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Hydrogen recirculation ejectors are commonly used to achieve anode exhaust recirculation in proton exchange membrane fuel cell systems to obtain higher fuel efficiency. By adopting variable-nozzle designs in traditional fixed-nozzle ejectors, recirculation rates under low loads and the operating range of ejectors can both be improved. In this study, the design methods of different variable-nozzle structures for a 40 kW-grade ejector are proposed. A 2D numerical model is subsequently constructed and experimentally validated to investigate the influence of nozzle structures, needle profiles and needle protrusion length on entraining performance and control linearity. The results indicate that the variable-nozzle designs take greater effects at lower loads in increasing the entrainment ratio. Convergent nozzles with short throats are optimal for variable-nozzle ejectors due to their more significant and linear performance improvement. Adopting frustum needles or radical-function needles further enhances the linearity to over 0.96 across all power levels, but increasing needle diameters results in a reduction in the entrainment ratio. Additionally, the maximum needle insertion depth should be kept below 5.0 mm to minimize performance loss caused by excessive needle protrusion. • A convergent nozzle with a short throat is optimal for variable-nozzle designs. •Frustum needles and radical-function needles both significantly improves the control linearity. •Increasing needle diameters or protruding length leads to the reduction in entraining ability. •The needle insertion depth should be kept below 5.0 mm to minimize performance loss. [ABSTRACT FROM AUTHOR]

Ejectors are ideal hydrogen recirculation devices for PEMFC systems but typically exhibit poor recirculation performance at low loads. For purpose of extending ejector's operating range in vehicular applications, the entraining performance across multiple loads should be focused. In this study, A 40 kW ejector was designed with a 1D theory and optimized using a 2D CFD model. Simulations were conducted to study the influence of various diameter and axial dimensions on the ejector's performance and flow characteristics. The results reveal that as the load increases from 20% to 100%, the suboptimal diffuser exit diameter decreases from 2.5 to 1.5 times the mixing chamber diameter, the optimal nozzle exit position increases from 0.59 to 0.63 times, and the optimal mixing chamber length increases from 2.2 to 4.3 times. A convergent nozzle with a short throat significantly improves low-load entraining performance and achieves the highest performance growth in the variable-nozzle design. Additionally, an optimization method for axial dimensions based on the proposed parameter flow uniformity was established, allowing for precise determination of the optimal dimensions through a few simulations. •Convergent nozzles outperform convergent-divergent nozzles in low-load entraining performance. • A convergent nozzle with a short throat is more suitable for the variable-nozzle design. • Optimal values of various diameter and axial dimensions at multiple loads were obtained. • The parameter flow uniformity is proposed, which can be used as criteria for determining optimal axial dimensions. [ABSTRACT FROM AUTHOR]

Periodic anode purges can remove excessive liquid water and nitrogen in the anode to mitigate hydrogen starvation in PEMFCs caused by flooding and nitrogen buildup. Experiments were conducted on a vehicular PEMFC stack to evaluate influences of operating conditions including current density, cathode flowrate, hydrogen recirculation and working pressures on performance decline during operations with anode purges. The accumulation of anode impurities was characterized by voltage decrease, voltage uniformity and anode pressure swing. The results reveal that anode flooding develops greatly with increasing current density. An optimal hydrogen recirculation pump speed of 1000 rpm substantially improves voltage stability and uniformity of the stack. High cathode pressure accelerates the impurity accumulation in the anode, while high anode pressure facilitates the removal of nitrogen. When the stack works with a constant pressure difference of 10–20 kPa between two electrodes, nitrogen buildup in the anode can be minimized and flooding becomes the primary contributor to performance decline under automotive operating conditions. As current density rises to 300–700 mA/cm2, the optimal pressure difference increases from 10.2 to 14.7 kPa. • An optimal recirculation rate greatly improves voltage stability and uniformity. • Anode nitrogen buildup can be minimized with a constant pressure difference. • The optimal pressure difference rises with the increase of current density. • Pressure swing at anode inlet reflects flooding development in the anode. [ABSTRACT FROM AUTHOR]

Higher-order interactions (HOIs) are ubiquitous in real systems, and HOIs among individuals complicate the exploration of species diversity for populations in ecosystems. Therefore, understanding how higher-order interactions affect biodiversity is essential but poses significant challenges. In this paper, we consider higher-order interactions in the competitive processes of spatial rock-paper-scissors (RPS) dynamics, specifically within spatially embedded hyper-lattices, and investigate what biodiversity can be driven by HOIs. Considering hyperedges, species in hyperedges can be different, and different relationships are considered, which can eventually demonstrate the strength of competition. With the competition intensity modulated by the sensitivity of HOIs, extensive simulations have shown that higher-order competitive processes can promote coexistence. We also found that stratification of species densities occurs when three species coexist due to HOIs, which are closely related to the increase of empty sites and disordered spiral entanglement. From investigating the extinction probability in a broad aspect, it has been found that, even if HOIs are working, the coexistence in the system is eventually broken at high mobility regimes. The intensified sensitivity to HOIs can somewhat alleviate extinction, although no striking change has occurred. Our findings may address that modeling predator-prey interactions incorporating HOIs is important for gaining insights into biodiversity, and we hope our study may provide a broad aspect for exploring complex ecosystems. • We introduced higher-order interactions (HOIs) in the competitive processes of a spatial rock-paper-scissors game. • We employed spatially embedded hyper-lattices for spatial dynamics. • Hyperedges constituted by various combinations of species and relationships demonstrate the strength of competition. • Introducing HOIs promotes species coexistence. • Increasing sensitivity to HOIs can mitigate extinction somewhat. [ABSTRACT FROM AUTHOR]

Rewards, as a form of positive reinforcement, effectively encourage cooperation. In this paper, we study a multi-population prisoner's dilemma game with asymmetric rewards, where agents in the same population play prisoner's dilemma game, and agents from the giver population can reward agents from the recipient population only if they make the same choice. In well-mixed populations, asymmetric rewards can facilitate cooperation. Similarly, asymmetric rewards on the regular square lattice can effectively prevent complete defection. In both well-mixed and structured populations, seemingly disadvantageous cooperative givers play an important role in the maintenance and spread of cooperation. Especially on lattice, cooperative givers with asymmetric rewards can be active in the system through diverse cases of cyclic dominance. Our findings provide deeper insights into the impact of asymmetry on cooperative behavior and the development of altruistic behavior in real-world scenarios. • We study the prisoner's dilemma game with asymmetric rewards in both well-mixed and regular square lattice. • In both well-mixed and structured populations, asymmetric rewards can significantly promote cooperation. • In the asymmetric system, the cooperative givers play an important role in the maintenance and spread of cooperation. [ABSTRACT FROM AUTHOR]

For analyzing ejector's performance in the system, an ejector for a 10 kW polymer electrolyte membrane fuel cell (PEMFC) system was first designed, manufactured, and a 10 kW PEMFC system bench was built up. A proportional valve and PI pressure feedback control method were adopted to control the hydrogen supply and anode inlet pressure. During the test, performances between dead-ended anode (DEA) mode and ejector mode were compared. Ejector's performances in the system, i.e., volume flow recirculated ratio, difference pressure, dynamic responses of primary pressure, anode inlet pressure, and recirculated gas flow rate during the purge process and current variation condition, were investigated. The results show that pressure adjustment is accurate, continuous, and fast using the proportional valve and PI pressure feedback control method. The hydrogen consumption rate in the ejector mode can reduce from 5% to 10% compared with the rate in the DEA mode except for the stack current 5 A and 10 A conditions. For better water removal out of the anode channel in ejector mode, the maximum stack power increases from 5.11 kW (DEA mode) to 9.56 kW (ejector mode). Anode pressure surge caused by the purge valve switching enhances the ejector's recirculated performance significantly. • An ejector for a 10 kW PEMFC system is designed, manufactured and evaluated. • The stack in ejector's mode shows a better performance than that in DEA mode. • Hydrogen recirculation can reduce the hydrogen consumption. • The proportional valve with the PI pressure feedback method can accurately control the anode inlet pressure. • Anode pressure surge can enhance ejector's recirculated performance. [ABSTRACT FROM AUTHOR]

Distributions of water and oxygen concentration are the two main factors that influence the consistency of current density in a polymer electrolyte membrane fuel cell. While the former type is relevant to the ohmic loss, the latter one associated with the mass transfer loss. In a self-humidified condition, higher demand for water management is requested as membrane drying often appears. To investigate the effects of flow pattern and hydrogen recirculation on the consistency of current density, the cell is tested under five different conditions, and a quasi-three-dimensional transient non-isothermal model is developed to explain different experimental phenomena in this study. Differences of distributions of current density, resistance and reaction gases are examined by comparing co-flow with counter-flow conditions, humidified with self-humidified conditions and dead-ended anode with hydrogen recirculation conditions. The results show that consistency reduces with the cell current density increasing, and gas humification is significantly beneficial. In co-flow configurations, the standard deviation of local current density increases from 0.02 at 0.2 A cm−2 to 0.14 at 1.2 A cm−2 under the humidified condition, increasing from 0.38 at 0.2 A cm−2 to 0.26 at 1.2 A cm−2 under the self-humidified condition. The water distribution of the cell in counter-flow configuration is more uniform than that in the co-flow configuration under the whole current density conditions. Hydrogen recirculation can improve the water content of segments near the inlet gas channel in the anode, and the consistency is the best when the current density is larger than 0.4 A cm−2. • A segmented single cell model is developed. • It has a higher demand for water management in a self-humidified condition. • Consistency in counter-flow configuration is better than that in co-flow way. • Recycled vapor in anode can improve consistency of local current density. [ABSTRACT FROM AUTHOR]

• Based on an activity-driven network, a model dividing individuals into two types, one is risk-ignorant, and the other is risk-averse who may reduce the potential risk of infection by being less social intensity is established. • The outbreak of an epidemic depends most on the proportion of risk-averse individuals. • A large number of risk-averse individuals who change their social intensity raises the theoretical threshold and reduces the epidemic size, thus suppressing the outbreak. • As risk-averse individuals increases, the epidemic is eliminated under small spreading rates. In human society, individual interactions intrinsically change, with profound implications for epidemics. The activity-driven model, a type of temporal network, offers an excellent framework to study epidemic processes in dynamical interaction. In this work, we study how social attitudes affect the transmission of infectious diseases in activity-driven networks. Here, we divide a population into "risk-ignorant" and "risk-averse", in which risk-averse individuals will reduce their social intensity (Social intensity refers to the number of social contacts in the social process) and risk-ignorant individuals will not. A parameter p controls the proportion of risk-averse individuals, and therefore risk-ignorant individuals by 1- p. With the aid of mean-field theory, we calculate epidemic thresholds, as well as validate theoretical predictions with extensive Monte Carlo simulations. It is shown numerically and theoretically that reducing the social intensity and increasing the number of risk-averse individuals are effective ways of controlling epidemic outbreaks. An appropriate proportion of the risk-averse individual will lead to an epidemic die-out, which is based on a small spreading rate. Our research provides a new perspective for understanding the effect of the population with different social attitudes in the epidemic process. [ABSTRACT FROM AUTHOR]

The maintenance of biological diversity has perpetually remained a central focus in the field of ecology. In the pursuit of enhanced survival rates, species have begun to explore cooperation with one another. However, the consequences of such collaboration remain largely unexplored. To delve into this matter, we introduce intraspecific cooperation within the framework of the classic rock-paper-scissors (RPS) game. In this model, the competition rate is intricately tied to interactions among individuals of the same species. A greater population of individuals from the same species tends to lead to an increased predation rate and a decreased prey rate. Through extensive simulations, we observe that (i) in the case of homogeneous intraspecific cooperation (all three species have intraspecific cooperation), increased cooperation between predators tends to increase the likelihood of species coexistence. In contrast, high levels of cooperation between prey appeared to decrease the favorability of species coexistence. Measurements of the characteristic length of spiral structures revealed that the characteristic length of spirals became longer when the intensity of prey cooperation increased. (ii) In the case of heterogeneous intraspecific cooperation (two species or only one species with intraspecific cooperation), neither an increase in the intensity of intraspecific cooperation of the predator nor an increase in the intensity of intraspecific cooperation of the prey is favorable for species coexistence. Our work underscores the critical role of intraspecific cooperation in maintaining biodiversity. • In rock-paper-scissors games, intraspecific cooperation promotes and jeopardizes biodiversity. • Under homogeneous intraspecific cooperation, predator cooperation promotes coexistence. • Under heterogeneous intraspecific cooperation, both predator and prey cooperation jeopardize coexistence. [ABSTRACT FROM AUTHOR]

In the real world, a single homogeneous or heterogeneous network is very rare, so we consider a compound model which contains two different types of subnetworks. The compound model may be applied to analyze the contagion dynamics of two different communities where they have a probability to communicate. The global infection threshold is obtained, and many factors affecting spread of epidemics are analyzed, including subnetwork density, subnetwork size, connecting probability and the maximum degree. An interesting phenomenon is that we find the transition points of the global threshold from increasing to decreasing, which was not mentioned in previous work. Therefore, we give many measures to improve infection threshold and prevent the spread of epidemics. The experimental results confirm the conclusions of epidemic analysis. • The spreading process of epidemics on a mixed model is studied. • The transition points of epidemic threshold from increasing to decreasing are given. • Many factors to affect the global epidemic threshold are analyzed. • Many measures to prevent the spread of epidemics are proposed. [ABSTRACT FROM AUTHOR]

• Aspiration-based exit option in prisoners dilemma game can promote cooperation. • In structured population, the intermediate aspiration level promotes cooperation, because defectors around the cooperative cluster exit the game, which weakens the exploitation of cooperators, and help the cooperators at the edge of the cooperative cluster to expand to inactive nodes or the defectors through network reciprocity. • The combined effect of aspiration level and dilemma strength affects the active state of players. Cooperation is promoted in the structured population when individual has the exit option and it is found that aspiration driven updating rules can also promote cooperation to a certain extent. The right to exit gives individuals the opportunity to get rid of exploitation, and the aspiration is the self-evaluation of individuals. Stimulated by these, we study the effect of aspiration driven exit on cooperation in the spatial prisoner dilemma game. In the game, the aspiration level and payoff of interactive determine the individual's state. When the individual gets more than aspiration level by interacting with other players, the individual will continue to participate in the game as an active player. On the contrary, when the payoff is lower than the aspiration level, individual exits the game as an inactive player. At the same time, inactive player who exits from the game will get random payoff and pay a certain cost. The promotion of cooperative behavior mainly depends on the aspiration level of players. An appropriate level of aspiration will lead to a high cooperation, which is based on the formation of cooperative clusters. These cooperators can get rid of the invasion of defectors, even if there is a great temptation of defection, this is because the inactive defectors who exit have cut off the interaction between the cooperative cluster and the defectors. Our research provides a feasible way to solve the social dilemma and will stimulate further application. [ABSTRACT FROM AUTHOR]

• We consider the repeated pairwise prisoner's dilemma game among two groups of agents. • We found that the mixed strategy-update rule (Q-learning-based update rule and Fermi-function-based update rule) can evaluate cooperation. • If the proportion of AI is moderate, cooperators among the whole population exhibit conditional behavior and moody conditional behavior. Recent studies show that different update rules are invariant regarding the evolutionary outcomes for a well-mixed population or homogeneous network. In this paper, we investigate how the Q-learning algorithm, one of the reinforcement learning methods, affects the evolutionary outcomes in square lattice. Especially, we consider the mixed strategy update rule, among which some agents adopt Q-learning method to update their strategies, the proportion of these agents (these agents are denoted as Artificial Intelligence (AI)) is controlled by a simple parameter ρ. The rest of other agents, the proportion is denoted by 1 − ρ, adopt the Fermi function to update their strategies. Through extensive numerical simulations, we found that the mixed strategy-update rule can facilitate cooperation compared with the pure Fermi- function-based update rule. Besides, if the proportion of AI is moderate, cooperators among the whole population exhibit conditional behavior and moody conditional behavior. However, if the whole population adopts the pure Fermi-function-based strategy update rule or the pure Q-learning-based strategy update rule, then cooperators among the whole population exhibit the hump-shaped conditional behavior. Our results provide a new insight to understand the evolution of cooperation from AI's view. [ABSTRACT FROM AUTHOR]

• Lupus-prone mouse has endothelial dysfunction. • RORα is decreased in aorta of lupus-prone mouse and in SLE medium treated HUVECs. • Melatonin prevents endothelial dysfunction in SLE by activating RORα. Atherosclerotic cardiovascular disease confers significant morbidity and mortality in patients with systemic lupus erythematosus (SLE). A substantial proportion of patients with SLE display accelerated endothelial dysfunction, which precedes cardiovascular disease. Melatonin and its nuclear receptor retinoid-related orphan receptor alpha (RORα) have been reported to have some protective effects on the development of atherosclerosis. However, the function of melatonin in SLE-induced endothelial dysfunction and the role that RORα plays are still unknown. In this study, we found that RORα protein expression was decreased in aortas of lupus-prone mice and in human umbilical vein endothelial cells (HUVECs) cultured with medium containing sera of patients with SLE. Melatonin-treated HUVECs showed a decrease of pro-inflammatory mRNAs [interleukin-1beta (IL-1β), interferon-gamma (IFN-γ), and tumor necrosis factor-alpha (TNF-α)] under the stimulation of SLE medium. Melatonin increased nitric oxide and antioxidant mRNAs (SOD1 , GPX1 , and CAT) and downregulated reactive oxygen species (ROS) level in HUVECs, which may subsequently delay endothelial senescence and promote HUVEC proliferation and repair after injury. Melatonin inhibited SLE medium-induced RAW264.7 macrophage migration. HUVECs pretreated with melatonin expressed less adhesion-related proteins (ICAM-1 and VCAM-1); as a result, these cells adhered to fewer peripheral blood monocytes. In addition, we also showed that the protective effects of melatonin on endothelial cells were largely diminished when RORα was knockdown in HUVECs. In conclusion, by targeting the nuclear receptor RORα, melatonin preserves normal functions of endothelium in SLE by its anti-inflammatory, antioxidant, and anti-senescence effects. RORα may have the potential to become a prophylactic or therapeutic target in preventing endothelial dysfunction and atherosclerotic cardiovascular disease in patients with SLE. [ABSTRACT FROM AUTHOR]