宽带多谐振偶极子天线设计

根据目前无线通信系统发展小型化与宽带化的趋势,设计了一款具有多谐振点的宽带偶极子辐射天线。首先通过特征模理论分析倒T型导体结构得到两个谐振模式;然后在不影响倒T型导体结构谐振特性的前提下,引入寄生谐振偶极子单元;最后在3个谐振模式的电流共同最大处添加集总端口,同时激励3个谐振模式,得到3个谐振点的宽带谐振天线。天线的仿真与实测结果基本吻合,最终的工作带宽为1.8～2.56 GHz (相对带宽为34.9%)。由此,所设计的天线不仅结构简单,且性能方面良好,可广泛应用于无线通信系统中。     

分子模拟技术在壳聚糖功能材料开发和应用中的研究进展

壳聚糖因其优良的生物相容性、可再生性、生物降解性以及絮凝、吸附性而被广泛应用于医药、能源、环保等领域。随着统计力学和计算机科学的快速发展,应用分子模拟研究壳聚糖材料的开发和应用已成为热点。本文综述了近年来分子模拟技术在该领域的研究进展,归纳了分子模拟的基本方法及特点,详述了以量子化学为基础的分子模拟软件Materials Studio在壳聚糖研究中的常用模块以及应用。在此基础上,介绍了利用分子模拟对壳聚糖分子结构、微观反应机理、相容性的分析与预测,以及壳聚糖在生物医用材料、燃料电池、缓蚀剂、水处理应用领域的分子模拟研究进展,总结分析了分子模拟方法在壳聚糖功能材料开发和应用中的优势以及在微观机理探索方面的不足,提出了采用多尺度模拟、与机器学习相结合等提高模拟结果准确性和计算速度的研究方法,为未来设计开发新型壳聚糖材料提供新的思路。     

亲水性PET共混材料的制备及性能研究

以机械共混法制备亲水性聚对苯二甲酸乙二醇酯(PET)共混材料,并通过接触角测定仪、差示扫描量热仪(DSC)和电子万能材料试验机等对共混材料的亲水性能、热性能和力学性能等进行研究与分析。结果表明,亲水处理剂聚乙二醇(PEG)、聚丙烯酸钠(PAAS)、聚乙烯吡咯烷酮(PVP)均能改善PET的亲水性能,影响PET的结晶性能,但亲水处理剂对PET的力学性能影响较小,其中PET/PEG共混材料的亲水性最优;随着PEG含量的增加,PET/PEG共混材料的亲水性先逐渐增强,当PEG含量高于5%后,共混材料的亲水性变化很小;且PET的结晶度随着PEG的加入呈现先增大后减小的趋势。     

益生菌对微生态系统的改善作用及其应用研究进展

人体微生态系统与宿主相互作用、相互影响,在维护机体健康方面发挥着重要作用。当饮食、环境或其他不利因素迫使微生态系统失去平衡时,机体抗感染能力降低,相关疾病也随之而来。益生菌即\     

基于比例和改进准谐振控制的MMC环流抑制策略

模块化多电平换流器（MMC）由于电容电压的波动会产生环流在相间流动,环流会增加能量损耗并对子模块中的绝缘栅双极晶体管（IGBTs）产生不良的影响。为抑制环流,基于环流的动态数学模型设计了一种能产生反向二倍频分量的比例控制器。针对环流中的高次谐波对传统的准谐振控制器进行了改进。对所提策略进行了仿真验证,仿真结果表明比例控制策略仅经过0.2 s后快速达到稳态抑制环流,改进后的准谐振控制策略相比于改进前THD值优化了3.56%,进一步降低了高频谐波分量,验证了所提策略的可靠性。     

基于统计聚类方法的儿童下肢肌电信号周期识别

为运用肌电信号分析髋脱位儿童和正常儿童的差异,提出一种基于统计的聚类方法,识别步态中下肢肌电信号的周期起始时刻.使用非参数贝叶斯模型将肌电信号序列聚类为状态序列,并通过k均值聚类算法将该状态序列标记为肌肉活跃和不活跃两种状态,将肌肉活跃状态的起始时刻作为肌电信号周期的起始位置,并且利用窗函数方法提高预测准确性.实验结果...     

High-performance thermosets with tailored properties derived from multi-arm stared vanillin and carbon fiber composites

Vanillin, a rigid compound can be separated from lignin, is a promising sustainable candidate for industrial and high performance polymers, while synthesis of hexa-epoxies is challenging. Meanwhile, carbon fiber reinforced bio-based polymers combining high performance are more difficult to be achieved because of the contradictions of liquidity and high rigidity in the polymer structure and performance. In this paper, a novel hexa-epoxy functionalized bio-based epoxy resin (HPVIGEP) with a multi-arm star structure, which simultaneously reduced the viscosity and improved thermo-mechanical properties. The rheological behavior analysis results of HPVIGEP indicated that the viscosity was 3406.9 mPa·s at 25°C, which dramatically decreased by 75.8% compared to DGEBA (14,096 mPa·s), leading to excellent processability and adaptability. At the same time, the study on mechanical properties revealed that the cured HPVIGEP manifested 30.6%, 33.7% and 49.0% in higher tensile strength, tensile modulus and storage modulus (30°C) than of cured commercial epoxy, respectively. The tensile strength and flexural strength of carbon fiber composites which were applied HPVIGEP were increased by 9.3% and 10.9%, respectively. In a word, this work provides the promise for the application of environmentally friendly bio-based composite materials.     

ICP-OES法测定辣条中的多种金属元素

此次试验旨在建立一种可靠的微波消解-电感耦合等离子体发射光谱(ICP-OES)法测定辣条中10种金属元素的方法。试验对仪器参数进行优化,随机购买市售50份样本,打碎混匀后,用微波消解-ICP-OES法对锰、铜、铁、铝、铅、银、镉、钼、镍、铬10种元素进行同时测定。结果表明,在优化试验条件下,各金属元素的线性关系良好,相关线性(r^2)在0.9998以上,方法的检出限为0.034~0.646 mg/kg。在加标量为0.005,0.010和0.020 mg/kg的3种梯度浓度下,回收率达到90.0%~102.0%,方法精密度RSD为0.82%~7.71%。该方法样品处理效率高,样品消解彻底,操作简单快速,谱线干扰少,线性范围宽,灵敏度高,能满足辣条样品中多种金属元素的同时测定。     

Two–step processing of thermoelectric (Ca0.9Ag0.1)3Co4O9/nano–sized Ag composites with high ZT

A two–step processing method, spark plasma sintering (SPS) combined with a heat–treatment, was used to fabricate (Ca_0.9Ag_0.1)₃Co₄O₉/nano–sized Ag composites. Sliver within the lattice generated hole carriers, and silver along the grain boundaries improved the transport path of the charge carriers. Samples sintered using SPS at different temperatures had very different thermoelectric properties. The results showed that when the sample was sintered at 1233 K, the maximum power factor reached 0.43 mW/(m·K²) along with an electrical resistivity of 8.61 mΩ·cm and a Seebeck coefficient of 196.90 μV/K, and the corresponding lattice thermal conductivity was 1.86 W/(m·K). This study shows how to improve the properties and broaden the application of Ca₃Co₄O₉ thermoelectric ceramics.