This study examined the effects of incorporating 8 weeks of bi-weekly lower limb elastic band based loaded plyometric training into the in-season regimen of junior handball players. Participants were ...assigned between control (
= 15, age: 18.1 ± 0.5 years, body mass: 73.7 ± 13.9 kg, height: 1.82 ± 0.06 m, body fat: 14.4 ± 6.0%) and experimental groups (
= 14, age: 17.7 ± 0.3 years, body mass: 76.8 ± 10.7 kg, height: 1.83 ± 0.04 m, body fat: 13.4 ± 3.8%). Measures obtained before and after the intervention included a cycle ergometer force-velocity test, squat and countermovement jump characteristics, sprints times, repeated change of direction and change of direction tests (COD), a 1-RM half-back squat, and anthropometric estimates of limb volumes. Gains in the experimental group relative to controls included absolute muscle power (W) (Δ 23.1%;
< 0.05; ES = 0.565), relative muscle power (W.kg
) (Δ 22.1%;
< 0.05; ES = 0.573), sprint times over 5 and 30 m (Δ-8.7%;
< 0.01; ES = 0.921 and Δ-7.2%;
< 0.05; ES = 0.573, respectively), COD times (Δ-9.2%;
< 0.05; ES = 0.561) and all repeated COD parameters except the fatigue index. However, a significant improvement by time interaction was observed in both groups on some anthropometric parameters (leg muscle volume and surface section thigh max), 1-RM half- back squat and vertical jump performance. We conclude that bi-weekly elastic band-loaded plyometric training improves the ability to sprint, COD and repeated COD relative to regular training, and thus it can be recommended to young male team handball players as a new method of plyometric training to improve important elements of their physical performance.
This paper introduces the concept of fault-tolerant control (FTC) of a multi-string battery energy storage system (BESS) in the dynamic reduction system of a traction substation load (DROPT). The ...major task of such a system is to reduce the maximum demand for contracted peak power, averaged for 15 min. The proposed concept, based on a multi-task control algorithm, takes into account: a three-threshold power limitation of the traction substation, two-level reduction of available power of a BESS and a multi-string structure of a BESS. It ensures the continuity of the maximum peak power demand at the contracted level even in the case of damage or disconnection of at least one chain of cells of the battery energy storage (BES) or at least one converter of the power conversion system (PCS). The proposed control strategy has been tested in a model of the system for dynamic reduction of traction substation load with a rated power of 5.5 MW. Two different BESS implementations have been proposed and several possible cases of failure of operations have been investigated. The simulation results have shown that the implementation of a multi-string BESS and an appropriate control algorithm (FTC) may allow for maintenance of the major assumption of DROPT, which is demanded power reduction (from 3.1 MW to 0.75 MW), even with a reduction of the BESS available power by at least 25% and more in the even in fault cases.
A hybrid chirped pulse amplification system composed by the monolithic fiber pre-amplifier and a two-stage single-pass single crystal fiber amplifier was demonstrated. A maximum power of 68 W at the ...repetition rate of 100 kHz was obtained. The laser pulses were amplified and then compressed using a 1600 line/mm grating pair compressor. A short pulse duration of 358 fs and a power of 54 W were obtained at 100 kHz, corresponding to a peak power of 1.508 GW, to the best of our knowledge, this is the highest peak power ever obtained from single crystal fiber at repetition rate above 100 kHz due to the consideration of the third order dispersion which was engraved in the stretcher and the tuning capacity of higher-order dispersion compensation of chirped fiber Bragg grating. Additionally, the beam quality better than 1.3 was obtained. This high peak power CPA system with excellent comprehensive parameters will find various applications in scientific research and industrial applications.
Liquid-solid triboelectric nanogenerator (LS-TENG) has emerged as a powerful tool in energy harvesting and motion detecting. There is a recognized need for improving the power output and ...signal-to-noise ratio of LS-TENG. The instantaneous discharging mechanism of LS-TENG is studied and experimentally realized by a controllable switch structure in this paper. The peak short circuit current and peak power output (at 1 MΩ) are increased by over 26 and 1700 times, respectively, with respect to the control LS-TENG working in the single electrode mode. This research provides a fresh insight in designing sensors with high signal-to-noise ratio and energy harvestors that have a superior performance in driving devices with low load resistance.
Liquid-solid triboelectric nanogenerator (LS-TENG) has emerged as a powerful tool in energy harvesting and motion detecting. There is a recognized need for improving the power output and signal-to-noise ratio of LS-TENG. The instantaneous discharging mechanism of LS-TENG is studied and experimentally realized by a controllable switch structure in this paper. The peak short circuit current and peak power output (at 1 MΩ) are increased by over 26 and 1700 times, respectively, with respect to the control LS-TENG working in the single electrode mode. This research provides a fresh insight in designing sensors with high signal-to-noise ratio and energy harvestors that have a superior performance in driving devices with low load resistance. Display omitted
•Enhanced short circuit current output compared to LS-TENG working in single electrode mode is obtained.•Greatly enhanced peak power output especially with low load resistance is obtained.•The proposed IDLS-TENG has a great application potential in self-powered sensors with high signal-to-noise ratio.
ABSTRACTHammami, M, Gaamouri, N, Shephard, RJ, and Chelly, MS. Effects of contrast strength vs. plyometric training on lower-limb explosive performance, ability to change direction and neuromuscular ...adaptation in soccer players. J Strength Cond Res 33(8)2094–2103, 2019—The aim was to compare the effects of 2 differing 8-week in-season strength training programs (contrast strength training CST vs. plyometric training PT) on selected performance tests (5 and 40 m sprints, S 4 × 5 m change of direction test, squat jump SJ and countermovement jump CMJ, leg peak power on a cycle-ergometer force-velocity test, 1 repetition maximal half-squat, and electromyographic EMG activity of the vastus lateralis, vastus medialis, and rectus femoris muscles during vertical jump tests). Forty male soccer players (age = 15.8 ± 0.4 years; body mass = 58.8 ± 6.3 kg; body height = 1.74 ± 0.06 m; body fat = 10.5 ± 1.9%) were divided between a contrast strength group (CSG, n = 14), plyometric group (PG, n = 14), and control group (CG, n = 12). Both training programs enhanced sprint performance (p < 0.001 in 5 m; p ≤ 0.05 in 40 m) and change of direction test scores (p < 0.001) relative to controls. The plyometric group and CSG increased SJ height relative to the CG, with a slightly greater response in CSG compared with PG (p ≤ 0.05). Most CMJ scores increased significantly in both CSG and PG relative to the CG, with no intergroup differences in training response. Most force-velocity scores increased significantly in the CSG relative to PG and CG. The EMG parameters also increased in the CSG relative to both PG and CG. In summary, most measures of athletic performance in male soccer players were enhanced after CST and PT. However, the improvement of physical performance was better with 8 weeks of CST than with PT. Thus, coaches should be encouraged to include CST as an element of in-season conditioning.
Probabilistic shaping for intensity modulation and direct detection (IM/DD) links is discussed and a peak power constraint determined by the limited modulation extinction ratio (ER) of optical ...modulators is introduced. The input distribution of 4-ary unipolar pulse amplitude modulation (PAM) symbols is optimized for short-reach transmission links without optical amplification nor in-line dispersion compensation. The resulting distribution is symmetric around its mean allowing to use probabilistic amplitude shaping (PAS) to generate symbols that are protected by forward error correction (FEC) and that have the optimal input distribution. The numerical analysis is confirmed experimentally for both an additive white Gaussian noise (AWGN) channel and a fiber channel, showing gains in transmission reach and transmission rate, as well as rate adaptability.
Purpose
The interpolated twitch technique (ITT) is often used to assess voluntary activation during isometric contractions; however, this may have limited relevance to dynamic contractions. Although ...the ITT has been applied to relatively slow isokinetic contractions (< 150°/s), it has received limited consideration during unconstrained velocity (i.e., isotonic) contractions, despite their relevance to natural movements. Here, we explored the ITT during isotonic knee extension contractions using a modified dynamometer.
Methods
Young males (
n
= 6) and females (
n
= 4) performed isometric and isotonic knee extension contractions of sub-maximal and maximal intensities with doublet (150 Hz) muscle belly stimulations to assess voluntary activation. Following each voluntary isotonic contraction (velocity range ~ 35°/s to ~ 275°/s), resting potentiated doublets were evaluated during passive joint rotation at the same angular velocity achieved during voluntary efforts, to account for force–velocity characteristics. Correlations between voluntary activation and the proportion of maximal torque or power were evaluated for isometric and isotonic contractions, respectively.
Results
Isometric voluntary activation was strongly correlated with increasing torque output (
r
= 0.96,
p
< 0.001). Doublet torque during passive joint rotation displayed a hyperbolic relationship with increasing angular velocity (
r
= 0.98,
p
< 0.001). Isotonic voluntary activation was strongly correlated with increasing power output (
r
= 0.89,
p
< 0.001). During maximal effort contractions, no differences were observed in voluntary activation between isometric and isotonic conditions (89.4% vs. 89.2%,
p
= 0.904).
Conclusions
The ITT is a valid approach to evaluate voluntary activation during an isotonic contraction using a modified dynamometer. Participants were able to achieve a similar high level of voluntary activation during isometric and isotonic contractions.
Charge recombination occurring inside the tribolayer limits the further improvement of triboelectric nanogenerator (TENG) output. While the doping of ferromagnetic medium in triboelectric materials ...has been proven effective in boosting the TENG output, its working mechanism in the tribolayer remains to be investigated. Herein, the dual tribolayer synergistic effect is demonstrated as a means of suppressing surface charge recombination, thus achieving a high peak power density of TENG based on a composite film of polymer/nickel nanoparticles. A dual tribolayer model is proposed to reveal the working mechanism of the ferromagnetic medium for suppressing charge recombination in the positive and negative tribolayer. The charge recombination ratio as a standardized assessment method is defined to quantify the surface charge loss. Owing to the dual tribolayer synergistic effect, the optimal TENG exhibits a record-high peak power density of 15.2 W m-2 Hz-1 with the ultra-low charge recombination ratio of 2.1%, representing a remarkable 3100% increase in comparison to pristine TENG in the atmospheric environment. A self-powered sitting posture monitoring system is developed based on the woven structured DT-TENGs benefiting from the dual-tribolayer synergistic effect. This work demonstrates the superior behavior of TENG in generating ultra-high-power output and provides a significant guidance in materials selection.
Display omitted
•The charge recombination ratio is proposed to quantify the surface charge loss.•Doped ferromagnetic NPs assists in suppressing surface charge recombination.•A synergistic effect is found for DT-TENG via ferromagnetic NPs, especially greatly suppressing charge recombination.•A record-high power density of the DT-TENG can reach 15.2 W m-2 Hz-1 by tribolayer modulation.•A self-powered sitting posture monitoring system with a woven structure DT-TENG is designed.
Purpose The study compared muscle peak power during pneumatic squat exercise with different percentages of load, corresponding to 80%, 100%, and 120% of body mass (BM), in male professional soccer ...players. Methods The study involved 40 male elite soccer players (25.2 ± 3.6 years; 179.6 ± 6.1 cm; 78.3 ± 5.2 kg; body fat 12.3 ± 3.3%) from a club of the Brazilian first division soccer league participating in national competitions organized by the Brazilian Soccer Confederation. Peak power was assessed by using a pneumatic squat machine (squat power test). The athletes applied different training loads during the squat power test (3 trials with 80% of BM followed by a 5-minute rest to perform attempts with 100% and 120%, respectively). Results The two-way ANOVA yielded main effects for group (F3,26 = 3.08, p < 0.04) and for timing of measurement F2,52 = 526.1, p < 0.0001), indicating a significant difference in the absolute peak power of goalkeepers when compared with defenders and midfielders at the loads corresponding to 80%, 100%, and 120% of BM. Intra-group comparison demonstrated a significant increase (p < 0.0001) in the absolute and relative peak power with loads corresponding to 120% of BM when compared with 80% and 100% of BM in all groups (defenders, goalkeepers, midfielders, and forwards). Conclusions The results confirm that loads corresponding to 120% of BM during pneumatic squat exercise contribute to greater absolute and relative peak power.
This study presents a technoeconomic analysis of renewables-based hydrogen production in Queensland, Australia under Optimistic, Reference and Pessimistic scenarios to address uncertainty in cost ...predictions. The goal of the work was to ascertain if the target fam-gate cost of AUD 3/kg (approx. USD 2/kg) could be reached. Economies of scale and the learning rate concept were factored into the economic model to account for the effect of scale-up and cost reductions as electrolyser manufacturing capacity grows. The model assumes that small-scale to large-scale wind turbine (WT)-based and photovoltaic (PV)-based power generation plants are directly coupled with an electrolyser array and utilises hourly generation data for the Gladstone hydrogen-hub region. Employing first a commonly used simplified approach, the electrolyser array was sized based on the maximum hourly power available for hydrogen production. The initial results indicated that scale-up is very beneficial: the levelised cost of green hydrogen (LCOH) could decrease by 49% from $6.1/kg to $3.1/kg when scaling PV-based plant from 10 MW to 1 GW, and for WT-based plant by 36% from $5.8/kg to $3.7/kg. Then, impacts on the LCOH of incorporating curtailment of ineffective peak power and electrolyser overload capacity were investigated and shown to be significant. Also significant was the beneficial effect of recognising that electrolyser efficiency depends on input power. The latter two factors have mostly been overlooked in the literature. Incorporating in the model the influence on the LCOH of real-world electrolyser operational characteristics overcomes a shortcoming of the simplified sizing method, namely that a large portion of electrolyser capacity is under-utilised, leading to unnecessarily high values of the LCOH. It was found that AUD 3/kg is achievable if the electrolyser array is properly sized, which should help to incentivise large-scale renewable hydrogen projects in Australia and elsewhere.
•Three electrolyser sizing methods examined to estimate LCOH.•Overload capacity and dynamic efficiency of the electrolyser incorporated, revealing their substantial impact.•Proper sizing of the electrolyser is required to reach LCOH = AUD 3/kg (USD 2/kg).•Scale-up from MW to GW power can approximately halve LCOH through reduced CAPEX.
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