Viscosity near phase transitions

Probably the most enticing observation in theoretical physics during the last decade was the discovery of the great amount of consequences obtained from the AdS/CFT conjecture put forward by Maldacena. In this work we review how this correspondence can be used to address hydrodynamic properties such as the viscosity of some strongly interacting systems. We also employ the Boltzmann equation for those systems closer to low-energy QCD, and argue that this kind of transport coefficients can be related to phase transitions, in particular the QGP/hadronic phase transition studied in heavy ion collisions.Comment: 9 pages, 1 figure. Contribution to the Gribov-80 Memorial Workshop. ICTP Trieste, Italy, May 26-28, 201

Trabajo, empleo y desempleo en la teoría económica: la nueva ortodoxia

En este artículo se realiza una revisión de la evolución de la Economía del trabajo y de sus presupuestos teóricos básicos. Se pone de manifiesto que los nuevos desarrollos teóricos plantean el análisis de los problemas relacionados con el empleo desde una perspectiva cada vez más microeconómica y alejada de las dinámicas macroeconómicas generales. Y que, además, las propuestas normativas que se sustentan sobre las mismas se muestran claramente ineficientes para solucionar el problema del desempleo precisamente por la estrechez de sus planteamientos.The aim of this article is to review the evolution of labour economics and its basic theoretical assumptions. This survey shows that new developments in labour economics focus more and more on issues concerning employment from a microecomic point of view, giving up more comprehensive and macroecomic approaches. It also shows that the normative proposals and employment policies that uphold on the microeconomic approaches are clearly insufficient to solve unemployment problem due to exactly the narrowness of this approach

Titanium scaffolds with multi-scale porosity obtained by controlled chemical and electrochemical treatments of porous solids from PM space holder technique

Junta de Andalucía (Spain) / FEDER (EU), through the project Ref. P12-TEP-140

Auxiliary Companies of the Horticultural Sector as a Competitiveness Element: The Case of Almeria (Spain)

The horticultural model of Almeria (Spain) based on the operation of greenhouses is an international reference and has been considered as an economic miracle. Alongside this agricultural development has been the deployment of the diverse productive activity of auxiliary companies. The objective of this article is to understand how these companies operate and analyze their factors of competitiveness, competing needs, and future competitive improvements, taking as reference four of the most important subsectors (machinery, greenhouse infrastructure, plastics, and seeds). The Delphi method was used and through a panel of experts the conditioning factors of each of the variables to be analyzed (factors, needs, and competitiveness improvements) was chosen. Of the 120 companies that were sent questionnaires, 72 participated. The sectors that make up the auxiliary companies are heterogeneous and therefore the results obtained have differed among them. The synergies between the greenhouse crops and the auxiliary companies are an example of diversification of productive activity that can be extrapolated to other production areas worldwide. The future of the auxiliary companies is linked to that of the intensive agriculture and the key variables must be underscored by competitiveness and sustainability

The radiation impedance of a current-carrying conductor in a JUNO-like Jovian orbit.

The so-called electrical power generation problem for exploration of the outer planets could be solved deploying an electrodynamic tether. Wave radiation by a conductor carrying a steady current in a polar, highly eccentric, low perijove orbit, as in the planned NASA Juno mission, is considered. The high Jupiter's oblateness produces fast apsidal precession over the meridional plane. In a cold plasma model, radiation occurs in the Alfven and Fast Magnetosonic modes, exhibiting large refraction index. The radiation impedance in both modes is determined for a representative arc in the orbits. Unlike the Earth ionospheric case, the low-dense and highly-magnetized Jovian plasma makes the electron-gyrofrequency to plasma-frequency ratio large [1]; this substantially modifies the power spectrum in either mode

Hydrogenation of furfural over supported Pd catalysts

Lignocellulosic biomass is the most abundant and economical non-fossil carbon source. Furthermore, it is not competitive with the food chain, coming from lignocellulosic wastes including agricultural and food processing, local urban solid and forestry wastes. However, these are made up of complex carbohydrates (mainly, cellulose and hemicellulose), which require to be broken down in their respective monomers. The hemicellulose is mainly composed of pentosans, which, after an initial hydrolysis step, are dehydrated to furfural. Furfural is an important platform molecule, since it has a wide range of applications, being considered the main chemical, aside from bioethanol, obtained from the sugar platform for the synthesis of chemicals, for plastics, agrochemical and pharmaceutical industries. In the present work, the hydrogenation of furfural in gas phase has been studied by using Pd as active phase, and different metal oxides as support, in order to elucidate the influence of the support on the catalytic performance. Furfural can be converted into chemicals with important applications in many different industrial fields. Thus, reduction of furfural can proceed through different pathways depending on the experimental conditions, where the nature of the catalysts plays a key role. In the case of Pd-based catalysts, the main products come from the decarbonylation of furfural.The catalytic results reveals that the nature of the support exerts an important influence on furfural conversion and yield. The highest conversion (92% after 5 h of TOS at 463 K) was attained with a Pd-SiO2 catalyst, with a furan yield of 70 mol%. This catalyst is the most selective to furan and a moderate deactivation is only observed after 5 h reaction. The catalytic performance demonstrates that decarbonylation reaction was the main pathway, although the formation of furfuryl alcohol and 2-methylfuran also suggests that the hydrogenation of the carbonyl group of furfural takes place.Universidad de Málaga. Campus de Excelencia Internacional Andalucía Tec

Cr-free Ni/MgO catalysts for hydrogenation of furfural

In the last century, the industrial development and the increase of the world population have caused the depletion of fossil reserves. This fact together with others factors have led to the search of alternative. Biomass is emerging as a widely available source to produce energy and, excluding fossil fuels, is the only source that can provide liquid fuels and chemicals. Lignocellulose is formed by cellulose, hemicellulose, lignin and other extractable components. In the case of hemicellulose, its hydrolysis leads to the formation of xylans and pentosans, which after dehydration can give rise to furfural. The high interest for furfural is attributed to its chemical structure, which provide high reactivity, making it potentially interesting for the synthesis of a vast variety of high value-added chemicals. Two of these important chemicals are furfuryl alcohol (FOL) and 2-methylfuran (MF), can be synthesized through hydrogenation of furfural, either in liquid or vapor phase. FOL is mainly used for the production of thermostatic resins, intermediates in the manufacture of lysines, vitamin C and dispersing agents. Meanwhile, MF is used in the synthesis of pesticides, in the pharmaceutical or perfume industries. Industrially, copper chromite catalyst is used, although the toxicity associated to the presence of chromium species has prompted the search of Cr-free catalysts. Therefore, much attention is being paid to the development of more sustainable and environmentally friendly catalysts, among them, catalytic systems based on Cu or Ni have demonstrated to be active and selective towards the formation of FOL and MF. The dispersion of metalspecies and their interaction with the support are key parameters that affect the catalytic activity and stabilityof catalysts. The use of metal oxides as supports can allow to obtain highly active and stable catalytic systems, and the electronic density of metal sites can be modified. The present work is aimed at the synthesis by Ni/MgO catalysts and the evaluation of their catalytic performance in the gas phase hydrogenation of furfural, at atmospheric pressure. x-Ni_MgO catalysts have been tested in the furfural hydrogenation, attaining the full furfural conversion with the 0.20-Ni_MgO catalyst, after 5 h of TOS, at 190 °C, by feeding a 5% furfural solution in cyclopentyl methyl ether, at a constant flow of hydrogen of 10 ml min-1. In all cases, catalysts are highly selective to furan. The analysis of the influence of the reaction temperature has revealed the existence of a volcano distribution, attaining the best catalytic performance at 190 °C. However, all catalysts suffer a progressive deactivation with TOS, by deposition of reactants and product.Universidad de Málaga. Campus de Excelencia Internacional Andalucía Tech Ministerio de Economía y Competitividad (Proyecto CTQ2015-64226-C3-3-R) Fondos FEDE

Minimum of η/s\eta/s and the phase transition of the Linear Sigma Model in the large-N limit

We reexamine the possibility of employing the viscosity over entropy density ratio as a diagnostic tool to identify a phase transition in hadron physics to the strongly coupled quark-gluon plasma and other circumstances where direct measurement of the order parameter or the free energy may be difficult. It has been conjectured that the minimum of eta/s does indeed occur at the phase transition. We now make a careful assessment in a controled theoretical framework, the Linear Sigma Model at large-N, and indeed find that the minimum of eta/s occurs near the second order phase transition of the model due to the rapid variation of the order parameter (here the sigma vacuum expectation value) at a temperature slightly smaller than the critical one.Comment: 22 pages, 19 figures, v2, some references and several figures added, typos corrected and certain arguments clarified, revised for PR