Quenched disorder and spin-glass correlations in XY nematics

We present a theoretical study of the equilibrium ordering in a 3D XY nematic system with quenched random disorder. Within this model, treated with the replica trick and Gaussian variational method, the correlation length is obtained as a function of the local nematic order parameter and the effective disorder strength. These results clarify what happens in the limiting cases of diminishing order parameter and disorder strength, that is near a phase transition of a pure system. In particular, it is found that quenched disorder is irrelevant as the order parameter tends to zero and hence does not change the character of the continuous XY nematic to isotropic phase transition. We discuss how these results compare with experiments and simulationsComment: 19 pages, 6 figures, corrected typo

Sistema integrado de produção agroecológica: uma experiência de pesquisa em agricultura orgânica.

O sistema integrado de produção agroecológica (SIPA). Alguns resultados de pesquisa no SIPA.bitstream/item/111699/1/CNPAB-Sistema-Integrado-de-Producao-Agroecologica-SIPA-DOC.-169-03.pd

Replica Symmetry Breaking in the Random Replicant Model

We study the statistical mechanics of a model describing the coevolution of species interacting in a random way. We find that at high competition replica symmetry is broken. We solve the model in the approximation of one step replica symmetry breaking and we compare our findings with accurate numerical simulations.Comment: 12 pages, TeX, 5 postscript figures are avalaible upon request, submitted to Journal of Physics A: Mathematical and Genera

Soja: desenvolvimento e selecao de germoplasma para regiões de baixas latitudes.

A soja no Piaui; Cultivar Tropical; Cultivar Timbira; Cultivar BR-10 (Teresina); BR-11 (Carajas); Cultivar BR 27 (Cariri); Cultivar BR-29 (Serido); Cultivar BR-32 (Nova Tropical); Cultivar BR/EMGOPA 312 (Potiguar); Cultivar BR-35 (Rio Balsas); Cultivar Embrapa 9 (Bays);Cultivar Embrapa 10 (Vale do Rio Doce); Cultivar Embrapa 31 (Mina); Cultivar 33 (Cariri RC); Cultivar Embrapa 34 (Teresina RC); Cultivar Embrapa 63 (Mirador); Cultivar MA/BR 64 (Parnaiba); Cultivar MA/BR 65 (Sambaiba); Cultivar MA/BRS 165 (Serudo RCH).bitstream/item/35895/1/Doc37.pd

Benefícios da adubação verde sobre a simbiose micorrízica e a produtividade de batata-doce.

Plantio das leguminosas e da batata doce. Produtividade da batata doce e simbiose micorrízica.bitstream/CNPAB-2010/27139/1/cot014.pd

Tetragonal tungsten bronze compounds: relaxor vs mixed ferroelectric - dipole glass behavior

We demonstrate that recent experimental data (E. Castel et al J.Phys. Cond. Mat. {\bf 21} (2009), 452201) on tungsten bronze compound (TBC) Ba$_2$Pr$_x$Nd$_{1-x}$FeNb$_4$O$_{15}$ can be well explained in our model predicting a crossover from ferroelectric ($x=0$) to orientational (dipole) glass ($x=1$), rather then relaxor, behavior. We show, that since a "classical" perovskite relaxor like Pb(Mn$_{1/3}$ Nb$_{2/3}$)O$_3$ is never a ferroelectric, the presence of ferroelectric hysteresis loops in TBC shows that this substance actually transits from ferroelectric to orientational glass phase with $x$ growth. To describe the above crossover theoretically, we use the simple replica-symmetric solution for disordered Ising model.Comment: 5 two-column pages, 4 figure

Características agronômicas e morfológicas das cultivares de soja desenvolvidas para as regiões de baixas latitudes.

Disponível via Word Wide Web. http: www.cpatsa.embrapa.b