Acute combined effects of concurrent physical activities on autonomic nervous activation during cognitive tasks

Backgrounds: The validity of heart rate variability (HRV) has been substantiated in mental workload assessments. However, cognitive tasks often coincide with physical exertion in practical mental work, but their synergic effects on HRV remains insufficiently established. The study aims were to investigate the combined effects of cognitive and physical load on autonomic nerve functions.Methods: Thirty-five healthy male subjects (aged 23.5 ± 3.3 years) were eligible and enrolled in the study. The subjects engaged in n-back cognitive tasks (1-back, 2-back, and 3-back) under three distinct physical conditions, involving isotonic contraction of the left upper limb with loads of 0 kg, 3 kg, and 5 kg. Electrocardiogram signals and cognitive task performance were recorded throughout the tasks, and post-task assessment of subjective experiences were conducted using the NASA-TLX scale.Results: The execution of n-back tasks resulted in enhanced perceptions of task-load feelings and increased reaction times among subjects, accompanied by a decline in the accuracy rate (p < 0.05). These effects were synchronously intensified by the imposition of physical load. Comparative analysis with a no-physical-load scenario revealed significant alterations in the HRV of the subjects during the cognitive task under moderate and high physical conditions. The main features were a decreased power of the high frequency component (p < 0.05) and an increased low frequency component (p < 0.05), signifying an elevation in sympathetic activity. This physiological response manifested similarly at both moderate and high physical levels. In addition, a discernible linear correlation was observed between HRV and task-load feelings, as well as task performance under the influence of physical load (p < 0.05).Conclusion: HRV can serve as a viable indicator for assessing mental workload in the context of physical activities, making it suitable for real-world mental work scenarios

The Analysis of Hand Movement Distinction Based on Relative Frequency Band Energy Method

For the purpose of successfully developing a prosthetic control system, many attempts have been made to improve the classification accuracy of surface electromyographic (SEMG) signals. Nevertheless, the effective feature extraction is still a paramount challenge for the classification of SEMG signals. The relative frequency band energy (RFBE) method based on wavelet packet decomposition was proposed for the prosthetic pattern recognition of multichannel SEMG signals. Firstly, the wavelet packet energy of SEMG signals in each subspace was calculated by using wavelet packet decomposition and the RFBE of each frequency band was obtained by the wavelet packet energy. Then, the principal component analysis (PCA) and the Davies-Bouldin (DB) index were used to perform the feature selection. Lastly, the support vector machine (SVM) was applied for the classification of SEMG signals. Our results demonstrated that the RFBE approach was suitable for identifying different types of forearm movements. By comparing with other classification methods, the proposed method achieved higher classification accuracy in terms of the classification of SEMG signals

Shear Failure Mechanism and Numerical Simulation Analysis of Rock-like Materials with an Embedded Flaw

In this study, the failure characteristics of self-made rock with internal flaws under shear were studied and a numerical simulation analysis was carried out. Firstly, based on basic physical and mechanical tests, the shear strength characteristics of rocks with built-in 3D defects were summarized. PFC3D simulation software was used to model the samples with flaws, and the microscopic parameters were calibrated according to the test results. From the simulation results, it was found that the generation mode of microcracks from the flaw tip was different. The microcracks of forward shear and reverse shear were mainly generated from the horizontal direction, while the microcracks of lateral shear gradually increased from the upper and lower ends of the flaw in the opposite direction. When the peak shear strength was reached, the total number of cracks was the largest in lateral shear and the smallest in forward shear. When studying the particle velocity vector field, it was found that when reaching the peak shear strength, the particles on both sides of the prefabricated flaw appeared to be in vortex motion. When α = 45° and σn = 2 MPa, the failure mode of forward shear and lateral shear was shear-tensile-shear (S-T-S), and that of reverse shear and the intact specimen was shear-shear-shear (S-S-S). The lateral shear tensile effect was the most obvious and was mainly concentrated in the middle part of the sample

Crack Coalescence Behavior of Rock-Like Specimens Containing Two Circular Embedded Flaws

AbstractExperimental research on the growth of internal flaws has rarely been reported due to the fact that it is difficult to cut internal flaws in specimens and cannot capture the initiation and propagation processes of internal flaws through direct observations. This paper proposed a method for creating internal flaws in specimens by utilizing the volatilization of camphor. A series of compression tests were performed on rock-like specimens including two embedded circular flaws, and CT techniques were used to investigate the internal damage behavior of flawed specimens. Experimental results illustrate that the strength and deformation properties of flawed specimens increase nonlinearly with the confining pressure as well as flaw inclination angle. Crack coalescence patterns and failure modes of flawed specimens depend on not only the confining pressure but also the flaw inclination angle. The crack coalescence pattern varies from wing crack coalescence to mixed tension-shear crack coalescence and then to the shear crack coalescence as the crack inclination angle increases. Confining pressure contributes to shear crack growth and has an inhibiting effect on the propagation of tension cracks. For specimens with the same flaw inclination angle, the failure mode changed from tension failure to mixed shear-tension failure or from mixed shear-tension failure to pure shear failure with the increase of confining pressure

Shear Failure Mechanism and Numerical Simulation Analysis of Rock-like Materials with an Embedded Flaw

In this study, the failure characteristics of self-made rock with internal flaws under shear were studied and a numerical simulation analysis was carried out. Firstly, based on basic physical and mechanical tests, the shear strength characteristics of rocks with built-in 3D defects were summarized. PFC3D simulation software was used to model the samples with flaws, and the microscopic parameters were calibrated according to the test results. From the simulation results, it was found that the generation mode of microcracks from the flaw tip was different. The microcracks of forward shear and reverse shear were mainly generated from the horizontal direction, while the microcracks of lateral shear gradually increased from the upper and lower ends of the flaw in the opposite direction. When the peak shear strength was reached, the total number of cracks was the largest in lateral shear and the smallest in forward shear. When studying the particle velocity vector field, it was found that when reaching the peak shear strength, the particles on both sides of the prefabricated flaw appeared to be in vortex motion. When α = 45° and σn = 2 MPa, the failure mode of forward shear and lateral shear was shear-tensile-shear (S-T-S), and that of reverse shear and the intact specimen was shear-shear-shear (S-S-S). The lateral shear tensile effect was the most obvious and was mainly concentrated in the middle part of the sample

Recent innovations in laser additive manufacturing of titanium alloys

Titanium (Ti) alloys are widely used in high-tech fields like aerospace and biomedical engineering. Laser additive manufacturing (LAM), as an innovative technology, is the key driver for the development of Ti alloys. Despite the significant advancements in LAM of Ti alloys, there remain challenges that need further research and development efforts. To recap the potential of LAM high-performance Ti alloy, this article systematically reviews LAM Ti alloys with up-to-date information on process, materials, and properties. Several feasible solutions to advance LAM Ti alloys are reviewed, including intelligent process parameters optimization, LAM process innovation with auxiliary fields and novel Ti alloys customization for LAM. The auxiliary energy fields (e.g. thermal, acoustic, mechanical deformation and magnetic fields) can affect the melt pool dynamics and solidification behaviour during LAM of Ti alloys, altering microstructures and mechanical performances. Different kinds of novel Ti alloys customized for LAM, like peritectic α-Ti, eutectoid (α + β)-Ti, hybrid (α + β)-Ti, isomorphous β-Ti and eutectic β-Ti alloys are reviewed in detail. Furthermore, machine learning in accelerating the LAM process optimization and new materials development is also outlooked. This review summarizes the material properties and performance envelops and benchmarks the research achievements in LAM of Ti alloys. In addition, the perspectives and further trends in LAM of Ti alloys are also highlighted

DataSheet1_Acute combined effects of concurrent physical activities on autonomic nervous activation during cognitive tasks.docx

Backgrounds: The validity of heart rate variability (HRV) has been substantiated in mental workload assessments. However, cognitive tasks often coincide with physical exertion in practical mental work, but their synergic effects on HRV remains insufficiently established. The study aims were to investigate the combined effects of cognitive and physical load on autonomic nerve functions.Methods: Thirty-five healthy male subjects (aged 23.5 ± 3.3 years) were eligible and enrolled in the study. The subjects engaged in n-back cognitive tasks (1-back, 2-back, and 3-back) under three distinct physical conditions, involving isotonic contraction of the left upper limb with loads of 0 kg, 3 kg, and 5 kg. Electrocardiogram signals and cognitive task performance were recorded throughout the tasks, and post-task assessment of subjective experiences were conducted using the NASA-TLX scale.Results: The execution of n-back tasks resulted in enhanced perceptions of task-load feelings and increased reaction times among subjects, accompanied by a decline in the accuracy rate (p Conclusion: HRV can serve as a viable indicator for assessing mental workload in the context of physical activities, making it suitable for real-world mental work scenarios.</p