• Journal of Electrical Engineering and Technology
• /
• 제12권1호
• /
• pp.288-294
• /
• 2017

This paper contains results of the theoretical studies of the electrical breakdown properties in sulfur hexafluoride. Since the strong interaction of high-energy electrons with the polyatomic sulfur hexafluoride molecule causes their rapid deceleration to the lower energy of electron capture and dissociative attachment, the breakdown is only possible at relatively high field strengths. From the breakdown voltage curves, the effective yields that characterize secondary electron productions have been estimated. Values of the effective yields are found to be more consistent if they are derived from the experimentally determined values of the ionization coefficient and the breakdown voltages. In addition, simulations were performed using an one-dimensional Particle-in-cell/Monte Carlo collision code. The obtained simulation results agree well with the available experimental data with an error margin of less than 10% over a wide range of pressures and the gap sizes. The differences between measurements and calculations can be attributed to the differences between simulation and experimental conditions. Simulation results are also compared with the theoretical predictions obtained by using expression that describes linear dependence of the breakdown voltage in sulfur hexafluoride on the pressure and the gap size product.

• 한국신재생에너지학회:학술대회논문집
• /
• 한국신재생에너지학회 2009년도 춘계학술대회 논문집
• /
• pp.516-520
• /
• 2009

This study describes aerodynamic characteristics for the HAWT (Horizontal Axis Wind Turbine) rotor blade using general CFD(Computational Fluid Dynamics) code. The boundary conditions for analysis are validated with the experimental result by the NREL (National Renewable Energy Laboratory)/NASA Ames wind tunnel test for S809 airfoil. In the case of wind turbine rotor blade, complex phenomena are appeared such as flow separation and re-attachment. Those are handled by using a commercial flow analysis tool. The 2-equation k-$\omega$ SST turbulence model and transition model appear to be well suited for the prediction. The 3-dimensional phenomena in the HAWT rotor blade is simulated by a commercial 3-D aerodynamic analysis tool. Tip vortex geometry and Radial direction flows along the blade are checked by the analysis.

• Nuclear Engineering and Technology
• /
• 제21권3호
• /
• pp.186-192
• /
• 1989

14$\times$14형 교체노심용 핵연료집합체 상단고정체 설계의 일환으로 핵연료집합체 운송 및 취급시의 하중조건하에서 여러 상단고정체 구조모델들에 대한 구조해석을 ANSYS code를 사용하여 수행하였다. 해석 모델에서는 3차원 등매개변수(isoparametric) 요소를 사용하였으며 설계조건들을 위배하지 않으면서 Adapter plate에 있는 구멍들의 배치를 조정하는 한편 Adapter plate에 부착되는 두름판(Enclosure)의 부착 방법을 개선함으로서 상단고정체의 구조적 강도를 증가시켰다. 이러한 개념들은 14$\times$14 교체노심용 핵연료 설계에 채택되었다.

• Journal of Radiation Protection and Research
• /
• 제40권2호
• /
• pp.87-91
• /
• 2015

We have employed X-ray photoelectron spectroscopy (XPS) technique to examine the combined effects of low-energy electron (LEE) irradiation and $Fe^{3+}$ ion on DNA damage. pBR322 plasmid DNA extracted from E. coli ER2420 was used for preparing DNA-$Fe^{3+}$ sample. The C1s XPS spectra were scanned for LEE-irradiated and LEE-unirradiated samples and then curve-fitted. For the samples with LEE irradiation only or with Fe ion only, no significant changes from pure DNA samples were observed - a single effect of either $Fe^{3+}$ ion or LEE irradiation did not cause a significant damage. However, when these two components were combined, the DNA damage was increased quite significantly, compared to the sum of DNA damages caused by $Fe^{3+}$ ion and by LEE irradiation independently. This observation is consistent with our previous results [Radiat. Res. 177, 775 (2012)] which was done using gel-electrophoresis technique. Partial interpretation of the observed spectrum peaks was also attempted.

• 한국태양에너지학회 논문집
• /
• 제31권6호
• /
• pp.132-138
• /
• 2011

Inducing the natural lighting into building has been commonly applied to the spaces where artistic objects are displayed to create better visual environment for the appreciation. The direct natural lighting, especially through top lighting system may, however, bring forth discoloing of highly light-sensitive materials such as paintings or demanding additional cooling load. In addition, it causes to create glare against appreciators or to yield in visual distraction due to the extreme contrast on the inner surfaces of the spaces. Shading device such as louver is capable of preventing such voidable cases with careful manipulation. This study aims to provide basic design guide-line when the flat-form louver has to be applied to top lighting system. Interaction between the daylight and louver was simulated by Reluxpro program with variation of the attachment location, the angle of the lover, surface reflectivity, to obtain the illumination of the floor surface. This study yields the louver just under the top lighting window with 90 degree angle gives the most desirable way of employment when the uniform illumination on the floor surface is required.

• Bulletin of the Korean Chemical Society
• /
• 제28권6호
• /
• pp.953-958
• /
• 2007

Anchoring quantum dots (QDs) onto thermodynamically stable, large band gap oxide semiconductors is a very important strategy to enhance their quantum yields for solar energy conversion in both visible and near-IR regions. We describe a general procedure for anchoring a few chalcogenide QDs onto the titanium oxide layer. To anchor the colloidal QDs onto a mesoporous TiO2 layer, linker molecules containing both carboxylate and thiol functional groups were initially attached to TiO2 layers and subsequently used to capture dispersed QDs with the thiol group. Employing the procedure, we exploited cadmium selenide (CdSe) and cadmium telluride (CdTe) quantum dots (QDs) as inorganic sensitizers for a large band gap TiO2 layer of dye-sensitized solar cells (DSSCs). Their attachment was confirmed by naked eyes, absorption spectra, and photovoltaic effects. A few QD-TiO2 systems thus obtained have been characterized for photoelectrochemical solar energy conversion.

• 한국태양에너지학회:학술대회논문집
• /
• 한국태양에너지학회 2009년도 추계학술발표대회 논문집
• /
• pp.74-79
• /
• 2009

The generation of electric power and plant facilities have been attempting to improve energy efficiency with many efforts as those being basis of our country's economy. In particular, the CHP(Combined Heat Power plant) system, is producing the electricity and process steam, has generally been using for the cogeneration plants. When CHP system operates, the steam has to maintain the high temperature and high pressure in order to have high efficiency of electric power production as much as possible. In addition, the exhausted steam from the turbine has to reform proper temperature to use the needed process. The major purpose of desuperheater is that the superheated steam changes into the saturated steam because it is more efficient and suitable for using the process, furthermore, it is more convenient and stable regarding the process temperature control. The design of the desuperheater obtained through the experiment and preceding analysis. This paper is verified by analysis that water spray nozzle(${\Phi}$=28mm) shows the best ability under the real power plant condition.

• 한국재료학회지
• /
• 제31권7호
• /
• pp.386-391
• /
• 2021

The formation of CaCO₃ in microalgal culture is investigated and applied for effective separation of microalgae. The presence of several cationic ions in the culture medium mediates the formation of 3 types of mineral precipitates depending on the concentration of mineral precursors, Ca²⁺ and CO₃^2-, amorphous nano-flakes, rhombohedral calcites, and spherical vaterites. While amorphous phased precipitates are formed for all concentrations of mineral precursor, only calcites are formed for 30 mM solutions of mineral precursor, and mixtures of calcites and vaterites are formed for 50 and 100 mM solutions of mineral precursor. The harvesting efficiency is also dependent on the concentration of the mineral precursor: from 90 % for 10 mM to 99 % for 100 mM after 60 mins' of gravitational sedimentation. The formation of nano-flakes on the surface of microalgal cells induces the flocculation of microalgae by breaking the stable dispersion. The negatively charged surface of the microalgal cell is compatible not only with nano-flake attachment but also with the growth of calcitic crystals in which microalgal cells are embedded.

• 풍력에너지저널
• /
• 제14권4호
• /
• pp.21-28
• /
• 2023

This study focuses on the analysis of slewing ball bearings in wind turbines. Slewing bearings have an outer diameter of several meters, and hundreds of balls are in contact with the raceway. Due to the large number of balls and raceway contact conditions, it is difficult to accurately analyze contact stresses using general analysis techniques. To analyze the contact stress of a slewing ball bearing, the sub-modeling method is applied, which is a technique that first analyzes the displacement of the entire model and then analyzes the local stress at the point of maximum displacement. In order to reduce the displacement analysis time of the entire ball bearing, the technique of replacing the ball with a nonlinear spring is adopted. The analytical agreement of the simplified model was evaluated by comparing it with a solid mesh model of the ball for three models with different spring attachment methods. It was found that for the condition where a large turnover moment is applied to the bearing, increasing the number of spring elements gives the closest results to modeling the ball with a solid mesh.

• Parasites, Hosts and Diseases
• /
• 제56권5호
• /
• pp.463-475
• /
• 2018

The present study was performed to observe histopathological effects of Oculotrema hippopotami Stunkard, 1924 infection in the eye of Hippopotamus amphibius, as well as to reveal new details of morphology and structural features of this monogenean and its comparison between 2 age stages of the parasite. This was done using both light and scanning electron microscopy, energy dispersive X-ray analysis (EDXA) and histopathology. The presence of a mixture of different generations (adult and sub-adult) in one host individual is common for Oculotrema Stunkard, 1924 in contrast to Polystoma Zeder, 1800. New metrical and graphical information obtained for adults and sub-adults compared with the previous studies. Here we show the presence of genital papillae in adults, metrical data on the distal part of the vas deferens. SEM micrographs of sperm ejaculatory structures and information about the flattened dorsal side of the body provided for the first time. Histopathological changes, such as necrosis and hemorrhage in host tissues as a result of O. hippopotami attachment structures are described. Structural analysis of different body parts of O. hippopotami of both age groups are also included. We show qualitative differences in the presence of hardening ions (S, P, Ca) in attachment structures (oral and haptor suckers) that increase with the age of the worm. The presence of sub-adults and adults on the same host, together with high levels of infection without high pathogenicity may account for Oculotrema being one of the most successful parasites among the Monogenea.