Active and stable project scheduling

The paper proposes a new classification of schedules for resource-constrained project scheduling problems with minimum and maximum time lags between project activities and regular and different types of nonregular objective functions. The feasible region of the scheduling problems represents a (generally disconnected) union of polytopes. In addition to the well-known concepts of active and semiactive schedules, pseudoactive and quasiactive as well as stable, semistable, pseudostable, and quasistable schedules are introduced. The (quasi-, pseudo-, semi-)active schedules are related to different types of left-shifts of sets of activities and correspond to minimal points of certain subsets of the feasible region. The (quasi-, pseudo-, semi-)stable schedules do not allow oppositely directed shifts and correspond to extreme points of certain subsets of the feasible region. The different sets of schedules contain optimal schedules for project scheduling problems which differ in their objective functions. The correspondence between those sets of schedules and vertices of specific polyhedral subsets of the feasible region can be exploited for analyzing schedule generation schemes which have been developed recently for finding solutions to the different classes of project scheduling problems.     

A new harvest operation cost model to evaluate forest harvest layout alternatives

In this paper we develop a new model for harvest operation costs that can be used to evaluate stands for potential harvest. The model is based on felling, extraction, and access costs and is unique in its consideration of the interaction between harvest area shapes and access roads. We illustrate the model and evaluate the impact of stand size, volume, and road cost when determining harvest layouts. We also present a generalized case where multiple unit road costs are considered in the same stand.     

OFDMA系统中基于有限反馈的资源公平调度算法

OFDMA是下一代无线通信系统中在下行链路上实现大容量通信的一种有前途的技术,其中的关键技术之一是在共享信道的用户间公平合理地分配子载波和功率。分析了功率约束下系统最大吞吐量的实现方法,提出了一种基于有限反馈的资源公平调度算法,这种算法具有系统所需反馈信息量少、用户间公平性好等性能,并通过仿真进行了验证。     

OFDM下行链路的跨层自适应传输算法

提出了一种适用于正交频分复用（OFDM）下行（前向）链路的跨层自适应传输算法．算法考虑了物理层的信道状态信息、功率约束以及数据链路层（DLL）的业务和用户的调度公平．基于比例公平原则和注水原理,给出了算法的6个具体步骤．仿真结果表明该跨层传输方案优于单纯在物理层采用子载波和功率分配自适应算法的方案,相对于后者能够提高用户数据包的传输成功率和降低包的传输时延,并能支持更多的用户．     

Balanced train timetabling on a single-line railway with optimized velocity

This paper aims to find an optimal balanced schedule with the least delay-ratio (i.e., the ratio of the total delay time and the total free-run time) by considering the impacts of the train velocity. A rigorous optimization model is proposed under the consideration of feasible speed constraint for finding the optimal velocity for each train on the railway line. To obtain an approximately optimal scheduling strategy, a combination of the improved TAS (ITAS) method and the genetic algorithm (GA), called GA-ITAS method, is in particular proposed to effectively solve the proposed model. The results of numerical experiments demonstrate the efficiency and effectiveness of the proposed approaches.     

基于规则和遗传算法的实验室排课算法研究

为解决实验室排课这一NP组合优化问题,设计了基于规则和遗传算法的实验室排课算法.首先对用到的数据库和数据结构进行了定义,然后采用遗传算法进行排课,最后引入排课规则解决对实验室按优先级排课的问题.同时,也给出了一种排课冲突的解决方法.实验证明该算法能很好地解决实验室排课问题.     

退化条件下的工期指派的单机排序问题

研究退化条件下的工期指派的单机排序问题。每个工件均有一个关于工期的连续非减的惩罚函数。工件的加工时间是退化的,即工件的加工时间是其开始加工时间的一个线性增函数,所有工件都有一个相同的退化率。目标是确定工件的最优加工顺序、最优工期和最优开始加工时间,使总工期、误工工件数及总完工时间之和最小。工件在工期之后完成则称为误工工件,工件在工期之前完成则是提前工件。工期指派分两种情况,一种是所有的工件工期都相等,另一种是不同的工件有不同的工期。对于上述两种情况分别给出了最优解的3个性质,并且证明了这个问题是多项式时间可解的。     

A note on the modelling of project networks with time constraints

In this note we show how to manage, by means of Generalized Precedence Relationships, some kinds of temporal constraints introduced by Chen et al. (1997) in project networks.     

Revisiting the PERT mean and variance

Difficulties with the interpretation of the parameters of the beta distribution let Malcolm et al. (1959) to suggest in the Program Evaluation and Review Technique (PERT) their by now classical expressions for the mean and variance for activity completion for practical applications. In this note, we shall provide an alternative for the PERT variance expression addressing a concern raised by Hahn (2008) regarding the constant PERT variance assumption given the range for an activity’s duration, while retaining the original PERT mean expression. Moreover, our approach ensures that an activity’s elicited most likely value aligns with the beta distribution’s mode. While this was the original intent of Malcolm et al. (1959), their method of selecting beta parameters via the PERT mean and variance is not consistent in this manner.