A sequential production line is defined as a set of sequential operations within a factory or distribution center whereby entities undergo one or more processes to produce a final product. Sequential production lines may gain efficiencies such as increased throughput or reduced work in progress by utilizing specific configurations while maintaining the chronological order of operations. One problem identified by the authors via a case study is that, some of the configurations, such as work cell or U-shaped production lines that have groups of buffers, often increase the space utilization. Therefore, many facilities do not take advantage of the configuration efficiencies that a work cell or U-shaped production line provide. To solve this problem, the authors introduce the concept of a buffer cluster. The production line implemented with one or more buffer clusters maintains the throughput of the line, identical to that with dedicated buffers, but with the clusters reduces the buffer storage space. The paper derives a time based parametric model that determines the sizing of the buffer cluster, provides a reduced time space for which to search for the buffer cluster sizing, and determines an optimal buffer clustering policy that can be applied to any N-server, N+1 buffer sequential line configuration with deterministic processing time. This solution reduces the buffer storage space utilized while ensuring no overflows or underflows occur in the buffer. Furthermore, the paper demonstrates how the buffer clustering policy serves as an input into a facility layout tool that provides the optimal production line layout.
In this paper we investigate the use of lot streaming in non-permutation flowshop scheduling problems. The objective is to minimize the makespan subject to the standard flowshop constraints, but where it is now permitted to reorder jobs between machines. In addition, the jobs can be divided into manageable sublots, a strategy known as lot streaming. Computational experiments show that lot streaming reduces the makespan up to 43% for a wide range of instances when compared to the case in which no job splitting is applied. The benefits grow as the number of stages in the production process increases but reach a limit. Beyond a certain point, the division of jobs into additional sublots does not improve the solution.
This paper formulates robust optimization models for the problem of finding near-optimal locations for new intermodal terminals and their capacities for a railroad company, which operates an intermodal network in a competitive environment with uncertain demands. To solve the robust models, a Simulated Annealing (SA) algorithm is developed. Experimental results indicate that the SA solutions (i.e. objective function values) were comparable to those obtained using GAMS, but the SA algorithm could obtain solutions faster and could solve much larger problems. In addition, the results verify that solutions obtained from the robust models were more effective in dealing with uncertain demand scenarios.
The social exchange perspective seeks to acknowledge, understand and predict the dynamics of social interactions. Empirical research involving social exchange constructs have grown to be highly technical including confirmatory factor analysis to assess construct distinctiveness and structural equation modeling to assess construct causality. Each study seemingly strives to assess how underlying social exchange theoretic constructs interrelate. Yet despite this methodological depth and resultant explanatory and predictive power, a significant number of studies report findings that, once synthesized, suggest an underlying persistent threat of conceptual or construct validity brought about by a search for epistemological parsimony. Further, it is argued that a methodological approach that embraces inherent complexity such as activity systems modeling facilitates the search for simplified models while not ignoring contextual factors.
It is well-known that subjects can exhibit a preference for increasing payments. Smith (2009a) [Smith, J. (2009a). Imperfect Memory and the Preference for Increasing Payments. Journal of Institutional and Theoretical Economics, 165(4), 684-700.] makes a related prediction that the difference between the preference for increasing wage payments and the preference for increasing non-wage payments will be largest for intermediate payments. We find evidence consistent with this prediction. Consistent with previous experiments, we find that the preference for increasing payments is increasing in the size of the payments. Also consistent with the literature, we find that the preference for increasing wage payments is stronger than the preference for non-wage payments. Our results contribute to the understanding of the optimal sequencing of wage payments over time.
This study intends to evaluate the impacts of implementing online marketing strategies on Iranian ecotourism industry. The study had eight hypotheses which were designed based on economic, sociological, and cultural aspects of Iranian ecotourism industry. The results indicate that the expansion of online marketing increased the number of foreign tourists who visited Iran’s natural tourist attractions, while it had no significant impact on the number of domestic tourists who visited these tourist attractions. The results also indicated that online marketing did not increase the amount of investment in Iranian ecotourism industry. Additionally, online ecotourism marketing did not have a significant influence on the total number of travels to Iran’s historical tourist attractions. Respondents believe implementing online marketing strategies in Iranian ecotourism industry helps Iran expand its cultural tourism in rural areas and it expands its hospitality industry; they also believe that online marketing helps to create more jobs in Iranian ecotourism industry and to improve working conditions in this industry.
Sending men to space has never been an ordinary activity, it requires years of planning and preparation in order to have a chance of success. The payoffs of reliable and repeatable space flight are many, including both Commercial and Military opportunities. In order for reliable and repeatable space flight to become a reality, catastrophic failures need to be detected and mitigated before they occur. It can be shown that small pieces of a design which seem ordinary can create devastating impacts if not designed and tested properly. This paper will address the use of a Failure Mode, Effects, and Criticality Analysis (FMECA) with modified Risk Priority Number (RPN) and its application to safety critical design components of shuttle liftoff. An example will be presented here which specifically focuses on the Solid Rocket Boosters (SRBs) to illustrate the FMECA approach to reliable space travel.
This paper studies the relationship between principals’ reward power and their conflict management styles. The five conflict management styles that we use in this study are based on Thomas-Kilmann Conflict Mode Instrument and include accommodating, avoiding, collaborating, competing, and compromising styles. This study can be classified as a regression analysis and is a descriptive study. Our statistical society for this research included all principals of high schools located in the city of Birjand. The results indicated that there was a significant relationship between principal’s reward power and accommodating conflict management style. The results also revealed that there was no significant relationship between principals’ reward power and the other four conflict management styles.
This paper summarizes the reaction of DABCO with the enol tosylate derivatives made from (L-Ser-L-Ser) and (L-Phe-L-Ser) diketopiperazines (DKP’s). The reaction between DABCO and EE-di-tosylate (L-Ser-L-Ser) DKP (2), results in the isomerization of the serine di-tosylate from EE-2 to ZZ-2. This is the first direct example of the utility of DABCO as a reagent demonstrating the successful isomerization in a DKP derivative. The E-enol tosylate of (L-Phe-L-Ser) DKP (4) upon reaction with DABCO provided a unique bis-ylidiene product (5).