-Secure in-network aggregation in Wireless Sensor Networks (WSNs) is a necessary and challenging task. In this paper, we first propose integration of system monitoring modules and intrusion detection modules in the context of WSNs. We propose an Extended Kalman Filter (EKF) based mechanism to detect false injected data. Specifically, by monitoring behaviors of its neighbors and using EKF to predict their future states (actual in-network aggregated values), each node aims at setting up a normal range of the neighbors' future transmitted aggregated values. This task is challenging because of potentially high packet loss rate, harsh environment, sensing uncertainty, etc. We illustrate how to use EKF to address this challenge to create effective local detection mechanisms. Using different aggregation functions (average, sum, max, and min), we present how to obtain a theoretical threshold. We further apply an algorithm of combining Cumulative Summation (CUSUM) and Generalized Likelihood Ratio (GLR) to increase detection sensitivity. To overcome the limitations of local detection mechanisms, we illustrate how our proposed local detection approaches work together with the system monitoring module to differentiate between malicious events and emergency events. We conduct experiments and simulations to evaluate local detection mechanisms under different aggregation functions.
Te 3 ) have been reported to exhibit a pressure-induced isostructural phase transition (IPT) in the low-pressure region (<5 GPa); however, the underlying mechanism is not fully understood yet. Here, we comparatively investigated the IPTs in a-Bi 2 Se 3 and a-Bi 2 Te 3 using high-pressure Bi L 3 -edge X-ray absorption fine structure spectroscopy, complemented with density functional theory (DFT) calculation. Near the IPT, the slope of the Bi L 3 -edge absorption energy shows a sudden decrease. In contrast to the monotonous shortening of the Bi-Bi bond-distance under compression, it is moreover rather surprising that the Bi-Se2 (Te2) and Bi-Se1 (Te1) bonddistances exhibit abnormal elongations around the IPT, which is synchronized with abrupt increases for their Debye-Waller factor. DFT calculation results show that near the IPT a structural distortion may appear for extremely small energy barrier. Those results indicate that each quintuple layer unit shrinks along the layer direction but elongates perpendicular to the layers at the onset of the IPT, which would be associated with a remarkable increase for the local structural disorder. Therefore, our findings suggest that the IPTs in a-Bi 2 Se 3 and a-Bi 2 Te 3 are coupled with a simultaneous charge redistribution and structural distortion accompanied with a static structural disorder increase.Sketch of the changes of local structure of centric Bi and lattice structure around the IPT.
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