基于多级单向哈希链的网格代理证书管理

代理证书是网格安全基础设施(GSI)中关键机制之一,用户需要通过代理证书访问网格服务,但目前的GSI方案中缺乏有效的代理证书管理机制。针对代理证书的生命周期控制不灵活、证书容易受到攻击等问题,该文提出一种基于多级单向哈希链的网格代理证书管理方案。多级单向哈希链由2层或2层以上哈希链构成,每个代理证书都由一个哈希值保护,其有效时间能够得到自适应控制,增强了网格代理证书管理的安全性和任务成功率。实验表明网格环境下该方案计算和通信开销较小。     

基于强化学习的频控阵-多输入多输出雷达发射功率分配方法

当前电磁环境日益复杂多变,新式干扰手段层出不穷,对雷达系统带来了极大的挑战和威胁。该文引入频谱干扰模型并提出了一种在频控阵-多输入多输出(FDA-MIMO)雷达与干扰机动态博弈框架下基于强化学习(RL)的发射功率分配优化方法,使雷达系统能够获得最大的信干噪比(SINR)。在此基础上,构造了频谱干扰模型。其次,雷达和干扰机之间存在一种Stackelberg博弈关系,且将雷达作为领导者,干扰机作为跟随者,建立动态博弈框架下的发射功率分配优化模型。采用深度确定性策略梯度(DDPG)算法,结合功率约束设计了奖赏函数,对雷达发射功率进行实时分配来获得最大的输出SINR。最后,仿真结果表明,在雷达与干扰机博弈的框架下,所提优化算法能够有效地对雷达发射功率进行优化,使雷达具备较好的抗干扰性能。     

一维河流水团示踪试验数据的模糊线性回归

将模糊线性回归的概念引入分析河流水团示踪试验数据、确定河流水质参数的计算过程中,建立计算河流水质参数的模糊线性回归模型,利用该模型能计算出不同置信水平下水质参数的取值范围。算例验证结果表明,应用模糊线性回归模型可以有效地确定河流的水质参数,且计算过程具有一定的稳定性、可靠性和灵活性,模糊线性回归模型是分析河流水团示踪试验数据、确定河流水质参数的一种有效的途径。     

基于卫星观测线距离的导弹主动段状态估计

分析了双星观测视线与弹道导弹主动段实际位置的关系,针对传统弹道导弹主动段状态估计算法中卫星观测角度值解耦难题,提出了基于导弹位置估计点与卫星观测视线距离的双星观测弹道导弹主动段状态最优估计方法,将红外卫星的观测角度二维信息融合为一维距离信息,避免了方位角及俯仰角耦合问题对最优估计算法的影响,保证能够得到高精度的状态估计,最后通过仿真实验验证了算法的有效性及准确性.     

基于证据空间有效性指标的聚类选择性集成

首先针对距离空间在描述数据复杂结构信息方面的不足给出证据空间的概念。然后基于证据空间扩展有效性指标Davies-Bouldin,同时利用聚类成员的类别相关矩阵度量差异性。最后以较高有效性和较大差异性为目标选择聚类成员并用于集成。实验结果显示所提方法能够有效提高聚类集成算法的有效性。     

基于MSC．Nastran的红外整流罩组件结构分析

基于有限元前后处理软件MSC．Patran及分析软件MSC．Nastran对红外整流罩组件进行了有限元分析,分析了大过载与气动加热情况下的组件应力分布,建立了详细的有限元模型,给出了有限元分析结果,验证了设计方案的可行性,并为改进设计提供了依据。     

Structure,dielectric properties of novel Ba(Zr,Ti)O3 based ceramics for energy storage application

(1-x) Ba(Zr_0.2Ti_0.8)O₃-x Na_0.5Bi_0.5TiO₃ (x = 0, 10, 20 30, 40, 50 mol%) (BZTN) ceramics are prepared by the traditional solid phase method. All BZTN ceramics exhibit a pseudo-cubic BZT based perovskite structure. Both the average grain size and the relaxor ferroelectricity of BZTN ceramics gradually increase with increasing NBT content. The W_rec of 3.22 J/cm³ and η of 91.2% is obtained for the BZTN40 ceramic at 241 kV/cm. BZTN40 ceramic also exhibits good temperature stability from room temperature to 150 °C and frequency stability from 1 Hz to 100 Hz. A P_D of 0.621 J/cm³ and a t_0.9 of 82 ns is obtained for the BZTN40 ceramic at 120 kV/cm. BZTN ceramics show application potential in energy storage and pulse power capacitors.     

High performance lead-free Na0.5K0.5NbO3 piezoelectric ceramics obtained via oscillatory hot-pressing

Lead-free Na_0.5K_0.5NbO₃ (KNN) piezoelectric ceramics is regarded as a potential candidate for PZT material, while high performance is difficult to be obtained due to its poor sinterability and non-stoichiometric component. In this work, oscillatory pressure-assisted hot pressing (OPAHP) is utilized to fabricate KNN ceramics with high density. The KNN ceramics sintered at 860 °C exhibits superior performance with piezoelectric parameter (d₃₃) of 142 pC/N, electromechanical coupling factors (k_p) of 0.41, and relative permittivity (ε^T₃₃/ε₀) of 472–620. Additionally, hardness and flexural strength are measured as 3.55 GPa and 99.13 MPa, respectively. This work indicates that OPAHP technique is effective for fabricating KNN piezoelectric ceramics with high performance.     

Structure-design strategy of 0–3 type (Bi0.32Sr0.42Na0.20)TiO3/MgO composite to boost energy storage density,efficiency and charge-discharge performance

A novel 0–3 type (Bi_0.32Sr_0.42Na_0.20)TiO₃/MgO composite is investigated in this work, which possesses a high stored energy storage density w_s˜2.50 J/cm³, recoverable energy storage density W_R˜2.09 J/cm³ with high efficiency η˜84% under low electric field (20 kV/mm). The excellent performance is owning to the increase of breakdown strength (BDS) value and the intrinsic mechanism for enhanced BDS value by MgO incorporation is disclosed by numerical simulations (COMSOL). Moreover, the studied composite exhibits excellent charge-discharge performance, the current density (C_D) and power density (P_D) are 1671 A/cm² and 150 MW/cm³, respectively, which are much superior to that of other ceramics. Besides, most of the stored energy is discharged within ˜0.15 μs via charge-discharge tests. This work not only provides a novel technique to designing bismuth-based ceramic capacitors with simultaneously high W_d, η and excellent charge-discharge performance, but also deepens the understandings of the role for the metallic oxide in the composite.     

Intergrowth Bismuth Layer-Structured Na0.5Bi2.5Nb2O9–Bi4Ti3O12 High Temperature Ferroelectrics Ceramics

Intergrowth superlattice structural Na_0.5Bi_2.5Nb₂O₉–Bi₄Ti₃O₁₂ (NBN–BIT) ceramics were synthesized by solid-state reaction method. In the temperature dependence of dielectric permittivity, two anomalies appeared at 663 and 780 °C, respectively. The dielectric loss tan δ of the NBN–BIT ceramics was very low, especially from room temperature to 400 °C. The ferroelectric hysteresis loop measurement revealed P _r and E _c of NBN–BIT ceramics are 10.5 μC/cm² and 18.5 kV/cm, the P _r nearly as twice as that of the NBN ceramics. The results show that ferroelectric properties of NBN–BIT ceramics increase comparing with pure NBN, and NBN–BIT ceramics are promising candidate materials for high temperature applications.