RESUMO
Laser-based inspection of trivalent chromium conversion coatings on rough, cold-rolled aluminium substrates is studied from a basic physics perspective by means of angle and wavelength dependent measurements. As a result, we show that the correlation between the scattered laser light and the coating weight of the conversion layer is dominated by the phenomenon of interference. The combined experimental and numerical approach of our study is based on an appropriate layer model which was developed from a set of reference measurements of confocal microscopy, electron microscopy and X-ray photoelectron spectroscopy. The aluminium alloy AA3003 with a trivalent chromium conversion coating serves as an example. Our derived model is capable to reconstruct the reflectance of a laser beam at grazing incidence even for a pronounced surface roughness of R q ≈ 300 n m , for different coating thicknesses less than 70 n m corresponding to coating weights between zero and 0.5 g / m 2 and for laser wavelengths from 405 n m to 785 n m . In our discussion we outline the possibility to transfer the results to other aluminium alloys and/or other metallic substrates, as well as their potential for industrial applications such as 100% inline-capability, costs, velocity and ruggedness.
RESUMO
Beam parameters of a probing laser source in an optical riblet sensor are studied by considering the high demands on a sensors' precision and reliability for the determination of deviations of the geometrical shape of a riblet. Mandatory requirements, such as minimum intensity and light polarization, are obtained by means of detailed inspection of the optical response of the riblet using ray and wave optics; the impact of wavelength is studied. Novel measures for analyzing the riblet shape without the necessity of a measurement with a reference sample are derived; reference values for an ideal riblet structure obtained with the optical riblet sensor are given. The application of a low-cost, frequency-doubled Nd:YVO4 laser pointer sufficient to serve as a reliable laser source in an appropriate optical riblet sensor is discussed.
RESUMO
PURPOSE: To determine the effect of hypofractionated stereotactic radiotherapy (hfSRT) on adult rat brain tissue (necrosis, impact on blood-brain barrier, signal changes on high-field magnetic resonance imaging [MRI]). MATERIAL AND METHODS: Adult male Wistar rats underwent MRI and CT scanning of the brain and respective images were introduced into the Novalis radiosurgery device (BrainLab, Feldkirchen, Germany). All animals (body weight 350 g) were irradiated weekly with doses of 2 x 10 Gy (n = 3 animals), 3 x 10 Gy (n = 3 animals) and 4 x 10 Gy (n = 3 animals), targeted to the left hippocampus after image-guided positioning. 4.7-T T2-weighted MRI scanning was performed in each animal. Animals were sacrificed 8, 12, and 16 weeks after hfSRT and brains were immersion-fixed in 4% paraformaldehyde for subsequent histopathologic analysis. RESULTS: In concordance with isodose distributions, pathologic signal hyperintensities in MRI were recorded from 4 x 10 Gy after 8 weeks, 3 x 10 Gy after 12 weeks, while 2 x 10 Gy induced slight detectable alterations only after 16 weeks. Subsequent histopathologic analysis revealed hippocampal cell necrosis with significantly earlier and stronger occurrence for higher doses (40 Gy > 30 Gy > 20 Gy). Pial microvessel permeability also increased after 40 Gy, whereas 30 Gy induced moderate changes. CONCLUSION: Partial-brain irradiation with hfSRT (Novalis System) was successfully adopted for small animals and histopathologic analysis confirmed its repositioning accuracy. The neuropathologic effects correlated with dose and observation time. The approach will be further developed for quality assurance in hfSRT of normal brain tissue, as well as novel treatment modalities in epileptic rats and orthotopic tumor models.
