Diurnal Variation of Gravity Wave Activity at Midlatitudes in the Ionospheric F Region     

Boška  J.  Šauli  P.  Altadill  D.  German Solé  J.  Alberca  L.F. 《Studia Geophysica et Geodaetica》2003,47(3):579-586

We investigate the short-term fluctuations in the period range from 15 to 180 minutes in the electron density variations of the F region ionosphere. Electron density profiles obtained at the ionospheric stations of Pruhonice (49.9° N, 14.5° E) and Ebro (40.8° N, 0.5° E) at five minute time sampling have been used for this analysis. The diurnal changes of the activity of the acoustic gravity wave fluctuations (AGW) show a clear enhancement during and several hours after sunrise. The periods of such AGW's are about 60 to 75 minutes and these waves propagates vertically through the ionosphere from a source located at an altitude of 180-220 km. The most likely source for these events seems to be passage of the Solar terminator.  相似文献   

Origin of nodular chert in the carbonate rocks of the Kaladgi group (younger precambrian), Karnataka,India     

S. Sathyanarayan  German Müller 《Sedimentary Geology》1980,25(3):209-221

Lensoid, irregular nodules and laminations of chert appear along the bedding planes and laminations of the Vidyanagar Dolomite Member of the Kaladgi Group, Karnataka, India. The field relations of the chert nodules with the host dolomite and evidence on polished hand-specimens clearly demonstrate that the cherts are secondary after dolomite. This contention finds extensive support from thin-sections which reveal floating relict dolomite fragments on a microcrystalline quartz mat, dolomite rhombs in various stages of progressive replacement, polycrystalline quartz rhombs apparently after dolomite. Chertification has also resulted in an aggrading neomorphic recrystallization of dolomicrite into dolomicrospar which rims the dislodged floating fragments of dolomite.Scanning electron microscopic studies revealed three distinct types of surfaces of chert; the polyhedral surface characteristic of microcrystalline quartz, the spongy surface characteristic of chalcedonic quartz (documented in thin-sections as semi-radiating to radiating aggregates of elongated crystals growing on the rhombic surfaces of dolomite, and the intermediate type showing both. The microcrystalline quartz seems to have originated through multinucleation at equally spaced centres on the dolomite mat, whereas the chalcedonic quartz originated by slow but direct and unhindered precipitation into cavities and residual pore-spaces, following dolomitisation. The silica invasion seems to have been accomplished by alkaline interstitial waters charged with silica.The occurrence and relation of chert-nodules with the host dolomite not only helps in unravelling their own origin, but also aids in drawing the dolomitisation curtain and in turn the post-dolomitisation diagenetic modifications of the host carbonates. It may be added, however, that the Kaladgi Carbonates have undergone mineralogical/textural modifications during diagenesis with superimposition of changes affected later, i.e. during tectonism which folded and cross-folded these sediments.  相似文献   

A suspended-particle rosette multi-sampler for discrete biogeochemical sampling in low-particle-density waters     

J.A. Breier  C.G. Rauch  K. McCartney  B.M. Toner  S.C. Fakra  S.N. White  C.R. German 《Deep Sea Research Part I: Oceanographic Research Papers》2009,56(9):1579-1589

To enable detailed investigations of early stage hydrothermal plume formation and abiotic and biotic plume processes we developed a new oceanographic tool. The Suspended Particulate Rosette sampling system has been designed to collect geochemical and microbial samples from the rising portion of deep-sea hydrothermal plumes. It can be deployed on a remotely operated vehicle for sampling rising plumes, on a wire-deployed water rosette for spatially discrete sampling of non-buoyant hydrothermal plumes, or on a fixed mooring in a hydrothermal vent field for time series sampling. It has performed successfully during both its first mooring deployment at the East Pacific Rise and its first remotely-operated vehicle deployments along the Mid-Atlantic Ridge. It is currently capable of rapidly filtering 24 discrete large-water-volume samples (30–100 L per sample) for suspended particles during a single deployment (e.g. >90 L per sample at 4–7 L per minute through 1 μm pore diameter polycarbonate filters). The Suspended Particulate Rosette sampler has been designed with a long-term goal of seafloor observatory deployments, where it can be used to collect samples in response to tectonic or other events. It is compatible with in situ optical sensors, such as laser Raman or visible reflectance spectroscopy systems, enabling in situ particle analysis immediately after sample collection and before the particles alter or degrade.  相似文献   

Heat,volume and chemical fluxes from submarine venting: A synthesis of results from the Rainbow hydrothermal field, 36°N MAR     

C.R. German  A.M. Thurnherr  J. Knoery  J.-L. Charlou  P. Jean-Baptiste  H.N. Edmonds 《Deep Sea Research Part I: Oceanographic Research Papers》2010,57(4):518-527

High-temperature hydrothermal activity occurs in all ocean basins and along ridge crests of all spreading rates. While it has long been recognized that the fluxes associated with such venting are large, precise quantification of their impact on ocean biogeochemistry has proved elusive. Here, we report a comprehensive study of heat, fluid and chemical fluxes from a single submarine hydrothermal field. To achieve this, we have exploited the integrating nature of the non-buoyant plume dispersing above the Rainbow hydrothermal field, a long-lived and tectonically hosted high-temperature vent site on the Mid-Atlantic Ridge. Our calculations yield heat and volume fluxes for high-temperature fluids exiting the seafloor of ～0.5 GW and 450 L s^?1, together with accompanying chemical fluxes, for Fe, Mn and CH₄ of ～10, ～1 and ～1 mol s^?1, respectively. Accompanying fluxes for 25 additional chemical species that are associated with Fe-rich plume particles have also been calculated as they are transported away from the Rainbow vent site before settling to the seabed. High-temperature venting has been found to recur at least once every ～100 km along all slow-spreading ridges investigated to-date, with half of all known sites on the Mid-Atlantic Ridge occurring as long-lived and tectonically hosted systems. If these patterns persist along all slow- and ultraslow-spreading ridges, high-temperature venting of the kind reported here could account for ～50% of the on-axis hydrothermal heat flux along ～30,000 km of the ～55,000 km global ridge crest.  相似文献   

Book reviews     

George Kish  Wolf Tietze  C. Paddick  Dietrich Barsch  Keith Clayton  Michael F. Thomas  Thomas Peucker  Alexander Zaporozec  Georg Matthess  German Müller  K. Ernstson  Olusegun Areola  Gerald M. Friedman  Maurice K. -Seguin  C. Koeman  Risto Aario 《GeoJournal》1979,3(4):410-416

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Improving neural network performance on the classification of complex geographic datasets   总被引：4，自引：0，他引：4  

Mark Gahegan  Gordon German  Geoff West 《Journal of Geographical Systems》1999,1(1):3-22

Neural Networks are now established computational tools used for search minimisation and data classification. They offer some highly desirable features for landuse classification problems since they are able to take in a variety of data types, recorded on different statistical scales, and combine them. As such, neural networks should offer advantages of increased accuracy. However, a barrier to their general acceptance and use by all but `experts' is the difficulty of configuring the network initially.  This paper describes the architectural problems of applying neural networks to landcover classification exercises in geography and details some of the latest developments from an ongoing research project aimed at overcoming these problems. A comprehensive strategy for the configuration of neural networks is presented, whereby the network is automatically constructed by a process involving initial analysis of the training data. By careful study of the functioning of each part of the network it is possible to select the architecture and initial weights on the node connections so the constructed network is `right first time'. Further adaptations are described to control network behaviour, to optimise functioning from the perspective of landcover classification. The entire configuration process is encapsulated by a single application which may be treated by the user as a `black box', allowing the network to the applied in much the same way as a maximum likelihood classifier, with no further effort being required of the user.  相似文献