Microseisms are the most energetic signals of Earth's ambient noise field. Locating the sources of microseisms helps us to understand arrivals on noise cross‐correlation functions (NCFs) and the asymmetric amplitude of Rayleigh waves on the positive and negative parts of the NCFs. Using a dense broadband seismic array in eastern China, we investigated temporal and spatial characteristics of Rayleigh wave microseisms in the frequency range of 45–155 mHz by conducting beamforming and Rayleigh wave amplitude‐azimuth variation analyses. Seasonal variations of incident direction are clearly observable at the primary microseisms frequency band (45–95 mHz) but are less prominent at the secondary microseisms frequency band (95–155 mHz). The beamforming and amplitude‐azimuth variation analyses also indicated that microseisms arriving at the array are dominantly from five back azimuthal bands. To locate the source areas of the observed microseisms, we combined noise data from two additional arrays in southern California and employed a multi‐array beamforming technique to constrain plausible microseisms' source areas. We found that microseisms of the five azimuthal bands were excited at the Southern Ocean, western coast of Europe, coastal areas of the North Pacific Ocean, the Kerguelen Islands in the southern Indian Ocean, and the Polynesia islands in the South Pacific Ocean, respectively.
Full-waveform inversion (FWI) is a powerful tool to reconstruct subsurface geophysical parameters with high resolution. As 3D surveys become widely implemented, corresponding 3D processing techniques are required to solve complex geological cases, while a large amount of computation is the most challenging problem. We propose an adaptive variable-grid 3D FWI on graphics processing unit devices to improve computational efficiency without losing accuracy. The irregular-grid discretization strategy is based on a dispersion relation, and the grid size adapts to depth, velocity, and frequency automatically. According to the transformed grid coordinates, we derive a modified acoustic wave equation and apply it to full wavefield simulation. The 3D variable-grid modeling is conducted on several 3D models to validate its feasibility, accuracy and efficiency. Then we apply the proposed modeling method to full-waveform inversion for source and residual wavefield propagation. It is demonstrated that the adaptive variable-grid FWI is capable of decreasing computing time and memory requirements. From the inversion results of the 3D SEG/EAGE overthrust model, our method retains inversion accuracy when recovering both thrust and channels.
It is well established that p-Hydroxycinnamic acids (HCAs), including ferulic, caffeic, sinapic, and p-coumaric acids, possess a characteristic phenylpropanoid C6-C3 backbone and account for about one-third of the phenolic compounds in our diet. HCAs are typically associated with various plant cell wall components, including mono-, di-, and polysaccharides, sterols, polyamines, glycoproteins, and lignins. Interestingly, enzymes produced by intestinal microbes liberate HCAs from these associations. HCAs are completely absorbed in their free form upon ingestion and undergo specific reactions upon absorption in the small intestine or liver. The gut epithelium, composed of intestinal epithelial cells (IECs), acts as a physical barrier against harmful bacteria and a site for regulated interactions between bacteria and the gut lumen. Thus, maintaining the integrity of the epithelial barrier is essential for establishing a physiochemical environment conducive to homeostasis. This review summarizes the protective effects of HCAs on the intestinal barrier, achieved through four mechanisms: preserving tight junction proteins (TJPs), modulating pro-inflammatory cytokines, exerting antioxidant activity, and regulating the intestinal microbiota.
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