Analysis of the moisture effect on the mechanical behaviour of an adhesively bonded joint under proportional multi-axial loads

The objective of the study is to identify the 3D behaviour of an adhesive in an assembly, and to take into account the effect of ageing in a marine environment. To that end, three different tests were employed. Gravimetric analyses were used to determine the water diffusion kinetics in the adhesive. Bulk tensile tests were performed to highlight the effects of humid ageing on the adhesive behaviour. Modified Arcan tests were performed for several ageing times to obtain the experimental database which was necessary to identify constitutive models. A Mahnken-Schlimmer type model was determined for the unaged state according to a procedure developed in a previous study. This identification used inverse techniques. It was based on the unaged modified Arcan results and on a coupling between an optimisation routine and finite-element analysis. Then, a global inverse identification procedure was developed. Its aim was to relate the unaged parameters to the moisture concentration and overcome the difficulties usually associated with ageing of bonded assemblies in a humid environment: a non-uniformity of the stress state and a gradient of mechanical properties in the adhesive. This procedure was similar to the one used in the first part but needed modified Arcan results for several ageing times. It also required an initial assumption for the evolution of the Mahnken-Schlimmer parameters with the moisture concentration.

Shared active site architecture between archaeal PolD and multi-subunit RNA polymerases revealed by X-ray crystallography

Archaeal replicative DNA polymerase D (PolD) constitute an atypical class of DNA polymerases made of a proofreading exonuclease subunit (DP1) and a larger polymerase catalytic subunit (DP2), both with unknown structures. We have determined the crystal structures of Pyrococcus abyssi DP1 and DP2 at 2.5 and 2.2 angstrom resolution, respectively, revealing a catalytic core strikingly different from all other known DNA polymerases (DNAPs). Rather, the PolD DP2 catalytic core has the same 'double-psi beta-barrel' architecture seen in the RNA polymerase (RNAP) superfamily, which includes multi-subunit transcriptases of all domains of life, homodimeric RNA-silencing pathway RNAPs and atypical viral RNAPs. This finding bridges together, in non-viral world, DNA transcription and DNA replication within the same protein superfamily. This study documents further the complex evolutionary history of the DNA replication apparatus in different domains of life and proposes a classification of all extant DNAPs.