ParisTech

About: ParisTech is a education organization based out in Paris, France. It is known for research contribution in the topics: Finite element method & Residual stress. The organization has 1888 authors who have published 1965 publications receiving 55532 citations. The organization is also known as: Paris Institute of Technology & ParisTech Développement.

Oxidation induced changes in viscoelastic properties of a thermostable epoxy matrix

Abstract: The thermal ageing of a neat epoxy matrix has been studied at 473 K in air by three complementary analytical techniques: optical microscopy, dynamic mechanical analysis and nano-indentation. Thermal oxidation is restricted in a superficial layer of about 195 μm of maximal thickness. It consists in a predominant chain scission process involving, in particular, chemical groups whose β motions have the highest degree of cooperativity and thus, are responsible for the high temperature side of β dissipation band. As a result, chain scissions decrease catastrophically the glass transition temperature, but also increase significantly the storage modulus at glassy plateau between T β and T α. This phenomenon is called “internal antiplasticization”. Starting from these observations, the Di Marzio and Gilbert’s theories have been used in order to establish relationships between the glass transition temperature and number of chain scissions, and between the storage modulus and β transition activity respectively. The challenge is now to establish a relationship between the β transition activity and the concentration of the corresponding chemical groups.

Influence of flank face on the condition of chatter self-excitation during turning

Abstract: This paper addresses a modelling approach for cutting tool and workpiece material interaction with ploughing taken into account. In the proposed model the distributed contact on the flank face is replaced by a concentrated additional cutting edge characterised by two physical parameters and bringing about a new delay term into the dynamical system. It is shown that under monoharmonic excitation of the tool on the direction orthogonal to the cutting velocity, it is possible to isolate the effect of the flank face and observe experimentally its parameters. The influence of the ploughing on the instability boundaries of continuous cutting is investigated. An analytical expression is obtained for the effective linear damping coefficient due to ploughing and depending on the cutting velocity.

Investigation of Associations of Yarrowia lipolytica , Staphylococcus xylosus , and Lactococcus lactis in Culture as a First Step in Microbial Interaction Analysis

Abstract: The interactions that may occur between microorganisms in different ecosystems have not been adequately studied yet. We investigated yeast-bacterium interactions in a synthetic medium using different culture associations involving the yeast Yarrowia lipolytica 1E07 and two bacteria, Staphylococcus xylosus C2a and Lactococcus lactis LD61. The growth and biochemical characteristics of each microorganism in the different culture associations were studied. The expression of genes related to glucose, lactate, and amino acid catabolism was analyzed by reverse transcription followed by quantitative PCR. Our results show that the growth of Y. lipolytica 1E07 is dramatically reduced by the presence of S. xylosus C2a. As a result of a low amino acid concentration in the medium, the expression of Y. lipolytica genes involved in amino acid catabolism was downregulated in the presence of S. xylosus C2a, even when L. lactis was present in the culture. Furthermore, the production of lactate by both bacteria had an impact on the lactate dehydrogenase gene expression of the yeast, which increased up to 30-fold in the three-species culture compared to the Y. lipolytica 1E07 pure culture. S. xylosus C2a growth dramatically decreased in the presence of Y. lipolytica 1E07. The growth of lactic acid bacteria was not affected by the presence of S. xylosus C2a or Y. lipolytica 1E07, although the study of gene expression showed significant variations.