Estimation of the mesoscopic thermoplastic dissipation in High-Cycle FatigueEstimation de la dissipation thermoplastique en fatigue à grand nombre de cycles

A series of High-Cycle Fatigue (HCF) criteria for polycrystalline materials is based on a multiscale interpretation, proposed initially by Dang Van, in which the principal concepts are a two scales model and a shakedown condition. The purpose of this Note is to extend the study of the different dissipative regimes during cyclic loading within this framework by using a self consistent homogenization scheme in coupled thermoplasticity. It is shown that the Sachs and Lin-Taylor schemes are not able to represent the thermal evolutions observed during fatigue tests. To cite this article: E. Charkaluk, A. Constantinescu, C. R. Mecanique 334 (2006).     

Simply Connected Minimal Surfaces in R3 Transverse to Horizontal Planes

We consider simply connected minimal surfaces in Euclidean space and we give a characterisation of the helicoid.     

Molecular dynamics simulation study on the interaction of KRN 7000 and three analogues with human CD1d

Many analogues of KRN 7000, a synthetic glycolipid (α-galactosylceramide) exhibiting immuno-stimulatory activity and antitumor properties, were previously synthesized and tested in order to understand the reasons for the resulting biological activity and Th1/Th2 cytokine profile. Principles have been established for the interaction of such glycolipids with the human CD1d molecule but the exact mechanism by which different ligands with the same polar head elicit distinct biological responses remains unclear. Based on these experiments and on the available crystal structures, protein-ligand interactions are explored using molecular dynamics simulations. Hydrogen bond interactions are examined with regard to the polar group orientation. The influence of modulations on the dynamic behavior of the CD1d-glycolipid complex is addressed. Overall, our data support the mechanism by which the shortening of the α-GalCer sphingosine chain causes a significant twist of the CD1d α1 helix structure from residue Phe84 that affects the position of CD1d residues involved in the TCR recognition.     

Competitive study of the reactions Br + RFI → IBr + RF and determination of bond dissociation energies D(RF−I) where RF = CF3, C2F5, n-;C3F7, i-C3F7, and n-C4F9

The overall photobromination reactions have been studied using a competitive technique. Relative Arrhenius parameters were obtained for the rate-determining step These were placed on an absolute basis using previous-absolute values of A and E for R_FI=CF₃I. The activation energies were used to calculate bond dissociation energies D(R? I) with the following results:

Simple waves in general elastic materials

The general theory of simple waves in Green-elastic and Cauchy-elastic materials is given. Such waves generate three-dimensional unsteady deformations. Boundary conditions producing such waves are derived together with conditions under which shocks occur. The theory is used to illustrate conditions behind acceleration fronts moving into homogeneously deformed regions and also the modes of propagation of fronts moving into a simple wave. The steady flow of an elastic material past a rigid developable surface is discussed. Simple waves which are principal waves are also discussed.     

Link between the geometrical and the spectral transformation approaches in scattering theory

We show how the Enss's geometrical proof of asymptotic completeness may be set on commutator properties.     

On the number of cycles possible in digraphs with large girth

We consider directed graphs which have no short cycles. In particular, if n is the number of vertices in a graph which has no cycles of length less than n ? k, for some constant k < ?n, then we show that the graph has no more than 3^k cycles. In addition, we show that for k ≤ ½n, there are graphs with exactly 3^k cycles. We thus are able to show that it is possible to bound the number of cycles possible in a graph which has no cycles of length less than f(n) by a polynomial in n if and only if f(n) ≥ n ? rlog(n) for some r.     

Non division dansA ∞(Ω)

Sans résumé