Passive micromixing can efficiently mix laminar flows through molecular and convective diffusion. Microstructures are expected to be efficient, easily integrated into micromixers, and suitable for micromixers over a wide range of Re. This paper presents the enhancement effects of the multiscale lateral microstructures on the flow field characteristics and mixing efficiency through numerical simulations at Re = 0.01–50. Inspired by the regulation of lateral microstructures on the local flow field, cross-scale staggered baffles (CSBs) were established and applied in typical passive micromixers. For low- Re conditions, the paired trapezoidal microstructures (PTMs) of the CSBs improved the mixing effect by increasing the local streamline tortuosity. For high- Re conditions, the PTMs of CSBs increased the number of expanding vortices in the microchannel, which could increase the size of the fluid interfaces, and an optimal mixing index with relatively little pressure drop was achieved. Moreover, the CSBs were applied to the serpentine curved channel, which caused large expanding vortices on the inner side of the curved channel, and then the state of the Dean vortices on the cross section of the curved channel changed. Therefore, compared with the conventional micromixer channel structure, lateral microstructures regulate the local flow field through the enhancement of the streamlines and the secondary flow effects, and lateral microstructures have great potential to improve the mixing efficiency over a wide range of Re.
To solve the long-existing difficult problems in extracting RNA and constructing a complementary DNA (cDNA) library for trace mites, we conducted a further comparative experiment among three RNA extraction methods (TRIzol method, Omega method, and Azanno method) based on our previous attempts at the construction of cDNA library of mites, with Psoroptes cuniculi still used as the experimental subject. By subsequently decreasing the number of mites, the least number of mites needed for RNA extraction of each method were found by criteria of completeness, concentration, and purity of the extracted RNA. Specific primers were designed according to the allergen Pso c1, Pso c2, and Actin gene sequences of Psoroptes to test the reliability of cDNA library. The results showed that Azanno method needed only 10 mites with sensitivity 204 times higher than previously used TRIzol method and 20 times higher than Omega method; clear RNA band was detected by agarose gel electrophoresis; and ultraviolet spectrophotometer determination showed that RNA concentration, 260/280, and 260/230 were in the range of 102 to 166 ng/μl, 1.83 to 1.99, and 1.49 to 1.72, respectively. Finally, specific primers detection showed that the amplified sequences had 98.33, 98.19, and 99.52% identities with those of P. cuniculi or Psoroptes ovis in GenBank, respectively, indicating that the cDNA library constructed using 10 mites was successful and it could meet the requirements for molecular biology research. Therefore, we concluded that Azanno method was more effective than TRIzol method and Omega method in RNA extraction and cDNA library construction of trace mites.
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