196 research outputs found
Ab initio Evidence for Giant Magnetoelectric Responses Driven by Structural Softness
We show that inducing structural softness in regular magnetoelectric (ME)
multiferroics -- i.e., tuning the materials to make their structure strongly
reactive to applied fields -- makes it possible to obtain very large ME
effects. We present illustrative first-principles results for BiFeO3 thin
films.Comment: 4 pages with 3 figures embedded. More information at
http://www.icmab.es/dmmis/leem/jorg
Magnetoelectric response of multiferroic BiFeO3 and related materials
We present a first-principles scheme for computing the magnetoelectric
response of multiferroics. We apply our method to BiFeO3 (BFO) and related
compounds in which Fe is substituted by other magnetic species. We show that
under certain relevant conditions -- i.e., in absence of incommensurate spin
modulation, as in BFO thin films and some BFO-based solid solutions -- these
materials display a large linear magnetoelectric response. Our calculations
reveal the atomistic origin of the coupling and allow us to identify the most
promising strategies to enhance it.Comment: 4 pages with 1 figure embedded. More information at
http://www.icmab.es/dmmis/leem/jorg
First-principles predictions of low-energy phases of multiferroic BiFeO3
We used first-principles methods to perform a systematic search for
potentially-stable phases of multiferroic BiFeO3. We considered a simulation
cell compatible with the atomic distortions that are most common among
perovskite oxides, and found a large number of local minima of the energy
within 100 meV/f.u. of the ferroelectric ground state. We discuss the variety
of low-symmetry structures discovered, as well as the implications of these
findings as regards current experimental (e.g., on thin films displaying {\em
super-tetragonal} phases) and theoretical (on models for BiFeO3's structural
phase transitions) work on this compound.Comment: 14 pages, 9 figures, accepted in PRB (contains small changes in the
text with respect to the first version
Steel profiles for repairing deteriorated timber beam ends
Se describe un procedimiento para la consolidación de viguetas de forjado de madera con deterioro en las cabezas mediante perfiles de acero conectados a la madera desde la cara superior del forjado. La pieza de refuerzo es un perfil en U de acero S275 conformado en frío con pletinas soldadas insertadas en la madera y conectada mediante tirafondos.
Se ensayaron 30 piezas a flexión obteniendo la rigidez y la capacidad de carga. Las probetas se dividieron en tres grupos. El primero compuesto por 10 piezas de madera laminada encolada de abeto con una sección de 180 x 200 mm y una longitud de 4.000 mm; el
segundo consistía en 10 piezas de madera aserrada de pino silvestre con la misma sección y longitud y, el tercero, estaba formado por otras 10 piezas de madera del género Pinus con una sección de 130 x 150 mm y 3.000 mm de longitud, procedentes de un edificio de Madrid con 120 años de antigüedad. Cada grupo de 10 piezas se dividió a su vez en dos grupos de 5 piezas. El primer subgrupo estaba formado por las piezas completas de madera y constituía el grupo de referencia. Las piezas del segundo subgrupo tenían una longitud inferior que se salvaba con una extensión del refuerzo metálico.
Los resultados indican que el sistema de refuerzo metálico permite resolver los problemas de falta de apoyo de la vigueta por deterioro de la madera que afecte en una longitud limitada (aproximadamente entre el 10 y el 20% de la longitud)
Multi-phonon scattering and Ti-induced hydrogen dynamics in sodium alanate
We use ab initio methods and neutron inelastic scattering (NIS) to study the
structure, energetics, and dynamics of pure and Ti-doped sodium alanate
(NaAlH_4), focusing on the possibility of substitutional Ti doping. The NIS
spectrum is found to exhibit surprisingly strong and sharp two-phonon features.
The calculations reveal that substitutional Ti doping is energetically
possible. Ti prefers to substitute for Na and is a powerful hydrogen attractor
that facilitates multiple Al--H bond breaking. Our results hint at new ways of
improving the hydrogen dynamics and storage capacity of the alanates.Comment: 5 pages, with 4 postscript figures embedded. Uses REVTEX4 and
graphicx macro
Primary immune thrombocytopenia: Experience of a specialised clinic
Introduction: Although primary immune thrombocytopenia (ITP) is rare in childhood, it is the most frequent cause of thrombocytopenia. There have been attempts to establish risk factors to predict the progression of the disease in order to optimise its management, which has changed in recent years due to, among other reasons, specialised care.
Material and methods: A retrospective, observational and analytical study was conducted on patients diagnosed with ITP over a 3-year period in a Paediatric Haematology specialist clinic.
Results: From the epidemiological, clinical and analytical point of view, the characteristics of this group are similar to others. Most of the patients (23/31, 74.2%) had ITP for less than 12 months, with there being no serious complications related to the disease or the treatment received. It was established that risk factors were related to being slowly evolving (lower event free survival (EFS)) with no statistical significance, female gender, age over 10 years, leukopenia absence of initial severe thrombocytopenia, and non-specialised care. The absence of a history of infection was significantly related to a lower EFS.
Conclusions: The epidemiological and analytical risk factors for a slowly evolving ITP are the same that described in the literature. Patients treated before the beginning of specialised care also had a lower EFS. These data seem to support the current recommendation that rare diseases should be managed in specialised units. (C) 2019 Published by Elsevier Espana, S.L.U. on behalf of Asociaci6n Espanola de Pediatria. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/)
Ab initio study of proper topological ferroelectricity in layered perovskite La2Ti2O7
We present a first-principles investigation of ferroelectricity in layered
perovskite oxide La2Ti2O7 (LTO), one of the compounds with highest Curie
temperature known (1770 K). Our calculations reveal that LTO's ferroelectric
transition results from the condensation of two soft modes that have the same
symmetry and are strongly coupled anharmonically. Further, the leading
instability mode essentially consists of rotations of the oxygen octahedra that
are the basic building block of the perovskite structure; remarkably, because
of the particular topology of the lattice, such O6 rotations give raise to a
spontaneous polarization in LTO. The effects discussed thus constitute an
example of how nano-structuring -- provided here by the natural layering of LTO
-- makes it possible to obtain a significant polar character in structural
distortions that are typically non-polar. We discuss the implications of our
findings as regards the design of novel multifunctional materials. Indeed, the
observed proper ferroelectricity driven by O6 rotations provides the ideal
conditions to obtain strong magnetoelectric effects.Comment: 13 pages with 4 figures embedded. More information at
http://www.icmab.es/dmmis/leem/jorg
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