• Nuclear Engineering and Technology
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• 제49권8호
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• pp.1758-1771
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• 2017

In this study, to determine the most effective alloy for shielding against gamma-rays, the gamma-ray shielding parameters of six types of cerrobend alloys have been investigated. Gamma-ray interaction with the cerrobend alloys has been discussed mainly in terms of total mass attenuation coefficient (${\mu}_t$), half value layer (HVL), tenth value layer (TVL), effective atomic number ($Z_{eff}$), and effective electron density ($N_{eff}$). These parameters have been calculated by theoretical approach using the ParShield program in a photon energy range between 0.1 MeV and 100 GeV. The dependence of these parameters on the incident photon energy and chemical composition of the cerrobend alloys has been studied.

• 한국화재소방학회논문지
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• 제23권1호
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• pp.1-6
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• 2009

본 연구의 목적은 화재 예측모델로 널리 사용되는 FDS(Fire Dynamics Simulation) ver. 4.07을 여객열차 화재예측에 적용하기 위하여 민감도 분석(Sensitivity analysis)을 수행하는 것이다. 주요 분석 변수(Parameter)는 격자 크기(Grid size)와 Solid angle number이다. 분석결과, 격자크기의 변화는 온도(Plume temperature 상부층 온도(Upper layer temperature), 연기층 높이(Layer height)결과 값에 약$10{\sim}20%$의 차이를 갖게 하는 주요 민감도 변수이며 Solid angle number는 민감도에 영향을 크게 미치지 않는 것으로 분석되었다. 또한, 0.05m의 Grid size가 0.1m보다 결과 해상도가 높은 것으로 나타났다.

• 한국정보전자통신기술학회논문지
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• 제12권1호
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• pp.92-98
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• 2019

본 논문에서는 몰포러지 연산을 기본으로 하는 몰포러지 신경망(MNN: Morphological Neural Network) 기반 딥러닝 시스템을 제안하였다. 딥러닝에 사용되는 레이어는 몰포러지 레이어, 풀링 레이어, ReLU 레이어, Fully connected 레이어 등이다. 몰포러지 레이어에서 사용되는 연산은 에로전, 다이레이션, 에지검출 등이다. 본 논문에서 새롭게 제안한 MNN은 기존의 CNN(Convolutional Neural Network)을 이용한 딥러닝 시스템과는 달리 히든 레이어의 수와 각 레이어에 적용되는 커널 수가 제한적이다. 레이어 단위 처리시간이 감소하고, VLSI 칩 설계가 용이하다는 장점이 있으므로 모바일 임베디드 시스템에 딥러닝을 다양하게 적용할 수 있다. MNN에서는 제한된 수의 커널로 에지와 형상검출 등의 연산을 수행하기 때문이다. 데이터베이스 영상을 대상으로 행한 실험을 통해 MNN의 성능 및 딥러닝 시스템으로의 활용 가능성을 확인하였다.

• 대한기계학회논문집B
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• 제29권7호
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• pp.837-845
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• 2005

In this paper, an investigation on high-Schmidt number (Sc=1670) mass transfer in turbulent flow around a rotating circular cylinder is carried out by Direct Numerical Simulation. The concentration field is computed for three different values of low Reynolds number, namely 161, 348 and 623 based on the cylinder radius and friction velocity. Statistical study reveals that the thickness of Nernst diffusive layer is very small compared with that of viscous sub-layer in the case of high Sc mass transfer. Strong correlation of concentration field with streamwise and vertical velocity components is observed. However, that is not the case with the spanwise velocity component. Instantaneous concentration visualization reveals that the length scale of concentration fluctuation typically decreases as Reynolds number increases. Statistical correlation between Sherwood number and Reynolds number is consistent with other experiments currently available.

• Nuclear Engineering and Technology
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• 제49권1호
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• pp.216-223
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• 2017

In this work, linear and mass attenuation coefficients, effective atomic number and electron density, mean free paths, and half value layer and $10^{th}$ value layer values of barium-bismuth-borosilicate glasses were obtained for 662 keV, 1,173 keV, and 1,332 keV gamma ray energies using MCNP-4C code and XCOM program. Then obtained data were compared with available experimental data. The MCNP-4C code and XCOM program results were in good agreement with the experimental data. Barium-bismuth-borosilicate glasses have good gamma ray shielding properties from the shielding point of view.

• 설비공학논문집
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• 제15권2호
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• pp.126-131
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• 2003

Convective instability driven by surface tension is analyzed in an initially quiescent water absorbing ammonia gas with heat transfer using the linear stability analysis. The propagation theory is adapted to find the critical conditions of the onset of Marangoni convection. In this theory, the solutal penetration depth is chosen as the length scale factor. The results show that the liquid layer becomes more stable with decreasing the Schmidt number and increasing the Lewis number. It is also found that there is a critical Biot number to make the liquid layer be most unstable, and there is a linear relationship between the thor-mal Marangoni number and the solutal Marangoni number.

• 한국환경복원기술학회지
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• 제7권3호
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• pp.35-47
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• 2004

In order to study changes in vegetation pursuant to rooftop revegetation plantation methods, plantation methods for rooftop revegetation were divided into two types through an analysis of recent trends. Then, Planted plants and invasive plants on sites where the planting methods were introduced were monitored. Planting methods were divided into mono-layer meadow cover type and multi-layer planting cover type. They showed some differences in terms of the availability of wetland, the structure of vegetation layers, the planted species, and the material of mulching. According to the results of monitoring the two sample sites for different plantation methods, the number of invasive plants was higher in multi-layer planting cover type and the ratio of naturalized plants was higher by 30% in average in mono-layer meadow cover type. The main reason for such a result is that the natural soil used in the multi-layer planting cover type likely contained some seeds. Moreover, it's harder for invasive plant seeds to germinate in volcanic rocks than in natural soil. Also, it is attributable to wetlands available in multi-layer planting cover type and diverse living environments created by multi-layer planting. The reason of the ratio of naturalized plants being higher by at least 10% in mono-layer meadow cover type is the character of naturalized plants being stronger in unfavorable conditions than nature plants are. Accordingly, the germination rate in the volcanic rock mulching has likely contributed in raising the introduction and germination of naturalized plants. The results showed that multi-layer planting cover type using wetland creation and nature soil can increase the number of invasive plants and lower the ratio of naturalized plants. However, since seeds contained in the natural soil can affect the growth of planted plants, this needs to be clarified, It was judged that mono-layer meadow cover type may affect more greatly on the germination and growth of invasive plants than on those of planted plants, Its potential adoption in highly urbanized areas was examined. By complementing with the mutual benefits of each plantation method, it appeared possible to shift to a rooftop revegetation system suitable to the site.

• 한국조경학회지
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• 제28권6호
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• pp.1-15
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• 2001

The purpose of this study is to figure out the structural characteristics of urban plant community and suggest restoration model of Quercus mongolica in the case of Korean national Capital Region. The investigation areas were selected from urban area of Mt. Nam at Chung-Gu, suburban areas of Mt. Bong at Eunpyoung-GU, Mt. Sungju at Buchon City and non-urban areas of Mt. Suri at Kunpu City and Mt. Chonma t namyangju-City. After the main study field had been classified into the evaluation of the ecological characteristics and the modeling of the vegetation. We analyzed to evaluate the ecological characteristics of the forest structure -- successional stage, naturalness, multi-layer structure of the forest and species diversity, and the plant community structures. We have proposed vegetation restoration model based on the selection of proper plants, the number of individuals, diameter short area of breast height, the shortest distance between plants in non-urban area. As for successional stage, It was judged that the ecological succession may not be followed like the present stage of the surveyed areas in urban, suburban and non-ruban areas. As for the retention of naturalness and multi-layer structures of vegetation, In Quercus mongolica community, Robinia pseudo-acacia and Ailanthus altissima occurred in each layers at Mt. Nam, Mt. Bong and Mt. Sungju, and Eupatorium rugosum occurred in herbaceous layer at Mt. Nam. Consequently, the ecological restoration plan following the structure of the vegetation in Mt. Chonma seemed to be advisable in Q. mongolica community, there were less number of species and individuals in urban areas than those of non-urban areas. Planting of trees following the simulated native plant community of non-urban areas seemed to be required to promote the plants in urban areas. Considering the number of individuals up to three layers in each 400$m^2$ area, it was composed of twenty nine in canopy layer, forth nine in understory layer, 367 in shrub layer and 33.7% herbaceous ground cover in the Q.mongolica community. The suggested restoration model in this study is nan applicable model for the introduction in the cities, and this study shows that continuous experiments and field investigation on this model should be performed in the future.

• International Journal of Control, Automation, and Systems
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• 제3권2호
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• pp.202-210
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• 2005

This paper presents a new neural network control for nonlinear bridge systems with earthquake excitation. We design multi-layer neural network controllers with a single hidden layer. The selection of an optimal number of neurons in the hidden layer is an important design step for control performance. To select an optimal number of hidden neurons, we progressively add one hidden neuron and observe the change in a performance measure given by the weighted sum of the system error and the control force. The number of hidden neurons which minimizes the performance measure is selected for implementation. A neural network was trained for mitigating vibrations of bridge systems caused by El Centro earthquake. We applied the proposed control approach to a single-degree-of-freedom (SDOF) and a two-degree-of-freedom (TDOF) bridge system. We assessed the robustness of the control system using randomly generated earthquake excitations which were not used in training the neural network. Our results show that the neural network controller drastically mitigates the effect of the disturbance.

• 한국환경복원기술학회지
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• 제22권4호
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• pp.47-64
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• 2019

The purpose of this study is to present the basic data for the management of National Park by surveying and analysing the change of vegetation of forest fire damaged area in Sogeumgang District, Gyeongju National Park. The covergae ratio, a number of species and dominant species changed overall in forest fire damaged area. The final result of the change is as follows. In case of coverage ratio in the shrub layer, Site 1 was 30%, 40% in Site 2, 50% in Site 3, 60% in Site 4 and 30% in Site 5. In the herb layer, Site 1 was 90%, 80% in Site 2, 90% in Site 3, 60% in Site 4 and 20% in Site 5. In case of the number of species in the shrub layer, Site 1 was 11 species, 8 species in Site 2, 6 species in Site 3, 10 species in Site 4, 7 species in Site 5, and in the herb layer, Site 1 was 22 species, 25 species in Site 2, 12 species in Site 3 and Site 4 each and 11 species in Site 5. In the dominant species, the shrub layer was Lespedeza maritima(Site 1, 2), Quercus serrata(Site 3), Quercus serrata and Lespedeza bicolor(Site 4) and Styrax japonicus(Site 5), the herb layer was Miscanthus sinensis var. purpurascens(Site 1, 3), Pteridium aquilinum var. latiusculum and Carex humilis var. nana(Site 2), Quercus serrata(Site 4) and Carex humilis var. nana andS tyrax japonicus(Site 5). The number of vascular plants was summarized as 91 taxa including 35 families, 69 genera, 78 species, 2 subspecies, 10 varieties and 1 form.