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991.
The meanders of a baroclinic coastal current in the Northwestern Mediterranean Sea have already been reported in the literature. These meanders can be surrounded by vortices. Such vortices have been observed in the western part of the Gulf of Lions but the location and the mechanism of their formation are poorly documented. In this paper, we use the current measurements of a one-year experiment, which was conducted in the eastern part of the Gulf of Lions to detect and characterize the vortex activity. A vortex detection algorithm based on few velocity data was developed. Current measurements were available at the sea surface (HF radars) and in the water column from 50 to 140 m depth (four current meter moorings). SST images and hydrologic data were also used. Results focus on observations that are coherent 50 m and at the surface. Vortices are anticyclonic, of submesoscale size and present maximal velocities of 30–50 cm/s. The drift speed of the vortices is comparable to but less than the velocity of the Northern Current. These observations enable to estimate the minimum vortex occurrence in this area. The presence of vortex structures is strongly correlated with a specific sequence of wind patterns. 相似文献
992.
Tine?Derez Tom?Van Der?Donck Oliver?Plümper Philippe?Muchez Gill?Pennock Martyn?R.?Drury Manuel?SintubinEmail author 《Contributions to Mineralogy and Petrology》2017,172(7):56
Fine extinction bands (FEBs) (also known as deformation lamellae) visible with polarized light microscopy in quartz consist of a range of nanostructures, inferring different formation processes. Previous transmission electron microscopy studies have shown that most FEB nanostructures in naturally deformed quartz are elongated subgrains formed by recovery of dislocation slip bands. Here we show that three types of FEB nanostructure occur in naturally deformed vein quartz from the low-grade metamorphic High-Ardenne slate belt (Belgium). Prismatic oriented FEBs are defined by bands of dislocation walls. Dauphiné twin boundaries present along the FEB boundaries probably formed after FEB formation. In an example of two sub-rhombohedral oriented FEBs, developed as two sets in one grain, the finer FEB set consists of elongated subgrains, similar to FEBs described in previous transmission electron microscopy studies. The second wider FEB set consists of bands with different dislocation density and fluid-inclusion content. The wider FEB set is interpreted as bands with different plastic strain associated with the primary growth banding of the vein quartz grain. The nanometre-scale fluid inclusions are interpreted to have formed from structurally bounded hydroxyl groups that moreover facilitated formation of the elongate subgrains. Larger fluid inclusions aligned along FEBs are explained by fluid-inclusion redistribution along dislocation cores. The prismatic FEB nanostructure and the relation between FEBs and growth bands have not been recognized before, although related structures have been reported in experimentally deformed quartz. 相似文献
993.
Van Lichtervelde Marieke Grand’Homme Alexis de Saint-Blanquat Michel Olivier Philippe Gerdes Axel Paquette Jean-Louis Melgarejo Joan Carles Druguet Elena Alfonso Pura 《Mineralogy and Petrology》2017,111(1):1-21
Mineralogy and Petrology - The Cap de Creus granitic pegmatites in the eastern Catalan Pyrenees were dated using in situ U-Pb geochronology by laser ablation ICP-MS on zircon and columbite-group... 相似文献
994.
Lourdes Vargas-Ramirez Emile Roche Philippe Gerrienne Henry Hooghiemstra 《Journal of Paleolimnology》2008,39(2):197-217
A pollen record from Puyehue area (40°S; 72°W) in the southern Lake District, Chile, indicates that prior to 13,410 14C yr BP (ca. 16,500–15,200 cal yr BP), cold resistant and hygrophilous vegetation, particularly Nothofagus forest and myricaceous vegetation, covered the area. From ca. 15,000 cal yr BP onward, the forest became increasingly dense.
Between 10,010 and 7450 14C yr BP (ca. 11,000–8000 cal yr BP), the expansion of Nothofagus obliqua and the spread of grasses suggests the climate became warmer and semi-arid. Lowland deciduous forest (Nothofagus obliqua, Aextoxicon punctatum, Laurelia sempervirens) and Valdivian rainforest (Nothofagus dombeyi, Eucryphia cordifolia, Caldcluvia paniculata, Aextoxicon punctatum, Laureliopsis philippiana) were abundant. During the next two thousand years, stable warm climatic conditions prevailed, and the diversity of the vegetation
increased. From 5760 to 1040 14C yr BP (ca. 6500–900 cal yr BP), the North Patagonian rainforest expanded. The presence of Pilgerodendron/Fitzroya, together with Nothofagus forest, suggests that humid conditions prevailed. During the last millennium, human impact intensified and regional vegetation
was disturbed, particularly the lowland deciduous forest and Valdivian rainforest. North-Patagonian and subantartic taxa,
such as Podocarpus nubigena, Pilgerodendron/Fitzroya, Nothofagus dombeyi type, Austrocedrus chilensis and Drimys winteri, occupied the low and high-altitude parts of the Cordillera. Five hundred years ago, shrub and grasses expanded in the Nothofagus forest, suggesting that forest became more open under cool–cold, and humid climatic conditions. These conditions prevail
to the present day.
This is the fourth in a series of eight papers published in this special issue dedicated to the 17,900 year multi-proxy lacustrine record of
Lago Puyehue, Chilean Lake District. The papers in this special issue were collected by M. De Batist, N. Fagel, M.-F. Loutre
and E. Chapron. 相似文献
995.
Jean-Marc?GuariniEmail author James?E.?Cloern Jody?Edmunds Philippe?Gros 《Estuaries and Coasts》2002,25(3):409-417
In this paper we describe a three-step procedure to infer the spatial heterogeneity in microphytobenthos primary productivity at the scale of tidal estuaries and embayments. The first step involves local measurement of the carbon assimilation rate of benthic microalgae to determine the parameters of the photosynthesis-irradiance (P-E) curves (using non-linear optimization methods). In the next step, a resampling technique is used to rebuild pseudo-sampling distributions of the local productivity estimates; these provide error estimates for determining the significance level of differences between sites. The third step combines the previous results with deterministic models of tidal elevation and solar irradiance to compute mean and variance of the daily areal primary productivity over an entire intertidal mudflat area within each embayment. This scheme was applied on three different intertidal mudflat regions of the San Francisco Bay estuary during autumn 1998. Microphytobenthos productivity exhibits strong (ca. 3-fold) significant differences among the major sub-basins of San Francisco Bay. This spatial heterogeneity is attributed to two main causes: significant differences in the photosynthetic competence (P-E parameters) of the microphytobenthos in the different sub-basins, and spatial differences in the phase shifts between the tidal and solar cycles controlling the exposure of intertidal areas to sunlight. The procedure is general and can be used in other estuaries to assess the magnitude and patterns of spatial variability of microphytobenthos productivity at the level of the ecosystems. 相似文献
996.
Philippe Robutel 《Celestial Mechanics and Dynamical Astronomy》1995,62(3):193-217
We present a direct method for the expansion of the planetary Hamiltonian in Poincaré canonical elliptic variables with its effective implementation in computer algebra. This method allows us to demonstrate the existence of simplifications occurring in the analytical expression of the Hamiltonian coefficients. All the coefficients depending on the ratio of the semi major axis can thus be expressed in a concise and canonical form. 相似文献
997.
The human perturbation of the carbon cycle via the release of fossil CO2 and land use change is now well documented and agreed to be the principal cause of climate change. We address three fundamental research areas that require major development if we were to provide policy relevant knowledge for managing the carbon-climate system over the next few decades. The three research areas are: (i) carbon observations and multiple constraint data assimilation; (ii) vulnerability of the carbon-climate system; and (iii) carbon sequestration and sustainable development. 相似文献
998.
Hennebelle Patrick Belloche Arnaud Whitworth Anthony André Philippe 《Astrophysics and Space Science》2004,292(1-4):355-360
We present numerical simulations of the evolution of low-mass, isothermal, molecular cores which are subjected to an increase in external pressure. If the external pressure increases very slowly, the core approaches instability quite quasi-statically. However, for faster compressions, a compression wave is driven into the core (Hennebelle, P., Whitworth, A., Gladwin, P. and André, P.: 2003a MNRAS 340, 870). Quantitative comparisons with observational velocity and density profiles are presented. The consequences of this compression for the fragmentation of the cloud is investigated and discussed. 相似文献
999.
Yvon Halbwachs Gabriel Courrioux Xavier Renaud Philippe Repusseau 《Mathematical Geology》1996,28(5):625-656
The consistent geometric and topological representation of a fault network is possible through a method based on the implementation of 3-dimensional Generalized maps (3-G-map) enabling all subdivisions of space to be represented. The fault network is modeled as an assemblage of polygonal faces from a set of geometric data on the faults and a knowledge of the relationships between the faults. The resultant model is expressed in terms of a 3-G-map in which volume, surface, and topological information is constructed taking into account computed intersections between faults and known interception relations. The fault network can be edited through an interactive 3-D viewer which provides several tools for navigating within the 3-G-map. Information relevant to a fault network, such as block geometry, connectivity, adjacencies, and connectivity relationships, can be obtained by exploring the data structure of the 3-G-map. The fault network architecture is made comprehensive through interactive modeling and visualization. 相似文献
1000.
This paper presents the second part of a work that aims at developing a mechanical model for the behaviour of propellant‐like materials under high confining pressure and strain rate. The model is to be employed to determine the temperature rise due to mechanical dissipation during a dynamic penetration event. Using the kinematical and thermodynamic background derived in the first part, a viscoelastic–viscoplastic–compaction model is put forward and identified. Viscoelasticity and compaction refer to the elastomeric nature of the material, while viscoplasticity, including implicit damage through dilatancy, reflects its granular nature. Some numerical exercises are performed, in view of determining the major model forces and weaknesses, and of assessing the numerical algorithm robustness. A penetration event is preliminarily simulated, and a temperature rise field predicted. Necessary model improvements are finally discussed, together with several ways of research for a longer term approach. Copyright © 2001 John Wiley & Sons, Ltd. 相似文献