Occurrence, distribution and risk assessment of antibiotics at various aquaculture stages in typical aquaculture areas surrounding the Yellow Sea

The pollution of antibiotics commonly existed throughout the entire aquaculture process,but the residues of antibiotics at different aquaculture stages have rarely been studied.This study investigated the occurrence,distribution and risk assessment of antibiotics at different aquaculture stages (the non-aquaculture stage,the early aquaculture stage,the middle aquaculture stage,and the late aquaculture stage) in two typical marine aquaculture areas(Mahegang River and Dingzi Bay) surrounding the Yellow Sea.Fluoroquinolones and tetracyclines were commonly used antibiotics in the aquaculture of these areas with high detection frequencies (17%to 83%).Compared among four aquaculture stages,the highest concentration of antibiotics (9032.08 ng/L) in aquaculture ponds was detected at the late aquaculture stage.And the antibiotic pollution level of natural water was directly related to the aquaculture stages.Similarly,at the aquaculture stages,the detection frequency of antibiotics in sediments was higher than that at the non-aquaculture stage.Based on the correlation analysis,the concentration of main antibiotics in water showed a positive correlation with total nitrogen (p<0.05) and chlorophyll a (p<0.01),while it showed a negative correlation with salinity (p<0.01) in coastal water of the Dingzi Bay.According to the risk assessment,with the development of aquaculture stages,the selection pressure of fluoroquinolones and tetracyclines on resistant bacteria had increased.And the ecological risks caused by sulfonamides and tetracyclines to aquatic organisms had also increased markedly.Overall,this study may provide a reference for formulating regulatory policies regarding antibiotic use at different aquaculture stages.

Effect of disconnector and high-voltage conductor on propagation characteristics of PD-induced UHF signals

UHF(ultra high frequency)method has been widely used in PD(partial discharge)detection for its high sensitivity.The resonance,distortion,and attenuation appearing in the propagation process of UHF signals in GIS(gas insulated switchgear)will influence the real situation of PD detection.Therefore,it is necessary to investigate the effect of GIS components such as disconnectors or high voltage conductors on the propagation characteristics of PD-induced UHF signals in various voltage classes GIS.The factors of PD signals propagation characteristics in axial and radial directions are both analysed to avoid the effect caused by placement of sensor in this paper.First,the simulation models of GIS are built based on FDTD(finite difference time domain)method.Then the propagation characteristics of PD-induced UHF signals are studied in the GIS with different disconnector gap lengths and different high voltage conductor radii.Finally,the reliability of the simulation results is verified by compared with laboratory tests.The disconnector gap and the change of conductor radii can both result in the signals attenuation which rises highest in the direction of 180°.The lower the GIS class voltage is,the larger the attenuation of signals after passing through disconnector gap is.

Promises and Challenges of Sn-Based Anodes for Sodium-Ion Batteries

Sn-based composites are considered as one of the promising anode materials for sodium-ion batteries(SIBs)due to their high theoretical capacities and suitable operation voltages.However,they suffer the huge volume change and unstable electrolyte/electrode interface during sodiation/desodiation,which causes structure collapse and serious capacity loss.In the past few years,great efforts have been made to ameliorate the performances of Sn by rationally designing electrode structures/components or optimizing electrolyte composition.Here,the underlying sodium-storage reactions in Sn are summarized based on the results from theoretical calculations and advanced characterizations.Then,the recent progresses of Sn-based composites,i.e.,Sn-based alloys,Sn/C composites,and Sn oxides/sulfides,with various structures for SIBs are discussed in details.After that,how the electrolyte affects solid-electrolyte interphase and the electrochemical performances is shown.Finally,the future directions for the applications of Sn-based composites in SIBs are suggested.Hence,this review provides a comprehensive scenario about the applications of Sn-based composites in SIBs.It will benefit the future development of alloy-type anodes in SIBs.