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Porous polyimide (PI) films with low dielectric constants and excellent thermal properties have been a pressing demand for the next generation of high-performance, miniature, and ultrathin microelectronic devices. A series of novel porous PI films containing fluorenyl-adamantane groups were prepared successfully via thermolysis of poly(ethylene glycol) (PEG) added in the PI matrix. The cross-sectional morphologies of porous PI films showed closed pores with diameters ranging from 135 to 158 nm, which were uniform and regular in shape without interconnectivity. These porous PI films exhibited excellent thermal properties with a glass-transition temperature at 376 °C whereas the 5% weight loss temperature in air excess of 405 °C due to enhanced rigidity afforded by fluorenyl-adamantane groups. Accompanied by thermolysis content of PEG increasing from 0 to 20 wt %, the density of porous PI films decreased, and the corresponding porosity grew significantly from 0 to 11.48%. Depending on porosity, the dielectric constant and dielectric loss of porous PI films significantly declined from 2.89 to 2.37 and from 0.050 to 0.021, respectively. These excellent properties benefit the as-prepared porous PI films for application as interlayer dielectrics, integrated circuit chips, or multichip modules in microelectronic fields. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47313. 相似文献
3.
本文总结了近年冶金炉渣氮酸盐容量的研究方法,氮在炉渣中存在形态与炉渣氧分压的关系,炉渣氮化物容量与温度及炉渣成分的关系,并给出设计钢液脱氮渣系的基本原则。 相似文献
4.
4G mobile communications: toward open wireless architecture 总被引:2,自引:0,他引:2
5.
A wireless LAN service integration architecture based on current wireless LAN hot spots is proposed so that migration to a new service becomes easier and cost effective. The proposed architecture offers wireless LAN seamless roaming in wireless LAN/cellular mobile networks. In addition, a link-layer-assisted mobile IP handoff mechanism is introduced to improve the network/domain switching quality in terms of handoff delay and packet loss. An application layer end-to-end authentication and key negotiation scheme is proposed to overcome the open-air connection problem existing in wireless LAN deployment. The scheme provides a general solution for Internet applications running on a mobile station under various authentication scenarios and keeps the communications private to other wireless LAN users and foreign network. A functional demonstration of the scheme is given. The research results can contribute to rapid deployment of wireless LANs. 相似文献
6.
李学闵 《玻璃钢/复合材料》1995,(5):43-46
本文结合玻璃秽管道在工程应用中所出现的质量问题,论述了FRP新产品应面向大市场,强化应用技术研究,确保产品质量,使产品与科学技术密切结合,以加快FRP工业发展。 相似文献
7.
高精度合成地震记录制作技术研究 总被引:24,自引:0,他引:24
制作高精度的合成地震记录是精细储层描述的基础,本文在分析合成地震记录原理的基础上,从地震剖面的极性判断、平均速度的选取,反射系数的准确提取,子波的精确估算等方面对制作合成记录的要点进行了分析,通过提高以上四方面的精度,提高了制作合成地震记录的精度,并提出了一套可行的合成地震记录的检查方法。 相似文献
8.
Continuous reverse k nearest neighbors queries in Euclidean space and in spatial networks 总被引:2,自引:0,他引:2
Muhammad Aamir Cheema Wenjie Zhang Xuemin Lin Ying Zhang Xuefei Li 《The VLDB Journal The International Journal on Very Large Data Bases》2012,21(1):69-95
In this paper, we study the problem of continuous monitoring of reverse k nearest neighbors queries in Euclidean space as well as in spatial networks. Existing techniques are sensitive toward objects
and queries movement. For example, the results of a query are to be recomputed whenever the query changes its location. We
present a framework for continuous reverse k nearest neighbor (RkNN) queries by assigning each object and query with a safe region such that the expensive recomputation is not required as long as the query and objects remain in their respective safe regions.
This significantly improves the computation cost. As a byproduct, our framework also reduces the communication cost in client–server
architectures because an object does not report its location to the server unless it leaves its safe region or the server
sends a location update request. We also conduct a rigid cost analysis for our Euclidean space RkNN algorithm. We show that our techniques can also be applied to answer bichromatic RkNN queries in Euclidean space as well as in spatial networks. Furthermore, we show that our techniques can be extended for
the spatial networks that are represented by directed graphs. The extensive experiments demonstrate that our techniques outperform
the existing techniques by an order of magnitude in terms of computation cost and communication cost. 相似文献
9.
SimRank has become an important similarity measure to rank web documents based on a graph model on hyperlinks. The existing
approaches for conducting SimRank computation adopt an iteration paradigm. The most efficient deterministic technique yields
O(n3)O\left(n^3\right) worst-case time per iteration with the space requirement O(n2)O\left(n^2\right), where n is the number of nodes (web documents). In this paper, we propose novel optimization techniques such that each iteration
takes O (min{ n ·m , nr })O \left(\min \left\{ n \cdot m , n^r \right\}\right) time and O ( n + m )O \left( n + m \right) space, where m is the number of edges in a web-graph model and r ≤ log2 7. In addition, we extend the similarity transition matrix to prevent random surfers getting stuck, and devise a pruning
technique to eliminate impractical similarities for each iteration. Moreover, we also develop a reordering technique combined
with an over-relaxation method, not only speeding up the convergence rate of the existing techniques, but achieving I/O efficiency
as well. We conduct extensive experiments on both synthetic and real data sets to demonstrate the efficiency and effectiveness
of our iteration techniques. 相似文献
10.
计算得到低碳马氏体形成时使残余奥氏体富碳所需扩散的时间约为7×10~(-3)—3×10~(-4)s。与条状马氏体形成的时间——10~(-3)—10~(-6)s比较,可见碳的扩散跟得上或稍落后于马氏体条的形成。残余奥氏体均匀富碳的时间落后于马氏体条的形成至少达1个数量级。这些表明低碳马氏体形成时可能存在碳的扩散,但后者不是马氏体相变的主要或必需过程。若低碳马氏体按上贝氏体形式长大,则计算所得其长大速率仅3×10~(-4)cm/s,比现有实验数据至少低2个数量级。本文工作再次证明低碳马氏体的形成机制和上贝氏体的不同。 相似文献