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Electrocardiogram Sampling Frequency Range Acceptable for Heart Rate Variability Analysis
권오환,정진우,김형빈,권인호,박송이,김지은,최유리 대한의료정보학회 2018 Healthcare Informatics Research Vol.24 No.3
Objectives: Heart rate variability (HRV) has gained recognition as a noninvasive marker of autonomic activity. HRV is considered a promising tool in various clinical scenarios. The optimal electrocardiogram (ECG) sampling frequency required to ensure sufficient precision of R–R intervals for HRV analysis has not yet been determined. Here, we aimed to determine the acceptable ECG sampling frequency range by analyzing ECG signals from patients who visited an emergency department with the chief complaint of acute intoxication or overdose. Methods: The study included 83 adult patients who visited an emergency department with the chief complaint of acute poisoning. The original 1,000-Hz ECG signals were down-sampled to 500-, 250-, 100-, and 50-Hz sampling frequencies with linear interpolation. R–R interval data were analyzed for time-domain, frequency-domain, and nonlinear HRV parameters. Parameters derived from the data on down-sampled frequencies were compared with those derived from the data on 1,000-Hz signals, and Lin’s concordance correlation coefficients were calculated. Results: Down-sampling to 500 or 250 Hz resulted in excellent concordance. Signals down-sampled to 100 Hz produced acceptable results for time-domain analysis and Poincaré plots, but not for frequency-domain analysis. Down-sampling to 50 Hz proved to be unacceptable for both time- and frequency-domain analyses. At 50 Hz, the root-mean-squared successive differences and the power of high frequency tended to have high values and random errors. Conclusions: A 250- Hz sampling frequency would be acceptable for HRV analysis. When frequency-domain analysis is not required, a 100-Hz sampling frequency would also be acceptable.
수전해용 Pt/PEM/Pt-Ru MEA의 전기화학적 특성
권오환,김경언,장인영,황용구,정장훈,문상봉,강안수 한국수소및신에너지학회 2008 한국수소 및 신에너지학회논문집 Vol.19 No.1
The membrane electrode assembly(MEA) was prepared by a nonequilibrium impregnation- reduction (I-R) method. Nafion 117 and covalently cross-linked sulfonated polyetherether with tungsto- phosphoric acid (CL-SPEEK/TPA30) prepared by our laboratory, were chosen as polymer electrolyte membrane(PEM). Pt(NH3)4Cl2, RuCl3 and reducing agent (NaBH4) were used as electrocatalytic materials.Electrochemical activity surface area(ESA) and specific surface area(SSA) of Pt cathodic electrode with Nafion 117 were 22.48 m2/g and 23.50 m2/g respectively under the condition of 0.8 M NaBH4. But Pt electrode prepared by CL-SPEEK/TPA30 membrane exhibited higher ESA 23.46 m2/g than that of Nafion 117. In case of Pt-Ru anodic electrode, the higher concentration of Ru was, the lower potential of oxygen reduction and region of hydrogen desorption was, and Pt-Ru electrode using 10 mM RuCl3 showed best properties of SSA 34.09 m2/g with Nafion 117. In water electrolysis performance, the cell voltage of Pt/PEM/Pt-Ru MEA with Nafion 117 showed cell property of 1.75 V at 1 A/cm2 and 80℃. On the same condition, the cell voltage with CL-SPEEK/TPA30 was the best of 1.73 V at 1 A/cm2.
Improved electrical conductivity of flexible carbon hybrid films with acid treatment
권오환,김진미,송희석,김병각,조성윤,김용석,원종찬,유영재 한국공업화학회 2015 한국공업화학회 연구논문 초록집 Vol.2015 No.1
In this work, we prepared the flexible hybrid film with graphite nanoplatelet (GNP) and a minimum use of SWNT. The hybrid film was prepared by casting method with varying the acid-treatment time of carbon fillers. It was observed that the hybrid films from acid-treated carbon filler show the highly increased electrical conductivity and unchanged the Seebeck coefficient due to the effective elimination of impurities. This process is expected for facile purification process of various carbon materials for flexible thermoelectric application based on hybrid materials.
Polyethyleneimine이 도핑된 n형 카본버키페이퍼의 제조 및 열전특성의 향상에 관한 연구
김진미,권오환,최환석,이성구,조성윤,유영재 한국공업화학회 2016 한국공업화학회 연구논문 초록집 Vol.2016 No.0
최근, 세계적으로 에너지자원의 고갈과 다양한 에너지 수요증가에 따른 새로운 에너지 자원의 확보 방안으로 각종 산업폐열을 이용한 열전발전기술에 대한 관심이 증대되고 있다. 따라서 본 연구에서는, 열전발전 재료로서 graphite nanoplatelet (GNP)과 single walled carbon nanotube (SWCNT)를 사용하여 나노카본기반의 열전 버키페이퍼를 제조하여 열전특성을 측정하였다. n형 열전발전 버키페이퍼를 제조하기 위해 카본 충전제와 polyethyleneimine (PEI)의 여과공정을 실시하였으며, 이를 통해 카본 충전제 사이의 공극에 PEI가 메워지게 되어 n도핑 효과를 낼 수 있도록 진행하였다. GNP와 SWCNT의 함량에 따른 전기전도도, 제벡계수를 측정하여 열전성능을 확인한 결과 높은 전기전도도를 가진 n형의 열전소재를 얻을 수 있었다. 또한 카본 분산 과정에서의 sodium dodecyl benzene sulfonate (SDBS)의 추가를 통하여 향상된 전기전도도를 갖는 카본 버키페이퍼를 제조할 수 있었다.