A one-dimensional Fermi accelerator model with moving wall described by a nonlinear van der Pol oscillator

A modification of the one-dimensional Fermi accelerator model is considered in this work. The dynamics of a classical particle of mass $m$, confined to bounce elastically between two rigid walls where one is described by a non-linear van der Pol type oscillator while the other one is fixed, working as a re-injection mechanism of the particle for a next collision, is carefully made by the use of a two-dimensional non-linear mapping. Two cases are considered: (i) the situation where the particle has mass negligible as compared to the mass of the moving wall and does not affect the motion of it; (ii) the case where collisions of the particle does affect the movement of the moving wall. For case (i) the phase space is of mixed type leading us to observe a scaling of the average velocity as a function of the parameter ($\c{hi}$) controlling the non-linearity of the moving wall. For large $\c{hi}$, a diffusion on the velocity is observed leading us to conclude that Fermi acceleration is taking place. On the other hand for case (ii), the motion of the moving wall is affected by collisions with the particle. However due to the properties of the van der Pol oscillation, the moving wall relaxes again to a limit cycle. Such kind of motion absorbs part of the energy of the particle leading to a suppression of the unlimited energy gain as observed in case (i). The phase space shows a set of attractors of different periods whose basin of attraction has a complicate organization

Mechanical Properties of Graphene Nanowiggles

In this work we have investigated the mechanical properties and fracture patterns of some graphene nanowiggles (GNWs). Graphene nanoribbons are finite graphene segments with a large aspect ratio, while GNWs are nonaligned periodic repetitions of graphene nanoribbons. We have carried out fully atomistic molecular dynamics simulations using a reactive force field (ReaxFF), as implemented in the LAMPPS (Large-scale Atomic/Molecular Massively Parallel Simulator) code. Our results showed that the GNW fracture patterns are strongly dependent on the nanoribbon topology and present an interesting behavior, since some narrow sheets have larger ultimate failure strain values. This can be explained by the fact that narrow nanoribbons have more angular freedom when compared to wider ones, which can create a more efficient way to accumulate and to dissipate strain/stress. We have also observed the formation of linear atomic chains (LACs) and some structural defect reconstructions during the material rupture. The reported graphene failure patterns, where zigzag/armchair edge terminated graphene structures are fractured along armchair/zigzag lines, were not observed in the GNW analyzed cases.Comment: Materials Research Society Symposia vol. 1658, mrsf13-1658-rr07-27 (2014

One-dimensional Silicon and Germanium Nanostructures With No Carbon Analogues

In this work we report new silicon and germanium tubular nanostructures with no corresponding stable carbon analogues. The electronic and mechanical properties of these new tubes were investigated through ab initio methods. Our results show that the structures have lower energy than their corresponding nanoribbon structures and are stable up to high temperatures (500 and 1000 K, for silicon and germanium tubes, respectively). Both tubes are semiconducting with small indirect band gaps, which can be significantly altered by both compressive and tensile strains. Large bandgap variations of almost 50% were observed for strain rates as small as 3%, suggesting possible applications in sensor devices. They also present high Young's modulus values (0.25 and 0.15 TPa, respectively). TEM images were simulated to help the identification of these new structures

Mechanical Properties and Fracture Dynamics of Silicene Membranes

As graphene became one of the most important materials today, there is a renewed interest on others similar structures. One example is silicene, the silicon analogue of graphene. It share some the remarkable graphene properties, such as the Dirac cone, but presents some distinct ones, such as a pronounced structural buckling. We have investigated, through density functional based tight-binding (DFTB), as well as reactive molecular dynamics (using ReaxFF), the mechanical properties of suspended single-layer silicene. We calculated the elastic constants, analyzed the fracture patterns and edge reconstructions. We also addressed the stress distributions, unbuckling mechanisms and the fracture dependence on the temperature. We analysed the differences due to distinct edge morphologies, namely zigzag and armchair

Ferramentas Educacionais e Análise Intervencional da Aprendizagem Significativa: Es tudos de Casos Aplicados no Ensino da Física Acústica na Disciplina de Conforto Ambiental

It is of fundamental importance the mastery of Physics contents for the understanding of Acoustic Comfort. In this sense, it is up to the teacher to become aware of students' prior knowledge, to give a new meaning to the cognitive structures that make it possible to transform their difficulties into learning potential. In this work, educational teaching / learning interventions were developed and focused on the Theory of Meaningful Learning. These case studies were carried out with several students in different classes in the same program. In addition to the pre- and post-intervention questionnaire, Computational Educational Tools were used in order to assess the previous concepts and the effectiveness and efficiency of the provided pedagogical intervention. Satisfactory results were obtained with a reduction of about 250% in terms of alternative conceptions to the scientific knowledge previously detected in the participating volunteer students. The analysis was based on the approach of Ausubel and collaborators' Meaningful Learning theories, contextualized to the content of Acoustic Physics and applied in the classes of the Environmental Comfort course in the Civil Engineering and Civil Construction Technology programs from 2012 to 2018

Eficiência da remoção de DQO, surfactantes e de óleos e graxas totais na estação de tratamento de esgoto vila city na cidade de Paranavaí – Paraná / Efficiency of removal of DQO, surfactants and total oils and grease in the sewage treatment plant vila city in the city of Paranavaí - Paraná

Avaliar a eficiência dos processos em uma Estação de Tratamento de Esgoto (ETE) é um instrumento fundamental na busca de uma sociedade mais sustentável. Este trabalho procurou avaliar parâmetros menos comuns, mas muito importantes para o equilíbrio sustentável do corpo hídrico receptor deste efluente, ainda que tratado: a DQO (demanda química de oxigênio), os surfactantes e os óleos e graxas. Foram avaliadas as concentrações destes parâmetros em diferentes etapas do processo de tratamento de esgoto da ETE Vila City, na cidade de Paranavaí-PR com o objetivo de se verificar a eficiência dos processos utilizados no tratamento do esgoto para adequação das concentrações destes aos valores referenciados pela legislação brasileira de lançamento de efluentes na coleção hídrica. Os valores obtidos para concentração destes parâmetros no período estudado indicam: remoção de cerca de 73% na concentração de DQO; remoção de cerca de 30% na concentração de óleos e graxas; média de remoção de cerca de menos de 8% na concentração de surfactantes

CONHECER, MENSURAR E GERIR O CAPITAL INTELECTUAL: UM ESTUDO DO PAPEL HUMANO NAS ORGANIZAÇÕES

O fator humano, na economia moderna, ganha destaque frente à competitividade dos mercados. A capacidade de inovação intrínseca e externa vem sendo apregoada pelo mercado e torna-se fator eliminatório nas equipes. A incorporação do colaborador de uma organização, no lugar do funcionário, leva ao reconhecimento de sua importância como fator produtivo diferencial. O valor de uma empresa pode ser mensurado de diversas formas. A forma mais eficiente deve abranger os valores tangíveis e intangíveis; nestes últimos, o fator humano age de forma primordial e indestacável. Compreender o que são os ativos intangíveis, a importância da era da informação em sua formação e iniciar o pensamento sobre as formas de gestão são os objetivos deste trabalho. A metodologia contou com pesquisa bibliográfica em obras de estudiosos sobre o tema, bem como na legislação pertinente. Observou-se, então, que, para que as organizações sobrevivam de forma eficiente no mercado e obtenham lugar de destaque, é essencial a gestão eficiente dos ativos intangíveis e, analisando em profundidade, estes têm como fator originário o capital intelectual, o qual unifica conhecimentos e habilidades e leva, diante de uma ótima gerência, a resultados ótimos para seus detentores (trabalhador-colaborador) e para a organização que o aloca.Palavras-chave: Competitividade. Gestão. Conhecimento