On the Introduction of an Agile, Temporary Workforce into a Tandem Queueing System

We consider a two-station tandem queueing system where customers arrive according to a Poisson process and must receive service at both stations before leaving the system. Neither queue is equipped with dedicated servers. Instead, we consider three scenarios for the fluctuations of workforce level. In the first, a decision-maker can increase and decrease the capacity as is deemed appropriate; the unrestricted case. In the other two cases, workers arrive randomly and can be rejected or allocated to either station. In one case the number of workers can then be reduced (the controlled capacity reduction case). In the other they leave randomly (the uncontrolled capacity reduction case). All servers are capable of working collaboratively on a single job and can work at either station as long as they remain in the system. We show in each scenario that all workers should be allocated to one queue or the other (never split between queues) and that they should serve exhaustively at one of the queues depending on the direction of an inequality. This extends previous studies on flexible systems to the case where the capacity varies over time. We then show in the unrestricted case that the optimal number of workers to have in the system is non-decreasing in the number of customers in either queue.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/47647/1/11134_2005_Article_2441.pd

Just One of the ‘PIIGS’ or a European Outlier? Studying Irish Emigration from a Comparative Perspective

The return of high levels of emigration has become one of the most debated and sensitive social topics in Ireland in recent years. But Irish emigration continues to be discussed in the singular rather than the plural. This paper compares Irish emigration to other Eurozone states that also encountered serious economic difficulties following the onset of the global financial crisis to highlight international trends and specify national differences. All of the ‘PIIGS’ experienced increased emigration after the crisis. Yet Irish citizens left in much greater numbers per capita than their Eurozone counterparts, with only Portugal bearing any similarities. This was because Irish emigrants possessed valuable transnational human, cultural and social capital that enabled them to access liberal labour markets outside the Eurozone. They possessed skills desired by attractive destination states; they spoke the same language and shared similar cultural traits as their hosts; and they were able to call upon recently renewed Irish networks to further facilitate their move abroad.Seventh Framework Programme (FP7)info:eu-repo/grantAgreement/EC/FP7/332409Cities, Migration and Global Interdependenc

Labeling and qualification of endothelial progenitor cells for tracking in tissue engineering: An in vitro study

Purpose: In order to track location and distribution of endothelial cells (ECs) within scaffolds in vitro, we chose lentiPGK-TdTomato transduction of human endothelial progenitor cells (EPCs) isolated and differentiated from cord blood. Because transduction could have a functional impact on cell behavior, we checked different parameters for qualification of labeled-EPCs as well as their use for potential applications in the context of vascular and bone tissue engineering.Methods: After isolation and expansion, EPCs were classically characterized then transduced with the lentiviral vector containing the TdTomato protein gene under the control of the phosphoglycerate kinase (PGK) promoter. Conventional karyotyping, differentiation capacity, viability, proliferation assays were performed with labeled and unlabeled EPCs. Scaffolds and co-cultures were explored with labeled EPCs, in static or shear stress conditions.Results: Our results show that cell labeling did not affect cell adhesion nor induce cell death. Cell labeling did not induce more chromosomal aberrations. Phenotypical characterization was not affected. In the context of tissue engineering applications, labeled EPCs maintained their ability to line 2D or 3D scaffolds, withstand physiological arterial shear stress, and form tubular networks in co-cultures with human osteoblast progenitor cells.Conclusions: It is possible to label human EPCs with TdTomato without affecting their behavior by the transduction procedure. This creates an important tool for numerous applications. Our results provide a qualification of labeled EPCs in comparison with unlabeled ones for vascular and bone tissue engineering