Performance analysis of a constrained resource sharing system

We consider a queueing system where the servers are arranged in a circle, and each arriving customer requires a pair of resources that is shared by its server with the respective neighbors on either side. If either resource is being used, the customer is denied service. Customers arrive at each server according to independent Poisson processes, and lengths of service times at each server have an exponential distribution. We derive a closed-form formula for the expected fraction of busy servers at any time in terms of the number of servers and the utilization factor (defined as the arrival rate times the mean service-time duration). This allows us to evaluate system performance when these parameters are varied, and to determine whether denying service to arrivals at alternate servers improves performance. We relate the system to Dijkstra's dining philosophers problem, which is an abstraction for resource sharing in an operating system. This revised version was published online in June 2006 with corrections to the Cover Date.     

求解资源约束项目调度问题的启发式算法综述

本文综述了求解RCPSP的启发式算法.首先在对各种优先权规则进行归纳的基础上,概述基于优先权规则的RCPSP启发式算法研究现状;其次,综述项目进度的表述方式及常用超启发式策略,汇总求解RCPSP的超启发式算法的研究成果.此外,简要介绍除上述两大类启发式算法之外的其他几种启发式算法;最后,对全文进行总结,并指出该领域几个有希望的研究方向.     

鄱阳湖区水资源承载力的分析

通过对鄱阳湖各县区的主要水资源指标的分析．选择了七个主要评价因素．采用主成分分析法对鄱阳湖区水资源承载能力进行综合评价分析。结果表明鄱阳湖区水资源承载力处中等偏上水平．进一步开发仍有很大的潜力。     

Production of propionic acid using a xylose utilizingPropionibacterium

The kinetics ofP. acidipropionici (ATCC25562), a xylose-utilizing rumen microorganism, was studied to assess its use for propionic acid production from wood hydrolyzates. Propionic acid has been shown to have a stronger inhibitory effect than acetic acid, with the undissociated acid form being responsible for the majority of the inhibitory effect. Thus, in batch tests with pH controlled at 6.0, the propionic acid concentration reaches 25 g/L and the acetic acid 7 g/L. Xylose uptake rate is dependent on the specific growth rate and glucose concentration. An immobilized cell columnar reactor at very high product yields (80%) proved adequate for propionic production. At cell concentrations of 95 g/L with high product concentration, volumetric productivities of 2.7 g/L·h were obtained in ultrafiltration cell recycle systems.     

A Coverage Model for Improving Public Transit System Accessibility and Expanding Access

Accessible and efficient service are vital features of well-utilized public transit systems. Modeling approaches to support the evaluation of transit operations for management and planning are essential for continued improvement. A hybrid coverage model is developed in this paper for simultaneously expanding service access and increasing accessibility. This paper discusses the use and integration of this model in a geographic information system environment for strategic planning. Analysis is presented for public transit service in Brisbane, Australia. The structured model provides flexibility in developing viable policies for addressing system improvements and service expansion, all of which are likely to promote increased utilization of public transit.     

塔里木盆地绿洲分布与水源的关系

通过对整个塔里木盆地绿洲分布与水系分布概况进行野外调查与室内数据分析,探讨塔里木盆地绿洲分布与水资源的关系,证明了绿洲与水资源的内在联系.二者的关系是:塔里木盆地绿洲分布由水系分布限定的.大部分大小绿洲都是位于在河流流域.塔里木盆地绿洲规模大小随水资源开发利用变化而不断地变化.     

Critical path analysis and resource constrained project scheduling — Theory and practice

Critical path techniques have been in documented use since the mid 1950's and are now widely used in most aspects of project planning and control. Interest in this area in recent years has been mainly concerned with making the best use of scarce resources throughout the duration of a project and a considerable amount of work has been undertaken in this area by both theorists and practitioners in project management. There is still however an apparent gap between the published theoretical work and the requirements of project schedulers and managers in the field and this paper briefly describes the different approaches taken, how they differ and suggests where future effort may be directed.     

F 2-FDG NMR imaging of the brain in rat

Images of the rat head reflecting glucose utilization were obtained using 2-fluoro-2-deoxy-D-glucose (2-FDG) and ¹⁹F nuclear magnetic resonance (NMR) imaging. Spatial heterogeneity of glucose utilization in the rat head was clearly demonstrated showing significantly higher glucose utilization in the brain as compared to the surrounding tissues. Although the potential adverse effects of the high doses of 2-FDG (400 mg/kg) needed to perform the study preclude immediate application of this technique to clinical quantitative glucose utilization studies, the present study shows potential for future development of glucose utilization imaging by NMR.     

MODELING THE DYNAMICS OF FISHERY STOCK RECOVERY: IMPLICATIONS FOR THE ASSESSMENT OF NATURAL RESOURCE DAMAGES

ABSTRACT. During the restoration planning phase of the natural resource damage assessment (NRDA) process, potential injuries to natural resources and services are evaluated in terms of the nature, degree and extent of injury so that the need for and scale of restoration actions can be ascertained. Injuries are quantified by comparing the condition of the injured natural resource relative to baseline (pre‐injury) conditions. The “Type A” procedures are used to quantify damages from smaller spills and rely on a standardized methodology and computer model to calculate injury and value of damages. In this model, fishery stock changes from injuries and resulting changes in user participation are not treated as dynamic. If true stock growth and re‐growth are indeed dynamic, then the Type A model is likely underestimating fishery losses. The purpose of this paper is to illustrate the potential for such underestimation by comparing simulated stock and harvest losses under dynamic treatment and a static treatment that more closely represents the way stock and service losses are estimated under the current NRDA process.     

论新疆干旱区水资源利用对生态环境影响的规律与良化途径

新疆水资源的转化与时空分布规律和水资源在此特殊干旱区的重要地位及自然、人文因子共同影响下,本地区水资源利用表现出宏观与微观上的明显“向水”趋势,并在各种用水方式的作用中形成若干新的人工水体生态系统,因此产生了一系列生态环境问题。本文在总结以往经验的基础上,就目前新疆水资源利用存在的主要问题,进行环境综合评价,进而寻求规律,扬长避短,提出合理开发利用新疆水资源的战略对策。