A novel method to estimate derailment probability due to track geometric irregularities using reliability techniques and advanced simulation methods

Track irregularities have a dramatic impact on the response and vibration of a railway vehicle and on the interaction between wheel and rail. The random nature of the track structure and constituent materials and the effects of other factors such as maintenance conditions and transit traffic give rise to the random nature of track irregularities. This research provides a method to estimate the derailment probability of a railway vehicle where track irregularities are assumed to be random, and the interaction of the track and the moving train is considered using advanced dynamic analysis. For this purpose, the limit state function of derailment was estimated using the response surface method and advanced simulation. The probability of derailment was then estimated using a Level 3 reliability method.     

Dual-Output Mach–Zehnder Modulator for Optical Access Networks

This paper employs dual-output Mach–Zehnder Modulator (MZM) for optical access networks without optical filters. Light waves generated from multiple laser sources are multiplexed and fed into dual-output MZM. Biasing the dual-output MZM at null point generates central carriers in one output port and first-order sidebands in another output port. Reflective semiconductor optical amplifier modulates both the central carriers and sidebands with wired and wireless data, respectively. The modulated optical signals are combined by polarization beam splitter and transmitted through 25-km single-mode fiber. The performance of the proposed scheme is proved by clear eye-diagrams and great bit error rate (BER) curves. Moreover, the power penalty at the BER of 10^-9 is less than 1 dB for both wired and wireless signals. Therefore, the proposed system simultaneously transmits wired and wireless signals.