Flexible and low-cost binderless capacitors based on p- and n-containing fibrous activated carbons from denim cloth wastes

Activated carbon cloths have been prepared from denim cloth wastes (DCWs) through chemical activation with H3PO4. The effect of the H3PO4/DCWs impregnation ratio and the carbonization temperature on the porous texture, the chemical composition, the fibers morphology, and the electrochemical performance has been studied. Low H3PO4/DCWs impregnation ratios lead to flexible and microporous activated carbons cloths, whereas more fragile and rigid activated carbon cloths with higher external surface area are produced upon increasing the amount of H3PO4. The increase in the carbonization temperature allows for obtaining a more ordered and conductive carbon structure. The activated carbon prepared at 900 ºC with a H3PO4/DCWs impregnation ratio of 0.5 (w/w) exhibits the best performance as electric double layer capacitor. This electrode shows a specific surface area of 2016 m2 g-1 and the highest registered gravimetric capacitance (227 F g-1). Moreover, its flexibility minimizes the ohmic resistance of the electrode, thus increasing the feasibility of working at higher current densities than the other synthesized electrodes.Universidad de Málaga. Campus de Excelencia Internacional Andalucía Tech; MINECO CTQ2015-68654-

Dynamical spacetimes and gravitational radiation in a Fully Constrained Formulation

This contribution summarizes the recent work carried out to analyze the behavior of the hyperbolic sector of the Fully Constrained Formulation (FCF) derived in Bonazzola et al. 2004. The numerical experiments presented here allows one to be confident in the performances of the upgraded version of CoCoNuT's code by replacing the Conformally Flat Condition (CFC) approximation of the Einstein equations by the FCF.Comment: 4 pages, 7 figures. Accepted for publication in Journal of Physics: Conference Series, Proceedings of the 8th Edoardo Amaldi Conference on Gravitational Wave

Methanol dehydration over ZrO2 supported-activated carbons

Resumen comunicación congreso internacionalDME is playing an important role due to its potential use as an alternative fuel in diesel engines. The use of this fuel produces lower NOx emissions, and less engine noise compared to traditional diesel fuels. Moreover, this compound is used as building block for many value-added chemicals such as lower olefins. DME is usually produced via catalytic dehydration of methanol over a solid acid. The use of activated carbons in catalytic processes, acting directly as catalyst and as catalyst support, is focussing much attention. They can be obtained from different types of lignocellulosic waste, producing not only an environmental but an economical profit. In this sense, the preparation of activated carbons with phosphoric acid produces catalytic supports with certain surface acidity, which have shown high activity for alcohol dehydration. In this study, ZrO2 supported activated carbons were prepared from an industrial byproduct as lignin for the methanol dehydration to DME. The activated carbon was prepared by chemical activation with H3PO4, using Alcell® lignin as precursor. The impregnation ratio value (H3PO4/lignin) used was 3. The impregnated sample was activated under N2 flow at 500 ºC for 2h, washed and dried. The activated carbon was loaded with different amounts of ZrO(NO3)2, dried at 120ºC for 24h, and calcined in air at 250ºC for 2h, obtaining ZrO2 loadings of 5 and 10%, respectively. For the sake of comparison, pure ZrO2 was also used. Catalytic tests were performed at atmospheric pressure in a fixed bed reactor, at different space times and partial pressures. The activated carbon (ACP) prepared shows a well-developed porous structure, with an apparent surface area higher than 2000 m2/g, and a high contribution of mesoporosity. After metal loading, a maximum decrease of 20% in all structural parameters of the ACP was observed.The results show that ZrO2 loading produces an enhancing in the catalytic activity of the carbon materials compared to the parent activated carbon (0.1 g·s/μmol, PCH3OH= 0.02 atm in helium and 350 ºC). In this sense, a methanol conversion of 25% was observed with the addition of 10% w/w ZrO2 (ACP-10Zr), at steady state conditions (Figure 1). ACP shows negligible conversion, at the same conditions and for pure ZrO2 the methanol conversion was of 10%. Very high selectivity to DME (~100%) was found at temperatures lower than 350 ºC. The methanol conversion increases with temperature, reaching a value of 67% at 475ºC, but a slight decrease in DME selectivity is observed, resulting in a higher production of light hydrocarbons, mainly CH4. The results suggest that the addition of only a 10% of ZrO2 over an activated carbon prepared by chemical activation with H3PO4 enhances significantly the performance of the catalyst, compared to pure ZrO2.Universidad de Málaga. Campus de Excelencia Internacional Andalucía Tech

An excision scheme for black holes in constrained evolution formulations: spherically symmetric case

Excision techniques are used in order to deal with black holes in numerical simulations of Einstein equations and consist in removing a topological sphere containing the physical singularity from the numerical domain, applying instead appropriate boundary conditions at the excised surface. In this work we present recent developments of this technique in the case of constrained formulations of Einstein equations and for spherically symmetric spacetimes. We present a new set of boundary conditions to apply to the elliptic system in the fully-constrained formalism of Bonazzola et al. (2004), at an arbitrary coordinate sphere inside the apparent horizon. Analytical properties of this system of boundary conditions are studied and, under some assumptions, an exponential convergence toward the stationary solution is exhibited for the vacuum spacetime. This is verified in numerical examples, together with the applicability in the case of the accretion of a scalar field onto a Schwarzschild black hole. We also present the successful use of the excision technique in the collapse of a neutron star to a black hole, when excision is switched on during the simulation, after the formation of the apparent horizon. This allows the accretion of matter remaining outside the excision surface and for the stable long-term evolution of the newly formed black hole.Comment: 14 pages, 9 figures. New section added and changes included according to published articl

Maximal slicings in spherical symmetry: local existence and construction

We show that any spherically symmetric spacetime locally admits a maximal spacelike slicing and we give a procedure allowing its construction. The construction procedure that we have designed is based on purely geometrical arguments and, in practice, leads to solve a decoupled system of first order quasi-linear partial differential equations. We have explicitly built up maximal foliations in Minkowski and Friedmann spacetimes. Our approach admits further generalizations and efficient computational implementation. As by product, we suggest some applications of our work in the task of calibrating Numerical Relativity complex codes, usually written in Cartesian coordinates.Comment: 25 pages, 6 figure

Use of quartz and rock crystal in Andalusian Late Prehistory. Status of the issue and analysis of a cultural phenomenon

Ante la escasez de estudios que aborden esta problemática, el presente trabajo pretende ofrecer una visión sintética y actualizada sobre la incidencia y contextos de uso desde el IV al II milenios ANE en el actual territorio andaluz tanto de prismas de cuarzo y cristal de roca como de otros elementos realizados sobre este mineral. A través del análisis de sus pautas de uso vemos que adquiere un evidente e importante simbolismo funerario por las sociedades prehistóricas, con una gran incidencia tanto a nivel geográfico como temporal. Se valora asimismo un notable número de contextos no funerarios donde los restos de talla de cristal de roca y algunos elementos significativos pueden ofrecer una lectura mucho más completa de su articulación en redes de interacción y el rol desempeñado por esta materia prima.Given the lack of studies which tackle this issue, this work aims to provide a synthetic and updated view of the impact and use contexts from the fourth to the second milennia BCE in the current Andalusian territory of quartz prisms and rock crystal as well as other elements made from this mineral. Through the analysis of its use patterns we may notice that it acquires an evident and important funerary simbolism from the prehistoric societies, with a great impact both on a geographic level and a temporal one. Moreover, a notable number of non-funerary contexts is also taken into account, where rock cristal chippings and other significative elements may offer a much more complete reading of its articulation within networks of interaction and the role played by this raw material

On the convexity of Relativistic Ideal Magnetohydrodynamics

We analyze the influence of the magnetic field in the convexity properties of the relativistic magnetohydrodynamics system of equations. To this purpose we use the approach of Lax, based on the analysis of the linearly degenerate/genuinely non-linear nature of the characteristic fields. Degenerate and non-degenerate states are discussed separately and the non-relativistic, unmagnetized limits are properly recovered. The characteristic fields corresponding to the material and Alfv\'en waves are linearly degenerate and, then, not affected by the convexity issue. The analysis of the characteristic fields associated with the magnetosonic waves reveals, however, a dependence of the convexity condition on the magnetic field. The result is expressed in the form of a generalized fundamental derivative written as the sum of two terms. The first one is the generalized fundamental derivative in the case of purely hydrodynamical (relativistic) flow. The second one contains the effects of the magnetic field. The analysis of this term shows that it is always positive leading to the remarkable result that the presence of a magnetic field in the fluid reduces the domain of thermodynamical states for which the EOS is non-convex.Comment: 14 pages. Submitted to Classical and Quantum Gravit

Interpretation of Iconic Texts Supported by the Theory of Umberto Eco and Peter McLaren

The purpose of the article presented here is to expose and relate the importance and implications of Umberto Eco's semiotic theory on the one hand, and on the other, the active role of the student as proposed by Peter McLaren. It is derived from the research that is being carried out with a view to strengthening the level of interpretive reading of iconic texts, in fifth grade students of the Rural School Center "Juana Berbesí" headquarters "La Platanala", in the municipality of Durania department of Norte de Santander. Methodologically it corresponds to a descriptive review of the theories and concepts proposed by the aforementioned authors, to highlight their applicability and usefulness in the teaching of the comprehensive reading of iconic texts, which is of interest in the educational field and leads to the conclusion that the behavior of these theories is relevant when applied in the classroom,  given their contributions to the change in the teaching processes of reading comprehension and the granting of the leading role of the student. Review that was derived from the analysis of the existing problem in the classroom in relation to the gaps present in the didactics of the understanding and interpretation of iconic texts, which is reflected in the limitations that students present to interpret and understand images, action that leads to decipher the message or the communicative intention that is in these. Limiting also for the development of oral or written expression skills, as well as other possibilities with which their imagination and creativity are stimulated. Based on the analysis of the theoretical proposals of the authors in question, the direction of alternatives and pedagogical strategies that contribute to strengthening the reading comprehension of students of primary basic education is achieved

Emerging models for the development of social mobile applications: people as a service, and social devices. A proof of concept.

Nowadays mobile devices have gained a great importance in our society and they are present everywhere. These devices have a huge amount of data about their owners and context data of their surroundings, and many communication channels. Nevertheless with current models mobile devices cannot take advantage of this situation. For these reasons, new models for mobile applications have appeared recently. People-as-a-Service (PeaaS) allows interactions between mobile devices in their surroundings, using sociological profiles of their owners to create communication between interested devices. Social Devices is a recent model that implements the PeaaS concept, taking advantage the devices are almost always with the user it creates a new kind of interactions between nearby devices with the main target of improve social relations. For this purpose each device is able to provide services to nearby devices and consume them, keeping the user’s data in the device and sharing it only when it is authorized. This concept could be integrated with technologies like Internet-of-Things and Ubiquitous Computing, allowing devices to connect with nearby objects like elevators, traffic lights or your own vehicle. In particular, there is a new platform that implements both concepts, which is the study object of this work: OrchestratorJS. The platform is still under development and is not too stable yet, furthermore there is no documentation available. The main target of this work is to explore the platform and to create a basic documentation which could be used for anybody interested on the in, acting as a starting point for future works

Alcohol decomposition on basic/acid lignin-derived submicron diameter carbon fibers

The use of lignin, the second most abundant polymer in nature, along with a simple and versatile technique, electrospinning, represents an advantageous and promising approach for the preparation of carbon fibers. In previous studies, we have demonstrated that the incorporation of H3PO4 to the initial lignin solution allows for shortening the carbon fibers preparation process and that the resulting carbon fibers present P-surface groups that are of great interest for heterogeneous catalysis. Different carbon fibers catalysts have been prepared by electropinning of Alcell lignin in the absence or presence of H3PO4 as chemical activating agent. Carbonization at different temperatures between 500 and 1600 ºC allows for preparing carbon fibers with a high variety of porosity and chemical surface properties. Diverse oxygen surface groups are presented on the carbon catalysts surface. The isopropanol decomposition has been used as a catalytic test to study the acid or basic character of the prepared carbon fibers. Carbon fibers without phosphorus surface groups generate acetone as the main product of the isopropanol decomposition reaction, from 400 to 600 ºC, suggesting the basic character of these catalysts. On the contrary, phosphorus-containing carbon fibers show high acid character, producing selectivity to propylene of 100 % at temperatures between 250 and 350 ºC. The most acid carbon fiber catalyst produced a high selectivity to ethylene and dimethyl ether for the decomposition of ethanol and methanol, respectively. The conversion enhancement that the presence of oxygen in the gas phase produced for all these reactions was also studied.Universidad de Málaga. Campus de Excelencia Internacional Andalucía Tech. MINECO (CTQ2015-68654-R). MINECO (PTA2015-11464-I)