Approximation and analysis of a call center with flexible and specialized servers

This paper describes a decomposition algorithm to estimate the performance of a call center with two types of customers and two server categories. In this system specialized servers can process only one customer type, while flexible servers handle both types. The algorithm divides the systems state space into regions, and simple approximate models find the conditional system performance within each region. While the procedure described here is tailored for a system with a priority queue discipline and two customer classes, it can be adapted for systems with FCFS queue disciplines and for systems with more than two customer types. Performance measures generated by the procedure are sufficiently accurate for many service system design decisions, such as setting telephone call center staffing levels and long-term capacity planning. The procedure is also extremely fast, and its computational requirements do not grow with system congestion. Numerical tests demonstrate that its running time is significantly lower than traditional numerical methods for generating approximations. As an example of its use, we employ the procedure to demonstrate the benefits of server flexibility in a particular telephone call center.The author thanks Gregory Dobson, who participated in the initial consulting project and problem formulation, as well as Paul Schweitzer, Harry Groenevelt, and two anonymous referees for their helpful suggestions.     

A direct method for cluster analysis

An algorithm based on a least-mean-square (LMS) criterion is presented. This algorithm partitions a multi-dimensional data set directly into a desired number of clusters. The result is compared favorably to existing methods in both performance and computational efficiency. An efficient method for determining a reasonable set of distributed initial cluster centers based on principal component analysis is also presented. This clustering algorithm is shown to converge to a unique minimum based on the LMS criterion and is demonstrated by digital computer simulation and applied to the analysis of vectorcardiograms.     

Au/锗/氧化硅纳米多层膜/p-Si结构的电致发光机制研究

用射频磁控溅射法制备了锗/氧化硅纳米多层膜,在室温下测量了Au/锗/氧化硅纳米多层膜/pSi结构的电致发光.利用位形坐标模型分析了锗/氧化硅纳米多层膜的发光中心,并用量子限制-发光中心模型对该纳米结构的电致发光过程作了研究,研究表明锗/氧化硅纳米多层膜的电致发光主要来自SiO2层的发光中心.     

Growth and optical properties of ZnO nanorods by introducing ZnO sols prior to hydrothermal process

ZnO nanorods of 25 nm with quite homogeneous size and shape have been fabricated by introducing ZnO sols as nucleation centers prior to the hydrothermal reaction. The samples were characterized by scanning electron microscope, transmission electron microscope, X-ray diffraction, photoluminescence and resonant Raman spectra. After ZnO sols are introduced, the width of the resulting nanorods decreases above an order of magnitude and the aspect ratio increases 5 times. The increase of the intensity ratio of ultraviolet to visible emissions in room-temperature photoluminescence spectrum and the decrease of the Raman linewidths show the improvement in the quality of ZnO nanorods. Influences of the number of seed nuclei and the aging time of ZnO sols on the morphology of ZnO nanorods are discussed.     

ON STOCHASTIC CONVERGENCE THEOREMS FOR THE FUZZY C-MEANS CLUSTERING PROCEDURE∗

The fuzzy c-means clustering algorithm has been well studied for equal weight distributions on a finite set. Suppose that this situation is generalized to an arbitrary probability distribution on a finite dimensional Euclidean space, assuming that the second moment of the distribution is finite. Now choose ever larger finite random samples from this distribution and compute the standard optimal membership functions for a fuzzy partition into c clusters. Then the convergence of the cluster center points is established in the Hausdorff sense with probability one, provided that there is a unique optimal center point set. These optimal center points are the fixed point of a simple operator, and there is a corresponding iterative algorithm that generalizes the usual procedure.     

Comparisons of tibial accelerations when walking on a wood composite vs. a concrete mezzanine surface

Mezzanine surfaces can be made from concrete, bar grate, or composite materials. Anecdotal data indicate that mezzanines in distribution centers made from composite materials, due to their increased compliance, may be a more comfortable working surface. Prior research suggested that a measure of tibial shock, peak tibial acceleration, could potentially discriminate the biomechanical differences between these surfaces. The objective of this study was to quantify differences in tibial accelerations as 27 people walked on mezzanines constructed from concrete and a wood composite material. Accelerometers were attached bilaterally to the shins of volunteers, and data were collected as they walked 30.5 m on each surface at their normal walking speed, a faster-than-normal walking speed, and a slower-than-normal walking speed. Peak acceleration values obtained from the leg with the highest values were compared. On average, the peak acceleration values were 5% higher on the concrete mezzanine as compared with the wood composite mezzanine (p = .036). These findings suggest that individuals working on mezzanines in distribution centers constructed from composite surfaces would potentially experience less discomfort associated with long exposure periods on these surfaces.     

氮化镓材料中的位错对材料物理性能的影响

氮化镓材料中的位错是制约GaN发光器件及电子器件的性能的一个关键因素。目前对于氮化镓材料中的位错的研究是一大热点。扼要综述了位错对于材料及器件的物理性能的影响：非辐射复合作用、造成器件的漏电流、缩短器件的寿命。并简要介绍了减少GaN外延层中的位错密度的几种方法。     

浸泡后多孔硅的结构及光致发光特性

用电化学腐蚀方法制备了多孔硅样品,在浸泡液中浸泡使其表层多孔层与样品分离,在样品表面形成了丰富的SiO2包裹纳米硅颗粒结构,研究了样品的光致发光(PL)特性.结果表明,与剥离前相比,表层多孔层剥离后PL谱的强度约有10倍的增幅,峰位主要在蓝紫光范围内.在300℃干氧中退火后,样品的发光强度下降为退火前的三分之一,随着退火温度的升高,发光强度有所增强.退火前后有不同的发光机理,退火前光激发主要在纳米硅内,然后在二氧化硅层中的发光中心辐射复合;退火后光激发和光辐射都发生在二氧化硅层中.     

Community mental health service use by older adults with dementia.

We considered the role of community-based public mental health services in providing care to older persons with Alzheimer's disease and other forms of dementia, and examined service outcomes within California's county-based public mental health system over a 3-year period. Treated prevalence rates, repeat service use rates, and service mix patterns were regressed onto individual, market, and contextual variables across 25 counties over 12 observation periods. The number of older adults with dementia who used community mental health services increased slightly over the observation periods, and service use was associated with age and Medicaid status. Service outcomes also were affected by complementary mental health and aging service systems within each county, as well as the poverty rate and location of the county. Future research is needed to clarify how administrative policies and service management practices contribute to increasing community mental health service use by persons with dementia. In the meantime, these findings can help program administrators and service providers understand the role of community-based mental health services in providing care to persons with dementia. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

能源互联网——信息与能源的基础设施一体化

能源是人类生存发展的重要物质基础,能源互联网作为未来可能的能源可持续发展解决方案正逐渐成为研究的热点和潮流。阐述了能源互联网的概念和特征,提出其基本架构,并从广域网,局域网和基础设施三个层面讨论信息与能源的基础设施一体化建设。综述了国内外能源互联网技术的发展现状,提出了能源路由器作为信息与能源的基础设施一体化的解决方案,并对基于能源路由器的能源互联网应用场景给出了详细描述。