Diffusive epidemic process: theory and simulation

We study the continuous absorbing-state phase transition in the one-dimensional diffusive epidemic process via mean-field theory and Monte Carlo simulation. In this model, particles of two species (A and B) hop on a lattice and undergo reactions B -> A and A + B -> 2B; the total particle number is conserved. We formulate the model as a continuous-time Markov process described by a master equation. A phase transition between the (absorbing) B-free state and an active state is observed as the parameters (reaction and diffusion rates, and total particle density) are varied. Mean-field theory reveals a surprising, nonmonotonic dependence of the critical recovery rate on the diffusion rate of B particles. A computational realization of the process that is faithful to the transition rates defining the model is devised, allowing for direct comparison with theory. Using the quasi-stationary simulation method we determine the order parameter and the survival time in systems of up to 4000 sites. Due to strong finite-size effects, the results converge only for large system sizes. We find no evidence for a discontinuous transition. Our results are consistent with the existence of three distinct universality classes, depending on whether A particles diffusive more rapidly, less rapidly, or at the same rate as B particles.Comment: 19 pages, 5 figure

Identificação de repelência à água em solos sob plantios florestais.

bitstream/CNPF-2009-09/40499/1/com_tec147.pd

Particle Creation by a Moving Boundary with Robin Boundary Condition

We consider a massless scalar field in 1+1 dimensions satisfying a Robin boundary condition (BC) at a non-relativistic moving boundary. We derive a Bogoliubov transformation between input and output bosonic field operators, which allows us to calculate the spectral distribution of created particles. The cases of Dirichlet and Neumann BC may be obtained from our result as limiting cases. These two limits yield the same spectrum, which turns out to be an upper bound for the spectra derived for Robin BC. We show that the particle emission effect can be considerably reduced (with respect to the Dirichlet/Neumann case) by selecting a particular value for the oscillation frequency of the boundary position

Wood characterization using the power spectral density and phase velocity of ultrasonic signals.

The application of non-destructive testing (NDT) in the analysis of trees in forest plantations permits the evaluation of the wood quality, the internal defects in development or pest attack and its characterization for application as solid wood and its products. These techniques have been constantly improved with the use of computers, electronics and agricultural control levels in order to provide tools to the specialists in integrated management. The ultrasound has been used in agriculture as NDT to determine the elasticity modulus of juvenile and mature wood of pinus and other species. This study aimed to the evaluation of new techniques for characterization of wood using parameters such as the power spectral density (PSD) and phase velocity of ultrasonic signals propagating in wood. The tests were performed using a pair of ultrasonic transducers with central frequency of 50 kHz (083-067-038, GE) which were connected to an ultrasonic pulser/receiver (5077PR, Olympus). The transmitting transducer was coupled to the samples of pinus using ultrasound gel and excited with negative pulses of short duration (5 μs) and high amplitude (-400 V) to generate longitudinal and shear waves. The ultrasound signals that propagated through the samples were received by the receiving transducer, amplified (20 to 40 dB), acquired in a digital scope (MSO4104B, Tektronix) and then transferred to a microcomputer. The tests have been done with 10 reference samples (healthy) and 10 attacked by wood wasps, with small holes in the bark. The transducers were placed on the samples in the axial, radial and inclined modes. The data were processed using the Matlab (Mathworks Inc.) to determine the power spectral density (PSD), the root mean square deviation index (cRMSDdB) and the phase velocity between the reference and attacked samples. The cRMSDdB calculated between the PSD of the reference and the attacked samples were generally higher for samples with higher degree of damage, however, in some cases, they were lower due to the presence of wood knots. The phase velocities were calculated in the frequency range 1-200 kHz and generally show higher values for the reference samples. The group velocities were also calculated and the results were in the range 1200-3000 m/s, indicating that these parameters can be used for wood characterization

Transformações químicas da matéria orgânica durante a compostagem de resíduos na indústria madeireira.

CHEMICAL TRANSFORMATIONS OF ORGANIC MATTER DURING THE COMPOSTING OF WOOD INDUSTRY WASTES (RESIDUES). Composting of sawdust and paper mill sludge, using a “Kneer” process reactor, was studied in an attempt to elaborate upon organic matter (OM) transformation during the process and to define parameters to measure the compost maturity level. Temperature, electron paramagnetic resonance (EPR) data, ash and C, H, N and S contents, and a spectroscopic method using ultraviolet-visible (UV-VIS) for alkaline (pH = 8.5) and solid samples was used to study the maturity of the compost samples. These parameters were measured in 6 humic acids (HA) extracted from the compost samples during 29 days. The results of this work show that the “Kneer” process is efficient in transforming ligno-celulitic residues in a short time (29 days), into an organic fertilizer material with application perspectives

Compostagem de resíduos florestais: um guia para produção de húmus através da reciclagem e aproveitamento de resíduos florestais.

Exemplifica a maneira moderna de se dar destino a rejeitos da indústria madeireira que, se não utilizados, ficariam como fonte de poluição e desequilíbrio ambiental.bitstream/item/40996/1/DC0087.pd

Fungos micorrízicos arbusculares como indicadores biológicos de alteração do solo na agricultura de derruba e queima e derruba sem queima na Amazônia.

O objetivo deste trabalho foi avaliar o potencial de emprego da densidade de esporos de fungos micorrízicos arbusculares (FMAs) como indicador biológico de alterações no solo devido ao manejo. Foram avaliados dois sistemas de uso da terra: agricultura tradicional de derruba e queima (corte/queima) e agricultura alternativa de derruba sem queima (corte/trituração) na Amazônia..