Yong-Yook Kim

Flexural-torsional coupled vibration of slewing beams using various types of orthogonal polynomials

Dynamic behavior of flexural-torsional coupled vibration of rotating beams using the Rayleigh-Ritz method with orthogonal polynomials as basis functions is studied. Performance of various orthogonal polynomials is compared to each other in terms of their efficiency and accuracy in determining the required natural frequencies. Orthogonal polynomials and functions studied in the present work are : Legendre, Chebyshev, integrated Legendre, modified Duncan polynomials, the special trigonometric functions used in conjunction with Hermite cubics, and beam characteristic orthogonal polynomials. A total of 5 cases of beam boundary conditions and rotation are studied for their natural frequencies. The obtained natural frequencies and mode shapes are compared to those available in various references and the results for coupled flexural-torsional vibrations are especially compared to both previously available references and with those obtained using NASTRAN finite element package. Among all the examined orthogonal functions, Legendre orthogonal polynomials are the most efficient in overall CPU time, mainly because of ease in performing the integration required for determining the stiffness and mass matrices.

Development of a virtual reality bicycle simulator for rehabilitation training of postural balance

Development of a virtual-reality training system based on an exercise bicycle and a personal-computer for rehabilitation of motor functions and balance capability in elderly patients has been described. The system can take three inputs from the bicycle: the pedaling speed, the direction of the handles, and the location of the center of pressure on the supporting base of the bicycle. These inputs allow user interactions with a virtual environment that increase motivation of the user. A series of experiments were conducted with three different visual feedback conditions: without visual feedback of balance information; with visual feedback of weight shift; or with visual feedback of the center of pressure. The assessment of balance parameters obtained from the experiments showed the improvement of balance capability on the bicycle. Especially, the visual feedback of weight shift most increased the effectiveness of the training. The findings suggest that the system might be used as a balance and motor function rehabilitation system with further objective measurements of balance ability of the patients in longer terms.

Dynamic Analysis and Structural Optimization of a Fiber Optic Sensor Using Neural Networks

The objective of this work is to apply artificial neural networks for solving inverse problems in the structural optimization of a fiber optic pressure sensor. For the sensor under investigation to achieve a desired accuracy, the change in the distance between the tips of the two fibers due to the applied pressure should not interfere with the phase change due to the change in the density of the air between the two fibers. Therefore, accurate dynamic analysis and structural optimization of the sensor is essential to ensure the accuracy of the measurements provided by the sensor. To this end, a normal mode analysis and a transient response analysis of the sensor were performed by combining commercial finite element analysis package, MSC/NASTRAN, and MATLAB. Furthermore, a parametric study on the design of the sensor was performed to minimize the size of the sensor while fulfilling a number of constraints. In performing the parametric study, the need for a relationship between the design parameters and the response of the sensor was fulfilled by using a neural network. The whole process of the dynamic analysis using commercial finite element analysis package and the parameter optimization of the sensor were automated within the MATLAB environment.

Experimental Studies on the Training of Postural Control Using an Unstable Platform

We performed experimental studies on the training of postural control using a training system which consists of an unstable platform, a computer, a computer interface, a monitoring device, and training programs. Using this system with the training programs that we have developed, we performed a variety of experiments of training the abilities of postural control of subjects. To evaluate the effects of the training, the parameters on how long a subject can maintain a focus on a target, the mean absolute deviation of the trace, and the fatigue of the muscles in lower limbs were measured. The experimental results showed that the training system can improve the ability of postural control of the subject. Therefore, the training system could be applied to clinical rehabilitation training for posture control as a new balance training system

A New Training System Using a Tilting Bed for an Early Rehabilitation

We propose a new training system using a tilting bed, a visual display and a force plate for an early rehabilitation. Conventional rehabilitation systems for postural control have not been applicable to the patients who have to be lying in bed all the time. The rehabilitation training using those systems is only possible when the patient can stand up by himself or herself. Moreover, there did not exist any device that could provide the sense of balance or the sensation of walking to the patients in bed. The software for the system consists of the training part and the analysis part. The training part has been developed to provide various training scheme that help improve postural control ability of the subjects via repeated training of moving COP. The training consists of the COP maintaining training and the COP movement training in mediolateral, anterior-lateral, and posterior-lateral directions. The analysis part performs the assessments on the COP moving time, COP maintaining time, and mean absolute deviation before and after the training for different tilt angles of the bed. Through the experiments on number of subjects with the system, we tried to find the effectiveness of the advanced early rehabilitation training system. The results showed that this system is an effective system for early rehabilitation training and that our system can be used as clinical equipment.

Probe classification of on-off type DNA microarray images with a nonlinear matching measure

We propose a nonlinear matching measure, called counting measure, as a signal detection measure that is defined as the number of on pixels in the spot area. It is applied to classify probes for an on-off type DNA microarray, where each probe spot is classified as hybridized or not. The counting measure also incorporates the maximum response search method, where the expected signal is obtained by taking the maximum among the measured responses of the various positions and sizes of the spot template. The counting measure was compared to existing signal detection measures such as the normalized covariance and the median for 2390 patient samples tested on the human papillomavirus (HPV) DNA chip. The counting measure performed the best regardless of whether or not the maximum response search method was used. The experimental results showed that the counting measure combined with the positional search was the most preferable.