Judging from the number of confirmed cases, deaths, cures and the time taken to restore normal social and economic order, China is undoubtedly one of the most successful countries in fighting the COVID-19 pandemic, which highlights strong policy capacity of Chinese government using policy tools to solve policy problems efficiently. Based on the policy tools theory put forward by Roy Rothwell and Walter Zegveld, this paper analyzes the specific policy tools used in the prodromal period, breakout period, chronic period and resolution period of China's COVID-19 pandemic and further summarizes three characteristics: The comprehensive use of policy tools, staging of the use of policy tools in different periods and the dominant position of supply-oriented policy tools.
The existing off-board active decoys face such common technical problems as short action time, limited jamming power, and difficult control over deployment situation and effective directive jamming beam direction. For this reason, this paper introduces a new mode and process of anti-missile combat, which places the radar active decoy on an unmanned surface vehicle (USV) to collaborate with the surface warship during the off-board active anti-missile combat. Following the principles of radar terminal guidance centroid jamming, a real-time calculation method for the effective area of off-board active jamming is developed, and the jamming position maneuver strategy under the collaboration of the USV and the surface warship is proposed to implement the off-board active anti-missile combat. The proposed strategy satisfies the needs of long-time, high-power, stable, and effective off-board jamming against incoming anti-ship missiles. This paper further verifies the effectiveness of the proposed strategy in the simulated and live firing confrontations. INDEX TERMS electronic countermeasures unmanned surface vehicle (ECM USV); off-board active decoy; centroid jamming; jamming-position maneuver.
A sensorless control approach for permanent magnet synchronous motor (PMSM) with contra-rotating dual rotors was researched in order to obtain simple configuration and reliable performance. First of all, the mathematical model was established on the basis of the characteristic of surface mounted PMSM with contra-rotating dual rotors. Then a rotating speed estimation algorithm of two rotors was presented based on high frequency voltage pulse injection method. After the rotating speed tracking observer was designed, the sensorless control system of PMSM with contrarotating dual rotors is accomplished. The experimental results verified that the proposed sensorless control approach is competent to PMSM with contra-rotating dual rotors in overall range of speed, and the results indicated that the control system has the advantages of exact tracking, strong robustness and quick response.
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