• 대한의용생체공학회:학술대회논문집
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• 대한의용생체공학회 1996년도 춘계학술대회
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• pp.6-9
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• 1996

In this paper, we attempted to analyze the contraction patterns of elbow flexor muscle during isometric, concentric and eccentric contraction. The analysis parameters are consisted of Sequency domain parameters (mean frequency, median frequency, skewness, kurtosis) and time domain parameters (zero crossing, positive maxima, integrated EMG). As a results, the analysis parameters have specific trends for muscles, muscle contraction patterns, muscle contraction angles. Especially, at the time domain analysis, IEMG is a dominant parameter for analysis of activation patterns, and the skewness, kurtosis are useful parameters for functional recognition.

• 대한한의학회지
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• 제35권4호
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• pp.24-35
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• 2014

Objectives: Although the autonomic nervous system (ANS) is thought to play an important role in treatment of obesity, no study has been conducted to investigate acupuncture's effects on this aspect of the ANS. This study aimed to describe the effects of acupuncture in the ANS by means of heart rate variability (HRV) analysis. Methods: A total of 46 obese women aged from 21 to 54 with body mass index ranging from 25.1 to $39.3kg/m^2$ were recruited and randomized into both the real acupuncture group (n=23) and sham acupuncture group (n=23). A total of 3 instances of HRV analysis were conducted before, during, and after treatment. Statistically significant differences between time and groups were analyzed using repeated measure analysis of variance. Results: All parameters of time domain analysis and frequency domain analysis except for the square root of the mean squared differences of successive normal sinus intervals (RMSSD) and very low frequency (VLF) showed significant differences between times. The mean of all R-R intervals (mean RR) showed significant level of interaction between time and group. Between groups, time domain analysis of standard deviation of the normal-to-normal intervals (SDNN), RMSSD and frequency domain analysis of total power (TP) and high frequency (HF) showed significant differences. Conclusions: The real acupuncture group showed deactivation of parasympathetic function and relative increase of sympathetic activity in obese subjects. Further studies are necessary to uncover the mechanisms of acupuncture in obesity treatment.

• 한국공작기계학회:학술대회논문집
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• 한국공작기계학회 2003년도 춘계학술대회 논문집
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• pp.79-85
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• 2003

One of unique characteristics of guided waves is a dispersive behavior that guided wave velocity changes with an excitation frequency and mode. In practical applications of guided wave techniques, it is very important to identify propagating modes in a time-domain waveform for determination of defect location and size. Mode identification can be done by measurement of group velocity in a time-domain waveform. Thus, it is preferred to generate a single or less dispersive mode But in many cases, it is difficult to distinguish a mode clearly in a time-domain waveform because of superposition of multi modes and mode conversion phenomena. Time-frequency analysis is used as efficient methods to identify modes by presenting wave energy distribution in a time-frequency. In this study, experimental guided wave mode identification is carried out in a steel plate using time-frequency analysis methods such as wavelet transform. The results are compared with theoretically calculated group velocity dispersion curves. The results are in good agreement with analytical predictions and show the effectiveness of using the wavelet transform method to identify and measure the amplitudes of individual guided wave modes.

• 한국전산구조공학회:학술대회논문집
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• 한국전산구조공학회 1994년도 봄 학술발표회 논문집
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• pp.137-144
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• 1994

In this study, a new procedure for solving 2-D dynamic problems of semi-infinite medium in time domain by boundary element method (BEM) is presented. Efficient modelling of the far field region, infinite boundary elements are introduced. The shape function of the infinite boundary element is a combination of decay functions and Laguerre functions. Though the present shape functions have been developed for the time domain analysis, they may be also applicable to the frequency domain analysis. Through the response analysis in a 2-D half space under a uniformly distributed dynamic load, it has been found that an excellent accuracy can be achieved compared with the analytical solution

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2013년도 춘계학술대회 논문집
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• pp.623-625
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• 2013

Tire hydroplaning is one of the most important tire performances, especially for safety on wet road surface. And nowadays various methods such as FEM and FVM analysis are being applied to design and improve tire hydroplaning performance, along with on-vehicle test of tire hydroplaning. Conventional evaluation of tire hydroplaning has been done by comparing peak lateral acceleration and vehicle speed in time domain. But in this paper, frequency domain analysis of lateral acceleration when hydroplaning at high speed has been carried out to get the quantitative comparison between test tires. And it is concluded that the frequency spectrum analysis of lateral acceleration gives much better discrimination, as compared to the conventional time domain analysis of lateral acceleration and vehicle speed.

• 한국공작기계학회논문집
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• 제12권5호
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• pp.94-100
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• 2003

One of unique characteristics of guided waves is a dispersive behavior that guided wave velocity changes with an excitation frequency and mode. In practical applications of guided wave techniques, it is very important to identify propagating modes in a time-domain waveform for determination of detect location and size. Mode identification can be done by measurement of group velocity in a time-domain waveform. Thus, it is preferred to generate a single or less dispersive mode But, in many cases, it is difficult to distinguish a mode clearly in a time-domain waveform because of superposition of multi modes and mode conversion phenomena. Time-frequency analysis is used as efficient methods to identify modes by presenting wave energy distribution in a time-frequency. In this study, experimental guided wave mode identification is carried out in a steel plate using time-frequency analysis methods such as wavelet transform. The results are compared with theoretically calculated group velocity dispersion own. The results are in good agreement with analytical predictions and show the effectiveness of using the wavelet transform method to identify and measure the amplitudes of individual guided wave modes.

• 한국소음진동공학회논문집
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• 제16권12호
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• pp.1224-1230
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• 2006

Pipe thinning is one of the major issues for the structural fracture of pipes of nuclear power plants. Therefore a method to inspect a large area of piping systems quickly and accurately is needed. In this paper, we proposed the method for monitoring pipe thinning. Our basic idea come from that a group velocity of impact wave is different as wall thickness. If the group velocity is measured, wall thickness can be estimated. To obtain the group velocity, time -frequency analysis is used. This is because an arrival time difference can be measured easily in time-frequency domain rather than time domain. To test the performance of this technique, experiments have been performed for a plate and U type pipe. Results show that the proposed technique is quite powerful in the monitoring pipe thinning.

• 대한의용생체공학회:의공학회지
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• 제28권1호
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• pp.55-65
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• 2007

This paper sought to investigate pupil size variability, pupil size parameters in terms of time domain and frequency domain, the autonomic activity change induced by posture change, degree of sleepiness and cognitive task (math task). With a specially designed pupil image acquisition system in the dark room, these three kinds of experiments were performed to induce a dominant state of sympathetic or parasympathetic activation. Electrocardiogram and pupil size were measured in all the experiments. Based on three experiments, we calculated heart rate variability. In the pupil size analysis, we calculated the mean and standard deviation of pupil size (in time domain), and proposed several frequency bands that exhibit different autonomic activation between different sessions. The results indicate that in terms of heart rate variability, posture change exhibited significant differences but not between sleepiness level, or between cognitive task. Pupil sizes differed only during the postures. And we found some frequency bands that correlated with autonomic activation in each experiment. While heart rate variability reflects posture change that need cardiac control, pupil size variability reflects not only posture induced autonomic activation but sleepiness and cognitive load, which is processed in the brain, in time and frequency domain parameter.

• Wind and Structures
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• 제24권5호
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• pp.481-500
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• 2017

A novel three-degree-of-freedom (DOF) forced vibration system has been developed for identification of aeroelastic (self-excited) load parameters used in time-domain response analysis of wind-excited flexible structures. This system is capable of forcing sinusoidal motions on a section model of a structure that is used in wind tunnel aeroelastic studies along all three degrees of freedom - along-wind, cross-wind, and torsional - simultaneously or in any combination thereof. It utilizes three linear actuators to force vibrations at a consistent frequency but varying amplitudes between the three. This system was designed to identify all the parameters, namely, aeroelastic- damping and stiffness that appear in self-excited (motion-dependent) load formulation either in time-domain (rational functions) or frequency-domain (flutter derivatives). Relatively large displacements (at low frequencies) can be generated by the system, if required. Results from three experiments, airfoil, streamlined bridge deck and a bluff-shaped bridge deck, are presented to demonstrate the functionality and robustness of the system and its applicability to multiple cross-section types. The system will allow routine identification of aeroelastic parameters through wind tunnel tests that can be used to predict response of flexible structures in extreme and transient wind conditions.

• Geomechanics and Engineering
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• 제6권6호
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• pp.531-544
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• 2014

Studies of earthquakes over the last 50 years and the examination of dynamic soil behavior reveal that soil behavior is highly nonlinear and hysteretic even at small strains. Nonlinear behavior of soils during a seismic event has a predominant role in current site response analysis approaches. Common approaches to ground response analysis include linear, equivalent linear and nonlinear methods. These methods of ground response analysis may also be categorized into time domain and frequency domain concepts. Simplicity in developing analytical relations and accuracy in considering soils' dynamic properties dependency to loading frequency are benefits of frequency domain analysis. On the other hand, nonlinear methods are complicated and time consuming mainly because of their step by step integrations in time intervals. In part Ι of this paper, governing equations for seismic response analysis of surcharged and layered soils were developed using fundamental of wave propagation theory based on transfer function and boundary conditions. In this part, nonlinear seismic ground response is analyzed using extended HFTD method. The extended HFTD method benefits Newton-Raphson procedure which applies regular iterations and follows soils' fundamental stress-strain curve until convergence is achieved. The nonlinear HFTD approach developed here are applied to some examples presented in this part of the paper. Case studies are carried in which effects of some influencing parameters on the response are investigated. Results show that the current approach is sufficiently accurate, efficient, and fast converging. Discussions on the results obtained are presented throughout this part of the paper.