ABSTRACT
It has long been established that plastic flow in the asthenosphere interacts constantly with the overlying lithosphere and plays a pivotal role in controlling the occurrence of geohazards such as earthquakes and volcanic eruptions. Unfortunately, accurately characterizing the direction and lateral extents of the mantle flow field is notoriously difficult, especially in oceanic areas where deployment of ocean bottom seismometers (OBSs) is expensive and thus rare. In this study, by applying shear wave splitting analyses to a dataset recorded by an OBS array that we deployed between mid-2019 and mid-2020 in the South China Sea (SCS), we show that the dominant mantle flow field has a NNW-SSE orientation, which can be attributed to mantle flow extruded from the Tibetan Plateau by the ongoing Indian-Eurasian collision. In addition, the results suggest that E-W oriented flow fields observed in South China and the Indochina Peninsula do not extend to the central SCS.
ABSTRACT
In this paper, a generalized flexure hinge model, that is, power-trigonometric function-shaped flexure hinges (PTFHs), is proposed. The power function and trigonometric function in the curve function are changed, which obtains different notch types of flexure hinges to meet the needs of flexure hinges in different scenarios. For the flexure hinge model, the notch curve equation of the hinge is presented first, and the influence of the degree of power function, degree of trigonometric function, and other parameters on the structure of the curve is analyzed. Then, the compliance and rotation precision equations of the flexure hinge are derived based on Castigliano's second theorem. Both equations are verified using the finite element method and achieve errors of less than 8.5%. Then, based on the flexure hinge equation, the influence of the size parameters on the compliance and rotation precision of the hinge is analyzed, and a new comparison method is proposed. Parameter ß is defined to analyze the influence of five parameters on ß. Through the comparison of PTFHs and three commonly used flexure hinges, the results prove that the proposed PTFHs have better comprehensive performance. Then, the flexure hinge is statically analyzed. Finally, a test system for flexure hinges is established to verify the performance of the model.
ABSTRACT
The North Pacific subtropical gyre (NPSG) plays a major role in present global ocean circulation. At times, the gyre has coursed through the South China Sea, but its role in the evolutionary development of that Sea remains uncertain. This work systematically describes a major shift in NPSG paleo-circulation evident from sedimentary features observed in seismic and bathymetric data. These data outline two contourite depositional systems-a buried one formed in the late Miocene, and a latest Miocene to present-day system. The two are divided by a prominent regional discontinuity that represents a major shift in paleo-circulation during the latest Miocene (~ 6.5 Ma). The shift coincides with the further restriction of the South China Sea with respect to the North Pacific due to the formation of the Luzon Strait as a consequence of further northwest movement of the Philippine Sea plate. Before that restriction, data indicate vigorous NPSG circulation in the South China Sea. Semi-closure, however, established a new oceanographic circulation regime in the latest Miocene. This work demonstrates the significant role of recent plate tectonics, gateway development, and marginal seas in the establishment of modern global ocean circulation.
ABSTRACT
To better solve the problem of target detection in marine environment and to deal with the difficulty of 3D reconstruction of underwater target, a binocular vision-based underwater target detection and 3D reconstruction system is proposed in this paper. Two optical sensors are used as the vision of the system. Firstly, denoising and color restoration are performed on the image sequence acquired by the vision of the system and the underwater target is segmented and extracted according to the image saliency using the super-pixel segmentation method. Secondly, aiming to reduce mismatch, we improve the semi-global stereo matching method by strictly constraining the matching in the valid target area and then optimizing the basic disparity map within each super-pixel area using the least squares fitting interpolation method. Finally, based on the optimized disparity map, triangulation principle is used to calculate the three-dimensional data of the target and the 3D structure and color information of the target can be given by MeshLab. The experimental results show that for a specific size underwater target, the system can achieve higher measurement accuracy and better 3D reconstruction effect within a suitable distance.
