Structural Dependence of the Molecular Mobility in the Amorphous Fractions of Polylactide

Fragility index and cooperativity length characterizing the molecular mobility in the amorphous phase are for the first time calculated in drawn polylactide (PLA). The microstructure of the samples is investigated from wide-angle X-ray scattering (WAXS) whereas the amorphous phase dynamics are revealed from broadband dielectric spectroscopy (BDS) and temperature-modulated differential scanning calorimetry (TMDSC). The drawing processes induce the decrease of both cooperativity and fragility with the orientation of the macromolecules. Post-drawing annealing reveals an unusual absence of correlation between the evolutions of cooperativity length and fragility. The cooperativity length remains the same compared to the drawn sample while a huge increase of the fragility index is recorded. By splitting the fragility index in a volume contribution and an energetic contribution, it is revealed that the amorphous phase in annealed samples exhibits a high energetic parameter, even exceeding the amorphous matrix value. It is assumed that the relaxation process is driven in such a way that the volume hindrance caused by the thermomechanical constraint is compensated by the acceleration of segmental motions linked to the increase of degrees of freedom. This result should also contribute to the understanding of the constraint slackening in the amorphous phase during annealing of drawn PLA, which causes among others the decrease of its barrier properties

The value of regionally focused comparative analysis

En este artículo, propongo que los estudios regionales de pocos casos tienen varias ventajas sobre los estudios transregionales de muchos casos si lo que buscamos es un análisis detallado que pueda proveer explicaciones ricas para los fenómenos políticos. Incluso si las conclusiones a las que lleguemos en estos estudios regionales de pocos casos sean difíciles de generalizar, en el trade-off entre intención y generalidad, prefiero el primero. Los estudios trans regionales de muchos casos y los regionales por supuesto que pueden nutrirse mutuamente, pero teniendo en cuenta que los primeros solo pueden establecer relaciones "acotadas" (thin) entre ciertas variables, cuya relación causal más precisa requerirá de un análisis más denso (thick). El mismo que puede lograrse con estudios regionales de pocos casos.In this article I propose that “Small N” regionally focused studies have many advantages over “Large N” cross regional studies if we seek detailed analyses that can provide meaningful explanations for political phenomena. Even if the conclusions found in regionally-focused work will be difficult to generalize, in the trade off between intention and generality I choose the former. Cross-regional and regional analysis could certainly inform each other, but having in mind that cross-regional analysis can only establish “thin” relations between certain variables, whose causal relation would require a more detailed and “thick” analysis. As the one provided by regionally-focused studies

L'éphéméride des élections 2007, du 1er septembre 2006 au 27 juin 2007

Rapport réalisé dans le cadre du Baromètre politique français 2007, Éphéméride des élections 2007 (1er septembre 2006-27 juin 2007

Study of poly(bisphenol A carbonate) relaxation kinetics at the glass transition temperature

In this work, the variations of the relaxation times are investigated above and below the glass transition temperature of a model amorphous polymer, the polycarbonate. Three different techniques (calorimetric, dielectric and thermostimulated currents) are used to achieve this goal. The relaxation time at the glass transition temperature was determined at the temperature dependence convergence of the relaxation times calculated with dynamic dielectric spectroscopy (DDS) for the liquid state and thermostimulated depolarisation currents (TSDC) for the vitreous state. We find a value of s(Tg) = 110 s for PC samples. The knowledge of the temperature dependence, s(T), and the value s(Tg) enables to determine the glass-forming liquid fragility index, m. We find m = 178 ± 5

Le vote des catholiques

Le vote des catholiques est souvent abordé par rapport aux enjeux de société. Il est nécessaire de l’aborder en soi. La religion renvoie à un système d’attitudes et de valeurs qui fait sentir ses effets sur le vote avec continuité depuis de nombreuses décennies. À la veille des élections de 2012, il est intéressant de savoir si les enquêtes montrent un vote catholique qui s’inscrit dans la continuité de ce qu’il a pu être lors de l’élection présidentielle de 2007.Note publiée sur le site du Cevipof "Elections 2012" In "Le recueil des notes du Cevipof - Les électorats sociologiques

The Construction of Indigenous Language Rights in Peru: A Language Regime Approach

From the 1990s onwards, many Latin American states have adopted constitutional reforms that recognise indigenous peoples’ rights. In this article, we address a much less studied aspect, the emergence of new language rights. Based on field research and process tracing, we study the case of Peru where indigenous language rights were created in the absence of ethnic parties and with a relatively weak indigenous movement. We argue that the country moved slowly away from a monolingual language regime towards the recognition of indigenous languages as official languages and the creation of language rights. We identify key moments of state transformation in the 1970s, the 1990s, and the 2000s as linked to successive building blocks in the creation of a multi-lingual language regime. In particular, the decentralisation reforms of the 2000s created new opportunities for subnational actors to further develop these rights in different regions of the country. We exemplify these dynamics by looking into the adoption of language rights in the regions of Cuzco and Ayacucho

Populists and Technocrats in Latin America: Conflict, Cohabitation, and Cooperation

The literature frequently presents populists and technocrats as antagonistic. Although undoubtedly there are good historical examples that confirm this tension, in this article we propose that the relations between economic technocrats and populists are less conflictive than usually assumed and cohabitation a more common outcome than expected. We argue that two conditions moderate conflict between populists and economic technocrats, leading not only to their cohabitation but to cooperation between them: the programmatic mandate of populists and the economic context of their rise to power. We analyse the relations of economic experts with nine populist presidents in contemporary Latin America to show this argument’s soundness

Selectivity for maltose and maltodextrins of maltoporin, a pore-forming protein of E. coli outer membrane

AbstractHomogeneous maltoporin (lamB protein), an Escherichia coli outer membrane spanning protein, was incorporated in phospholipid planar bilayers. It generates aqueous channels distinct from those formed by the non-specific porin (OmpF) or by phosphoporin (phoE protein). The single conductance, 150 pS in 1 M NACl, is much smaller than that of the porins. The channels, which are poorly selective for cations and voltage independent, are specifically inhibited by maltose and maltodextrins. This inhibition, observed in the absence of maltose binding protein, demonstrates that the selectivity of maltoporin for maltose and maltodextrins is an intrinsic property of the protein

Effect of Random Ethylene Comonomer on Relaxation of Flow-Induced Precursors in Isotactic Polypropylene

The effect of comonomer on structure and relaxation of flow-induced precursors was investigated in a series of isotactic polypropylene and random propylene−ethylene copolymers. The polymers were subjected to flow by fiber pulling and allowed to relax above their nominal melting temperature for specific times. The type of morphology developed after cooling revealed whether flow-induced precursors were still present or the melt had fully reequilibrated. Precursors were long-lived and, at fixed temperature, decayed significantly faster with higher ethylene content. The critical time for precursor relaxation followed an Arrhenius-type dependence with temperature. The apparent energy of activation for precursor dissolution decreased with increasing comonomer content, indicating that the rate-limiting step of the relaxation process becomes less difficult with higher ethylene fraction. This effect is attributed to ethylene co-units acting as disruptors of precursor structure and is discussed in terms of quasi-crystalline nature and characteristic chain stem length of precursor bundles. Includes supplemental materials

Seismic Fault Preserving Diffusion

This paper focuses on the denoising and enhancing of 3-D reflection seismic data. We propose a pre-processing step based on a non linear diffusion filtering leading to a better detection of seismic faults. The non linear diffusion approaches are based on the definition of a partial differential equation that allows us to simplify the images without blurring relevant details or discontinuities. Computing the structure tensor which provides information on the local orientation of the geological layers, we propose to drive the diffusion along these layers using a new approach called SFPD (Seismic Fault Preserving Diffusion). In SFPD, the eigenvalues of the tensor are fixed according to a confidence measure that takes into account the regularity of the local seismic structure. Results on both synthesized and real 3-D blocks show the efficiency of the proposed approach.Comment: 10 page