An mmWave Dual-Band Integrated Substrate Gap Waveguide Single Cavity Filter with Frequency Selectivity

A novel dual-band ISGW cavity filter with enhanced frequency selectivity is proposed in this paper by utilizing a multi-mode coupling topology.Its cavity is designed to control the number of modes,and then the ports are determined by analyzing the coupling relationship between these selected modes.By synthesizing the coupling matrix of the filter,a nonresonating node(NRN)structure is introduced to flexibly tune the frequency of modes,which gets a dualband and quad-band filtering response from a tri-band filter no the NRN.Furthermore,a frequency selective surface(FSS)has been newly designed as the upper surface of the cavity,which significantly improves the bad out-of-band suppression and frequency selectivity that often exists in most traditional cavity filter designs and measurements.The results show that its two center frequencies are f01=27.50 GHz and f02=32.92GHz,respectively.Compared with the dual-band filter that there is no the FSS metasurface,the out-of-band suppression level is improved from measured 5 dB to18 dB,and its finite transmission zero(FTZ)numbers is increased from measured 1 to 4 between the two designed bands.Compared with the tri-band and quadband filter,its passband bandwidth is expanded from measured 1.17%,1.14%,and 1.13% or 1.31%,1.50%,0.56%,and 0.57% to 1.71% and 1.87%.In addition,the filter has compact,small,and lightweight characteristics.

Nitrogen-Doped Carbon Nanotube-Supported Pd Catalyst for Improved Electrocatalytic Performance toward Ethanol Electrooxidation

In this study, hydrothermal carbonization(HTC)was applied for surface functionalization of carbon nanotubes(CNTs) in the presence of glucose and urea. The HTC process allowed the deposition of thin nitrogen-doped carbon layers on the surface of the CNTs. By controlling the ratio of glucose to urea, nitrogen contents of up to 1.7 wt%were achieved. The nitrogen-doped carbon nanotube-supported Pd catalysts exhibited superior electrochemical activity for ethanol oxidation relative to the pristine CNTs.Importantly, a 1.5-fold increase in the specific activity was observed for the Pd/HTC-N1.67%CNTs relative to the catalyst without nitrogen doping(Pd/HTC-CNTs). Furtherexperiments indicated that the introduction of nitrogen species on the surface of the CNTs improved the Pd(0)loading and increased the binding energy.

On Latency Reductions in Vehicle-to-Vehicle Networks by Random Linear Network Coding

In the Internet of vehicles(IoV),direct communication between vehicles,i.e.,vehicle-tovehicle(V2V)may have lower latency,compared to the schemes with help of Road Side Unit(RSU)or base station.In this paper,the scenario where the demands of a vehicle are satisfied by cooperative transmissions from those one in front is considered.Since the topology of the vehicle network is dynamic,random linear network coding is applied in such a multisource single-sink vehicle-to-vehicle network,where each vehicle is assumed to broadcast messages to others so that the intermediate vehicles between sources and sink can reduce the latency collaboratively.It is shown that the coding scheme can significantly reduce the time delay compared with the non-coding scheme even in the channels with high packet loss rate.In order to further optimize the coding scheme,one can increase the generation size,where the generation size means the number of raw data packets sent by the source node to the sink node in each round of communication.Under the premise of satisfying the coding validity,we can dynamically select the Galois field size according to the number of intermediate nodes.It is not surprised that the reduction in the Galois field size can further reduce the transmission latency.

An ISGW Filtering Antenna with Spurious Modes and Surface Wave Suppression for Millimeter Wave Communications

In this paper,an integrated substrate gap waveguide(ISGW)filtering antenna is proposed at millimeter wave band,whose surface wave and spurious modes are simultaneously suppressed.A secondorder filtering response is obtained through a coupling feeding scheme using one uniform impedance resonator(UIR)and two stepped-impedance resonators(SIRs).To increase the stopband width of the antenna,the spurious modes are suppressed by selecting the appropriate sizes of the ISGW unit cell.Furthermore,the ISGW is implemented to improve the radiation performance of the antenna by alleviating the propagation of surface wave.And an equivalent circuit is investigated to reveal the working principle of ISGW.To demonstrate this methodology,an ISGW filtering antenna operating at a center frequency of 25 GHz is designed,fabricated,and measured.The results show that the antenna achieves a stopband width of 1.6f0(center frequency),an out-of-band suppression level of 21 dB,and a peak realized gain of 8.5 dBi.

Training Mode of Personnel Majoring in Network Engineering Based on Three Main Lines

Network engineering is an emerging major across many disciplines,so there is yet to be an established personnel training program for this field.Moreover,there is a lack of reference material concerning personnel training.Therefore,it is especially urgent to explore a model suitable for personnel training in network engineering and study relevant personnel training systems.In this paper,the present situation of network engineering personnel training in China is analyzed,and basic orientation and training targets of network engineering major are explored.We find that network engineering personnel training is based on three main combinations:theory and practice,learning and innovation under the social computing environment,and classroom and employment experience,thereby providing constructive experience for training high-quality personnel specializing in network engineering.

ρ-Al_2O_3添加量对原位反应结合碳化硅膜支撑体性能的影响

以黑色碳化硅为骨料,添加不同含量的ρ-Al_2O_3,在1430℃、无压条件下,用碳化硅表面氧化产生的SiO_2与Al_2O_3反应制备多孔碳化硅膜支撑体,研究了ρ-Al_2O_3添加量对碳化硅支撑体粘结相组成及性能的影响。结果表明,ρ-Al_2O_3添加量由3wt%增加到15wt%时,试样烧结后粘结相中莫来石相增多,石英相减少但不能完全消除,支撑体的显气孔率降低,孔径减小,透气度由1127.8 m3·cm/(m^2·h·kPa)下降到210.4 m^3·cm/(m^2·h·kPa);支撑体抗弯强度先增大后降低,ρ-Al_2O_3添加量为9wt%时,支撑体抗弯强度为25.1 MPa,透气度为372.7 m3·cm/(m^2·h·kPa),支撑体的综合性能满足高温含尘气体过滤的要求。

质量单位千克复现初探

新定义的启用意味着千克原器将逐渐被以自然常数为基础的量子基准取代,基于新定义的千克单位复现将很快被提上议事日程.本文阐述了射线晶体密度法(X-ray crystal density,XRCD),即原子计数法测量阿伏伽德罗常数的基本原理和方法,包括晶格常数、同位素、浓缩硅、硅球直径及表面氧化层测量等.探讨了以原子计数法复现质量单位千克的基本技术路线和方案,并就复现方案进行了不确定度评估,将为国际单位制改制之后我国质量量值复现提供技术参考.

Direct transformation of ZIF-8 into hollow porous carbons and hollow carbon composites

Hollow porous carbons(HPCs)are a class of porous materials with advantages of high surface to volume ratio,large interior cavities,low density,and short diffusion length,which are promising in various applications.Direct carbonization of carbon precursors is the simplest and the most cost-effective method to prepare porous carbons,however,it often leads to non-hollow structures.Herein,we demonstrate the preparation of HPCs through a direct carbonization method with a two-step heating process of zeolitic imidazolate framework-8(ZIF-8)and tetrafluoroterephthalonitrile(TFTPN).During the carbonization,ZIF-8 nanoparticles first react with TFTPN at low temperature to create polymer coatings on the surface,which are then converted into HPCs at elevated temperature.The obtained HPCs show hierarchically porous structure with high specific surface areas and pore volumes.Additionally,this method has been adopted to fabricate Au@HPCs yolk–shell composites,exhibiting good catalytic performance in nitrobenzene reduction.The developed synthesis strategy can enrich the toolbox for the preparation of novel HPCs and their composites.