Staffing Call Centers with Uncertain Arrival Rates and Co‐sourcing

In a call center, staffing decisions must be made before the call arrival rate is known with certainty. Once the arrival rate becomes known, the call center may be over‐staffed, in which case staff are being paid to be idle, or under‐staffed, in which case many callers hang‐up in the face of long wait times. Firms that have chosen to keep their call center operations in‐house can mitigate this problem by co‐sourcing; that is, by sometimes outsourcing calls. Then, the required staffing N depends on how the firm chooses which calls to outsource in real time, after the arrival rate realizes and the call center operates as a M/M/N + M queue with an outsourcing option. Our objective is to find a joint policy for staffing and call outsourcing that minimizes the long‐run average cost of this two‐stage stochastic program when there is a linear staffing cost per unit time and linear costs associated with abandonments and outsourcing. We propose a policy that uses a square‐root safety staffing rule, and outsources calls in accordance with a threshold rule that characterizes when the system is “too crowded.” Analytically, we establish that our proposed policy is asymptotically optimal, as the mean arrival rate becomes large, when the level of uncertainty in the arrival rate is of the same order as the inherent system fluctuations in the number of waiting customers for a known arrival rate. Through an extensive numerical study, we establish that our policy is extremely robust. In particular, our policy performs remarkably well over a wide range of parameters, and far beyond where it is proved to be asymptotically optimal.     

主题关联性阅读模式的建构——兼论语境参数论与TEM-8语篇阅读

探讨了语篇生成之主题关联性机制,并从语境参数论出发,结合TEM-8阅读考试真题分析阐述了建立主题关联性阅读模式的可行性与重要性,强调语境参数对于语篇阅读理解的重要意义.这是提高英语语篇阅读效率与TEM-8阅读考试成绩的有效途径.     

On Minimum Distance Estimation Using Kolmogorov-Lévy Type Metrics

Let X ₁, . . ., X_n be independent identically distributed random variables with a common continuous (cumulative) distribution function (d.f.) F , and F^_n the empirical d.f. (e.d.f.) based on X ₁, . . ., X_n . Let G be a smooth d.f. and Gθ = G (·–θ) its translation through θ∈ R . Using a Kolmogorov-Lévy type metric ρ_α defined on the space of d.f.s. on R , the paper derives both null and non-null limiting distributions of √ n [ ρ_α ( F_n , Gθ_n ) – ρ_α ( F, G_θ )], √ n (θ _n –θ) and √ nρ_α ( Gθ , Gθ ), where θ _n and θ are the minimum ρ_α -distance parameters for F_n and F from G , respectively. These distributions are known explicitly in important particular cases; with some complementary Monte Carlo simulations, they help us clarify our understanding of estimation using minimum distance methods and supremum type metrics. We advocate use of the minimum distance method with supremum type metrics in cases of non-null models. The resulting functionals are Hadamard differentiable and efficient. For small scale parameters the minimum distance functionals are close to medians of the parent distributions. The optimal small scale models result in minimum distance estimators having asymptotic variances very competitive and comparable with best known robust estimators.     

铁基非晶合金非晶形成能力的分子动力学模拟

采用分子动力学方法,模拟了Fe60Cr20Mo20和Fe50Cr20Mo20M10(M=Ni, W) 铁基非晶合金的形成过程,通过加热至熔融态再淬火的方法计算出了Fe60Cr20Mo20、Fe50Cr20Mo20Ni10和Fe50Cr20Mo20W10三种合金形成非晶的临界冷速及一系列热力学参数。结果表明,三种合金形成非晶的临界冷速分别为15.7 K/ps、3.62 K/ps和1.04 K/ps,四元合金较三元合金形成非晶所需的临界冷速大大降低,而W元素的添加更能提高合金的非晶形成能力。另外,通过热力学参     

论唐代“诗客曲子词”的体式特征及其对词体演进的贡献

在词体滥觞的中晚唐时期,词所倚之"声"是俗乐"曲子"[1](P117)。其文体结构的形成与发展必得与"曲子"相辅相成,且深受曲体结构的约束。最初的"诗客"作"曲子",并非要将歌词当作一种单独的文体从曲子里剥离出来,相反却力求兼顾,以使文乐谐美。唐代文人既注重"倚声"谐唱以制词,又出于创作惯性引近体诗律为句,迈出了词体"律化"的第一步。"诗客曲子词"的出现,从文学和音乐两个方面提升了曲子辞的艺术成就,使文与乐更加紧密地结合在一起,为宋词的繁荣奠定了基础。     

中国银行业成本效率实证研究(1999-2010)——基于SFA测度方法的应用

以1999-2010年12年间国内14家商业银行样本数据为基础, 基于随机前沿效率分析原理, 利用参数估计SFA(Stochastic Frontier Approach)分析法, 评估金融改革以来银行成本效率的分布及演化趋势。研究表明:(1)样本期内银行整体成本效率呈先改善后趋于平稳态势, 近年来无明显波动。(2)国有商业银行成本效率下降显著, 无效率项影响明显;股份制商业银行成本效率除个别银行外, 大多数呈改善趋势;国有与股份制银行之间成本效率差异呈扩大趋势, 应予以重视。(3)未能发现资产规模、权益与银行成本效率之间的显著性相关关系。(4)国有商业银行成本效率存在明显改善空间, 内部治理和运营管理改革有待进一步强化。     

天线调谐器反Г形阻抗匹配网络适配

介绍天线调谐器反Г形阻抗匹配网络的结构形式和匹配区域;分析反Г形网络各参数取不同值时对HF双极天线的适配性,给出参数变化随频率、VSWR门限变化时对HF双极天线输入阻抗的适配曲线,为设计天线调谐器阻抗匹配网络和决定天线调谐器适配天线类型提供参考.     

从亚里士多德伦理学看贝娄小说《拉维尔斯坦》

《拉维尔斯坦》是美国小说家、1976年诺贝尔文学奖获得者索尔·贝娄的代表性小说。借助亚里士多德伦理学解读《拉维尔斯坦》,可以发现该小说体现了幸福在于沉思的生活的观点。     

天线调谐器反Г形阻抗匹配网络适配HF双极天线分析

介绍天线调谐器反Г形阻抗匹配网络的结构形式和匹配区域;分析反Г形网络各参数取不同值时对HF双极天线的适配性,给出参数变化随频率、VSWR门限变化时对HF双极天线输入阻抗的适配曲线,为设计天线调谐器阻抗匹配网络和决定天线调谐器适配天线类型提供参考.     

冰箱蒸发器管路特性自动检测系统研制

介绍了冰箱中蒸发器和毛细管等管路器件特性自动测试系统的设计原理。运用管中气流的理论,分析了温度和压力对管路阻力综合参数的影响,提出了管路阻力综合参数和泄漏系数的检测方法。用差压、流量变送器和数字集成温度传感器,通过三星单片机进行数据采集和运算处理,研制了管路器件泄漏和阻力综合参数测试系统,样机运行的测试结果表明,该管路测试系统的设计是成功的。