Using clustering as pre-processing in the framework of signal unmixing for exhaustive exploration of archaeological artefacts in Raman imaging.

Analytical chemistry on archaeological material is an essential part of modern archaeological investigations and from year to year, instrumental improvement has made it possible to generate data at a high spatial and temporal frequency. In particular, Raman spectral imaging can be successfully applied in archaeological research by its simplicity of implementation to study past human societies through the analysis of their material remains. This technique makes it possible to simultaneously obtain spatial and spectral information by preserving sample integrity. However, because of the inherent complexity of the samples in Archaeology (e.g. seniority, fragility, lack or full absence of any information about its composition), chemical interpretation can be difficult at first glance. Indeed, specific problems of spectral selectivity related to unexpected chemical compounds could appear due to their state of conservation. Furthermore, detecting minor compounds becomes challenging as major components impose their contributions in the acquired spectra. Therefore, a relevant chemometric approach has been introduced in this context to characterize distinct spectral sources in a Raman imaging dataset of an archaeological specimen - a mosaic fragment. The fragment was unearthed during the Ruscino archaeological dig on the outskirts of Perpignan, France. It dates back to the oppidum period. The aim is to extract selective spectral information from pixel clustering analysis in order to enhance the initial optimisation step within the Multivariate Curve Resolution and Alternating Least-Squares (MCR-ALS) algorithm, a well-known signal unmixing technique. The underlying principle of the MCR-ALS is that the acquired spectra can be expressed as linear combinations of pure spectra of all individual components present in the chemical system under study. Sometimes it can be difficult to obtain the desired results through the algorithm, particularly if initial estimates of spectral or concentration profiles are inaccurate due to complex signals, noise or lack of selectivity, resulting in rank deficiency (i.e. a poor estimation of the total number of pure signals). For this reason, an innovative threshold-based clustering algorithm, combined with multiple Orthogonal Projection Approaches (OPA), has been developed to improve matrix rank investigation and thus the initialisation step of the MCR-ALS approach before optimisation. The effective analysis of Raman imaging data for an archaeological mosaic played a crucial role in uncovering significant chemical information about a particular biogenic material. This insight sheds light on the origins of mortar manufacture during the oppidum period.

Benefits of Chemometric and Raman Spectroscopy Applied to the Kinetics of Setting and Early Age Hydration of Cement Paste.

The addition of water is used to past by internal post-curing of hardening cement. Hydration and curing of cementitious are widely identified by non-destructive 1H nuclear magnetic resonance (NMR) measurements of transverse relaxation time and self-diffusion. However, those non-destructive analytical methodologies do not give a truly chemical characterization of the cement matrix during the hydration and curing process. Indeed, the NMR studies only the water dynamics of hydrating cement with internal post-curing. Recent research indicated chemometrics coupled with Raman spectroscopy allows for a better understanding of chemical processes. Recent advances in computing gave industries and research centers the opportunity to generate cost effective data. In this work, an original method is presented, which uses both a data analysis and a non-invasive, non-destructive Raman monitoring of the hydration reaction of a Portland cement. Data was then analyzed by means of chemometrics methods (principal components analysis (PCA), independent components analysis (ICA), and multivariate curve resolution-alternated least-squares (MCR-ALS) with SIMPLe-to-use Interactive Self-modelling Mixture Analysi (SIMPLISMA) and Orthogonal Projection Approach (OP initialization). Results were compared to the ones obtained with thermogravimetric analysis of this cement paste. Besides the consistency of results from both analytical measurements, chemometrics coupled to Raman spectroscopy accurately revealed the details of the setting without any samples collection. The acquisition frequency allowed a proper identification of the occurrence of each of the various phases involved in the hydration and setting process.

Advanced Radar Absorbing Ceramic-Based Materials for Multifunctional Applications in Space Environment.

In this review, some results of the experimental activity carried out by the authors on advanced composite materials for space applications are reported. Composites are widely employed in the aerospace industry thanks to their lightweight and advanced thermo-mechanical and electrical properties. A critical issue to tackle using engineered materials for space activities is providing two or more specific functionalities by means of single items/components. In this scenario, carbon-based composites are believed to be ideal candidates for the forthcoming development of aerospace research and space missions, since a widespread variety of multi-functional structures are allowed by employing these materials. The research results described here suggest that hybrid ceramic/polymeric structures could be employed as spacecraft-specific subsystems in order to ensure extreme temperature withstanding and electromagnetic shielding behavior simultaneously. The morphological and thermo-mechanical analysis of carbon/carbon (C/C) three-dimensional (3D) shell prototypes is reported; then, the microwave characterization of multilayered carbon-filled micro-/nano-composite panels is described. Finally, the possibility of combining the C/C bulk with a carbon-reinforced skin in a synergic arrangement is discussed, with the aid of numerical and experimental analyses.

Profiling proteins in nutraceutical formulations: characterization of the constituents.

Several nutraceutical preparations containing proteins, amino acids and other small molecules are nowadays present on the market. In this work we propose NMR spectroscopy such as (1)H NMR, (1)H-(1)H TOCSY and DOSY for their constituents characterization, identification and profiling, comparing these results with those obtained by electrophoretic technique such as SDS-PAGE. The (1)H NMR spectroscopy was applied for measurements of the amino acids and other small compounds added from the manufacturer. Further the autocorrelation function obtained from the one dimensional spectrum was used without the complete assignment of the resonances of the NMR spectrum of proteins for the evaluation of the folding quality and stability. Finally the DOSY NMR technique was performed on the samples for the characterization of the mean molecular weight range of proteins. All this features considered together create an important set of data useful for the evaluation of the protein profiling and the characterization of such formulations.

Spectroscopic characterization of urea aqueous solutions: experimental phase diagram of the urea-water binary system.

Raman spectroscopy was used to analyze mixtures of urea and water in order to identify the influence of the urea concentration on the solution's freezing point. Our approach consisted in the analysis of urea aqueous solutions and the determination of their phase transitions at low temperatures. Hence, Raman spectra of these solutions were acquired in a -30 to 10 °C temperature range. This enabled us to build the experimental phase diagram of the urea-water binary system.

Experimental study of NaCl aqueous solutions by Raman spectroscopy: towards a new optical sensor.

Raman spectroscopy was used to study the NaCl aqueous solutions around the solid-liquid phase transition. Special attention was devoted to the modification induced by the salt on the OH stretching band of water. Investigations were carried out in the temperature range between -21 and 10 degrees C, for concentrations from 0 to 200 g/L. We demonstrated that micro-Raman spectroscopy can be used as a marker, allowing the determination of the salt concentration of an aqueous solution with an error close to +/-5%.

Optical sensor for characterizing the phase transition in salted solutions.

We propose a new optical sensor to characterize the solid-liquid phase transition in salted solutions. The probe mainly consists of a Raman spectrometer that extracts the vibrational properties from the light scattered by the salty medium. The spectrum of the O-H stretching band was shown to be strongly affected by the introduction of NaCl and the temperature change as well. A parameter SD defined as the ratio of the integrated intensities of two parts of this band allows to study the temperature and concentration dependences of the phase transition. Then, an easy and efficient signal processing and the exploitation of a modified Boltzmann equation give information on the phase transition. Validations were done on solutions with varying concentration of NaCl.

Vitamin B6 deficiency and dietary fats: effects on lipid composition and glutathione peroxidase activity in rat liver.

Dietary selenium, vitamin B6 and fatty acids modulate both tissue acyl composition by regulating polyunsaturated fatty acid metabolism and antioxidant defences by influencing glutathione peroxidase activity. Alteration in the intake of one of them could therefore lead to different results depending on the intake of the others. To clarify this complex relationship, in the present study we have evaluated the modifications occurring in fatty acid composition and glutathione peroxidase activity in total liver and liver microsomes of rats fed diets containing the same amount of selenium, but different vitamin B6 content and fatty acid composition. Our data indicate that both acyl composition and glutathione peroxidase activity are greatly influenced not only by vitamin B6 deficiency, but also by the diet unsaturation degree. This study underlines that not only selenium availability but also other nutrients can modulate glutathione peroxidase activity.