An analysis and preliminary experiment of the discharge characteristics of RF ion source with electromagnetic shielding

Combined with two-dimensional(2D)and three-dimensional(3D)finite element analysis and preliminary experimental tests,the effects of size and placement of the electromagnetic shield of the radio-frequency(RF)ion source with two drivers on plasma parameters and RF power transfer efficiency are analyzed.It is found that the same input direction of the current is better for the RF ion source with multiple drivers.The electromagnetic shield(EMS)should be placed symmetrically around the drivers,which is beneficial for the plasma to distribute uniformly and symmetrically in both drivers.Furthermore,the bigger the EMS shield radius is the better generating a higher electron density.These results will be of guiding significance to the design of electromagnetic shielding for RF ion sources with a multi-driver.

Comparison of experimental and theoretical radiation shielding parameters of several environmentally friendly materials

In this study, the gamma radiation shielding features of several environmentally friendly materials were investigated. For this purpose, several attenuation parameters, such as the mass attenuation coefficient (l=q), radiation protection efficiency (RPE), and effective atomic number (Zeff) were determined experimentally and compared with numerical data obtained using WinXCom software. In the measurements, the emitted gamma photons were counted by a gamma spectrometer equipped with an HPGe detector using 22Na, 54Mn, 57Co, 60Co, 133Ba, and 137Cs radioactive point sources in the energy region of 81–1333 keV. The obtained results indicate that the l=q and RPE values of the samples decrease with an increase in photon energy. The experimental values are in good agreement with those obtained using WinXCom software. The RPE and Zeff results show that among the studied materials, the NaY0.77Yb0.20Er0.03F4 sample has the best gamma radiation shielding effectiveness.

基于SE-SBM的机采棉加工工艺配置效率评价

针对目前机采棉加工工艺优化过程中缺乏从系统角度定量评估工艺配置效率的情况,把机采棉加工工艺系统看作一个具有输入输出的系统,以机采棉生产投入、工艺配置情况作为输入指标,以机采棉加工质量和皮棉产量等产出水平作为输出指标,建立了基于SE-SBM(Super Efficiency Slacks-based Measure)的工艺配置效率评价模型。以新疆某棉花加工企业的9条机采棉加工生产线为例,通过收集数据和利用DEA-Slover5.0软件计算,对其工艺配置效率进行了评估和比较,再根据所得结论确定了改进方向和额度,并提出了有针对性的建议。所构建的指标体系和评价方法可用于评估不同机采棉加工生产线的工艺配置效率,能为实施机采棉加工工艺设计和优化改进提供决策参考。

中国规模生猪养殖的环境效率分析——基于SE-SBM模型

探究我国各区域规模生猪养殖的环境效率,对指导生猪产业绿色发展具有重要的意义。文章基于2010—2020年我国24个生猪主产省的面板数据,运用SE-SBM模型对我国规模生猪养殖进行环境效率测算。结果显示:规模生猪养殖的环境效率与养殖规模成正比;中、大规模生猪养殖的环境效率在波动中提升,小规模持续稳定在较低水平;东、中部地区规模生猪养殖的发展要优于西部地区;山东省、河北省和重庆市的规模生猪养殖对其他省市具有一定的示范作用;仔畜、疫病防控投入冗余以及化学需氧量和全氮排放过量是规模生猪养殖产生效率损失的主要原因。推动生猪规模化养殖,需适当地引导生猪养殖适度规模发展,着力减少资源耗能和污染排放。

Electromagnetic Shielding and Absorption Properties of Fiber Reinforced Cementitious Composites

In order to investigate the electromagnetic shielding effectiveness （SE） and absorbing properties of fiber reinforced concrete, steel fiber, carbon fiber and synthetic polyvinyl alcohol （PVA） fiber reinforced concrete were researched. The results show that with the increase of fiber Volume fraction, the SE and trend of frequency change of corresponding fiber reinforced concrete are enhanced. When the volume content of steel fiber is 3%, the SE of concrete is above 50 dB and its frequency is above 1.8 GHz. Moreover, in the range of 8-18 GHz, steel fiber, carbon fiber and PVA fiber all can improve the microwave absorption properties of concrete. The concrete with 0.5% carbon fiber can achieve the best absorbing property, the minimum reflectivity is about -7 dB; while steel fiber optimal volume fraction is 2%. The reflectivity curve of PVA fiber reinforced concrete fluctuates with the frequency, and the minimum value of the reflectivity is below -10 dB. The results show that fiber reinforced concrete could be used as EMI（electromagnetic interference） prevention buildings by attenuating and reflecting electromagnetic wave energy.

Constant envelope FrFT OFDM: spectral and energy efficiency analysis

Constant envelope with a fractional Fourier transformorthogonal frequency division multiplexing(CE-FrFT-OFDM)is a special case of a constant envelope OFDM(CE-OFDM),both being energy efficient wireless communication techniques with a 0 dB peak to average power ratio(PAPR).However,with the proper selection of fractional order,the first technique has a high bit error rate(BER)performance in the frequency-time selective channels.This paper performs further analysis of CE-FrFT-OFDM by examining its spectral efficiency(SE)and energy efficiency(EE)and compare to the famous OFDM and FrFT-OFDM techniques.Analytical and comprehensive simulations conducted show that,the CE-FrFT-OFDM has five times the EE of OFDM and FrFT-OFDM systems with a slightly less SE.Increasing CE-FrFT-OFDM’s transmission power by increasing its amplitude to 1.7 increases its SE to match that of the OFDM and FrFT-OFDM systems while slightly reducing its EE by 20%to be four times that of OFDM and FrFTOFDM systems.OFDM and FrFT-OFDM’s amplitude fluctuations cause rapid changing output back-off(OBO)power requirements and further reduce power amplifier(PA)efficiency while CE-FrFTOFDM stable operational linear range makes it a better candidate and outperforms the other techniques when their OBO exceeds 1.7.Higher EE and low BER in time-frequency selective channel are attracting features for CE-FrFT-OFDM deployment in mobile devices.

Spectral and Energy Efficiency of Line-of-Sight OAM-MIMO Communication Systems

Not only high spectral efficiency(SE)but also high energy efficiency(EE)are required for future wireless communication systems.Radio orbital angular momentum(OAM)provides a new perspective of mode multiplexing to improve SE.However,there are few studies on the EE performance of OAM mode multiplexing.In this paper,we investigate the SE and EE of a misaligned uniform concentric circle array(UCCA)-based multi-carrier multimode OAM and multiple-input multiple-output(MCMM-OAM-MIMO)system in the line-ofsight(LoS)channel,in which two transceiver architectures implemented by radio frequency(RF)analog synthesis and baseband digital synthesis are considered.The distance and angle of arrival(AoA)estimation are utilized for channel estimation and signal detection,whose training overhead is much less than that of traditional MIMO systems.Simulation results validate that the UCCA-based MCMM-OAM-MIMO system is superior to conventional MIMOOFDM system in the EE and SE performances.

Exploiting Spectral-Energy Efficiency Tradeoff with Fairness in Non-Orthogonal Multiple Access Systems

The spectral efficiency(SE)and energy efficiency(EE)tradeoff while ensuring rate fairness among users in non-orthogonal multiple access(NOMA)systems is investigated.In order to characterize the SE-EE tradeoff with rate fairness,a multi-objective optimization(MOO)problem is first formulated,where the rate fairness is represented with theα-fair utility function.Then,the MOO problem is converted into a single-objective optimization(SOO)problem by the weighted sum method.To solve the converted non-convex SOO problem,we apply sequential convex programming,which helps to propose a general power allocation algorithm to realize the SE-EE tradeoff with rate fairness.We prove the convergence of the proposed algorithm and the convergent solution satisfies the KKT conditions.Simulation results demonstrate the proposed power allocation algorithm can achieve various levels of rate fairness,and higher fairness results in degraded performance of SE-EE tradeoff.A pivotal conclusion is reached that NOMA systems significantly outperform orthogonal multiple access systems in terms of SE-EE tradeoff with the same level of rate fairness.

Cr应力缓释层对柔性Cu_(2)ZnSn(S,Se)_(4)薄膜太阳电池性能的影响

柔性Cu_(2)ZnSn(S,Se)_(4)(CZTSSe)薄膜太阳电池中的应力是阻碍其发展的一大瓶颈。采用磁控溅射法在柔性Ti衬底和Mo背电极之间引入不同厚度的Cr缓释层,研究其对CZTSSe薄膜应力的影响。结果表明,当Cr应力缓释层厚度为80 nm时,薄膜的结晶质量最好,电池具有最佳的光电性能,相比没有Cr应力缓释层存在的情况,薄膜的残余应力从-7.15 GPa降低至-3.61 GPa,电池的光电转换效率(PCE)从2.89%提高至4.65%,增加了60.9%。Cr应力缓释层的引入不会影响CZTSSe薄膜的晶体结构,相反可有效提高薄膜的结晶质量,降低薄膜的残余应力,最终提高电池的光电性能。

水系锌电池Se@Zn负极的制备及性能

采用原位化学反应策略,在Zn电极表面生长出Se单质,通过XRD、XPS、SEM和能谱表征,结果表明Se在Zn电极表面的成功合成,且Se在锌电极表面均匀分布。将Se@Zn电极和裸Zn电极分别组装为对称电池和以MnO2为正极的全电池进行性能比较,结果表明,Se@Zn对称电池在1 mA/cm^(2)下可以运行1000小时以上,并保持27mV的极化电压。Se@Zn||MnO_(2)全电池在2A/g电流密度下容量为136mA·h/g,在1000次循环后,Se@Zn||MnO_(2)全电池仍接有近100%的库仑效率,容量保持率为88%。

高质量发展视角下中国物业上市企业服务效率评价

物业服务是民生建设的重要内容,对增进民生福祉、构建和谐社会具有重要意义,物业企业作为其基本服务单元,探究高质量发展视角下以增效提质、与时俱进、人民满意为标尺的服务效率就显得尤为重要。文章以全国43家物业上市企业作为截面样本,以高质量发展为研究视角,引入ESG理念,重构物业服务效率评价指标体系,采用SE-DEA模型对其物业服务效率进行测度与比较,并按不同的ESG等级分析制约物业服务效率的因素,由此提出中国物业服务上市企业服务效率提升的对策与建议。

基于改进YOLOv8的煤矿输送带异物检测

现有基于深度学习的输送带异物检测模型较大,难以在边缘设备部署,且对不同尺寸异物和小目标异物存在错检、漏检情况。针对上述问题,提出一种基于改进YOLOv8的煤矿输送带异物检测方法。采用深度可分离卷积、压缩和激励(SE)网络将YOLOv8主干网络中C2f模块的Bottleneck重新构建为DSBlock,在保持模型轻量化的同时提升检测性能;为增强对不同尺寸目标物体信息的获取能力,引入高效通道注意力(ECA)机制,并对ECA的输入层进行自适应平均池化和自适应最大池化操作,得到跨通道交互MECA模块,以增强模块的全局视觉信息,进一步提升异物识别精度;将YOLOv8的3个检测头修改为4个轻量化小目标检测头,以增强对小目标的敏感性,有效降低小目标异物的漏检率和错检率。实验结果表明:改进YOLOv8的精确度达91.69%,mAP@50达92.27%,较YOLOv8分别提升了3.09%和4.07%;改进YOLOv8的检测速度达73.92帧/s,可充分满足煤矿输送带异物实时检测的需求;改进YOLOv8的精确度、mAP@50、参数量、权重大小和每秒浮点运算数均优于SSD,Faster-RCNN,YOLOv5,YOLOv7-tiny等主流目标检测算法。

盾构法隧道开挖面稳定性下的多目标优化研究

盾构法隧道开挖过程中开挖面稳定性保持非常重要,开挖面稳定性下提升工程进度、保障工程质量等目标具有重要的工程意义。目前,针对开挖面稳定性下的多目标优化控制的研究不足。选择掘进效率作为工程进度的指标,选择掘进过程引起的最大地表沉降作为工程质量指标。采用分层序列法和NSGA-II多目标优化算法,将盾构开挖面稳定作为第一层优化目标,工程进度与工程质量作为第二层优化目标,研究盾构开挖面稳定下多目标优化。在一段连续穿越堤坝、空地、敏感建筑三个场景的施工隧道中应用本研究方法,结果表明,优化后的盾构推力维持在上下限区间内,提高了施工效率和减少了地表沉降。本文方法能够根据实际工况自适应的调整和优化控制策略,提高了在实际工程中的适应性和灵活性。为类似盾构隧道工程提供了参考和指导。

医用X射线防护材料的研究进展

介绍了医用X射线与生物系统的相互作用机理及物理防护原理,分析了具有医用X射线屏蔽能力的柔性复合材料的研究进展。探讨了铅、铋、钨等防X射线功能颗粒及聚合物基材的性能特征,总结了涂层法、溶胶-凝胶法、纺丝法等成型方法的优缺点。研究表明,现有X射线防护材料在提升防护效果和使用便捷性方面具有重要意义,但面临性能优化和成本控制方面的挑战。未来研究应聚焦新型功能颗粒的开发、复合材料结构设计的优化及环保高效屏蔽材料的探索等方面,以进一步提升医用X射线防护材料的性能,拓宽其应用前景。

交流高压静电防护服装标准的解读

为推动标准的有效推广和实施,以及交流高压静电防护服装的科学制备和合理适用,对GB/T18136—2008《交流高压静电防护服装及试验方法》和DL/T 1238—2013《1000 kV交流系统用静电防护服装》中的关键技术指标进行了探讨。对比分析了两个标准的异同点,并提出了合理化建议,为标准的修订提供参考。认为:应进一步增加衣料撕破强力、透湿量、色牢度、甲醛含量、pH值、接缝强力等考核指标,并明确相关考核指标的测试参数。

基于CutMix数据增强与多约束损失函数的YOLOv7盾构隧道渗漏水检测

盾构隧道强度投影图像中渗漏水尺寸不一致且像素占比偏小,现有目标检测模型的关键特征学习能力较弱,存在渗漏水病害目标检测精度偏低的问题。本文提出了基于CutMix数据增强与多约束损失函数的改进YOLOv7盾构隧道渗漏水检测方法。首先采用镶嵌CutMix方法对隧道图像进行数据增强,将多张不同的训练样本进行随机裁剪,拼接融合成具有综合特征的新样本;然后以YOLOv7网络为骨架结构,引入高效通道注意力模块,提高渗漏水关键特征的自主学习与表达能力;最后引入多约束几何条件的损失函数,提高预测框几何形状的精度,从而提升模型预测精度。在光线良好、光线不佳和存在遮挡等复杂环境情况下,选取Fast R-CNN、SSD、YOLOv5、YOLOv7这4种算法进行对比,试验表明,本文算法渗漏水检测精度达85.90%,平均精度比同类算法分别提高5.55%、8.89%、3.93%、2.75%,具有较高的稳健性和泛化能力。

基于SE-DEA模型的中国生猪规模养殖环境效率时空差异研究

本文在利用相关资料数据计算得到生猪规模养殖的投入、产出的基础上,构建SE-DEA模型,对中国17个生猪主产区2004—2014年规模养殖的环境效率进行测算,比较各主产区不同规模养殖的环境效率,分析不同规模下各区域环境效率的时序变化特征。结果表明:整体上生猪规模养殖环境效率呈现出明显的区域和规模差异,中部和西南优势区比东北及沿海优势区的养殖环境效率更高,大规模养殖环境效率最高,小规模次之,中规模最低;沿海优势区较为适合发展中小规模养殖,东北优势区较为适合发展大规模养殖,中部地区较为适合发展中小规模养殖,西南优势区较为适合发展小规模及大规模养殖。

考虑非合意产出的省际水资源利用效率及驱动因素研究——基于SE-SBM与Tobit模型的考察

水资源短缺与水生态恶化成为制约我国水资源利用的主要问题,提高水资源利用效率是解决水资源可持续利用的根本途径,也契合经济新常态与供给侧改革,研究水资源利用效率问题具有必要性和现实意义。国家相继实施最严格水管理制度,确立水资源利用三条红线,从水资源消耗总量和强度采取水资源管理双控行动,将"河长制"提升为全国性治水方略。本文选取资本、劳动力、用水总量为投入指标,以实际GDP与废水排放总量作为期望与非期望产出,利用非期望产出SE-SBM模型估算2003—2015年各省市水资源利用效率,并采用Tobit模型探究水资源利用效率的驱动因素。结果显示,水资源利用效率总体上呈现先下降后上升的U型发展趋势,虽研究时限内绝大多数省区水资源利用效率均有大幅度提升,东、中、西部水资源利用效率存在显著差异,京津沪等省份水资源利用效率最高,西北省份效率最低,通过变异系数分析比较得出区域差异呈现不断收敛的趋势,水资源利用效率驱动因素上,地区经济的发展水平、水资源的丰富程度、工农业结构、政府干预强度与水资源利用效率呈现负相关,进出口需求对其影响并不显著。提高水资源利用效率,国家要充分考虑各区域的实际情况,因地制宜地制定水资源利用效率目标及水资源管理政策,应大力发展节水技术,发挥价格杠杆在水资源利用效率中的作用,利用正向空间溢出效应,推动跨区域合作,以弱代强,推动省际水资源治理协同发展。

基于DEA与SE-SBM模型的资源型城市碳排放效率及影响因素研究——以全国106个资源型地级市为例

根据我国资源型城市的分类,选取106个资源型城市(成长型13个、成熟型58个、衰退型22个、再生型13个)作为研究对象,综合运用DEA模型和SE-SBM模型对其碳排放效率进行研究。研究发现,不同阶段的资源型城市碳排放效率存在显著差异,而同一类型资源型城市碳排放效率在规模有效性、技术有效性、规模收益和综合效率等方面仍表现出差异化;通过Tobit回归分析发现,经济发展水平、产业结构和城市化率对碳排放效率有不同程度的正向影响,能源强度与碳排放效率则呈现明显的负相关性。研究认为,提高资源型城市的碳排放效率应根据资源型城市不同发展阶段的特性、差异性和碳排放相关影响因素进行调整。最后针对资源型城市不同阶段的碳排放特征和影响因素提出针对性建议。