Absorption spectrum in the wings of the potassium second resonance doublet broadened by helium

We have measured the reduced absorption coefficients occurring in the wings of the potassium 4S-5P doublet lines at 404.414 nm and at 404.720 nm broadened by helium gas at pressures of several hundred Torr. At the experimental temperature of 900 K, we have detected a shoulder-like broadening feature on the blue wing of the doublet which is relatively flat between 401.8 nm and 402.8 nm and which drops off rapidly for shorter wavelengths, corresponding to absorption from the X doublet Sigma+ state to the C doublet Sigma+ state of the K-He quasimolecule. The accurate measurements of the line profiles in the present work will sharply constrain future calculations of potential energy surfaces and transition dipole moments correlating to the asymptotes He-K(5p), He-K(5s), and He-K(3d).Comment: 2 figure

Effects of aeolian processes on water infiltration in sandy Sahelian rangeland in Burkina Faso

In Sahelian ago-ecosystems, sandy microdunes often provide a privileged habitat for primary production and can also be potential initial points for the regeneration of eroded surfaces. The aim of this study is to understand the role of sandy aeolian deposits in the retention of rain and runoff water on overgrazed Sahelian hillslopes. It focuses on the interactions between wind and water processes. Water is beneficial to the development of vegetation if it (i) infiltrates through soil surfaces; (ii) reaches a sufficient depth so that it does not rapidly evaporate; and (iii) is accessible to plant roots. In this study, the wetting-front depth (WFD) proved to be a relevant indicator of these three criteria. Investigations were conducted within three plots with surface area of 14,000, 376 and 36 m(2) and grids of observations of 4, 0.5 and 0.2 m, respectively. The largest plot was a micro-catchment patched with sandy aeolian deposits. The two other plots were isolated microdunes with a typical asymmetric shape. A cone penetrometer was used to estimate the WFD and survey its spatial variability. Soil surface conditions (micro-relief, plant cover, crusted areas) were also estimated following the typology of Casenave and Valentin (Casenave, A., Valentine, C., 1992. A runoff capability classification system based on surface features criteria in semi-arid areas of West Africa. Journal of Hydrology 130, 231-249). At the catchment scale, WFD values ranged from 0-0.82 m. The deepest infiltration occurred within sandy deposits which supported an herbaceous cover of > 50% (drying surface type) and along rills filled with coarse sands (runoff surface type). Minimum WED values were observed on bare crusted surfaces with gentle slopes (erosion surface type). At the microdune scale, the important penetration depths coincided with bare windward surfaces with steep slopes. This unexpected result seems to be due to the combined effect of wind deflation and splash erosion, which would hamper the development of impervious crusts. These results could have significant impacts for better understanding of rangeland sandy soil in semi-arid areas. (c) 2006 Elsevier B.V. All rights reserved

Aile quasistatique et satellite bleu du doublet 4s-5p du potassium perturbé par le néon

Les profils d’absorption et d’émission du doublet 42S-52P (4044/47 Å) du potassium perturbé par le néon ont été enregistrés par une technique de fluorescence induite par laser et comparés aux profils calculés par la théorie quasistatique à partir d’un nouveau potentiel modèle. On observe un satellite bleu dont la position coïncide remarquablement (⩽ 1 Å) avec celle prévue par le potentiel. Comparée aux intensités calculées, l’intensité observée dans l’aile bleue est la moitié alors qu’elle est le double dans l’aile rouge

Bruit des systemes de transmissions mecaniques Etude des mecanismes de generation du bruit et des moyens mis en oeuvre pour le reduire

Available at INIST (FR), Document Supply Service, under shelf-number : 18477, issue : a.1992 n.93 / INIST-CNRS - Institut de l'Information Scientifique et TechniqueSIGLEFRFranc