Competing tunneling and capacitive paths in Co-ZrO2 granular thin films

The ac electrical response is studied in thin films composed of well-defined nanometric Co particles embedded in an insulating ZrO2 matrix which tends to coat them, preventing the formation of aggregates. In the dielectric regime, ac transport originates from the competition between interparticle capacitive Cp and tunneling Rt channels, the latter being thermally assisted. This competition yields an absorption phenomenon at a characteristic frequency 1/(RtCp), which is observed in the range 1010 000 Hz. In this way, the effective ac properties mimic the universal response of disordered dielectric materials. Temperature and frequency determine the complexity and nature of the ac electrical paths, which have been successfully modeled by an Rt-Cp network.

Synthesis, structural order and magnetic behavior of self-assembled epsilon-Co nanocrystal arrays

The synthesis of magnetic nanoparticles with monodispere size distributions, their self assembly into ordered arrays and their magnetic behavior as a function of structural order (ferrofluids and 2D assemblies) are presented. Magnetic colloids of monodispersed, passivated, cobalt nanocrystals were produced by the rapid pyrolysis of cobalt carbonyl in solution. The size, size distribution (std. dev.< 5%) and the shape of the nanocrystals were controlled by varying the surfactant, its concentration, the reaction rate and the reaction temperature. The Co particles are defect-free single crystals with a complex cubic structure related to the beta phase of manganese (epsilon-Co). In the 2D assembly, a collective behavior was observed in the low-field susceptibility measurements where the magnetization of the zero field cooled process increases steadily and the magnetization of the field cooling process is independent the temperature. This was different from the observed behavior in a sample comprised of disordered interacting particles. A strong paramagnetic contribution appears at very low temperatures where the magnetization increases drastically after field cooling the sample. This has been attributed to the Co surfactant-particle interface since no magnetic atomic impurities are present in these samples.

Discours économique et évolution institutionnelle, les apports de J. R. Commons

John Roger Commons est, de manière quasi systématique, considéré comme l'un des pères fondateurs de l'ancien institutionnalisme américain. On souligne tout aussi couramment l'influence que la philosophie pragmatiste a pu avoir sur ses travaux, du moins en ce qui concerne son ouvrage de 1934. Plus rares sont les commentateurs soulignant le rôle qu'a le langage, a fortiori le langage de l'économiste, dans l'analyse qu'il fait de l'évolution institutionnelle. Notre but sera de souligner ce fait : pour Commons, dire c'est faire, dans la lignée de la linguistique performativiste, dire c'est agir sur l'évolution institutionnelle. Abstract : John Roger Commons is well known as one of the founders of old institutionnalism. It is current to emphazise his philosophical roots : the american pragmatism, at least in his masterpiece of 1934. On the other hand, it is less frequent to point out the important role that the langage, and a fortiori economics' langage, has in his understanding of institutional evolution. Our aim will be to spotlight this point : for Commons, we can do things with words, on the way of performativist linguistic, when we use words, we influence institutional evolution.