Parallel and Cross-Sectional Hamstring Injuries in Sprint Running

This issue of Journal of Sport and Health Science contains a point-counterpoint discussion of hamstring injuries in sprint running by the groups of Drs. Liu and Yu.1–4 They propose different mechanisms of muscle injuries in general, and hamstring injuries in sprint running specifically. Yu et al.2,4 present evidence suggesting that hamstring injuries are primarily caused by excessive muscle strain during eccentric contraction. In maximal effort sprint running, excessive muscle strains occur at the end of the swing phase. In contrast, Liu et al.1,3 point out that, in addition to excessive hamstring strain, high stresses in the late swing and early stance phase and the transition between swing and stance may also contribute to hamstring injuries when the hamstrings actively assist hip extension and knee flexion. Both groups provide supporting published, scientific evidence for their contention. Yet, the entire discussion is based on the assumption that the hamstring muscles contract uniformly in all phases of sprint running. However, the different heads of the hamstring muscles have different insertion sites, structure, and fiber type distributions. Therefore, it is safe to assume that the individual heads fulfill different functions and that they do not elongate at the same rate and that stress across them is not uniform. Using magnetic resonance imaging in combination with finite element modeling, Fiorentino and colleagues5 reported that non-uniformity in fiber strains may also be a contributing factor for hamstring injuries, especially when sprinting at high speeds. We propose that this fiber strain and strain rate non-uniformity at fast sprint speeds could lead to “parallel injury”, tissue separation, and misalignment of myofibrils along the muscle fibers (e.g., see Lee and Healy, 2012, for a detailed image6). Along these lines, Morgan7 proposed the so-called “Popping Sarcomeres Hypothesis”, which is based on the idea that repeated high stresses during eccentric contractions leads to “tearing” of sarcomeres, and the local damage of sarcomeres leads to more damage in adjacent sarcomeres and neighboring myofibrils due to the sudden increase in localized stress. We propose that the “Popping Sarcomeres” phenomenon could lead to “cross-sectional” hamstring injuries in which the damage occurs tangential to the fiber orientation and produces disruptions of the Z-lines and misaligned A-bands (see Morgan, 1990, for exemplar image7). Parallel and cross-sectional hamstring injuries may have different underlying causes and may provide a post hoc possibility for evaluating how the injury occurred. In severe hamstring injuries (Grade II or more), one might expect simultaneous parallel and cross-sectional injuries. The detailed mechanisms of hamstring injuries in sprint running remain a question of debate, and it might be time to look at this issue from an altogether different point of view. Considering that hamstring strains and strain rates might be non-uniform across the different heads, it appears feasible that the non-uniform strains and strain rates may lead to “parallel” injuries, whereas non-uniform stresses might lead to “cross-sectional” injuries. Considering different and multiple hamstring muscle injury mechanisms in sprint running may lead to more targeted training strategies and provide new insights into the prevention and rehabilitation of hamstring injuries

Active vibration control of support sting in wind tunnel by using adaptive method

The low-frequency and large-amplitude coupled vibration of the support sting in wind tunnel affects the accuracy of the wind tunnel test’s data. An active vibration control system of support sting in wind tunnel is demonstrated using adaptive control method in this paper. Following the establishment of the finite element model, and the extraction of parameter matrix, the original model is reduced to lower-mode model which contains first two pitching modes based on DC gain ranking method. The active control model is proposed based on model reference adaptive control method (RACM) to control the low-frequency vibration of supporting sting in wind tunnel. Research results have justified the effectiveness of the controlled system and provided insight into the practical application of the proposed method

Generalized Conditional Feedback System with Model Uncertainty

Model uncertainty creates a largely open challenge for industrial process control, which causes a trade-off between robustness and performance optimality. In such a case, we propose a generalized conditional feedback (GCF) system to largely eliminate conflicts between robustness and performance optimality. This approach leverages a nominal model to design an optimal control in the virtual domain and defines an ancillary feedback controller to drive the physical process to track the trajectory of the virtual domain. The effectiveness of the proposed GCF scheme is demonstrated in a simulation for six typical industrial processes and three model-based control methods, and in a half-quadrotor system control test. Furthermore, the GCF scheme is open to existing optimal control and robust control theories

Kinetics of the decomposition reaction of phosphorite concentrate

Apatite is the raw material, which is mainly used in phosphate fertilizer, and part are used in yellow phosphorus, red phosphorus, and phosphoric acid in the industry. With the decrease of the high grade phosphorite lump, the agglomeration process is necessary for the phosphorite concentrate after beneficiation process. The decomposition behavior and the phase transformation are of vital importance for the agglomeration process of phosphorite. In this study, the thermal kinetic analysis method was used to study the kinetics of the decomposition of phosphorite concentrate. The phosphorite concentrate was heated under various heating rate, and the phases in the sample heated were examined by the X-ray diffraction method. It was found that the main phases in the phosphorite are fluorapatiteCa5(PO4)3F, quartz SiO2,and dolomite CaMg(CO3)2.The endothermic DSC peak corresponding to the mass loss caused by the decomposition of dolomite covers from 600°C to 850°C. The activation energy of the decomposition of dolomite, which increases with the increase in the extent of conversion, is about 71.6~123.6kJ/mol. The mechanism equation for the decomposition of dolomite agrees with the Valensi equation and G-B equation

Lattice Boltzmann Simulations of Thermal Convective Flows in Two Dimensions

In this paper we study the lattice Boltzmann equation (LBE) with multiple-relaxation-time (MRT) collision model for incompressible thermo-hydrodynamics with the Boussinesq approximation. We use the MRT thermal LBE (TLBE) to simulate the following two flows in two dimensions: the square cavity with differentially heated vertical walls and the Rayleigh-Benard convection in a rectangle heated from below. For the square cavity, the flow parameters in this study are the Rayleigh number Ra = 103-106, and the Prandtl number Pr = 0.71; and for the Rayleigh-Benard convection in a rectangle, Ra = 2 . 103, 104 and 5 . 104, and Pr = 0.71 and 7.0