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    • European Journal of Operational Research
    Authors: Thuy Anh Ta; Wyean Chan; Fabian Bastin; Pierre L’Ecuyer;  Advisor: -;  Co-Author: - (2021)

    We study a solution approach for a staffing problem in multi-skill call centers. The objective is to find a minimal-cost staffing solution while meeting a target level for the quality of service to customers. We consider a common situation in which the arrival rates are unobserved random variables for which preliminary forecasts are available in a first stage when making the initial staffing decision. In a second stage, more accurate forecasts are obtained and the staffing may have to be modified at a cost, to meet the constraints. This leads to a challenging two-stage stochastic optimization problem in which the quantities involved in the (nonlinear) constraints can only be estimated via simulation, so several independent simulations are required for each first-level scenario. We p...
    • A simulation-based decomposition approach for two-stage staffing optimization in call centers under arrival rate uncertainty
    Authors: Ta, Thuy Anh;  Advisor: Chan, Wyean; Bastin, Fabian; L’Ecuyer, Pierre;  Co-Author: - (2021)

    We study a solution approach for a staffing problem in multi-skill call centers. The objective is to find a minimal-cost staffing solution while meeting a target level for the quality of service to customers. We consider a common situation in which the arrival rates are unobserved random variables for which preliminary forecasts are available in a first stage when making the initial staffing decision. In a second stage, more accurate forecasts are obtained and the staffing may have to be modified at a cost, to meet the constraints. This leads to a challenging two-stage stochastic optimization problem in which the quantities involved in the (nonlinear) constraints can only be estimated via simulation, so several independent simulations are required for each first-level scenario. We p...
    • Numerical analysis of deformation and breakup of a compound droplet in microchannels
    Authors: Nguyen, Cuong T.;  Advisor: Vu, Hung V.; Vu, Truong V.; Truong, Thuan V.; Ho, Nang X.; Pham, Binh D.; Nguyen, Vinh T.; Nguyen, Hoe D.;  Co-Author: - (2021)

    Compound droplets with different sizes are increasingly used in industrial production and academic research. This study aims to improve understanding of the dynamical behaviors of the compound droplet moving in microchannels. The compound droplet consisting of one inner core is initially concentric and placed at the entrance of a circular channel with a cone at the downstream region. Following this primary channel is a secondary channel that is circular and straight. Manipulation of the droplet is assisted by a flow introduced via the gap between two channels. The numerical results show that when passing through these confined channels, the droplet experiences a finite deformation or breakup mode. In each mode, the deformation or breakup of the compound droplet is also different whe...