Pecuária versus diversificação da produção nos projetos de assentamentos no Sudeste Paraense.

bitstream/item/28085/1/com.tec.97.pd

Gapless Excitation above a Domain Wall Ground State in a Flat Band Hubbard Model

We construct a set of exact ground states with a localized ferromagnetic domain wall and with an extended spiral structure in a deformed flat-band Hubbard model in arbitrary dimensions. We show the uniqueness of the ground state for the half-filled lowest band in a fixed magnetization subspace. The ground states with these structures are degenerate with all-spin-up or all-spin-down states under the open boundary condition. We represent a spin one-point function in terms of local electron number density, and find the domain wall structure in our model. We show the existence of gapless excitations above a domain wall ground state in dimensions higher than one. On the other hand, under the periodic boundary condition, the ground state is the all-spin-up or all-spin-down state. We show that the spin-wave excitation above the all-spin-up or -down state has an energy gap because of the anisotropy.Comment: 26 pages, 1 figure. Typos are fixe

Fertirrigação na cultura da bananeira no Sudeste Paraense.

bitstream/item/63611/1/Oriental-Doc183.PD

Stoner gap in the superconducting ferromagnet UGe2

We report the temperature ($T$) dependence of ferromagnetic Bragg peak intensities and dc magnetization of the superconducting ferromagnet UGe2 under pressure ($P$). We have found that the low-$T$ behavior of the uniform magnetization can be explained by a conventional Stoner model. A functional analysis of the data produces the following results: The ferromagnetic state below a critical pressure can be understood as the perfectly polarized state, in which heavy quasiparticles occupy only majority spin bands. A Stoner gap $\Delta(P)$ decreases monotonically with increasing pressure and increases linearly with magnetic field. We show that the present analysis based on the Stoner model is justified by a consistency check, i.e., comparison of density of states at the Fermi energy deduced from the analysis with observed electronic specific heat coeffieients. We also argue the influence of the ferromagnetism on the superconductivity.Comment: 5 pages, 4 figures. to be published in Phys. Rev.

O método de parcagem como alternativa agroecológica para a integração agricultura/pecuária da produção familiar do sudeste paraense.

bitstream/item/19059/1/Doc-220.pdfDisponível também 0n-line

On rationality of the intersection points of a line with a plane quartic

We study the rationality of the intersection points of certain lines and smooth plane quartics C defined over F_q. For q \geq 127, we prove the existence of a line such that the intersection points with C are all rational. Using another approach, we further prove the existence of a tangent line with the same property as soon as the characteristic of F_q is different from 2 and q \geq 66^2+1. Finally, we study the probability of the existence of a rational flex on C and exhibit a curious behavior when the characteristic of F_q is equal to 3.Comment: 17 pages. Theorem 2 now includes the characteristic 2 case; Conjecture 1 from the previous version is proved wron

Quantifying the GCM-related uncertainty for climate change impact assessment of rainfed rice production in Cambodia by a combined hydrologic - rice growth model

The effects of climate change on agriculture are a major concern for global food security. In this study, the impacts of climate change on rainfed rice production in the granary of Cambodia were examined on a basin scale by developing and applying a combined model consisting of a crop model and a basin-scale distributed hydrological model. The response of rice production to soil-water availability was simulated for past (1981–2000) and future (2041–2060, 2081–2100) periods. From 34 general circulation models (GCMs) that participated in the Coupled Model Intercomparison Project Phase 5 (CMIP5), 5 GCMs were selected by evaluating monthly rainfall in the past. Although annual rainfall was projected to increase by all five selected GCMs, notable decreases in rainfed rice production were projected with 3 GCMs, while small changes were projected with the other 2 GCMs. The main factor restricting future rice production was soil water availability, brought by the projected change in the seasonal distribution of rainfall and the projected more severe dry spells in the early monsoon season. The results suggest the importance of the selection and bias correction of GCMs to force rice crop models and of the simulation of soil water flow on a basin scale for the assessment of rain-fed rice production. In particular, improvements in projections of rainfall amounts over shorter periods rather than annual or seasonal periods, which fit within the time scales of rice plant growth, were suggested to be important

Polymers in Curved Boxes

We apply results derived in other contexts for the spectrum of the Laplace operator in curved geometries to the study of an ideal polymer chain confined to a spherical annulus in arbitrary space dimension D and conclude that the free energy compared to its value for an uncurved box of the same thickness and volume, is lower when $D < 3$, stays the same when $D = 3$, and is higher when \mbox{$D > 3$}. Thus confining an ideal polymer chain to a cylindrical shell, lowers the effective bending elasticity of the walls, and might induce spontaneous symmetry breaking, i.e. bending. (Actually, the above mentioned results show that {\em {any}} shell in $D = 3$ induces this effect, except for a spherical shell). We compute the contribution of this effect to the bending rigidities in the Helfrich free energy expression.Comment: 20 pages RevTeX, epsf; 4 figures; submitted to Macromoledule

Processing conditions for (Nd, Eu, Gd)-Ba-Cu-O ternary bulk superconductors

Abstract(Nd, Eu, Gd)-Ba-Cu-O ternary bulk superconductors have high potential for practical applications since they exhibit very high critical current densities and thus high field trapping capabilities. (Nd, Eu, Gd)-Ba-Cu-O superconductors are synthesized in a reduced oxygen atmosphere, which requires a control of oxygen partial pressure and needs a special device for hot seeding. In the present study, for simplicity, we employed Ar gas flow into the furnace to control oxygen partial pressure instead of flowing oxygen-controlled gas. Hence, it was necessary to modify the melt processing conditions to produce a single domain. Through the optimization of seeding temperature and cooling rate, we obtained the processing conditions, in which a single domain bulk (Nd, Eu, Gd)-Ba-Cu-O of 20mm diameter could be synthesized