Collective modes of a quasi two-dimensional Bose condensate in large gas parameter regime

We have theoretically studied the collective modes of a quasi two-dimensional (Q2D) Bose condensate in the large gas parameter regime by using a formalism which treats the interaction energy beyond the mean-field approximation. In the calculation we use the perturbative expansion for the interaction energy by incorporating the Lee, Huang and Yang (LHY) correction term. The results show that incorporation of this higher order term leads to detectable modifications in the mode frequencies.Comment: 10 pages, 2 figure

A laboratory-numerical approach for modelling scale effects in dry granular slides

Granular slides are omnipresent in both natural and industrial contexts. Scale effects are changes in physical behaviour of a phenomenon at different geometric scales, such as between a laboratory experiment and a corresponding larger event observed in nature. These scale effects can be significant and can render models of small size inaccurate by underpredicting key characteristics such as ow velocity or runout distance. Although scale effects are highly relevant to granular slides due to the multiplicity of length and time scales in the flow, they are currently not well understood. A laboratory setup under Froude similarity has been developed, allowing dry granular slides to be investigated at a variety of scales, with a channel width configurable between 0.25-1.00 m. Maximum estimated grain Reynolds numbers, which quantify whether the drag force between a particle and the surrounding air act in a turbulent or viscous manner, are found in the range 102-103. A discrete element method (DEM) simulation has also been developed, validated against an axisymmetric column collapse and a granular slide experiment of Hutter and Koch (1995), before being used to model the present laboratory experiments and to examine a granular slide of significantly larger scale. This article discusses the details of this laboratory-numerical approach, with the main aim of examining scale effects related to the grain Reynolds number. Increasing dust formation with increasing scale may also exert influence on laboratory experiments. Overall, significant scale effects have been identified for characteristics such as ow velocity and runout distance in the physical experiments. While the numerical modelling shows good general agreement at the medium scale, it does not capture differences in behaviour seen at the smaller scale, highlighting the importance of physical models in capturing these scale effects

Le piezocone améliorations apportées à la reconnaissance des sols

Lorsqu'un capteur de pression est incorporé dans un pénétromètre statique électrique, cet ensemble est appelé piézocône.Les auteurs donnent l'état des connaissances de cet essai relativement récent. Ils décrivent les précautions à prendre pour faire des mesures fiables de la pression interstitielle générée par la pénétration du cône. Ils montrent l'intérêt du piézocône pour obtenir des profils stratigraphiques précis, pour connaître la résistance au cisaillement des argiles, pour apprécier le potentiel de liquéfaction au séisme de couches sableuses, et pour faire des prédictions de temps de consolidation de couches compressibles chargées in situ (courbe Kh en fonction de t50)