• 한국진공학회지
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• 제20권5호
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• pp.381-386
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• 2011

실리콘(silicon) 기판위에 전기화학증착법(electrochemical deposition)을 이용하여 성장된 ZnO (zinc oxide) 나노로드 표면에 $SiO_2$ (silicon dioxide)를 전자빔증발법(e-beam evaporation)을 이용하여 증착하였으며, 이는 자연적으로 경사입사(oblique angle) 증착이 이루어져 $SiO_2$ 나노로드가 자발 형성되어, ZnO/$SiO_2$ 가지형 나노계층구조형태가 제작될 수 있음을 확인하였다. 실험을 위해서 $SiO_2$ 증착률을 0.5 nm/s로 고정하고 $SiO_2$ 증착시간을 변화시켰으며, 각각 나노구조의 형태와 광학적 특성을 분석하였다. 실리콘 기판위에 전기화학증착법으로 성장된 ZnO 나노로드는 수직으로 정렬된 1차원의 나노구조의 기하학적 형태를 갖고 있어, 입사되는 빛의 파장이 300 nm에서 535 nm인 영역에서 10% 미만의 반사방지(antireflection) 특성을 보였으며, $SiO_2$ 증착시간이 100 s일 때의 ZnO/$SiO_2$ 가지형 나노계층구조에서는 점차적 변화를 갖는 유효 굴절률 분포로 인해 개선된 반사 방지 특성을 확인하였다. 이러한 반사방지 특성과 branch 계층형태의 나노구조형태는 광전소자 및 태양광 소자 응용에 있어서 유용한 소재로 사용될 수 있다.

• 원예과학기술지
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• 제18권1호
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• pp.22-27
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• 2000

배를 캐나다 등 외국에 수출할 시는 수출 상대국의 검역요건에 맞추어 주어야 한다. 수출국 특히 캐나다에 수출되는 배의 검역상 문제점을 찾아 그 해결법을 제시하고자 수출 조건에서 수출 단계별 검역규제병해충을 조사하였다. 조사 결과 복숭아명나방과 복숭아순 나방이 발견되었으나 이들은 저온처리로 인하여 모두 사멸되었다. 해충은 복숭아심식나방류 유충이 과실로 이동되는 시기에 방제를 소홀히 한 생산지 과실에서 발견되었으므로 복숭아명나방 등 심식나방류 유충이 과실로 이동되는 시기에 예찰을 철저히 하여 적기방제 하는 것이 필요하다. 한편 병원균은 과실의 선과 작업과 이동할 때 생긴 압상, 자상 등 상처를 통하여 Penicillium sp. 및 Alternaria sp.의 부생균이 감염된 것이 발견되고 검역병원균은 발견되지 않았다. 그러나 이들 병원균도 비록 비검역병원균이라고 하지만 부패과실이 일정비율 초과할 경우 수출자가 수입자에게 이를 보상하여야 하므로 수출배 중 외피가 얇은 황금배 등은 수확 후 운송과정과 선과장 선과 작업 중에 특별한 주의가 요구된다.

• International Journal of Air-Conditioning and Refrigeration
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• 제11권2호
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• pp.51-60
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• 2003

In the nuclear power plant, emergency core coolant system (ECCS) is furnished at reactor coolant system (RCS) in order to cool down high temperature water in case of emergency. However, in this coolant system, thermal stratification phenomenon can occur due to coolant leaking in the check valve. The thermal stratification produces excessive thermal stresses at the pipe wall so as to yield thermal fatigue crack (TFC) accident. In the present study, effects of turbulence penetration on the thermal stratification into T-branches with square cross-section in the modeled ECCS are analysed numerically. Standard k-$\varepsilon$ model is employed to calculate the Reynolds stresses in momentum equations. Results show that the length and strength of thermal stratification are primarily affected by the leak flow rate of coolant and the Reynolds number of duct. Turbulence penetration into the T-branch of ECCS shows two counteracting effects on the thermal stratification. Heat transport by turbulence penetration from main duct to leaking flow region may enhance thermal stratification while the turbulent diffusion may weaken it.

• Journal of the Korean Wood Science and Technology
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• 제44권6호
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• pp.890-896
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• 2016

Paulownia tomentosa is one of fast-growing wood species in Korea. In order to evaluate the solid bioenergy properties of Paulownia tree, this study examined the heating value, moisture content (MC), pH and proximate analysis of stem, branch, root, bark and leaf. The heating values of wood parts were slightly higher than those of bark and leaf, and that of branch was the highest among all the samples. The higher moisture content of bark and leaf referred to their lower heating value. Also, the pH of stem, branch and root was similar and lower than those of bark and leaf. The ash content of bark and leaf was much higher than that of wood parts, which is the one of the reasons for effect on the lower heating value and higher pH. While, the volatile matter content (VMC) of bark and leaf was lower than those of wood parts. The bark showed the highest fixed carbon content (FCC), while the FCC of stem was the lowest among all the samples. The obtained results are encouraging that the Paulownia tree could be totally utilized as alternative fuels for bioenergy production.

• Journal of Electrical Engineering and Technology
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• 제6권2호
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• pp.147-153
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• 2011

This paper proposes a methodology using a tool based on the branch-parameter continuation power flow (BCPF) in order to restore the power flow solvability in unsolvable contingencies. A specified contingency from a set of transmission line contingencies is modeled, considering the transient analysis and practice in the Korean power system. This tool traces a solution path that satisfies the power flow equations with respect to the variation of the branch parameter. At a critical point, in which the branch parameter can move on to a maximum value, a sensitivity analysis with a normal vector is performed to identify the most effective compensation. With the sensitivity information, the location of the reactive power compensation is determined and the effectiveness of the sensitivity information is verified to restore the solvability. In the simulation, the proposed framework is then applied to the Korean power system.

• Structural Engineering and Mechanics
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• 제74권6호
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• pp.809-819
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• 2020

For the first time, the influence of in-plane magnetic field on wave propagation of Graphene Nano-Platelets (GNPs) polymer composite nanoplates is investigated here. The impact of three- parameter Kerr foundation is also considered. There are two different reinforcement distribution patterns (i.e. uniformly and non-uniformly) while the material properties of the nanoplate are estimated through the Halpin-Tsai model and a rule of mixture. To consider the size-dependent behavior of the structure, Eringen Nonlocal Differential Model (ENDM) is utilized. The equations of wave motion derived based on a higher-order shear deformation refined theory through Hamilton's principle and an analytical technique depending on Taylor series utilized to find the wave frequency as well as phase velocity of the GNPs reinforced nanoplates. A parametric investigation is performed to determine the influence of essential phenomena, such as the nonlocality, GNPs conditions, Kerr foundation parameters, and wave number on the both longitudinal and flexural wave characteristics of GNPs reinforced nanoplates.

• Structural Engineering and Mechanics
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• 제68권3호
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• pp.359-368
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• 2018

This paper deals with the dynamic stability of nanocomposite pipes conveying pulsating ferrofluid. The pipe is reinforced by carbon nanotubes (CNTs) where the agglomeration of CNTs are considered based on Mori-Tanaka model. Due to the existence of CNTs and ferrofluid flow, the structure and fluid are subjected to axial magnetic field. Based on Navier-Stokes equation and considering the body forced induced by magnetic field, the external force of fluid to the pipe is derived. For mathematical modeling of the pipe, the first order shear deformation theory (FSDT) is used where the energy method and Hamilton's principle are used for obtaining the motion equations. Using harmonic differential quadrature method (HDQM) and Bolotin's method, the motion equations are solved for calculating the excitation frequency and dynamic instability region (DIR) of the structure. The influences of different parameters such as volume fraction and agglomeration of CNTs, magnetic field, structural damping, viscoelastic medium, fluid velocity and boundary conditions are shown on the DIR of the structure. Results show that with considering agglomeration of CNTs, the DIR shifts to the lower excitation frequencies. In addition, the DIR of the structure will be happened at higher excitation frequencies with increasing the magnetic field.

• Advances in Energy Research
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• 제4권1호
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• pp.87-106
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• 2016

In this research, optimum design of the combined solar collector, geothermal heat pump and thermal seasonal storage system for heating and cooling a sample greenhouse is studied. In order to optimize the system from technical point of view some new control strategies and functions resulting from important TRNSYS output diagrams are presented. Temperatures of ground, rock bed storage, outlet ground heat exchanger fluid and entering fluid to the evaporator specify our strategies. Optimal heat storage is done with maximum efficiency and minimum loss. Mean seasonal heating and cooling COPs of 4.92 and 7.14 are achieved in series mode as there is no need to start the heat pump sometimes. Furthermore, optimal parallel operation of the storage and the heat pump is studied by applying the same control strategies. Although the aforementioned system has higher mean seasonal heating and cooling COPs (4.96 and 7.18 respectively) and lower initial cost, it requires higher amounts of auxiliary energy either. Soil temperature around ground heat exchanger will also increase up to $1.5^{\circ}C$ after 2 years of operation as a result of seasonal storage. At the end, the optimum combined system is chosen by trade-off between technical and economic issues.

• Ocean and Polar Research
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• 제22권1호
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• pp.37-43
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• 2000

Epiphytic communities on marine plants of Seychelles (Indian Ocean Island group associated with East Africa) were investigated in January - March of 1989 during the $15^{th}$ biological voyage of the research vessel cademic Alexander Nesmeyanov. A seagrass species, Thalassodendron ciliatum, and macroalgae (Sargassum spp. and Halimeda spp.) were tested for host substrates and biomass of their dominant epiphytes were assessed. Also, in order to understand the effect of shading and nutrient filtering by epiphytes, two series of photosynthetic rates were compared for Th. ciliatum host leaves having 10% and no epiphytes. Total of 84 species of algae and main taxons of benthic animals were identified from three different host plants. An average biomass of the epiphytes on Th. cihiatum was $184.6g\;kg^{-1}$ and dominant species were green alga Halimeda opuntia, red algae Dictyurus occidentalis and Gelidiella myrioclada. These dominant species and their biomass were remarkably varied with depth increment. On Sargassum spp., an average biomass of the epiphytes was $0.18g\;kg^{-1}$ and the maximum biomass was never exceeded $0.16g\;kg^{-1}$. In the case of Halimeda spp. an average biomass of the epiphytes was $8.0g\;kg^{-1}$, and dominant species were Peyssonnelia dubyi, sponges and decapods. Photosynthetic rates of Th. ciliatum were significantly reduced in the leaves having 10% epiphytes (1.72 times lower, t=6.718, p<0.001).

• Journal of Mechanical Science and Technology
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• 제20권7호
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• pp.1030-1042
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• 2006

An experimental study has been performed to investigate the off-take phenomena at the header-feeder systems (horizontal header pipe with multiple feeder branch pipes) in a CANDU (CANadian Deuterium Uranium) reactor with the branch orientation varies ${\pm}36^{\circ}\;or\;{\pm}72^{\circ}$. In order to evaluate the applicability of the conventional correlations used in the safety analysis code, RELAP5-Mod3, the test facility is designed with the 1/2 scale of the. CANDU 6. It was found that the data set for the top, bottom and side branches are in a good agreement with the correlations used. However, for the specific angled branches, ${\pm}36^{\circ}\;and\;{\pm}72^{\circ}$, the onsets of off-take data and quality data showed large deviation with the conventional model inside RELAP5-MOD3. Furthermore, based on the uncertainty analysis, the conventional 2.5 power law needs to be modified. The present experimental data set can be useful for the construction of the general correlation considering the arbitrary branch orientation.