Raman-scattering study of the phonon dispersion in twisted bi-layer graphene

Bi-layer graphene with a twist angle \theta\ between the layers generates a superlattice structure known as Moir\'{e} pattern. This superlattice provides a \theta-dependent q wavevector that activates phonons in the interior of the Brillouin zone. Here we show that this superlattice-induced Raman scattering can be used to probe the phonon dispersion in twisted bi-layer graphene (tBLG). The effect reported here is different from the broadly studied double-resonance in graphene-related materials in many aspects, and despite the absence of stacking order in tBLG, layer breathing vibrations (namely ZO' phonons) are observed.Comment: 18 pages, 4 figures, research articl

Biological and Health-promoting Activity of Vinification Byproducts Produced in Spanish Vineyards

Several by-products are produced in the Spanish agricultural system. Among them, fresh and vinifiedgrape skins represent an abundant source of phenols with a potential nutraceutical value. Fresh grape skinextracts (FGSE) and vinification of grape skin extracts (VGSE) obtained by a microwave-assisted methodhave been chemically and biologically characterised. Their role in the maintenance of genetic stabilitywas stated by in vivo genotoxic and antigenotoxic evaluations (Drosophilla melanogaster wing spot test), aswell as by their potential chemopreventive effect (in an HL60 in vitro model). Total phenolic, anthocyaninand resveratrol contents were chemically characterised in the two extracts, showing some qualitativedifferences. Both extracts and resveratrol were not mutagenic in the Drosophila somatic mutation andrecombination tests, and exerted antigenotoxic activities against hydrogen peroxide. They also showedcytotoxic activity to HL60 leukaemia cells, with an IC50 of 4.5μL/mL, 4.6μL/mL and 98μM respectively andinduced apoptotic internucleosomic fragmentation in the HL60 cell line

Facile Synthesis of High Quality Graphene Nanoribbons

Graphene nanoribbons have attracted attention for their novel electronic and spin transport properties1-6, and because nanoribbons less than 10 nm wide have a band gap that can be used to make field effect transistors. However, producing nanoribbons of very high quality, or in high volumes, remains a challenge. Here, we show that pristine few-layer nanoribbons can be produced by unzipping mildly gas-phase oxidized multiwalled carbon nanotube using mechanical sonication in an organic solvent. The nanoribbons exhibit very high quality, with smooth edges (as seen by high-resolution transmission electron microscopy), low ratios of disorder to graphitic Raman bands, and the highest electrical conductance and mobility reported to date (up to 5e2/h and 1500 cm2/Vs for ribbons 10-20 nm in width). Further, at low temperature, the nanoribbons exhibit phase coherent transport and Fabry-Perot interference, suggesting minimal defects and edge roughness. The yield of nanoribbons was ~2% of the starting raw nanotube soot material, which was significantly higher than previous methods capable of producing high quality narrow nanoribbons1. The relatively high yield synthesis of pristine graphene nanoribbons will make these materials easily accessible for a wide range of fundamental and practical applications.Comment: Nature Nanotechnology in pres

Avaliação da silagem do híbrido de sorgo BR 601 com aditivos: alterações nos teores de matéria seca, frações fibrosas e digestibilidade "in vitro" da matéria seca.

Avaliou-se o padrão de fermentação de silagens do híbrido de sorgo forrageiro BR 601 com ou sem aditivos. Foram adotados os tratamentos: silagem sem aditivo (testemunha) e silagens adicionadas com 0,5% de uréia, 0,5% de carbonato de cálcio, 0,5% de uréia mais 0,5% de carbonato de cálcio e com inoculante bacteriano. Os materiais foram ensilados em silos de “PVC” e abertos com um, três, cinco, sete, 14, 28 e 56 dias de ensilagem. Determinaram-se as variações nos teores de matéria seca (MS), os teores de fibra em detergente neutro (FDN), hemicelulose, celulose, fibra em detergente ácido (FDA), lignina e a digestibilidade “in vitro” da MS (DIVMS). Adotou-se o delineamento inteiramente casualizado, em um esquema fatorial 5 x 7, sendo as médias comparadas pelo teste SNK a 5%. As silagens tratadas com a associação entre uréia e carbonato de cálcio apresentaram as maiores perdas de MS. Os aditivos não promoveram alterações nos teores de FDN, hemicelulose e celulose e na DIVMS. Ocorreu diferença entre a silagem testemunha e as silagens com aditivo, com a evolução do processo fermentativo, quanto aos teores de FDA e lignina

The metallicities of UM151, UM408 and A1228+12 revisited

We present the results of new spectrophotometry and heavy element abundance determinations for 3 dwarf galaxies UM151, UM408 and A1228+12 (RMB132). These galaxies have been claimed in the literature to have very low metallicities, corresponding to log(O/H)+12 < 7.65, that are in the metallicity range of some candidate local young galaxies. We present higher S/N data for these three galaxies. UM151 and UM408 have significantly larger metallicities: log(O/H)+12 = 8.5 and 7.93, respectively. For A1228+12 our new log(O/H)+12 = 7.73 is close to that recalculated from earlier data (7.68). Thus, the rederived metallicities allow us to remove these objects from the list of galaxies with Z < 1/20 Z_Sun.Comment: LaTeX, 8 pages with 3 Postscript figures, A&A in pres

Anyonic behavior of quantum group gases

We first introduce and discuss the formalism of $SU_q(N)$-bosons and fermions and consider the simplest Hamiltonian involving these operators. We then calculate the grand partition function for these models and study the high temperature (low density) case of the corresponding gases for $N=2$. We show that quantum group gases exhibit anyonic behavior in $D=2$ and $D=3$ spatial dimensions. In particular, for a $SU_q(2)$ boson gas at $D=2$ the parameter $q$ interpolates within a wider range of attractive and repulsive systems than the anyon statistical parameter.Comment: LaTeX file, 19 pages, two figures ,uses epsf.st

"Narrow" Graphene Nanoribbons Made Easier by Partial Hydrogenation

It is a challenge to synthesize graphene nanoribbons (GNRs) with narrow widths and smooth edges in large scale. Our first principles study on the hydrogenation of GNRs shows that the hydrogenation starts from the edges of GNRs and proceeds gradually toward the middle of the GNRs so as to maximize the number of carbon-carbon $\pi$-$\pi$ bonds. Furthermore, the partially hydrogenated wide GNRs have similar electronic and magnetic properties as those of narrow GNRs. Therefore, it is not necessary to directly produce narrow GNRs for realistic applications because partial hydrogenation could make wide GNRs "narrower"

Optical-phonon resonances with saddle-point excitons in twisted-bilayer graphene

Twisted-bilayer graphene (tBLG) exhibits van Hove singularities in the density of states that can be tuned by changing the twisting angle $\theta$. A $\theta$-defined tBLG has been produced and characterized with optical reflectivity and resonance Raman scattering. The $\theta$-engineered optical response is shown to be consistent with persistent saddle-point excitons. Separate resonances with Stokes and anti-Stokes Raman scattering components can be achieved due to the sharpness of the two-dimensional saddle-point excitons, similar to what has been previously observed for one-dimensional carbon nanotubes. The excitation power dependence for the Stokes and anti-Stokes emissions indicate that the two processes are correlated and that they share the same phonon.Comment: 5 pages, 6 figure

Dados agronômicos de seis genótipos de sorgo (Sorghum bicolor (L.) Moench) para a produção de silagem.

Foram utilizados seis genótipos de sorgo (Sorghum bicolor (L) Moench) de porte alto e colmo seco, colhidos no estádio de grão leitoso/pastoso, com o objetivo de avaliar a altura média das plantas, número de plantas por hectare, proporção panícula/folha/ colmo, dados de produção de matéria verde, matéria seca e matéria seca digestível por hectare. Os híbridos 1 e 2 são as testemunhas comerciais (BRS610 e VOLUMAX, respectivamente), enquanto que os outros quatro são novos materiais desenvolvidos pela EMBRAPA Milho e Sorgo. Utilizou-se o teste SNK para comparação entre médias, com um delineamento experimental inteiramente ao acaso. Houve grande variação no número de plantas por hectare nos genótipos avaliados. Eles não apresentaram diferença estatística na produção de Matéria Verde/hectare. Os híbridos apresentaram correlação positiva entre produção de MS/ha e altura das plantas [r= 0,52 (p= 0,05)]. O híbrido 2 apresentou maior produção de Matéria Seca e Matéria Seca Digestível/ha. Não houve diferença estatística nas proporções de panícula/folha/colmo, com valores que oscilaram de 42,61 a 55,14; 20,75 a 25.73 e 22,85 a 32,75% na MS, respectivamente