• Radiation Oncology Journal
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• 제13권3호
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• pp.277-283
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• 1995

목적 : 임상 방사선치료에서 병소선량은 인체 연부조직의 방사선흡수와 유사한 수조펜텀에서 측정환산된 흡수선량자료를 이용하여 얻어지고 있으며, 방사선 치료부위내 공기층 또는 밀도가 낮은 폐조직 주위에 종양이 존재할 경우 공기층과 만나는 종양의 경계면 선량은 rebuild-up에 의해 낮아질 수 있으나 현재까지 연구 발표된 것은 많지 않다. 이에 본 연구에서는 6, 10 메가볼트 광자선을 이용하여 조직 불균질층 경계면 선량을 실험적으로 측정하여 종양선량에 미치는 영향을 분석하여 방사선 치료선량 결정에 이용하고자 하였다. 방법 : 고에너지 광자선의 조사면내 조직 불균질성에 의한 선량변화를 얻기 위하여 조직층에 해당되는 폴리스티렌 고체펜텀의 두께가 각각 10, 30, 50 mm 인 경우 공기층의 두께를 10, 20, 30, 50 mm 로 변화시켜서, 이러한 조직층과 공기층을 지나 종양의 가장자리에 해당되는 수조펜텀의 표면에 도달되는 방사선량을 평행평판형전리함으로 측정하였다. 방사선 조사면적은 임상에서 비교적 많이 이용되는 $5{\times}5,\;10{\times}10,\;20{\times}20\;cm^2$를 사용하였다. 결과 : 방사선 조사면적 $5{\times}5\;cm^2$ 이고 조직층 두께 30 mm 일때 6 메가볼트 광자선에서 공기층 두께변화에 따른 표면선량 변화는 표준선량보다 공기층 10 mm 에서는 $1.1\%$, 50 mm 에서는 $29.1\;\%$ 낮아졌으며 공기층 두께가 두꺼워질수록 방사선량 감소가 현저했다. 같은 조건에서 10 메가볼트 광자선에서 선량변화는 표준선량보다 $4.2\%$에서 $33.9\%$ 까지 낮아졌다. 동일 깊이에서 표준심부선량에 대한 불균질 조직층 선량의 비인 OER 은 조사면적 10{\times}10\;cm^2$ 이상에서는 1 보다 크거나 1 에 가까운 값을 보였다. 결론 : 방사선 조사면적이 커지면 공기층과 인접한 조직 경계면의 선량감소는 거의 나타나지 않으며, $10{\times}10\;cm^2$ 이하의 소조사면 치료시 조직 경계면의 종양에 대한 치료선량 평가에는 rebuild-up 효과를 고려하여야 될 것으로 생각된다. 임상에서 6 메가볼트 광자선을 사용하여 공기층이 존재하는 구강과 인후두 종양을 치료할 때, 공기층에 인접한 점막층 (1-3 mm) 의 선량은 표준선량에 비해 $29\%$ 까지 적게 도달될 수 있으므로 방사선 치료선량 결정에 이러한 곁과를 필히 고려하여야 될 것으로 사료된다.

• 한국추진공학회:학술대회논문집
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• 한국추진공학회 2011년도 제36회 춘계학술대회논문집
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• pp.1-2
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• 2011

Hybrid rockets have lately attracted attention as a strong candidate of small, low cost, safe and reliable launch vehicles. A significant topic is that the first commercially sponsored space ship, SpaceShipOne vehicle chose a hybrid rocket. The main factors for the choice were safety of operation, system cost, quick turnaround, and thrust termination. In Japan, five universities including Hokkaido University and three private companies organized "Hybrid Rocket Research Group" from 1998 to 2002. Their main purpose was to downsize the cost and scale of rocket experiments. In 2002, UNISEC (University Space Engineering Consortium) and HASTIC (Hokkaido Aerospace Science and Technology Incubation Center) took over the educational and R&D rocket activities respectively and the research group dissolved. In 2008, JAXA/ISAS and eleven universities formed "Hybrid Rocket Research Working Group" as a subcommittee of the Steering Committee for Space Engineering in ISAS. Their goal is to demonstrate technical feasibility of lowcost and high frequency launches of nano/micro satellites into sun-synchronous orbits. Hybrid rockets use a combination of solid and liquid propellants. Usually the fuel is in a solid phase. A serious problem of hybrid rockets is the low regression rate of the solid fuel. In single port hybrids the low regression rate below 1 mm/s causes large L/D exceeding a hundred and small fuel loading ratio falling below 0.3. Multi-port hybrids are a typical solution to solve this problem. However, this solution is not the mainstream in Japan. Another approach is to use high regression rate fuels. For example, a fuel regression rate of 4 mm/s decreases L/D to around 10 and increases the loading ratio to around 0.75. Liquefying fuels such as paraffins are strong candidates for high regression fuels and subject of active research in Japan too. Nakagawa et al. in Tokai University employed EVA (Ethylene Vinyl Acetate) to modify viscosity of paraffin based fuels and investigated the effect of viscosity on regression rates. Wada et al. in Akita University employed LTP (Low melting ThermoPlastic) as another candidate of liquefying fuels and demonstrated high regression rates comparable to paraffin fuels. Hori et al. in JAXA/ISAS employed glycidylazide-poly(ethylene glycol) (GAP-PEG) copolymers as high regression rate fuels and modified the combustion characteristics by changing the PEG mixing ratio. Regression rate improvement by changing internal ballistics is another stream of research. The author proposed a new fuel configuration named "CAMUI" in 1998. CAMUI comes from an abbreviation of "cascaded multistage impinging-jet" meaning the distinctive flow field. A CAMUI type fuel grain consists of several cylindrical fuel blocks with two ports in axial direction. The port alignment shifts 90 degrees with each other to make jets out of ports impinge on the upstream end face of the downstream fuel block, resulting in intense heat transfer to the fuel. Yuasa et al. in Tokyo Metropolitan University employed swirling injection method and improved regression rates more than three times higher. However, regression rate distribution along the axis is not uniform due to the decay of the swirl strength. Aso et al. in Kyushu University employed multi-swirl injection to solve this problem. Combinations of swirling injection and paraffin based fuel have been tried and some results show very high regression rates exceeding ten times of conventional one. High fuel regression rates by new fuel, new internal ballistics, or combination of them require faster fuel-oxidizer mixing to maintain combustion efficiency. Nakagawa et al. succeeded to improve combustion efficiency of a paraffin-based fuel from 77% to 96% by a baffle plate. Another effective approach some researchers are trying is to use an aft-chamber to increase residence time. Better understanding of the new flow fields is necessary to reveal basic mechanisms of regression enhancement. Yuasa et al. visualized the combustion field in a swirling injection type motor. Nakagawa et al. observed boundary layer combustion of wax-based fuels. To understand detailed flow structures in swirling flow type hybrids, Sawada et al. (Tohoku Univ.), Teramoto et al. (Univ. of Tokyo), Shimada et al. (ISAS), and Tsuboi et al. (Kyushu Inst. Tech.) are trying to simulate the flow field numerically. Main challenges are turbulent reaction, stiffness due to low Mach number flow, fuel regression model, and other non-steady phenomena. Oshima et al. in Hokkaido University simulated CAMUI type flow fields and discussed correspondence relation between regression distribution of a burning surface and the vortex structure over the surface.

• 청정기술
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• 제27권4호
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• pp.350-358
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• 2021

본 연구결과에서 연소로 내 온도가 848.27 ~ 1,026.80 ℃ 범위로써 평균 976.61 ℃으로 나타났으며, 온도증가에 따라 NOx 농도는 증가하는 경향으로 나타났다. 요소 사용량은 291.00 ~ 693.00 kg d^-1로 평균 542.34 kg d^-1로 나타났으며, 요소 사용량의 증가에 따라 NOx 농도는 감소하는 경향으로 나타났다. 체류시간이 3.38 ~ 9.17 s로 평균 약 5.22 s로써 설계시 고려한 2 s이내 보다 약 2.61 배 크게 나타났다. 이는 SRF 투입량 허가조건인 1,950 kg h^-1 대비 평균 SRF 투입량이 약 55.71%인 1,086 kg h^-1로써 연소실 면적은 일정하나 SRF 연소량의 감소에 따라 배가스량 감소에 따른 체류시간이 증가하는 것으로 판단된다. O₂/CO 비는 847.05 ~ 14,877.34로 평균 3,111.30으로 나타났고, O₂/CO 비 증가에 따라 NOx 농도는 다소 증가하는 경향으로 나타났다. 온도증가와 O₂/CO 비의 증가에 공기 중 질소 성분과의 연소반응이 증가하여 NOx 농도가 다소 증가하였으며, 요소 투입량 증가와 체류시간이 증가할수록 배가스의 NOx와의 반응량이 증가하여 처리 후의 NOx 농도는 다소 감소하는 경향으로 나타났다. TMS 자료에 의한 굴뚝 출구에서의 NOx 농도는 7.88 ~ 34.02 ppm으로 평균 19.92 ppm으로써 배출허용기준 60 ppm 이내로 배출되었다. NOx 배출계수는 1.058 ~ 1.795 kg ton^-1으로써 평균 1.450 kg ton^-1으로 나타났다. 본 연구결과 NOx 배출계수는 기타 고체연료인 최대 배출계수 5.830 kg ton^-1 약 24.87%로 나타났으며, 기타 합성수지류와 기타 사업장폐기물의 배출계수인 1.817 kg ton^-1, 3.322 kg ton^-1 대비 각각 79.80%, 43.65%로 나타났다. 기 유사 연구결과인 NIER 고시(2005-9)의 RDF 배출계수인 1.400 kg ton^-1과 유사하게 나타났으며, 최대로 나타난 SRF의 경우인 배출계수 13.210 kg ton^-1에 비해 약 10.98%로 나타났다. 따라서 NOx의 배출계수는 편차가 크게 나타났다.

• Journal of Ecology and Environment
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• 제42권4호
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• pp.210-218
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• 2018

Background: Soil respiration (Rs) is a major factor of the absorption and accumulation of carbon through photosynthesis in the ecosystem carbon cycle. This directly affects the amount of net ecosystem productivity, which affects the stability and sustainability of the ecosystem. Understanding the characteristics of Rs is indispensable to scientifically understand the carbon cycle of ecosystems. It is very important to study Rs characteristics through analysis of environmental factors closely related to Rs. Rs is affected by various environmental factors, such as temperature, precipitation, soil moisture, litter supply, organic matter content, dominant plant species, and soil disturbance. This study was conducted to analyze the effects of micro-topographical differences on Rs in forest vegetation by measuring the Rs on the ridge and southern slope sites of the broadly established Quercus mongolica forest in the central Korean area. Method: Rs, Ts, and soil moisture data were collected at the southern slope and ridge of the Q. mongolica forest in the Mt. Jeombong area in order to investigate the effects of topographical differences on Rs. Rs was collected by the closed chamber method, and data collection was performed from May 2011 to October 2013, except Winter seasons from November to April or May. For collecting the raw data of Rs in the field, acrylic collars were placed at the ridge and southern slope of the forest. The accumulated surface litter and the soil organic matter content (SOMC) were measured to a 5 cm depth. Based on these data, the Rs characteristics of the slope and ridge were analyzed. Results: Rs showed a distinct seasonal variation pattern in both the ridge and southern slope sites. In addition, Rs showed a distinct seasonal variation with high and low Ts changes. The average Rs measurements for the two sites, except for the Winter periods that were not measured, were $550.1\;mg\;CO_2m^{-2}h^{-1}$ at the ridge site and $289.4\;mg\;CO_2m^{-2}h^{-1}$ at the southern slope, a difference of 52.6%. There was no significant difference in the Rs difference between slopes except for the first half of 2013, and both sites showed a tendency to increase exponentially as Ts increased. In addition, although the correlation is low, the difference in Rs between sites tended to increase as Ts increased. SMC showed a large fluctuation at the southern slope site relative to the ridge site, as while it was very low in 2013, it was high in 2011 and 2012. The accumulated litter of the soil surface and the SOMC at the depth range of 0~5 cm were $874g\;m^{-2}$ and 23.3% at the ridge site, and $396g\;m^{-2}$ and 19.9% at the southern slope site. Conclusions: In this study, Rs was measured for the ridge and southern slope sites, which have two different results where the surface litter layer is disturbed by strong winds. The southern slope site shows that the litter layer formed in autumn due to strong winds almost disappeared, and while in the ridge site, it became thick due to the transfer of litter from the southern slope site. The mean Rs was about two times higher in the ridge site compared to that in the southern slope site. The Rs difference seems to be due to the difference in the amount of litter accumulated on the soil surface. As a result, the litter layer supplied to the soil surface is disturbed due to the micro-topographical difference, as the slope and the change of the community structure due to the plant season cause heterogeneity of the litter layer development, which in turn affects SMC and Rs. Therefore, it is necessary to introduce and understand these micro-topographical features and mechanisms when quantifying and analyzing the Rs of an ecosystem.

• 대한방사선치료학회지
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• 제32권
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• pp.53-59
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• 2020

목 적: 본 연구의 목적은 타깃 용적의 변화에 따라 MLC 로그 파일 기반 소프트웨어(Mobius)와 기존의 팬텀-전리함(ArcCheck) 선량 검증 방법 간에 차이를 비교 분석하는데 목적이 있다. 대상 및 방법: 반지름이 0.25cm, 0.5cm, 1cm, 2cm, 3cm, 4cm, 5cm, 6cm, 7cm, 8cm, 9cm, 10cm까지 총 12개의 球(구) 모양 타깃이 있는 플랜을 생성하고 Mobius와 ArcCheck을 사용한 선량 검증을 각각 3번씩 실시하였다. 조사된 데이터를 점선량 오차값과 감마 통과율(3%/3mm)을 평가지표로 하여 비교 분석하였다. 결 과: Mobius의 점선량 오차값은 반지름 0.25cm에서 -9.87%, 0.5cm에서 -4.39%로 나타났고, 나머지 타깃 용적에서 오차값은 3% 이내로 나타났다. 감마 통과율은 반지름 9cm에서 95%, 10cm에서 93.9%로 나타났고, 나머지 타깃 용적에서는 95% 이상의 통과율을 보였다. ArcCheck에서 점선량 평균 오차값은 모든 타깃 용적에서 2% 내외의 일치율을 보였다. 감마 통과율 역시 모든 타깃 용적에서 98% 이상의 통과율을 보였다. 결 론: 반지름 0.5cm 이하의 작은 타깃이나 반지름 9cm 이상의 큰 타깃에서는 MLC 로그 파일 기반 DQA의 불확실성을 고려하여, 팬텀-전리함 기반 DQA를 상호 보완해서 사용함으로써 점선량, 감마 지표, DVH, 타깃 포함 등의 종합적인 분석으로 선량 전달 검증을 하는 것이 바람직하다고 사료된다.