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 & Finite element method. The organization has 2717 authors who have published 5585 publications receiving 175925 citations.

Analytical Armature Reaction Field Prediction in Field-Excited Flux-Switching Machines Using an Exact Relative Permeance Function

Abstract: In this paper, an analytical approach for the prediction of the armature reaction field of field-excited flux-switching (FE-FS) machines is presented. The analytical method is based on the magnetomotive force (MMF)-permeance theory. The doubly-salient air-gap permeance, developed here, is derived from an exact solution of the slot permeance. Indeed, the relative slot permeance is obtained by solving Maxwell's equations in a subdomain model and applying boundary and continuity conditions. In addition, during a no-load study, we found that, regarding the stator-rotor teeth combination, phase distributions were modified. Hence, in this paper, phase MMF distributions, for q phases, several stator-rotor combinations and also phase winding distribution (single- or double-layers) are proposed. We compare extensively magnetic field distributions calculated by the analytical model with those obtained from finite-element analyses. Futhermore, the model is used to predict the machine inductances. Once again, FE results validate the analytical prediction, showing that the developed model can be advantageously used as a design tool of FE-FS machine.

4-Pyridyl-9,9'-spirobifluorenes as Host Materials for Green and Sky-Blue Phosphorescent OLEDs

Abstract: We report herein new pyridine-substituted spirobifluorene (SBF) dyes, i.e., 4-(9,9′-spirobi[fluoren]-4-yl)pyridine (4-4Py-SBF), 3-(9,9′-spirobi[fluoren]-4-yl)pyridine (4-3Py-SBF), and 2-(9,9′-spirobi[fluoren]-4-yl)pyridine (4-2Py-SBF), built on the association of the 4-substituted spirobifluorenyl core and various regioisomers of pyridine. These organic semiconductors possess high triplet energy levels (ET around 2.7 eV) in accordance with their use as hosts for green and sky-blue phosphorescent organic light-emitting diodes (PhOLEDs). These dyes have been synthesized from the 4-bromo-spirobifluorene (4-Br-SBF) platform, obtained from a new and efficient synthetic approach using the promising building block 4-bromofluorenone as a key intermediate. Synthesis, structural, thermal, electrochemical, and photophysical properties of the three dyes have been investigated in detail and compared to other model compounds, namely, 4-phenyl-SBF (4-Ph-SBF), 2-phenyl-SBF (2-Ph-SBF), and 2,4-pyridyl-SBF (2-4Py-SBF), in ...