150 research outputs found
Metal-insulator transition in NdEuNiO compounds
Polycrystalline NdEuNiO () compounds
were synthesized in order to investigate the character of the metal-insulator
(MI) phase transition in this series. Samples were prepared through the sol-gel
route and subjected to heat treatments at 1000 C under oxygen
pressures as high as 80 bar. X-ray Diffraction (XRD) and Neutron Powder
Diffraction (NPD), electrical resistivity , and Magnetization
measurements were performed on these compounds. The results of NPD and XRD
indicated that the samples crystallize in an orthorhombic distorted perovskite
structure, space group . The analysis of the structural parameters
revealed a sudden and small expansion of 0.2% of the unit cell volume
when electronic localization occurs. This expansion was attributed to a small
increase of 0.003 \AA{} of the average Ni-O distance and a simultaneous
decrease of of the Ni-O-Ni superexchange angle. The
measurements revealed a MI transition occurring at temperatures
ranging from to 336 K for samples with and 0.50,
respectively. These measurements also show a large thermal hysteresis in
NdNiO during heating and cooling processes suggesting a first-order
character of the phase transition at . The width of this thermal
hysteresis was found to decrease appreciably for the sample
NdEuNiO. The results indicate that cation disorder
associated with increasing substitution of Nd by Eu is responsible for changing
the first order character of the transition in NdNiO.Comment: 19 pages, 9 figure
Caracterización de las propiedades nanométricas de un silicato de aluminio y sodio amorfo: desarrollo del protocolo OECD 318
En los últimos años, el aumento de la producción y el uso generalizado de nanomateriales manufacturados han acrecentado la probabilidad de encontrarlos en sistemas naturales acuosos. Esta situación ha dado lugar a un debate sobre si los protocolos actuales de prueba reglamentarios para los materiales son suficientes y adecuados para evaluar el destino final y el impacto de los nanomateriales en los sistemas naturales de interés.En 2011, la Comisión Europea adoptó la Recomendación (2011/696/EU) en la definición de nanomaterial, categorizándolo como aquel material que al menos una de sus dimensiones es menor a 100 nm.A pesar de los avances técnicos desarrollados en los últimos años, no se dispone de un procedimiento operativo universal y estandarizado para preparar una muestra arbitraria y medir la distribución de tamaño de sus partículas constituyentes.Cada material requiere de un tratamiento específico, aunque hay ciertos aspectos comunes y esenciales que deben tenerse en cuenta a la hora de preparar la muestra para su análisis.La OECD (Organización para la Cooperación y el Desarrollo Económico) ha desarrollado diferentes guías de pruebas para la caracterización de los nanomateriales. En este Trabajo Fin de Máster se desarrolla el protocolo OECD 318 sobre la estabilidad de dispersión de nanomateriales en medios ambientes simulados, utilizando para ello el SODASIL®P95 un silicato de aluminio y sodio amorfo fabricado por Industrias Químicas del Ebro (IQE).A través de este protocolo y los demás ensayos realizados de caracterización del material se ha podido evaluar el alcance del SODASIL®P95 en medios acuosos. Se ha determinado una baja estabilidad de dispersión para el material en condiciones ambientales de: pH alcalinos, una alta concentración salina y la ausencia de materia orgánica disuelta. Así mismo el material se ha categorizado como muy poco soluble según la EFSA (Autoridad Europea de Seguridad Alimentaria) siguiendo el protocolo desarrollado del OECD 105. Además, mediante ensayos de centrifugación se ha determinado la concentración de silicio en el rango nanométrico y por medio de microscopía electrónica (SEM/TEM) se ha intentado determinar la morfología de las partículas primarias, agregados y aglomerados formados por el material.<br /
Determinación de los perfiles sensoriales característicos de la aceituna Aloreña
Aloreña olives are unique to and typical of the Guadalhorce region (Málaga, Spain). They possess some specific characteristics which make them an excellent product that is differentiated from the other olive varieties. The sensory profile technique was used to study the sensory attributes which best characterize the three processing styles of Aloreña table-olives. The characteristic descriptors are identified according to the round-table method and multivariate analysis. Sensory profile data obtained were analyzed using a mix of Nested Design ANOVA and Factorial ANOVA and by a canonical analysis. The effect of the factor processing style was significant only for three descriptors: fruit odor, bitter taste and firmness (p < 0.05) whereas the effect of the samples nested in each processing style was significant for all the attributes (p < 0.001). Duncan’s post hoc test and the canonical analysis showed that all samples were different within each processing style.La aceituna Aloreña es una variedad de aceituna de mesa autóctona de la comarca del Valle del Guadalhorce (Málaga, España) que posee unas características propias que la distingue del resto de variedades, siendo las propiedades sensoriales las que mejor la diferencian. Para estudiar los atributos sensoriales que mejor definen a los tres tipos de elaboración de la aceituna Aloreña (verdes frescas, tradicionales y curadas) se utiliza la técnica del perfil sensorial. La selección de atributos sensoriales se realiza mediante discusión grupal en mesa redonda y utilizando análisis multivariante. Los datos obtenidos de los perfiles sensoriales se analizan utilizando un modelo mixto de análisis de la varianza (anidado x factorial) y un análisis canónico. Los resultados del análisis de varianza indican que las principales diferencias entre estilos de elaboración se deben a los atributos frutado, sabor amargo y firmeza (p < 0.05) y que las diferencias entre muestras, dentro de cada estilo de elaboración, se deben a todos los atributos estudiados (p < 0.001). El test de medias de Duncan y el análisis canónico muestran que todas las muestras son diferentes dentro de cada estilo de elaboración
Crossover in the nature of the metallic phases in the perovskite-type RNiO_3
We have measured the photoemission spectra of NdSmNiO,
where the metal-insulator transition and the N\'{e}el ordering occur at the
same temperature for and the metal-insulator transition
temperature () is higher than the N\'{e}el temperature for . For , the spectral intensity at the Fermi level is high in the
metallic phase above and gradually decreases with cooling in the
insulating phase below while for it shows a pseudogap-like
behavior above and further diminishes below . The results
clearly establish that there is a sharp change in the nature of the electronic
correlations in the middle () of the metallic phase of the
NiO system.Comment: 4 pages, 4 figure, submitted to Phys. Rev.
Dissecting galactic bulges in space and time I: The importance of early formation scenarios vs. secular evolution
This article has been accepted for publication in Monthly Notices Royal Astronomical Society ©: 2014 The Authors. Published by Oxford University Press on behalf of the Royal Astronomical Society. All rights reservedThe details of bulge formation via collapse, mergers, secular processes or their interplay remain unresolved. To start answering this question and quantify the importance of distinct mechanisms, we mapped a sample of three galactic bulges using data from the integral field spectrograph WiFeS on the ANU's 2.3-m telescope in Siding Spring Observatory. Its highresolution gratings (R ~ 7000) allow us to present a detailed kinematic and stellar population analysis of their inner structures with classical and novel techniques. The comparison of those techniques calls for the necessity of inversion algorithms in order to understand complex substructures and separate populations. We use line-strength indices to derive single stellar population equivalent ages and metallicities. Additionally, we use full spectral fitting methods, here the code STECKMAP, to extract their star formation histories. The high quality of our data allows us to study the 2D distribution of different stellar populations (i.e. young, intermediate and old). We can identify their dominant populations based on these age-discriminated 2D light and mass contribution. In all galactic bulges studied, at least 50 per cent of the stellar mass already existed 12 Gyr ago, more than currently predicted by simulations. A younger component (age between ~1 and ~8 Gyr) is also prominent and its present day distribution seems to be affected much more strongly by morphological structures, especially bars, than the older one. This in-depth analysis of the three bulges supports the notion of increasing complexity in their evolution, likely to be found in numerous bulge structures if studied at this level of detail, which cannot be achieved by mergers alone and require a non-negligible contribution of secular evolutionMKS acknowledges the support of the Instituto
de Astrofísica de Canarias via an Astrophysicist Resident
fellowship and Ignacio Martín-Navarro, Andra Stroe and Stéphane
Courteau for useful discussions. RC acknowledges the Ministerio
de Ciencia e Innovación by means of their FPI program (grant AYA-
2010-21322-C03-03 and AYA-2013-48226-C3-3-P). JFB acknowledges
support from the Ramón y Cajal Program and from the FP7
Marie Curie Actions of the European Commission, via the Initial
Training Network DAGAL under REA grant agreement number
289313. TRL thanks the support of the Spanish Ministerio de Educación,
Cultura y Deporte by means of the FPU fellowship. This research
has been supported by the Spanish Ministry of Economy and
Competitiveness (MINECO; grants AYA2010-21322-C03-02 and
AYA2009-11137) and by the Spanish Ministry of Science and Innovation
(MICINN; grants AYA2011-24728 and Consolider-Ingenio
CSD2010-00064) and by the Junta de Andalucía (FQM-108
LEARNING BY DOING ON COMPUTATIONAL FLUID DYNAMICS
ABSTRACT This work involves the methodology used in the University of Valladolid for Mechanical Engineering students to learn Computational Fluid Dynamics playing an active role. Students pretend to be engineers in a consulting or design office carrying out a fluid mechanics scale down projects. Later they act as reviewers evaluating a project from a colleague. There is a deeper understanding of the topic when they need to discuss the strategies to accomplish the project, to write a technical report and finally to justify the evaluation of other works. Furthermore, they develop their critical thought, writing skills and synthesis capacity. Multimedia material from other institutions that review the concepts learned in the course can be a suitable way to improve the understanding of concepts. INTRODUCTION The computational fluid dynamics (CFD) is a key tool in mechanical engineering because of the useful information provided at a very low cost that reduces the a posteriori parametric experimental studies. Learning CFD is an important investment for Mechanical Engineering undergraduate students. They need to know the methodology and to identify the weaknesses and strength of commercial codes
Astrobiological field campaign to a volcanosedimentary mars analogue methane producing subsurface protected ecosystem: Imuruk Lake (Alaska)
Viking missions reported adverse conditions for life in Mars surface. High hydrogen signal obtained by Mars orbiters has increased the interest in subsurface prospection as putative protected Mars environment with life potential. Permafrost has attracted considerable interest from an astrobiological point of view due to the recently reported results from the Mars exploration rovers. Considerable studies have been developed on extreme ecosystems and permafrost in particular, to evaluate the possibility of life on Mars and to test specific automated life detection instruments for space missions. The biodiversity of permafrost located on the Bering Land Bridge National Preserve has been studied as an example of subsurface protected niche of astrobiological interest. Different conventional (enrichment and isolation) and molecular ecology techniques (cloning, fluorescence "in situ" probe hybridization, FISH) have been used for isolation and bacterial identificationThe expedition to Imuruk Lake was supported by Centro de Astrobiología-INTA (Spain). The laboratory experimental procedures were supported by Grant AYA 2010–20213 “Desarrollo de Tecnología para la identificación de vida de forma automática” from the Spanish Governmen
Changes in western Mediterranean thermohaline circulation in association with a deglacial Organic Rich Layer formation in the Alboran Sea
We thank the constructive comments of three anonymous reviewers that substantially improved this manuscript. JNPA has been funded by a Postdoctoral fellowship Beatriu de Pinós funded by the AGAUR from the Generalitat de Catalunya and the European Union through the Marie Curie-COFUND actions. LDP acknowledges support from the Ramón y Cajal program (MINECO, Spain), JF from the Serra Húnter Programme (Generalitat de Catalunya) and IC from the ICREA-Academia program from the Generalitat de Catalunya. We are indebted to Albert Català and Montse Guart (University of Barcelona), and Joaquim Perona and Regina Roca (CCiT-UB) for their support with the laboratory work.Supplementary data to this article can be found online at
https://doi.org/10.1016/j.quascirev.2019.106075.The accumulation of an Organic Rich Layer (ORL) during the last deglaciation in the Alboran Sea (western Mediterranean Sea) and its link to changes in deep and intermediate water circulation are here investigated. Benthic foraminiferal assemblages and the shallow infaunal foraminifer Uvigerina peregrina δ13C record support the establishment of sustained high organic matter fluxes, and thus eutrophic conditions at the sea floor, during the late phase of the ORL (Younger Dryas to early Holocene periods). Since organic matter fluxes were lower (mesotrophic conditions) during the Bølling-Allerød period, they cannot be solely responsible for the ORL initiation. Geochemical, sedimentological and micropalaeontological proxies support a major weakening of the deep-water convection in the Gulf of Lion as the main driver for the development of poorly-ventilated conditions from intermediate depths (946 m) to the deep western Mediterranean basin that promoted the beginning of the ORL deposition. Nevertheless, a better ventilation at intermediate depths was established during the late ORL, while the deep basin remained poorly ventilated. We propose that our data reflect the arrival of a new better-ventilated intermediate water mass analogue to the current Levantine Intermediate Water (LIW) and/or a new intermediate water mass from the Gulf of Lion. The ultimate source of this water mass needs to be further explored but chronologies of the changes recorded here indicate that intermediate and deep ventilation phases were decoupled between the western and eastern Mediterranean basins during the deglaciation and early-middle Holocene.This work was funded by the projects TIMED (Call ref: ERC-CoG-2015; proposal number 683237) of the European Research Council (Consolidator Grants), CHIMERA (CTM2016-75411-R), CGL2015-66835-P and RTI2018-099489-B-I00 of the Ministerio de Economía y Competitividad of Spain. The Research Group GRC Geociències Marines (2017 SGR 315) of the Generalitat de Catalunya is also acknowledged, as well as the Research Groups RNM-178 and RNM-190 (Junta de Andalucía)
Charge disproportionation in YNiO : ESR and susceptibility study
We present a study of the magnetic properties of YNiO in the
paramagnetic range, above and below the metal-insulator (MI) transition. The dc
susceptibility, (measured up to 1000 K) is a decreasing function of
T for 150 K (the N\'{e}el temperature) and we observe two different
Curie-Weiss regimes corresponding to the metallic and insulator phases. In the
metallic phase, this behaviour seems to be associated with the small ionic
radius of Y% . The value of the Curie constant for T T allows
us to discard the possibility of Ni localization. An electron spin
resonance (ESR) spectrum is visible in the insulator phase and only a fraction
of the Ni ions contributes to this resonance. We explain the ESR and behaviour for T T in terms of charge disproportionation of
the type 2Ni Ni+Ni that is compatible with the
previously observed structural transition across T.Comment: 10 pages, 4 figures, submitted to Phys. Rev.
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