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Some of the earliest biomechanics research focused on running and the ground reaction forces generated with each step. Research in running gait accelerated in the 1970′s as the growing popularity in running increased attention to the musculoskeletal injuries sustained by runners. Despite decades of high-quality research, running remains the most common cause of exercise-related musculoskeletal injuries and rates of overuse running-related injuries (RRI) have not appreciably declined since the research began. One leading area of running gait research focuses on discrete variables derived from the vertical ground reaction force, such as the vertical loading rate. Across sub-disciplines of running gait research, vertical loading rate is often discussed as the primary and undisputed variable associated with RRI despite only low to moderate evidence that retrospectively or prospectively injured runners generate greater vertical loading rates than uninjured counterparts. The central thesis of this review is that relying on vertical loading rate is insufficient to establish causal mechanisms for RRI etiology. To present this argument, this review examines the history of the ‘impacts cause injury’ hypothesis, including a historical look at ground reaction forces in human running and the research from which this hypothesis was generated. Additionally, a synthesis of studies that have tested the hypothesis is provided and recommendations for future research are discussed. Although it is premature to reject or support the ‘impacts cause injury’ hypothesis, new knowledge of biomechanical risk factors for RRI will remain concealed until research departs from the current path or adopts new approaches to previous paradigms.

Background Phthalic acid esters, including diethyl phthalate (DEP), which are considered as top-priority and hazardous pollutants, have received significant attention over the last decades. It is vital for industries to select the best treatment technology, especially when the DEP concentration in wastewater is high. Meanwhile, anaerobic biofilm-based reactors are considered as a promising option. Therefore, in the present study, for the biological removal of DEP from synthetic wastewater, two different anaerobic biofilm-based reactors, including anaerobic fixed film baffled reactor (AnFFBR) and up-flow anaerobic fixed film fixed bed reactor (UAnFFFBR), were compared from kinetic and performance standpoints. As in the previous studies, only the kinetic coefficients have been calculated and the relationship between kinetic coefficients and their interpretation has not been evaluated, the other aim of the present study was to fill this research gap. Results In optimum conditions, 90.31 and 86.91% of COD as well as 91.11 and 88.72% of DEP removal were achieved for the AnFFBR and UAnFFFBR, respectively. According to kinetic coefficients (except biomass yield), the AnFFBR had better performance as it provided a more favorable condition for microbial growth. The Grau model was selected as the best mathematical model for designing and predicting the bioreactors’ performance due to its high coefficients of determination (0.97 < R 2). With regard to the insignificant variations of the calculated Grau kinetic coefficients (K G) when the organic loading rate (with constant HRT) increased, it can be concluded that both of the bioreactors can tolerate high organic loading rate and their performance is not affected by the applied DEP concentrations. Conclusions Both the bioreactors were capable of treating low-to-high strength DEP wastewater; however, according to the experimental results and obtained kinetic coefficients, the AnFFBR indicated higher performance. Although the AnFFBR can be considered as a safer treatment option than the UAnFFFBR due to its lower DEP concentrations in sludge, the UAnFFFBR had lower VSS/TSS ratio and sludge yield, which could make it more practical for digestion. Finally, both the bioreactors showed considerable methane yield; however, compared to the UAnFFFBR, the AnFFBR had more potential for bioenergy production. Although both the selected bioreactors achieved nearly 90% of DEP removal, they can only be considered as pre-treatment methods according to the standard regulations and should be coupled with further technology.

The mechanical and acoustic emission characteristics of rock-like materials under non-uniform loads were investigated by means of a self-developed mining-induced stress testing system and acoustic emission monitoring system. In the experiments, the specimens were divided into three regions and different initial vertical stresses and stress loading rates were used to simulate different mining conditions. The mechanical and acoustic emission characteristics between regions were compared, and the effects of different initial vertical stresses and different stress loading rates were analysed. The results showed that the mechanical properties and acoustic emission characteristics of rock-like materials can be notably localized. When the initial vertical stress and stress loading rate are fixed, the peak strength of region B is approximately two times that of region A, and the maximum acoustic emission hit value of region A is approximately 1–2 times that of region B. The effects of the initial vertical stress and stress loading rate on the peck strain, maximum hit value, and occurrence time of the maximum hit are similar in that when either of the former increase, the latter all decrease. However, peck strength will increase with the increase in loading rate and decrease with the increase in initial vertical stress. The acoustic emission hits can be used to analyse the damage in rock material, but the number of acoustic emission hits cannot be used alone to determine the degree of rock damage directly.

Most of the existing researches on energy evolution in the process of rock deformation and failure mainly revolve around a specific stage (before or after the peak). However, there are few studies involving the impacts of lithology and loading rate on the energy evolution in the whole process from deformation to failure, especially the studies on non-linear characteristics of rock energy, which is the frontier of study on the mechanism of rock failure. In this context, this study further explores the influencing rule of lithology and loading rate on the energy evolution process of loaded rock. By employing the MTS 815 rock mechanics test system and conducting 18 groups of tests on yellow sandstone, limestone and marble, the research reveals the evolution process and distribution law of elastic energy resilience density along with the stress. Then the micro-mechanism of accumulation and dissipation of rock energy are analyzed. A non-linear evolution model (Logistic equation) is proposed that demonstrates how the energy density of loaded rock changes with axial stress. This model can also explore the bifurcation and chaos characteristics of rock energy evolution, and further reveals the rule that the iterative growth factor of energy density changes with lithology, stress level and loading rate. The results are conducive to deepening the understanding on the differences in engineering characteristics of rocks with different lithologies, and play a guiding role in the prevention and control against dynamic disasters of rocks in the engineering field.

HighlightsA dynamic constitutive model for rock materials suited to dynamic cyclic loading was established.The numerical tests on a hard rock under true triaxial dynamic cyclic loading with different loading rates were conducted.The dynamic deformation and mechanical properties of a hard rock were studied.

Abstract The large capacity production and low utilization rate increase the difficulty of fruit and vegetable wastes (FVW) treatment. Efficient and targeted recovery strategies can solve these problems. This study investigated and proposed combined strategies via pH and organic loading rate (OLR) to target and enhance ethanol- and butyrate-dominant acidogenic production in the FVW mixed culture fermentation. Under pH 4.0, OLR 18 gCOD/(L∙d), and mesophilic (35 °C), ethanol-dominant fermentation was formed. The long-term operation (168 days) showed that the highest ethanol yield was 0.33 g/gCOD which was greater than that in other studies. Also, the hydrolysis rate of ethanol-type fermentation reached 74.5%. Besides, butyrate-type fermentation was stable at yield 0.39 g/gCOD following conditions: pH 6.0, OLR 28 gCOD/(L∙d), and 35 °C, of which hydrolysis and acidogenic rate were 78.0% and 62.0%, respectively. The high relative abundance of Lactobacillus, Olsenella, and Bifidobacterium played positive role in achieving ethanol, butyrate, and lactate production among various metabolic pathways. The results revealed the pH value together with OLR was the valid parameter to affect product formation and composition during FVW fermentation.

Rockburst is a kind of rock failure phenomenon during which the internal elastic strain energy of surrounding rock mass is released dynamically under external load, and the loading rate is an essential influencing factor of potential for bursting. To investigate the effects of loading rate on rockburst proneness from energy storage and surplus perspectives, conventional uniaxial compression tests are conducted on granite under four orders of magnitude loading rate. The failure process and mode of granite specimens were recorded in real time with a high-speed camera with microsecond shooting speed. The variation trend of the internal elastic strain energy of granite specimens under four loading rates was obtained by performing the single-cycle loading–unloading uniaxial compression test. The experimental results show that the elastic strain energy linearly increases as the input strain energy increases under each loading rate, which meet the linear energy storage law. Based on the linear energy storage law, the peak elastic strain energy of each granite specimen can be accurately obtained. According to the mass and range of ejected rock debris after specimen failure, the bursting liability of each specimen was evaluated by the far-field ejection mass ratio (MF) from a qualitative point of view. Meanwhile, the residual elastic energy index (AEF) and the other three criteria were used to evaluate the potential for bursting of granite specimens under different loading rates. The comparison results show the rockburst proneness of granite specimens increases with the loading rate and that the evaluation results of MF and AEF are unified from qualitative and quantitative aspects, respectively. The fundamental reason for the consistent results is that these two indexes have a common essence of elastic strain energy release.HighlightsThe mechanical properties of granite are significantly influenced by loading rate.The loading rate does not affect the existence of linear energy storage law and the compression energy storage coefficient is independent of loading rate.The rockburst liability of granite increases with the loading rate.At different loading rates, the far-field ejection mass ratio and residual elastic energy index offer consistent qualitative and quantitative evaluations for the rockburst proneness of granite.

Post-traumatic knee osteoarthritis (PTOA) develops rapidly after anterior cruciate ligament reconstruction (ACLR) and both high and low vertical ground reaction force (vGRF) loading rates are associated with cartilage degeneration. However, the gait characteristics that influence vGRF linear and instantaneous loading rates after ACLR are unknown. Sixty-nine individuals with ACLR (sex: 72 % female, age: 20 ± 3 years, and time since ACLR: 26 ± 16 months) walked at a self-selected pace from which the vGRF linear (slope from heel strike to peak) and instantaneous (peak of the first time derivative) loading rates were calculated. Lasso regressions were utilized to objectively identify a subset of predictor variables that influence vGRF linear and instantaneous loading rates. The identified predictors were then utilized in multiple regressions to determine the unique variance attributable to each predictor by computing Δr2 when that predictor was removed from the model. Greater gait speed (Δr2=0.019), greater medial hamstring preparatory amplitude (Δr2=0.022), and lesser peak posterior ground reaction force (pGRF) (Δr2=0.103) were associated with greater vGRF linear loading rate. Greater gait speed (Δr2=0.072), greater medial hamstring preparatory amplitude (Δ r2 = 0.016), greater anterior ground reaction force (aGRF) immediately after heel strike (Δr2=0.054), and lesser peak pGRF (Δr2=0.019) were associated with greater vGRF instantaneous loading rates. Lesser pGRF and greater aGRF immediately after heel strike explain additional variance in vGRF linear and instantaneous loading rates beyond that explained by gait speed. Future investigations should evaluate the relationship between the aGRF immediately after heel strike and pGRF with indicators of cartilage degeneration.

Individuals with anterior cruciate ligament reconstruction (ACLR) often exhibit a “stiffened knee strategy” or an excessively extended knee during gait, characterized by lesser knee flexion excursion and peak internal knee extension moment (KEM). The purpose of this study was to determine the effect of real-time biofeedback (RTBF) cuing an acute change in peak vertical ground reaction force (vGRF) during the first 50% of the stance phase of walking gait on: (1) root mean square error (RMSE) between actual vGRF and RTBF target vGRF; (2) perceived difficulty; and (3) knee biomechanics. Acquisition and short-term recall of these outcomes were evaluated. Thirty individuals with unilateral ACLR completed 4 separate walking sessions on a force-measuring treadmill that consisted of a control (no RTBF) and 3 experimental loading conditions using RTBF including: (1) 5% vGRF increase (high-loading), (2) 5% vGRF decrease (low-loading) and (3) symmetric vGRF between limbs. Bilateral biomechanical outcomes were analyzed during the first 50% of the stance phase, and included KEM, knee flexion excursion, peak vGRF, and instantaneous vGRF loading rate (vGRF-LR) for each loading condition. Peak vGRF significantly increased and decreased during high-loading and low-loading, respectively compared to control loading. Instantaneous vGRF-LR, peak KEM and knee flexion excursion significantly increased during the high-loading condition compared to low-loading. Perceived difficultly and RMSE were lower during the symmetrical loading condition compared to the low-loading condition. Cuing an increase in peak vGRF may be beneficial for increasing KEM, knee flexion excursion, peak vGRF, and vGRF-LR in individuals with ACLR. Clinical Trials Number: NCT03035994.

Hydrogen-assisted (HA) fatigue crack growth (FCG) occurs in ferritic steels, wherein H-dislocation interaction plays a vital role. We aim to model the HAFCG mechanism based on the within the crack tip zone. Our modeling framework is as follows: H is condensed into crack tip and trapped by dislocations; these H significantly decrease dislocation mobility; stress relief via crack blunting is suppressed; localized brittle fracture triggers HAFCG. This model was substantiated experimentally in H gas at various load frequencies and temperatures. Theoretical formulations were established considering the thermal equilibrium of H-trapping and dislocation breakaway from the H atmosphere.