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Jeon, HoJun,Lee, Hyeongjin,Kim, GeunHyung Mary Ann Liebert 2014 Tissue engineering. Part C, Methods Vol.20 No.12
<P>Melt-plotted poly(e-caprolactone) (PCL) has been widely applied in various tissue regenerations. However, its hydrophobic nature has hindered its usage in wider tissue engineering applications. In this study, we present the development of a porous and multilayered PCL scaffold, which shows outstanding hydrophilic properties and has a roughened surface consisting of homogeneously distributed nanosized pits. The scaffold was obtained using an innovative oxygen plasma treatment. This technology can induce variable nanoscale surface roughness, which is difficult from traditional plasma treatment. Osteoblast-like cells were cultured on the scaffolds and several cellular responses (cell viability, fluorescence images [live/dead cells, nucleus, and actin cytoskeleton], ALP activity, and calcium mineralization) were assessed for untreated PCL and conventionally plasma-treated PCL scaffolds. The data indicated that an appropriate roughness (654 +/- 91 nm) of the PCL scaffold processed with the new plasma treatment induced more advantageous responses for the cells, compared with untreated scaffolds and traditional plasma-treated scaffolds.</P>
압전기(PZT)가 결합된 플러팅 시스템을 이용한 3차원 PCL 지지체 제작
전호준(Hojun Jeon),고석진(Sukjin Ko),윤현(Hyeon Yoon),안승현(SeungHyun Ahn),김근형(GeunHyung Kim) 대한기계학회 2009 대한기계학회 춘추학술대회 Vol.2009 No.11
The RP can provide great control of the internal features of a scaffold, the resolution and minimum feature size are usually constrained by processing parameters and material properties. Recently, a flow in the small-sized nozzle of the plotting system should be required along smoothly to obtain small-sized polymer strand of the 3D scaffold. To attain the stable flow in small-sized nozzle, we adapted a PZT system to the melt-plotting RP system. The effects of the various amplitude and frequencies were investigated in respect of the strand size and the fabricated scaffolds were characterized in mechanical properties. The scaffold of aided PZT system had higher mechanical properties than normal plotting system due to the inducement of molecular orientation of the strand by the vibrating system. From these results, we can convince that this technique is a feasible new method for fabricating high-quality 3D polymeric scaffolds.
플라즈마 애칭을 이용한 나노 표면 구조를 가지는 마이크로 파이버 제작
전호준(HoJun Jeon),안승현(SeungHyun Ahn),이형진(Hyeongjin Lee),여명구(MyungGu Yeo),김용복(YongBok Kim),김민성(Min Seong Kim),이경호(KyoungHo Lee),김근형(GeunHyung Kim) 대한기계학회 2014 대한기계학회 춘추학술대회 Vol.2014 No.11
In a recent study, a hierarchical structure of coexistent nano- and microstructures induced high cellular activities, such as proliferation and differentiation. In this study, an easy and versatile method of generating a nano-sized patterned surface on a nonwoven mat of electrospun poly(e-caprolactone) (PCL) fibers is described. A hierarchical structured pattern could be achieved on the surface of the PCL fiber coated with collagen solution using a modified plasma-treatment method with nano-sized template (800 nm). This new type of plasma-treated PCL fiber mat has high potential as a biomaterial, and can be employed for various tissue engineering applications.
초발수성 식물표면에 존재하는 마이크로/나노구조 복제를 위한 전기장을 이용한 나노임프린팅 방법
전호준(HoJun Jeon),진규현(Gyuhyon Jin),윤현(Hyeon Yoon),김근형(GeunHyung Kim) 대한기계학회 2009 대한기계학회 춘추학술대회 Vol.2009 No.11
The technologies to fabricate micro/nano-patterned surface, such as electron beam lithography and nanoimprinting techniques, have been investigated several years. However, the nano-imprinting technology requiring high pressure during the process is not affordable to replicate micro/nano-surface of plant leaf due to the low stiffness of the leaf. In this study, we researched new technology to produce the hydrophobic nature of plant leaves on the surface of polydimethylsiloxane (PDMS). The micro/nano-patterned PDMS was fabricated by means of field-aided nano-imprint lithography (FA-NIL) technique. By varying the processing conditions of FA-NIT, we could obtain an optimized processing condition to attain hydrophobic surface of lotus leaf. The surface of the replicated PDMS was characterized using a scanning electron microscope (SEM) and surface roughness apparatus. We find that FA-NIL might be a good method to generate the soft micro/nano size structures, plant leaf.
진호준(HoJun Jin),전규현(Jeon GyuHyun),전승호(Seungho Jeon),서정택(Jung Taek Seo) ICT플랫폼학회 2023 ICT플랫폼학회 하계학술발표대회논문집 Vol.10 No.1
본 논문에서는 사물인터넷(IoT) 도메인에 대한 다단계 공격 탐지 프로세스를 제안한다. IoT는 봇넷 공격을 대상으로 하는 공격이 급증하고 있지만, 이에 대응하는 방법에 대한 연구가 부족하다. 우리의 목표는 IoT에서 공격을 빠르게 감지하고 대응할 수 있는 구조를 만드는 것을 목표로 한다. 또한 제안된 프로세스를 통해 IoT 위협 모델링에 대한 연구를 시작하고자 한다. 이 논문은 IoT 도메인에서 봇넷 공격을 분석, 탐지 및 대응하기 위한 5단계 프로세스를 제안한다. 논문의 핵심 제안 구간인 프레임워크에서는 MITRE ATT&CK의 Tactics와 Technique를 IoT에 맞게 본 논문에서는 제안한다. 프레임워크를 기반으로 봇넷 공격의 유형을 분석하고, 이를 통해 Defense Rules을 제안하고자 한다. IoT 대상 봇넷 탐지 프로세스를 통해 IoT 공격이 발생하고 난 이후 빠른 대응을 통한 대처 시스템 프로세스가 개발되는 것을 향후 연구의 목표로 한다.
Hot Deformation Behavior of V Micro‑Alloyed TWIP Steel During Hot Compression
Hojun Gwon,Sunmi Shin,Jongbae Jeon,Taejin Song,Sungkyu Kim,Bruno C. De Cooman 대한금속·재료학회 2019 METALS AND MATERIALS International Vol.25 No.3
High manganese twinning induced plasticity (TWIP) steel is an attractive material for automotive applications as its usecould result in an improved vehicle fuel efficiency and a superior passenger safety. Due to the limited research on the hotdeformation behaviour of High Mn steel, the selection of suitable operating conditions for the hot rolling process is challenging. The present contribution focusses on the hot deformation behaviour and the dynamic recrystallization kinetics of Vmicro-alloyed high manganese TWIP steel, by means of single-hit compression test in the temperature range of 850–1000 °Cand the strain rate range of 0.1–10 s−1. The activation energy for hot deformation and the processing map of a V-free TWIPsteel and a V-added TWIP steel were compared by analysing their stress–strain curves. The V-added TWIP steel exhibiteda higher activation energy than the V-free TWIP steel, i.e. 383.4 kJ/mol versus 372.5 kJ/mol. Processing maps based ona dynamic material model indicated that the hot workability of TWIP steel was decreased by micro-alloying with V. Theeffect of V on the hot deformation behaviour of TWIP steels was also analysed by means of its effect on the microstructureusing the SEM-EBSD technique. The V-added TWIP steel was characterized by a higher peak stress at a lower peak strainas compared to the V-free TWIP steel, indicating that the onset of dynamic recrystallization was accelerated by the additionof V. The rapid dynamic recrystallization kinetics resulted in a smaller recrystallized grain size in the hot deformed microstructureof the V-added TWIP steel.
Study on Distortion and Field of View of Contents in VR HMD
Hojun Son,Hyoung joon Jeon,Soonchul Kwon 한국인터넷방송통신학회 2017 Journal of Advanced Smart Convergence Vol.6 No.1
Recently, VR HMD (virtual reality head mounted display) has been utilized for virtual training, entertainment, vision therapy, and optometry. In particular, virtual reality contents are increasingly used for vision therapy and optometry. Accordingly, high-quality virtual reality contents such as a natural vision of life is required. Therefore, it is necessary to study the content production according to the optical characteristics of the VR HMD. The purpose of this paper is to suggest a proper FOV (field of view) of contents according to the distortion rate. We produced virtual reality contents and obtained distorted images by virtual camera. The distortion rate is calculated by using the distorted image. It is proved that the optimal FOV of the VR content with the minimum distortion is 90 ~ 100°. The results of this study are expected to be applied to the production of high quality contents.
Evaluation of cryogenic mechanical properties of aluminum alloy using small punch test
Hojun Cha,Seungmin Jeon,Donghyeon Yoon,Jisung Yoo,Seunggun Lee,Seokho Kim 한국초전도저온학회 2023 한국초전도저온공학회논문지 Vol.25 No.4
The Small Punch Test (SPT) was developed to evaluate the softening and embrittlement of materials such as power plants and nuclear fusion reactors by taking samples in the field. Specimens used in the SPT are very thin and small disk-shaped compared to specimens for general tensile test, and thus have economic advantages in terms of miniaturization and repeatability of the test. The cryogenic SPT can also be miniaturized and has a significantly lower heat capacity than conventional universal test machines. This leads to reduced cooling and warm-up times. In this study, the cryogenic SPT was developed by modifying the existing room temperature SPT to be cooled by liquid nitrogen using a super bellows and a thermal insulation structure. Since the cryogenic SPT was first developed, basic experiments were conducted to verify the effectiveness of it. For the validation, aluminum alloy 6061-T6 specimens were tested for mechanical properties at room and cryogenic temperature. The results of the corrected tensile properties from the SPT experiment results were compared with known room temperature and cryogenic properties. Based on the correction results, the effectiveness of the cryogenic SPT test was confirmed, and the surface fracture characteristics of the material were analyzed using a 3d image scanner. In the future, we plan to conduct property evaluation according to the development of various alloy materials.