Remaining useful life (RUL) prediction plays a crucial role in prognostics and health management (PHM). Recently, the adaptive model-based RUL prediction, which is proven effective and flexible, has gained considerable attention. Most research on adaptive degradation models focuses on the Wiener process. However, since the degradation process of some products is accumulated and irreversible, the inverse Gaussian (IG) process that can describe monotonic degradation paths is a natural choice for degradation modelling. This article proposes a nonlinear adaptive IG process along with the corresponding state space model considering measurement errors. Then, an improved particle filtering algorithm is presented to update the degradation parameter and estimate the underlying degradation state under the nonGaussian assumptions in the state space model. The RUL prediction depending on historical degradation data is derived based on the results of particle methods, which can avoid high-dimensional integration. In addition, the expectationmaximization (EM) algorithm combined with an improved particle smoother is developed to estimate and adaptively update the unknown model parameters once newly monitored degradation data become available. Finally, this article concludes with a simulation study and a case application to demonstrate the applicability and superiority of the proposed method.INDEX TERMS Adaptive model, inverse Gaussian process, measurement errors, remaining useful life.

A layered compound with superior selectivity and removal ability toward 90Sr over a wide pH range.

The study of the reaction between plutonium and nitrogen is helpful to further understand the interaction between plutonium and air gas molecules. For the nitridation reaction of plutonium, there is no report on the microscopic reaction mechanism of this system at present. Therefore, the microcospic mechanism of gas phase reaction of Pu with N2 is studied in this paper based on the density functional theory (DFT) using different functions. In this paper, the geometry of stationary points on the potential energy surface is optimized. In addition, the transition states are verified by the frequency analysis method and the intrinsic reaction coordinate (IRC) method. Finally, we obtain the reaction potential energy curve and the micro reaction pathways. The analysis of reaction mechanism shows that the reaction of Pu with N2 has two pathways. The pathway-1 (Pu+N2→R1→TS1→PuN2) has a T-shaped transition state and the pathway-2 (Pu+N2→R2→TS2→PuN+N) has a L-shaped transition state. Moreover, both transition states have only one virtual frequency. The energy analysis shows that pathway-1 is the main reaction pathway. The nature of the Pu-N bonding evolution along the pathways is studied by atoms in molecules (AIM) and electron localization function (ELF) topological approaches. In order to analyse the role of 5f orbital of plutonium atom in the reaction, the variation of density of state along the pathways is performed. The results show that the 5f orbital makes major contributions to the formation of Pu-N bonds. Meanwhile, the influence of different temperatures on the reaction rate is revealed by calculating the rate constants of the two reaction pathways.