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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 (p0.05) and chlorophyll a (p0.01), while it showed a negative correlation with salinity (p0.01) 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.

Benefits of replacing ordinary Portland cement with industrial solid wastes are promising for reducing cement production and solving environmental problems associated with industrial solid wastes. In this study, an experimental investigation was conducted to evaluate the performance of sustainable concrete containing different industrial solid wastes (e.g., waste glass, coal gangue, fly ash, and slag), with the attention on the mechanical strength, chloride transport property, and pore structure characteristics. Three water to binder ratios (i.e., 0.38, 0.48, and 0.65) and three replacement levels (i.e., 10%, 20%, and 30%) were considered in this work. The test results show that regardless of the content and type of industrial solid wastes, the inclusion of industrial solid wastes generally exerts a negative influence on the mechanical properties, especially under high water to binder ratios. However, acceptable mechanical strength can still be achieved in these sustainable concretes. In addition, the inclusion of industrial solid wastes could enhance the chloride diffusion resistance of concrete, and also the concrete with waste glass powder showed the best performance. Furthermore, the incorporation of industrial solid wastes has a refinement effect on the microstructure of the matrix, manifesting as decreased cumulative pore volume and compacted microstructural morphology.

In this work, effect of the oscillation frequency on the oil surface flashover characteristics under lightning impulse voltage is experimentally studied. Four lightning impulse (OLI) waves with different oscillation frequencies and 1.2/50 µs standard lightning impulse (SLI) wave are used in this study. The experiment results show that flashover voltages under OLI are larger than those under SLI and the flashover time lags under OLI are longer than those under SLI. Additionally, the flashover voltage tends to increase and the time lag tends to be shorter as the oscillation frequency increases. According to the experimental results and the discharge theory of liquids, we believe that the waveform oscillation frequency affects both the effective electron generation time lag and the formative time lag. This work provides a reference for the waveform selection of the on-site withstand voltage test and explains the physical mechanism of the oil flashover discharge from the perspective of impulse waveform oscillation.

This paper enhanced the integration-type E&S model and the dynamic E&S model for integrating the impact of DC-biased field and eddy current on vector magnetic properties of electrical steel sheet. B and H of electrical steel sheet are measured under DC-biased and rotating fields. Based on the measured results, the databases of reluctivity and hysteresis coefficients of both the enhanced integration-type E&S model and the improved dynamic E&S model are established for predicting H waveform under any given operating condition. By comparing the H waveform calculated by the enhanced integration-type E&S model and the improved dynamic E&S model with the experimental H waveform, it is found that both two models have good reliability and the improved dynamic E&S model has slightly better accuracy than the enhanced integration-type E&S model.

Polycyclic aromatic hydrocarbon (PAH) pollution caused by marine oil spills and antibiotic pollution caused by aquaculture industries were common environmental problems in the Yellow River Estuary, China. But few data are reported on the bioaccumulation and influencing factors of these two types of contaminants in aquaculture simultaneously. This study investigated the occurrence and bioaccumulation of PAHs and antibiotics in aquaculture areas of the Yellow River Estuary, and explored the factors affecting the bioaccumulation. 3-ring PAHs and fluoroquinolones were dominant contaminants in the study area. The concentrations of PAHs and antibiotics in lipid-rich tissues (fish viscus, shrimp head, and crab ovary) was higher than that in muscle. It indicated that the lipid content was an important factor affecting the bioaccumulation capacity. Physicochemical parameters (K

This study presents experimental results on the influence of cellulose particles on the breakdown characteristics of transformer oil in a highly non-uniform field under lightning impulse voltage. The experimental results show that as the particle content increases, the breakdown voltage reduces with little change in the breakdown time lag. At the same cellulose particle content, the oil breakdown voltage under oscillating lightning impulse (OLI) is lower than that under standard lightning impulse (SLI) and the breakdown time lag under OLI is longer than that under SLI. The impulse wave oscillation has a large effect on the accumulation of particles around the high voltage electrode and cellulose particles affect the development of the streamer process. At mid to high particle content the accumulation of particles around the high voltage electrode causes a decrease in the conductivity of the surrounding oil. This work contributes to the understanding of the effect of cellulose particles in oil and breakdown and on oscillating waveforms and provides guidance for lightning impulse tests on oil-immersed power transformers in the field.

In this paper the behavior of partial discharges (PDs) on epoxy insulation under AC and impulse superimposed voltages are experimentally investigated in SF 6 gas. The lightning impulse (LI) and the switching impulse (SI) voltages with different polarity are superimposed on different phases of the AC voltage. PDs are measured by three sensors, a 50 Ω measurement impedance, an ultra-high frequency sensor and a photomultiplier tube. The max PD amplitude, PD pulse number and PD duration under AC voltage after an impulse voltage are summarized and analyzed. The effect of the impulse superposition phase, the impulse type and the impulse polarity on the characteristics of AC PDs are discussed. Results show that after a positive impulse voltage was applied on the positive semi-wave of AC voltage (0 to 180°), PDs in the negative half cycle of the AC voltage can be remarkably excited. A negative impulse voltage was applied on the negative semi-wave (180 to 360°), AC PDs can be initiated in the positive half cycle of AC voltage. PDs excited by a LI voltage is severe than excited by a SI. PDs excited by a positive impulse is intense than excited by a negative impulse.

This article proposes an enhanced dynamic vector magnetic hysteresis model for describing the effect of dc-biased field and eddy current on vector magnetic quantities. A governing equation combining the proposed model is derived for finite-element analysis of magnetic characteristics distribution of transformer core under dc-biased excitation. The numerical results of the transformer core by using the enhanced model with consideration of dc-biased excitation and eddy current are compared with the numerical results obtained by using the magnetizing curve. It proves that the proposed model can consider vector magnetic properties and iron loss of electrical steel sheet under both dc-biased and rotating magnetic fields during numerical analysis.

This work presents a laboratory and field study on the performance of the asphalt binder and mixture modified by pre-treated crumb rubber. Initially, a mechano-chemical method was employed to pre-treat crumb rubber, intending to increase its surface activity and compatibility with asphalt binder. Subsequently, the properties of asphalt binders and mixtures modified by the pre-treated crumb rubber were evaluated systematically. Test results showed that the incorporation of pre-treated crumb rubber resulted in the reduced penetration value, higher softening point, enhanced tensile performance, improved elastic recovery, and greater aging resistance of asphalt binder. Additionally, the asphalt mixtures modified by pre-treated crumb rubber demonstrated excellent road performance. Furthermore, the developed asphalt mixtures were successfully applied in practical engineering, validating the feasibility and practicality of the modified asphalt mixture by pre-treated crumb rubber.

This letter proposed a new lightning impulse test method for power transformers based on oscillating lightning impulse(OLI) waveform. The OLI has high generation efficiency and is easy to generate for field test. Partial discharge detection and transfer function analysis are used to evaluate the transformer insulation condition during the impulse test. The OLI waveform for transformer test satisfied with the requirements of the standard is obtained by altering the value of resistance and inductance in the circuit. The experiment was carried out on a transformer scale model to prove the validity of the proposed method. The results show that the current pulse method and the UHF method detect the PDs simultaneously as the insulation defect is excited at high voltage. Meanwhile, the transfer function changes due to the discharge in winding. It provides a new test and insulation diagnose method with application prospects for transformer lightning impulse test on site.

In this letter, a test platform capable of generating superimposed voltage with controllable phase is presented. Surface partial discharge(PD) of epoxy insulation was measured and analyzed in SF6. The applied voltage is AC and switching impulse superimposed voltage. Results show that only PD of the negative cycles of the AC voltage is excited or accelerated after impulse. With AC voltage at 90% of partial discharge inception voltage(PDIV), AC PDIV is reduced after imposing the switching impulse. When AC voltage is kept at 110% of PDIV, AC PDs are obviously promoted after impulse.

A novel partial discharge (PD) detection method for transformers on site adopting its component as ultra-high frequency (UHF) sensor is proposed. The bushing tap, iron core, and high-voltage (HV) winding can be used as internal UHF sensor for UHF PD detection. The experiments are carried out on an 80-kV transformer model to prove the validity of this method. The results show that the proposed method has good detection sensitivity and anti-disturbance performance, and can measure the PD signals without additional sensor. It solves the problem of the lack of available unused valves for internal UHF sensor installation while the external sensor is susceptible to interference. It provides a novel method with application prospects for PD detection of transformers in field.

A cavity is a typical defect in a solid insulator which may cause the appearance of partial discharge (PD) activity in power equipment [1–4]. It is mainly caused by imperfections in the manufacturing process as well as by the creep during equipment operation [5]. In epoxy resin insulators, the creep brings irreversible deformations that increase with time at elevated temperatures and external stress [6,7]. Once a cavity has been formed, the PD can lead to insulation failure. Many studies on PDs in void defects, a type of gas-filled cavity, have been performed by pasting together three epoxy laminates and demonstrated factors that affect their intensity, including void size, shape and interface roughness [8–12]. However, such a test void is quite different in its structure and composition from what we further consider in this article, i.e., cavities appearing during actual insulator operation. Moreover, the pressure in a real cavity is usually very low, because of air leakage and polymerization shrinkage, whereas the test void typically remains under atmospheric pressure. Considering the above mentioned differences, we prepared experimental model insulators, containing various low-pressure cavities. The insulators were manufactured by means of automatic pressure gelation (APG) technique by changing the pressure and temperature during the resin pouring process, which allowed for simulating a more realistic operating environment.

Power transformers are known as one of the most important equipment in power system. The experiment was carried out on a 35kV transformer, which is an actual structural scale model for simulating large oil-immersed power transformers. The turn-to-turn insulation defect was set in its high voltage winding to study the PD characteristics under lightning impulse voltages, including standard lightning impulse (SLI) voltage and oscillating lightning impulse (OLI) voltages with different oscillating frequencies. The results show that there are two types of partial discharge, the main discharge and the reverse discharge. The pulse current method was more sensitive to the main discharge detection. In addition to detecting a large amplitude main discharge, the UHF method can detect many reverse discharge signals as well. The PD number under OLI is significantly larger than that under SLI. The 50% probability PD inception voltage $(\mathbf{PDIV}_{\mathbf{50}})$ is analyzed based on the measurement results. The $\mathbf{PDIV}_{\mathbf{50}}$ increases with the increasing of oscillating frequency of the OLI voltage.

Voltage surges arising lightning discharges are one of the chief causes of failure in the transformer winding due to the non-linear distribution of the voltage along the transformer winding. This paper extends the former researches in one aspect by including the voltage distribution under the oscillating lightning impulse voltage (OLI) in comparison with that of standard lightning impulse (SLI). A lumped parameter model of a transformer winding is built and the simulations are carried out to study the voltage distribution across a transformer winding when excited with SLI of different front and tail time and its corresponding OLI of same front and tail time. The voltage between each coil and the ground and the voltage between coils is determined. It is discovered that the oscillation frequency of the winding under OLI is consistent with the frequency of the applied voltage at first and then with the natural frequency. The voltage between coils is highest at coils 1-5. The coil to ground voltage under OLI is generally smaller than that under SLI. This research can be used as a cornerstone for the application of OLI voltage for the on-site insulation dielectric strength test.

The effect of the repeated lightning impulses accumulative effect on partial discharges (PDs) characteristics of epoxy insulation surface is experimentally investigated in SF 6 gas. After the epoxy insulation specimen is subjected by 0, 200, 400, 600, 800 times of lightning impulses ( $1.2/50\mu\mathrm{s}$ ), respectively, PDs on epoxy insulation surface are measured. The surface morphology of the epoxy insulation specimen is observed by the scanning electron microscopy (SEM) after impulse. The amplitude of the impulse is about twice the PD inception voltage (PDIV). PDIV, average PD pulse number and average PD magnitude per cycle of the AC voltage are counted and analyzed after impulse. Results show that with the increase of the number of impulse, the PDIV under AC voltage is gradually decreases. Average PD pulse number and PD magnitude is increase. PDs in the negative half-cycle of the AC voltage is more intense than the positive half-cycle. The area of the epoxy insulation surface close to the high-voltage electrode becomes rougher as the number of the impulse increases.

Zircon (ZrSiO4) ceramics were widely used in the field of nuclear waste immobilization because of their excellent properties. However, the SiO2/ZrSiO4 ceramics were usually obtained in the preparation of ZrSiO4. The actinides immobilization behavior of SiO2/ZrSiO4 ceramics is unclear. Herein, Nd-doped 0.2SiO2/Zr1-xNdxSiO4-x/2 (0≤x ​≤ ​0.1) ceramics were fabricated and the effects of Nd-doping and sintering temperature on their phase and microstructure evolution were investigated. The obtained ceramics were characterized by XRD, SEM, BSE and EDS. Results show that 0.2SiO2/Zr1-xNdxSiO4-x/2 ceramics with 0≤x ​

A partial discharge (PD) detection method for SF6 insulated inverted current transformers (SIICTs) adopting an inner shield case as an ultra-high frequency (UHF) sensor is proposed in this paper. The inner shield case is a component of the SIICT. Its structure is similar to that of an antenna and can be used as a UHF sensor to measure the PD UHF signal. A 110 kV current transformer is used as an experimental object and the voltage standing-wave ratio of the inner shield case is calculated. The validity and sensitivity of this method are proved by experiments with ac voltage. This PD detection method solves the problem that the UHF sensor is difficult to mount inside current transformers and provides a novel method for PD detection of SIICTs.

Maricultured organisms are chronically exposed to water containing antibiotics but the bioaccumulative behavior of antibiotics in exposed organisms at different growth stages has received little attention. Here, we investigated the concentrations and tissue-specific bioaccumulation characteristics of 19 antibiotics during three growth stages (youth stage, growth stage, and adult stage) of various organisms (Scophthalmus maximus, Penaeus vannamei, Penaeus japonicus, and Apostichopus japonicus) cultivated in typical marine aquaculture regions, and explored the factors that could affect the bioaccumulation of antibiotics. Tetracyclines (TCs) and fluoroquinolones (FQs) were the dominant antibiotics in all organisms, and the total concentrations of the target antibiotics in fish (S. maximus) were significantly higher than those in shrimp (P. vannamei and P. japonicus) and sea cucumber (A. japonicus) (p 0.01). The bioaccumulation capacity of a class of statistically significant antibiotics in most samples was strongest during the youth stage and weakest during the adult stage. The antibiotics exhibited higher bioaccumulation capacity in lipid-rich tissues (fish liver and shrimp head) or respiratory organs (fish gill) than muscle. Our results also reveal significant metabolic transformation of enrofloxacin in fish. Different from previous studies, the logarithm bioaccumulation factor (log BAF) was positively correlated with log D

Effect of the oscillation on the breakdown characteristics of the oil-impregnated paper under different lightning impulse voltage waves are studied experimentally in this work. IEC60060-3 standard and the waveform requirements of the on-site impulse withstand voltage test are considered, and four lightning impulse waves with different oscillation frequencies and 1.2/50μs standard lightning impulse wave are applied during the experiment. The experimental results show that the breakdown voltage under 1.2/50μs impulse is lower than that under the oscillating impulse. Under the oscillating waves, as the oscillating frequency increases, the number of breakdown points distributed at the peak of the non-first cycle increases, the minimum breakdown time gradually shortens, and the breakdown voltage shows a decreasing trend. The possible breakdown process of paper and the influence mechanism of different waveform parameters are discussed in detail. The explanation could be that changes on the impulse waveform parameters affect the movement, trap and accumulation of the positive charges ionized inside the oil micro-cavity, causing differences in the breakdown results. This study deepens the understanding of the breakdown mechanism of paper from the perspective of the waveform parameters effect and can provide a theoretical reference for the explanation of on-site impulse withstand voltage test results.

Power transformer is one of the most important equipment in power system. Its reliability directly affects the safe operation of power network. A partial discharge (PD) detection method for transformers adopting the end shield of the bushing as ultra-high frequency (UHF) sensor is developed in this paper. The bushing end shield can be used as the internal UHF sensor to measure the PD UHF signals. The experiments are carried out on an 80kV transformer model with three types of defect models set inside. The validity and sensitivity of this method are proved by experiments with AC voltage. The results show that the proposed method has high detection sensitivity and it can measure the PD signals without additional sensor. The UHF method has good anti-interference performance and is not affected by corona discharge outside the transformer. This PD detection method solves the problem that the internal UHF sensor has security risks while the external sensor is susceptible to interference. It provides a new method for PD detection of transformers in field.

Excessive nitrogen (N) loadings from human activities have led to increased eutrophication and associated water quality impacts in China's coastal wetlands. Denitrification accounts for significant reduction of inorganic N to nitrous oxide (N2O) or dinitrogen gas (N2), and thereby curtails harmful effects of N pollution in coastal and marine ecosystems. However, the molecular drivers and limiting steps of denitrification in coastal wetlands are not well understood. Here, we quantified the abundances of functional genes involved in N cycling and determined denitrification rates using 15N paring technique in the coastal wetland sediments of Bohai Economic Rim in eastern China. Denitrification accounting for 80.7 ± 12.6% of N removal was the dominant pathway for N removal in the coastal wetlands. In comparison, anaerobic ammonium oxidation (ANAMMOX) removed up to 36.9 ± 7.3% of inorganic N. Structural equation modeling analysis indicated that the effects of ammonium on denitrification potential were mainly mediated by the relative abundances of nosZ/nirS, nirS/(narG + napA) and amoA/nirK. Denitrification was limited by the relative strength of two steps, namely N2O reduction to N2 and nitrite (NO2−) reduction to nitric oxide (NO). Our results suggest that the relative abundances of functional genes which are more stable than sediment chemical compounds in the context of environmental changes are indictive of denitrification potential in coastal wetlands.