Comparison of two measurement devices for obtaining horizontal force-velocity profile variables during sprint running

This study established the magnitude of systematic bias and random error of horizontal force-velocity (F-v) profile variables obtained from a 1080 Sprint compared to that obtained from a Stalker ATS II radar device. Twenty high-school athletes from an American football training group completed a 30 m sprint while the two devices simultaneously measured velocity-time data. The velocity-time data were modelled by an exponential equation fitting process and then used to calculate individual F-v profiles and related variables (theoretical maximum velocity, theoretical maximum horizontal force, slope of the linear F-v profile, peak power, time constant tau, and horizontal maximal velocity). The devices were compared by determining the systematic bias and the 95% limits of agreement (random error) for all variables, both of which were expressed as percentages of the mean radar value. All bias values were within 6.32%, with the 1080 Sprint reporting higher values for tau, horizontal maximal velocity, and theoretical maximum velocity. Random error was lowest for velocity-based variables but exceeded 7% for all others, with slope of the F-v profile being greatest at ±12.3%. These results provide practitioners with the information necessary to determine if the agreement between the devices and the magnitude of random error is acceptable within the context of their specific application.

A 3-dimensional finite element analysis to evaluate the impact of force direction, insertion angle, and cortical bone thickness on mini-screw and its surrounding bone

Background. The present study aimed to assess the stress and strain distribution on mini-screws and the surrounding bone in cases of different cortical bone thicknesses (CBTs), mini-screw insertion angles, and force directions using finite element analysis (FEA). Methods. Inventor professional version 8 software was used to construct 24 three-dimensional assemblies of mini-screws inserted with different insertion angles (30º, 60º, and 90º) in alveolar bone blocks with different CBTs (0.5, 1, 1.5, and 2 mm). The models simulated mini-screws inserted in bones with different CBTs and different insertion angles. A 2-N load was applied in two directions to mini-screw heads. The resultant stresses of the applied load were collected from the output of the ANSYS program. Results. The results indicated that force direction affected bone strains as the horizontal force generated more strains on cortical bone than the oblique one. Force applied to 60º inserted mini-screws generated much more strains on cortical bone than 90º and 30º inserted mini-screws. In a 60º inserted mini-screw, the horizontal force generated about 45% more strains on cortical bone than the oblique one. The exerted microstrain on bone decreased as CBT increased. Conclusion. It can be concluded that inserting mini-screws at 60º to the bone surface should be avoided as it generates much more strains on cortical bone than 90º and 30º, especially when a force parallel to the bone surface is applied.

Numerical study on breaking solitary wave force on box-girder bridge

Solitary wave is often used to simulate tsunami propagating in deep water and breaking solitary wave is often used to simulate tsunami bore propagating in shallow water or on land. The breaking solitary wave force on box-girder, which has been widely used in bridge engineering in coastal areas of China, receives few attentions. This study aims to investigate characteristics and generation mechanism of breaking solitary wave force on box-girder numerically. A numerical wave flume with a 1:20 slope was built firstly, then the solitary wave generation ability, wave deformation and wave breaking on the slope, as well as wave force calculation precision, are validated. The water depth 0.6 m, the slope gradient 1:20 and the distance between slope top and box-girder 2.0 m remain unchanged, while the wave height and clearance changes in different cases. The time histories of horizontal force and vertical force on box-girder can be divided into three and four stages respectively according to their characteristics. The surface of box-girder is decomposed into a series of panels to facilitate exploring tsunami bore force generation mechanism. Results show horizontal force is dominated by static pressure on upstream vertical panels and vertical force is mainly contributed by static pressure on upstream horizontal panels and on panels in the chambers. Tsunami bore overtopping the box-girder deck impacts the top panel vigorously and results in the peak value of negative vertical force.

Maintenance of ankle power and decreased inter-limb asymmetry during sprint running in fatigued multi-speed athletes

The ability to shift from walking and jogging to sprinting gaits, even when fatigued after prolonged effort, would have been as useful to our hunter-gatherer ancestors as it is in modern day sports. During prolonged jogging, joint moment and work are reduced in the distal (ankle) joint but increased at proximal (hip/knee) joints as fatigue progresses, and might be expected to occur in sprinting. Fatigue is also thought to increase inter-limb kinematic and force production asymmetries, which are speculated to influence injury risk. However, the effects of running-related fatigue on sprint running gait have been incompletely studied, so these hypotheses remain untested. We studied 3-D kinematics and ground reaction force production in dominant (DL) and non-dominant (NDL) legs during both non-fatigued and fatigue sprinting in habitual but uncoached running athletes. Contrary to the tested hypotheses, relative between-leg differences were greater in non-fatigued than fatigued sprinting. When not fatigued, DL produced greater propulsive impulse through both greater positive and negative work being performed at the ankle, whilst NDL produced more vertical impulse, possibly resulting from the greater hip flexion observed prior to the downwards acceleration of the foot towards the ground. Whilst few changes were detected in DL once fatigued, NDL shifted towards greater horizontal force production, largely resulting from an increase in plantarflexion (distal-joint) moments and power. After fatiguing running, therefore, inter-limb asymmetry was reduced and no distal-to-proximal shift in work/power was detected during sprinting. Speculatively, these adaptations may help to attenuate decreases in running speed whilst minimising injury risk.

Analysis of Soil Resistance under Horizontal Load of Rigid Antislide Pile

In order to study the bearing characteristics and failure mechanism of the rigid antislide pile under horizontal load, the stress of rigid antislide pile under transverse axial large displacement load is analyzed by using elastic-plastic theory, finite element analysis, and model test. The theoretical formula of the proximal plastic earth pressure near the pile with the depth of soil under the horizontal force is obtained. The results show that the standard is insensitive to the variation of soil parameters and the influence of soil parameters on allowable soil resistance in front of pile should be considered. With the increase of the horizontal force of the pile top, the soil near the pile is destroyed in this process gradually, which is the decline of the cross section of the maximum soil resistance of the pile. When the horizontal displacement of pile top is 20 mm and 70 mm, the soil resistance value and the ultimate soil resistance value in front of the pile can be selected, respectively. The plastic zone develops to the front and bottom of the pile at the same speed, at an angle of 45° with the direction of gravity. When the displacement reaches 34 mm, the plastic zone develops to the deeper depth obviously. The results can provide a theoretical basis for the design and application of antislide piles during the process of slope protections.

Free Falling Szilard Engine, Entropic Forces and Landauer’s principle; Revisiting the Principle of Equivalence

Gedanken experiments illustrating exemplifications of the Landauer principle in the free falling Einstein elevator are treated. Double-well simplest information system embedded into the free falling elevator is addressed. Infinitesimal horizontal force applied to the particle m transfers it from position “0” to position “1”, emerging from the free falling double-well system confining mass m. When thermal noise is considered, the potential barrier of kBT should be surmounted for the erasing of one bit of information. Entropic forces arising in the free falling elevator are considered. The maximal change in the entropy of free-joint polymer chain attached to the free falling elevator is estimated as ΔSmax≅kB, and it is remarkably independent of the mass attached to the chain and the parameters of the chain itself. Free falling minimal Szilard engine is treated. The informational re-interpretation of the minimal Szilard process is shaped as follows: the energy kBTln2 necessary for erasing of 1 bit of information is spent for lifting up mass, whatever, is the value of this mass. Appropriate choice of frames enables elimination of gravity in the considered system; however elimination of the thermal noise (dissipation processes) by the same procedure is impossible.