@article{KellnerUtz2019, author = {Florian Kellner and Sebastian Utz}, title = {Sustainability in supplier selection and order allocation: combining integer variables with Markowitz portfolio theory}, journal = {Journal of Cleaner Production}, volume = {214}, pages = {462 -- 474}, doi = {10.1016/j.jclepro.2018.12.315}, year = {2019}, }