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51.
研究了空间铷钟和被动型氢钟的地面批量和寿命试验测试结果,以及卫星在轨试验所达到的最新性能结果。基于这些星载钟的试验结果,对全球卫星导航系统的地面时间站的关键设备及其相关算法作了简要描述,并介绍了一种新颖的在轨技术,即从星载原子钟组(ONCLE)直接产生高度稳健的时间频率信号。 相似文献
52.
Roberto Bertoni Wade H. Jeffrey Mireille Pujo-Pay Louise Oriol Pascal Conan Fabien Joux 《Aquatic Sciences - Research Across Boundaries》2011,73(3):377-387
The scaling of the solar ultraviolet radiation (UVR, 280–400 nm) effect on phyto- and bacterio-plankton at the ecosystem level
is difficult since its estimate is often based on short-time incubation experiments performed at fixed depths, neglecting
the previous days’ radiation history and the variable radiation caused by vertical mixing. To examine this issue, we measured
primary (PP) and bacterial (BP) production in samples from coastal water in the Northwest Mediterranean Sea incubated at fixed
depths or moving vertically within the water column (0–8 m) with a periodicity of 22 min, exposed to full sun, PAR or maintained
in dark. Three experiments were carried out on consecutive days to measure day-to-day variations in planktonic response. In
surface waters, PP was inhibited by ~32 to 42% by UVR, and BP was inhibited by ~50 to 70% by solar radiation (UVR + PAR).
We observed a general decrease in the integrated inhibition of PP due to UVR for both fixed and moving incubations over the
3 days from ~27% of inhibition to non-significant inhibition. In contrast, large discrepancies were observed in the integrated
inhibition of BP due to solar radiation (UVR + PAR) between fixed and moving incubations. Whereas both type of incubations
gave similar estimation of solar radiation inhibition on day 1 (~25%), inhibition became much higher for fixed incubation
compared to moving incubation on days 2 and 3. Differences in responses between days suggest that light history, spectral
quality, photoadaptation or acclimation may be important factors in daily observed responses. Our results also underline,
for the first time, the importance of the vertical mixing in the BP inhibition by solar radiation. 相似文献
53.
Afroosa M. Rohith B. Paul Arya Durand Fabien Bourdallé-Badie Romain Joseph Sudheer Prerna S. Shenoi S. S. C. 《Ocean Dynamics》2022,72(7):523-538
Ocean Dynamics - An intraseasonal see-saw has been observed in the Indo-Pacific barotropic sea level anomaly during boreal winters. This see-saw carries a significant amount of energy and is... 相似文献
54.
The evolution of flood activity with global warming remains uncertain. To better assess flood–climate relationships, lake sediments are increasingly being investigated because they could provide regional flood histories long enough to cover past climate changes. However, site‐specific sedimentary processes may bias flood reconstructions. The aim of this article is to investigate these effects through the reconstruction of two distinct flood records from independent, neighbouring sedimentary basins of the same lake (Lake Allos in the Mediterranean French Alps), i.e. under the same climate conditions. Understanding of sedimentary processes is crucial in order to adapt the sampling strategy and the flood‐intensity proxy to each sedimentary system and, thereby, reconstruct a complete and reliable flood history. Thanks to this detailed approach, the main trends of the regional flood variability can be reproduced; i.e. periods of high flood‐frequency, ranges of flood‐frequency values and timing of the most intense events. In detail, some differences appeared associated to the various stream capacities to erode and transport flood sediments to the lake system, implying variable sensitivity of sedimentary systems in recording floods. Comparing regional flood records based on independent sedimentary systems from similar environments could thus be a complementary approach to assessing past flood intensity. Such an approach could open particularly interesting perspectives because reconstructing the long‐term evolution of flood intensity is a key challenge in the geosciences. 相似文献
55.
Anne Mouchet Fabien Cornaton Éric Deleersnijder Éric J. M. Delhez 《Ocean Dynamics》2016,66(3):367-386
The concept of age is widely used to quantify the transport rate of tracers - or pollutants - in the environment. The age focuses only on the time taken to reach a given location and disregards other aspects of the path followed by the tracer parcel. To keep track of the subregions visited by the tracer parcel along this path, partial ages are defined as the time spent in the different subregions. Partial ages can be computed in an Eulerian framework in much the same way as the usual age by extending the Constituent oriented Age and Residence Time theory (CART, www.climate.be/CART). In addition to the derivation of theoretical results and properties of partial ages, applications to a 1D model with lateral/transient storage, to the 1D advection-diffusion equation and to the diagnosis of the ventilation of the deep ocean are provided. They demonstrate the versatility of the concept of partial age and the potential new insights that can be gained with it. 相似文献
56.
57.
The response of soil erosion and sediment export to land-use change in four areas of Europe: The importance of landscape pattern 总被引:7,自引:0,他引:7
Martha M. Bakker Gerard Govers Anne van Doorn Fabien Quetier Dimitris Chouvardas Mark Rounsevell 《Geomorphology》2008,98(3-4):213
The response of erosion and sediment export to past land-use change has been studied in four agricultural areas of Europe. Three of these areas were subject to land abandonment or de-intensification and one to intensification of land-use practices. Erosion and sediment yield were modeled using the WaTEM/SEDEM model, which combines the RUSLE equation with a sediment routing algorithm. Spatial relationships between the RUSLE C-factor (i.e. land-use) and other erosion and sediment export-determining factors (slope, soil erodibility and distance to rivers) were investigated, as these account for non-linearity in the response of erosion and sediment export to land-use change.Erosion and sediment export have decreased enormously in the de-intensified areas, but slightly increased in the intensively cultivated area. The spatial pattern of land-use change in relation to other erosion and sediment export-determining factors appears to have a large impact on the response of soil erosion and sediment export to land-use change. That the drivers of abandonment of arable land and erosion coincide indicates that de-intensification leads to a more favourable landscape pattern with respect to reduction of erosion and sediment export. This mechanism applies not only within the study areas, but also among the European study areas where the process of intensification of some areas and de-intensification of others might result in an overall decrease of erosion and sediment yield through time. 相似文献
58.
Interfacial interactions, namely interfacial tension, wettability, capillarity and interfacial mass transfer are known to govern fluid distribution and behavior in porous media. Therefore the interfacial interactions between CO2, brine and oil and/or gas reservoirs have a significant influence on the effectiveness of any CO2 storage operations. However, data and knowledge of interfacial properties in storage conditions are scarce. This issue becomes particularly true in the case of deep saline aquifers where limited, economically driven, data collection and archiving are available. In this paper, we present a complete set of brine–CO2 interfacial tension data at pressure, temperature and salinity conditions, representative of a CO2 storage operation. A semi-empirical correlation is proposed to calculate the interfacial tension from the experimental data. Wettability is studied at pore scale, using glass micromodels in order to track fluids distribution as a function of the thermodynamic properties and wettability conditions for water–CO2 systems. With this approach, we show that, in strongly hydrophilic porous media, the CO2 does not wet the solid surface whereas; if the porous media has less hydrophilic properties the CO2 significantly wets the surface. 相似文献
59.
Integrating geological concepts, such as relative positions and proportions of the different lithofacies, is of highest importance in order to render realistic geological patterns. The truncated plurigaussian simulation method provides a way of using both local and conceptual geological information to infer the distributions of the facies and then those of hydraulic parameters. The method ( Le Loc'h and Galli 1994 ) is based on the idea of truncating at least two underlying multi-Gaussian simulations in order to create maps of categorical variable. In this article, we show how this technique can be used to assess contaminant migration in highly heterogeneous media. We illustrate its application on the biggest contaminated site of Switzerland. It consists of a contaminant plume located in the lower fresh water Molasse on the western Swiss Plateau. The highly heterogeneous character of this formation calls for efficient stochastic methods in order to characterize transport processes. 相似文献
60.
Daniel Käser Tobias Graf Fabien Cochand Rob McLaren René Therrien Philip Brunner 《Ground water》2014,52(6):827-836
Recent models that couple three‐dimensional subsurface flow with two‐dimensional overland flow are valuable tools for quantifying complex groundwater/stream interactions and for evaluating their influence on watershed processes. For the modeler who is used to defining streams as a boundary condition, the representation of channels in integrated models raises a number of conceptual and technical issues. These models are far more sensitive to channel topography than conventional groundwater models. On all spatial scales, both the topography of a channel and its connection with the floodplain are important. For example, the geometry of river banks influences bank storage and overbank flooding; the slope of the river is a primary control on the behavior of a catchment; and at the finer scale bedform characteristics affect hyporheic exchange. Accurate data on streambed topography, however, are seldom available, and the spatial resolution of digital elevation models is typically too coarse in river environments, resulting in unrealistic or undulating streambeds. Modelers therefore perform some kind of manual yet often cumbersome correction to the available topography. In this context, the paper identifies some common pitfalls, and provides guidance to overcome these. Both aspects of topographic representation and mesh discretization are addressed. Additionally, two tutorials are provided to illustrate: (1) the interpolation of channel cross‐sectional data and (2) the refinement of a mesh along a stream in areas of high topographic variability. 相似文献