Avaliação da força de cisalhamento de fibras longas de piaçava em poliéster insaturado

Composites made from plant fiber and polymer matrix present an important point regarding the interaction between these two materials. This interaction has great infl uence on the final properties of the composite, because they are connection points that constitute the composite material itself. The att raction between the polymer matrix and the piassava fiber should be as large as possible to transmit to the composite a strong link between these att ractive materials, overcoming as far as possible the forces binding the polymer matrix and the fiber. The critical length of the piassava fiber embedded in the polymer matrix also has great importance in the construction of composites reinforced with these fibers. The evaluation of the interfacial shear strength between the matrix and the polyester piassava fibers was studied in this work.Key words: polymer, shear, composite, vegetable fiber.Compósitos confeccionados com fibras vegetais e matriz polimérica apresentam um ponto importante com relação à interação entre esses dois materiais. Essa interação tem grande influência nas propriedades finais do compósito, pois são pontos de ligação-união entre os elementos que constituem o próprio material compósito. A atração entre a matriz polimérica e a fibra de piaçava deve ser a maior possível de forma a transmitir a esse tipo de compósito uma forte ligação atrativa entre esses materiais, superando, na medida do possível, a força de tração da matriz polimérica e da fibra. O comprimento crítico da fibra de piaçava embutida na matriz polimérica também apresenta importância relevante na construção de compósitos reforçados com essas fibras, pois permite buscar as melhores propriedades do material compósito em função do tamanho da fibra do material. A avaliação da força de cisalhamento interfacial da matriz poliéster em relação às fibras de piaçava foi estudada neste trabalho.Palavras-chave: polímero, cisalhamento, compósito, fibra vegetal

Monte Carlo Simulation of Epitaxial Growth

A numerical Monte Carlo (MC) model is described in detail to simulate epitaxial growth. This model allows the formation of structural defects, like substitutional defects and vacancies, and desorption of adsorbed atoms on the surface. The latter feature supports the study of epitaxial growth at very high kinetic regime. The model proposed here is applied to simulate the homoepitaxial growth of Si. The results obtained fit well to the experimental reports on (0 0 1) silicon homoepitaxy. The easy implementation of a large number of microscopic processes and the three-dimensional spatial information during the film growth suggests that the model can be applied to simulate the growth of binary, ternary, or more compounds and even the growth of superlattices and heterostructures

Author Correction: Non-local effect of impurity states on the exchange coupling mechanism in magnetic topological insulators

A Correction to this paper has been published: https://doi.org/10.1038/s41535-021-00314-

Non-local effect of impurity states on the exchange coupling mechanism in magnetic topological insulators

Since the discovery of the quantum anomalous Hall (QAH) effect in the magnetically doped topological insulators (MTI) Cr:(Bi,Sb)2Te3 and V:(Bi,Sb)2Te3, the search for the magnetic coupling mechanisms underlying the onset of ferromagnetism has been a central issue, and a variety of different scenarios have been put forward. By combining resonant photoemission, X-ray magnetic circular dichroism and density functional theory, we determine the local electronic and magnetic configurations of V and Cr impurities in (Bi,Sb)2Te3. State-of-the-art first-principles calculations find pronounced differences in their 3d densities of states, and show how these impurity states mediate characteristic short-range pd exchange interactions, whose strength sensitively varies with the position of the 3d states relative to the Fermi level. Measurements on films with varying host stoichiometry support this trend. Our results explain, in an unified picture, the origins of the observed magnetic properties, and establish the essential role of impurity-state-mediated exchange interactions in the magnetism of MTI