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The aim of this study has been to develop a data-driven analytical methodology for prediction of isolated track geometry defects, based on the measurement data obtained from a field study. Within the study, a defect-based model has been proposed to identify the degradation pattern of isolated longitudinal level defects. The proposed model considered the occurrence of shock events in the degradation path. Furthermore, the effectiveness of tamping intervention in rectifying the longitudinal level defects was analysed. The results show that the linear model is an appropriate choice for modelling the degradation pattern of longitudinal level defects. In addition, a section-based model has been developed using binary logistic regression to predict the probability of occurrence of isolated defects associated with track sections. The model considered the standard deviation and kurtosis of longitudinal level as explanatory variables. It has been found that the kurtosis of the longitudinal level is a statistically significant predictor of the occurrence of isolated longitudinal level defects in a given track section. The validation results show that the proposed binary logistic regression model can be used to predict the occurrence of isolated defects in a track section.

Cognitive radio network (CRN) is an emerging technology that can increase the utilization of spectrum underutilized by primary users (PUs). In the literature, most exiting investigations on CRNs have focused on how secondary users (SUs) can coexist harmlessly with the PUs. Despite the importance of such a coexistence issue, it is also crucial to investigate the coexistence of SUs because (i) the PUs usually rarely use the licensed spectrum and (ii) the advantages of CRN will significantly increase the number of SUs in the future. To address this challenging issue, we propose, in this paper, an optimal randomized spectrum access scheme, whose main ideas include the following: (i) an SU shares its sensing results with neighboring SUs and (ii) with the regional sensing results, an SU will access available channels with a non-uniform probability distribution. We first formulate a multichannel optimal randomized multiple access (MC-ORMA) problem that aims to maximize the throughput of the CRN; we then develop efficient distributed algorithms to solve the MC-ORMA problem; we derive the closed-form value of collision probability for each SU; and finally, we conduct extensive numerical experiments and compare our theoretical analysis with simulation results to demonstrate the advantages of our scheme.MAXDIV: AN OPTIMAL RSA WITH MAXIMUM DIVERSITY SCHEME FOR CRNS 833 Although the aforementioned design goal is very important to CRN, we argue that it is also crucial to further investigate the coexistence of SUs with the objective of maximizing the utilization of spectrum resources. The first motivation is the fact that in a common CRN scenario, PUs rarely use the licensed spectrum (e.g., with only 5-15% utilization). Moreover, in some CRN scenarios, such as the TV broadcast channels [5], the activities of PUs are predictable and can even be known in advanced. The second motivation is that the current situation of CRN is quite similar to that of Wi-Fi 10 years ago. In wireless local area network, the spectrum resources would be shared among many wireless devices; the collisions of the devices hugely decrease the throughput of the wireless network. Therefore, many researches were paid on this issue, and many efficient schemes were proposed in that time. However, in CRN, the situation is different. SUs may not directly use the spectrum resources because they may be occupied by licensed users. The first conflict is between PUs and SUs. The second one is the conflict among SUs, that is, how to access the available spectrums that have been verified by spectrum sensing. At this point, the second conflict is similar to the Wi-Fi network one decade ago. It is reasonable to envision that the number of CR-equipped devices will soar in the foreseeable future. As a result, coexistence among SUs is also a critical issue to improve the CRN's throughput.In this paper, the optimal coexistence problem of SUs in a CRN will be addressed. In particular, a novel approach has been proposed to optimally access spectrum, whose main ideas include the...

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