New understanding of the shape-memory response in thiol-epoxy click systems: towards controlling the recovery process

Our research group has recently found excellent shape-memory response in “thiol-epoxy” thermosets obtained with click-chemistry. In this study, we use their well-designed, homogeneous and tailorable network structures to investigate parameters for better control of the shape-recovery process. We present a new methodology to analyse the shape-recovery process, enabling easy and efficient comparison of shape-memory experiments on the programming conditions. Shape-memory experiments at different programming conditions have been carried out to that end. Additionally, the programming process has been extensively analysed in uniaxial tensile experiments at different shape-memory testing temperatures. The results showed that the shape-memory response for a specific operational design can be optimized by choosing the correct programming conditions and accurately designing the network structure. When programming at a high temperature (T » Tg), under high network mobility conditions, high shape-recovery ratios and homogeneous shape-recovery processes are obtained for the network structure and the programmed strain level (eD). However, considerably lower stress and strain levels can be achieved. Meanwhile, when programming at temperatures lower than Tg, considerably higher stress and strain levels are attained but under low network mobility conditions. The shape-recovery process heavily depends on both the network structure and eD. Network relaxation occurs during the loading stage, resulting in a noticeable decrease in the shape-recovery rate as eD increases. Moreover, at a certain level of strain, permanent and non-recoverable deformations may occur, impeding the completion and modifying the whole path of the shape-recovery process.Postprint (author's final draft

Actuación de resolutores de primero y segundo año de secundaria en la resolución de un problema matemático: un estudio exploratorio

Los sistemas de representación y la resolución de problemas matemáticos es un tema de interés para la Didáctica de la Matemática porque se pone en juego una serie de conocimientos, conceptos, modelos, métodos, estrategias, experiencias y relaciones que implican un pensamiento elaborado complejo que consigue que, a partir de unos datos conocidos, encontrar otros datos desconocidos. En este estudio, describimos la actuación de resolutores cuando resuelven un problema matemático, de manera espontánea con lápiz y papel. Cuando algún estudiante resuelve un problema mediante lápiz y papel deja la huella de los pasos seguidos en su resolución. Esos pasos están cargados de información importante que el resolutor presenta haciendo uso de algún sistema de representación que le es conocido y le permite comunicar su pensamiento

Estudio de la adherencia a un protocolo para el manejo del traumatismo craneoencefalico en un servicio de urgencias pediátrico

[ES] Se presenta un estudio retrospectivo sobre una cohorte de niños con diagnóstico de traumatismo craneal (TC), cuyo objetivo principal es estudiar la epidemiología del TC en nuestro entorno y la adherencia a un nuevo protocolo de diagnóstico y tratamiento en urgencias, basado en la evidencia científica existente sobre el tema. Para el primer objetivo se analiza la base de datos global de los 1182 TC atendidos durante el año 2016 y para analizar la adherencia al protocolo, se realiza una revisión de historias clínicas de una muestra aleatoria de 202 pacientes. El autor del estudio encuentra que 9 (0,7%) niños presentaron una lesión intracraneal (LIC) y 13 una fractura craneal aislada. Se practicó TAC a 52 (4,4%) y radiografía de cráneo únicamente a 6 (0,5%) pacientes. Un total de 212 (17,9%) pacientes fueron ingresados en observación, hospitalizándose 15 (1,3%), 7 de ellos en cuidados intensivos. Analizando la muestra, el investigador encuentra que la adherencia al protocolo actual es del 81,2%, mostrando que el 88% de los incumplimientos se produjo en el grupo de 66 (32,6%) niños clasificados como de riesgo moderado de lesión intracraneal. Treinta pacientes (42%) de este grupo no recibieron el periodo de observación hospitalaria establecido, mínimo 2 horas, a pesar de cumplir con alguno de los factores de riesgo descritos. Sin embargo, ninguno de ellos consultó de nuevo en el servicio y todos tuvieron una evolución favorable. En el global de la muestra la indicación de pruebas de imagen se ajustó al protocolo y la evolución de los pacientes fue buena. Concluye que la adherencia al protocolo es alta y que el manejo de los pacientes siguiendo esta pauta, es seguro. IDIOMA: ESPAÑOL

The eigenvalue characterization for the constant sign Green’s functions of (k,n−k)(k,n−k) problems

This paper is devoted to the study of the sign of the Green’s function related to a general linear nth-order operator, depending on a real parameter, Tn[M]Tn[M], coupled with the (k,n−k)(k,n−k) boundary value conditions. If the operator Tn[M¯]Tn[M¯] is disconjugate for a given M̄, we describe the interval of values on the real parameter M for which the Green’s function has constant sign. One of the extremes of the interval is given by the first eigenvalue of the operator Tn[M¯]Tn[M¯] satisfying (k,n−k)(k,n−k) conditions. The other extreme is related to the minimum (maximum) of the first eigenvalues of (k−1,n−k+1)(k−1,n−k+1) and (k+1,n−k−1)(k+1,n−k−1) problems. Moreover, if n−kn−k is even (odd) the Green’s function cannot be nonpositive (nonnegative). To illustrate the applicability of the obtained results, we calculate the parameter intervals of constant sign Green’s functions for particular operators. Our method avoids the necessity of calculating the expression of the Green’s function. We finalize the paper by presenting a particular equation in which it is shown that the disconjugation hypothesis on operator Tn[M¯]Tn[M¯] for a given M̄ cannot be eliminatedAlberto Cabada was partially supported by Ministerio de Educación, Cultura y Deporte, Spain, and FEDER, project MTM2013-43014-P. Lorena Saavedra was partially supported by Ministerio de Educación, Cultura y Deporte, Spain, and FEDER, project MTM2013-43014-P, and Plan I2C scholarship, Consellería de Educación, Cultura e O.U., Xunta de Galicia, and FPU scholarship, Ministerio de Educación, Cultura y Deporte, Spain. The authors would also like to express their special thanks to the reviewer of the paper for his/her remarks, which considerably improved the content of this paperS

Lower and upper solutions for even order boundary value problems

In this paper, we prove the existence of solutions of nonlinear boundary value problems of arbitrary even order using the lower and upper solutions method. In particular, we point out the fact that the existence of a pair of lower and upper solutions of a considered problem could imply the existence of solution of another one with different boundary conditions. We consider Neumann, Dirichlet, mixed and periodic boundary conditionsThe authors were partially supported by Xunta de Galicia (Spain), project EM2014/032 and AIE, Spain and FEDER, grant MTM2016-75140-PS

Characterization of constant sign Green's function for a two-point boundary-value problem by means of spectral theory

This article is devoted to the study of the parameter’s set where the Green’s function related to a general linear nth-order operator, depending on a real parameter, Tn[M], coupled with many different two point boundary value conditions, is of constant sign. This constant sign is equivalent to the strongly inverse positive (negative) character of the related operator on suitable spaces related to the boundary conditions. This characterization is based on spectral theory, in fact the extremes of the obtained interval are given by suitable eigenvalues of the differential operator with different boundary conditions. Also, we obtain a characterization of the strongly inverse positive (negative) character on some sets, where non homogeneous boundary conditions are considered. To show the applicability of the results, we give some examples. Note that this method avoids the explicit calculation of the related Green’s function.This research was Partially supported by AIE Spain and FEDER, grants MTM2013-43014-P, MTM2016-75140-P. The second author was supported by FPU scholarship, Ministerio de Educaci´on, Cultura y Deporte, SpS

Phenomenological characterization of sequential dual-curing of off-stoichiometric "thiol-epoxy" systems: Towards applicability

An extensive characterization of a sequential dual-curing system based on off-stoichiometric “thiol-epoxy” mixtures was carried out using thiol compounds of different functionality. The intermediate and final materials obtained after each curing stages at different thiol-epoxy ratios were studied by means of thermomechanical and rheological experiments. The storage and loss modulus and the loss factor tan d were monitored during the curing process to analyse gelation and network structure build-up. The critical ratio for gelation was determined making use of the ideal Flory-Stockmayer theory and compared with experimental results. Intermediate materials obtained in the vicinity of the theoretical critical ratio did not have the mechanical consistency expected for partially crosslinked materials, did not retain their shape and even experienced undesired flow upon heating to activate the second curing reaction. The rheological results showed that the critical ratio is higher than the predicted value and that a softening during the second curing stage affects the shape-retention at this ratio. From the thermomechanical results, a wide range of intermediate and final materials with different properties and applicability can be obtained by properly choosing the thiol-epoxy ratio: from liquid-like to highly deformable intermediate materials and from moderately crosslinked (deformable) to highly crosslinked (brittle) final materials.Postprint (author's final draft

Estudio del nivel de confort en el transporte ferroviario mediante ADAMS/RAIL

El objetivo principal de este proyecto es calcular los niveles de confort que se producen cuando un tren viaja por una vía en diferentes condiciones de circulación. De forma más particular, las situaciones que se van a estudiar son: Variando el número de vagones. Se van a realizar simulaciones con trenes de un vagón y dos vagones. Modificando los radios de curvatura de la vía. Se van a utilizar en las simulaciones diferentes trazados, todos ellos con un tramo recto y las diferentes curvas con radios de curvatura de 200, 300, 400 y 500 metros. Cambiando la velocidad inicial del tren. Estas velocidades comienzan con 15 m/s y van aumentando hasta alcanzar la condición de descarrilamiento o hasta superar el mayor índice de confort. Es necesario estudiar los procedimientos que se utilizan habitualmente para calcular los niveles de confort que se producen cuando un ser humano se ve expuesto ante vibraciones y variaciones de aceleración. Además, es importante conocer las repercusiones que generan las vibraciones sobre el organismo. Para realizar las simulaciones necesarias en las diferentes situaciones de circulación, es preciso entender el funcionamiento del programa de simulación virtual Adams/Rail.Ingeniería Técnica en Mecánic

Student-Generated Videos to Promote Understanding of Chemical Reactions

Published as part of the Journal of Chemical Education virtual special issue “Teaching Changes and Insights Gained in the Time after COVID-19”.[Abstract] Students were tasked with the creation of videos of ordinary reactions to promote significant learning of complex concepts underlying chemical transformations. Interactive infographics were used to deliver instructions. Afterward, students planned the experimental setup for the reaction execution and video recording using their mobile phones. The videos and an online questionnaire, also created by the students, were shared with other class members using the visual platform Padlet. The reasoning required to elaborate the questions contributed to a better understanding of the principles underpinning the chemical equation. An exit survey showed that planning and performing the activity were not time-consuming for the students. Marks attained by the students in questions related to chemical reactions improved after completing the activity