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This paper presents a baseline-free quantitative method for the imaging of corrosion flaws present in thin plates with under-sampled data. This method is based on the Hybrid Algorithm for Robust Breast Ultrasound Tomography (HARBUT) which is itself inherently baseline-free. However, in order to ensure that the incident field component becomes negligible in the reconstruction, a calibration step is necessary. Indeed, it is essential to rescale the data with respect to the acoustic model whether it be simulation data or experimental data. This calibration is usually performed by manually choosing a ray for which the domain of propagation is assumed sound. This can be problematic because this method is not automatic. Moreover, if the chosen ray happens to pass through a flaw, the resulting image will be of poor quality. This paper proposes an autocalibration method for the rescaling step. The field of application is Structural Health Monitoring (SHM) of critical structures with heavy constraints on both sensor intrusiveness and diagnostic reliability. In order to limit intrusiveness, a sub-sampled array of embedded guided waves sensors within the structure is used. Extensions to HARBUT are introduced to compensate for the aliasing caused by the undersampling. The benefits of these extensions are then assessed with numerical simulations and experimental datasets measured by a PZT network. [ABSTRACT FROM AUTHOR]

Heavy neutral leptons (HNLs) appear in many extensions of the Standard Model of particle physics. In this study, we investigate to which extent the NA62 experiment at CERN could improve the existing bounds on the HNL mixing angle |Ue|² by performing a missing mass search in K+→π0e+N decays in flight. We show that the limit |Ue|²≃2×10-6 can be reached with the currently available data in the mass range 125-144 MeV, which is currently not well covered by production searches. Future data, together with a dedicated trigger and/or improvements in rejection of out-of-acceptance photons, can improve this limit by another order of magnitude. [ABSTRACT FROM AUTHOR]