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Absorption-based polymeric solid-phase microextraction (SPME) fibers with poly(dimethylsiloxane) (PDMS) coatings were used to determine the partitioning coefficients of polychlorinated biphenyls (PCBs) between the sorptive fiber coatings and water. Previous models showing very good correlations between octanol-water partitioning coefficients (K(ow)) and absorption-based fiber-water partitioning coefficients (K(dv)) for low-molecular-weight analytes failed to predict K(dv) values for PCBs. In fact, K(dv) values for PCBs were 1-7 orders of magnitude lower than those predicted by K(ow) and actually showed a strong negative correlation between K(ow) and K(dv) for higher molecular weight analytes (MW >∼200). K(dv) values obtained using PDMS fibers with 7- and 100-μm coatings also disagree, demonstrating that K(dv) cannot be used to describe the partitioning behavior of PCBs between PDMS and water. However, when PCB partitioning coefficients were calculated on the basis of surface area (K(ds)), the K(ds) values obtained using 7- and 100-μm PDMS fibers agreed reasonably well, demonstrating that surface adsorption is the primary mechanism controlling PCB (and likely other higher molecular weight solutes) partitioning from water to SPME sorbents.

When machining a small hole with high aspect ratio in EDM, it is hard for the flushing liquid entering the bottom gap and the debris could hardly be removed, which results in the accumulation of debris and affects the machining efficiency and machining accuracy. The assisted ultrasonic vibration can improve the removal of debris in the gap. Based on dynamics simulation software, Fluent, a three-dimensional (3D) model of debris movement in the gap flow field of EDM small hole machining assisted with side flushing and ultrasonic vibration is established in this paper. The laws of different amplitudes and frequencies and different aspect ratios on debris distribution and movement are quantitatively analyzed. The motion height of debris was observed under different conditions. The research results show that periodic ultrasonic vibration can promote the movement of debris, which is beneficial to the removal of debris in the machining gap. When compared to traditional small hole machining in EDM, the debris in the machining gap were greatly reduced, which ensures the stability of the machining process and improves the machining efficiency.

A novel mitochondria-targeted ratiometric fluorescent probe for colorimetric and ratiometric sensing of endogenously generated SO2 derivatives is presented, with a perfect combination of water-solubility and reactivity.