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A high-sensitive and transverse-stress compensated methane sensor based on a photonic crystal fiber long-period grating (PCF-LPG) is proposed. The outermost layer of the PCF consists of six large sideholes, five of which are coated with methane-sensitive compound film to achieve methane measurement. Such side-hole structure is helpful for gas sensitive reaction, but not conducive to avoiding external stress interference. Therefore, the last large hole is plated with silver layer to eliminate the cross-sensitivity effect through adding a Surface Plasmon Resonance (SPR) sensing channel with the consideration of photo-elastic effect and material deformation. Results show that the methane gas sensitivity can reach up to 6.39nm/% with the transverse-stress compensation. The sensor is very simple and effective, which provides a new method of gas measurement combined with different actual conditions.

With the rapid development of the Internet of Things, the emerging botnet attacks have become more rampant and harmful. In order to detect botnet, the method based on artificial intelligence is proposed in the paper, which detects the domain name of the core C&C server in the botnet. The corresponding detection model is established and 9 types of features are given for the algorithm. Particularly, we apply the pronunciation features and TLD features into machine learning to improve the accuracy of botnet detection. We use statistical methods to reduce the false positive rate. The results of statistical method are fed back to the corpus, so that generalization ability of the machine learning model is continuously strengthened. After continuous optimization, the final model accuracy can reach up to 99.38%, the false positive rate is 0.28%, and the false negative rate is 1.86% in the testing environment. Meanwhile, our detection method can also effectively detect more than 2000 botnet C&C domain names from the real-world network environment in 4 months.

A temperature-compensated methane sensor with high sensitivity based on magnetic fluids infiltrated photonic crystal fiber is proposed. The methane concentration sensitivity is 20.07nm/% with a good linearity of 0.99999.

In this note, we investigate the problem of stabilization for second order switched systems by means of output feedback control and switching design. Under mild conditions, we design the output feedback and switching signal to exponentially stabilize the switched systems. Meanwhile, we optimize the switching signal to achieve nonovershooting of the output.

In this note, we investigate the problem of bounded-input bounded-output (BIBO) stability for continuous-time switched linear systems under arbitrary switching. We show that BIBO stability is equivalent to exponential stability under mild assumptions, which is an extension of the well-known relationship between external and internal stability for linear systems.