Search

The 3M PetriFilmTM rapid aerobic count plate method (3M test plate method) and filter membrane method were used to quantitatively determine the total number of bacterial colonies in the beverage, and the consistency of the two methods was analyzed. Seven kinds of bacteria including Escherichia coli, Staphylococcus aureus, Paenibacillus ehimensis, Bacillus subtilis, Asia Siamensis, Candida albicans and Aspergillus niger were used to artificially inoculate and test the beverage samples. The experimental results showed that for different strains and different pollution levels, the linear fitting degree of 3M test plate method and filter membrane method was better (determination coefficient R2>0.95). And the recovery rate of 3M test plate method was more than 70%, and the RSD values (2.9%~34.3%) were within the prescribed range of Pharmacopoeia of the People's Republic of China 2020, indicating that 3M test plate method had better accuracy and precision. For the specificity test of bacterial and fungal contamination and the repeatability test of different batches of 3M test plates, the recovery rate of 3M test plate method was more than 70%, and the RSD values (3.6%~34.3%) were within the acceptable range, showing good specificity and repeatability. The results of 3M test plate method and filter membrane method were analyzed by using relatively trueness and accuracy profileanalysis method. The results showed that the two methods had good consistency and equivalence. Based on the above analysis results, 3M test plate method is equivalent to filter membrane method to determine the total number of colonies in beverages.

In order to study the effects of W content on the structure and mechanical properties of Cu-W thin films, these films were prepared by magnetron sputtering process using mosaic combination targets. The composition, structure and surface morphology of the thin films were characterized, respectively, by energy dispersive spectroscopy(EDS), X-ray diffraction(XRD), high-resolution transmission electron microscope(HRTEM), scanning electron microscope(SEM) and atomic force microscope(AFM). The yield strength(σ0.2), critical strain for crack initiation(εc), elastic modulus(E) and microhardness(H) of the thin films were tested using micro-force testing system and nano indentation instrument, respectively. Results showed that the composition of the thin films could be controlled by adjusting the proportion of the W target area. When the proportion of the W target area was increased from 5% to 25%, the W content in the Cu-W thin films was observed to gradually increase from 2.30%(atomic fraction, the same below) to 15.10%, accompanied by the formation of an fcc Cu(W) metastable quasi-solid solution. As the W content increased, the average grain size of the Cu-W thin films was seen to gradually decrease from 28 nm to 18 nm, the quasi-solid solubility was noted to gradually increase from 1.30%W to 9.50%W, and an improvement in the surface smoothness of the thin films was recorded. With the increase of W content, it was found that the yield strength(σ0.2) and microhardness(H) of the Cu-W thin films increased significantly, the elastic modulus exhibited a slight increase, while the critical strain for crack initiation(εc) experienced a decrease. The Cu-15.10% W thin film was determined to possess the smallest average grain size and the highest surface smoothness, along with the highest yield strength, hardness and elastic modulus(σ0.2 = 0.86 GPa, H = 6.1 GPa, E = 123.5 GPa); the critical strain for crack initiation(εc) value was 0.84%, indicating the best comprehensive mechanical performance.