• 한국안광학회지
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• 제18권4호
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• pp.465-471
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• 2013

목적: 정시안에 유발된 부등상시에서 영향인자들이 입체시에 미치는 효과를 알아보고자 하였다. 방법: 안질환 및 전신질환이 없고, 원용 완전교정 굴절력이 등가구면 굴절력 ${\pm}0.50$ D 이내이며, 교정시력이 1.0 이상, AWAYA 부등상시도 1% 이하의 대학생 20명(평균연령 $22.50{\pm}2.72$세, 남자 14명, 여자 6명)을 대상자로 선정하였다. 대상자의 우위안을 원형구멍카드법(Hole in card method)으로 확인한 후, 우위안 또는 비우위안에 각각 -7.00 D ~ +7.00 D의 콘택트렌즈를 착용시켜 굴절부등시를 유발하고 이를 교정하는 안경을 착용하여 부등상시를 유발한 후 Random Dot Stereo Acuity Test with LEA symbols$^{(R)}$(Vision Assessment Corporation$^{TM}$, USA)를 이용하여 입체시를 측정하였다. 결과: 우위안에 부등상시를 유발한 경우, 굴절부등시 유발을 위한 착용 콘택트렌즈 굴절력이 큰 경우, (+) 콘택트렌즈 착용 후 (-) 안경렌즈로 교정한 경우, 남자인 경우에서 부등상시 유발에 따른 입체시의 저하가 더욱 크게 나타났다. 결론: 부등상시는 입체시의 저하를 일으킬 수 있으므로 굴절부등시 교정 시에는 이를 고려하여야 한다.

• 한국안광학회지
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• 제15권2호
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• pp.137-144
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• 2010

목적: 본 연구는 프리즘 밸러스트 디자인 원데이 토릭 소프트 콘택트렌즈의 임상적 성능을 평가하고 안경교정 상태와 시기능의 질을 비교하기 위해 실시하였다. 방법: 대상자는 구면 -2.75 D이고 -0.75 DC에서 -2.25 DC 사이의 직난시를 갖는 건강한 대학생 15명(30안)을 대상으로 프리즘 밸러스트 디자인 렌즈를 양안에서 처방하여 2주간 착용시켰다. 대상자들은 토릭렌즈의 임상성능(렌즈 안정 위치, 중심안정, 렌즈 움직임, 타이트한 정도, 렌즈 안정성, 회전 회복, 자각증상)을 평가하고 양안시 검사 값 및 대비감도를 초기 방문과 2주간 적응 후 검사하여 안경교정 상태와 비교였다. 결과, 프리즘 밸러스트 디자인의 토릭 소프트 콘택트렌즈를 2주간 착용한 후에 렌즈 방향안정, 회전 회복, 자각증상을 평가한 결과, 적응 전보다 향상되었다. 양안시 검사 값과 대비감도가 안경 착용 상태와 비교할 때 통계적으로 유의한 차이가 없는 것으로 나타났다. 결론: 프리즘 밸러스트 디자인의 토릭 소프트 콘택트렌즈를 착용한 후 임상적 기능이 증진하였다. 양안시 검사값과 대비감도가 안경교정 상태와 차이가 없는 것으로 평가되었다. 본 연구를 통해서 토릭 소프트 콘택트렌즈 착용자가 안경교정 자와 유사한 시생활을 영위할 수 있는 것으로 사료된다.

• 한국세라믹학회지
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• 제42권8호
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• pp.554-560
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• 2005

The engineering ceramic needs the properties of high strength, hardness, corrosion-resistance and heat-resistance in order to withstand thermal shock or applied nonuniform stresses without failure. The densely coated porous ceramics can be used for machine component, electromagnetic component, bio-system component and energy-system component by their high-performances from superior coating properties and light-weight characteristics due to the structure including pore by itself. In this study we controlled the porosity of silica and alumina, $8.2\~25.4\%$ and $23.4\~36.0\%$, respectively, by the control of sintering temperature and starting powder size. We made bilayer structures, consisting of a transparent glass coating layer bonded to a thick substrate of different porous ceramics by a thin layer of epoxy adhesive, facilitated observations of crack initiation and propagation. The elastic modulus mismatch could be controlled using different porous ceramics as the substrate layer. Then we applied 150 N force using WC sphere with a radius of 3.18 mm by Hertzian indentation. As a result, the crack initiation in the coating layer was delayed at lower porosity in the substrate layer, and the damage in the coating layer was relatively smaller at the bilayer structure coated on higher elastic substrate.

• Applied Microscopy
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• 제43권1호
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• pp.34-39
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• 2013

Glandular and nonglandular trichomes on the leaf surface of Plectranthus tomentosa were investigated by variable pressure field emission scanning electron microscopy (VP-FESEM). The segments of the plant's leaves were directly mounted without any specimen preparation, and examined at ambient temperature using a variable pressure secondary electron (SE) detector under ca. 15 Pa. Foliar trichomes maintained their shapes and structures without severe surface collapse or charging. The adaxial leaf surface was abundantly covered with different types of trichome. Nonglandular trichomes consisted of a basal cell and a long (up to ca. $300{\mu}m$) stalk. Meanwhile, capitate glandular trichomes had a secretory head and a short or long stalk. Peltate glandular trichomes with globose secretory heads were observed in close contact with the leaf epidermis. Spherical projections on the secretory head showed the secretion process of glandular trichomes. In addition to the trichomes, oval stomata were distributed on the abaxial leaf surface. These results suggest that ambient VP-FESEM can be used to classify the dehydration-sensitive foliar trichomes of succulent plants by SE imaging. At the FESEM resolution, this approach facilitates the rapid and detailed morphological analysis of a variety of trichomes in diverse plant taxa with reduced labor and preparation.

• 한국재료학회지
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• 제17권6호
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• pp.331-336
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• 2007

The pure Mg powder compacts were successfully fabricated using SPS process. The machined chip powder showed flake shaped morphology with coarse surfaces, while gas atomized powders were spherical in morphology with smooth surfaces. In this study, SPS process was used to consolidate the pure Mg powder because this process allows high density consolidation in a short time. The results showed that increased sintering temperature from $350^{\circ}C$ to $500^{\circ}C$ with pressure of 30MPa, the maximum values of the density was increased from 98.1% to 99.8% of theoretical density, respectively. However, density of the sintered chip powders was higher than that of gas-atomized powder due to larger contact areas between particles.

• 상하수도학회지
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• 제27권4호
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• pp.439-444
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• 2013

Excessive phosphorus in aquatic systems causes algal bloom resulting in eutrophication, DO depletion, decline in recreational value of water and foul tastes. To treat wastewater containing phosphorus including effluent of wastewater treatment plant, the continuous experiments were performed by using electrochemical way. The spherical ZVI and silica sand which act as physical filter are packed at appropriate volume ratio of 1:2. Electric potential is applied externally which can be changed as per the operational requirement. The results indicate that optimum hydraulic retention time of 36 minutes (10 mL/min at 1 L reactor) was required to meet the effluent standards. Lower concentrations of phosphorus (<10 mg/L as phosphate) were removed by precipitation by contact with iron. Thus, additional electric potential was not required. In order to remove high concentration phosphorus around 150 mg/L as phosphate, external electric potential of 600 V was applied to the reactor.

• 한국분무공학회지
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• 제11권2호
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• pp.89-97
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• 2006

An inviscid axisymmetric model capable of predicting droplet bouncing and the detailed pre-impact motion, influenced by the ambient pressure, has been developed using boundary element method (BEM). Because most droplet impact simulations of previous studies assumed that a droplet was already in contact with the impacting substrate at the simulation start, the previous simulations could not accurately describe the effect of the gas compressed between a failing droplet and the impacting substrate. To properly account for the surrounding gas effect, an effect is made to release a droplet from a certain height. High gas pressures are computationally observed in the region between the droplet and the impact surface at instances just prior to impact. The current simulation shows that the droplet retains its spherical shape when the surface tension energy is dominant over the dissipative energy. When increasing the Weber number, the droplet surface structure is highly deformed due to the appearance of the capillary waves and, consequently, a pyramidal surface structure is formed; this phenomenon was verified with our experiment. Parametric studies using our model include the pre-impact behavior which varies as a function of the Weber number and the surrounding gas pressure.

• Nuclear Engineering and Technology
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• 제32권4호
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• pp.410-423
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• 2000

A two-dimensional numerical model is developed and applied to the LAVA-EXV tests performed at the Korea Atomic Energy Research Institute (KAERI) to investigate the external cooling effect on the thermal margin to failure of a reactor pressure vessel (RPV) during a severe accident. The computational program was written to predict the temperature profile of a two-dimensional spherical vessel segment accounting for the conjugate heat transfer mechanisms of conduction through the debris and the vessel, natural convection within the molten debris pool, and the possible ablation of the vessel wall in contact with the high temperature melt. Results of the sensitivity analysis and comparison with the LAVA-EXV test data indicated that the developed computational tool carries a high potential for simulating the thermal behavior of the RPV during a core melt relocation accident. It is concluded that the main factors affecting the RPV failure are the natural convection within the debris pool and the ablation of the metal vessel, The simplistic natural convection model adopted in the computational program partly made up for the absence of the mechanistic momentum consideration in this study. Uncertainties in the prediction will be reduced when the natural convection and ablation phenomena are more rigorously dealt with in the code, and if more accurate initial and time-dependent conditions are supplied from the test in terms of material composition and its associated thermophysical properties.

• Tribology and Lubricants
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• 제10권3호
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• pp.18-28
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• 1994

Sliding friction between a spherical pin of 8mm in diameter and flat (disk) substrates coated with vacuum-deposited thin film was measured under ultra high vacuum pressure for various materials, various rates of film supply (8~210 nm/min), various sliding velocities (1.5~67.0 mm/s). It was found that the most effective lubrication was obtained when the adhesion between $Si_3N_4$ pin and SUS440C disk was high and that between $Si_3N_4$ pin and $Si_3N_4$ disk was low. When In film was used as a lubricant between $Si_3N_4$ pin and stainless steel disk, the friction coefficient had a value as low as 0.04. In this case, the normal load W and the sliding speed V were expressed as 10N and 24 mm/s for $10^{-6}Pa$. The dependence of $\mu$ on the thickness h of the Ag film, which was used as a lubricant between $Si_3N_4$ pin and SUS440C (Q) disk was expressed as $\mu$=0.12 for W=10N and V=24mm/s when the film was thicker than 100nm. A brief discussion on these relations is presented from the viewpoint of the real contact area.

• Tribology and Lubricants
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• 제30권5호
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• pp.291-294
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• 2014

Multiple additives can help improve the performance of generally used lubricants. These additives include MoS2, cadmium, chloride, indium, sulfide, and phosphide, which are harmful to both humans and the environment. Thus, researchers in this industry have been trying to reduce the use of these additives by finding alternatives. Nanodiamonds are one of these candidates. Nanodiamond particles are very hard, chemically stable, and highly heat-conductive. This research involved uniformly dispersing nanodiamond particles in marine engine oils via a matrix synthesis method at various concentrations (0, 0.1, 0.3, 0.5, and 1.0 wt). Friction and wear tests involved constant loads on ball-on-disk specimens, where the ball was AISI 51200 steel, the disk was AISI 1020 steel, and the sliding speed was 0.217 m/s. The lowest wear occurred at a suitable concentration of nanodiamonds (0.3 wt). However, excessive amounts of nanodiamonds caused them to act as abrasive debris because of their hardness, which increased the wear amount. The friction coefficient decreased as the nanodiamond concentration increased because their octagonal, almost spherical shape caused them to act as rolling contact elements between two surfaces.