Key Production Parameters to Obtain Transparent Nanocellular PMMA

Transparent nanocellular polymethylmethacrylate (PMMA) with relative density around 0.4 is produced for the first time by using the gas dissolution foaming technique. The processing conditions and the typical characteristics of the cellular structure needed to manufacture this novel material are discovered. It is proved that low saturation temperatures (−32 °C) combined with high saturation pressures (6, 10, 20 MPa) allow increasing the solubility of PMMA up to values not reached before. In particular, the highest CO2 uptake ever reported for PMMA, (i.e., 48 wt%) is found for a saturation pressure of 20 MPa and a saturation temperature of −32 °C. Due to these processing conditions, cell nucleation densities of 1016 nuclei cm−3 and cell sizes clearly below 50 nm are achieved. The nanocellular polymers obtained, with cell sizes ten times smaller than the wavelength of visible light and very homogeneous cellular structures, show a significant transparency

Indicadores del desarrollo e implantación de la sociedad de la información: un capítulo pendiente

En este escrito se pretende reflexionar sobre la importancia que conlleva la elección de los indicadores del desarrollo e implantación de la Sociedad de la Información. Dicha elección no es en ningún caso neutral y puede implicar sesgos que obvien desiguaThis work tries to reflect on the inherent importance of the indicators made for assessing the development and implementation of the "Information Society". A particular choice isn't neutral or aseptic, and it can hide a lot of interests behind it, concea

Protocolo de introducción de software libre a personal docente e investigador universitario y diseño de un proyecto formativo

Se presenta un protocolo de introducción de un determinado software (bajo las definiciones de la Free Software Foundation y de la Open Source Initiative) en el Departamento de Educación de la Universidad de Las Palmas de Gran Canaria. Dicho protocolo puede servir de ejemplo para la migración hacia este tipo de software en comunidades docentes e investigadoras no relacionadas directamente con la informática, pero que pueden convertirse en diseñadores y colaboradores de la creación de esta tecnología. Se ha elaborado un plan de actuación y proyecto formativo que incluye una evaluación previa de necesidades e intereses, la construcción de un cuestionario semiestructurado como instrumento de recogida de información, la selección de unos contenidos y materiales y la evaluación de la transferencia. Algunos datos de este estudio preliminar confirman que centrarse en las necesidades y una formación orientada hacia la transferencia son elementos esenciales para el éxito de un proyecto de este tipo.We present a software introduction protocol, developed within the Education Department of the Las Palmas de Gran Canaria University. The software we try to introduce is licenced under the “Free Software Foundation and/or Open Source Initiative” terms. This protocol could be useful for a migration to this kind of software in research and educational institutions. We show here our plan and a formative project that include an assessment, the making of a test as a tool for data mining, a content and material selection and the evaluation of the transfer. Some results show that is essencial to center the efforts in professorʹs needs and the best formative choice is teaching for transfer

Transparent nanocellular PMMA: Characterization and modeling of the optical properties

In this work, the optical properties of transparent nanocellular polymethylmethacrylate (PMMA) have been studied, experimental and theoretically. Transmittance measurements of samples presenting different cell sizes (14, 24, 39 and 225 nm) and a constant relative density of around 0.45 have been carried out obtaining values as high as 0.94 for the sample with the smaller cell size and a thickness of 0.05 mm. In addition, the light absorption coefficient has been measured as a function of cell size and wavelength. It has been found that the transmittance has a strong dependence with the wavelength, presenting these transparent materials Rayleigh scattering. On the other hand, the transmission of visible light through these nanocellular materials has been modelled for the first time. The developed model reproduces with good accuracy the trends observed in the experimental results and provides remarkable insights into the physics mechanisms controlling the optical behavior of these materials

A cognitive-based approach to President Obama´s educational discourse through the lens of his State of the Union Addresses (2009-2016)

In order to gain a cultural understanding of the discourse on education used by President Obama, this article examines the source domains commonly used to refer to education in his State of the Union Addresses, from the time he took office in 2009 to 2016 when he will leave office. The study will proceed by applying insights from Conceptual Metaphor Theory (CMT), within the field of cognitive linguistics, supplemented by the Metaphor Identification Procedure (MIP) developed by the Pragglejazz Group. The source domains identified and discussed are: COMPETITION and ECONOMICS. In fact, the strong coherence in Obama's speeches relies on the use of the story of competition as the concept that is repeated in and across speeches and that works as a persuasive device by framing reality and directing the audience's thinking, perception and even action

Satisfacción usuaria en el Centro Gineco-obstetrico de Hospital de Linares

65 p.El presente trabajo de tesis tiene por objetivo principal evaluar la satisfacción de las usuarias obstétricas beneficiarias del Sistema Chile Crece Contigo que resolvieron su parto en el Centro de Responsabilidad Gineco-Obstétrico del Hospital de Linares, a través de la realización de una investigación de mercado. Este estudio entonces, tiene como finalidad medir la percepción de las usuarias sobre la calidad de la atención que recibió, es importante señalar que ésta percepción tiene importantes implicancias éticas, y socio-culturales de cada persona que es atendida. Para la realización de éste estudio se aplicó como instrumento una encuesta validada por expertos del sistema Chile Crece Contigo, modificada, la que se aplicó a 190 de 215 usuarias que recibieron atención de su pre-parto, parto y puerperio, entre el 01 y el 30 de Septiembre del año 2009 en el Centro de Responsabilidad Gineco-Obstétrico. La encuesta, en escala Likert de 5 puntos, se aplicaba al término de sesiones educativas grupales al momento del alta y los datos demográficos se obtienen del libro de registro de partos. Los resultados obtenidos de la aplicación de la encuesta se ingresaron, tabularon y se realizó un análisis factorial utilizando el software SPSS (Statistics Packing for Social Science) con el fin de reducir los datos. A través de éste análisis se puede concluir que el factor mejor evaluado por las usuarias fue la relación con el equipo de atención, el respeto por la intimidad de la triada, la infraestructura y la información que reciben tanto de los procesos técnicos como asistenciales, es importante valorar la participación en la toma de decisiones en relación a su salud. Las variables menos satisfactorias tenían que ver con tiempos de espera, con la percepción que tienen las usuarias que los funcionarios de la salud en general son autoritarios y no podían expresar sus malestares por temor a no ser comprendidos, también se puede ver que las usuarias sentían que no se les ofrecían todas las alternativas para adoptar posiciones más cómodas, o poder deambular si fuese su preferencia

Modeling the heat transfer by conduction of nanocellular polymers with bimodal cellular structures

Nanocellular polymers are a new generation of materials with the potential of being used as very efficient thermal insulators. It has been proved experimentally that these materials present the Knudsen effect, which strongly reduces the conductivity of the gas phase. There are theoretical equations to predict the thermal conductivity due to this Knudsen effect, but all the models consider an average cell size. In this work, we propose a model to predict the thermal conductivity due to the conduction mechanisms of nanocellular materials with bimodal cellular structures, that is, with two populations of cells, micro and nanocellular. The novelty of our work is to consider not only the average cell size, but the cell size distribution. The predictions of the model are compared with the experimental conductivity of two real bimodal systems based on poly(methyl methacrylate) (PMMA), and it is proved that this new model provides more accurate estimations of the conductivity than the models that do not consider the bimodality. Furthermore, this model could be applied to monomodal nanocellular polymers. In particular, for monomodal materials presenting a wide cell size distribution and at low densities, the model predicts important variations in comparison with the current models in the literature. This result indicates that the cell size distribution must be included in the estimations of the thermal conductivity of nanocellular polymer

How Women Are Imagined Through Conceptual Metaphors in United Nations Security Council Resolutions on Women, Peace and Security

United Nations Security Council Resolution 1325 is a landmark pronouncement on the Women, Peace and Security Agenda. Not only does this resolution highlight the important role of the involvement of women in peace processes, but it also stresses the importance of their equal participation in all efforts for the maintenance and promotion of peace. Furthermore, it also triggers the approval of some other resolutions, which are all further elaborations on that first document. The aim of this paper is to analyse, from a cognitive linguistic perspective, the way in which women are actually narrated in these pronouncements by means of the two conceptual metaphors that are most often repeated: WOMEN ARE VICTIMS, typically found in earlier resolutions, and WOMEN ARE AGENTS OF CHANGE, as the metaphor that has gained more strength and visibility as new resolutions have continued to appear. As metaphors are the cognitive lenses we use to make sense of abstract concepts, it is important that we look closely at each of those metaphors to see how they shape the characterization of women in times of armed conflict and post-conflict and, in doing so, how they guide our understanding and behaviour towards them

Nanocellular Polymers with a Gradient Cellular Structure Based on Poly(methyl methacrylate)/Thermoplastic Polyurethane Blends Produced by Gas Dissolution Foaming

Graded structures and nanocellular polymers are two examples of advanced cellular morphologies. In this work, a methodology to obtain low-density graded nanocellular polymers based on poly(methyl methacrylate) (PMMA)/ thermoplastic polyurethane (TPU) blends produced by gas dissolution foaming is reported. A systematic study of the effect of the processing condition is presented. Results show that the melt-blending results in a solid nanostructured material formed by nanometric TPU domains. The PMMA/ TPU foamed samples show a gradient cellular structure, with a homogeneous nanocellular core. In the core, the TPU domains act as nucleating sites, enhancing nucleation compared to pure PMMA and allowing the change from a microcellular to a nanocellular structure. Nonetheless, the outer region shows a gradient of cell sizes from nano- to micron-sized cells. This gradient structure is attributed to a non-constant pressure profile in the samples due to gas desorption before foaming. The nucleation in the PMMA/ TPU increases as the saturation pressure increases. Regarding the effect of the foaming conditions, it is proved that it is necessary to have a fine control to avoid degeneration of the cellular materials. Graded nanocellular polymers with relative densities of 0.16–0.30 and cell sizes ranging 310–480 nm (in the nanocellular core) are obtained

Overcoming the Challenge of Producing Large and Flat Nanocellular Polymers: A Study with PMMA

Although nanocellular polymers are interesting materials with improved properties in comparison with conventional or microcellular polymers, the production of large and flat parts of those materials is still challenging. Herein, gas dissolution foaming process is used to produce large and flat nanocellular polymethylmethacrylate samples. In order to do that, the foaming step is performed in a hot press. The methodology is optimized to produce flat samples with dimensions of 100 × 100 × 6 mm3, relative densities in the range 0.25–0.55 and cell sizes around 250 nm. Additionally, foaming parameters are modified to study their influence on the final cellular structure, and the materials produced in this paper are compared with samples produced by using a most conventional approach in which foaming step is conducted in a thermal bath. Results obtained show that an increment in the foaming temperature leads to a reduction in relative density and an increase of cell nucleation density. Moreover, differences in the final cellular structure for materials produced by both foaming routes are studied, proving that although there exist some differences, the mechanisms governing the nucleation and growing are the same in both processes, leading to the production of homogeneous materials with very similar cellular structures