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In recent years, the application prospect of urban logistics unmanned aerial vehicles has attracted extensive attention. The high-density operation of UAVs requires autonomous separation maintenance capability. To achieve autonomous separation maintenance, it is necessary to conduct autonomous track prediction and formulate the required separation accordingly. Based on the target level of safety requirements for UAV operation, aiming at the autonomous separation maintenance ability of UAVs and considering the accuracy of track prediction, a method to calculate the required separation between UAVs is proposed. This study consists of two parts. Firstly, based on historical data, the position prediction error of the flight track is investigated. Using a machine learning model, a two-stage track prediction method, which involves classification followed by prediction, is proposed for urban logistics UAV track data. Subsequently, based on the track prediction error distribution, by designing a gas model and a position error probability model, a separation-formulating model for urban logistics UAVs in free flight is proposed in which UAV maneuverability is considered. By applying this model, the required separation is formulated for UAVs. When the required separation is set to 48.5 m, the overall collision risk meets the TLS requirements. The research provides a feasible method for establishing autonomous separation for urban logistics UAVs.

The title compound, C14H12ClNO, is a Schiff base derived from the condensation of equimolar quantities of 5-chlorosalicylaldehyde and 1-benzylamine. The molecule has a trans configuration with respect to the imine C=N double bond. The N atom is involved in an intramolecular O—H...N hydrogen bond.

The title complex, [Cu2(C14H11ClNO)2Cl2], has a centrosymmetric dinuclear structure where two symmetry-related copper(II) metal centres are bridged by the O atoms of two phenoxy groups. Each copper(II) centre displays a distorted tetrahedral coordination provided by one N atom and two O atoms from two Schiff base ligands and by one Cl atom. The Cu...Cu separation is 3.0702 (9) Å.

The asymmetric unit of the title compound, [Ni(C7H4ClO2)2], contains one half-molecule. The NiII ion, lying on an inversion centre, is four-coordinated by O atoms of 5-chlorosalicylaldehydate ligands in a square-planar geometry.

The scarcity of good-quality water is forcing the use of brackish water for irrigation in many areas around the world. Alternate fresh- and brackish water irrigation is a feasible irrigation method (IM). A pot experiment was carried out with three brackish water IMs and at three levels (1, 3 and 5 g NaCl L−1). The various levels of brackish waters were irrigated at the seedling stage, the jointing and tasseling stage and the after tasseling stage, respectively. The responses of maize (Zea mays L.) to alternate irrigation were investigated through gas exchange and chlorophyll fluorescence. The results showed that the alternate use of fresh- and brackish water reduced the increasing soil salinity caused by brackish water irrigation. The changes in net photosynthesis rate (Pn), stomatal conduction (gs), intercellular CO2 concentration (Ci) and chlorophyll content (SPAD) values revealed that maize was more resistant to brackish water at the after tasseling stage. Moreover, significant reductions in maximum quantum yield (Φpo), effective quantum yield of photochemical energy conversion (Φ2), photochemical quenching (qp), non-photochemical quenching of variable chlorophyll fluorescence (qN) and non-photochemical chlorophyll fluorescence quenching (NPQ) of photosystem II, grain yield and biomass weight of maize subjected to high NaCl level brackish water at the jointing and tasseling stage were observed. This implied that maize plants were extremely sensitive to brackish water irrigation during the jointing and tasseling stage, and freshwater should be applied at this growth period. Our results would be helpful for sustainable maize production using alternate irrigation with fresh- and brackish water in arid and semi-arid areas.