Design of magnetic spirals in layered perovskites: extending the stability range far beyond room temperature

In insulating materials with ordered magnetic spiral phases, ferroelectricity can emerge due to the breaking of inversion symmetry. This property is of both fundamental and practical interest, in particular with a view to exploiting it in low-power electronic devices. Advances towards technological applications have been hindered, however, by the relatively low ordering temperatures $T_\mathrm{spiral}$ of most magnetic spiral phases, which rarely exceed 100 K. We have recently established that the ordering temperature of a magnetic spiral can be increased up to 310 K by the introduction of chemical disorder. Here we explore the design space opened up by this novel mechanism by combining it with a targeted lattice control of some magnetic interactions. In Cu-Fe layered perovskites we obtain $T_\mathrm{spiral}$ values close to 400 K, comfortably far from room temperature and almost 100 K higher than using chemical disorder alone. Moreover, we reveal a linear, universal relationship between the spiral's wave vector and the onset temperature of the spiral phase. This linear law ends at a paramagnetic-collinear-spiral triple point, which defines the highest spiral ordering temperature that can be achieved in this class of materials. Based on these findings, we propose a general set of rules for designing magnetic spirals in layered perovskites using external pressure, chemical substitutions and/or epitaxial strain, which should guide future efforts to engineer magnetic spiral phases with ordering temperatures suitable for technological applications.Comment: 5 figures, 35 pages, to be appeared on Science Advanc

Plan de cuidados estandarizados del paciente hospitalizado con síndome post-uci. atención integral del equipo multidisciplinar

Sufrir una enfermedad en situación crítica, a menudo supone un gran impacto para los pacientes que logran sobrevivir a la misma. El síndromePost-UCI, es una entidad clínica que no solo comprende el conjunto de complicaciones resultado de la estancia en UCI, sino también la repercusiónque esta puede provocar en todos los ámbitos de la vida del paciente durante años.Pasada una década desde su planteamiento, cobra especial importancia como posible consecuencia de la crisis sanitaria del SARS COV-2.<br /

Dynamic Disorder Restriction of Methylammonium (MA) Groups in Chloride-Doped MAPbBr 3 Hybrid Perovskites: A Neutron Powder Diffraction Study

The hybrid methylammonium (MA) lead halide MAPbX 3 perovskites present an appealing optoelectronic behavior with applications in high-efficiency solar cells. The orientation of the organic MA units may play an important role in the properties, given the degrees of freedom for internal motion of MA groups within the PbX 6 network. The present neutron powder diffraction study reveals the dynamic features of the MA units in the hybrid perovskite series MAPb(Br 1−x Cl x ) 3 , with x=0, 0.33, 0.5, 0.67, and 1. From difference Fourier maps, the H and C/N positions were located within the PbX 6 lattice; the refinement of the crystal structures unveiled the MA conformations. Three different orientations were found to exist as a function of the chlorine content (x) and, therefore, of the cubic unit-cell size. These conformations are stabilized by H-bond interactions with the halide ions, and were found to agree with those reported from theoretical calculations.Fil: Lopez, Carlos Alberto. Instituto de Ciencia de Materiales de Madrid; España. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - San Luis. Instituto de Investigaciones en Tecnología Química. Universidad Nacional de San Luis. Facultad de Química, Bioquímica y Farmacia. Instituto de Investigaciones en Tecnología Química; ArgentinaFil: Álvarez Galván, María Consuelo. Consejo Superior de Investigaciones Científicas; EspañaFil: Martínez Huerta, María Victoria. Consejo Superior de Investigaciones Científicas; EspañaFil: Fernández Díaz, María Teresa. Institut Laue Langevin; FranciaFil: Alonso, José Antonio. Instituto de Ciencia de Materiales de Madrid; Españ

Structural Phase Transitions of Hybrid Perovskites CH₃NH₃PbX₃ (X = Br, Cl) from Synchrotron and Neutron Diffraction Data

Methylammonium (MA) lead trihalide perovskites, that is, CH3NH3PbX3 (X = I, Br, Cl), have emerged as a new class of light-absorbing materials for photovoltaic applications. Indeed, since their implementation in solar-cell heterojunctions, they reached efficiencies above 23%. From a crystallographic point of view, there are many open questions that should be addressed, including the role of the internal motion of methylammonium groups within PbX6 lattice under extreme conditions, such as low/high temperature or high pressure. For instance, in MAPbBr3 perovskites, the octahedral tilting can be induced upon cooling, lowering the space group from the aristotype Pm3¯m to I4/mcm and Pnma. The band gap engineering brought about by the chemical management of MAPb(Br,Cl)3 perovskites has been controllably tuned: the gap progressively increases with the concentration of Cl ions from 2.1 to 2.9 eV. In this chapter, we review recent structural studies by state-of-the-art techniques, relevant to the crystallographic characterization of these materials, in close relationship with their light-absorption properties

Talentos matemáticos: análisis de una muestra

Durante décadas se han diagnosticado como talentos matemáticos, estudiantes que piensan e interpretan las matemáticas de un modo genuino, original y único, mediante problemas matemáticos ideados para sujetos de mayor edad que ellos. En la actualidad, diferentes autores plantean una definición del talento matemático basada en características, destacando que estos sujetos, a menudo, son capaces de proporcionar resoluciones inusualmente rápidas y exactas ante la propuesta de problemas matemáticos, y además, cuentan con suficientes habilidades para establecer relaciones entre tópicos, conceptos e ideas careciendo de una orientación educativa formal y dirigida. En esta investigación pretendemos determinar qué instrumentos son los más idóneos para identificar a niños con talento matemático a partir de una muestra (189 sujetos) ya preseleccionada para participar en el Proyecto Estalmat-Galicia. A esta muestra se le administraron dos instrumentos; una prueba matemática conformada por seis problemas de desarrollo y la batería de aptitudes mentales primarias de Thurstone (pma)For decades, students who think and interpreted maths in a genuine, original and unique mode, through mathematical problems designed for subjects older than them, have been diagnosed as mathematical talents. Nowadays, different authors suggest a definition of mathematical talent based in features, stressing that these subjects are often able to provide unusually fast and accurate answers to mathematical problems proposed, and also have sufficient skills to set up relations between topics, concepts and ideas without a formal educational and directed guidance. In this study we want to determine which instruments are best suited to identify children with mathematical talent from a sample (189 subjects) pre-selected to participate in the Project called Estalmat-Galicia. Two instruments were administered to this sample: a mathematical proof formed by six developmental problems and the battery of mental skills of primary Thurstone (PMA)S

Al-Doped SrMoO3 Perovskites as Promising Anode Materials in Solid Oxide Fuel Cells

Two perovskite materials with SrMo1−xAlxO3−δ (x = 0.1, 0.2) compositions have been synthesized by reduction from the corresponding scheelite phases, with SrMo1−xAlxO4−δ stoichiometry; the pertinent characterization shows that the defective perovskites can be used as anode materials in solid oxide fuel cells, providing maximum output power densities of 633 mW/cm2 for x = 0.2. To correlate structure and properties, a neutron powder diffraction investigation was carried out for both perovskite and scheelite phases. Both perovskites are cubic, defined in the Pm-3m space group, displaying a random distribution of Mo and Al cations over the 1a sites of the structure. The introduction of Al at Mo positions produced conspicuous amounts of oxygen vacancies in the perovskite, detected by neutrons. This is essential to induce ionic diffusion, providing a mixed ionic and electronic conduction (MIEC), since in MIEC electrodes, charge carriers are combined in one single phase and the ionic conductivity can be one order of magnitude higher than in a conventional material. The thermal expansion coefficients of the reduced and oxidized samples demonstrated that these materials perfectly match with the La0.8Sr0.2Ga0.83Mg0.17O3−δ electrolyte, La0.4Ce0.6O2−δ buffer layer and other components of the cell. Scanning electron microscopy after the test in a real solid oxide fuel cell showed a very dense electrolyte and porous electrodes, essential requirements for this type of fuel. SrMo1−xAlxO3−δ perovskites are, thus, a good replacement of conventional biphasic cermet anodes in solid oxide fuel cells

Habilidades matemáticas y verbales: diferencias de género en una muestra de 6º de Primaria y de 1º de ESO

El abordaje de las diferencias entre hombres y mujeres, niños y niñas, ha interesado, a lo largo del tiempo, a distintas ramas del saber. La situación social, educativa y política, en diferentes países, hace que este tópico no pierda actualidad. Los resultados de diversas investigaciones constatan diferencias en manifestaciones conductuales y en distintos campos del conocimiento entre unos y otras y, al intentar averiguar las causas, se continúa recurriendo a factores ligados a la biología o a factores sociales, culturales y educativos. El presente estudio se ha llevado a cabo con una muestra de 505 sujetos, 306 niños y 199 niñas de 6º de Primaria y 1º de la E.S.O. Esta muestra fue seleccionada en más de 150 colegios de Galicia para asistir a una prueba conjunta de matemáticas con vistas a participar en un programa de Estimulación del Talento Matemático, (ESTALMAT-Galicia) en la Facultad de Matemáticas de la USC. El instrumento utilizado ha sido el PMA. Los resultados apuntan que no existen diferencias significativas en cuanto a la ejecución de los factores del PMA entre niños y niñas, las únicas diferencias significativas fueron en el factor numérico y en el razonamiento, tomando toda la muestra. Se hizo un análisis más exhaustivo en aquellos que puntuaban por encima del percentil 95 y los resultados fueron muy similaresThe variety of approaches in finding the differences between men and women and boys and girls has been a topic of interest for the different branches of learning throughout time. The social, educational and political situation in several countries is one of the many reasons why this topic has not lost its importance or is still relevant today. The results from several researches ascertain differences in behavioral manifestations and in different fields of knowledge between both males and females. In trying to discover the causes of this the research is continually resorting to biological, social, cultural and educational factors. The present study has been carried out with a simple of 505 subjects, 306 boys and 199 girls from 6º de Primaria and 1º de la E.S.O (Middle School). This sample was selected in more than 150 schools in Galicia, Spain to assist with a test that was given in conjuncture in mathematics with the objective of participating in a program for Stimulation of Mathematical Talent (ESTALMAT-GALICIA) in the Faculty of Mathematics at the University of Santiago de Compostela (USC). The instrument used was the PMA. The results point out that taking into consideration the whole sample, there are no significant differences in regards to the execution of the PMA factors between boys and girls. The only significant differences were in the numerical and reasoning factors. A more comprehensive analysis was done in those samples that scored above a 95 percentile and the results were very similarS

On the crystal structure thermal evolution of formamidinium lead tribromide, CH(NH2)2PbBr3

Although methylammonium lead triiodide (CH3NH3PbI3) is recognized as the best candidate for photovoltaic applications, unfortunately it undergoes fast degradation when exposed to moisture and mild temperatures. Among hybrid organic-inorganic perovskites, formamidinium lead tribromide (FA: formamidinium, CH(NH2)2+) is an excellent alternative given its long-term stability. Here we present a structural study from synchrotron X-ray and neutron diffraction of an undeuterated FAPbBr3 specimen, carried out to follow its crystallographic behaviour in the 1-298 K temperature range. Two phase transitions are identified; at 256-261 K from the cubic structure observed at RT (Pm3m), to a tetragonal symmetry (P4/mbm), and at 159-160 K to an orthorhombic phase (space group Pnma). Our neutron diffraction data allowed us to unveil the configuration of the organic FA units and their full localization within the mentioned temperature range, thus improving the crystallographic description of this compound. The evolution with temperature of the H-bonds between the organic molecule and the inorganic cage is followed. The UV-Vis diffuse reflectance spectrum shows a band gap of 2.23 eV, making it a suitable material for optoelectronic devices.Fil: Abia, Carmen. Instituto de Ciencia de Materiales de Madrid; España. Institut Laue Langevin; FranciaFil: Lopez, Carlos Alberto. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - San Luis. Instituto de Investigaciones en Tecnología Química. Universidad Nacional de San Luis. Facultad de Química, Bioquímica y Farmacia. Instituto de Investigaciones en Tecnología Química; Argentina. Instituto de Ciencia de Materiales de Madrid; EspañaFil: Álvarez Galván, María Consuelo. Consejo Superior de Investigaciones Científicas; EspañaFil: Canadillas Delgado, Laura. Institut Laue Langevin; FranciaFil: Fernández Díaz, María Teresa. Institut Laue Langevin; FranciaFil: Alonso, José Antonio. Instituto de Ciencia de Materiales de Madrid; Españ

An onto-semiotic approach to geometrical reasoning and spatial visualization

En el marco de una investigación sobre evaluación y desarrollo de capacidades de visualización y razonamiento espacial, presentamos el análisis de una tarea propuesta a una muestra de 400 estudiantes de magisterio. El análisis se realiza aplicando la noción de configuración de objetos y procesos introducida en el enfoque ontosemiótico del conocimiento y la instrucción matemática, la cual aporta posibilidades analíticas complementarias respecto de otras nociones cognitivas. La identificación de las redes de objetos intervinientes y emergentes en la resolución de la tarea permite formular hipótesis sobre conflictos potenciales de significado de los sujetos y explicar las dificultades en términos de los conocimientos y procesos de interpretación requeridosAs part of an investigation on the evaluation and development of visualization skills and spatial reasoning, we present the analysis of a task used with a sample of 400 student teachers. The analysis is carried out applying the notion of configuration of objects and processes introduced in the "onto-semiotic approach" to mathematical knowledge and instruction, which provides complementary analytical possibilities with respect to other cognitive tools. The identification of the networks of intervening and emergent objects in the resolution of the task allows us to formulate hypothesis on potential subjects' conflicts of meaning and to explain the difficulties in terms of the required knowledge and processes of interpretationTrabajo realizado parcialmente en el marco del proyecto de investigación, SEJ2007-60110/EDUC, financiado por el Ministerio de Educación y Ciencia y los Fondos Europeos de Desarrollo Regional (MEC-FEDER)S

Bilateral anterior ischemic optic neuropathy after bilateral neck dissection

Mar&amp;iacute;a J Su&amp;aacute;rez-Fern&amp;aacute;ndez, Antonio Clariana-Mart&amp;iacute;n, Enrique Menc&amp;iacute;a-Guti&amp;eacute;rrez, Esperanza Guti&amp;eacute;rrez-D&amp;iacute;az, Teresa Gracia-Garc&amp;iacute;a-MiguelOphthalmology Department, 12 de Octubre Hospital, Complutense University, Madrid, SpainPurpose: The risk of visual loss after nonocular surgeries is very low, between 0.2% and 4.5%. According to the American Society of Anesthesiologists, ischemic optic neuropathy has been reported mostly after spinal surgery (54.2%), followed by cardiac surgery and radical neck dissection (13.3%). It may occur in association with some conditions that include systemic hypotension, acute blood loss and hypovolemia.Case report: A 46-year-old woman, whose diagnosis was laryngeal squamous cell carcinoma, complained of visual loss in her right eye two days after surgery (laryngectomy with bilateral radical neck dissection and left jugular ligature) and one day later in her left eye. The diagnosis was nonarteritic anterior ischemic optic neuropathy.Conclusion: Anterior ischemic optic neuropathy related to nonocular surgery is usually bilateral and its prognosis is very poor, resulting in blindness or severe visual loss. Although rare, patients should be warned about this complication, which has a profound impact on quality of life, since no therapeutic measure, including correction of hypotension and anemia, seems to improve the prognosis of this complication.Keywords: ischemic optic neuropathy, visual loss, radical neck dissection, blood los