The movement of water droplets in clouds around the nose of an atmospheric research aircraft

The dynamic interaction between droplets and the airflow around the hemispherical nose of an aircraft was evaluated. The effect of the aircraft nose on droplet sampling for cloud research is explained. The proportion of different droplet sizes and their concentration at each point around the aircraft nose were determined. In a cloud, interaction between droplets is negligible. Each particle acts, for the calculation of the forces applied to it, as if it is alone in the air. The airflow carrying the droplets, on the average, is not influenced by their presence. The trajectory of each droplet was studied separately after calculating dry airflow. Concentrations were found with a Lagrangian method, using two trajectories computed directly close to one another. Theory confirms that to within 3% experimentally measured concentrations are representative of those in a cloud

Les figures d'Alexandre dans la littérature persane : entre assimilation, moralisation et ironie

13 pages, preprint d'un article à paraître dans l'ouvrage collectif Epopées du monde. Contribution à un panorama (presque) complet, textes réunis et présentés par E. Feuillebois, avec une conclusion de Florence Goyet, sous presse chez Classiques Garnier, 2011The article investigates Persian sources of information regarding Alexander, and the different lectures of the sources by literature, giving birth to diametrically opposing literary characters: Ferdowsi's tragic hero, Nezâmi's ideal king and prophet, and the anti-hero in popular novels.L'article examine les sources d'informations des Persans sur le personnage historique d'Alexandre, et les lectures qui en ont été faites par la littérature, donnant naissance à des personnalités littéraires diamétralement opposées : le héros tragique de Ferdowsi, le souverain idéal et la figure prophétique de Nezâmi, l'anti-héros du roman populaire

Lubrication approximation for micro-particles moving along parallel walls

Lubrication expressions for the friction coefficients of a spherical particle moving in a fluid between and along two parallel solid walls are explicitly evaluated in the low-Reynolds-number regime. They are used to determine lubrication expression for the particle free motion under an ambient Poiseuille flow. The range of validity and the accuracy of the lubrication approximation is determined by comparing with the corresponding results of the accurate multipole procedure. The results are applicable for thin, wide and long microchannels, or quasi-two-dimensional systems.Comment: 4 pages, 5 figure

Transverse flow in thin superhydrophobic channels

We provide some general theoretical results to guide the optimization of transverse hydrodynamic phenomena in superhydrophobic channels. Our focus is on the canonical micro- and nanofluidic geometry of a parallel-plate channel with an arbitrary two-component (low-slip and high-slip) coarse texture, varying on scales larger than the channel thickness. By analyzing rigorous bounds on the permeability, over all possible patterns, we optimize the area fractions, slip lengths, geometry and orientation of the surface texture to maximize transverse flow. In the case of two aligned striped surfaces, very strong transverse flows are possible. Optimized superhydrophobic surfaces may find applications in passive microfluidic mixing and amplification of transverse electrokinetic phenomena.Comment: 4 page

La nouvelle artistique de l’époque romantique au miroir de la presse

Cet article propose une analyse de la « nouvelle artistique » « Le Peintre », écrite par l’écrivain romantique Vladimir Odoevskij en 1839 et traditionnellement interprétée, à l’instar de l’ensemble du corpus des « nouvelles artistiques » romantiques et postromantiques, comme une démonstration qu’il est impossible de réaliser des valeurs artistiques supérieures dans le monde ordinaire. L’article propose de relire à nouveaux frais ce texte typique, en utilisant une grille de lecture élaborée au croisement des sciences sociales et de la critique littéraire dans l’étude d’autres littératures européennes : cette méthode suggère que l’interprétation de tels textes a été longtemps conditionnée par le support sur lequel ces œuvres parvenaient au lecteur, mais qu’un retour au contexte originel de publication permet de les considérer d’une manière nouvelle. Dans cette perspective, il devient ainsi possible de lire la « nouvelle artistique » composée par Odoevskij, non comme une forme de désillusion envers les idéaux romantiques, mais comme la seule manière de les maintenir et de les diffuser.This paper offers an analysis of the ‘artist story’ ‘The Painter’, written by the Romantic Vladimir Odoevskij in 1839: this short story is usually interpreted as are all the genre of the Romantic and post-Romantic ‘artist stories’ and considered as a demonstration that it is impossible to realize superior artistic values in the ordinary world. This paper applies to Odoevskij’s short story a new way of reading such well-known texts, using the frame constructed in collaboration between social sciences and literary criticism in the studies of other European literature: such a method suggests that for many years the interpretation of theses texts has proceeded from the material support on which these works were read by the modern public, but that returning to the original conditions of publication helps reading them anew. In this perspective, it becomes possible to consider the ‘artist story’ composed by Odoevskij, not as a form of disillusion towards Romantic ideals, but as the only way to perpetuate them and make them public

Effective slip over superhydrophobic surfaces in thin channels

Superhydrophobic surfaces reduce drag by combining hydrophobicity and roughness to trap gas bubbles in a micro- and nanoscopic texture. Recent work has focused on specific cases, such as striped grooves or arrays of pillars, with limited theoretical guidance. Here, we consider the experimentally relevant limit of thin channels and obtain rigorous bounds on the effective slip length for any two-component (e.g. low-slip and high-slip) texture with given area fractions. Among all anisotropic textures, parallel stripes attain the largest (or smallest) possible slip in a straight, thin channel for parallel (or perpendicular) orientation with respect to the mean flow. For isotropic (e.g. chessboard or random) textures, the Hashin-Strikman conditions further constrain the effective slip. These results provide a framework for the rational design of superhydrophobic surfaces.Comment: 4+ page