The actual impedance of non-reflecting boundary conditions : implications for the computation of resonators

Non-reflecting boundary conditions are essential elements in the computation of many compressible flows: such simulations are very sensitive to the treatment of acoustic waves at boundaries. Non-reflecting conditions allow acoustic waves to propagate through boundaries with zero or small levels of reflection into the domain. However, perfectly non-reflecting conditions must be avoided because they can lead to ill-posed problems for the mean flow. Various methods have been proposed to construct boundary conditions which can be sufficiently non-reflecting for the acoustic field while still making the mean-flow problem well posed. This paper analyses a widely-used technique for non-reflecting outlets (Rudy and Strikwerda, Poinsot and Lele). It shows that the correction introduced by these authors can lead to large reflection levels and non-physical resonant behaviors. A simple scaling is proposed to evaluate the relaxation coefficient used in theses methods for a non-reflecting outlet. The proposed scaling is tested for simple cases (ducts) both theoretically and numerically

Characterization of the detection chain of the Micro-channel X-ray Telescope

This paper describes the first performance tests and characterization of the detection chain of the Microchannel X-ray Telescope (MXT), one of the instruments on board the French-Chinese mission SVOM for the study of Gamma-Ray Bursts. The MXT detector consists of a back-illuminated 450 μm-thick fully-depleted framestore silicon pnCCD, operating in the 0.2 − 10 keV energy range. Featuring an imaging area of ≈ 4 cm2, the device is read out in parallel by two CAMEX ASICs and is powered and controlled by its dedicated Front-End Electronics. A complete setup based on a cryostat and a multi-energy X-ray source have been designed for the characterization of the detection chain. The tests, performed at ≈ −65 ◦C, demonstrate a spectral resolution of (82 ± 2) eV at 1.5 keV as well as a < 200 eV low-level threshold. Both of those results are in compliance with the performance requirements of the instrument

AIRS: ARIEL IR spectrometer status

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