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연속적 결측이 존재하는 기온 자료에 대한 결측복원 기법의 비교
김희경,강인경,이재원,이영섭,Kim, Hee-Kyung,Kang, In-Kyeong,Lee, Jae-Won,Lee, Yung-Seop 한국통계학회 2016 응용통계연구 Vol.29 No.3
장기간의 기후 자료가 누적되다 보면 자료의 수집과정에서 시스템적 오류나 측정 장비의 고장 등으로 인하여 연속적 결측이 종종 발생하게 된다. 연속적인 결측 형태를 갖는 경우 시계열 결측 자료를 대체하는 것에 어려움이 따른다. 이러한 경우 참조시계열을 이용하여 결측값을 대체할 수 있다. 참조시계열은 결측이 발생한 시계열과 관련성이 높은 주변지점의 시계열로 구성할 수 있다. 본 연구에서는 결측값을 대체시킬 수 있는 3가지 결측복원 기법-수정된 정규화비율 방법, 회귀 방법, IDW 방법-을 비교하는 시뮬레이션을 수행하였다. 우리나라 14개 지점의 기후관측소의 일평균기온값을 대상으로 비교한 결과 남쪽 해안가에 위치한 기후관측소의 자료에 대해서는 IDW 방법이 가장 정확한 것으로 나타났으며, 그 외 지역의 기후관측소 자료에 대해서는 회귀 방법이 가장 정확한 것으로 나타났다. Consecutive missing values are likely to occur in long climate data due to system error or defective equipment. Furthermore, it is difficult to impute missing values. However, these complicated problems can be overcame by imputing missing values with reference time series. Reference time series must be composed of similar time series to time series that include missing values. We performed a simulation to compare three missing imputation methods (the adjusted normal ratio method, the regression method and the IDW method) to complete the missing values of time series. A comparison of the three missing imputation methods for the daily mean temperatures at 14 climatological stations indicated that the IDW method was better thanx others at south seaside stations. We also found the regression method was better than others at most stations (except south seaside stations).
Fabrication method of dual-pore scaffold using Polyethylene oxide, Polycaprolactone and NaCl
Hee Kyeong Kim(김희경),Yong Sang Cho(조용상),Young-Sam Cho(조영삼) 대한기계학회 2014 대한기계학회 춘추학술대회 Vol.2014 No.11
In this study, PEO (polyethylene oxide), which is water-soluble polymer, was added to overcome the problem that NaCl particles were not leaching out at PCL (polycaprolactone)/NaCl scaffold if dispensing-type SFF (solid freeform fabrication) apparatus was utilized to fabricate. Before fabrication of dual-pore scaffold, PEO, PCL and NaCl powders with certain size were prepared. Afterward, PEO, PCL and NaCl powders were mixed via stirrer for 24hours. After that, mixed powders were filled in the barrel of bio-plotter. Subsequently, mixed PEO, PCL and NaCl powders were plotted under consistent pressure and melting temperature. Built scaffold was soaked into the D.I. water to leach out PEO and NaCl particles for 24hours in the sonicator and dried in the desiccator. The porosity of fabricated scaffolds was measured. Moreover, morphology of fabricated scaffold was observed through FE-SEM.
비교적 큰 나노구조 표면에서 박테리아 부착 및 살균 메커니즘
김희경(Hee Kyeong kim),박준기(Jun Gi Park),Suvd Erdene Ganbaatar,서경덕(Kyoung Duck Seo),조영삼(Young-Sam Cho),박현하(Hyun-Ha Park) 대한기계학회 2021 대한기계학회 춘추학술대회 Vol.2021 No.11
Biofilms formed due to the attachment of bacteria to the surface are causing various problems in medical design and fabrication of a generation of bactericidal materials. Recently, mechano-bactericidal using a contact killing mechanism by mimicking the wings of cicada or dragonfly is being studied. Mechano-bactericidal has a mechanism in which the bacterial membrane is destroyed as the bacteria attached to the surface are stretched by the nanostructure. The bactericidal ability of the nanostructure is determined by the spacing, height, geometric structure of the nanostructure. The nanostructures reported so far mimic the wings of cicadas and dragonflies, and have high density and pointed nanostructures. Tear of the bacterial membrane by the nanopillars can induce bacteria to kill. The pointed nanostructures can pierce the bacterial membrane and kill the attached bacteria. However, this mechanism is predicted to kill due to the tearing by stretching of the bacterial membrane by relatively large nanopillars.