电化学置换反应制备石墨烯基纳米无定型锑复合阳极用于高性能钠离子电容器的构筑

锑(Sb),因其具有较高的理论比容量(660 mAh·g^(-1))、较低储钠电位(0.5–0.8 V vs.Na/Na^(+))和较高的密度(6.68 g·cm^(-3))等特点,被认为是一种理想的钠离子电容器的阳极材料。然而,在Na^(+)脱嵌过程中,Sb电极会发生较大的体积变化,导致其容量快速衰减以及倍率性能变差,阻碍了Sb电极的实际应用。因此,本文提出一种可用于制备锚定在具有碳涂层的二维石墨烯表面的无定型Sb纳米颗粒的电化学置换方法。所制备Sb/石墨烯复合材料具有典型的二维复合结构,可大幅增加与电解液界面接触面积,缩短离子扩散路径,促进离子迁移与电子转移。进一步利用该复合材料作为阳极,自制活性炭作为阴极,构建出一种新型钠离子电容器。研究证实,该钠离子电容器工作电压可达4.0 V,可输出140.75 Wh·kg^(-1)的最大能量密度和12.43 kW·kg^(-1)的最高功率密度。综上,该研究结果可为钠离子储能器件用高容量锑基阳极材料的优化设计提供可借鉴的思路。

A Correlation-Based Stochastic Model for Massive MIMO Channel

In this paper,the channel impulse response matrix(CIRM)can be expressed as a sum of couplings between the steering vectors at the base station(BS)and the eigenbases at the mobile station(MS).Nakagami distribution was used to describe the fading of the coupling between the steering vectors and the eigenbases.Extensive measurements were carried out to evaluate the performance of this proposed model.Furthermore,the physical implications of this model were illustrated and the capacities are analyzed.In addition,the azimuthal power spectrum(APS)of several models was analyzed.Finally,the channel hardening effect was simulated and discussed.Results showed that the proposed model provides a better fit to the measured results than the other CBSM,i.e.,Weichselberger model.Moreover,the proposed model can provide better tradeoff between accuracy and complexity in channel synthesis.This CIRM model can be used for massive MIMO design in the future communication system design.

宣肺败毒颗粒临床应用专家共识

宣肺败毒颗粒是在经典名方基础上化裁而成的用于治疗新型冠状病毒感染的有效方药。为进一步规范临床医师对宣肺败毒颗粒的合理使用,提高临床疗效,提高合理用药水平,发挥更大作用,特邀请来自临床一线专家,针对宣肺败毒颗粒的功能主治、用法用量、不良反应及注意事项等进行讨论,形成共识。共识认为:宣肺败毒颗粒具有宣肺化湿、清热透邪、泻肺解毒的功效;可用于治疗新冠病毒感染轻型、普通型、重型患者及流感等其他常见上呼吸道感染性疾病;急性气管炎-支气管炎及社区获得性下呼吸道感染性疾病等属湿毒郁肺者;可缓解慢性阻塞性肺疾病急性加重所引发的咳嗽、咯痰等症状,临床疗效确切,安全性好。按照循证医学原则,该专家共识将会定期进行更新。

Magnetic triangular bubble lattices in bismuth-doped yttrium iron garnet

Magnetic bubbles have again become a subject of significant attention following the experimental observation of topologically nontrivial magnetic skyrmions. In recent work, tailoring the shape of the bubbles is considered a key factor for their dynamics in spintronic devices. In addition to the reported circular, elliptical, and square bubbles, here we observe triangular bubble domains in bismuth-doped yttrium iron garnet(Bi-YIG) using Kerr microscopy. The bubble domains evolve from discrete circular to latticed triangular and hexagonal shapes. Further, the orientation of the triangular bubbles in the hexagonal lattices can be flipped by decreasing the magnetic field. The sixfold in-plane magnetic anisotropy of Bi-YIG(111) crystal, which is presumably the mechanism underlying the triangular shape of the bubbles, is measured as1179 erg/cm~3. The study of the morphologies of topologically trivial bubbles in YIG offers insight into nontrivial spin textures, which is appealing for future spintronic applications.

面向6G的无线通信信道特性分析与建模

针对6G全覆盖、全频谱、全应用的发展愿景,对面向6G的全频谱全场景无线信道测量、信道特性与信道模型方面的进展进行了全面概述,侧重于毫米波、太赫兹、光波段、卫星、无人机、海洋、水声、高铁、车对车、大规模/超大规模天线、轨道角动量以及工业物联网等通信信道,并展示了6G信道的相关测量与建模结果。最后,指出了6G无线信道测量与建模研究的未来挑战。

Neighbor-Aware Multiple Access Protocol for 5G m MTC Applications

In order to support massive Machine Type Communication(mMTC) applications in future Fifth Generation(5G) systems,a key technical challenge is to design a highly effective multiple access protocol for massive connection requests and huge traffic load from all kinds of smart devices,e.g.bike,watch,phone,ring,glasses,shoes,etc..To solve this hard problem in distributed scenarios with massive competing devices,this paper proposes and evaluates a Neighbor-Aware Multiple Access(NAMA) protocol,which is scalable and adaptive to different connectivity size and traffic load.By exploiting acknowledgement signals broadcasted from the neighboring devices with successful packet transmissions,NAMA is able to turn itself from a contention-based random access protocol to become a contention-free deterministic access protocol with particular transmission schedules for all neighboring devices after a short transition period.The performance of NAMA is fully evaluated from random state to deterministic state through extensive computer simulations under different network sizes and Contention Window(CW)settings.Compared with traditional IEEE802.11 Distributed Coordination Function(DCF),for a crowded network with 50 devices,NAMA can greatly improve system throughput and energy efficiency by more than 110%and210%,respectively,while reducing average access delay by 53%in the deterministic state.

Guest editorial: special issue on high mobility wireless communications

The high-speed railway and high-way networks are now expanding at a phenomenal speed in Chinaand in many other parts of the world. The related broadband wireless communication over high-speed trains and highway vehicles is a very challenging task due to hostile transmission channel conditions. The demand for such services is growing rapidly, following the proliferation of laptop/tablet computers and smart phones. This motivates the research on wireless communications in the high mobility environments.

AG Channel Measurements and Characteristics Analysis in Hilly Scenarios for 6G UAV Communications

As an important part of sixth generation(6G)integrated space-air-ground-sea networks,unmanned aerial vehicle(UAV)communications have aroused great attention and one of its typical application scenarios is the hilly environments.The related UAV air-ground(AG)channel characteristics analysis is crucial for system design and network evaluation of future UAV communications in hilly scenarios.In this paper,a recently conducted channel measurements campaign in a hilly scenario is presented,which is conducted at the center frequencies of 2.585 GHz and 3.5 GHz for different flight trajectories.Based on the measurement data,some key channel characteristics are analyzed,including path loss(PL),shadow fading(SF),Rician K-factor,root mean square(RMS)delay spread(DS),and temporal auto-correlation function(ACF).Finally,the comparison of typical channel characteristics under circular and straight trajectories is given.The related results can provide a theoretical reference for constructing future UAV communication system in hilly scenarios.

Channel Measurements and Models for 6G

In the early stage of 6G research,carrying out research on channel measurements and models is one of the fundamental and prerequisite works,as well as full of the challenges.Driven by the demand for multiple frequency bands,versatile scenarios,and various new technologies in the future,6G channels are expanding in multiple dimensions such as the space-time-frequency domains.Those all make 6G channel measurement and modeling research face a series of new challenges,e.g.,non-stationarity in multiple dimensions,the obvious increase in modeling complexity,and changes in theoretical premises and assumptions.It is therefore clear that more efforts are needed to understand propagation characteristics,especially in the new scenes and applications,and to develop a new paradigm for 6G channel modeling.

A Study on the Driving Factors of Food Production in Huang-Huai-Hai Plain Based on Path Analysis

The effects of 14 factors on food production in Huang-Huai-Hai Plain are analyzed by path analysis in this paper,and then the linear regression models of them are established by SPSS software. The results show that electricity consumption for agriculture,growing area of crops,the affected area,annual average temperature and arable land area at the end of the year have great effects on food production. Finally some recommendations are put forward to improve the food production in Huang-Huai-Hai Plain such as improving the level of agricultural mechanization,stabilizing food production,preventing natural disasters and increasing the effective irrigation area.

Carbon nanotube-supported mixed-valence Mn_(3)O_(4) electrodes for high-performance lithium-oxygen batteries

Lithium-oxygen batteries(LOBs)have extensive applications because of their ultra-high energy densities.However,the practical application of LOBs is limited by several factors,such as a high overpotential,poor cycle stability,and limited rate capacity.In this paper,we describe the successful uniform loading of Mn_(3)O_(4) nanoparticles onto multi-walled carbon nanotubes(Mn_(3)O_(4)@CNT).CNTs form a conductive network and expose numerous catalytically active sites,and the one-dimensional porous structure provides a convenient channel for the transmission of Li+and O2 in LOBs.The electronic conductivity and electrocatalytic activity of Mn_(3)O_(4)@CNT are significantly better than those of MnO@CNT because of the inherent driving force facilitating charge transfer between different valence metal ions.Therefore,the Mn_(3)O_(4)@CNT cathode obtains a low overpotential(0.76 V at a limited capacity of 1000 mAh g^(-1)),high initial discharge capacity(16895 mAh g^(-1) at 200 mA g^(-1)),and long cycle life(97 cycles at 200 mA g^(-1)).This study provides evidence that transition metal oxides with mixed-valence states are suitable for application as efficient cathodes for LOBs.

Progress and perspectives on two-dimensional silicon anodes for lithium-ion batteries

Silicon(Si)anodes with extremely high theoretical capacities are considered indispensable for next-generation high-energy lithium-ion batteries(LIBs).However,several intractable problems,including pulverization,poor electrical contact,and continuous side reactions caused by the large volume change of Si during lithia-tion/delithiation,lead to a short cycle life and poor rate capability,thus hindering the commercial use of Si anodes in LIBs.Two-dimensional(2D)Si with a unique graphene-like structure has a short ion diffusion path-way,small volume change during lithiation,and efficient redox site utilization,making it more promising than bulk Si or Si with other versatile structures for use in LIBs.Theoretical analysis demonstrated that the low energy barrier on the surface of 2D Si accelerates the transport of Li+.However,the issues surrounding 2D Si,includ-ing the tedious and user-unfriendly synthesis,ease of restacking,and atmospheric sensitivity,limit its practical applications,which are discussed in this review.Furthermore,possible solutions to these remaining challenges and new directions are provided,with the aim of designing practical and high-performance 2D Si anodes for next-generation LIBs.

Advanced all-solid-state lithium-selenium batteries enabled by selenium-nitrogen doped hierarchic meso-microporous carbon nanospheres composite cathode

Selenium,an element belonging to the same group in the periodic table as sulfur,has a high electronic conductivity(1×10^(-5)S/cm)and a high volumetric energy density(3253 mA h/cm^(3)),which is a prospective cathode material for high-energy all-solid-state rechargeable batteries.However,its wide use is hindered by large volume expansion and low utilization rate.In this work,Se-infused nitrogen-doped hierarchical meso-microporous carbon composites(Se/NHPC)are prepared by a melt-diffusion process.Amorphous Se is uniformly dispersed in meso-micropores of NHPC with a high mass loading of 81%.All-solid-state Li-Se batteries fabricated by using Se/NHPC as the cathode,a Li-In alloy as the anode,and Li_(6)PS_(5)Cl as the solid-state electrolyte,deliver a highly reversible capacity of 621 m Ah/g(92%of theoretical capacity),a good rate capability and a high capacity retention value of 80.9%after 100 cycles.It is found that the capacity decay of Se cathode is mainly related to the interfacial degradation and the separation of Se from the carbon substrate,as suggested by the continuous increase of interfacial resistance and the structural transformation from amorphous Senchains to Se8rings initial discharge/charge cycle and then to the trigonally crystalline Se chains structure after the long-term cycles.

Molecule‑Level Multiscale Design of Nonflammable Gel Polymer Electrolyte to Build Stable SEI/CEI for Lithium Metal Battery

The risk of flammability is an unavoidable issue for gel polymer electrolytes(GPEs).Usually,flameretardant solvents are necessary to be used,but most of them would react with anode/cathode easily and cause serious interfacial instability,which is a big challenge for design and application of nonflammable GPEs.Here,a nonflammable GPE(SGPE)is developed by in situ polymerizing trifluoroethyl methacrylate(TFMA)monomers with flame-retardant triethyl phosphate(TEP)solvents and LiTFSI–LiDFOB dual lithium salts.TEP is strongly anchored to PTFMA matrix via polarity interaction between-P=O and-CH_(2)CF_(3).It reduces free TEP molecules,which obviously mitigates interfacial reactions,and enhances flame-retardant performance of TEP surprisingly.Anchored TEP molecules are also inhibited in solvation of Li^(+),leading to anion-dominated solvation sheath,which creates inorganic-rich solid electrolyte interface/cathode electrolyte interface layers.Such coordination structure changes Li^(+)transport from sluggish vehicular to fast structural transport,raising ionic conductivity to 1.03 mS cm^(-1) and transfer number to 0.41 at 30℃.The Li|SGPE|Li cell presents highly reversible Li stripping/plating performance for over 1000 h at 0.1 mA cm^(−2),and 4.2 V LiCoO_(2)|SGPE|Li battery delivers high average specific capacity>120 mAh g^(−1) over 200 cycles.This study paves a new way to make nonflammable GPE that is compatible with Li metal anode.

基于超图聚簇和干扰限制区域理论的全双工D2D车载通信资源管理方案

在蜂窝车用无线通信(cellular vehicular-to-everything,C-V2X)系统中,车辆快速移动导致D2D链路的网络拓扑不稳定,频繁重构的网络拓扑增加了同频干扰问题的复杂度和拓扑管理信令的数量,造成基站的计算能力和带宽资源浪费.本文建立以簇为核心的全双工D2D(full-duplex device-to-device,FD-D2D)车载通信模型,提出基于超图聚簇(hypergraph clustering,HG-C)和干扰限制区域(interference limited area,ILA)理论的FD-D2D车载通信资源管理方案.利用链路依赖度(degree of link dependence,DLD)和车辆用户(Vehicle users,VUE)的计算能力提高簇的生存时间,降低基站的开销.同时,利用动态功率控制和复用区域映射辅助基站分配资源,削弱复用相同蜂窝链路的V-D2D(vehicular device-to-device)链路间和对蜂窝链路的同频干扰,提高频谱效率.最后,基于交通仿真建模软件VISSIM产生实时交通流数据,从而验证本文所提资源管理方案,结果表明:基站承担的网络拓扑管理任务量至少降低50%,与传统蜂窝D2D车载通信相比,频谱平均复用次数增加0.5次以上,频谱效率增加10%.

Electrocatalytic hydrogen evolution performance of modified Ti_(3)C_(2)O_(2)doped with non-metal elements:A DFT study

Developing highly conductive,stable,and active hydrogen evolution reaction(HER)catalysts is a critical step towards establishing the hydrogen economy.However,there are few catalysts,except for noble metals,that can meet all the requirements.Recently,two-dimensional(2D)transition metal carbon/nitride(MXene)materials have shown excellent performance in catalysis,and have attracted wide attention from researchers.In this study,the effectiveness of non-metal element(B,C,N,P,and S)-doped Ti_(3)C_(2)O_(2)MXene in the electrocatalytic hydrogen evolution reaction was investigated using density functional theory(DFT)calculations.Non-metal atoms as elec-tron donors can provide additional electrons to the O functional group on the catalyst surface,thereby reducing charge transfer from H to O and the interaction between H and O.The Gibbs free energy(ΔG H)of non-metal element-doped Ti_(3)C_(2)O_(2)is closer to 0 than that of pristine Ti_(3)C_(2)O_(2),demonstrating better hydrogen evolution performance.Furthermore,in the hydrogen evolution path,the desorption process is more inclined to the Hey-rovsky mechanism,and doping greatly reduces the energy barrier of the reaction,thereby improving the catalytic efficiency.The present results prove that doping with non-metallic elements is an effective means of improving the catalytic activity of Ti_(3)C_(2)O_(2)for hydrogen evolution.