动态用户最优配流问题的投影算法研究

本文首先建立了动态用户最优配流问题的变分不等式模型,并对此模型用投影算法来求解.本文中的模型满足Wordrop第一原理要求,所给算法在每一个小时段都能给出路段流入率、流出率及路段流量,从而为行人出行提供可靠的、实时的信息,所给数值实验也说明该模型和算法是可行且有效的.     

多维动态用户最优出行选择的变分不等式模型

针对出行行为的出行模式,出发时间/路径选择三个方面,建立了基于路段的理想动态用户最优的变分不等式模型,该模型将用户的出行方案制定和实施作为一个整体进行考虑,表明了在满足动态用户最优选择条件下,交通流在出行模式、出发时间和出行路径上取得一致的动态均衡性,通过必要性和充分性的论证,得到了变分不等式模型和动态用户最优出行模式/出发时间/路径选择均衡条件的等价性,对模型解的存在惟一性成立需要满足的条件作了讨论,提出了求解的嵌套对角化算法,在此基础上,使用一个简单算例对模型进行了验证.     

基于出行时间可靠性的交通配流问题

提出一类由需求随机性所导致的基于出行时间可靠性的交通配流问题.由于每一天交通需求的随机变化,出行者的出行时间不是确定的,而是随机变量.假设出行者在过去经验的基础上能够得知出行时间的随机分布,提出一类新准则去刻画出行者在出行时间不确定情况下的路径选择行为.这种准则可以表示为一种以路径流量为变量的变分不等式模型.对于这类新的模型,给出了解的存在性证明,并且引入一个启发式的算法去求解该问题.数值算例展示了模型在应用上的特性和算法的有效性.     

基于横向和纵向公平偏好的二层供应链网络均衡决策

在上层为制造商、下层为多个竞争型零售商和需求市场的二层供应链网络中,分析了多个零售商间横向公平偏好、零售商与制造商间纵向公平偏好行为。构建了下层零售商考虑横向和纵向公平偏好的Nash均衡模型,并且得到上层和下层供应链网络的Stackelberg-Nash博弈模型,利用罚函数法求解得到二层供应链网络均衡决策。定性分析了零售商横向、纵向公平偏好权重和纵向公平参考系数对均衡决策的影响,并通过数值算例验证。最后对供应链各决策者给出应对公平偏好负效用的合理化建议。     

O-D需求估计的双层规划模型及基于灵敏度分析的求解算法

本文在考虑三种交通模式 (一般机动车,公交车,自行车)的基础上,建立了一般拥挤网络多模式OD需求估计问题的双层规划模型,给出了一个基于灵敏度分析的启发式求解算法,并进行了数值试验。试验结果表明,本文所给的模型和算法不仅能较好地给出OD需求的估计值,而且同时还给出了各模式路段流量的估计值。     

考虑顾客选择行为的逆向物流网络设计问题研究

逆向物流网络设计是企业获得经济利益和提高竞争力的战略决策之一.本文在进行逆向物流网络设计时,考虑了企业和顾客有不同的利益,通过双层规划建模来描述物流网络设计问题.上层模型为双目标模型,描述企业同时优化物流总成本和服务水平,下层模型描述顾客选择回收点的行为.设计了求解算法,得到一组Pareto解构成的效率边界,通过分析效率边界,确定企业的物流网络结构.最后用算例验证了模型和算法的有效性.     

求解非线性二层规划问题的模拟植物生长算法

本文以植物向光性生长理论为启发式准则,提出了一种求解非线性二层规划问题的智能优化算法。在该算法中,将二层规划上层解空间和下层反应集分别作为植物的两个生长环境,建立以生长规则为基础的植物系统演绎方式和以植物向光性理论为基础的概率生长模型,两者结合所形成的优化模式,实现了模拟植物从初始状态到完整形式的终态(没有新的树枝生长),从而得到二层规划问题的解。该方法具有搜索精度较高,求解稳定性较强的特点,通过与国外学者在非线性二层规划实际测试问题的最优值进行精度比较,表明模拟植物生长算法是有效可行的。     

价格-数量调节网络交通流演化模型

首次运用经济学非瓦尔拉斯均衡中的价格-数量调节原理和方法,建立网络交通流动态演化模型.假设出行者在路径选择决策时,不但受路径出行时间(价格)的影响,而且还受到路径剩余通行能力(数量)的影响,并将这种路径选择行为形成的稳定交通流模式定义为价格-数量混合调节用户均衡.论文分别建立了价格调节演化模型和数量调节演化模型,进而构建了价格-数量共同调节演化模型,证明了演化模型的稳定状态等价于价格-数量调节用户均衡,且价格调节用户均衡和数量调节用户均衡均为价格-数量调节用户均衡的特例.论文最后以一个简单的测试网络为例对文中建立的演化模型进行了计算分析,结果显示三种演化模型均可较理想地模拟路径流随时间变化的过程,且模型稳定状态分别对应三种用户均衡交通流模式.     

基于累积前景理论的出发时间选择SDUO模型

以早高峰工作出行为研究对象,基于累积前景理论建立了一个随机动态用户最优(SDUO)交通分配模型,模型可以同时选择出发时间和出行路径,给出了等价的变分不等式,设计了求解算法并通过算例进行了验证。结果显示,路径及OD对之间的动态出发流量、出发时间选择满意函数均与到达工作地点的价值函数形态相似,绝大多数出行者(96.45%)都能在"可以接受的最早到达时刻"与"工作开始时刻"之间到达。模型拓展了传统出发时间选择模型中"时间窗"的概念和出行者完全理性假设的局限,在有限理性框架下考察出行者的决策行为,模型及算法可以为出行行为分析、动态路径诱导,以及拥挤收费和错时上下班等交通管理措施的制订提供理论依据。     

模糊车辆路径问题的一种混合遗传算法

在对模糊车辆路径问题进行简单描述的基础上,通过引入决策者主观偏好值的概念,给出了解决该问题的基本思路,建立了具有模糊特征的车辆路径问题的模糊机会规划模型,提出了求解该问题的一种基于模糊模拟的混合遗传算法。同时,在最小化总行驶距离的目标下,通过随机模拟方法研究了决策者主观偏好值的选择对最终决策目标的影响作用,并给出了其最佳取值范围。     

Introduction to Special Section on Sensitivity Analysis and Summary of NCSU/USDA Workshop on Sensitivity Analysis

This guest editorial is a summary of the NCSU/USDA Workshop on Sensitivity Analysis held June 11–12, 2001 at North Carolina State University and sponsored by the U.S. Department of Agriculture's Office of Risk Assessment and Cost Benefit Analysis. The objective of the workshop was to learn across disciplines in identifying, evaluating, and recommending sensitivity analysis methods and practices for application to food‐safety process risk models. The workshop included presentations regarding the Hazard Assessment and Critical Control Points (HACCP) framework used in food‐safety risk assessment, a survey of sensitivity analysis methods, invited white papers on sensitivity analysis, and invited case studies regarding risk assessment of microbial pathogens in food. Based on the sharing of interdisciplinary information represented by the presentations, the workshop participants, divided into breakout sessions, responded to three trigger questions: What are the key criteria for sensitivity analysis methods applied to food‐safety risk assessment? What sensitivity analysis methods are most promising for application to food safety and risk assessment? and What are the key needs for implementation and demonstration of such methods? The workshop produced agreement regarding key criteria for sensitivity analysis methods and the need to use two or more methods to try to obtain robust insights. Recommendations were made regarding a guideline document to assist practitioners in selecting, applying, interpreting, and reporting the results of sensitivity analysis.     

Distinguishing traumatic, vicarious and routine operational stressor exposure and attendant adverse consequences in a sample of police officers

Problems in studying occupational stress within the police service are identified and the paucity of work on operational duties as potential stressors are discussed. The present study reports the results of a factor analysis of operational stressors (N = 601 serving British police officers) that revealed three factors: exposure to death and disaster; violence and injury; sexual crime. These were demonstrated to be reliable scales and were included in logistic regression models together with a range of demographic and psychological variables. Models were applied to men and women separately, which showed there to be different predictors of the likelihood of suffering distress (measured by the General Health Questionnaire, GHQ) in terms of the officer's gender and operational role. Overall the model for women officers was better at predicting psychological distress than that for men. These findings are related to aspects of the police occupational culture. Further discussion is offered that conceptualizes police operational stressors as traumatic, routine and vicarious. Finally, some implications are drawn for the provision of stress intervention in the light of this differentiation.     

Criteria for selecting a production control philosophy

Logistic objectives constitute a compromise between having short leadtimes and a low volume of work in progress on the one hand and a high resource loading and due date obligation on the other. Miscellaneous production planning approaches offered today provide different combinations of logistic objectives for satisfying a manufacturing strategy. To combine the strength of the various approaches into a unified system, a new approach based on a dynamic and distributed production planning methodology is proposed. To customize the approach, various analyses and specifications have to be made and for that reason some important characteristics and criteria for analysing production control philosophies will be given.     

The social construction of the meaning of acute stressors: a qualitative study of the personal accounts of police officers using a stress counselling service

The police profession is one in which acute stressors are encountered more frequently than in other occupations. Using the personal accounts of 35 police officers attending an in-house stress counselling clinic, the aim of the present study was to provide a qualitative examination of how the institutional context of policing influenced the ways in which acute stressors signified to individual police officers experiencing felt distress. Using the framework of Rational Emotive Behaviour Therapy as an analytical tool, it is argued that beliefs contributing to the experience of felt distress are related to the way in which policing as both an identity and an activity is constructed through the police organizational culture. Not only do these constructions influence the ways in which officers perceive themselves and their environments, but they also operate at the collective level to 'normalize' some emotional responses and to 'pathologize' others which, it is argued, could impact upon the outcomes of interventions such as stress counselling.     

The moderating role of social support in Karasek's job strain model

This paper examines whether social support is a boundary-determining criterion in the job strain model of Karasek (1979). The particular focus is the extent to which different sources of social support, work overload and task control influence job satisfaction, depersonalization and supervisor assessments of work performance. Hypotheses are tested using prospective survey data from 80 clerical staff in a university setting. Results revealed 3-way interactions among levels of support (supervisor, co-worker, non-work), perceived task control and work overload on levels of work performance and employee adjustment (self-report). After controlling for levels of negative affect in all analyses, there was evidence that high levels of supervisor support mitigated against the negative effects of high strain jobs on levels of job satisfaction and reduced reported levels of depersonalization. Moreover, high levels of non-work support and co-worker support also mitigated against the negative effects of high strain jobs on levels of work performance. The results are discussed in terms of the importance of social support networks both at, and beyond, the work context.     

Job insecurity, coping resources and personality dispositions in occupational strain

This paper presents research on the relationships between the work-related stressor of perceived job insecurity and various indicators of occupational strain, taking into account employees' personality dispositions (trait negative and positive affectivity) and coping resources. Respondents were 222 Australian public servants surveyed during organizational restructuring that involved downsizing and threat to job certainty. The research was formulated within an adaptation of Osipow, Doty, and Spokane's (1985) framework of stress-strain-coping that included the possible direct as well as moderating effects of personality dispositions in reporting occupational strain (Parkes, 1990). Findings from hierarchical regression analyses indicate consistent significant independent effects of personality dispositions, coping resources and perceived job insecurity on various indicators of strain. There was also support for the moderating roles of negative affectivity and self-care in the relation between perceived job insecurity and physical strain. Implications for the role of dispositional factors, especially negative affectivity, and the utility of various coping resources in accounting for occupational strain in times of threatened job security are discussed.     

Job stress, job strain, and psychological withdrawal among Dutch university staff: towards a dualprocess model for the effects of occupational stress

This study examined the antecedents of job strain (emotional exhaustion, health complaints) and withdrawal behaviour (e.g. lowered organizational commitment) among a cross-sectional sample of 131 academic staff members of the law department of a large Dutch university. Conservation of resources theory (Hobfoll, 1989) provided the theoretical background for this study. Strains and withdrawal behaviours were expected to be most prominent among those who reported having few resources and/or who reported high job demands. Structural equation modelling revealed that this was indeed the case. As predicted, differential patterns of effects emerged for job demands and job resources. Analysis of the effects of four job-specific stressors revealed that especially the structural aspects of a staff member's teaching task (e.g. the number of students in their classes) contributed strongly to perceived job demands. Theoretical and practical implications of the study are discussed.     

Employees' perceptions of organizational restructuring: the role of social support

Organizational change and restructuring is often perceived as leading to increased occupational stress, impacting negatively on the psychological well-being of employees. This pragmatic study investigates the role of social support and dispositional affect as moderators of role stress post-restructuring for employees in a public utility company. A total of 176 employees, including 37 managers, 60 graded staff and 78 industrial staff completed a self-report questionnaire, approximately 1 year postrestructuring, retrospectively assessing role conflict, ambiguity, overload and positive and negative feedback pre- and post-restructuring. Results suggested that overall role stress increased for managers/ senior officers and graded staff, but not for industrial staff. Social support was linked with lower role stress, more positive feedback and less negative feedback at post-restructuring. For certain role stressors this impact was moderated by dispositional affect, but the effect was not consistent across occupational groups. Positive affect enhanced the effect of manager support in reducing role conflict for graded staff, and the effect of co-worker support in increasing positive feedback and reducing negative feedback for industrial staff. Findings suggest that managers should pay particular attention to support and feedback for employees during periods of chronic occupational stress following organizational restructuring.     

The Danish psychosocial work environment and symptoms of stress: the main, mediating and moderating role of sense of coherence

The aim of this cross-sectional study was to explore the main, mediating and moderating role of sense of coherence (SOC) on stress symptoms and on the association between perceived psychosocial work environment and stress symptoms. The sample includes 2053 Danish employees from 52 workplaces. Hierarchical regression models were applied for each measure of stress. The results strongly supported the presence of a main effect for SOC. People with high levels of SOC experienced fewer stress symptoms. A mediating effect of SOC was also supported. Thus, SOC in part explained the association between work environment and stress symptoms. In addition, some support for a moderating effect of SOC was found, suggesting that people with higher SOC coped more efficiently with work environmental strain that people with lower SOC. Taken together the regression models explained 11-32% of the variance in stress symptoms. The results suggest that measures of individual factors such as SOC should be included in analyses of the effects of work environmental factors on stress and well-being.     

Control at work: a generalized resource factor for the prevention of musculoskeletal symptoms?

During the last two decades two potent groups of predictors for work-related musculoskeletal problems have been identified: physical work load and poor psychosocial working conditions. However, little is known about their combined effects. In this study the buffering effect of control at work with respect to the negative effects of psychological demands and physical work load on musculoskeletal problems is examined. All study variables were sampled from 431 people working in geriatric nursing homes in Germany by means of questionnaires. Main effects and interactions were tested with multiple regression analysis. The results showed that control buffered the effects of high psychological demands, but not of high physical work load; the buffering effect of control was observed only when physical work load was low. The combined effects of demands and physical work load were over-additive. Thus, the power of different predictors for musculoskeletal symptoms depended on the level of other predictors. This suggests that the efficiency of certain strategies for the prevention of musculoskeletal problems is likely to depend on the level of risk factors, with different strategies being appropriate for different levels of risk.