Orientation imaging using spatially resolved acoustic spectroscopy R Smith, S Sharples, W Li et al. Abstract. Wood is a biological growth medium. It is orthotropic with longitudinal, radial and tangential axes. Furthermore, standing trees adapt themselves to environmental growth conditions, and their material properties vary with age. These changes result in variations that are much more complex than anisotropy. Studying wood quality and intraspecific variability is useful for clonal selection and for the genetic improvement of plantations. In this study, two logs of Picea abies underwent transmission tomography. The mean diameter was 16 cm (26-year-old tree) and the moisture content was 22%. The effect of the presence of bark and artificial defects was investigated. The tomographic device was specifically built for tree imaging. The imaging process was automatic with 900 ultrasonic acquisitions in 40 minutes (emission at 55 kHz with 5 periods of square wave form). The main conclusions were: speed near the bark is higher than in the centre because of the existence of juvenile wood combined with the moisture content gradient (moisture content lower near the bark). Likewise, damping near the bark is lower than in the centre. A significant relationship was observed between slowness and attenuation (R²=0.50); when the speed increased, damping decreased. No clear effect of the presence of bark was shown on the tomographic images. The bark was thin (3 to 5 mm thick) compared to the wavelength (26 mm). The 10, 20 and 50 mm artificial holes were clearly visible on the tomographic images. However, quantitative tomography does not enable the precise location of defects.
International audienceThe quality of the Ultrasonic Computed Tomography (UCT) imaging device, in term of spatial resolution, sensitivity or dynamic, is a function of the wavelength, the number of transducers, the ultrasonic field generated and the inversion algorithm. This latter factor was studied using four inversion techniques for the tomography of trees. Two new methods, Partial Least Squares method - PLS, and Layer Stripping - LS, are compared to two classical methods, Filtered Backprojection - FBP, and Simultaneous Iterative Reconstruction Technique - SIRT. An original numerical phantom of tree was used and the effects of the variation of the number of transducers and the noise level were analyzed. The PLS was found to converge slowly but reached a high performance for the reconstruction of the projection values (slowness). PLS method was also characterized by a fast computation time. However, the PLS method gave a poor image quality (high sensitivity to noise level and presence of outlier values). The main advantage of the LS method was its high robustness to the noise level. The computing time was however the weakest point of LS method. A combination of the two classic FBP-SIRT methods seemed the most suitable except for the computation time. However, an improvement of the convergence conditions of PLS method (very fast computing time; including also curved rays), with the use of SIRT method, would constitute a promising solution
The detoxification and sterilization radicular surfaces that have been produced by periodontal diseases could be accomplished after polishing (root planing) using the thermal elevation resulting from CO2 laser on continuous emission. In vitro experiments reveal that thermal elevations reached on the surfaces or in the depth are proportional to the dispersed energy. The thermal elevation in the depth (0.5-1 mm from the impact point) remained moderate because of the water absorption potentials of the radiations. Energies from 2 to 4.5 J can help obtain the combination of surface temperature elevation, which allows detoxification, and of a thermal elevation in the depth, compatible with vital tissues. This energy has to be delivered at an application time under 0.6 sec in continuous mode.
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