Dynamic assessment of stable operation capability and performance efficiency for air-ground cooperative networks under various shock scenarios, such as adverse weather and equipment failures, is critical for ensuring network reliability. This paper proposes a multi-state air-ground cooperative network reliability evaluation and multi-stage performance analysis approach for city aviation and railway infrastructure. First, a comprehensive network architecture is established that incorporates aviation and railway passenger transport systems along with their operational interdependencies. Subsequently, a multi-state failure-recovery process model is developed to characterize network reliability under different shock scenarios. Next, a three-tier cost analysis framework is introduced to quantify revenue losses, image losses, and operational costs under various shock scenarios. A multi-stage performance model is then proposed, integrating resistive, degraded, recovery, and comprehensive performance efficiency indicators to capture dynamic network behavior throughout the entire disruption cycle. The primary advantage of this framework lies in its capability to systematically assess network reliability while providing actionable insights for performance optimization through targeted improvement strategies. Experimental validation using air-ground cooperative networks from three adjacent provinces in China demonstrates the effectiveness of the proposed approach. For the Air-Dominant and Rail-Supplementary (ADRS) and Bilayer Air-Rail Parallel (BARP) network modes, after implementing improvement strategies, the comprehensive performance efficiency improved by 0.0154 and 0.0872 respectively under general failure scenarios, and by 0.0563 and 0.0542 respectively under extreme failure scenarios.
Proton exchange membrane fuel cell (PEMFC) stacks with dead-ended anode often suffer from anode flooding and inefficient hydrogen utilization. This study investigates the combined effects of anode operational parameters on an air-cooled PEMFC stack integrated with micro heat pipe arrays. Through experiments and an algorithm-based multi-objective optimization, key performance metrics under different hydrogen supply pressure, and purging strategy are analyzed and the optimal operating strategy is carried out. Results show that increasing the hydrogen supply pressure from 40 kPa to 90 kPa improves output power by 5.2 % and reduces the voltage fluctuation coefficient (VFC) by 75 %, enhancing voltage stability. However, cell voltage uniformity deteriorates with increasing current; as current rises from 5 A to 40 A, inter-cell voltage variation increases by 140 %. Moreover, reducing the purging ratio from 5.88 % to 1.96 % leads to 43.5 % and 41.7 % increases in VFC and standard deviation, respectively, indicating decreased voltage stability. To balance power output, voltage stability, and hydrogen efficiency, a multi-objective optimization framework is developed. At 40 A, the optimized parameters yield a 7.9 % increase in power and a 3.5 % improvement in hydrogen utilization, while maintaining the VFC below 5 %. These findings provide practical insights for optimizing anode operating conditions of PEMFC technology.
With the ongoing exploitation of fossil resources, oil extraction is increasingly shifting toward decentralized and small-scale oil extraction stations. These stations commonly rely on diesel generator-powered electric heating or air-source heat pumps (ASHP) for heat supply, resulting in high energy consumption and significant carbon emissions. To achieve low-carbon and efficient heating in oilfields while ensuring a reliable heat supply under low-temperature conditions, this study proposes a dual-source multi-mode photovoltaic-thermal (PVT) heat pump system. The system innovatively integrates PVT modules, finned-tube heat exchangers (FTHE), and a cascade refrigeration system. It also introduces four operating modes to ensure efficient performance under varying conditions: PVT direct-drive boost mode, dual-source cooperative mode, air-source single-stage and cascade mode. An experimental setup of the dual-source multi-mode PVT heat pump system was constructed and tested. Experimental results demonstrate that the proposed system can supply hot water at 62.5 degrees C at an ambient temperature of -23.9 degrees C. Through mode switching, the system stably and efficiently provides 55 degrees C hot water across different operating conditions. When the PVT module participates in the circulation, the average coefficient of performance (COP) increases by 21.98%, and the average heating capacity improves by 59.15%. The proposed system ensures a stable heat supply by leveraging the synergy of multiple energy sources while substantially lowering both operational energy consumption and carbon emissions.
In this article, a single-channel frequency-modulated continuous-wave (FMCW) radar based on a 1-bit time-modulated array (TMA) is proposed. By utilizing the spectrum folding phenomenon introduced by harmonics dechirping, the frequency spectrums of beat signals generated by different harmonics are distributed in independent frequency areas, thereby avoiding target ambiguity caused by spectrum crossing and achieving the single-channel estimation of target range, velocity, and direction. The theory of range, velocity, and direction estimation based on the multiharmonic power reconstruction (MHPR) method is established. Meanwhile, the constraint condition among modulation frequency, target range, and target velocity for avoiding target ambiguity is derived. Compared with conventional single-channel FMCW radar based on switched antenna array (SAA), which employs time-division multiplexing, the proposed system improves the array reception efficiency significantly by using 1-bit time-modulation modules to enable all antenna elements to simultaneously receive echo signals. Moreover, the advantage of the proposed system is that the echo signals are received continuously in the time domain, which avoids the velocity-direction coupling problem introduced by time-division reception in a conventional single-channel system. Hence, the independent detection of range, velocity, and direction for high-speed moving targets can be achieved in the proposed system. Numerical simulations are provided to verify the performance of the proposed system, and a C-band eight-element 1-bit TMA is constructed to experimentally verify its feasibility. Simulation results show that compared with the SAA radar, the beat signal power is increased, and the beat frequency estimation error is reduced. The direction-finding accuracy is improved for high-speed targets.
Airborne radar forward-looking imaging (FLI) is a crucial technique with applications in various fields. To enhance imaging performance, super-resolution (SR) methods from array signal processing are introduced, enabling high-resolution FLI. Among SR approaches, compressed sensing (CS) combined with array radar offers a promising approach. However, conventional CS reconstruction algorithms require prior knowledge of sparsity, which is often unavailable in practice. Although some algorithms, like the sparsity adaptive matching pursuit (SAMP), do not require sparsity, their performance can be hindered by ineffective stopping criteria. To address this, we propose a modified algorithm based on SAMP, named MSAMP. MSAMP employs a novel stopping criterion and a more suitable reconstruction process tailored for airborne radar FLI without requiring sparsity. Compared to some existing FLI algorithms, such as orthogonal matching pursuit (OMP) and iterative adaptive approach (IAA), MSAMP demonstrates low time complexity and competitive reconstruction performance.
