Observations of the daytime boundary layer in deep alpine valleys

Peer reviewe

Observations of the daytime boundary layer in deep alpine valleys

Peer reviewe

Modelling photochemistry in alpine valleys

Peer reviewe

A KINEMATIC STUDY OF BUTTERFLY TURN IN ELITE SWIMMERS

The aims of this work were (i) to evaluate the different phases of the butterfly turn during a 200 m race (in long course), (ii) to determine if the wall contact times were related to swim velocity, (iii) to compare the turn variables of the European champion with the other swimmers studied. Two studies were carried out, the first one was to: (i) test 22 swimmers ranked in 3 groups according to their performance. The most significant results revealed that the third turn was performed quicker by GI (the faster group) than by G3 (the slower group), both before (

Estimating the diffusive heat flux across a stable interface forced by convective motions

Original article can be found at: http://www.nonlin-processes-geophys.net/volumes_and_issues.html Copyright Author(s) 2010. This work is distributed under the Creative Commons Attribution 3.0 License.Entrainment at the top of the convectively-driven boundary layer (CBL) is revisited using data from a high-resolution large-eddy simulation (LES). In the range of values of the bulk Richardson number RiB studied here (about 15–25), the entrainment process is mainly driven by the scouring of the interfacial layer (IL) by convective cells. We estimate the length and time scales associated with these convective cells by computing one-dimensional wavenumber and frequency kinetic energy spectra. Using a Taylor assumption, based upon transport by the convective cells, we show that the frequency and wavenumber spectra follow the Kolmogorov law in the inertial range, with the multiplicative constant being in good agreement with previous measurements in the atmosphere. We next focus on the heat flux at the top of the CBL, , which is parameterized in classical closure models for the entrainment rate we at the interface. We show that can be computed exactly using the method proposed by Winters et al. (1995), from which the values of a turbulent diffusivity across the IL can be inferred. These values are recovered by tracking particles within the IL using a Lagrangian stochastic model coupled with the LES. The relative difference between the Eulerian and Lagrangian values of is found to be lower than 10%. A simple expression of we as a function of is also proposed. Our results are finally used to assess the validity of the classical "first-order'' model for we. We find that, when RiB is varied, the values for we derived from the "first-order'' model with the exact computation of agree to better than 10% with those computed directly from the LES (using its definition). The simple expression we propose appears to provide a reliable estimate of we for the largest values of RiB only.Peer reviewe

Combination of carbon nanotubes and two-photon absorbers for broadband optical limiting

New systems are required for optical limiting against broadband laser pulses. We demonstrate that the association of non-linear scattering from single-wall carbon nanotubes (SWNT) and multiphoton absorption (MPA) from organic chromophores is a promising approach to extend performances of optical limiters over broad spectral and temporal ranges. Such composites display high linear transmission and good neutral colorimetry and are particularly efficient in the nanosecond regime due to cumulative effects.Comment: 5 avril 200