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김시진(Sijin Kim),김학철(Hakchul Kim),김계환(Kyehwan Kim),박영훈(Younghoon Park),박선정(Sunjung Park),이동근(Donggeun Lee),김진곤(JinKon Kim),문희장(Heejang Moon),유영준(Youngjun You),권민찬(Minchan Kwon) 한국추진공학회 2016 한국추진공학회 학술대회논문집 Vol.2016 No.5
본 연구는 하이브리드 로켓 모터의 수중추진기관 적용을 위한 초기연구로 Lab-scale 하이브리드 로켓 모터를 이용하여 수중연소시험을 수행하였다. 3 m x 1 m x 1 m 크기의 수조 내 바닥면에서 55 cm 위에 연소기를 위치하여 수중연소시험을 수행하였으며 아크릴판으로 제작된 파열판(rupture disk)을 이용하여 연소실 초기 기밀을 유지하였다. 산화제는 액체아산화질소(LN2O), 연료는 HDPE를 사용하였고 KNSB 추진제를 이용하여 점화하였으며 연소시험은 총 5초간 진행되었다. 수중연소시험 결과 설계 추력에 근접하는 추력을 얻을 수 있음을 확인하였다. In this study, underwater combustion test was performed using a lab-scale hybrid rocket motor. The purpose of this study is to find out the feasibility of underwater propulsion using hybrid rocket system. Combustor was located underwater above 55cm from the bottom of water tank where the size of water tank is 3m X 1m X 1m. The combustor was sealed by installing acrylic plate rupture disk at the nozzle exit. LN2O and HDPE were used as oxidizer and solid fuel respectively, while the KNSB propellant was used as the ignitor source. The combustion duration was set to 5 seconds, and it was confirmed that the measured thrust of underwater combustion test was close to the design thrust.
Prediction of Settling Velocity of Nonspherical Soil Particles Using Digital Image Processing
Kim, Donggeun,Son, Younghwan,Park, Jaesung Hindawi Limited 2018 Advances in civil engineering Vol.2018 No.-
<P>Digital image processing (DIP) is used to measure shape properties and settling velocity of soil particles. Particles with diameters of 1 to 10 mm are arbitrarily sampled for the test. The size of each particle is also measured by a Vernier caliper for comparison with the classification results using the shape classification table. The digital images were taken with a digital camera (Canon EOS 100d). Shape properties are calculated by image analysis software. Settling velocity of soil particles is calculated by displacement and time difference of images during settling. The fastest settling particles are spherical shaped. Shape factors well explain the difference of settling velocity by a particle shape. In particular, the aspect ratio has a high negative correlation with residual of settling velocity versus mean diameter. Especially, DIP has a higher applicability than classification using the shape classification table because it can measure a number of particles at once. The settling velocity of soil particles is expressed as a function of mean diameter and aspect ratio.</P>
Kim, Jeonggeon,Goo, Yong-Rack,Choi, Indae,Kim, Songkil,Lee, Donggeun Elsevier 2019 INTERNATIONAL JOURNAL OF HEAT AND MASS TRANSFER - Vol.131 No.-
<P><B>Abstract</B></P> <P>A particle-reinforced composite material is a matrix with thermally conductive particles that has a diverse range of applications from electronics to energy harvesting/storage systems. In the engineering design of a particle-reinforced composite material for application, it is crucial to accurately and practically predict its effective thermal conductivity. Here, we report the development of a simple analytical model for predictions with improved accuracy and applicability. Comprehensive evaluation of existing models was first conducted to clarify their limitations in prediction accuracy and applicability to various experimental conditions. To overcome the challenges of the existing models, our new model was derived to consider the effect of shape, particle aggregation, and mutual interaction of particles on effective thermal conductivity. Lattice Boltzmann simulations were conducted to obtain a quasi-universal coefficient representing interactions of particles, whereas a shape coefficient characterizing microstructures of aggregated particles was obtained from experimental data available from literature. As a result, our model prediction outperformed the existing models in its prediction accuracy, and it could be applicable to any experimental circumstances where previous model predictions are inappropriate to use.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Comprehensive evaluation showed that existing models had their conditional limitations. </LI> <LI> The models were unacceptably degraded under conditions for electronics applications. </LI> <LI> We developed a new model to accurately predict effective thermal conductivity. </LI> <LI> The new model was self-consistent and described asymptotic behaviors of existing models. </LI> <LI> With an additional correlation, the new model was reasonably applicable to any conditions. </LI> </UL> </P>
Donggeun Kim,Sangwoo Park,Donggoo Kang,Joonki Paik 대한전자공학회 2020 IEIE Transactions on Smart Processing & Computing Vol.9 No.1
A single shot multibox detector (SSD) is used as a baseline for many object detection networks, since it can provide sufficiently high accuracy in real time. However, it cannot deal with objects of various sizes, because features used in an SSD are not robust to multi-scale objects. To solve this problem, we present an improved feature pyramid for using multi-scale context information. The proposed feature pyramid fuses only adjacent features of the conventional SSD to achieve high accuracy without decreasing the processing speed. Our detector, with a 320×320 input, achieved 79.1% mean average precision (mAP) at 63 frames per second on a Pascal Visual Object Classes Challenge 2007 test set using a single Nvidia 1080 Ti graphics processing unit. This result shows better performance than existing SSDs.
Kim, Donggeun,Son, Younghwan,Park, Jaesung,Kim, Taejin,Jeon, Jihun Hindawi Limited 2019 Advances in civil engineering Vol.2019 No.-
<P>The objective of this study is to monitor the water content of soil quickly and accurately using a UAV. Because UAVs have higher spatial and temporal resolution than satellites, they are currently becoming more useful in remote sensing areas. We developed a water content estimation equation using the color of the soil and suggested a calibration method for field application. Since the resolution of the images taken by the UAV is different according to the altitude, the water content estimation formula is developed by using the images taken at each altitude. In order to calibrate the color difference according to lighting conditions, the calibration method using field data were proposed. The results of the study showed an altitude-specific estimation equation using RGB values of the UAV image through linear regression. The appropriate number of field data needed for calibration for site application of the estimation equation was found between 4 and 10. On-site application results of the proposed calibration method showed RMSE accuracy of 1.8 to 2.9%. Thus, the water content estimation and calibration method proposed in this study can be used in effectively monitoring the water content of soil using UAVs.</P>
Kim, Hyun-Sook,Suh, Kwang Sik,Sul, Donggeun,Kim, Byung-Jo,Lee, Seung Kwan,Jung, Woon-Won D.A. Spandidos 2012 INTERNATIONAL JOURNAL OF MOLECULAR MEDICINE Vol.29 No.2
<P>Osteoblastic bone formation and osteoclastic bone resorption are in balance to maintain a constant, homeostatically controlled amount of bone. Excessive bone resorption by osteoclasts is involved in the pathogenesis of bone-related disorders. In the present study, we evaluated the inhibitory effects of glabridin, a flavonoid purified from licorice root, on the receptor activator of nuclear factor-κB ligand (RANKL)-induced osteoclast differentiation and its molecular mechanisms in murine osteoclast progenitor RAW264.7 cells. Glabridin significantly inhibited RANKL-induced tartrate-resistant acid phosphatase (TRAP) activity, the formation of multinucleated osteoclasts and resorption-pit formation. In mechanistic studies of the anti-osteoclastogenic potential of glabridin, we found that glabridin inhibited RANKL-induced expression of c-Fos and subsequent expression of NFATc1, which is a master regulator of osteoclastogenesis. Interestingly, glabridin inhibited the RANKL-induced expression of signaling molecules (TRAF6, GAB2, ERK2, JNK1 and MKK7) and osteoclast survival-related signaling pathways such as c-Src, PI3K and Akt2. Glabridin also inhibited the bone resorptive activity of mature osteoclasts by inhibiting osteoclast-associated genes (cathepsin?K, MMP-9, CAII, TCIRG1, OSTM1 and CLCN7). Taken together, our data suggest that glabridin holds great promise for use in preventing osteoclastogenesis by inhibiting RANKL-induced activation of signaling molecules and subsequent transcription factors in osteoclast precursors and these findings may be useful for evaluating treatment options in bone-destructive diseases.</P>
Role of Autophagy in Endothelial Damage and Blood–Brain Barrier Disruption in Ischemic Stroke
Kim, Kyeong-A,Shin, Donggeun,Kim, Jeong-Hyeon,Shin, Young-Jun,Rajanikant, G.K.,Majid, Arshad,Baek, Seung-Hoon,Bae, Ok-Nam American Heart Association, Inc. 2018 Stroke Vol.49 No.6
<P>The global burden of neurological diseases including stroke has significantly increased, 1 and an urgent need exists to develop new treatment strategies. Impairment of autophagic regulation has been observed in diseases including neurodegenerative diseases and ischemic stroke, suggesting that modulation of autophagy could be a potential therapeutic target. 2 Endothelial cells (ECs) maintain homeostasis by regulating the vascular tone and permeability and endothelial dysfunction is associated with diverse cardiovascular diseases (CVDs). The integrity of the blood-brain barrier (BBB), which shows selective permeability for substances into the brain, is significantly impaired under ischemic stroke. This review focuses on autophagy in endothelial dysfunction in the context of ischemic stroke and potential targets for therapeutic manipulation.</P>
LATTICE INSTABILITIES OF BaTiO 3 /SrTiO 3 ARTIFICIAL SUPERLATTICE
KIM, LEEJUN,KIM, JUHO,WAGHMARE, UMESH,JUNG, DONGGEUN,LEE, JAICHAN Gordon and Breach Science Publishers 2005 Integrated ferroelectrics Vol.73 No.-
<P>We have investigated lattice instabilities of ultra-short period BaTiO 3 /SrTIO 3 (BTO/ STO) artificial superlattice (double-perovskite 10-atom unit cell) as a function of epitaxial strain using first-principles density functional theory (DFT) calculations based on pseudopotentials and a plane-wave basis. We find a structural transition from the tetragonal phase at compressive strain to the monoclinic phase at tensile strain. In the tetragonal phase, the Ti ions displacement patterns of the BTO/STO superlattice show ferrielectric phase behavior. Likewise, those of the monoclinic BTO/STO superlattice along [001] direction are very similar to the tetragonal BTO/STO superlattice. However, the displacement patterns in the xy -plane BTO/STO superlattice exhibit different behavior which both Ti ions displace parallely along [110] direction and against direction of oxygen displacements. It means that the monoclinic phase of BTO/STO superlattice is ferrielectric along [001] direction similar to tetragonal BTO/STO superlattice, but is ferroelectric in the xy- plane.</P>