一种基于风险传播的信息系统风险评估方法

传统信息系统的风险评估方法未考虑节点的状态变化和风险的传播方向,且评估结果的准确性受专家主观性的影响,对此,提出了一种基于风险传播的信息系统风险评估方法.首先,确定节点的初始状态转移概率矩阵,并根据攻击属性对矩阵进行修正,得到节点状态转移概率;其次,基于系统风险传播网络拓扑图和节点属性值计算节点在各方向的传播概率;然后,利用三参数区间数方法获取节点威胁事件的量化值;最后,根据风险评估方法计算各节点的风险值.实验结果表明,基于风险传播方法的评估流程更客观、合理,可提高信息系统风险评估的整体性和准确性.     

Luminescence modulation of the Eu3+ doped Srn+1SnnO3n+1 (n=1, 2, 5, ∞) ceramics based on photochromism and its application in anti-counterfeiting technology

The structure and optical properties of Sr_n+1Sn_nO_3n+1 ceramics greatly depend on the n value. Thus, we fabricated four compositions, namely Sr_n+1Sn_nO_3n+1:Eu³⁺ (n = 1, 2, 5, ∞) ceramics, and their crystal structure, photoluminescence, photochromism and luminesce modulation properties have been investigated. It is found that excellent photochromism and luminesce modulation properties are found in Sr₂SnO₄:Eu³⁺ and Sr₃Sn₂O₇:Eu³⁺ ceramics. After 280-nm light irradiation, the Sr₂SnO₄:Eu³⁺ ceramics transform into gray purple from primal white. Meanwhile, luminescence intensity decrement ratio ΔI_dec of the colored Sr₂SnO₄:Eu³⁺ reaches a high value of 80.8% under optimized irradiation wavelength. The decreased luminescence intensity of Eu³⁺ can be completely recovered via 450-nm light irradiation. The ΔI_dec of Sr₃Sn₂O₇:Eu³⁺ ceramic reaches 53.1%, and the decreased luminesce intensity can not be covered by light irradiation, only can be covered by a high temperature stimulus at 400 °C. Finally, we successfully fabricated a flexible membrane using Sr₂SnO₄:Eu³⁺ and PDMS for anti-counterfeiting applications.     

激光选区熔化纳米SiC/AlSi7Mg复合材料微观组织及力学性能EI北大核心CSCD

采用机械混合法制备纳米SiC/AlSi7Mg混合粉末,利用激光选区熔化技术(selective laser melting,SLM)成形纳米SiC颗粒增强AlSi7Mg复合材料,观察和分析试样的相对密度、物相和微观组织,并测试材料的硬度和拉伸性能。结果表明:SLM成形纳米SiC/AlSi7Mg复合材料试样的相对密度随着扫描速度和扫描间距的增大均呈现先增加后减少的趋势,相对密度最高可达99.75%;试样微观组织与SLM成形铝合金相似,Si相呈网状结构均匀嵌入α-Al基体中,且在Al基体中存在与Si分布相似的纳米SiC团聚物及Mg_(2)Si相;与AlSi7Mg相比,复合材料微观组织由柱状晶转化为等轴晶,且晶粒明显细化(平均晶粒尺寸为1.36μm);由于SiC的加入,产生细晶强化和固溶强化,试样的硬度和强度均明显提高,硬度最高达到137.3HV,抗拉强度达到448.3 MPa,屈服强度达到334.7 MPa,但伸长率下降至3.9%,断裂模式主要为脆性断裂。     

新型细水雾添加剂成分对灭火性能影响研究

为研究自制细水雾添加剂中主要成分对灭火性能的影响,在开放空间,进行了不同工作压力、不同浓度、不同燃料条件下含添加剂细水雾的灭火研究,实验获取了灭火时间、火焰形态、火焰温度等灭火参数。通过对柴油和汽油两种不同燃料的灭火实验发现,使用含添加剂的细水雾对低沸点、高蒸发速率的汽油灭火效果同样较好。根据加入不同浓度的氟表面活性剂的实验结果比照发现,氟表面活性剂是自制添加剂中起到主要提升灭火性能作用的物质,它通过改变细水雾物理性质使加入自制添加剂的细水雾的灭火性能显著提高。对比调整自制添加剂各物质含量的实验数据,进一步确定添加剂各成分最佳灭火性能浓度。     

Advanced high-temperature resistant (RT-1000 °C) aluminum phosphate-based adhesive for titanium superalloys in extreme environments

To facilitate the repairing and connecting processes for titanium superalloys, an advanced high-temperature resistant adhesive that can be converted to a composite of intermetallics and ceramics was prepared by modifying aluminum phosphate-based adhesive with various additives. The composition evolution of the adhesive, the structure changes in the bonding layer, the reaction process at interfaces and the fracture mode of joints are comprehensively studied to explore the bonding mechanism. The results showed that the chemical bonding based on the formation of TiSi and Ti₅Si₄ started to work at 600 °C, and became the crucial bonding mechanism at higher temperatures. A diffusion reaction layer with size up to 6 μm effectively alleviated the difference of composition and performance between alloy substrate and adhesive. From RT to 900 °C, the coefficient of thermal expansion (CTE) of adhesive matched well with that of alloy substrates, and the difference of their CTE was always lower than 2 × 10⁻⁶ k⁻¹. The bonding strength reached ~16 MPa after pre-treatment at 900 °C without pressure, and remained over 13 MPa within the common operating temperature range (400–600 °C) of TC4 alloys. Without any pre-treatment, the adhesive could still provide above 5 MPa in range of RT-600 °C.     

Advanced high-temperature (RT-1100°C) resistant adhesion technique for joining dissimilar ZrO2 ceramic and TC4 superalloys based on an inorganic/organic hybrid adhesive

To meet the high demand for ceramic/superalloy composite structural components in various fields, an advanced high-temperature adhesion technique was firstly developed by preparing a novel inorganic/organic hybrid adhesive suitable for ZrO₂ and TC4. Chemical bonding started to work at ～600°C, and became the crucial bonding mechanism at elevated temperatures. The formation of ZrSiO₄ and Ti₅Si₃ at the interfaces of two substrates not only increased the interfacial connection strength, but also formed two gradient layers with a size of ～2 μm to effectively alleviate the difference of composition and performance between the adhesive and substrates. In the temperature range of 500–900°C, the matching degree of CTE among ZrO₂, adhesive and TC4 is higher, and the maximum difference does not exceed 3×10^-6 K^-1. Meanwhile, the formation of a composite structure containing various ceramics (ZrO₂, SiC and ZrB₂) and intermetallics (Ni–Si, Al–Ni), and the improvement of structural compactness of adhesive from 500 to 900°C greatly improved the bonding strength to the maximum value of 31.4 MPa at 900°C. Also, the adhesive pretreated at 900°C showed good thermal cycling resistance, and the strength was still higher than 15 MPa after 50 cycles. For cured adhesive, when used directly in an extreme environment, it can provide bonding strength not less than 5 MPa in the whole temperature range, indicating that the adhesive possessed potential emergency repair convenience. This work significantly broadened the application of high-temperature-resistant adhesion technology in the connection of dissimilar ceramics and alloys.     

基于平衡氧浓度的飞机燃油箱可燃性降低仿真研究

氧气从燃油中逸出，使燃油箱空余空间中氧气浓度上升，增加了燃油蒸气点燃爆炸的风险，使得飞机燃油箱处于不安全的状态，可使用降低可燃性的方法使燃油箱惰化。使用富氮气体（NEA）使飞机燃油箱空余空间氧体积分数降至14.5%以下，确保燃油箱中的氧气浓度不足以支持燃烧，使燃油箱处于惰化状态。采用NEA惰化的方式，建立油箱空余空间氧浓度模型，考虑氧气从燃油中析出，建立随高度变化的燃油箱可燃性降低（FRM）模型。仿真结果表明，燃油箱的可靠可燃性随着FRM模型的最小故障间隔时间（MTBF）的增加而减小，得出满足可靠可燃性的最小MTBF；确定MTBF，通过仿真，得出FRM模型满足性能可燃性所需的最小流量：下降阶段满足要求所需的最小高流量和其他飞行阶段满足要求所需的最小低流量。     

基于知识表示的森林灭火直升机机型配备研究

针对森林灭火中直升机机源不足的问题,通过分析直升机森林灭火作业因素和应具备的基本条件,利用产生式规则理论方法设计并表示森林灭火飞行直升机机型配备知识,建立基于图论路径问题的推理算法实现灭火机型的推理,提出了优化灭火方案并充分利用现有机型资源,通过实际案例分析,验证了方法的科学性和有效性,研究结果可为森林航空灭火指挥调度和机型配置提供参考和借鉴。     

Improved numerical integration method for flowrate of ultrasonic flowmeter based on Gauss quadrature for non-ideal flow fields

Multipath ultrasonic flowmeters with large diameter are widely used in industry. And their measurement performances are sensitive to velocity profiles in conduits. Gauss–Jacobi and Optimized Weighted Integration for Circular Sections (OWICS) method are commonly applied in flow measurement of multipath ultrasonic flowmeters, both of which assume ideal flow in pipes. They are not proper for non-ideal flow measurement. Therefore, an improved numerical integration method for flowrate based on Gauss quadrature is proposed. With this method, optimum relative path heights and corresponding weights are determined according to specific disturbed flows. By comparison Gauss–Jacobi, OWICS with the improved method, the validity of the proposed method is verified for typical disturbed flows based on both theoretical analysis and experiments, and measurement performances of ultrasonic flowmeters are improved significantly.