15,584 research outputs found
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 times . 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 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
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