双模容错计算机的设计与实现

高可靠性的计算机应用环境需要计算机具备容错功能,并要求采用高等级的处理器芯片。该文以高等级的Power PC处理器PC8245为基础,以FPGA为核心,设计双模容错的计算机。由于应用空间限制,该计算机采用了分布式冗余仲裁结构,仲裁逻辑同时运行在主计算机和备份计算机的FPGA中。分析了分布式冗余仲裁算法的有限状态机,论述了通信接口的冗余控制机制。     

Fabrication and characterization of 3-D Cf/ZrC composites by low-temperature liquid metal infiltration

Three-dimensional braided carbon fiber-reinforced ZrC matrix composite, 3-D C_f/ZrC, were prepared by liquid metal infiltration process at 1200 °C using a Zr₂Cu intermetallic compound as infiltrator. The microstructure and properties of the composites were investigated. The results indicated that ZrC with a yield of 35.2 ± 1.8 vol.% was certified as the major phase of the composites. The formation of ZrC was controlled by a solution-precipitation mechanism. The obtained composites exhibited good mechanical properties, with a flexural strength of 293.0 ± 12.1 MPa, a flexural modulus of 82.7 ± 6.4 GPa and a fracture toughness of 9.8 ± 0.9 MPa m^1/2. The mass and linear ablation rates of the composites exposed to oxyacetylene torch were 0.0013 ± 0.0005 g s⁻¹ and −0.0009 ± 0.0003 mm s⁻¹, respectively. The formation of a dense ZrO₂ protective layer and the evaporation of residual Cu contributed mainly to the excellent ablation resistance.     

含能材料的损伤本构模型研究进展

主要从宏观力学现象和微观统计力学两个角度介绍了国内外含能材料损伤力学模型的发展现状。通过比较各模型的描述观点和应用范围,认为需要建立多尺度分析模型,系统研究各种形式加载条件下含能材料的损伤演化规律及关联性,才能建立更合理的本构模型描述含能材料的力学行为。     

A novel starch-enhanced melamine-formaldehyde aerogel with low volume shrinkage and high toughness

A new hybrid aerogel with low volume shrinkage and high toughness was prepared by aqueous condensation of melamine, starch and formaldehyde and extracting the solvent from the wet gel with carbon dioxide under the supercritical condition. The sizes of the wet gel and aerogel were measured by vernier calipers and the volume shrinkage of the aerogel was as low as 1.8%. The results from BET and SEM indicated that the hybrid aerogel belonged to the mesoporous material, which showed a typical three-dimensional porous structure with a specific surface area about 366.2 m²/g and pore diameter about 12.9 nm. To study the mechanical properties of the hybrid aerogel, we measured the compressive stress as a function of strain and the hybrid aerogel demonstrated excellent elasticity and mechanical durability.     

一种新的DDoS攻击预警方法

DDoS攻击的研究是网络安全研究领域的一个研究热点。预测DDoS攻击发生的概率,对于早期防御和响应DDoS攻击具有重要意义。提出了一种基于概率有限状态自动机的DDoS攻击预警模型,给出了一种计算攻击成功概率和攻击期望威胁度的方法。实验表明,方法能有效地计算出DDoS攻击成功概率和期望威胁度,实现早期防御。     

Effect of interfacial residual thermal stress on the fracture behavior of Cf/B4C composites prepared by spark plasma sintering

Carbon fiber reinforced boron carbide (Cf/B₄C) composites were fabricated with different Cfs contents by spark plasma sintering (SPS). The interfacial residual thermal stress (RTS) distribution in the Cf/B₄C composites and its effects on the fracture behavior of the composites was investigated based on Raman spectroscopy and finite-element (FE) calculation. The results show that the maximum RTS of Cf in as-produced composites were obtained at the edge of fibers. The B₄C matrix among fibers suffered a high compressive and tensile RTS simultaneously in radial and tangential directions, which caused the formation of micro-cracks and became the origin of fracture failure of the Cf/B₄C composites. The maximum relative density 98.7% and bending strength of 391.41 MPa were obtained when the Cf content was 2.5% while the maximum fracture toughness of 5.46 MPa·m^1/2 at 5% Cf content of Cf/B₄C sample. The sharp decreases of bending strength when increasing content of Cf cloth was mainly caused by high RTS in the composites.     

喷墨打印中的银导电墨水综述

介绍了应用在电子喷墨打印技术中的两枑导电银墨水：纳米颗粒墨水和金属有机先驱体墨水的组成体系、制备方法和性能影响因素;结合国外悁究前沿简要介绍了当前两枑墨水的悁究现状和发展方向。最后对两枑墨水的综合性能进行了对比,并指出了导电墨水未来的挑战。