회전구동부 충격 흡수를 위한 고탄성 쿠션 개발

남윤욱 ( Yoonwook Nam ),손기중 ( Kijoong Son ),박범희 ( Bumhee Park ) 한국품질경영학회 2017 한국품질경영학회 학술대회 Vol.2017 No.1

Nuclear Reactor Transient Analysis by Continuous-Energy Monte Carlo Calculation Based on Predictor-Corrector Quasi-Static Method

Jo, YuGwon,Cho, Bumhee,Cho, Nam Zin Academic Press 2016 Nuclear science and engineering Vol.183 No.2

<P>The continuous-energy Monte Carlo (MC) method is gaining attention not only for nuclear reactor statics but also for transient analysis, as computing power increases with the use of massive parallel computers. This paper presents a practical and accurate MC transient analysis method for heterogeneous, continuous-energy reactor transient problems, based on the predictor-corrector quasi-static (PCQS) method. The transient fixed-source problem of the PCQS method is solved by MC calculation with fission source iteration, where the partial current-based coarse-mesh finite difference (p-CMFD) method is used both to accelerate the convergence of the fission source distributions and to diagnose whether the fission source iteration diverges because of too large a macro-time-step size used for a positive reactivity insertion. To improve the convergence of the fission source iteration, exponential transformation is also applied. In addition, the variances of MC tallies can be reduced by increasing the number of active fission source iterations. For method and code verification, the PCQS method for the MC calculation with fission source iteration is compared with the implicit Euler method for a method-of-characteristics calculation on a two-dimensional TWIGL problem. For both multigroup energy and continuous-energy three-dimensional test problems, the proposed method efficiently reduces computing time with a large macro-time-step size, while the accuracy of the solutions is maintained, compared with those calculated with smaller macro-time-step sizes.</P>

Synthesis of nanograined ZnO nanorods functionalized with NiO nanoparticles and their enhanced hydrogen sensing properties

Jeong Gyujin,Kim Sanghyun,Nam Bumhee,Lee Chongmu 한국물리학회 2021 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.78 No.4

NiO nanoparticle (NP)-functionalized nanograined ZnO nanorods (NRs) were grown by using the thermal evaporation of ZnSe powders; this was followed by the thermal oxidation of the ZnSe NRs to synthesize ZnO NRs and a solvothermal process for NiO functionalization. The diameters of the grains in the synthesized nanograined ZnO NRs are in the range of 50–150 nm. The ZnO grains were not spherical, but they were shaped like rice grains. The diameters and the lengths of the ZnO NRs were in the range of 40–50 nm and 1–6 μm, respectively. The diameters of the NiO NPs were in the range of 40–80 nm. A multiple-networked chemiresistive sensor was fabricated by pouring the IPA solution containing NiO NPdecorated nanograined ZnO NRs onto SiO2/ Si substrates with a patterned electrode. A pristine nanograined ZnO NR sensor was also prepared in a similar manner. The NiO NP-functionalized nanograined ZnO NR sensor exhibited a greater and faster response to H2, as compared to its pristine nanograined ZnO counterpart; it also showed higher selectivity toward H2 against other reducing gases, as compared to the pristine nanograined ZnO counterpart. Herein, the origin of the enhanced sensing performance of the NiO NP-functionalized nanograined ZnO sensor is discussed in detail.

High Thermal Conductive Natural Rubber Composites Using Aluminum Nitride and Boron Nitride Hybrid Fillers

( June-young Chung ),( Bumhee Lee ),( In-kyung Park ),( Hyun Ho Park ),( Heon Seob Jung ),( Joon Chul Park ),( Hyun Chul Cho ),( Jae-do Nam ) 한국고무학회 2020 엘라스토머 및 콤포지트 Vol.55 No.1

Herein, we investigated the thermal conductivity and thermal stability of natural rubber composite systems con­taining hybrid fillers of boron nitride (BN) and aluminum nitride (AlN). In the hybrid system, the bimodal distribution of polygonal AlN and planar BN particles provided excellent filler-packing efficiency and desired energy path for phonon transfer, resulting in high thermal conductivity of 1.29 W/mK, which could not be achieved by single filler composites. Fur­ther, polyethylene glycol (PEG) was compounded with a commonly used naphthenic oil, which substantially increased ther­mal conductivity to 3.51 W/mK with an excellent thermal stability due to facilitated energy transfer across the filler-filler interface. The resulting PEG-incorporated hybrid composite showed a high thermal degradation temperature (T₂) of 290℃, a low coefficient of thermal expansion of 26.4 ppm/℃, and a low thermal distortion parameter of 7.53 m/K, which is well over the naphthenic oil compound. Finally, using the Fourier's law of conduction, we suggested a modeling methodology to evaluate the cooling performance in thermal management system.

NO2 sensing properties of WO3-decorated In2O3 nanorods and In2O3-decorated WO3 nanorods

이중무,현승균,Tae-Kyoung Ko,Bumhee Nam 나노기술연구협의회 2019 Nano Convergence Vol.6 No.40

n2O3 nanoparticle (NP)-decorated WO3 nanorods (NRs) were prepared using sol–gel and hydrothermal methods. The In2O3 NRs and WO3 NPs were crystalline. WO3 NP-decorated In2O3 NRs were also prepared using thermal evaporation and hydrothermal methods. The NO2 sensing performance of the In2O3 NP-decorated WO3 NR sensor toward NO2 was compared to that of the WO3 NP-decorated In2O3 NR sensor. The former showed a high response to NO2 due to a significant reduction of the conduction channel width upon exposure to NO2. In contrast, the latter showed a far less pronounced response due to limited reduction of the conduction channel width upon exposure to NO2. When the sensors were exposed to a reducing gas instead of an oxidizing gas (NO2), the situation was reversed, i.e., the WO3 NP-decorated In2O3 NR exhibited a stronger response to the reducing gas than the In2O3 NP-decorated WO3 NR sensor. Thus, a semiconducting metal oxide (SMO) with a smaller work function must be used as the decorating material in decorated heterostructured SMO sensors for detection of oxidizing gases. The In2O3 NP-decorated WO3 NR sensor showed higher selectivity for NO2 compared to other gases, including reducing gases and other oxidizing gases, as well as showed high sensitivity to NO2.

Effects of Particle Size on the NO2 Gas Sensing Properties of NiO Nanoparticle-Decorated SnO2 Nanorods

Choi Kyeongbin,Jeong Gyujin,Hyun Soong Keun,Nam Bumhee,Ko Tae Kyung,Lee Chongmu 한국물리학회 2020 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.77 No.6

This study reports the effects of NiO nanoparticle (NP) size on the sensing performance of NiO NP-decorated SnO2 nanorods (NRs). NiO NP-decorated SnO2 NRs were synthesized using a two-step process: 1) thermal evaporation of tin powders in an oxidizing atmosphere based on the vapor-liquid-solid growth mechanism and 2) solvothermal decoration of SnO2 NRs with NiO NPs. X-ray diffraction and transmission electron microscopy analyses revealed that both the SnO2 NRs and the NiO NPs were polycrystalline. Scanning electron microscopy images showed that the diameters of the NRs ranged from 100 to 200 nm and that those of the small and the large NiO NPs ranged from 20 to 30 nm and from 80 to 180 nm, respectively. The small NiO NP-decorated SnO2 NRs showed stronger response to NO2 than did the large NiO NP-decorated SnO2 NRs over the concentration range of 0.5 - 100 ppm. Decoration of SnO2 NRs with small NiO NPs resulted in enhanced sensing performance whereas decoration of SnO2 NRs with large NiO NPs deteriorated the sensing performance. The superior NO2 gas sensing performance of the small NiO NP-decorated SnO2 NR sensor as compared to that of the large NiO NP-decorated SnO2 NR sensor was attributed to a higher ratio of n-SnO2 to p-NiO and a higher number of p-n heterojunctions for the same volume of NiO in the former than in the latter. In addition, the small NiO NP-decorated SnO2 NR sensors showed selectivity toward NO2 against other competing gases such as SO2, CO2, CO, H2, C7H8 and C6H6.