Ultra-long range correlations of the dynamics of jammed soft matter

We use Photon Correlation Imaging, a recently introduced space-resolved dynamic light scattering method, to investigate the spatial correlation of the dynamics of a variety of jammed and glassy soft materials. Strikingly, we find that in deeply jammed soft materials spatial correlations of the dynamics are quite generally ultra-long ranged, extending up to the system size, orders of magnitude larger than any relevant structural length scale, such as the particle size, or the mesh size for colloidal gel systems. This has to be contrasted with the case of molecular, colloidal and granular ``supercooled'' fluids, where spatial correlations of the dynamics extend over a few particles at most. Our findings suggest that ultra long range spatial correlations in the dynamics of a system are directly related to the origin of elasticity. While solid-like systems with entropic elasticity exhibit very moderate correlations, systems with enthalpic elasticity exhibit ultra-long range correlations due to the effective transmission of strains throughout the contact network.Comment: To appear in Soft Matte

Hybrid magnetic iron oxide nanoparticles with tunable field-directed self-assembly

We describe the synthesis of hybrid magnetic ellipsoidal nanoparticles that consist of a mixture of two different iron oxide phases, hematite (α-Fe2O3) and maghemite (γ- Fe2O3), and characterize their magnetic field-driven self-assembly. We demonstrate that the relative amount of the two phases can be adjusted in a continuous way by varying the reaction time during the synthesis, leading to strongly varying magnetic properties of the particles. Not only does the saturation magnetization increase dramatically as the composition of the spindles changes from hematite to maghemite, but also the direction of the induced magnetic moment changes from being parallel to the short axis of the spindle to being perpendicular to it. The magnetic dipolar interaction between the particles can be further tuned by adding a screening silica shell. Small-angle X-ray scattering (SAXS) experiments reveal that at high magnetic field, magnetic dipole–dipole interaction forces the silica coated particles to self- assemble into a distorted hexagonal crystal structure at high maghemite content. However, in the case of uncoated maghemite particles, the crystal structure is not very prominent. We interpret this as a consequence of the strong dipolar interaction between uncoated spindles that then become arrested during field-induced self- assembly into a structure riddled with defects

Pablo Neruda a 110 años de su nacimiento

Fue un poeta. No dudó en arrojarse a las aguas de la contradicción a fin de construir su propia arquitectura verbal. Puso en valor el destino de los pueblos y sus habitantes

"Na Cadencia Bonita do Samba": Accomplishing Suingue in Toronto

What happens when Afro-Brazilian sounds like samba are lifted from their context of origin and performed by and for non-Brazilians in Canada? In particular, what happens to the samba groove--"cadência" or "suingue" as Brazilians call it--and what does this suingue do, or not do, to those performing? I explore such questions by focusing on two interrelated matters pertaining to what the editors of this volume refer to as a presumed Brazilian improvisative consciousness: the pedagogical dynamics of samba transmission, and the dialectics of freedom and restraint in samba’s creative processes, particularly in the context of Canadian samba. This article is informed by my ongoing field research with performers of Afro-Brazilian music in Toronto and surrounding areas who play in large, amateur ensembles such as Batucada Carioca, of which I am a member

Pratiques professionnelles et représentations en prévention et promotion de la santé

Depuis plusieurs années, la prévention et la promotion de la santé se trouvent au cœur des poli- tiques de santé publique. Une pluralité d’interventions se déploient, amenant à une redéfinition des champs d’exercice et une évolution des pratiques professionnelles. Cette étude qualitative, réalisée auprès de professionnels, explore les pratiques, les savoirs et représentations mobilisés dans l’intervention en prévention et promotion de la santé et tend à repérer les processus sous-jacents à la circonscription de ces deux champs d’exercice. Les résultats montrent une difficulté à délimiter le « territoire » de la prévention et de la promotion de la santé. Les savoirs construits sont davantage caractérisés par une « mise en pratique » plutôt que fondés sur une conception théorique. Il existe une tension entre politiques publiques et valeurs professionnelles. Cette étude invite à réinterroger des notions essentielles (prévention et promotion de la santé) inhérentes à des champs d’exercice en santé publique. Enfin, ce travail met en perspective la manière dont les professionnels s’approprient et incarnent la prévention et promotion de la santé sur leur terrain d’exercice, réélaborent et transmettent des savoirs en ce sens. L’amélioration de la connaissance des pratiques et des représentations constitue une démarche heuristique de compréhension des réalités complexes de terrain