Effects of chemical structure and morphology of graphene-related materials (GRMs) on melt processing and properties of GRM/polyamide-6 nanocomposites

In this work, different graphene-related materials (GRMs) and polyamide-6 (PA6) were melt compounded by twin screw extrusion. The GRMs prepared were graphene nanoplatelets (GNPs), graphene oxide (GO), reduced graphene oxide (rGO) and silane functionalised reduced graphene oxide (f-rGO). The GRMs had comparable lateral size (20-30μm), but different thickness and surface chemistry which resulted in different behaviour in processing of melt flow, maximum loading in the PA6 matrix (15%wt for GNPs, 10%wt for GO, 2%wt for rGO and 2.5%wt for f-rGO) as well as mechanical properties. A second extrusion phase produced formulations with lower concentration of GRMs. In the case of f-rGO/PA6, the melt flow index increased by over 76% at 0.5%wt loading compared with the pure PA6 resin, facilitating processing and dispersion of the flakes within the matrix and increasing the elastic modulus and tensile strength by 39%. However, high filler content above 10% has been achieved only for GNPs improving the elastic modulus by 50% at 15%wt

Layer-by-Layer Assembly of Efficient Flame Retardant Coatings Based On High Aspect Ratio Graphene Oxide and Chitosan Capable of Preventing Ignition of PU Foam

The layer-by-layer (LbL) technique is adopted for the construction of multilayers encompassing chitosan and graphene oxide (GO) platelets capable of improving the flame retardant properties open cell PU foams. The LbL assembly follows a linear growth regime as evaluated by infrared spectroscopy and yields a multilayer structure where GO platelets are embedded within a chitosan continuous matrix. 3 and 6 bi-layers (BL) can efficiently coat the complex 3D structure of the foam and substantially improve its flame retardant properties. 3BL only add 10% to the original mass and can suppress the melt dripping during flammability and reduce both the peak of heat release rate by 54% and the total smoke released by 59% in forced combustion tests. Unprecedented among other LbL assemblies employed for FR purposes, the deposition 6BL is capable of slowing down the release of combustible volatile to the limits of non-ignitability thus preventing ignition in half of the specimens during cone calorimetry tests. This has been ascribed to the formation of a protective coating where the thermally stable char produced by chitosan serves as a continuous matrix embedding GO platelets, which control volatile release while mechanically sustaining the PU foam structure

The Quest for Global Justice in Health: A Review of Global Health Law by Lawrence 0. Gostin

We are witnessing the emergence of a new world health order. Health occupies an increasingly relevant place in the global agenda. An unprecedented health transition is leading to a new model characterized by expanded international and national funding for health and the involvement of a growing pluralism of actors

The effect of rippling on the mechanical properties of graphene

Graphene is the stiffest material known so far but, due to its one-atom thickness, it is also very bendable. Consequently, free-standing graphene exhibit ripples that has major effects on its elastic properties. Here we will summarize three experiments where the influence of rippling is essential to address the results. Firstly, we observed that atomic vacancies lessen the negative thermal expansion coefficient of free-standing graphene. We also observed an increase of the Young's modulus with global applied strain and with the introduction of small density defects that we attributed to the decrease of rippling. Here, we will focus on a surprising feature observed in the data: the experiments consistently indicate that only the rippling with wavelengths between 5-10nm influences the mechanics of graphene. The rippling responsible of the negative TEC and anomalous elasticity is thought to be dynamic, i.e. flexural phonons. However, flexural phonons with these wavelengths should have minor effects on the mechanics of graphene, therefore other mechanisms must be considered to address our observations. We propose static ripples as one of the key elements to correctly understand the thermomechanics of graphene and suggest that rippling arises naturally due to a competition of symmetry breaking and anharmonic fluctuations

Tug-of-War games and the infinity Laplacian with spatial dependence

In this paper we look for PDEs that arise as limits of values of Tug-of-War games when the possible movements of the game are taken in a family of sets that are not necessarily euclidean balls. In this way we ¯nd existence of viscosity solutions to the Dirichlet problem for an equation of the form ¡hD 2 v ¢ Jx(Dv); Jx(Dv)i(x) = 0, that is, an in¯nity Laplacian with spatial dependence. Here Jx(Dv(x)) is a vector that depends on the the spatial location and the gradient of the solution.Fil: Gomez, Ivana Daniela. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico - CONICET - Santa Fe. Instituto de Matemática Aplicada; Argentina;Fil: Rossi, Julio Daniel. Universidad de Buenos Aires; Argentina

Uso de la Biblia como estrategia pedagógica para fomentar la investigación

The present article has as aim implement the use of the bible as pedagogic strategy to promote the investigation, using a methodology of qualitative type developed from the Investigation as Pedagogic Strategy (IEP), in which the technology of the observation was applied and as I orchestrate a structured interview applied to 40 students of the degrees of 6 ° to 9 ° degree between the ages of 12-16 years performing activities such as debates, roll plays and socialization spaces. From the application it was obtained that students consider that the Bible as a pedagogical means of learning if it allows to acquire new knowledge and in a didactic way strengthening and promoting research.El presente artículo tiene como objetivo implementar el uso de la biblia como estrategia pedagógica para fomentar la investigación, utilizando una metodología de tipo cualitativo desarrollado desde la Investigación como Estrategia Pedagógica  (IEP).  El desarrollo de la investigación, incluyó como técnicas de recolección de información la observación y la entrevista en profundidad; los cuales fueron aplicados a 40 estudiantes de los grados de 6° a 9° con edades comprendidas entre los 12 y los 16 años.  Adicionalmente, se realizaron actividades como debates, roll plays y espacios de socialización. A partir de los resultados obtenidos se llegó a la conclusión de que los estudiantes consideran que la Biblia como medio pedagógico de aprendizaje que permite adquirir nuevos conocimientos de manera didáctica fortaleciendo y fomentando la investigación

Dependence of the location of the Martian magnetic lobes on the interplanetary magnetic field direction: Observations from Mars Global Surveyor

We use magnetometer data from the Mars Global Surveyor (MGS) spacecraft during portions of the premapping orbits of the mission to study the variability of the Martian-induced magnetotail as a function of the orientation of the interplanetary magnetic field (IMF). The time spent by MGS in the magnetotail lobes during periods with positive solar wind flow-aligned IMF component B IMF suggests that their location as well as the position of the central polarity reversal layer (PRL) are displaced in the direction antiparallel to the IMF cross-flow component B IMF. Analogously, in the cases where B IMF is negative, IMF the lobes are displaced in the direction of B ⟂ . This behavior is compatible with a previously published analytical model of the IMF draping, where for the first time, the displacement of a complementary reversal layer (denoted as IPRL for inverse polarity reversal layer) is deduced from first principles.Fil: Romanelli, Norberto Julio. Consejo Nacional de Investigaciónes Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Astronomía y Física del Espacio. - Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Astronomía y Física del Espacio; ArgentinaFil: Bertucci, Cesar. Consejo Nacional de Investigaciónes Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Astronomía y Física del Espacio. - Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Astronomía y Física del Espacio; ArgentinaFil: Gomez, Daniel Osvaldo. Consejo Nacional de Investigaciónes Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Astronomía y Física del Espacio. - Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Astronomía y Física del Espacio; ArgentinaFil: Mazelle, C.. Université Paul Sabatier; Franci

Implementación de un sistema de reconocimiento de voz en el lenguaje Nasa Yuwe basado en Redes Neuronales Convolusionales

Introduction: This paper presents the Implementation of an algorithm for voice recognition in the Nasa Yuwe language based on Convolutional Neural Networks (CNN), developed at the Universidad del Cauca in the year 2022. Problem: The Nasa Yuwe language is phonetically rich, as it has 32 vowels and 34 consonants, which leads to confusion in pronunciation and therefore difficulties in recognizing voice patterns. Objective: To implement a speech recognition algorithm for the Nasa Yuwe language supported in CNN. Methodology: The preprocessing of the audio signals was carried out to subsequently obtain the characteristics through the scalograms of the Mel coefficients. Finally, an architecture of the CNN is proposed for the classification process. Results: A DataSet is built from the scalograms of the voice patterns, and the CNN training process is carried out. Conclusion: The implementation of a Voice Recognition System based on CNN provides low margins of error in the word classification process of the Nasa Yuwe language. Originality: The proposed voice recognition system is the first and only one of its kind that has been carried out so far, with the purpose of collaborating in the process of teaching, preserving and learning the Nasa Yuwe language. Limitations: It is necessary to increase the number of voice patterns provided by native speakers, and there is a need to implement other technological tools that allow for the conservation and dissemination of the Nasa Yuwe language.Introducción:  Este artículo presenta la Implementación de un algoritmo para el reconocimiento de voz en el lenguaje Nasa Yuwe basado en Redes Neuronales Convolusionales (RNC), desarrollado en la Universidad del Cauca en el año 2022. Problema: La riqueza fonética del lenguaje Nasa Yuwe es grande, al poseer 32 vocales, y 34 consonantes, lo que lleva a confusiones en la pronunciación y por lo tanto a dificultades en el reconocimiento de patrones de voz. Objetivo:  Implementar un algoritmo de reconocimiento de voz, para el lenguaje Nasa Yuwe soportado en RNC. Metodología:  Se realizó el preprocesamiento de las señales de audio para posteriormente obtener las características por medio de los escalogramas de los coeficientes de Mel.  Finalmente se propone una arquitectura de la RNC para el proceso de clasificación. Resultados:  Se construye un DataSet a partir de los escalograma de los patrones de voz, y se realiza el proceso de entrenamiento de la RNC. Conclusión:  La implementación de un SRV basado RNC, proporciona bajos márgenes de error en el proceso de clasificación de palabras del lenguaje Nasa Yuwe. Originalidad:  El sistema de reconocimiento de voz planteado es el primero y único en su clase que se ha realizado hasta el momento, con el propósito de colaborar en el proceso de enseñanza, conservación y aprendizaje del lenguaje Nasa Yuwe. Limitaciones:  Se requiere aumentar el número de patrones de voz aportados por hablantes nativos, y se plantea la necesidad de implementar otras herramientas tecnologías que permitan la conservación y difusión del lenguaje Nasa Yuwe

Polyelectrolytes Enabled Reduced Graphite Oxide Water Dispersions: Effects of the Structure, Molecular Weight, and Charge Density

The polyelectrolyte (PE)-based water dispersion of graphene-related materials (GRMs) represents an interesting intermediate for the development of advanced materials by sustainable processes. Although the proof of concept has been demonstrated, there is a lack of knowledge for what concerns the effects of parameters typical of PEs such as functionalization, molecular weight, and charge density. In this work, we evaluate the effects of such parameters on the quality and long-term stability of reduced graphite oxide (rGO) dispersion in aqueous media prepared by ultrasound sonication in the presence of different PEs. Four PEs were evaluated: polyacrylic acid (PAA), branched poly(ethylenimine) (BPEI), sodium carboxymethyl cellulose (CMC), and poly(sodium 4-styrenesulfonic acid) (PSS). The prepared dispersions were thoroughly characterized by means of UV-visible spectroscopy, thermogravimetric analysis, dynamic light scattering, and Raman spectroscopy. The highest concentrations of rGO were achieved by BPEI with a molecular weight of 25,000 and 270,000 Da (33 and 26 mu g/mL, respectively). For other PEs, the rGO concentration was found to be independent of the molecular weight. The PAA-based dispersions displayed the best through-time stability while yielding homogeneous dispersion with a smaller average size and narrower size distribution