The LLC half-bridge resonant converter has attracted extensive research attention due to its advantages of achieving high efficiency and high power density. However, the resonant process is more complicated, where the main difficulty is to precisely calculate resonant parameters. In this paper, the fundamental harmonic approximation (FHA) method is employed to analyze the resonant process of the converter. In particular, the working mode and the mathematical model of the LLC half-bridge resonant converter are established, where a new method is proposed to determine the operating frequency of LLC based on voltage gain and transformer loss. Based on the proposed method, the converter parameters can be optimized and the drawbacks of manually selecting the frequency can be avoided.Finally, a 200-W LLC converter laboratory prototype is established and the experimental results verify the effects of parameter optimization.
The effect of N-acyl-homoserine lactone (AHL)-based quorum sensing (QS) on biogenic amine (BA) formation by Pantoea agglomerans was studied. Agrobacterium tumefaciens A136 and KYC55-based bioassays confirmed AHLs production by Pantoea agglomerans. The production ability of AHLs was quantified on the basis of β-galactosidase activity. The influence of temperature (10°C and 20°C) and pH (5.5 and 6.5) on β-galactosidase activity and BAs production by Pantoea agglomerans was determined. Acidification of the environment adversely affected the growth and β-galactosidase activity of Pantoea agglomerans, and AHLs production and BAs accumulation by Pantoea agglomerans was inhibited at low temperature. A significant correlation between β-galactosidase activity and BAs (putrescine, histamine, putrescine and tryptamine) was identified (P < 0.01). Based on the results of this study, the AHL-based QS system influences the concentrations and types of BAs produced by Pantoea agglomerans.
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