Percolation-induced frost formation

We report the observation of an unconventional mechanism for frost formation. On a smooth hydrophobic surface cooled much below the water freezing temperature (−9 °C), we find that, instead of the classical freezing of individual supercooled condensed droplets, frost can occur through a multi-step 2-dimensional percolation-driven mechanism. This in-plane propagation process provides a model to investigate more complex bulk phase transformations such as those occurring in atmospheric supercooled clouds. It can also lead to a new method to control and design in-plane solidification at a nanoscale level

Comparing Economic Dynamics of Oyster and Mussel Farming, with Particular Emphasis on their Profitability: An Application in the Mont-Saint-Michel Bay (France)

This paper sets out an evaluation of profitability differentials within shellfish farming activities of the Mont-Saint-Michel Bay. The objective is to examine whether profitability differentials have consequences in terms of economic dynamics and of management arrangements. The paper divides into four parts. The first part presents a retrospective analysis of shellfish farming activities in the Bay, which are nowadays dominated by Pacific oyster (Crassostrea gigas) and Blue mussel (Mytilus edulis). The second part consists in measuring the economic performances of enterprises. The indicators are based on the data provided by two surveys conducted in 2002 (mussel-farming) and 2004 (oyster-farming); methodological difficulties due in particular to the status of shellfish farming land are addressed here. The third part examines the determinants of the profitability for each sector, the profitability being the result of a combination of factors such as natural productivity, technical practices, production costs and products pricing. The last part discusses the implications of profitability differentials. Profitability differentials seem to be correctly reflected in land prices, but not necessarily in the annual ground fees perceived by the Administration. However, shellfish farming profitability should be included in redistributive mechanisms, as its relation to primary resources exploitation and management is not neutral. Thus, empirical evidence suggests that profitability differentials create bargaining powers which influence the results of negotiation between actors regarding the management of the Mont-Saint-Michel Bay

Droits à produire transférables

Cet article propose une analyse de l’évolution du système d’accès au foncier conchylicole en France ainsi qu’une étude de son fonctionnement actuel. Il traite la question de la répartition des moyens de production dans un secteur dominé par le modèle de l’exploitation familiale et ayant vocation à maintenir une base sociale créatrice d’emplois dans certaines zones d’activité du littoral. Le régime d’accès au foncier conchylicole s’apparente à un système de droits à produire transférables. Cependant, le développement spontané du marché des concessions conchylicoles dans un contexte de faible intervention de l’administration provoque des effets non désirés dont la manifestation est ici vérifiée empiriquement, sur données quantitatives et qualitatives. La discussion finale porte sur la recherche d’outils de régulation et d’indicateurs économiques pour un meilleur fonctionnement du marché des concessions.This paper sets out an historical analysis of the rights-based system applied to the French shellfish-farming sector and a study of the current operating way of this system. It addresses the issue of the distribution of production means within an industry whose two main characteristics are the familial exploitation model and the specific social objectives like jobs creation in some coastal areas. The shellfish farming rights-based system has evolved toward a transferable production-rights system. However, the spontaneous emergence of a market for production-rights in the context of a weak administrative intervention is likely to generate unintended effects, whose occurrence is tested using quantitative and qualitative data. The final discussion searches for the economic indicators and the regulation tools which could improve the efficiency of the shellfish farming concessions market

Dew condensation on desert beetle skin

Some tenebrionind beetles inhabiting the Namib desert are known for using their body to collect water droplets from wind-blown fogs. We aim to determine whether dew water collection is also possible for desert insects. For this purpose, we investigated the infra-red emissivity, and the wetting and structural properties, of the surface of the elytra of a preserved specimen of Physasterna cribripes (Tenebrionidæ) beetle, where the macro-structure appears as a series of “bumps”, with “valleys” between them. Dew formation experiments were carried out in a condensation chamber. The surface properties (infra-red emissivity, wetting properties) were dominated by the wax at the elytra surface and, to a lower extent, its micro-structure. We performed scanning electron microscope on histological sections and determined the infra-red emissivity using a scanning pyrometer. The emissivity measured (0.95 ± 0.07 between 8–14 μm) was close to the black body value. Dew formation occurred on the insect’s elytra, which can be explained by these surface properties. From the surface coverage of the condensed drops it was found that dew forms primarily in the valleys between the bumps. The difference in droplet nucleation rate between bumps and valleys can be attributed to the hexagonal microstructure on the surface of the valleys, whereas the surface of the bumps is smooth. The drops can slide when they reach a critical size, and be collected at the insect’s mouth

The shear viscosity of carbon fibre suspension and its application for fibre length measurement

The viscosity of short carbon fibre suspensions in glycerol aqueous solution was measured using a bespoke vane-in-cup viscometer, where the carbon fibre has an aspect ratio from 450 to 2209. In the semi-concentrated regime, nL3 ranging from 20 to 4400, the suspensions demonstrated strong shear-thinning characteristics particularly at higher concentrations. The shear-thinning characteristic is strongly related to the crowding factor proposed by Kerekes, indicating that non-hydrodynamic interactions occur in the suspensions. The influence of fibre bending on viscosity emerges when the bending ratio is lower than 0.0028. An empirical model based on transient network formation and rupture was proposed and used to correlate the relative viscosity with fibre concentration nL3 and shear rate. Based on the model, a viscosity method is established to analyse the fibre length by measuring the viscosity of the fibre suspension using a bespoke vane-in-cup viscometer

Micro grooved surface improve dew collection

This work presents an experimental study on the atmospheric water condensation on micro-grooved substrates. The influence of several physical and geometric parameters (relative humidity, substrate inclination with horizontal, groove size) on the process of condensation and drainage is presented. The process is studied by weighing collected water and visualizing the drops formed on the substrate. The grooves appear to markedly increase the collected amount of water by promoting drop coalescence and lowering pinning forces, resulting in early shedding when compared to a smooth surface with same wetting properties.papers presented to the 12th International Conference on Heat Transfer, Fluid Mechanics and Thermodynamics, Costa de Sol, Spain on 11-13 July 2016

Percolation-induced frost formation

We report the observation of an unconventional mechanism for frost formation. On a smooth hydrophobic surface cooled much below the water freezing temperature (−9 °C), we find that, instead of the classical freezing of individual supercooled condensed droplets, frost can occur through a multi-step 2-dimensional percolation-driven mechanism. This in-plane propagation process provides a model to investigate more complex bulk phase transformations such as those occurring in atmospheric supercooled clouds. It can also lead to a new method to control and design in-plane solidification at a nanoscale level