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1.
Arnaud M. Aubourg E. Bareyre P. Br';ehin S. Caridroit R. de Kat J. Dispau G. Djidi K. Gros M. Lachièze-Rey M. Laigneau Y. Laurent B. Lesquoy E. Lavocat Ph. Magneville C. Mazeau B. Milsztajn A. Moscoso L. Pasquaud J. Paul B. Perrin P. Petibon J. Piret Y. Queinnec F. Rich J. Spiro M. de Trogoff J. Vigroux L. Zylberajch S. Ansari R. Cavalier F. Moniez M. Beaulieu J. P. Ferlet R. Grison Ph. Vidal-Madjar A. Adrianzyk G. Berger J. P. Burnage R. Delclite J. C. Kohler D. Magnan R. Richaud A. Guibert J. Moreau O. Tajahmady F. Baranne A. Maurice E. Prévôt L. Gry C. 《Experimental Astronomy》1994,4(3-4):265-278
A 20cm
2
CCD mosaic camera has been especially built to search for dark galactic halo objects by the gravitational microlensing effect. The sensitive area is made of 16 edge-buttable CCDs developped by Thomson-CTS, with 23×23 µm
2
pixels. The 35 kg camera housing and mechanical equipment is presented. The associated electronics and data acquisition system are described in a separate paper. The camera resides at the focal plane of a 40 cm, f/10, Ferson reflector. The instrument has been in operation since December 1991 at the La Silla Observatory (ESO). 相似文献
2.
Wolfram Neutsch Herbert Kalisch Horst Fichtner S. Ranga Sreenivasan Maurice Shevalier 《Astrophysics and Space Science》2003,288(3):391-408
The study of the expansion of the solar wind out of a system of coronal holes is continued. To this end, we consider the numerical
integration of partial differential equations for problems with icosahedral symmetry, in general. First, employing Weyl theory,
orbifold coordinates are introduced. Second, the icosahedral coordinates are discussed in detail. Third, following an analysis
of the properties of these coordinates and the derivation of a few expressions useful for grid construction, various alternatives
for the distribution of lattice points required for numerical integration are considered. A comparison of these numerical
grids motivates the choice of a specific grid optimized for the numerical integration carried out in the accompanying paper
by Kalish et al.(2002).
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
3.
4.
Domenico Voltolina Leslie N. Brown Maurice G. Robinson 《Estuarine, Coastal and Shelf Science》1985,21(6):817-822
The results of eight sets of repeated observations on the vertical variations of the chlorophyll maximum layer in a shallow lagoon during a red tide show that these were more frequently hydrologically induced, rather than due to active vertical migrations of the red tide-forming organism. These results are discussed and compared to those existing in the literature, with special regard to the role of light and nitrogen in conditioning vertical migrations in red tide-forming dinoflagellates. 相似文献
5.
A large amount of interest has recently been expressed pertaining to the quantity of physically adsorbed water by the Martian regolith. Thermodynamic calculations based on experimentally determined adsorption and desorption isotherms and extrapolated to subzero temperatures indicate that physical adsorption of more than one or two monomolecular layers is highly unlikely under Martian conditions. Any additional water would find ice to be the state of lowest energy and therefore the most stable form. To test the validity of the thermodynamic calculations we have measured adsorption and desorption isotherms of sodium montmorillonite at ?5°C. To a first approximation it was found to be valid. 相似文献
6.
The chemical composition of fogwater has been studied in the city of Strasbourg (France) from 1990 to 1999. During these years, fogwater samples have been collected and analysed for major ions and trace metals. This paper reports on the analysis of the collected dataset. The analysis revealed a significant decrease in acidity of approximately one pH unit over the course of the study. This decrease in acidity appears to be linked to a decrease in SO2(g) and the resulting SO42−. Trace metal concentrations have also strongly decreased over the 10-year period. Pb concentrations, following the elimination of leaded gasoline, decreased by more than one order of magnitude. 相似文献
7.
Direct observations of aluminosilicate weathering in the hyporheic zone of an Antarctic Dry Valley stream 总被引:1,自引:0,他引:1
Patricia A. Maurice Diane M. McKnightLaura Leff Julia E. FulghumMichael Gooseff 《Geochimica et cosmochimica acta》2002,66(8):1335-1347
This study focused on chemical weathering and bacterial ecology in the hyporheic zone of Green Creek, a McMurdo Dry Valley (Antarctica) stream. An in situ microcosm approach was used to observe dissolution features on the basal-plane surface of muscovite mica. Four mica chips were buried in December 1999 and dug up 39 d later. Atomic force microscopy (AFM) of the basal-plane surfaces revealed small, anhedral ∼10-Å-deep etch pits covering ∼4% of the surfaces, from which an approximate basal-plane dissolution rate of 8.3 × 10−18 mol muscovite cm−2 s−1 was calculated (on the basis of the geometric surface area) for the study period. This is an integrated initial dissolution rate on a fresh surface exposed for a relatively brief period over the austral summer and should not be compared directly to other long-term field rates. The observation of weathering features on mica agrees with previous stream- and watershed-scale studies in the Dry Valleys, which have demonstrated that weathering occurs where liquid water is present, despite the cold temperatures.AFM imaging of mica surfaces revealed biofilms including numerous small (<1 μm long), rounded, oblong bacteria. The AFM observations agreed well with X-ray photoelectron microscopy results showing increased organic C and N. Bacteriologic analysis of the hyporheic zone sediments also revealed <1-μm-long bacteria. α-Proteobacteria were observed, consistent with the oligotrophic conditions of the hyporheic zone. Nitrate-reducing bacteria were found, in agreement with a previous tracer test at Green Creek that suggested nitrate reduction occurs in the hyporheic zone. The results of this study thus provide direct evidence of dynamic geochemical and microbial processes in the hyporheic zone of a Dry Valley stream despite the extreme conditions; such processes were inferred previously from stream-scale hydrogeochemical studies. 相似文献
8.
Landslides pose serious hazards in the Mercantour Massif and the French Riviera in southeastern France. The context for landslide development is a particularly favourable one, both in terms of the geomorphic and structural setting of this Alpine region, and of the climatic, hydrologic and seismic factors that trigger such failures. High mountain relief and steep slopes constitute a very favourable setting for failures affecting massive basement rocks and a very heterogeneous sedimentary cover whose resistance has been weakened by weathering, tectonic stresses, and cambering due to gravity. Among trigger factors, the important appears to be the precipitation regime. Rainfalls are commonly concentrated into short high-intensity downpours or into bursts of sustained falls over periods of several days, leading to soil saturation and lubrication of potential failure planes. Snowmelt also contributes to these lubrication processes. Earthquakes affecting this region are also a potentially important landslide trigger. However, while a lot of work has been done on the relationship between extreme climatic events and landslide activity, much less is known of the trigger effects of earthquakes.Both the background factors that promote landslide development and the factors that trigger such failures are discussed within a time frame of landslide development. Progressive changes in soil strength due to weathering, rock cambering and shattering processes lead to long-term reduction in resistance. Superimposed on these progressive changes are episodic triggerings related to rainfall and snowmelt episodes or earthquakes. Landslides may occur as shallow, low-volume “one-time” events or may be part of a progressive long-term failure. The former generally affect unconsolidated or clay-rich sedimentary rocks, especially on the coastal hillslopes of the French Riviera. A notable exception of a major, voluminous “one-time” event was the submarine landslide of the Var Delta in 1979. This landslide, like numerous other smaller subaerial landslides onland, was largely a result of human activities. This landslide occurred following extensive modification of the Var Delta and, notably, reclamation of the steep, fine-grained delta front. Deforestation, quarrying, urbanisation and road network developments are various ways in which human activity has destabilized the coastal hillslopes, favouring the development of numerous shallow landslides following each episode of heavy rainfall.Progressive landslides on the upper hillslopes of the Mercantour Massif have developed over long time spans (order of 101 to 105 yrs) and have involved more complex interactions between lithological controls, slope characteristics and trigger factors. The Collelongue and Bois de Malbosc landslides have evolved into now stable failures buttressed by resistant migmatitic diorites or amphibolites. The more voluminous and well monitored Clapière landslide is a relatively simple rotational landslide of the toe-failure type. This active landslide poses a serious to inhabitants and infrastructure in the Tinée Valley. The importance of continued field monitoring, modelling and mapping of landslides and their hazards is emphasised. 相似文献
9.
Concentrated plasticity (CP) models are frequently used in static and dynamic building analysis and have been implemented in available commercial software. This investigation deals with three different CP‐models, a simplified macroelement model (SEM) for a complete building story, a frame element with elasto‐plastic interaction hinges (PH), and a frame element with fiber hinges (FB). The objectives of this work are to evaluate the quality of the earthquake responses predicted by these models and to identify important aspects of their implementation and limitations for their use in dynamic analysis. The three elements are tested in a single‐story asymmetric plan building and in a three‐story steel building. Results show that base shear and global response values are usually computed with better accuracy than interstory deformations and local responses. Besides, the main limitation of elasto‐plastic CP models is to control the displacement offsets that result from perfect elasto‐plastic behavior. On the other hand, calibration of the SEM‐model shows that global responses in steel structures may be computed within 20% error in the mean at a computational cost two orders of magnitude smaller than that of the other CP elements considered. However, the three element models considered lead to increasing levels of accuracy in the dynamic response and their use depends on the refinement of the analysis performed. Copyright © 2005 John Wiley & Sons, Ltd. 相似文献
10.
Laurence Le Callonnec Alain Person Maurice Renard René Létolle Nathalie Nebout Leila Ben Khelifa Ivan Rubanov 《Comptes Rendus Geoscience》2005,337(12):1035-1044
The withdrawal of the Aral Sea tributaries (Amu and Syr Daria) for cultures has led to significant falls of its level and an important increase in its salinity. During the Holocene, a succession of low and high water inputs occurred. Silty deposits correspond to the high levels and carbonates to the low levels. This study makes a distinction between the Syr Daria and the Amu Daria water inputs during low-level periods by using mineralogical and chemical compositions of the carbonates deposits. Waters from the Syr Daria are more sulphatic and have a low iron content in comparison with that of the Amu Daria. The Syr Daria was the major tributary around 7500, 4956 and 970 yr?BP, whereas around 6200 and 3610 yr?BP, inflow also from the Amu Daria is observed. To cite this article: L. Le Callonnec et al., C. R. Geoscience 337 (2005). 相似文献