Tratamiento numérico de una teoría de plasticidad por gradiente de deformación basada en un modelo de cosserat

The current trend towards miniaturization in the microelectronic industry has promulgated the development of theories aimed at explaining the behavior of materials used on a small scale. In the particular case of metals, a class of non-classical theories of continuous media mechanics has recently been used in order to explain a wide range of micrometric scale observations. However, the practical use of the proposed theories remains limited due to difficulties in their numerical implementation. First, when these are to be implemented in formulations by finite elements based on displacements, the need for high orders of continuity in interpolation functions is generated in order to maintain the convergence properties in the algorithm. These limitations generate strong restrictions on the geometries of the available elements. On the other hand, the inelastic models available for small-scale applications have been formulated as deformation theories (total) limiting their applicability to problems under proportional load conditions. In this article two contributions are made in the case of a Cosserat continuum with torque voltages. First, a numerical scheme based on a strategy of penalty functions combined with reduced integration is described to appropriately address the problem of higher order terms present in the Cosserat theory. This scheme results in a new finite element that can be directly coupled to commercial distribution programs that accept user subroutines. Secondly, a theory of fl ow of plasticity is proposed incorporating size effects overcoming some of the obstacles of deformation theories. The resulting constitutive model and its corresponding time integration scheme are coupled to the new element formulated and implemented in ABAQUS user subroutines. The validity of the strategy is demonstrated by simulations of the micro fl exion test on nickel sheets reported in the literature.La tendencia actual hacia la miniaturización en la industria microelectrónica ha promulgado el desarrollo de teorías orientadas a explicar el comportamiento de materiales usados en pequeña escala. En el caso particular de los metales, recientemente se ha usado una clase de teorías no clásicas de la mecánica de los medios continuos con el fin de explicar una amplia gama de observaciones a escala micrométrica. Sin embargo el uso práctico de las teorías propuestas permanece limitado debido a dificultades a la hora de su implementación numérica. En primer lugar, cuando éstas van a ser implementadas en formulaciones por elementos finitos basadas en desplazamientos se genera la necesidad de altos órdenes de continuidad en las funciones de interpolación con el fin de mantener las propiedades de convergencia en el algoritmo. Estas limitaciones generan fuertes restricciones en las geometrías de los elementos disponibles. De otro lado, los modelos inelásticos disponibles para aplicaciones a pequeña escala han sido formulados como teorías de deformación (total) limitando su aplicabilidad a problemas bajo condiciones proporcionales de carga. En el presente artículo se hacen dos contribuciones para el caso de un continuo de Cosserat con tensiones de par. Primero se describe un esquema numérico basado en una estrategia de funciones de penalización combinadas con integración reducida para abordar apropiadamente el problema de los términos de orden superior presentes en la teoría de los Cosserat. Este esquema da como resultado un nuevo elemento finito que puede ser directamente acoplado a programas de distribución comercial que acepten subrutinas de usuario. En segundo lugar se propone una teoría de flujo de plasticidad incorporando efectos de tamaño superando algunos de los obstáculos de las teorías por deformación. El modelo constitutivo resultante y su correspondiente esquema de integración en el tiempo son acoplados al nuevo elemento formulado e implementados en subrutinas de usuario de ABAQUS. La validez de la estrategia es demostrada mediante simulaciones del ensayo de microflexión en láminas de níquel reportados en la literatura

Tratamiento numérico de una teoría de plasticidad por gradiente de deformación basada en un modelo de cosserat

The current trend towards miniaturization in the microelectronics industryhas pushed for the development of theories intended to explain the behaviorof materials at small scales. In the particular case of metals, a class ofavailable non–classical continuum mechanics theories has been recently employedin order to explain the wide range of observed behavior at the micronscale. The practical use of the proposed theories remains limited due to issuesin its numerical implementation. First, in displacement–based finite elementformulations the need appears for higher orders of continuity in the interpolationshape functions in order to maintain the convergence rate upon meshrefinement. This limitation places strong restrictions in the geometries of theavailable elements. Second, the available inelastic constitutive models for smallscale applications have been cast into deformation theory formulations limitingthe set of problems to those exhibiting proportional loading only. In thisarticle two contributions are made for the particular case of a Cosserat couplestress continuum. First it describes a numerical scheme based on a penaltyfunction/reduced integration approach that allows for the proper treatment ofthe higher order terms present in Cosserat like theories. This scheme results in a new finite element that can be directly implemented into commercial finiteelement codes. Second, a flow theory of plasticity incorporating size effects isproposed for the case of rate independent materials overcoming the limitationsin the deformation theory formulations. The constitutive model and its correspondingtime–integration algorithm are coupled to the new proposed finiteelement and implemented in the form of a user element subroutine into thecommercial code ABAQUS. The validity of the approach is shown via numericalsimulations of the microbending experiment on thin Nickel foils reportedin the literature.PACS: 81.40.Lm, 81.40.Jj, 46MSC: 82B21, 65N30La tendencia actual hacia la miniaturización en la industria microelectrónica ha promulgado el desarrollo de teorías orientadas a explicar el comportamiento de materiales usados en pequeña escala. En el caso particular de los metales, recientemente se ha usado una clase de teorías no clásicas de la mecánica de los medios continuos con el fin de explicar una amplia gama de observaciones a escala micrométrica. Sin embargo el uso práctico de las teorías propuestas permanece limitado debido a dificultades a la hora de su implementación numérica. En primer lugar, cuando éstas van a ser implementadas en formulaciones por elementos finitos basadas en desplazamientos se genera la necesidad de altos órdenes de continuidad en las funciones de interpolación con el fin de mantener las propiedades de convergencia en el algoritmo. Estas limitaciones generan fuertes restricciones en las geometrías de los elementos disponibles. De otro lado, los modelos inelásticos disponibles para aplicaciones a pequeña escala han sido formulados como teorías de deformación (total) limitando su aplicabilidad a problemas bajo condiciones proporcionales de carga. En el presente artículo se hacen dos contribuciones para el caso de un continuo de Cosserat con tensiones de par. Primero se describe un esquema numérico basado en una estrategia de funciones de penalización combinadas con integración reducida para abordar apropiadamente el problema de los términos de orden superior presentes en la teoría de los Cosserat. Este esquema da como resultado un nuevo elemento finito que puede ser directamente acoplado a programas de distribución comercial que acepten subrutinas de usuario. En segundo lugar se propone una teoría de flujo de plasticidad incorporando efectos de tamaño superando algunos de los obstáculos de las teorías por deformación. El modelo constitutivo resultante y su correspondiente esquema de integración en el tiempo son acoplados al nuevo elemento formulado e implementados en subrutinas de usuario de ABAQUS. La validez de la estrategia es demostrada mediante simulaciones del ensayo de microflexión en láminas de níquel reportados en la literatura.PACS: 81.40.Lm, 81.40.Jj, 46MSC: 82B21, 65N3

Numerical optimization of hybrid dielectric/HTS resonators for surface impedance evaluation of HTS films

This work describes an alternative to the traditional dielectric resonator topology used for measuring surface impedance in high temperature superconducting (HTS) films. A gap is introduced above the dielectric so that only the lower film is in direct contact with it. This arrangement has been used extensively for mechanical tuning of dielectric resonators and, when used for surface impedance measurement, it can be designed to make the losses in the upper film small relative to the overall resonator losses. Then, measured results are mostly due to one of the films and not the average of two. The specifics of a resonator design for measuring 2-inch wafers are presented. An analysis and optimization of the resonator is done using a numerically efficient mode-matching algorithm.Peer ReviewedPostprint (published version

An Evolutionary Artificial Neural Network approach for spatio-temporal wave height time series reconstruction

This paper proposes a novel methodology for recovering missing time series data, a crucial task for subsequent Machine Learning (ML) analyses. The methodology is specifically applied to Significant Wave Height (SWH) time series in the field of marine engineering. The proposed approach involves two phases. Firstly, the SWH time series for each buoy is independently reconstructed using three transfer function models: regression-based, correlation-based, and distance-based. The distance-based transfer function exhibits the best overall performance. Secondly, Evolutionary Artificial Neural Networks (EANNs) are utilised for the final recovery of each time series, using as inputs highly correlated buoys that have been intermediately recovered. The EANNs are evolved considering two metrics, the novel squared error relevance area, which balances the importance of extreme and around-mean values, and the well-known mean squared error. The study considers SWH time series data from 15 buoys in two coastal zones in the United States. The results demonstrate that the distance-based transfer function is generally the best transfer function, and that EANNs outperform a range of state-of-the-art ML techniques in 12 out of the 15 buoys, with a number of connections comparable to linear models. Furthermore, the proposed methodology outperforms the two most popular approaches for time series reconstruction, BRITS and SAITS, for all buoys except one. Therefore, the proposed methodology provides a promising approach, which may be applied to time series from other fields, such as wind or solar energy farms in the field of green energy

Measurements and analysis of microwave nonlinearities in ferroelectric thin film transmission lines

This work evaluates the microwave nonlinear properties of ferroelectric BaSrTiO thin films by measuring the frequency response of several coplanar transmission lines and interdigital capacitor structures as a function of the applied electric field from 150 Hz to 40 GHz. From these measurements, we obtain the distributed nonlinear capacitance C(Vdc) as a function of dc bias. We also measure the harmonic generation at microwave frequencies in ferroelectric transmission lines, and use an accurate circuit model to obtain C(Vrf), the nonlinear capacitance as a function of RF bias. Information about the tuning speed of the film is obtained from a comparison between the two nonlinear capacitances. Characterization of this mechanism is also required to assess the spurious signal generation in ferroelectric-based devicesPeer Reviewe

Media representation of minors who migrate on their own: The 'MENA' in the Spanish press

This article analyses Spanish media treatment of a certain type of immigrant: the unaccompanied foreign minor ('MENA' in Spanish). The media play an important role in creating and disseminating ideas and images amongst the general public, thereby promoting the articulation of sets of meanings called discourses. The main goal of this research is to identify the discursive approaches that have been constructed around the term “MENA” in the main Spanish daily newspapers. To this end, we gathered and analysed all the news reports published between January 2017 and October 2019 by the digital editions of the four most widely-read newspapers in Spain (La Vanguardia, El País, El Mundo and ABC). This analysis was performed using text mining techniques (an important field in data science) such as term frequency, inverse document frequency, and correlation networks between words. Our results show that the term “MENA” evokes a criminalising, moralistic, welfare-dependent discourse that is articulated from an adult-centric, nationalist perspective. The study concluded that the conservative press uses the acronym more frequently than the left-wing media. However, no significant discursive differences were observed between conservative and progressive press in terms of the language used, which often had negative connotations that stigmatised the young people concerned

Gamifying the Classroom for the Acquisition of Skills Associated with Machine Learning: A Two-Year Case Study

Machine learning (ML) is the field of science that combines knowledge from artificial intelligence, statistics and mathematics intending to give computers the ability to learn from data without being explicitly programmed to do so. It falls under the umbrella of Data Science and is usually developed by Computer Engineers becoming what is known as Data Scientists. Developing the necessary competences in this field is not a trivial task, and applying innovative methodologies such as gamification can smooth the initial learning curve. In this context, communities offering platforms for open competitions such as Kaggle can be used as a motivating element. The main objective of this work is to gamify the classroom with the idea of providing students with valuable hands-on experience by means of addressing a real problem, as well as the possibility to cooperate and compete simultaneously to acquire ML competences. The innovative teaching experience carried out during two years meant a great motivation, an improvement of the learning capacity and a continuous recycling of knowledge to which Computer Engineers are faced to

Barreras psicosociales para la vinculación laboral de excombatientes

In the framework of the signing of the peace agreement between FARC-EP and the Colombian government, the concern arises about how the processes of labor inclusion of demobilized combatants are taking place and what role psychosocial barriers for peace play. Thus, a documentary review was made of the main findings that some researchers have had regarding the reintegration processes of the demobilized population within the labor world and the psychosocial barriers that have been built in Colombia so that these processes can be fully developed. The findings show that the labor sector, being immersed in the social constructions and discourses on demobilized people, has also established stigmatization and rejection processes within its hiring processes, which strongly evidence the presence of psychosocial barriers to reintegration, reconciliation and peace within the organizations.En el marco de la firma del acuerdo de paz entre las FARC-EP y el gobierno colombiano, surge la inquietud de cómo se están dando los procesos de inclusión laboral de los desmovilizados y qué papel juegan las Barreras psicosociales para la paz, por lo que se hizo una revisión documental de los principales hallazgos que han tenido algunos investigadores con respecto a los procesos de reintegración de la población desmovilizada dentro del mundo laboral y las barreras psicosociales que se han construido en Colombia para que estos procesos puedan desarrollarse plenamente. Los hallazgos evidencian que, el sector laboral al estar inmerso dentro de las construcciones y discursos sociales sobre las personas desmovilizadas, han instaurado también procesos de estigmatización y rechazo dentro de sus procesos de contratación, que permiten evidenciar fuertemente la presencia de barreras psicosociales para la reintegración, la reconciliación y la paz, dentro de las organizaciones

La opinión pública colombiana sobre el acuerdo de paz 2016-2020: punitivismo, desconfianza y ostracismo

Después de varias décadas de conflicto armado en Colombia, el Gobierno colombiano y las Farc-EP firmaron, en 2016, el Acuerdo Final para la terminación del conflicto y la construcción de una paz estable y duradera. No obstante, este acuerdo no fue refrendado por la ciudadanía, en un plebiscito celebrado ese mismo año. En 2018, ganó las elecciones presidenciales un candidato que prometió cambiar las condiciones del Acuerdos Final y modificar uno de sus principales instrumentos: la Jurisdicción Especial para la Paz (JEP). En ese contexto esta investigación se pregunta: ¿cuál es la opinión de los colombianos sobre el Acuerdo Final y la JEP? La investigación indaga en las opiniones de los colombianos a través de un análisis estadístico comparativo de tres encuestas de opinión de 2016, 2018 y 2020. Los resultados detallan los cambios actitudinales ocurridos en esos años, como la disminución del rechazo frontal a los Acuerdos de Paz y el leve incremento de las posibilidades de reintegración de los excombatientes a la vida civil. También, expone algunas reticencias al cambio, como la desconfianza persistente, la reafirmación del rechazo al indulto de los excombatientes (punitivismo) y a su participación política (ostracismo)

Comprehensive circuit model of autolimiting superconductor devices

©2017 IEEE. Personal use of this material is permitted. Permission from IEEE must be obtained for all other uses, in any current or future media, including reprinting/republishing this material for advertising or promotional purposes, creating new collective works, for resale or redistribution to servers or lists, or reuse of any copyrighted component of this work in other works.This paper presents a phenomenological equivalent circuit to model the phenomenon occurring when a section of superconducting transmission line transits from a superconducting state to a normal state. This phenomenon allows the use of superconductors for the design of autolimiting structures based on superconducting transmission line sections. Although this autolimiting effect happens when the current density achieved in the superconductor exceeds the critical current inherent to the superconducting material, heating effects also play a significant role in this behavior. The equivalent circuit presented in this work accounts for both electric and thermal effects, and the interaction between them. The circuit model is then used for the evaluation of a practical microwave and frequency selective IMUX configuration.Peer ReviewedPostprint (author's final draft