Die Vervollkommnung des Nachweises von Methylalkohol in ?thylalkohol

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Stress-based upper-bound method and convex optimization: case of the Gurson materialMéthode cinématique par les contraintes et optimisation convexe : cas du matériau de Gurson

A nonlinear interior point method associated with the kinematic theorem of limit analysis is proposed. Associating these two tools enables one to determine an upper bound of the limit loading of a Gurson material structure from the knowledge of the sole yield criterion. We present the main features of the interior point algorithm and an original method providing a rigorous kinematic bound from a stress formulation of the problem. This method is tested by solving in plane strain the problem of a Gurson infinite bar compressed between rough rigid plates. To cite this article: F. Pastor et al., C. R. Mecanique 334 (2006).     

Detection and confirmation of saxitoxin analogues in freshwater benthic Lyngbya wollei algae collected in the St. Lawrence River (Canada) by liquid chromatography–tandem mass spectrometry

The presence of cyanotoxins in benthic Lyngbya wollei algae samples collected in a fluvial lake along the St. Lawrence River, Canada, was investigated using a multi-toxins method. Hydrophilic interaction liquid chromatography (HILIC) and reverse phased liquid chromatography (RPLC) were coupled to triple quadrupole mass spectrometry (LC-QqQMS) for quantification and to quadrupole-time of flight mass spectrometry (LC-QqTOFMS) for screening and confirmation. The presence of two saxitoxin analogues, LWTX-1 and LWTX-6, was confirmed in benthic Lyngbya wollei algae samples. Concentration of LWTX-1 was between 209 ± 5 and 279 ± 9 μg g^?1. No other targeted cyanotoxin (such as anatoxin-a, nodularin, microcystin-LR, microcystins-RR and saxitoxin) was found in the samples. The presence of LWTX-6 was observed by using a screening approach based on an in-house database of cyanotoxins, an algorithm of identification and high resolution mass spectrometry measurements on the precursor and product ions. This work demonstrates the need for more research on the fate of benthic cyanotoxins in aquatic ecosystems such the St. Lawrence River.     

Zum Nachweis und zur quantitativen Bestimmung des Formaldehyds

Analytical and Bioanalytical Chemistry -     

Zum Nachweis und zur quantitativen Bestimmung des Formaldehyds

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Limit analysis and conic programming: ‘porous Drucker–Prager’ material and Gurson's modelAnalyse limite et optimisation conique : étude d'un matériau de Drucker–Prager poreux

Extending a previous work on the Gurson model for a ‘porous von Mises’ material, the present study first focuses on the yield criterion of a ‘porous Drucker–Prager’ material with spherical cavities. On the basis of the Gurson micro-macro model and a second order conic programming (socp) formulation, calculated inner and outer approaches to the criterion are very close, providing a reliable estimate of the yield criterion. Comparison with an analytical criterion recently proposed by Barthélémy and Dormieux—from a nonlinear homogenization method—shows both excellent agreement when considering tensile average boundary conditions and substantial improvement under compressive conditions. Then the results of an analogous study in the case of cylindrical cavities in plane strain are presented. It is worth noting that obtaining these results was made possible by using mosek, a recent commercial socp code, whose impressive efficiency was already seen in our previous works. To cite this article: M. Trillat et al., C. R. Mecanique 334 (2006).