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

Comparative genomics of the rhodococcus genus shows wide distribution of biodegradation traits

The genus Rhodococcus exhibits great potential for bioremediation applications due to its huge metabolic diversity, including biotransformation of aromatic and aliphatic compounds. Comparative genomic studies of this genus are limited to a small number of genomes, while the high number of sequenced strains to date could provide more information about the Rhodococcus diversity. Phylogenomic analysis of 327 Rhodococcus genomes and clustering of intergenomic distances identified 42 phylogenomic groups and 83 species-level clusters. Rarefaction models show that these numbers are likely to increase as new Rhodococcus strains are sequenced. The Rhodococcus genus possesses a small “hard” core genome consisting of 381 orthologous groups (OGs), while a “soft” core genome of 1253 OGs is reached with 99.16% of the genomes. Models of sequentially randomly added genomes show that a small number of genomes are enough to explain most of the shared diversity of the Rhodococcus strains, while the “open” pangenome and strain-specific genome evidence that the diversity of the genus will increase, as new genomes still add more OGs to the whole genomic set. Most rhodococci possess genes involved in the degradation of aliphatic and aromatic compounds, while short-chain alkane degradation is restricted to a certain number of groups, among which a specific particulate methane monooxygenase (pMMO) is only found in Rhodococcus sp. WAY2. The analysis of Rieske 2Fe-2S dioxygenases among rhodococci genomes revealed that most of these enzymes remain uncharacterizedThis research was funded by GREENER-H2020 (EU), grant number 826312 and MICINN/FEDER EU, grant number RTI2018-0933991-B-I00. D.G.-S. was granted by the MECD FPU fellowship program, grant number FPU14/0396

Low-density PMMA/MAM nanocellular polymers using low MAM contents: Production and characterization

Low-density nanocellular polymers are required to take advantage of the full potential of these materials as high efficient thermal insulators. However, their production is still a challenging task. One promising approach is the use of nanostructured polymer blends of poly(methyl methacrylate) (PMMA) and a block copolymer poly(methyl methacrylate)-poly(butyl acrylate)-poly(methyl methacrylate) (MAM), which are useful for promoting nucleation but seem to present a severe drawback, as apparently avoid low relative densities. In this work, new strategies to overcome this limitation and produce low-density nanocellular materials based on these blends are investigated. First, the effect of very low amounts of the MAM copolymer is analysed. It is detected that nanostructuration can be prevented using low copolymer contents, but nucleation is still enhanced as a result of the copolymer molecules with high CO2 affinity dispersed in the matrix, so nanocellular polymers are obtained using very low percentages of the copolymer. Second, the influence of the foaming temperature is studied. Results show that for systems in which there is not a clear nanostructuration, cells can grow more freely and smaller relative densities can be achieved. For these studies, blends of PMMA with MAM with copolymer contents from 10 wt% and as low as 0.1 wt% are used. For the first time, the production strategies proposed in this work have allowed obtaining low density (relative density 0.23) nanocellular polymers based on PMMA/MAM blends. Graphical abstrac

El efecto del deseo de control en el desarrollo de competencias

Uno de los objetivos propuestos en el nuevo paradigma de la educación superior es la adquisición y desarrollo de competencias que faciliten la inserción de los estudiantes en el mundo laboral. Este proceso de adquisición y desarrollo no sólo se lleva a cabo en el contexto educativo sino que hay ciertas variables de carácter individual que pueden intervenir en este proceso. Una de esas variables es el deseo de control. El objetivo del presente trabajo es conocer el efecto de las diferencias individuales en el deseo de control sobre el desarrollo de competencias. Han participado en el estudio 69 estudiantes universitarios con edades comprendidas entre los 18 y 26 años. Los resultados muestran que el deseo de control puede jugar un papel clave en la adquisición, entrenamiento y desarrollo de competencias en estudiantes universitarios.One of the proposed aim of the new higher education´s paradigm is the obtaining and development of competences which favour the entry into employment of students. This obtaining and development process is not only carried out in the educational context but there could be individual variables that can take part in this process. One of these variables is the desire of control. The aim of this study is to know the effect of individual differences in desire of control related to their competences development. There were 69 students participating in the study, aged between 18 and 26 years old. Results have shown that desire of control can play a key role in the obtaining, the coaching and the development competences of students.peerReviewe

Measuring the desire for control: a Spanish version of Burger and Cooper's Scale

The following study will present findings on the validity of the adaptation of the Burger and Cooper’s Desirability of Control Scale into Spanish. Two samples are present: the first involving 1,999 people to study their psychometric properties. In the second sample, 111 people were included to estimate test/ retest reliability. Cultural adaptation was performed using the translation & back-translation method. Item analysis, internal consistency and test/retest reliability were assessed, then evidence of the validity of the internal structure was determined by using exploratory and confirmatory factor analysis. Subject recruitment was performed to gather the 1,999 subjects stratified by age, gender quotas as designed in the sampling plan. Of the subjects, 51% were female, average age of 45 years old (SD = 17.5). All items from the original scale were understood correctly, while five items presented ceiling effect. Cronbach’s alpha = .736 and a test-retest correlation r = .713 were obtained. The factor structure indicated the presence of four dimensions: forecast, autonomy, power and influence and reactance which were reassured in the confirmatory analysis (χ2/df = 4.805, CFI =.932, TLI =.954, RMSEA = .062). The basic dimensions of the scale have shown to be stable and well-defined, though not perfect. The scope, possible applications of the scale and further research are later proposed and discussed.Se presenta la adaptación y validación al español de la Escala de Deseo de Control de Burger y Cooper. Se emplearon dos muestras. Para estudiar las propiedades psicométricas de la escala se contó con una primera muestra de 1999 (Medad = 45 años, DS = 17,5; 51% mujeres). Para estimar la fiabilidad test-retest se contó con una segunda muestra de 111 personas. La adaptación cultural se llevó a cabo mediante el procedimiento de traducción–retrotraducción. Se presentan las evidencias de validez de la estructura interna de la escala mediante los resultados de sendos análisis factoriales, exploratorio y confirmatorio. El análisis de ítems reveló que todos los elementos presentaron unos valores aceptables, aunque cinco de ellos mostraron efecto techo. El Alfa de Cronbach fue de .736 y la Fiabilidad test–retest fue de .713. La estructura factorial indicó la presencia de cuatro dimensiones: previsión, autonomía, poder e influencia y reactancia. La estructura fue corroborada en el análisis confirmatorio (χ2/df = 4.805, CFI = .932, TLI = .954, RMSEA = .062). Las dimensiones de la escala son estables y específicas, aunque no perfectas. Se discute el alcance y posibles aplicaciones de la escala y se proponen futuras investigaciones

Modelo de evaluación de la gestión logística en empresas

Diversos estudios apuntan a que el desarrollo de cualquier área de gestión empresarial requiere tanto de la existencia de sistemas de gestión para los procesos implicados, como de modelos de evaluación y diagnóstico basados en su correspondiente sistema de gestión. En el área de la gestión logística, la literatura científica y diversos trabajos técnicos ya recogen la existencia de un sistema de gestión logística (modelo CPLA). Por tanto, este trabajo desarrolla un modelo de evaluación basado en el modelo CPLA de gestión logística, contando además con la experiencia de aplicación en más de 30 empresas de diversos sectores industriales

Understanding the role of MAM molecular weight in the production of PMMA/MAM nanocellular polymers

Nanostructured polymer blends with CO2-philic domains can be used to produce nanocellular materials with controlled nucleation. It is well known that this nanostructuration can be induced by the addition of a block copolymer poly(methyl methacrylate)-poly(butyl acrylate)-poly(methyl methacrylate) (MAM) to a poly(methyl methacrylate) (PMMA) matrix. However, the effect of the block copolymer molecular weight on the production of nanocellular materials is still unknown. In this work, this effect is analysed by using three types of MAM triblock copolymers with different molecular weights, and a fixed blend ratio of 90 wt% PMMA and 10 wt% of MAM. Blends were produced by extrusion. As a result of the extrusion process, a non-equilibrium nanostructuration takes place in the blends, and the micelle density increases as MAM molecular weight increases. Micelle formation is proposed to occur as result of two mechanisms: dispersion, controlled by the extrusion parameters and the relative viscosities of the polymers, and self-assembly of MAM molecules in the dispersed domains. On the other hand, in the nanocellular materials produced with these blends, cell size decreases from 200 to 120 nm as MAM molecular weight increases. Cell growth is suggested to be controlled by the intermicelle distance and limited by the cell wall thickness. Furthermore, a theoretical explanation of the mechanisms underlying the limited expansion of PMMA/MAM systems is proposed and discussed

Mi entrada en el mundo docente

Este documento es el referente a mi Trabajo Fin de Máster, mediante el cual se explica mi experiencia vivida al cursar el Máster de Educación por la Universidad de Zaragoza. Empezaré hablando de mis inquietudes personales en el apartado de introducción. Ahí también haré un repaso del contexto legislativo y las diferentes teorías que he considerado más importantes para sustentar el grueso de mi trabajo. Seguidamente hay un apartado en el que justifico mi trabajo basándome en una serie de tareas que he realizado a lo largo del máster. En el siguiente apartado reflexionaré sobre mis períodos de prácticas en instituto, haciendo referencia a los trabajos más importantes del apartado anterior y explicando qué utilidad he sacado de cada uno. Finalmente propondré una serie de vías por las que quiero conducir mi formación y expondré conclusiones a las que me ha conducido esta experiencia