Evaluation of scheduling strategies for a dynamic job shop in a tool-shared,flexible manufacturing environment

A two-phase approach is used to examine the impact of job scheduling rules and tool selection policies for a dynamic job shop system in a tool-shared, flexible manufacturing environment. The first phase develops a generalized simulation model and analyses 'simple' job scheduling rules and tool selection policies under various operating scenarios. The results from this investigation are then used to develop and analyse various bi-criteria rules in the second phase of this study. The results show that the scheduling rules have the most significant impact on system performance, particularly at high shop load levels. Tool selection policies affect some of the performance measures, most notably, proportion of tardy jobs, to a lesser degree. Higher machine utilizations can be obtained at higher tool duplication levels but at the expense of increased tooling costs and lower tool utilization. The results also show that using different processing time distributions may have a significant impact on shop performance.     

A nonparametric hypothesis test for heteroscedasticity

In this paper, a hypothesis test for heteroscedasticity is proposed in a nonparametric regression model. The test statistic, which uses the residuals from a nonparametric fit of the mean function, is based on an adaptation of the well-known Levene's test. Using the recent theory for analysis of variance when the number of factor levels goes to infinity, the asymptotic distribution of the test statistic is established under the null hypothesis of homocedasticity and under local alternatives. Simulations suggest that the proposed test performs well in several situations, especially when the variance is a nonlinear function of the predictor.     

Subsampling-extrapolation bandwidth selection in bivariate kernel density estimation

This paper focuses on bivariate kernel density estimation that bridges the gap between univariate and multivariate applications. We propose a subsampling-extrapolation bandwidth matrix selector that improves the reliability of the conventional cross-validation method. The proposed procedure combines a U-statistic expression of the mean integrated squared error and asymptotic theory, and can be used in both cases of diagonal bandwidth matrix and unconstrained bandwidth matrix. In the subsampling stage, one takes advantage of the reduced variability of estimating the bandwidth matrix at a smaller subsample size m (m < n); in the extrapolation stage, a simple linear extrapolation is used to remove the incurred bias. Simulation studies reveal that the proposed method reduces the variability of the cross-validation method by about 50% and achieves an expected integrated squared error that is up to 30% smaller than that of the benchmark cross-validation. It shows comparable or improved performance compared to other competitors across six distributions in terms of the expected integrated squared error. We prove that the components of the selected bivariate bandwidth matrix have an asymptotic multivariate normal distribution, and also present the relative rate of convergence of the proposed bandwidth selector.     

Prediction of future failures times based on Type-I hybrid censored samples of random sample sizes

In this article, we consider the prediction of future failure times based on Type-I hybrid censored samples. Point predictors and prediction intervals using different procedures are discussed for a general model. The exponential and Rayleigh distributions are used as illustrative examples to show the most simplified forms of the so obtained predictors as well as prediction intervals. Intensive simulation study and a real life dataset are presented to illustrate our findings and results.     

Moving targets: determinants of nutritional preferences and habitat use in an urban ant community

Urban environments are often associated with reduced biodiversity, presumably because they are typically more fragmented, warmer, and drier than nearby non-urban environments. However, urban landscapes offer significant complexity that have allowed some taxonomic groups to flourish. Understanding how urban-exploiting animals navigate this spatiotemporal heterogeneity is important given the continued global urban land expansion. Here, we examined the factors influencing resource-use in an urban community of ants, which represent a widespread and important taxon in urban ecosystems. In particular, we sought to integrate ants’ nutritional, thermal, and spatial niches to better understand how urban animals successfully access critical resources throughout their active season. Meteorological season (spring, summer, and fall) and/or species (n?=?9) influenced ants’ preferences for nutrition (ratio of ingested protein-to-carbohydrate ratio), as well as the temperature, type (impervious vs. non-impervious), and shade status (shaded vs. non-shaded) of surfaces used during activity. Our data also indicate links among habitat variables, as well as between nutritional preferences and habitat use. Together, our results suggest that species and seasonality influence ecological (combined nutritional, thermal, and spatial) niches in an urban community. We encourage future work in urban ecosystems that continues to integrate more features of the ecological niche, and to examine the outcomes of variation in niches (e.g., non-overlapping niches may explain both the persistence of some native animals and the success of invaders).     

The middling mobile: finding place in the liquid city

The middling mobile, differentiated by their modest and unsure mobility, are a vast of bulk of people who intend or expect to move on. As they travel, they tread differing intensities of rhythm and social embeddedness felt to be chaotic, constraining, liberating, or comforting. Owing to their aspirations to ‘get out’ of a rhythmic life, or to move somewhere familiar, the middling mobile use movement and rootedness to navigate and manage everyday life in the liquid city. My analysis offers a holistic exposition of a life that flows between mobility/immobility and rhythmic/arrhythmic forms, and the transitions between them.     

Multidimensional self-esteem as a mediator of the relationship between sports participation and victimization: a study of African American girls

The purpose of this study that focused on African American high school girls was threefold. First, the relationship of sports participation and victimization was explored. Second, the impact of sports participation on self-esteem was assessed. Third, the role of self-esteem and its disaggregated components (social acceptance, competence, and self-confidence) as mediators of the relationship between sports participation and victimization was examined. In accordance with the sport protection hypothesis, it was hypothesized that sports participation would be related to enhanced self-esteem and reduce victimization. Results suggest that sports participation appears to have some relationship to lower rates of victimization. There was also support for our assertion that sports participation was related to enhanced self-esteem. Finally, overall self-esteem and, specifically, the individual component competence mediated the relationship between sports participation and victimization.     

Innovation in user-centered skills and performance improvement for sustainable complex service systems

In order to leverage individual and organizational learning and to remain competitive in current turbulent markets it is important for employees, managers, planners and leaders to perform at high levels over time. Employee competence and skills are extremely important matters in view of the general shortage of talent and the mobility of employees with talent. Two factors emerged to have the greatest impact on the competitiveness of complex service systems: improving managerial and employee's knowledge attainment for skills, and improving the training and development of the workforce. This paper introduces the knowledge-based user-centered service design approach for sustainable skill and performance improvement in education, design and modeling of the next generation of complex service systems. The rest of the paper cover topics in human factors and sustainable business process modeling for the service industry, and illustrates the user-centered service system development cycle with the integration of systems engineering concepts in service systems. A roadmap for designing service systems of the future is discussed. The framework introduced in this paper is based on key user-centered design principles and systems engineering applications to support service competitiveness.     

Residential Remittances and Food Security in the Upper West Region of Ghana

In recent years, out migration from the Upper West Region to the southern belt of Ghana for farming has become commonplace. The natural question that has arisen is: what is the potential impact of remittances from this migration pattern on food security in the region? Using multivariate ordered logistic regression this study assesses the linkage between remittances and household food security (derived using the HFIAS) among urban and rural households (n=1,438) in the region. The findings show that urban remittance‐receiving households and rural remittance and non‐remittance receiving households were more likely (OR=2.44, p<0.05; OR=2.46, p<0.001; and OR=1.49, p<0.1, respectively) to report being more severely food‐insecure than urban non‐remittance receiving households. The findings demonstrate that household strategies such as migration and remittances on their own are not sufficient to ameliorate the precarious food insecurity situation of the region. The study calls for development of alternative livelihoods in the region.