27 research outputs found
The Magnetothermal Instability in the Intracluster Medium
The electron mean free path in the intracluster medium (ICM) of galaxy
clusters is much larger than the gyroradius; thus, heat is transported
anisotropically along magnetic field lines. We show that the intracluster
medium is unstable to the magnetothermal instability (MTI) using MHD
simulations with anisotropic thermal conduction. As a result of the MTI, we
find that the temperature profile of the ICM can be substantially modified on
timescales of several billion years while the magnetic field is amplified by
dynamo action up to more than fifty times the original energy. We also show
that the instability drives field lines to become preferentially radial leading
to conduction that is a highly efficient fraction of the Spitzer conductivity.
As such, we present the first self-consistent calculation of the effective
thermal conductivity in the ICM.Comment: Submitted to Ap
Effect of the Coriolis Force on the Hydrodynamics of Colliding Wind Binaries
Using fully three-dimensional hydrodynamic simulations, we investigate the
effect of the Coriolis force on the hydrodynamic and observable properties of
colliding wind binary systems. To make the calculations tractable, we assume
adiabatic, constant velocity winds. The neglect of radiative driving,
gravitational deceleration, and cooling limit the application of our models to
real systems. However, these assumptions allow us to isolate the effect of the
Coriolis force, and by simplifying the calculations, allow us to use a higher
resolution (up to 640^3) and to conduct a larger survey of parameter space. We
study the dynamics of collidng winds with equal mass loss rates and velocities
emanating from equal mass stars on circular orbits, with a range of values for
the ratio of the wind to orbital velocity. We also study the dynamics of winds
from stars on elliptical orbits and with unequal strength winds. Orbital motion
of the stars sweeps the shocked wind gas into an Archimedean spiral, with
asymmetric shock strengths and therefore unequal postshock temperatures and
densities in the leading and trailing edges of the spiral. We observe the
Kelvin-Helmholtz instability at the contact surface between the shocked winds
in systems with orbital motion even when the winds are identical. The change in
shock strengths caused by orbital motion increases the volume of X-ray emitting
post-shock gas with T > 0.59 keV by 63% for a typical system as the ratio of
wind velocity to orbital velocity decreases to V_w/V_o = 2.5. This causes
increased free-free emission from systems with shorter orbital periods and an
altered time-dependence of the wind attenuation. We comment on the importance
of the effects of orbital motion on the observable properties of colliding wind
binaries.Comment: 12 pages, 17 figures, accepted for publication in Ap
Density Probability Distribution Functions in Supersonic Hydrodynamic and MHD Turbulence
We study the probability distribution function (PDF) of the mass density in
simulations of supersonic turbulence with properties appropriate for molecular
clouds. For this study we use Athena, a new higher-order Godunov code. We find
there are surprisingly similar relationships between the mean of the
time-averaged PDF and the turbulent Mach number for driven hydrodynamic and
strong-field MHD turbulence. There is, however, a large scatter about these
relations, indicating a high level of temporal and spatial variability in the
PDF. Thus, the PDF of the mass density is unlikely to be a good measure of
magnetic field strength. We also find the PDF of decaying MHD turbulence
deviates from the mean-Mach relation found in the driven case. This implies
that the instantaneous Mach number alone is not enough to determine the
statistical properties of turbulence that is out of equilibrium. The scatter
about the mean-Mach relation for driven turbulence, along with the large
departure of decaying turbulence PDFs from those of driven turbulence, may
illuminate one factor contributing to the large observed cloud-to-cloud
variation in the star formation rate per solar mass.Comment: 4 pages, 2 figures, published in ApJL; corrected sign in eqn. (4
Line Hops and Side Hold Rotation Tests Load Both Anterior and Posterior Shoulder: A Biomechanical Study
Background: Clinical tests should replicate the stressful positions encountered during sport participation. Evaluating the kinetic and electromyographical demands of clinical tests enables clinicians to choose appropriate tests for specific sports.
Purpose: To describe the shoulder forces and muscle activation levels during closed chain functional tests of Line Hops (LH) and Side Hold Rotation (SHR).
Study Design: Descriptive biomechanical study.
Methods: Ten asymptomatic participants were examined in a university laboratory. Two functional tests were evaluated using three-dimensional video analysis and electromyography to measure shoulder forces, moments, and muscular activity levels.
Results: SHR produced a peak average posterior translation force of 4.84 N/kg (CI95 4.32-5.36N/kg) and a peak average anterior translational force of 1.57 N/kg (CI95 1.10-2.01N/kg). High levels of serratus anterior (98% maximum voluntary isometric contraction (MVIC) and infraspinatus (52 %MVIC) were recorded during SHR. LH produced a posterior translational force of 4.25 N/kg (CI95 3.44–5.06N/kg). High levels of serratus anterior (105 %MVIC) and infraspinatus (87 %MVIC) were recorded during the push off phase of this activity.
Conclusions: LH and SHR placed large posterior translational forces that approached half of a person\u27s bodyweight on shoulder structures. SHR produced an anterior translation force at extremes of horizontal abduction placing approximately 18% of bodyweight on shoulder structures. The LH test required the serratus anterior to provide power to push the upper torso of the ground while both the serratus and the infraspinatus provides scapular and humeral stability, respectively.
Level of Evidence: 4: Case series
Injury Rates in Major League Baseball during the 2020 COVID-19 Season
Background: The 2020 Major League Baseball (MLB) season was drastically altered because of the COVID-19 pandemic. The changes included an extended layoff between March and July as well as a shortened preseason.
Purpose/Hypothesis: To determine the incidence and epidemiology of MLB injuries in the abbreviated 2020 season compared with prior seasons. We hypothesized that there was an increase in the overall injury rate in the 2020 season compared with the 2018-2019 seasons and that it equally affected all body regions.
Study Design: Descriptive epidemiology study.
Methods: The MLB transactions database was queried to find players who had been placed on the injury list between 2018 and 2020. Injuries were categorized into upper extremity, lower extremity, spine/core, and other injuries. Incidence per 1000 athlete-exposures was calculated for the prior 2 seasons (2018-2019) and for the 2020 season separately. Incidence for each category was also calculated separately for pitchers and fielders. Incidence rate ratios (IRRs) and confidence intervals were used to compare injury rates in 2018-2019 versus 2020. The z test for proportions was used to determine significant differences between injury incidences.
Results: In 2020, the overall incidence rate per 1000 athlete-exposures was almost twice the rate compared with the 2 seasons before COVID-19 (8.66 vs 5.13; IRR, 1.69 [95% CI, 1.53-1.87]; P \u3c .001). Injury incidence increased similarly in 2020 for both pitchers (IRR, 1.68 [95% CI, 1.47-1.91]; P \u3c .001) and fielders (IRR, 1.68 [95% CI, 1.45-1.96]; P \u3c .001). Increases in injury incidence were seen in the upper extremity, spine/core, and other injury categories; however, the incidence of the lower extremity did not change significantly.
Conclusion: There was a significant increase in injury incidence for both pitchers and fielders in 2020. Injury rates increased in anatomic zones of the upper extremity and spine/core but were not significantly changed in the lower extremity. The overall increase in injury rate suggests that irregular or insufficient sport-specific preparation prior to the start of the season placed athletes at a greater risk of injury when play resumed
Line Hops and Side Hold Rotation Tests Load Both Anterior and Posterior Shoulder: A Biomechanical Study
# Background
Clinical tests should replicate the stressful positions encountered during sport participation. Evaluating the kinetic and electromyographical demands of clinical tests enables clinicians to choose appropriate tests for specific sports.
# Purpose
To describe the shoulder forces and muscle activation levels during closed chain functional tests of Line Hops (LH) and Side Hold Rotation (SHR).
# Study Design
Descriptive biomechanical study
# Methods
Ten asymptomatic participants were examined in a university laboratory. Two functional tests were evaluated using three-dimensional video analysis and electromyography to measure shoulder forces, moments, and muscular activity levels.
# Results
SHR produced a peak average posterior translation force of 4.84 N/kg (CI~95~ 4.32-5.36N/kg) and a peak average anterior translational force of 1.57 N/kg (CI~95~ 1.10-2.01N/kg). High levels of serratus anterior (98% maximum voluntary isometric contraction (MVIC) and infraspinatus (52 %MVIC) were recorded during SHR. LH produced a posterior translational force of 4.25 N/kg (CI~95~ 3.44–5.06N/kg). High levels of serratus anterior (105 %MVIC) and infraspinatus (87 %MVIC) were recorded during the push off phase of this activity.
# Conclusions
LH and SHR placed large posterior translational forces that approached half of a person’s bodyweight on shoulder structures. SHR produced an anterior translation force at extremes of horizontal abduction placing approximately 18% of bodyweight on shoulder structures. The LH test required the serratus anterior to provide power to push the upper torso of the ground while both the serratus and the infraspinatus provides scapular and humeral stability, respectively.
# Level of Evidence
4: Case serie
Detecting feigned ADHD using the MMPI-2-RF
Access to thesis permanently restricted to Ball State community onlyAccess to abstract permanently restricted to Ball State community onlyThesis (M.A.)Department of Psychological Scienc