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1.
基于机械零件的增材制造设计,用仿自然式方法设计了一种金刚石晶格结构,对晶胞相对密度和等效弹性模量建立了数学模型,并拟合得到二者关系式,一系列的仿真验证结果显示理论研究所得关系式具有一定的正确性;对金刚石晶格填充结构提出变密度假设,并用仿真和压缩试验的方法进行了验证,结果显示,填充单元密度以受力点为中心渐渐减小的变密度结构拥有更好的抗压性能,同时验证了本文得出的等效弹性模量数学模型具有一定的正确性和适用性.本研究结果可应用于承压机械零件的实体夹层填充,对机械零件进行应力匹配变密度设计,以达到机械结构轻量化的目标. 相似文献
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Chuncheng Wei Zhen Liu Yun Wu Yeqing Liu Heng Zhang Peng Wang Qiyan Sun Lijuan Zhou 《Ceramics International》2021,47(13):18693-18698
Laminated Si3N4/SiCw ceramics were successfully prepared by tape casting and hot-pressing. Its mechanical properties were measured and the impact resistance was discussed. The toughness of the laminated Si3N4/SiCw ceramics was 13.5 MPa m1/2, which was almost 1.6 times that of Si3N4/SiCw composite ceramics, namely 8.5 MPa m1/2. Moreover, the indentation strength of laminated Si3N4/SiCw ceramics was not sensitive to increasing indentation loads and exhibited a rising R-curve behaviour, indicating that the laminated Si3N4/SiCw ceramics had excellent impact resistance. The improved toughness and impact resistance of laminated Si3N4/SiCw ceramics was attributed to the residual stress caused by a thermal expansion coefficient mismatch between the different layers, resulting in crack deflection and bridging of SiC whiskers in the interface layer, thus consuming a large amount of fracture work. 相似文献
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人体所必需的营养素除了蛋白质、脂类、糖类等能量物质外,维生素也是不可或缺的营养物质,是评价其营养质量的关键指标。检测食品中的维生素含量,是有效保证其质量与安全的必要条件。因此,对现有国家标准食品中维生素的检测方法进行综述,总结各方法的前处理及检出限等,为增强检测工作效率,以及食品检测方法的研究和发展提供参考。 相似文献
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Yujie Chen Yiping Song Zhen Zhang Yali Chen Qiliang Deng Shuo Wang 《Advanced functional materials》2021,31(41):2104885
Various products, including foods and pharmaceuticals, are sensitive to temperature fluctuations. Thus, temperature monitoring during production, transportation, and storage is critical. Facile indicators are required to monitor temperature conditions via color changes in real time. This study aimed to prepare and apply thiol-functionalized covalent organic frameworks (COFs) as a novel indicator for monitoring thermal history and temperature abuse. The COFs underwent obvious color changes from bright yellow to purple after exposure to different temperatures for varying durations. The reaction kinetics are analyzed under isothermal conditions, which reveal that the order of reaction rates is k−20°C < k4°C < k20°C < k35°C < k55°C. The activation energy (Ea) of the COFs is calculated using the Arrhenius equation as 50.71 kJ moL−1. The COFs are capable of sensitive color changes and offer a broad temperature tracking range, thereby demonstrating their application potential for the monitoring of temperature and time exposure history during production, transportation, and storage. This excellent performance thermal history indicator also shows promise for expanding the application field of COFs. 相似文献
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使用碳纤维复合材料设计某乘用车悬架控制臂,对4个区域的铺层结构进行优化设计.首先以各角度铺层厚度为设计变量对控制臂模态频率、质量和各工况应变能进行优化;然后以前三阶模态频率为目标,弯曲刚度参数作为设计变量优化铺层顺序.针对设计变量间存在的工艺约束条件使样本空间不规则且优化变量较多的问题,利用聚类分析进行试验设计确定训练近似模型需要的样本点,并用高斯过程回归方法建立近似模型以减少计算时间,验证模型R2在0.9以上.两步优化后,对比复合材料初始铺层各性能指标均有不同程度改善,复合材料质量减少11.4%;对比原钢制控制臂,各性能均满足要求,质量降低37.1%. 相似文献
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殷华英 《承德石油高等专科学校学报》2021,23(1):37-40
无线开关是智能家居环境中重要的一个组成部件,通过它,用户可以实现远程对电器的控制和管理.针对开发的一款无线电源开关,根据其工作原理,设计出对应的一套指令系统,并在AP和STA两种模式下对该指令系统进行了测试,验证了本指令系统的正确性和合理性. 相似文献
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Katja F. Hellendahl Felix Kaspar Dr. Xinrui Zhou Zhaoyi Yang Prof. Dr. Zhen Huang Prof. Dr. Peter Neubauer Dr. Anke Kurreck 《Chembiochem : a European journal of chemical biology》2021,22(11):2002-2009
Selenium-modified nucleosides are powerful tools to study the structure and function of nucleic acids and their protein interactions. The widespread application of 2-selenopyrimidine nucleosides is currently limited by low yields in established synthetic routes. Herein, we describe the optimization of the synthesis of 2-Se-uridine and 2-Se-thymidine derivatives by thermostable nucleoside phosphorylases in transglycosylation reactions using natural uridine or thymidine as sugar donors. Reactions were performed at 60 or 80 °C and at pH 9 under hypoxic conditions to improve the solubility and stability of the 2-Se-nucleobases in aqueous media. To optimize the conversion, the reaction equilibria in analytical transglycosylation reactions were studied. The equilibrium constants of phosphorolysis of the 2-Se-pyrimidines were between 5 and 10, and therefore differ by an order of magnitude from the equilibrium constants of any other known case. Hence, the thermodynamic properties of the target nucleosides are inherently unfavorable, and this complicates their synthesis significantly. A tenfold excess of sugar donor was needed to achieve 40−48 % conversion to the target nucleoside. Scale-up of the optimized conditions provided four Se-containing nucleosides in 6–40 % isolated yield, which compares favorably to established chemical routes. 相似文献