Preseason Lower Extremity Functional Test Scores Are Not Associated With Lower Quadrant Injury - A Validation Study With Normative Data on 395 Division III Athletes

Background: Preseason performance on the lower extremity functional test (LEFT), a timed series of agility drills, has been previously reported to be associated with future risk of lower quadrant (LQ = low back and lower extremities) injury in Division III (D III) athletes.Validation studies are warranted to confirm or refute initial findings. Hypothesis/Purpose: The primary purpose of this study was to examine the ability of the LEFT to discriminate injury occurrence in D III athletes, in order to validate or refute prior findings. It was hypothesized that female and male D III athletes slower at completion of the LEFT would be at a greater risk for a non-contact time-loss injury during sport. Secondary purposes of this study are to report other potential risk factors based on athlete demographics and to present normative LEFT data based on sport participation. Methods: Two hundred and six (females = 104; males = 102) D III collegiate athletes formed a validation sample. Athletes in the validation sample completed a demographic questionnaire and performed the LEFT at the start of their sports preseason. Athletic trainers tracked non-contact time-loss LQ injuries during the season. A secondary analysis of risk based on preseason LEFT performance was conducted for a sample (n = 395) that consisted of subjects in the validation sample (n = 206) as well as athletes from a prior LEFT related study (n = 189). Study Design: Prospective cohort Results: Male athletes in the validation sample completed the LEFT [98.6 (± 8.1) seconds] significantly faster than female athletes [113.1 (± 10.4) seconds]. Male athletes, by sport, also completed the LEFT significantly faster than their female counterparts who participated in the same sport. There was no association between preseason LEFT performance and subsequent injury, by sex, in either the validation sample or the combined sample. Females who reported starting primary sport participation by age 10 were two times (OR = 2.4, 95% CI: 1.2, 4.9; p = 0.01) more likely to experience a non-contact time-loss LQ injury than female athletes who started their primary sport at age 11 or older. Males who reported greater than three hours per week of plyometric training during the six-week period prior to the start of the preseason were four times more likely (OR = 4.0, 95% CI: 1.1, 14.0; p = 0.03) to experience a foot or ankle injury than male athletes who performed three or less hours per week. Conclusions: The LEFT could not be validated as a preseason performance measure to predict future sports injury risk. The data presented in this study may aid rehabilitation professionals when evaluating an injured athlete’s ability to return to sport by comparing their LEFT score to population norms

A Variational Perspective on Accelerated Methods in Optimization

Accelerated gradient methods play a central role in optimization, achieving optimal rates in many settings. While many generalizations and extensions of Nesterov's original acceleration method have been proposed, it is not yet clear what is the natural scope of the acceleration concept. In this paper, we study accelerated methods from a continuous-time perspective. We show that there is a Lagrangian functional that we call the \emph{Bregman Lagrangian} which generates a large class of accelerated methods in continuous time, including (but not limited to) accelerated gradient descent, its non-Euclidean extension, and accelerated higher-order gradient methods. We show that the continuous-time limit of all of these methods correspond to traveling the same curve in spacetime at different speeds. From this perspective, Nesterov's technique and many of its generalizations can be viewed as a systematic way to go from the continuous-time curves generated by the Bregman Lagrangian to a family of discrete-time accelerated algorithms.Comment: 38 pages. Subsumes an earlier working draft arXiv:1509.0361

Evaluation of flow and scalar transport characteristics of small public drinking water disinfection systems using computational fluid dynamics

2011 Spring.Includes bibliographical references.This study focuses on the evaluation of flow and scalar transport characteristics of small disinfection systems, primarily through computational fluid dynamics (CFD) as well as physical conservative tracer studies. Original research was performed on a pipe loop, series of pressurized tanks, and two separate open surface tank contact systems and a case study was performed on a baffled tank system. The flow dynamics for each of these respective disinfection systems were evaluated using CFD. The flow dynamics govern the transport of any quantity (e.g., a passive scalar, conservative tracer, or chlorine-containing species) through the system visualized through plotting the effluent concentration (e.g., passive scalar for computational models and conservative tracer for physical experiments) through time forming what is commonly referred to as a residence time distribution (RTD), or flow-through, curve. Physical experiments provided validation for the CFD models that give a more complete view of hydraulic efficiency thus overcoming the common "black-box" approach to contact tank design using only the theoretical detention time (TDT) (defined as the system volume V divided by the volumetric flow rate Q). The differing geometries of contact tank systems yield significantly different flow paths with varying degrees of separation, recirculation, inlet and outlet effects, and wall effects prompting the need for the evaluation of hydraulic efficiency to be unique to the system. Yet current practice evaluates the hydraulic efficiency of disinfection contact tank systems based on the TDT and the rising limb of the RTD curve, designated by the United States Environmental Protection Agency (USEPA) as baffle factor (BF). Research presented in this study using CFD models and physical tracer studies shows that evaluation methods based upon TDT tend to overestimate, severely in some instances, the actual hydraulic efficiency as obtained from the systems' flow and scalar transport dynamics and subsequent RTD curves. The main objectives of this study were to determine the systems' respective hydraulic efficiencies and to analyze an alternative measure of hydraulic efficiency, the ratio t10/t90, where t10 and t90 are the time taken for 10 and 90 percent of the input concentration to be observed at the outlet of a system. The pipe loop system was dominated by advection and thus showed little variance in the values of BF and t10/t90. Analysis of the series of pressurized tank systems showed significant regions of turbulent mixing and recirculation corresponding to a system that was much less efficient than the pipe loop system. BF values for the pressurized tank systems were nearly 100 percent greater than t10/t90 values as a result of a system behavior further from plug flow. The open surface tank systems exhibited the most uneven flow paths and lowest efficiencies seen in this study with BF and t10/t90 values differing by at least 100 percent. These systems exhibited significant degrees of short-circuiting and recirculation largely due to their inlet and outlet configurations. Finally, the baffled tank system showed an increase in system efficiency with the number of baffles (e.g., increase in advective forces) and a corresponding decrease in the variance between BF and t10/t90 values. Overall, the research presented in this thesis provides an extensive evaluation for the flow and scalar characteristics of the described small public drinking water disinfection systems allowing for the development of t10/t90 as a more representative evaluation of hydraulic efficiency

Phytoforensics: Applications in vapor intrusion assessment

Vapor intrusion (VI) occurs when contaminants in the vapor phase migrate in the shallow subsurface and enter buildings through cracks, seams, and gaps and has been recognized as a serious human-health threat as occupants are exposed to potentially harmful concentrations over long periods of time. The VI pathway has recently (2017) been identified as a primary exposure pathway and implemented into the Hazard Ranking System for inclusion on the Nation Priorities List. However, assessing VI and human exposure is not simple and current methods are time-, cost-, and labor-intensive; intrusive; and temporally and spatially variability. Trees are ideal candidates for environmental biomonitors because they are ubiquitous, active samplers of vapor and groundwater and because they are thought to sample over large spatial and temporal scales, effectively averaging variability. Sampling trees is noninvasive and does not require the construction of sampling ports in homes, increasing the likelihood of obtaining property access and VI data. Tree samples are representative of the shallow subsurface with a footprint similar to a residential building. Directional tree sampling can also be used to elucidate shallow subsurface contamination from a single tree, and tree sampling is shown to be correlated with VI samples, especially when environmental samples are averaged over months and years. However, non-uniform distributions of tree-core samples likely resulted in large interpolation error in areas where trees are sparse. Although these findings demonstrate that tree sampling can augment traditional VI assessment methods, tree sampling is best applied as a screening tool because of the many parameters, and their associate uncertainties, that control mass transfer of contaminants in the subsurface and entry into plants and the built environment --Abstract, page iv

Conservative Scattering of Reissner-Nordstr\"om Black Holes at Third Post-Minkowskian Order

Using a recently developed effective field theory formalism for extreme mass ratios [2308.14832], we present a calculation of charged black hole scattering at third post-Minkowskian order. The charges and masses are kept arbitrary, and the result interpolates from the scattering of Schwarzschild to extremal charged black holes, and beyond to charged particles in electrodynamics -- agreeing with previously reported results in all such limits. The computation of the radial action is neatly organized in powers of the mass ratio. The probe (0SF) contributions are readily computed by direct integration of the radial momentum, and we use the effective field theory to compute the subleading (1SF) contributions via background-field Feynman rules supplemented by an operator encoding recoil of the background. Together these contributions completely determine the conservative physics at order~$\mathcal{O}(G^{3})$.Comment: 36 pages, 3 figure

Evaluation and parameterization of stably stratified turbulence: insights on the atmospheric boundary layer and implications for wind energy, An

2014 Fall.Includes bibliographical references.This research focuses on the dynamics of turbulent mixing under stably stratified flow conditions. Velocity fluctuations and instabilities are suppressed by buoyancy forces limiting mixing as stability increases and turbulence decreases until the flow relaminarizes. Theories that ubiquitously assume turbulence collapse above a critical value of the gradient Richardson number (e.g. Ri > Ric) are common in meteorological and oceanographic communities. However, most theories were developed from results of small-scale laboratory and numerical experiments with energetic levels several orders of magnitude less than geophysical flows. Geophysical flows exhibit strong turbulence that enhances the transport of momentum and scalars. The mixing length for the turbulent momentum field, LM, serves as a key parameter in assessing large-scale, energy-containing motions. For a stably stratified turbulent shear flow, the shear production of turbulent kinetic energy, P, is here considered to be of greater relevance than the dissipation rate of turbulent kinetic energy, ε. Thus, the turbulent Reynolds number can be recast as Re ≡ k2/(ν P) where k is the turbulent kinetic energy, allowing for a new perspective on flow energetics. Using an ensemble data set of high quality direct numerical simulation (DNS) results, large-eddy simulation (LES) results, laboratory experiments, and observational field data of the stable atmospheric boundary layer (SABL), the dichotomy of data becomes apparent. High mixing rates persist to strong stability (e.g. Ri ≈ 10) in the SABL whereas numerical and laboratory results confirm turbulence collapse for Ri ~ O(1). While this behavior has been alluded to in literature, this direct comparison of data elucidates the disparity in universal theories of stably stratified turbulence. From this theoretical perspective, a Reynolds-averaged framework is employed to develop and evaluate parameterizations of turbulent mixing based on the competing forces of mean shear and buoyancy frequency, S and N, respectively. Length scale estimates for LM are given by LkS ≡ k1/2/S and LkN ≡ k1/2/N, where LkS provides an accurate estimate for eddy viscosity, νt, under neutral to strongly stable conditions for SABL data. The relative influence of shear and buoyancy are given by the ratio of the respective time scales, S-1 and N-1, with the pertinent time scale of the large-scale motions, TP ≡ k/P, through the parameters STP and NTP. LkS's range of applicability is further assessed in a STP-NTP parameter space. In developing these parameterizations, the stress-intensity ratio, c2, is evaluated using high-Re stably stratified data and is shown to exhibit a near constant value (c2 ≈ 0.25) for stably stratified geophysical turbulence. These findings provide a clear trajectory for numerical modeling of stably stratified geophysical shear turbulence without reliance on stability or damping functions, tuning parameters, or artificial parameterizations. An initial modeling study of moderate-Re channel and Ekman layer flows using the proposed parameterizations confirms this supposition. Finally, it is in this new light that large-scale implications of wind energy can now be considered. As a first step in this process, computational fluid dynamics (CFD) studies of wind turbine interactions are carried out under neutrally stratified conditions. Simulations clearly show that actuator line models provide efficacy in wake generation, interaction, and restoration and highlight model requirements for stably stratified conditions. Results suggest that standard horizontal spacings of 5-10 rotor diameters yield significant reductions in power output and increases turbulence intensity and fatigue loading