Centre vortex effects on the overlap quark propagator

We investigate the role of centre vortices in dynamical mass generation using overlap fermions. The exact chiral symmetry that the overlap fermion action possesses yields a distinctive response to the underlying topology of the gauge field, leading to novel results. We study the quark propagator and associated mass function on gauge field backgrounds featuring the removal of centre vortices as well as on vortex-only backgrounds. The effect of cooling vortex-only backgrounds on the overlap quark propagator is also presented.D. Trewartha, W. Kamleh and D. Leinwebe

A CASE STUDY OF STRIDE FREQUENCY AND SWING TIME IN ELITE ABLE-BODIED SPRINT RUNNING: IMPLICATIONS FOR AMPUTEE DEBATE

Recent research into trans-tibial double-amputee sprint performance has debated the possible inherent advantages, disadvantages and limitations to sprinting with prosthetic limbs compared to healthy limbs. Biomechanical data gathered throughout a training season from an elite able-bodied sprinter provide a new perspective on this debate. Peak stride frequency was measured at 2.62 Hz, and the corresponding swing time was estimated to be 0.287 s in the able-bodied sprinter. Published swing time and stride frequency values from the double-amputee at maximum velocity, thought to be beyond biological limits, therefore may not be so, although previously published research has provided evidence that some joint kinetic values from the double-amputee have not been shown in elite able-bodied sprinting

Cervical spine injuries: A whole-body musculoskeletal model for the analysis of spinal loading

This is the final version of the article. Available from Public Library of Science via the DOI in this record.Cervical spine trauma from sport or traffic collisions can have devastating consequences for individuals and a high societal cost. The precise mechanisms of such injuries are still unknown as investigation is hampered by the difficulty in experimentally replicating the conditions under which these injuries occur. We harness the benefits of computer simulation to report on the creation and validation of i) a generic musculoskeletal model (MASI) for the analyses of cervical spine loading in healthy subjects, and ii) a population-specific version of the model (Rugby Model), for investigating cervical spine injury mechanisms during rugby activities. The musculoskeletal models were created in OpenSim, and validated against in vivo data of a healthy subject and a rugby player performing neck and upper limb movements. The novel aspects of the Rugby Model comprise i) population-specific inertial properties and muscle parameters representing rugby forward players, and ii) a custom scapula-clavicular joint that allows the application of multiple external loads. We confirm the utility of the developed generic and population-specific models via verification steps and validation of kinematics, joint moments and neuromuscular activations during rugby scrummaging and neck functional movements, which achieve results comparable with in vivoand in vitrodata. The Rugby Model was validated and used for the first time to provide insight into anatomical loading and cervical spine injury mechanisms related to rugby, whilst the MASI introduces a new computational tool to allow investigation of spinal injuries arising from other sporting activities, transport, and ergonomic applications. The models used in this study are freely available at simtk.org and allow to integrate in silico analyses with experimental approaches in injury prevention.Funding: This project is funded by the Rugby Football Union (RFU) Injured Players Foundation. The funder had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript

A CASE STUDY OF STRIDE FREQUENCY AND SWING TIME IN ELITE ABLEBODIED SPRINT RUNNING: IMPLICATIONS FOR AMPUTEE DEBATE

Recent research into trans-tibial double-amputee sprint performance has debated the possible inherent advantages, disadvantages and limitations to sprinting with prosthetic limbs compared to healthy limbs. Biomechanical data gathered throughout a training season from an elite able-bodied sprinter provide a new perspective on this debate. Peak stride frequency was measured at 2.62 Hz, and the corresponding swing time was estimated to be 0.287 s in the able-bodied sprinter. Published swing time and stride frequency values from the double-amputee at maximum velocity, thought to be beyond biological limits, therefore may not be so, although previously published research has provided evidence that some joint kinetic values from the double-amputee have not been shown in elite able-bodied sprinting

Quark propagation in the instantons of lattice QCD

We quantitatively examine the extent to which instanton degrees of freedom, contained within standard Monte-Carlo generated gauge-field configurations, can maintain the characteristic features of the mass and renormalization functions of the nonperturbative quark propagator. We use over-improved stout-link smearing to isolate instanton effects on the lattice. Using a variety of measures, we illustrate how gauge fields consisting almost solely of instantonlike objects are produced after only 50 sweeps of smearing. We find a full vacuum, with a packing fraction more than three times larger than phenomenological models predict. We calculate the overlap quark propagator on these smeared configurations, and find that even at high levels of smearing the majority of the characteristic features of the propagator are reproduced. We thus conclude that instantons contained within standard Monte-Carlo generated gauge-field configurations are the degrees of freedom responsible for the dynamical generation of mass observed in lattice QCD.Daniel Trewartha, Waseem Kamleh, Derek Leinweber, and Dale S. Robert

Measuring impacts and informing modelling processes

Primarily using rugby union situations as case study examples for the practical demonstration, the initial part of the session will discuss both familiar and emerging techniques to measure the biomechanics of sport impact situations. We will cover some of the issues that need to be accounted for to acquire robust data in such complex environments, and we will discuss how experimental measures can be either used in their own right to develop knowledge of impact biomechanics or can provide data to input a modelling pipeline and for model validation purposes

Centre vortices are the seeds of dynamical chiral symmetry breaking

Using lattice QCD, we reveal a fundamental connection between centre vortices and several key features associated with dynamical chiral symmetry breaking and quark confinement. Calculations are performed in pure SU(3) gauge theory using the chiral overlap fermion action. Starting from the original Monte Carlo gauge fields, a vortex identification procedure yields vortex-removed and vortex-only backgrounds. We examine the static quark potential, the quark mass function, the hadron spectrum, the local topological charge density, and the distribution of instanton-like objects on the original, vortex-removed and vortex-only ensembles. The removal of vortices consistently results in the removal of the corresponding feature associated with dynamical chiral symmetry breaking. Remarkably, we observe that after some smoothing, in each of these cases, the vortex-only degrees of freedom are able to encapsulate the pertinent features of the original gauge fields

Analysis of cervical spine loading in rugby scrummaging: a computer simulation approach

Musculoskeletal modelling is widely used in biomechanics for the analysis and simulation of human motion. A modelling approach allows estimates of the internal load on specific anatomical structures, and the individual muscle forces that govern movement execution. Within the analysis of impact events in rugby union, modelling can help the understanding of the mechanisms of acute and chronic cervical spine injuries, starting from experimental measures of external load on the player, and progressing to the estimation of stresses acting on the internal cervical structures. During this part of the applied session, we will use a novel musculoskeletal model and previously collected experimental data (forces and kinematics) to analyse the cervical spine loading experienced during a rugby scrum. An open-source biomechanical software (OpenSim 3.2) will be used to set up and run inverse and forward dynamics pipelines to calculate joint moments and joint reaction forces, and to analyse “what if…” scenarios

The influence of instantons on the quark propagator

Extent: 6p.We use over-improved stout-link smearing to investigate the presence and nature of instantons on the lattice. We find that smearing can remove short-range effects with little damage to the longrange structure of the gauge field, and that after around 50 sweeps this process is complete. There are more significant risks for very high levels of smearing beyond 100 sweeps. We are thus able to produce gauge configurations dominated by instanton effects. We then calculate the overlap quark propagator on these configurations, and thus the non-perturbative mass function. We find that smeared configurations preserve the majority of dynamical mass generation, and conclude that instantons are primarily responsible for the dynamical generation of mass.Daniel Trewartha, Waseem Kamleh, Derek Leinweber, Peter Moranhttp://pos.sissa.it/cgi-bin/reader/conf.cgi?confid=16

Evaluation of tackling biomechanics in rugby:video incident analysis and experimental set up

This study consisted of a video incident analysis of rugby tackles leading to spinal injuries, where players’ behaviours and observed loading mechanisms were coded for each incident. The key features of these events were summarised, revealing the role of highspeed impacts, illegal tackles, and poor tackle technique in injury-causing tackles. In addition, lateral bending moments and lateral flexion movements were more prevalent than suggested by previous research. This investigation informed an experimental protocol for the analysis of simulated rugby tackles, with the final goal to obtain measures of cervical spine biomechanics during tackles. Data captured from this protocol could also be input into a full-body musculoskeletal model to provide descriptions of internal cervical spine loading in different tackle event scenarios