Ising Ferromagnet: Zero-Temperature Dynamic Evolution

The dynamic evolution at zero temperature of a uniform Ising ferromagnet on a square lattice is followed by Monte Carlo computer simulations. The system always eventually reaches a final, absorbing state, which sometimes coincides with a ground state (all spins parallel), and sometimes does not (parallel stripes of spins up and down). We initiate here the numerical study of ``Chaotic Time Dependence'' (CTD) by seeing how much information about the final state is predictable from the randomly generated quenched initial state. CTD was originally proposed to explain how nonequilibrium spin glasses could manifest equilibrium pure state structure, but in simpler systems such as homogeneous ferromagnets it is closely related to long-term predictability and our results suggest that CTD might indeed occur in the infinite volume limit.Comment: 14 pages, Latex with 8 EPS figure

Análise matemática e biológica dos modelos de estimativa de perdas de rendimento na cultura devido à interferência de plantas daninhas.

As plantas daninhas acarretam reduções no rendimento das culturas agrícolas. Os modelos matemáticos de estimativa de perda de rendimento na cultura devido à interferência dessas plantas podem ser instrumentos úteis à tomada de decisão de manejo. Se for possível prever as perdas de rendimento, será possível decidir se é viável ou não a aplicação de uma medida de controle. Há na literatura vários modelos matemáticos empíricos de regressão lineares, não-lineares e polinomiais usados para estimar as perdas de rendimento devido às plantas daninhas. O presente trabalho teve como objetivo apresentar uma análise dos modelos matemáticos presentes na literatura utilizados para estimar as perdas de rendimento que as plantas daninhas acarretam à cultura, considerando o ajuste matemático às observações e a descrição biológica do comportamento dessas perdas

GHASP: an Hα\alpha kinematic survey of spiral galaxies - X. Surface photometry, decompositions and the Tully-Fisher relation in the Rc-band

We present Rc-band surface photometry for 170 of the 203 galaxies in GHASP, Gassendi H-Alpha survey of SPirals, a sample of late-type galaxies for which high-resolution Fabry-Perot H{\alpha} maps have previously been obtained. Our data set is constructed by new Rc-band observations taken at the Observatoire de Haute-Provence (OHP), supplemented with Sloan Digital Sky Survey (SDSS) archival data, obtained with the purpose of deriving homogeneous photometric profiles and parameters. Our results include Rc-band surface brightness profiles for 170 galaxies and $ugriz$ profiles for 108 of these objects. We catalogue several parameters of general interest for further reference, such as total magnitude, effective radius and isophotal parameters -- magnitude, position angle, ellipticity and inclination. We also perform a structural decomposition of the surface brightness profiles using a multi-component method in order to separate disks from bulges and bars, and to observe the main scaling relations involving luminosities, sizes and maximum velocities. We determine the Rc-band Tully Fisher relation using maximum velocities derived solely from H$\alpha$ rotation curves for a sample of 80 galaxies, resulting in a slope of $-8.1 \pm 0.5$, zero point of $-3.0 \pm 1.0$ and an estimated intrinsic scatter of $0.28 \pm 0.07$. We note that, different from the TF-relation in the near-infrared derived for the same sample, no change in the slope of the relation is seen at the low-mass end (for galaxies with $V_{max} < 125$ km/s). We suggest that this different behaviour of the Tully Fisher relation (with the optical relation being described by a single power-law while the near-infrared by two) may be caused by differences in the stellar mass to light ratio for galaxies with $V_{max} < 125$ km/s.Comment: 17 pages, 11 figure

Forest growth dynamics of managed forests in the Southwestern Brazilian Amazon.

The objective of this work was to present the growth forest dynamics results obtained in two sites located in Acre and Amazonas states in the southwestern Brazilian Amazon.Abstracts of the XXV IUFRO World Congress

Manejo e exploração sustentável de florestas naturais tropicais: opções, restrições e alternativas.

Introdução; Conceito e manejo florestal e sustentabilidade; Características das florestas naturais tropicais; Formas de manejo florestal; Manejo de produtos não-madeireiros; Manejo de uso múltiplo; Manejo florestal em área com população; Modelo geral para pequena propriedade; condições gerais para o manejo florestal; Condições imediatas para implantação do manejo florestal.bitstream/CNPF-2009-09/40472/1/doc110.pd

Modeling and simulation of micro direct methanol Fuel Cells

Fuel cells have unique technological attributes: efficiency, absence of moving parts and low emissions. The Direct Methanol Fuel Cell (DMFC) has attracted much attention due to its potential applications as a power source for transportation and portable electronic devices. With the advance of micromachining technologies, miniaturization of power sources became one of the trends of evolution of research in this area. Based on the advantages of the scaling laws, miniaturization promises higher efficiency and performance of power generating devices, so, MicroDMFC is an emergent technology. Models play an important role in fuel cell development since they facilitate a better understanding of parameters affecting the performance of fuel cells. In this work, a steady state, one-dimensional model accounting for coupled heat and mass transfer, along with the electrochemical reactions occurring in a fuel cell, already developed and validated for DMFC in [1-3], is used to predict Micro DMFC performance. The model takes in account all relevant phenomena occurring in a DMFC. Polarization curves predicted by the model are compared with experimental data existing in literature and the model shows good agreement, mainly for lower current densities. The model is used to predict some important parameters to analyze fuel cell performance, such as water transport coefficient and leakage current density. This easily to implement simplified model is suitable for use in real-time MicroDMFC simulations

Post-Newtonian equation for the energy levels of a Dirac particle in a static metric

We study first the Hamiltonian operator H corresponding to the Fock-Weyl extension of the Dirac equation to gravitation. When searching for stationary solutions to this equation, in a static metric, we show that just one invariant Hermitian product appears natural. In the case of a space-isotropic metric, H is Hermitian for that product. Then we investigate the asymptotic post-Newtonian approximation of the stationary Schroedinger equation associated with H, for a slow particle in a weak-field static metric. We rewrite the expanded equations as one equation for a two-component spinor field. This equation contains just the non-relativistic Schroedinger equation in the gravity potential, plus correction terms. Those "correction" terms are of the same order in the small parameter as the "main" terms, but are numerically negligible in the case of ultra-cold neutrons in the Earth's gravity.Comment: 12pt LaTeX, 17 pages. v2: version accepted for publication in Phys.Rev.D: comments on scalar product changed, using a recent paper; discussion of PN expansions simplified (no change of units any more); numerical estimates for ultra-cold neutrons in the Earth's gravit

Positivity issues for the pinch-technique gluon propagator and their resolution

Although gauge-boson propagators in asymptotically-free gauge theories satisfy a dispersion relation, they do not satisfy the K\"allen-Lehmann (KL) representation because the spectral function changes sign. We argue that this is a simple consequence of asymptotic freedom. On the basis of the QED-like Ward identities of the pinch technique (PT) we claim that the product of the coupling $g^2$ and the scalar part $\hat{d}(q^2)$ of the PT propagator, which is both gauge invariant and renormalization-group invariant, can be factored into the product of the running charge $\bar{g}^2(q^2)$ and a term $\hat{H}(q^2)$ both of which satisfy the KL representation although their product does not. We show that this behavior is consistent with some simple analytic models that mimic the gauge-invariant PT Schwinger-Dyson equations (SDE) provided that the dynamic gauge boson mass is sufficiently large. The PT SDEs do not depend directly on the PT propagator through $\hat{D}$ but only through $\hat{H}$.Comment: 13 pages, revtex4. Same physics, shortened; version accepted for publication in Phys. Rev.