对服务率可变的T-SPH/M/1/N排队基于广义特征值方法的分析

本文讨论服务率依赖于当前系统中顾客数的有限T-SPH/M/1/N排队,其中TSPH表示连续时间可数状态吸收生灭过程吸收时间的分布.对该排队模型,可以用水平无限位相有限的拟生灭(QBD)过程进行建模.通过用广义特征值方法对该QBD过程进行分析,得到了T-SPH/M/1/N排队的平稳到达队长分布.另外,为了说明我们方法的有效性,还用几个数值例子对模型进行了分析,以刻画参数变化对系统性能的影响.     

多服务速率多重休假M/G(M/G)/1可修排队

本文通过对系统中顾客数设置门限N,考虑研究了服务台的服务速度依门限发生变化且当服务台未服务顾客(休假或故障)时到达顾客仅以概牢p进入系统的多重休假可修M／G(M／G)／1排队系统。通过L-变换、母函数以及补充变量方法得到了队长分布的瞬态解、稳态解及一些可靠性结果,并指出当两个服务速度相等时该模型与前人研究的M／G／1(E,MV）排队一致。     

M~x/M/N可修排队系统

本文研究了顾客批量到达且服务台忙时与闲时故障率不同的多服务台可修排队系统,推导出了系统的稳态平衡方程以及稳态概率值的求解思路.由于N≥2时手工计算的复杂性,使用Mathematica软件编程实现了稳态概率值的求取,并最终得到了系统有效服务台数的稳态分布、稳态队长的母函数以及平均队长等重要的系统指标.     

介质/金属/介质多层透明导电薄膜研究进展

综述了介质/金属/介质(dielectric/metal/dielectric,D/M/D)多层透明导电膜材料的特点、制备方法、研究进展与应用现状,重点比较讨论了ITO/Ag/ITO、ZnS/Ag/ZnS的膜系结构、光电性能、化学稳定性、热稳定性等特点,以及与国内外的研究差距.ITO/Ag/ITO、ZnS/Ag/ZnS是目前光电性能最好,且无需引入过渡层的两种D/M/D膜系,但有关其热稳定性的评价和研究存在不同的观点.用资源丰富、价格便宜、无毒的掺铝氧化锌(ZAO)薄膜取代含有价格昂贵的贵金属铟的掺锡氧化铟(ITO)薄膜,ZAO/Ag/ZAO膜系结构的设计、薄膜制备、光电性能与IMI的对比研究是目前国内外D/M/D研究中的热点课题和D/M/D发展的主要方向.     

CUSUM Statistical Monitoring of M/M/1 Queues and Extensions

Many production and service systems can be modeled as queueing systems. Their operational efficiency and performance are often measured using queueing performance metrics (QPMs), such as average cycle time, average waiting length, and throughput rate. These metrics need to be quantitatively evaluated and monitored in real time to continuously improve the system performance. However, QPMs are often highly stochastic, and hence are difficult to monitor using existing methods. In this article, we propose the cumulative sum (CUSUM) schemes to efficiently monitor the performance of typical queueing systems based on different sampling schemes. We use M/M/1 queues to illustrate how to design the CUSUM chart and compare their performance with several alternative methods. We demonstrate that the performance of CUSUM is superior, responding faster to many shift patterns through extensive numerical studies. We also briefly discuss the extensions of CUSUM charts to more general queues, such as M/G/1, G/G/1, or M/M/c queues. We use case studies to demonstrate the applications of our approach. Supplementary materials for this article are available online.     

新型高性能粉末高温合金的研究与发展

粉末高温合金由于在高温下表现出一系列优越的性能而成为制造高推重比航空发动机涡轮盘等部件的首选材料,本研究总结和分析了国外第三代新型高性能粉末高温合金的研究成果,重点描述了这些合金的制备工艺和力学性能,并提出研制高性能粉末高温合金的重点发展方向.     

On enhancing the mechanical properties of aluminum P/M alloys

Sintered aluminum alloys are an attractive material for the automobile industry, both because of the low specific gravity and high strength-to-weight ratio of aluminum itself, and the fabrication advantages associated with a powder metallurgy process. However, properties such as impact, stiffness, corrosion and wear resistance are often poor, thereby restricting the widespread use of these materials. Recent work by the authors has shown that hardness, wear resistance and tensile properties of a P/M Al–Cu–Mg ternary master alloy can be improved using a novel diffusion/supersolidus liquid phase sintering process. Improvements were due to in-situ microalloying during sintering, in particular, the influence of Ag and Sn. To complement this work, the present investigation addresses the response of a commercial alloy, AA2014, to the microalloying process. Results show that sintered densities for the commercial alloy were relatively unaffected by the presence of either Ag or Sn, and were superior to the ternary master alloy. Hardness and tensile properties were also improved relative to those obtained for the ternary, and were comparable to wrought 2014. Examination of final microstructure of Ag modified AA2014 using TEM showed the presence of Ω as the principal precipitate, but only after extended sintering times. This particular precipitate is believed to contribute to enhanced hardness. The apparent absence of Ω for short sintering times was due to the presence of silicon in the commercial product. However, the corrosion behavior of the P/M AA2014 was superior to the wrought product and thus the process is presented as a potential P/M alternative to using ingot metallurgy techniques for microalloying.     

附有选择性服务与无等待能力的M/G/1排队系统稳定性分析

研究附有选择性服务与无等待能力的M/G/1排队系统。通过对描述其系统行为的偏微分方程组的规范化,将其转化为Banach空间中抽象的Cauchy问题。然后,利用强连续有界线性算子半群理论,证明了系统的非负稳定解恰是系统算子的0本征值对应的非负本征向量。同时通过研究系统算子的谱特征,证明了系统算子的谱点均位于复平面的左半平面且虚轴上除0外无谱,进而得到系统的渐近稳定性,特别在范数意义下系统的动态解收敛到稳态解。     

一般限量服务M/G/1型单重休假排队系统的随机分解

本文研究了M／G／1型一般限量服务单重休假排队系统,根据稳态下M／G／1型非空竭服务休假排队系统的队长的随机分解的一般结构,提出简便算法一结构分析法,并且在先到先服务规则下(FCFS)求得稳态下队长的随机分解的概率母函数(GFP)和服务时间的随机分解的Laplace变换(LST),还充分地讨论了系统平稳的条件及其概率含义。     

粉末冶金低合金钢的制备和性能研究进展

分别从粉末制备、成形工艺、烧结工艺及其组织控制等方面较系统地介绍了国内外粉末冶金低合金钢的制备情况,并展望了其将来的研究方向和前景.     

Single Run Optimization of Discrete Event Simulations—An Empirical Study Using the M/M/l Queue

Simulation modeling has been widely used to analyze complex stochastic systems, such as, to compute some performance measures of a modem manufacturing facility. Often, we are interested in optimizing these performance measures of the system wth respect to some controllable parameters. Traditional methods to find an optimum of a sirnulation model usually require making a number of simulation runs, which can be computationally intensive. This study proposes a stochastic optimization method to optimize a simulation model in a single simulation run, with the potential of large savings in computational effort. Two algorithms based on this method are developed and evaluated empirically using an M/M/l queue problem. Experimental results show that the algorithms, especially one of them, are promising and that this approach merits further investigation     

基于 Min($N,D,V$)——策略和单重休假的 $M/G/1$ 排队系统队长分布的瞬态和稳态解

本文主要研究服务员单重休假且在休假时间中根据 Min($N,D,V$)--控制策略可立即中断休假的 $M/G/1$ 排队系统．运用全概率分解技术和拉普拉斯变换工具，讨论在任意初始状态条件下队长的瞬态和稳态性质，得到了队长分布瞬态解的拉普拉斯变换表达式．在此基础上，直接获得了便于作数值计算的队长分布稳态解的递推表达式．进一步，给出了稳态队长的随机分解结构、附加队长分布的显示表达式，以及在一些特殊情形下的相应结果．最后，通过数值实例考察了附加队长分布对系统参数的敏感性，分析参数不同取值对系统运行性能的影响．     

夹杂物对粉末高温合金疲劳性能的影响

粉末高温合金FGH95是发动机用的优选材料。通过对该合金的疲劳性能试验和扫描电镜微观观察,发现合金中含有由铝、氧、镁、钛、硅和钇等元素组成的夹杂物。无论室温或者高温条件下,合金的疲劳裂纹源均从夹杂物处萌生,并且夹杂物尺寸越大,距离表面越近,所对应的疲劳寿命越低。     

粉末高温合金中夹杂物特性及其质量控制

研究了粉末高温合金中夹杂物特性及对材料断裂行为的影响 ,研究内容包括 :夹杂物的性质及来源、夹杂物在材料变形过程中的形变特征、夹杂物对材料疲劳断裂行为的影响等 ,同时研究了盘件在生产过程中夹杂物质量控制方法 .     

镍基粉末高温合金冶金工艺的研究与发展

叙述和分析了镍基粉末高温合金冶金工艺三十多年来在制粉末处理工艺，成型工艺，热处理工艺等方面的研究成果和存在的问题，总结了粉末高温合金冶金工艺今后的主要发展方向。     

压制压力对粉末冶金钢组织和性能的影响

压制压力是制造粉末冶金材料的关键工艺因素之一,本文根据45#钢的铁碳配比,选取了5个压制压力（130,260,360,470,600MPa）,在其他工艺条件如烧结温度、烧结压力、烧结气氛、保温时间、冷却方式相同的情况下,来考察这5个工艺水平对于粉末冶金钢组织和性能的影响。试验结果表明,随着压制压力的增大,烧结体的晶粒尺寸变小并趋于均匀,材料的冲击断裂方式也由韧性断裂转变为混合断裂方式,同时烧结体的密度、硬度也随着压力的增大而出现先增大后趋于平缓的趋势。     

Joint decisions for R/M integrated supply chain using system dynamics methodology

In the remanufacturing/manufacturing (R/M) integrated supply chain, the decisions of the manufacturer, the wholesaler, the retailer, the parts producer, the raw materials supplier, the collector, and the disassembly centre are interactional. In this paper, a system dynamics model is proposed to examine the long-term behaviour of the R/M integrated supply chain with reuse, remanufacturing, and recycling. The optimal decision sets of the remanufacturing ratio and the setup period of remanufacturing (r) are given, the joint decisions of all members of R/M integrated supply chain under optimal r are presented by the simulation results, and the impacts of optimal r on the joint decisions are analysed.     

基体合金对连续M40石墨纤维/Al复合材料纤维损伤及断裂机制的影响

选用M40石墨纤维为增强体,采用真空气压浸渗法制备了纤维体积分数为40%,基体合金分别为ZL102、ZL114A、ZL205A及ZL301合金的连续M40/Al复合材料,并用NaOH溶液萃取出M40纤维,研究了基体合金对连续M40/Al复合材料纤维损伤和断裂机制的影响。结果表明:不同的基体合金对M40纤维造成的损伤差异较大,从M40/ZL301复合材料中萃取的纤维拉伸强度最高,其拉伸强度为1 686 MPa,约为纤维原丝拉伸强度的38.3%;而从M40/ZL102复合材料中萃取的纤维拉伸强度最低,其拉伸强度仅为687 MPa,且纤维表面粗糙程度不一。不同M40/Al复合材料的断裂机制存在明显差别,M40/ZL102和M40/ZL114A复合材料断裂时无纤维拔出及界面脱粘,裂纹横向穿过纤维导致复合材料在低应力下失效;M40/ZL205A复合材料则表现为少量纤维拔出,界面轻微脱粘;同时,M40/ZL301复合材料表现为大量纤维拔出,裂纹沿界面纵向扩展,界面脱粘明显,纤维充分发挥其承载作用,复合材料的拉伸强度最高,达到了670.2 MPa。      

铝硅合金、铁基粉末冶金、灰口铸铁耐磨性对比

选用压铸铝硅合金、铁基粉末冶金、灰口铸铁进行摩擦对比试验。结果表明,在给定的滑动摩擦条件下压铸铝硅合金的耐磨性最高,加工硬化能力最强;铁基粉末冶金仅次于压铸铝硅合金;灰口铸铁的耐磨必琢加工硬化能力最差。     

渗铜量对颗粒强化铁基材料显微组织的影响

采用烧结-熔渗和后续热处理工艺制备了Co-Cr-Mo-Si颗粒强化的铁基粉末冶金材料,利用光学显微镜、扫描电镜和能谱分析技术,研究了不同渗铜量对材料显微组织的影响.研究表明:Co-Cr-Mo-Si硬颗粒单独存在于基体中,起颗粒强化的作用;未渗铜时,孔洞多,硬颗粒与基体界面清晰可见,结合强度差,随着渗铜量的增多,合金元素扩散程度提高,硬颗粒与基体界面结合强度好;材料的孔隙度减小,碳化物弥散分布程度提高;采用熔渗工艺并合理控制渗铜量,可获得组织均匀化、各相界面结合较好的铁基粉末冶金材料.