Molten salt as ultrastrong polar solvent enables the most straightforward pyrolysis towards highly efficient and stable single-atom electrocatalyst

Currently,pyrolysis as the most widely used method still has some key issues not well resolved for synthesis of carbon-supported single-atom catalysts(C-SACs),e.g.,the sintering of metal atoms at high temperature as well as the high cost and complicated preparations of precursors.In this report,molten salts are demonstrated to be marvellous medium for preparation of C-SACs by pyrolysis of small molecular precursors(ionic liquid).The ultrastrong polarity on one hand establishes robust interaction with precursor and enables better carbonization,resulting in largely enhanced yield.On the other hand,the aggregation of metal atoms is effectively refrained while no nanoparticle or cluster is formed.By this strategy,a C-SAC with atomically dispersed Fe-N_(4) sites and a high specific area over 2000 m^(2) g^(-1) is obtained,which illustrates high ORR activity in both acid and alkaline media.Moreover,this SAC exhibits superior methanol tolerance and stability after acid soaking at 85℃ for 48 h.It is believed that the molten-salts-assisted pyrolysis can be developed into a routine strategy as it not only can largely simply the synthesis of C-SACs,but also can be extended to prepare other types of SACs.

交通信号放行模式在西宁市特勤安保中分类运用的思考

论文概括了国内交通特勤任务中交通信号放行方式主要类型,并就全自动智能放行和半自动智能放行进行了详细说明,同时总结了近年来西宁市交通警察支队交通特勤安保工作的主要做法,最后结合西宁市公安局交通警察支队实际情况,给出了特勤安保中交通信号放行方式的选择方法。

Asymmetrically ligated single atomic nickel sites for efficient hydrogen peroxide electrosynthesis

Atomic transition-metal-nitrogen-carbon electrocatalysts hold great promise as alternatives to benchmark Pt in the oxygen reduction reaction.The pristine metal centers with quasi square-planar D_(4h) configuration,however,still suffer from unfavorable energetics and thereby strong activity/selectivity trade-off during the catalytic process.Here we present a ligand-field engineering of single-atom Ni-N-C catalysts to boost the sluggish kinetics via rationally constructing prototypical asymmetrically ligated Ni-N_(3)O_(1) sites.The as-obtained Ni-supported multi-walled carbon nanotubes with molten salt-treated(defined as Ni/CNS)catalyst delivered an excellent H_(2)O_(2) selectivity(>90%)within a wide potential window(0.2–0.7 V vs.reversible hydrogen electrode(RHE))and robust stability(for 10 h)in alkaline medium.Combined electron paramagnetic resonance and theoretical analysis rationalize this finding and demonstrate that the broken symmetry facilitates the electron transfer of a σ* to O–O orbital as compared to the Ni-N_(4) counterpart,playing an indispensable role in efficient O_(2) activation.

Hierarchical design of FeCo-based microchains for enhanced microwave absorption in C band

Microwave absorbing materials(MAMs)has been intensively investigated in order to meet the requirement of electromagnetic radiation control,especially in S and C band.In this work,FeCo-based magnetic MAMs are hydrothermally synthesized via a magnetic-field-induced process.The composition and morphology of the MAMs are capable of being adjusted simultaneously by the atomic ratio of Fe2+to Co2+in the precursor.The hierarchical magnetic microchain,which has a core–shell structure of twodimensional FexCo1−xOOH nanosheets anchored vertically on the surface of a one-dimensional(1D)Co microchain,shows significantly enhanced microwave absorption in C band,resulting in a reflection loss(RL)of lower than−20 dB at frequencies ranging from 4.4 to 8.0 GHz under a suitable matching thickness.The magnetic coupling of Co microcrystals and the double-loss mechanisms out of the core-shell structure are considered to promote the microwave attenuation capability.The hierarchical design of 1D magnetic MAMs provides a feasible strategy to solve the electromagnetic pollution in C band.

Simultaneous enhancement of coercivity and electric resistivity of Nd-Fe-B magnets by Pr-Tb-Al-Cu synergistic grain boundary diffusion toward high-temperature motor rotors

To high-power permanent magnetic motors,it is critical for Nd-Fe-B magnets to maintain the desirable coercivity at high-temperature operating conditions.To address this,two approaches have been proven effective:(1)enhancing the room temperature coercivity;(2)reducing the eddy current loss.However,these two items are difficult to be simultaneously achieved.Here,the grain boundary diffusion(GBD)of the Pr-Tb-Al-Cu-based source is applied to enhance the coercivity and electric resistivity at room temperature from 1101 kA m-1 and 2.13×10–6Ωm to 1917 kA m-1 and 2.60×10–6Ωm,and those at 120°C from 384 kA m-1 and 4.31×10–6Ωm to 783 kA m-1 and 4.86×10–6Ωm,respectively.Such optimization is ascribed to the improved formation depth of Tb-rich 2:14:1 shells with large magnetocrystalline anisotropy and the increased intergranular Pr-based oxides with high electric resistivity,induced by the coordination effects of Tb and Pr,as proven by the atomic-scale observations and the first principles calculations.It thus results in the simultaneously improved output power and energy efficiency of the motor because of the combination of magnetic thermal stability enhancement and eddy current loss reduction,as theoretically confirmed by electromagnetic simulation.

Electroreduction of hexavalent chromium using a porous titanium flow-through electrode and intelligent prediction based on a back propagation neural network

Flow-through electrodes have been demonstrated to be effective for electroreduction of Cr(VI),but shortcomings are tedious preparation and short lifetimes.Herein,porous titanium available in the market was studied as a flow-through electrode for Cr(VI)electroreduction.In addition,the intelligent prediction of electrolytic performance based on a back propagation neural network(BPNN)was developed.Voltametric studies revealed that Cr(VI)electroreduction was a diffusion-controlled process.Use of the flow-through mode achieved a high limiting diffusion current as a result of enhanced mass transfer and favorable kinetics.Electroreduction of Cr(VI)in the flow-through system was 1.95 times higher than in a parallel-plate electrode system.When the influent(initial pH 2.0 and 106 mg/L Cr(VI))was treated at 5.0 V and a flux of 51 L/(h·m2),a reduction efficiency of~99.9%was obtained without cyclic electrolysis process.Sulfate served as the supporting electrolyte and pH regulator,as reactive CrSO72−species were formed as a result of feeding HSO4−.Cr(III)was confirmed as the final product due to the sequential three-electron transport or disproportionation of the intermediate.The developed BPNN model achieved good prediction accuracy with respect to Cr(VI)electroreduction with a high correlation coefficient(R2=0.943).Additionally,the electroreduction efficiencies for various operating inputs were predicted based on the BPNN model,which demonstrates the evolutionary role of intelligent systems in future electrochemical technologies.

无人机景象匹配视觉导航技术综述

高精度定位与导航是实现无人机自主飞行、高效侦察与精确打击的关键技术之一.景象匹配视觉导航技术因其设备结构简单、被动式、定位精度高等特点,能与惯性系统组合构成自主性很强的高精度导航系统.通过分析当前基于景象匹配的无人机视觉导航技术研究现状,发现国外研究主要集中于单独利用视觉图像信息进行飞机姿态、导航信息提取以及联合IMU等传感器的组合导航系统;国内该领域的研究鲜见报道,但对该技术所涉及的惯性组合导航、视觉/激光测距三维地图重建、视觉导航着陆应用等技术进行了大量研究.本文总结了无人机景象匹配视觉导航技术的特点、分类与研究方法,得出在不同时间、不同视角、不同光照、不同分辨率、不同平台以及不同传感器等条件下,在高精度、强实时、鲁棒、连续视觉导航任务中,无人机景象匹配视觉导航需突破的关键技术.

SINS/GNSS integrated navigation system based on maximum versoria filter

In the missile-borne Strapdown Inertial Navigation System/Global Navigation Satellite System(SINS/GNSS)integrated navigation system,due to the factors such as the high dynamics,the signal blocking by obstacles,the signal intefereces,etc.,there always exist pulse interferences or measurement information interruptions in the satellite receiver,which make nonstationary measurement process.The traditional Kalman Filter(KF)can tackle the state estimation problem under Gaussian white noise,but its performance will be significantly reduced under nonGaussian noises.In order to deal with the non-Gaussian conditions in the actual missile-borne SINS/GNSS integrated navigation systems,a Maximum Versoria Criterion Extended Kalman Filter(MVC-EKF)algorithm is proposed based on the MVC and the idea of M-estimation,which assigns a smaller weight to the anomalous measurements so as to suppress the influence of anomalous measurements on the state estimation while maintaining a relatively low calculation cost.Finally,the integrated navigation simulation experiments prove the effectiveness and robustness of the proposed algorithm.

Autonomous maneuver strategy of swarm air combat based on DDPG

Unmanned aerial vehicles(UAVs)have been found significantly important in the air combats,where intelligent and swarms of UAVs will be able to tackle with the tasks of high complexity and dynamics.The key to empower the UAVs with such capability is the autonomous maneuver decision making.In this paper,an autonomous maneuver strategy of UAV swarms in beyond visual range air combat based on reinforcement learning is proposed.First,based on the process of air combat and the constraints of the swarm,the motion model of UAV and the multi-to-one air combat model are established.Second,a two-stage maneuver strategy based on air combat principles is designed which include inter-vehicle collaboration and target-vehicle confrontation.Then,a swarm air combat algorithm based on deep deterministic policy gradient strategy(DDPG)is proposed for online strategy training.Finally,the effectiveness of the proposed algorithm is validated by multi-scene simulations.The results show that the algorithm is suitable for UAV swarms of different scales.

Carrier dynamics in CsPbI_3 perovskite microcrystals synthesized in solution phase

All-inorganic cesium lead halide perovskites （CsPbX3, X=CF, Br-, I-） could provide comparableoptoelectronic properties as a promising class of materials for photovoltaic cell （PV）, photodetector andlight-emitting diode （LED） with enhanced thermal and moisture stabilities compared to organic-inorganic lead halide species. However, fabrication of CsPbI3 perovskite via facile solution process hasbeen difficult due to instability of CsPbl3 in the perovskite cubic phase in ambient air. Herein, we reportthe synthesis of CsPbl3 perovskite microcrystals by low-temperature, catalyst-free, solution-phasemethod. By applying the time-resolve spectroscopic technique, we determine the carrier diffusioncoefficient of 0.6-1.2 cm2/s, the intrinsic carrier lifetimes of 200-1300 ns and diffusion length of4-10 μm in different individual CsPbl3 perovskite microcrystals. Our results suggest the CsPbl3 perovskitemicrocrystals synthesized by solution process exhibit high quality feature and are suitable forapplications in optoelectronic devices.