Site-dependent hydrogenation on graphdiyne

Graphene is one of the most important materials in science today due to its unique and remarkable electronic, thermal and mechanical properties. However in its pristine state, graphene is a gapless semiconductor, what limits its use in transistor electronics. In part due to the revolution created by graphene in materials science, there is a renewed interest in other possible graphene-like two-dimensional structures. Examples of these structures are graphynes and graphdiynes, which are two-dimensional structures, composed of carbon atoms in sp2 and sp-hybridized states. Graphdiynes (benzenoid rings connecting two acetylenic groups) were recently synthesized and some of them are intrinsically nonzero gap systems. These systems can be easily hydrogenated and the relative level of hydrogenation can be used to tune the band gap values. We have investigated, using fully reactive molecular dynamics (ReaxFF), the structural and dynamics aspects of the hydrogenation mechanisms of graphdiyne membranes. Our results showed that the hydrogen bindings have different atom incorporation rates and that the hydrogenation patterns change in time in a very complex way. The formation of correlated domains reported to hydrogenated graphene is no longer observed in graphdiyne cases.Comment: Submitted to Carbo

Quantum theory of spectral diffusion induced electron spin decoherence

A quantum cluster expansion method is developed for the problem of localized electron spin decoherence due to dipolar fluctuations of lattice nuclear spins. At the lowest order it provides a microscopic explanation for the Lorentzian diffusion of Hahn echoes without resorting to any phenomenological Markovian assumption. Our numerical results show remarkable agreement with recent electron spin echo experiments in phosphorus doped silicon.Comment: 5 pages, 1 figur

Chaos and Synchronized Chaos in an Earthquake Model

We show that chaos is present in the symmetric two-block Burridge-Knopoff model for earthquakes. This is in contrast with previous numerical studies, but in agreement with experimental results. In this system, we have found a rich dynamical behavior with an unusual route to chaos. In the three-block system, we see the appearance of synchronized chaos, showing that this concept can have potential applications in the field of seismology.Comment: To appear in Physical Review Letters (13 pages, 6 figures

The multidimensional role of social entrepreneurship: A case study approach within an international project context

Social entrepreneurship creates social value and has a multidimensional impact (e.g. economic, environmental, cultural). This is related to the complexity and multidimensional approaches to current societal problems such as climatic changes and socioeconomic crises. The paper explores this multidimensionality by presenting three Portuguese case studies of social entrepreneurship operating in diverse domains. The study is based on primary and secondary data on the selected social enterprises. The analysis explores the motivations and constraints in forming a social enterprise and the impact of entrepreneurial activity. There is evidence of multiple roles played by these entrepreneurial agents, and, therefore, their critical role in the response to the problems that current societies face.info:eu-repo/semantics/publishedVersio

Efeito do aumento de CO2 e de estresses abióticos em milho e sorgo.

O aumento da concentração do CO2 atmosférico deverá ter um impacto nas plantas cultivadas, especialmente quando este for combinado com estresses abióticos. Apesar de plantas C4, como o milho e sorgo, sofrerem um menor impacto na presença de elevado CO2 atmosférico é importante conhecer as alterações que podem ocorrer no metabolismo das plantas, uma vez que essas têm se mostrado benéficas no sentido de manter ou aumentar a produtividade das espécies estudas até o momento. Esta publicação tem como objetivo informar sobre o cenário atual do aumento da concentração de CO2 atmosférico, bem como o efeito desse aumento nas plantas e sua interação com alguns estresses abióticos, como a seca e o uso de nitrogênio em milho e sorgobitstream/item/51819/1/doc-121.pd

Concentração e qualidade de DNA's de açaizeiro tipo branco (Euterpe oleracea mart.) obtidos da Embrapa Amazônia Oriental.

O açaizeiro (Euterpe oleracea Mart.) é uma palmeira perene, tropical e frutífera cujo habitat natural se encontra nas várzeas da Amazônia, onde o Pará vincula como principal produtor e consumidor. Destaca-se mundialmente pela polpa congelada e diversos subprodutos. Essa palmeira é constituída por algumas variedades que diferem especialmente, pelo tamanho e coloração dos frutos, dentre elas tem-se o açaí branco que vem sendo objeto de vários estudos nas instituições da Amazônia. Objetivou-se determinar a concentração e a qualidade de DNA?s de açaizeiros tipo branco obtidos na Embrapa Amazônia Oriental. Foram coletados folíolos de folhas de 222 plantas de açaí tipo branco conservado no Banco Ativo de Germoplasma da Embrapa Amazônia Oriental. A extração de DNA foi feita pelo método de CTAB (Brometo de Cetil Trimetilamônio) utilizando o protocolo de Doyle e Doyle com modificações. Os DNA?s foram quantificados em gel de agarose a 0,8% com o auxílio de três concentrações de DNA lambda (50, 100 e 200 ng/ul) como padrão e as imagens obtidas foram capturadas e lidas no software Labimage. As concentrações foram analisadas por estatísticas descritivas. As 222 amostras de DNA apresentaram 100% de aproveitamento, mas os pellets obtidos apresentaram tamanhos distintos e foram diluídos em volumes distintos, variando entre 50 a 250µl. As quantidades dos DNA?s obtidos variaram de 101,37 a 620,27 ng.μl -1 apresentando média de 269,39 ng.μl -1. As bandas obtidas apresentaram arrastes e presença de RNA, sendo submetidas a tratamentos para melhoria das qualidades. Portanto, pode-se considerar que os DNA?s de açaizeiro tipo branco obtidos possuem excelentes concentrações e qualidades.VII ENAAg

Opacity of graphene independent of light frequency and polarization due to the topological charge of the Dirac points

The opacity of graphene is known to be approximately given by the fine-structure constant $\alpha$ times $\pi$. We point out the fact that the opacity is roughly independent of the frequency and polarization of the light can be attributed to the topological charge of the Dirac points. As a result, one can literally see the topological charge by naked eyes from the opacity of graphene, and moreover it implies that the fine-structure constant is topologically protected. A similar analysis suggests that 3D topological insulator thin films of any thickness also have opacity $\pi\alpha$ in the infrared region owing to the topological surface states, indicating that one can see the surface states by naked eyes through an infrared lens. For 3D Dirac or Weyl semimetals, the optical absorption power is linear to the frequency in the infrared region, with a linearity given by the fine-structure constant and the topological charge of Weyl points.Comment: 9 pages, 3 figure