Ab initio studies of thermodynamic and electronic properties of phosphorene nanoribbons

We present a density functional theory study of the thermodynamic and electronic properties of phosphorene nanoribbons. We consider a variety of terminations and reconstructions of ribbon edges, both with and without hydrogen passivation, and calculate an ab intio phase diagram that identifies energetically preferred edges as a function of temperature and hydrogen partial pressure. These studies are also accompanied by detailed electronic structure calculations from which we find that ribbons with hydrogenated edges are typically direct gap semiconductors with fundamental gaps that are in excess of phosphorene, the gaps varying inversely with ribbon width. In contrast, ribbons with bare or partially passivated edges either have metallic edges or are semiconducting with band gaps that are smaller than those of their hydrogenated counterparts due to the appearance of midgap edge states. Overall, our studies provide a basis for tailoring the electronic properties of phosphorene nanoribbons by controlling the edge termination via processing conditions (temperature and hydrogen partial pressure) as well as by confinement of carriers via control over ribbon width

Opening and tuning of band gap by the formation of diamond superlattices in twisted bilayer graphene

We report results of first-principles density functional theory calculations, which introduce a new class of carbon nanostructures formed due to creation of covalent interlayer C-C bonds in twisted bilayer graphene (TBG). This interlayer bonding becomes possible by hydrogenation of the graphene layers according to certain hydrogenation patterns. The resulting relaxed configurations consist of two-dimensional (2D) superlattices of diamondlike nanocrystals embedded within the graphene layers, with the same periodicity as that of the Moiré pattern corresponding to the rotational layer stacking in TBG. The 2D diamond nanodomains resemble the cubic or the hexagonal diamond phase. The detailed structure of these superlattice configurations is determined by parameters that include the twist angle, ranging from 0° to ∼15°, and the number of interlayer C-C bonds formed per unit cell of the superlattice. We demonstrate that formation of such interlayer-bonded finite domains causes the opening of a band gap in the electronic band structure of TBG, which depends on the density and spatial distribution of interlayer C-C bonds. We have predicted band gaps as wide as 1.2 eV and found that the band gap increases monotonically with increasing size of the embedded diamond nanodomain in the unit cell of the superlattice. Such nanostructure formation constitutes a promising approach for opening a precisely tunable band gap in bilayer graphene

Ab initio studies of thermodynamic and electronic properties of phosphorene nanoribbons

We present a density functional theory study of the thermodynamic and electronic properties of phosphorene nanoribbons. We consider a variety of terminations and reconstructions of ribbon edges, both with and without hydrogen passivation, and calculate an ab intio phase diagram that identifies energetically preferred edges as a function of temperature and hydrogen partial pressure. These studies are also accompanied by detailed electronic structure calculations from which we find that ribbons with hydrogenated edges are typically direct gap semiconductors with fundamental gaps that are in excess of phosphorene, the gaps varying inversely with ribbon width. In contrast, ribbons with bare or partially passivated edges either have metallic edges or are semiconducting with band gaps that are smaller than those of their hydrogenated counterparts due to the appearance of midgap edge states. Overall, our studies provide a basis for tailoring the electronic properties of phosphorene nanoribbons by controlling the edge termination via processing conditions (temperature and hydrogen partial pressure) as well as by confinement of carriers via control over ribbon width

Evaluation of biomass and coal co-gasification of brazilian feedstock using a chemical equilibrium model

Coal and biomass are energy sources with great potential for use in Brazil. Coal-biomass cogasification enables the combination of the positive characteristics of each fuel, besides leading to a cleaner use of coal. The present study evaluates the potential of co-gasification of binary coal-biomass blends using sources widely available in Brazil. This analysis employs computational simulations using a reliable thermodynamic equilibrium model. Favorable operational conditions at high temperatures are determined in order to obtain gaseous products suitable for energy cogeneration and chemical synthesis. This study shows that blends with biomass ratios of 5% and equivalence ratios ≤ 0.3 lead to high cold gas efficiencies. Suitable gaseous products for chemical synthesis were identified at biomass ratios ≤ 35% and moisture contents ≥ 40%. Formation of undesirable nitrogen and sulfur compounds was also analyzed

Tuning the band structure of graphene nanoribbons through defect-interaction-driven edge patterning

We report a systematic analysis of pore-edge interactions in graphene nanoribbons (GNRs) and their outcomes based on first-principles calculations and classical molecular-dynamics simulations. We find a strong attractive interaction between nanopores and GNR edges that drives the pores to migrate toward and coalesce with the GNR edges, which can be exploited to form GNR edge patterns that impact the GNR electronic band structure and tune the GNR band gap. Our analysis introduces a viable physical processing strategy for modifying GNR properties by combining defect engineering and thermal annealing

Análise comparativa de agitadores para um reator de polimerização em fase gás usando CFD

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Peering into the formation of template-free hierarchical flowerlike nanostructures of SrTiO3

The development of efficient advanced functional materials is highly dependent on properties such as morphology, crystallinity, and surface functionality. In this work, hierarchical flowerlike nanostructures of SrTiO3 have been synthesized by a simple template-free solvothermal method involving poly(vinylpyrrolidone) (PVP). Molecular dynamics simulations supported by structural characterization have shown that PVP preferentially adsorbs on {110} facets, thereby promoting the {100} facet growth. This interaction results in the formation of hierarchical flowerlike nanostructures with assembled nanosheets. The petal morphology is strongly dependent on the presence of PVP, and the piling up of nanosheets, leading to nanocubes, is observed when PVP is removed at high temperatures. This work contributes to a better understanding of how to control the morphological properties of SrTiO3, which is fundamental to the synthesis of perovskite-type materials with tailored properties

Orientações para Realização de Exames de Ressonância Magnética Nuclear em Pacientes com Dispositivos Eletrônicos Cardíacos

Estima-se que até 75% dos pacientes com dispositivos cardíacos eletrônicos implantáveis (DCEIs) terão indicação de exame de ressonância nuclear magnética (RNM) ao longo da vida. Pelas características dos dispositivos, esses foram excluídos historicamente do rol de pacientes considerados elegíveis ao exame

A list of land plants of Parque Nacional do Caparaó, Brazil, highlights the presence of sampling gaps within this protected area

Brazilian protected areas are essential for plant conservation in the Atlantic Forest domain, one of the 36 global biodiversity hotspots. A major challenge for improving conservation actions is to know the plant richness, protected by these areas. Online databases offer an accessible way to build plant species lists and to provide relevant information about biodiversity. A list of land plants of “Parque Nacional do Caparaó” (PNC) was previously built using online databases and published on the website "Catálogo de Plantas das Unidades de Conservação do Brasil." Here, we provide and discuss additional information about plant species richness, endemism and conservation in the PNC that could not be included in the List. We documented 1,791 species of land plants as occurring in PNC, of which 63 are cited as threatened (CR, EN or VU) by the Brazilian National Red List, seven as data deficient (DD) and five as priorities for conservation. Fifity-one species were possible new ocurrences for ES and MG states

Associação entre a ooforectomia bilateral precoce e o desenvolvimento do parkinsonismo e Doença de Parkinson em mulheres na pré-menopausa

O parkinsonismo é um distúrbio do sistema nervoso de maior incidência masculina do que feminina, visto que, por mecanismos fisiológicos, o estrogênio possui efeitos neuroprotetores, com funções como aumento da dopamina, um neurotransmissor essencial para o controle das funções motoras. Além disso, previne a formação dos corpúsculos de Lewy e da agregação da α-sinucleína, responsáveis pela progressão da Doença de Parkinson. Por isso, a doença se apresenta diferentemente nas mulheres. A remoção cirúrgica de ambos os ovários em mulheres na pré-menopausa para a prevenção do câncer de ovário parece favorecer o surgimento da doença, tendo em vista a perda da produção do hormônio protetor. Assim, o objetivo do estudo é analisar a associação entre a ooforectomia bilateral precoce e o desenvolvimento de parkinsonismo e Doença de Parkinson em mulheres na pré-menopausa. Trata-se de uma revisão bibliográfica sistemática, do tipo quantitativa, que utilizou as plataformas do PubMed, SciELO e Cochrane Library como bases de dados para seleção dos artigos, todos na língua inglesa. Foram utilizadas literaturas publicadas com recorte temporal de 2017 a 2022. De acordo com as literaturas analisadas, a ooforectomia bilateral precoce em mulheres na pré-menopausa aumenta o risco do desenvolvimento de parkinsonismo. Desse modo, a diminuição dos procedimentos cirúrgicos profiláticos para câncer de ovário nas pacientes com risco médio de malignidade reduziria o risco dessa condição