A series of semi‐interpenetrating polymer networks (semi‐IPNs) based on polyurethane and polydimethylsiloxane were prepared. They are formed by crosslinking the polydimethylsiloxane prepolymer with 3‐aminopropyltriethoxysilane in the presence of linear polyurethane. Investigations were carried out by swelling measurement, dynamic mechanical analysis, Fourier transform infrared experiments, and scanning electron microscopy. It is concluded that the crosslinking of the polydimethylsiloxane network is restricted by the presence of the polyurethane, and the grafting level between the two components is low. The system is phase separated, and there is dual phase continuity in the midrange composition.

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Fatigue cracks are usually initiated by small geometrical irregularities or material inhomogeneities that give rise to sharp local stress concentrations. In the early stages of fatigue, small cracks often remain hidden from conventional ultrasonic detection by stronger scattering from the very same structural imperfection that produced them in the first place. A new experimental method was developed to selectively increase the sensitivity of ultrasonic echographic techniques for such hidden fatigue cracks by exploiting one of their most characteristic features, their susceptibility for closure under compressive stress. Thermo-optical modulation by pulsed infrared laser irradiation was introduced to produce a temporary compressive thermal stress on the surface of the specimen. The resulting dynamic closure of microcracks was detected by a high-frequency ultrasonic surface wave technique. It is demonstrated that this method can be used to effectively distinguish fatigue cracks from other structural imperfections present in the material.

In this paper, an anti-jamming method, which turns the single objective optimization problem into a multi-objective optimization problem by utilizing 2-norm, is proposed. The proposed jamming suppression method can reduce the wide nulls and wrong nulls problems, which are generated by the common adaptive nulling methods. Therefore a better signal-noise-ratio (SNR) can be achieved, especially when the jammers are close to satellite signals. It can also improve the robustness of the algorithm. The effectiveness of the proposed method is evaluated by simulation and practical outdoor experiments with the GPS L1 band C/A signals. The experimental results show that with the dedicated method, the nulls targeting at the corresponding jammers become narrower and the wrong nulls can be eliminated.