• Journal of the Korean Society of Propulsion Engineers
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• v.18 no.5
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• pp.70-78
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• 2014

A numerical study has been conducted to investigate flow and heat transfer characteristics of supersonic second throat exhaust diffusers for high altitude simulation. By changing pressure and configuration, flow and cooling characteristics of the diffuser have been studied. At the normal operation of the diffuser, there were high temperature regions over 3,000 K without cooling, especially near wall and in subsonic diffuser part. If the cooling system of the diffuser is added, flow velocity is increased due to the cooled wall temperature.

• Journal of the Korean Ceramic Society
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• v.39 no.3
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• pp.286-293
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• 2002

Microstructure and the electrical porperties of a ZnO-based multilayered chip-type varistor(abbreviated as MLV) with Ag/Pd(7:3) inner electrode have been studied as a function of firing of temperature. At 1100$^{\circ}$C, inner electrode layers began to show nonuniform thickness and small voids, which resulted in significant disappearance of the electrode pattern and delamination at 1100$^{\circ}$C. MLVs fired at 950$^{\circ}$C showed large degradation in leakage current, probably due to incomplete redistribution of liquid and transition metal elements in pyrochlore phase decomposition. Those fired at 1100$^{\circ}$C and above, on the other hand, revealed poor varistor characteristics and their reproductibility, which are though to stem from the deformation of inner electrode pattern, the reaction between electrode materials and ZnO-based ceramics, and the volatilization of $Bi_2O_3$. Throughout the firing temperature range of 950∼1100$^{\circ}$C, capacitance and leakage current increased while breakdown voltage and peak current decreased with the increase of firing temperature, but nonlinear coefficient and clamping ratio kept almost constant at ∼30 and 1.4, respectively. In particular, those fired between 1000$^{\circ}$C and 1050$^{\circ}$C showed stable varistor characteristics with high reproducibility. It seems that Ag/Pd(7:3) alloy is one of the electrode materials applicable to most ZnO-based MLVs incorporating with $Bi_2O_3$ when cofired up to 1050$^{\circ}$C.

• Journal of Conservation Science
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• v.17 s.17
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• pp.73-82
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• 2005

The Bunhwangsaseoktop is the oldest stone brick pagoda in Silla Period. The pagoda body is made by piling small brick-shaped stones trimmed from black andesite and the first-story core has a shrine, which is made by granite. In 1915 it was repaired on a large scale, but now is severely damaged. Many kind of the stone decay like flaking, granular disintegration have occurred especially on the granite surface of the pagoda. In this study have been investigated the stone decay type and its cause in relation to efflorescence on the body part. Various analysis show that the deterioration on the granite is due to the same materials that lead to efflorescence on the body stone surface. The soluble salt like sodium nitrate, calcium sulfate and sodium sulfate come from white joint mortar. This salt solution is recrystallized in the outside of the pagoda, but most of them flow down with rain. In This process the porous granite absorbes the dissolved salts with moisture into the inside by capillary action. In order to reduce this problem, therefore, white joint moral is changed with other less soluble materials. And it is necessary to take steps to prevent water from seep into the inside of the stone, because this water dissolves the white joint mortar.

• Journal of Conservation Science
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• v.31 no.4
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• pp.351-360
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• 2015

This is the result of the study on the temporary fortifier using sublimation type Consolidate is Cyclododecane to prepare plan for reinforcement of the surface part that can be damaged during the dismantling of stone cultural heritages. To supplement the disadvantages of the existing reinforcement methods using intumescent urethane foam, Cyclododecane was diluted in solvent to reinforce the surface and inside desquamation, and after dismantling the framework, it sublimated by imposing heat of about $60^{\circ}C$. Such method can guarantee the strength needed for reinforcement of the damaged surface with outstanding reversibility of Cyclododecane being entirely sublimated. But, it shows big difference of effect according to the solvent, so it shall be diluted in petroleum ether or heated in a double boiler. Therefore, considering the working conditions at the site, it seems the most appropriate to use petroleum ether double boiler heating method for injection and filling of the desquamation part and temporary reinforcement processing with Cyclododecane diluted in petroleum ether for surface spraying.

• Proceedings of the Korean Vacuum Society Conference
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• 2014.02a
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• pp.274-274
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• 2014

금속칼코게나이드 화합물중 하나인 $MoS_2$는 초저 마찰계수의 금속성 윤활제로 널리 사용되고 있으며 흑연과 비슷한 판상 구조를 지니고 있어 기계적 박리법을 통한 그래핀의 발견 이후 2차원 박막 합성법에 대한 활발한 연구가 진행되고 있다. 최근 다양한 응용이 진행 중인 그래핀의 경우 높은 전자이동도, 기계적 강도, 유연성, 열전도도 등 뛰어난 물리적 특성을 지니고 있으나 zero-bandgap으로 인한 낮은 on/off ratio는 thin film transistor (TFT), 논리회로(logic circuit) 등 반도체 소자 응용에 한계가 있다. 하지만 $MoS_2$는 벌크상태에서 약 1.2 eV의 indirect band-gap을 지닌 반면 단일층의 경우 1.8 eV의 direct-bandgap을 나타내고 있다. 또한 단일층 $MoS_2$를 이용하여 $HfO_2/MoS_2/SiO_2$ 구조의 트랜지스터를 제작하였을 때 $200cm^2/v^{-1}s^{-1}$의 높은 mobility와 $10^8$ 이상의 on/off ratio 나타낸다는 연구가 보고되어 있어 박막형 트랜지스터 응용을 위한 신소재로 주목을 받고 있다. 한편 2차원 $MoS_2$ 박막을 합성하기 위한 대표적인 방법인 기계적 박리법의 경우 고품질의 단일층 $MoS_2$ 성장이 가능하지만 대면적 합성에 한계를 지니고 있으며 화학기상증착법(CVD)의 경우 공정 gas의 분해를 위한 높은 온도가 요구되므로 박막형 투명 트랜지스터 응용을 위한 플라스틱 기판으로의 in-situ 성장이 어렵기 때문에 이를 보완할 수 있는 $MoS_2$ 박막 합성 공정 개발이 필요하다. 특히 Plasma enhanced chemical vapor deposition (PECVD) 방법은 공정 gas가 전기적 에너지로 분해되어 chamber 내부에서 cold-plasma 형태로 존 재하기 때문에 박막의 저온성장 및 대면적 합성이 가능하며 고진공을 바탕으로 합성 중 발생하는 오염 요소를 효과적으로 제어할 수 있다. 본 연구에서는PECVD를 이용하여 plasma power, 공정압력, 공정 gas의 유량 등 다양한 공정 변수를 조절함으로써 저온, 저압 조건하에서의 $MoS_2$ 박막 성장 가능성을 확인하였으며 전구체로는 Mo 금속과 $H_2S$ gas를 사용하였다. 또한 향후 flexible 소자 응용을 위한 플라스틱 기판의 녹는점을 고려하여 공정 온도는 $300^{\circ}C$ 이하로 설정하였으며 합성된 $MoS_2$ 박막의 두께 및 화학적 구성은 Raman spectroscopy를 이용하여 확인 하였다. 공정온도 $200^{\circ}C$와 $150^{\circ}C$에서 성장한 $MoS_2$ 박막의 Raman peak의 경우 상대적으로 낮은 공정온도로 인하여 Mo와 H2S의 화학적 결합이 감소된 것을 관찰할 수 있었고 $300^{\circ}C$의 경우 약 $26{\sim}27cm^{-1}$의 Raman peak 간격을 통해 5~6층의 $MoS_2$ 박막이 형성 된 것을 확인할 수 있었다.

• Journal of the Korea Concrete Institute
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• v.14 no.4
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• pp.449-456
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• 2002

Recently, the application of high strength and high performance concrete has been gradually increased as an important construction material for high rise and huge scaled construction. However, high performance concrete has undesirable characteristics of spalling subjected to high temperature due to its dense microstructure content. A spalling by fire brings surface failure and falling off concrete member. It is considered that spalling by fire should be taken into account for the safety of the concrete structure under fire. Therefore, in this paper, tests are carried out using high performance concrete containing polypropylene(PP) fiber in order to improve the fire resistance performance. PP fiber contents and member sizes are varied. According to experimental results, as for the influence of PP fiber contents, all the test specimens without PP fiber show entire failure in W/C of 35％, while they show nearly sound shape except some kinds of surface fracture in W/C of 55％. When PP fiber is contained more than 0.07％, favorable prevention effects of spatting by fire are obtained. As for the effects of test specimens size, it tends to increase the possibilities of spatting by fire as test specimens become larger. And spatting by fire at the edge of test specimens occurs more frequently than at the surface of test specimens. Residual compressive and tensile strength shows 45∼65 ％ of its original strength at W/C of 35％, and 30∼40％ at W/C of 55 ％.

• Journal of Chest Surgery
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• v.29 no.12
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• pp.1342-1346
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• 1996

A right thoracotomy was used for the reoperation or mitral valve of 15 patients who had previously undergone a cardiac operation through a median sternotomy. In our experience. this approach provided dn excellent exposure of the nlitral valve and easy cannulations of both cavie with minimal dissection, ilvoiding any damage of cardiac and major vessels during re-sternotomy Arterial cannulation was performed in the ascending aorta in 13 patients And in the femoral artery in 2 patients. In earlier cases, venous cannulation was done in the SVC And IVC through the right atrium and snared. In later cases, this could be done without snaginly of both cavae or by placing a silgle light-angled catheter into the right atrium. Crystalloid cardioplegic solution was infused for myocardial protection. Hypothermia was controlled at 20\ulcorner$25^{\circ}C$. For defibrillation, internal paddles were used In one patient while sterilized external paddles were used in 10 patients. In the remaining four patients. however. the heart beat spontaneously The respirator could be weaned within 48 hours alter the operation and no pulmonary complication was observed. One out of the 15 patients expired due to sudden attack of ventricular tarchycardid developed ten days after the operation, but the rest of the patients were discharged with good condition.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 1996.10a
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• pp.65-70
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• 1996

엔진소음을 소음특성에 따라 분류하면 공력소음(Aerodynamic Noise), 연소소음(Combustion Noise), 기계적인 소음(Mechanical Noise)으로 나눌 수 있으며 소음원의 종류에 따라 분류하면 배기계소음(Exhaust System Noise)으로 나눌 수 있으며 소음원의 종류에 따라 분류하면 배기계소음(Exhaust System Noise), 흡기계소음(Intake System Noise), 냉각계소음(Cooling System Noise), 엔진표면소음(Engine System Noise)등으로 분류할 수 있다. 이러한 여러소음중 엔진 내부의 유동에 의한 흡배기계통으로의 소음방출은 자동차 실 내외 소음의 중요한 문제로 대두되는데, 이를 줄이기 위해 그 동안 소음기 등의 서브시스템의 형태와 그 위치조정에 관한 연구가 수행되어 왔다. 그러나 이것이 비용 또는 성능에 영향을 미치므로 본질적인 소음원을 규명해 내는 것이 필요하게 되었다. 흡배기계의 소음은 엔진의 흡입, 배기행 정시 피스톤의 운동에 의해 팽창 및 압축파 형태의 압력파(pressure wave)로 발생하게 되고, 밸브근방에서는 유동의 박리(separation)에 의해 발생하게 된다. 소음기 등의 서브시스템에서도 유동의 박리에 의해 발생하게 되며 특히 배기행정시 발생하는 압력파는 비선형영역에 있게된다. 흡기소음은 배기에 비해 그 크기가 작아서 그동안 등한시 되어왔으나 이것이 소비자의 불평요인으로 작용하므로써 이에 대한 연구도 활발히 수행되어야 한다. Bender, Bramer[1]는 흡배기계 소음의 외부 방사에 관하여 전반적으로 기술하였고 Sierens등[2]은 흡기계에서 1차원 MOC(Method of Characteristics)방법으로 비정상 유동해석을 하고 실험결과와 비교하였다. J.S.Lamancusa 등[3]은 흡기 소음원을 실험을 통해 예측하였고, 흡기소음도 비선형 거동을 보인다고 밝혔다. Yositaka Nishio 등[4]은 새로운 흡기실험장치를 고안하여 공명기(resonator)의 위치 변화에 의한 저소음 흡기계를 설계 초기단계에서부터 적용하려 하였다. 일반적으로 흡배기계의 복잡한 형상 때문에 대부분 실험을 통해 문제를 해결하려 하였고, 수치해석은 피스톤의 운동을 배제한 단순화한 흡배기계의 정상상태 유동해석이 주를 이루어왔다. Taghaui and Dupont 등[5]은 KIVA코드를 사용하여 흡기포트와 연소실 그리고 밸브의 움직임을 동시에 고려한 수치해석을 도입하였다. 하지만 이들이 밸브의 운동을 고려하기 위해 사용한 이동격자는 격자점은 시간에 따라 변화하지만 그 격자의 수가 일정하게 유지되어 있어서 밸브의 완전개폐를 해석할 수가 없다. 강희정[6]은 단일 실린더와 단일 배기밸브를 갖는 문제로 단순화하여 피스톤과 밸브의 움직임을 고려하므로써 배기행정 후 소음이 어떻게 전파해 나가는가를 연구하였다. 본 연구에서도 최소밸브간격과 최대밸브간격 사이에서만 계산이 가능하나 흡기의 경우는 밸브가 닫힐 때 생기는 압력파가 중요하므로 실린더와 밸브사이에 벽면조건을 주어 밸브의 개폐를 모사하였다.

• Korean Journal of Heritage: History & Science
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• v.45 no.1
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• pp.86-101
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• 2012

The constituting rocks of Multi-storied Round shape stone Pagoda of Unjusa Temple are lithic tuff and rhyolite tuff breaccia which show green or grey and also rock fragment with poor roundness are present in the structure. lithic tuff is composed of feldspar and quartz which are glassy texture and cryptocrystalline and also micro crystalline are scattered. phenocryst quartz and feldspar in the substrate composed of feldspar and opaque minerals are found in rhyolite tuff breaccia. dust, exfoliation, cavity, fracture and crack are observed in all the stone of the pagoda and the result of Infrared Thermography shows partial inter cavities have developed severely which may cause further exfoliation. In addition, a great deal of various grey, green, and yellow brown lichen as well as bryophyte are present at the upper part of eastern and western roof stone located above the third floor. Discolors remarkably shown at stereobate and roof stone are identified as inorganic pollutants such as manganese oxide, iron oxide and iron hydroxide. The stone of the pagoda of the Chemical Index of Alteration (CIA) and the Weathering Potential Index (WPI) are 55.69 and 1.12 respectively and this corresponds to a highly weathered stage. The measured values, average ultrasonic velocity 2,892m/s, coefficient of weathering 0.4k and compressive strength $1,096kg/cm^3$, suggest that the rock strength and durability are weakened.

• Journal of the Korean Society of Food Science and Nutrition
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• v.46 no.3
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• pp.394-399
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• 2017

To resolve environmental pollution caused by synthetic packaging materials, biodegradable films have been studied as an alternative. In this study, we prepared rockfish skin gelatin (RFG) and nano-clay (Cloisite $Na^+$ and Cloisite 10A) composite films to compare the effects of nano-clay on the physical properties of RFG film. Gelatin was extracted from rockfish skin and used to prepare RFG film with sorbitol as a plasticizer. Tensile strength (TS), water vapor permeability (WVP), and water solubility (WS) of the RFG film were 15.0 MPa, $2.70{\times}10^{-9}g\;m/m^2\;s\;Pa$, and 53.8%, respectively. Addition of nano-clay to the RFG film increased TS and decreased WVP and WS. The X-ray diffraction analysis and scanning electron microscopic results suggest that RFG/nano-clay composite films formed an exfoliated structure. These results indicate that RFG/nano-clay composite films can be applied as biodegradable packaging materials in the food industry.