Estudo das propriedades dos concretos confeccionados com cimento CP V - ARI e CP II - F32, sob diferentes temperaturas de mistura e métodos de cura

Orientador: Prof. Dr. Kleber F. PortellaDissertação (mestrado) - Universidade Federal do Paraná, Setor de Tecnologia, Curso de Pós-Graduação em Engenharia de Materiais e ProcessosInclui referências: p. 90-95Área de concentração: Engenharia e Ciência de MateriaisResumo: O estudo das propriedades do concreto é imprescindível na busca da melhoria da qualidade do material. Sabe-se que o concreto está sujeito a sofrer modificações em suas propriedades em função de uma enorme gama de variáveis. O entendimento de como estão relacionadas essas variáveis e as modificações no material se faz necessário. Nesse trabalho são analisadas as influências da temperatura de mistura, do tipo de cimento e o método de cura nas propriedades do concreto. Para avaliar as alterações do material são utilizadas metodologias como: ensaios físico-químicos dos materiais, inspeção visual, ensaios de resistência à compressão, propriedades elétricas, comportamento térmico, análises microscópicas e de difração de raios X. Com o uso dessas metodologias pode-se verificar que os fatores estudados influenciam de forma significativa nas propriedades do concreto. Concretos misturados nas temperaturas estudadas, 10, 20 e 60 °C, apresentaram alterações na resistência à compressão em função destas temperaturas. Misturas a temperaturas mais elevadas proporcionam concretos com maior resistência mecânica nas primeiras idades, podendo esses resultados serem modificados no decorrer do tempo. A quantidade e distribuição dos poros na microestrutura variaram conforme o caso estudado, onde cp's misturados nas maiores temperaturas apresentaram maior incidência de poros. Diferentes fases do material foram identificadas em função da temperatura de mistura e do método de cura. No método de cura à temperatura elevada identificou-se que os cp's analisados apresentam maior probabilidade corrosiva, se comparados aos cp's curados em câmara úmida a 23 °C.Abstract: The study of concrete properties is essential in the search for its quality improvement. It's known that the concrete is subjected to property modifications in terms of an enormous range of variables. Understanding how variables are related to the modifications in the material is necessary. In this work, the influences of the mixing temperature, as well as of the cement type and the curing method in the properties of the concrete are analyzed. To evaluate the alterations in the material, the following methodologies are used: physical-chemical analysis of the materials, visual inspection, compressive strength, electrical properties tests, thermal behavior, microscopical analyses and x-ray diffraction. With the use of these methodologies it can be verified that the studied factors have significant influence in the properties of the concrete. Concrete mixed at different temperatures 10, 20 and 60 °C, presented alterations in the compressive strength. The mixtures made at the highest temperatures provided concretes with higher mechanical resistance in the early ages, with a varying behavior in time. The amount and distribution of pores in the microstructure varied according to the studied case, where specimens mixed at the highest temperatures presented a greater incidence of pores. Different phases of the material were identified as function of the mixing temperature and the curing method. In the curing at high temperatures it was identified that analyzed specimens presented greater probability of corrosion

Species fractionation in atomic chains from mechanically stretched alloys.

Bettini et al (2006 Nat. Nanotechnol. 1 182-5) reported the first experimental realization of linear atomic chains (LACs) composed of different atoms (Au and Ag). The different contents of Au and Ag were observed in the chains from what was found in the bulk alloys, which raises the question of what the wire composition is, if it is in equilibrium with a bulk alloy. In this work we address the thermodynamic driving force for species fractionation in LACs under tension, and we present the density-functional theory results for Ag-Au chain alloys. A pronounced stabilization of the wires with an alternating Ag-Au sequence is observed, which could be behind the experimentally observed Au enrichment in LACs from alloys with high Ag content

Machine Learning-based Analysis of Electronic Properties as Predictors of Anticholinesterase Activity in Chalcone Derivatives

In this study, we investigated the correlation between the electronic properties of anticholinesterase compounds and their biological activity. While the methodology of such correlation is well-established and has been effectively utilized in previous studies, we employed a more sophisticated approach: machine learning. Initially, we focused on a set of $22$ molecules sharing a common chalcone skeleton and categorized them into two groups based on their IC50 indices: active and inactive. Utilizing the open-source software Orca, we conducted calculations to determine the geometries and electronic structures of these molecules. Over a hundred parameters were collected from these calculations, serving as the foundation for the features used in machine learning. These parameters included the Mulliken and Lowdin electronic populations of each atom within the skeleton, molecular orbital energies, and Mayer's free valences. Through our analysis, we developed numerous models and identified several successful candidates for effectively distinguishing between the two groups. Notably, the most informative descriptor for this separation relied solely on electronic populations and orbital energies. By understanding which computationally calculated properties are most relevant to specific biological activities, we can significantly enhance the efficiency of drug development processes, saving both time and resources.Comment: to be submitted to Journal of Chemical Information and Modelin