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In view of the heat transfer problems of gap flows near the shock-wave interference region of hypersonic vehicles, a two-dimensional model of the shock generator and gap was established. By using CFD technology, the internal flow heat transfer characteristics with shock waves in the front, middle and back of the gap were studied. The results showed that compared to the flow fields without shock wave, the vortex structure of the flow inside the gap changes obviously when the shock wave acts on the front and middle of the gap, resulting in a sharp increase in the flow intensity and heat inside the gap. However, when the shock wave acts on the rear part of the gap, the vortex structure inside the gap does not change significantly, and the far-end wall heat flux near the gap lip decreases locally, which is beneficial to the shape protection of the thermal protection structure. The results clearly indicated that it is necessary to avoid the position where shock wave acts on the front and middle part of gap in structural thermal protection design.

The co-application of water, fertilizer, and air is a new water-saving irrigation method based on drip irrigation technology, which can effectively alleviate the phenomenon of soil rhizosphere hypoxia, improve water and fertilizer utilization efficiency, and inhibit the clogging of irrigation equipment in drip irrigation systems. The performance of drip irrigation systems is one of the important factors affecting the effectiveness of the co-application of water, fertilizer, and air. However, the impact of factors such as the aeration method, fertilization device, and working parameters on the performance of drip irrigation systems for the co-application of water, fertilizer, and air is still unclear. Therefore, based on two typical aeration methods, i.e., micro-nano and Venturi aeration, the performance of a drip irrigation system under the co-application of water, fertilizer, and air was studied by comparing and analyzing the effects of different aeration methods, working pressures of the drip irrigation system, and the pressure difference between the inlet and outlet of fertilizer irrigation on the spatial distribution uniformity of water, fertilizer, and air in the drip irrigation pipeline network. The results showed that the pressure difference between the inlet and outlet of fertilization irrigation had no significant impact on system performance, while the working pressure significantly affected system performance. Compared with the effective effect of Venturi aeration on system performance, micro-nano aeration can significantly affect drip irrigation system performance and effectively improve drip irrigation system performance. The micro-nano-aerated drip irrigation system with the co-application of water, fertilizer, and air under a working pressure of 0.1 MPa has better system performance. The research results are of great significance for revealing the mechanism underlying the impact of the co-application of water, fertilizer, and air on the performance of drip irrigation systems and constructing efficient drip irrigation technology for the co-application of water, fertilizer, and air.

This study investigates the combined effect of microplastics and cadmium on the decomposition of litter, the structure of fungal communities, and the feeding behavior of invertebrates in an aquatic ecosystem. Through a series of microcosm experiments, we demonstrate that exposure to MPs and Cd significantly reduced the decomposition of leaf litter. Notably, the cumulative impact of combined MP and Cd exposure was found to be greater than their individual effects. During this process, the carbon–nitrogen ratio of the litter increased, while dehydrogenase activity and fungal biomass were inhibited. Additionally, the relative abundance of Ascomycota and Basidiomycota fungi decreased, weakening their role in the decomposition of leaf litter. Conversely, MPs and Cd reduced the relative content of leaf litter lignin, improving its quality as food, thereby leading to an increase in the feeding rate of invertebrates. This dual effect indicates that micropollutants suppress the decomposition of litter by regulating microbial metabolic activity and fungal community structure but promote invertebrate feeding. Our findings provide crucial insights into the adverse effects of MPs and Cd on the structure and diversity of aquatic fungal communities, which could have long-term impacts on the food webs and nutrient cycling progress of aquatic ecosystems.

Microplastic pollution is a research hotspot around the world. This study investigated the characteristics of microplastic pollution in the freshwater environments of 21 major cities across China. Through indoor and outdoor experimental analysis, we have identified the spatial and temporal distribution characteristics of microplastic pollution in China’s freshwater environments. Our findings indicate that the average concentration of microplastics in China’s freshwater environments is 3502.6 n/m3. The majority of these microplastics are fibrous (42.5%), predominantly smaller than 3 mm (28.1%), and mostly colored (64.7%). The primary chemical components of these microplastics are polyethylene (PE, 33.6%), polyvinyl chloride (PVC, 21.5%), polypropylene (PP, 16.8%), and polystyrene (PS, 15.6%). The abundance of microplastics in China’s freshwater environments generally tends to increase from west to east and from south to north, with the lowest concentration found in Xining, Qinghai (1737.5 n/m3), and the highest in Jiamusi, Heilongjiang (5650.0 n/m3). The distribution characteristics of microplastics are directly related to land use types, primarily concentrated in areas of intense human activity, including agricultural, transport, and urban land. Seasonal changes affect the abundance of microplastics, peaking in summer, followed by spring and autumn, mainly due to variations in rainfall, showing a positive correlation.

Aquatic litter decomposition is highly dependent on contributions and interactions at different trophic levels. The invasion of alien aquatic organisms like the channeled apple snail (Pomacea canaliculata) might lead to changes in the decomposition process through new species interactions in the invaded wetland. However, it is not clear how aquatic macroinvertebrate predators like the Chinese mitten crab (Eriocheir sinensis) will affect the nutrient cycle in freshwater ecosystems in the face of new benthic invasion. We used the litter bag method to explore the top-down effect of crabs on the freshwater nutrient cycle with the help of soil zymography (a technology previously used in terrestrial ecosystems). The results showed significant feeding effects of crabs and snails on lotus leaf litter and cotton strips. Crabs significantly inhibited the intake of lotus litter and cotton strips and the ability to transform the environment of snails by predation. Crabs promoted the decomposition of various litter substrates by affecting the microbial community structure in the sediment. These results suggest that arthropod predators increase the complexity of detrital food webs through direct and indirect interactions, and consequently have an important impact on the material cycle and stability of freshwater ecosystems. This top-down effect makes macrobenthos play a key role in the biological control and engineering construction of freshwater ecosystems.

Abstract Background Vigilance refers to the behavior of animals scanning their surroundings with a main purpose of anti-predation. Whether vigilance can serve the function of anti-predation depends on its unpredictability, meaning instantaneous randomness, sequential randomness, and independence, the three assumptions from Pulliam model (J Theor Biol 38:419, 1973). Here we tested two of these three assumptions in reproductive Black-necked Cranes (Grus nigricollis) in Tibetan Plateau: instantaneous randomness and sequential randomness. Methods Observations were carried out in July and September of 2014, July and August in 2017 in Selincuo National Nature Reserve, Tibet, with the help of focal sampling method. For instantaneous randomness, we used Kolmogorov–Smirnov test for its negative exponential distribution; for sequential randomness, we used Run test, correlation analysis, and generalized linear model to see if an inter-scan and its previous scan were correlated. Results Not similar to some recent studies, we did not find a significant predictable vigilance in this crane. Most inter-scan intervals (86/100, 86.0%) passed negative exponential distribution test, meaning vigilance sequences with instantaneous randomness; most inter-scan intervals (91/100, 91.0%) passed sequential random test, showing vigilance sequences were random organized. Conclusion Our results suggest that keeping a vigilance pattern with unpredictability is beneficial to the survival of the Black-necked Cranes, which are facing with both cruel natural environments and high predation risks.

Soil invertebrates and microorganisms are two major drivers of litter decomposition. Even though the importance of invertebrates and microorganisms in biogeochemical soil cycles and soil food webs has been studied, the effects of invertebrates on fungi are not well understood compared to other organisms. In this work, we investigated the effects of soil invertebrates on fungi as a factor that cannot be ignored in the study of nutrient cycling. The result showed the grazing of isopods on white-rot fungi was transitive and persistent. The grazed fungi appeared “compensatory” growing. The biomass of fungi increased after grazing. The activities of enzymes associated with nutrient cycling were increased under grazing. The zymography images showed the enzyme hotspots and activities also increased significantly in the grazing area. The results suggest that invertebrate grazing can significantly increase the fungal biomass and enzyme activity, accelerating litter decomposition in the unreached grazer area. The grazing effects of invertebrate plays an important role in promoting the nutrient cycling of the forest ecosystem. We believe that this study will be a good reference related to showing the relationship between soil invertebrates, fungi and soil biogeochemical cycles.

Environmental conditions strongly affect experimental animals. As a model organism, zebrafish has become important in life science studies. However, the potential effect of living environment on their behavior and physiology is often overlooked. This work aimed to determine whether tank size affects zebrafish behavior and physiology. Tests on shelter leaving, shelter seeking, shoaling, stamina, and pepsin and cortisol levels were conducted. Results showed that zebrafish behavior is easily affected by changes on the tank size. Fish that lived in small tanks behaved less boldly, had poor stamina, and spent much time on movement. Sex differences in behavior were only evident in the shelter seeking tests. Tank size had no effect on pepsin and cortisol, but cortisol concentrations in males were lower than those in females. This study suggests that zebrafish behavior is easily influenced by their living environment, and future related studies should consider their living space.

Rest contributes a large part of animals' daily life, and animals usually rest in two ways, standing or in recumbence. Small or medium sized ungulates bed to rest in most cases, and standing rest is very rare and hardly seen. Here we described a standing rest behavior of Tibetan antelopes (Pantholops hodgsonii) living on the Tibet Plateau which has not been reported before. We named the standing rest behavior Puppet behavior, since the antelope stand still for a certain time. Of the 304 individuals observed, 48.3% (98/203) of adult and sub-adult males expressed the Puppet behavior, whereas only 6.3% (6/96) of females did, indicating an obvious sexual difference. Puppet behavior occurred more frequently at noon and in the afternoon on sunny and cloudy days, meaning that daytime and weather were both influential factors. Puppet behavior was usually accompanied with rumination and sometimes ended with leg-shaking. Our results suggest that Puppet behavior may be an adaptive form of rest, which may serve a thermoregulatory and anti-predation function, and may be simpler and safer than recumbent rest.