Investigation of the internal structure of hemp fibres using optical coherence tomography and focused ion beam transverse Abstract The use of plant fibres in composite applications requires an efficient characterisation of their mechanical properties and thus an accurate description of their internal structure.The review of literature points out that there is still a lack of data on the organisation and structure of bast fibres. In this study, we propose to investigate the internal structure of hemp fibres using two experimental techniques: Focused Ion Beam (FIB) microscopy and Optical Coherence Tomography (OCT). Results indicate that OCT, a nondestructive and non-invasive technique, is a powerful technique to quickly and easily describe the internal structure of fibres and also to discriminate single fibres from bundle of fibres. In this paper, we also show that among technical hemp fibres and for a same range of external diameters (of about 20-30 microns), two types of internal structures can be observed: (i) elementary fibres with a thick wall and a small lumen and (ii) bundle of small fibres with an external diameter of a few microns. According to data of literature, these two structures were identified as being respectively primary fibres and bundle of secondary fibres. This result is of great importance for the mechanical characterization of the bast hemp fibres. Indeed, this means that during the test campaigns, the batch of isolated fibres is undoubtedly composed of both single primary fibres and bundle of secondary fibres. It certainly participates to the high scattering in results.

No abstract

International audienceWe report here on the ability of elastic light scattering in discriminating Gram+, Gram-and yeasts at an early stage of growth (6h). Our technique is non-invasive, low cost and does require neither skilled operators nor reagents. Therefore it is compatible with automation. It is based on the analysis of the scattering pattern (scatterogram) generated by a bacterial microcolony growing on agar, when placed in the path of a laser beam. Measurements are directly performed on closed Petri dishes. The characteristic features of a given scatterogram are first computed by projecting the pattern onto the Zernike orthogonal basis. Then the obtained data are compared to a database so that machine learning can yield identification result. A 10-fold cross-validation was performed on a database over 8 species (15 strains, 1906 scatterograms), at 6h of incubation. It yielded a 94% correct classification rate between Gram+, Gram-and yeasts. Results can be improved by using a more relevant function basis for projections, such as Fourier-Bessel functions. A fully integrated instrument has been installed at the Grenoble hospital's laboratory of bacteriology and a validation campaign has been started for the early screening of SA and MRSA (Staphylococcus aureus, methicillin-resistant S. aureus) carriers. Up to now, all the published studies about elastic scattering were performed in a forward mode, which is restricted to transparent media. However, in clinical diagnostics, most of media are opaque, such as blood-supplemented agar. That is why we propose a novel scheme capable of collecting back-scattered light which provides comparable results