Un nouveau gisement de granite orbiculaire dans le Massif Central français: le granite du Signal de Randon (Lozère)     

Jean -Pierre Couturié 《Contributions to Mineralogy and Petrology》1973,42(4):305-312

This orbicular granite contains ovoïds of an exceptional composition, comprising a core of biotite, surrounded by an envelope of plagioclase, enclosed in turn by an envelope of potassium feldspar. The latter also occurs as isolated idiomorphic megacristals between the ovoïds.Because of the spectacularly clear mineralogical relationships of the rock, it is possible to work out the order of crystallization of the minerals, the magmatic differentiation of syenitic orbicules and that of the leucogranitic groundmass with an aplito-pegmatitic texture.A magmatic process is proposed to explain the origin of the rock.

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Les déterminations de l'indice de triclinicité des feldspaths potassiques ont été effectuées par Yves Blanc, Clermont-Ferrand (diffractométrie X, d'après G. Sabatier, 1963).  相似文献   

Wassermilben aus dem Amazonasgebiet (Hydrachnellae,Acari)     

Dr. R. Braun  Dr. H. Sioli  Karl Viets 《Aquatic Sciences - Research Across Boundaries》1954,16(2):161-247

Zusammenfassung Erstmalig aus dem Amazonasgebiet wurden nach den SammlungenSioli undBraun die Hydrachnellae untersucht. Von den 104 festgestellten Arten bzw. Unterarten waren 64 neu für die Wissenschaft; 5 neue Genera bzw. Subgenera wurden aufgestellt. Durch 171 ausgewertete F?nge wurden 1033 Individuen ermittelt, eine im Vergleich mit anderen Sammlungen geringe Menge sowohl im ganzen gesehen, als auch die Individuen pro Fang betrachtet, als auch im Hinblick auf die hohe Zahl der neuen Formen in der kleinen Individuenmenge. Als Ursache dieser Diskrepanz werden neben extensivem Sammelverfahren chemisch-physikalische Faktoren der Gew?sser vermutet. Die Amazonas-Wassermilben werden nach Biotopen-stehende und fliessende Gew?sser-untersucht; dazu kommen Angaben über Frequenz, über jahreszeitliche Verteilung und das Verh?ltnis der Geschlechter. Der besondere Chemismus der Amazonasgew?sser-die im allgemeinen niedrigen pH-Werte-, dazu die klimatisch bedingte inkonstanz mancher Faktoren scheint bei der wohl grossen Toleranz der Wassermilben diesen Faktoren gegenüber weniger direkt, vielleicht aber indirekt die Nahrungstiere und damit das zahlenm?ssige Auftreten der Hydrachnellae zu beeinflussen. Ein Vergleich der Wassermilben aus den bislang untersuchten tropischen Gebieten kann noch nicht zu allgemeinen Ergebnissen gelangen, weil einheitlich zutreffende Vergleichspunkte noch kaum gegeben sind.  相似文献   

On the stability of a slow deflagration front at the surface of a degenerate star     

A. Braun  R. Z. Yahel 《Astrophysics and Space Science》1980,69(1):217-225

On the surface of a degerate star, a slow nuclear combustion process with a wake of escaping matter can exist. The evolution of this process has been studied by solving the nonadiabatic, time-dependent hydrodynamic equations. It has been found that this flow is almost stationary and is stable against small spherical symmetric perturbations.  相似文献   

Education challenges in the North Sea area     

Ducrotoy JP 《Marine pollution bulletin》2003,47(1-6):246-252

This paper introduces the North Sea as a fast evolving coastal ecosystem. The variability of natural conditions relates to the global climatic change and to human disturbances, which originate regionally. Education is an integral part of the strategy to improve environmental awareness. Considering contemporary challenges for educating the wider public about the main issues of environmental concern, attention is paid to various plans, which are being developed in North-Western Europe from primary schools to universities. "Learning for life" relies on an opening of the vocation of traditional universities and on the creation of a European university. Sharing resources in a competitive environment is one response given by British universities in the framework of a Discipline Network in Coastal Sciences and Management in 1996-2000. Networking is truly the key to a fast evolving teaching and learning context, notably in relation to ever developing information and communication technologies. The dissemination of scientific information is primordial in this context; a case study relating to the European project "Marine biodiversity in Europe" (BIOMARE) demonstrates the need for an elaborated strategy leading to socio-economic considerations. Empowering communities and governance are the main possible outcomes of such an enlarged approach to education, involving teachers, students, researchers, professionals, and volunteers. Proposals are made for amplifying the involvement of non-scientists into scientific research and its applications to management. Finally, a case is made for facilitating the mobility of all concerned, with a view to annihilate language and cultural barriers.  相似文献   

Assessment of gully erosion rates through interviews and measurements: a case study from northern Ethiopia   总被引：3，自引：0，他引：3  

Jan Nyssen  Jean Poesen  Maude Veyret‐Picot  Jan Moeyersons  Mitiku Haile  Jozef Deckers  Joke Dewit  Jozef Naudts  Kassa Teka  Gerard Govers 《地球表面变化过程与地形》2006,31(2):167-185

Gullying has been widespread in the Ethiopian Highlands during the 20th century. It threatens the soil resource, lowers crop yields in intergully areas through enhanced drainage and desiccation, and aggravates flooding and reservoir siltation. Knowing the age and rates of gully development during the last few decades will help explain the reasons for current land degradation. In the absence of historical written or photographic documentation, the AGERTIM method (Assessment of Gully Erosion Rates Through Interviews and Measurements) has been developed. It comprises measurements of contemporary gully volumes, monitoring of gully evolution over several years and semi‐structured interview techniques. Gully erosion rates in the Dogu'a Tembien District, Tigray, Ethiopia, were estimated in three representative case‐study areas. In Dingilet, gullying started around 1965 after gradual environmental changes (removal of vegetation from cropland in the catchment and eucalyptus plantation in the valley bottom); rill‐like incisions grew into a gully, which increased rapidly in the drier period between 1977 and 1990. The estimated evolution of the total gully volume in the other areas show patterns similar to those of the Dingilet gully. Average gully erosion rate over the last 50 years is 6·2 t ha^?1 a^?1. Since 1995, no new gullies have developed in the study area. Area‐specific short‐term gully erosion rates are now on average 1·1 t ha^?1 a^?1. The successful application of the AGERTIM method requires an understanding of the geomorphology of the study area and an integration of the researchers with the rural society. It reveals that rapid gully development in the study area is some 50 years old and is mainly caused by human‐induced environmental degradation. Under the present‐day conditions of ‘normal’ rain and catchment‐wide soil and water conservation, gully erosion rates are decreasing. Copyright © 2006 John Wiley & Sons, Ltd.  相似文献   

The use of riparian vegetated filter strips to reduce river sediment loads: an overestimated control measure?   总被引：1，自引：0，他引：1  

Gert Verstraeten  Jean Poesen  Katleen Gillijns  Gerard Govers 《水文研究》2006,20(20):4259-4267

The spatially distributed soil erosion and sediment delivery model WATEM/SEDEM was used to simulate the impact of riparian vegetated filter strips (RVFSs) on river sediment delivery at different spatial scales. For a field plot with a straight slope, sediment reduction by the RVFSs is comparable to results obtained through experimental set‐ups elsewhere (i.e. >70%). However, at the scale of an entire catchment, sediment reduction is much less (i.e. ±20%) due to (1) overland flow convergence, which reduces the sediment trapping efficiency of an RVFS, and (2) because part of the sediment bypasses the RVFSs through ditches, sewers and road surfaces. These results suggest that, at the catchment scale, RVFSs should be accompanied with other conservation techniques that are more appropriate for reducing river sediment loads, and that also reduce on‐site soil erosion. Copyright © 2006 John Wiley & Sons, Ltd.  相似文献   

Runoff and water erosion modelling using WEPP on a Mediterranean cultivated catchment   总被引：1，自引：0，他引：1  

Damien Raclot  Jean Albergel 《Physics and Chemistry of the Earth》2006,31(17):1038-1047

Soil erosion due to water is a major environmental problem in many parts of the world. Most of Mediterranean countries are concerned because of their specific climate and soils sensitivity, but also because of the recent intensification of human activities and agricultural practices. Accurate estimation of soil water erosion for various land-use and climate scenarios is so an important key to define sustainable management policies. In the last decades, several studies have been carried out to build models suitable for quantifying soil erosion. Among these models, the Water Erosion Prediction Project (WEPP, Flanagan, D.C., Nearing, M.A., 1995. USDA-Water Erosion Prediction Project: Hillslope profile and watershed model documentation. NSERL Report 10, USDA-ARS National Soil Erosion Research Laboratory, West Lafayette, IN, USA.) is a physically based, distributed-parameter model that has been developed and mainly validated in USA. Only few studies have investigated its applicability to environmental conditions that differs from those where the model was developed. The aim of this work is to test the efficiency of WEPP model to predict soil erosion at catchment scale in a Mediterranean semi-arid area. Continuous simulations have been conducted between 1995 and 2002 on an cultivated experimental catchment located upstream from a hill reservoir (Kamech catchment, 2.45 km², Cap Bon, Tunisia) where runoff and soil erosion measurements are available at the outlet. Comparison between predictions and measurements shows significant differences. Processes related to seasonal effects (as cracking soils) are pointed out as a weakness of WEPP model for Mediterranean conditions.  相似文献   

北京地区单双频地基GPS大气水汽遥测试验与研究   总被引：5，自引：3，他引：5       下载免费PDF全文

谢璞  张朝林  王迎春  楚艳丽  张京江  王京丽  李矩  Ying Hwa Kuo  John Braun 《应用气象学报》2006,17(Z1):28-34

该文对北京地区单双频地基GPS大气水汽监测网布网依据、单频与双频地基GPS测量数据解算技术应用、GAMIT和Bernese地基GPS数据分析处理软件应用、远程遥控GPS数据采集与通讯系统、资料分析与数值同化应用等方面的工作进展进行简要介绍,重点讨论了单双频地基GPS大气水汽资料的解算技术及其应用效果。结果表明:在北京天气敏感区通过单双频地基GPS接收机合理组网布局,可构建并利用高分辨率电离层延迟订正技术将单频接收机的大气水汽监测精度提高到实用水平,为强降水天气预报提供有价值的产品。  相似文献   

Estimating Crustal Heterogeneity from Double-difference Tomography     

Jean -Luc Got  Vadim Monteiller  Jean Virieux  Paul Okubo 《Pure and Applied Geophysics》2006,163(2-3):405-430

Seismic velocity parameters in limited, but heterogeneous volumes can be inferred using a double-difference tomographic algorithm, but to obtain meaningful results accuracy must be maintained at every step of the computation. MONTEILLER et al. (2005) have devised a double-difference tomographic algorithm that takes full advantage of the accuracy of cross-spectral time-delays of large correlated event sets. This algorithm performs an accurate computation of theoretical travel-time delays in heterogeneous media and applies a suitable inversion scheme based on optimization theory. When applied to Kilauea Volcano, in Hawaii, the double-difference tomography approach shows significant and coherent changes to the velocity model in the well-resolved volumes beneath the Kilauea caldera and the upper east rift. In this paper, we first compare the results obtained using MONTEILLER et al.'s algorithm with those obtained using the classic travel-time tomographic approach. Then, we evaluated the effect of using data series of different accuracies, such as handpicked arrival-time differences (``picking differences'), on the results produced by double-difference tomographic algorithms. We show that picking differences have a non-Gaussian probability density function (pdf). Using a hyperbolic secant pdf instead of a Gaussian pdf allows improvement of the double-difference tomographic result when using picking difference data. We completed our study by investigating the use of spatially discontinuous time-delay data.  相似文献   

The glacial inception as recorded in the NorthGRIP Greenland ice core: timing, structure and associated abrupt temperature changes     

Amaelle Landais  Valérie Masson-Delmotte  Jean Jouzel  Dominique Raynaud  Sigfus Johnsen  Christof Huber  Markus Leuenberger  Jakob Schwander  Bénédicte Minster 《Climate Dynamics》2006,26(2-3):273-284

The mechanisms involved in the glacial inception are still poorly constrained due to a lack of high resolution and cross-dated climate records at various locations. Using air isotopic measurements in the recently drilled NorthGRIP ice core, we show that no evidence exists for stratigraphic disturbance of the climate record of the last glacial inception (∼123–100 kyears BP) encompassing Dansgaard–Oeschger events (DO) 25, 24 and 23, even if we lack sufficient resolution to completely rule out disturbance over DO 25. We quantify the rapid surface temperature variability over DO 23 and 24 with associated warmings of 10±2.5 and 16±2.5°C, amplitudes which mimic those observed in full glacial conditions. We use records of δ¹⁸O of O₂ to propose a common timescale for the NorthGRIP and the Antarctic Vostok ice cores, with a maximum uncertainty of 2,500 years, and to examine the interhemispheric sequence of events over this period. After a synchronous North–South temperature decrease, the onset of rapid events is triggered in the North through DO 25. As for later events, DO 24 and 23 have a clear Antarctic counterpart which does not seem to be the case for the very first abrupt warming (DO 25). This information, when added to intermediate levels of CO₂ and to the absence of clear ice rafting associated with DO 25, highlights the uniqueness of this first event, while DO 24 and 23 appear similar to typical full glacial DO events.  相似文献