Magnetic structure factor of correlated moments in small-angle neutron scattering

The interplay between structural and magnetic properties of nanostructured magnetic materials allows one to realize unconventional magnetic effects, which results in a demand for experimental techniques to determine the magnetization profile with nanoscale resolution. Magnetic small-angle neutron scattering (SANS) probes both the chemical and magnetic nanostructure and is thus a powerful technique, e.g., for the characterization of magnetic nanoparticles. Here, we show that the conventionally used particle-matrix approach to describe SANS of magnetic particle assemblies, however, leads to a flawed interpretation. As a remedy, we provide general expressions for the field-dependent two-dimensional magnetic SANS cross section of correlated moments. It is shown that for structurally disordered ensembles the magnetic structure factor is in general, and contrary to common assumptions, (i) anisotropic also in zero field and (ii) that even in saturation the magnetic structure factor deviates from the nuclear one. These theoretical predictions explain qualitatively the intriguing experimental, polarized SANS data of an ensemble of dipolar-coupled iron oxide nanoparticles.This project has received funding from the European Commission Framework Programme 7 under Grant Agreement No. 604448 (NanoMag)

Supraferromagnetic correlations in clusters of magnetic nanoflowers

Magnetic nanoflowers are densely packed aggregates of superferromagnetically coupled iron oxide nanocrystallites, which excel during magnetic hyperthermia experiments. Here, we investigate the nature of the moment coupling within a powder of such nanoflowers using spin-resolved small-angle neutron scattering. Within the powder, the nanoparticles are agglomerated to clusters, and we can show that the moments of neighboring nanoflowers tend to align parallel to each other. Thus, the whole system resembles a hierarchical magnetic nanostructure consisting of three distinct levels, i.e., (i) the ferrimagnetic nanocrystallites as building blocks, (ii) the superferromagnetic nanoflowers, and (iii) the supraferromagnetic clusters of nanoflowers. We surmise that such a supraferromagnetic coupling explains the enhanced magnetic hyperthermia performance in the case of interacting nanoflowers.This project received funding from the European Commission Framework Programme 7 under Grant Agreement No. 604448 (NanoMag), the National Research Fund of Luxembourg (No. CORE SANS4NCC Grant), and the Spanish Government (No. MAT2017-83631-C3-R)

Nonlinear susceptibilities as a probe to unambiguously distinguish between canonical and cluster spin glasses

Treating the randomly Fe-substituted optimally hole-doped manganite La0.7Pb0.3(Mn1−yFey)O3 (y=0.2,0.3) as a test case, we demonstrate that a combined investigation of both odd and even harmonics of the ac magnetic response permits an unambiguous distinction between the canonical and cluster spin glasses. As expected for a spin glass (SG), the nonlinear ac magnetic susceptibilities χ3(T,ω) and χ5(T,ω) (odd armonics) diverge at the SG freezing temperature Tg=80.00(3) K [Tg=56.25(5) K] in the static limit and, like the imaginary part of the linear susceptibility, follow dynamic scaling with the critical exponents β=0.56(3) [β=0.63(3)], γ=1.80(5) [γ=2.0(1)], and zν=10.1(1) [zν=8.0(5)] in the sample with composition y=0.2 (y=0.3). The nonlinear susceptibility χNL, which has contributions from both χ3 and χ5, satisfies static scaling with the same choice of Tg, β, and γ. Irrespective of the Fe concentration, the values of the critical exponents γ, ν, and η are in much better agreement with those theoretically predicted for a three-dimensional (d=3) Heisenberg chiral SG than for a d=3 Ising SG. The true thermodynamic nature of the “zero-field” spin-glass transition is preserved even in finite magnetic fields. Unlike odd harmonics, even harmonics χ2(T,ω) and χ4(T,ω) make it evident that, apart from the macroscopic length scale of the spin-glass order in the static limit, there exists a length scale that corresponds to the short-range ferromagnetic order.This work was supported by the Department of Science and Technology, India, through Grant No. IR/S5/IU-01/2006, and by the Spanish Ministry for Education through the grant No. SAB 2010-0091. S.N.K. is thankful to the Department of Science and Technology, India, for financial support through the J. C. Bose National Fellowship. Y.B. thanks the Council for Scientific and Industrial Research, India, for the financial support through a Senior Research Fellowship. The authors thank J. M. Barandiaran and J. Gutiérrez for providing the samples

A review of river habitat characterisation methods: indices vs. characterisation protocols

RESUMEN. Una gran variedad de metodologías se han propuesto para la caracterización de los hábitats fluviales a fin de cumplir con diferentes objetivos medioambientales. Esta diversidad de métodos puede ser vista como una ventaja para hacer frente a diferentes objetivos ambientales. Sin embargo, el seguimiento a medio o largo plazo de las características físicas del hábitat fluvial carece de una metodología estandarizada, lo cual contrasta con otros métodos mucho mejor establecidos para el seguimiento de otros componentes del ecosistema fluvial. Se han hecho algunos intentos para estandarizar los métodos de caracterización de los hábitats fluviales, y estos incluyen el estándar europeo para la evaluación de las características hidromorfológicas de los ríos (CEN, 2002), y el desarrollo del módulo de evaluación fisicoquímica dentro del sistema australiano de evaluación fluvial (AusRivAS). Uno de los primeros pasos para avanzar en el desarrollo y uso de métodos para la caracterización de los hábitats fluviales en los programas de seguimiento a medio y largo plazo es revisar las prácticas actuales a fin de poder abordar las deficiencias e introducir mejoras. En el presente trabajo se revisan más de 50 métodos que se han utilizado para caracterizar los hábitats fluviales en todo el mundo, utilizando el estándar europeo como referencia para comparar los métodos. Los métodos de caracterización de los hábitats fluviales se diferencian principalmente por tres razones: (1) los objetivos para los que fueron diseñados, (2) el tiempo que demanda su aplicación y (3) unos miden mientras otros evalúan las características del hábitat. Las características del cauce y de la zona ribereña son consideradas por un mayor número de métodos que las características de la llanura de inundación. Además, entre todas las características del hábitat fluvial descritas, la estabilidad de las orillas, el sustrato del lecho, las estructuras artificiales, la estructura de la vegetación ribereña, las dimensiones del cauce, el tipo de flujo o el caudal, los usos del suelo adyacentes y las barras de sedimentos son las más comúnmente registradas. Se concluye que los métodos de medición de las características del hábitat fluvial que recogen información cuantitativa cubriendo diferentes escalas espaciales podrían ser los más eficaces, ya que proporcionan bases de datos más amplias que permiten utilizar la información para diversos objetivos. Por último, algunos tipos de ríos, como los ríos intermitentes, requieren un mayor estudio para poder identificar correctamente los atributos físicos y la metodología adecuada para realizar el seguimiento de las características del hábitat.ABSTRACT. A wide variety of methodologies have been proposed for characterising river habitats in order to meet different environmental objectives. However, mid- to long-term monitoring of the physical characteristics of river habitats lacks a standardised methodology. This contrasts with well-established methods for monitoring other river ecosystem components. Some attempts have been made to standardise the methods for characterising river habitats including the European Guidance Standard for Assessing the Hydromorphological Characteristics of Rivers (CEN, 2002) and the Physical and Chemical AssessmentModule within the Australian River Assessment System (AusRivAS). One of the first steps toward advancing the development and use of methods for characterising river habitats in mid- to long-term monitoring programs is to review current practices so that deficiencies can be identified and addressed. In the present work, we review more than 50 methods that have been used to characterise river habitats worldwide. This review uses the European standard as a reference benchmark for comparison with existing methods of river habitat characterisation. Methods of characterising river habitats differ mainly with respect to three features: (1) the objectives for which they were designed, (2) the time required for their application and (3) whether they measure characteristics or evaluate them. Channel and riparian zone characteristics are more extensively covered than floodplain characteristics. Moreover, of all the described river habitat characteristics, bank stability, channel substrate, artificial structures, riparian vegetation structure, channel dimensions, flow types or flow status, adjacent land uses and bars are the most commonly recorded.We conclude that assessment methods of river habitat characteristics that gather quantitative information at a range of spatial scales could be the most effective, as they provide relatively extensive data sets that can be used to analyse information for several purposes. Finally, some types of rivers, such as intermittent rivers, require further work in order to identify their physical habitat characteristics and the proper monitoring methodology

Separation of CO2-N2 gas mixtures: Membrane combination and temperature influence

Novel mixed matrix membranes (MMM) with different characteristics are experimentally evaluated in a two-stage membranes-in-series bench-scale setup for the separation of CO2-N2 gas mixtures. For stage 1, a high permeability (higher than 1000 Barrer) and low selectivity (about 5–10) membrane is chosen: the [emim][Ac]-Chitosan (IL-CS) hybrid membrane developed in our laboratory and the Pervap 4060 (Sulzer) composite membrane. For stage 2, we chose our Zeolite A/PTMSP MMM, whose selectivity is higher than 20 even at up to 343 K, the CO2 permeability not lower than 5000 Barrer, which allows skipping the use of the intermediate compressor. The influence of membrane intrinsic properties (i.e. selective membrane material), number of modules in series, and feed concentration on separation performance is evaluated experimentally. In this system, a 10% CO2 feed is concentrated to 43%, 26 and 40% for the Zeolite A/PTMSP MMM – Zeolite A/PTMSP MMM, IL-CS – Zeolite A/PTMSP and Pervap 4060 – Zeolite A/PTMSP in stage 1 and stage 2, respectively. The agreement of the experimental results with a mathematical model at the low CO2 feed concentration of flue gas allows estimating the membrane area needed for each membrane material to achieve a given CO2 purity and removal efficiency. The very large membrane areas needed to reach the 90% CO2 purity and removal efficiency target are drastically reduced if the CO2 removal efficiency required is set to 70%, especially for the combinations with different membranes in each stage, which gives scope for attempting further development of novel membrane materials for CO2capture processes.This work is partially based on a concept from Eliot S. Gerber (U. S.A.), for which he is gratefully acknowledged. The authors are also grateful for the financial support from the Spanish Ministry of Economy and Competitiveness (MINECO) under project CTQ2012-31229. A.F.B. and C.C.C. also thank the MINECO for the Early Stage Researcher (BES2013-064266) and ‘‘Ramón y Cajal” (RYC2011-0855) contracts, respectively

Analysis of technical efficiency in Spanish maritime transport companies: 2012-2018

RESUMEN: El objetivo de este estudio es analizar la eficiencia técnica de las empresas de transporte marítimo españolas y sus factores determinantes utilizando la metodología de análisis de fronteras de producción determinista y estocástica durante el periodo 2012-2018. Analizando los niveles de eficiencia técnica de las empresas de transporte marítimo, los resultados nos muestran un incremento a lo largo del periodo considerado. Siendo 2014 el año donde se encuentra el dato más bajo de eficiencia técnica y en 2017 el más alto. El estudio se centra en el análisis de los determinantes de tales niveles de eficiencia técnica, para los cuales se han seleccionado varios ratios financieros además de observar si las empresas tienen presencia internacional o solamente se limitan al ámbito nacional. Nos muestra cómo afectan de manera significativa y positiva el ratio margen de beneficio y los ratios de solvencia y liquidez. Sin embargo, la presencia de negocio fuera de España afecta de manera negativa.ABSTRACT: The main of this study is to analyze the technical efficiency of the Spanish maritime transport companies and their de determinant factors using the deterministic and stochastic production frontier analysis methodology during the period 2012-2018. Analyzing the levels of technical efficiency of maritime transport companies, the results show us an increase throughout the period considered. 2014 being the year where the lowest technical efficiency data is found and in the 2017 the highest. The study focuses on the analysis of those determinants of such levels of technical efficiency, for which several financial ratios have been selected in addition to observing whether the companies have an international presence or are only limited to national sphere. It show us how significantly and positively affecting profit margin ratio and solvency and liquidity ratios. However, we see how the presence of business outside of Spain have a negative effect.Grado en Economí

Effect of humidity on CO2/N2 and CO2/CH4 separation using novel robust mixed matrix composite hollow fiber membranes: experimental and model evaluation

In this work, the performance of new robust mixed matrix composite hollow fiber (MMCHF) membranes with a different selective layer composition is evaluated in the absence and presence of water vapor in CO2/N2 and CO2/CH4 separation. The selective layer of these membranes is made of highly permeable hydrophobic poly(trimethyl-1-silylpropine) (PTMSP) and hydrophilic chitosan-ionic liquid (IL-CS) hybrid matrices, respectively, filled with hydrophilic zeolite 4A particles in the first case and HKUST-1 nanoparticles in the second, coated over compatible supports. The effect of water vapor in the feed or using a commercial hydrophobic PDMSXA-10 HF membrane has also been studied for comparison. Mixed gas separation experiments were performed at values of 0 and 50% relative humidity (RH) in the feed and varying CO2 concentration in N2 and CH4, respectively. The performance has been validated by a simple mathematical model considering the effect of temperature and relative humidity on membrane permeability.This research was funded by the Spanish Ministry of Science, Innovation and Universities (www.ciencia.gob.es) under project CTQ2016-76231-C2-1-R

Urdiales, grotte

Le siteLa grotte d’Urdiales est localisée dans le village du même nom, dans la localité de Castro Urdiales, dans la zone est de la communauté autonome de Cantabrie (Espagne). Elle s’ouvre dans le réseau karstique du « Alto de San Andrés », petite colline calcaire du Crétacé inférieur (calcaire aptien) qui renferme également la grotte décorée d’El Cuco. Si celle-ci est connue depuis plusieurs décennies (García Guinea 1968), ce n’est qu’en 1999 qu’a été découverte la grotte d’Urdiales. Ce sont..

El Cuco, grotte

Le siteLa grotte d’El Cuco se trouve à l’ouest du Haut de San Andres, dans la ville de Castro Urdiales (Cantabrie). La grotte a été découverte au cours des années 1960 par un amateur local. Les manifestations graphiques pariétales ont été étudiées par M.A. García Guinea (1968). Au début du xxie siècle, leur révision a été entreprise par E. Muñoz, R. Montes, A. Gómez et P. Rasines (2007), qui ont incorporé de nouvelles manifestations, notamment quelques peintures rouges.La cavité, orientée à ..