Search Results (7)

In the process of plant protection for fruit trees using rotary-wing UAVs, challenges such as droplet drift, insufficient canopy penetration, and low agrochemical utilization efficiency remain prominent. Among these, the uncertainty in the spatio-temporal distribution of downwash airflow is a key factor contributing to non-uniform droplet deposition and increased drift. To address this issue, we developed a wind field numerical simulation model based on an improved hierarchical leaf density model to clarify the spatio-temporal characteristics of downwash airflow, the scale of turbulence regions, and their effects on internal canopy airflow under varying flight altitudes and different rotor speeds. Field experiments were conducted in orchards to validate the accuracy of the model. Simulation results showed that the average error between the simulated and measured wind speeds inside the canopy was 8.4%, representing a 42.11% reduction compared to the non-hierarchical model and significantly improving the prediction accuracy. The coefficient of variation (CV) was 0.26 in the middle canopy layer and 0.29 in the lower layer, indicating a decreasing trend with an increasing canopy height. We systematically analyzed the variation in turbulence region scales under different flight conditions. This study provides theoretical support for optimizing UAV operation parameters to improve droplet deposition uniformity and enhance agrochemical utilization efficiency. Full article

Due to terrain and transportation constraints, some open cast mines have to choose a weak basement as their tailings dumping grounds. Therefore, ensuring the bearing capacity and slope stability of dumping grounds on the weak basement is of great significance for the production capacity and economic benefits of open cast mining. To ensure the safety of surrounding facilities and the normal production of open cast mines, the bearing capacity of the dumping ground of a certain open cast mine was calculated using the oblique strip method and verified by numerical simulation. On this basis, the potential failure mode of the dumping ground base was analyzed, and the ultimate bearing capacity of the dumping ground under current conditions was calculated. The results are as follows: (1) The ultimate bearing capacity of the current dumping ground base is 3781 kPa, and the failure mode of the base is overall shear sliding along the base of the dumping ground. (2) When the slope foot increases from 12° to 18°, the stability coefficient and critical bearing capacity coefficient of the slope base decrease by about 21% and 46%, respectively. The slope angle has a greater impact on the bearing capacity of the base, and the height of the slope body has a relatively small impact, with almost no width effect. (3) Compared with the classic Terzaghi method and Prandtl method, the ultimate bearing capacity of the dumping ground base determined using the oblique strip method proposed in this paper is closer to the numerical simulation results, with an error of no more than 5%, a consistent critical sliding surface, and results that are relatively consistent with the engineering practice monitoring of the surface uplift part. The calculation results of the bearing capacity of the weak basement of open cast mine dumping grounds using the oblique strip method are reliable. Full article

A crab steering system aiming at improving the steering flexibility and operation efficiency of the high clearance sprayer was designed. First, a steering transmission mechanism of the high clearance sprayer was designed according to the operational and structural characteristics of the sprayer. Meanwhile, a crab steering hydraulic system based on load sensing was designed, and a mathematical model of the steering transmission mechanism and hydraulic system was established to describe the working characteristics of the crab steering system. On the basis of analyzing the operating environment of the sprayer and the operating characteristics of crab steering mode, a control strategy and algorithm of the crab steering system were proposed. The simulation model of the crab steering control system was built according to the established mathematical model, and the simulation analysis of the crab steering system was carried out. The simulation results showed that under the excitation of step signal, the average deviation of the two front wheels is 0.063°, and the absolute value of the maximum deviation is 2.75°, which is within the allowable range of deviation and meets the crab steering demand of the sprayer. Additionally, in order to verify the effectiveness of the designed system, an actual vehicle test platform of the crab steering system was built based on the 3WPG-3000 high clearance self-propelled sprayer independently developed by the research group, and the field test results revealed that the average deviation of the four wheels was 0.285°, the maximum absolute deviation was 2.587°, the rotation deviation was small, within the allowable and reasonable range. Altogether, the results of the simulation and field test verify the accuracy, stability and practicability of the crab steering system, which effectively improved the maneuverability of the sprayer. Full article

The emergence of high antimicrobial-resistant and hypervirulent Klebsiella pneumoniae (hvKp) clones in clinics has become a cause of concern in recent years. Despite the global spread of the clonal complex (CC) 258, hvKp of other non-CC258 subgroups also emerged. Here, by performing a retrospective study from July 2019 to August 2020 in a Chinese hospital, we obtained 25 K. pneumoniae isolates belonging to CC15. By antimicrobial susceptibility testing and whole genome sequencing and analysis, we obtained the resistant phenotypes and genotypes of these isolates. Twenty-one isolates (84%) were carbapenem-resistant, and eighteen were bla_KPC-2 positive. In addition, ten isolates were identified as putative hvKp and seven were carbapenem-resistant hvKp. Nine isolates carried the pLVPK-like virulence plasmid, which contains the fragment including rmpA2, peg-589, iutA, and iucABCD. Another isolate carried iucA. Phylogenetic analysis revealed that the isolates belonged to four lineages, and the putative hvKp isolates were identified in three of these. Two independent sublineages of putative hvKp were caused by the acquisition of pLVPK-like virulence plasmid. Based on comparative genomic analysis, the number of pairwise single nucleotide polymorphisms amongst the four sublineages, Lineage 1a, 1b, 2a, and 2b, were 1–43, 2–13, 129–279, and 3–4, respectively, indicating clonal transmission of Lineage 1a, 1b, and 2b. These results indicate that multiple lineages of CC15 carbapenem-resistant hvKp have emerged in the hospital and caused nosocomial transmission, and that the spreading of virulence plasmids among classic K. pneumoniae subtypes might become more common and happen more easily. These findings highlight the importance of surveillance of local epidemics of non-CC258 subgroups in hospitals. Full article

National parks, as an important type of nature protected areas, are the cornerstone that can effectively maintain biodiversity and mitigate global climate change. At present, China is making every effort to build a nature-protection system, with national parks as the main body, and this approach considers China′s urgent goals of obtaining carbon neutrality and mitigating climate change. It is of great significance to the national carbon-neutralization strategy to accurately predict the carbon sink capacity of national park ecosystems under the background of global change. To evaluate and predict the dynamics of the carbon sink capacity of national parks under climate change and different management measures, we combined remote-sensing observations, model simulations and scenario analyses to simulate the change in the carbon sink capacity of the proposed Kunlun Mountain National Park ecosystem over the past two decades (2000–2020) and the change in the carbon sink capacity under different zoning controls and various climate change scenarios from 2020 to 2060. Our results show that the carbon sink capacity of the proposed Kunlun Mountain National Park area is increasing. Simultaneously, the carbon sink capacity will be improved with the implementation of park management and control measures; which will be increased by 2.04% to 2.13% by 2060 in the research area under multiple climate change scenarios. The research results provide a scientific basis for the establishment and final boundary determination of the proposed Kunlun Mountain National Park. Full article

There are 376 million migrants, which account for more than 25% of the population in China according to the newest national demographic census, most of whom are from undeveloped areas to developed urban regions. Migrants’ social integration was one of the most important issues when the country aimed to build an inclusive society. As a form of human capital, the effect of migrants’ health status on social integration has rarely been explored until now, especially empirically. Previous studies have usually ignored health indicators when discussing the determinants of migrants’ social integration, and understanding the role of migrants’ physical health and mental health on their social integration is significant for efforts to ensure inclusive urbanization. For filling this research gap, the China Migrants Dynamic Survey dataset was used to uncover the role of migrants’ health status, including physical health and mental health, in their degree of social integration, and a further comparison of impact was conducted among rural–urban and urban–urban migrants. Through the empirical analysis, our results indicated the following. First, both better physical and mental health lead to higher social integration levels, and a one-point increase in physical and mental health improves the odds of good social integration by 33.27% and 5.98% for belonging and 66.05% and 6.35% for harmony, respectively. Second, health status is equally important for rural–urban and urban–urban migrants’ social integration, and the significant positive effect was consistent across groups, although some other impact factors may exhibit differences. Third, the effect of health status on social integration was moderated by social participation, which was more obvious for mental health than physical health. According to our findings, we discuss the measures to promote migrants’ health status and additional countermeasures to improve their social integration level. Full article

Ag₃PO₄/g-C₃N₄ heterojunctions, with different g-C₃N₄ dosages, were synthesized using an in situ deposition method, and the photocatalytic performance of g-C₃N₄/Ag₃PO₄ heterojunctions was studied under simulated sunlight conditions. The results revealed that Ag₃PO₄/g-C₃N₄ exhibited excellent photocatalytic degradation activity for rhodamine B (Rh B) and phenol under the same light conditions. When the dosage of g-C₃N₄ was 30%, the degradation rate of Rh B at 9 min and phenol at 30 min was found to be 99.4% and 97.3%, respectively. After five cycles of the degradation experiment for Rh B, g-C₃N₄/Ag₃PO₄ still demonstrated stable photodegradation characteristics. The significant improvement in the photocatalytic activity and stability of g-C₃N₄/Ag₃PO₄ was attributed to the rapid charge separation between g-C₃N₄ and Ag₃PO₄ during the Z-scheme charge transfer and recombination process. Full article