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21.
《Ceramics International》2022,48(20):29561-29571
Currently, materials with outstanding absorption abilities, such as thin size, better absorbing power, and light weight are the need of industry to resolve the electromagnetic issues. However, the research on optimizing the composition of the material, microstructure and the structure of the absorber are also the important factors for enhancing the absorption features. A metamaterial microwave absorber (MMA) based on nano ferrites with desirable absorption peaks is proposed and simulated. Sol-gel auto combustion route is used to prepare the nanosized Sm doped Co ferrite with Co1+xSmxFe2-2xO4 at x = 0.00, 0.03, 0.06, 0.09, respectively. XRD, VSM, FESEM, and VNA were employed to evaluate the structural, magnetic, morphological, and dielectric features. Rietveld refinement of the XRD patterns of samples was evaluated. Refined parameters show the spinel phase's emergence and the Fe2O3 phase. Grain size and crystallite size were increased with Sm doping in Co ferrite. Electromagnetic studies depicted that the highest dielectric constant value was found at x = 0.09 and the minimum value at x = 0.03, respectively. Sm doped Co ferrite at x = 0.09 depicted high Q values at higher frequencies. The coercivity values first decreased and then increased. All samples exhibit variations in coercivity and magneto-crystalline anisotropy constant. This variation was attributed to the super-exchange interactions and strong LS coupling of the cations. The multiple absorption peaks are attained for TE-polarization, and the absorptivity is considerably improved for x = 0.09. The proposed absorber simulated from CST depicted the absorption peaks of the S-band and C-band of the microwave regime. The synergistic effects among the metamaterial and ferrite layers may enhance the absorption feature and would be useful for satellite communication applications. 相似文献
22.
以二氧化硅为起始原料,与乙二醇、氢氧化钾反应,生成高反应活性的五配位硅钾化合物,并以此为原料与对苄氯苯乙烯反应制备出含双键官能团的四配位硅单体;然后与甲基丙烯酸甲酯进行自由基聚合反应,得到了支链含硅的共聚物。最后对合成的四配位硅单体及共聚物进行了IR、TG、DSC、GPC结构表征。IR表明,四配位硅单体在1629.6 cm-1处的C=C伸缩振动吸收峰在共聚物中消失;TG表明四配位硅单体在67℃就开始失重,437℃有机部分基本失重完毕,而共聚物在150℃左右开始失重,550℃有机部分失重完毕;DSC表明,共聚物的玻璃化温度为55.0℃;GPC分析表明,共聚物的分子量为3千左右。 相似文献
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24.
文章综述了MMA防水涂料、MMA彩色防滑路面、MMA地坪涂料和MMA混凝土修复材料等系列产品的研究进展情况。 相似文献
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26.
Telma Barroso Mrcio Temtem Teresa Casimiro Ana Aguiar-Ricardo 《The Journal of Supercritical Fluids》2009,51(1):57-66
Porous membranes were developed in a two step process using supercritical CO2 technology. Copolymers of methyl methacrylate (MMA) and methacrylic acid (MAA) were synthesized for the first time in supercritical carbon dioxide (scCO2), being identified by 1H NMR and FT-IR. The influence of the feed monomer ratio on their morphology, average molecular weight and Tg was studied. These PMMA-co-PMAA copolymers were then used in the preparation of thin pH-responsive membranes by scCO2-assisted phase inversion method. The prepared films were characterized by scanning electron microscopy, mercury porosimetry, dynamical mechanical analysis, swelling and contact angle measurements, in order to study their morphology, pH-responsive character, hydrophilicity and viscoelastic properties by changing the monomer ratio composition of the copolymer from 5 to 50 wt% of MAA with respect to the total mass of monomers. PMMA-co-PMAA membranes were then tested for a potential application as protein filtration devices. Bovine serum albumin (BSA) was used as a model protein and permeation measurements were performed at three different pHs (4.5, 5.0 and 7.4). The PMMA–PMAA (90:10) membrane showed a good performance in terms of BSA amount filtrated, with distinct profiles at different pH, and consequently capable to assume an efficient role in protein filtration processes. 相似文献
27.
丝素蛋白纤维的接枝聚合Ⅴ.甲基丙烯酸甲酯(MMA)在丝绸表面的接枝聚合 总被引:1,自引:0,他引:1
本文研究了甲基丙烯酸甲酯(MMA)在丝绸织物表面的无引发接枝聚合反应和影响该聚合反应的各重要因素。研究结果表明,用不同浓度的碱处理过的丝绸具有不同的热性能且对接枝聚合反应有十分重要的影响,C_u~(2+)的加入对这种影响有很好的稳定作用.付里叶衰减全反射红外光谱研究结果表明,用碱处理过的丝绸,其表面结构呈不稳定状态,随着表面结构的变化,接枝聚合反应有不同的行为. 相似文献
28.
一种适用于水声信道盲均衡算法及仿真 总被引:6,自引:0,他引:6
对于高阶QAM信号,常数模算法的收敛误差不为零,而多模算法的收敛速度慢,提出了一种混合常数模算法,并将该算法应用于水声信道盲均衡。该算法根据均衡器输出信号模值与其判决模值之间的距离,设置一判决域。根据该判决域,算法的迭代过程在常数模和多模算法之间自动切换,且收敛后自动切换到多模算法。该算法收敛速度快,且均方误差小,特别适合高于高阶QAM信号的盲均衡,通过对水声信道均衡的计算机仿真,验证了该算法的优点及对多途干扰抑制的有效性。 相似文献
29.
一种改进的基于Web的移动代理的设计 总被引:1,自引:0,他引:1
移动代理系统的特点是移动性,自治性和智能性。在移动代理技术拥有完整性保护后,移动代理就可以免于被恶意的主机和其他代理攻击。传统的移动代理是由固定的代码段组成的,提出了一种改进的移动代理方法(MMA),这种方法可以在执行需求时动态添加新的代理代码模块,也可以删除冗余的代码模块。在基于Web的系统中这种方法比传统的静态方法更加灵活有效。 相似文献
30.
Mahadevaiah T. Demappa 《应用聚合物科学杂志》2007,103(6):3498-3505
The kinetics of polymerization of methylmethacrylate initiated by cerium(IV)–lactic acid redox system was studied in an aqueous medium in the temperature range of 25–50°C. The rate of polymerization (Rp) and the rate of cerium(IV) disappearance have been measured. The effects of some water‐miscible organic solvents, cationic, anionic, nonionic surfactants, and complexing agents on the rate of polymerization were investigated. The temperature dependence of the rate was studied, and the activation parameters were computed using the Arrhenius and Eyring plots. The effects of inorganic and organic solvents on polymerization were also investigated. All of them depressed both the initial rate and limiting conversion. A mechanism consistent with the experimental data, involving cerium(IV)–lactic acid complex formation, which generates free radicals, is suggested. The chain termination step of the polymerization reaction is by mutual interaction of the growing macromolecules. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 3498–3505, 2007 相似文献