超声颗粒监测中聚焦的必要性及相应参数的确定方法

分析了超声波颗粒监测中探头聚焦的必要性,并介绍了与聚焦探头有关的聚焦参数（Ｆｚ,Ｂｗ）的理论确定方法。     

高可靠、强实时分布式系统的切换技术研究

本文首先给出某高可靠、强实时分布式系统及系统的两种切换方案的简要描述，然后对切换技术的实现进行讨论；最后，在建立强实时双工系统的可靠性模型基础上，对系统的两种切换方案进行分析与比较。研究结果表明：对于本系统，机组级切换优于结点机级切换，且可以减少程序的复杂度，提高系统的可靠性与实时性。     

航天测控通信系统可靠性分析的Krylov子空间投影算法

基于Markov模型对航天测控通信系统进行可靠性分析的过程中,若系统中测控通信设备数量较多,模型中的状态空间随设备数量呈指数增长,将会导致数值计算困难.提出了一种基于Krylov子空间技术的可靠性分析方法,将大规模问题投影至小规模子空间中,求得问题的近似解.实验结果证明,Krylov子空间方法的计算速度及精度优于Ross方法和前向Euler法(forward Euler method,FEM).     

考虑弹体动态特性的机动效率约束导引律

针对考虑交会角和过载约束导引律在大机动时能量损失大的问题,提出一种考虑导弹机动效率的多约束制导律。应用最优二次型原理推导出考虑一阶弹体延迟的时变导引系数闭环次优制导形式,将导弹机动时刻阻力系数引入时变权系数,并通过迭代确定机动效率约束边界。将时变约束表示成剩余时间与弹体延迟时间的函数,代入制导指令,进行弹道仿真。结果表明,对于常值与机动目标,文中制导律与过载约束导引律同只考虑交会角约束的导引律相比,对目标均能实现末端弹道成型要求,而考虑机动效率的制导指令分配更为合理,在避免指令加速度饱和的同时有效降低了拦截末端速度损耗,提高制导精度与毁伤效果。且该制导律中时变权系数无须配平求解,在保证精度的同时极大地提高了迭代速度。     

基于旋量方法的高超声速飞行器三维非线性伪最优制导律设计

针对高超声速飞行器制导过程中的通道耦合问题,设计一种基于旋量方法的三维非线性伪最优制导律。引入角度矢量、视线旋量、视线旋量速度等概念,通过等价性证明,得出视线旋量、视线旋量速度控制分别与视线方位、视线角速度控制具有一致性的结论,从而将制导问题转化为视线旋量和旋量速度的控制问题;基于旋量方法构建弹目视线旋量、视线旋量速度模型,构建得到飞行器制导的三维非线性模型;为避免直接求解Riccati微分方程过程的复杂性,引入伪控制变量,将三维非线性制导模型转化为线性制导模型;分别针对无终端约束和有终端约束情况,基于二次型最优方法得到三维非线性伪最优制导律。该制导律避免了通道解耦,其制导参数又满足一定物理意义下的最优性。仿真结果验证了所设计制导律的有效性。     

雷达虚拟维修训练中交互系统的通用性

基于USB接口技术对"通用雷达装备虚拟维修训练系统(URVMTS)"的人机交互系统进行研究,通过合理的软、硬件设计实现了系统的通用性。不同的实装操作部件经过适当的信号调理均可以通过该系统方便地实现与雷达虚拟样机之间的交互。着重介绍了交互系统的通用性设计与实现方法,包括系统的通用性设计方案,USB硬件电路的通用性设计及相应的软件开发。     

后方油库整体生存概率分析计算

针对我军后方油库特点,探讨了油库整体生存概率计算的基本思路和方法,分析了各类分项目标生存概率的计算方法,采用层次分析对后方油库各分项目标权值进行了详细分析计算,可为后方油库伪装防护效能评估提供依据。     

Optimal policies for M/M/m queue with two different kinds of (N,T)‐policies

In this paper, two different kinds of (N, T)‐policies for an M/M/m queueing system are studied. The system operates only intermittently and is shut down when no customers are present any more. A fixed setup cost of K > 0 is incurred each time the system is reopened. Also, a holding cost of h > 0 per unit time is incurred for each customer present. The two (N, T)‐policies studied for this queueing system with cost structures are as follows: (1) The system is reactivated as soon as N customers are present or the waiting time of the leading customer reaches a predefined time T, and (2) the system is reactivated as soon as N customers are present or the time units after the end of the last busy period reaches a predefined time T. The equations satisfied by the optimal policy (N*, T*) for minimizing the long‐run average cost per unit time in both cases are obtained. Particularly, we obtain the explicit optimal joint policy (N*, T*) and optimal objective value for the case of a single server, the explicit optimal policy N* and optimal objective value for the case of multiple servers when only predefined customers number N is measured, and the explicit optimal policy T* and optimal objective value for the case of multiple servers when only predefined time units T is measured, respectively. These results partly extend (1) the classic N or T policy to a more practical (N, T)‐policy and (2) the conclusions obtained for single server system to a system consisting of m (m ≥ 1) servers. © 2000 John Wiley & Sons, Inc. Naval Research Logistics 47: 240–258, 2000     

Optimizing the defensive characteristics of mild steel via the electrodeposition of ZnSi3N4 reinforcing particles

The effect of ZnSi₃N₄ deposition prepared via direct electrolytic co-deposition on mild steel was studied as a result its inherent vulnerability to corrosion in an aggressive environment and failure on the application of load. The experiment was conducted varying the mass concentration of silicon nitride (Si₃N₄) between 7 and 13 g at cell voltage of 0.3 and 0.5 V, at constant temperature of 45 °C. The morphologies of the coated surfaces were characterized using high resolution Nikon Optical Microscope and Scanning Electron Microscope (SEM) revealing that the particles of the ZnSi₃N₄ were homogeneously dispersed. The corrosion behaviour was studied using potentiodynamic polarization technique in 3.65% NaCl solution and the microhardness was examined using Brinell hardness testing technique. The result of the corrosion experiment confirmed an improved corrosion resistance with a reduction in corrosion rate from 9.7425 mm/year to 0.10847 mm/year, maximum coating efficiency of 98.9%, maximum polarization resistance of 1555.3 Ω and a very low current density of 9.33 × 10⁻⁶ A/cm². The negative shift in the E_corr revealed the cathodic protective nature of the coating. The microhardness was also found to have increased from 137.9 HBN for the unmodified steel to a maximum value of 263.3 HBN for the 0.5Zn13Si₃N₄ coated steel representing 90.9% increment in hardness as a result of the matrix grain refining and dispersion-strengthening ability of the incorporated Si₃N₄ particles.     

基于子空间投影波束形成技术的导航接收机抗干扰算法研究

阵列天线空时自适应处理通过联合空域和时域的自适应滤波处理技术能够有效提高导航接收机的窄带和宽带干扰抑制性能。利用导航信号淹没在干扰信号和热噪声的特点，本文提出先将天线阵列接收的空时信号矢量向干扰子空间的正交子空间投影以实现干扰抑制，当接收机对投影后的参考阵元数据捕获成功后，利用捕获估计的本地扩频码相位作为参考信号依据最小均方误差准则进行波束形成。仿真结果表明该抗干扰算法在零陷强干扰的同时使主波束指向导航信号来波方向，有效提高了阵列输出信干噪比，并降低了空时自适应处理对导航信号伪码相关峰形状和载波跟踪性能的影响。