Due to the large number of spam user registrations, the Captcha for new user registration has been changed to a more challenging verification, and validation of email address is also required. New users need to click the activation link sent to the user's email address. However, some email address hosting providers (such as Yahoo) are not compatible with our SMTP. The webmaster will review new accounts daily and manually activate your account. At the same time, the author can send a registration request or directly submit the manuscript to the editor's email: bzhang@futureenergysp.com.