Experimental and Numerical Study of Wind and Turbulence in a Near-Field Dispersion Campaign at an Inhomogeneous Site     

Xiao Wei  Eric Dupont  Eric Gilbert  Luc Musson-Genon  Bertrand Carissimo 《Boundary-Layer Meteorology》2016,160(3):475-499

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A static drilling riser model using free boundary conditions     

Luc Huyse  Mansa C. Singh  Marc A. Maes 《Ocean Engineering》1997,24(5):431-444

A static three-dimensional analytical method for drilling risers experiencing large displacements and slip at the top joint is presented. The riser is described in cylindrical coordinates as a three-dimensional tensioned string, without bending or torsional stiffness. The vertical vessel displacement is not taken into account. The equilibrium configuration is obtained from the stationary condition of the total potential energy functional. Kinematic boundary conditions are introduced for the radial displacement only. The riser orientation at the top directly follows from the natural boundary conditions based on the variational treatment of the energy functional.  相似文献   

Sedimentary record of redox-sensitive elements (U, Mn, Mo) in a transitory anoxic basin (the Thau lagoon, France)   总被引：4，自引：0，他引：4  

Franoise Elbaz-Poulichet  Jean Luc Seidel  Didier Jzquel  Edouard Metzger  Franois Prvot  Caroline Simonucci  Grard Sarazin  Eric Viollier  Henri Etcheber  Jean-Marie Jouanneau  Olivier Weber  Olivier Radakovitch 《Marine Chemistry》2005,95(3-4):271-281

In order to further document the relation between redox conditions and the sedimentary record of Mn, U and Mo in a transitory anoxic water basin, their distribution has been studied along two profiles in the Thau lagoon (France). Sediments and pore-water have been sampled at two contrasting sites located, respectively, in the shellfish-farming area and in the centre of the lagoon. In the shellfish-farming area, the particulate organic carbon (POC) data indicate a more rapid organic matter mineralisation compared to the centre of the lagoon. This results in a sharper redox gradient characterized by the appearance of H₂S in pore-water a few millimetres below the sediment–water interface. In the centre of the lagoon, H₂S appears at a depth of 35 cm.In both cores, sedimentary Mn is relatively depleted through out the whole sedimentary column and varies with the proportion of clay minerals. After an initial release into solution at the sediment–water interface in relation to Mn-oxide reductive dissolution, authigenic U is immobilized when sulphides appear. Despite the occurrence of anoxic conditions at the sediment–water interface at the site influenced by shellfish farming, the burial of U is reduced by bioturbation, which raises reducing sediments to the surface. In the centre of the lagoon, Mo profiles reflect continuous diffusion into pore water and immobilization at 15 cm probably in anoxic microenvironments. At shellfish farms, dissolved Mo undergoes removal with sulphides but contrary to U, sedimentary Mo does not appear to be strongly affected by bioturbation. The profile indicates an increase in the frequency of anoxia crises during the second half of the 20th century.  相似文献   

A gamma‐ray spectroscopy survey of Omani meteorites          下载免费PDF全文

Patrick Weber  Beda A. Hofmann  Tamer Tolba  Jean‐Luc Vuilleumier 《Meteoritics & planetary science》2017,52(6):1017-1029

The gamma‐ray activities of 33 meteorite samples (30 ordinary chondrites, 1 Mars meteorite, 1 iron, 1 howardite) collected during Omani‐Swiss meteorite search campaigns 2001–2008 were nondestructively measured using an ultralow background gamma‐ray detector. The results provide several types of information: Potassium and thorium concentrations were found to range within typical values for the meteorite types. Similar mean ²⁶Al activities in groups of ordinary chondrites with (1) weathering degrees W0‐1 and low ¹⁴C terrestrial age and (2) weathering degree W3‐4 and high ¹⁴C terrestrial age are mostly consistent with activities observed in recent falls. The older group shows no significant depletion in ²⁶Al. Among the least weathered samples, one meteorite (SaU 424) was found to contain detectable ²²Na identifying it as a recent fall close to the year 2000. Based on an estimate of the surface area searched, the corresponding fall rate is ~120 events/10⁶ km²*a, consistent with other estimations. Twelve samples from the large JaH 091 strewn field (total mass ~4.5 t) show significant variations of ²⁶Al activities, including the highest values measured, consistent with a meteoroid radius of ~115 cm. Activities of ²³⁸U daughter elements demonstrate terrestrial contamination with ²²⁶Ra and possible loss of ²²²Rn. Recent contamination with small amounts of ¹³⁷Cs is ubiquitous. We conclude that gamma‐ray spectroscopy of a selection of meteorites with low degrees of weathering is particularly useful to detect recent falls among meteorites collected in hot deserts.  相似文献   

Permineralization process promotes preservation of Holocene macrofossil charcoal in soils     

Guillaume De Lafontaine  Pierre‐Luc Couillard  Serge Payette 《第四纪科学杂志》2011,26(6):571-575

The use of macrofossil soil charcoal as a palaeoecological tool to reconstruct past vegetation, climate or fire history has gained much interest in recent years. Yet little is known about taphonomy of charcoal in soils. Here we assessed the putative loss of palaeoecological information due to charcoal fragmentation after burial. We found no significant loss of charcoal mass with time. Instead, we found a significant positive relationship between the mass of charcoal particles and their age. Permineralization of charcoal particles older than ca. 5200 a explained the increased charcoal mass with time in mineral soils. The permineralization process increased the density of charcoal particles (resulting in a twofold particles mass increase) and thus offers a protection against subsequent degradation. Our results suggest high stability of palaeoecological information from charcoal macrofossils buried in mineral soils at least over the Holocene timescale. Copyright © 2011 John Wiley & Sons, Ltd.  相似文献   

Hydrological regimes in a tropical valley of New Caledonia (SW Pacific): Impacts of wildfires and invasive fauna     

Caroline Marie Clémence Tramier  Pierre Genthon  Quentin Réginald Camille Paul Delvienne  Nicolas Luc Sauvan  Jean-Jérôme Olivier Cassan  Etienne Ebrard  Pascal Sébastien Dumas  Yann Queffélean 《水文研究》2021,35(3):e14071

In New Caledonia wildfires and invasive mammals (deer and wild pigs) constitute the major agents of land surface degradation. Our study reveals the linkage between land cover and water balance on the northeast coast of New Caledonia (2400 mm annual rainfall) located on a micaschist basement. The hydrological regime of characteristic and representative land surfaces is assessed using a 1-year record from three 100 m² plots each, located in a forest area degraded by an invasive fauna, in a woody savannah which is regularly burned, and in a healthy forest area. The three plots present highly contrasting hydrological regimes, with annual and maximum runoff/rain ratios during a rain event of, respectively, 0.82, 0.16, 0.03, and 2.7, 0.7, 0.2, for the degraded forest, the savannah and the healthy forest. Such results suggest that subsurface flow originating from the contributing area above the degraded forest plot should exfiltrate inside the plot. A conceptual model for the degraded forest plot shows that water exfiltrating inside the plot represents 61% of the observed runoff. In savannahs, water should mainly be transferred downstream by subsurface flow within a thick organic soil layer limited by an impervious clay layer at a 20–30 cm depth. Savannahs are generally located above forests and generate the transfer of rainwater to downslope forests. Exfiltration into the forests can be the result of this transfer and depends on the thickness and permeability of the forest topsoils and on topographic gradients. Water exfiltration in forest areas highly degraded by pigs and deer enhances erosion and increases further degradation. It probably also limits percolation in the areas located downstream by increasing the amount of superficial runoff concentrated in gullies.  相似文献   

SN 1994W: an interacting supernova or two interacting shells?     

Luc Dessart  D. John Hillier  Suvi Gezari  Stéphane Basa  Tom Matheson 《Monthly notices of the Royal Astronomical Society》2009,394(1):21-37

We present a multi-epoch quantitative spectroscopic analysis of the Type IIn supernova (Type IIn SN) 1994W, an event interpreted by Chugai et al. as stemming from the interaction between the ejecta of a SN and a  0.4 M_⊙  circumstellar shell ejected 1.5 yr before core collapse. During the brightening phase, our models suggest that the source of optical radiation is not unique, perhaps associated with an inner optically thick cold dense shell and outer optically thin shocked material. During the fading phase, our models support a single source of radiation, an hydrogen-rich optically thick layer with a near-constant temperature of ∼7000 K that recedes from a radius of  4.3 × 10¹⁵  at a peak to  2.3 × 10¹⁵ cm  40 d later. We reproduce the hybrid narrow-core broad-wing line profile shapes of SN 1994W at all times, invoking an optically thick photosphere exclusively (i.e. without any external optically thick shell). In SN 1994W, slow expansion makes scattering with thermal electrons a key escape mechanism for photons trapped in optically thick line cores, and allows the resulting broad incoherent electron-scattering wings to be seen around narrow-line cores. In SNe with larger expansion velocities, the thermal broadening due to incoherent scattering is masked by the broad profile and the dominant frequency redshift occasioned by bulk motions. Given the absence of broad lines at all times and the very low ⁵⁶Ni yields, we speculate whether SN 1994W could have resulted from an interaction between two ejected shells without core collapse. The high conversion efficiency of kinetic to thermal energy may not require a SN-like energy budget for SN1994W.  相似文献   

Search for finite dimensional attractors in atmospheric turbulence   总被引：1，自引：0，他引：1  

Rudolf O. Weber  Peter Talkner  Gérard Stefanicki  Luc Arvisais 《Boundary-Layer Meteorology》1995,73(1-2):1-14

The question is investigated whether the dynamics of turbulent wind fields in the atmospheric boundary layer can be satisfactorily described by a low-dimensional deterministic system. Special emphasis is laid on the detection of a possibly existing, underlying strange attractor. Fast response wind measurements of an ultrasonic anemometer with a sampling rate of 21 Hz were carried out over periods of several days in the near surface boundary layer. The correlation dimension of the resulting time series, several million data points long, is estimated by means of the Grassberger-Procaccia algorithm. No sign of a low dimensional attractor can be detected. By comparison with different types of random noise, the existence of an attractor with dimension lower than six can be excluded in the present data sets.  相似文献   

Book reviews     

Rudnicki  John W.  Zheng  Gutuan  Koch  Manfred  Hanyga  Andrzej  Fujinawa  Yukio  Tabeart  Frazer  Kimbrough  David L.  Lovison-Golob  Lucía  Dore  Anthony  Blecki  Jan  Sroczynska-Kozuchowska  Magdalena 《Pure and Applied Geophysics》1993,140(3):537-556

Pure and Applied Geophysics -  相似文献   

Rossby similarity and turbulent formulations     

Régis Du Vachat  Luc Musson-Genon 《Boundary-Layer Meteorology》1982,23(1):47-68

The structure of the Planetary Boundary Layer in the stationary case is investigated. The dynamic equations are written in an universal form deduced from Rossby Similarity. Then the system is closed using two semi-empirical formulations for the turbulent fluxes (Prandtl's formulation and the turbulent energy scheme) with a mixing-length chosen to be compatible with Rossby Similarity. For each formulation the system is solved using a new numerical procedure to compute universal profiles of wind and also the Similarity functions A and B in terms of stability. These profiles and functions are then compared to experimental data and good agreement is obtained. Investigating simpler formulations, it appears that good results are obtained with a simple two-layer model, patching a diabatic Ekman spiral with surface-layer profiles. Its formulation is analytical and it can incorporate constant baroclinicity.  相似文献