Agricultura urbana, condición para el desarrollo sostenible y la mejora del paisaje

Este artículo resulta de investigaciones en torno al “enverdecimiento” de las ciudades y las oportunidades de la agricultura urbana para la alimentación de una población en constante aumento que no trabaja la tierra. También es fruto de actividades de mejora de ambientes urbanos realizadas con la Escuela de Ingenieros Agrónomos de la Universidad Politécnica de Madrid. A través de casos de agricultura urbana, entendiendo por ella el conjunto de prácticas para la producción de alimentos y plantas ornamentales dentro de las ciudades y en sus entornos, se analizan alternativas para la recuperación de espacios construidos e incremento de la calidad de vida de la población. Todo ello se traduce, además, en creación de riqueza y mejora del paisaje urbano, siempre desde criterios de sostenibilidad que favorecen el desarrollo local desde la Cumbre de la Tierra de Río de 1992 y la Conferencia sobre Desarrollo Sostenible Río+20 de 2013.

A low molecular weight hydro and organogelator derived from an isohexide and sol-gel transcription of the alcogel

Heating 2,5-di-O-methanesulfonyl-1,4:3,6-dianhydro-D-sorbitol (1) in a range of solvents led to the formation of a gel state at low concentrations. 1 was found to gel aromatics, alcohols and water. The structure of 1 in the solid state was solved by single crystal X-ray crystallography; no strong hydrogen bonds or associated solvents were found in the crystal. Electron micrographs revealed the morphology of the gels to be predominantly rod-like. The ethanol alcogel was used to template silica by sol-gel transcription.

The Co-Entrapment of a Homogeneous Catalyst and an Ionic Liquid by a Sol-gel Method: Recyclable Ionogel Hydrogenation Catalysts

Molecular hydrogenation catalysts have been co-entrapped with the ionic liquid [Bmim]NTf(2) inside a silica matrix by a sot-gel method. These catalytic ionogels have been compared to simple catalyst-doped glasses, the parent homogeneous catalysts, commercial heterogeneous catalysts, and Rh-doped mesoporous silica. The most active ionogel has been characterised by transmission electron microscopy, X-ray photoelectron spectroscopy, and solid state NMR before and after catalysis. The ionogel catalysts were found to be remarkably active, recyclable and resistant to chemical change.

Ionic liquids as solvent and solvent additives for the synthesis of sol-gel materials

The ionic liquid (IL) 1-butyl-3-methylimidazolium chloride was used as a drying control chemical additive in the synthesis of silica sol-gel materials with and without methanol as a co-solvent. The resulting gels were characterized by using thermogravimetric analysis, differential scanning calorimetry, infrared spectroscopy and water sorption kinetics. Calcined gels were analyzed using scanning electron microscopy and nitrogen adsorption isotherms for surface area and pore volume determination. Non-calcined gels were monolithic and showed general cloudiness with lesser degrees observed at higher IL volumes. Calcinations resulted in the formation of powders with increased available surface area as the amount of IL volume was increased. This is consistent with an increase in respective pore volume but a general decrease in average pore size. The resulting materials exhibited conventional structural microdomains, in contrast to periodicity reported when other ionic liquids were used as templates.

Study of the luminescence of tris(2-thenoyltrifluoroacetonato)lanthanide(III) complexes covalently linked to 1,10-phenanthroline-functionalized hybrid sol-gel glasses

The solubility and uniform distribution of lanthanide complexes in sol-get glasses can be improved by covalently linking the complexes to the sol-gel matrix. In this study, several lanthanide beta-diketonate complexes (Ln = Nd, Sm, Eu, Tb, Er, Yb) were immobilized on a 1,10-phenanthroline functionalized sol-gel glass. For the europium(Ill) complex, a sol-gel material of diethoxydimethylsilane (DEDMS) with polymer-like properties was derived. For the other lanthanide complexes, the sol-gel glass was prepared by using a matrix of tetramethoxysilane (TMOS) and DEDMS. Both systems were prepared under neutral reaction conditions. High-resolution emission and excitation spectra were recorded. The luminescence lifetimes were measured. (c) 2004 Elsevier B.V. All rights reserved.

Sol-gel-entrapped nano silver catalysts-correlation between active silver species and catalytic behavior

Silver colloids prepared by reducing AgNO3 in aqueous solution with sodium citrate were embedded in alumina following two different preparation procedures resulting in samples containing 3 and 5 wt.% silver. Characterization of these materials using TEM. XPS, XAES, CP/MAS NMR, XRD, and adsorption-desorption isotherms of nitrogen showed that embedding the pre-prepared silver colloids into the alumina via the sol-gel procedure preserved the particle size of silver. However, as XAES demonstrates, the catalysts prepared in a sol-gel with a lower amount of water led to embedded colloids with a higher population of Ag+ species. The catalytic behaviors of the resultant catalysts were well correlated with the concentration of these species. Thus, the active silver species of the catalysts containing more Ag+ species selectively converts NO to N-2. However, subsequent thermal aging leads to an enhancement of the conversion of NO parallel to slight alteration of the selectivity with the appearance of low amounts of N2O despite an increase of Ag+ species. Accordingly, an optimal surface Ag-0/Ag+ ratio is probably needed, independently of the size of silver particles. It was found that this optimal ratio strongly depends on the operating conditions during the synthesis route. (C) 2010 Elsevier Inc. All rights reserved.

Performance, représentation et (il)lisibilité du genre dans la fiction sandienne des années 1830

Dans son premier roman, Indiana (1832), Sand établit un réseau de correspondances entre la langue, la performance et l'identité sexuelle qui n'ont pas encore fait l'objet d'une étude approfondie. Or, ces correspondances sous-tendent d'autres romans des années 1830, notamment Lélia (1833), Le Secrétaire intime (1834) et Gabriel (1839). Deux concepts – la performance et la lisibilité – fondent en fait les réflexions de Sand sur la représentation et le genre. Il s'agit dans cet article d'étudier ce réseau d'associations et d'explorer son évolution dans la fiction sandienne des années 1830. Cette analyse permettra de souligner comment, chez Sand, la performativité du genre met en question et trouble la représentation mimétique.