Identifying the key N species for electrocatalytic oxygen reduction reaction on N-doped graphene

The state of nitrogen in nitrogen-doped graphene(NG)promoting the conversion of molecular oxygen to hydrogen peroxide was investigated.The oxygen reduction reaction(ORR)reactivity of graphitic-N,pyrrolic-N,pyridinic-N in NG was predicted by density functional theory(DFT).A series of NG samples with different contents of these doped nitrogen types were prepared by the low-temperature thermal reduction method and used for the ORR evaluation.The H_(2)O_(2)yield,2e−ORR current efficiency,H_(2)O_(2)selectivity,electron transfer number(n)were systematically studied.The 2e−ORR selectivity was positively correlated with the N content,approaching 100%with increasing N content(0.40 V vs.reversible hydrogen electrode(RHE)),whereas the comparative energy efficiency showed a volcano-type trend related to N content,reaching a maximum of 94%.In addition,N species validation experiments proved the key role of pyrrolic-N in the synthesis of H_(2)O_(2).Compared with a pure graphene catalyst,further contaminant degradation studies on NG electrodes with different pyrrolic-N contents revealed that the lower pyrrolic-N the higher removal of p-nitrophenol(PNP).This work provides insight into the mechanism of ORR on metal-free catalysts and a facile approach to optimize this important environmental catalytic strategy.

A Nowcasting Technique Based on Application of the Particle Filter Blending Algorithm

To improve the accuracy of nowcasting, a new extrapolation technique called particle filter blending was con- figured in this study and applied to experimental nowcasting. Radar echo extrapolation was performed by using the radar mosaic at an altitude of 2.5 km obtained from the radar images of 12 S-band radars in Guangdong Province, China. The first bilateral filter was applied in the quality control of the radar data; an optical flow method based on the Lucas-Kanade algorithm and the Harris corner detection algorithm were used to track radar echoes and retrieve the echo motion vectors; then, the motion vectors were blended with the particle filter blending algorithm to estimate the optimal motion vector of the true echo motions; finally, semi-Lagrangian extrapolation was used for radar echo extrapolation based on the obtained motion vector field. A comparative study of the extrapolated forecasts of four precipitation events in 2016 in Guangdong was conducted. The results indicate that the particle filter blending al- gorithm could realistically reproduce the spatial pattern, echo intensity, and echo location at 30- and 60-min forecast lead times. The forecasts agreed well with observations, and the results were of operational significance. Quantitat- ive evaluation of the forecasts indicates that the particle filter blending algorithm performed better than the cross-cor- relation method and the optical flow method. Therefore, the particle filter blending method is proved to be superior to the traditional forecasting methods and it can be used to enhance the ability of nowcasting in operational weather forecasts.

Fault Feeder Identification in Non-effectively Grounded Distribution Network with Secondary Earth Fault

Secondary earth faults occur frequently in power distribution networks under harsh weather conditions.Owing to its characteristics,a secondary earth fault is typically hidden within the transient of the first fault.Therefore,most researchers tend to focus on a feeder with single fault while disregarding secondary faults.This paper presents a fault feeder identification method that considers secondary earth faults in a non-effectively grounded distribution network.First,the wavelet singular entropy method is used to detect a secondary fault event.This method can identify the moment at which a secondary fault occurs.The zero-sequence current data can be categorized into two fault stages.The first and second fault stages correspond to the first and secondary faults,respectively.Subsequently,a similarity matrix containing the time-frequency transient information of the zero-sequence current at the two fault stages is defined to identify the fault feeders.Finally,to confirm the effectiveness and reliability of the proposed method,we conduct simulation experiments and an adaptability analysis based on an electromagnetic transient program.

Er-doped all-fiber laser mode-locked by graphitic carbon nitride nanosheets

Few-layer graphitic carbon nitride （g-C-N-） nanosheets were fabricated and utilized as a saturable absorber for mode-locking in an Er-doped fiber laser with net normal dispersion. Tile g-CaN,-/polyvinyl alcohol （PVA） hybrid-film-based saturable absorber has a modulation depth of 4.01% and a saturation intensity of 7.5 MW/cm2. By integrating g-C3N4-PVA mode-locker into the laser cavity, a mode-locked operation could be obtained. The achieved mode-locking pulse centered at 1530.3 nm has a pulse width of 530 ps. Its repetition rate is 40.8 MHz, and the corresponding signal-to-noise ratio is about 55 dB.