The helicon wave plasma (HWP) sources have well-known advantages of high efficiency and high plasma density, with broad applications in many areas. The crucial mechanism lies on mode transitions, which has been an outstanding issue for years. We have built a fluid simulation model and further developed the Peking University Helicon Discharge (PHD) code. The mode transitions also known as density jumps of a single-loop antenna discharge are reproduced in simulations for the first time. It is found that large-amplitude SHWs are responsible for the mode transitions, similar to those of a resonant cavity for laser generation. This paper intends to give a complete and quantitative standing helicon wave (SHW) resonance theory to explain the relationship of the mode transitions and the SHWs. The SHW resonance theory reasonably explains several key questions in helicon plasmas, such as mode transition and efficient power absorption, and helps to improve future plasma generation methods.

Landslide disaster monitoring has always been an important research topic. In this study, we used the finite element numerical method to simulate the Meiping landslide dynamic process. The mechanical properties and geometric structure of the landslide were constructed based on the geology and the displacement field of the Meiping landslide. From the interactive simulation, we adjusted the landslide bottom to optimize the existing model and performed some individual calculations for external factors, such as water level and precipitation, which affect the landslide slip condition. The results show that the rapid decrease in water level and rainfall are the major factors in the displacement of the Meiping landslide. Through the dynamic simulation, we can enhance understanding of landslide development and make some useful progress in predicting landslide disaster.

The moment magnitude (Mw) 6.4 and 7.1 Ridgecrest earthquake sequence that occurred on July 4 and 6, 2019, ruptured a conjugate fault system within the eastern California shear zone. In addition to the ∼50 km surface ruptures, the sequence activated a series of structures with lengths ranging from 1 to 10 km, which are well illuminated by phase gradient maps of Synthetic Aperture Radar (SAR) interferograms. The deformation patterns and mechanisms of these fractures have been well studied, yet the controlling factors of their spatial distribution are less discussed, which are important for understanding how the accumulated strain is released via distributed faulting in the earthquake cycle. Here, we use multi-source SAR images to derive three-dimensional (3D) surface displacement along the main ruptures and the east–west strain across the detected small fractures caused by the 2019 Ridgecrest earthquake sequence. We find that the distribution of these fractures is related to the displacement pattern along the main rupture. Specifically, more fractures appeared in areas with larger slips normal to the main rupture as well as in the junction of the conjugated ruptures. We also conduct uniaxial loading rock experiments to evaluate the strain distribution before the samples were broken. Rock experiments show that rupturing of a conjugated fault system may produce local strain concentration along the main rupture, indicating the important role of the orthogonal faults in generating small fractures with different striking angles and deformation patterns. The 2019 Ridgecrest earthquake sequence exhibits complicated crust behaviors by rupturing an immature fault system, implying that the simple elastic rebound theory may be insufficient to model the coseismic deformation during the earthquake cycle, particularly in the zone with weak crust.

The application of construction waste as an aggregate in subgrade backfilling is an important recycling option. This study analyzed a subgrade backfill material consisting of lime-fly ash construction waste mixture (LFCWM). Compaction and California bearing ratio (CBR) tests were performed on LFCWM under different cement-aggregate ratios (CARs, 3:7, 4:6, 5:5, 8:2). Different normal stresses (100, 200, and 300 kPa) and aggregate sizes (20%, 40%, 60%, 80% of P4.75) were also evaluated. The experimental results indicated that: (1) when the CAR was 4:6, the optimum water content and the maximum dry density reached their maximum values of 10.1% and 2.03 g/cm3, respectively, the maximum CBR value was 42.5%, and the shear strength reached its maximum value. (2) With an increase in shear displacement, the shear stress showed a rapid initial increase, then a slow decrease, and finally tended to stabilize. (3) Normal stress had a positive effect on the shear strength of the mixture. (4) When P4.75 was 40%, the shear strength of LFCWM was the maximum. The research results have been successfully applied to road engineering, providing an important reference for the application of construction waste aggregate in roadbed engineering.

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