Fenómenos de retracción y comportamiento frente a la corrosión de materiales base cemento de bajo pH basados en OPC o CAC

Prior to using low-pH cementitious materials in underground repositories for high level waste, the characteristics determining their long-term durability must be analysed in depth. In this sense, different shrinkage tests have been made on mortar and concrete specimens using low-pH cement formulations based on ordinary portland cement (OPC) or calcium aluminate cement (CAC), with high mineral admixtures contents. They showed similar autogenous shrinkage than samples without mineral admixtures but higher drying shrinkage when materials based on OPC with high silica fume contents were considered. Besides, as the use of reinforced concrete could be required in underground repositories, the susceptibility of reinforcement to corrosion when using low-pH cementitious materials based on OPC was analyzed, considering carbon steel and galvanized steel. In the formers corrosion was detected due to the low pore solution pH but any problem was detected when galvanized reinforcement were used.Previo al empleo de materiales con cementos de bajo pH en almacenamientos geológicos profundos (AGP) de residuos radiactivos de alta actividad, características relacionadas con su durabilidad a largo plazo deben ser verificadas. Así, su estabilidad volumétrica se ha analizado en morteros y hormigones de bajo pH basados en OPC o CAC, con elevados contenidos de adiciones minerales. Estos presentaron retracciones autógenas similares a las medidas en materiales convencionales, pero retracciones por secado mayores en los basados en OPC y altos contenidos de humo de sílice. Dado que en zonas de los AGP podría emplearse hormigón armado, también se evaluó la susceptibilidad a la corrosión de aceros al carbono y aceros galvanizados en materiales de bajo pH basados en OPC. Se detectó un inicio temprano de corrosión en los primeros debido al bajo pH presente en el fluido de los poros de estos materiales, sin detectarse problemas al emplear aceros galvanizados

El Coeficiente de Pulimento Acelerado y su relación con parámetros petrográficos (contraste de dureza y composición modal) y la microrrugosidad superficial de áridos naturales y artificiales

The goal of this work was first to establish the relationships between the PSV values and the microstructural and mineralogical features of the aggregates and surface micro-roughness, and then to establish the behavioural differences between natural and artificial aggregates. The results obtained indicate that the surface micro-roughness and the different PSV values of the natural aggregates are strongly governed by the existence of minerals with different degrees of hardness, together with the proportion of these minerals. In contrast, the different degree of porosity in artificial aggregates (a furnace slag) was seen to be responsible for its high surface micro-roughness and PSV values. Finally, the PSV and a petrographic parameter (Overall Hardness Contrast, ΔH) were seen to be related by an exponential curve (PSV=39.726ΔH0.057) with an extremely good fit, providing a good tool to estimate PSVs in natural and artificial aggregates from petrographic parameters.El objetivo de este trabajo es establecer, por un lado, las relaciones existentes del CPA con las características petrográficas de los áridos, así como su microrrugosidad superficial y, por otro, las diferencias de comportamiento entre áridos naturales y artificiales. Los resultados indican que en los áridos naturales la microrrugosidad superficial y el diferente valor del CPA están determinados, en gran medida, por las diferencias de dureza de sus minerales y también por la proporción en la que estos minerales se encuentran en las distintas litologías. Sin embargo, en los áridos artificiales (escorias de fundición) su elevada porosidad es la responsable de su marcada microrrugosidad superficial y su elevado valor del CPA. Finalmente, se relaciona el CPA con un parámetro petrográfico (Contraste de Dureza Global, ΔH) mediante una curva exponencial, cuyo excelente índice de regresión hace que sea factible estimar mediante el estudio petrográfico de un árido su valor del CPA (CPA=39,726ΔH0,057)

Self-sustained enzymatic cascade for the production of 2, 5-furandicarboxylic acid from 5-methoxymethylfurfural

Background: 2, 5-Furandicarboxylic acid is a renewable building block for the production of polyfurandicarboxylates, which are biodegradable polyesters expected to substitute their classical counterparts derived from fossil resources. It may be produced from bio-based 5-hydroxymethylfurfural or 5-methoxymethylfurfural, both obtained by the acidic dehydration of biomass-derived fructose. 5-Methoxymethylfurfural, which is produced in the presence of methanol, generates less by-products and exhibits better storage stability than 5-hydroxymethylfurfural being, therefore, the industrial substrate of choice. Results: In this work, an enzymatic cascade involving three fungal oxidoreductases has been developed for the production of 2, 5-furandicarboxylic acid from 5-methoxymethylfurfural. Aryl-alcohol oxidase and unspecific peroxygenase act on 5-methoxymethylfurfural and its partially oxidized derivatives yielding 2, 5-furandicarboxylic acid, as well as methanol as a by-product. Methanol oxidase takes advantage of the methanol released for in situ producing H2O2 that, along with that produced by aryl-alcohol oxidase, fuels the peroxygenase reactions. In this way, the enzymatic cascade proceeds independently, with the only input of atmospheric O2, to attain a 70% conversion of initial 5-methoxymethylfurfural. The addition of some exogenous methanol to the reaction further improves the yield to attain an almost complete conversion of 5-methoxymethylfurfural into 2, 5-furandicarboxylic acid. Conclusions: The synergistic action of aryl-alcohol oxidase and unspecific peroxygenase in the presence of 5-methoxymethylfurfural and O2 is sufficient for the production of 2, 5-furandicarboxylic acid. The addition of methanol oxidase to the enzymatic cascade increases the 2, 5-furandicarboxylic acid yields by oxidizing a reaction by-product to fuel the peroxygenase reactions

Crystallization of para-Hydrogen: a quantum phase transition at finite temperature?

4 págs.; 3 figs.; Open Access funded by Creative Commons Atribution Licence 3.0; 7th Meeting of the Spanish Neutron Scattering Association (SETN)Recent neutron scattering measurements have revealed that para-Hydrogen prepared in its fundamental state solidifies in a crystal that do not show temperature response (temperature independent molecular displacement and first rotational level linewidth as well as negligible thermal expansion). Here, it is argued that such unique behaviour in the crystal phase can be understood if the crystallization is driven by pure quantum fluctuations.Work supported in part by grants MAT2007-65711-C04-01 and MAT2012-33633 from the Spanish Ministerio de Economía y Competitividad.Peer Reviewe

Hierarchy of QM SUSYs on a Bounded Domain

We systematically formulate a hierarchy of isospectral Hamiltonians in one-dimensional supersymmetric quantum mechanics on an interval and on a circle, in which two successive Hamiltonians form N=2 supersymmetry. We find that boundary conditions compatible with supersymmetry are severely restricted. In the case of an interval, a hierarchy of, at most, three isospectral Hamiltonians is possible with unique boundary conditions, while in the case of a circle an infinite tower of isospectral Hamiltonians can be constructed with two-parameter family of boundary conditions.Comment: 15 pages, 3 figure

Phase diagram and influence of defects in the double perovskites

The phase diagram of the double perovskites of the type Sr_{2-x} La_x Fe Mo O_6 is analyzed, with and without disorder due to antisites. In addition to an homogeneous half metallic ferrimagnetic phase in the absence of doping and disorder, we find antiferromagnetic phases at large dopings, and other ferrimagnetic phases with lower saturation magnetization, in the presence of disorder.Comment: 4 pages, 3 postscript figures, some errata correcte

A comprehensive examination of the local- and long-range structure of Sb6O13 pyrochlore oxide

The crystal structure of the Sb6O13 oxide, exhibiting a defect pyrochlore crystal structure with atomic vacancies, has been studied using a complete set of state-of-the-art techniques. The degree of antimony disproportionation in Sb3+ and Sb5+ valence states has been directly determined around 36% and 64%, respectively, using X-ray absorption near edge structure (XANES). These findings are in excellent agreement with our Rietveld analysis of synchrotron X-ray (SXRD) and neutron powder diffraction (NPD) results. Moreover, the highly distorted Sb3+ coordination due to its lone electron pair has been critically revisited. The bonding distances and coordination of Sb3+ and Sb5+ species closely agree with an extensive dynamic and crystallographic determination using the Extended X-ray Absorption Fine Structure (EXAFS) technique. Most importantly, the specific local disorder of the two distinctive Sb ions has been crosschecked monitoring their unusual Debye–Waller factors.Fil: Mayer, Sergio Federico. Instituto de Ciencia de Materiales de Madrid; España. Universidad Tecnológica Nacional. Facultad Regional Córdoba. Centro de Investigación en Nanociencia y Nanotecnología; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Rodrigues, Joao Elias. Universidade de Sao Paulo; Brasil. Instituto de Ciencia de Materiales de Madrid; EspañaFil: Marini, C.. CELLS–ALBA Synchrotron; EspañaFil: Fernández-Díaz, M.T.. Institut Laue Langevin; FranciaFil: Falcón, H.. Universidad Tecnológica Nacional. Facultad Regional Córdoba; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Centro de Investigación y Tecnología Química. Universidad Tecnológica Nacional. Facultad Regional Córdoba. Centro de Investigación y Tecnología Química; ArgentinaFil: Asensio, M. C.. Consejo Superior de Investigaciones Científicas; España. Instituto de Ciencia de Materiales de Madrid; EspañaFil: Alonso, J. A.. Instituto de Ciencia de Materiales de Madrid; Españ

A comprehensive examination of the local- and long-range structure of Sb6O13 pyrochlore oxide

The crystal structure of the Sb6O13 oxide, exhibiting a defect pyrochlore crystal structure with atomic vacancies, has been studied using a complete set of state-of-the-art techniques. The degree of antimony disproportionation in Sb3+ and Sb5+ valence states has been directly determined around 36% and 64%, respectively, using X-ray absorption near edge structure (XANES). These findings are in excellent agreement with our Rietveld analysis of synchrotron X-ray (SXRD) and neutron powder diffraction (NPD) results. Moreover, the highly distorted Sb3+ coordination due to its lone electron pair has been critically revisited. The bonding distances and coordination of Sb3+ and Sb5+ species closely agree with an extensive dynamic and crystallographic determination using the Extended X-ray Absorption Fine Structure (EXAFS) technique. Most importantly, the specific local disorder of the two distinctive Sb ions has been crosschecked monitoring their unusual Debye–Waller factors.Fil: Mayer, Sergio Federico. Instituto de Ciencia de Materiales de Madrid; España. Universidad Tecnológica Nacional. Facultad Regional Córdoba. Centro de Investigación en Nanociencia y Nanotecnología; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Rodrigues, Joao Elias. Universidade de Sao Paulo; Brasil. Instituto de Ciencia de Materiales de Madrid; EspañaFil: Marini, C.. CELLS–ALBA Synchrotron; EspañaFil: Fernández-Díaz, M.T.. Institut Laue Langevin; FranciaFil: Falcón, H.. Universidad Tecnológica Nacional. Facultad Regional Córdoba; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Centro de Investigación y Tecnología Química. Universidad Tecnológica Nacional. Facultad Regional Córdoba. Centro de Investigación y Tecnología Química; ArgentinaFil: Asensio, M. C.. Consejo Superior de Investigaciones Científicas; España. Instituto de Ciencia de Materiales de Madrid; EspañaFil: Alonso, J. A.. Instituto de Ciencia de Materiales de Madrid; Españ

Effect of the mother tree age and acorn weight in the regenerative characteristics of Quercus faginea

[EN] The establishment of oak trees is often a slow and difficult process. Hence, it is necessary to determine the characteristics that can lead to improving their regeneration. In this genus, seed size is highly variable both at the interspecific and intraspecific levels, and the effects of intrapopulation variability are not well understood, being even less so for Quercus faginea. In this study, the effects of the age of the mother tree, seed weight and the interaction between these two factors on seed germination, emergence and growth (biomass) were analysed. For this purpose, 16 trees—8 young and 8 old—were selected with the intent to cover the entire range of acorn weights produced in this population. Among the main results, it should be noted that: (1) in older trees, it is easier to find larger acorns; (2) the percentage and the speed of germination of the acorns of young trees is greater than that of old trees; (3) the percentage and the speed of seedling emergence of young trees is greater than that of old trees; and (4) cotyledon weight is the variable that most influences biomass, quite often in a positive way. Therefore, maintaining intrapopulation variability seems to be an approach that most favours the persistence of these populations