1. Karelian Institute, University of Eastern Finland, 80101 Joensuu, Finland
2. Department of Economics and Statistics, University of Salerno, 84084 Fisciano, Italy
3. CF Energy Service SRL, Altavilla Silentina, 84045 Salerno, Italy
4. School of Information Technology, Zhejiang Financial College, Hangzhou 310018, China
5. Department of Agricultural Sciences, University of Naples Federico II, 80055 Portici, Italy