基于NB分类器重访概率预测的Web缓存替换策略

Web缓存是用来解决网络访问延迟和网络拥塞问题，缓存替换策略直接影响缓存的命中率。为此，提出一种朴素贝叶斯（NB）分类器重访概率预测的Web缓存替换策略；根据用户之前访问日志，通过分区操作提取多项特征来表示每次访问的对象，并构建特征数据集；训练NB分类器，用来确定缓存中对象被再次访问的概率，为对象分配权重；结合LRU策略来合理删除一些对象。仿真结果表明，提出的策略在保证较高命中率的同时有效降低了执行时间。     

适用于移动自组织网络的信息安全动态评估模型

在信息安全风险评估领域,针对传统静态评估手段难以适应移动自组织网络的动态拓扑结构的缺陷,提出了一种新的动态再评估模型。该模型将整个系统抽象为构件和访问路径组成的拓扑结构,将构件间的关系抽象为三类关联类型和四类组合类型,并给出不同关系条件下的安全度量方法。当系统发生变化后,以变化的构件为中心,确定其变化的影响范围和新的关系类型,只对相邻构件进行再评估,进而得到局部和全局的新安全度量。实验结果显示,所提出评估模型具有更高的评估效率,能大幅大减少评估成本。     

Soot deposition effects and microwave regeneration modelling of diesel particulate filtration system

Regeneration of accumulated soot particles in the substrate walls of the diesel particulate filtration system is one of the major challenges faced by the automotive industry. This study investigated the conversion efficiency and filtration behaviour of the after treatment system comprising of diesel oxidation catalysis (DOC) and diesel particulate filtration (DPF) system. The average conversion efficiency of hydrocarbons was close to 54% and filtration efficiency of the particle number emissions was around 92%. Characterization of the DOC and DPF substrate were conducted using microscopic imaging, Fourier transform infrared spectroscopy (FTIR) and particle size analysis (PSA). The results of FTIR study indicated the presence of carcinogenic agents trapped in the porous walls of the filter substrate. A model for microwave based regeneration system is proposed in this article and CFD analysis were conducted to determine the temperature and electric field distribution in the DPF substrate for a regeneration time of 180 s. Results of simulation showed that the microwave radiations raise the temperature close to soot oxidation temperature (873 K), ensuring effective regeneration.     

低压环境下航空电缆材料燃烧特性的研究

在高高原实验室(61 kPa、4 290 m)和广汉实验室(96 kPa、520 m),分别开展常低压条件下FXL型航空电缆的对比燃烧实验。通过热辐射加热箱、烟密度及成分测试仪和氧指数仪等设备,测量点燃时间、烟密度、质量损失速率和CO、CO2及O2等浓度变化。实验结果表明:在96 kPa和61 kPa两种实验环境下,低压下最小点燃时间及温度的数值更大,两者的温度和时间差分别为15℃和4.8 s;烟密度曲线快速升高后趋于平衡,61 kPa条件下的发烟量小于96 kPa;O2体积浓度随着加热时间先下降后升高,而CO2的变化趋势相反。在61 kPa条件下,CO曲线会出现双峰现象且更明显;随着氧浓度增加,质量损失速率加快且呈线性关系;压力因素对燃烧影响减弱且燃烧持续时间差值变小。研究结果揭示了低压环境对航空电缆的燃烧影响,为增强航空安全提供参考。     

机身/发动机数控组件测试系统的研制

针对国内尚未拥有机身/发动机数控组件维修、测试能力的现状,并结合该组件当前故障率,提出一种基于虚拟仪器技术的维修测试平台。该平台以GPIB仪器、VXI模块为依托完成硬件设计,利用labview驱动模块实现对各类测试仪器的控制,并进一步完成软件设计。针对此平台进行误差分析的结果表明：该系统测试精度较高,参数误差均在性能指标范围内,能够满足机身/发动机数控组件的维修测试需求。     

轮轨材料/硬度匹配研究进展与展望

车轮与钢轨硬度是影响轮轨磨损的主要因素之一,合理的轮轨材料与硬度匹配对于减轻轮轨磨损、延长服役寿命具有十分关键的作用。当前我国铁路运营过程中存在2种硬度钢轨匹配4种硬度车轮的现象,材料匹配行为复杂。针对铁路轮轨材料和硬度的选用与匹配,至今尚无统一合理的规定与标准。从轮轨材料硬度出发,首先分析了国内外轮轨材料发展与硬度匹配的使用现状,发现不同国家和地区轮轨材料硬度的选用存在较大差异。具体表现为:日本新干线使用的车轮硬度远高于钢轨(H_R/H_W<1),欧洲高速铁路上H_R/H_W值接近1,而中国高速铁路系统中,轮轨种类多,硬度区间大。其次,总结了轮轨硬度匹配研究进展,明确材料硬度和轨轮硬度比(H_R/H_W)对磨损与滚动接触疲劳损伤都具有显著影响,但并没有形成统一的结论,且以往的材料选用经验并不完全适用于当前的铁路系统。然后,针对现阶段轮轨材料与硬度匹配研究,探讨了材料加工硬化、合金钢微观组织、表面热处理工艺、复杂服役环境与车轮运行参数等因素的潜在影响。最后,提出...     

Ablation behavior of inorganic particle-filled polybenzoxazine composite coating irradiated by high-intensity continuous laser

Further utilization of aircraft structural materials is threatened by the fact that high-intensity continuous lasers are widely used in the field of military defense. To protect the aircraft structure from laser damage, ammonium polyphosphate filled polybenzoxazine composite coatings were prepared on the substrate. The anti-laser ablation characteristics of the coatings were investigated. Results showed that the addition of the inorganic filler improved the anti-laser ablation performance of polybenzoxazine. The back-surface temperature of substrates covered with the composite coatings was more 50% lower than that in the case of a pure polybenzoxazine coating after laser ablation. Further, the residue of the composite coating could be vertically divided into three distinct regions, with the dense surface char layer and the porous pyrolysis layer acting as shielding layers for the laser beam and preventing any heat-related transformations from occurring. The addition of the inorganic particles improved the surface reflectivity of the coatings resulting in much more laser energy dissipation. The decreased pyrolysis rate ensured that the pneumatic cooling effect of pyrolysis gas was more lasting and stable, owing to which the composite coatings could act as effective thermal protection layer for longer. These results confirmed that the inorganic filler modified polybenzoxazine coating exhibits excellent anti-laser properties and are suitable for protecting structural materials from laser-related damage.     

Comparative susceptibility of Corcyra cephalonica (Lepidoptera: Pyralidae) eggs to carbon dioxide and nitrogen at different temperatures

The aim of this study was to evaluate the susceptibility of the egg stage of the rice moth Corcyra cephalonica to modified atmospheres (MAs) enriched with CO₂ or N₂ at 25, 30 and 35 °C combined with various exposure times. The tested modified atmospheres containing CO₂ were 20% CO₂, 16% O₂ and 64% N₂; 40% CO₂, 12% O₂ and 48% N_2; 60% CO₂, 8% O₂ and 32% N₂ and 80% CO₂, 4% O₂ and 16% N₂. The tested modified atmospheres containing N₂ were 97% N₂ and 3% O₂ and 98% N₂ and 2% O₂. The results showed that the hatchability responding to modified atmospheres enriched with either CO₂ or N₂ decreased significantly with an increase in exposure time, gas content (%) and temperature. All tested combinations provided complete (100%) egg control in less than 4 days. Based on 100% mortality, shorter exposures were obtained with 80% CO₂ than with N₂ at most tested temperatures. The modified atmospheres enriched with 98% N₂ were more effective than 97% N₂ against C. cephalonica eggs, especially at 35 °C. It is recommended to use high levels of CO₂ in air (80%) and N₂ (98%) in controlling 0–24-h-eggs of C. cephalonica within 24–36 h for CO₂ and 18–72 h for N₂.     

基于K-L距离的改进D-S证据合成方法

提出了一种证据距离为基础的冲突证据合成方法.通过改进的K-L距离得到证据间间距,进一步通过相关算法转化为证据权值,权值反映了证据的重要程度,以权值为系数对原始的基本可信度分配函数进行重新分配,再通过改进的合成公式,得到证据合成结果.最后通过具体的算例比较,说明新方法的合成结果更确定,更符合实际情况.     

一种使用离散时间尺度变换技术的合成宽带雷达成像系统

基于离散时间尺度变换技术,提出了一种新的适用于合成宽带信号的机载雷达成像系统。为了消除多普勒散布效应,该系统使用了尺度变换矩阵,将同一目标在不同子带上的多普勒频率变换到一个已知的频率上,以便每一个子带可使用相同的传统多普勒滤波器组形式去获得无失真的合成距离像。同时,利用FFT及CZT算法,进一步推导出尺度变换矩阵的一种快速实现算法。实验仿真结果验证了所提方法的有效性。