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당뇨병 환자에서 Power Spectrum Analysis 를 이용한 자율신경계 이상의 검정
이두하(Du Ha Lee),황형기(Hyoung Ki Hwang),이형우(Hyoung Woo Lee),김영조(Young Jo Kim),심봉섭(Bong Sup Shim),이현우(Hyun Woo Lee),신동구(Dong Ku Shin),이상학(Sang Hak Lee),이준하(Jun Ha Lee) 대한내과학회 1991 대한내과학회지 Vol.41 No.5
N/A In order to assess the autonomic nervous system activity in normal subjects and in diabetic patients affected by different degrees of diabetic autonomic neuropathy, we applied autoregressive power spectral analysis to 35 diabetic patients and 15 normal controls. This analysis was then compared to conventional methods by CAN score tests. Each subject was placed on a bed and connected to electro-cardiographic electrodes. After 15-minute rest in a sitting position, the electrocardiogram (ECG) recorded 512 heartbeats in a supine position. Thereafter, the same measure was taken in a standing position. During the test, the subjects quietly breathed in synchronosity with a 15/min (0.25 Hz) metronome signal to obtain stationary respiratory activity without frequency change or phase drift. R-wave detection by fast peak detection algorithm and spectrum computation by Fast Fourier transform enabled the study of the power spectrum of heart rate fluctuations. The power of fluctuations at different frequencies was the result of sympathetic and vagal input into the sinoatrial node. The autoregressive power spectral density of RR interval variability contained 2 major components: a high frequency (0.25 Hz), which is a quantitative marker of cardiac vagal activity, and a low frequency (<0.15 Hz), which is a quantitative marker of sympathetic activity with vagal modulation. A marked reduction in HF spectral density was found in diabetic patients relative to the normal controls (p<0.001). When neural activity was provoked through standing, less decreased HF spectral density and less increased LF spectral density were noted in diabetic patients relative to the normal controls (p<0.01). When diabetic autonomic neuropathy was advanced, HF and LF spectral density changes were lost. This method is simple, repeatible, objective, and quantitative. It may facilitate the screening of diabetic patients for autonomic neuropathy and enable convenient quantitative fallow-up.
Kwon, Sung-Ku,Kim, Du-Hyun The Korea Association of Crystal Growth 1999 한국결정성장학회지 Vol.9 No.5
In-situ cleaning and subsequent silicon epitaxial film growth were performed in a load-locked reactor equipped with Hg-grid UV lamp and PBN heater to obtain the smooth and contaminant-free underlying surface and develop low-temperature epitaxial film growth process. The removals of organic and native oxide were investigated using UV-excited $O_2$ and $NF_{3}/H_{2}$, and the effect of the surface condition was examined on the quality of silicon epitaxial film grown at temperature as low as $750^{\circ}C$. UV-excited gas phase cleaning was found to be effective in removing the organic and native oxide successfully providing a smooth surface with RMS roughness of 0.5$\AA$ at optimal condition. Crystalline quality of epitaxial film was determined by smoothness of cleaned surface and the presence of native oxide and impurity. Crystalline defects such as dislocation loops or voids due to the surface roughness were observed by XTEM.
Mechanical properties and durability of PMMA impregnated mortar
Priya Nair,이원묵,Du Hyun Ku,이철우,Jung Soon Park,Hun Young Park 한국화학공학회 2010 Korean Journal of Chemical Engineering Vol.27 No.1
Polymer impregnated concrete (PIC) is known to exhibit better strength and durability characteristics than the other classes of polymer cement composites. In the work described herein the monomer was impregnated into cement mortar and polymerized by two methods - the conventional thermal method and using microwaves. The mechanical properties and durability characteristics of the samples and on exposure to chemical environments were then evaluated. The above studies revealed that the strengths of PIC specimens were almost 2-3 times better than those of conventional cement mortars. The chemical resistance was also found to be superior even on prolonged exposure to the chemical media. This may be attributed to the protective layer formed by the polymer on the cement mortar, which prevents the external chemical media from interacting with the cement particles. The properties of the PIC specimens prepared by both methods have also been compared and discussed in this paper.
Kong, Hong Jin,Beak, Du Hyun,Lee, Dong Won,Lee, Seong Ku The Optical Society 2005 Optics letters Vol.30 No.24
<P>We have found that it is possible to preserve the temporal waveform of the reflected wave generated from stimulated Brillouin scattering (SBS) by using a prepulse technique. The waveform of the SBS wave usually shows a steep rising edge in the ordinary SBS process. It has been found that the waveform of the reflected wave depends on both the prepulse energy and the time delay between the main pulse and the prepulses. A prepulse energy of 5 mJ and a time delay of 5 ns have been measured to be the optimum values under the experimental conditions. This prepulse method is useful in developing a multistage system employing several SBS cells in series for high-power laser applications.</P>