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381.
382.
The proposals for a European policy framework for Geographic Information (GI) recently put forward by Directorate General XIII raise three sets of issues about measures required to facilitate the dissemination of GI in the European Union: (1)'hot topics' such as privacy and the legal protection of databases that apply to information generally; (2) GI issues such as reference data and metadata services that may require action by the European Commission; and (3) perceived barriers to the development of a European GI market. This paper examines the views of 20 experts responsible for the provision and management of GI in key organizations throughout Europe. A Delphi-style strategy was used to identify the relative importance of the issues raised by the proposals and to ascertain the level of agreement as to the importance of these issues between the experts. The results show that issues relating to copyright, the protection of intellectual property rights, data quality, and data access policies were ranked highly by most of the respondents. A lack of awareness, education, and training (as opposed to the lack of public domain data and metadata services) were viewed as the main barriers to the deveiopment of the GI market in Europe. 相似文献
383.
Constant sets for several turbulence closure models,based on data for the atmospheric boundary layer, areproposed. They differ from those currently used inengineering situations but are self-consistent andtuned to represent atmospheric boundary-layerturbulence. The proposed constant sets are tested in a simple,one-dimensional, neutrally-stratified planetaryboundary-layer flow over a horizontally homogeneousand aerodynamically rough flat surface. Comparisons ofmodel results with similarity theory and large-eddysimulation show promise for improving boundary-layerpredictions. 相似文献
384.
The effect of rain on air-water gas exchange 总被引:5,自引:0,他引:5
385.
Microprobe analyses of the oxide mineral assemblages from monzonitic,granodioritic, and granitic units of the Finnmarka igneous complex,Oslo area, Norway, disclose a remarkable trend of Mn enrichmentin ilmenite with differentiation. Ilmenite-pyrophanite solidsolutions containing up to 63 mole per cent MnTiO3 have developedunder apparently unusually oxidizing conditions, a conclusiondeduced in part from the fact that Fe2+ is more readily oxidizedthan Mn2+ and was thus preferentially extracted. Several differentmineral reactions may have been involved in this process. Geothermometricapplications of oxide Mn contents must be made with caution. Additional mineralogic complexities, e.g. ilmenite lamellaein magnetite, magnetite lamellae in ilmenite, and, in the granite,the breakdown of ilmenite to rutile+hematite, all provide insightinto the conditions of emplacement and cooling history of thecomplex. 相似文献
386.
PETER WIGLEY 《Sedimentology》1973,20(2):295-304
The Sr2+ content of Barbudan limestones is proportional to the aragonite content. The Sr2+ content of calcite which has replaced aragonite varies from 3000 p.p.m. in the youngest limestones to 50 p.p.m., average values are approximately 300 p.p.m. The (mSr2+/mCa2+)L ratios from well waters within the limestone fall within the predicted values assuming KSrC~0·1. The high (mSr2+/mCa)2+L ratios expected by a lower value of KSrC do not occur. The build up of (mSr2+/mCa2+)L ratios seen in waters from Barbados is not seen in the well waters from Barbuda. The Sr2+ content of calcite is generally lower than is seen in Barbados, but similar to that seen in parts of the Miami Oolite. Diagenesis of aragonite in Barbudan limestones is probably occurring in a more open system than in Barbados. 相似文献
387.
388.
New insight into the evolution of large-volume turbidity currents: comparison of turbidite shape and previous modelling results 总被引:2,自引:0,他引:2
The Marnoso Arenacea Formation provides the most extensive correlation of individual flow deposits (beds) yet documented in an ancient turbidite system. These correlations provide unusually detailed constraints on bed shape, which is used to deduce flow evolution and assess the validity of numerical and laboratory models. Bed volumes have an approximately log‐normal frequency distribution; a small number of flows dominated sediment supply to this non‐channelized basin plain. Turbidite sandstone within small‐volume (<0·7 km3) beds thins downflow in an approximately exponential fashion. This shape is a property of spatially depletive flows, and has been reproduced by previous mathematical models and laboratory experiments. Sandstone intervals in larger‐volume (0·7–7 km3) beds have a broad thickness maximum in their proximal part. Grain‐size trends within this broad thickness maximum indicate spatially near‐uniform flow for distances of ∼30 km, although the flow was temporally unsteady. Previous mathematical models and laboratory experiments have not reproduced this type of deposit shape. This may be because models fail to simulate the way in which near bed sediment concentration tends towards a constant value (saturates) in powerful flows. Alternatively, the discrepancy may be the result of relatively high ratios of flow thickness and sediment settling velocity in submarine flows, together with very gradual changes in sea‐floor gradient. Intra‐bed erosion, temporally varying discharge, and reworking of suspension fallout as bedload could also help to explain the discrepancy in deposit shape. Most large‐volume beds contain an internal erosion surface underlain by inversely graded sandstone, recording waxing and waning flow. It has been inferred previously that these characteristics are diagnostic of turbidites generated by hyperpycnal flood discharge. These turbidites are too voluminous to have been formed by hyperpycnal flows, unless such flows are capable of eroding cubic kilometres of sea‐floor sediment. It is more likely that these flows originated from submarine slope failure. Two beds comprise multiple sandstone intervals separated only by turbidite mudstone. These features suggest that the submarine slope failures occurred as either a waxing and waning event, or in a number of stages. 相似文献
389.
Rates and Processes of Potassic Magma Evolution beneath Sangeang Api Volcano, East Sunda Arc, Indonesia 总被引:11,自引:3,他引:11
TURNER SIMON; FODEN JOHN; GEORGE RHIANNON; EVANS PETER; VARNE RICK; ELBURG MARLINA; JENNER GEORGE 《Journal of Petrology》2003,44(3):491-515
U-series isotopes can provide unique insights into the physicalprocesses of magma evolution by constraining the time scalesover which they operate. This, however, requires rock suitesthat provide a clear and complete record of the liquid lineof descent. Sangeang Api volcano, in the east Sunda arc, providessuch an opportunity because it erupts potassic lavas (SiO2 相似文献
390.
ANSGAR GRESHAKE WOLFGANG KL
CK PETER ARNDT MISCHA MAETZ GEORGE J. FLYNN SASA BAJT ADDI BISCHOFF 《Meteoritics & planetary science》1998,33(2):267-290
Abstract— Depending on their velocity, entry angle and mass, extraterrestrial dust particles suffer certain degrees of heating during entry into Earth's atmosphere, and the mineralogy and chemical composition of these dust particles are significantly changed. In the present study, pulse-heating experiments simulating the atmospheric entry heating of micrometeoroids were carried out in order to understand the mineralogical and chemical changes quantitatively as well as to estimate the peak temperature experienced by the particles during entry heating. Fragments of the CI chondrites Orgueil and Alais as well as pyrrhotites from Orgueil were used as analogue material. The experiments show that the volatile elements S, Zn, Ga, Ge, and Se can be lost from 50 to 100 μm sized CI meteorite fragments at temperatures and heating times applicable to the entry heating of similar sized cosmic dust particles. It is concluded that depletions of these elements relative to CI as observed in micrometeorites are mainly caused by atmospheric entry heating. Besides explaining the element abundances in micrometeorites, the experimentally obtained release patterns can also be used as indicators to estimate the peak heating of dust particles during entry. Using the abundances of Zn and Ge and assuming their original concentrations close to CI, a maximum heating of 1100–1200 °C is obtained for previously analyzed Antarctic micrometeroites. Thermal alteration also strongly influenced the mineralogy of the meteorite fragments. While the unheated samples mainly consisted of phyllosilicates, these phases almost completely transformed into olivine and pyroxene in the fragments heated to ≥800 °C. Therefore, dust particles that still contain hydrous minerals were probably never heated to temperatures ≥800 °C in the atmosphere. During continued heating, the grain size of the newly formed silicates increased and the composition of the olivines equilibrated. Applying these results quantitatively to Antarctic micrometeorites, typical peak temperatures in the range of 1100–1200 °C during atmospheric entry heating are deduced. This temperature range corresponds to the one obtained from the volatile element concentrations measured in these micrometeorites and points to an asteroidal origin of the particles. 相似文献