List of Articles Hierarchical Models Open Access Article Abstract Page Full-Text 1 - Developing a New Bi-Objective Functions Model for a Hierarchical Location-Allocation Problem Using the Queuing Theory and Mathematical Programming Parham Azimi Abulfazl Asadollahi 10.22094/joie.2018.350.0 20.1001.1.22519904.2019.12.2.12.1