Heartbeat classification fusing temporal and morphological information of ECGs via ensemble of classifiers

©2019. This manuscript version is made available under the CC-BY-NC-ND 4.0 license https://creativecommons.org/licenses/by-nc-nd/4.0/. This version of the article: Mondéjar-Guerra, V., Novo, J., Rouco, J., Penedo, M. G., & Ortega, M. (2019). “Heartbeat classification fusing temporal and morphological information of ECGs via ensemble of classifiers” has been accepted for publication in Biomedical Signal Processing and Control, 47, 41–48. The Version of Record is available online at: https://doi.org/10.1016/j.bspc.2018.08.007.[Abstract]: A method for the automatic classification of electrocardiograms (ECG) based on the combination of multiple Support Vector Machines (SVMs) is presented in this work. The method relies on the time intervals between consequent beats and their morphology for the ECG characterisation. Different descriptors based on wavelets, local binary patterns (LBP), higher order statistics (HOS) and several amplitude values were employed. Instead of concatenating all these features to feed a single SVM model, we propose to train specific SVM models for each type of feature. In order to obtain the final prediction, the decisions of the different models are combined with the product, sum, and majority rules. The designed methodology approaches are tested on the public MIT-BIH arrhythmia database, classifying four kinds of abnormal and normal beats. Our approach based on an ensemble of SVMs offered a satisfactory performance, improving the results when compared to a single SVM model using the same features. Additionally, our approach also showed better results in comparison with previous machine learning approaches of the state-of-the-art.This work was partially supported by the Research Project RTC-2016-5143-1, financed by the Spanish Ministry of Economy, Industry and Competitiveness and the European Regional Development Fund (ERDF). Also, this work has received financial support from the ERDF and the Xunta de Galicia, Centro singular de investigación de Galicia accreditation 2016–2019, Ref. ED431G/01; and Grupos de Referencia Competitiva, Ref. ED431C 2016-047.Xunta de Galicia; ED431G/01Xunta de Galicia; ED431C 2016-04

Geometrically controlled ratchet effect with collective vortex motion

© 2015 IOP Publishing Ltd and Deutsche Physikalische Gesellschaft. Rectified flux motion arising from the collective effect of many interacting vortices is obtained in a specially designed superconducting device. Ratchet structures with different asymmetric pinning potentials are generated by tuning the size, depth, and distribution of triangular blind-antidots in a high-temperature superconducting film. We experimentally and theoretically demonstrate that the amplitude and sign of the rectified vortex motion can be finely tuned with the pattern geometry. Two different dynamical regimes depending on the nature of vortices initiating the dissipation are identified, which can control the rectified vortex motion.This work has been supported by MINECO(MAT2014-51778-C2-1R, MAT2012-35370, CSD2007-0041, IPT- 2011-1090-920000), Generalitat de Catalunya (SGR2014-00753, 2014SGR150, XaRMAE), EU-FP7 NMP-LA- 2012-280432 EUROTAPES project and Cost Action MP1201.VR acknowledges the JAE-CSIC PhD grant. AS acknowledges funding from an ICREA Academia award.Peer Reviewe

Competition between superconductor : ferromagnetic stray magnetic fields in YBa2Cu3O7−x films pierced with Co nano-rods

Altres ajuts: Cost Actions MP1201 and CM1301 (CELINA). A. Sanchez acknowledges a grant from ICREA Academia, funded by the Generalitat de Catalunya. We are grateful to I. Rivas and R. Valero from LMA-INA (Zaragoza, Spain) for experimental help in the cobalt growth and Ar+milling processes, and Dr C. Magén and Dr. P. Algarabel from LMA-INA (Zaragoza, Spain) for facilitating the use of their high performance computing server to perform the micromagnetic simulations. We acknowledge R. Morales from UPV/EHU and Ikerbasque, A. Fernández-Pacheco from U. Cambridge and S. Valencia from Helmholtz-Zentrum, Berlin for fruitful discussions.Superconductivity and ferromagnetism are two antagonistic phenomena that combined can lead to a rich phenomenology of interactions, resulting in novel physical properties and unique functionalities. Here we propose an original hybrid system formed by a high-temperature superconducting film, patterned with antidots, and with ferromagnetic nano-rods grown inside them. This particular structure exhibits the synergic influence of superconductor (SC) - ferromagnetic (FM) stray fields, in both the superconducting behaviour of the film and the three-dimensional (3D) magnetic structure of nano-rods. We show that FM stray fields directly influence the critical current density of the superconducting film. Additional functionalities appear due to the interaction of SC stray fields, associated to supercurrent loops, with the non-trivial 3D remanent magnetic structure of FM nano-rods. This work unravels the importance of addressing quantitatively the effect of stray magnetic fields from both, the superconductor and the ferromagnet in hybrid magnetic nano-devices based on high temperature superconductors

Combining Freestanding Ferroelectric Perovskite Oxides with Two-Dimensional Semiconductors for High Performance Transistors

[EN] We demonstrate the fabrication of field-effect transistors based on single-layer MoS2 and a thin layer of BaTiO3 (BTO) dielectric, isolated from its parent epitaxial template substrate. Thin BTO provides an ultrahigh-κ gate dielectric effectively screening Coulomb scattering centers. These devices show mobilities substantially larger than those obtained with standard SiO2 dielectrics and comparable with values obtained with hexagonal boron nitride, a dielectric employed for fabrication of high-performance two-dimensional (2D) based devices. Moreover, the ferroelectric character of BTO induces a robust hysteresis of the current vs gate voltage characteristics, attributed to it polarization switching. This hysteresis is strongly suppressed when the device is warmed up above the tetragonal-to-cubic transition temperature of BTO that leads to a ferroelectric-to-paraelectric transition. This hysteretic behavior is attractive for applications in memory storage devices. Our results open the door to the integration of a large family of complex oxides exhibiting strongly correlated physics in 2D-based devices.European Research Council (ERC) through the project 2DTOPSENSE (GA 755655) European Union’sHorizon 2020 research and innovation program (Graphene Core2-Graphenebased disruptive technologies and Grant Agreement 881603 Graphene Core3-Graphene-based disruptive technologies) EU FLAG-ERA through the project To2Dox (JTC-2019-009) Comunidad de Madrid through the project CAIRO-CM project (Y2020/NMT-6661) Spanish Ministry of Science and Innovation through the projects PID2020-118078RBI00 RTI2018-099054-J-I00 and IJC2018-038164-I, PRE2018-084818 Key Research and Development Program of Shaanxi (Program No.2021KW-02).Peer reviewe

Geometrically controlled ratchet effect with collective vortex motion

Rectified flux motion arising from the collective effect of many interacting vortices is obtained in a specially designed superconducting device. Ratchet structures with different asymmetric pinning potentials are generated by tuning the size, depth, and distribution of triangular blind-antidots in a high-temperature superconducting film. We experimentally and theoretically demonstrate that the amplitude and sign of the rectified vortex motion can be finely tuned with the pattern geometry. Two different dynamical regimes depending on the nature of vortices initiating the dissipation are identified, which can control the rectified vortex motion

Ferroionic inversion of spin polarization in a spin-memristor

Magnetoelectric coupling in artificial multiferroic interfaces can be drastically affected by the switching of oxygen vacancies and by the inversion of the ferroelectric polarization. Disentangling both effects is of major importance toward exploiting these effects in practical spintronic or spinorbitronic devices. We report on the independent control of ferroelectric and oxygen vacancy switching in multiferroic tunnel junctions with a La_(0.7)Sr_(0.3)MnO_3 bottom electrode, a BaTiO_3 ferroelectric barrier, and a Ni top electrode. We show that the concurrence of interface oxidation and ferroelectric switching allows for the controlled inversion of the interface spin polarization. Moreover, we show the possibility of a spin-memristor where the controlled oxidation of the interface allows for a continuum of memresistance states in the tunneling magnetoresistance. These results signal interesting new avenues toward neuromorphic devices where, as in practical neurons, the electronic response is controlled by electrochemical degrees of freedom

Controlled sign reversal of electroresistance in oxide tunnel junctions by electrochemical-ferroelectric coupling

The persistence of ferroelectricity in ultrathin layers relies critically on screening or compensation of polarization charges which otherwise destabilize the ferroelectric state. At surfaces, charged defects play a crucial role in the screening mechanism triggering novel mixed electrochemical-ferroelectric states. At interfaces, however, the coupling between ferroelectric and electrochemical states has remained unexplored. Here, we make use of the dynamic formation of the oxygen vacancy profile in the nanometerthick barrier of a ferroelectric tunnel junction to demonstrate the interplay between electrochemical and ferroelectric degrees of freedom at an oxide interface. We fabricate ferroelectric tunnel junctions with a La_0.7Sr_0.3MnO_3 bottom electrode and BaTiO_3 ferroelectric barrier. We use poling strategies to promote the generation and transport of oxygen vacancies at the metallic top electrode. Generated oxygen vacancies control the stability of the ferroelectric polarization and modify its coercive fields. The ferroelectric polarization, in turn, controls the ionization of oxygen vacancies well above the limits of thermodynamic equilibrium, triggering the build up of a Schottky barrier at the interface which can be turned on and off with ferroelectric switching. This interplay between electronic and electrochemical degrees of freedom yields very large values of the electroresistance (more than 10^6% at low temperatures) and enables a controlled switching between clockwise and counterclockwise switching modes in the same junction (and consequently, a change of the sign of the electroresistance). The strong coupling found between electrochemical and electronic degrees of freedom sheds light on the growing debate between resistive and ferroelectric switching in ferroelectric tunnel junctions, and moreover, can be the source of novel concepts in memory devices and neuromorphie computing

Treatment with tocilizumab or corticosteroids for COVID-19 patients with hyperinflammatory state: a multicentre cohort study (SAM-COVID-19)

Objectives: The objective of this study was to estimate the association between tocilizumab or corticosteroids and the risk of intubation or death in patients with coronavirus disease 19 (COVID-19) with a hyperinflammatory state according to clinical and laboratory parameters. Methods: A cohort study was performed in 60 Spanish hospitals including 778 patients with COVID-19 and clinical and laboratory data indicative of a hyperinflammatory state. Treatment was mainly with tocilizumab, an intermediate-high dose of corticosteroids (IHDC), a pulse dose of corticosteroids (PDC), combination therapy, or no treatment. Primary outcome was intubation or death; follow-up was 21 days. Propensity score-adjusted estimations using Cox regression (logistic regression if needed) were calculated. Propensity scores were used as confounders, matching variables and for the inverse probability of treatment weights (IPTWs). Results: In all, 88, 117, 78 and 151 patients treated with tocilizumab, IHDC, PDC, and combination therapy, respectively, were compared with 344 untreated patients. The primary endpoint occurred in 10 (11.4%), 27 (23.1%), 12 (15.4%), 40 (25.6%) and 69 (21.1%), respectively. The IPTW-based hazard ratios (odds ratio for combination therapy) for the primary endpoint were 0.32 (95%CI 0.22-0.47; p < 0.001) for tocilizumab, 0.82 (0.71-1.30; p 0.82) for IHDC, 0.61 (0.43-0.86; p 0.006) for PDC, and 1.17 (0.86-1.58; p 0.30) for combination therapy. Other applications of the propensity score provided similar results, but were not significant for PDC. Tocilizumab was also associated with lower hazard of death alone in IPTW analysis (0.07; 0.02-0.17; p < 0.001). Conclusions: Tocilizumab might be useful in COVID-19 patients with a hyperinflammatory state and should be prioritized for randomized trials in this situatio

Controlling Vortex Pinning and Dynamics of Nanostructured YBCO Thin Films Grown by Chemical Solution Deposition

Desde el descubrimiento de los Superconductores de Alta Temperatura (SCAT), se ha realizado un gran esfuerzo con tal de optimizar las propiedades eléctricas de estos materiales. A diferencia de los Superconductores convencionales de Baja Temperatura (SCBT), algunos de los SCAT son capaces de alcanzar el estado superconductor a la temperatura de ebullición del nitrógeno (77K) haciéndolos mucho más atractivos en cuanto a aplicaciones tecnológicas dados los reducidos costes de operación. Una de las principales aplicaciones de los SCAT es el transporte eléctrico. La ausencia de resistencia eléctrica de estos materiales cuando están por debajo de su temperatura crítica, Tc, hacen que puedan transportar hasta 10 veces más de potencia que los cables convencionales, o proporcionar una misma potencia con niveles muy inferiores de voltaje. Por otro lado, los SCAT han sido profundamente estudiados en el ámbito de la electrónica. En particular, nanohilos de SCAT pueden ser escalados a tamaños menores debido a sus pequeñas longitudes intrínsecas. Además, sus rápidos coeficientes de relajación permiten altos niveles de adquisición en experimentos de fotodetección cuando éstos son comparados con SCBT. No obstante, una de las características más importantes en el estudio de los SCAT es la presencia de líneas de flujo magnético cuantificadas, denominadas vórtices, en su diagrama de fase. Su mayor diferencia con respecto a los SCBT surge cuando se tienen en cuenta las altas excitaciones térmicas. Como consecuencia, una gran variedad de defectos de anclaje son necesarios con la finalidad de evitar (o controlar) la dinámica de los vórtices y por lo tanto, la disipación eléctrica resultante. El control del anclaje y la dinámica de los vórtices es la finalidad de esta tesis donde los principales resultados están presentados en los capítulos 3, 4 y 5. Previamente, en el capítulo 1 presentamos las principales propiedades superconductoras y en particular, las referidas al comportamiento de los vórtices en muestras de YBa2Cu3O7-x (YBCO -superconductor con el más amplio rango de operación-) crecidas por el método de deposición de soluciones químicas (DSQ). En el capítulo 2 exponemos las técnicas experimentales utilizadas así como los procedimientos de medida. En el capítulo 3, un gran análisis sobre el anclaje de vórtices es presentado. Un fenómeno sin precedentes en el anclaje de vórtices es demostrado el cual permite mejorar la densidad de corriente crítica y su anisotropía en presencia de fases secundarias no-superconductoras dentro de la matriz de YBCO. Además, un análisis de la dinámica de los vórtices con respecto a los defectos naturales de muestras de YBCO-DSQ es expuesto. En los capítulos 4 y 5 nos focalizamos en el control de la dinámica de los vórtices en capas finas de YBCO. En el capítulo 4 demostramos un sentido preferencial para el movimiento de los vórtices cuando nanoestructuras asimétricas son diseñadas en la capa de YBCO. Como consecuencia, una rectificación AC-DC es obtenida. En el capítulo 5, los estudios están centrados en la interacción entre materiales superconductores y ferromagnéticos. Se demuestra como introduciendo nanocilindros ferromagnéticos dentro de la matriz del YBCO, un enorme control sobre la densidad de corriente crítica es posible en función del estado magnético de los nanocilindros. Las conclusiones generales están expuestas y resumidas en el último capítulo. Finalmente, el procedimiento analítico utilizado en una simulación teórica presentada en el capítulo 5 es explicado en el apéndice.Since the discovery of High-Temperature Superconductors (HTS) a huge effort has been devoted in order to optimize the electric power properties of these materials. As a difference from conventional Low-Temperature Superconductors (LTS), some HTS are able to achieve the superconducting state at the boiling point of nitrogen (77K), making these materials much more attractive for technological applications due to their reduced operating costs. One of the main applications of HTS is the electrical transport. Due to the zero electrical resistance of these materials when they are below the critical temperature, Tc, they can transmit up to 10 times more power than conventional cables or can carry equivalent power at much lower voltages. On the other hand, HTS materials have been deeply studied in the field of electronics. In particular, HTS nanowires can be functionally scaled to smaller sizes due to their extremely short intrinsic lengths. Furthermore, their characteristic fast relaxation rates offer higher counting rates in photodetection experiments when compared to LTS. However, one of the most important issues to take into account in the study of HTS, is the presence of quantified magnetic flux lines, referred as vortex, into their phase diagram. The main difference from LTS concerning the vortex behavior arises from the high thermal excitations. Consequently a great variety of different pinning centers are needed in order to avoid (or control) the vortex dynamics and therefore, the resulting electrical dissipation. Controlling vortex pinning and dynamics is the aim of this thesis where the main results are presented in chapters 3, 4 and 5. Previously, in chapter 1 we present the main superconducting properties, and in particular, the regarding to vortex behavior in YBa2Cu3O7-x (YBCO -HTS with the widest operating range-) samples grown following the Chemical Solution Deposition (CSD) technique. In chapter 2 we show the experimental techniques used in our analysis and the measurement procedure. In chapter 3, a huge analysis of vortex pinning is presented. An unprecedented phenomenon for vortex pinning is demonstrated which allows improving the critical current density and its anisotropy in the presence of non-superconducting secondary phases into the YBCO matrix. Furthermore, an analysis of the vortex dynamics with YBCO-CSD natural defects is performed. In chapters 4 and 5 we have focused in controlling vortex dynamics in YBCO thin films. In chapter 4 a preferential sense for the vortex movement is demonstrated when asymmetric nanostructures are patterned in the YBCO layer. Consequently, a controlled AC-DC rectification is obtained. In chapter 5, the studies are centered in the interaction between superconducting and ferromagnetic materials. It is demonstrated that by inserting ferromagnetic nanorods into the YBCO matrix, a huge control of the critical current density is possible as a function of the magnetic state of the nanorod. General conclusions of the thesis are presented and summarized in the last chapter. Finally, the analytical procedure used in a theoretical simulation presented in chapter 5 is exposed in the appendix