Search results for " surface"
showing 10 items of 2838 documents
Non subanalyticity of sub-Riemannian Martinet spheres
2001
Abstract Consider the sub-Riemannian Martinet structure (M,Δ,g) where M= R 3 , Δ= Ker ( d z− y 2 2 d x) and g is the general gradated metric of order 0 : g=(1+αy) 2 d x 2 +(1+βx+γy) 2 d y 2 . We prove that if α≠0 then the sub-Riemannian spheres S(0,r) with small radii are not subanalytic.
Investigation of the vibrational dynamics of the HCN/CNH isomers through high order canonical perturbation theory
2000
International audience; Molecular vibrations of the molecule HCN/CNH are examined using a combination of a minimum energy path Hamiltonian and high order canonical perturbation theory , as suggested in a recent work [D. Sugny and M. Joyeux, J. Chem. Phys. 112, 31 (2000)]. In addition, the quantum analog of the classical CPT is presented and results obtained therefrom are compared to the classical ones. The MEP Hamiltonian is shown to provide an accurate representation of the original potential energy surface and a convenient starting point for the CPT. The CPT results are subsequently used to elucidate the molecular dynamics: It appears that the isomerization dynamics of HCN/CNH is very tri…
Recent changes in measured wind in the NE Atlantic and variability of correlation with NAO
2010
The paper deals with wind measurements, recorded since the 1950s, at twelve meteorological stations along a transect near the westernmost European border, between 64° and 44° N. Extreme wind speed tends to decrease sharply near the northern boundary (at Reykjavick), near the middle of the study area (at Shannon and Valentia) and near the southern boundary (at Brest and Cap Ferret), to increase at Thorshavn, with less significant trends at the other stations. Average wind speeds confirm the above tendencies, with an additional increasing speed at Lerwick, Kirkwall, Malin Head, Belle-Ile and Cap Ferret. To compare changes in wind activity, the data have been subdivided into three periods: unt…
Modelling of interference fits with taking into account surfaces roughness with homogenization technique
2013
International audience; The assembly technique by shrink fit is increasingly used today because it allows for the assembly of two pieces without any intermediary part simply by the tightening effect given by the difference in diameters of the two parts assembled. The definition of assemblies depends on calculation models available in the standard. They make very restrictive assumptions that limit the geometrical defects and the surface finish. It is increasingly common to use a finite element method to better adapt the model to the complex forms of industrial parts. However, the standard is limited with regard to the consideration of roughness which results in a loss of tightening. An easy …
Etude de la stabilité de films industriels de PLA et de leur modification de surface pour des applications en tant qu'emballage alimentaire biodégrad…
2017
Poly(lactic acid) (PLA) is a biodegradable and renewable polyester, which is considered as the most promising eco-friendly substitute of conventional plastics. It is mainly used for food packaging applications, but some drawbacks still reduce its applications. On the one hand, its low barrier performance to gases (e.g. O2 and CO2) limits its use for applications requiring low gas transfer, such as modified atmosphere packaging (MAP) or for carbonate beverage packaging. On the other hand, its natural water sensitivity, which contributes to its biodegradation, limits its use for high moisture foods with long shelf life.Other biopolymers such as wheat gluten (WG) can be considered as interesti…
An empirical method to determine the free surface energy of solids at different deformations and temperatures regimes : An application to Al.
2005
Abstract We have performed molecular dynamics (MD) simulations using the three low index surfaces of Al to determine the variation of the surface energy as a function of deformation and temperature. We have also developed an empirical formulation for the surface free energy as a function of deformation. The observed difference between the numerical and analytical results has led us to divide the deformation into a mechanical and a thermal contribution. From this observation, we have obtained an expression for the surface free energy placing the temperature dependence on the bulk and surface elastic constants. Our simulations permitted us to analyze the multilayer relaxation for the particul…
Syntheses of TiO2 anatase nanocrystals with controlled size distribution. Influence of the crystallites size on the Raman spectrum and investigation …
2006
The determination of the size and the size distribution of anatase TiO2 nanopowders using Raman spectroscopy is presented. Several synthesis methods (soft chemistry, water-in-oil microemulsion, continuous hydrothermal synthesis) are used in order to control the size (from 3 to 20 nm), shape, phase and size distribution. The shift and width of the anatase Eg peak are often used to obtain the nanoparticles size. Homever, this peak is also sensitive to nonstoichiometry and others parameters. Low-frequency Raman scattering does not suffer from this problem. Size distibutions obtained by Raman spectroscopy and MET micrographs are compared. Finally, in situ Raman spectroscopy is used to study the…
Initial stages of metal oxides thin films growth by MOCVD: physicochemical characterisation of the film/substrate interface
2006
The initial stages of Metalorganic Chemical Vapour Deposition (MOCVD) of TiO2 thin films on Si(100) were studied in situ by surface analyses (XPS, ARXPS, AES). An original experimental set-up was built for this purpose and developed. Information obtained from these in situ experiments was completed by ex situ characterisations (HRTEM, SIMS, GIXRD...).The formation of an interfacial SiOy<2 layer resulting of the interaction of the precursor Ti(OCH(CH3)2)4 with the substrate takes place before the formation of stoichiometric TiO2 and leads to the presence of carbon at the interface. At the deposition temperature, 675 °C, silicon diffusion within the TiO2 external layer was also revealed. Conc…
Extraction de primitives à partir d'images de lumière structurée
2013
National audience; Les attributs géométriques tels que la courbure ou la normale constituent des informations complémentaires aux points 3D obtenus suite à la numérisation d'une surface ou d'un objet. Dans la chaine 3D classique, présentant une structure séquentielle, ces informations sont déterminées à partir du nuage de points dense (issus par exemple d'un scanner 3D). Par la suite, elles sont utilisées pour diminuer la quantité d'information et permettre ainsi d'aboutir à un modèle simplifié (compressé ou modélisé sous forme de primitives). Dans cet article, nous nous intéressons à la possibilité d'extraire certains des attributs mentionnés plus haut, directement à partir des images 2D o…
A NEW POTENTIAL FUNCTION FOR SELF INTERSECTING GIELIS CURVES WITH RATIONAL SYMMETRIES
2009
International audience; We present a new potential field equation for self-intersecting Gielis curves with rational rotational symmetries. In the literature, potential field equations for these curves, and their extensions to surfaces, impose the rotational symmetries to be integers in order to guarantee the unicity of the intersection between the curve/surface and any ray starting from its center. Although the representation with natural symmetries has been applied to mechanical parts modeling and reconstruction, the lack of a potential function for Rational symmetry Gielis Curves (RGC) remains a major problem for natural object representation, such as flowers and phyllotaxis. We overcome thi…