Papers by Author: Byung Young Moon

Abstract: Gait analysis is essential to identify accurate cause and knee condition from patients who display abnormal walking. Traditional linear tools can, however, mask the true structure of motor variability, since biomechanical data from a few strides during the gait have limitation to understanding the system. Therefore, it is necessary to propose a more precise dynamic method. The chaos analysis, a nonlinear technique, focuses on understanding how variations in the gait pattern change over time. Healthy eight subjects walked on a treadmill for 100 seconds at 60 Hz. Three dimensional walking kinematic data were obtained using two cameras and KWON3D motion analyzer. The largest Lyapunov exponent from the measured knee angular displacement time series was calculated to quantify local stability. This study quantified the variability present in time series generated from gait parameter via chaos analysis. Gait pattern is found to be chaotic. The proposed Lyapunov exponent can be used in rehabilitation and diagnosis of recoverable patients.

Abstract: Submicron silica powders were prepared by w/o emulsion method using inexpensive sodium silicate, ammonium sulfate and Triton N-57 as SiO2 source, precipitant and emulsifier, respectively. Nano-sized silica powders with narrow size distribution were prepared at a low temperature of 25°C for 1h by ultrasonic irradiation of the reactants using a commercial ultrasonic cleaner operating at a frequency of 47kHz, whereas silica powders with larger size and broad size distribution were synthesized using the same reactants at the same temperature and for the same time by the conventional process without ultrasounds. The particle size and size distribution of the silica powders obtained by the ultrasonic process were smaller and narrower than those by the conventional process, indicating that the application of ultrasound in the synthesis of silica powders by the w/o emulsion method is an efficient way to have powders with smaller and narrower particle size distribution.

Abstract: The use of linear and second order stress extrapolation to obtain KI and KII in two-dimensional finite element models of a thick plate containing an edge crack was examined. Three loading cases were studied, including classical Mode I and Mode II problems and a problem of tribological contact. Linear extrapolation was observed to yield accurate predictions of KI in cases of dominant Mode I loading. In Mode II situations, notably where the crack faces experienced compressive normal stresses, second order extrapolation was observed to improve estimates of KII

Abstract: This study developed and evaluated a shoe cushioning system to reduce impact force patterns during running. The shoe cushioning system is composed with a polyurethane pocket, which contains water and porous grains to absorb the force against the weight inside the pocket. Load-displacement curves for the shoe cushioning system were obtained from an instrumented testing machine and the results were compared with various pockets that have air, water or grains. Mechanical testing showed that the pocket with 5 g particles was the best for the shoe cushioning system. This founding will be helpful to designing the shoe.

Abstract: Anterior cruciate ligament(ACL) is liable to a major injury that often results in a functional impairment requiring surgical reconstruction. The success of reconstruction depends on such factors as attachment positions, initial tension of ligament and surgical methods of fixation. The purpose of this study is to find isometric positions of the substitute during flexion/extension. A threedimensional knee model was constructed from CT images and was used to simulate length change during knee flexion/extension. The results showed that minimum length changes were 1.9~5.8 mm(average 3.6±1.4 mm). The proposed method can be utilized and applied to optimal reconstruction for ACL deficient knee.

Abstract: Nanosized silica powders were synthesized via w/o emulsion method using sodium silicate as SiO2 source under ultrasonic process. The powders were prepared under conventional process and ultrasonic process using the same reactants at ambient temperature for 1h varying the concentration of Na2SiO3 solution while fixing the concentration of surfactant in cyclohexane. The particle size of the silica powder decreased with decreasing the concentration of sodium silicate solution under both conditions, with and without ultrasounds. However, the particle size and size distribution of the silica powder with ultrasounds were smaller and narrower than those without ultrasounds, establishing that ultrasound treatments decrease the particle size and become narrow in particle size distribution.