The influence of inhomogeneity on the propagation of ultrasound in wood

The use of ultrasound for determining the elastic constants of materials is a well-established science for homogeneous materials such as metals. However, its extension to anisotropic, inhomogeneous materials such as wood has proved more problematic. Wood is modelled as an orthorhombic material with the influence of inhomogeneities generally being neglected. For this paper the potential influence of inhomogeneities on waves propagating in the radial direction was considered. Within ring density and ultrasonic velocity measurements were made. A model for ultrasound propagation in the radial direction was then constructed which treats the annual ring structure in the radial direction as a layered structure and predicts the occurrence of stop bands in the frequency domain. Evidence for the existence of such stop bands is considered

Sitka Spruce Quality Estimation using Neural Networks

This paper describes an automated classifier for the identification of good wood and knotty wood from computer tomography (CT) images of logs. Such a system is intended to allow better assessment of saw logs before being cut into timber. We describe a new empirical model for the growth of Sitka Spruce (Picea Stichensis (Bong, Carr)) whose operation is adapted to Irish conditions. The use of Hopfield networks for 2D cross-section image reconstruction from CT data obtained from the model is investigated. We also used a multi-layer feedforward neural network trained with fast-backpropagation to identify good wood from knotty wood. The Hopfield approach to image reconstruction was seen as being unsuitable for application with the wood industry. However, the use of a feedforward neural network for wood classification produced very promising results when trained on our tree model. It is expected that results from real wood data would be even more accurate

Measurements of the absolute concentrations of HCO and (CH2)-C-1 in a premixed atmospheric flat flame by cavity ringdown spectroscopy

Singlet methylene (1CH2) and the formyl radical (HCO) have been studied in a premixed flat flame of CH4 and air by cavity ring-down spectroscopy at 1 atm. The absorption lines lie in the same spectral region for both species. The 1CH2 radicals were probed via the 1B1 (0,13,0) ¿ã1A1 (0,0,0) band at 622 nm and the HCO radicals via the Ã2A' (0,9,0) ¿ 2A¿ (0,0,0) band at 615 nm. Absolute concentrations of 1CH2 and HCO have been obtained at various heights above the burner and compared to numerical simulations using both the GRI-Mech 2.11 and 3.0 mechanisms, showing relatively good agreement

Measurements of absolute concentrations of CH in a premixed atmospheric flat flame by cavity ring-down spectroscopy

Absolute concentrations of CH in a premixed, atmospheric flat flame of CH4 and air have been determined with cavity ring-down spectroscopy (CRDS). CH is excited from the X2¿ to the A2¿ state at 430 nm. Since at atmospheric pressure the CH radical is present only in a very narrow layer at the flame front, specific problems due to the finite size of the laser beam and thermal deflection are encountered. An intensified CCD camera was used as an aid to be able to take these effects into account. Distributions of [CH] were obtained for two different stoichiometries (f = 1.2 and 1.1) in a burner-stabilized flame. Signal-to-noise ratios indicate that [CH] number densities down to 4 × 1011 cm-3, corresponding to 1.5 ppb (S/N = 2) can be detected easily at 1 atm. Flame uniformity was verified with an Abel inversion technique. The rotational flame temperature was derived from Boltzmann distributions. The results were compared to modeling calculations using GRI-Mech 2.11 and 3.0. The predictions for both models show higher maximum [CH] located further away from the burner. The computed maximum [CH] is predicted in both cases at a higher temperature. Analyses of the effect of errors in the experimental settings and direct absorption measurements of [OH] have been used to verify positional differences. The results indicate that the differences may be attributed to reaction mechanisms

Sitka Spruce Quality Estimation using Neural Networks

This paper describes an automated classifier for the identification of good wood and knotty wood from computer tomography (CT) images of logs. Such a system is intended to allow better assessment of saw logs before being cut into timber. We describe a new empirical model for the growth of Sitka Spruce (Picea Stichensis (Bong, Carr)) whose operation is adapted to Irish conditions. The use of Hopfield networks for 2D cross-section image reconstruction from CT data obtained from the model is investigated. We also used a multi-layer feedforward neural network trained with fast-backpropagation to identify good wood from knotty wood. The Hopfield approach to image reconstruction was seen as being unsuitable for application with the wood industry. However, the use of a feedforward neural network for wood classification produced very promising results when trained on our tree model. It is expected that results from real wood data would be even more accurate. 1

Cavity ring down spectroscopy of CH, CH2, HCO, and H2CO in a premixed flat flame at both atmospheric and sub-atmospheric pressure

Density distributions of CH, CH2, HCO and H2CO have been measured in a premixed CH4/air flat flame by Cavity Ring Down Spectroscopy (CRDS). At atmospheric pressure problems are encountered due to the narrow spatial distribution of these species. Rotational flame Temperatures have been derived from the spectral line intensities of CH. Additional distributions of the species are recorded in a low-pressure set up at 2x104 Pa. The results at both pressures are compared to modeling calculations using GRI-Mech 2.11 and 3.0 showing a relatively good agreement. Deviations are attributed to the applied reaction mechanisms

Cavity ring down spectroscopy of CH, CH2, HCO, and H2CO in a premixed flat flame at both atmospheric and sub-atmospheric pressure

Density distributions of CH, CH2, HCO and H2CO have been measured in a premixed CH4/air flat flame by Cavity Ring Down Spectroscopy (CRDS). At atmospheric pressure problems are encountered due to the narrow spatial distribution of these species. Rotational flame Temperatures have been derived from the spectral line intensities of CH. Additional distributions of the species are recorded in a low-pressure set up at 2x104 Pa. The results at both pressures are compared to modeling calculations using GRI-Mech 2.11 and 3.0 showing a relatively good agreement. Deviations are attributed to the applied reaction mechanisms