• 한국화재소방학회논문지
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• 제23권1호
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• pp.55-62
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• 2009

층류영역의 분출유량에서 큰 가진강도 효과를 얻기 위해 연료관 관 공명주파수로 가진된 비예혼합 분류 화염의 일반적인 가진 연소특성을 실험적으로 조사하였다. 화염 안정화 특성에서는 두 가지 형태의 부상 특성이 존재하는 사실을 알았는데, 화염이 부상되는 가진강도 크기에서 한 쪽은 감소, 다른 영역에서는 증가하는 것으로 나타나 각각 서로 다른 부상기구가 존재함을 확인할 수 있었다. 특히 부상되지 않고 노즐에 부착된 분출유량 영역에서의 가진 연소특성을 가진 강도에 따른 화염 길이와 형상, 유동장 응답 특성 그리고 노즐 출구에서의 유속 분포를 중심으로 집중 조사하였다. 특이한 현상으로는 가진 강도 증가에 따라 화염의 신장과 in-burning 현상 그리고 화염 내 거동 와동들의 말림방향이 서로 역전되는 현상 등이 발견되었다. 노즐 출구의 유속분포와 가시화 기법을 통해 이러한 현상들이 노즐관 관벽 안쪽서부터 음의 속도가 발생하기 시작함에 따라 주변 산화제인 공기가 노즐관 안으로 유입되는 현상과 관련되는 것으로 파악되었다.

• 대한방사선기술학회지:방사선기술과학
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• 제27권4호
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• pp.31-35
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• 2004

PVDF[poly(vinylidene fluoride)] 압전소자로 제작된 초음파 변환기를 이용하여 초음파 spectroscopy 측정시스템을 제작하였다. 이 장치를 이용하여 MBBA(p-methoxy benzylidene-p-n-butylaniline) 액정의 nematic-isotropic 상전이 현상을 관측한 결과 상전이 온도가 $47^{\circ}C$임을 확인하였으며, 기존의 광학적 방법에 의해 관측된 값과 잘 일치하였다. 한편으로 상전이 점의 주파수 의존성을 확인하였으나 이는 관측되지 않았으며, 단지 PVDF 압전소자의 공진주파수인 2 MHz에서 초음파의 진폭이 최대로 나타났으며, 다른 주파수에서는 진폭이 감소함을 알 수 있었다. 이와 같이 온도의 변화에 따른 액정의 상전이 현상을 초음파 감쇠의 변화로 확인하여 보았다. 이것은 액정의 상전이 메카니즘을 해석함에 있어 PVDF 초음파 변환기를 이용한 spectroscopy 측정 시스템은 매우 유용한 도구로 이용될 수 있음을 확인하였으며, 의료용으로 이용할 경우 겸상세포 빈혈증이나 동맥 경화증과 같은 질병 진단에 이용 가능하리라 여겨진다.

• 전자공학회논문지SC
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• 제39권3호
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• pp.228-238
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• 2002

본 논문은 메탈 할라이드 램프용 고주파 변조 방식 전자식 안정기의 디지털 제어기에 관한 것이다. 제안한 디지털 제어기에는 소프트 스타팅, 무부하 보호, 과전류 보호, 전력 제어 알고리즘이 포함되어 있다. 또한 제안한 디지털 제어기는 고주파 변조 제어 및 공명 현상회피 알고리즘을 수행한다. ASIC을 이용한 저가 양산을 위하여 제안한 제어기는 마이크로프로세서를 이용하지 않고 단지 FPGA만을 사용하여 설계하였다. 본 논문에서는 구체적인 디지털 제어 알고리즘들을 기술하였으며 프로토 타입의 150w 메탈 할라이드 램프용 전자식 안정기의 실험 결과를 나타내었다.

• 한국해안해양공학회지
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• 제6권2호
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• pp.139-149
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• 1994

본 논문에서는 항만 부진동현상을 예측할 수 있는 무한요소를 이용한 유한요소기법에 대해서 연구하였다. 지배방정식으로는 완경사방정식을 사용하였으며, 고체경계면에서의 에너지 손실효과를 고려하기 위하여 부분반사조건을 도입하였다. 외부영역 무한경계조건을 효율적으로 처리하기 위하여 새로운 무한요소를 개발하였다. 개발된 무한요소의 형상함수는 해석적 도유함수의 급수해의 진행파항을 나타내는 제 1종 Hankel 함수의 점근적 형태를 사용하여 결정하였다. 수치해석상의 효율성을 제고하기 위하여 무한요소의 시스템행렬 구성시 나타나는 무한방향으로의 적분을 해석적으로 수행하였다. 기존의 수리실험 및 타 수치모형 결과와의 비교를 통하여 본 연구에서 개발한 무한요소에 기초한 수치모형의 타당성을 입증하였다. 또한 해석의 효율성과 정도에 직접적으로 영향을 주는 무한요소의 위치결정에 대한 수치실험도 수행하였다.

• 전기학회논문지
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• 제66권12호
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• pp.1844-1851
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• 2017

As the capacity of the wireless power transmission increases, a higher supply current which may induce current in nearby conductive parts requires. Induced current may affect electric shock to the human body and malfunction of the electrical equipment. In order to prevent such induced phenomena as a risk factor, shielding is required between the source of the wireless power transmission and the conductive parts. The resonance frequency for the large capacity wireless power transmission has the wavelength of several hundred meters, so most environments are included in the near-field area. By wave impedance, the electric field has higher density in the near-field area and needs to be analyze for protecting. For this purpose, it is necessary to select a substance having a larger electric conductivity and optimized shielding structure. In this paper, an aluminum base shielding structure was presented to conduct experiments on thickness, position, and heat dissipation. In the 35 kW, 60 kHz environments, the optimized 5T Al base shielding structure attenuates the induced current to 43 %.

• Bulletin of the Korean Chemical Society
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• 제2권2호
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• pp.71-75
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• 1981

Vacuum ultraviolet photolysis of ethyl bromide was studied at 104.8-106.7 nm (11.4-11.6 eV) in the pressure range of 0.2-18.6 torr at $25^{\circ}$ using an argon resonance lamp with and without additives, i.e., NO and He. Since the ionization potential of $CH_3CH_2Br$ is lower than the photon energy, the competitive processes between the photoionization and the photodecomposition were also investigated. The observations indicated that 50% of absorbed light leads to the former process and the rest to the latter one. In the absence of NO the principal reaction products for the latter process were found to be $CH_4, C_2H_2, C_2H_4, C_2H_6, and C_3H_8$. The product quantum yields of these reaction products showed two strikingly different phenomena with an increase in reactant pressure. The major products, $C_2H_4$ and $C_2H_6$, showed positive effects with pressure whereas the effects on minor products were negative in both cases, i.e., He and reactant pressures. Addition of NO completely suppresses the formation of all products except $C_2H_4$ and reduces the $C_2H_4$ quantum yield. These observations are interpreted in view of existence of two different electronically excited states. The initial formation of short-lived Rydberg transition state undergoes HBr molecular elimination and this state can across over by collisional induction to a second excited state which decomposes exclusively by carbon-bromine bond fission. The estimated lifetime of the initial excited state was ${\sim}4{\times}10^{-10}$ sec. The extinction coefficient for $CH_3CH_2Br$ at 104.8-106.7 nm and $25{\circ}$ was determined to be ${varepsilon} = (1/PL)ln(I_0/I_t) = 2061{\pm}160atm^{-1}cm6{-1}$ with 95% confidence level.

• 대한방사선기술학회지:방사선기술과학
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• 제41권6호
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• pp.553-560
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• 2018

PET-CT and PET-MRI which integrates CT using ionized radiation and MRI using phenomena of magnetic resonance are determined to have the limitation to apply the semi-quantitative index, standardized uptake value (SUV), with the same level due to the fundamental differences of image capturing principle and reorganization, hence, their correlations were analyzed to provide their clinical information. To 30 study subjects maintaining pre-treatment, $^{18}F-FDG$ (5.18 MBq/㎏) was injected and they were scanned continuously without delaying time using $Biograph^{TM}$ mMR 3T (Siemens, Munich) and Biograph mCT 64 (Siemens, Germany), which is an integral type, under the optimized condition except the structural differences of both scanners. Upon the measurement results of $SUV_{max}$ setting volume region of interest with evenly distributed radioactive pharmaceuticals by captured images, $SUV_{max}$ mean values of PET-CT and PET-MRI were $2.94{\pm}0.55$ and $2.45{\pm}0.52$, respectively, and the value of PET-MRI was measured lower by $-20.85{\pm}7.26%$ than that of PET-CT. Also, there was a statistically significant difference in SUVs between two scanners (P<0.001), hence, SUV of PET-CT and PET-MRI cannot express the clinical meanings in the same level. Therefore, in case of the patients who undergo cross follow-up tests with PET-CT and PET-MRI, diagnostic information should be analyzed considering the conditions of SUV differences in both scanners.

• International Journal of Naval Architecture and Ocean Engineering
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• 제12권1호
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• pp.213-225
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• 2020

Floating Offshore Wind Turbines (FOWT) installed in the deep sea regions where stable and strong wind flows are abundant would have significantly improved energy production capacity. When designing FOWT, it is essential to understand the stability and motion performance of the floater. Water tank model tests are required to evaluate these aspects of performance. This paper describes a model test and numerical simulation for a 750-kW semi-submersible platform wind turbine model-II. In the previous model test, the 750-kW FOWT model-I suffered slamming phenomena from extreme wave conditions. Because of that, the platform freeboard of model-II was increased to mitigate the slamming load on the platform deck structure in extreme conditions. Also, the model-I pitch Response Amplitude Operators (RAO) of simulation had strong responses to the natural frequency region. Thus, the hub height of model-II was decreased to reduce the pitch resonance responses from the low-frequency response of the system. Like the model-I, 750-kW FOWT model-II was built with a 1/40 scale ratio. Furthermore, the experiments to evaluate the performance characteristics of the model-II wind turbine were executed at the same location and in the same environment conditions as were those of model-I. These tests included a free decay test, and tests of regular and irregular wave conditions. Both the experimental and simulation conditions considered the blade rotating effect due to the wind. The results of the model tests were compared with the numerical simulations of the FOWT using FAST (Fatigue, Aerodynamics, Structures, and Turbulence) code from the National Renewable Energy Laboratory (NREL).

• 마이크로전자및패키징학회지
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• 제29권1호
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• pp.55-59
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• 2022

본 논문에서는 플라즈몬 공명 현상을 통하여 나노 입자 주변의 전기장을 증폭시키며, 흡광률을 높일 수 있는 구조를 시간영역 유한차분(FDTD)시뮬레이션을 이용하여 나노입자를 평면에 배열하였을 때와 비교하여 나노 구조에 배열하였을 때의 전기장과 흡광도를 비교하였다. 또한 나노구조의 폭을 240 nm ~ 300 nm로 조절하여 입자간의 간격이 좁을수록 광 흡수율이 높음을 보이고자 하였다. 또한 UV 임프린트를 통하여 나노 입자와 나노 구조를 표면에 함께 형성시키는 방법에 대한 연구를 진행하였다. 해당 구조에 입자를 형성하기 위하여 스프레이 코팅을 이용하여 나노 입자를 구조 제작에 사용되는 몰드에 먼저 배열한 후, UV 임프린팅을 통해 제작하였고 나노구조와 입자가 함께 형성됨을 Scanning Electron Microscopy 로 확인하였다.

• Asian Journal of Atmospheric Environment
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• 제7권2호
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• pp.65-71
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• 2013

Japanese cedar (Cryptomeria japonica) pollinosis is the most popular pollinosis in Japan. It has been reported that Cryptomeria japonica pollen allergenic species are suspended as fine particles in the urban atmosphere. These allergenic fine particles are responsible for inducing asthma by breaking into the lower respiratory tract. It has also been found that pollinosis symptoms on the sufferers appear mainly at night-time by the results from epidemiological studies. However, the exact reason for these phenomena is not yet clarified. In this study, the diurnal and nocturnal behaviours of Cryptomeria japonica pollen grains and their allergenic species in the urban area of Saitama city of Kanto Plain were investigated. Airborne pollen grains and allergenic Cry j 1 concentrations in total suspended particulate matter (TSP) were investigated at two sampling sites, a heavy traffic road (roadside site) and at the balcony of the $10^{th}$ floor of the Building of Research and Project of Saitama University (general urban site). The latter sampling site where located about 300 m away from the roadside site was used as a general urban site unaffected by automobile traffic. The airborne pollen counts were measured with a real-time pollen monitor. Cry j 1 particles were collected with two high volume air samplers, and these concentrations were measured by surface plasmon resonance method with a Biacore J system. The diurnal variation of the airborne pollen counts was similar to the trends of temperature and wind speed during the day-time; whereas its tendency with wind speed trend was not observed during the night-time. Airborne pollen counts were lower with northern wind than with southern wind because the pollen comes from the mountainous areas, and the mountains in the south are closer, about half the distance to the northern mountains. It is suggested that the peaks of airborne pollen counts during night-time in the sampling site occurred by transport of pollen grains released during day-time in the mountainous forest areas, located c.a. 100 km away from the sampling site. On the roadside site the allergenic Cry j 1 concentrations were higher than at the general urban site, nevertheless pollen grains counts were lower. These results suggested that worsening of pollinosis symptoms during night-time in urban area was caused by transport of pollen grains during day-time in the mountainous forest areas. Moreover, pollen allergenic species become different morphology from pollen grain at roadside site, and the subsequent pollen grains re-suspension by automobile traffic.