Synthesis and characterization of a positive‐working,aqueous‐base‐developable photosensitive polyimide precursor

A positive‐working, aqueous‐base‐developable photosensitive polyimide precursor based on poly(amic ester)‐bearing phenolic hydroxyl groups and a diazonaphthoquinone photosensitive compound was developed. The poly(amic ester) was prepared from a direct polymerization of 2,2′‐bis‐(3‐amino‐4‐hydroxyphenyl)hexafluoropropane and bis(n‐butyl)ester of pyromellitic acid in the presence of phenylphosphonic dichloride as an activator. Subsequently, the thermal imidization of the poly(amic ester) precursor at 300°C produced the corresponding polyimide. The inherent viscosity of the precursor polymer was 0.23 dL/g. The cyclized polyimide showed a glass‐transition temperature at 356°C and a 5% weight loss at 474°C in nitrogen. The structures of the precursor polymer and the fully cyclized polymer were characterized by Fourier transform infrared spectroscopy and ¹H‐NMR. The photosensitive polyimide precursor containing 25 wt % diazonaphthoquinone photoactive compound showed a sensitivity of 150 mJ/cm² and a contrast of 1.65 in a 3 μm film with 1.25 wt % tetramethylammonium hydroxide developer. A pattern with a resolution of 10 μm was obtained from this composition. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 86: 352–358, 2002     

The effects of intercepted solar radiation on sunflower (<Emphasis Type="Italic">Helianthus annuus</Emphasis> L.) seed composition from different head positions

The effect of intercepted solar radiation during fruit filling on seed weight and oil content from seeds of three sectors of the head in two sunflower (Helianthus annuus L.) hybrids of low and high potential oil percentage was investigated. Seed weight in each sector depended on both the level of radiation intercepted (modified by shading and thinning plants) and the genotype grown. A higher level of intercepted solar radiation increased seed weight in each sector. Central seeds of shaded plants showed the lowest weight. The seed and kernel oil content hierarchy among the three sectors was modified only in the hybrid with high potential oil content. For each head sector, variations in seed oil content associated with changes in the level of intercepted radiation could be accounted for by changes in the kernel oil content, not in the kernel/seed ratio. Significant relationships were found between seed oil and kernel oil contents when analyses between treatments (R>0.86) and sectors (R>0.92) were carried out. These relationships together with the growing conditions of plants during seed filling, the genotype, and the seed position on the head are essential factors that should be taken into account when selecting seeds in sunflower breeding programs since they affect the commercial/industrial quality of seeds.     

移动代理同态加密主动保护技术研究

针对移动代理(MA)在异质网络环境中的安全问题,提出了一种同态加密主动保护策略。加密后的移动代理可在其它网络平台上运行而无需解密,MA及产生的结果数据最终由MA生成者解密,从而减少了中间环节的加、解密时间。该方案采用加乘同态加密三地址码操作数,组合函数加密三地址码操作码的保护策略,同时验证了加密、解密算法的正确性及安全性。实验结果表明,对比数据迷乱方法,该方案节省执行时间近1/3,并能及时侦测恶意主机。     

美国的欧洲分阶段适应性导弹防御方案发展浅析

欧洲分阶段适应性导弹防御方案是美国全球导弹防御系统的重要组成部分。介绍了美国在欧洲部署分阶段适应性导弹防御系统的建立背景,概括了其新进展,阐述了其发展面临的国际、国内和技术3方面的制约因素,最后对其发展前景作了评析。     

Mixtures of poly(vinyl chloride) and copolyesters based on ε‐caprolactone and L‐lactide: Miscibility,thermal stability,and weathering resistance

Properties of the blends of Poly(vinyl chloride) (PVC) and poly(ε‐caprolactone) (PCLO) and copolyesters based on ε‐caprolactone and L‐lactide (LLA) prepared by rolling were studied. Incorporating the LLA units into the structure of PCLO the content of the crystalline phase was controlled. Miscibility of the blends was assessed using DMA, and basic mechanical properties were correlated with the type and content of the polymer plasticizer. The PVC blends containing up to 20 wt parts polyesters were miscible. The presence of the LLA units in the copolyester influenced negatively the thermal stability. On the other hand even small content of copolyester in the blend enhanced the resistivity against aging. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

The effect of nano-structured alumina coating on the bond strength of resin-modified glass ionomer cements to zirconia ceramics

The purpose of this study was to evaluate the effect of Y-TZP ceramic surface functionalization with a nano-structured alumina coating on bond strength of the resin modified glass ionomer dental cement. A total of 160 disc-shaped specimens were produced and randomly divided into two groups of 80. Half of the discs in each group received an alumina coating which was fabricated by exploiting the hydrolysis of aluminum nitride (AlN) powder. The shear bond strengths of the resin-modified glass ionomer cement FUJI+ (GC Japan) and the composite resin luting agent RelyX Unicem (3M ESPE, USA) were then studied for the coated and uncoated surfaces The SEM analyses revealed that the application of an alumina coating to the Y-TZP ceramics created a highly retentive surface for bonding. The bond strengths for the coated groups in both cements were significantly higher than the uncoated groups.     

Aspen Plus在氨合成流程模拟中的应用

Aspen Plus软件是应用最多的化工流程模拟软件之一,在化工设计过程中占有重要地位。应用此软件对某化工厂氨合成工艺进行模拟计算,选择合适的物性方法,通过调整撕裂物流使计算收敛。最后将Aspen Plus软件模拟结果与实际运行结果进行对比,结果基本一致,说明Aspen Plus软件在该模拟计算中得到了精确可靠的结果。     

船体材料腐蚀与防护措施的研究进展

对船体材料在海洋环境中受到的主要腐蚀类型及其腐蚀机理进行了综述,重点包括化学腐蚀、电化学腐蚀、空泡腐蚀及海洋生物腐蚀等方面。然后,通过对腐蚀机理及耐蚀环境的分析,分别从耐蚀材料的选择、表面改性技术的应用、涂层保护材料的发展、阴极保护及防污涂料的应用等影响方面,综合阐述了目前我国船体材料防护措施的发展方向及未来重点研究的领域。