Mines ParisTech

About: Mines ParisTech is a education organization based out in Paris, France. It is known for research contribution in the topics: Finite element method & Microstructure. The organization has 6564 authors who have published 11676 publications receiving 359898 citations. The organization is also known as: École nationale supérieure des mines de Paris & École des mines de Paris.

On necessary and sufficient conditions for differential flatness

Abstract: This paper is devoted to the characterization of differentially flat nonlinear systems in implicit representation, after elimination of the input variables, in the differential geometric framework of manifolds of jets of infinite order. We extend the notion of Lie-Backlund equivalence, introduced in Fliess et al. (IEEE Trans Automat Contr 44(5):922–937, 1999), to this implicit context and focus attention on Lie-Backlund isomorphisms associated to flat systems, called trivializations. They can be locally characterized in terms of polynomial matrices of the indeterminate $${\frac{d}{dt}}$$, whose range is equal to the kernel of the polynomial matrix associated to the implicit variational system. Such polynomial matrices are useful to compute the ideal of differential forms generated by the differentials of all possible trivializations. We introduce the notion of a strongly closed ideal of differential forms, and prove that flatness is equivalent to the strong closedness of the latter ideal, which, in turn, is equivalent to the existence of solutions of the so-called generalized moving frame structure equations. Two sequential procedures to effectively compute flat outputs are deduced and various examples and consequences are presented.

Development of the local approach to fracture over the past 25 years: Theory and applications

Abstract: This review paper is devoted to the local approach to fracture (LAF) for the prediction of the fracture toughness of structural steels. The LAF has been considerably developed over the past two decades, not only to provide a better understanding of the fracture behaviour of materials, in particular the failure micromechanisms, but also to deal with loading conditions which cannot easily be handled with the conventional linear elastic fracture mechanics and elastic-plastic fracture mechanics global approaches. The bases of this relatively newly developed methodology are first presented. Both ductile rupture and brittle cleavage fracture micromechanisms are considered. The ductile-to-brittle transition observed in ferritic steels is also briefly reviewed. Two types of LAF methods are presented: (i) those assuming that the material behaviour is not affected by damage (e.g. cleavage fracture), (ii) those using a coupling effect between damage and constitutive equations (e.g. ductile fracture). The micromechanisms of brittle and ductile fracture investigated in elementary volume elements are briefly presented. The emphasis is laid on cleavage fracture in ferritic steels. The role of second phase particles (carbides or inclusions) and grain boundaries is more thoroughly discussed. The distinction between nucleation and growth controlled fracture is made. Recent developments in the theory of cleavage fracture incorporating both the effect of stress state and that of plastic strain are presented. These theoretical results are applied to the crack tip situation to predict the fracture toughness. It is shown that the ductile-to-brittle transition curve can reasonably be well predicted using the LAF approach. Additional applications of the LAF approach methods are also shown, including: (i) the effect of loading rate and prestressing; (ii) the influence of residual stresses in welds; (iii) the mismatch effects in welds; (iv) the warm-prestressing effect. An attempt is also made to delineate research areas where large improvements should be made for a better understanding of the failure behaviour of structural materials.

Rapid on-line sampler-injector : a reliable tool for HT-HP sampling and on-line GC analysis

Abstract: Withdrawing of representative and reliable microsamples down to 1/100th mg is far from trivial, especially for extreme conditions such as high temperature and high pressure conditions or very corrosive media. The new Rapid On-Line Sampler- Injector presented herein was designed and set-up to largely extend sampling capabilities in hazardous media. It is largely use d in our laboratory to measure vapour-liquid equilibria. It has a lot of applications, both in production (process control in pet ro- leum, chemical, nuclear plants, etc.) and academic and industrial researches and development (laboratory instruments, pilot plants…).

For What It’s Worth: An Introduction to Valuation Studies

Abstract: Welcome to Valuation Studies! We are very glad that you have set your eyes on the very !rst editorial of this new journal. The aim of this inaugural editorial is manifold. We aim, !rstly, to provide some re"ections about the starting of this journal. This will bring us both to the issue of the perceived topicality of the study of valuation as a social practice as well as our provisional answers to the many questions embedded in the very embarking on such an endeavour. (Why a new journal? Why open access? Why a transdisciplinary scope? Etc.) Secondly, we want to take the opportunity to discuss what we take as the scope of the journal. We feel that the topic of valuation as a social practice would bene!t from a large amount of openness. Yet, there are also limits to the amount of diversity that can be fruitfully embraced within the (digital) covers of any journal. Thirdly, we would also like to address the many questions concerning valuation of academic work that relentlessly surface in an endeavour such as this one. (Will the contributions be any good? Will the journal provide a good arena for scholarly discussions about valuation and the study of it? Will an article published in Valuation Studies given any value in the valuation practices performed by the universities to evaluate faculty and candidates for positions? Etc.) Finally, we would want to touch upon the issue of further actions, ours as well as of others. Valuation Studies 1(1) 2013: 1–10