CentraleSupélec

About: CentraleSupélec is a based out in . It is known for research contribution in the topics: MIMO & Wireless network. The organization has 1330 authors who have published 2344 publications receiving 30533 citations. The organization is also known as: CentraleSupelec & CentraleSupelec of the Paris-Saclay University.

Use of ZnO thin films as sacrificial templates for metal organic vapor phase epitaxy and chemical lift-off of GaN

Abstract: Continued development of GaN-based light emitting diodes is being hampered by constraints imposed by current non-native substrates. ZnO is a promising alternative substrate but it decomposes under the conditions used in conventional GaN metal organic vapor phase epitaxy (MOVPE). In this work, GaN was grown on ZnO/c-Al2O3 using low temperature/pressure MOVPE with N2 as a carrier and dimethylhydrazine as a N source. Characterization confirmed the epitaxial growth of GaN. The GaN was lifted-off the c-Al2O3 by chemically etching away the ZnO underlayer. This approach opens up the way for bonding of the GaN onto a support of choice.

International Benchmark on Numerical Simulations for 1D, Nonlinear Site Response (PRENOLIN): Verification Phase Based on Canonical Cases

Abstract: PREdiction of NOn‐LINear soil behavior (PRENOLIN) is an international benchmark aiming to test multiple numerical simulation codes that are capable of predicting nonlinear seismic site response with various constitutive models. One of the objectives of this project is the assessment of the uncertainties associated with nonlinear simulation of 1D site effects. A first verification phase (i.e., comparison between numerical codes on simple idealistic cases) will be followed by a validation phase, comparing the predictions of such numerical estimations with actual strong‐motion recordings obtained at well‐known sites. The benchmark presently involves 21 teams and 23 different computational codes. We present here the main results of the verification phase dealing with simple cases. Three different idealized soil profiles were tested over a wide range of shear strains with different input motions and different boundary conditions at the sediment/bedrock interface. A first iteration focusing on the elastic and viscoelastic cases was proved to be useful to ensure a common understanding and to identify numerical issues before pursuing the nonlinear modeling. Besides minor mistakes in the implementation of input parameters and output units, the initial discrepancies between the numerical results can be attributed to (1) different understanding of the expression “input motion” in different communities, and (2) different implementations of material damping and possible numerical energy dissipation. The second round of computations thus allowed a convergence of all teams to the Haskell–Thomson analytical solution in elastic and viscoelastic cases. For nonlinear computations, we investigate the epistemic uncertainties related only to wave propagation modeling using different nonlinear constitutive models. Such epistemic uncertainties are shown to increase with the strain level and to reach values around 0.2 (log_(10) scale) for a peak ground acceleration of 5 m/s^2 at the base of the soil column, which may be reduced by almost 50% when the various constitutive models used the same shear strength and damping implementation.

Reverberation chambers a la carte: An overview of the different mode-stirring techniques

Abstract: Reverberation chambers (RC), a name inspired in room acoustics, are also known in literature as reverberating, reverb, mode-stirred or mode-tuned chambers. In their basic form, they consist of a shielded metallic enclosure, forming a cavity resonator, together with some mode-stirring mechanism. The main goal of such stirring mechanism is to generate an amplitude-varying electromagnetic field that is ideally statistically uniform.

Acoustically perturbed turbulent premixed swirling flames

Abstract: The dynamics of a turbulent premixed confined swirling flame is investigated using large eddy simulation. The flame response is determined by introducing an external acoustic forcing at two modulation frequencies corresponding to characteristic values of the flame transfer function obtained experimentally. These values were found to give different responses in terms of gain in a previous series of experiments. The underlying physical mechanisms identified experimentally are investigated numerically. Simulations confirm that swirl number fluctuations and vortex roll-up govern the flame response. It is also confirmed that the first mechanism is associated with a mode conversion process taking place when acoustic waves impinge on the swirler unit. The axial acoustic velocity disturbance on the upstream side of the swirler generates an axial acoustic wave and an azimuthal convective disturbance in the downstream flow. These combined disturbances are retrieved in the simulation and their effect on the swirl number is extracted. Calculations also indicate that vortex shedding synchronized by the acoustic forcing takes place at the injector lip outlet. Vortices originating from this region are convected in the jet shear layer, impinge on the flame, and roll-up the flame tip. This process interferes with oscillations in the flame angle induced by swirl number fluctuations. The phasing of the flame angle with respect to the instant of vortex shedding from the injector lips determines the lifetime of the vortex before interaction with the flame and controls the strength of this interaction. When this lifetime is reduced, the vortex cannot fully develop and the flame response remains weak. For larger lifetimes, the vortex can fully develop and produce larger heat release rate perturbations. This process depends on the forcing frequency, which determines the phasing between swirl number fluctuations and vortices generation.