Sport-Related Injuries in Canadian Interuniversity Athletics: A Descriptive Epidemiologic Analysis of Knee Injuries, 2014-2017

The purpose of this study was to identify and establish the extent of sport-related injury in Canadian university varsity athletics, focusing on knee injury and significant sport injury. Of the SRIs reported, 20% were significant in nature and 23.2% were knee injuries. A larger percentage of knee SRIs were significant compared non-knee SRIs. Those suffering a knee injury were 4.5 times more likely to suffer a significant injury than those afflicted with non-knee injuries. Mens volleyball athletes are two times more likely to suffer a knee injury, once controlled for sport group. Once controlled for sport, mens hockey athletes are 2.3 times more likely to suffer a significant injury than any other sport (Table 4). Mens basketball has the highest rate of injury (3.32 per athlete) during this reporting period and football has the highest rate of significant knee injury at 0.27 per athlete (Table 1)

A New Godunov Scheme for MHD, with Application to the MRI in disks

We describe a new numerical scheme for MHD which combines a higher order Godunov method (PPM) with Constrained Transport. The results from a selection of multidimensional test problems are presented. The complete test suite used to validate the method, as well as implementations of the algorithm in both F90 and C, are available from the web. A fully three-dimensional version of the algorithm has been developed, and is being applied to a variety of astrophysical problems including the decay of supersonic MHD turbulence, the nonlinear evolution of the MHD Rayleigh-Taylor instability, and the saturation of the magnetorotational instability in the shearing box. Our new simulations of the MRI represent the first time that a higher-order Godunov scheme has been applied to this problem, providing a quantitative check on the accuracy of previous results computed with ZEUS; the latter are found to be reliable.Comment: 11 pages, style files included, Conference Proceedings: "Magnetic Fields in the Universe: from Laboratory and Stars to Primordial Structures", More information on Athena can be found at http://www.astro.princeton.edu/~jstone/athena.htm

Nonlinear Evolution of the Magnetohydrodynamic Rayleigh-Taylor Instability

We study the nonlinear evolution of the magnetic Rayleigh-Taylor instability using three-dimensional MHD simulations. We consider the idealized case of two inviscid, perfectly conducting fluids of constant density separated by a contact discontinuity perpendicular to the effective gravity g, with a uniform magnetic field B parallel to the interface. Modes parallel to the field with wavelengths smaller than l_c = [B B/(d_h - d_l) g] are suppressed (where d_h and d_l are the densities of the heavy and light fluids respectively), whereas modes perpendicular to B are unaffected. We study strong fields with l_c varying between 0.01 and 0.36 of the horizontal extent of the computational domain. Even a weak field produces tension forces on small scales that are significant enough to reduce shear (as measured by the distribution of the amplitude of vorticity), which in turn reduces the mixing between fluids, and increases the rate at which bubbles and finger are displaced from the interface compared to the purely hydrodynamic case. For strong fields, the highly anisotropic nature of unstable modes produces ropes and filaments. However, at late time flow along field lines produces large scale bubbles. The kinetic and magnetic energies transverse to gravity remain in rough equipartition and increase as t^4 at early times. The growth deviates from this form once the magnetic energy in the vertical field becomes larger than the energy in the initial field. We comment on the implications of our results to Z-pinch experiments, and a variety of astrophysical systems.Comment: 25 pages, accepted by Physics of Fluids, online version of journal has high resolution figure

Suitability of Nickel Chromium Wire Cutters as Deployable Release Mechanisms on CubeSats in Low Earth Orbit

This paper investigates the suitability of a nickel chromium wire cutter (NCWC) for use on the GASPACS (Get Away Special Passive Attitude Control Satellite) Mission. It is intended that when activated the NCWC will cut through a restraining wire and thereby release the stored energy of the deployable AeroBoom. Flight worthiness is based on favorable performance during functional testing to address known issues with the NCWC, such as wire burn through and cutting issues. In-depth testing discussed in this paper includes: Manufacturability of the NCWC, including analysis of possible acceptable performance errors induced from inefficiencies in the assembly process, functional testing of a prototype NCWC under flight conditions, and analyzing the safety margin between the flight running conditions and the point of failure (destructive testing). The results from these tests support the conclusion that the current design of the NCWC will successfully support the GASPACS mission in deploying its AeroBoom Experiment

The Magnetic Rayleigh-Taylor Instability in Three Dimensions

We study the magnetic Rayleigh-Taylor instability in three dimensions, with focus on the nonlinear structure and evolution that results from different initial field configurations. We study strong fields in the sense that the critical wavelength l_c at which perturbations along the field are stable is a large fraction of the size of the computational domain. We consider magnetic fields which are initially parallel to the interface, but have a variety of configurations, including uniform everywhere, uniform in the light fluid only, and fields which change direction at the interface. Strong magnetic fields do not suppress instability, in fact by inhibiting secondary shear instabilities, they reduce mixing between the heavy and light fluid, and cause the rate of growth of bubbles and fingers to increase in comparison to hydrodynamics. Fields parallel to, but whose direction changes at, the interface produce long, isolated fingers separated by the critical wavelength l_c, which may be relevant to the morphology of the optical filaments in the Crab nebula.Comment: 14 pages, 9 pages, accepted by Ap

A Mass Media Campaign to Promote Divorce Adjustment

Introduction. This study produced and evaluated a mass media campaign designed to promote emotional adjustment to divorce. Hypotheses. (a) Sending a promotional newsletter to divorced persons will increase their reported utilization of the campaign. (b) Divorced persons who report heavy utilization of the campaign will report greater emotional improvement than divorced persons who report light or no utilization of the campaign. Method. A field experiment was conducted in rural northern Utah. The names of all recently (less than 12 months) divorced persons were obtained from the county clerk and randomly divided into an experimental group, who received a newsletter promoting the media campaign, and a control group. The five-week media campaign included 10 radio shows, 16 newspaper articles, and 29 television shows. After the campaign, 101 subjects were interviewed regarding their media use. They also completed a posttest and retrospective pretest of anxiety, depression, hostility (measured by the Symptom Check List 90-R), and attachment. Results. The campaign was reportedly used by 77.2% of the subjects. Hypothesis 1 was weakly supported. Subjects who received the newsletter reported using statistically significantly more media events (X = 4.95) than subjects who did not receive the newsletter (X = 3.12). However, the percentage of variance in media use associated with newsletter receipt was only 3.2%. Hypothesis 2 was partially supported. Heavy campaign users (3+ events) reported statistically significantly greater improvements in anxiety, depression, and hostility (but not attachment) than light users (0-2 events). The percentage of variance in emotional improvements associated with media use ranged from 1 to 5%. Those who reportedly spent time with significant others after the divorce reported significantly greater emotional improvements than those who did not spend time with others. The highest degree of reported emotional improvement was reported by those who reported both heavy media use and time spent with significant others, while the lowest degree of emotional improvement was reported by subjects who reported little or no media use and no time spent with confidants