in this paper, we consider a cooperative cognitive radio network in which there is an ofdm primary link and multiple single carrier secondary links.the primary link is required to maintain its secrecy rate above a predefined threshold. if the secrecy rate requirement is not satisfied, the secondary system help primary link to maintain its secrecy rate requirement. in doing so, the secondary trans...

Sternal tumors are very rare and challenging. Secondary sternal tumors are more common than primary tumors. These tumors are usually refractory to chemotherapy and radiotherapy, and surgery is the best choice for their treatment. In this study, we reported the collected data of 15 patients with primary and secondary tumors of the sternum, histological type, as well as kind of resection and reco...

  Objective: Secondary caries is a common problem in dental treatments and its occurrence is attributed to several factors. The present study aimed at assessing the prevalence of secondary caries in posterior teeth of patients presenting to the Department of Operative Dentistry, Shahid Beheshti Dental School.   Methods: This descriptive study was conducted on 350 patients with 1,339 posterior t...

a module m is called epi-retractable if every submodule of m is a homomorphic image of m. dually, a module m is called co-epi-retractable if it contains a copy of each of its factor modules. in special case, a ring r is called co-pli (resp. co-pri) if rr (resp. rr) is co-epi-retractable. it is proved that if r is a left principal right duo ring, then every left ideal of r is an epi-retractable ...