Gills of hydrothermal vent annelids: Structure, ultrastructure and functional implications in two alvinellid species     

Claude Jouin  Franoise Gaill 《Progress in Oceanography》1990,24(1-4)

The anatomy, fine structure, diffusion distances and respiratory surface areas of the gills of two species of the polychaete family Alvinellidae have been investigated. Each gill consists of a stem on which are inserted two opposite rows of respiratory elements: flat sickle-shaped lamellae in Alvinella pompejana and cylindrical filaments in Paralvinella grasslei. Both lamellae and filaments have a ciliated mucous epidermis, a central layer of supporting and muscle cells and are devoid of coelomic cavity. Each respiratory element possesses one afferent and one efferent marginal vessel, united to each other distally, and connected proximally to separate longitudinal vessels running in the stem. Superficial parallel blood spaces connect the marginal vessels across the lamella or filament. Deeper, between the basal laminae of the epidermis and that of the central cell layer, a blood sinus is also present. The marginal vessels and the superficial blood spaces actually are intraepidermal extensions of this deep blood sinus. The diffusion distances are very small owing to the intraepidermal position of the respiratory blood spaces. The specific gill surface areas in A. pompejana and P. grasslei are the largest known today in polychaetes, respectively 12 and 47 cm² per g wet weight. The distinctive features of the gills are possibly related to a low oxygen content of the ambient seawater. Numerous crystalline granules scattered in the gill epidermis suggest that this epithelium has a detoxifying function.  相似文献   

Compressibility and permeability of sand–kaolin mixtures. Experiments versus non‐linear homogenization schemes     

Claude Boutin  Grzegorz Kacprzak  Doanh Thiep 《国际地质力学数值与分析法杂志》2011,35(1):21-52

This study deals with the behaviour of mixtures of sand and saturated kaolin paste considered as composite materials made of permeable and deformable (with non‐linear behaviour) matrix (the kaolin paste) with rigid and impervious inclusions (the sand grains). Oedometric and permeability tests highlight the key role of the state of the clay paste, and show the existence of a threshold of sand grain concentration above which a structuring effect influences both compressibility and permeability. At the light of these experiments two homogenization schemes (with simplifying assumptions to make the problem manageable) are considered to model these two parameters. Qualitative and quantitative comparisons with experimental data point out their respective domain of interest and limitations: a tangent homogenization scheme is shown to be sufficient to describe the macroscopic properties for dilute sand concentration; above the concentration threshold, the structuring effect is captured by the new homogenization scheme developed in this paper. Copyright © 2010 John Wiley & Sons, Ltd.  相似文献   

Measure of the exponential splitting of the homoclinic tangle in four-dimensional symplectic mappings     

Elena Lega  Massimiliano Guzzo  Claude Froeschlé 《Celestial Mechanics and Dynamical Astronomy》2009,104(1-2):191-204

Using four-dimensional symplectic maps as a model problem, we numerically compute the unstable manifolds of the hyperbolic manifolds of the phase space related to the single resonances. We measure an exponential dependence of the size of the lobes of these manifolds through many orders of magnitude of the perturbing parameter. This is an indirect numerical verification of the exponential decay of the normal form, as predicted by the Nekhoroshev theorem. The variation of the size of the lobes turns out to be correlated to the diffusion coefficient.  相似文献   

A numerical study of the hyperbolic manifolds in a priori unstable systems. A comparison with Melnikov approximations     

Elena Lega  Massimiliano Guzzo  Claude Froeschlé 《Celestial Mechanics and Dynamical Astronomy》2010,107(1-2):115-127

Using numerical methods we study the hyperbolic manifolds in a model of a priori unstable dynamical system. We compare the numerically computed manifolds with their analytic expression obtained with the Melnikov approximation. We find that, at small values of the perturbing parameter, the topology of the numerically computed stable and unstable manifolds is the same as in their Melnikov approximation. Increasing the value of the perturbing parameter, we find that the stable and unstable manifolds have a peculiar topological transition. We find that this transition occurs near those values of the perturbing parameter for which the error terms of Melnikov approximations have a sharp increment. The transition value is also correlated with a change in the behaviour of dynamical quantities, such as the largest Lyapunov exponent and the diffusion coefficient.  相似文献   

Local and remote impacts of a tropical Atlantic salinity anomaly   总被引：1，自引：1，他引：0  

Juliette Mignot  Claude Frankignoul 《Climate Dynamics》2010,35(7-8):1133-1147

The climatic impacts of an enhanced evaporation prescribed during 50 years in the tropical Atlantic are investigated in a coupled ocean–atmosphere general circulation model. Locally, the salinity increase leads to a rapid deepening and cooling of the surface mixed layer. This induces a deepening of the equatorial undercurrent and an intensification of the south equatorial current. A remote atmospheric response to the tropical Atlantic perturbation is detected in the North Atlantic sector after ten years. It has the form of a robust wave-like tropospheric perturbation seemingly excited by the weakening of atmospheric deep convection over the Amazonian basin. Meanwhile, the salt anomaly is carried northward by the mean oceanic circulation. It is traced up to the convection sites and then on its return path at depth towards lower latitudes. Consistent with the density increase, deep convection is enhanced after the arrival of the salt anomaly and the Atlantic meridional overturning circulation (AMOC) intensifies about 20 years after the beginning of the perturbation. The adjustment of the tropical Atlantic to the AMOC intensification then modifies its initial response to the freshwater forcing, leading to a weaker cooling in the northern tropical Atlantic than in the southern tropical Atlantic, a slight northward shift of the tropical Atlantic precipitation pattern and an intensification of the North Brazil current. On the other hand, no significant anomalous precipitations are found in the Pacific. The initial remote atmospheric response is also modulated, by an NAO-like response to the AMOC intensification.  相似文献   

Rivières & rivaux. Les frontières de l'eau,par Vazken Andréassian et Jean Margat     

Claude Cosandey 《水文科学杂志》2013,58(8)

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⁸⁷Rb-⁸⁷Sr age of fragments and soils from the lunar sea of fertility     

Jean Louis Birck  Claude J Allegre 《Geochimica et cosmochimica acta》1973,37(9):2025-2031

The Luna 16 materials were dated by the Rb-Sr method.An internal isochron age of 3.4 ± 0.2 has been determined for a 6 mg fragment.The Luna 16 total soil is poorer in radiogenic Sr than any other analyzed soil from the Moon. Apollo 14 and 15 soils have also been studied; all of them fall nearly on a 4.65 b.y. isochron with the ADOR initial ${}^{87}\text{Sr}{}^{86}\text{Sr}$ ratio.A comparison of the integrated $\text{Rb}\text{Sr}$ of the basalt source region and the $\text{Rb}\text{Sr}$ of the rocks suggests that these basaltic fragments have been generated with only minor $\text{Rb}\text{Sr}$ fractionation.The existence of an old Rb-rich subcrust which contaminated the basalts is also in agreement with the present results.  相似文献   

Etude de la thermoluminescence de la meteorite Saint Severin     

Georges Valladas  Claude Lalou 《Earth and Planetary Science Letters》1973,18(1):168-171

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Proneofiber, a new genus of vole (Cricetidae: Rodentia) from the Pleistocene Seymour Formation of Texas,and its evolutionary and stratigraphic significance     

Claude W. Hibbard  Walter W. Dalquest 《Quaternary Research》1973,3(2):269-274

A new genus and species of a microtine rodent, Proneofiber guildayi, is named on the basis of rooted teeth with cement from the warm Gilliland local fauna, Seymour Formation of Pleistocene age, Knox County, Texas. Proneofiber guildayi is considered to be ancestral to Neofiber, the round-tailed water rat, now living in the extreme southeastern United States. The presence of Pleistocene faunas prior to the first continental glaciation and the existence of three Pearlette-like volcanic ashes in the Plains Region suggest a revision of the age assignment of Pleistocene deposits from the nonglaciated region.  相似文献   

Late Pleistocene to Holocene eruptive activity of Pico de Orizaba,Eastern Mexico     

Armann Hoskuldsson  Claude Robin 《Bulletin of Volcanology》1993,55(8):571-587

The Late Pleistocene to Holocene eruptive history of Pico de Orizaba can be divided into 11 eurptive episodes. Each eruptive episode lasted several hundred years, the longest recorded being about 1000 years (the Xilomich episode). Intervals of dormancy range from millenia during the late Pleistocene to about 500 years, the shortest interval recorded in the Holocene. This difference could reflect either changes in the volcano's activity or that the older stratigraphic record is less complete than the younger. Eruptive mechanisms during the late Pleistocene were characterized by dome extrusions, lava flows and ash-and-scoria-flow generating eruptive columns. However, in Holocene time plinian activity became increasingly important. The increase in dacitic plinian eruptions over time is related to increased volumes of dacitic magma beneath Pico de Orizaba. We suggest that the magma reservoir under Pico de Orizaba is stratified. The last eruptive episode, which lasted from about 690 years bp until ad 1687, was initiated by a dacitic plinian eruption and was followed by effusive lava-forming eruptions. For the last 5,000 years the activity of the volcano has been gradually evolving towards such a trend, underlining the increasing importance of dacitic magma and stratification of the magma reservoir. Independent observations of Pico de Orizaba's glacier early this century indicate that some increase in volcanic activity occurred between 1906 and 1947, and that it was probably fumarolic.  相似文献