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In this work, the spreading of a solder droplet on a substrate agitated by ultrasonic vibration was recorded by a high-speed camera. The dynamics and physical processes of the spreading, such as corrugate formation and atomization, were investigated. Results showed the solder droplet was able to spread on a nonwetting substrate, and it presented periodic expanding-shrinking spreading characteristics with a periodicity of dozens of acoustic periods. Corrugates formed as a result of the capillary wave propagation on the droplet, and the formation became intensive on a violently vibrating surface. Atomization preferentially occurred at the spreading front during solder expansion, where the liquid solder appeared as a film and burst on the whole droplet with strong vibration. High ultrasonic power resulted in fast spreading and a large spreading diameter. In particular, the solder droplet exhibited fast spreading and a large spreading diameter on the TC4 alloy with high characteristic impedance. The Sn-4Cu solder with large viscosity spread slowly and exhibited a small spreading diameter.

The eastern South China Block (ESCB) is characterized by intense magmatism in the late Mesozoic. To further investigate the mechanism of late Mesozoic magmatism, we apply the tomographic method to construct a P-wave velocity model down to 750 km by using 40,989 P-wave arrival times collected from 687 teleseismic events recorded by 191 stations. Our model shows that (1) a high-Vp anomaly is observed beneath the lower Yangtze Block (YZB) and northern Cathaysia Block (CAB) in the crust and uppermost mantle, which could represent the present lithosphere; (2) two high-Vp anomalies are observed in the upper mantle beneath the YZB, which could be the detached lithosphere and the relict of the subducted SCB; (3) the break-off of the subducted Eurasian Plate has penetrated the 410 km discontinuity beneath central and northern Taiwan Island; (4) the stagnant Paleo-Pacific Plate in the MTZ is mainly beneath the lower YZB; (5) the low-Vp anomaly in the upper mantle that is immediately above the stagnant Paleo-Pacific Plate may represent the thermal asthenosphere caused by plate dehydration; and (6) the low-Vp anomaly beneath the southern CAB extends from the crust downward to the MTZ, which may represent an ‘upward channel’ for thermal materials. Based on our results and those of previous studies, we suggest that late Mesozoic magmatism in the ESCB could be highly associated with the subduction of the Paleo-Pacific Plate and its eastward rollback. We also suggest that thermal/chemical erosion may be responsible for lithospheric thinning in the ESCB.

The Cathaysia Block is located in South China, along the western margin of the Pacific plate, and well known for its widespread granitoids and rich poly-metallic mineralization. Despite the numerous studies conducted in this region, some key questions are still in debate, which revolve around the detailed crustal architecture, the boundary between the western and eastern part of Cathaysia Block, and the geodynamic evolution and metallogenic settings in the Cathaysia Block. In this study, we have conducted a dense broad-band seismic observation in the Cathaysia Block, and obtained the fine crustal structure of it by using P-wave receiver functions and analyzing other geophysical and geological studies comprehensively. Our study has following findings: (1) the crust of the Cathaysia Block is ~31.5 km thick, thinner than that of the global continent, and is interpreted to have been thinned since the Late Mesozoic; (2) the Vp/Vs ratio of the Cathaysia Block is lower than that of the global continent, which implies there is no extensive underplating beneath the Cathaysia Block, or that the magma may be confined at bottom of the crust and formed a velocity gradient belt around Moho; (3) Zhenghe-Dapu fault is marked as the structural boundary between the western and eastern Cathaysia Block; (4) the western and eastern Cathaysia Block have different intra-crustal structures, petrochronology features and mineralization settings; (5) the subduction of the paleo-Pacific plate and the following roll-back could be responsible for the geodynamic evolution of the crustal deformation, as well as the widespread magmatism and mineralization.

The eastern South China Block is characterized by multi-stage intra-continental collisions and orogeny from the Paleozoic to early Mesozoic, and strong magmatism and metallogenesis since the late Mesozoic. In order to further study the tectonics, magmatism and metallogenesis, we constructed a new model of crustal thickness and Vp/Vs ratio for the crust beneath the eastern South China Block using H-κ stacking of teleseismic P-wave radial receiver functions from 845 broadband seismic stations. New knowledge of the crustal structure and properties pertinent to the tectonics and metallogenesis is as follows: (1) the average crustal thickness beneath the eastern South China Block is 33 km. It is thinner and varies smoothly in the Cathaysia Block and Jiangnan Orogen, and gradually thickens to the northwest and reaches ~40 km in the Yangtze Block; (2) the average crustal Vp/Vs ratio of the eastern South China Block is ~1.72, lower than the global average value ~1.78. This implies an absence of a mafic lowermost crustal layer; (3) the Jiangnan Orogen is characterized by a conspicuous belt of lower Vp/Vs ratios, different from the Yangtze and Cathaysia Blocks on either side. This is interpreted as caused by synorogenic crustal thickening and the subsequent lower crustal delamination; (4) the crustal thickness and the Vp/Vs ratios in the eastern South China Block are negatively correlated, also indicating tectonic thickening of a felsic upper and middle crust. This is consistent with folding and thrusting during orogenesis and the later delamination of the mafic lower crust; (5) the Anhua-Luocheng fault is considered to be the southwestern segment of the boundary between the Yangtze Block and Jiangnan Orogen; (6) lithospheric extension caused by subduction of the Pacific Plate and the corresponding slab rollback during the late Mesozoic can explain the crustal thickness, the Vp/Vs ratio distribution patterns and the metallogenesis in the eastern South China Block.

Modeling and verifying real-world cyber-physical systems is challenging, which is especially so for complex systems where manually modeling is infeasible. In this work, we report our experience on combining model learning and abstraction refinement to analyze a challenging system, i.e., a real-world Secure Water Treatment system (SWaT). Given a set of safety requirements, the objective is to either show that the system is safe with a high probability (so that a system shutdown is rarely triggered due to safety violation) or not. As the system is too complicated to be manually modeled, we apply latest automatic model learning techniques to construct a set of Markov chains through abstraction and refinement, based on two long system execution logs (one for training and the other for testing). For each probabilistic safety property, we either report it does not hold with a certain level of probabilistic confidence, or report that it holds by showing the evidence in the form of an abstract Markov chain. The Markov chains can subsequently be implemented as runtime monitors in SWaT., Comment: Accepted by FM 2018