• 한국전산유체공학회:학술대회논문집
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• 한국전산유체공학회 2009년 추계학술대회논문집
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• pp.129-134
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• 2009

In the present study, the characteristic of flow distribution in the channel of a plate heat exchanger is investigated numerically. In order to accomplish the efficient and fast analyses of the flow characteristics in the channel, a semi-microscopic analysis has been performed using a porous media model. For semi-microscopic analysis using porous media, the flow resistance coefficients are obtained through the result of pressure drop in the experimental data. The results showed that the variation of mass flow rate, geometry and chevron angle strongly depend on the flow distribution in the channel. Particularly, the chevron angle is most important factor for uniform flow distribution.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 2002년도 봄 학술발표회 논문집
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• pp.189-194
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• 2002

Many researches in the past have shown that a majority initial cracking in concrete are caused during early age period. Therefore, the close examination of early age concrete behavior under various stress conditions is necessary to fully understand the cracking mechanism of concrete. In this study early age cement paste specimen is axially strained up to 20% of its original length by laterally reinforcing it. This type of test is called "Tube Squash Test" and has been previously used to apply up to 50% axial strain on concrete. Microscopic analyses (XRD, FESEM, EDS and DSE/TG) are performed on 20% axially strained early age cement paste specimen. The analysis results show that the microscopic structures and material characteristics of 20% axially strained cement paste remained same as the unstrained cement paste.

• 한국공작기계학회논문집
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• 제15권6호
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• pp.50-57
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• 2006

The investigation of microscopic precision in high speed endmilling is necessary for machinability evaluation, and the environmentally conscious machining technology have more important position in recent machining process. The microscopic precision of workpiece is influenced by machining environments variation as cutting fluid type and lubricant method. In this study, the cutting forces according to variation of cooling and lubrication are investigated by specially designed tool dynamometer. And the surface roughness, micro hardness and residual stress are evaluated according to machining environment. The characteristics of damaged layer in environmentally conscious machining and conventional machining using cutting fluid are compared experimentally.

• 한국가시화정보학회지
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• 제16권1호
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• pp.48-53
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• 2018

In this study, the effect of injection pressure on the column diameter and droplet velocity of liquid jet with the weakly turbulent Rayleigh-like breakup mode is experimentally studied using digital microscopic holography (DMH). The injection nozzle has the diameter of $50{\mu}m$ and injection pressure is varied from 0.1 to 0.4 MPa. When the micro liquid jet is injected into still air, the double-pulsed holograms was recorded on a CCD sensor and numerically reconstructed in order to obtain well focused images. In this study, the liquid column diameter from $50{\mu}m$ orifice nozzle is shown to be changed slightly but the droplet velocity is increased proportionally as the injection pressure is increased.

• International Journal of Naval Architecture and Ocean Engineering
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• 제9권1호
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• pp.66-76
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• 2017

This paper is concerned with investigating the plastic material properties of steel plate formed by line heating method, and is aimed at implementing more rational design considering the accidental limit states such as collision or grounding. For the present study, line heating test for marine grade steel plate has been carried out with varying plate thickness and heating speed, and then microscopic examination and tensile test have been carried out. From the microscopic, it is found that the grain refined zones like ferrite and pearlite are formed all around the heat affected zone. From the tensile test results, it is seen that yield strength, tensile strength, fracture strain, hardening exponent and strength coefficient vary with plate thickness and heat input quantity. The formulae relating the material properties and heat input parameter should be, therefore, derived for the design purpose considering the accidental impact loading. This paper ends with describing the extension of the present study.

• 대한화학회지
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• 제62권3호
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• pp.243-252
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• 2018

이 연구에서는 중학교 2학년 학생들의 물질의 특성에 대한 거시적, 미시적 수준의 개념을 비교하였다. 기초 입자 개념 검사와 녹는점, 용해도, 밀도 개념에 대한 거시적, 미시적 수준의 개념 검사를 개발하여 371명의 중학생들을 대상으로 실시하였다. 학생들의 응답을 거시적 수준과 미시적 수준의 개념 이해 여부에 따라 네 가지로 범주화하고 범주별 비율과 특징을 분석하였다. 연구 결과, 거시적 수준의 개념을 이해한 학생들은 미시적 수준에서 다양한 오개념을 가지고 있는 경우가 많았다. 많은 학생들은 물질의 특성과 관련한 미시적 수준의 개념뿐 아니라 거시적 수준의 개념 이해에도 어려움을 겪었다. 거시적 수준의 개념을 이해하지 못한 학생들은 대부분 미시적 수준에서 거시적 수준의 응답과 일치하는 응답을 하지 못하였다. 기초 입자 개념 문항에 옳은 응답을 한 학생들도 물질의 특성 관련 개념을 이해하는 데 어려움을 겪었으나, 거시적 수준의 개념을 이해한 경우 미시적 수준의 개념도 함께 이해한 비율이 높았다. 연구 결과를 바탕으로 물질의 특성 관련 개념의 효과적인 교수학습 및 향후 교육과정의 개선을 위한 교육적 시사점을 논의하였다.

• 한국윤활학회:학술대회논문집
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• 한국윤활학회 2000년도 제32회 추계학술대회 정기총회
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• pp.318-331
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• 2000

Electrical and tribological behaviours of a copper-graphite brush in a slipring-brush assembly were investigated to evaluate the characteristics of electric signal transmission between a slipring and a brush. Five brush materials containing different amounts of copper and graphite were studied. The result showed that a copper-graphite brush at a particular graphite content exhibited the most stable frictional and electrical behaviour suggesting an optimum amount of a solid lubricant in a metal-graphite brush system. Microscopic observation and the surface analysis showed good agreements with this phenomena. In addition, the deviation of the friction coefficient and electric signal distortion has a close relationship with a microscopic mechanical vibration and the change of a real contact area.

• 대한수의학회지
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• 제24권2호
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• pp.245-266
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• 1984

As a fundamental study to increase the reproductive efficiency in cattle, highly motile sperm were separated and collected from raw semen, extended semen and frozen semen by different methods using various concentrations of bovine serum albumin or Tyrode's solution. Various characteristics and light microscopic and electron-microscopic morphology of sperm separated by different methods were compared. The results obtained were as follows; 1. The sperm separated from raw semen using bovine serum albumin showed significantly high value in motility, motile sperm count, percent of normal sperm and progressive motility, as compared with control sperm and revealed the highest sperm recovery rate when separated with 6% bovine serum albumin. 2. The sperm motility, percent of normal sperm and progressive motility of the highly motile sperm frozen after being separated from raw semen with bovine serum albumin, showed significantly high value than those of a control sperm and especially found the highest value when separated with 20% bovine serum albumin. 3. Light-microscopic percent of abnormality was significantly low in the prefrozen and postfrozen highly motile sperm separated with bovine serum albumin, as compared with control sperm. 4. Electron-microscopic finding of the highly motile sperm separated with bovine serum albumin showed low percent of deformity in the dilatation and vesiculation of cell membrane, in dilatation and density loss of acrosome than in those of control sperm. 5. It was impossible to separate the highly motile sperm from frozen semen with bovine serum albumin, but it was possible with Tyrode's solution. 6. Recovery rate of highly motile sperm from raw semen extended semen and frozen semen was the highest when the sperm pellet stood in Tyrde's solution for 80 minutes. 7. The highly motile sperm separated from raw semen, extended semen and frozen semen with Tyrode's solution showed significantly high value in motility, progressive motility and percent of normal sperm, as compared with control sperm. 8. Highly motile sperm, when separated from raw semen, extended semen and frozen semen with Tyrode's solution, showed significantly low percent of microscopic abnormality as compared with control sperm.

• 한국방재학회 논문집
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• 제8권1호
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• pp.31-37
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• 2008

기존의 교통영향평가 지침으로 규정된 사업 시행 전후의 교통흐름은 가로구간의 경우 교통량, V/C, 평균통행속도와 서비스수준, 교차로의 경우 서비스 수준 등의 교통류 분석지표에 의하여 분석되고 있다. 이러한 교통류 분석지표는 확률론적(stochastic)인 교통류의 특성을 효율적으로 번영하지 못하며, 특히 개별 가로구간과 교차로에 국한하여 분석됨으로서 사업 시행으로 인한 교통영향 분석 범위 전체 구간의 교통흐름을 종합적으로 분석하기에는 미흡하다. 본 연구는 차량추종모형(Car-Following Theory)에 의한 미시적 시뮬레이션(microscopic-simulation) 기법을 적용하여, 개별 구간과 교차로 분석 범위를 넘어서 사업 대상 교통영향 반경 내의 교통흐름을 가시적(visual)하게 보여줄 수 있는 방안과 이를 바탕으로 공간적 범위 설정 개선방안, 개선대책 수립에 따른 효과분석 방안 등 다양한 분석결과를 도출하였다.

• 대한의생명과학회지
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• 제25권4호
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• pp.367-371
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• 2019

In this study, the author observed the fungal characteristics of T. verrucosum which is commonly known as the cattle ringworm fungus in the farms of Hoengseong, Gangwon-do. After isolating 20 strains of T. verrucosum from cattle, they were cultured on SDA, PDA media and the fungal characteristics were concluded through visual observation of the colonies, microscopic findings, hair perforation test and urease test. The size of the colonies cultured on SDA media at 37 C was on an average 5 mm at 1 week, 33 mm at 2 weeks, 42 mm at 3 weeks and 58 mm after 4 weeks. Observing the characteristics of the colonies, 17 strains of T. album showing central bold radial folds, 2 strains of T. ochraceum having l throughout the colonies and 1 strain of T. discoides with rapid growth rate and gray-white cotton patterns were found. On microscopic observations of the cultured colonies on SDA, PDA media, macroconidia and microconidia were not found in T. verrucosum and hyphae and chlamydospore were only seen in T. album types. Out of 20 strains of T. verrucosum, hair perforation test was positive on only 3 strains and urease test was positive on all of the 20 strains.