The appearance of mechanical cracks originated from anisotropic expansion and shrinkage of electrode particles during Li de/intercalation is a major cause of the capacity fading in Li-ion batteries. Well-designed and controlled nanostructures of electrodes have shown a prominent prospect for solving this obstacle. Here, we report a novel and convenient strategy for the preparation of graphene nanoscroll wrapping NbO nanoparticles (denoted as T-NbO/G). First, high energy ball milling is conducted to acquire softly agglomerated T-NbO nanoparticles owing to its spontaneous reduction of surface energy among these single particles. Then freeze-drying leads to the formation of graphene nanoscroll, which easily realizes the in situ wrapping over softly agglomerated T-NbO nanoparticles. Extended cycling tests demonstrate that such T-NbO/G yields a high reversible specific capacity of 222 mA h g over 700 cycles at 1C. The dominated surface capacitive insertion processes possessing favorable kinetics enable T-NbO/G to exhibit excellent rate performance, which achieve a capacity of 110 mA h g at 10C. A combined ex situ X-ray diffraction, scanning electron microscopy, and transmission electron microscopy investigation reveal that the long-term cycling stability of T-NbO/G is attributed to the excellent structural stability of the electrode, in which the synergistic effect between the softly agglomerated T-NbO nanoparticles and graphene nanoscroll prevents the formation of mechanical cracks.
Surveillance system is becoming an indispensable system on construction sites with the fast development of computer vision techniques, thus an optimal placement of surveillance cameras is essential for the successful performance of this system. However, to develop effective models and solutions for large‐scale camera placement still remain as opening challenges. Therefore, this study investigated two fundamental placement problems and proposed a multiobjective placement problem, where the maximum‐coverage problem is to monitor the construction layout as much as possible with a limited budget; the minimum‐cost problem is to minimize the cost given a layout required to be fully covered; and the multiobjective problem is to identify the Pareto fronts of cost and coverage ratio of the system. To solve these problems, the objective space and search space were discretized, and the deterministic and heuristic approaches were revised and developed to provide effective solutions. Finally, experiments in a practical project in Hong Kong were conducted to verify the sufficiency of the developed algorithms and findings revealed potential implementations in many scenarios.
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