Toughening of brittle materials by ductile inclusions

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Acoustic emission analysis of composite pressure vessels under constant and cyclic pressure

International audienceThe use of acoustic emission (AE) for the detection of damage in carbon fibre composite pressure vessels was evaluated for constant and cyclic internal gas pressure loading conditions. AE was capable of monitoring the initiation and accumulation of damage events in a composite pressure vessel (CPVs), although it was not possible to reliably distinguish carbon fibre breakage from other microscopic damage events (e.g. matrix cracks, fibre/matrix interfacial cracks). AE tests performed on the carbon fibre laminate used as the skin of pressure vessels revealed that the development of damage is highly variable under constant pressure, with large differences in the rupture life and acoustic emission events at final failure. Numerical analysis of the skin laminate under constant tensile stress revealed that the high variability in the stress rupture life is due mainly to the stochastic behaviour of the carbon fibre rupture process

Helium trapping in carbide precipitates in a tempered F82H ferritic–martensitic steel

The microstructural changes of a tempered F82H ferritic–martensitic steel following He implantation at 60 and 500 °C have been examined by transmission electron microscopy (TEM) and atom probe tomography (APT). After irradiation at 500 °C, numerous He bubbles were formed throughout the matrix, whereas after irradiation at 60 °C, no bubbles were seen to form in the matrix. In both irradiations, He bubbles were observed to have formed within large carbide precipitates, determined by APT compositional analysis to be M23C6. The observed preferential He bubble formation in carbides during low temperature He irradiation occurs as a result of the diffusing He being trapped in the carbide due to the strong He–C bond. As the He concentration increases in the carbide due to trapping, He bubbles are formed

Daughter Cell Assembly in the Protozoan Parasite Toxoplasma gondii

The phylum Apicomplexa includes thousands of species of obligate intracellular parasites, many of which are significant human and/or animal pathogens. Parasites in this phylum replicate by assembling daughters within the mother, using a cytoskeletal and membranous scaffolding termed the inner membrane complex. Most apicomplexan parasites, including Plasmodium sp. (which cause malaria), package many daughters within a single mother during mitosis, whereas Toxoplasma gondii typically packages only two. The comparatively simple pattern of T. gondii cell division, combined with its molecular genetic and cell biological accessibility, makes this an ideal system to study parasite cell division. A recombinant fusion between the fluorescent protein reporter YFP and the inner membrane complex protein IMC1 has been exploited to examine daughter scaffold formation in T. gondii. Time-lapse video microscopy permits the entire cell cycle of these parasites to be visualized in vivo. In addition to replication via endodyogeny (packaging two parasites at a time), T. gondii is also capable of forming multiple daughters, suggesting fundamental similarities between cell division in T. gondii and other apicomplexan parasites

A Dutch treat:randomized controlled experimentation and the case of heroin-maintenance in the Netherlands

In 1995, the Dutch Minister of Health proposed that a randomized clinical trial (RCT) with heroin-maintenance for severe abusers be conducted. It took nearly four years of lengthy debates before the Dutch Parliament consented to the plan. Apart from the idea of prescribing heroin, the minister and her scientific advisers had to defend the quite high material and non-material costs that would arise from employing the randomized controlled design. They argued that the RCT represented the truly scientific approach and was the royal way to unambiguous results. In the present article, I question this common dual justification of RCTs. First, I situate the historical origins and the basic assumptions of the ideal experiment in 20th-century economic liberalism. Secondly, using the Dutch heroin experiment as an example, I discuss human-science experimentation as an attempt to create reality rather than merely record it. Finally, I discuss some surprising responses by heroin users. These responses display the assumptions of RCTs discussed in the historical section, and underline the importance of the culture of heroin use. In the epilogue, 1 suggest that cultural aspects of heroin consumption can best be studied by thorough ethnographic research