Suchergebnisse

Tesis Doctoral le?da en la Universidad Rey Juan Carlos de Madrid en 2015. Director de la Tesis: Javier Guill?n Caram?s ; Este trabajo trata de la modificaci?n del contrato de obra p?blica. Desciende desde lo general, la ejecuci?n del contrato, hasta lo particular, su novaci?n modificativa. Se analizan los supuestos que influyen y conducen a la alteraci?n de las prestaciones asumidas por la Administraci?n y por el Contratista tras la perfecci?n del contrato. He tratado de evidenciar las razones que han conducido a la legislaci?n hasta el actual estado de la cuesti?n y qu? soluciones han planteado los legisladores nacional y comunitario para poner fin a esta controversia que existe desde que naci? la contrataci?n administrativa. Desde un punto de vista cr?tico se ha analizado la futura reglamentaci?n que previsiblemente se aprobar? en la pr?xima legislatura y que a, mi modo de ver, en materia de modificaci?n contractual, da un paso atr?s con respecto al actual sistema y evita, una vez m?s, dar una soluci?n definitiva a este antiqu?simo e irresoluble problema.

The aim of this work is to establish the influence of different ultrasonic frequencies ranging from 20 to 1142 kHz on the efficiency of the US/Fe2O3/SBA-15/H2O2 (sono-Fenton) system. The frequency of 584 kHz has been established as the optimum ultrasonic irradiation for the degradation of aqueous phenol solutions by the sono-Fenton system and the effect of different variables, such as hydrogen peroxide concentration or catalyst loadings in the reaction was studied by factorial design of experiments. Catalyst loadings of 0.6 g/L and hydrogen peroxide concentration, close to the stoichiometric amount, show high organic mineralization, accompanied by excellent catalyst stability in a wide range of concentrations of aqueous phenol solutions (0.625 to 10 mM). Additionally, the catalyst can be easily recovered by filtration for reuse in subsequent reactions without appreciable loss of activity. The coupling of US (584 kHz)/Fe-SBA-15/H2O2 at room temperature is revealed as a promising technique for wastewater treatment. Additionally, a new sono-Fenton variant, the so-called latent remediation has also been studied, using ultrasonic irradiation only as pretreatment for 15 minutes in an attempt at reducing the cost of the degradation process. It has been observed that latent remediation provides TOC degradation of around 21 % after 15 min sonication followed by 6 h silent reaction while the typical sono-Fenton reaction affords 29 % TOC reduction after 6h sonication. Keywords: Ultrasound, Sono-Fenton; Phenol; SBA-15. ; Financial support of Regional Government of Madrid provided through the project "Red Madrile?a de Tratamientos Avanzados de Aguas Residuales con Contaminantes no biodegradables" (REMTAVARES) and the Spanish government provided through projects CTM2005-01053 and CONSOLIDER INGENIO 2010 program is gratefully acknowledged. R. Molina thanks Ministerio de Ciencia e Innovaci?n for a research fellowship through the Jos? Castillejo Program. Y. Segura is also grateful to the Juan de la Cierva program. The authors ...

El abordar un tema de esta trascendencia pone a pensar a un colectivo de asociados de Coomeva a partir de la ?tica solidaria. Esta disciplina implica la formulaci?n de las competencias claves de un nuevo modelo de liderazgo, provisto de un prop?sito clave y animado con una pasi?n por el servicio a los dem?s. El prop?sito es desatar las fuerzas constructoras de una nueva civilizaci?n, pensamiento esbozado por el fil?sofo Luis Razeto, de quien hemos extra?do la esencia de su propuesta en todo el recorrido de la ponencia, se?alando que s?lo un individuo con el ejercicio de su autonom?a, no apegado al sistema y observador del mismo para proponer cambios transformadores, con esp?ritu Solidario en el cual el servicio por los dem?s no tiene l?mite en procurar el bien com?n y creativo en su desempe?o, puede ser el dirigente que debe liderar la econom?a solidaria hacia el lugar que le corresponde como alternativa de desarrollo social y econ?mico de la nueva civilizaci?n.

The present work reviews the role of biogas as advanced biofuel in the renewable energy system, summarizing the main raw materials used for biogas production and the most common technologies for biogas upgrading and delving into emerging biological methanation processes. In addition, it provides a description of current European legislative framework and the potential biomethane business models as well as the main biogas production issues to be addressed to fully deploy these upgrading technologies. Biomethane could be competitive due to negative or zero waste feedstock prices, and competitive to fossil fuels in the transport sector and power generation if upgrading technologies become cheaper and environmentally sustainable.