Transport Properties through Double Barrier Structure in Graphene

The mode-dependent transmission of relativistic ballistic massless Dirac fermion through a graphene based double barrier structure is being investigated for various barrier parameters. We compare our results with already published work and point out the relevance of these findings to a systematic study of the transport properties in double barrier structures. An interesting situation arises when we set the potential in the leads to zero, then our 2D problem reduces effectively to a 1D massive Dirac equation with an effective mass proportional to the quantized wave number along the transverse direction. Furthermore we have shown that the minimal conductivity and maximal Fano factor remain insensitive to the ratio between the two potentials V_2/V_1=\alpha.Comment: 18 pages, 12 figures, clarifications and reference added, misprints corrected. Version to appear in JLT

Interplay between edge states and simple bulk defects in graphene nanoribbons

We study the interplay between the edge states and a single impurity in a zigzag graphene nanoribbon. We use tight-binding exact diagonalization techniques, as well as density functional theory calculations to obtain the eigenvalue spectrum, the eigenfunctions, as well the dependence of the local density of states (LDOS) on energy and position. We note that roughly half of the unperturbed eigenstates in the spectrum of the finite-size ribbon hybridize with the impurity state, and the corresponding eigenvalues are shifted with respect to their unperturbed values. The maximum shift and hybridization occur for a state whose energy is inverse proportional to the impurity potential; this energy is that of the impurity peak in the DOS spectrum. We find that the interference between the impurity and the edge gives rise to peculiar modifications of the LDOS of the nanoribbon, in particular to oscillations of the edge LDOS. These effects depend on the size of the system, and decay with the distance between the edge and the impurity.Comment: 10 pages, 15 figures, revtex

Physiological quality of soybean and wheat seeds produced with alternative potassium sources

O uso de fontes não convencionais para fornecimento de K às plantas tem sido amplamente estudado, mas os efeitos de materiais alternativos na qualidade fisiológica das sementes não são conhecidos. Este estudo teve como objetivo avaliar a qualidade fisiológica de sementes de soja e trigo em função da aplicação fontes de potássio em uma sucessão de culturas. O delineamento experimental foi o de blocos ao acaso com quatro repetições. Os tratamentos constaram de três fontes de K (KCl, rocha alcalina e fonolito moído, com 58%, 11% e 8.42% de K2O, respectivamente) aplicados em quatro doses (0, 25, 50 e 100 kg K2O ha-1). As doses de potássio foram aplicadas na soja e seu efeito residual foi avaliado na cultura do trigo, cultivado em sucessão. Logo após a colheita, as sementes de soja e trigo foram avaliadas pelos testes de teor de água, massa de sementes, germinação, primeira contagem, condutividade elétrica, comprimento de plântulas e massa da matéria seca de plântulas. Plantas de soja adubadas com fontes alternativas para fornecimento de K produzem sementes com maior massa e menor permeabilidade de membranas comparado às com KCl; maior qualidade fisiológica de sementes de soja e massa de sementes de trigo são obtidas com maiores doses de K2O independente da fonte.The use of unconventional sources of K for plants has been widely studied, but the effects of alternative materials on physiological seed quality are still relatively unknown. The objective of this study was to evaluate the physiological quality of soybean and wheat seeds after using different potassium sources in a crop succession. The experimental design was a completely randomized block with four replications. Treatments consisted of three K sources (KCl, alkaline rock and ground phonolite, with 58%, 11% and 8.42% of K2O, respectively) applied in four doses (0, 25, 50 and 100 kg K2O ha-1). Potassium doses were applied in soybean and their residual effects were evaluated on the following wheat crop. Soybean and wheat seeds were evaluated immediately after harvesting by tests for moisture content, seed weight, germination, first count, electrical conductivity, seedling length and seedling dry matter. Soybean plants fertilized with alternative sources of K produced heavier seeds with a lower coat permeability compared to KCl; the physiological quality of soybean seeds and the weight of wheat seeds increase due to higher K2O doses, independently of their source.UNESP FCA Department of Plant Production/AgricultureUNESP FCA Department of Plant Production/Agricultur