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Forward head posture (FHP) is a serious problem causing head and neck disability, but the characteristics of muscle activity during long-term postural maintenance are unclear. This study aimed to investigate a comparison of electromyography (EMG) activation properties and subjective fatigue between young adults with and without habitual FHP. In this study, we examined the changes in the spatial and temporal distribution patterns of muscle activity using high-density surface EMG (HD-SEMG) in addition to mean frequency, a conventional measure of muscle fatigue. Nineteen male participants were included in the study (FHP group (n = 9; age = 22.3 ± 1.5 years) and normal group (n = 10; age = 22.5 ± 1.4 years)). Participants held three head positions (e.g., forward, backward, and neutral positions) for a total of 30 min each, and the EMG activity of the trapezius pars descendens muscle during posture maintenance was measured by HD-SEMG. The root mean square (RMS), the modified entropy, and the correlation coefficient were calculated. Additionally, the visual analogue scale (VAS) was evaluated to assess subjective fatigue. The RMS, VAS, modified entropy, and correlation coefficients were significantly higher in the FHP group than in the normal group ( p  < 0.001). With increasing postural maintenance time, the modified entropy and correlation coefficient values significantly decreased, and the mean frequency and VAS values significantly increased ( p  < 0.001). Furthermore, the forward position had significantly higher RMS, correlation coefficient, modified entropy, and VAS values than in the neutral position ( p  < 0.001). The HD-SEMG potential distribution patterns in the FHP group showed less heterogeneity and greater muscle activity in the entire muscle and subjective fatigue than those in the normal group. Excess muscle activity even in the neutral/comfortable position in the FHP group could potentially be a mechanism of neuromuscular conditions in this population.

An elastomer composite with controllable stiffness, known as a magnetorheological elastomer (MRE), is used in a dynamic vibration absorber whose natural frequency is tuned adaptively to the disturbance frequency through the application of an external magnetic field. The field-dependent property test of the fabricated MRE sample shows that the stiffness changes by more than six times compared to the baseline property value at a 40% iron powder volume concentration. The MRE is then used to fabricate a frequency-tunable dynamic absorber for mitigating transient vibrations of a one-degree-of-freedom system. Investigations show that the proposed absorber outperforms a conventional passive-type absorber throughout the tunable frequency range.

Acute myeloid leukaemia (AML) is a haematologic malignancy with high relapse rates in both adults and children. Leukaemic stem cells (LSCs) are central to leukaemopoiesis, treatment response and relapse and frequently associated with measurable residual disease (MRD). However, the dynamics of LSCs within the AML microenvironment is not fully understood. This study utilized three-dimensional cellular automata (CA) modelling to simulate LSC behaviour and treatment response under induction chemotherapy. Our study revealed: (i) a correlation between LSC persistence post-induction chemotherapy and risk of AML relapse; (ii) MRD negativity based on LSC count may not reliably predict outcomes, supporting clinical evidence that patients with MRD-negative status can still be at risk of relapse; (iii) prolonged persistence of LSCs post-chemotherapy without disruption of normal haematopoiesis, aligning with clinical observations of dormant AML clones; (iv) early LSC dynamics post-induction chemotherapy, characterized by stochastic behaviours and movement velocities, are insufficient predictors of long-term prognosis; and (v) a distinct spatiotemporal organization of LSCs in later phases post-induction chemotherapy is correlated with long-term outcomes. Our modelling results provide a theoretical and clinical framework for AML research, and future clinical data validation could refine the utility of CA modelling for oncological studies.

In this research, a novel variable stiffness vibration isolator that uses magnetorheological elastomers (MREs) accompanied with a fuzzy semiactive vibration control was developed. Firstly, the viscoelastic characteristics of MREs in shear mode were clarified systematically in order to achieve a mathematical basis for the controller development. Secondly, the fuzzy semiactive vibration control with a strategy based on the Lyapunov theory and dynamic characteristic of MREs was proposed for minimizing the movement of the isolator. In the conventional semiactive algorithm, the command applied current of MRE-based isolator is set at either minimum or maximum value which causes high acceleration and jerk peaks periodically, thus leading to the degeneration of the overall system quality. However, the fuzzy semiactive algorithm presented here is able to produce the sufficient applied current and thus viscoelastic force is desirably produced. The effectiveness of the developed isolator was evaluated numerically by MATLAB simulation and experimentally in comparison with the performances of a passive system and a system with on-off type semiactive controller. The results showed that the developed controller was successful in overcoming the disadvantages of conventional on-off semiactive control.

Acute myeloid leukaemia (AML) is a haematologic malignancy with high relapse rates in both adults and children. Leukaemic stem cells (LSCs) are central to leukaemopoiesis, treatment response and relapse and frequently associated with measurable residual disease (MRD). However, the dynamics of LSCs within the AML microenvironment is not fully understood. This study utilized three-dimensional cellular automata (CA) modelling to simulate LSC behaviour and treatment response under induction chemotherapy. Our study revealed: (i) a correlation between LSC persistence post-induction chemotherapy and risk of AML relapse; (ii) MRD negativity based on LSC count may not reliably predict outcomes, supporting clinical evidence that patients with MRD-negative status can still be at risk of relapse; (iii) prolonged persistence of LSCs postchemotherapy without disruption of normal haematopoiesis, aligning with clinical observations of dormant AML clones; (iv) early LSC dynamics post-induction chemotherapy, characterized by stochastic behaviours and movement velocities, are insufficient predictors of long-term prognosis; and (v) a distinct spatiotemporal organization of LSCs in later phases post-induction chemotherapy is correlated with long-term outcomes. Our modelling results provide a theoretical and clinical framework for AML research, and future clinical data validation could refine the utility of CA modelling for oncological studies.

PurposeThe aim of this study was to examine the effect of vibration on motor unit (MU) firing behavior and physical performance of antagonist muscles in healthy young adult males.MethodsFourteen males (age = 24.3 ± 3.6 years) were included in this study. There were two conditions, one in which participants received 80 Hz vibration in the distal tendon of the hamstring for 30 s and the control condition (no vibration). High-density surface electromyography (HD-SEMG) signals and maximal voluntary contraction (MVC) of knee extensor muscles were evaluated before and after the respective conditions and recorded from the vastus lateralis muscle during submaximal ramp-up and sustained contractions at 30% MVC. Convolution blind source separation was used to decompose the HD-SEMG signals into individual MU firing behaviors.ResultsIn total, 739 MUs were detected (control; 360 MUs and vibration; 379 MUs), and a total of 312 matched MUs were identified across both submaximal contraction conditions (control: 150 MUs; vibration: 162 MUs). Vibration significantly increased the discharge rate (p = 0.047) and decreased the recruitment threshold before and after intervention (p = 0.001) but not in the control condition. Furthermore, the recruitment threshold is a factor that influences discharge rate. Significant correlations were observed between the recruitment threshold and both the ∆ discharge rate and the ∆ recruitment threshold under the vibration condition (p < 0.001).ConclusionVibration increased in the discharge rate and decreased the recruitment threshold of the antagonist muscle. These findings suggested that vibration contributes to immediate changes in the neural control of antagonist muscles.

For most existing semiactive systems, it is commonly known that the stability and tracking performance will deteriorate in a real application due to the input constraints and nonlinearity in the system. In this study, in order to overcome the above shortcomings, a novel bench-scale suspension plant using a magnetorheological elastomer (MRE)-based absorber accompanied with an adaptive and global neural-network-based tracking controller is introduced. The adaptive neural network (ANN) is used to estimate the uncertain dynamics of the quarter-car model. The novel scheme consists of three parts, including a conventional ANN controller dominating the active region of neurons, a robust controller serving as a temporary controller to pull back the state into the active region when the neural approximation falls outside, and a switch to be used to monitor the activation of the neural part and switch the control authority between the above two controllers. The controller ensures that a globally uniform ultimate boundedness can be achieved. Furthermore, an auxiliary design system was added to the controller in order to deal with the effects of input constraints, and the state was analyzed for the tracking of the stabilization. The control scheme ensures that the output of the system converges to the vicinity of a reference trajectory and all the signals are globally, uniformly, and ultimately bounded. The simulation and experimental results demonstrate that the proposed controller can effectively suppress the vibrations of the semiactive quarter car.

A passive-type dynamic vibration absorber (DVA) is basically a mass-spring system that suppresses the vibration of a structure at a particular frequency. Since the natural frequency of the DVA is usually tuned to a frequency of particular excitation, the DVA is especially effective when the excitation frequency is close to the natural frequency of the structure. Fixing the physical properties of the DVA limits the application to a narrowband, harmonically excited vibration problem. A frequency-tunable DVA that can modulate its stiffness provides adaptability to the vibration control device against non-stationary disturbances. In this paper, we suggest a broadband frequency-tunable DVA whose natural frequency can be extended by 300% to the nominal value using the magnetorheological elastomers (MREs). The frequency adjustability of the proposed absorber is first shown. The real-time vibration control performance of the frequency-tunable absorber for an acoustically excited plate having multiple resonant peaks is then evaluated. Investigations show that the vibration of the structure can be effectively reduced with an improved performance by the DVA in comparison to the conventional passive- type absorber.

To downsize the clamp area and increase the output power of the harvester, we developed a miniature piezoelectric vibration energy harvester with combining a Z-shaped folded spring and a mechanically-switching SSHI (synchronized switch harvesting on inductor). The overall harvester size is 4×2×3 cm3. The FEM analysis revealed that the output power increases and the value of the 1st and 2nd resonance frequencies move closer as the angle of the Z-shaped spring decreases, therefore, the smaller angle would be more promising. The experimental results showed that the maximum output power of our harvester for the 1st (20.2 Hz) and 2nd (53.0 Hz) resonance frequencies at the applied acceleration of 4.9 m/s2 are 088 and 0.98 mW, respectively. The reason for a marked enhancement of the output power for the 2nd resonance frequency is attributed to the vertical movement of the 2nd vibrational mode which applies larger mechanical stress to the piezo ceramic and achieves better electrical contact between the tip of the Z-shaped spring and the spring plunger.