Sizing of riprap for spill-through abutments

An experimental investigation of riprap stability at spill-through abutments has been carried out in two similar horiontal-bed flumes, avoiding riprap failure modes other than shear failure and erosion failure. Tests were conducted for two common abutment side slopes, subcritical flow regime, short to intermediate abutment lenghts and high bed roughness. The aim of the experiments was to determine the size of stone riprap necessary to resist (a) shear failure in aprons placed at the base of spill-through abutments, and (b) erosion failure over their side slopes. Results are compared with predictions of stone riprap size given by expressions found in the literature. The predictor of Pagan-Ortiz is confirmed as being appropriate for shear failure at abutment aprons and can be adapted to account for erosion failure over abutment side slopes. Alternatively, two news expressions, written in terms of the (critical) approach flow intensity required to make the riprap stones move, are suggested

Toe protection for spill-through and vertical-wall abutments

This study addresses the design of riprap aprons as a scour countermeasure near abutments under clear-water conditions. It deals with the lateral extent of riprap aprons and the geometry of the scour hole prevailing at the apron edge. The study applies to riprap aprons acting as granular filters. The scour depth appears to be independent for a sufficiently long relative abutment length. Scour holes develop farther away from spill-through abutments than from vertical-wall abutments; the distance between the point of maximum scour depth and the abutment increases with the relative abutment length. The effect of contraction on this distance was not identified. The angle defining the position of the deepest scour point is close to 308. Neither the abutment shape nor the flow contraction seems to influence the minimum stable apron width

Transfert de charge de protons avec formation d'atomes d'hydrogène fortement excités

A study was made of the formation of highly excited hydrogen atoms, having principal quantum numbers n ≽ 9, by charge exchange of 20-150 keV protons in the gases H2, Ar, He. The relative yield of highly excited atoms was determined by ionizing them in a strong electric field. It was found a maximum for the yield of these atoms at the same order of the energy, in the case of H2 and Ar.On étudie la formation d'atomes d'hydrogène excités sur des niveaux n ≽ 9, par échange de charge de protons d'énergie 20 à 150 keV, passant à travers différents gaz : H2, Ar, He. La production relative des atomes excités est déterminée par leur ionisation au moyen d'un champ électrique intense. Les résultats montrent que la production maximale d'atomes excités est obtenue pour la même valeur de l'énergie des ions, dans le cas où l'échange de charge se fait avec des gaz hydrogène et d'argon

Sections efficaces d'émission des raies de Balmer Hα, H β, Hγ produites par impact de protons 10-100 keV sur N2 et O2

Absolute cross sections have been measured for the emission of the Balmer Hα, Hβ, Hγ lines produced by 10-100 keV proton impact on N2 and O2. The polarization of the Hα and Hβ lines has been determined for these gases from 10 to 60 keV. The cross sections show a similar dependence on impact energy for different lines, except at low energy for Hβ and Hγ in N2.Nous avons mesuré des valeurs absolues des sections efficaces d'émission des raies de Balmer Hα, Hβ, Hγ produites par collisions de protons d'énergie 10 keV ≤ E ≤ 100 keV sur les cibles N2 et O2. La polarisation des raies Hα et Hβ a été déterminée pour 10 keV ≤ E ≤ 60 keV. Les sections efficaces montrent une même dépendance en fonction de l'énergie pour les différentes raies, excepté à basse énergie pour les raies Hβ et Hγ dans N2

An optical diffractive method for characterizing SSFLC field induced director patterns in the SmC* phase

International audienceChevron and quasi-bookshelf textures in Surface Stabilized Ferroelectric Liquid Crystals, as well as intermediate transition textures, correspond to distinct birefringence modulations and result in distinct diffraction properties which are theoretically analysed. The experimental study of the polarization and illumination properties of diffraction patterns allows us to distinguish the actual texture of a liquid crystal among the above possible textures