On the Temperature Distribution Inside a Tree Under Fire Conditions

A simple and efficient numerical scheme is presented for the prediction of temperature field distribution inside a tree trunk subjected to ground fire conditions. The trunk is modeled by a cylinder of circular cross section and unit length, through which the time-dependent heat conduction equation is numerically integrated. The model is partly validated in laboratory and then applied to the case of a prescribed ground fire inside a Pinus pinmter stand

Ab-initio prediction of the electronic and optical excitations in polythiophene: isolated chains versus bulk polymer

We calculate the electronic and optical excitations of polythiophene using the GW approximation for the electronic self-energy, and include excitonic effects by solving the electron-hole Bethe-Salpeter equation. Two different situations are studied: excitations on isolated chains and excitations on chains in crystalline polythiophene. The dielectric tensor for the crystalline situation is obtained by modeling the polymer chains as polarizable line objects, with a long-wavelength polarizability tensor obtained from the ab-initio polarizability function of the isolated chain. With this model dielectric tensor we construct a screened interaction for the crystalline case, including both intra- and interchain screening. In the crystalline situation both the quasi-particle band gap and the exciton binding energies are drastically reduced in comparison with the isolated chain. However, the optical gap is hardly affected. We expect this result to be relevant for conjugated polymers in general.Comment: 15 pages including 4 figures; to appear in Phys. Rev. B, 6/15/200

Aspectos técnicos e econômicos da terminação de cordeiros a pasto e em confinamento.

SISTEMAS DE TERMINAÇÃO DE CORDEIROS; FATORES INERENTES AO CORDEIRO QUE INTERFEREM NOS RESULTADOS DA FASE DE TERMINAÇÃO; FATORES AMBIENTAIS A SEREM CONSIDERADOS NA ESCOLHA DO SISTEMA DE TERMINAÇÃO DE CORDEIROS; ASPECTOS ECONÔMICOS DA TERMINAÇÃO DE CORDEIROS À PASTO E EM CONFINAMENTO; TIPO DE TERMINAÇÃO DE CORDEIROS E AS ALTERNATIVAS PARA UMA PRODUÇÃO DE CARNE OVINA DIFERENCIADA

Solubility isotope effects in aqueous solutions of methane

The isotope effect on the Henry's law coefficients of methane in aqueous solution (H/D and C-12/C-13 substitution) are interpreted using the statistical mechanical theory of condensed phase isotope effects. The missing spectroscopic data needed for the implementation of the theory were obtained either experimentally (infrared measurements), by computer simulation (molecular dynamics technique), or estimated using the Wilson's GF matrix method. The order of magnitude and sign of both solute isotope effects can be predicted by the theory. Even a crude estimation based on data from previous vapor pressure isotope effect studies of pure methane at low temperature can explain the inverse effect found for the solubility of deuterated methane in water. (C) 2002 American Institute of Physics

Efeito da substituição parcial da silagem de milho por silagem de gliricidia sobre o desempenho de cordeiras Santa Inês alimentadas em confinamento.

O estudo foi realizado com o objetivo de avaliar o efeito da substituicao parcial da silagem de milho por silagem de gliricidia (Gliricidia sepium) no crescimento ponderal de cordeiras Santa Ines alimentadas em confinamento. O peso medio inicial das cordeiras foi de 20,0 Kg. A dieta basica dos animais foi constituida por silagem de milho e concentrado (milho + farelo de soja) em tres tratamentos, ocorrendo, em dois deles, a substituicao parcial da silagem de milho por silagem de gliricidia na ordem de 20 ou 40% da materia seca da fracao volumosa da dieta. Os animais foram mantidos em baias coletivas com 8 animais, sendo o animal a unidade experimental, totalizando 24 cordeiras. Os valores encontrados para peso inicial e peso final (Kg) nao diferiram estatisticamente (P¡Â0,05) entre os tratamentos estudados, porem houve diferenca estatistica para as medias de ganho medio diario de peso (g/animal/dia), sendo o tratamento com maior inclusao de silagem de gliricidia melhor em relacao ao tratamento com ausencia de gliricidia. Os resultados obtidos mostram que a utilizacao de silagem de gliricidia em substituicao a silagem de milho, proporciona um melhor desempenho de cordeiras em confinamento

Continuous Percolation Phase Transitions of Two-dimensional Lattice Networks under a Generalized Achlioptas Process

The percolation phase transitions of two-dimensional lattice networks under a generalized Achlioptas process (GAP) are investigated. During the GAP, two edges are chosen randomly from the lattice and the edge with minimum product of the two connecting cluster sizes is taken as the next occupied bond with a probability $p$. At $p=0.5$, the GAP becomes the random growth model and leads to the minority product rule at $p=1$. Using the finite-size scaling analysis, we find that the percolation phase transitions of these systems with $0.5 \le p \le 1$ are always continuous and their critical exponents depend on $p$. Therefore, the universality class of the critical phenomena in two-dimensional lattice networks under the GAP is related to the probability parameter $p$ in addition.Comment: 7 pages, 14 figures, accepted for publication in Eur. Phys. J.

Some doubts on the validity of the foreground Galactic contribution subtraction from microwave anisotropies

The Galactic foreground contamination in CMBR anisotropies, especially from the dust component, is not easily separable from the cosmological or extragalactic component. In this paper, some doubts will be raised concerning the validity of the methods used to date to remove Galactic dust emission in order to show that none of them achieves its goal. First, I review the recent bibliography on the topic and discuss critically the methods of foreground subtraction: the cross-correlation with templates, analysis assuming the spectral shape of the Galactic components, the "maximum entropy method", "internal linear combination", and "wavelet-based high resolution fitting of internal templates". Second, I analyse the galactic latitude dependence from WMAP data. The frequency dependence is discussed with the data in the available literature. The result is that all methods of subtracting the Galactic contamination are inaccurate. The galactic latitude dependence analysis or the frequency dependence of the anisotropies in the range 50-250 GHz put a constraint on the maximum Galactic contribution in the power spectrum to be less than a ~10% (68% C. L.) for a ~1 degree scale, and possibly higher for larger scales. The origin of most of the signal in the CMBR anisotropies is not Galactic. In any case, the subtraction of the Galaxy is not accurate enough to allow a "precision Cosmology"; other sources of contamination (extragalactic, solar system) are also present.Comment: 24 pages, 1 figure, accepted to be published in J. Astrophys. Ast