First-principles study of the effect of charge on the stability of a diamond nanocluster surface

Effects of net charge on the stability of the diamond nanocluster are investigated using the first-principles pseudopotential method with the local density approximation. We find that the charged nanocluster favors the diamond phase over the reconstruction into a fullerene-like structure. Occupying the dangling bond orbitals in the outermost surface, the excess charge can stabilize the bare diamond surface and destabilize the C-H bond on the hydrogenated surface. In combination with recent experimental results, our calculations suggest that negative charging could promote the nucleation and further growth of low-pressure diamond.open8

Análise histoquímica foliar do amendoim: genótipos 'Tatu' e SO-909 Leaf histochemical analyses of peanut: genotypes 'Tatu' and SO-909

Este trabalho teve por finalidade a análise histoquímica foliar de dois genótipos de amendoim (Arachis hypogaea L.), do tipo botânico Valência: SO-53 ('Tatu') e SO-909 (PI-259747), cuja literatura demonstra apresentarem respostas diferentes de resistência às principais moléstias fúngicas foliares do Brasil. Seções transversais das seguintes estruturas - pulvino, haste peciolar, raque, pulvínulo e folíolo - e seções paradérmicas de folíolos coletados em dois anos agrícolas consecutivos, foram analisadas quanto à presença de alcalóides, amido, calose, celulose pura, celulose com pectina, cera, cristais, cutina, lignina, mucilagem, óleo, resina, tanino e ureídeos (micrograma) por folíolo (grama). As diferenças qualitativas histoquímicas observadas nos diversos tecidos, como a freqüência de tanino, alcalóide, pectina e óleo, supostamente, podem ser responsáveis pela resistência ou suscetibilidade dos genótipos às moléstias fúngicas foliares. Para fins de caracterização, mostrou-se eficiente a avaliação de pureza de celulose.<br>Leaf histochemical analyses were made in two genotypes of Arachis hypogaea L., of the Valencia group, which present different responses to some of the peanut foliar diseases. The analyses were performed on cross sections of the pulvini, petiole, rachis, pulvinulus and leaflets. The following constituents were observed: alkaloids, callose, cellulose with pectin, cristal, cutin, lignin, mucilage, oil, pure cellulose, resin, starch, tannin, wax and weight of ureides by leaflets. Some histochemical characteristics such the amount of tannin, alkaloids, pectin and oil can be produce different responses of peanut to foliar fungal diseases, and can be used in the characterization of peanut genotypes like the amount of pure cellulose and cellulose with pectin