• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.33 no.8
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• pp.84-91
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• 2005

An experimental investigation has been carried out to examine heat-transfer characteristics of an axisymmetric, under-expanded, sonic jet impinging on a flat plate and the local measurement of surface pressures and heat transfer coefficients on a plate have been achieved together with a visualization test of shock structure in a jet. Heat transfer coefficients on a plate have been found to be changed significantly depending on the under-expansion ratio as much as the nozzle-to-plate distance. These phenomena could be explained by the wall pressure measurement and the shock visualization.

• Journal of the Society of Disaster Information
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• v.20 no.1
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• pp.40-46
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• 2024

Purpose: In this study, in order to ensure the evacuation safety of plant facilities, we analyze the relationship between the height of smoke removal boundary walls, the presence or absence of smoke removal equipment, and evacuation safety. Method: Using fire and evacuation simulations, evacuation safety was analyzed through changes in the height of the smoke removal boundary wall, air supply volume and exhaust volume according to vertical dista. Result: In the case of visible drawings, if only 0.6m of boundary wall is used, the time below 5m reaches the shortest, and 1.2m of boundary width is 20% longer than when using smoke removal facilities. In the case of temperature, 1.2m is 20% longer than 0.6m when only the boundary width is used without smoke removal facilities. Conclusion: It was found that increasing the length of the smoke removal boundary wall could affect visibility, and installing a smoke removal facility would affect temperature. Therefore, it is determined that an appropriate smoke removal plan and smoke removal equipment should be installed in consideration of the process characteristics.

• Journal of the Korean Vacuum Society
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• v.17 no.4
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• pp.365-373
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• 2008

We have succeeded in synthesizing vertically aligned thin multi-walled carbon nanotubes (VA thin-MWCNTs) by a catalytic chemical vapor deposition (CCVD) method onto Fe/Al thin film deposited on a Si wafers using an optimum amount of hydrogen sulfide ($H_2S$) additive. Scanning electron microscope (SEM) images revealed that the as-synthesized CNT arrays were vertically well-oriented perpendicular to the substrate with relatively uniform length. Transmission electron microscope (TEM) observations indicated that the as-grown CNTs were nearly catalyst-free thin-MWCNTs with small outer diameters of less than 10nm. The average wall number is about 5. We suggested a possible growth mechanism of the VA thin-MWCNT arrays. The VA thin-MWCNTs showed a low turn-on electric field of about $1.1\;V/{\mu}m$ at a current density of $0.1\;{\mu}A/cm^2$ and a high emission current density about $2.5\;mA/cm^2$ at a bias field of $2.7\;V/{\mu}m$. Moreover, the VA thin-MWCNTs presented better field emission stability without degradation over 20 hours (h) at the emission current density of about $1\;mA/cm^2$.

• Solar Energy
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• v.14 no.2
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• pp.75-90
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• 1994

Thermal energy transport in a two-dimensional horizontal and vertical channel with an isothermal rectangular beam attached to one adiabatic wall is investigated from the numerical solution of Navier-Stokes and energy equations. The solutions have been obtained for dimensionless aspect equations. The solutions have been obtained for dimensionless aspect ratios of beam, H/B=$0.25{sim}4$, Reynolds numbers, Re=$50{\sim}500$ and Grashof numbers, Gr=$0{\sim}5{\times}10^4$. The mean Nusselt number, $\overline{Nu}$ for horizontal and vertical channels shows same value at Gr=0 and increases as Gr increases and decreases as H/B increases at Re=100. $\overline{Nu}$ of vertical channel shows higher in $0.25{\leq}H/B<1.1$ and lower in $1.1{\leq}H/B{\leq}4.0$ than that of horizontal channel at $Gr=10^4$, Re=100. $\overline{Nu}$ of vertical channel shows higher in $0.25{\leq}H/B<1.1$ and lower in $1.1{\leq}H/B=1.0$ than that of horizontal channel at Re=100, $0<Gr{\leq}5{\times}10^4$. A comparison between the experimental and numerical results shows good agreement.

• Journal of the Korea Concrete Institute
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• v.21 no.5
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• pp.549-556
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• 2009

This research analyzed the structural efficiency and application by improving the 100 mm width vertical joint to 150 mm and developing three connection methods to reduce the difficulty in assembling and handling PC walls. Moreover, nonlinear finite analysis was used for analyzing. From the analysis results, when double width connection was applied, the PC wall showed larger load capacity and ductility due to the steel bar sharing loads efficiently. Moreover, as the dimension of loops and the number of bars increased, the maximum load capacity increased as well. Also, among the double width connections, the largest capacity showed in the order of welding, ring and C type loop. However, in case of welding type loop connection, the ring type loop is more stable due to changes in different site conditions. Therefore, thorough quality control of welding is necessary.

• Proceedings of the Korean Vacuum Society Conference
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• 2011.08a
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• pp.387-387
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• 2011

탄소 나노튜브(Carbon nanotubes, CNTs)는 육각형 모양의 구조로서 오직 탄소만으로 이루어진 소재이다. CNT는 열전도율이 다이아몬드보다 약 2배 우수하고, 전기 전도는 구리에 비해 1,000배 높으며, 강도는 강철보다 100배나 뛰어나다. CNT의 이러한 특성을 이용한 트랜지스터, 태양전지, 가스 검출을 위한 고감도 센서, 나노 섬유, 고분자-탄소나노튜브 고기능 복합체 등 많은 분야에서 연구가 활발히 진행되고 있다. 또한 수직으로 성장된 탄소 나노튜브는 일반적인 재료에서는 보기 드물게 힘들게 직경이 나노 크기인 반면 길이는 수 mm까지 합성 되기 때문에 앞서 언급한 분야로의 활용이 더욱 유리하며, 그 중에서도 나노 섬유, 나노 복합체로서의 활용에 극히 유용하다. 이러한 이유로 수직 배열된 CNT 합성에 많은 연구가 집중 되고 있다. 여러 합성 방법 중 성장 변수를 비교적 용이하게 조절 가능한 열 화학 기상 증착법(Thermal chemical vapor deposition, TCVD)을 이용하여 수직 배열된 수 mm의 CNT를 합성한 연구 결과들이 보고된 바 있다. 그러나 앞선 연구결과들은 CNT의 성장속도가 느릴 뿐만 아니라 합성 시간이 길어질수록 성장 속도가 감소하는 경향을 보였다. 반면, 마이크로웨이브 플라즈마 화학 기상 증착법(Microwave plasma CVD, MPCVD)은 기존의 다른 TCVD에 비해 낮은 온도에서 CNT를 합성할 수 있는 장점을 가지며, 고출력(~600 W 이상)의 플라즈마를 사용하기 때문에 성장률이 높고 고밀도의 CNT 합성이 가능하다. 본 연구에서는 철을 촉매금속으로 사용하고 MPCVD을 이용하여 얇은 다중벽 CNT를 합성하였다. 철은 직류 마그네트론 스퍼터(D.C magnetron sputter)를 사용하여 증착하였다. 합성시 가스는 탄소 공급원인 메탄($CH_4$)과 함께 플라즈마 공급원인 수소($H_2$)를 사용하였다. 또한 산소($O_2$)의 주입 여부에 따른 CNT의 성장 속도와 성장 길이를 비교하였다. 산소를 주입하였을 때, CNT의 성장 속도와 길이 모두 크게 향상됨을 확인 할 수 있었다. 이는 촉매금속 표면의 비정질 탄소의 흡착으로 인해 활성화된 촉매금속의 반응시간을 증가시키기 때문이다. 성장된 CNT는 주사전자 현미경(Scanning Electron Microscopy, SEM)과 라만 분광법(Raman spectroscopy)을 통해 표면형상과 결정성을 분석하였다.

• The Journal of Korean Academy of Prosthodontics
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• v.48 no.2
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• pp.111-121
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• 2010

Purpose: This 3D-FEA study was performed to investigate the influence of marginal bone loss pattern around the implant to the stress distribution. Material and methods: From the right second premolar to the right second molar of the mandible was modeled according to the CT data of a dentate patient. Teeth were removed and an implant ($\Phi\;4.0{\times}10.0mm$) was placed in the first molar area. Twelve bone models were created; Studied bone loss conditions were horizontal bone loss and vertical bone loss, assumed bone loss patterns during biologic width formation, and pathologic vertical bone loss with or without cortification. Axial, buccolingual, and oblique force was applied independently to the center of the implant crown. The Maximum von Mises stress value and stress contour was observed and von Mises stresses at the measuring points were recorded. Results: The stress distribution patterns were similar in the non-resorption and horizontal resorption models, but differed from those in the vertical resorption models. Models assuming biologic width formation showed altered stress distribution, and weak bone to implant at the implant neck area seams accelerates stress generation. In case of vertical bone resorption, contact of cortical bone to the implant may positively affect the stress distribution.

• Restorative Dentistry and Endodontics
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• v.34 no.4
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• pp.350-355
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• 2009

Bond strength depends on characteristics of bonding surface and restorative technique. The majority of studies dealing with dentin bond strength were carried out on flat bonding surface, therefore, difference of bond strength between axial wall and pulpal wall is not clear yet. This study evaluated bonding difference between cavity walls in class I composite resin restoration with different filling techniques. Twenty extracted caries-free human third molars were used. Cavities were prepared in 6 ${\times}$4 ${\times}$3 mm box-type and divided into four groups according to filling technique and bonding surface: Group I; bulk filling - pulpal wall, Group II; bulk filling - axial wall, Group III; incremental filling - pulpal wall, Group IV; incremental filling - axial wall. Cavities were filled with Filtek $Z250^{(R)}$(3M/ESPE., USA) and Clearfill SE $bond^{(R)}$(Kuraray, Japan). After 24 hour-storage in $37^{\circ}C$water, the resin bonded teeth were sectioned bucco-lingualy at the center of cavity. Specimens were vertically sectioned into 1.0 ${\times}$1.0 mm thick serial sticks perpendicular to the bond surface using a low-speed diamond saw (Accutom 50, Struers, Copenhagen, Denmark) under water cooling. The trimmed specimens were then attached to the testing device and in turn, was placed in a universal testing machine (EZ test, Shimadzu Co., Kyoto, Japan) for micro-tensile testing at a cross-head speed of 1 mm/min. The results obtained were statistically analyzed using 2-way ANOVA and t-test at a significance level of 95%. The results were as follows: 1. There was no significant difference between bulk filling and incremental filling. 2. There was no significant difference between pulpal wall and axial wall, either. Within the limit of this study, it was concluded that microtensile bond strength was not affected by the filling technique and the site of cavity walls.

• Journal of Korean Tunnelling and Underground Space Association
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• v.12 no.2
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• pp.129-144
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• 2010

The earth pressure acting on the vertical shaft is less than that acting on the retaining wall due to three dimensional arching effect. Thus, it might be essential to estimate the earth pressure actually acting on the shaft when designing the vertical shaft. In this paper, large-sized model tests were conducted as Part II of companion papers to verify the newly suggested earth pressure equation proposed by Kim et al. (2009: Part I of companion papers) that can be used when designing the vertical shaft in cohesionless soils as well as in c-$\phi$ soils and multi-layered soils. The newly developed model test apparatus was designed to be able to simulate staged shaft excavation. Model tests were performed by varying the radius of vertical shaft in dry soil. Moreover, tests on c-$\phi$ soils and on multi-layered soils were also performed; in order to induce apparent cohesion to the cohesionless soil, we add some water to the dry soil to make the soil partially-saturated before depositing by raining method. Experimental results showed a load transfer from excavated ground to non-excavated zone below dredging level due to arching effect when simulating staged excavation. It was also found that measured earth pressure was far smaller than estimated if excavation is done at once; the final earth pressure measured after performing staged excavation was larger and matched with that estimated from the newly proposed equation. Measured results in c-$\phi$ soils and in multi-layered soils showed reduction in earth pressures due to apparent cohesion effect and showed good matches with analytical results.

• Proceedings of the Korean Society of Surveying, Geodesy, Photogrammetry, and Cartography Conference
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• 2007.04a
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• pp.179-182
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• 2007

In this study, we proposed a way to detect trees using virtual grid and to discriminate vertical wall points from building tops based on effective segmentation of LIDAR point cloud utilizing scan line characteristics. Trees were detected by their surface roughness value calculated based on virtual grid and vertical building wall points were discriminated from building tops with one dimensional filtering of scan line during segmenting point cloud. In results, we could distinguish trees from buildings and bind virtical wall points to prevent them from faltly acting on point segmentation process.