Multi-objective layout optimization for an orbital propellant depot

Structural and Multidisciplinary Optimization - The overall layout optimization design of an orbital propellant depot involves the optimization of shape, size, and positions of propellant tanks in...     

MoSi2-based oxidation protective coatings for SiC-coated carbon/carbon composites prepared by supersonic plasma spraying

To protect carbon/carbon (C/C) composites against oxidation, MoSi₂-based oxidation protective coatings for SiC-coated carbon/carbon composites were prepared on them by supersonic plasma spraying. The MoSi₂-based coatings primarily consist of MoSi₂, Mo₅Si₃ and glassy SiO₂. Only a few pinholes and some microcracks are observed on the surface and no through-thickness cracks penetrate the cross-section. Weight loss of the MoSi₂-based coated specimens is only 1.14% after 400 h oxidation in air at 1773 K and the coated C/C composites remain intact after 11 thermal cycles between 1773 K and room temperature. The outstanding anti-oxidation ability is mainly attributable to the formation of SiO₂-based layer on the surface of MoSi₂-based coatings.     

Multilayer oxidation protective coating for C/C composites from room temperature to 1500 °C

To prevent carbon/carbon (C/C) composites from oxidation, a multilayer oxidation resistant coating was prepared. The inner SiC coating was prepared by pack cementation, and the outer SiC-MoSi₂ three-layer coating was obtained by slurry coating using silicon-sol as the caking agent. X-ray diffraction, scanning electron microscopy and energy dispersive X-ray spectroscopy were used to analyze the phase, microstructure and element distribution of the as-prepared coating. The results show that, the as-received multilayer coating has a crack-free structure with the thickness of about 300 μm. It is provided with excellent oxidation resistance from room temperature to 1500 °C in air and can protect C/C composites from oxidation for more than 120 h at 900 °C and more than 110 h at 1500 °C in air. The weight loss of the coated samples during oxidation tests mainly resulted from the oxidation of Mo₅Si₃ and the volatilization of SiO₂ in the coating.     

石蜡裂解制α-烯烃工艺技术研究

采用优质的54#半精炼石蜡,将乙烯裂解二次注汽技术融合在石蜡裂解技术中,避免了裂解炉结焦;考察了单程裂解、炉前甩残蜡循环裂解、炉后甩残蜡循环裂解在相同的工艺条件下的产品质量、产品收率及存在的问题;验证了新的炉后甩残蜡循环裂解是较好的工艺路线,在较高的水蜡比15%(质量分数),高温600℃、低烃分压和短停留时间(2s左右)条件下,能生产出高质量的α-烯烃产品(总烯烃质量分数在97%以上,α-烯烃含量为88%).     

石蜡裂解烯烃羰基合成高碳醇试验研究

以石蜡裂解烯烃为原料,羰基钴膦配合体为催化剂,通过高压釜式装置和5t/a羰基合成模式装置合成了高碳醇。与长链烷烃脱氢烯烃为原料制高碳醇的工艺比较,该工艺的烯烃转化率、烷烃收率、醇收率和物料平衡方面优于或相当于长链烷烃脱氢烯烃生产工艺,该工艺可以降低生产成本,提供了一条重要的新的高碳醇合成原料来源。     

多智能体系统在焊接柔性制造系统中的应用

焊接柔性制造系统 (WFMS)已经成为焊接自动化生产的一个重要的发展趋势。面对这样高度集成 ,高度复杂的自动化生产系统 ,采用单一的基于定量数学模型的传统控制理论和技术的控制系统已经不能对其实施有效的控制了。分布式人工智能 (DAI)领域中的多智能体系统 (MAS)的理论和技术已经应用于柔性制造系统。由于WFMS内在的分散性 (时间、空间和功能上的分散性 )以及它与MAS的内在联系和相似性 ,使得MAS成为WFMS的最佳控制策略之一。文章介绍了DAI中的MAS的概念和特点 ,讨论了MAS的网络结构及组织结构。针对WFMS的结构特点和焊接生产工艺特点 ,详细讨论了MAS系统和WFMS系统之间的内在联系以及MAS应用于WFMS的可行性。     

无机盐溶胶-凝胶法制备超细ZrB2-ZrC复合粉体

利用ZrO2-B2O3-C体系中碳热还原的基本原理,分别采用氧氯化锆、硼酸和酚醛树脂作为ZrO2,B2O3和C的来源,利用溶胶-凝胶法制备出超细ZrB2-ZrC复合粉体.采用热分析仪,X射线衍射和透射电镜对前驱粉体煅烧中的热力学过程,复合粉体的物相以及粒径和形貌进行了分析和表征.结果表明,ZrB2、ZrC相在1300°C开始生成,1500°C煅烧1h后碳热还原反应基本完成.复合粉体的平均粒径在200nm左右,比表面积达87m2g-1,加入1.0wt%的聚乙二醇作为分散剂时,粉体的团聚现象得到很大的改善.     

Full-Length cDNA Cloning,Molecular Characterization and Differential Expression Analysis of Lysophospholipase I from Ovis aries

Lysophospholipase I (LYPLA1) is an important protein with multiple functions. In this study, the full-length cDNA of the LYPLA1 gene from Ovis aries (OaLypla1) was cloned using primers and rapid amplification of cDNA ends (RACE) technology. The full-length OaLypla1 was 2457 bp with a 5′-untranslated region (UTR) of 24 bp, a 3′-UTR of 1740 bp with a poly (A) tail, and an open reading frame (ORF) of 693 bp encoding a protein of 230 amino acid residues with a predicted molecular weight of 24,625.78 Da. Phylogenetic analysis showed that the OaLypla1 protein shared a high amino acid identity with LYPLA1 of Bos taurus. The recombinant OaLypla1 protein was expressed and purified, and its phospholipase activity was identified. Monoclonal antibodies (mAb) against OaLypla1 that bound native OaLypla1 were generated. Real-time PCR analysis revealed that OaLypla1 was constitutively expressed in the liver, spleen, lung, kidney, and white blood cells of sheep, with the highest level in the kidney. Additionally, the mRNA levels of OaLypla1 in the buffy coats of sheep challenged with virulent or avirulent Brucella strains were down-regulated compared to untreated sheep. The results suggest that OaLypla1 may have an important physiological role in the host response to bacteria. The function of OaLypla1 in the host response to bacterial infection requires further study in the future.     

一种基于粗糙集的网络安全评估模型

准确掌握计算机网络系统的安全水平对于保障网络系统的正常运行具有重要意义.当前大多数网络安全评估系统缺乏对数据的深入分析,难以形成对网络安全状况的整体认识.本文提出了一种利用粗糙集理论挖掘网络安全评估规则,进而利用评估规则构建网络安全评估决策系统的算法模型.研究了网络安全评估问题的粗糙集描述,给出了模糊属性决策表的约简方法.利用一个简化的网络安全评估数据集,验证了本文提出的决策规则提取方法,结果表明该方法可以得到与实际情况相符的决策规则.     

网络攻击效果在线评估模型与算法研究

为了顺利实现预定的攻击目标，在线评估攻击效果并制定适当的攻击策略都是非常重要的。本文讨论了网络攻击效果与目标网络系统安全性之间的关系，提了一种基于网络安全性改变量的攻击效果定义方法；重点研究了网络攻击效果在线评估的评估模型和评估算法；提出了网络攻击效果的评价准则和评估指标体系；设计并给出了网络攻击效果在线评估系统的框架模型；详细讨论了网络攻击效果在线评估的评估算法、状态图生成算法、攻击效果预测算法和攻击方案决策算法。