Stefan Tautz  Volker Heine  Martin T. Dove  Xiaojie Chen 《Physics and Chemistry of Minerals》1991,18(5):326-336

A molecular dynamics simulation of quartz at different temperatures both in the a and in the phase has been conducted. The - phase transition could be observed. A phonon analysis of the -phase confirms and rounds out in a quantitative way the origin of the incommensurate (ic) modulated phase. In particular it traces the optic soft mode at becoming (to a good approximation) a so-called rigid unit mode (RUM) at q0, and elucidates its coupling to the transverse acoustic mode which precipitates the incommensurate transition. This success underpins and illuminates the concept of RUMs and their role in structural phase transitions.  相似文献   

Palaeobotanical evidence of wildfires in the Late Palaeozoic of South America – Early Permian, Rio Bonito Formation, Paraná Basin, Rio Grande do Sul, Brazil     

Andr Jasper  Dieter Uhl  Margot Guerra-Sommer  Volker Mosbrugger 《Journal of South American Earth Sciences》2008,26(4):435-444

Fossil charcoal, as direct evidence of palaeowildfires, has repeatedly been reported from several plant-bearing deposits from the Late Palaeozoic of the Northern Hemisphere. In contrast charcoal reports from the Late Palaeozoic deposits of the Southern Hemisphere are relatively rare in comparison to the Northern Hemisphere. Although the presence of pyrogenic coal macerals has repeatedly been reported from Late Palaeozoic coals from South America, no detailed anatomical investigations of such material have been published so far. Here is presented an anatomical analysis of charcoal originating from Early Permian sediments of the Quitéria Outcrop, Rio Bonito Formation, Paraná Basin, located in the central-eastern portion of Rio Grande do Sul, Brazil. This charcoal comes from two different coaly facies, and it was possible to scrutinize between three types, based on anatomical characters of the charcoal. Two of these charcoal types can be correlated to gymnosperm woods, and the other type corresponds to strongly permineralized bark with characteristic features of lycopsids. The presence of charcoal in different facies, ranging from parautochtonous to allochtonous origin, indicates that different vegetation types, i.e. plants which grew under wet conditions in the lowland as well as in the more dry hinterland, have experienced wildfires. Taking into account previous petrographic and lithological analyses from the facies in which the charcoal occurs and from the conditions of the wood and bark fragments, it was possible to speculate that the intensity of such wildfires most probably corresponds to forest-crown fires. Moreover, it is possible to state that wildfires have been a more or less common element in distinct Late Palaeozoic terrestrial ecosystems in the South American part of Gondwana. The data support previous assumptions on the occurrence of wildfires in the Early Permian of the Paraná Basin which were based solely on coal-petrographic data.  相似文献   

Spring-spawning herring (Clupea harengus L.) in the southwestern Baltic Sea: do they form genetically distinct spawning waves?     

Hede Jorgensen  Hanne B.; Hansen  Michael Moller; Loeschcke  Volker 《ICES Journal of Marine Science》2005,62(6):1065-1075

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Arctic Coastal Dynamics (ACD): an introduction     

Volker Rachold  Feliks E. Are  David E. Atkinson  Georgy Cherkashov  Steven M. Solomon 《Geo-Marine Letters》2005,25(2-3):63-68

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The solubility of [4H]Si defects in α-quartz and their role in the formation of molecular water and related weakening on heating     

J. D. C. McConnell  J. S. Lin  Volker Heine 《Physics and Chemistry of Minerals》1995,22(6):357-366

The nature of the solubility of water as [4H]_Si defects in quartz, and their role in providing a source of molecular water on heating, is investigated. Existing ab inito energy calculations on the incorporation of water in quartz are used to show that energetically 4H for Si substitution is likely to constitute the most prevalent mode of water uptake on the atomic scale in quartz under equilibrium conditions, and that the planar defects previously observed by a number of different authors by electron microscopy in wet quartz are likely to be planar rafts of aggregated [4H]_Si defects which are formed on supersaturation. These new conclusions call into question the previous identification of the planar defects as high pressure water clusters and require that their role in the production of molecular water in the context of recent theories of hydrolytic weakening be re-assessed. Accordingly the existing ab initio results have been used to establish the characteristics of the phase diagram for the system quartz-water in the temperature and pressure range of interest in hydrolytic weakening. Additional electron-optical experiments on wet quartz show that, on annealing at temperature in the electron microscope, similar planar defects develop in wet quartz by a diffusion process. In the context of existing theories of hydrolytic weakening it is now proposed that the conversion of [4H]_Si defects to molecular water, where this is dictated by the equilibrium phase diagram, leads to a relatively large increase in volume and to the appearance of the bubbles of free water and the nucleation of associated prismatic dislocation loops of Burgers vector b=1/3 a $\langle 11\bar 20\rangle $ as previously observed. Ultimately the development of these loops leads to dislocation-induced plasticity.  相似文献   

Electrical resistivity structure of the eastern Moroccan Atlas System and its Tectonic implications     

G. Schwarz  H. G. Mehl  F. Ramdani  V. Rath 《International Journal of Earth Sciences》1992,81(1):221-235

The electrical resistivity structure of the crust and upper mantle of the Atlas Mountain System was studied using magnetotelluric and geomagnetic deep soundings. Field experiments were done in eastern Morocco along a traverse from the Anti Atlas to the Rides Rifaines in two campaigns in 1983 and 1988.Zones of very low electrical resistivity could be identified in the various structural settings at different depth ranges, most likely connected directly to the tectonic evolution of the mountain belts. A mid-crustal low resistivity layer with total conductance (thickness-resistivity ratio) of about 2000 Siemens stretches from the southern border of the High Atlas towards the Middle Atlas. This layer seems to characterize the base of crustal detachment, e.g., the plane for large horizontal overthrusting, and supports the idea of thick- and thin-skinned tectonics involved in Atlasic mountain building. In the western Middle Atlas an upper-crustal low resistivity layer (at depth < 10 km) was found in the area where volcanic activity was present, pointing towards a direct relation between low electrical resistivity and volcanic or postvolcanic events. North of the Middle Atlas resistivity structures change totally: The Pre and parts of the Sub-Rif have a highly conductive cover, presumably connected to the molasse basin. Total conductance was calculated to reach 6000 Siemens. No further conductive structures, like, e.g., the ones found beneath the High and Middle Atlas, are seen within the resistive crust, but at much greater depth within the upper mantle.

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Zusammenfassung Im marokkanischen Atlas-System wurde der elektrische Widerstand der Kruste und des oberen Mantels mit magnetotellurischen und erdmagnetischen Tiefen-Sondierungen erkundet. Die Feldmessungen wurden in den Jahren 1983 und 1988 im östlichen Marokko entlang einer Traverse vom Anti Atlas bis in das Rif durchgeführt.In den einzelnen strukturellen Einheiten wurden in unterschiedlichen Krustentiefen Schichten sehr kleiner elektrischer Widerstände entdeckt, die direkt mit der tektonischen Entwicklung des Atlasgebirges verknüpft zu sein scheinen. Zwischen dem Südrand des Hohen Atlas und dem Mittleren Atlas im Norden erstreckt sich eine Zone sehr kleiner Widerstände (integrierte Leitfähigkeit etwa 2000 Siemens) in mittleren Krustentiefen. Diese Schicht scheint einen Bereich krustaler Ablösung zu kennzeichnen und kann als Basis einer weitspannigen Überschiebung angenommen werden. Diese Form der »thick- & thin-skinned« Tektonik scheint wesentlich am Prozess der Gebirgsbildung im Atlas beteiligt zu sein. Im westlichen Mittleren Atlas, im Bereich des jungen Vulkanismus, wurde eine gutleitende Zone in der oberen Kruste (Tiefe < 10 km) gefunden. Diese Beobachtung legt einen direkten Zusammenhang zwischen erhöhter elektrischer Leitfähigkeit und vulkanischen bzw. postvulkanischen Ereignissen nahe. Nördlich des Mittleren Atlas ändern sich die Widerstandsstrukturen sehr stark: Im Prä- und teilweise auch noch im Sub-Rif liegt eine sehr gut leitende Deckschicht (integrierte Leitfähigkeit etwa 6000 Siemens) über einem hochohmigen Basement. In der Kruste des Rif werden keine weiteren, tieferliegenden Schichten erhöhter Leitfähigkeit gefunden, wie sie z.B. unter dem Hohen Atlas vorliegen. Dagegen gibt es Hinweise auf Zonen hoher Leitfähigkeit im oberen Mantel.

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Résumé Dans l'Atlas marocain la résistivité électrique de la croûte et du manteau supérieur a été étudiée à l'aide des sondages magnétotelluriques et géomagnétiques. Ces travaux ont été effectués le long d'une traverse menant de l'Anti-Atlas jusqu'au Rif durant les années 1983 et 1988.Dans différentes profondeurs de la croûte terrestre des zones de résistances électriques très basses ont pu être découvertes ce qui peut être attribué à l'évolution tectonique de l'Atlas. Une couche de résistances très basses (conductance vers 2000 Siemens) s'étend entre le bord au sud du Haut Atlas et l'Atlas Moyen au nord. Cette couche peut être le signe d'un détachement de l'écorce et d'une poussée très vaste. Cette forme tectonique »thick- & thin-skinned« semble être essentiellement responsable du processus de la formation orogénique de l'Atlas. Une zone de bonne conductance se trouve dans la croûte terrestre supérieure (profondeur < 10 km) dans l'ouest de l'Atlas Moyen aux environs de l'activité volcanique caractérisant une relation directe entre une haute conductance électrique et des événements volcaniques et post-volcaniques. Vers le nord de l'Atlas Moyen les structures de résistance subissent un changement total: Au Pré- et partiellement aussi au Subrif se trouve une bonne couche guide (conductance vers 6000 Siemens). Aucune autre couche de conductance supérieure — comme au-dessous du Haut Atlas — n'a été découverte dans la croûte du Rif. On en décèle, par contre, dans le manteau supérieur.

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Streams in the Harz National Parks (Germany) — a hydrochemical and hydrobiological evaluation     

Uta Langheinrich  Dirk Bhme  Uwe Wegener  Volker Lüderitz 《Limnologica》2002,32(4):309-321

Between 1995 and 2001, 16 measuring points at small and medium sized brooks in the Harz National Parks were sampled. The samples have been evaluated by means of hydrochemistry and macroinvertebrate biology. Although nearly all streams are largely uncontaminated by oxygen-consuming substances, they are settled only by a small number of macroinvertebrate species. There is a clear correlation between this number and pH. The reduction in species number with decrease of pH is mainly caused by the absence of most Ephemeroptera, some Coleoptera and Trichoptera. Comparing biological evaluation of acidity with physico-chemical measurements, a unacceptable underestimation was found. The reason could be that different sensitivities to acidification between regional populations seem to exist.

Despite of the low species number, there is a very specific macroinvertebrate fauna that emphasizes the conservation value of the Harz National Parks.  相似文献