To explore the effect of tea polysaccharides on the gut microbiota and their short-chain fatty acid (SCFA) metabolic products, we used the faecal microbiota to simulate the gut microbiota in vitro, and cultured them to obtain a preculture solution. Ultrapure water, tea polysaccharides, and glucose were added to the precultured solution for anaerobic fermentation. Samples of each group were harvested at 0, 6, 12, and 24th hour during fermentation to test the contents of the SCFAs. In addition, high-throughput 16S rRNA sequencing was performed to analyse the microbiota in the fermentation medium. Results showed that the faecal microbiota used tea polysaccharides to generate SCFAs. When compared with the fermentation group with the addition of ultrapure water, the group with the addition of tea polysaccharides increased the relative abundance of Firmicutes, and decreased the relative abundance of Bacteroidetes at the phylum level. The relative abundances of Butyricimonas, Roseburia, Eubacterium rectale group, Ruminococcus 1, Lachnospira, and Parasutterella increased significantly at the genus level. Based on the LEfSe analysis of key microbiota at the genus level, significant differences between the groups were observed. It was clear that tea polysaccharides selectively enriched the microbiota to produce SCFAs, and the correlation between the SCFAs and faecal microbiota was confirmed.
By using the vehicle-track interaction model and the wear calculation model, the development characteristics of rail profile wear and the longitudinal characteristics of rail wear development of the track-vibration-absorber fastener tangential track at different passing speeds were analyzed. The results of rail profile wear analysis show that with the increase of iteration times, the wear ranges and wear depths of left and right rails at the corrugation trough/crest position are close. Meantime, the wear depths of rail profile and wave depth amplitudes at the corrugation trough/crest position in discrete passing speed modes are significantly lower than those in constant passing speed mode. The results of rail longitudinal wear analysis show that with the increase of vehicle running times, the characteristic frequencies of corrugation do not change under different passing speed modes, which reflects the fixed frequency feature of corrugation, and the irregularity levels corresponding to characteristics frequencies of rail longitudinal wear under the three passing speed modes show a decreasing trend in turn. Compared with the constant passing speed mode, the discrete passing speed modes can significantly decrease the rail profile wear and the development degree of rail wear at the characteristic frequencies.
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