Rules for manuscript withdrawal: If the authors would like to withdraw their manuscript before acceptance, please inform the editorial office and proceed with relevant procedures as soon as possible. Once the manuscript is accepted, withdrawal of the manuscript is not allowed in principle. If the authors definitely need to withdraw the manuscript due to personal reasons, an application for manuscript withdrawal is required as well as associated fee compensations such as a review fee, editing fee, polishing fee, and typesetting fee. After two instances of manuscript withdrawal subsequent to acceptance due to the authors’ personal reasons, the authors will be automatically added to the blacklist of our journal alliance.