Trajectory Generation and Tracking Control for Aggressive Tail-Sitter Flights

We address the theoretical and practical problems related to the trajectory generation and tracking control of tail-sitter UAVs. Theoretically, we focus on the differential flatness property with full exploitation of actual UAV aerodynamic models, which lays a foundation for generating dynamically feasible trajectory and achieving high-performance tracking control. We have found that a tail-sitter is differentially flat with accurate aerodynamic models within the entire flight envelope, by specifying coordinate flight condition and choosing the vehicle position as the flat output. This fundamental property allows us to fully exploit the high-fidelity aerodynamic models in the trajectory planning and tracking control to achieve accurate tail-sitter flights. Particularly, an optimization-based trajectory planner for tail-sitters is proposed to design high-quality, smooth trajectories with consideration of kinodynamic constraints, singularity-free constraints and actuator saturation. The planned trajectory of flat output is transformed to state trajectory in real-time with consideration of wind in environments. To track the state trajectory, a global, singularity-free, and minimally-parameterized on-manifold MPC is developed, which fully leverages the accurate aerodynamic model to achieve high-accuracy trajectory tracking within the whole flight envelope. The effectiveness of the proposed framework is demonstrated through extensive real-world experiments in both indoor and outdoor field tests, including agile SE(3) flight through consecutive narrow windows requiring specific attitude and with speed up to 10m/s, typical tail-sitter maneuvers (transition, level flight and loiter) with speed up to 20m/s, and extremely aggressive aerobatic maneuvers (Wingover, Loop, Vertical Eight and Cuban Eight) with acceleration up to 2.5g

A Comparative Study on Damage Mechanism of Sandwich Structures with Different Core Materials under Lightning Strikes

Wind turbine blades are easily struck by lightning, a phenomenon that has attracted more and more attention in recent years. On this subject a large current experiment was conducted on three typical blade sandwich structures to simulate the natural lightning-induced arc effects. The resulting damage to different composite materials has been compared: polyvinyl chloride (PVC) and polyethylene terephthalate (PET) suffered pyrolysis and cracks inside, while the damage to balsa wood was fibers breaking off and large delamination between it and the resin layer, and only a little chemical pyrolysis. To analyze the damage mechanism on sandwich structures of different materials, a finite element method (FEM) model to calculate the temperature and pressure distribution was built, taking into consideration heat transfer and flow expansion due to impulse currents. According to the simulation results, PVC had the most severe temperature and pressure distribution, while PET and balsa wood were in the better condition after the experiments. The temperature distribution results explained clearly why balsa wood suffered much less chemical pyrolysis than PVC. Since balsa wood had better thermal stability than PET, the pyrolysis area of PET was obviously larger than that of balsa wood too. Increasing the volume fraction of solid components of porous materials can efficiently decrease the heat transfer velocity in porous materials. Permeability didn’t influence that much. The findings provide support for optimum material selection and design in blade manufacturing

Metabolic Dynamics During Loquat Fruit Ripening and Postharvest Technologies

Loquat is an important fruit widely cultivated worldwide with high commercial value. During loquat fruit development, ripening, and storage, many important metabolites undergo dramatic changes, resulting in accumulation of a diverse mixture of nutrients. Given the value of loquat fruit, significant progresses have been achieved in understanding the metabolic changes during fruit ripening and storage, as well as postharvest technologies applied in loquat fruit in recent years. The objective of the present review is to summarize currently available knowledge and provide new references for improving loquat fruit quality

Analysis of Microbial Communities in Three Rounds of High-temperature Daqu Using Metagenomic Technology

Metagenomic sequencing technology was used to analyze the microbial community structures and functional composition in three rounds of Daqu. The results showed that the average assembly length of the 25 samples was 100.5 Mb, a total of 439 000 gene catalogs were detected, and 5 104 species were identified. The results of species annotation showed that Kroppenstedtia eburnea was the dominant species, and the subdominant species were multiple Bacillus species. There was no significant difference in microbial community diversity between samples from the first feeding (Xiasha) and those from the first round of fermentation, and the β-diversity of the microbial community in samples from the second feeding (Zaosha) was higher than that in samples from Xiasha and the first round of fermentation. The results of gene functional annotation showed that the most abundant genes in Daqu were related to metabolism, while the most representative genes were related to carbohydrate metabolism and amino acid metabolism. The number of glycoside hydrolase genes in Zaosha samples was largest and the activities of related enzymes were highest. The above results indicated that the microbial community structures and functional composition in the three rounds of Daqu were basically consistent, whereas there was a difference in functional performance between the Zaosha samples and the other two samples

Investigation of indoor airbourne bacteria in the severe cold region in China: Genera, levels, and the influencing factors of concentration

In regions experiencing severe cold, inadequate ventilation during winter months often leads to increased concentrations of indoor pollutants. While there have been several studies on indoor particulate matter and inorganic pollutants in such regions, bioaerosol pollution has not been as extensively investigated. This study examines the indoor bioaerosol situation in a university located in one of the severe cold regions in China, focusing on bacteria as a representative pollutant. It investigated random samples of an office and a dormitory (including washrooms) and spanned heating and nonheating periods. The findings indicated that bacterial abundance in the dormitory and office was approximately equivalent. The predominant airborne bacterial communities identified were Proteobacteria, Bacteroidota, Actinobacteriota, Firmicutes, and Myxococcota. Opening windows effectively reduced bacterial concentrations during both heating and nonheating periods. When windows remained closed, bacterial concentrations exceeded the standard by 9.1% during the nonheating period and by 14.3% during the heating period. Furthermore, temperature and relative humidity influenced bacterial particle size, activity, and consequently, aerosol concentrations. In the office, the highest percentage of bioaerosols was observed in particle sizes <1.1 and 1.1–2.1 μm, with smaller percentages observed in other particle sizes. Conversely, the percentage of particle sizes 2.1–3.3 μm in the dormitory was higher. The highest bacterial aerosol concentrations were detected in the morning in both the dormitory and office, during heating and nonheating periods. Bacterial concentrations in the office were lower on weekends than on weekdays, whereas in the dormitory, concentrations were higher on weekends than on weekdays. The above results indicate that indoor bacterial aerosol pollution is serious in winter in severe cold regions, which needs more attention

Rapid evolutionary divergence of Gossypium barbadense and G. hirsutum mitochondrial genomes

Background The mitochondrial genome from upland cotton, G. hirsutum, was previously sequenced. To elucidate the evolution of mitochondrial genomic diversity within a single genus, we sequenced the mitochondrial genome from Sea Island cotton (Gossypium barbadense L.). Methods Mitochondrial DNA from week-old etiolated seedlings was extracted from isolated organelles using discontinuous sucrose density gradient method. Mitochondrial genome was sequenced with Solexa using paired-end, 90 bp read. The clean reads were assembled into contigs using ABySS and finished via additional fosmid and BAC sequencing. Finally, the genome was annotated and analyzed using different softwares. Results The G. barbadense (Sea Island cotton) mitochondrial genome was fully sequenced (677,434-bp) and compared to the mitogenome of upland cotton. The G. barbadensemitochondrial DNA contains seven more genes than that of upland cotton, with a total of 40 protein coding genes (excluding possible pseudogenes), 6 rRNA genes, and 29 tRNA genes. Of these 75 genes, atp1, mttB, nad4, nad9, rrn5, rrn18, and trnD(GTC)-cp were each represented by two identical copies. A single 64 kb repeat was largely responsible for the 9 % difference in genome size between the two mtDNAs. Comparison of genome structures between the two mitochondrial genomes revealed 8 rearranged syntenic regions and several large repeats. The largest repeat was missing from the master chromosome in G. hirsutum. Both mitochondrial genomes contain a duplicated copy of rps3 (rps3-2) in conjunction with a duplication of repeated sequences. Phylogenetic and divergence considerations suggest that a 544-bp fragment of rps3 was transferred to the nuclear genome shortly after divergence of the A- and D- genome diploid cottons. Conclusion These results highlight the insights to the evolution of structural variation between Sea Island and upland cotton mitochondrial genomes

Crosstalk Between Autophagy and Cerebral Ischemia

With the use of advanced electron microscopy and molecular biology tools, several studies have shown that autophagy is involved in the development of ischemic stroke. A series of molecular mechanisms are involved in the regulation of autophagy. In this work, the possible molecular mechanisms involved in autophagy during ischemic stroke were reviewed and new potential targets for the study and treatment of ischemic stroke were provided