• The Journal of Internal Korean Medicine
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• v.19 no.2
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• pp.7-16
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• 1998

Background and Purpose The increasing evidence for neurally mediated cardiac damage and sudden death has focused attention on the central autonomic control of cardiac function. Power spectral analysis of heart rate variability(HRV) can detect autonomic consequences of stroke. We performed power spectral analysis of heart rate variability from 24-hour holter recording to identify cerebral hemispheric lateralization and gender effect in cardiac autonomic control. Methods Data were obtained from 24-hour holter recordings in 30 consecutive patients with hemispheric brain infarction in the subacute phase. We analysed the time domain and frequency domain measures of HRV and ST segment by hemispheric lateralization and Gender. Results ST segment was depressed in women compared with man. There was no statistically significant differences between right and left hemisphere stroke patients in any standard index of HRV and ST segment changes. Conclusions These data are partial consistent with evidence from the recent literature that two cerebral hemispheres and gender have a differential influence on the nature and severity of cardiac dysfunction. We think the prospective and definite study was necessary.

• Korean Journal of Acupuncture
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• v.33 no.4
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• pp.176-182
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• 2016

Objectives : This study was designed to analyze the characteristic of heart rate variability(HRV) changes between Deficiency Pattern and Excess Pattern in Stroke Patients admitted to the hospital. Methods : We measured heart rate variability of stroke patients who were admitted to the Department of Korean Internal medicine, Stroke and Neurological Disorders Center from February 1, 2015 to May 30, 2016. We recruited a total of 28 stroke patients and heart rate variability tests were performed on the first day of admission, 2weeks after admission, and 4 weeks after admission. Results : VLF and LF/HF ratio significantly increased over time in Deficiency Pattern group compared with those in the Excess Pattern group. Conclusions : This results suggest that the parasympathetic function of Deficiency Pattern group is lower than that of the Excess Pattern group, resulting in imbalance of the autonomic nervous system.

• The Bulletin of The Korean Astronomical Society
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• v.41 no.1
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• pp.36.2-37
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• 2016

We study the long-term radio variability of 43 radio bright AGNs by exploiting the data base of the University of Michigan Radio Astronomy Observatory (UMRAO) monitoring program. The UMRAO database provides high quality lightcurves spanning 25 - 32 years in time at three observing frequencies, 4.8, 8, and 14.5 GHz. We model the periodograms (temporal power spectra) of the observed lightcurves as simple power-law noise (red noise, spectral power $P(f){\propto}f^{-{\beta}}$ using Monte Carlo simulations, taking into account windowing effects (red-noise leak, aliasing). The power spectra of 39 (out of 43) sources are in good agreement with the models, yielding a range in power spectral index (${\beta}$) from ${\approx}1$ to ${\approx}3$. We find a strong anti-correlation between ${\beta}$ and the fractal dimension of the lightcurves, which provides an independent check of the quality of our modelling of power spectra. We fit a Gaussian function to each flare in a given lightcurve to obtain the flare duration. We discover a correlation between ${\beta}$ and the median duration of the flares. We use the derivative of a lightcurve to obtain a characteristic variability timescale which does not depend on the assumed functional form of the flares, incomplete fitting, and so on. We find that, once the effects of relativistic Doppler boosting on the observed timescales are corrected, the variability timescales of our sources are proportional to the black hole mass to the power of ${\alpha}=1.70{\pm}0.49$. We see an indication for AGNs in different regimes of accretion rate, flat spectrum radio quasars and BL Lac objects, having different scaling relations with ${\alpha}{\approx}1$ and ${\approx}2$, respectively. We find that modelling the periodograms of four of our sources requires the assumption of broken powerlaw spectra. From simulating lightcurves as superpositions of exponential flares we conclude that strong overlap of flares leads to featureless simple power-law periodograms of AGNs at radio wavelengths in most cases (The paper is about to be submitted to ApJ).

• Journal of the Korean Society of Radiology
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• v.16 no.5
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• pp.545-551
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• 2022

This study analyzed the correlation between stress measurements calculated through HRV signals and thyroid function test items. 181 healthy adults without disease who visited Clinic K were the subjects of this study. Stress resistance (SR) and stress index (SI) were calculated using the acquired HRV signal, and TSH, Free T4, and T3 were used as thyroid function test items. For the measured values, the relationship between each item was statistically analyzed through Pearson correlation analysis. From the results, it was confirmed that Free T4 and SR had a positive correlation (r=0.18) and a negative correlation with SI (r=-0.16). Through this, it was confirmed that there is a significant relationship between thyroid function and HRV signal.

• Journal of The Korean Society of Integrative Medicine
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• v.9 no.2
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• pp.23-33
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• 2021

Purpose : This study aimed to investigate the effects of dual-task training according to the variability of the walking environment on balance, gait, and function in patients with stroke. Methods : Twenty-five patients with stroke were randomly assigned to experimental group I (n=12) and experimental group II (n=13). Experimental group I and II performed obstacle and non-obstacle walking training, respectively, along with cognitive tasks for 21 minutes per session, 3 times a week for 6 weeks. Both groups received additional general physical therapy for 30 minutes per session. The functional reach test (FRT), gait analyzer (G-Walk), and functional independence measure (FIM) were used to evaluate balance, gait and function of pre- and post-interventions, respectively, while gait cadence, gait velocity, and stride length were evaluated using a gait analyzer. Results : In the within-group comparison of FRT, all the two groups showed significant post-intervention improvements (p<.05). In within-group comparison of gait cadence, all the two groups showed significant post-intervention improvements (p<.05). In within-group comparison of gait velocity, all the two groups showed significant post-intervention improvements (p<.05). In within-group comparison of stride length, experimental group I showed significant post-intervention improvements (p<.05), while experimental group II did not show significant post-intervention improvements (p>.05). In within-group comparison of FIM scores, experimental group I showed significant post-intervention improvements (p<.05), while experimental group II did not show significant post-intervention improvements (p>.05). There was a significant difference in the change of FIM scores pre- and post-intervention (p<.05) in the between-group comparison. Conclusion : The results of this study show that dual-task training with cognitive tasks and walking training can improve the balance, gait and function of patients with stroke, and obstacle walking training is effective for improving functions including activities of daily living compared to non-obstacle walking training.

• Structural Engineering and Mechanics
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• v.9 no.2
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• pp.141-152
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• 2000

Based on the discussion about some empirical coherency models resulted from earthquake-induced ground motion recordings at the SMART-1 array in Taiwan, and a heuristic model of the coherency function from elementary notions of stationary random process theory and a few simplifying assumptions regarding the propagation of seismic waves, a practical coherency model for spatially varying ground motions, which can be applied in aseismic analysis and design, is proposed, and the regressive coefficients are obtained using least-square fitting technique from the above recordings.

• Ocean and Polar Research
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• v.41 no.3
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• pp.121-133
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• 2019

Natural variability associated with a variety of large-scale climate modes causes regional differences in sea level rise (SLR), which is particularly remarkable in the Pacific Ocean. Because the superposition of the natural variability and the background anthropogenic trend in sea level can potentially threaten to inundate low-lying and heavily populated coastal regions, it is important to quantify sea level variability associated with internal climate variability and understand their interaction when projecting future SLR impacts. This study seeks to identify the dominant modes of sea level variability in the tropical Pacific and quantify how these modes contribute to regional sea level changes, particularly on the two strong El $Ni{\tilde{n}}o$ events that occurred in the winter of 1997/1998 and 2015/2016. To do so, an adaptive data analysis approach, Ensemble Empirical Mode Decomposition (EEMD), was undertaken with regard to two datasets of altimetry-based and in situ-based steric sea levels. Using this EEMD analysis, we identified distinct internal modes associated with El $Ni{\tilde{n}}o$-Southern Oscillation (ENSO) varying from 1.5 to 7 years and low-frequency variability with a period of ~12 years that were clearly distinct from the secular trend. The ENSO-scale frequencies strongly impact on an east-west dipole of sea levels across the tropical Pacific, while the low-frequency (i.e., decadal) mode is predominant in the North Pacific with a horseshoe shape connecting tropical and extratropical sea levels. Of particular interest is that the low-frequency mode resulted in different responses in regional SLR to ENSO events. The low-frequency mode contributed to a sharp increase (decrease) of sea level in the eastern (western) tropical Pacific in the 2015/2016 El $Ni{\tilde{n}}o$ but made a negative contribution to the sea level signals in the 1997/1998 El $Ni{\tilde{n}}o$. This indicates that the SLR signals of the ENSO can be amplified or depressed at times of transition in the low-frequency mode in the tropical Pacific.

• Journal of the Korean Association of Geographic Information Studies
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• v.12 no.2
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• pp.120-131
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• 2009

This study measured the centripetal force and effective scope of the population spread from urban center and subcenters in order to diagnose the urban spatial structure of the formation of a multicentric city structure in Busan. The study analyzed the variability of the determination coefficient value (R square) with a negative exponential function derived from the population density model by extending the circular region into 5-km units. The aim of this study was to measure changes in the effective scope of the population centripetal force of the urban center and subcenter in 5-year intervals from 1995 to 2005 using census data. The explanatory adequacy of the population density function was examined with the bias of the function to calculate the distance error between the real location of the urban center and the optimal location, according to the population density function. To summarize the results, the value for the area of Jungangdong showed a continuous reduction, whereas Seomyeon (Bujeondong) maintained explanatory adequacy without a large change. As a whole, Busan was in the process of continuous diversification, in spite of its reduced population. Therefore, it appears necessary to strengthen the function of the urban center and subcenter and to supply adequate dwelling zones close to downtown to form a more efficient urban spatial structure. The results of the present study will be utilized as basic data for the formulation of a political approach to the efficient reorganization of spatial structure by correlating concrete spatial information with the population variability of Busan's urban center and subcenter.

• Sleep Medicine and Psychophysiology
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• v.11 no.2
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• pp.100-105
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• 2004

Objectives: Major depression is associated with an increased risk of cardiovascular mortality. One possible explanation for this association is that major depression influences autonomic neurocardiac regulation. However, previous studies on the relationship between heart rate variability (HRV) and major depression have revealed conflicting results. The purpose of this study is to clarify that major depressive patients compared to healthy controls show a reduction in HRV as an expression of reduced modulation of vagal activity to the heart. Methods: According to DSM-IV, the time and frequency domain HRV indices (5-min resting study) of 30 patients with major depressive disorder were compared with those of 30 healthy controls. Standardized HRV tests enable quantitative estimation of autonomic nervous system function. Results: After controlling for age and gender, subjects with major depression showed a higher heart rate and significantly lower modulation of cardiovagal activity compared to controls. The total power (TP) band, very low frequency (VLF: 0.003-0.04 Hz) band, low frequency (LF: 0.04-0.15 Hz) band, and high frequency (HF: 0.15-0.4 Hz) band were significantly reduced in subjects with major depression compared to control subjects. Conclusion: Patients with major depression may suffer from functional disturbances in the interaction between the sympathetic and parasympathetic autonomic systems.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.24 no.4
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• pp.383-389
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• 2011

In this paper, a statistical calibration method is proposed in order to identify the variability of complex modulus for a rubber material due to operational temperature and experimental/model errors. To describe temperature- and frequency-dependent material properties, a fractional derivative model and a shift factor relationship are used. A likelihood function is defined as a product of the probability density functions where experimental values lie on the model. The variation of the fractional derivative model parameters is obtained by maximizing the likelihood function. Using the proposed method, the variability of a synthetic rubber material is estimated and applied to a rubber mount problem. The dynamic characteristics of the rubber mount are calculated using a finite element model of which material properties are sampled from Monte Carlo simulation. The calculated dynamic stiffnesses show very large variation.