École normale supérieure de Cachan

About: École normale supérieure de Cachan is a education organization based out in Cachan, Île-de-France, France. It is known for research contribution in the topics: Decidability & Nonlinear system. The organization has 2717 authors who have published 5585 publications receiving 175925 citations.

Avoiding 5-axis singularities using tool path deformation

Abstract: This paper deals with a topical method for avoiding the tool to traverse singular positions in 5-axis machining. It is well known that the inverse kinematics transformation generates singular positions for which incoherent movements of rotary axes appear. However, in the paper, we show that due to uncertainties on the positioning, the singular position is actually characterized by a cone. We thus adopt the concept of singular cone. Following, we propose a method to deform the tool path so that the tool does not traverse the singular cone during machining. This method takes advantage of the description of the tool trajectory as B-spline curves. Therefore, the deformation corresponds to the displacements of certain control points wisely chosen. As the corrected tool path must still verify the machining tolerance, the displacement is limited by the admissible displacement which can be calculated in function of the geometrical characteristics of the tool and of the specified machining tolerance. The deformation method we propose can be extended so that the contact point is preserved. Our purpose is illustrated through the example of the machining of a surface in 5-axis high-speed machining (HSM). This illustration shows the efficiency of our method: incoherent movements are eliminated after tool path deformation and the dynamic performance of the machine tool is improved.

Synthesis, crystal structures, and nonlinear optical (NLO) properties of new Schiff-base nickel(II) complexes. Toward a new type of molecular switch?

Abstract: An H2L Schiff-base ligand that was obtained from the monocondensation of diaminomaleonitrile and 4-(diethylamino)salicylaldehyde is reported together with four related nickel(II) complexes formulated as [Ni(L)(L‘)] (L‘ = MePhCHNH2, iPrNH2, Py, and PPh3). Crystal structures have been solved for H2L, [Ni(L)(MePhCHNH2)], and [Ni(L)(iPrNH2)]. Surprisingly, the complexation process leads to the formation of a rather unusual nickel amido (−NH−NiII) bond by deprotonation of the primary amine of H2L. A reduction of the quadratic hyperpolarizability (β) from 38 × 10-30 to 17.5 × 10-30 cm5 esu-1 is evidenced on H2L upon metal complexation by the electric-field-induced second-harmonic (EFISH) technique. Qualitative ZINDO/SCI quantum chemical calculations indicate that, in [Ni(L)(MePhCHNH2)], the β orientation strongly depends on the laser wavelength. In particular, a β rotation strictly equal to 90° could be obtained with 1.022 μm incident light on passing from [Ni(L)(MePhCHNH2] to a hypothetical [Ni(HL)(MePhCHNH2]+...

Large Time Asymptotics for Partially Dissipative Hyperbolic Systems

Abstract: This work is concerned with (n-component) hyperbolic systems of balance laws in m space dimensions. First, we consider linear systems with constant coefficients and analyze the possible behavior of solutions as t → ∞. Using the Fourier transform, we examine the role that control theoretical tools, such as the classical Kalman rank condition, play. We build Lyapunov functionals allowing us to establish explicit decay rates depending on the frequency variable. In this way we extend the previous analysis by Shizuta and Kawashima under the so-called algebraic condition (SK). In particular, we show the existence of systems exhibiting more complex behavior than the one that the (SK) condition allows. We also discuss links between this analysis and previous literature in the context of damped wave equations, hypoellipticity and hypocoercivity. To conclude, we analyze the existence of global solutions around constant equilibria for nonlinear systems of balance laws. Our analysis of the linear case allows proving existence results in situations that the previously existing theory does not cover.