Jia Li-Qun, Sun Xian-Ting, Zhang Mei-Ling, Zhang Yao-Yu, Han Yue-Lin. Generalized Hojman conserved quantity deduced from generalized Lie symmetry of Appell equations for a variable mass mechanical system in relative motionJ. Acta Physica Sinica, 2014, 63(1): 010201. DOI: 10.7498/aps.63.010201