Doctor of Philosophy

dissertationRailroad workers experience a unique exposure to walking on ballast and uneven ground walking is a possible risk factor for knee osteoarthritis. However, the effect of ballast on workers is still not clear, especially for mechanical joint loads. Published research on walking on ballast principally examines temporal gait parameters and joint kinematics. The aim of this research is to investigate the change of knee contact force (KCF) during walking on ballast as surface condition, surface configuration, and uphill or downhill limbs by using an new OpenSim model. There are two significant contributions of this research. First, a new OpenSim gait model with robust knee structures was developed, which included patella structures, a six degrees of freedom knee joint, and four main knee ligaments. Second, KCF was investigated when walking on ballast. Temporal gait parameters were found to be different between uphill and downhill limbs. A trend was observed that the second peak KCF decreased in ballast conditions compared with no ballast. The timing of the first peak KCF was different among no ballast, main ballast and walking ballast. Knee muscle cocontraction was higher in walking ballast compared with no ballast in both peak KCFs. Knee muscle cocontraction was also higher for the uphill limb than the downhill limb. Lateral collateral ligament force was larger and medial collateral ligament force was smaller for the downhill limb compared with the uphill limb in both peak KCFs. The effect of surface configuration was significant for some ligament bundles, including iv anterior cruciate ligament and medial collateral ligament in the first peak KCF, and lateral collateral ligament in the second peak KCF. There are two additional findings in this research. First, the ankle kinematics was found to be sensitive to toe marker placement error and muscle forces responded the residual variance of joint kinematics in various degrees based on the muscle function. Second, a method to combine ground reaction data from different trials was described, which can successfully simulate the gait cycle and obtain the results of joint moments and muscle forces in a certain acceptable range

Capillary-based multiplexed isothermal nucleic acid-based test for sexually transmitted diseases in patients

We demonstrate a multiplexed loop mediated isothermal amplification (LAMP) assay for infectious disease diagnostics, where the analytical process flow of target pathogens genomic DNA is performed manually by moving magnetic beads through a series of plugs in a capillary. Heat is provided by a water bath and the results read by the naked eye, enabling applications in low resource settings