Non-homogeneous servers in emergency medical systems: Practical applications using the hypercube queueing model

In this paper, we study the effects of considering homogeneous versus non-homogeneous servers in applications of the hypercube queueing model. This is important since approximate methods available for solving the model for homogeneous servers are computationally much less time-consuming than the exact methods required for the non-homogeneous case. Illustrative examples are initially presented to show the degree to which using homogeneous versus non-homogeneous servers can differ. Then, two ambulance deployment applications dealing with Brazilian emergency medical systems, in a city and along a highway, are analyzed. The basic operational characteristics of non-homogeneous systems were compared to the respective predictions produced under the simplifying assumption of homogeneous servers. It was found that, even when the degree of non-homogeneity of the servers is not highly significant, homogeneity may lead to poor predictions of the actual operational characteristics of non-homogeneous systems.     

The M/G/∞ Queueing Model for Optimistic Concurrency Control

The M / G /∞ queue with Optimistic Concurrency Control (OCC) is a model for a special form of parallel transaction processing in a real-time database. Transactions arrive according to a Poisson process and require some generally distributed execution time. One of the differences with ordinary multi- and infinite-server queueing models is that under OCC the successful completion of one transaction may immediately cause the failure of one or more of the other transactions. This happens if the completing transaction has overwritten a data-item that is in use by another transaction in progress. As soon as this failure is detected the failed transaction is restarted. So the total service time of a transaction consists of its final successful run and the time spent on unsuccessful runs.
In this study we develop an approximation for the distribution of the total service time, and test the approximation against simulation. Although in practice the number of servers is never unlimited, this study provides valuable insight in the asymptotics with respect to the number of servers. The approximation clearly demonstrates the very limited performance gain from an increase of the number of servers.     

Emergence of anti-coordination through reinforcement learning in generalized minority games

In this paper we propose adaptive strategies to solve coordination failures in a prototype generalized minority game model with a multi-agent, multi-choice environment. We illustrate the model with an application to large scale distributed processing systems with a large number of agents and servers. In our set up, agents are assigned responsibility to complete tasks that require unit time. They request servers to process these tasks. Servers can process only one task at a time. Agents have to choose servers independently and simultaneously, and have access to the outcomes of their own past requests only. Coordination failure occurs if more than one agent simultaneously requests the same server to process tasks at the same time, while other servers remain idle. Since agents are independent, this leads to multiple coordination failures. In this paper, we propose strategies based on reinforcement learning that minimize such coordination failures. We also prove a null result that a large category of probabilistic strategies which attempts to combine information about other agents’ strategies, asymptotically converge to uniformly random choices over the servers.

     

Multi-server Batch-service Systems

In this paper we analyse a multi-server batch-service queueing model. Customers arrive one by one according to a Poisson process. They are served in batches under the following threshold policy: when a server becomes available a new batch of waiting customers is taken into service as soon as their number reaches a threshold a . The maximum allowable batch size is equal to b . Two classes of batch service time distributions are considered: Coxian-2 and Erlang- r distributions. In both cases the queueing model can be described by a Markov process. For this process it is shown that the equilibrium probabilities for states with all servers busy can be expressed as a finite sum of geometric terms. This form is used to derive a closed form expression for the waiting time distribution.     

基于Java的软交换计费服务器文件自动处理的设计与实现

在众多计费服务器上删除大量历史话单文件费时费力。基于Java语言编写自动删除话单历史文件的程序,并通过Windows的任务计划进行定时调度执行,可实现历史话单自动删除,大大提高了系统维护工作的效率。     

Land use-transport models in regional development planning

A land use-transport model of the Lowry-type is described along with several applications of the model to regional planning problems in the Toronto region of Ontario. The particular model used has several unique features. It may be disaggregated by socio-economic group, the population serving employment sub-model may be disaggregated into a number of employment sectors and transport mode-specific travel behaviour estimated. Applications of the model to public policy program formulation within the region are illustrated by three examples.     

Activity signature functions for high-frequency data analysis

We define a new concept termed activity signature function, which is constructed from discrete observations of a continuous-time process, and derive its asymptotic properties as the sampling frequency increases. We show that the function is a useful device for estimating the activity level of the underlying process and in particular for deciding whether the process contains a continuous martingale. An application to $ /DM exchange rate over 1986–1999 indicates that a jump-diffusion model is more plausible than a pure-jump model. A second application to internet traffic at NASA servers shows that an infinite variation pure-jump model is appropriate for its modeling.     

利用WINGDOWS SERVER2003 R2做服务器群集

什么是服务器群集?服务器集群就是指将很多服务器集中起来一起进行同一种服务,在客户端看来就象是只有一个服务器集群可以利用多个计算机进行并行计算从而获得很高的计算速度,也可以用多个计算机做备份,从而使得任何一个机器坏了整个系统还是能正常运行。     

混凝土保护层厚度的调查与分析

本文通过大量的工程实例数据,分析造成其梁、板保护层厚度不合格的原因;分析了不同保护层厚度对简支梁力学性能的影响,并利用ANSYS有限元软件对4根不同保护层厚度情况下的钢筋混凝土梁进行了有限元分析。研究表明,保护层厚度是否满足要求对保证工程质量具有重要的作用,因此应重视保护层的保证措施;保护层检测时,应注意选取合适的检测部位以及检测数量,保证检测环境的稳定;较大的保护层厚度可以较好地保护钢筋,但是梁的挠度增加,进而降低其承载能力。故应选用合适的保护层厚度,从而降低工程造价。     

Gradual location set covering with service quality

Location set covering models were first described in the early 1970s. In their simplest form, they minimize the number of facilities necessary to completely cover a set of customers in some given space, where covering means providing service within a predetermined distance. This paper considers extensions of the basic model that soften the covered/not covered dichotomy and replace it with gradual covering. The models discussed in this work include the quality of service as a criterion. The models are formulated and compared with each other with respect to their size and features. A small series of computational tests concludes the paper.     

国家历史文化名城土地覆盖研究

在对国内外土地覆盖相关研究综述的基础上,介绍了国家历史文化名城、城市地区等相关概念以及本文的数据来源;分析了国家历史文化名城的土地覆盖结构与土地覆盖特征;根据联合国环境规划署和世界粮农组织的土地覆盖分类系统,将国家历史文化名城地区归纳为四大类:陆地植被覆盖类型、水域植被覆盖类型、陆地非植被覆盖类型以及水域非植被覆盖类型。     

A synthesis of the production function and the shift-share model : A new regional modelling approach

The purpose of this paper is to suggest a new approach to regional modelling and show the way by which regional expansion paths of output and employment can be developed. Basically, the theoretical model is a synthesis of the production function for the industry (or region), the shift-share model, and a set of hypotheses and a number of identifies concerning the growth components of employment. The growth components of employment specified by the shift-share model and explained by the hypotheses enter and modify the production function in the sense that the shift-share model is linked directly to the production function in which the labor factor appears disaggregated into three distinct components (regional-share, industrial-mix, and national growth component). The theoretical model was tested for the manufacturing industry of the Greek economy. The policy implications of this model center around the fact that policy-makers can affect regional economic variables towards the desired level and direction.     

Scheduling spatially distributed jobs with degradation: Application to pothole repair

This paper considers scheduling spatially distributed jobs with degradation. A mixed integer programming (MIP) model is developed for the linear degradation case in which no new jobs arrive. Properties of the model are analyzed, following which three heuristics are developed, enhanced greedy, chronological decomposition and simulated annealing. Numerical tests are conducted to: (i) establish limits of the exact MIP solution, (ii) identify the best heuristic based on an analysis of performance on small problem instances for which exact solutions are known, (iii) solve large problem instances and obtain lower bounds to establish solution quality, and (iv) study the effect of three key model parameters. Findings from our computational experiments indicate that: (i) exact solutions are limited to instances with less than 14 jobs; (ii) the enhanced greedy heuristic followed by the application of the simulated annealing heuristic yields high quality solutions for large problem instances in reasonable computation time; and (iii) the factors “degradation rate” and “work hours” have a significant effect on the objective function. To demonstrate applicability of the model, a case study is presented based on a pothole repair scenario from Buffalo, New York, USA. Findings from the case study indicate that scheduling spatially dispersed jobs with degradation such as potholes requires: (i) careful consideration of the number of servers assigned, degradation rate and depot location; (ii) appropriate modeling of continuously arriving jobs; and (iii) appropriate incorporation of equity consideration.     

以客户为导向的第三方物流服务商选择方法

首先，运用AHP分析评价客户和待选第三方物流服务商；然后，综合前一阶段的评价结果，建立一个多目标混合整数规划模型；最后，通过与传统选择方法比较验证了此方法的合理性。     

Industrial relations in South-Eastern Europe: disaggregating the contexts

This study critically evaluates industrial relations (IR) in South-Eastern Europe and points towards future practical and research-oriented opportunities in the region. A survey of organizational policies and practices has been used to explore the state of IR in both private and public organizations in this region. Specifically, the data, collected in 2009–2010 (including the latest changes due to the economic crisis), cover 840 different organizations located in Slovenia, Serbia, Bulgaria, Greece and Cyprus. We discuss the development of ‘regional-specific’ IR policies, the ‘importing’ of varieties of capitalism models, the diffusion of the European Union social model and the role of foreign MNCs in changing IR in the region.     

医院中心机房设计原则及管理方法浅析

随着医院信息化的不断发展、深入,医院计算机中心机房的设计及管理日显重要,医院计算机中心机房设备由大量的微电子设备、精密机械设备和机电设备组成,包括服务器、路由器、核心交换机等重要设备,是确保医院信息系统7×24h不间断安全稳定运行的重要基础和保障。     

Forest Harvesting to Optimize Timber Production and Water Runoff

Timber and water runoff are joint forest products, and augmentation of runoff can occur when timber harvest uses smaller but costlier cut blocks. If runoff from a forested catchment area drains into a water-scarce region, then this interesting question arises: how best can harvesting in the catchment area be tailored to increase runoff to the water-scarce region? To examine the economics of joint production for a forested area in Canada, a linear programming model maximizing net present value of timber production and water runoff is run for three block sizes. Including a moderate or high value for water runoff leaves the optimal harvest pattern unchanged and does not cover the additional costs of smaller blocks. Yet, smaller blocks yield other benefits to society which, if valued monetarily, might make them preferred. To realize the benefits of smaller blocks would likely require public sector involvement for devising institutions/contracts linking the user of increased runoff with the harvester whose practices are modified.     

Application controlled caching for web servers

Today's web servers must have the ability to deal with large data sets, and their performance mainly depends on the control mechanism of the disc cache. Though the cache replacement algorithms in operating systems generally perform well, application-specific policies can often perform much better. In this paper, we present the application-controlled caching in user space (ACCUS) mechanism for web server disc caching. With this mechanism, an application can schedule the service requests based on the cache status of the requested files to improve its performance so that the system can gain a high parallelism of CPU processing, networking I/O and disc I/O. An application can service the cached files with a higher priority to the ones not cached, which helps reduce the latency caused by disc I/O blocking. Meanwhile, the application can enforce a policy for domain-specific cache management to obtain a higher cache hit ratio. ACCUS is implemented in two web servers of different models, Flash and userver. Despite the great differences in architectures, the empirical results show that both servers can achieve high throughput under heavy workloads with ACCUS enabled. Performance analysis for two other typical web servers, Apache? and Zeus Web Server are also conducted and the results indicate that ACCUS can achieve significant improvement in performance.     

Transversals, systems of distinct representatives, mechanism design, and matching

A transversal generated by a system of distinct representatives (SDR) for a collection of sets consists of an element from each set (its representative) such that the representative uniquely identifies the set it belongs to. Theorem 1 gives a necessary and sufficient condition that an arbitrary collection, finite or infinite, of sets, finite or infinite, have an SDR. The proof is direct, short. A Corollary to Theorem 1 shows explicitly the application to matching problems. In the context of designing decentralized economic mechanisms, it turned out to be important to know when one can construct an SDR for a collection of sets that cover the parameter space characterizing a finite number of economic agents. The condition of Theorem 1 is readily verifiable in that economic context. Theorems 2–5 give different characterizations of situations in which the collection of sets is a partition. This is of interest because partitions have special properties of informational efficiency.     

A log-linear approach to disaggregated micro-level population forecasts

"This paper proposes the use of a log-linear model to obtain long-range micro-level population projections from the aggregative projections. The proposed model is tested using U.S. data. The total population of households is decomposed into 120 subgroups on the basis of the household's region of location, age, size and the female's employment status. The estimated number of households from the log-linear technique is compared against the random-walk and time-trend methods. A comparison of the size of the observed and estimated subgroups for the years 1960 and 1980 suggests that the log-linear technique is superior to the other two methods. Five different measures of errors are used to evaluate the projections."