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

Rehabilitación del entrenador de automatización Industrial ED-4031 en el Centro Tecnológico Simón Bolívar, Managua 2020

El presente Estudio nace con el objetivo de rehabilitar el entrenador de automatización industrial (ED-4031) ubicado en el Centro Tecnológico Simón Bolívar en Managua, debido a que este se encontraba inactivo impidiendo que los estudiantes de este centro de formación técnica realicen sus prácticas de automatización de un proceso industrial con los equipos que este centro posee

Crisis del calzado en el barrio Restrepo, Bogotá análisis y perspectivas

Se realizó un análisis en el sector del barrio Restrepo para verificar cuales podrían ser las falencias de la industria que han venido en declive y generando la quiebra de empresas pertenecientes al sector del calzado. Entre los resultados se encontró que una de las posibles causas son la falta de competencia, renovación de su producción y mano de obra calificada. Las cuales se analizará para dar a cabo una viabilidad para la mejora del sector en su competitividad interna como externa. Se verificará industrias donde su maquinaria para fabricar calzado de alta calidad y la técnicas de uso que le dan a esto productos tener competencia en el mercado les pueda tomar para modernizar la industria del calzado en el sector del Restrepo.RESUMEN ABSTRACT INTRODUCCIÓN 1 TÍTULO 2 PROBLEMA 2.1 DESCRIPCIÓN DEL PROBLEMA 2.2 FORMULACIÓN DEL PROBLEMA 3 OBJETIVOS DE LA INVESTIGACIÓN 3.1 OBJETIVO GENERAL 3.2 OBJETIVOS ESPECÍFICOS 4 JUSTIFICACIÓN Y DELIMITACIÓN DE LA INVESTIGACIÓN 4.1 JUSTIFICACIÓN 4.2 DELIMITACIÓN 5 MARCO DE REFERENCIA DE LA INVESTIGACIÓN 5.1 MARCO TEÓRICO 5.1.1 Innovación 5.1.1.1 Principales tipos de innovación 5.1.3 Estrategia 5.1.4 Competitividad 5.2 MARCO CONCEPTUAL 5.3 MARCO LEGAL 5.4 MARCO HISTÓRICO 6 MARCO METODOLÓGICO 6.1 TIPO DE INVESTIGACIÓN 6.2 MATERIALES Y MÉTODOS 6.3 VALIDEZ Y CONFIABILIDAD 6.4 TÉCNICAS E INSTRUMENTOS DE RECOLECCIÓN DE DATOS 6.4.1 Fuentes primarias 6.4.2 Fuentes secundarias 6.5 TÉCNICAS DE PROCESAMIENTO Y ANÁLISIS DE DATOS 7 SECTOR DEL CALZADO EN BOGOTÁ DESDE EL AÑO 2005 AL 2013 8 ANÁLISIS DE LA TENDENCIA MUNDIAL EN LA INDUSTRIA DEL CALZADO Y PERSPECTIVAS PARA BOGOTÁ FRENTE AL MAYOR EXPORTADOR DE CALZADO (CHINA) 8.1.1 Tendencia mundial del Calzado 8.1.2 Calzado en Bogotá 8.1.2.1 Informalidad y dumping 8.1.2.3 Insuficiencia de materias primas 8.1.3 Calzado en China 9 ANÁLISIS DEL CLÚSTER EN EL SECTOR DE CALZADO EN BOGOTÁ 9.1 QUÉ HA LLEVADO AL QUE EL SECTOR DEL CALZADO EN BOGOTÁ SE HAYA VISTO OBLIGADO A CREAR SUS PROPIOS CLÚSTER 10 PROPUESTA PARA MEJORAR EL SECTOR DEL CALZADO DESDE UN PUNTO DE VISTA ECONÓMICO EN EL SECTOR DEL RESTREPO BOGOTÁ Asociatividad entre productores y proveedores de materias primas Reducir el peligro de residir en un solo mercado Desarrollo de la cadena de valor Innovación desarrollo e investigación para mejorar la producción Marketing e internacionalización Financiación a pequeñas y medianas empresas CONCLUSIONES RECOMENDACIONES REFERENCIAS BIBLIOGRÁFICASPregradoProfesional en Comercio InternacionalComercio Internaciona

Micronization as a solution for enhancing the thermal insulation of nanocellular poly(methyl-methacrylate) (PMMA)

Producción CientíficaThis work shows a route to reduce the thermal conductivity of nanocellular poly(methyl-methacrylate) (PMMA). This approach is based on micronizing to replace the continuous solid phase by a discontinuous one. PMMA powders with densities of 147–195 kg/m3, formed by particles of 100 microns with nanometric cells inside them, are produced by milling. Micronization allows increasing the overall porosity maintaining the cell size. Results prove that after milling it is possible to obtain open cell nanoporous PMMA powders with thermal conductivity below that of the bulk materials (15% reduction). The reduction is not only due to a density decrease, but a result of the new structure of the powder material. The discontinuity of the solid phase and the increase in radiation extinction are the key factors allowing this improvement. This route is confirmed as a promising alternative to enhance the performance of nanocellular polymers.Junta de Castilla y Leon (grant VA202P20)Ministerio de Ciencia, Innovación y Universidades (projects RTI2018-098749-B-I00, PTQ2019-010560 and PRE2019-088820)Instituto para la Competitividad Empresarial de Castilla y León - Fondo Europeo de Desarrollo Regional (projects PAVIPEX. 04/18/VA/008 and FICACEL. 11/20/VA/0001

Evaluation of methods to accurately characterize the thermal conductivity of micro-and nanocellular polymers based on poly(methyl-methacrylate) (PMMA) produced at lab-scale

Producción CientíficaThe characterization of the thermal conductivity of new and enhanced thermal insulators developed at lab-scale is a challenge. The small dimensions of the prototypes make impossible the use of the conventional techniques because steady-state methods require large samples. Furthermore, the accuracy of transient methods to measure the thermal conductivity is not clear. In this work, we compare four different approaches to measure the thermal conductivity of small prototypes of nanocellular poly(methyl-methacrylate) (PMMA). Both steady-state and transient techniques are used. Results show that the transient plane source method is not suitable for the characterization of these materials (the deviation from the steady-state methods is on average higher than 15%). In addition, two different approaches for measuring the thermal conductivity of small samples via a steady-state technique are proposed and validated.Junta de Castilla y León (grant VA202P20)Ministerio de Ciencia, Innovación y Universidades (projects RTI2018-098749-B-I00 and PTQ2019-010560)Instituto para la Competitividad Empresarial de Castilla y León - Fondo Europeo de Desarrollo Regional (projects PAVIPEX. 04/18/VA/008 and FICACEL. 11/20/VA/0001

Experiencia percibida de la fatiga en población clínica y general: descriptores y reactividad asociada

The aim of this study is the analysis of different descriptors and reactions related to the experience of fatigue. Two groups were compared: a clinical sample (n = 92, 31 males, mean age = 38.87) and a non-clinical (n = 225, 135 males, mean age = 32.45) sample. The total sample was composed of 317 participants (52% males), ranging in age from 18 to 76 years. Findings show the experience of fatigue was mainly related to somatic terms (76% of the total sample). Specific results were found only for the clinical group: (a) significant relationships between fatigue and anxiety, χ2(1) = 34.71, p < .01; tension, χ2(1) = 16.80, p < .01; and sadness, χ2(1) = 24.59, p < .01; (b) higher intensity of fatigue (F = 84.15, p = .001), and predominance of the cognitive components of fatigue. Results showed that fatigue in subjects with a clinical disorder (versus those without) was associated both, to negative emotional states, and to a higher intensity of fatigue, especially in its cognitive elements. Important clinical implications for its assessment and intervention are discussed

Efectos de la fatiga anticipatoria y la sintomatología emocional en la percepción de fatiga física y cognitiva

El objetivo de este estudio fue doble, primero, analizar los efectos de la fatiga anticipatoria, la sintomatología emocional y la pertenencia a un grupo clínico sobre la percepción de fatiga física y mental; segundo, explorar el potencial efecto moderador de la anticipación de la fatiga en las relaciones entre la sintomatología o la condición clínica y la sensación percibida de fatiga. Se analiza mediante un diseño ex post facto y correlacional los efectos parciales y condicionados de las variables predictivas mediante diferentes análisis de regresión jerárquica. Participaron 317 sujetos (29% procedentes de población clínica). Se evaluó la fatiga anticipatoria (Escala elaborada ad hoc), la experiencia percibida de fatiga (Escala de Fatiga de Chalder et al., 1993), y la sintomatología emocional (GHQ-28 de Goldberg, 1996). Los resultados mostraron efectos significativos de la fatiga anticipatoria y la sintomatología emocional, predominantemente de la sintomatología depresiva sobre la percepción de fatiga física y mental. La pertenencia a un grupo clínico predecía de forma significativa y exclusiva la fatiga cognitiva. Además, la fatiga anticipatoria moderaba el efecto del grupo (clínico versus general) sobre la fatiga cognitiva. En conclusión, la sintomatología, principalmente la depresiva, y la fatiga anticipatoria, tienen un valor predictivo significativo en la experiencia percibida de la fatiga física y mental. La anticipación de fatiga moderaba el efecto del grupo clínico sobre la experiencia de fatiga cognitiva una vez controlada la sintomatología depresiva.The two fold aim of this study was first, to analyze the effects of anticipatory fatigue, emotional symptomatology and belonging to a clinical group on the physical and cognitive perception of fatigue, and second, to explore the potential moderating effect of anticipatory fatigue on the relationship between symptomatology or clinical condition and perceived fatigue. The conditional and partial effects of independent variables were analyzed by hierarchical regression in an ex-post-facto correlational design. The sample was composed of 317 participants (29% from a clinical population). Anticipatory fatigue (by an ad hoc scale), and perception of fatigue (by the Chalder Fatigue Scale) were measured. Emotional symptoms were assessed by Goldberg’s GHQ-28 questionnaire. Anticipatory fatigue and emotional symptoms (mainly depressive) had significant effects on cognitive and physical fatigue. Belonging to the clinical group significantly and exclusively predicted cognitive fatigue. Furthermore, anticipatory fatigue moderated between-group effects (clinical versus general) and cognitive fatigue. In brief, emotional symptoms (mainly depressive) and anticipatory fatigue significantly predicted perceived cognitive and physical fatigue. Anticipation of fatigue moderated the effect of clinical group on cognitive fatigue after controlling for depressive symptomatolog

El papel mediador de la sintomatología emocional entre la fatiga anticipatoria y la percepción de la fatiga

Background: Clinical research stresses the importance of cognitive variables for predisposition, onset, and especially, perpetuation of perceived fatigue. The aim was to analyze the mediating effects of emotional symptomatology (somatic, depressive and anxiety) between anticipatory fatigue and perception of physical and cognitive fatigue. Methods: The sample was composed of 317 participants (29% from a clinical population) aged 18 to 76. Anticipatory fatigue and perception of fatigue were measured by fatigue scales. Emotional symptoms were assessed by the General Health Questionnaire, GHQ-28. Results: Depressive symptomatology mediated the relationship between anticipatory fatigue and cognitive fatigue in both groups, and also somatic symptoms/somatization in patients. The indirect effect of physical fatigue was observed only in the clinical group, with depressive symptoms partially mediating the anticipatory fatigue and cognitive fatigue relationship. Conclusions: Anticipatory fatigue has a partial indirect effect on total physical fatigue, and full indirect effect on cognitive fatigue, mediated by depressive and somatic symptoms. Anticipatory fatigue is a relevant cognitive factor in the design of psychological intervention for improvement of cognitive and physical fatigue.Antecedentes: la investigación clínica resalta la importancia de variables cognitivas en la predisposición, inicio y mantenimiento de la fatiga percibida. Se analizan los efectos de mediación de la sintomatología emocional entre la fatiga anticipatoria y la percepción de la fatiga física y cognitiva. Métodos: la muestra se compone de 317 participantes (29% de población clínica) de 18 a 76 años. La fatiga anticipatoria y la percepción de la fatiga se midieron a través de escalas de fatiga y los síntomas emocionales a través del Cuestionario GHQ-28. Resultados: la sintomatología depresiva media la relación entre fatiga anticipatoria y la fatiga cognitiva en ambos grupos, y también para el grupo de pacientes cuando además los síntomas son somáticos. En el caso de la fatiga física, el efecto indirecto se da solo para el grupo clínico, siendo la sintomatología depresiva la variable que media parcialmente la relación. Conclusiones: la fatiga anticipatoria tiene un efecto indirecto parcial sobre la fatiga física e indirecto total sobre la fatiga cognitiva, mediado por los síntomas depresivos y somáticos. Este factor cognitivo es relevante en el diseño de la intervención psicológica para la disminución de la fatiga cognitiva y física

Effect of the molecular structure of TPU on the cellular structure of nanocellular polymers based on PMMA/TPU blends

Producción CientíficaIn this work, the effects of thermoplastic polyurethane (TPU) chemistry and concentration on the cellular structure of nanocellular polymers based on poly(methyl-methacrylate) (PMMA) are presented. Three grades of TPU with different fractions of hard segments (HS) (60%, 70%, and 80%) have been synthesized by the prepolymer method. Nanocellular polymers based on PMMA have been produced by gas dissolution foaming using TPU as a nucleating agent in different contents (0.5 wt%, 2 wt%, and 5 wt%). TPU characterization shows that as the content of HS increases, the density, hardness, and molecular weight of the TPU are higher. PMMA/TPU cellular materials show a gradient cell size distribution from the edge of the sample towards the nanocellular core. In the core region, the addition of TPU has a strong nucleating effect in PMMA. Core structure depends on the HS content and the TPU content. As the HS or TPU content increases, the cell nucleation density increases, and the cell size is reduced. Then, the use of TPUs with different characteristics allows controlling the cellular structure. Nanocellular polymers have been obtained with a core relative density between 0.15 and 0.20 and cell sizes between 220 and 640 nm.Ministerio de Ciencia, Innovación y Universidades (Proyects RTI2018-098749-B-I00 and PTQ2019-010560)Ente Regional de la Energía de Castilla y León (Proyecto EREN_2019_L4_UVA

Effect of the Molecular Structure of TPU on the Cellular Structure of Nanocellular Polymers Based on PMMA/TPU Blends

From MDPI via Jisc Publications RouterHistory: accepted 2021-09-07, pub-electronic 2021-09-10Publication status: PublishedFunder: Junta de Castilla y León; Grant(s): I.Sanchez-CalderonFunder: Ministerio de Ciencia, Innovación y Universidades; Grant(s): RTI2018-098749-B-I00, PTQ2019-010560 (Victoria Bernardo-García)Funder: EREN; Grant(s): Ente Regional de la Energía de Castilla y León EREN_2019_L4_UVAIn this work, the effects of thermoplastic polyurethane (TPU) chemistry and concentration on the cellular structure of nanocellular polymers based on poly(methyl-methacrylate) (PMMA) are presented. Three grades of TPU with different fractions of hard segments (HS) (60%, 70%, and 80%) have been synthesized by the prepolymer method. Nanocellular polymers based on PMMA have been produced by gas dissolution foaming using TPU as a nucleating agent in different contents (0.5 wt%, 2 wt%, and 5 wt%). TPU characterization shows that as the content of HS increases, the density, hardness, and molecular weight of the TPU are higher. PMMA/TPU cellular materials show a gradient cell size distribution from the edge of the sample towards the nanocellular core. In the core region, the addition of TPU has a strong nucleating effect in PMMA. Core structure depends on the HS content and the TPU content. As the HS or TPU content increases, the cell nucleation density increases, and the cell size is reduced. Then, the use of TPUs with different characteristics allows controlling the cellular structure. Nanocellular polymers have been obtained with a core relative density between 0.15 and 0.20 and cell sizes between 220 and 640 nm