The effect of low cycle fatigue (LCF) predamage on the subsequent very high cycle fatigue (VHCF) behavior is investigated in TC21 titanium alloy. LCF predamage is applied under 1.8% strain amplitude up to various fractions of the expected life and subsequent VHCF properties are determined using ultrasonic fatigue tests. Results show that 5% of predamage insignificantly affects the VHCF limit due to the absence of precrack, but decreases the subsequent fatigue crack initiation life estimated by the Pairs law. Precracks introduced by 10% and 20% of predamage significantly reduce the subsequent VHCF limits. The crack initiation site shifts from subsurface-induced fracture for undamaged and 5% predamaged specimens to surface precrack for 10% and 20% predamaged specimens in very high cycle region. Furthermore, the predicted fatigue limits based on the El Haddad modified model for the predamaged specimens agree with the experimental results.

Stachyose is a functional oligosaccharide, acting as a potential prebiotic for colonic fermentation. To understand the mechanism of how stachyose promotes the growth of probiotic bacterium, we analyzed the differences of the proteome of Lactobacillus acidophilus grown on stachyose or glucose. By a combination of two-dimensional electrophoresis and mass spectrometry analysis, we observed 16 proteins differentially abundant under these two conditions and identified 9 protein spots. Six of these proteins were highly abundant when stachyose was used as the sole carbon source. They included the phosphotransferase system, the energy coupling factor (ECF) transporter and the mannose-6-phosphate isomerase, involved in the uptake and catabolism of stachyose in Lactobacillus acidophilus CICC22162. Supportively, these observations were validated by quantitative RT-PCR analysis and enzymatic activity determination. Positive correlation was found between the content of the proteins and their mRNA levels. Additionally, we explored the recognition mechanism for stachyose binding to the newly identified ECF transporter by MD simulations and free energy analysis. Taken together, these results provide new insights into the mechanism of stachyose in promoting the growth of probiotic bacterium.

C20H16N2O4, monoclinic, P21 (no. 4), a = 8.0094(5) Å, b = 6.7689(3) Å, c = 29.577(2) Å, β = 95.809(6)°, V =1595.27(16) Å3, Z = 4, Rgt(F) = 0.0457, wRref(F2) = 0.1209, T = 293 K.