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The previous Decentralised Cognitive Medium Access Control (DC-MAC) protocol allows Secondary Users (SUs) to independently search for spectrum access opportunities without the need for a central coordinator. DC-MAC assumes that the detection scheme is ideal at the Physical (PHY) layer. In fact, a more complex detection algorithm is impractical in distributed spectrum sharing scenarios. Energy Detection (ED) at the PHY layer has become the most common method because of its low computational and implementation complexities. Thus, it is essential to integrate the DC-MAC with ED at the PHY layer. However, ED requires the Minimum Sampling Time (MST) duration to achieve the target detection probability in low Signal-to-Noise Ratio (SNR) environments. Otherwise, it cannot achieve the expected detection performance. In this paper, we derive an accurate expression of MST for ED in low SNR environments. Then, we propose an Optimised DC-MAC (ODC-MAC) protocol which is based on MST, and which amends the aforementioned problems of DC-MAC with ED. Moreover, the closed-form expressions for the unreliable data transmission probability are derived for both DC-MAC and ODC-MAC. We show that the simulation results agree well with the theoretical analyses. The proposed ODC-MAC can improve the data transmission reliability and enhance the throughput compared to the performance of the traditional DC-MAC.

Summary: The cytogenetics and clinical stigmata in 5 cases of Turner’s syndrome were studied. Three of them were non-mosaic i(Xq) and two with partial monosome of a X chromosome short are (Xp21). whose DNA replication patterns of inactive X chromosome were analyzed by RBG technique. Results showed that differences between the replication patterns in cases of X chromosome deletion (Xp21) and normal females existed; that the behavior of abnormal X expressed nonrandom inactivation. It was suggested that the phenotype may be closely related with both X chromosome replication pattern and its inactivation behavior, which might be useful in genetic counselling.

An extended 5-generation family has been investigated in which 32 of the 111 family members were diagnosed as having retinitis pigmentosa (RP). The proband was a 58-year old male in whom night-blindness was first observed in early childhood, with almost loss of vision by 52 years of age. The symptoms observed in other family members included night-blindness, impaired vision and visual field loss. Dementia, digital abnormalities, deaf-mutism and mental retardation were variously diagnosed in a number of individuals with RP. The affected and unaffected family members were tested for mutations in a range of candidate genes. The 8 exons of three candidate genes have been analyzed by polymerase chain reaction-single strand conformation polymorphism (PCR-SSCP) and DNA sequencing techniques. A novel mutation was identified in the rhodopsin gene at codon 52 of exon 1 (TTC-TAC) that resulted in a substitution of Phe to Tyr.