Microscopic Theory of Damon-Eshbach Modes in Ferromagnetic Films

The surface spin wave branches in ferromagnetic films are studied using a microscopic theory which considers both magnetic dipole-dipole and Heisenberg exchange interactions. The dipole terms are expressed in a Hamiltonian formalism, and the dipole sums are calculated in a rapidly convergent form. The Damon-Eshbach surface modes are analyzed for different directions of the spin-wave propagation and also for different ratios of the strength of the dipole interactions relative to the exchange interactions. Numerical results are presented using parameters for Fe and GdCl$_3$.Comment: 9 pages including figures, Revtex, to appear in the proceedings of the ICM 200

Brazilian elections: voting for a scaling democracy

The proportional elections held in Brazil in 1998 and 2002 display identical statistical signatures. In particular, the distribution of votes among candidates includes a power-law regimen. We suggest that the rationale behind this robust scaling invariance is a multiplicative process in which the voter's choice for a candidate is governed by a product of probabilities.Comment: 4 pages, 2 figure

Electronic oscillations in paired polyacetylene chains

An interacting pair of polyacetylene chains are initially modeled as a couple of undimerized polymers described by a Hamiltonian based on the tight-binding model representing the electronic behavior along the linear chain, plus a Dirac's potential double well representing the interaction between the chains. A theoretical field formalism is employed, and we find that the system exhibits a gap in its energy band due to the presence of a mass-matrix term in the Dirac's Lagrangian that describes the system. The Peierls instability is introduced in the chains by coupling a scalar field to the fermions of the theory via spontaneous symmetry breaking, to obtain a kink-like soliton, which separates two vacuum regions, i.e., two spacial configurations (enantiomers) of the each molecule. Since that mass-matrix and the pseudo-spin operator do not commute in the same quantum representation, we demonstrate that there is a particle oscillation phenomenon with a periodicity equivalent to the Bloch oscillations.Comment: 4 pages, 1 figure.to appear in Solid State Communication

SWINE WASTE PHYTOREMEDIATION USING DUCKWEED (Landoltia punctata, Les & Crawford) IN A FULL SCALE PLANT

Banner Apresentado em Congresso: 11th International Conference, Heraklion, Crete, Greece PhytotechnologiesThe large amount of nitrogen and phosphorous compounds found in pig manure has caused ecological imbalances, with eutrophication of major river basins in the producing regions. Therefore, the aquatic macrophytes group named duckweeds (Araceae; Lemnoideae) have been successfully used for phytoextraction and rhizodegradation of nutrient and heavy metals from swine waste, generating further a biomass with high protein content. The present study evaluated the phytoremediation of nitrogen and phosphorus from swine waste using the duckweed Landoltia punctata and also their protein biomass production as by-product