Development of a biomechanically validated turf testing rig

The aim of this study was to develop an artificial turf testing rig that applied biomechanically validated vertical, shear and torque loads to the surface. Results of initial testing on 3rd generation artificial turf and natural grass soccer pitches are presented

Tidal Stresses and Energy Gaps in Microstate Geometries

We compute energy gaps and study infalling massive geodesic probes in the new families of scaling, microstate geometries that have been constructed recently and for which the holographic duals are known. We find that in the deepest geometries, which have the lowest energy gaps, the geodesic deviation shows that the stress reaches the Planck scale long before the probe reaches the cap of the geometry. Such probes must therefore undergo a stringy transition as they fall into microstate geometry. We discuss the scales associated with this transition and comment on the implications for scrambling in microstate geometries.Comment: 22 pages, 1 figur

Arithmetic Progressions with Restricted Digits

For an integer $b \geqslant 2$ and a set $S\subset \{0,\cdots,b-1\}$, we define the Kempner set $\mathcal{K}(S,b)$ to be the set of all non-negative integers whose base-$b$ digital expansions contain only digits from $S$. These well-studied sparse sets provide a rich setting for additive number theory, and in this paper we study various questions relating to the appearance of arithmetic progressions in these sets. In particular, for all $b$ we determine exactly the maximal length of an arithmetic progression that omits a base-$b$ digit

Higher-Dimensional Algebra VII: Groupoidification

Groupoidification is a form of categorification in which vector spaces are replaced by groupoids, and linear operators are replaced by spans of groupoids. We introduce this idea with a detailed exposition of "degroupoidification": a systematic process that turns groupoids and spans into vector spaces and linear operators. Then we present three applications of groupoidification. The first is to Feynman diagrams. The Hilbert space for the quantum harmonic oscillator arises naturally from degroupoidifying the groupoid of finite sets and bijections. This allows for a purely combinatorial interpretation of creation and annihilation operators, their commutation relations, field operators, their normal-ordered powers, and finally Feynman diagrams. The second application is to Hecke algebras. We explain how to groupoidify the Hecke algebra associated to a Dynkin diagram whenever the deformation parameter q is a prime power. We illustrate this with the simplest nontrivial example, coming from the A2 Dynkin diagram. In this example we show that the solution of the Yang-Baxter equation built into the A2 Hecke algebra arises naturally from the axioms of projective geometry applied to the projective plane over the finite field with q elements. The third application is to Hall algebras. We explain how the standard construction of the Hall algebra from the category of representations of a simply-laced quiver can be seen as an example of degroupoidification. This in turn provides a new way to categorify - or more precisely, groupoidify - the positive part of the quantum group associated to the quiver.Comment: 67 pages, 14 eps figures; uses undertilde.sty. This is an expanded version of arXiv:0812.486

Design and Development Process for a novel Technology Capable of Providing a New Breaking Force Attenuating Sports Surface

AbstractLower limb loading rate is a major contributor to athletic injury because it represents the stress being absorbed by an athlete's lower limbs that makes them vulnerable to stress fractures, as well as knee and ankle joint injuries. This research therefore sought to identify a means by which lower limb loading rates could be reduced and therefore the risk of overloading injury reduced. A sports surface that encourages elastic deformation during contact in both the horizontal anterior-posterior direction and the horizontal medial-lateral direction through a process of horizontal deformation and displacement may result in reduced foot and limb loading. This surface should maximise horizontal energy attenuation in order to reduce the risk of injury while at the same time provide satisfactory energy return to avoid player fatigue.Effective product research and development methods centre on the ways in which the activities can be effectively planned, controlled and implemented. The process can be regarded as a sequence of activities and decisions which progress a problem solving process from the initial identification of the problem, through to a final implementable design solution. The process of design is fundamentally an iterative method, which comprises the articulation of the problem which is to be solved, collecting and codifying pertinent information, the divergent exploration of potential problem solutions, convergence towards a favourable solution, and finally, the detailed implementation and optimisation of the design solution.The creative process followed, has resulted in the design of a novel, and commercially improved modular plastic tile sports surface system. This has been realised through the development of an innovative, sustainable, shock attenuating tile and connector geometry, which aims to reduce braking forces on the sports surface to acceptable levels, and thus reduce the risk of athlete injury. This research is significant as currently no sports surface exists which specifically targets horizontal force reduction, as a means to reduce injury rates

PREDICTING TEAM WORKLOAD AND PERFORMANCE USING TEAM AUTONOMIC ACTIVITY

The development of a team measure of autonomic activity has a wide variety of applications. During team training, an index of team autonomic activity could potentially have added value for real-time feedback, team selection and performance evaluation. The primary purpose of this study was to investigate the relation between autonomic activity measures, workload, and performance, on both an individual and team level. Specifically, this study sought to determine whether changes in workload could be detected in measures of autonomic activity and whether changes in the autonomic measures related to changes in performance. 34 teams of two (35 males, 33 females) completed a processing plant simulation during 4 varying levels of individual and team difficulty. Sympathetic and parasympathetic nervous system activity was measured throughout the task using an electrocardiogram (ECG) and an impedance cardiogram (ICG), in addition to the NASA-TLX. SNS and PNS measures were combined to produce a team autonomic activity measure that was used to predict team workload and performance. Results showed that workload and performance varied across the task difficulty levels with higher difficulty producing higher workload and worse performance. Regressions conducted predicting team performance from team autonomic activity showed that team autonomic activity accounted for 10% of the variance in team performance scores. Further exploratory analyses showed interesting relations between autonomic activity and performance when examining the task difficulty levels separately. These analyses discovered that during the mixed individual difficulty levels, one team member\u27s physiology was consistently correlated with the other team member\u27s performance. In conclusion, the current study showed that team performance can be predicted from team autonomic activity, and that individual team member physiology has the potential to provide an index of team related behaviors (e.g. mutual performance monitoring and back-up behaviors)

THE ROLE OF HEAD MOVEMENTS IN SIMULATOR SICKNESS GENERATED BY A VIRTUAL ENVIRONMENT

Virtual environments (VEs) are being used in a variety of applications, including training, rehabilitation and clinical treatment. To effectively utilize VEs in these situations it is important to try to understand some of the effects of VE exposure. The purpose of this study was to investigate head and body movements in virtual and real environments during building clearing and the relationship between these movements and simulator sickness. The data for the current study were drawn from a larger team training study which investigated the use of VEs for training building clearing. The goal of the first part of this study was to compare head movements made in a real world (RW) environment to head movements made in a VE (Analysis I). The goal of second part of this study was to examine the relationship between head movements and simulator sickness in a VE (Analysis II). The first analysis used two independent samples t-tests to examine the differences between head movements made in a VE and head movements made in a RW environment. The t-tests showed that subjects in the VE moved their heads less, t(23.438)=12.690, p\u3c0.01, and less often, t(46)=8.682, p\u3c0.05, than subjects in the RW. In the second analysis, a 3 x 20 ANOVA found a significant difference between groups with low, med, and high simulator sickness scores, F(2,21)=4.221, p\u3c0.05, ήp2= 0.287, where subjects who reported being the most sick tended to restrict their head movements more than the other two groups. For VEs to progress as a useful tool, whether for training, therapy, etc., it will be necessary to identify the variable(s) that cause people to become motion sick and restrict their head movement during VE exposure. Future studies should seek to investigate more continuous measures of sickness, perhaps psychophysiological measures, and possible effects of a negative transfer of training due to the restriction of head movements in VEs