Conrado Borraz-Sánchez Roger Z. Ríos-Mercado A Hybrid Meta-heuristic Approach for Natural Gas Pipeline Network Optimization. 54-65 2005 conf/hm/2005 Hybrid Metaheuristics http://dx.doi.org/10.1007/11546245_6 db/conf/hm/hm2005.html#Borraz-SanchezR05