Materials nanocomposits a partir de whiskers de cel•lulosa i matriu polimèrica de cautxú

De acuerdo con los objetivos generales del proyecto y plan de trabajo previsto, para esta anualidad, se obtuvieron fibras y microfibras de celulosa a partir de dos fuentes: celulosa vegetal de pino y eucalipto y celulosa bacterial. Las microfibrillas han sido utilizadas como material de refuerzo para la fabricación de materiales compuestos a partir de caucho natural, policaprolactona y polivinil alcohol. Las muestras se fabricaron mediante la técnica de "casting" en medio acuoso y temperatura ambiente. Las muestras fueron caracterizados en sus propiedades mecánicas, físicas y térmicas. Se observó que, en general, la adición de las microfibrillas de celulosa en las matrices poliméricas provoca una mejora sustancial en las propiedades mecánicas del material en comparación con el polímero sin reforzar. Los resultados pueden resumirse de la siguiente manera: 1.Fabricación de materiales compuestos a base de caucho natural y fibras de celulosa. Se obtuvieron fibras y nanofibras de celulosa que fueron modificadas químicamente y usadas como refuerzo en matriz de caucho. Los resultados mostraron mejora de propiedades mecánicas del material, principalmente en los materiales compuestos reforzados con nanofibras. 2. Obtención de whiskers de celulosa y su utilización como material de refuerzo en una matriz de policaprolactona. Se obtuvieron whiskers de celulosa a partir de pasta blanqueada. La adición en una matriz de policaprolactona produjo materiales compuestos con propiedades mecánicas superiores a la matriz, con buena dispersión de los whiskers. 3. Obtención de fibras de celulosa bacterial y nanofibras de celulosa, aislamiento y utilización sobre una matriz de polivinil alcohol. Se obtuvo celulosa bacterial a partir de la bacteria Gluconacetobacter xylinum. Además se fabricaron nanofibras de celulosa a partir eucalipto blanqueado. La celulosa bacterial como material de refuerzo no produjo importantes mejoras en las propiedades mecánicas de la matriz; en cambio se observaron mejoras destacables con la nanofibra como refuerzo.

Mean intrinsic tensile properties of stone groundwood fibers from softwood

Stone groundwood (SGW) is a fibrous matter commonly prepared in a high yield process, and mainly used for papermaking applications. In this work, the use of SGW fibers is explored as reinforcing element of polypropylene (PP) composites. Due to its chemical and superficial features, the use of coupling agents is needed for a good adhesion and stress transfer across the fiber-matrix interface. The intrinsic strength of the reinforcement is a key parameter to predict the mechanical properties of the composite and to perform an interface analysis. The main objective of the present work was the determination of the intrinsic tensile strength of stone groundwood fibers. Coupled and non-coupled PP composites from stone groundwood fibers were prepared. The influence of the surface morphology and the quality at interface on the final properties of the composite was analyzed and compared to that of fiberglass PP composites. The intrinsic tensile properties of stone groundwood fibers, as well as the fiber orientation factor and the interfacial shear strength of the current composites were determined

Does Reasoning Enhance Learning?

Utilizing the well-known Ultimatum Game, this note presents the following phenomenon. If we start with simple stimulus-response agents, learning through naive reinforcement, and then grant them some introspective capabilities, we get outcomes that are not closer but farther away from the fully introspective game-theoretic approach. The cause of this is the following: there is an asymmetry in the information that agents can deduce from their experience, and this leads to a bias in their learning process.

Does eeasoning enhance learning?

Utilizing the well-known Ultimatum Game, this note presents the following phenomenon. If we start with simple stimulus-response agents,learning through naive reinforcement, and then grant them some introspective capabilities, we get outcomes that are not closer but farther away from the fully introspective game-theoretic approach. The cause of this is the following: there is an asymmetry in the information that agents can deduce from their experience, and this leads to a bias in their learning process.

Are agent-based simulations robust? The wholesale electricity trading case

Agent-based computational economics is becoming widely used in practice. This paperexplores the consistency of some of its standard techniques. We focus in particular on prevailingwholesale electricity trading simulation methods. We include different supply and demandrepresentations and propose the Experience-Weighted Attractions method to include severalbehavioural algorithms. We compare the results across assumptions and to economic theorypredictions. The match is good under best-response and reinforcement learning but not underfictitious play. The simulations perform well under flat and upward-slopping supply bidding,and also for plausible demand elasticity assumptions. Learning is influenced by the number ofbids per plant and the initial conditions. The overall conclusion is that agent-based simulationassumptions are far from innocuous. We link their performance to underlying features, andidentify those that are better suited to model wholesale electricity markets.

Trade-off between formal and informal care in Spain

The remarkable growth of older population has moved long term care to the front ranks of the social policy agenda. Understanding the factors that determine the type and amount of formal care is important for predicting use in the future and developing long-term policy. In this context we jointly analyze the choice of care (formal, informal, both together or none) as well as the number of hours of care received. Given that the number of hours of care is not independent of the type of care received, we estimate, for the first time in this area of research, a sample selection model with the particularity that the first step is a multinomial logit model. With regard to the debate about complementarity or substitutability between formal and informal care, our results indicate that formal care acts as a reinforcement of the family care in certain cases: for very old care receivers, in those cases in which the individual has multiple disabilities, when many care hours are provided, and in case of mental illness and/or dementia. There exist substantial differences in long term care addressed to younger and older dependent people and dependent women are in risk of becoming more vulnerable to the shortage of informal caregivers in the future. Finally, we have documented that there are great disparities in the availability of public social care across regions.

Thermoplastic Starch-based Composites Reinforced with Rape Fibers: Water Uptake and Thermomechanical Properties

Fully biodegradable composite materials were obtained through reinforcement of a commercially available thermoplastic starch (TPS) matrix with rapeseed fibers (RSF). The influence of reinforcement content on the water sorption capacity, as well as thermal and thermo-mechanical properties of composites were evaluated. Even though the hydrophilic character of natural fibers tends to favor the absorption of water, results demonstrated that the incorporation of RSF did not have a significant effect on the water uptake of the composites. DSC experiments showed that fibers restricted the mobility of the starch macromolecules from the TPS matrix, hence reducing their capacity to crystallize. The viscoelastic behaviour of TPS was also affected, and reinforced materials presented lower viscous deformation and recovery capacity. In addition, the elasticity of materials was considerably diminished when increasing fiber content, as evidenced in the TMA and DMTA measurements

Enhanced electron-electron correlations in nanometric epitaxial SrRuO3 epitaxial films

Epitaxial and fully strained SrRuO3 thin films have been grown on SrTiO3(100). At initial stages the growth mode is three-dimensional- (3D-)like, leading to a finger-shaped structure aligned with the substrate steps and that eventually evolves into a 2D step-flow growth. We study the impact that the defect structure associated with this unique growth mode transition has on the electronic properties of the films. Detailed analysis of the transport properties of nanometric films reveals that microstructural disorder promotes a shortening of the carrier mean free path. Remarkably enough, at low temperatures, this results in a reinforcement of quantum corrections to the conductivity as predicted by recent models of disordered, strongly correlated electronic systems. This finding may provide a simple explanation for the commonly observed¿in conducting oxides-resistivity minima at low temperature. Simultaneously, the ferromagnetic transition occurring at about 140 K, becomes broader as film thickness decreases down to nanometric range. The relevance of these results for the understanding of the electronic properties of disordered electronic systems and for the technological applications of SrRuO3¿and other ferromagnetic and metallic oxides¿is stressed.

Anàlisi i disseny d'una aplicació web per a un banc del temps

Els bancs del temps són eines que permeten l'intercanvi de serveis entre persones d'una mateixa localització geogràfica. El tret més característic és que aquest serveis s'intercanvien sense utilitzar diners, agafant el temps propi d'una persona com a moneda de canvi. Es poden intercanviar tot tipus de serveis: passejar gossos, fer companyia a persones majors, classes de repàs, assessorament informàtic, etc. Aquest projecte proposa la creació d'un portal web que permeti i gestioni el funcionament d'un banc del temps, tant a nivell d'usuari com a nivell d'administració.

Bio-inspired Mechanisms for Artificial Self-organised Systems

Self-organization is a growing interdisciplinary field of research about a phenomenon that can be observed in the Universe, in Nature and in social contexts. Research on self-organization tries to describe and explain forms, complex patterns and behaviours that arise from a collection of entities without an external organizer. As researchers in artificial systems, our aim is not to mimic self-organizing phenomena arising in Nature, but to understand and to control underlying mechanisms allowing desired emergence of forms, complex patterns and behaviours. Rather than attempting to eliminate such self-organization in artificial systems, we think that this might be deliberately harnessed in order to reach desirable global properties. In this paper we analyze three forms of self-organization: stigmergy, reinforcement mechanisms and cooperation. The amplification phenomena founded in stigmergic process or in reinforcement process are different forms of positive feedbacks that play a major role in building group activity or social organization. Cooperation is a functional form for self-organization because of its ability to guide local behaviours in order to obtain a relevant collective one. For each forms of self-organisation, we present a case study to show how we transposed it to some artificial systems and then analyse the strengths and weaknesses of such an approach

Recerca avaluativa sobre el programa “LÍMITS”

Des de la comunitat científica s’ha posat de manifest la necessitat d’avaluar els programes d’intervenció per a la millora de la parentalitat, especialment en el context de la infància i adolescència en risc. En aquesta recerca es presenten els resultats de l’avaluació del programa Límits aportant evidències d’eficàcia i efectivitat, que permeten identificar i descriure les seves fortaleses, així com també aquells elements que poden ser objecte de millora. El programa Límits és una proposta estructurada d’intervenció preventiva de caire selectiu amb grups de famílies de joves d’entre 14 i 18 anys que passen pel circuit de la justícia juvenil. El programa ha estat funcionant des del 2007, en diverses edicions, a tot el territori català aplegant una experiència i trajectòria remarcable que ha incidit en 351 persones i 245 famílies. El programa consta de vuit sessions en grup d’entre dotze i quinze participants, dinamitzat per dos monitors, en les que es treballen diferents estratègies a partir de l’abordatge de continguts relacionats amb les relacions i els lligams, la comunicació, els conflictes, l’establiment de normes i la disciplina. Per dur a terme l’avaluació del programa Límits s’ha partit d’un disseny quasi-experimental, pretest–postest aplicat a un grup programa (GP) i a grup col·laborador (GC) i de manera diferida (dos mesos després de la seva finalització) només al GP per constatar si s’han assolit els resultats previstos. Quan s’analitza l’evolució del GP s’observen millores en les habilitats d’autocontrol de les emocions, el reforç positiu i les relacions familiars. Tanmateix, des del punt de vista de les famílies no s’han observat canvis significatius en la millora de la percepció d’auto eficàcia del rol parental respecte el GC abans i després del programa. La percepció majoritària és que els objectius que planteja el programa són excessivament ambiciosos i en conseqüència, difícilment assolibles. Els responsables consideren que, en alguns casos, el perfil de famílies derivades al programa no és el més adequat perquè presenten problemàtiques molt més agudes a les desitjables per aquest tipus d’intervenció. Com a punts forts, es destaca que el programa és útil als ulls dels responsables i tècnics perquè genera una presa de consciència del problema i de la necessitat de canvi per part de les famílies. Els participants diuen transferir a la vida real algunes habilitats apreses especialment la comunicació i millora de les relacions familiars. Els tècnics aplicadors coincideixen amb la percepció de les famílies tot i declarar percentatges lleugerament inferiors. També és vist com un complement professional a la seva tasca que ajuda a fer un millor seguiment dels casos, i permet seguir treballant amb posterioritat amb les famílies.

Investigación evaluativa sobre el programa "LÍMITES"

Desde la comunidad científica se ha puesto de manifiesto la necesidad de evaluar los programas de intervención para la mejora de la parentalidad, especialmente en el contexto de la infancia y la adolescencia en riesgo. En esta investigación se presentan los resultados de la evaluación del programa Límites aportando evidencias de eficacia y efectividad, que permiten identificar y describir sus fortalezas, así como también aquellos elementos que pueden ser objeto de mejora. El programa Límites es una propuesta estructurada de intervención preventiva de carácter selectivo, con grupos de familias de jóvenes de entre 14 y 18 años que pasan por el circuito de la justicia juvenil. El programa ha estado funcionando desde 2007 en todo el territorio catalán, y ha incidido en un total de 351 personas y 245 familias. El programa consta de ocho sesiones en grupo en las que se trabajan contenidos relacionados con las relaciones y los vínculos, la comunicación, los conflictos, el establecimiento de normas y la disciplina. Para llevar a cabo la evaluación del programa Límites se ha partido de un diseño cuasi-experimental, pretest-postest aplicado a un grupo programa (GP) y grupo colaborador (GC) y de manera diferida (dos meses después de su finalización) sólo en el GP, para constatar si se han alcanzado los resultados previstos. Cuando se analiza la evolución del GP se observan mejoras en las habilidades de autocontrol de las emociones, el refuerzo positivo y las relaciones familiares. Sin embargo, desde el punto de vista de las familias no se han observado cambios significativos en la mejora de la percepción de auto eficacia del rol parental respecto al GC antes y después del programa. La percepción mayoritaria es que los objetivos que plantea el programa son excesivamente ambiciosos y en consecuencia, difícilmente alcanzables. Los responsables consideran que, en algunos casos, el perfil de familias derivadas al programa no es el más adecuado puesto que presenten problemáticas mucho más agudas a las deseables para este tipo de intervención. Como puntos fuertes, se destaca que el programa es útil a los ojos de los responsables y técnicos porque genera una toma de conciencia del problema y de la necesidad de cambio por parte de las familias. Los participantes dicen transferir a la vida real algunas habilidades aprendidas, especialmente la comunicación y mejora de las relaciones familiares. Los técnicos aplicadores coinciden con la percepción de las familias, a pesar de declarar porcentajes ligeramente inferiores. También es visto como un complemento profesional a su tarea que ayuda a hacer un mejor seguimiento de los casos, y permite seguir trabajando con posterioridad con las familias.

High-Performance-Tensile-Strength Alpha-Grass Reinforced Starch-Based Fully Biodegradable Composites

Though there has been a great deal of work concerning the development of natural fibers in reinforced starch-based composites, there is still more to be done. In general, cellulose fibers have lower strength than glass fibers; however, their specific strength is not far from that of fiberglass. In this work, alpha-fibers were obtained from alpha-grass through a mild cooking process. The fibers were used to reinforce a starch-based biopolymer. Composites including 5 to 35% (w/w) alpha-grass fibers in their formulation were prepared, tested, and subsequently compared with those of wood- and fiberglass-reinforced polypropylene (PP). The term “high-performance” refers to the tensile strength of the studied composites and is mainly due to a good interphase, a good dispersion of the fibers inside the matrix, and a good aspect ratio. The tensile strength of the composites showed a linear evolution for fiber contents up to 35% (w/w). The strain at break of the composites decreased with the fiber content and showed the stiffening effects of the reinforcement. The prepared composites showed high mechanical properties, even approaching those of glass fiber reinforced composites

Analysis of the tensile modulus of polypropylene composites reinforced with stone groundwood fibers

One of the most relevant properties of composite materials to be considered is stiffness. Fiberglass has been used traditionally as a fibrous reinforcing element when stiff materials are required. However, natural fibers are been exploited as replacements for synthetic fibers to satisfy environmental concerns. Among the different natural fibers, wood fibers show the combination of relatively high aspect ratio, good specific stiffness and strength, low density, low cost, and less variability than other natural fibers of such those from annual crops. In this work, composites from polypropylene and stone groundwood fibers from softwood were prepared and mechanically characterized under tensile loads. The Young’s moduli of the ensuing composites were analyzed and their micromechanics aspects evaluated. The reinforcing effect of stone groundwood fibers was compared to that of conventional reinforcement such fiberglass. The Halpin-Tsai model with the modification proposed by Tsai-Pagano accounted fairly for the behavior of PP composites reinforced with stone groundwood fibers. It was also demonstrated that the aspect ratio of the reinforcement plays a role in the Young’s modulus of injection molded specimens

Modelo de comportamiento en sevicio para estructuras reticulares de hormigón. Parte I: Descripción del modelo y ejemplos de aplicación

A general method for instantaneous and time-dependent serviceability analysis of plane concrete frames is presented. The methodology is based in an extension of the classic matrix formulation for bars. The main aspects influencing the behaviour of the structural concrete are considered: cracking, creep, shrinkage or prestress losses. To simulate the effect of cracking a smeared model (developed in Part II) based on the modification of the tensile branch of the concrete stress-strain relationship is adopted. The general approach considered permits the application to different materials and constitutive laws. Sequential construction (sectional and structural), incorporation of reinforcement, consideration of the loads history; placing and removing shores, and restraining or releasing in boundary conditions are considered. Some examples are included to highlight the capabilities of the model