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김낙환,이응혁,안홍기,홍승홍 대한전기학회 2003 전기학회논문지 D Vol.52 No.9(D)
- In this paper, we designed the PC-based analyzer of the power spectral density that could estimate the heart rate variability from time series data of R-R interval. The power spectral density estimated that it applied the autoregressive model to the measured electrocardiogram during a short period. Also, the characteristics of the designed analyzer are that it could process of the signal filtering, the generation and recomposition of time series and the feature extraction at the same time. Especially the analyzer reconstructed which applied the lowpass filter of the time series composed by the linear interpolation so as to enhance the signal-to-noise feature.We could estimate the power spectral density that confirmed a variety of power peak with low frequency range and high frequency rang of autonomic nerve by the heart rate variability.
김낙환,Kim, Nak-Hwan 한국과학기술단체총연합회 1998 과학과 기술 Vol.31 No.3
오늘날 국경없는 경제전쟁에서 살아남기 위해서는 국가경쟁력 특히 기술경쟁력을 강화하는 길밖에 없다. 정부는 지난해 말 어려워진 경제현실을 극복하기 위한 조치로 과하기술장관회의에서 과학기술혁신 5개년 계획을 확정했다. 총 투자규모 8조원으로 편성, 국가 종합과학기술력을 21세기 초가지 선진7개국 수준으로 제고하는 것으로 하는 이 혁신 계획의 내용을 살펴본다.
심박변동의 스펙트럼해석을 위한 자기회귀 모델차수 선택 알고리즘에 관한 연구
김낙환,신재호,한영환,이응혁,민홍기,홍승홍,Kim, Nag-Hwan,Shin, Jae-Ho,Han, Young-Hwan,Lee, Eung-Huk,Min, Hong-Ki,Hong, Sung-Hong 대한전자공학회 2001 電子工學會論文誌-SC (System and control) Vol.38 No.6
본 논문에서는 자기회귀모델을 이용한 심박변동의 파워스펙트럼해석에서 복잡한 계산과정을 수행하지 않으면서 심박변동의 특성을 반영한 간단한 모델차수법을 제안하였다. 자기회귀모델을 이용한 심박변동의 단구간 시계열에 대한 파워스펙트럼해석은 모델차수에 따라 스펙트럼 추정의 분해능이 변화한다. 제안한 모델차수법과 기존의 AIC와 고정차수법에 대하여 비교실험을 하였다. 실험결과, AIC 보다 계산과정이 매우 간단해졌으며 낮은 분해능의 문제를 해결하였고 고정차수의 단점인 시계열의 특성에 대응한 모델차수를 선택 할 수 있었다. 또한 제안된 방법으로 파워스펙트럼말도를 추정한 결과 AIC에서 나타나는 낮은 분해능 문제 와 적은 시계열 개수에서 나타나는 고정차수에 의한 잡음성 파워성분 저l거 등이 가능함을 확인하였다. In this paper, we proposed the simple and selective method for the order of model that reflected the feature of the heart rate variability without the complicated calculation in the power spectral analysis of heart rate variability using autoregressive model. The power spectral analysis of short-term of heart rate variability using autoregressive have been problem to resolution of spectral estimates by the selective model order. As a result that the proposed method for the order comparative tested with the AIC and the fixed order method, the calculation process could become very simple and select the order which correspond with the feature of the time series. We verified it could removed the noisy power components by the fixed order.
Effect of Ramp on Joint Moment of Attendants during Manual Control of Wheelchairs
김낙환 대한임상통증학회 2022 Clinical Pain Vol.21 No.1
Objective: This study aimed to predict the injury risk to attendants by simulating and analyzing the joint moment that occurs during wheelchair transportation for five different ramp ratios and five different velocities. Method: Three-dimensional musculoskeletal models and rigid structure of a standard wheelchair were developed using the AnyBody Modeling System. The ramp ratio was set to 1:6 (the steepest), 1:8, 1:10, 1:12, and 1:14 (the gentlest). The wheelchair speeds were set to 0.4, 0.5, 0.6, 0.7, and 0.8 m/s. Both the uphill and downhill movement conditions were investigated. Results: Most of the joint moments that occur in the wrist joint, elbow and shoulder while driving uphill increased or decreased proportionally to the slope and speed of the ramp. However, the external moment of the wrist occurring downhill was largely influenced by the slope, and the joint moment of the shoulder showed a dynamic pattern of change in the middle of the ramp in spite of constant driving speed. Conclusion: The influence that occurs during deceleration while wheelchair driving on a ramp is primarily on the proximal shoulder joint, and the influence of the release control in the middle of driving primarily causes loads on the distal wrist and forearm. A high risk of damage exists because the moment change value of the load on the shoulder joint is relatively large and increases with inclination. The increase in wrist abduction moment for deceleration while driving downhill also suggests the possibility of damage.
AR모델을 이용한 심전도와 맥파의 심박변동 스펙트럼 해석
김낙환,이은실,민홍기,이응혁,홍승홍,Kim NagHwan,Lee EunSil,Min HongKi,Lee EungHyuk,Hong SeungHong 한국융합신호처리학회 2000 융합신호처리학회 논문지 (JISPS) Vol.1 No.1
The analysis of power spectrum based on linear AR model is applied widely to quantize the response of autonomic nerve noninvasively, In this paper, we estimate the power spectrum density for heartrate variability of the electrocadiogram and pulse wave for short term data(less than two minute), The time series of heart rate variability is obtained from the time interval(RRI, PPI) between the feature point of the electrocadiogram and pulse wave for normal person, The generated time series reconstructed into new time series through polynomial interpolation to apply to the AR mode. The power spectrum density for AR model is calculated by Burg algorithm, After applying AR model, the power spectrum density for heart rate variability of the electrocadiogram and the pulse wave is shown smooth spectrum power at the region of low frequence and high frequence, and that the power spectrum density of electrocadiogram and pulse wave has similar form for same subject.