Annular cracks in thin films of nanoparticle suspensions drying on a fiber

We report an experimental study of the crack pattern formed during the drying of a colloidal suspension. A horizontal fiber, which provides a one dimensional, boundary-free substrate, is coated by a film of micronic thickness. The geometry imposes a remarkable annular crack pattern and allowing precise measurements of the crack spacing over a short range of film thickness (between 2 and 10 $\mu$m) which varies linearly with the film height. We compare our experimental data with a model proposed by Kitsunezaki which suggests that the variation of the crack spacing with the film thickness depends on the ratio between a critical stress at cracking and a critical stress for slipping on the substrate. By measuring the friction force of the colloidal gels on a hydrophobic surface through a cantilever technique, we can deduce the critical crack stress for these colloidal gels simply by measuring the crack spacing of the pattern.Comment: Accepted in EP

Instability and morphology of polymer solutions coating a fiber

We report an experimental study on the dynamics of a thin film of polymer solution coating a vertical fiber. The liquid film has first a constant thickness and then undergoes the Rayleigh-Plateau instability which leads to the formation of sequences of drops, separated by a thin film, moving down at a constant velocity. Different polymer solutions are used, i.e. xanthan solutions and polyacrylamide (PAAm) solutions. These solutions both exhibit shear-rate dependence of the viscosity, but for PAAm solutions, there are strong normal stresses in addition of the shear-thinning effect. We characterize experimentally and separately the effects of these two non-Newtonian properties on the flow on the fiber. Thus, in the flat film observed before the emergence of the drops, only shear-thinning effect plays a role and tends to thin the film compared to the Newtonian case. The effect of the non-Newtonian rheology on the Rayleigh-Plateau instability is then investigated through the measurements of the growth rate and the wavelength of the instability. Results are in good agreement with linear stability analysis for a shear-thinning fluid. The effect of normal stress can be taken into account by considering an effective surface tension which tends to decrease the growth rate of the instability. Finally, the dependence of the morphology of the drops with the normal stress is investigated and a simplified model including the normal stress within the lubrication approximation provides good quantitative results on the shape of the drops.Comment: Accepted in Journal of Fluid Mechanic

Access and Benefit Sharing under the Convention on Biological Diversity and Its Protocol : What Can Some Numbers Tell Us about the Effectiveness of the Regulatory Regime?

The Convention on Biological Diversity (CBD), adopted in 1992 and entered into force at the end of 1993, established a global regime on access to genetic resources (GR) and sharing of benefits arising from their utilization (Access and Benefit Sharing (ABS) regime). Its protocol—the Nagoya Protocol (NP)—which entered into force 21 years later in 2014, clears up some terminological ambiguities of the Convention, clarifies and develops several procedural and instrumental elements of the regime, and obliges States Parties to implement some of its provisions, including the core instrument of the regime: the bilateral ABS agreement between users and providers of GR, that became a condition for obtaining access to the resource. However, scholars who analyzed the ABS regime as well as its official bodies find, and sometimes deplore, the small number of ABS agreements concluded so far, under the CBD as under the NP. This paper has two objectives: First, to assess the effectiveness of the ABS regime implemented by the CBD and the NP on the basis of its central instrument: the ABS agreements concluded between users and providers of GR. The aim is to accurately document the number of ABS agreements concluded since the entry into force of the regime. To our knowledge, such a counting that is neither piecemeal nor has an estimate yet been produced. To do so, I combine several sources, including first hand data collected from the official information agencies—the National Focal Points (NFP)—of each of the States Parties to the NP. Second, I provide a critical summary of the existing explanations of the low number of ABS agreements concluded and I evaluate the corresponding causal mechanisms, relying on the results I obtained regarding the number of permits and agreements

De l’intégration scolaire à l’inclusion scolaire: quels obstacles et quels leviers du point de vue des enseignants ordinaires ?

Dans le cadre de ce travail, nous avons choisi d’étudier le passage de l’intégration scolaire à l’inclusion scolaire. Nous nous sommes intéressées plus particulièrement aux obstacles et aux leviers qu’identifient les enseignants ordinaires à ce passage. Pour répondre à nos différentes questions de recherche, nous avons opté pour la méthode qualitative et la passation d’entretiens semi-directifs. A cet effet, nous nous sommes rendues auprès de huit enseignants ordinaires du canton de Fribourg. Tout d’abord, nous avons questionné le sens que donnent les enseignants ordinaires aux concepts d’intégration scolaire et d’’inclusion scolaire, puis comment ces mêmes enseignants voient le passage progressif entre les deux, les conditions et les obstacles à ce passage, et finalement, leurs besoins quant à cette transition. Ces entretiens nous ont permis de répondre à nos questions de recherche. Bien que les enseignants semblent penser que le passage de l’intégration scolaire à l’inclusion est souhaitable, ils énoncent passablement de conditions à mettre en place. Selon eux, ces dernières impliquent de nombreux changements à différents niveaux. Pour se sentir prêts à ce passage, les enseignants ordinaires interrogés énoncent divers besoins. Finalement, nous avons discuté les résultats en distinguant les obstacles et les leviers. Ceux-ci n’étant pas directement interrogés, nous les avons extraits des différents résultats