A map for heavy inertial particles in fluid flows

We introduce a map which reproduces qualitatively many fundamental properties of the dynamics of heavy particles in fluid flows. These include a uniform rate of decrease of volume in phase space, a slow-manifold effective dynamics when the single parameter $s$ (analogous of the Stokes number) approaches zero, the possibility of fold caustics in the "velocity field", and a minimum, as a function of $s$, of the Lyapunov (Kaplan-Yorke) dimension of the attractor where particles accumulate.Comment: 10 pages, 5 figure

Avaliação da produção e de doenças em genótipos de mandioca em área de várzea do Rio Solimões.

As podridões radiculares em mandioca (Manihot esculenta Grantz) têm ocasionado sérios problemas na produção de mandioca no Estado do Amazonas. Os sintomas manifestam-se em plantas jovens e adultas afetando a região do colo, raiz e haste. O objetivo da pesquisa foi avaliar a produção de raiz e a ocorrência de podridões radiculares em genótipos de mandioca do Banco Ativo de Germoplasma (BAG) na área de várzea do Rio Solimões, do Campo Experimental do Caldeirão, pertencente à Embrapa Amazônia Ocidental. O levantamento da incidência da doença foi por meio da identificação visual na planta e raiz. Foram avaliados 67 genótipos, dos quais 21 se destacaram. Destes, 42,8% permaneceram com as 10 plantas/parcela, enquanto nos demais (57,2%) morreu apenas uma planta. Entre os genótipos que se destacaram, constatou-se que as infecções na planta e raiz foi maior com os fungos Phytophthora drechsleri + Fusarium sp. (42,9%), seguida por P. drechsleri (38,1%) e sadias (19,0%). Os acessos IM-1688; IM-1995; IM-2007 e IM-2042 não apresentaram raiz podre

Influência do período de colheita na produção de raiz e fécula de mandioca (Manihot esculenta Crantz) no Amazonas.

Este trabalho teve como objetivo selecionar cultivares de mandioca com melhor desempenho produtivo, submetidas a duas épocas de colheita em condições de terra firme no Amazonas

A semiquantitative approach to the impurity-band-related transport properties of GaMnAs nanolayers

We investigate the spin-polarized transport of GaMnAs nanolayers in which a ferromagnetic order exists below a certain transition temperature. Our calculation for the self-averaged resistivity takes into account the existence of an impurity band determining the extended ("metallic" transport) or localized (hopping by thermal excitation) nature of the states at and near the Fermi level. Magnetic order and resistivity are inter-related due to the influence of the spin polarization of the impurity band and the effect of the Zeeman splitting on the mobility edge. We obtain, for a given range of Mn concentration and carrier density, a "metallic" behavior in which the transport by extended carriers dominates at low temperature, and is dominated by the thermally excited localized carriers near and above the transition temperature. This gives rise to a conspicuous hump of the resistivity which has been experimentally observed and brings light onto the relationship between transport and magnetic properties of this material

Avaliação da produção e da incidência da podridão radicular em genótipos de mandioca (Manihot esculenta Crantz) cultivados em dois sistemas de preparo de solo.

Este trabalho teve como objetivo avaliar a produção de raízes e a incidência da podridão radicular em sete genótipos cultivados em dois sistemas de preparo de solo

Soil–Atmosphere Exchange of Nitrous Oxide, Nitric Oxide, Methane, and Carbon Dioxide in Logged and Undisturbed Forest in the Tapajos National Forest, Brazil

Selective logging is an extensive land use in the Brazilian Amazon region. The soil–atmosphere fluxes of nitrous oxide (N2O), nitric oxide (NO), methane (CH4), and carbon dioxide (CO2) are studied on two soil types (clay Oxisol and sandy loam Ultisol) over two years (2000–01) in both undisturbed forest and forest recently logged using reduced impact forest management in the Tapajos National Forest, near Santarem, Para, Brazil. In undisturbed forest, annual soil–atmosphere fluxes of N2O (mean ± standard error) were 7.9 ± 0.7 and 7.0 ± 0.6 ng N cm−2 h−1 for the Oxisol and 1.7 ± 0.1 and 1.6 ± 0.3 ng N cm−2 h−1 for the Ultisol for 2000 and 2001, respectively. The annual fluxes of NO from undisturbed forest soil in 2001 were 9.0 ± 2.8 ng N cm−2 h−1 for the Oxisol and 8.8 ± 5.0 ng N cm−2 h−1 for the Ultisol. Consumption of CH4 from the atmosphere dominated over production on undisturbed forest soils. Fluxes averaged −0.3 ± 0.2 and −0.1 ± 0.9 mg CH4 m−2 day−1 on the Oxisol and −1.0 ± 0.2 and −0.9 ± 0.3 mg CH4 m−2 day−1 on the Ultisol for years 2000 and 2001. For CO2 in 2001, the annual fluxes averaged 3.6 ± 0.4 μmol m−2 s−1 on the Oxisol and 4.9 ± 1.1 μmol m−2 s−1 on the Ultisol. We measured fluxes over one year each from two recently logged forests on the Oxisol in 2000 and on the Ultisol in 2001. Sampling in logged areas was stratified from greatest to least ground disturbance covering log decks, skid trails, tree-fall gaps, and forest matrix. Areas of strong soil compaction, especially the skid trails and logging decks, were prone to significantly greater emissions of N2O, NO, and especially CH4. In the case of CH4, estimated annual emissions from decks reached extremely high rates of 531 ± 419 and 98 ± 41 mg CH4 m−2 day−1, for Oxisol and Ultisol sites, respectively, comparable to wetland emissions in the region. We calculated excess fluxes from logged areas by subtraction of a background forest matrix or undisturbed forest flux and adjusted these fluxes for the proportional area of ground disturbance. Our calculations suggest that selective logging increases emissions of N2O and NO from 30% to 350% depending upon conditions. While undisturbed forest was a CH4 sink, logged forest tended to emit methane at moderate rates. Soil–atmosphere CO2 fluxes were only slightly affected by logging. The regional effects of logging cannot be simply extrapolated based upon one site. We studied sites where reduced impact harvest management was used while in typical conventional logging ground damage is twice as great. Even so, our results indicate that for N2O, NO, and CH4, logging disturbance may be as important for regional budgets of these gases as other extensive land-use changes in the Amazon such as the conversion of forest to cattle pasture