The hydrophilic hollow construction of HZIF-8 enhanced the water retention of composite membrane and reduced the proton transfer resistance throughout HZIF-8. More importantly, the proton conducting ...routes at both the GO@HZIF-8 surfaces and GO@HZIF-8/Nafion interfaces became relatively connective benefitting from the tethering function of GO. These combinedly resulted in outstanding proton transportation ability of composite membrane.
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•GO@HZIF-8 was constructed as an efficient proton transfer accelerator.•Proton transfer of composite PEM was effectively accelerated by GO@HZIF-8.•Composite PEM exhibited distinctly promoted fuel blocking ability.•Maximum current density and power density of composite PEM were greatly improved.
Interconnected hollow metal–organic framework (MOF) network (GO@HZIF-8) was designed as an efficient proton transfer accelerator in Nafion membrane. GO@HZIF-8 was constructed by in situ synthesis of ZIF-8 onto graphene oxide (GO) and succedent etching with tannic acid (TA). The hollow construction and surface TA functionalization of hollow ZIF-8 (HZIF-8) bestowed composite membrane with superior water retention. This was highly beneficial to the rapid proton transfer. Besides, the hollow construction could effectively reduce the proton transfer resistance onto GO@HZIF-8. More importantly, the interconnective architecture between HZIF-8 by the tethering function of GO and the interfacial hydrogen bond interaction between GO@HZIF-8 and Nafion resulted in connective proton transfer routes at GO@HZIF-8 surfaces and GO@HZIF-8/Nafion interfaces. These dramatically accelerated the proton transfer of GO@HZIF-8/Nafion composite membrane, enabling a considerable proton conductivity (PC) of 0.301 S cm−1 under 90 °C, 95 % RH, ∼1.33-fold greater than that of the pure Nafion membrane (RN). Moreover, the composite membrane exhibited a peak power density of 45.8 mW cm−2, ∼1.22-fold higher than that of RN. These results menifest that constructing hollow MOF network possesses grand prospect in the construction of high performance proton exchange membranes (PEMs).
Work-matched high-intensity intermittent cycling training (HIICT) reportedly improves VO2max regardless of the combination of loads and cadences. However, the effect of work-matched HIICT with ...different combinations of loads and cadences on anaerobic work capacity is unknown. This study aims to investigate the effects of work-matched HIICT with different loads and cadences on Wingate anaerobic test (WAnT) performance, which is an index of anaerobic work capacity. University athletes performed HIICT either with high-load / 60 rpm (HL60, n = 8) or low-load / 120 rpm (LL120, n = 8). HIICT consisted of eight sets of pedaling for 20 s with 10 s of passive rest between each set. Initial exercise intensity was set at 135% of VO2peak and decreased by 5% after every two sets. HIICT was performed for 18 sessions during the 6-week period. Pre and post the training period, peak power, peak rpm, average power, and time to reach peak power during WAnT and VO2peak were measured. According to two-way analysis of variance (time × group), the main effect of time was observed in VO2peak, peak power, peak rpm, and average power during WAnT (p < 0.05). However, time × group interaction was not observed for any indices (p > 0.05). Conversely, time × group interaction was observed in time to reach peak power during WAnT, and significantly shortened only in HL60 (p < 0.05). These results suggest the effectiveness of work-matched HIICT with high-load / low cadence on WAnT performance.
Key points
Critical power represents an important threshold for neuromuscular fatigue development and may, therefore, dictate intensities for which exercise tolerance is determined by the magnitude ...of fatigue accrued.
Peripheral fatigue appears to be constant across O2 delivery conditions for large muscle mass exercise, but this consistency is equivocal for smaller muscle mass exercise.
We sought to determine the influence of blood flow occlusion during handgrip exercise on neuromuscular fatigue development and to examine the relationship between neuromuscular fatigue development and W ′.
Blood flow occlusion influenced the development of both peripheral and central fatigue, thus providing further evidence that the magnitude of peripheral fatigue is not constant across O2 delivery conditions for small muscle mass exercise.
W ′ appears to be related to the magnitude of fatigue accrued during exercise, which may explain the reported consistency of intramuscular metabolic perturbations and work performed for severe‐intensity exercise.
The influence of the muscle metabolic milieu on peripheral and central fatigue is currently unclear. Moreover, the relationships between peripheral and central fatigue and the curvature constant (W ′) have not been investigated. Six men (age: 25 ± 4 years, body mass: 82 ± 10 kg, height: 179 ± 4 cm) completed four constant power handgrip tests to exhaustion under conditions of control exercise (Con), blood flow occlusion exercise (Occ), Con with 5 min post‐exercise blood flow occlusion (Con + Occ), and Occ with 5 min post‐exercise blood flow occlusion (Occ + Occ). Neuromuscular fatigue measurements and W ′ were obtained for each subject. Each trial resulted in significant peripheral and central fatigue. Significantly greater peripheral (79.7 ± 5.1% vs. 22.7 ± 6.0%) and central (42.6 ± 3.9% vs. 4.9 ± 2.0%) fatigue occurred for Occ than for Con. In addition, significantly greater peripheral (83.0 ± 4.2% vs. 69.0 ± 6.2%) and central (65.5 ± 14.6% vs. 18.6 ± 4.1%) fatigue occurred for Occ + Occ than for Con + Occ. W ′ was significantly related to the magnitude of global (r = 0.91) and peripheral (r = 0.83) fatigue. The current findings demonstrate that blood flow occlusion exacerbated the development of both peripheral and central fatigue and that post‐exercise blood flow occlusion prevented the recovery of both peripheral and central fatigue. Moreover, the current findings suggest that W ′ may be determined by the magnitude of fatigue accrued during exercise.
In this article, the peak-power expression of dissipative-soliton-resonance (DSR) pulse is derived, in a normal-dispersion fiber laser, by using the equation for the resonance curve and the ...relationship between the parameters of cubic–quintic complex Ginzburg–Landau (CGLQ) equation and the cavity parameters. According to the peak-power expression, the peak power of DSR pulses is inversely proportional to the average dispersion and the square of the gain bandwidth, is proportional to the square of the saturation power. That is to say, we can improve the peak power of DSR pulse in three ways: Firstly, increase the saturation power in the case of sinusoidal-saturable-absorber transmission curve; secondly, decrease the gain bandwidth properly; thirdly, decrease the average dispersion suitably. In addition, the further results of numerical simulations are obtained by using pulse-tracing technique, which are in good agreement with the theoretical derivation of peak power of DSR pulses. This means that our work can serve as a guideline to design high-peak-power DSR fiber laser.
An accurate battery model is the prerequisite for reliable state estimate of vanadium redox battery (VRB). As the battery model parameters are time varying with operating condition variation and ...battery aging, the common methods where model parameters are empirical or prescribed offline lacks accuracy and robustness. To address this issue, this paper proposes to use an online adaptive battery model to reproduce the VRB dynamics accurately. The model parameters are online identified with both the recursive least squares (RLS) and the extended Kalman filter (EKF). Performance comparison shows that the RLS is superior with respect to the modeling accuracy, convergence property, and computational complexity. Based on the online identified battery model, an adaptive peak power estimator which incorporates the constraints of voltage limit, SOC limit and design limit of current is proposed to fully exploit the potential of the VRB. Experiments are conducted on a lab-scale VRB system and the proposed peak power estimator is verified with a specifically designed “two-step verification” method. It is shown that different constraints dominate the allowable peak power at different stages of cycling. The influence of prediction time horizon selection on the peak power is also analyzed.
•Model parameters are online adapted to keep accuracy and robustness.•An online peak power estimator is proposed by considering multiple constraints.•Online model identification is experimentally verified.•A “two-step verification” method is designed to verify the peak power estimation.•The method is robust to battery aging and operating condition variation.
•Flexible charging, battery degradation, nonlinear charging profile, and TOU plan are incorporated to make BEB fleet and charging schedules.•An integrated optimization model for timetable shifting ...and joint fleet and charging scheduling is formulated.•A two-stage solution method is suggested to combine the column generation technique and timetable shifting algorithm.•Full-flexible charging and timetable shifting strategies can efficiently improve the utilization rate and reduce peak power demand.
In a battery electric bus (BEB) network, buses are scheduled to perform timetabled trips while satisfying time, energy consumption, charging, and operational constraints. Increasing research efforts have been dedicated to the integrated optimization of multiple planning tasks to reduce system costs. At a high integration level, this study determines the BEB scheduling and charging planning with flexible charging and timetable shifting strategies. We first formulate an integrated arc-based model to minimize the total costs considering the power grid pressure cost and subsequently reformulate it into a two-stage model, for which we develop an effective solution method. The first stage minimizes the total operational costs including the fleet, charging, and battery degradation costs based on the column generation technique, and the second stage minimizes the peak power demand through two timetable shifting strategies. It is found through numerical experiments that the proposed integrated optimization model and solution method can achieve significant improvement in the utilization rate and reductions in the fleet size, operational costs, and peak power demand compared to the two baseline models.
Since the Information and Communications Technologies (ICT) were designed without taking the energy-saving into account, the unexpected excessive energy consumption of the fourth-generation (4G) and ...pre-4G wireless networks causes serious carbon dioxide emissions. To achieve green wireless networks, the fifth-generation (5G) wireless networks are expected to significantly increase the network energy efficiency while guaranteeing the quality of service (QoS) for time-sensitive multimedia wireless traffics. In this paper, we develop the statistical delay-bounded QoS driven green power allocation schemes to maximize the effective power efficiency (EPE), which is defined as the statistical-QoS-guaranteed throughput (effective capacity) per unit power, over single-input single-output (SISO) and multipleinput multiple-output (MIMO)-channels based 5G mobile wireless networks. For the SISO-channel based 5G wireless networks, our developed QoS-driven green power allocation scheme converges to the despicking water-filling scheme (despicking channel inversion scheme) when the QoS constraint becomes very loose (stringent). We further develop and analyze the statistical-QoS-driven green power allocation scheme to maximize the EPE over the multiplexing-MIMO based 5G mobile wireless networks. The obtained numerical results show that our developed statistical QoS-driven green power allocation schemes can optimize the EPE over 5G mobile wireless networks, thus enabling the effective implementation of green 5G wireless networks.
Hydrogen-rich water (HRW) is used as a supplement to improve performance and reduce fatigue in athletes. However, the potentially beneficial effects of HRW intake could be mediated by the training ...status of athletes. The purpose of the study was to analyse the ergogenic effect of intake of HRW for one week on aerobic and anaerobic performance, both in trained and untrained individuals. Thirty-seven volunteers participated in the study and were divided into two experimental groups: trained cyclists and untrained subjects. A double-blind crossover design was performed in which all subjects took a placebo (PW) and nano-bubble HRW (pH: 7.5; hydrogen concentration: 1.9 ppm; oxidation-reduction potential (ORP): -600 mV). At the end of 7-day intake, performance was assessed by an incremental VO
2
max test and by a maximum anaerobic test. After HRW intake, only trained cyclists improved their performance in the anaerobic test with an increase in peak power (from 766.2 ± 125.6 to 826.5 ± 143.4 W;
d
= .51) and mean power (from 350.0 ± 53.5 to 380.2 ± 71.3 W;
d
= .51), and a decrease in the fatigue index (from 77.6 ± 5.8 to 75.1 ± 5.9%;
d
= .45). The findings demonstrate that the ergogenic effect of HRW is mediated by the training status, and that 7-day intake of HRW would be an effective strategy for improving anaerobic performance in trained cyclists.
•The equivalent circuit model is estimated for battery states estimation.•Battery peak current is analyzed by multi-constrained conditions.•A novel multi-time-scale observer is used to estimate SOE ...and SOP concurrently.•The accuracy of the proposed method is verified under different conditions.
The battery state of energy and state of power are two important parameters in battery usage. The state of energy represents the residual energy storage in battery and the state of power represents the ability of battery discharge/charge. To estimate the two states with high accuracy, the characteristics of battery maximum available capacity and open-circuit voltage are analyzed under different working temperatures. Meanwhile, the equivalent circuit model of the battery is employed to embody the battery dynamic performance. To improve the accuracy of the battery states estimation, the multi-time-scale filter is applied in battery model parameters identification and battery states prediction. Besides, the state of power is analyzed by multi-constrained conditions to ensure battery work with safety. The proposed approach is verified by experiments operated on lithium-ion battery under new European driving cycle profiles and dynamic test profiles. The experimental results indicate the proposed method can estimate the battery states with high accuracy for actual application. In addition, the factors affecting the change of battery states are analyzed.
Energy communities (ECs) are essential tools to meet the Energy Transition goals but, to fully unleash their potential, they require a coordinated operation and design that the community itself may ...be ill-equipped to manage. Aggregators and Energy Service COmpanies (ESCOs) can perform this support role, but only provided that their goals are aligned to those of the community, not to incur in the agency problem. In this study, we propose a business model for aggregators of ECs, and its optimization problem, accounting for all crucial aspects: (i) alleviating the risk of the agency problem, (ii) fairly distributing the reward awarded to the EC, (iii) estimating the fair payment for the aggregator services, and (iv) defining appropriate exit clauses ruling what happens when a user leaves the EC. A mathematical model is developed, employing several fair game-theoretic reward distribution schemes, some of which are proposed here for the first time. A case study is developed, and results show that the aggregator enables reducing costs by 16% and improving renewable penetration and self/shared consumption by 35%–51% with respect to the base case. Our results suggest that the aggregator fair retribution is around 16%–24% the added benefit produced with respect to the base case, and that stable reward distribution schemes, such as Shapley/Core, Variance/Core or Nucleolus, are stable and recommended. Moreover, the results highlight the unwanted effect that some non-cooperative ECs may have an added benefit without providing any positive effect to the power system. Our work provides a methodology and preliminary results that can help policy makers and developers in tailoring national-level policies and market-offerings.
•Cooperative and non-cooperative optimal sizing of Energy Communities: a comparison.•Business model with fair stable profit allocation and withdrawal/termination clauses.•Comparison of Shapley Value, Core, Nucleolus, MinVariance and novel hybrid methods.•Role, value and fair remuneration of aggregators based on literature review.•Effects on the total peak power that affects the distribution network.
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