Nuevos materiales nanocompuestos multifuncionales preparados mediante "Solution Blow Spinning" con potenciales propiedades eléctricas especiales

En la siguiente tesis doctoral se han diseñado, preparado y caracterizado nuevos materiales nanocompuestos con propiedades dieléctricas especiales. En particular estos materiales compuestos estuvieron constituidos por un a matriz polimérica de polifluoruro de vinilideno, PVDF, y un relleno basado en nanotubos de carbono de pared múltiple, MWCNT. Se prepararon los materiales buscando distintas configuraciones en términos macrocópicos jugando con la composición de los materiales nanocompuestos y utilizando un proceso de fabricación aditiva que permitió ir configurando los materiales finales en términos de disposición de varias capas de manera sucesiva. Para preparar los materiales se utilizó una técnica relativamente nueva denominada hilado por soplado o en inglés “solution blow spinning”, SBS. La producción mediante SBS se realizó utilizando un dispositivo diseñado y construido por el Grupo de materiales compuestos poliméricos e interfases de la Universidad Carlos III de Madrid, GMCPI. Como primera etapa antes de proceder a la fabricación de materiales se tuvo que optimizar las condiciones del proceso de SBS para obtener materiales constituidos fundamentalmente por fibras de diámetros submicrométricos con uniforme dispersión de los MWCNT en el interior del polímero. Mediante SBS se prepararon materiales de PVDF con MWCNT considerando diferentes configuraciones en términos de la disposición de capas con distinta concentración (0%, 0.2%, 0.5%, 1%, 2%, 3% y 4% en peso de MWCNT) por aplicación sucesiva de diferentes suspensiones sobre un colector cilíndrico giratorio. Los materiales así preparados fueron caracterizados tal y como se obtuvieron de la preparación directa a partir de SBS y después de haber sido sometidos a un segundo proceso de prensado en caliente. Se estudió la estructura, morfología y comportamiento térmico de los materiales preparados, así como sus propiedades dieléctricas en un intervalo amplio de frecuencias, con el fin de encontrar y comprender las posibles correlaciones existentes. La morfología de los materiales se estudió en función de la composición de las diferentes capas realizando inspecciones por microscopía electrónica de barrido, SEM, en diferentes posiciones de los materiales a lo largo de una sección transversal del material con mayor número de capas (300, 700 y 1900 μm). Se pudo ver que, independientemente de la región de observación la morfología era fundamentalmente fibrilar con algunas acumulaciones de material en forma de ovillos y que la cantidad relativa de dichos ovillos aumentaba a medida el punto de observación se encontraba más cercano a la superficie del material donde se encontraba la concentración más alta en nanotubos de carbono, lo que sugiere que la presencia de nanotubos de carbono induce variaciones en la morfología aumentando la proporción de ovillos a medida que aumenta la concentración de MWCNT. La caracterización estructural de los materiales se llevó a cabo mediante difracción de rayos X (DRX) y espectroscopia infrarroja por transformada de Fourier en el modo de reflexión totalmente atenuada (ATR-FTIR). Se pudo comprobar que la utilización de SBS para preparar estos materiales induce preferencialmente la formación de fase beta en el PVDF que además se ve potenciada con la presencia y concentración de nanotubos de carbono. Para estudiar el comportamiento térmico de los materiales se utilizó calorimetría diferencial de barrido (DSC), realizando un estudio de los procesos de fusión y cristalización. En este caso no solos e pudo corroborar que la fase principal del PVDF era la beta sino que además se pudo distinguir entre las fusiones asociadas a las fases beta y alfa del PVDF, punto éste sujeto a mucha controversia a lo largo de los años. Finalmente se realizó un estudio del comportamiento dieléctrico de los materiales preparados utilizando un analizador de impedancia (SOLARTRON 1260A). En términos generales, se pudo observar que al añadir nanotubos de carbono siempre hay un aumento de permitividad. Además, una configuración del material tal que se genere un gradiente composicional desde el centro con concentración cero de nanotubos (PVDF puro) hasta los extremos con mayor concentración favorece aún más el aumento de permitividad. Lo datos obtenidos permitieron también encontrar un método sencillo para diseñar materiales con valores de permitividad eléctrica concretos o a la carta. Finalmente, cuando se reduce la porosidad de los materiales tras someterlos a un proceso de prensado el efecto potenciador de permitividad es menor debido a la existencia de menor polarización superficial pues esta se reduce a desaparecer en gran medida las fibras. También se estudió el comportamiento mecánico de los materiales sin prensar mediante ensayos convencionales de tracción. Las variaciones observadas en el comportamiento mecánico fueron debidas fundamentalmente a cambios composicionales de las capas que configuran el material y no a la propia configuración de capas, ni a los cambios de porosidad. Finalmente, se realizaron estudios sobre el comportamiento flexoeléctrico de los materiales preparados. Para ello se diseñó una máquina automatizada para realizar ensayos flexoeléctricos que permitía a través de la lectura en un osciloscopio tener datos de respuesta en voltaje de los materiales por aplicación de una deformación cíclica en los materiales. Se pudo demostrar que la resistencia a la deformación dependía de tres factores, el diseño del material en términos macroscópicos (en el caso que nos ocupa configuración e capas de diferente composición), de la composición en sí, en términos de concentración de nanotubos y de la dispersión de dichos nanotubos. Todos los materiales bajo estudio basados en PVDF dieron lugar a respuesta flexoeléctrica clara y medible indicativo de que cualquiera podría utilizarse como sensor de presión. Se puede decir también que la respuesta flexoeléctrica de los materiales bajo estudio depende tanto de la morfología interna de los materiales como de la naturaleza y composición de los mismos. Finalmente indicar que los materiales porosos, en general, aparte de dar lugar a respuestas flexoeléctricas más intensas también son más eficientes en términos de disipación de energía.In the following doctoral thesis, new nanocomposite materials with special dielectric properties have been designed, prepared and characterized. In particular, these composite materials consisted of a polymeric matrix based on polyvinylidene fluoride, PVDF, and a filler based on multiple-walled carbon nanotubes, MWCNT. The materials were prepared looking for different configurations in macroscopic terms, playing with the composition of the nanocomposite materials and using an additive manufacturing process that allowed the final materials to be configured in terms of the arrangement of several layers in succession. A relatively new technique called solution blow spinning, SBS, was used to prepare the materials. Production with SBS was carried out using a device designed and built by the Group of polymer composite materials and interphases of the Carlos III University of Madrid, GMCPI. As a first stage, before carrying out with the materials fabrication, the conditions of the SBS process was optimized to obtain materials consisting mainly of fibers with submicrometric diameters and with uniform dispersion of the MWCNTs within the polymer. Using SBS, PVDF materials were prepared filled with MWCNT considering different configurations in terms of the arrangement of layers with different concentrations (0%, 0.2%, 0.5%, 1%, 2%, 3% and 4% by weight of MWCNT) by the application of different suspensions successively on a rotating cylindrical collector. The materials thus prepared were characterized as they were obtained from the direct preparation from SBS and after having been subjected to a hot-pressing process. The structure, morphology and thermal behavior of the prepared materials, as well as their mechanical and dielectric properties in a wide range of frequencies, were studied in order to find and understand the possible existing correlations. The morphology of the materials was studied as a function of the composition of the different layers, performing inspections by scanning electron microscopy, SEM, at different positions of the materials along a cross section of the material with a greater number of layers (300, 700 and 1900 μm). It could be seen that, regardless of the observation region, the morphology was mainly fibrillar with some accumulations of material in the form of tangles or coils and that the relative quantity of these coils increased as the point of observation was closer to the surface of the material where the highest concentration was found in carbon nanotubes, which suggests that the presence of carbon nanotubes induces variations in morphology, increasing the proportion of coils as the concentration of MWCNT increases. The structural characterization of the materials was carried out by X-ray diffraction (XRD) and Fourier transform infrared spectroscopy in attenuated total reflectance mode (ATR-FTIR). It was found that the use of SBS to prepare these materials preferentially induces the formation of beta phase in PVDF, which is also enhanced by the presence and concentration of carbon nanotubes. Differential scanning calorimetry (DSC) was used to study the thermal behavior of the materials, carrying out a study of the processes of fusion and crystallization. In this case, it was not only possible to corroborate that the main phase of PVDF was the beta one, but also, it was possible to distinguish between the melting associated to the beta and alpha phases of PVDF, an issue that has been subjected to much controversy over the years. Finally, a study of the dielectric behavior of the materials prepared was carried out using an impedance analyzer (SOLARTRON 1260A). In general terms, it could be observed that when adding carbon nanotubes there is always an increase in permittivity. Furthermore, a configuration of the material such that a compositional gradient is generated from the center with zero nanotube concentration (pure PVDF) to the surface with the highest concentration further favors the increase in permittivity. The data obtained also allowed us to find a simple method to design materials with tailored electrical permittivity values. Finally, when the porosity of the materials is reduced after subjecting them to a pressing process, the permittivity enhancing effect was lower due to the existence of less surface polarization since the presence of fibers is greatly reduced. The mechanical behavior of un-pressed materials was also studied by conventional tensile tests. The variations observed in the mechanical behavior were mainly due to compositional changes of the layers that make up the material and not to the layer configuration itself.- Ministerio de Economía y Competitividad [MAT2014-59116-C2] - Universidad Carlos III de Madrid: Fondos de Investigación de Fco. Javier González Benito [2012/00130/004] - Universidad Carlos III de Madrid Acción estratégica en Materiales compuestos e interfases [2011/00287/002] - Facultad de Ciencias, Departamento de Química de la Universidad de Navarra (Dr. Gustavo González-Gaitano. Espectroscopía infrarroja por transformada de Fourier y difracción de rayos X. - Mi más profundo agradecimiento al Consejo Nacional de Ciencia y Tecnología (CONACYT) México, por el soporte brindado en el proceso de formación doctoral (Convocatoria 291179).Programa de Doctorado en Ciencia e Ingeniería de Materiales por la Universidad Carlos III de MadridPresidente: Dania Olmos Díaz.- Secretario: Gustavo González Gaitano.- Vocal: Daniel Villanueva Vásque

Geometrical design for pure current-driven domain wall nucleation and shifting

Nucleation of domain walls by current-driving a single domain wall, confined to the junction area of two symmetrical strips, is investigated using systematic micromagnetic simulations. Secondary domain walls (equivalently, bits encoded in domains) are simultaneously nucleated and driven by alternatively applying current pulses between two terminals in the structure. Simulations show that nanosecond-duration current pulses nucleate and drive series of robust up/down domains even under realistic conditions. These results demonstrate a technique for sequentially nucleating and shifting domain walls without using attached external bit lines, fields or modifying the ferromagnetic strip.Comment: 11 pages, 3 figure

Current-Driven Domain Wall Motion in Curved Ferrimagnetic Strips Above and Below the Angular Momentum Compensation

Current driven domain wall motion in curved Heavy Metal/Ferrimagnetic/Oxide multilayer strips is investigated using systematic micromagnetic simulations which account for spin-orbit coupling phenomena. Domain wall velocity and characteristic relaxation times are studied as functions of the geometry, curvature and width of the strip, at and out of the angular momentum compensation. Results show that domain walls can propagate faster and without a significant distortion in such strips in contrast to their ferromagnetic counterparts. Using an artificial system based on a straight strip with an equivalent current density distribution, we can discern its influence on the wall terminal velocity, as part of a more general geometrical influence due to the curved shape. Curved and narrow ferrimagnetic strips are promising candidates for designing high speed and fast response spintronic circuitry based on current-driven domain wall motion

A tribute to José María ("Chema") Cantú

José María ("Chema") Cantú (1938-2007), nacido en México, fue un líder pionero, amado y respetado en genética médica y humana y bioética en América Latina. Se graduó como médico en México y luego se formó en genética médica y humana en Francia y los Estados Unidos. Fue instrumental en el desarrollo de un programa de investigación, capacitación y genética de primera categoría en genética médica y humana en Guadalajara, en el noroeste de México. Actuó enérgicamente a nivel nacional, regional e internacional para promover el desarrollo científico a través de la colaboración y la educación en ciencias y humanidades, al mismo tiempo que se esforzaba por la justicia, la paz, el amor y los derechos humanos. Él alcanzó algunos de los honores más altos que un científico y un humanista podían aspirar así como el reconocimiento de las comunidades que él sirvió. Cientos de discípulos de América Latina y del mundo se han inspirado en su visión de un mundo mejor a través de la conjunción de la ciencia, el respeto a la humanidad, la ética y el amor.José María (“Chema”) Cantú (1938-2007), born in Mexico, was a pioneering, loved and respected leader in medical and human genetics and bioethics in Latin America. He graduated as a physician in Mexico and then trained in medical and human genetics in France and the United States. He was instrumental in developing a first-rate research, training and genetic services program in medical and human genetics in Guadalajara, in northwestern Mexico. He acted forcefully at national, regional and international levels to promote scientific development through collaboration and education in science and humanities, while he simultaneously strived for justice, peace, love and human rights. He attained some of the highest honors a scientist and humanist could aspire to as well as the recognition of the communities he served. Hundreds of disciples throughout Latin America and the world have been inspired by his vision of a better world through the conjunction of science, respect for humankind, ethics and love

Temperature and relative humidity estimation and prediction in the tobacco drying process using artificial neural networks

Producción CientíficaThis paper presents a system based on an Artificial Neural Network (ANN) for estimating and predicting environmental variables related to tobacco drying processes. This system has been validated with temperature and relative humidity data obtained from a real tobacco dryer with a Wireless Sensor Network (WSN). A fitting ANN was used to estimate temperature and relative humidity in different locations inside the tobacco dryer and to predict them with different time horizons. An error under 2% can be achieved when estimating temperature as a function of temperature and relative humidity in other locations. Moreover, an error around 1.5 times lower than that obtained with an interpolation method can be achieved when predicting the temperature inside the tobacco mass as a function of its present and past values with time horizons over 150 minutes. These results show that the tobacco drying process can be improved taking into account the predicted future value of the monitored variables and the estimated actual value of other variables using a fitting ANN as proposed.Centro para el Desarrollo Tecnológico Industrial (CDTI), proyecto "Mejora de la competitividad del sector del tabaco en Extremadura: nuevos procesos y productos" (under project IDI-20100986)Junta de Castilla y León, financiado por el Plan Regional de Proyectos de Investigación (proyecto VA034A10-2

Geometrical design for pure current-driven domain wall nucleation and shifting

[EN]Nucleation of domain walls by current-driving a single domain wall, confined to the junction area of two symmetrical strips, is investigated using systematic micromagnetic simulations. Secondary domain walls (equivalently, bits encoded in domains) are simultaneously nucleated and driven by alternatively applying current pulses between two terminals in the structure. Simulations show that nanosecond-duration current pulses nucleate and drive series of robust up/down domains even under realistic conditions. These results demonstrate a technique for sequentially nucleating and shifting domain walls without using attached external “bit lines,” fields, or modifying the ferromagnetic strip

Current-Driven Domain Wall Motion in Curved Ferrimagnetic Strips Above and Below the Angular Momentum Compensation

[EN] Current driven domain wall motion in curved Heavy Metal/Ferrimagnetic/Oxide multilayer strips is investigated using systematic micromagnetic simulations which account for spinorbit coupling phenomena. Domain wall velocity and characteristic relaxation times are studied as functions of the geometry, curvature and width of the strip, at and out of the angular momentum compensation. Results show that domain walls can propagate faster and without a significant distortion in such strips in contrast to their ferromagnetic counterparts. Using an artificial system based on a straight strip with an equivalent current density distribution, we can discern its influence on the wall terminal velocity, as part of a more general geometrical influence due to the curved shape. Curved and narrow ferrimagnetic strips are promising candidates for designing high speed and fast response spintronic circuitry based on current-driven domain wall motion.Projects SA114P20 and SA299P18 from Junta de Castilla y Leon (JCyL) MAT2017-87072-C4-1-P and PID2020-117024GB-C41 from the Ministry of Economy, Spanish government MAGNEFI, from the European Commission (European Union

The evolution of agrarian prices received and paid by the farmers in Spain (2000-2009)

La evolución de los precios de los alimentos en años recientes se ha evaluado en numerosos estudios considerando: el análisis de los márgenes comerciales y la evolución temporal de los precios, si bien, la mayoría de ellos centrados en la óptica del consumidor. En este artículo se analizó la evolución temporal de los precios de los alimentos en España en el período 2000-2009 desde el punto de vista del agricultor y ganadero. Concretamente se utilizó información relacionada con los precios percibidos, precios pagados y el índice de precios de consumo (IPC), y con técnicas de análisis de series temporales se analizó la existencia de relaciones de equilibrio a largo plazo entre las series. Los resultados reflejan una relación de equilibrio a largo plazo entre: los precios percibidos y pagados; el IPC y los precios percibidos. Las principales conclusiones muestran que, a pesar de los desequilibrios existentes a corto plazo, a largo plazo los precios percibidos y pagados tienden a una situación de equilibrio. Un elemento importante en la evolución del IPC lo constituyen los precios percibidos por los productos en el sector primario. Sin embargo, la fijación de los precios de los insumos (pagados) en el sector primario; lejos de regirse en el largo plazo por la evolución del IPC; no muestra una relación significativa con dicho indicador.The recent evolution of the foods prices has been evaluated in several studies considering: the commercial margins analysis and the prices temporal evolution although more of them have been developed using the consumer optics. In this paper, the temporal evolution of the foods prices in Spain has been analysed in the period 2000-2009 considering the farmer optics. Concretely, information in relation with the prices received by the farmers, the prices paid by them and the consumer price index (CPI) has been used. Then, using a time series analysis, the long run relationships between series have been analysed. The results show a long run balance between the prices received and paid by the farmer and between the CPI and the received prices. The main conclusions show that, in spite of the existing imbalances in the short term, in the long term the received and paid prices tend to a balance situation. An important element in the evolution of the CPI is the prices received by the products in the primary sector. Nevertheless, the inputs price fixation in the primary sector in the long term does not show a significant relationship with the CPI.Fil: Andrés Martínez, María Encarnación. Universidad de Castilla-La Mancha. Facultad de Ciencias Económicas y Empresariales de Albacete.Fil: Alfaro Navarro, José Luis. Universidad de Castilla-La Mancha. Facultad de Ciencias Económicas y Empresariales de Albacete.Fil: López Ruiz, Víctor Raúl. Universidad de Castilla-La Mancha. Facultad de Ciencias Económicas y Empresariales de Albacete

Meson-exchange currents and superscaling analysis with relativistic effective mass of quasielastic electron scattering from C-12

This work has been partially supported by the Ministerio de Economia y Competitividad (Grant No. FIS2017-85053-C2-1-P) and by the Junta de Andalucia (Grant No. FQM-225). V.L.M.-C. acknowledges a contract funded by Agencia Estatal de Investigacion and European Social Fund.We reanalyze the scaling properties of inclusive quasielastic electron scattering from 12C by subtracting from the data the effects of two-particle emission. A model of relativistic meson-exchange currents (MEC) is employed within the mean field theory of nuclear matter, with scalar and vector potentials that induce an effective mass and a vector energy to the nucleons. A new phenomenological quasielastic scaling function is extracted from a selection of the data after the subtraction of the 2p-2h contribution. The resulting superscaling approach with relativistic effectivemass (SuSAM*) can be used to compute the genuine quasielastic cross section without contamination of the 2p-2h channel that can then be added separately to obtain the total quasielastic plus two-nucleon emission response.Spanish Government FIS2017-85053-C2-1-PJunta de Andalucia FQM-225Agencia Estatal de InvestigacionEuropean Social Fund (ESF

A vibroacoustic model of the stationary railway wheel for sound radiation prediction through an axisymmetric approach

[EN] In the literature, different dynamic models of the railway wheel have been developed to predict its sound radiation; however, there are still certain aspects that can be improved. Specifically, the high computational cost of these models, either because they solve the fluidstructure interaction or because they solve the dynamics and acoustics of the three-dimensional wheel, makes it difficult to carry out numerous simulations with the aim of achieving quieter designs. In the present work, a vibroacoustic model of the stationary wheel is developed through an axisymmetric approach, yielding an efficient and comprehensive acoustic prediction tool. The calculation methodology consists of, firstly, adopting an axisymmetric approach to solve the vibratory dynamics of the wheel from its cross-section, using finite element techniques; subsequently, the acoustic radiation of the three-dimensional wheel is calculated from the dynamics of the aforementioned section through an analytical formulation. Finally, the vibroacoustic model developed is validated via comparison with commercial software that solves the fluid-structure interaction, showing the aforementioned computational advantages that the former has over the latter.The authors gratefully acknowledge the financial support of Agencia Estatal de Investigación and European Regional Development Fund (grant FPU18/03999, project TRA2017-84701-R and project PID2020-112886RA-I00).Andrés Ruiz, V.; Martínez Casas, J.; Carballeira Morado, J.; Denia Guzmán, F. (2022). A vibroacoustic model of the stationary railway wheel for sound radiation prediction through an axisymmetric approach. En Proceedings of the YIC 2021 - VI ECCOMAS Young Investigators Conference. Editorial Universitat Politècnica de València. 320-325. https://doi.org/10.4995/YIC2021.2021.12584OCS32032