We report on experiments and modeling of the interactions between delayed visual feedback and postural control in human quiet stance. A heuristic model is derived based on physiological and psychophysical parameters. The level of agreement found between the data and the model was found to be very good for power spectral densities, probability density functions and mean-squared displacements (or Hurst exponents). The stochastic delayed differential model identifies critical time scales of postural corrections. We also investigate properties of the model such as stability, small delay approximations and the power spectral density. Lastly, we use nonlinear time series techniques to investigate the temporal structure of the experimental postural dynamics. We propose the first dynamical model of visually assisted posture control.

<p> Although coordination has been identified as a fundamental element necessary for the successful achievement of walking, this aspect of gait has yet to be embraced into instrumented gait analysis, perhaps in part due to the lack of a normative reference and unfamiliarity of mathematical methods that are best suited to capture this essential behavior. Therefore, this work focused on expanding clinical gait analysis techniques by validating nonlinear methods that describe the influence of neurological control on the musculoskeletal system. This body of work investigated the coordination dynamics during gait in both prospective and retrospective subjects free of gait pathology, subjects with spastic cerebral palsy, and subjects with a lower limb amputation using motion capture and mathematical models to help elucidate the complexities of gait and enhance therapeutic interventions. This investigation quantified coordination strategies employed by an unimpaired subject when presented with various walking conditions and challenges mimicking various inhibitions associated with performing the task of swing limb advancement. Two novel indices of coordination dynamics were created to provide a concise metric and ease their inclusion into future research applications. The first normative reference dataset of these coordination measures was created from a large cohort of unimpaired subjects. While there is presently not a gold standard method for quantifying coordination during gait, the exciting correlations between the proposed measures and select clinical performance tasks indicate the coordination measures quantify essential inter-segmental coordination dynamics of walking. The theoretical pendular software model created shows swing limb advancement is not a purely passive motion, but instead an actively controlled motion. Comparisons between the various cohorts revealed the proposed measures of coordination are more suitable for characterizing motor control strategies contributing to a gait pattern, quantify organization of individual segments, identify mechanisms of change, and reveal the loci of impairment(s). The proposed measures of coordination dynamics are capable of distinguishing between different gait pathologies and patterns associated with altered limb advancement during the swing period of gait. Results from this multidisciplinary work have the strong potential to directly impact the clinical treatment of persons with aberrant coordination dynamics during gait.</p>

<p>The Neanderthal (<i>Homo neanderthalensis</i>) femur is distinct from that of recent modern humans (<i>Homo sapiens</i>). Broadly speaking, the Neanderthal femur is more &ldquo;robust&rdquo;, meaning that it appears to be biomechanically stronger, and it is more curved, which may enhance the predictability of the stresses and strains experienced by the bone. It has been hypothesized that the Neanderthal morphology is an adaptation to withstand elevated and repetitive loads associated with increased mobility. This study tests the mobility hypothesis using comparative and biomechanical methods. Specifically, this study sought to test the mobility hypothesis by a) determining whether or not a relationship exists between skeletal variables and day range (a surrogate for mobility) in living primates, and b) using finite element analysis to quantify differences in biomechanical strength between Neanderthals and modern humans while simulating loads associated with bipedal walking, traumatic loads, and stumbling. </p><p> The hypothesis that extant primates with longer day ranges exhibit more robust and more curved bones, used here as an indication of predictability of deformation, is rejected. The hypothesis that Neanderthal femora are as strong as or stronger than recent modern human femora is partially rejected. Under loading regimes simulating normal walking, it is unclear which femur is stronger. The human femur is stronger under simulated traumatic loads. The Neanderthal femur is stronger under loads simulating stumbling. The human femur is more predictable along the neck and at midshaft; the Neanderthal femur is more predictable along proximal and distal diaphyseal sections. The femoral neck is the weakest location on the modern human femur, whereas the distal lateral metaphysis is typically the weakest location on the Neanderthal femur. </p><p> Although a relationship between curvature and robusticity variables could not be confirmed using an extant primate sample, the unexpected results of the Neanderthal/human femur comparisons suggest that because regions of peak stress differ considerably between the species as a result of the differences in morphology, each may be adapted to the specific and typical demands imposed by their respective habitats and lifestyles. </p>

<p> This thesis consists of four major studies: a study of incipient flight behaviors in young birds over ontogeny (chapter 1); a detailed study of maneuvering using physical models of a likely ancestral bird morphology (chapter 2); a comparative study of maneuvering ability in several stem-group birds, within a phylogenetic context (chapter 3); and development of basic engineering theory to quantify the turbulence sensitivity of shapes to environmental turbulence of given scales and spectral content. The studies have identified: 1) shifts in function from asymmetric to symmetric movements in young birds, contrary to predictions from alternative hypotheses and occurring before wing-assisted incline running; 2) shifts in function, tied to angle of attack, of asymmetric appendage postures in creating yawing and rolling moments; and 3) migration of control effectiveness as tails are shortened and other features change, during the early evolution of birds. The work plugs some considerable gaps in current prevailing theories (e.g. Dial, 2003; Tobalske et al., 2011) and provides a test of hypotheses of flight evolution not based in outdated "trees-down'' or "ground-up'' paradigms from the past, but rather based on the universal need of airborne animals to maneuver (Dudley and Yanoviak, 2011; Maynard-Smith, 1953).</p><p> This work seeks to understand early flight evolution from a maneuvering perspective; every animal in the air must maneuver, and by understanding "powered'' flight as simply a point along a spectrum of <i>maneuvering</i> flight (Dudley and Yanoviak, 2011), unifying breakthroughs are made. It is hoped that the multifaceted approach taken here, with ontogenetic series, aerodynamic studies, and phylogenetic approaches, is robust against the shortcomings of any one approach individually: confounding ontogeny with evolution (as may be the case in others' studies of alternative hypotheses, e.g. Dial, 2003); inferring implausible functions from paleontological material in the absence of proper benchmarking against live animals; or misdiagnosis of how forms work in the absence of functional studies.</p>

<p> The screwdriver is a tool that has been among the most widely used hand tools for decades and continues to be used in the workplace to perform a variety of fastening tasks. Advancements in fastener technology have been complemented by the development of new types of screwdriver bits. While designs may vary, so do the force application requirements placed on the tool user. The primary objective of this experiment is to analyze the relationship between user torque and screwdriver bit design. A further objective is to utilize the results to develop an effort metric by which bits of different designs can be compared. In this experiment, three types of screwdriver bit designs (straight, Phillips, and combination of straight/Phillips (ECX)) were tested to determine how the design affects the amount and type of force applied by the user when performing a fastening task. The designs were tested to simulate fastener tightening and loosening operations. Sixteen participants were tested in this study. Although there was no significant effect, the data suggest that the Phillips bit design allow subjects to exert the maximum torque and the minimum axial force. This divergence suggests that the Phillips bit may have a higher biomechanical effort ratio, which is greater torque for the same or lower axial force. Finally, the data suggest there is little difference in user torque exertion between the ECX bit and the straight bit designs. Subjective assessment indicated that users overwhelmingly preferred the Phillips bit design. Bit designs requiring less axial force for the same torque exertion level reduce the overall muscular effort of the user, allowing work to be completed more efficiently and may reduce the risk of musculoskeletal disorder affecting the wrist, elbow, and shoulder. Results may also assist designers by allowing them to select fasteners that provide sufficient mechanical integrity of the design while maximizing user effectiveness.</p>

<p> This thesis research is focused on advancing image processing techniques and algorithms used for detecting skin melanoma. We have modified previous image processing approaches and developed computational algorithms for quantifying morphological features of a mole image. Applying the algorithms to 20 mole images downloaded from educational websites, we have identified three cut-off ratios to distinguish melanoma images from benign mole images. More specifically, the higher the boundary irregularity ratio, and/or the asymmetry ratio, and/or the color variation ratio, the high chance the mole is melanoma leading. The irregularity ratio cutoff is identified as 1.96, suggesting 96% more circumference length than that of a circle with the same area. One finds that the cut-off ratio for assessing asymmetry of the mole image is 0.109, representing the degree of asymmetry as approximately 11% to place a mole image into the melanoma group. Evaluation of the color variation of the moles leads to a cut-off ratio of the color variation as 0.334. Statistical analyses have been performed to determine the confidence of cut-off ratios, varying from 63% to 81%, for placing a mole image into its correct groups. The algorithms have also been implemented to assess "changes" of mole images over time observed by a dermatologist. Using a &plusmn;14% as the definition of changes, the algorithm identifies 9 of the 10 mole images as changed over time. Among the irregularity, asymmetry, color variation, and size ratios, 5 out of the 9 moles have shown changes in one ratio, 2 out the 9 moles have experience changes in two ratios, 1 mole has shown changes in three ratios, and only 1 mole shows changes in all four ratios. The computational results are consistent with the general observations that human eyes are sensitive to size changes and color variation changes, and may not be very good to distinguish changes in border irregularity and asymmetry. The developed algorithms can be helpful to assist a physician in evaluating subtle changes of mole images that may not be very sensitive to the eyes.</p>

Abstract not available.

<p> We address outflow boundary conditions for blood flow modeling. In particular, we consider a variety of fundamental issues in the structured tree boundary condition. We provide a theoretical analysis of the numerical implementation of the structured tree, showing that it is sensible but must be performed with great care. We also perform analytical and numerical studies on the sensitivity of model output on the structured tree's defining geometrical parameters. The most important component of this dissertation is the derivation of the new, generalized structured tree boundary condition. Unlike the original structured tree condition, the generalized structured tree does not contain a temporal periodicity assumption and is thus applicable to a much broader class of blood flow simulations. We describe a numerical implementation of this new boundary condition and show that the original structured tree is in fact a rough approximation of the new, generalized condition.</p><p> We also investigate parameter selection for outflow boundary conditions, and attempt to determine a set of structured tree parameters that gives reasonable simulation results without requiring any calibration. We are successful in doing so for a simulation of the systemic arterial tree, but the same parameter set yields physiologically unreasonable results in simulations of the Circle of Willis. Finally, we investigate the extension of recently introduced PDF methods to smooth solutions of systems of hyperbolic balance laws subject to uncertain inputs. These methods, currently available only for scalar equations, would provide a powerful tool for quantifying uncertainty in predictions of blood flow and other phenomena governed by first order hyperbolic systems. </p>

Abstract not available.

Olympic weightlifting has been subject to rigorous academic and applied sporting research for over 40 years. Biomechanists have concerned themselves with Olympic weightlifting due to the complex coordination requirements coupled with high levels of full-body muscular activity. Motivated by Enoka's (1988) research on load- and skill-related changes; we used modern three-dimensional motion capture to assess selected mechanical characteristics of the snatch lift across varied lifting intensities. Our research variables included peak moment powers about the joints of the lower extremity, bilateral shoulder symmetry, and range of anterior-posterior system centre of mass (COM) movement as barbell load was varied across 80, 85, and 90% of each lifter's maximum. The five subjects were elite-level Olympic weightlifters (mean age 23 +/- 4.18 years, mean mass 77.6 +/- 5.81 kg). Multiple dependent t-tests (one for each joint pair) with Bonferroni corrections were applied between left and right peak powers to assess symmetry in the lower extremities. No significant differences were found, t(df =14) = 0.068, 0.038, and 0.039. Significance statistics wereall > p (alpha/n) = 0.0167 about the ankle, knee, and hip joint pairs, respectively. This confirmed assumptions of previous researchers that peak moment powers in elite-level lifters were symmetrical between joint pairs of the lower extremity. Exploiting the symmetry results, we simplified further analyses by considering only the left side of the body. Repeated-measures ANOVA revealed no significant differences in average peak moment power in three dimensions about the joints of the left lower extremity across barbell intensities. In the flexion extension plane of motion, left ankle F (2, 8) = 2.594, p = 0.135, knee F (2,8) = 0.133, p = 0.878, and hip F (2, 8) = 0.420, P = 0.671). Similar results followed for motion about the y and z axes of motion. Results indicated between 80-90% of maximal barbell load, no differences existed in average peak moment powers about the joints of the lower extremity. These results confirmed the findings of Enoka (1988) and showed lifters do not accommodated heavier barbell loads through increased peak moment powers in the lower extremities. Shoulder symmetry was assessed through graphical and numerical methods. All trials showed Pearson's correlations of r > 0.95, which indicated strong similarity between left and right shoulder trajectories. Bilateral shoulder position remained highly stable across barbell intensities, as participants did not modify shoulder symmetry across the tested intensity range. Range of anterior-posterior system COM movement showed no significant differences across barbell intensities (F (2, 4) = 0.765, P = 0.523). While the range of anterior-posterior system COM motion did not vary across barbell intensities, various motion trends were observed. The anterior-posterior range of system COM motion was quite small, but perturbations in system COM trajectory could be detrimental to subsequent lift phases as the barbell load approaches maximum. In conclusion, peak moment powers about the joints of lower extremities did not vary significantly across snatch lifts of 80-90% maximal capacity. Thus, training programs designed to improve athletic power through the use of weightlifting movements should not exceed the 80% limit for snatch based exercises. Statistical tests revealed no significant differences between average peak moment powers between left and right joint pairs of the lower extremities. The peak moment powers during the snatch lift were not asymmetrical. Our research demonstrated elite-level weightlifters exhibiting strong linear correlation in shoulder position across the 8090% range of barbell loads. System COM showed no significant variation in anterior-posterior range of motion across barbell intensities. This research confirmed the results previously established by Enoka (1988) regarding power response to load variation.