Breaking Conditions Research Articles

Active motor-cognitive recovery supports reactive agility performance in trained athletes.

Active breaks are suggested to support recovery and performance in sports. Previous research in ball and team sports focused on motor performance such as repetitive sprinting or change of direction. This does not account for the interaction between motor and cognitive task demands in sports. Therefore, this study is the first to investigate the effectiveness of an active motor-cognitive break to support reactive agility performance. Twenty (7 female and 13 male) healthy trained young adults (mean age: 26years) performed an active or passive 5 min break following a fatiguing protocol of six 100m reactive agility runs with an intermittent break of 40s. Prior to the experiment (pre), after fatigue (post), and following the rest condition (retention), a reactive agility test was performed using the SKILLCOURT technology. In addition, lactate, heartrate, and physical exertion were recorded. Active rest contained two motor-cognitive training tasks on the SKILLCOURT combining low to moderate physical intensity with conflict inhibition and decision-making. During passive rest, participants remained seated. When comparing post and retention agility tests, results indicate significantly stronger performance gains following the active when compared to the passive break condition (p=0.02 and ηp 2=0.24). This was not associated with any differences in physiological parameters such as lactate, heart rate, or RPE (p≥0.25). The results suggest that active motor-cognitive breaks support recovery and improve sport-related reactive agility performance. Performance gains in the active break are likely attributable to cognitive performance effects rather than physiological recovery, which may benefit athletes especially in ball and team sports.

Faster than real-time, phase-resolving, data-driven model of wave propagation and wave–structure interaction

A machine learning time-series prediction approach is proposed for wave propagation and wave load prediction. Under unidirectional wave conditions and variable bathymetry, given a wave gauge upstream, a model is shown to reproduce wave elevation or wave forces downstream under irregular steep and either non-breaking or breaking conditions. Attempts to perform the opposite calculation, predicting upstream conditions from downstream measurements, results in higher error, likely due to information loss under breaking conditions. For choice of machine learning approach, comparisons show that the Time-series Dense Encoder (TiDE) approach results in a good balance between model complexity, stability, computational time, and error. Over a flat bottom, time-series of wave elevation can be predicted up to 10 wavelengths away, though with a degraded accuracy compared to shorter distances. Similar results are shown for time-series of forces on a vertical cylinder, showing better results than a simple Morison approach, as used in engineering tools such as OpenFAST, but with a similarly fast computational time. Generalizations show that training on irregular wave data permit extrapolations to periodic wave cases. Finally, the same method also is also demonstrated at field-scale, comparing results between two offshore buoys.

Impact of tunneling parameters on disc cutter wear during rock breaking in transient conditions

The assessment of disc cutter wear in subway shield construction beneath operational airports is a critical endeavor for evaluating the structural integrity of shield machines. This study delved into the linear tunnel project linking Station T1 to T3 within the Baiyun airport, focusing on the intricate relationship between tunneling parameters during rock-machine interactions and the impact of disc cutter installation radius on wear amount. In addition, dynamic impact transient rock-breaking tests of shield disc cutters were performed under the coupled thermo-hydro-mechanical triaxial conditions to ensure the validity of the relationship between mass-point velocity and the transient rock-breaking behavior of the disc cutter. The analysis revealed that when the shield thrust was between 17000 kN and 21000 kN, the total thrust of the shield had a significant effect on the advancement speed and cutterhead torque. Notably, the wear amount of the cutter increased approximately linearly with the installation radius, while the wear of the gauge cutter was also affected by the inclination angle. Furthermore, the study uncovered a linear correlation between the cutting length of the disc cutter and the magnitude of wear. Within a cutting length range between 440 km and 2276 km, the disc cutter's installation position had minimal impact on the wear coefficient. Simultaneously, this study employed the mass-point velocity to simulate the thrust and rolling forces in the equivalent shield tunneling processes. The findings underscored a positive correlation between disc cutter wear and shield advancement speed, cutterhead rpm, and mass-point velocity. When the mass-point velocity of the shield reached the maximum value of 0.666 m/s, the wear of the shield disc cutter also reached the maximum value of 27.5 mm, providing the quantitative reference for evaluating the influences of shield tunneling parameters on the cutter wear under transient impact rock breaking conditions.

Real-time in-situ coatings corrosion monitoring using machine learning-enhanced triboelectric nanogenerator

Current methods for monitoring coating corrosion are limited by their inability to provide real-time data and dependence on external power sources. This study presents a novel in-situ corrosion monitoring system using a solid-liquid triboelectric nanogenerator (TENG) that converts mechanical energy into electrical signals for self-powered sensing. TENG signals and electrochemical impedance spectra were measured on a dopamine-modified lignin-polydimethylsiloxane coating on steel in 1 M NaCl solution under no corrosion, indentation, pitting, and broken conditions, respectively. We extract time-frequency features from the TENG signals to predict the coating’s corrosion condition by applying a customised convolutional neural network (CNN). By extracting time-frequency features from the TENG signals and applying a custom CNN, a prediction accuracy of 99 % for corrosion classification was achieved. Furthermore, the CNN regression model predicted coating impedance values with a high coefficient of determination (R² = 0.98), demonstrating its effectiveness in tracking corrosion progression. The developed TENG also facilitates defect localisation via a matrix electrode beneath the coating. Our approach introduces a promising real-time technology for in-situ corrosion monitoring.

Hard rock fragmentation by dynamic conical pick indentation under confining pressure

Mechanical mining and excavation in deep metal mines can be regarded as the process of crushing hard rock by conical pick indentation. In this study, a confining pressure loading device was designed and used to carry out dynamic conical pick indentation crushing tests under confining pressure conditions on three types of granite with varying strengths, using the Split Hopkinson Pressure Bar (SHPB). The objective was to quantitatively investigate the effect of confining pressure and rock strength on the indentation crushing characteristics of deep hard rocks. The results indicate that as the confining pressure increases from 5 MPa to 20 MPa, the dimensional parameters such as volume, diameter and depth of the impact groove decrease linearly, while parameters such as the specific energy, indentation force, indentation index and energy utilization rate progressively increase. The increase in the confining pressure inhibits the formation of internal cracks in the rock, enhancing its resistance to pick indentation, which in turn makes rock fragmentation more difficult. This creates unfavorable conditions for efficient rock breaking. Furthermore, rock strength plays a crucial role in the pick indentation process. The higher the rock strength, the greater its resistance to pick indentation, leading to increased energy consumption, accelerated wear of the conical picks, and reduced efficiency in rock breaking.

Filled elastomers sliding over smooth obstacles: Experiments and modeling in large deformations

The objective of this paper is to shed light on the mechanical response of filled elastomers in sliding contact. Compared to situations encountered by tires in breaking conditions, the study only considers smooth obstacles in order to analyze the contribution of finite deformations and of the complex viscosity of filled elastomers without facing all the complexity of surface roughness. For this purpose, a new experiment is introduced that allows to measure the friction on the surface of a filled elastomer that is subjected to large local deformation through a cyclic contact loading applied by sliding indenters. The setup uses smooth spherical indenters sliding on the material of interest within a temperature controlled water tank. The relevance of adhesion forces is reduced by using Teflon as a dry lubricant and Sinnozon as a surfactant. To analyze the experimental results, full-field simulations of the experiments are carried out within the setting of finite viscoelastodynamics by making use of two types of viscoelastic constitutive models for the filled elastomer: (i) a classical viscoelastic model combining a Mooney–Rivlin equilibrium elasticity and Maxwell branches with constant viscosities and (ii) an internal-variable-based viscoelastic model that was introduced in Kumar and Lopez-Pamies (2016) for unfilled elastomers and that is extended herein to account for the more complex viscous response of filled elastomers.

Study of arc and magnetic field parameters under delayed breaking condition of DB-DC VCB

Taking the mechanical double-break DC vacuum circuit breaker (DB DC VCB) as the research object, the magnetic field and temperature field distribution between the breaks and the plasma characteristics under the working condition of gap difference caused by actuator dispersion are investigated to explore the difference in arc characteristics between the two breaks. Based on the system of Maxwell and magnetohydrodynamic (MHD) equations, a non-simultaneous breaking model of the DB DC VCB is established, and parameters such as magnetic flux density, plasma velocity, inter-contact pressure, and ion and electron temperatures are calculated. The simulation results show that the cathode surface field emission effect is stronger in the small gap break (delayed breaking break). Besides, in the small gap break, the arc temperature is higher, the rate of decrease of temperature is lower, the electron velocity is higher, the magnetic flux density is lower, the regulatory ability of the magnetic field is weaker, and the plasma diffusion speed is slower. In the arc ignition stage, the arc aggregation state duration of the small gap break is longer than that of the normal break, which means the arc in the small gap break gets diffused and arc energy dissipation becomes harder. Therefore, the arc energy density of the delayed breaking break is greater, the arc morphology transition time is longer, the residual particle concentration after arc extinguishing is higher, and the probability of re-strike breakdown increases with the increase in gap difference. Improving the synchronization of the actuator could improve the breaking ability of the DB DC VCB. Index terms—plasma arc, double-break direct current vacuum circuit breaker (DB-DC VCB), transverse magnetic field (TMF), magnetohydrodynamic (MHD) model.

Experimental investigation of equilibrium and temporal scour around the round head of the rubble mound breakwater in case of breaking and non-breaking waves

In this study, local sediment movements caused by regular wave effects around the head section of rubble mound breakwater were investigated experimentally. The experiments were performed in a wave channel with a length of 33 m, a width of 3.6 m and a depth of 1.2 m. A plunger-type wave generator was located at the offshore side, generating regular waves of varying heights and periods. Uniform sandbed material of three different grain sizes was used, alongside two distinct breakwater slopes and six different wave characteristics. Experiments were performed under both breaking and non-breaking wave conditions. Time-dependent scour depth and water level measurements were determined by using measuring equipment working with an ultrasonic method. In the paper, new empirical relations were derived for temporal relative scour depths and the non-dimensional time scale parameter and the non-dimensional time scale parameter. The determination coefficient and scatter index of these derived relations were calculated and evaluated statistically. It was observed that the relations are in good agreement with those obtained from experiments. Additionally, the findings indicate that wave breaking significantly reduces the equilibrium scour depth.

Sufficient conditions of blowup to a shallow water wave equation

The blow-up features of a shallow water wave equation on the line R are investigated. The L2 conservation law is utilized to derive several estimates of solutions for the equation. Sufficient conditions for wave breaking and lifespan of the solutions are established. Our main results contain parts of the wave breaking conditions for the Fornberg–Whitham and Degasperis–Procesi equations in the previous literatures.

Analysis of Breaking Characteristics of C4F7N/CO2 Mixture Gas in Circuit Breaker

In recent years, the C4F7N mixed gas has attracted considerable attention for its outstanding insulation and arc-extinguishing capabilities, positioning it as a potential substitute for sulfur hexafluoride, SF6. However, there remains a limited understanding of the arc-extinguishing and insulation performance of C4F7N/CO2 mixed gas. In addition, there is limited research on high-current breaking in circuit breakers. Therefore, this study aims to investigate the arc characteristics and breaking behavior of 10%C4F7N/90%CO2 and 15%C4F7N/85%CO2 mixed gases using a magnetohydrodynamic model based on the 252kV air pressure circuit breaker. The dynamic characteristics of this mixed gas are compared with pure SF6 under short-circuit current breaking conditions, while analyzing different parameters of the C4F7N configuration. The results indicate that the mixed gas exhibits lower levels in terms of arc temperature, axial diffusion distance and pressure difference at the moment of arc initiation compared to pure SF6. Furthermore, increasing the inflating pressure can effectively enhance the breaking performance of the circuit breaker with 0.6 MPa, making it more suitable. Additionally, increasing the proportion of C4F7N in the mixed gases will cause the arc temperature to rise slightly at the initial arc and current crossing zero, but decrease at the peak current. The core pressure also rises significantly, with a greater pressure difference established in the compressor at moment of arc initiation. This study provides a reference for the design of an environmentally friendly circuit breaker and the selection of the mixed gas ratio.

The effect of secondary cutting on the chip breaking in turning with (Ti,W)C cermet cutting tools

This study proposes a secondary cutting technique to address the chip breaking issue of cermet cutting tools. A cemented carbide blade is superimposed to cut off the chips while cutting with (Ti,W)C cermet tools, this approach allows for achieving chip breaking while maintaining excellent machining surface integrity. In this paper, the influence of the distance between the secondary cutting tool and the major cutting edge and the thickness of the tool on the chip breaking is studied, by using the combination of finite element simulation and experimental verification. The results indicate that the secondary cutting technique transforms the chips from long helical chips into dual-C-type chips. The distance between the secondary cutting tool and the major cutting edge is the primary factor affecting chip breaking. The reason is that the free end of the chip is subjected to the reaction force of the secondary cutting tool, which hinders the increase of the chip curl radius, increases the internal strain, and achieves the chip breaking condition. The thickness of the secondary cutting tool is also a significant factor influencing chip breaking, when the thickness reaches the critical value of 1.8 mm, the tool transitions from obstructive action to cutting action. When the cutting material is 45 steel, the cutting speed is 300 m/min, the feed rate is 0.142 mm/r, and the cutting depth is 0.2 mm, the distance between the secondary cutting tool and the major cutting edge is 1.5 mm, and the tool thickness is 1.3 mm, the chip breaking effect is the best, the main types of chips is dual-C type chips, with a chip length of 7.1 mm ± 0.3 mm and a chip fracture curl radius of 1.8 mm ± 0.1 mm. At this point, the surface roughness can be reduced to as low as 0.98 μm, good surface integrity is ensured while chip breaking.

Numerical study of wave run-up on sea dikes with vegetated foreshores

Integrating coastal vegetation into sea dikes is a nature-based approach aimed at combining disaster prevention with ecological sustainability in coastal areas. This study investigates the impact of vegetation on the wave run-up on dikes through numerical analysis. The numerical model used in the study solves the Reynolds-averaged Navier–Stokes equations by adding a vegetation resistance force to account for momentum loss. A stabilized k–ω shear stress transport model considering the vegetation effect was adopted for turbulence closure. A series of numerical simulations was carried out on the wave run-up (Ru) on dikes, focusing on the effects of different vegetation heights, densities, zone lengths, and dike slopes under various wave conditions. The results indicate that vegetation can significantly decrease Ru and may cause the wave to change from breaking to nonbreaking on dikes. The Ru behaviors depend on whether waves break and can be well characterized by the Iribarren number and dimensionless wave momentum flux parameter under breaking and nonbreaking conditions, respectively. Finally, the multivariate non-linear regression (MNLR) and artificial neural network (ANN) methods were adopted to explore a prediction model for evaluating Ru. Comparisons showed that the prediction performance of the ANN model is superior to that of the MNLR model. The ANN model has the potential as a promising predictive tool for obtaining wave run-up on dikes with vegetated foreshores under breaking and nonbreaking conditions.

Out of the loop: Taking a one-week break from social media leads to better self-esteem and body image among young women

This study experimentally tested the effects of taking a one-week break from social media (SM) on body image and self-esteem among young women. Female undergraduate students (N = 66) were randomly assigned to either take a one-week break from SM or continue their normal use (control condition). State self-esteem and body satisfaction were measured at baseline (Time 1) and one week later (Time 2). As predicted, participants in the break condition reported higher body satisfaction and higher state self-esteem (total, performance, social, and appearance domains) at Time 2 than did those in the control condition, controlling for Time 1 scores. The benefits of taking a break from SM on body satisfaction were especially pronounced for women with higher baseline levels of thin-ideal internalization. The findings demonstrate the short-term benefits of taking a break from SM for one week on self-esteem and body image among young women.

UAV based comprehensive modelling approach for flood hazard assessment and mitigation planning

The assessment of flood hazard in semi-arid region under the scare data situation is a challenging task under the changing climatic situation. Therefore, the present research is carry out for Rel river catchment, Gujrat, India as case study and presented the comprehensive approach to identify the possible flood extend and flood mitigation measures for better flood assessment. The UAV based high resolution (3.6 cm × 3.6 cm) DEM is generated for most flood vulnerable area (i.e. Dhanera city), whereas scare precipitation data under ungauged condition is generated using GEE and National Aeronautics and Space Administration (NASA) Global Precipitation Measurement Mission (GPM) system. The HEC-HMS based hydrologic model is utilized for simulation of stream flow under the observed data, however, the 2D HEC-RAS based open-source model is used for flood assessment in 2D under extreme flood, dam break and levees condition. The flood decision making maps i.e water surface elevation, flood inundation, flood arrival time, and flood velocity are prepared for flood event 2017. The six flood hazard classes were selected from H1 (Low) to H6 (High) categories. The hazard maps of flood for different scenario i.e., 2D hydrodynamic analysis, 2D dam breach, 2D analysis with extended levees, and Dam break analysis with extended levees are derived. The model was validated with observed river gauge (water level) and discharge data at Dhanera City of flood 2017. The developed UAV based comprehensive modelling approach for flood hazard and mitigation planning provides the systematic approach for flood hazard assessment and would be adopted as a system framework for flood risk assessment for any similar case worldwide.

Fundamental and dipole gap solitons and their dynamics in the cubic–quintic fractional nonlinear Schrödinger model with a [formula omitted]-symmetric lattice

The interplay of two linear controlled terms – fractional diffraction and parity-time (PT) symmetric lattice – gives rise to unique and interesting linear Bloch gap structures within where the nonlinear localized gap modes may exist. In this study, we explore the formation and dynamics of one-dimensional gap solitons in the cubic–quintic physical model combining the fractional diffraction and PT symmetric lattice. Two classes of gap solitons, which we name the fundamental gap solitons and dipole ones, are constructed and their stability regions within the first finite gap of the associated linear Bloch spectrum are identified by means of linear-stability analysis and direct perturbed numerical simulations. We stress that the gap solitons are always unstable under the condition of PT symmetry breaking (the imaginary part of which is above 0.5). The excitations of the stable two classes of gap solitons are also investigated by using the adiabatic variation of the system’s parameters. The results predicted here shed some light on soliton physics in physical systems with combined fractional diffraction and PT symmetric lattice and the competing nonlinearities.

An overtopping formula for shallow water vertical seawalls by SWASH

There is now wide evidence that phase-resolving numerical models can capture the general physics of the overtopping process even under complex hydrodynamics. Based on this outcome, an extensive parametric study has been carried out with the model SWASH, to develop a design formula that uniformly predicts the overtopping rate at vertical seawalls for both breaking and non-breaking wave conditions. The use of the numerical model has allowed to vary the experimental conditions smoothly, avoiding the typical limitation of laboratory experiments. Furthermore, particular tests have been performed to assess whether, and up to which extent, the mean overtopping discharge is affected by the low frequency components of the incident wave spectrum.The formula relates the overtopping rate to a new water level statistic, which represents the average of the highest one-fourth wave displacements at the toe of the wall; it has initially been derived for planar beaches and then extended to the case of slope varying foreshores. A comparison with an array of 200 laboratory experiments confirms that the new parametrization can reduce the scatter of data compared to the EurOtop equation.

Size-resolved aerosol at a Coastal Great Lakes Site: Impacts of new particle formation and lake spray.

The quantification of aerosol size distributions is crucial for understanding the climate and health impacts of aerosols, validating models, and identifying aerosol sources. This work provides one of the first continuous measurements of aerosol size distribution from 1.02 to 8671 nm near the shore of Lake Michigan. The data were collected during the Lake Michigan Ozone Study (LMOS 2017), a comprehensive air quality measurement campaign in May and June 2017. The time-resolved (2-min) size distribution are reported herein alongside meteorology, remotely sensed data, gravimetric filters, and gas-phase variables. Mean concentrations of key aerosol parameters include PM2.5 (6.4 μg m-3), number from 1 to 3 nm (1.80x104 cm-3) and number greater than 3 nm (8x103 cm-3). During the field campaign, approximately half of days showed daytime ultrafine burst events, characterized by particle growth from sub 10 nm to 25-100 nm. A specific investigation of ultrafine lake spray aerosol was conducted due to enhanced ultrafine particles in onshore flows coupled with sustained wave breaking conditions during the campaign. Upon closer examination, the relationships between the size distribution, wind direction, wind speed, and wave height did not qualitatively support ultrafine particle production from lake spray aerosol; statistical analysis of particle number and wind speed also failed to show a relationship. The alternative hypothesis of enhanced ultrafine particles in onshore flow originating mainly from new particle formation activity is supported by multiple lines of evidence.

Influence of Intraoperative Active and Passive Breaks in Simulated Minimally Invasive Procedures on Surgeons' Perceived Discomfort, Performance, and Workload.

Laparoscopic surgeons are at high risk of experiencing musculoskeletal discomfort, which is considered the result of long-lasting static and awkward body postures. We primarily aimed to evaluate whether passive and active work breaks can reduce ratings of perceived discomfort among laparoscopic surgeons compared with no work breaks. We secondarily aimed to examine potential differences in performance and workload across work break conditions and requested the surgeons evaluate working with passive or active work breaks. Following a balanced, randomized cross-over design, laparoscopic surgeons performed three 90 min laparoscopic simulations without and with 2.5 min passive or active work breaks after 30 min work blocks on separate days. The simulation included the following tasks: a hot wire, peg transfer, pick-and-place, pick-and-tighten, pick-and-thread, and pull-and-stick tasks. Ratings of perceived discomfort (CR10 Borg Scale), performance per subtask, and perceived workload (NASA-TLX) were recorded, and the break interventions were evaluated (self-developed questionnaire). Statistical analyses were performed on the rating of perceived discomfort and a selection of the performance outcomes. Twenty-one participants (9F) were included, with a mean age of 36.6 years (SD 9.7) and an average experience in laparoscopies of 8.5 years (SD 5.6). Ratings of perceived musculoskeletal discomfort slightly increased over time from a mean level of 0.1 to 0.9 but did not statistically significantly differ between conditions (p = 0.439). Performance outcomes of the hot wire and peg transfer tasks did not statistically significantly differ between conditions. The overall evaluation by the participants was slightly in favor regarding the duration and content of active breaks and showed a 65% likelihood of implementing them on their own initiative in ≥90 min-lasting laparoscopic surgeries, compared with passive breaks. Both passive and active breaks did not statistically significantly influence ratings of perceived discomfort or perceived workload in a 90 min simulation of laparoscopic surgery, with an overall low mean level of perceived discomfort of 0.9 (SD 1.4). As work breaks do not lead to performance losses, rest breaks should be tested in real-life situations across a complete working shift, where perceived discomfort may differ from this laboratory situation. However, in this respect, it is crucial to investigate the acceptance and practicality of intraoperative work breaks in feasibility studies in advance of assessing their effectiveness in follow-up longitudinal trials.

Simulation study on arc motion process of 38 A low-voltage AC contactor under AC-4 conditions

In the process of breaking an AC contactor, the ablation of the contact by the arc current is an important factor affecting its electrical life, so the evolution of arc shape in the arc extinguishing chamber has an important influence on its breaking performance. To explore the influence of arc motion characteristics on its breaking characteristics, based on the theory of magnetohydrodynamics and considering the contact motion process, a three-dimensional air arc simulation model is established for the arc extinguishing chamber of an AC contactor with a fixed current of 38 A and the arc motion characteristics of the arc during breaking are analyzed. To verify the accuracy of the simulation model, a test platform was built. Under the same breaking conditions, the arc shape, arc voltage, and arc current were measured, and the experimental results were consistent with the simulation results. On this basis, an optimization scheme of the arc extinguishing component is proposed and its influence on the arc motion process is analyzed.

Influence of wind and waves on ambient noise and bubble entrainment depth in the semi-enclosed Baltic Sea

Semi-enclosed, fetch-limited waters create unique conditions for wind wave development and breaking. Parameters of breaking waves influence bubble entrainment depth and associated noise, which is why they differ in semi-enclosed sea compared to open waters. While the established noise-wind speed relationship holds in oceanic conditions, it differs in land-constrained basins like the Baltic Sea. To explore noise level, bubble entrainment depth and wind speed relationships, we conducted noise and sub-surface bubble measurements, coupled with wind observations, in the selected area of the Baltic Sea during two consecutive summers. A novel method was employed to estimate bubble entrainment depth under conditions of strong backscatter. Model data of wave field parameters were employed to assess their influence on noise level and bubble entrainment depth. Results suggest stronger connections between noise level and wind speed, as well as wave height, compared to wave age and wind sea steepness. The same patterns hold true for the correlation between bubble entrainment depth and both wind speed and wave field parameters. The parameterized noise level-wind speed relationship differs from that obtained for oceanic conditions and also varies across measurement periods. Observed differences were shaped by varying wind-wave conditions, notably differences in wind speed, direction, wave height, and the presence of swell. The noise level-bubble entrainment depth relation is reported for the first time for Baltic Sea conditions. For a thorough analysis of the influence of these factors on noise and bubbles, longer measurements under diverse wind-wave conditions are required to account for site-specific wave field characteristics.