Dear authors, readers, and librarians, our volume 19 issue 2 of 2020 has been published. It is a little bit late due to several circumstances. We made an improvement in this issue. Our articles are mainly in English to accommodate our international authors and readers.

We are sincerely grateful for the work done by our esteemed reviewers and appreciate the authors for their excellent papers submitted to this journal.

Finally, have fun reading this issue. We do hope that it will bring new research perspectives.