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Marine DC power grid typically sustains high current when shorted and its electric characteristics are extremely susceptible to influence by the stray parameters. Given the limitations of cabin space, it is necessary for the bus-tie switch of the DC grid to be miniaturized and in a symmetrical topology while the same level of fault shutdown protection performance is maintained. To this end, this paper presents the rule that how support capacitors and busbar's stray parameters impact short-circuit current, which was analyzed through a combination of simulation and testing at multiple operating points of a typical DC power grid. Specifically, to ensure the safety of devices, breaking time of the solid-state circuit breaker should not exceed 200 μs, and addressing the transient overvoltage suppression in case of bus- tie switch breaking is identified as a key technical issue. Based on the analysis results, it proposes a solid-state circuit breaker with a mirror-symmetrical bus-tie switch topology suitable for marine application scenarios and with the optimized performance based on simulation, to integrate the bus-tie switch and chopper multiplexing as a solution for voltage oscillation upon the bus-tie switch breaking-off. Based on the practical short-circuit tests, it is verified that the designed bus-tie switch is capable of meeting continuous DC power supply conditions on the normal side DC power grid when the busbar and branch are short-circuited. The onboard test results show that the solid-state circuit breaker can achieve a breaking-off capacity in the order of 100 μs, the optimized design of bus-tie switch topology meets the short-circuit protection requirements of marine DC power grid, and the delay for the bus-tie switch to break-off in case of short-circuit fault can mitigate breaking overvoltage fluctuation, thus better guaranteeing system safety.

Due to the strictly restricted free area, vehicles have difficulties to pass through mine narrow corridors. To solve this problem, this paper presents a trajectory planning method based on optimal control. Narrow corridor model and vehicle single-track kinematics model are adopted to construct the trajectory planning model based on optimal control with an approximate space-discretization strategy considering factors like vehicle passage time, vehicle-boundary collision and vehicle actuator range. By vehicle kinematics integral, the control variable sequence solved by the above trajectory planning model leads to an initial optimal trajectory. Taking the discretization impact on trajectory continuity into account, the final target trajectory is formed after smooth the initial optimal trajectory by quadratic programming. Simulation results show that the trajectory generated by the proposed method is effective in narrow corridor scene, and the generated trajectory is continuous and smooth. Compared with the baseline method, the average maximum curvature reduces from 0.094 m-1 to 0.040 m-1 and the average passing time reduces from 6.18 s to 4.80 s in evaluate scenarios.

Objective To investigate the expression of heparanase-2 (HPSE2) in gastric cancer tissues, and explore its effect on the survival and prognosis of the cancer and invasion and migration of the cancer cells. Methods Immunohistochemical staining of HPSE2 was performed on gastric cancer tissue chip to examine the expression level of HPSE2 in gastric cancer and paracancerous tissues. The correlation of HPSE2 expression level with clinical features, survival, prognosis and prognostic factors were analyzed. The lentival vectors of HPSE2 overexpression were constructed, and then transfected in gastric cancer cell lines SGC7901 and MKN28. The effect of HPSE2 overexpression on invasion and migration of gastric cancer cells were detected using Transwell analysis. Results The mean pathological score of HPSE2 was 4.56 in gastric cancer tissue, and 7.18 in paracancer tissues, showing that the expression was significantly lower in gastric cancer than paracancer tissues (P < 0.05). The expression level of HPSE2 was closely correlated with the tumor size, lymph node metastasis, and clinical staging. The patients with higher HPSE2 expression had obviously shorter median survival time and cumulative survival rate than those with lower expression (P < 0.05). Cox proportional risk model showed that clinical stage, tumor size and HPSE2 protein expression were risk factors for prognosis of gastric cancer patients (P < 0.05). Overexpression of HPSE2 could remarkably inhibit the invasion and migration of gastric cancer cells. Conclusion HPSE2 is lowly expressed in gastric cancer tissues, and is associated with the tumor size, lymph node metastasis, survival and prognosis of gastric cancer. Overexpression of HPSE2 could inhibit the invasion and migration of gastric cancer cells.