Online scheduling on unbounded parallel-batch machines to minimize maximum flow-time

We consider online scheduling on m unbounded parallel-batch machines to minimize maximum flow-time of the jobs. We show that no online algorithm can have a competitive ratio less than 1+αm, where αm is the positive root of α²+(m+1)α−1=0, and this lower bound is still valid even when all jobs have the same processing times. Then we provide an online algorithm of competitive ratio 1+1/m. When the jobs have the same processing times, we present a best possible online algorithm of competitive ratio 1+αm.     

Effect of latex and superplasticiser on Portland cement mortar in the fresh state

This report deals with the individual and combined effect of latex and superplasticiser on Portland cement mortar in the fresh state. The compatibility of five commercial superplasticisers with four latexes of the vinyl polymer group and SBR latex in varying dosages was studied with respect to setting time, consistency of fresh cement pastes, subjective workability (surface texture, segregation), bleeding, air content, water reduction capacity and the flow-time relationship of fresh mortar. It has been observed that superplasticisers of melamine formaldehyde and a blend of melamine and naphthalene formaldehyde eliminated shortcomings like delayed setting, high air entrainment in the fresh latex-modified system whereas lignosulphonate and a blend of lignosulphonate and naphthalene formaldehyde aggravated it. In a consequent report, performances in the hardened state will be discussed.     

基于改进遗传算法的单机成组作业调度

提出了单机成组作业调度的改进遗传算法。优化目标为总流程时间的单机成组作业调度问题明显是NP-hard问题,此问题的多项式求解方法不能求取最优解,而一些启发式算法也只能求出此问题的次优解。为获得单机成组作业最优调度,通过采用整数实值编码,随机采样选择,单点交叉以及变异检查,设计了单机成组作业调度的改进遗传算法。仿真结果表明,算法能够找到此问题的最优解,其性能优于加权最短加工时间(WSPT)启发式算法。改进遗传算法能够灵活解决各种单目标调度及多目标调度问题。     

New simple constructive heuristic algorithms for minimizing total flow-time in the permutation flowshop scheduling problem

This paper develops a set of new simple constructive heuristic algorithms to minimize total flow-time for an $n$-jobs×$m$-machines permutation flowshop scheduling problem. We first propose a new iterative algorithm based on the best existing simple heuristic algorithm, and then integrate new indicator variables for weighting jobs into this algorithm. We also propose new decision criteria to select the best partial sequence in each iteration of our algorithm. A comprehensive numerical experiment reveals that our modifications and extensions improve the effectiveness of the best existing simple heuristic without affecting its computational efficiency.     

城市供水系统突发性污染监测

以监测到供水系统中突发性污染为目标,提出一种城市供水系统监测点优化布置的方法.在定义最短水流时间矩阵和污染覆盖矩阵的基础上,针对复杂管网求解最短水流时间矩阵困难的问题,利用动态规划求解最短水流时间矩阵,并由此得到给定监测等级下的污染覆盖矩阵.以监测覆盖范围最大为目标函数,并引入重复覆盖度的概念,运用遗传算法优化布置监测点.算例结果表明,用动态规划求解复杂管网的最短水流时间矩阵易于编程实现,并有较高的时间效率;遗传算法能够快速地搜索到最优监测点的布置方案,达到在给定监测等级下最大限度地监测整个管网突发性污染的目的;通过与穷举法结果的对比,证明了本方法的正确性.     

Fully polynomial time approximation scheme for the weighted flow-time minimization on a single machine with a fixed non-availability interval

In a recent paper [Theoretical Computer Science 363, 257–265], He, Zhong and Gu considered the non-resumable case of the scheduling problem with a fixed non-availability interval under the non-resumable scenario. They proposed a polynomial time approximation scheme (PTAS) to minimize the total completion time.In this paper, we propose a fully polynomial-time approximation scheme to minimize the total weighted completion time. The FPTAS has O(n²/ε²) time complexity, where n is the number of jobs and ε is the required error bound. The proposed FPTAS outperforms all the previous approximation algorithms designed for this problem and its running time is strongly polynomial.     

On-line maintenance job scheduling and assignment to resources in distributed systems by heuristic-based optimization

A heuristic-based optimization algorithm is proposed in this paper for on-line scheduling and assignment of preventive maintenance jobs to processors, to minimize under availability constraints, on a given time-window, the total cost of the maintenance operations of a distributed system. This algorithm minimizes the cost of discharge of preventive maintenance tasks or jobs, while assigning the tasks along with balancing the processors load. It is shown that the problem is NP-hard. To solve it, the concept of job emergency is introduced and the priority rule for total flow time (PRTF) criterion is used in an adapted heuristic job-scheduling model. In addition, the algorithm considers the constraints of precedence among consecutive standby jobs and their emergency. It is depicted the specific properties of the proposed heuristic allowing jobs scheduling in the right order. Computational results illustrate the efficiency of the approach implemented on different system configurations.     

基于改进禁忌搜索算法的单机成组作业调度

提出了单机作业调度的改进禁忌搜索算法。以总流程时间最短为优化目标的具有作业分类与机器设置时间的单机成组作业高度问题是NP难问题,此问题的多项式求解方法不能保证求取最优解。基于改进禁忌搜索算法,建立了具有提交时间与分类设置时间的单机成组作业调度模型,可搜索到该问题的最优解。仿真实验表明,改进禁忌搜索算法能够搜索到最优解,其性能优于WSPT启发式算法,并且运行时间短,可应用于大规模调度问题。     

Optimal maintenance headcount allocation: an application of Chebyshev Goal Programming

In a semiconductor wafer fabrication facility (as well as virtually any type of factory), the allocation of maintenance technicians to tool sets (or clusters of tools) plays a crucial role in the determination of tool set availability. Tool availability, in turn, determines factory capacity and serves to drive factory performance in terms of outs, inventory, cycle time and WIP velocity. With tools now composing 70% or more of the cost of current (i.e. 300?mm wafer) multi-billion dollar facilities, even seemingly slight increases in tool set availability can translate into savings on the order of millions or hundreds of millions of dollars. In this paper, an approach for deriving the allocation of maintenance technicians for this problem by means of Chebyshev Goal Programming is described and illustrated.