Gravitation-enabled Forward Acceleration during Flap-bounding Flight in Birds

Flap-bounding, a form of intermittent flight, is often exhibited by small birds over their entire range of flight speeds. Its purpose is unclear during low to medium speed （2 m·s^-1-8 m·s^-1） flight： aerodynamic models suggest continuous flapping would require less power output and lower cost of transport. To explore its functional significance at low speeds, we measured body trajectory and kinematics of wings and tail of two zebra finches （Taeniopygia guttata） during flights between two perches in a laboratory. The flights consisted of three phases： initial, descending and ascending. Zebra finch first accelerated using continuous flapping, then descended, featuring intermittent bounds. The flight was completed by ascending using nearly-continuous flapping. When exiting bounds in descending phase, they achieved higher velocity than that of pre-bound forward by swinging their body forward similar to pendular motion with conserved me- chanical energy. We recorded takeoffs of three black-capped chickadees （Poecile atricapillus） in the wild and also found similar kine- matics. Our modeling of power output indicated finch achieved higher velocity （13%） with lower cost of transport （9%） when descending, compared with continuous flapping in previously studied pigeons. Flap-bounding could be useful for unmanned aerial vehicle design by mimicking descending flight to achieve rapid take-off and transition to forward flight.

A novel approach for assessing color harmony of historical buildings via street view image

While new buildings continue to emerge in the process of urbanization,historical buildings,as valuable legacies carrying national historical memory,play an important role in the urban landscape.Previous studies have shown that color harmony is a crucial factor in coordinating urban landscapes.However,the evaluation of color harmony in historic areas and buildings lacks effective quantitative standards,often overlooking factors such as complementary color harmony and the compatibility of analogous colors.This study aims to build a new method to evaluate the color harmony of historical buildings through street view technology,semantic segmentation algorithms,quantification of color harmony methods based on image property detection and classification,questionnaire verification,and takes Shanghai’s historical buildings as an example to explore.Our study categorizes six types of color harmony indexes for Shanghai street-facing historic buildings into three levels,with the top tier serving as a benchmark for excellence and the lowest tier highlighting areas in need of urban environmental improvement.This study uniquely considers color compatibility within hue ranges and expanded relationship types like complementary harmony.This approach,applicable to cities globally,offers practical tools for urban planners and conservators in managing and preserving historic areas and buildings.