Fabrication of dental gutta-percha points by injection molding process

Seunghyun Ko,Yong-Hoon Jeong,Tae-Gon Jung,Myong-Hyun Baek 대한치과재료학회 2022 대한치과기재학회 학술대회 Vol.2022 No.11

Preparation of synthetic graphite from waste PET plastic

Seunghyun Ko,Yeon Ju Kwon,Jea Uk Lee,Young-Pyo Jeon 한국공업화학회 2020 Journal of Industrial and Engineering Chemistry Vol.83 No.-

The development of new technologies for converting waste plastics into value-added products isattracting widespread attention because of the global plastic waste crisis. In this study, we present anovel route for the upcycling of waste plastics, wherein synthetic graphite is prepared from a wastepolyethylene-terephthalate (PET) bottle through a facile and scalable method. PET was successfullyconverted to graphite via a synthetic method of pyrolysis at 900 C followed by boron-assisted catalyticgraphitization at 2400 C. This technique overcame the intrinsic non-graphitizable property of PET andyielded graphite showing high crystallinity with the maximum crystallite size of 20.9 nm in Lc and thed(002) spacing of 3.373 Å. In particular, it showed a much higher degree of graphitization (80.6%) than that(68.9%) derived from a well-known AR mesophase pitch (Mitsubishi). In addition, via a microwave-assisted liquid-phase exfoliation, the PET-derived graphite was successfully exfoliated as graphene sheetswith the average lateral size of 410 nm. We expect that our work can guide the innovative upcycling ofwaste plastics to invaluable synthetic graphite, which has many potential applications such as anodematerials in secondary batteries andfillers for carbon composites, and may serve as an alternative sourcefor graphene production.

Modified oxidative thermal treatment for the preparation of isotropic pitch towards cost-competitive carbon fiber

Ko, Seunghyun,Choi, Jong-Eun,Lee, Chul Wee,Jeon, Young-Pyo THE KOREAN SOCIETY OF INDUSTRIAL AND ENGINEERING 2017 JOURNAL OF INDUSTRIAL AND ENGINEERING CHEMISTRY -S Vol.54 No.-

<P><B>Abstract</B></P> <P>A modified oxidative thermal treatment was developed to increase the softening point of a pitch precursor while minimizing the pitch yield loss. An O<SUB>2</SUB>/N<SUB>2</SUB> mixed gas was used as the reaction gas, and the softening point and pitch yield variations were measured at different O<SUB>2</SUB> concentrations. As a result, when softening point increased from 130 to 249°C, the pitch yield remained almost constant (only 0.6% drop). Structural analysis performed via MALDI-TOF, FTIR, and <SUP>1</SUP>H and <SUP>13</SUP>NMR showed that condensation reaction between pitch molecules in the presence of O<SUB>2</SUB>-containing gas followed a different mechanism depending on the O<SUB>2</SUB> concentration. In addition, the precursors were spun into pitch fibers and carbonized at 1100°C. During the spinning, they exhibited excellent spinnability without breakage for more than 10min of spinning. The obtained carbon fibers showed high tensile strengths comparable to that of a commercial isotropic-pitch-derived carbon fiber (0.83GPa). The current study showed that the modified thermal treatment is useful for the preparation of cost-competitive pitch precursors suitable for carbon fiber production.</P> <P><B>Highlights</B></P> <P> <UL> <LI> An O<SUB>2</SUB>/N<SUB>2</SUB> mixed gas was used as the reaction gas, and the softening point and pitch yield variations were measured at different O<SUB>2</SUB> concentrations. </LI> <LI> When softening point increased from 130 to 249°C, the pitch yield remained almost constant (only 0.6% drop). </LI> <LI> Pitches prepared by the modified oxidative thermal treatment exhibited excellent spinnability without breakage for more than 10min of spinning. </LI> <LI> The obtained carbon fibers showed high tensile strengths comparable to that of a commercial isotropic-pitch-derived carbon fiber (0.83GPa). </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>

Improved understanding of the molecular structure of pyrolysis fuel oil: towards its utilization as a raw material for mesophase pitch synthesis

Seunghyun Ko,Jong‑Eun Choi,Hyejin Yim,Jin Miyawaki,Seong‑Ho Yoon,Young‑Pyo Jeon 한국탄소학회 2019 Carbon Letters Vol.29 No.3

Structural characterization of pyrolysis fuel oil (PFO) was conducted via 1H NMR and 13C NMR to elucidate its molecular structure and evaluate the feasibility of using PFO as a raw material for mesophase pitch synthesis. The average structural parameters were calculated based on the data from elemental analysis and matrix-assisted laser desorption/ionization time of flight mass spectrometry (MALDI-TOF-MS), as well as 1H NMR and 13C NMR data. The resultant structural features of PFO were compared with those of fluidized catalytic cracking-decant oil (FCC-DO). Based on the calculated parameters, we proposed average molecular models of PFO and FCC-DO. The molecular model of PFO showed that it had an aromatic structure consisting of three aromatic rings and one naphthenic ring fused with one pericondensed and two catacondensed aromatic carbons, as well as a short alkyl side chain (with only a methyl group). This structural feature of PFO demonstrated that it is highly favorable for use as a raw material for mesophase pitch synthesis. The empirical findings in this study provide an in-depth understanding of the molecular structure of PFO as well as FCC-DO and can offer insights for future research on the utilization of PFO and other petroleum heavy oils.

K-Means 클러스터링을 적용한 향상된 CS-RANSAC 알고리즘

고승현 ( Seunghyun Ko ),윤의녕 ( Ui-nyoung Yoon ),( Jumabek Alikhanov ),조근식 ( Geun-sik Jo ) 한국정보처리학회 2017 정보처리학회논문지. 소프트웨어 및 데이터 공학 Vol.6 No.6

이미지를 기반으로 하는 증강현실 시스템에서 가상의 객체를 실제 영상에 저작할 때 생기는 이질감을 줄이기 위해서는 실제 영상에 저작된 가상객체의 방향과 위치에 대해 정확하게 추정을 해야 하며, 이때 호모그래피를 사용한다. 호모그래피를 추정하기 위해서는 SURF와 같은 특징점을 추출하고 추출된 특징점들을 통해 호모그래피 행렬을 추정한다. 호모그래피 행렬의 추정을 위해서 RANSAC 알고리즘이 주로 사용되고 있으며, 특히 RANSAC에 제약 조건 만족 문제(Constraint Satisfaction Problem)와 여기에 사용되는 제약조건을 동적으로 적용하여 속도와 정확도를 높인 DCS-RANSAC 알고리즘이 연구되었다. DCS-RANSAC 알고리즘에서 사용된 이미지 그룹 데이터는 수동적인 방법을 통해 직관적으로 분류되어 있지만 특징점 분포 패턴이 다양하지 않고, 이미지들을 정확하게 분류하기가 어려워서 이로 인해 알고리즘의 성능이 저하되는 경우가 있다. 따라서 본 논문에서는 K-means 클러스터링을 적용하여 이미지들을 자동으로 분류하고 각 이미지 그룹마다 각기 다른 제약조건을 적용하는 KCS-RANSAC 알고리즘을 제안한다. 제안하는 알고리즘은 머신러닝 기법인 K-means 클러스터링을 사용하여 전처리 단계에서 이미지를 특징점 분포 패턴에 따라 자동으로 분류하고, 분류된 이미지에 제약조건을 적용하여 알고리즘의 속도와 정확도를 향상시켰다. 실험결과 본 논문에서 제안하는 KCS-RANSAC이 DCS-RANSAC 알고리즘에 비해 수행시간이 약 15% 단축되었고, 오차율은 약 35% 줄어들었으며, 참정보 비율은 약 14% 증가되었다. Estimating the correct pose of augmented objects on the real camera view efficiently is one of the most important questions in image tracking area. In computer vision, Homography is used for camera pose estimation in augmented reality system with markerless. To estimating Homography, several algorithm like SURF features which extracted from images are used. Based on extracted features, Homography is estimated. For this purpose, RANSAC algorithm is well used to estimate homography and DCS-RANSAC algorithm is researched which apply constraints dynamically based on Constraint Satisfaction Problem to improve performance. In DCS-RANSAC, however, the dataset is based on pattern of feature distribution of images manually, so this algorithm cannot classify the input image, pattern of feature distribution is not recognized in DCS-RANSAC algorithm, which lead to reduce it`s performance. To improve this problem, we suggest the KCS-RANSAC algorithm using K-means clustering in CS-RANSAC to cluster the images automatically based on pattern of feature distribution and apply constraints to each image groups. The suggested algorithm cluster the images automatically and apply the constraints to each clustered image groups. The experiment result shows that our KCS-RANSAC algorithm outperformed the DCS-RANSAC algorithm in terms of speed, accuracy, and inlier rate.

머신러닝 기법을 적용한 CS-RANSAC 알고리즘

고승현 ( Seunghyun Ko ),윤의녕 ( Ui-nyoung Yoon ),주마백 ( Jumabek Alikhanov ),조근식 ( Geun-sik Jo ) 한국정보처리학회 2016 한국정보처리학회 학술대회논문집 Vol.23 No.2

증강현실에서 영상과 증강된 콘텐츠 간의 이질감을 줄이기 위해서 정확한 호모그래피 행렬을 추정해야 하며, 정확한 호모그래피 행렬을 추정할때 RANSAC 알고리즘이 널리 사용된다. 그러나 RANSAC 알고리즘은 랜덤 샘플링 과정을 반복적으로 거치기 때문에 불필요한 연산 과정이 발생하고 이로 인해 알고리즘의 효율이 저하된다. 이러한 단점을 극복하기 위해 DCS-RANSAC 알고리즘이 제안 되었다. 제안된 DCS-RANSAC 알고리즘은 이미지를 특징점 분포 패턴에 따라 그룹으로 분류하고 각 그룹에 제약조건 문제를 적용하여 불필요한 연산 과정을 줄이고 정확도를 향상시킨 알고리즘이다. 그러나 DCS-RANSAC 알고리즘에서 사용된 이미지 그룹 데이터는 수동적인 방법을 통해 직관적으로 분류되어 있지만 특징점 분포 패턴이 다양하지 않아 분류시 정확도가 저하되는 경우가 있다. 위의 문제점을 해결하기 위해 본 논문에서는 머신러닝 기법을 통해 이미지들을 자동으로 분류하고 각 그룹마다 각기 다른 제약조건을 적용하는 MCS-RANSAC 알고리즘을 제안한다. 제안하는 알고리즘은 머신러닝 기법을 사용하여 전처리 단계에서 이미지를 분류하고 분류된 이미지에 제약조건을 적용시켜 알고리즘의 처리시간을 줄이고 정확도를 향상시켰다. 실험 결과 본 논문에서 제안하는 MCS-RANSAC은 DCS-RANSAC 알고리즘에 비해 수행시간이 약 6% 단축되었고 호모그래피 오차율은 약 15% 줄어들었으며 참정보 비율은 2.8% 증가한 것으로 확인되었다.

Quench Analysis of a Superconducting Magnet for RISP 28 GHz ECR Ion Source

Seunghyun Song,Tae Kuk Ko,Sukjin Choi,In Seok Hong,Hyoungku Kang,Min Cheol Ahn Institute of Electrical and Electronics Engineers 2015 IEEE transactions on applied superconductivity Vol.25 No.3

<P>This paper presents quench analysis of a superconducting magnet system for 28 GHz electron cyclotron resonance (ECR) ion source. The magnet system consists of a hexapole coil and four solenoid coils located outside of the hexapole one. All coils were wound with NbTi wire and impregnated by epoxy. To analyze the characteristic of superconducting coil when the quench occurs, a numerical code was developed. The analysis procedures are as follows. First, normal zone propagation (NZP) velocity which is as a function of magnetic field was calculated. Second, a fraction of the winding volume was obtained by transient analysis, considering longitudinal and transverse NZP velocities. Third, a generated resistance and temperature rising over time were simulated. Lastly, current trace of the coil was calculated. The current trace calculated by simulation well agrees with the test result. Also the result of hot-spot temperature is reasonable. Since simulated hot-spot temperature and experimental result are 60.32 K and 63 K when the operating current is 169 A. The normal zone resistances are also identical for 1.13 s which is the convergence time of simulation. The final resistances are about 10.2 Ω and 11.23 Ω. Therefore it is expected that the analysis code can be used to estimate the characteristic of superconducting magnet when the quench occurs.</P>

Voltage disturbance detection method for HTS tape using electromagnetically coupled coils

Seunghyun Song,Jiho Lee,Woo Seung Lee,Hongwoo Jin,Young Jin Hwang,Tae Kuk Ko 한국초전도저온학회 (구 한국초전도저온공학회) 2014 한국초전도저온공학회논문지 Vol.16 No.1

High durability conductive textile using MWCNT for motion sensing

Ko, Jaehwan,Jee, Seunghyun,Lee, Joo Hyeon,Kim, Sun Hee Elsevier 2018 Sensors and actuators. A Physical Vol.274 No.-

<P><B>Abstract</B></P> <P>A conductive textile was fabricated by vacuum-filtration using conductive ink prepared from multi-walled carbon nanotubes. The fabricated conductive textile was evaluated as its resistance varied while it was subjected to repeat stretching at strain rates of 0% to 20%. The textile samples showed resistance variations of less than ±3% after 10,000 cycles of stretching, and the pulse of the resistance variation at a strain rate of 0%–20% remained uniform during the stretching cycles. A motion-sensing glove fabricated with the conductive textile showed that the pulse of the oscilloscope changed accurately with movements of the fingers. These results show that the conductive textile prepared in this study can be applied to motion-sensing products.</P> <P><B>Highlights</B></P> <P> <UL> <LI> A conductive textile was fabricated by vacuum-filtration of water-based MWCNTs ink. </LI> <LI> The conductive textile showed resistance variations of less than ±3% after 10,000 cycles of stretching. </LI> <LI> A motion-sensing glove fabricated with the textile showed that signal changed accurately with movements of the fingers. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>

Quench Detection Method for HTS Coils Using Electromagnetically Coupled Coils

Seunghyun Song,Jiho Lee,Woo Seung Lee,Hongwoo Jin,Jeyull Lee,Young Jin Hwang,Tae Kuk Ko Institute of Electrical and Electronics Engineers 2015 IEEE transactions on applied superconductivity Vol.25 No.3

<P>Generally, in order to detect the quench of the superconducting field coil for the superconducting rotating machine, signal wires for voltage taps are indispensably needed. However, the problem of the conventional method is wire twisting as the superconducting field coil rotates. Therefore, in this paper, authors suggest a new method to detect the quench of the superconducting field coil using electromagnetically coupled coils. The suggested method consists of two superconducting pancake and copper solenoid coils. Two superconducting pancake coils play roles of a field coil and external (alternating) field generation for the rotating machine. In addition, two copper solenoid coils are used to transmit the voltage wirelessly and receive the transmitted voltage using electromagnetic induction. In order to verify the feasibility of this method, experiments are performed according to the transporting current flowing through two superconducting pancake coils and separation distance between two copper solenoid coils. The result shows that it is expected to apply this method to the superconducting rotating machines for the detection of quench without direct connection of voltage taps.</P>