Impedance matching optimization of SiCf/Si3N4–SiOC composites for excellent microwave absorption properties

SiC fiber reinforced ceramic matrix composites (SiC_f-CMCs) are considered to be one of the most promising materials in the electromagnetic (EM) stealth of aero-engines, which is expected to achieve strong absorption and broad-band performance. Multiscale structural design was applied to SiC_f/Si₃N₄–SiOC composites by construction of micro/nanoscale heterogeneous interfaces and macro double-layer impedance matching structure. SiC_f/Si₃N₄–SiOC composites were fabricated by using SiC fibers with different conductivities and SiOC–Si₃N₄ matrices with gradient impedance structures to improve impedance matching effectively. Owing to its unique structure, SiC_f/Si₃N₄–SiOC composites (A3-composites) achieved excellent EM wave absorption performance with a minimum reflection coefficient (RC_min) of ?25.1 dB at 2.45 mm and an effective absorption bandwidth (EAB) of 4.0 GHz at 2.85 mm in X-band. Moreover, double-layer SiC_f/Si₃N₄–SiOC with an improved impedance matching structure obtained an RC_min of ?56.9 dB and an EAB of 4.2 GHz at 3.00 mm, which means it can absorb more than 90% of the EM waves in the whole X-band. The RC is less than ?8 dB at 2.6–2.8 mm from RT to 600 °C in the whole X-band, displaying excellent high-temperature absorption performance. The results provide a new design opinion for broad-band EM absorbing SiC_f-CMCs at high temperatures.     

Affective matches of fabric and lighting chromaticity

This study investigates the impact of lighting colors on subjective judgments of fabric: in particular, whether the influence of lighting varies depending on fabric types and color combinations. We conducted two visual assessments. In Study 1 (N = 44), eight illuminants and six types of fabric were presented as cloth stimuli. Derived from the literature review, four sets of adjectives (humble-luxurious, cool-warm, old-new, and not preferred-preferred) were used as metrics. In Study 2 (N = 41), five sets of fabric color combination swatches were assessed under lighting conditions that were identical to those of Study 1. Three bipolar scales (ordinary-characterful, classic-modern, and soft-rigid), were employed from factor analysis along with three unipolar scales (luxurious, preferred, harmonious with lighting). The results showed that hue characteristics of lighting and cloth types influenced participants' perceptions of the fabric. Overall, white lighting with 4000 K was the most preferred and luxurious lighting across various types of clothes, while a pinkish white with 4700 K (duv = −0.0127) was the best matched in every color combination. In addition, there were interaction effects between lighting colors, clothes types, and fabric color combinations with regard to each of the perceptual qualities. This study provides empirical evidence for optimally match lighting colors with fabric in the presentation of fabric goods.     

大数据环境下基于K中心点优化算法的Web服务组合

在当前Web服务海量增加、现有Web服务选择算法低效、用户匹配度差的基础上，针对K中心点算法存在的质点偏移、准确率低和容易发生畸变等问题，提出一种大数据环境下基于K中心点优化算法的Web服务组合方法。该方法是在大数据环境下，根据不同用户需求满意度及Web服务QoS参数，对基于优化初始聚类中心的K中心点算法的Web服务选择及最优Web服务组合进行研究。同时针对不同的选择方法对服务动态选择及组合的准确度、迭代更新次数、候选集选择时间及选择总时间进行实验分析，验证了本文研究方法的有效性和可靠性。     

城市燃气的分步置换

提出了一种城市燃气分步置换的新思路及其具体实施办法，在天然气利用工程中有良好的推广应用前景，可以产生显著的经济、环保和社会效益。     

混凝土温度跟踪养护仪的研制及应用

对混凝土试样实施温度跟踪养护,可以模拟混凝土在某种保温环境中,在自身水化热的影响下,其水化产物、体积稳定性和力学性能的变化规律.基于虚拟仪器的思想,研制了混凝土温度跟踪养护仪.试验结果表明:该温度跟踪养护仪可依据设定的温度变化历程很好地完成对混凝土试样的养护,同时,相对于恒温(T=20℃)条件下养护的混凝土试样,对混凝土试样实施温度跟踪养护可提高其抗压、抗折强度和弹性模量.     

田湾核电站预应力钢束全比例灌浆试验

介绍田湾核电站反应堆厂房内安全壳预应力体系灌浆工艺,材料特点,以及浆体的配合比、搅拌程序、灌注程序和质量控制指标。     

剖析配电系统中低压断路器的级联问题

阐述了低压配电系统设计中,为保证上下级低压断路器保护动作的选择性方面应考虑的因素,以及对实现选择性方法,使保障配电系统达到了安全运行的要求。     

轴向柱塞泵摩擦副材料的摩擦磨损实验研究

轴向柱塞泵是液压系统中的核心元件,斜盘式轴向柱塞泵的寿命及可靠性直接取决于斜盘-滑靴副、缸体-配流盘副和缸体-柱塞副3种摩擦副的材料、配对情况及工艺参数的选择。使用MWF-10往复式摩擦磨损实验机进行实验,记录硬材料(38Cr Mo Al,20Cr Mn Ti,30Cr Mo VA)与软材料(HMn58-3,QAl9-4,QT500-7)所组成的摩擦副的磨损情况。基于正交实验法的分析,得到配对材料表面粗糙度和硬度对磨损量和摩擦因数的影响。当摩擦副配对材料为HMn58-3(Ra0.2)/20Cr Mn Ti(Ra0.2)时软材料的磨损量最小,硬材料表面粗糙度对摩擦因数和磨损量的影响最大。     

基于匹配函数的云测试资源匹配算法研究

在云测试领域,用户需求与云资源间的匹配关系MR复杂且相互影响,导致缺少有效的针对云资源匹配方法的研究,而实现两者间的有效匹配对于满足用户需求和提高服务效率具有重要意义。首先对用户需求和云资源进行数学建模,然后综合考虑资源的性能、成本、可靠性、复杂性以及均衡性等影响因素,结合需求与资源间属性的距离偏好提出了相应的匹配函数和基于匹配函数的云测试资源匹配算法CTRMAMF,最后基于某工程实例,验证了该算法在解决用户需求与资源间最优匹配问题上的可行性。     

基于片上变压器耦合的CMOS功率放大器设计

设计了一个2 GHz全集成的CMOS功率放大器(PA),该PA的匹配网络采用片上变压器实现,片上变压器用来实现单端信号和差分信号之间的转换和输入、输出端的阻抗匹配。采用ADS Momentum软件对片上变压器进行电磁仿真,在2 GHz频点,输入、级间和输出变压器的功率传输效率分别为74.2%,75.5%和78.4%。该PA基于TSMC 65 nm CMOS模型设计,采用Agilent ADS软件进行电路仿真,仿真结果表明:在2.5 V供电电压、2 GHz工作频率点,PA的输入、输出完全匹配到50Ω(S11=–22.4 d B、S22=–13.5 d B),功率增益为33.2 d B,最高输出功率达到23.4 d Bm,最高功率附加效率(PAE)达到35.3%,芯片面积仅为1.01 mm2。