Editors-in-Chief
B. Fraboni and G. García López
The authors wish to thank the anonymous reviewers for their helpful comments and suggestions. They are also grateful to EPJP for their corrections pertaining to the English language.

E. Tala-Tebue, University of Dschang, Bandjoun, Cameroon

ISSN: 2190-5444 (Electronic Edition)

© Società Italiana di Fisica and
Springer-Verlag

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