INFLUENCE OF PLAYING LEVEL ON THE KINEMATICS AND KINETICS OF THE RUGBY SCRUM

The aim of this study was to examine the force production, lower body kinematics and kinetics of front row rugby union forwards during the engagement phase of a simulated rugby union scrum. Twenty-eight male front row players were divided into three groups; professional, senior and junior amateur players. Players performed five trials based on the International Rugby Board scrum engagement sequence. Three dimensional motion analysis and force plate data were used to determine joint angles and reaction forces both on the scrum machine and on the ground. Professional front row forwards generated significantly greater force during the engagement phase compared to both senior and junior amateur players. Professional players had a significantly greater knee abduction angle and generated larger peak hip joint power compared to both junior and senior players

Stiffness of Contacts Between Rough Surfaces

The effect of self-affine roughness on solid contact is examined with molecular dynamics and continuum calculations. The contact area and normal and lateral stiffnesses rise linearly with the applied load, and the load rises exponentially with decreasing separation between surfaces. Results for a wide range of roughnesses, system sizes and Poisson ratios can be collapsed using Persson's contact theory for continuous elastic media. The atomic scale response at the interface between solids has little affect on the area or normal stiffness, but can greatly reduce the lateral stiffness. The scaling of this effect with system size and roughness is discussed.Comment: 4 pages, 3 figure

Quasi-Static Contact and Sliding of Crystalline Materials

The mechanical properties of solid-solid contact are important in both engineered systems and in the explanation of everyday phenomena. However, predicting those properties from the surface geometry is a challenge for several reasons. The surface of a solid is typically rough, exhibiting effectively random geometry extending from the long-wavelength topography down to the atomic-scale structure. The surfaces often remain separated over most of their area. Even within a single region of contact, the solids can deform into one of many possible configurations. In this thesis we use quasi-static molecular dynamics simulation to determine the mechanical properties of crystalline contacts. We help develop the Green's function molecular dynamics method to enable simulations to reach the necessary wide range of length-scales. We focus on simple interatomic potentials and models to isolate the underlying mechanical phenomena. We design simulations that test with atomic-scale resolution the normal contact of rough solids and the quasi-static sliding of clean crystalline contacts. We find for rough solids at typical normal loads that the average surface separation decreases as a logarithm of load. Correspondingly, the mechanical stiffness associated with the rough surface is proportional to the load. In both the continuum case and the atomistic case, the fraction of the surface in repulsive contact increases approximately linearly with load. In the atomistic case, the dimensionless proportionality constant can be increased several times by nanometer-scale features. Surface steps frequently found on crystalline materials can dramatically increase contact area by increasing the amount of plastic rearrangement and, in turn, decreasing the average surface stress. The static friction of a contact between elastic crystals depends sensitively on contact size, crystal orientation, and the microscopic friction law at the interface. In non-adhesive commensurate simulations, we show that the friction coefficient decreases over several decades as $(a^2/Rb)^{-2/3}$ where a is the contact radius, $R$ is the sphere radius, and $b$ is the Burgers vector of dislocations that are produced. Incommensurate contacts, despite exhibiting complex deformations while sliding, show surprisingly universal characteristics in the large size limit. We discuss the elastic breakdown of superlubricity by showing the rapid rise in friction from lowering the material modulus of large incommensurate contacts

Statistical properties of 3D cell geometry from 2D slices

Although cell shape can reflect the mechanical and biochemical properties of the cell and its environment, quantification of 3D cell shapes within 3D tissues remains difficult, typically requiring digital reconstruction from a stack of 2D images. We investigate a simple alternative technique to extract information about the 3D shapes of cells in a tissue; this technique connects the ensemble of 3D shapes in the tissue with the distribution of 2D shapes observed in independent 2D slices. Using cell vertex model geometries, we find that the distribution of 2D shapes allows clear determination of the mean value of a 3D shape index. We analyze the errors that may arise in practice in the estimation of the mean 3D shape index from 2D imagery and find that typically only a few dozen cells in 2D imagery are required to reduce uncertainty below 2\%. This framework could be naturally extended to estimate additional 3D geometric features and quantify their uncertainty in other materials

The identification of risk factors for ankle sprains sustained during netball participation

Objectives: Ankle sprains account for a large percentage of injuries sustained in netball. The identification of risk factors for ankle sprain is the preliminary action required to inform future prevention strategies. Design: Prospective study. Participants: Ninety-four netball players from club and inter-district teams. Methods: Preseason data were collected for; vertical jump height, perceived ankle instability, sprain history, arthrometry inversion-eversion angles, star excursion balance test reach distances, the number of foot lifts during unilateral stance and demi-pointe balance test results. Participants were followed for the duration of one netball season and ankle sprains were recorded. Results: Eleven sprains were recorded for eleven players using a time-loss definition of injury. Ankle sprains occurred at an incidence rate of 1.74/1000 h of netball exposure. One risk factor was identified to increase the odds of sustaining an ankle sprain during netball participation – a reach distance in the posterior-medial direction of the star excursion balance test of less than or equal to 77.5% of leg length (OR = 4.04, 95% CI = 1.00–16.35). Conclusions: The identified risk factor can be easily measured and should be considered for preseason injury risk profiling of netball players. Netball players may benefit from training programs aimed at improving single leg balance

Office-based optical coherence tomographic imaging of human vocal cords

Optical coherence tomography (OCT) is an evolving noninvasive imaging modality and has been used to image the larynx during surgical endoscopy. The design of an OCT sampling device capable of capturing images of the human larynx during a typical office based laryngoscopy examination is discussed. Both patient’s and physician\u27s movements were addressed. In vivo OCT imaging of the human larynx is demonstrated. Though the long focal length limits the lateral resolution of the image, the basement membrane can still be readily distinguished. Office-based OCT has the potential to guide surgical biopsies, direct therapy, and monitor disease. This is a promising imaging modality to study the larynx

Human feeder cell line for derivation and culture of hESc/hiPSc

AbstractWe have generated a human feeder cell line from early second trimester Placental Stromal Fibroblasts (ihPSF) stably over-expressing the polycomb protein BMI-1. These feeder cells retain the ability to maintain human Embryonic Stem cells (hESc) over long-term culture whereas hTERT or BMI-1/hTERT immortalised feeder cell lines do not. ihPSFs were able to support the derivation of a new hESc line in near xenofree (free of non-human animal components) conditions and support continued culture of newly derived hESc and human induced Pluripotent Stem (hiPS) cell lines in complete xenofree conditions necessary for clinical use