The equations of motion of an insect with flapping wings are derived and then simplified to that of a flying body using the "rigid body" assumption. On the basis of the simplified equations of motion, the longitudinal dynamic flight stability of four insects (hoverfly, cranefly, dronefly and hawkmoth) in hovering flight is studied (the mass of the insects ranging from 11 to 1,648 mg and wingbeat frequency from 26 to 157 Hz). The method of computational fluid dynamics is used to compute the aerodynamic derivatives and the techniques of eigenvalue and eigenvector analysis are used to solve the equations of motion. The validity of the "rigid body" assumption is tested and how differences in size and wing kinematics influence the applicability of the "rigid body" assumption is investigated. The primary findings are: (1) For insects considered in the present study and those with relatively high wingbeat frequency (hoverfly, drone fly and bumblebee), the "rigid body" assumption is reasonable, and for those with relatively low wingbeat frequency (cranefly and howkmoth), the applicability of the "rigid body" assumption is questionable. (2) The same three natural modes of motion as those reported recently for a bumblebee are identified, i.e., one unstable oscillatory mode, one stable fast subsidence mode and one stable slow subsidence mode. (3) Approximate analytical expressions of the eigenvalues, which give physical insight into the genesis of the natural modes of motion, are derived. The expressions identify the speed derivative M u (pitching moment produced by unit horizontal speed) as the primary source of the unstable oscillatory mode and the stable fast subsidence mode and Z w (vertical force produced by unit vertical speed) as the primary source of the stable slow subsidence mode.
The Beijing-Tianjin-Hebei (BTH) region has encountered increasingly severe and frequent haze pollution during recent decades. This study reveals that the El Niño–Southern Oscillation (ENSO) has distinctive impacts on interannual variations of haze pollution over BTH in early and late winters. The impact of ENSO on the haze pollution over the BTH is strong in early winter, but weak in late winter. In early winter, ENSO-related sea surface temperature anomalies generate double-cell Walker circulation anomalies, with upward motion anomalies over the tropical central-eastern Pacific and tropical Indian Ocean, and downward motion anomalies over tropical western Pacific. The ascending motion and enhanced atmospheric heating anomalies over the tropical Indian Ocean trigger atmospheric teleconnection propagating from North Indian Ocean to East Asia, and result in generation of an anticyclonic anomaly over northeast Asia. The associated southerly anomalies to the west side lead to more serious haze pollution via reducing surface wind speed and increasing low-level humidity and thermal inversion. Strong contribution of the Indian Ocean heating anomalies to the formation of the anticyclonic anomaly over northeast Asia in early winter can be confirmed by atmospheric model numerical experiments. In late winter, vertical motion and precipitation anomalies are weak over tropical Indian Ocean related to ENSO. As such, ENSO cannot induce clear anticyclonic anomaly over northeast Asia via atmospheric teleconnection, and thus has a weak impact on the haze pollution over BTH. Further analysis shows that stronger ENSO-induced atmospheric heating anomalies over tropical Indian Ocean in early winter is partially due to higher mean SST and precipitation there.
The dealing/recycling of Ni‐containing wastewater pollution has aroused great attention both from environmental science and resource utilization perspectives. Herein, a classic CaFe‐layered double hydroxide (CaFe‐LDH) stabilizer, which exhibits a super‐stable mineralization efficiency for removing Ni2+ ions with a maximum saturated removal capacity of 321 mg g−1 is prepared. This stabilizer can remove not only 10 000 mg L−1 Ni2+ ions to a few mg L−1, but also 1 mg L−1 Ni2+ ions to 2 µg L−1. Moreover, the CaFe‐LDH shows great mineralization capability for the real Ni‐containing electroplating solution. It is demonstrated by ex situ X‐ray diffraction and extended X‐ray absorption fine structure characterization that the isomorphous substitution of Ca2+ by Ni2+ in the laminate of LDH dominates the mineralization process, and the CaFe‐LDH is transformed to the corresponding NiCaFe‐LDH accordingly. Further application of the resultant NiCaFe‐LDH shows improved electrocatalytic oxygen evolution reaction and photocatalytic CO2 reduction activities. This work paves great way for Ni2+ ion removal from wastewater and utilization of the recycled Ni resource.
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