With the advantage of high mobility, Unmanned Aerial Vehicles (UAVs) are used to fuel numerous important applications in computer vision, delivering more efficiency and convenience than surveillance cameras with fixed camera angle, scale and view. However, very limited UAV datasets are proposed, and they focus only on a specific task such as visual tracking or object detection in relatively constrained scenarios. Consequently, it is of great importance to develop an unconstrained UAV benchmark to boost related researches. In this paper, we construct a new UAV benchmark focusing on complex scenarios with new level challenges. Selected from 10 hours raw videos, about 80, 000 representative frames are fully annotated with bounding boxes as well as up to 14 kinds of attributes (e.g., weather condition, flying altitude, camera view, vehicle category, and occlusion) for three fundamental computer vision tasks: object detection, single object tracking, and multiple object tracking. Then, a detailed quantitative study is performed using most recent state-of-the-art algorithms for each task. Experimental results show that the current state-of-the-art methods perform relative worse on our dataset, due to the new challenges appeared in UAV based real scenes, e.g., high density, small object, and camera motion. To our knowledge, our work is the first time to explore such issues in unconstrained scenes comprehensively.

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To improve the microstructure of low-temperature-processed CsPbIBr2 films, a chlorobenzene (CB) and isopropyl alcohol (IPA) mixed solution is used as an antisolvent to fabricate CsPbIBr2 films. It is found that the modified film by the mixed antisolvent demonstrates a better morphology, crystallinity, absorption of sunlight, less trap-state density (N trap), and suppressed carrier recombination. The modified perovskite solar cells (PSCs) without a hole-transport layer (HTL) achieve a champion efficiency of 7.05%, being much higher by 28.18% than that of the Reference-PSCs without an antisolvent. Moreover, the HTL of undoped zinc phthalocyanine (ZnPc) prepared by solution processing is used to promote charge transfer and protect the CsPbIBr2 film from damage caused by humid air at the CsPbIBr2/carbon interface. The best PSC with a structure of FTO/TiO2/CsPbIBr2/ZnPc/carbon yields a champion efficiency of 8.48% (Reference-PSC, 5.50%) with an open-circuit voltage of 1.23 V. The modified PSCs without encapsulation demonstrate improved humidity stability and retain about 90% (Reference-PSC, ∼70%) of their initial efficiency after storage at a 20% relative humidity in air for 30 days. In addition, the modified PSCs possess good light and thermal stability. Our work provides a feasible low-temperature (150 °C) process to prepare CsPbIBr2 films with the preferred orientation and stable, efficient all-inorganic PSCs (200 °C).

Abstract:High-voltage direct current (HVDC) lines with line-commutated converter (LCC) are being increasingly employed to transmit bulk wind power over long distance. However, this may cause the sub-synchronous torsional interaction (SSTI) between the wind farms and the LCC-HVDC system. The SSTI characteristics of wind farms with fixed-speed induction generator (FSIG) wind turbines connected to LCC-HVDC are investigated in this paper. To simplify the calculations, a modular modeling method is proposed for building the small-signal mathematical model of the investigated system. Small-signal analysis, participation factor analysis, and impact of dominant factors analysis are then applied to investigate the SSTI characteristics under different operating conditions. Three oscillation modes associated with the SSTI are identified in the entire system through small-signal and participation factor analysis, comprising two torsional modes and an electromechanical mode. Impact of dominant factors analysis shows that the system becomes less stable as the wind farm capacity grows and the distance between FSIG wind farm and the rectifier station increases. Moreover, the above analysis suggests that wind farms with FSIG connected to LCC-HVDC lines may not cause unstable SSTI. The electromagnetic transient simulations based on PSCAD/EMTDC (Power Systems Computer-Aided Design/Electromagnetic Transients including DC) verify these results.