Suihu Dang

Distributed optical fiber acoustic sensing is a versatile technology based on phase-sensitive optical time domain reflectometry, capable of distributed monitoring of multi-point disturbances along a length of the optical fiber, which has been widely implemented in diverse science and engineering fields. However, for ultra-long sensing distances, the system suffers from several signal fading mechanisms, especially those produced by interference and polarization fluctuation. As a result, the local signal intensity will be greatly attenuated, causing the phase signal to jump, making it difficult to continuously and effectively collect the disturbance signal. An adaptive phase correction method for fading suppression in distributed optical fiber acoustic sensing systems is proposed in this paper. The fading-point position is obtained through differential analysis of the amplitude signal and its outlier detection. Phase correction is performed using a moving-window adjacent interpolation to achieve fading suppression. Experiments conducted in a controlled laboratory environment show that, for the piezoelectric transducer vibration signals, applying the fading suppression method results in an average increase of 12.49 dB in signal-to-noise ratio. The time required of a single moving-window processing is only 3.1 ms. During lake trials, the signal-to-noise ratio of an underwater acoustic disturbance signal increases by 20.36 dB after applying the fading suppression method, demonstrating that the proposed method suppressed the signal distortion caused by fading effectively and could completely restore the disturbance signal.

Its outstanding mechanical and thermodynamic characteristics make SrAl₂O₄ a highly desirable ceramic material for high-temperature applications. However, the effects of elevated pressure on the structural and other properties of SrAl₂O₄ are still poorly understood. This study encompassed structural, elastic, electronic, dynamic, and thermal characteristics. Band structure calculations indicate that the direct band gap of SrAl₂O₄ is 4.54 eV. In addition, the Cauchy pressures provide evidence of the brittle characteristics of SrAl₂O₄. The mechanical and dynamic stability of SrAl₂O₄ is evident from the accurate determination of its elastic constants and phonon dispersion relations. In addition, a comprehensive analysis was conducted of the relationship between specific heat and entropy concerning temperature variations.

In this work, graphene-like ZnO (g-ZnO)-based two-dimensional (2D) heterostructures (ZnO/WS₂ and ZnO/WSe₂) were designed as water-splitting photocatalysts based on the hybrid density functional. The dependence of photocatalytic properties on the rotation angles and biaxial strains were investigated. The bandgaps of ZnO/WS₂ and ZnO/WSe₂ are not obviously affected by rotation angles but by strains. The ZnO/WS₂ heterostructures with appropriate rotation angles and strains are promising visible water-splitting photocatalysts due to their appropriate bandgap for visible absorption, proper band edge alignment, and effective separation of carriers, while the water oxygen process of the ZnO/WSe₂ heterostructures is limited by their band edge positions. The findings pave the way to efficient g-ZnO-based 2D visible water-splitting materials.

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Based on the analysis of the evanescent wave from total internal reflection, a light-emitting diode (LED) structure with a plasmonic Ag nanostructure and indium tin oxide (ITO) grating was proposed to enhance the extraction efficiency. The two-dimensional finite-difference time-domain method was used to study the spectral properties of the hybrid structure and the effects of structure parameters on extraction enhancement. The results demonstrate that the plasmonic Ag nanostructure can couple the evanescent wave to a propagation wave around the GaN/ITO interface, and then the photons are scattered out of the LED chips by the ITO grating with high extraction efficiency. Under the optimal parameters, the light extraction efficiency can reach approximately three times the original value at a relatively longer wavelength.