Reliability of linear multistate multiple sliding window systems

This paper proposes a new model that generalizes the linear consecutive k‐out‐of‐r‐from‐n:F system to multistate case with multiple failure criteria. In this model (named linear multistate multiple sliding window system) the system consists of n linearly ordered multistate elements (MEs). Each ME can have different states: from complete failure up to perfect functioning. A performance rate is associated with each state. Several functions are defined for a set of integer numbers ρ in such a way that for each r ∈ ρ corresponding function f_r produces negative values if the combination of performance rates of r consecutive MEs corresponds to the unacceptable state of the system. The system fails if at least one of functions f_r for any r consecutive MEs for r ∈ ρ produces a negative value. An algorithm for system reliability evaluation is suggested which is based on an extended universal moment generating function. Examples of system reliability evaluation are presented. © 2005 Wiley Periodicals, Inc. Naval Research Logistics, 2005.     

System reliability based on diffusion models for fatigue crack growth

Diffusion processes are commonly used to describe the dynamics of complex systems arising in a wide range of application fields. In this paper we propose, on the basis of diffusion processes, two models concerned with the stochastic behavior of fatigue cracks in a system. They are then used to get the distribution of the failure time, the first time the crack size of at least one of the cracks exceeds a given value. Several properties of our proposed models are presented, and the unknown parameters are estimated by the method of maximum likelihood. From these an estimate of failure time distribution is obtained. In this part, contrary to common practice, we do not assume availability of failure data. © 2004 Wiley Periodicals, Inc. Naval Research Logistics, 2005     

Basic scheduling problems with raw material constraints

One of the achievements of scheduling theory is its contribution to practical applications in industrial settings. In particular, taking finiteness of the available production capacity explicitly into account, has been a major improvement of standard practice. Availability of raw materials, however, which is another important constraint in practice, has been largely disregarded in scheduling theory. This paper considers basic models for scheduling problems in contemporary manufacturing settings where raw material availability is of critical importance. We explore single scheduling machine problems, mostly with unit or all equal processing times, and L_max and C_max objectives. We present polynomial time algorithms, complexity and approximation results, and computational experiments. © 2005 Wiley Periodicals, Inc. Naval Research Logistics, 2005.     

Signal‐to‐interference‐plus‐noise ratio estimation for wireless communication systems: Methods and analysis

The Signal‐to‐Interference‐plus‐Noise Ratio (SINR) is an important metric of wireless communication link quality. SINR estimates have several important applications. These include optimizing the transmit power level for a target quality of service, assisting with handoff decisions and dynamically adapting the data rate for wireless Internet applications. Accurate SINR estimation provides for both a more efficient system and a higher user‐perceived quality of service. In this paper, we develop new SINR estimators and compare their mean squared error (MSE) performance. We show that our new estimators dominate estimators that have previously appeared in the literature with respect to MSE. The sequence of transmitted bits in wireless communication systems consists of both pilot bits (which are known both to the transmitter and receiver) and user bits (which are known only by the transmitter). The SINR estimators we consider alternatively depend exclusively on pilot bits, exclusively on user bits, or simultaneously use both pilot and user bits. In addition, we consider estimators that utilize smoothing and feedback mechanisms. Smoothed estimators are motivated by the fact that the interference component of the SINR changes relatively slowly with time, typically with the addition or departure of a user to the system. Feedback estimators are motivated by the fact that receivers typically decode bits correctly with a very high probability, and therefore user bits can be thought of as quasipilot bits. For each estimator discussed, we derive an exact or approximate formula for its MSE. Satterthwaite approximations, noncentral F distributions (singly and doubly) and distribution theory of quadratic forms are the key statistical tools used in developing the MSE formulas. In the case of approximate MSE formulas, we validate their accuracy using simulation techniques. The approximate MSE formulas, of interest in their own right for comparing the quality of the estimators, are also used for optimally combining estimators. In particular, we derive optimal weights for linearly combining an estimator based on pilot bits with an estimator based on user bits. The optimal weights depend on the MSE of the two estimators being combined, and thus the accurate approximate MSE formulas can conveniently be used. The optimal weights also depend on the unknown SINR, and therefore need to be estimated in order to construct a useable combined estimator. The impact on the MSE of the combined estimator due to estimating the weights is examined. © 2004 Wiley Periodicals, Inc. Naval Research Logistics, 2004     

Bounding the optimal burn‐in time for a system with two types of failure

Burn‐in is a widely used method to improve the quality of products or systems after they have been produced. In this paper, we consider the problem of determining bounds to the optimal burn‐in time and optimal replacement policy maximizing the steady state availability of a repairable system. It is assumed that two types of system failures may occur: One is Type I failure (minor failure), which can be removed by a minimal repair, and the other is Type II failure (catastrophic failure), which can be removed only by a complete repair. Assuming that the underlying lifetime distribution of the system has a bathtub‐shaped failure rate function, upper and lower bounds for the optimal burn‐in time are provided. Furthermore, some other applications of optimal burn‐in are also considered. © 2004 Wiley Periodicals, Inc. Naval Research Logistics, 2004     

极化域—空域联合谱估计

首次提出极化域-空域联合谱的概念,拓广了电磁波特征参量的谱描述方法.结合具体的极化敏感阵列定义了极化域-空域联合谱,用MUSIC方法得到联合谱函数表达式.研究了联合谱的估计的重要性能指标估计精度和分辨力,估计精度用克拉美劳限CRB(cramer-Rao Bound)来具体度量,分辨力由极化域-空域模糊函数以及模糊图来描述.最后仿真结果验证了该方法的有效性和理论分析的正确性.     

离散系统的绝对稳定性

给出了离散系统绝对稳定性问题的充分条件:约束条件下的矩阵不等式的正定解;基于这一思路可以构造控制器来镇定一类非线性系统;最后还给出了设计实例以说明结果的有效性。     

康特洛维奇的数值方法在矩形薄板横向弯曲振动中的应用

本文提出的解决矩形薄板弯曲振动问题的康特洛维奇的数值方法,大大减少了所需要的计算机内存。通过算例表明它具有比较高的计算精度和计算速度,是一种有前途的计算方法。     

CRF与规则相结合的军事命名实体识别研究

作战命令的分词是作战指令自动化生成、文图转换等各种指挥自动化技术的重要基础。在作战指令进行分词处理的过程中,军事命名实体的识别是技术难点之一。命名实体是信息的主要载体,它的识别是军事信息抽取的关键。提出了一种基于CRF模型与规则相结合的命名实体识别方法,结合基本特征与外部词典特征,提高了实体识别效率;在后期进行规则优化,最终实现高效的命名实体识别。实验证明,该方法是行之有效的。能够成功解决命名实体的自动识别问题。