基于选频技术的高效高均匀性微波加热

近年来,微波加热以其高效性和内部加热等优点在各领域得到广泛应用。然而,微波加热的不均匀性限制了其大规模工业应用的发展。高均匀性和高效率是微波加热领域研究的重点。效率低会造成能源的浪费,而不均匀加热会导致加热品质差、甚至热失控等现象。本文提出一种双端口选频加热方法,通过在腔体中内置两个正交极化天线方式进行馈电。并且利用扫频来分析各频点的加热效率以及不同频率对加热效果的影响。最后选择性地对其中高效率的频点进行选频加热,使其在维持加热高效率的前提下提高加热的均匀性。     

Software effort estimation accuracy prediction of machine learning techniques: A systematic performance evaluation

Software effort estimation accuracy is a key factor in effective planning, controlling, and delivering a successful software project within budget and schedule. The overestimation and underestimation both are the key challenges for future software development, henceforth there is a continuous need for accuracy in software effort estimation. The researchers and practitioners are striving to identify which machine learning estimation technique gives more accurate results based on evaluation measures, datasets and other relevant attributes. The authors of related research are generally not aware of previously published results of machine learning effort estimation techniques. The main aim of this study is to assist the researchers to know which machine learning technique yields the promising effort estimation accuracy prediction in software development. In this article, the performance of the machine learning ensemble and solo techniques are investigated on publicly and non-publicly domain datasets based on the two most commonly used accuracy evaluation metrics. We used the systematic literature review methodology proposed by Kitchenham and Charters. This includes searching for the most relevant papers, applying quality assessment (QA) criteria, extracting data, and drawing results. We have evaluated a state-of-the-art accuracy performance of 35 selected studies (17 ensemble, 18 solo) using mean magnitude of relative error and PRED (25) as a set of reliable accuracy metrics for performance evaluation of accuracy among two techniques to report the research questions stated in this study. We found that machine learning techniques are the most frequently implemented in the construction of ensemble effort estimation (EEE) techniques. The results of this study revealed that the EEE techniques usually yield a promising estimation accuracy than the solo techniques.     

A metallic 3D printed K‐band quasi‐pyramidal‐horn antenna array

A K‐band (18‐27 GHz) antenna array is presented in this article. By deposing the quasi‐pyramidal‐horn upon a print circuit board (PCB), a traveling‐wave quasi‐pyramidal‐horn antenna is formed. Parasitic rings are introduced to decrease the quality factor for an extended bandwidth. The antenna element demonstrates impedance bandwidth 18.6 to 23.3 GHz. The gain is 10.3 dBi at 20.4 GHz with a stable radiation pattern. The impedance bandwidth of a 2 × 2 array is 18.3 to 22.7 GHz, with a maximum gain of 15.2 dBi at 20.4 GHz. The simulated and measured radiation patterns on E‐ and H‐planes at 20.4 GHz agree well. Taking advantage of the 3D printing technology, the quasi‐pyramidal horn is fabricated by selective laser melting using aluminum alloy for time‐saving and process simplicity. The proposed design highlights the hybrid usage of PCB and metallic 3D printing technology in fabricating microwave devices. It is a capable candidate for wireless communication.     

具有谐波抑制功能的共面波导轻薄整流天线

为解决对无人机、平流层飞艇等空中移动目标无线输能时机载接收端整流天线质量大,占居飞行器有效载荷多的难题,设计了一种具有谐波抑制功能的共面波导轻薄圆极化整流天线。该整流天线采用集中式整流方式,通过将整流电路直接集成在微带天线接地板上,实现了质量轻,尺寸小,剖面低,易共形的圆极化整流天线。该天线工作在5.8 GHz,采用共面波导耦合馈电,并在馈线上直接加载共面波导谐振结构进行谐波抑制,具有较宽的工作带宽。整流电路采用倍压整流形式,利用贴片电容作为直通滤波器进行直流滤波,电路结构简单。该整流天线结构紧凑,质量仅6.28 g,剖面厚度0.5 mm,最佳整流效率63.84%,测试结果与仿真结果吻合良好,验证了该设计的可行性。     

High‐gain planar array designed by using fragmented slots

A novel planar array antenna is proposed. It utilizes fragmented slots as its radiation elements and explores employing this highly flexible structure for achieving high gain. Each fragmented slot is gridded into 8 × 8 rectangular pixels, whose dimensions as well as conducting or nonconducting properties are optimized by the Genetic Algorithm (GA) in parallel on a PC cluster. A prototype antenna with 4 × 4 slots was designed, fabricated and measured. Both the simulation and measurement results show that this antenna possesses a high gain of 20.5 dBi at its working frequency of 5.8 GHz, and thus the corresponding aperture efficiency is up to 95%, which is much higher than that of the planar arrays with rectangular slots or split‐ring resonator (SRR) slots. © 2013 Wiley Periodicals, Inc. Int J RF and Microwave CAE 24:382–388, 2014.     

一个紧凑的梯形领结无芯RFID标签的设计

提出了一种紧凑、低成本、可完全印制的缝隙加载领结型无芯射频识别标签的设计。标签由2个梯形金属贴片组成,2组谐振频率邻近的缝隙谐振器分别加载在2个贴片上。在不增加缝隙间相互耦合的前提下,标签在超宽带频段内容纳的数据位数提高了1倍,在35 mm×33 mm的合理尺寸内,12个缝隙谐振器对应12位数据。仿真给出了标签的雷达散射截面积曲线,实测是在双站天线配置下进行,在频域内测出了传输系数s21。实测和仿真结果一致,验证了本设计的合理性。该标签具有高数据位数和低成本,因其只需1个导电层,所以能被直接印刷在ID卡甚至纸张上。     

A High‐Temperature Na‐Ion Battery: Boosting the Rate Capability and Cycle Life by Structure Engineering

High‐temperature sodium ion batteries (SIBs) have drawn significant heed recently for large‐scale energy storage. Yet, conventional SIBs are in the depths of inferior charge/discharge efficiency and cyclability at elevated temperatures. Rational structure design is highly desirable. Hence, a 3D hierarchical flower architecture self‐assembled by carbon‐coated Na₃V₂(PO₄)₃ (NVP) nanosheets (NVP@C‐NS‐FL) is fabricated via a microwave‐assisted glycerol‐mediated hydrothermal reaction combined with a post heat‐treatment. The growth mechanism of NVP@C‐NS‐FL is systematically investigated, by forming a microspherical glycerol/polyglycerol‐NVP complex initially and then converting into flower‐like architecture during the subsequent annealing at a low temperature ramping rate. Benefiting from the integrated structure, fast Na⁺ transportation, and highly effective heat transfer, the as‐obtained NVP@C‐NS‐FL exhibits an excellent high‐temperature SIB performance, e.g., 65 mAh g^?1 (100 C) after 1000 cycles under 60 °C. When coupled with NaTi₂(PO₄)₃ anode, the full cell can still display superior power capability of 1.4 kW kg^?1 and long‐term cyclability (2000 cycles) under 60 °C.     

无线能量传输中平顶波束的分析应用

平顶波束在无线能量传输中能够保证接收端功率密度的均匀性,对提高接收效率以及简化整流电路的设计具有重要意义。该文首先基于Orchard综合,控制Schelkunoff单位圆零点位置,得到了实现平顶波束的条件;然后通过引入Sinc函数,给出了平顶波束的解与平顶宽度的对应关系;最后利用微扰法编程计算,讨论了平顶宽度与矩形系数、波纹系数、副瓣电平之间的数值关系。以一款10元阵为例,实现了副瓣低于且宽度很窄的平顶波束,验证了该文方法和结论的有效性。     

Exergoeconomic Based Optimization of a Gas Fired Steam Power Plant Using Genetic Algorithm

This research paper mainly deals with exergy, economic, and environmental investigation of a 250 MW steam power plant located in Iran. In order to model this power plant, energy balance equations are used and each part of the power plant is modeled accordingly. Further by introducing the boiler as the main source of irreversibility, two approaches are presented to improve the boiler performance, reduction of excess air, and temperature reduction of gasses leaving the stacks. To study the effect of these two approaches, an objective function including the cost rate of exergy destruction of boiler, fuel cost, and cost rate of environmental impact is presented. The optimization process is done using a genetic algorithm. It is concluded that by optimizing, 20% reduction in the overall cost rate and 88% reduction in the cost rate of environmental impact can be achieved.     

构建基于Windows和MPI的Beowulf并行计算系统

利用普通微机构建并行计算集群(常称为Beowulf系统),能够以低廉的价格获得强大的计算能力。文章介绍了利用16台微机构建一套Beowulf并行计算系统,节点微机上运行Windows2000操作系统,采用MPI(Message-Passing-Interface)的MPICH最新版本:MPICH.NT1.2.3作为并行计算的支撑环境,并以100Mbps高速交换式以太网作为互连网络。通过编制的并行计算程序对该Beowulf系统进行了并行效率的实际测试,测试结果表明该Beowulf系统能够达到非常高的并行加速比和并行效率。