One-step synthesis of nano-porous monolithic polyimide aerogel

Kim, Jinyoung,Kwon, Jinuk,Kim, Seung-Ik,Kim, Myeongsoo,Lee, Daero,Lee, Sangrae,Kim, Gunhwi,Lee, Juheon,Han, Haksoo Elsevier 2016 Microporous and mesoporous materials Vol.234 No.-

<P><B>Abstract</B></P> <P>A facile one-step method for synthesis of a porous monolithic polyimide aerogel was successfully developed. The specific thermal curing, slow desiccating process and swelling method were used in synthesizing monolithic polyimide aerogel without any additional chemical reaction to create a connected structure among the polyimide-based spherical aerogel microparticles. Using this method, the monolithic polyimide aerogel can be easily fabricated whilst using no additional chemicals for crosslinking. This type of polyimide aerogel was produced homogeneously by the polyimidization of pyromellitic dianhydride (PMDA) and 4,4′-oxydianiline (ODA). The synthesized porous monolithic polyimide aerogel has many good properties which could be used in various industries, as it maintained a high thermal decomposition temperature (10% weight decomposition temperature: T<SUB>d10%</SUB>) of approximately 577 °C and a glass transition temperature (T<SUB>g</SUB>) of 432 °C, with bulk density of 490.7 kg/m<SUP>3</SUP>, porosity of approximately 45% and average pore size of 4 nm (by nitrogen adsorption test) of polymer and 157 nm (by mercury intrusion method) of space observed in FE-SEM image. Also, the monolithic polyimide aerogel had an excellent oil-adsorbing capacity of 150%, and the adsorbed oil could be separated easily using a simple drying process. The dried monolithic polyimide aerogel showed significant recoverability and reusability of adsorbed oil. In addition, the monolithic polyimide aerogel exhibited high mechanical resistance such that the structure can withstand a high pressure greater than 122.3 kPa, under which the monolithic polyimide aerogel (MPA) was compressed but did not break. This type of MPA shows excellent thermal, mechanical properties and great processability, and could be the new candidate for high performance materials in various industries, especially catalyst field.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Unlike other aerogel synthesis, in this study, the polyimide aerogel monolith is created without adding any other chemicals. </LI> <LI> The polyimide aerogel monolith has excellent thermal, mechanical properties and great processability for application in various industries. </LI> <LI> The polyimide aerogel monolith synthesized with homogeneity fully maintained in very convenient and easy method. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>

초분광 영상 기반 CDOM 흡수계수 결정 및 분광특성 분석

김진욱(Jinuk Kim),장원진(Wonjin Jang),김진휘(Jin Hwi Kim),박용은(Yongeun Park),김성준(Seongjoon Kim) 대한환경공학회 2022 대한환경공학회 학술발표논문집 Vol.2022 No.11

Oversampling 기반 Machine Learning 기법별 백제보 상류하천구간의 CDOM 흡수계수 예측

김진욱 ( Jinuk Kim ),장원진 ( Wonjin Jang ),김진휘 ( Jinhwi Kim ),박용은 ( Yongeun Park ),김성준 ( Seongjoon Kim ) 한국농공학회 2022 한국농공학회 학술대회초록집 Vol.2022 No.-

금강 백제보는 준공 이후 긴 체류시간과 깊은 수심으로 인해 상류에서 유입된 유기물질로 인한 녹조 번성이 유리한 유역이다. 유기물질을 조절하기 위해 최근 머신러닝과 원격감지 기술로 CDOM(Colored Dissolved Organic Matter)을 모니터링하기 위한 연구가 진행되고 있다. 한편, 머신러닝을 통해 CDOM을 예측할 때 데이터 품질과 양에 따라 결과 값이 달라지며, 백제보는 모니터링 기간 중 CDOM 값은 전체기간 동안 2.0~11.0 m^-1의 분포를 가지며, 5 m^-1 이상의 고농도 구간 자료 개수가 18개로 전체(105개)의 17%를 보였다. 따라서 본 연구에서는 녹조 번성이 심했던 2016~2017년의 백제보의 초분광영상을 이용하여, oversampling 기법 중 하나인 SMOTE(Synthetic Minority Over-sampling Technique)와 ADASYN(Adaptive Synthesis Sampling Approach) 기법을 통해 불균형 문제를 해결하고, 여러 머신러닝 기법을 적용하여 CDOM을 모니터링하고자 하였다. 고농도와 저농도 비율을 고려하여 Train 데이터와 Test 데이터를 70:30으로 분할 한 후, Train 데이터에 대해 SMOTE와 ADASYN 기법을 적용해 고농도 데이터를 생성하였다. 머신러닝은 OLS(Ordinary Least Squres), SVR(Support Vector Regression), RFR(Random Forest Regression), LGB(Light Gradient Boosting Regression), ANN(Artificial Neural Network)을 적용하여 평하가였다. 평가결과 SMOTE+RFR의 overall 결과는 Train R² 0.826, Test R² 0.439를 보였으며 best case에서는 Train R² 0.831, Test R² 0.882으로 가장 높은 예측력을 보였다. 해당 결과를 활용하여 공간분포를 실시하였으며, 공간적으로 유기물이 밀집된 지역과 아닌 지역을 판별하였다. 본 연구결과를 활용하여 하천 내 유기 오염물질 관리를 위한 설계를 지원하는데 사용할 수 있을 것으로 판단된다.

열가소성 플라스틱의 미소박리시험 시료 제작법 비교 연구

김상훈(Sanghoon Kim),엄찬혁(Chanhyeok Um),김수영(Suyoung Kim),하진욱(Jinuk Ha),정선경(Sunkyoung Jeong),김늘새롬(Neulsaerom Kim),김재훈(Jaehoon Kim),고윤기(Yoonki Ko) 한국자동차공학회 2017 한국자동차공학회 학술대회 및 전시회 Vol.2017 No.11

대용량 Water dynamometer CFD 성능 예측

김상윤(Sangyoon Kim),김병하(Byungha Kim),이영호(Youngho Lee),김영춘(Yeongchun Kim),홍기원(Giwon Hong),김진욱(Jinuk Kim),정동화(Donghwa Jung) 한국유체기계학회 2020 한국유체기계학회 학술대회 논문집 Vol.2020 No.11

Inference on the Joint Center of Rotation by Covariance Pattern Models

( Jinuk Kim ) 한국운동역학회 2018 한국운동역학회지 Vol.28 No.2

Objective: In a statistical linear model estimating the center of rotation of a human hip joint, which is the parameter related to the mean of response vectors, assumptions of homoscedasticity and independence of position vectors measured repeatedly over time in the model result in an inefficient parameter. We, therefore, should take into account the variance-covariance structure of longitudinal responses. The purpose of this study was to estimate the efficient center of rotation vector of the hip joint by using covariance pattern models. Method: The covariance pattern models are used to model various kinds of covariance matrices of error vectors to take into account longitudinal data. The data acquired from functional motions to estimate hip joint center were applied to the models. Results: The results showed that the data were better fitted using various covariance pattern models than the general linear model assuming homoscedasticity and independence. Conclusion: The estimated joint centers of the covariance pattern models showed slight differences from those of the general linear model. The estimated standard errors of the joint center for covariance pattern models showed a large difference with those of the general linear model.

Inference on the Joint Center of Rotation by Covariance Pattern Models

Kim, Jinuk Korean Society of Sport Biomechanics 2018 한국운동역학회지 Vol.28 No.2

Objective: In a statistical linear model estimating the center of rotation of a human hip joint, which is the parameter related to the mean of response vectors, assumptions of homoscedasticity and independence of position vectors measured repeatedly over time in the model result in an inefficient parameter. We, therefore, should take into account the variance-covariance structure of longitudinal responses. The purpose of this study was to estimate the efficient center of rotation vector of the hip joint by using covariance pattern models. Method: The covariance pattern models are used to model various kinds of covariance matrices of error vectors to take into account longitudinal data. The data acquired from functional motions to estimate hip joint center were applied to the models. Results: The results showed that the data were better fitted using various covariance pattern models than the general linear model assuming homoscedasticity and independence. Conclusion: The estimated joint centers of the covariance pattern models showed slight differences from those of the general linear model. The estimated standard errors of the joint center for covariance pattern models showed a large difference with those of the general linear model.

Optimization of a high pressure turbine blade tip cavity with conjugate heat transfer analysis

Jinuk Kim,Young-Seok Kang,Dongwha Kim,Jihyeong Lee,Bong-Jun Cha,Jinsoo Cho 대한기계학회 2016 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.30 No.12

The current study aims to understand the aero-thermal performance of a cooled cavity tip in a single stage transonic turbine. The squealer tip of the uncooled turbine blade was reduced to an aerodynamic loss with suppressing leakage flow. However, the aerodynamic loss study of the cooled turbine blade tip is rare. It is necessary to study the tip cavity of the cooled turbine blade. Depth, front blend radius and aft blend radius of the cavity were set as design variables, and 30 cases were chosen using design of experiments. These cases were calculated with conjugate heat transfer method. Approximation model was made using the Kriging method, and tip cavity shape was optimized with multidisciplinary design optimization. Average total pressure loss behind the trailing edge and cooling effectiveness of blade tip surface were set to the objective function. The aerodynamic optimization model decreased 1.6 % of total pressure loss, the heat transfer optimization model increased 1.3 % point of cooling effectiveness and aero-thermal optimization model were found. Volume of tip cavity becomes larger when three design variables are grown. Amount of tip leakage flow and its distribution over the tip region increases and total pressure loss and cooling effectiveness increase. In terms of heat transfer, blade tip without cavity is advantageous. Total pressure loss coefficient, however, also increases over 5 %. To improve both aero-thermal characteristics of cooled blade tip, the design using the multidisciplinary design optimization is recommended.

Immediate Effect of Kinesiology Taping on Gait Function in Stroke Patients with Foot Drop

Jinuk Kim 국제물리치료연구학회 2020 Journal of International Academy of Physical Ther Vol.11 No.2

Background: Recently, the kinesiology taping (KT) method was reported to be effective in improving walking ability in foot drop patients after stroke, but the clinical basis is still unclear. Objectives: The KT method was compared with ankle-foot orthotics (AFO) to investigate gait ability in foot drop patients after stroke. Design: Crossover study design. Methods: In this study, 11 stroke patients with foot drop participated. Walking ability of all subjects for both conditions (KT and AFO) was measured using the GAITRite system. The order of application of the two conditions was determined randomly by drawing lots. Wilcoxon signed-rank test was used to compare walking ability between the two conditions. The level of statistical significance was set at P<.05. Results: There were no significant differences between the KT and AFO methods in terms of velocity, cadence, step length, and stride length (P>.05, all). Conclusion: This study recommends KT as an alternative to the AFO, since KT provides evidence of preventing of foot drops and improving gait ability in stroke patient.

A Statistical Model for Marker Position in Biomechanics

Kim, Jinuk Korean Society of Sport Biomechanics 2017 한국운동역학회지 Vol.27 No.1

Objective: The purpose of this study was to apply a general linear model in statistics to marker position vectors used to study human joint rotational motion in biomechanics. Method: For this purpose, a linear model that represents the effect of the center of hip joint rotation and the rotation of the marker position on the response was formulated. Five male subjects performed hip joint functional motions, and the positions of nine markers attached on the thigh with respect to the pelvic coordinate system were acquired at the same time. With the nine marker positions, the center of hip joint rotation and marker positions on the thigh were estimated as parameters in the general linear model. Results: After examining the fitted model, this model did not fit the data appropriately. Conclusion: A refined model is required to take into account specific characteristics of longitudinal data and other covariates such as soft tissue artefacts.