Las actitudes hacia las matemáticas: construcción y validación de un instrumento para su medida

La medida de las actitudes hacia las matemáticas supone un campo de gran valor dentro de lo que seconoce como dominio afectivo matemático por el número de investigaciones y por la amplitud de sus relaciones. No obstante, los instrumentos disponibles en la actualidad para medir estas actitudes están en la mayoría de los casos validados mediante procedimientos psicométricos poco robustos y. en algunas ocasiones. con tamaños muestra! es no muy elevados. A partir de una muestra de 4807 alumnos de todos los niveles no universitarios y siguiendo tanto el acercamiento de la Teoría Clásica de los Test como los modelos de ecuaciones estructurales (modelos de medida) y el planteamiento de la Teoría de Respuesta a los Ítems (modelo de respuesta graduada) se presenta un instrumento de medida de las actitudes hacia las matemáticas sólido y robusto y con evidencias contrastadas de validez y fiabilidad

Graphitic carbon nanostructures from cellulose

Graphitic carbon nanostructures have been synthesized from cellulose via a simple methodology that essentially consists of the steps: (i) hydrothermal treatment of cellulose at 250 °C and (ii) impregnation of the carbonaceous product with a nickel salt followed by thermal treatment at 900 °C. The formation of graphitic carbon nanostructures seems to occur by a dissolution–precipitation mechanism in which amorphous carbon is dissolved in the catalyst nanoparticles and then precipitated as graphitic carbon around the catalyst particles. The subsequent removal of the nickel nanoparticles and amorphous carbon by oxidative treatment leads to graphitic nanostructures with a coil morphology. This material exhibits a high degree of crystallinity and large and accessible surface area.The financial support for this research work provided by the Spanish MCyT (MAT2008-00407) is gratefully acknowledged. M. S. acknowledges the assistance of the Spanish MCyT for the award of a Postdoctoral Mobility contract.Peer reviewe

Superior Capacitive Performance of Hydrochar-Based Porous Carbons in Aqueous Electrolytes

This is the accepted version of the following article: Fuertes, A. B. and Sevilla, M. (2015), Superior Capacitive Performance of Hydrochar-Based Porous Carbons in Aqueous Electrolytes. ChemSusChem, 8: 1049–1057. doi: 10.1002/cssc.201403267, which has been published in final form at http://dx.doi.org/10.1002/cssc.201403267. This article may be used for non-commercial purposes in accordance with the Wiley Self-Archiving PolicyBiomass-based highly porous carbons with excellent performances in aqueous electrolyte-based supercapacitors have been developed. The synthesis of these materials is based on the chemical activation of biomass-based hydrochar. The addition of melamine to the activation mixture leads to porous carbons with a porosity consisting of micropores/small mesopores. Furthermore, melamine promotes the introduction of nitrogen heteroatoms in the carbon framework, along with abundant oxygen functionalities, to improve the wettability. The materials produced in the presence or absence of melamine exhibit high specific capacitances in aqueous electrolytes (>270 F g−1 in H2SO4 and >190 F g−1 in Li2SO4). Additionally, the mesopores present in the melamine-based micro-/mesoporous carbons notably improve the ion-transport kinetics, especially in Li2SO4. Furthermore, in Li2SO4, they remain stable up to a cell voltage of 1.6 V; thus exhibiting superior energy and power characteristics than those in H2SO4.This research work was supported by the Spanish MINECO (MAT2012-31651). M. S. thanks the Spanish MINECO for her Ramón y Cajal contract.Peer reviewe

Direct Synthesis of Highly Porous Interconnected Carbon Nanosheets and Their Application as High-Performance Supercapacitors

An easy, one-step procedure is proposed for the synthesis of highly porous carbon nanosheets with an excellent performance as supercapacitor electrodes. The procedure is based on the carbonization of an organic salt, i.e., potassium citrate, at a temperature in the 750–900 °C range. In this way, carbon particles made up of interconnected carbon nanosheets with a thickness of <80 nm are obtained. The porosity of the carbon nanosheets consists essentially of micropores distributed in two pore systems of 0.7–0.85 nm and 0.95–1.6 nm. Importantly, the micropore sizes of both systems can be enlarged by simply increasing the carbonization temperature. Furthermore, the carbon nanosheets possess BET surface areas in the ∼1400–2200 m2 g–1 range and electronic conductivities in the range of 1.7–7.4 S cm–1 (measured at 7.1 MPa). These materials behave as high-performance supercapacitor electrodes in organic electrolyte and exhibit an excellent power handling ability and a superb robustness over long-term cycling. Excellent results were obtained with the supercapacitor fabricated from the material synthesized at 850 °C in terms of both gravimetric and volumetric energy and power densities. This device was able to deliver ∼13 Wh kg–1 (5.2 Wh L–1) at an extremely high power density of 78 kW kg–1 (31 kW L–1) and ∼30 Wh kg–1 (12 Wh L–1) at a power density of 13 kW kg–1 (5.2 kW L–1) (voltage range of 2.7 V).This research work was supported by the Spanish MINECO (MAT2012-31651). M.S. acknowledges the award of a Ramón y Cajal contract.Peer reviewe

Fabrication of porous carbon monoliths with a graphitic framework

[EN] Macro/mesoporous carbon monoliths with a graphitic framework were synthesized by carbonizing polymeric monoliths of poly(benzoxazine-co-resol). The overall synthesis process consists of the following steps: (a) the preparation of polymeric monoliths by co-polymerization of resorcinol and formaldehyde with a polyamine (tetraethylenepentamine), (b) doping the polymer with a metallic salt of Fe, Ni or Co, (c) carbonization and (d) the removal of inorganic nanoparticles. The metal nanoparticles (Fe, Ni or Co) formed during the carbonization step catalyse the conversion of a fraction of amorphous carbon into graphitic domains. The resulting carbon monoliths contain >50 wt.% of graphitic carbon, which considerably improves their electrical conductivity. The use of tetraethylenepentamine in the synthesis results in a nitrogen-containing framework. Textural characterization of these materials shows that they have a dual porosity made up of macropores and mesopores (∼2–10 nm), with a BET surface area in the 280–400 m2 g−1 range. We tested these materials as electrodes in organic electrolyte supercapacitors and found that no conductive additive is needed due to their high electrical conductivity. In addition, they show a specific capacitance of up to 35 F g−1, excellent rate and cycling performance, delivering up to 10 kW kg−1 at high current densities.The financial support for this research work provided by the Spanish MCyT (CQT2011-24776 and MAT2012-31651) is gratefully acknowledged. M. S. thanks the Spanish MCyT for the award of a Ramón y Cajal contract.Peer reviewe

Procedimiento para la preparación de membranas de carbono para la separación de gases permanentes

Referencia OEPM: P9801024.-- Fecha de solicitud: 18/05/1998.-- Titular: Consejo Superior de Investigaciones Científicas (CSIC).Procedimiento para la preparación de membranas de carbono para la separación de gases permanentes. El procedimiento incluye las siguientes etapas principales: disolución de un polímero precursor en un líquido para la obtención de una disolución polimérica transparente, deposición de la disolución sobre un soporte de carbono, introducción del substrato recubierto homogéneamente en un líquido en el cual precipita, formándose la membrana polimérica. Su aplicación principal es para la separación de gases permanentes.Peer reviewe

Carboxyl-functionalized mesoporous silica–carbon composites as highly efficient adsorbents in liquid phase

[EN] Mesoporous silica–carbon composites functionalized with acidic oxygen groups were prepared by oxidation of a layer of carbon deposited inside the silica pores. The synthesis procedure involved the following steps: (a) removal of the silica surfactant, (b) impregnation of the silica pores with a carbon precursor, (c) carbonization and (d) oxidation with ammonium persulfate. The resulting silica–carbon composites contained around 25–30 wt.% of carbonaceous matter with a high density of acid oxygen groups attached to the deposited carbon layer (i.e. –COOH, –Cdouble bond; length as m-dashO and –OH). The structural characteristics of the parent silica were retained by the oxidized composite materials, which exhibit a high surface area, a large pore volume and a well-ordered porosity made up of uniform mesopores. The oxygen-functionalized silica–carbon composites were found to be excellent adsorbents of basic dyes (e.g. methylene blue) and heavy metals (i.e. Cu2+, Zn2+ and Pb2+) in aqueous media.This work was supported by the Spanish MICINN (Project CQT2011-24776). M.S. and P.V-V. acknowledge Ramon y Cajal and JAE-Predoc contracts, respectively.Peer reviewe

Construcción de las bases para la implementación de un programa de orientación profesional en relaciones laborales y en ciencias del trabajo

Con el propósito de construir las bases para una posterior implementación de orientación profesional, tanto en la Diplomatura de Relaciones Laborales como en la Licenciatura de Ciencias del Trabajo, se llevó a cabo un estudio con una amplia muestra de sujetos cuya población estaba constituida por todo el alumnado que había terminado una de las dos titulaciones, o las dos, que imparte nuestro centro (Facultad de Ciencias del Trabajo de la Universidad de Valladolid, Campus de Palencia) durante los tres últimos años. Este trabajo incluye la administración de un cuestionario en el que, además de una serie de items de tipo sociodemográfico, había otros que preguntaban la opinión de nuestros ex-alumnos/as sobre el plan de estudios que habían cursado y sobre las posibles carencias de éste. Se les preguntó igualmente qué añadirían o quitarían del plan de estudio de cara a conseguir una formación más completa, formación que, por otra parte, les facilitará una más exitosa búsqueda de empleo en el mercado de trabajo. Finalmente, se comentan los resultados obtenidos y se extraen las conclusiones pertinentes.______________________________In order to build the foundations for further implementation of a program of vocational guidance, both in the Bachelor of Industrial Relations in the Bachelor of Science Labour, we made a study with a large sample consisting of the entire student body he had completed one of these two studies, or both, in our center (Faculty of Labour Science of the University of Valladolid, Palencia Campus) over the past three years. This work includes the administration of a questionnaire which, in addition to a number of items of type sociodemographic, there were others who wondered what our ex students on curriculum and sent on possible shortcomings there of. They were also asked what they would add or remove of the curriculum towards achieving a more complete training, training, on the other hand, they provide a more successful job search in the labour market. Finally, we discussed the results and drew out the appropriate conclusions