Vassilis M. Papadakis

Optical coherence tomography complemented by hyperspectral imaging for the study of protective wood coatings

Optical coherence tomography (OCT) is a contactless and non-destructive testing (NDT) technique based on low-coherence interferometry. It has recently become a popular NDT-tool for evaluating cultural heritage. In this study, protective coatings on wood and their penetration into the wood structure were measured with a customized infrared fiber optic OCT instrument. In order to enhance the understanding of the OCT measurements of coatings on real wooden samples, an optimization of the measuring and analyzing methodology was performed by developing an averaging approach and by post-processing the data. The collected information was complemented by data obtained with hyperspectral imaging to allow data from local OCT A-scans to be used in mapping the coating thicknesses over larger areas.

Monitoring chemical degradation of thermally cycled glass-fibre composites using hyperspectral imaging

Nowadays, the application of glass-fibre composites in light-weight structures is growing. Although mechanical characterizations of those structures are commonly performed in testing, chemical changes of materials under stresses have not yet been well documented. In the present work coupon tests and Hyperspectral Imaging (HSI) have been used to categorise possible chemical changes of glass-fibre reinforced polymers (GFRP) which are currently used in the aircraft industry. HSI is a hybrid technique that combines spectroscopy with imaging. It is able to detect chemical degradation of surfaces and has already been successfully applied in a wide range of fields including astronomy, remote sensing, cultural heritage and medical sciences. GFRP specimens were exposed to two different thermal loading conditions. One thermal loading condition was a continuous thermal exposure at 120°C for 24h, 48 h and 96h, i.e. ageing at a constant temperature. The other thermal loading condition was thermal cycling with three different numbers of cycles (4000, 8000, 12000) and two temperature ranges (0°C to 120°C and -25°C to 95°C). The effects of both conditions were measured using both HSI and interlaminar shear (ILSS) tests. No significant changes of the physical properties of the thermally cycled GFRP specimens were detected using interlaminar shear strength tests and optical microscopy. However, when using HIS, differences of the surface conditions were detected. The results showed that the different thermal loading conditions could be successfully clustered in different colours, using the HSI linear unmixing technique. Each different thermal loading condition showed a different chemical degradation level on its surface which was indicated using different colours.

Sea bream interactions toward the aquaculture net due to the presence of micro-fouling

Abstract The technology of floating sea cages that is largely used in the Mediterranean aquaculture provides optimal conditions for the development of marine fouling. The present study investigates the influence of micro-fouling developed on a net, on sea bream behavior. Negative effects of biofouling were not tested since the study was performed under laboratory conditions and for short experimental period. The net condition (micro-fouling filaments) is further examined in comparison with a similar green–brown colored and a white net pen. From the results obtained, it can be concluded that micro-fouling filaments highly induce net biting. In contrast, the colored net tested in this study negatively affected sea bream interactions on the net. Results lead to the conclusion that the fouling filaments are more important to sea bream attraction than the net color, while both variables affect species behavior.

Behavioural Differences in Tank-Held European Sea Bass under Dark/Light Environment

Light is an important abiotic factor that has been associated with fish biology and behaviour. Most fish depends on their vision system to perform activities such as foraging Meager & Luchiari et al. [1,2] breeding. Particularly, biorhythms have been related to feeding time, either in nature or aquaculture as well as under restricted feeding conditions [3]. In recent years, artificial light has been introduced in both fisheries [4] and aquaculture [5] towards attraction to specific areas and population guide for manipulation and avoidance of unfavorable conditions [6,7].

Spectral imaging of Dutch gilt leather for improved conservation strategies

Gilt leather was one of the most fashionable and costly types of wall hangings in the Western world in the 16th to 18th centuries. Despite its appearance, it is not real gold that creates the golden shine, but typically a silver leaf which is coated with an orange-brown lacquer to obtain a golden lustre. Gilt leather has its origins in North-Africa, and the technique was widely practiced in Southern Europe through the middle ages and Renaissance. By the mid-17th century Dutch gilt leather had a similar fame to Delftware and Dutch paintings. Despite this only a small fraction of the large amounts of gilt leather wall hangings produced in Europe has been preserved. Gilt leather is a layered composite of organic and inorganic materials, including leather, animal glue, silver leaf, varnish, oil paint – materials which fall within different conservation disciplines. The aging of gilt leather is characterized by the specific degradations of each of the applied materials, and the possible interactions between them. Some common conservation treatments practiced in the past, such as oiling the leather, have negative side effects, such as gloss and colour change (darkening) and stiffening of the support. Furthermore, most of the surviving gilt leather decorative sections show traces of surface cleaning, such as abrasion, re-varnishing or the application of other protective coatings. Hyperspectral imaging has a wide range of applications in astronomy, biology, chemistry, medicine and quality control. Within the domain of art history, archaeology and conservation, hyperspectral imaging has been used since the 1990’s, mostly for the examination of paintings and manuscripts. It has proved a successful tool for revealing things that are invisible to the naked eye, for example varnish layers, overpaints or underdrawings. In this study the research team investigated a collection of gilt leather objects at SRAL (Stichting Restauratie Atelier Limburg, Maastricht) using an imaging monochromator IMSPECTOR V10E (Specim©, spatial resolution 1300 pixels, wavelength range 400-1000 nm, bandwidth 2.8nm). Scanning of selected case study objects was performed with an automated 3D scanning platform, developed at TU Delft. The objective lens enabled imaging of an approximately 100 mm of field of view. The sample was illuminated by 3 tungsten lamps (30W Halogen) at a 45° angle to avoid specular reflections and to ensure that only diffuse scattering caused by the surface roughness and scattering centres underneath the surface were recorded by the camera. The technique is non-invasive and non-destructive to the studied object. The data was recorded in February 2016 and is currently being analysed using the TIPP software platform, developed at TU Delft. This software platform includes algorithms to perform filtering and un-mixing of hyperspectral data cubes, along with memory management for large data sets and tools for data visualization. Data processing will be performed within the next months, with the objective of mapping areas of surface chemical degradation or change in composition due to earlier conservation treatments. Results will be included in the full paper.