Weak versus strong wave turbulence in the MMT model

Within the spirit of fluid turbulence, we consider the one-dimensional Majda-McLaughlin-Tabak (MMT) model that describes the interactions of nonlinear dispersive waves. We perform a detailed numerical study of the direct energy cascade in the defocusing regime. In particular, we consider a configuration with large-scale forcing and small scale dissipation, and we introduce three non- dimensional parameters: the ratio between nonlinearity and dispersion, {\epsilon}, and the analogues of the Reynolds number, Re, i.e. the ratio between the nonlinear and dissipative time-scales, both at large and small scales. Our numerical experiments show that (i) in the limit of small {\epsilon} the spectral slope observed in the statistical steady regime corresponds to the one predicted by the Weak Wave Turbulence (WWT) theory. (ii) As the nonlinearity is increased, the WWT theory breaks down and deviations from its predictions are observed. (iii) It is shown that such departures from the WWT theoretical predictions are accompanied by the phenomenon of intermittency, typical of three dimensional fluid turbulence. We calculate the structure-function as well as the probability density function of the wave field at each scale and show that the degree of intermittency depends on {\epsilon}.Comment: 7 pages, 6 figure

Henry-Rusell Hitchcock y Philip Johnson: The International Style: architecture since 1922 , y otros textos. La Bauhaus en la crítica de Hitchcock

Henry-Rusell Hitchcock y Philip Johnson: The International Style: architecture since 1922 , y otros textos. La Bauhaus en la crítica de Hitchcoc

Synthesis of a Structured Material Based on Compact Spheres Coated with Zn or Mg Spinel

In this work, a synthesis method of coating with thin layers of MgAl2O4 or ZnAl2O4 over alpha-Al2O3 spheres were developed.The method consisted in the deposition of a primer of bohemite on the spheres, followed by the impregnation with a solution of Mg or Zn nitrates, and further thermal treatments in order to obtain MAl2O4 (M: Mg or Zn). This method was modified to improve the thickness and purity of the layer material. With this method, layers of uniform and adequate thickness and good adhesion were achieved. Pt catalysts prepared with these materials as supports displayed good catalytic performances in the n-butanedehydrogenation reaction, especially those obtained with purified supports.Fil: Bocanegra, Sonia Alejandra. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe. Instituto de Investigaciones en Catálisis y Petroquímica ; ArgentinaFil: Ballarini, Adriana Daniela. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe. Instituto de Investigaciones en Catálisis y Petroquímica ; ArgentinaFil: Scelza, Osvaldo Antonio. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe. Instituto de Investigaciones en Catálisis y Petroquímica ; ArgentinaFil: de Miguel, Sergio Ruben. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe. Instituto de Investigaciones en Catálisis y Petroquímica ; Argentin

La repoblación forestal en España: las especies utilizadas desde 1877 a partir de las cartografías forestales

En España, la actividad repobladora moderna comenzó en la segunda mitad del siglo xix. Este artículo analiza qué uso se hizo de las diferentes especies forestales en el periodo comprendido entre 1877 y 2013. Un periodo que subdividimos en tres etapas: 1877-1939, 1940-1984 y 1985-2013. Como fuentes documentales, utilizamos las series estadísticas forestales oficiales y las cartografías forestales de 1966 y 1997, que informan de una superficie repoblada que es, respectivamente, un 33% y 18% superior a la indicada por aquéllas. Ello confirma la importancia que tuvo la repoblación en la transformación del paisaje. Las cartografías forestales, cuya utilidad para corregir las deficiencias de las estadísticas oficiales queda así confirmada, también recogieron la rápida expansión en el territorio de las especies de crecimiento rápido, como el eucalipto, el pino de Monterrey, el pino gallego y el chopo, que en 1997 ocupaban el 46% de la superficie total repoblada. El resto de las repoblaciones se realizaron con especies autóctonas del género Pinus, que fueron las más utilizadas en las tres etapas. Sin embargo, en la última etapa las especies mediterráneas del género Quercus fueron las más usadas en las repoblaciones realizadas por particulares.The modern reforestation of Spain began in the second half of the nineteenth century. The aim of this study is to analyze the tree species involved and the three different historical stages that occurred between 1877 and 2013. This analysis is based on the official statistical series and national forest maps (NFMs) published in 1966 and 1997. Using NFMs, the estimated total reforested area was found to be, respectively, 33 and 18% higher than the estimates available in the official statistics for the corresponding historical periods. This highlights the great importance that reforestation has had in shaping the Spanish landscape, as well as the value of NFMs in filling the gaps arising from data based entirely on statistical series only. The NFMs of 1966 and 1997 explain the rapid spread of fast-growing species such as eucalyptus, Monterrey and Maritime pines and poplars, which represent up to 46% of the total reforested area according to the NFM of 1997. However, native pine have been the predominant species in reforestation throughout this historical period although, from 1993 onwards, the use of native hardwoods, especially certain species of oak, came to dominate reforestation projects on privately-owned land. The national reforestation maps presented here allow further research on the spatial-temporal evolution of the reforested areas in order to gain further insights into the resulting forested stands and landscapes

Modification of selectivity and carbon deposition during the initial stages of the n-butane dehydrogenation over mono and bimetallic catalysts

The initial carbon deposition and the generation of dehydrogenating selectivity during the initial steps of the reaction are investigated for Pt and PtSn catalysts supported on pure and Na-doped alumina by using a pulse technique (injection of n-butane pulses). Results demonstrate that Pt supported on pure alumina is not a proper dehydrogenation catalyst. It shows a high hydrogenolytic and cracking behavior and an important carbon formation that deactivates the catalyst. However the combined presence of tin and sodium inhibits not only the carbon deposition reactions but also the C-C breaking reactions, increasing in an important way the dehydrogenating selectivity to the different butenes to a value about 80%.Fil: Bocanegra, Sonia Alejandra. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico - CONICET -Santa Fe. Instituto de Investigaciones en Catálisis y Petroquímica; ArgentinaFil: Scelza, Osvaldo Antonio. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico - CONICET -Santa Fe. Instituto de Investigaciones en Catálisis y Petroquímica; ArgentinaFil: de Miguel, Sergio Ruben. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico - CONICET -Santa Fe. Instituto de Investigaciones en Catálisis y Petroquímica; Argentin