More and more printed circuit boards (PCBs) will be used in electric aircraft to achieve higher power density of the on-board electric system, while PCBs in aircraft are more likely to generate partial discharges (PDs) due to external factors such as compact structure and low air pressure. Therefore, this article proposes a fluorescent fiber-based method for detecting and evaluating PDs on PCBs. The detection method is effectively immune against the presence of the electromagnetic, acoustic, and vibration interference. Based on the optical detection, the evolution regularities of PCB surface appearance changes, optical PRPD patterns, and optical pulses during the aging process of PCB under different air pressure are analyzed in this article. Then, 12 assessment features are extracted for the PD aging process, and the contribution of these 12 features to the severity assessment at different air pressures is obtained using the minimal-redundancy-maximal-relevance (mRMR) algorithm. Finally, different numbers of PD features are tested for PD severity assessment by the support vector machine (SVM) algorithm. The evaluation results show that the severity assessment method proposed in this article can achieve an assessment accuracy of at least 91.1% and up to 94.4% under all three air pressures, which has good application and guidance value.

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We performed effective mass measurements employing microwave-induced resistance oscillation in a tunable-density GaAs/AlGaAs quantum well. Our main result is a clear observation of an effective mass increase with decreasing density, in general agreement with earlier studies which investigated the density dependence of the effective mass employing Shubnikov-de Haas oscillations. This finding provides further evidence that microwave-induced resistance oscillations are sensitive to electron-electron interactions and offer a convenient and accurate way to obtain the effective mass.

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We investigate quantum Hall stripes under an in-plane magnetic field B in a variable-density two-dimensional electron gas. At filling factor ν=9/2, we observe one, two, and zero Binduced reorientations at low, intermediate, and high densities, respectively. The appearance of these distinct regimes is due to a strong density dependence of the Binduced orienting mechanism which triggers the second reorientation, rendering stripes parallel to B. In contrast, the mechanism which reorients stripes perpendicular to B showed no noticeable dependence on density. Measurements at ν=9/2 and 11/2 at the same, tilted magnetic field allow us to rule out the density dependence of the native symmetry-breaking field as a dominant factor. Our findings further suggest that screening might play an important role in determining stripe orientation, providing guidance in developing theories aimed at identifying and describing native and B induced symmetry-breaking fields.@en