Probabilistic approaches to compute uncertainty intervals and sensitivity factors of ultrasonic simulations of a weld inspection

For comprehension purpose, numerical computations are more and more used to simulate the propagation phenomena observed during experimental inspections. However, the good agreement between experimental and simulated data necessitates the use of accurate input data and thus a good characterization of the inspected material. Generally the input data are provided by experimental measurements and are consequently tainted with uncertainties. Thus, it becomes necessary to evaluate the impact of these uncertainties on the outputs of the numerical model. The aim of this study is to perform a probabilistic analysis of an ultrasonic inspection of an austenitic weld containing a manufactured defect based on advanced techniques such as polynomial chaos expansions and computation of sensitivity factors (Sobol, DGSM). The simulation of this configuration with the finite element code ATHENA2D was performed 6000 times with variations of the input parameters (the columnar grain orientation and the elastic constants of the material). The 6000 sets of input parameters were obtained from adapted statistical laws. The output parameters (the amplitude and the position of the defect echo) distributions were then analyzed and the 95% confidence intervals were determined.     

New strategies to study the chemical nature of wine oligomeric procyanidins

Tannins represent a key element in red wine flavors, so researchers have made a lot of effort to try to understand the role of their structure in wine taste in recent decades. We report some new routes to achieve a true structure–taste relationship for the major tannins found in wine, which are procyanidins in their monomeric or oligomeric state. All these routes use synthetic standards. New advances in their synthesis and their analyses using chromatographic methods, NMR spectroscopy, and mass spectrometry to obtain more precise information about their chemical structure, including their stereochemistry and their precise degree of polymerization and galloylation, are described.     

On Parsimonious Edge-Colouring of Graphs with Maximum Degree Three

In a graph G of maximum degree Δ, let γ denote the largest fraction of edges that can be Δ edge-coloured. Albertson and Haas showed that ${\gamma \geq \frac{13}{15}}$ when G is cubic. We show here that this result can be extended to graphs with maximum degree 3, with the exception of a graph on 5 vertices. Moreover, there are exactly two graphs with maximum degree 3 (one being obviously the Petersen graph) for which ${\gamma = \frac{13}{15}.}$ This extends a result given by Steffen. These results are obtained by using structural properties of the so called δ-minimum edge colourings for graphs with maximum degree 3.     

The Kendrick analysis for polymer mass spectrometry

The mass spectrum of a polymer often displays repetitive patterns with peak series spaced by the repeating unit(s) of the polymeric backbones, sometimes complexified with different adducts, chain terminations, or charge states. Exploring the complex mass spectral data or filtering the unwanted signal is tedious whether performed manually or automatically. In contrast, the now 60‐year‐old Kendrick (mass defect) analysis, when adapted to polymer ions, produces visual two‐dimensional maps with intuitive alignments of the repetitive patterns and favourable deconvolution of features overlaid in the one‐dimensional mass spectrum. This special feature article reports on an up‐to‐date and theoretically sound use of Kendrick plots as a data processing tool. The approach requires no prior knowledge of the sample but offers promising dynamic capabilities for visualizing, filtering, and sometimes assigning congested mass spectra. Examples of applications of the approach to polymers are discussed throughout the text, but the same tools can be readily extended to other applications, including the analysis of polymers present as pollutants/contaminants, and to other analytes incorporating a repetitive moiety, for example, oils or lipids. In each of these instances, data processing can benefit from the application of an updated and interactive Kendrick analysis.     

Modeling procyanidin self-association processes and understanding their micellar organization: a study by diffusion NMR and molecular mechanics

The colloidal behavior of eight synthetic procyanidins (three monomers, four dimers, and a trimer) has been investigated in water or in a winelike medium using DOSY NMR spectroscopy and molecular dynamics simulations. Different behavior was observed for monomers and oligomers. Monomers self-associate with a high affinity constant (37-53 M(-1)) to form micelles at low cmc (critical micelle concentration) values (1-5 g.L(-1)). These micelles undergo a time-dependent coalescence process to form hazes and precipitates. As for dimers and the trimer, self-association also occurs but with a lower affinity (approximately 6 M(-1)) and at higher cmc values (10-20 g.L(-1)) to form small micelles (<5 nm) that remain stable throughout the experiment. The presence of 10% ethanol does not significantly affect the self-association constant for monomers and oligomers but increases their cmc values by approximately 50% and decreases the micelle size by a factor 2. However, the presence of 20 mM NaCl appears to negate the effect of ethanol. This study helps to clarify the role of procyanidin monomers versus oligomers in wine turbidity and demonstrates that procyanidin oligomers are fully available to interact with saliva proteins.     

Sustainable Heck-Matsuda reaction with catalytic amounts of diazonium salts: an experimental and theoretical study

The palladium-catalyzed Heck-Matsuda reaction with a catalytic amount of an in-situ-generated diazonium salt proceeded under mild and sustainable conditions. The reaction proceeded at room temperature, under base-free conditions, and only generated tBuOH, H(2)O, and N(2) as by-products. Ortho-substituted diazonium salts were more-efficiently coupled to methyl acrylate than their corresponding para isomers, which required the addition of anisole as an additive. In support of these experimental data, we carried out theoretical studies to gain a deeper understanding of these reaction outcomes.     

Neutron spin echo measurements of monolayer and capillary condensed water in MCM-41 at low temperatures

Neutron spin echo measurements of monolayer and capillary condensed heavy water (D(2)O) confined in MCM-41 C10 (pore diameter 2.10 nm) were performed in a temperature range of 190-298 K. The intermediate scattering functions were analyzed by the Kohlrausch-Williams-Watts stretched exponential function. The relaxation times of confined D(2)O in the capillary condensed state follow remarkably well the Vogel-Fulcher-Tammann equation between 298 and 220 K, whereas below 220 K they show an Arrhenius type behavior. That is, the fragile-to-strong (FTS) dynamic crossover occurs, which has never been seen in experiments on bulk water. On the other hand, for monolayer D(2)O, the FTS dynamic crossover was not observed in the temperature range measured. The FTS dynamic crossover observed in capillary condensed water would take place in the central region of the pore, not near the pore surface. Because the tetrahedral-like water structure in the central region of the pore is more preserved than that near the pore surface, the FTS dynamic crossover would be concerned with the tetrahedral-like water structure.