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Hybrid parabolic trough concentrators were considered as the basis of co-generation systems, which mainly based on the Simultaneous production of thermal and electrical energy. In this paper, a thermal model of two cogeneration systems consisting parabolic trough collector, combined with a cylindrical thermoelectric generator was presented. The collector of the present configurations forms an annular channel between the inner side of absorber tube and upper surface of tubular thermoelectric generator. A heat transfer fluid (Therminol VP1 or hot water) is passed along the annular channel using a pump with low consumption, which mainly energized by the produced power from the tubular thermoelectric generator. Also, the heat transfer fluid (Therminol VP1 or Hot water) temperature is mainly based on the temperature adjustment principle, where the heat transfer fluid flow rate is adjusted according to sun irradiation to keep the heat transfer fluid temperature at 400 °C for Therminol VP1 or at 95 °C in the case of water. To examine the effects of solar concentration ratio and sun irradiation on the thermal and electrical performance of the hybrid system, a set of nonlinear equations were developed and coded in MATLAB software (R2015a). The power output and electrical efficiency of the tubular thermoelectric generator, the overall efficiency and net power as well as hot water storage of the hybrid systems were separately presented and discussed for all three solar concentration ratios and ten sun irradiation values. To validate the predicted results of the numerical model, two available research works have been used. The comparison of results obtained with results of the exact solution indicates a good agreement. The novel integration technique shows major improvements in thermal and electrical performance of both hybrid systems. As a results, the overall efficiency of the first hybrid system (Here, Therminol VP1 serves as a heat transfer fluid) reached to 70.550% corresponding to 306.5826 L/Day of Therminol VP1 at 400 °C and about 585 W of additional power. These values in the case of water serves as a heat transfer fluid up to 76.913%, 1058.467 L/D of hot water at 95 °C and 97.032 W of additional electrical power, respectively.

In this paper, an experimental test rig has been developed by utilising the free-piston linear generator (FPLG) principle of a dual-piston air-driven system. The mechanical energy of the FPLG is converted into electric power through a linear generator. The piston motion, root mean square (RMS) power output, operating frequency, system stability and the conversion efficiency of the FPLG at various inlet pressure and valve opening duration (VOD) are duly discussed in the paper. It is noticed that the piston displacement (stroke) is associated with the VOD and inlet pressure, which have the greatest effect on the FPLG motion characteristics. A long VOD leads to a high piston speed, causing high peak power output. However, the RMS power shows an approximately linear decline with the increase in VOD due to the free-piston dwelling for a certain time at the dead centre position before the exhaust process starts. The FPLG can be achieved a maximum RMS power of 120 W when the inlet pressure is 8 bar and VOD is 30 ms. When the inlet pressure changed from 8 bar to 5 bar, the FPLG operating frequency shows a similar trend and values because it is associated with the piston velocity and stroke. The FPLG Cycle-to-Cycle variation (COV) is low when the inlet pressure is high, and the system stability increases with decreases in VOD. As the VOD increases, the indicated efficiency and work to electrical efficiency increase, whereas the thermal to work efficiency decreases. The maximum indicated efficiency, work to electrical efficiency and thermal to work efficiency achieved are 59.9%, 14.7% and 14.6 %, respectively.

Background Standardized tests are currently available to assess power output in elite rowers. However, there are no valid and reliable tests to assess power output in amateur rowers. Objective This study aimed to determine the validity and reliability of a 6-min rowing ergometer test (6-minRT) as a predictor of power output (PO) in amateur male rowers. Methods Twelve male amateur rowers were part of the study. All participants were instructed to perform an incremental test (IT), a 6-minRT test, and a retest. The validity of the 6-minRT was determined by comparing maximum oxygen uptake (VO2max) and power output (PO) between the IT and 6-minRT. Reliability included the coefficient of variation (CV), intra-class correlation coefficient (ICC), and mean standard error between the 6-minRT test and retest. The significance level was p < 0.05. Results There was no significant difference in VO2max in both IT and 6-minRT (p = 0.18), while the mean power output (Pmean) generated in the 6-minRT equaled 91.96% of the maximal aerobic power (MAP) generated in the IT (p = 0.004). Reliability analysis for the 6-minRT showed a CV = 0.50% and ICC = 0.97 for distance, a CV = 1.85% and ICC = 0.96 for Pmean. Conclusion From a ventilatory and mechanical point of view, the 6-minRT is a maximally valid test for establishing MAP in amateur rowers. Also, the 6-minRT evidences a high degree of agreement between days. Therefore, the 6-minRT is a valid and reliable test for assessing PO in amateur male rowers.

Based on the model of irreversible single resonance energy-selective electron heat engine established in the previous literature, this paper applies finite-time thermodynamic theory and NSGA-II algorithm to perform multi-objective optimization. Single-, bi-, tri- and quadru-objective optimizations are performed when the energy boundary and the resonance width are taken as the optimization variables, and the power output, thermal efficiency, efficient power and ecological function are taken as the optimization objectives. The deviation indexes of different optimization objective combinations are obtained by using LINMAP, TOPSIS and Shannon entropy approaches. The results show that the values of energy boundary and resonance width can be reasonably selected according to the design requirements of the system. When power output and efficiency are optimized, the minimal deviation index is obtained by TOPSIS approach and the value is 0.0748, which is the most ideal design scheme. [ABSTRACT FROM AUTHOR]

Although microbial fuel cells (MFCs) have been developed over the past decade, they still have a low power production bottleneck for practical engineering due to the ineffective interfacial bioelectrochemical reaction between exoelectrogens and anode surfaces using traditional carbonaceous materials. Constructing anodes from biomass is an effective strategy to tackle the current challenges and improve the efficiency of MFCs. The advantage features of these materials come from the well-decorated aspect with an enriched functional group, the turbostratic nature, and porous structure, which is important to promote the electrocatalytic behavior of anodes in MFCs. In this review article, the three designs of biomass-derived carbon anodes based on their final products (i.e., biomass-derived nanocomposite carbons for anode surface modification, biomass-derived free-standing three-dimensional carbon anodes, and biomass-derived carbons for hybrid structured anodes) are highlighted. Next, the most frequently obtained carbon anode morphologies, characterizations, and the carbonization processes of biomass-derived MFC anodes were systematically reviewed. To conclude, the drawbacks and prospects for biomass-derived carbon anodes are suggested. [ABSTRACT FROM AUTHOR]

The present study investigated whether acute capsaicin (CAP) supplementation improves mean power output (MPO) and peak velocity (PV) during the performance of the free bench press exercise (FBP). Twelve (n = 12) male Brazilian Jiu-Jitsu (BJJ) athletes (age: 24.3 ± 1.5 years, height: 1.74 ± 0.1 m, body mass: 75.7 ± 10.1 kg) participated in this randomized, placebo (PLA)-controlled, double-blind, crossover trial. For each condition, 45 min after CAP (12 mg purified) or PLA (12 mg of Celulomax E) consumption, the participants performed four sets of five repetitions of FBP at a load of 60% of body mass with five-min rest intervals. The MPO (t = 5.6, df = 11, p = 0.001, EF = 0.3, IC 95% = −0.55 to 1.05) and PV (t = 5.4, df = 11, p = 0.001, EF = 0.5, IC 95% = −0.32 to 1.30) were significantly higher with CAP supplementation versus PLA. Acute CAP supplementation appears to improve MPO and PV during FBP in male BJJ athletes. [ABSTRACT FROM AUTHOR]

A one-dimensional dual-pressure steam turbine (ST) model for the marine Rankine cycle is built in this paper. Based on constructal theory, the optimal design of the dual-pressure ST is performed with a fixed total volume of the high- and low-pressure STs. The total power output (PO) of the dual-pressure ST is maximized. Seventeen parameters, including the dimensionless average diameters (DADs) of the stages, steam inlet angles (SIAs) of the stages, average reaction degrees (ARDs) of the stages, and volume ratio of the high-pressure ST are taken as optimization variables. The optimal structure parameters of the stages are gained. It reveals that the total PO of the dual-pressure ST is increased by 2.59% by optimizing the average diameter of the Curtis stage, and the change in the total PO is not obvious by optimizing the average diameter of the third stage of the low-pressure ST. Both the total PO and the corresponding efficiency of the dual-pressure ST are increased by 10.8% after simultaneously optimizing 17 variables with the help of the Matlab optimization toolbox. The novelty of this paper is introducing constructal theory into turbine performance optimization by varying seventeen structure, thermal and flow parameters, and the result shows that the constructal optimization effect is remarkable. Optimal designs of practical STs can be guided by the optimization results gained in this paper. [ABSTRACT FROM AUTHOR]

The acute and delayed hormonal and blood cell responses to a high-intensity interval training (HIIT) session, were examined before and after a 3-week intervention (9 HIIT sessions of 4–6 × 30 s high-intensity cycling bouts) in eight recreationally active male volunteers (age: 24.3 ± 1.4 y, VO2max: 41.2 ± 3.2 ml/kg/min). Blood samples were collected before and 0.5, 24, 48 h following the first and last training session. Before training, the HIIT session induced acute increases in cortisol, prolactin and TSH concentration, while free-T4 peaked 24 h later (p < 0.001) and testosterone remained unchanged. White blood cell count was increased 0.5 h after exercise (p < 0.001), while lymphocyte percentage decreased 24 h post exercise (p < 0.01). After three weeks of HIIT, cortisol, WBC and lymphocyte responses were decreased by ~42% (p = 0.002), 8.6% (p = 0.032) and 9.6% (p = 0.039), respectively, despite an increase in total work. These findings show that short-term HIIT may induce rapid adaptations of the hypothalamic-pituitary-adrenal axis and may blunt exercise-induced immune responses. [ABSTRACT FROM AUTHOR]

Background: There is a universal need to increase the number of adults meeting physical activity (PA) recommendations to help improve health. In recent years, electrically assisted bicycles (e‐bikes) have emerged as a promising method for supporting people to initiate and maintain physical activity levels. To the best of our knowledge, there have been no meta‐analyses conducted to quantify the difference in physiological responses between e‐cycling with electrical assistance, e‐cycling without assistance, conventional cycling, and walking. Methods: A systematic review and meta‐analysis was conducted following PRISMA guidelines. We identified short‐term e‐bike studies, which utilized a crossover design comparing physiological outcomes when e‐cycling with electrical assistance, e‐cycling without electrical assistance, conventional cycling, or walking. Energy expenditure (EE), heart rate (HR), oxygen consumption (VO2), power output (PO), and metabolic equivalents (METs) outcomes were included within the meta‐analysis. Results: Fourteen studies met our inclusion criteria (N = 239). E‐cycling with electrical assistance resulted in a lower energy expenditure (EE) [SMD = −0.46 (−0.98, 0.06), p = 0.08], heart rate (HR) [MD = −11.41 (−17.15, −5.68), p < 0.000, beats per minute], oxygen uptake (VO2) [SMD = −0.57 (−0.96, −0.17), p = 0.005], power output (PO) [MD = −31.19 (−47.19 to −15.18), p = 0.000, Watts], and metabolic equivalent (MET) response [MD = −0.83 (−1.52, −0.14), p = 0.02, METs], compared with conventional cycling. E‐cycling with moderate electrical assistance resulted in a greater HR response [MD 10.38 (−1.48, 22.23) p = 0.09, beats per minute], and VO2 response [SMD 0.34 (−0.14, 0.82) p = 0.16] compared with walking. Conclusions: E‐cycling was associated with increased physiological responses that can confer health benefits. [ABSTRACT FROM AUTHOR]

Solid oxide fuel cell (SOFC) has the potential to convert biomass to electrical power cleanly and efficiently by integrating with in situ gasification of biomass. It is necessary to keep a balance between maximizing the power output of fuel cells and minimizing the pretreatment of biomass. Herein, we report the comparison of output performance between the apple tree branches (ATB) dried at 110°C and the one pyrolyzed at 500°C in SOFCs. The results show that the peak power densities (PPD) of SOFCs operated at 850°C were 157 and 238 mW cm−2 for the dried and the pyrolyzed samples, respectively. And the corresponding apparent fuel utilizations for them were 18.1% and 24.6%, respectively. However, if counting the pyrolysis yield (~28 wt%), the overall fuel utilization of the pyrolyzed sample declined from 24.6% to ~6.9%. In addition, if loading the steel slag (SS)‐based catalyst catalyst to the dried sample, its PPD at 850°C were almost doubled to 303 mW cm−2, but the fuel utilization reduced to 9.2%. Meanwhile, SOFCs using the medium‐density fiberboard (MDF) as fuel exhibited the parallel trends in electrochemical performance and fuel utilization. [ABSTRACT FROM AUTHOR]

The aim of this study was to investigate the effect of four different inertial loads (0.025, 0.050, 0.075, and 0.100 kg⋅m²) on concentric (CON) power, eccentric (ECC) power, and ECC overload in the flywheel Romanian deadlift (RDL). Fourteen recreationally trained males (27.9 ± 6.4 years, 90 ± 10.7 kg, 180.7 ± 5.5 cm) volunteered for the study. They had a minimum of two years of resistance training experience, although none had experience in flywheel inertia training (FIT). All participants performed the flywheel RDL on a flywheel device (kBox 3, Exxentric, AB TM, Bromma, Sweden). Each set was performed using different inertial loads, those being 0.025, 0.050, 0.075, and 0.100 kg⋅m². For CON, ECC power, and ECC overload, there was a significant difference (p < 0.001) between inertial loadings. In conclusion, results highlight that lower inertial load leads to higher peak CON and ECC power values, precisely 0.025 kg⋅m². Regarding ECC overload, medium to higher loads (0.050, 0.075, and 0.100 kg⋅m²) will lead to higher values. [ABSTRACT FROM AUTHOR]

The purpose of this study was to assess 1) how treadmill slope variance affected external power output (PO) and propulsion technique reliability; and 2) how PO is associated with propulsion technique. Eighteen individuals with spinal cord injury performed two wheelchair treadmill exercise blocks (0% and 1% treadmill slope, standardized velocity) twice on two separate days. PO, velocity, and 14 propulsion technique variables were measured. In a follow-up study, N = 29 performed wheelchair treadmill drag tests. Target and actual slope were documented and PO, intraclass correlation coefficients (ICC) and smallest detectable differences (SDD) were calculated. Within and between visits, the reliability study ICCs were perfect for velocity (1.0), weak for PO (0.33-0.46), and acceptable (>0.70) for five (0% slope) and 10 (1% slope) propulsion technique variables, resulting in SDDs of 35-196%. Measured PO explained 56-90% of the variance in key propulsion technique variables. In the follow-up, PO ICCs were weak (0.43) and SDDs high. Bias between target and actual slope appeared random. In conclusion, PO variability accounts for 50-90% of the variability in propulsion technique variables when speed and wheelchair set-up are held constant. Therefore, small differences in PO between interventions could mask the effect of the interventions on propulsion technique. [ABSTRACT FROM AUTHOR]

Rooftop solar arrays are a way of harvesting the energy from sun rays falling on the roof of buildings. These arrays can help buildings to generate power for themselves, either completely or partially fulfilling their energy needs. These systems however have their own sets of factors that can cause losses in them and reduce their power output. In this research work, the effect of mutual shading and design parameters are studied. The rooftop solar arrays with different parameters are simulated that help to estimate results closely agreeable with practical outcomes. The software 'DIVA for Rhino' was used to perform the simulations. The effect of various parameters such as the inclination of the roof surface, inter-row spacing of the panels, and their inclination, were studied. The degree of mutual shading was observed by varying these parameters. The power outputs and payback periods of the simulated systems were compared and their trends were observed to give a better understanding of how these factors affect rooftop solar arrays. The shading loss was high for higher panel inclination values coupled with smaller inter-row spacing. A higher roof inclination reduced the level of shading loss as it reduced the panel inclination with respect to the roof surface. The roof surface area increases with its inclination, which means more space for solar panels and hence a higher array power output. The results of the simulations will help in better decision-making during the construction of rooftop solar arrays as it helps to see the extent to which each of these parameters affects them. • Rooftop PV arrays were simulated. • This paper examines the effects of various design parameters on mutual shading. • The software 'DIVA for Rhino' was used to perform the simulations. • Annual power generation of the PV arrays was simulated. • Payback periods of the PV arrays were calculated. [ABSTRACT FROM AUTHOR]

The aim of this study was to investigate the effect of four different inertial loads (0.025, 0.050, 0.075, and 0.100 kg· m²) on concentric (CON) power, eccentric (ECC) power, and ECC overload in the flywheel Romanian deadlift (RDL). Fourteen recreationally trained males (27.9 ± 6.4 years, 90 ± 10.7 kg, 180.7 ± 5.5 cm) volunteered for the study. They had a minimum of two years of resistance training experience, although none had experience in flywheel inertia training (FIT). All participants performed the flywheel RDL on a flywheel device (kBox 3, Exxentric, AB TM, Bromma, Sweden). Each set was performed using different inertial loads, those being 0.025, 0.050, 0.075, and 0.100 kg·m². For CON, ECC power, and ECC overload, there was a significant difference (p < 0.001) between inertial loadings. In conclusion, results highlight that lower inertial load leads to higher peak CON and ECC power values, precisely 0.025 kg· m². Regarding ECC overload, medium to higher loads (0.050, 0.075, and 0.100 kg·m²) will lead to higher values.

Based on irreversible Porous Medium cycle model established in the previous literature, this paper investigates cycle optimal performance by taking cycle power density as optimization objective and applying finite time thermodynamics. Various parameters are used to examine relationships among power density and thermal efficiency versus compression ratio. The cycle performance is compared under maximum power density circumstance and maximum power output circumstance. Compared with condition of maximum power output, the Porous Medium cycle engine gets higher thermal efficiency and smaller size under the maximum power density condition. One-, two-, three- and four-objective optimizations of the cycle are performed by using NSGA-II algorithm, choosing compression ratio as design variable, and choosing dimensionless power density, dimensionless power output, thermal efficiency, and dimensionless ecological function as optimization objectives. Using three decision schemes, LINMAP, TOPSIS and Shannon entropy, deviation indices under different optimization objective combinations are compared. For six two-objective optimizations, power output and thermal efficiency optimization has the smallest deviation index, 0.1215. For four three-objective optimizations, power output, ecological function and power density optimization has the smallest deviation index, 0.1235. For four-objective optimization, the deviation index is 0.1419. The appropriate solution should be selected according to the actual application.

In this study, experimental and numerical examinations of the performance of the conventional photovoltaic panel, concentrated photovoltaic (CPV) system and water-cooled CPV system were performed. The tests are conducted under the climatic conditions of the city of Duhok, North of Iraq, on a sunny day on September 25, 2019. During the experiments, the average ambient temperature and average solar radiation were 32.6 °C and 930 W/m2, respectively. As well, MATLAB/Simulink modeling is developed by using PV module equations and the manufacturing data sheet. The empirical results showed that the ultimate panel temperature of the PV panel, concentrated PV system and water-cooled concentrated PV system is 57.5, 64.1 and 36.5 °C, respectively. In addition, the power output of the water-cooled CPV system and CPV system was improved respectively by 24.4% (effective 23%) and 10.65%. In addition, electrical efficiency was increased from 14.2% to 17% by using reflectors and water cooling with the PV panel. In the case of the water-cooled CPV system, open circuit voltage and short circuit current were increased by 9% and 5.2%, respectively. Moreover, the comparison between the experimental and numerical results agrees well.

Purpose: To describe the demand of recent World Cup (WC) races comparing top-10 (T10) and non-top-10 (N-T10) performances using power data. Methods: Race data were collected in 1-d World Cup races during the 2012-2015 road cycling seasons. Seven female cyclists completed 49 WC races, finishing 25 times in T10 and 24 times in N-T10. Peak power (1 s) and maximal mean power (MMP) for durations of 5, 10, 20, and 30 s and 1, 2, 5, 10, 20, 30, and 60 min expressed as power to weight ratio were analyzed in T10 and N-T10. The percentage of total race time spent at different power bands was compared between T10 and N-T10 using 0.75-W⋅kg-1 power bands, ranging from <0.75 to >7.50 W⋅kg-1. The number of efforts in which the power output remained above 7.50 Wvkg-1 for at least 10 s was recorded. Results: MMPs were significantly higher in T10 than in N-T10, with a large effect size for durations between 10 s and 5 min. N-T10 spent more time in the 3.01- to 3.75-W•kg-1 power band when compared to T10 (P = .011); conversely, T10 spent more time in the 6.75- to 7.50- and >7.50-W⋅kg-1 power bands (P = .009 and .005, respectively) than N-T10. A significantly higher number of short and high-intensity efforts (≥10 s, >7.5 W⋅kg-1) was ridden by T10 than N-T10 (P = .002), specifically, 46 ± 20 and 30 ± 15 efforts for T10 and N-T10, respectively. Conclusions: The ability to ride at high intensity was determinant for successful road-cycling performances in WC races. [ABSTRACT FROM AUTHOR]

A large number of power meters have been produced on the market for nearly 20 y according to user requirements. Purpose: To determine the validity, sensitivity, reproducibility, and robustness of the PowerTap (PWT), Stages (STG), and Garmin Vector (VCT) power meters in comparison with the SRM device. Methods: A national-level male competitive cyclist completed 3 laboratory cycling tests: a submaximal incremental test, a submaximal 30-min continuous test, and a sprint test. Two additional tests were performed, the first on vibration exposures in the laboratory and the second in the field. Results: The VCT provided a significantly lower 5-s power output (PO) during the sprint test with a low gear ratio than the SRM did (-36.9%). The STG PO was significantly lower than the SRM PO in the heavy-exercise-intensity zone (zone 2, -5.1%) and the low part of the severe- intensity zone (zone 3, -4.9%). The VCT PO was significantly lower than the SRM PO only in zone 2 (-4.5%). The STG PO was significantly lower in standing position than in the seated position (-4.4%). The reproducibility of the PWT, STG, and VCT was similar to that of the SRM system. The STG and VCT PO were significantly decreased from a vibration frequency of 48 Hz and 52 Hz, respectively. Conclusions: The PWT, STG, and VCT systems appear to be reproducible, but the validity, sensitivity, and robustness of the STG and VCT systems should be treated with some caution according to the conditions of measurement. [ABSTRACT FROM AUTHOR]

Purpose: To assess the dose-response relationships between different training-load methods and aerobic fitness and performance in competitive road cyclists. Method: Training data from 15 well-trained competitive cyclists were collected during a 10-wk (December-March) preseason training period. Before and after the training period, participants underwent a laboratory incremental exercise test with gas-exchange and lactate measures and a performance assessment using an 8-min time trial (8MT). Internal training load was calculated using Banister TRIMP, Edwards TRIMP, individualized TRIMP (iTRIMP), Lucia TRIMP (luTRIMP), and session rating of perceived exertion (sRPE). External load was measured using Training Stress Score (TSS). Results: Large to very large relationships (r = .54-.81) between training load and changes in submaximal fitness variables (power at 2 and 4 mmol/L) were observed for all training-load calculation methods. The strongest relationships with changes in aerobic fitness variables were observed for iTRIMP (r = .81 [95% CI .51-.93, r = .77 [95% CI .43-.92]) and TSS (r = .75 [95% CI .31-.93], r = .79 [95% CI .40-.94]). The strongest dose-response relationships with changes in the 8MT test were observed for iTRIMP (r = .63 [95% CI .17-.86]) and luTRIMP (r = .70 [95% CI .29-.89). Conclusions: Training-load quantification methods that integrate individual physiological characteristics have the strongest dose-response relationships, suggesting this to be an essential factor in the quantification of training load in cycling. [ABSTRACT FROM AUTHOR]

Purpose: To describe the within-season external workloads of professional male road cyclists for optimal training prescription. Methods: Training and racing of 4 international competitive professional male cyclists (age 24 ± 2 y, body mass 77.6 ± 1.5 kg) were monitored for 12 mo before the world team-time-trial championships. Three within-season phases leading up to the team-time-trial world championships on September 20, 2015, were defined as phase 1 (Oct-Jan), phase 2 (Feb-May), and phase 3 (June-Sept). Distance and time were compared between training and racing days and over each of the various phases. Times spent in absolute (<100, 100-300, 400-500, >500 W) and relative (0-1.9, 2.0-4.9, 5.0-7.9, >8 W/kg) power zones were also compared for the whole season and between phases 1-3. Results: Total distance (3859 ± 959 vs 10911 ± 620 km) and time (240.5 ± 37.5 vs 337.5 ± 26 h) were lower (P < .01) in phase 1 than phase 2. Total distance decreased (P < .01) from phase 2 to phase 3 (10911 ± 620 vs 8411 ± 1399 km, respectively). Mean absolute (236 ± 12.1 vs 197 ± 3 W) and relative (3.1 ± 0 vs 2.5 ± 0 W/kg) power output were higher (P < .05) during racing than training, respectively. Conclusion: Volume and intensity differed between training and racing over each of 3 distinct within-season phases. [ABSTRACT FROM AUTHOR]

The main aim of this study was to analyze the effect of resistance training programs differing in set configuration on mechanical force-velocity profiles. Thirteen participants performed 10 unilateral knee extension training sessions over 5 weeks. Each limb was randomized to one of the following set configurations: traditional (4 sets of 8 repetitions at maximum intended velocity, 10RM load, 3-min pause between sets) or interrepetition rest (32 maximum intended velocity repetitions, 10RM load, 17.4 s of rest between each repetition). Velocity of each repetition was recorded throughout the program. Before and after training, individual linear force velocities were calculated, and the following parameters were obtained: force and velocity axis intercept, slope, and estimated maximum power. Mean velocity was higher throughout the program for interrepetition rest configuration (0.54 ± 0.01 vs. 0.48 ± 0.01 m⋅s-1 for interrepetition rest, and traditional configuration respectively; main effect of set configuration: P < .001). There was a significant increase in force and velocity intercepts, but a steeper negative slope after both training protocols (main effect of time: P < .001 for every variable). Differences in resistance training velocity did not affect the adaptations. Our results suggest that, in a short-term program, maximum intended rather than actual velocity is a key factor to modulate strength adaptations. [ABSTRACT FROM AUTHOR]

Purpose: To analyze the effect of the pedaling activity in different 4-min time trials (TT4s) (laboratory and field conditions) and compare TT4 and maximal aerobic power (MAP) determined from the classical incremental exercise test in laboratory. It was hypothesized that the exercises performed on the field would determine higher physical (power output [PO]) and mental involvements due to different environmental conditions. Methods: Sixteen male cyclists underwent an incremental test to exhaustion and 3 TT4s under different conditions: cycle ergometer (CE), level ground (LG), and uphill (UP). Results: Correlation was observed for PO with a trivial effect size and narrow limits of agreement between MAP and CE TT4 (r = .96, P < .001). The comparison between the CE, LG, and UP tests indicates that PO was significantly higher in UP than in CE (+8.0%, P < .001) and LG (+11.0%, P < .001). Conclusions: The results suggest that PO depends on the nature of the pedaling activity. Moreover, PO under CE TT4 is a relevant predictor of MAP. It seems important to measure MAP by taking into account the cycling conditions, considering that coaches and scientists use this parameter to assess the aerobic potential of athletes and determine the exercise intensities useful for monitoring adaptation to training. [ABSTRACT FROM AUTHOR]

Older women participated in a 12-week high-speed resistance training program under two supervisor-to-subject ratio methods (i.e., high versus low supervision) to assess its effects on muscle strength, power, functional performance, and quality of life assessed before (T1) and after (T2) intervention. Women were divided into either the control group (CG, n = 15), high supervision group (HSG, n = 30), or low supervision group (LSG, n = 28). The training program included exercises requiring high-speed concentric muscle actions. No differences were observed among groups at T1. Between T1 and T2, the HSG showed a higher (p < .05) improvement in muscle strength (ES = 0.36–1.26), power (ES = 0.5–0.88), functional performance (ES = 0.52–0.78), and quality of life (ES = 0.44–0.82) compared with LSG and CG. High-speed resistance training under closer supervision is more effective for improving muscle strength, power, functional performance, and quality of life in older women. [ABSTRACT FROM AUTHOR]

Using a one-dimensional code, we computed the power (enthalpy discharge rate) of a twelve-cell mechanical draft cooling tower (MDCT) using over two hundred visible condensed water vapor plume volume measurements derived from images, weather data, and tower operating conditions. The plume images were simultaneously captured by multiple stationary digital cameras surrounding the cooling tower. An analysis technique combining structure from motion (SfM), a neural-network-based image segmentation algorithm, and space carving was used to quantify the volumes. Afterwards, the power output was computed using novel techniques in the one-dimensional code that included cooling tower exhaust plume adjacency effects implemented with a modified version of the entrainment function, weather data averaged from eleven stations, and fan operations at the times when plume volumes were measured. The model was then compared with the averaged observed power output, and it validated well with an average error ranging from 6 to 12%, depending on the meteorological data used in the simulations. This methodology can possibly determine power plant fuel consumption rates by applying visible imagery.

Lead-containing piezoelectric materials typically show the highest energy conversion efficiencies, but due to their toxicity they will be limited in future applications. In their bulk form, the piezoelectric properties of lead-free piezoelectric materials are significantly lower than lead-containing materials. However, the piezoelectric properties of lead-free piezoelectric materials at the nano scale can be significantly larger than the bulk scale. This review looks at the suitability of ZnO nanostructures as candidate lead-free piezoelectric materials for use in piezoelectric nanogenerators (PENGs) based on their piezoelectric properties. Of the papers reviewed, Neodymium-doped ZnO nanorods (NRs) have a comparable piezoelectric strain constant to bulk lead-based piezoelectric materials and hence are good candidates for PENGs. Piezoelectric energy harvesters typically have low power outputs and an improvement in their power density is needed. This review systematically reviews the different composite structures of ZnO PENGs to determine the effect of composite structure on power output. State-of-the-art techniques to increase the power output of PENGs are presented. Of the PENGs reviewed, the highest power output belonged to a vertically aligned ZnO nanowire (NWs) PENG (1-3 nanowire composite) with a power output of 45.87 μW/cm2 under finger tapping. Future directions of research and challenges are discussed.

The Future of Energy is focused on the consolidation of new energy technologies. Among them, Fuel Cells (FCs) are on the Energy Agenda due to their potential to reduce the demand for fossil fuel and greenhouse gas emissions, their higher efficiency (as fuel cells do not use combustion, their efficiency is not linked to their maximum operating temperature) and simplicity and absence of moving parts. Additionally, low-power FCs have been identified as the target technology to replace conventional batteries in portable applications, which can have recreational, professional, and military purposes. More recently, low-power FCs have also been identified as an alternative to conventional batteries for medical devices and have been used in the medical field both in implantable devices and as micro-power sources. The most used power supply for implantable medical devices (IMD) is lithium batteries. However, despite its higher lifetime, this is far from enough to meet the patient’s needs since these batteries are replaced through surgeries. Based on the close synergetic connection between humans and microorganisms, microbial fuel cells (MFCs) were targeted as the replacement technology for batteries in IMD since they can convert the chemical energy from molecules presented in a living organism into electrical energy. Therefore, MFCs offer the following advantages over lithium batteries: they do not need to be replaced, avoiding subjecting IMD users to different surgeries and decreasing medical costs; they do not need external recharging as they operate as long as the fuel is supplied, by the body fluids; they are a more environmentally friendly technology, decreasing the carbon dioxide and other greenhouse gases emissions resulting from the utilization of fossil fuels and the dependency on fossil fuels and common batteries. However, they are complex systems involving electrochemical reactions, mass and charge transfer, and microorganisms, which affect their power outputs. Additionally, to achieve the desired levels of energy density needed for real applications, an MFC system must overcome some challenges, such as high costs and low power outputs and lifetime.

Background: Post-activation performance enhancement (PAPE) is a physiological phenomenon that acutely improves voluntary muscular performance following a conditioning activity. A large and growing body of literature has investigated different strategies to induce a PAPE stimulus; however, little attention has been given to whether acute caffeine ingestion could augment the effect of PAPE on subsequent performance. This study evaluated the acute effects of caffeine ingestion and back squat conditioning activity on subsequent countermovement jump (CMJ) performance in female semi-professional volleyball players. Methods: Fourteen resistance-trained female volleyball players (26 ± 3 years) performed 3 different testing conditions in randomized order: where each ingested 6 mg/kg of caffeine (CAF) or placebo (PLAC) and performed a single set of back squats at 80%1RM until mean movement velocity dropped by 10% as the conditioning activity or a control (CTRL) condition where participants did not ingest any supplement and did not perform the conditioning activity. CMJ height was examined at baseline and in 2 min intervals until 10 min postconditioning activity. Furthermore, due to the wide inter-individual variation in optimal recovery time of PAPE response, the baseline and best post-conditioning activity performance were also analyzed. Results: The Friedman test revealed a significant difference in jump height within CTRL (p = 0.002) and CAF (p = 0.001) conditions, but no significant difference was found within the PAP condition. The post hoc showed a significant decrease in jump height in 8th min in CTRL condition (p = 0.022, effect size [ES] = −0.31), a significant increase in jump height in 2nd min in CAF condition (p = 0.013, ES = 0.3), without differences in PLAC condition in comparison to baseline values. Moreover, a significant jump height increases from baseline to best performance post conditioning activity value for CAF (p = 0.001, ES = 0.39) and PLAC (p = 0.001, ES = 0.3) condition, but no significant difference was found for the CTRL condition. Conclusions: The single set of heavy-loaded back squats with controlled velocity used as a conditioning activity in the current study enhanced subsequent CMJ performance in female volleyball players with no additional effect of caffeine. [ABSTRACT FROM AUTHOR]

Background: Mixed-reality sports are increasingly reaching the highest level of sport, exemplified by the first Virtual Tour de France, held in 2020. In road races, power output data are only sporadically available, which is why the effect of power output on race results is largely unknown. However, in mixed-reality competitions, measuring and comparing the power output data of all participants is a fundamental prerequisite for evaluating the athlete's performance. Objective: This study investigates the influence of different power output parameters (absolute and relative peak power output) as well as body mass and height on the results in mixed-reality competitions. Methods: We scrape data from all six stages of the 2020 Virtual Tour de France of women and men and analyze it using regression analysis. Third-order polynomial regressions are performed as a cubic relationship between power output and competition result can be assumed. Results: Across all stages, relative power output over the entire distance explains most of the variance in the results, with maximum explanatory power between 77% and 98% for women and between 84% and 99% for men. Thus, power output is the most powerful predictor of success in mixed-reality sports. However, the identified performance-result gap reveals that other determinants have a subordinate role in success. Body mass and height can explain the results only in a few stages. The explanatory power of the determinants considered depends in particular on the stage profile and the progression of the race. Conclusion: By identifying this performance-result gap that needs to be addressed by considering additional factors like competition strategy or the specific use of equipment, important implications for the future of sports science and mixed-reality sports emerge. [ABSTRACT FROM AUTHOR]

During the traditional reverse electrodialysis (RED) process, second only to concentration polarization phenomenon, the spacer shadow effect that blocks the ionic transport as a consequence of the use of non-permselective spacers has an undesirable impact on the practical power output. In this work, a configuration of ion-permselective spacer is proposed to eliminate the spacer shadow effect to improve the power density. By combining direct current and alternating current experimental methods, the spacer shadow and concentration polarization effects are measured. At the same time, their impact on stack resistance and power out are analyzed quantatively under different hydrodynamic conditions and spacer configurations to optimize the RED process performance. Compared with traditional spacers, the use of ion-permselective spacers makes the spacer shadow effect reduced by more than 95% inversely with a stronger concentration polarization phenomenon, which results in a higher power density due to remarkable decrease in stack resistance. In order to further suppress the concentration polarization, increasing flow rate and reducing pore size of channel are both feasible, which meanwhile leads to a further reduction in shadow effect. Yet, the variation of channel shape has little impact on the shadow and concentration polarization effects. The maximum power output of 0.81 W/m2 is harvested with pore size of 4.5 mm and cell pair of 3 at flow rate of 40 L/h under the investigated conditions and is improved by 50% in comparison to non-permselective spacers. [ABSTRACT FROM AUTHOR]

The ergogenic effects of carbohydrate (CHO) and caffeine (CAF) mouth rinse (MR) methods on anaerobic performance remains unclear. Therefore, the aim of this study was to investigate the effects of CHO, CAF, and CHO + CAF combination solutions in mouth on repeated vertical jumping (RVJ) performance in highly trained male athletes. Eight male athletes (mean age: 22 years) underwent test sessions four times with minimum 24-h intervals under fasting conditions. Participants rinsed their mouths with four different 25-ml solutions, namely, CHO (6.4% maltodextrin = 1.6 g), CAF (1.2% caffeine = 300 mg), placebo (PLA, saccharin), or CHO + CAF (6.4%+1.2%) combination, for 10 s and performed a 30-s RVJ test twice with a 5-min interval. Peak power output, vertical jump height, blood lactate level, fatigue index, and rate of perceived exertion of the RVJ tests for different intervention sessions were compared. The statistical significance level was set at p ≤ 0.05. Analyses demonstrated that CHO- (Δ: 3.4), CAF- (Δ: −0.8), and CHO + CAF-MR (Δ: −1.8) interventions led to similar RVJ performance changes compared to PLA. All differences in the dependent variables were statistically insignificant and had moderate and lower effect sizes between interventions (p > 0.05, g < 0.94). Our study did not elicit sufficient evidence to recommend highly trained male athletes the use of CHO- and CAF-MR separately or in combination to enhance jump performance. However, the fact that some differences have medium to large effect sizes suggests that the issue is still worth to be a potential topic for further research. Highlights Effects of CHO + CAF-MR on anaerobic performance in highly trained athletes have not been investigated using performance tasks requiring high technical skills. There is not enough evidence to suggest that CHO, CAF and CHO + CAF-MR interventions have beneficial effects on RVJ performance compared to PLA in highly trained male athletes. Some statistically insignificant differences have medium to large effect sizes. Therefore, the issue is still worth to be a potential topic for further research. [ABSTRACT FROM AUTHOR]

This study utilised on-water graded exercise tests (GXT) to determine the power output (PO) corresponding to the first and second lactate thresholds (LT1PO and LT2PO), subsequently examining their relationship to the mean maximal power (MMP) and race time achieved across three on-water sprint kayak time-trials. Twelve well-trained sprint kayak athletes completed an on-water GXT and a 200-, 500- and 1000-m time-trial utilising novel instrumented paddle technology. Stepwise multiple regression was used to determine whether equations incorporating 200-, 500- and 1000-m MMP data could be used as an alternative method for estimating LT1PO and LT2PO. On-water GXT derived LT1PO and LT2PO were 151 ± 34 and 194 ± 39 W, respectively. For the 200-, 500- and 1000-m time-trials, MMP were 528 ± 143, 358 ± 92 and 287 ± 67 W, respectively. Athletes' LT1PO and LT2PO had very-large inverse relationships to 200-, 500- and 1000-m time-to-completion (r = −.71 to −.85, P ≤.010) and very-large, to near-perfect positive relationships to 200-, 500- and 1000-m MMP (r =.81 to.94, P ≤.001). The equation incorporating 1000-m MMP alone provided the best prediction of LT1PO and LT2PO, explaining 78% and 88% of the variance, and yielding a standard error of estimate (SEE) of 11.3% and 7.1% for these measures, respectively. The results of this study provide further evidence to support the ecological validity of recently developed on-water GXTs graded by PO, since LT1PO and LT2PO were significantly correlated to 200-, 500- and 1000-m performance. Practitioners could also predict LT2PO with reasonable accuracy based solely from a 1000-m time-trial; potentially providing an alternative, non-invasive, competition-specific protocol for threshold determination. Highlights The fact that LT1PO and LT2PO had very-large, to near-perfect positive relationships to 200-, 500- and 1000-m MMP suggests that coaches should consider these relative submaximal aerobic-fitness variables when evaluating the performance of sprint kayak athletes, regardless of their race specialty. While the SEE and 95% limits of agreement (95%LoA) values for the prediction of LT1PO may be too large to be practically meaningful, measures of LT2PO could be predicted with a reasonable level of accuracy based upon 1000-m MMP. The ability to inform athletes' LT2PO from a single 1000-m time-trial is advantageous since it would provide a more feasible, and time-efficient testing protocol within the athletes' training schedule compared to GXTs, potentially allowing coaches and practitioners to monitor changes in LT2PO, and subsequently review individual training zones, more regularly. Given that LT1PO and LT2PO derived from on-water GXTs had very-large, to nearly perfect relationships to 200-, 500- and 1000-m performance, practitioners may prefer to use on-water, rather than laboratory-based GXTs given their greater practical significance and ecological validity. [ABSTRACT FROM AUTHOR]

Prediction of power output plays a vital role in the installation and operation of photovoltaic modules. In this paper, two photovoltaic module technologies, amorphous silicon and copper indium gallium selenide installed outdoors on the rooftop of the University of Dodoma, located at 6.5738° S and 36.2631° E in Tanzania, were used to record the power output during the winter season. The average data of ambient temperature, module temperature, solar irradiance, relative humidity, and wind speed recorded is used to predict the power output using a non-linear autoregressive artificial neural network. We consider the Levenberg-Marquardt optimization, Bayesian regularization, resilient propagation, and scaled conjugate gradient algorithms to understand their abilities in training, testing and validating the data. A comparison with reference to the performance indices: coefficient of determination, root mean square error, mean absolute percentage error, and mean absolute bias error is drawn for both modules. According to the findings of our investigation, the predicted results are in good agreement with the experimental results. All the algorithms performed better, and the predicted power out of both modules using the Bayesian regularization algorithm is observed to exhibit good processing capabilities compared to the other three algorithms that are evident from the measured performance indices. [ABSTRACT FROM AUTHOR]

The actuator disc model (ADM) incorporated into the k-ε turbulence model of EI Kasmi is able to simulate the wind farm wakes with high fidelity, which is essential for layout optimization and the evaluation of power production in modern wind farms. However, the effects of the parameter C4ε in the k-ε model of EI Kasmi on turbulent kinetic energy (TKE) in the superposition areas and the recovery of wind farm wake velocity have rarely been studied. To this end, the k-ε model of EI Kasmi is coupled with the advanced ADM in PHOENICS to investigate the influence of the parameter C4ε on the wake simulation of wind farms (e.g., two offshore wind farms, one onshore wind farm). It is concluded that a decreased parameter C4ε makes the generation range of TKE in the vicinity of the rotor smaller, but the TKE near the rotor becomes larger, and the wake recovery rate of the downstream turbine is less affected by the near wake. As the interwind turbine spacing increases, the influence area of TKE in the wake region of each downstream machine gradually reduces, and atmospheric turbulence plays a dominant role in wake recovery. A decreased parameter C4ε can effectively promote the inflow wind velocity and power output of downstream turbines. The power output simulated compares well with the measured power value when the parameter C4ε = 0.15. [ABSTRACT FROM AUTHOR]

Muscles convert chemical energy to mechanical work. Mechanical performance of a muscle is often assessed by the muscle's ability to shorten and generate power over a range of loads or forces, characterized by the force–velocity and force–power relationships. The hyperbolic force–velocity relationship of muscle, for a long time, has been regarded as a pure empirical description of the force–velocity data. Connections between mechanical manifestation in terms of force–velocity properties and the kinetics of the crossbridge cycle have only been established recently. In this review, we describe how the model of Huxley's crossbridge kinetics can be transformed to the hyperbolic Hill equation, and link the changes in force–velocity properties to molecular events within the crossbridge cycle driven by ATP hydrolysis. This allows us to reinterpret some findings from previous studies on experimental interventions that altered the force–velocity relationship and gain further insight into the molecular mechanisms of muscle contraction under physiological and pathophysiological conditions. [ABSTRACT FROM AUTHOR]

Background: Mixed-reality sports are increasingly reaching the highest level of sport, exemplified by the first Virtual Tour de France, held in 2020. In road races, power output data are only sporadically available, which is why the effect of power output on race results is largely unknown. However, in mixed-reality competitions, measuring and comparing the power output data of all participants is a fundamental prerequisite for evaluating the athlete’s performance.Objective: This study investigates the influence of different power output parameters (absolute and relative peak power output) as well as body mass and height on the results in mixed-reality competitions.Methods: We scrape data from all six stages of the 2020 Virtual Tour de France of women and men and analyze it using regression analysis. Third-order polynomial regressions are performed as a cubic relationship between power output and competition result can be assumed.Results: Across all stages, relative power output over the entire distance explains most of the variance in the results, with maximum explanatory power between 77% and 98% for women and between 84% and 99% for men. Thus, power output is the most powerful predictor of success in mixed-reality sports. However, the identified performance-result gap reveals that other determinants have a subordinate role in success. Body mass and height can explain the results only in a few stages. The explanatory power of the determinants considered depends in particular on the stage profile and the progression of the race.Conclusion: By identifying this performance-result gap that needs to be addressed by considering additional factors like competition strategy or the specific use of equipment, important implications for the future of sports science and mixed-reality sports emerge.

Muscles convert chemical energy to mechanical work. Mechanical performance of a muscle is often assessed by the muscle’s ability to shorten and generate power over a range of loads or forces, characterized by the force–velocity and force–power relationships. The hyperbolic force–velocity relationship of muscle, for a long time, has been regarded as a pure empirical description of the force–velocity data. Connections between mechanical manifestation in terms of force–velocity properties and the kinetics of the crossbridge cycle have only been established recently. In this review, we describe how the model of Huxley’s crossbridge kinetics can be transformed to the hyperbolic Hill equation, and link the changes in force–velocity properties to molecular events within the crossbridge cycle driven by ATP hydrolysis. This allows us to reinterpret some findings from previous studies on experimental interventions that altered the force–velocity relationship and gain further insight into the molecular mechanisms of muscle contraction under physiological and pathophysiological conditions.

Background: Caffeine, widely recognized as an ergogenic aid, has undergone extensive research, demonstrating its effectiveness to enhance endurance performance. However, there remains a significant gap in systematically evaluating its effects on time trial (TT) performance in cyclists., Purpose: This meta-analysis aimed to determine the efficacy of caffeine ingestion to increase cycling TT performance in cyclists and to evaluate the optimal dosage range for maximum effect., Methods: A search of four databases was completed on 1 December 2023. The selected studies comprised crossover, placebo-controlled investigations into the effects of caffeine ingestion on cycling TT performance. Completion time (Time) and mean power output (MPO) were used as performance measures for TT. Meta-analyses were performed using a random-effects model to assess the standardized mean differences (SMD) in individual studies., Results: Fifteen studies met the inclusion criteria for the meta-analyses. Subgroup analysis showed that moderate doses of caffeine intake (4-6 mg/kg) significantly improved cycling performance (SMD Time  = -0.55, 95% confidence interval (CI) = -0.84 ~ -0.26, p  < 0.01, I 2  = 35%; SMD MPO  = 0.44, 95% CI = 0.09 ~ 0.79, p  < 0.05, I 2  = 39%), while the effects of low doses (1-3 mg/kg) of caffeine were not significant (SMD Time  = -0.34, 95% CI = -0.84 ~ 0.17, p  = 0.19, I 2  = 0%; SMD MPO  = 0.31, 95% CI = -0.02 ~ 0.65, p  = 0.07, I 2  = 0%)., Conclusion: A moderate dosage (4-6 mg/kg) of caffeine, identified as the optimal dose range, can significantly improve the time trial performance of cyclists, while a low dose (1-3 mg/kg) does not yield improvement. In addition, the improvements in completion time and mean power output resulting from a moderate dose of caffeine are essentially the same in cycling time trails.

Emerging trends in technological innovations, data analysis and practical applications have facilitated the measurement of cycling power output in the field, leading to improvements in training prescription, performance testing and race analysis. This review aimed to critically reflect on power profiling strategies in association with the power-duration relationship in cycling, to provide an updated view for applied researchers and practitioners. The authors elaborate on measuring power output followed by an outline of the methodological approaches to power profiling. Moreover, the deriving a power-duration relationship section presents existing concepts of power-duration models alongside exercise intensity domains. Combining laboratory and field testing discusses how traditional laboratory and field testing can be combined to inform and individualize the power profiling approach. Deriving the parameters of power-duration modelling suggests how these measures can be obtained from laboratory and field testing, including criteria for ensuring a high ecological validity (e.g. rider specialization, race demands). It is recommended that field testing should always be conducted in accordance with pre-established guidelines from the existing literature (e.g. set number of prediction trials, inter-trial recovery, road gradient and data analysis). It is also recommended to avoid single effort prediction trials, such as functional threshold power. Power-duration parameter estimates can be derived from the 2 parameter linear or non-linear critical power model: P(t) = W′/t + CP (W′—work capacity above CP; t—time). Structured field testing should be included to obtain an accurate fingerprint of a cyclist's power profile. [ABSTRACT FROM AUTHOR]

Hebisz, RG, Hebisz, P, and Zatoń, MW. Heart rate variability after sprint interval training in cyclists and implications for assessing physical fatigue. J Strength Cond Res 36(2): 558–564, 2022—This study evaluated the time- and frequency-domain indexes of heart rate variability (HRV) during sprint interval exercise test (SIXT) and identify the onset of fatigue by HRV concurrent with changes in average (Pavg) and peak (Ppeak) power output, total oxygen uptake (V̇ o 2tou), and blood hydrogen (H+) and lactate (La−) concentrations. Twenty-seven cyclists performed 4 sets of SIXT in which each set consisted of four 30-second maximal sprints interspersed with 90 seconds of low-intensity cycling. Each set was separated by 25–40 minutes of recovery. Before beginning each set, HRV was analyzed by time (mean normal-to-normal RR intervals [RRNN], SD of normal-to-normal RR intervals [SDNN], and square root of the mean squared difference between successive normal-to-normal RR intervals [RMSSD]) and frequency (total spectral power [T] and very low- [VLF], low- [LF], and high-frequency [HF] spectral power) domain methods. Pavg, Ppeak, and V̇ o 2tou were recorded in each set, and H+ and La− were measured after each set. RRNN, SDNN, and VLF decreased in the second set, whereas all time and frequency indexes of HRV decreased in the third and fourth set. Pavg and H+ decreased, while V̇ o 2tou increased in the fourth set. Ppeak decreased in the second, third, and fourth set. Correlations were found between the changes in the time and frequency indexes of HRV with H+, La−, and V̇ o 2tou. The results indicate that HRV does not reflect the onset of physical fatigue in SIXT as was observed in Pavg and no correlation was found between the changes in HRV with Pavg and Ppeak. [ABSTRACT FROM AUTHOR]

Previous studies have shown the abundance of tidal energy resources in Indonesia. However, some sites have yet to be considered. The Lepar Strait, for example, is located between Bangka and Lepar Islands. This paper describes a field survey and numerical modelling conducted in the Lepar Strait. The modelling was performed using Delft3D, with the aim of determining potential sites for harvesting tidal current energy and estimate the generated power. In the modelling, the domain decomposition method was employed for model downscaling, allowing grid resolution reaching 130 x 130 m2, which is sufficient to represent the narrow gaps between tiny islands in the area of interest. The National Bathymetric (Batnas) from the Geospatial Information Agency (BIG) and the International Hydrographic Organization (IHO) tide constituents were applied for the bathymetry and tide elevation boundaries. The comparison between the surveyed and modelled data showed a good agreement. The RMSE and r for water level are > 0.95 and < 0.15, and the RMSE for velocity was <0.19. Furthermore, an energetic flow reaching 1.5 m/s was found at the Northern part of Lepar Strait, situated at the narrow gaps. The Gorlov Helical Turbine was selected in this study due to shallow water and low mean velocity. In the 2019 model, the power density and power output at the best potential sites were 2,436.94 kWh/m2 and 1,870.41 kWh, respectively. This number is higher than those previously found in Kelabat Bay. Nonetheless, it is still far below the currently promising project in Larantuka and Lombok Straits. Future research is recommended, to conduct a detailed field measurement campaign and assess the impact of energy extraction in more detail. [ABSTRACT FROM AUTHOR]

This research was performed to optimize the performance characteristics of the Nigerian Jebba Hydropower Plant in order to enhance its generation of electricity. Pertinent hydropower data were hourly collected from the plant from 8:00 am to 5:00 pm between 2016 and 2018. The coefficient of determination obtained from the response surface methodology (RSM) showed that discharge, pressure drop, stator temperature and water pressure strongly influenced the generation of estimated power. Also, the contour and surface plots suggested that the discharge (D) 8200.00–8600.00 m3/s and pressure drop (Pd) ranging from 27.50–28.50 m gave the optimal power generation indicating that both factors must be kept high when the hydropower plant is in operation. The instability of power generation was attributed to the reduction in the net available head as turbine inlet decreased. The study, therefore, showed that net power output, speed of the turbine, and efficiency of the hydropower plant could be optimized with increase discharge and gross head. Predicted optimal values for discharge, pressure drop, stator temperature, and water pressure were 8783.3667 m3, 28.59 m, 58.00°C, and 31.00 N/m2 respectively. [ABSTRACT FROM AUTHOR]

Limited information is available regarding the role of anaerobic metabolism capacity on GOLD 1 and 2 COPD patients during upper limb exercise. We aimed to compare the upper limb anaerobic power capacity, blood lactate concentration, cardiovascular and respiratory responses, in male COPD patients versus healthy subjects during the 30-s Wingate anaerobic test (WAnT). The rate of fatigue and time constant of the power output decay (τ, tau) were also calculated and a regression analysis model was built to assess the predictors of τ in these patients. Twenty-four male COPD patients (post-bronchodilator FEV1 73.2 ± 15.3% of predicted) and 17 healthy subjects (FEV1 103.5 ± 10.1% of predicted) underwent the WAnT. Measurements were performed at rest, at the end of the WAnT, and during 3′ and 5′ of recovery time. Peak power (p = 0.04), low power (p = 0.002), and mean power output (p = 0.008) were significantly lower in COPD patients than in healthy subjects. Power output decreased exponentially in both groups, but at a significantly faster rate (p = 0.007) in COPD patients. The time constant of power decay was associated with resistance (in ohms) and fat-free mass (r2 = 0.604, adjusted r2 = 0.555, and p = 0.002). Blood lactate concentration was significantly higher in healthy subjects at the end of the test, as well as during 3′ and 5′ of recovery time (p < 0.01). Compared with healthy subjects, COPD patients with GOLD 1 and 2 presented lower upper limb anaerobic capacity and a faster rate of power output decrease during a maximal intensity exercise. Also, the WAnT proved to be a valid tool to measure the upper limb anaerobic capacity in these patients. [ABSTRACT FROM AUTHOR]

Solar energy is at the forefront of renewable energy sources. Depending on the increasing energy need, the use of clean energy sources is inevitable in terms of human health and the environment. The application of solar chimney power plants (SCPPs) is one of the not very old and promising systems. SCPPs are systems that attract attention with their long life and simple working principles. SCPPs have three basic elements: collector, chimney and turbine, and optimizing these elements in terms of design and operational parameters plays a key role in the performance parameters of the system such as power output and efficiency. This study, which references the Manzanares pilot plant, aims at the collector dimensioning of the system to achieve the optimum power output and efficiency from the plant and to assess the upper thermodynamic limits of the Manzanares pilot plant. The most challenging aspect of SCPPs, in general, is their high cost, and large collector areas constitute a notable fraction of this cost. Therefore, for performance and cost optimization, collector dimensioning is of vital importance and reveals the innovative aspect of this study. For this purpose, a 3D 90° computational fluid dynamics model is created with ANSYS engineering software. RNG k-e turbulence model and discrete ordinates solar ray-tracing algorithm are applied to the model. In the study, solutions are taken in the dimensions of the pilot plant with an ambient temperature of 290 K and two different radiation intensities of 800 and 1000 W/m2. The collector radius (Rcoll) is increased up to 2 times the reference size and its effect on the system is evaluated. It is found that the plant, which produces an electrical power of 46.6 kW at 800 W/m2, will generate 138.3 kW of electrical power if the Rcoll is doubled. The optimum collector radius rate (Xcoll) is found to be in the range of 1.00–1.50. For the greater values of Xcoll than 1.50 (183 m), it is observed that the exponential increase in power output stops, and cost-related upper thermodynamic limits are achieved. [ABSTRACT FROM AUTHOR]