Thermoelectric performance of MoSi(2)As(4) monolayer

Thermoelectric performance of MoSi2As4 monolayer is investigated using density functional theory combined with Boltzmann transport theoy. The maximal power factors of n- and p-type by PBE (HSE06) functional are 7.73 (48.31) and 32.84 (30.50) mW m-1 K-2 at the temperature of 1200 K, respectively. The lattice thermal conductivity is less than 30 W m-1 K-1 above 800 K. The thermoelectric figure of merit can reach 0.33 (0.58) and 0.90 (0.81) using PBE (HSE06) functional for n- and p-type under appropriate carrier concentration at 1200K, respectively. Thus, the p-type MoSi2As4 monolayer is predicted to be a potential candidate for high-temperature thermoelectric applications.

Can Popular High-Intensity Interval Training (HIIT) Models Lead to Impossible Training Sessions?

High-Intensity Interval Training (HIIT) is a time-efficient training method suggested to improve health and fitness for the clinical population, healthy subjects, and athletes. Many parameters can impact the difficulty of HIIT sessions. This study aims to highlight and explain, through logical deductions, some limitations of the Skiba and Coggan models, widely used to prescribe HIIT sessions in cycling. We simulated 6198 different HIIT training sessions leading to exhaustion, according to the Skiba and Coggan-Modified (modification of the Coggan model with the introduction of an exhaustion criterion) models, for three fictitious athlete profiles (Time-Trialist, All-Rounder, Sprinter). The simulation revealed impossible sessions (i.e., requiring athletes to surpass their maximal power output over the exercise interval duration), characterized by a few short exercise intervals, performed in the severe and extreme intensity domains, alternating with long recovery bouts. The fraction of impossible sessions depends on the athlete profile and ranges between 4.4 and 22.9% for the Skiba model and 0.6 and 3.2% for the Coggan-Modified model. For practitioners using these HIIT models, this study highlights the importance of understanding these models’ inherent limitations and mathematical assumptions to draw adequate conclusions from their use to prescribe HIIT sessions.

Post-activation performance enhancement after inclusion of opponent versus no opponent during isoinertial crossover step exercise: A randomized crossover trial

This study sought to determine whether the inclusion of an opponent on an isoinertial crossover step task influenced the post-activation response and power production. Twenty adult male team-sports athletes participated in a randomized crossover trial. We used a novel design in which the performance of an isoinertial flywheel exercise was tested with or without the inclusion of sport-specific constraints (inclusion of an opponent vs. no opponent) in one of the two sequences (sequence one: constraint manipulation followed by no constraint manipulation; and sequence two: no constraint manipulation followed by constraint manipulation). Maximal power was recorded during exercise; then the coefficient of variation of maximal power was estimated. Post-activation responses were measured using unilateral jump height and change-of-direction time. Also, ankle dorsiflexion range of motion was measured. The use of an isoinertial flywheel resulted in improved ankle dorsiflexion and the capacity to repeat change-of-direction. Furthermore, the inclusion of an opponent was associated with a higher variability of the power output in the concentric phase of the movement. Importantly, performing the crossover step task in front of an opponent was also linked to a positive correlation between unilateral countermovement jump and power output. We conclude that the inclusion of typical constraints of the performance environment may have induced movement adaptations to accommodate the unpredictability associated with the actions of the opponent.

Optical Fiber Sensor for Temperature and Strain Measurement Based on Multimode Interference and Square-Core Fiber

A variety of specialty fibers such as no-core fiber (NCF) have already been studied to reveal their sensing abilities. In this work, we investigate a specialty fiber, square-core fiber, for temperature and strain sensing. A simple single-mode–multimode–single-mode (SMS) fiber sensor was fabricated, consisting of a 30-cm-long square-core fiber. The experimental results indicate that the maximal wavelength-temperature and wavelength-strain sensitivities are −15.3 pm/∘C and −1.5 pm/με, respectively, while the maximal power-temperature and power-strain sensitivities are 0.0896 dBm/∘C and 0.0756 dBm/με. Analysis of the results suggests that the fiber sensor has the potential to be used as a high-sensitivity temperature sensor with a low strain sensitivity.

Great power comes at a high (locomotor) cost: the role of muscle fascicle length in the power versus economy performance trade-off

Muscle design constraints preclude simultaneous specialization of the vertebrate locomotor system for explosive and economical force generation. The resulting performance trade-off between power and economy has been attributed primarily to individual differences in muscle fiber type composition. While certainly crucial for performance specialization, fiber type likely interacts with muscle architectural parameters, such as fascicle length, to produce this trade-off. Longer fascicles composed of more serial sarcomeres can achieve faster shortening velocities, allowing for greater power production. Long fascicles likely reduce economy, however, because more energy-consuming contractile units are activated for a given force production. We hypothesized that longer fascicles are associated with both increased power production and locomotor cost. In a set of 11 power- and 13 endurance-trained recreational athletes, we measured 1) muscle fascicle length via ultrasound in gastrocnemius lateralis, gastrocnemius medialis, and vastus lateralis, 2) maximal power during cycling and countermovement jumps, and 3) running cost of transport. We estimated muscle fiber type noninvasively based on the pedaling rate at which maximal cycling power occurred. As predicted, longer gastrocnemius muscle fascicles were correlated with greater lower-body power production and cost of transport. Multiple regression analyses revealed that variability in maximal power was explained by fiber type (48% for cycling; 25% for jumping) and average fascicle length (18% for cycling; 12% for jumping), while average fascicle length accounted for 15% of the variation in cost of transport. These results suggest that, at least for certain muscles, fascicle length plays an important role in the power versus economy performance trade-off.

Experimental Analysis of the Arrays of Macro Fiber Composite Patches for Rotational Piezoelectric Energy Harvesting from a Shaft

Four arrays of three MFC patches, glued onto a rotating shaft, were compared in laboratory research. The first array was based on a delta circuit and equipped with one three-phase rectifier; the second array was based on a star circuit and equipped with one three-phase rectifier; the third array was based on parallel connection and equipped with three full-bridge rectifiers; and the fourth array was based on a series connection and equipped with three full-bridge rectifiers. The array based on a delta circuit generated the highest value of maximal electric power in comparison to the rest of arrays. It was experimentally observed that the arrays based on delta or star circuits of MFC patches and equipped with one three-phase rectifier generated a higher value of maximal power than arrays based on the connections of three full-bridge rectifiers, connected in parallel or in series. The array based on parallel connection generated the highest maximal value of current in comparison to rest of arrays for low values of load resistance (from 10 kΩ to 40 kΩ depending on the experiment). For higher values of load resistance arrays based on delta circuits and star circuits generated higher values of current than the array based on parallel connection.

Topology optimized thermoelectric generator: a parametric study

Typical thermoelectric generator legs are brittle which limits their application in vibratory and shear environments. Research is conducted to develop compliant thermoelectric generators (TEGs) capable of converting thermal loads to power, while also supporting shear and vibratory loads. Mathematical structural, thermal, and power conversion models are developed. Topology optimization is employed to tailor the TEG design yield maximal power production while sustaining the applied shear and vibratory loads. As a specific example, results are presented for optimized TEG legs with a void volume fraction of 0.2 that achieve compliance shear displacement of 0.0636 (from a range of 0.0504 to 0.6079). In order to achieve the necessary compliance to support the load, the power reduction is reduced by 20% relative to similarly sized void free TEG legs.

Spring-resonance-assisted maximal power tracking control of a direct-drive wave energy converter

In this paper, to finely accommodate large-range wave frequencies on same sea areas, a spring resonance mechanism is created to facilitate maximal power tracking control of a direct-drive wave energy converter (DWEC) that is expected to be equipped on same sea areas, whereby the spring-resonance-assisted module is devised by mover-coaxial springs and reshapes the resonant-frequency pertaining to a specific spectrum. By virtue of modeling the spring-resonance-assisted DWEC system, a finite-time disturbance observer (FDO) is deployed to rapidly compensate environmental disturbances. Accordingly, the FDO-based integral sliding-mode (ISM) control framework is proposed, to accurately achieve the resonance between the DWEC buoy and wave, thereby contributing to spring-resonance-assisted maximal power tracking control (SR-MPTC) of the DWEC. Simulation studies and comprehensive comparisons demonstrate that the proposed SR-MPTC scheme performs remarkably fast adaptation and accurately maximal power tracking in the presence of disturbances and spring resonance assistance.