• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 1998.10a
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• pp.32-32
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• 1998

고체 추진제 로켓의 연소시에 발생되는 산화 알루미늄(A1$_2$O$_3$) 입자는 로켓 추진 노즐에서 팽창과정의 효율을 저하시키는 요소가 되며, 이러한 비효율성은 연소 가스와 입자간의 비평형 상태 효과와 기본적인 속도와 열적 차이에 의해서 발생된다고 보고되었다. 또한 연소시 발생된 산화 알루미늄 입자는 높은 열과 큰 운동량을 가지고 로켓 노즐 내부를 유동하게 되며, 매우 많은 량이 짧은 시간에 고온 고속으로 노즐 벽면이나 기타 구조물에 충돌 및 점착하기 때문에 로켓 노즐내의 표면이 손상을 입게 되고, 로켓의 방향 제어 및 조정 안정성이 저하되며, 구조적인 강도가 약화 될 수 있다. 또한 산화 알루미늄 액적들의 경우 노즐 벽면에 고착되게 되면 로켓의 중량 증가로 인해서 추력의 손실을 초래할 수 있다. 따라서 이러한 연소 부산물들의 운동 경로와 충돌 위치 및 표면에서의 충돌량과 그리고 충돌에 따른 마모량 및 점착 그리고 열전달 특성을 예측하는 것이 필수적이다.

• Cement
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• s.38
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• pp.16-21
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• 1970

시멘트공업경영은 자본집약산업으로 그 규모는 일정수준의 단위까지 팽창되지 않으면 안되는 시장경쟁적 여건을 포함하고 있는데 특히 시멘트제품의 수급비탄력성은 방대한 규모의 생산시설과 여기에 투입된 노동을 유휴화시키고 이로 인한 기업의 고정비부담을 가중시키므로 적자의 가장 큰 요인으로 작용하고 있다. 이와 같은 유휴비용중 특히 노무비부담이 큰 비중을 점하고 있는데 현세멘트공업계의 임금제도는 저생산저임금형태로 기업과 종업원에게 공히 유용한 요소가 되고 있다. 이러한 시멘트의 계절적인 수요변동에 따라 성수기에 있어서는 노동의 부족을 나타내고 비성수기에 있어서는 확대된 부분이 축소된 것만큼 인원을 감소시켜야하므로 노사간의 불화와 기업공신력의 상실등을 야기시키게 되어 기업측이나 종업원측으로 보아서도 서로의 손실임에는 틀림없다. 따라서 이와 같은 문제는 합리적인 임금제도 및 영리의 결여에서 오는 것인 만큼 기업과 종업원에 공히 이득을 가져와 줄 수 있는 성과급제도의 도입적용에 시급히 필요하다고 하겠다.

• Proceedings of the Korean Information Science Society Conference
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• 2001.04a
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• pp.319-321
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• 2001

무선망을 이용한 데이터 통신 서비스에 대한 수요가 빠르게 늘고, 인터넷(Internet)의 팽창과 일반화에 따라 무선데이터망에서 TCP/IP 통신 응용을 효율적으로 지원하는 것이 중요한 문제로 대두되고 있다. 그러나 무선망은 유선망과 달리 높은 오류율이 나타난다. 그러므로 상대적으로 데이터의 오류율과 손실률이 낮은 유선망을 기반으로 설계된 기존의 TCP 기법들은 무선망에서 적절하게 작동하지 못한다. 이를 해결하기 위해서 Snoop과 Spoofing 등의 방법들이 제안되어 왔는데 Snoop의 경우 유선 링크의 대역폭을 낭비할 수 있는 가능성이 있고 Spoofing 등의 방법들이 제안되어 왔는데 Snoop의 경우 유선 링크의 대역폭을 낭비할 수 있는 가능성이 있고 Spoofing의 경우 기지국의 버퍼 요구량이 크다는 문제가 있다. 이에 본 논문에서는 기지국에서 Snoop과 Spoofing을 동시에 기용하여 무선 링크에서의 패킷 전송 성공 여부에 따라 이 두 가지 모듈을 선택적으로 사용함으로써 기지국의 버퍼 요구 정도를 줄이면서 TCP 성능을 향상시킬 수 있는 방법을 제안하였다.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.26 no.5
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• pp.455-462
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• 2015

In this paper, we suggested multiband antenna that can be equipped on a inflatable life-jacket, operating VHF-DSC band(156 MHz), COSPAS-SARSAT band(406 MHz) and GPS band(1,575 MHz) for search and rescue survivors quickly. The GPS band antenna was implemented with a square ring-slot planar antenna, and the COSPAS-SARSAT and VHF-DSC band antenna were implemented meander type dipole antennas. In order to place the antenna on a life-jacket, we installed it on 0.2 mm thickness FR-4 substrate to obtain a flexibility. It appeared that the antenna has -14.6 dB, -30.9 dB, and -18 dB return loss in COSPAS-SARSAT, GPS, and VHF-DSC band, respectively. In addition, its gain has 0.83 dBi, 2.1 dBi in COSPAS-SARSAT and GPS band, respectively.

• Applied Microscopy
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• v.32 no.2
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• pp.149-156
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• 2002

For investigation of the activated carbon in the rat liver toxicated by lead. Aniamls used $7{\sim}8$ weeks to Sparague-Dewley rat (150 g). The lead acetate (500 ppm) were injected and activated carbon (40 mg/kg) were treated orally for four and eight weeks, respectivelly, and observed by the electron microscope. The group with only lead for 4 weeks, The mitochondria and rough endoplasmic reticulum (rER) were extended and ribosomes dropped from the rER. The group with lead-activated carbon for 4 weeks, The number of lysosomes increased. The shapes of nucleus and rough endoplasmic reticulum observed almost similar with nomally. The group with only lead for 8 weeks, The mitochondria and rough endoplasmic reticulum (rER) were more extended. The group with lead-activated carbon for 8 weeks, the nucleus and rough endoplasmic reticulum was observed nomally.

• Journal of the Korea Convergence Society
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• v.10 no.6
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• pp.7-14
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• 2019

In this paper, we propose a Cascade Classifier face detection method using the Haar-like feature, which is complemented by the Flood Fill algorithm for lossy areas due to illumination and shadow in YCbCr color space extraction. The Cascade Classifier using Haar-like features can generate noise and loss regions due to lighting, shadow, etc. because skin color extraction using existing YCbCr color space in image only uses threshold value. In order to solve this problem, noise is removed by erosion and expansion calculation, and the loss region is estimated by using the Flood Fill algorithm to estimate the loss region. A threshold value of the YCbCr color space was further allowed for the estimated area. For the remaining loss area, the color was filled in as the average value of the additional allowed areas among the areas estimated above. We extracted faces using Haar-like Cascade Classifier. The accuracy of the proposed method is improved by about 4% and the detection rate of the proposed method is improved by about 2% than that of the Haar-like Cascade Classifier by using only the YCbCr color space.

• Journal of Biomedical Engineering Research
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• v.24 no.1
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• pp.37-44
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• 2003

This experimental study is aimed at evaluating the hydrodynamic performance of newly designed self-expandable graft stents under steady flow condition. Two graft stents with different coating materials and a bare TiNi metallic stent for comparison test were used in the experiment. Pressure variation and velocity distribution at the upstream and downstream of the stents were measured at flow rates of 5, 10, and 15 l/min, respectively. Pressure loss due to insertion of the stent increased with increasing flow rate exponentially as expected. At a flow rate of 15 l/min, pressure loss of Polyure-thane(PU)-coated graft stent was 6 times higher than that of TiNi metallic stent, while the pressure loss of a porous Polytetrafluoroethylene(PTFE)-coated graft stent was comparable to a bare TiNi metallic stent. Velocity profiles of the porous PTFE-coated graft stent were similar to those of a bare TiNi metallic stent regardless of flow rate. Furthermore, the velocity profile of PU-coated graft stent revealed an asymmetrical and relatively low central velocity at a higher flow rate than 10 1/min, expecially, where the effects resulted in increases of wall shear stress and normal stress. The worse hydrodynamic behavior of PU-coated graft stent than the other two stents might be attributed to formation of folds due to poor flexibility of coated material when inserting the graft stent into the pipe with a more smaller size, which later gave rise non-symmetry of flow area, increase of surface roughness and jet flow via the crevice between the stent and cylinder wall.

• Journal of the Korea Concrete Institute
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• v.24 no.5
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• pp.605-612
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• 2012

Spalling of concrete occurs due to vapor pressure ignited explosion, temperature difference across a section, and combination of these factors. Factors affecting spalling can be classified into internal and external factors such as material property and environmental condition, respectively, have to be considered to precisely understand spalling behavior. An external environmental factor such as differences in heating rate cause internal humidity cohesion and different vapor pressure behavior. Therefore, spalling property, vapor pressure and thermal strain property were measured from concrete with compressive strengths of 30 MPa, 50 MPa, 70 MPa, 90 MPa, and 110 MPa, applied with ISO-834 standard heating curve of $1^{\circ}C/min$ heating rate. The experimental results showed that spalling occurred when rapid heating condition was applied. Also, when concrete strength was higher, the more cross section loss from spalling occurred. Also, spalling property is influenced by first pressure cancellation effect of thermal expansion caused by vapor pressure and heating rates.

• Journal of Navigation and Port Research
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• v.39 no.4
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• pp.285-291
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• 2015

Exposure to cold sea water can be life-threatening to the drowned individual. Although appropriate life jacket can be usually be provided for the buoyance at the drowning accident, heat loss can make the drowned individual experience the hypothermia. Inflatable life jackets filled with inflatable air pocket can increase the thermal protection as well as the buoyancy force. Because it is important to know how the human body behaves unde the different life jacket, present study compares the thermal insulation capacity of solid type life jacket with that of inflatable life jacket. In order to represent the insulation capacity of life jacket, thermal resistance is estimated based on the assumption of steady-state. Also, a transient three-dimensional thermal distribution of the thigh is analyzed by using finite element method implementing the Pennes bioheat equation. The finite element model is a segmental, multi-layered representation of the body section which considers the heat conduction within tissue, bone, fat and local blood flow rate.

• Tunnel and Underground Space
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• v.21 no.4
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• pp.297-306
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• 2011

In this paper, we performed thermodynamic energy balance analysis of the underground lined rock cavern for compressed air energy storage (CAES) using the results of multi-phase heat flow analysis to simulate complex groundwater-compressed air flow around the cavern as well as heat transfer to concrete linings and surrounding rock mass. Our energy balance analysis demonstrated that the energy loss for a daily compression and decompression cycle predominantly depends on the energy loss by heat conduction to the concrete linings and surrounding rock mass for a sufficiently air-tight system with low permeability of the concrete linings. Overall energy efficiency of the underground lined rock caverns for CAES was sensitive to air injection temperature, and the energy loss by heat conduction can be minimized by keeping the air injection temperature closer to the ambient temperature of the surroundings. In such a case, almost all the heat loss during compression phase was gained back in a subsequent decompression phase. Meanwhile, the influence of heat conductivity of the concrete linings to energy efficiency was negligible.