A comprehensive understanding of spatially non-uniform degradation under high current density conditions is essential for health management of proton exchange membrane fuel cell (PEMFC). In this study, a segmented PEMFC is subjected to a 600-hour durability test at 2.0 A & sdot;cm-2. PEMFC is uniformly divided into 11 equal segments (S1-S11, 21 mm each) along air flow direction from inlet to outlet. At end-of-life (EOL), the average platinum particle radius increases to 2.52 nm in segment S11 and 3.35 nm in segment S1. This non-uniform platinum irreversible degradation reduces current density in segments S1-S4, while increases current density in segments S5-S11. Meanwhile, during operation periods, the current density decreases in segments S1 and S8S11 but increases in segments S2-S7, confirming the spatially non-uniform reversible degradation. To interpret these observations, a three-dimensional degradation model is developed incorporating platinum Oswald ripening, coalescence and ionomer sulfonate adsorption. The model reveals that the difference in ionomer water content between operation periods and recovery steps accelerates sulfonate coverage onto platinum, with coverage ratio reaching 0.15-0.437 in segments S1-S2 and S8-S11, thereby inducing severe reversible degradation. Reversible degradation modifies the spatial evolution of electrochemical active surface area (ECSA) under irreversible degradation, shifting ECSA distribution from an initially low-inlet/high-outlet pattern to a middle-peaked profile. In contrast, the spatial trend of proton conductivity degradation remains consistent with that driven by irreversible degradation. This study provides a predictive PEMFC model for non-uniform degradation under high current density, offering guidance for the development of PEMFC health management and degradation mitigation strategies.
Continuous tracking and high-precision localization of objects within specified regions using space-based optical remote sensing systems represents a critical frontier for future space surveillance capabilities. To address this, this paper formulates a real-time multi-fold regional coverage constellation scheduling problem based on MEO satellite constellations, enabling real-time multi-fold coverage of various regions of interest on demand. To solve this problem, we propose a coverage vision-based DRL algorithm, which integrates satellite ground coverage distribution image as coverage vision into the mission planning framework, thereby avoiding the need for manual feature engineering, while also achieving improved learning efficiency compared to traditional state based DRL methods. The algorithm design employs a Recurrent PPO framework that incorporates Long Short-Term Memory networks to capture temporal dependencies in sequential observations, and implements invalid action masking within the PPO policy update to enforce satellite attitude maneuver constraints. Simulation results demonstrate that, compared with classical metaheuristic algorithms, the proposed method achieves superior performance in both coverage effectiveness and computational efficiency. (c) 2025 COSPAR. Published by Elsevier B.V. All rights are reserved, including those for text and data mining, AI training, and similar technologies.
The Chinese Space Station Survey Telescope (CSST) is an upcoming Stage-IV sky survey telescope, distinguished by its large field of view (FoV), high image quality, and multi-band observation capabilities. It can simultaneously conduct precise measurements of the Universe by performing multi-color photometric imaging and slitless spectroscopic surveys. The CSST is equipped with five scientific instruments, i.e., Multi-band Imaging and Slitless Spectroscopy Survey Camera (SC), Multi-Channel Imager (MCI), Integral Field Spectrograph (IFS), Cool Planet Imaging Coronagraph (CPI-C), and THz Spectrometer (TS). Using these instruments, CSST is expected to make significant contributions and discoveries across various astronomical fields, including cosmology, galaxies and active galactic nuclei (AGN), the Milky Way and nearby galaxies, stars, exoplanets, Solar System objects, astrometry, and transients and variable sources. This review aims to provide a comprehensive overview of the CSST instruments, observational capabilities, data products, and scientific potential.
An efficient approximation-based optimization framework is proposed for concurrent topology and mixed-variable sizing (discrete- and continuous-valued) problems. Unlike conventional metaheuristics that directly explore the combinatorial space at high computational cost, the method constructs a series of explicit subproblems using an adjusted branched multi-point approximation technique. Move limits for topology and both types of size variables are adaptively controlled to ensure stability. An improved genetic algorithm with hybrid encoding and multi-level operators is designed to solve each approximate subproblem. The initial population is generated based on the concept of adjacent individuals,and tailored crossover and mutation operators subsequently maintain the proximity of solutions to prior optima,balancing approximation stability and population diversity. The strategy is verified through benchmark cases including truss structures, rib-stiffened shells, composite laminates, and sandwich panels and further applied to satellite structural optimization. The results demonstrate that the framework achieves competitive solution quality with only several to dozens of structural and sensitivity analyses required, which is far fewer than direct metaheuristic searches, thus significantly improving optimization efficiency for complex engineering structures.
In this paper, a novel rigid-flexible coupled satellite with a fixed space net is studied, which has significant advantages in deep space exploration, space-based power generation and space debris removal. The flexible space net is characterized by large deformation and low-frequency vibration, which severely impact the satellite attitude. A dynamic model of a continuous rigid-flexible system that considers the geometric nonlinearity of the space net is established. Furthermore, to account for the low-frequency vibration characteristics and locally fixed boundary conditions of the space net, two sets of vibration displacement functions for its in-plane and out-of-plane vibrations are proposed to discretize the continuous system. The accuracy of the established dynamic model is subsequently verified in both the frequency and time domains using a finite element model (FEM) and multibody dynamics (MBD), respectively. Several numerical examples are studied to analyze the complex dynamic behavior and reveal the motion mechanism of the rigid-flexible coupled system. The simulation results demonstrate that the tangential vibration of the space net primarily affects the satellite's roll and yaw attitude, whereas the radial and axial vibrations mainly influence the pitch attitude. Additionally, the contribution of tangential vibration to the satellite's three-axis attitude disturbance is approximately 42.3%, whereas the contributions of radial and axial vibrations are approximately 27.3% and 30.4%, respectively.
