• 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.

• Structural Engineering and Mechanics
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• 제19권5호
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• pp.519-533
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• 2005

The numerical simulations on the influence of mesoscopic structures on the macroscopic strength and fracture characteristics are carried out based on that the concrete is assumed to be a three-phase composite composed of matrix (mortar), aggregate and bond between them by using a numerical code named MFPA. The finite element program is employed as the basic stress analysis tool when the elastic damage mechanics is used to describe the constitutive law of meso-level element and the maximum tensile strain criterion and Mohr-Coulomb criterion are utilized as damage threshold. It can be found from the numerical results that the bond between matrix and aggregate has a significant effect on the macroscopic mechanical performance of concrete.

• Biomolecules & Therapeutics
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• 제7권4호
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• pp.347-353
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• 1999

Osteoarthrosis was induced in rabbit knees through resecton of anterior cruciate ligament. Sodium hyaluronate (1%) was administerated into articular space at the dose levels of 0.1 mg/kg once a week using 1ml sylinge and 26G needle for test groups. Saline was administrated for control groups. After 6 and 12 weeks, animals were sacrificed to conduct macroscopic observation and histopathologic examination. The articular lesions were evaluated and test groups were compared with control groups. No significant differencies were showed between test groups and control groups at macroscopic observation in both 6- and 12- week groups. In histopathologic examination, control groups showed higher osteoarthrosis than test groups. The articular surfaces of control groups showed fibrillation, denudation, pannus formation and hypocellularity. The articular surfaces of test groups showed fibrillaton and hypercellularity. These indicate that sodium hyaluronate has inhibitory effects on osteoarthrosis at least in rabbit and could be used for treatment of osteoarthrosis.

• 대한한방소아과학회지
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• 제31권2호
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• pp.57-63
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• 2017

Objectives The purpose of this case study is to report the effect of Yukmijihwangtang-gamibang on recurrent hematuria in childhood. Methods The subject was a male child with macroscopic hematuria. This patient was only treated with oriental herbal medicine. The improvement was observed by subjective symptoms and routine urinalysis. Results After the treatment with Yukmijihwangtang-gamibang, the symptoms of macroscopic hematuria were relieved. The occult blood test was negative as well. The number of red blood cells in urine was within the normal range. He was less tired but hematuria did not recur even after intense exercise. Conclusions This study showed that Korean medical treatment with using herbal medicine such as Yukmijihwangtanggamibang can be an effective treatment option for asymptomatic macroscopic hematuria.

• Journal of Mechanical Science and Technology
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• 제18권7호
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• pp.1222-1235
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• 2004

This study examines the influence of geometry on the internal flow and macroscopic behavior of the spray in Diesel nozzles. For this investigation, two bi-orifice nozzles were employed: one cylindrical and one conical. The first step is to use a non-destructive characterization method which is based on the production of silicone moulds so that the precise internal geometry of the two nozzles can be measured. At this stage the nozzles have been characterized dimensionally and therefore the internal flow can be studied using CFD calculations. The results gained from this experiment make it possible also to ascertain the critical cavitation conditions. Once the critical cavitation conditions have been identified, the macroscopic parameters of the spray can be studied in both cavitating and non-cavitating conditions using a test rig pressurized with nitrogen and with the help of a image acquisition system and image processing software. Consequently, research can be carried out to determine the influence that cavitation has on macroscopic spray behavior. From the point of view of the spray macroscopic behavior, the main conclusion of the paper is that cavitation leads to an increment of the spray cone angle. On the other hand, from the point of view of the internal flow, the hole outlet velocity increases when cavitation appears. This phenomenon can be explained by the reduction in the cross section of the liquid phase in the outlet section of the hole.

• 드라이브 ㆍ 컨트롤
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• 제16권2호
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• pp.80-90
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• 2019

Fuel cell hybrid electric vehicle is an attractive solution to reduce pollutants, such as noise and carbon dioxide emission. This study presents an approach for energy management and control algorithm based on energetic macroscopic representation for a fuel cell hybrid electric vehicle that is powered by proton exchange membrane fuel cell, battery and supercapacitor. First, the detailed model of the fuel cell hybrid electric vehicle, including fuel cell, battery, supercapacitor, DC-DC converters and powertrain system, are built on the energetic macroscopic representation. Next, the power management strategy was applied to manage the energy among the three power sources. Moreover, the control scheme that was based on back-stepping sliding mode control and inversed-model control techniques were deduced. Simulation tests that used a worldwide harmonized light vehicle test procedure standard driving cycle showed the effectiveness of the proposed control method.

• Tribology and Lubricants
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• 제5권1호
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• pp.28-35
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• 1989

The wear tests of ceramic materials in dry rolling contact were carried out at room temperature to investigate their macroscopic wear characteristics. Both point contact and line cootact were adapted in the wear tests of them. Ceramic materials used in these tests were silicon nitride, silicon carbide, cermet of TiN and TiC, titania, and alumina. The wear test of the bearing steel was carried out to compare to the wear test results of the ceramic materials. The results showed that the wear rate of silicon nitride was smaller than any other ceramic materials and bearing steel. In the steady wear, the wear volume of ceramic materials increases linearly with the rolling distance. It was also found from the experimental results that fracture toughness and surface roughness dominate the wear process of ceramic materials in dry rolling contact.

• 한국분무공학회지
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• 제17권3호
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• pp.121-127
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• 2012

The study is to investigate the mixing stability, fuel properties, and macroscopic spray characteristics of diesel-gasoline blended fuels in a common-rail injection system of a diesel engine. The test fuels were mixed diesel with gasoline fuel, which were based volume fraction of gasoline from 0 to 100% in 20% intervals. In order to analyze the blended effect of gasoline to diesel fuel, the properties of test fuels such as density, viscosity, and surface tension were measured. In addition, the spray behavior characteristics were studied by investigating the spray tip penetration and spray angle using a spray images through a spray visualization system. It was revealed that the density, kinematic viscosity and surface tension of diesel-gasoline blending fuels were decreased with the increase of gasoline fuel. The injection quantity of test fuels were almost similar level at short energizing duration condition. On the other hand, the increase of energizing duration shows the decrease of injection quantity compared to short energizing duration. The test blending fuels have similar growth in Spray tip penetration and Spray cone angle.

• 한국재료학회지
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• 제26권7호
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• pp.370-375
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• 2016

Tensile tests and creep tests were carried out at high temperatures on an Al-$Al_4C_3$ alloy prepared by mechanical alloying technique. The material contains about 2.0% carbon and 0.9% oxygen in mass percent, and the volume fractions of $Al_4C_3$ and $Al_2O_3$ particles are estimated at 7.4 and 1.4%, respectively, from the chemical composition. Minimum creep rate decreased steeply near two critical stresses, ${\sigma}_{cl}$ (the lower critical stress) and ${\sigma}_{cu}$ (the upper critical stress), with decreasing applied stress at temperatures below 723 K. Instantaneous plastic strain was observed in creep tests above a critical stress, ${\sigma}_{ci}$, at each test temperature. ${\sigma}_{cu}$ and ${\sigma}_{ci}$ were fairly close to the 0.2% proof stress obtained by tensile tests at each test temperature. It is thought that ${\sigma}_{cl}$ and ${\sigma}_{cu}$ correspond to the microscopic yield stress and the macroscopic yield stress, respectively. The lower critical stress corresponds to the local yield stress needed for dislocations to move in the soft region within subgrains. The creep strain in the low stress range below 723 K arises mainly from the local deformation of the soft region. The upper critical stress is equivalent to the macroscopic yield stress necessary for dislocations within subgrains or in subboundaries; this stress can extensively move beyond subboundaries under a stress above the critical point to yield a macroscopic deformation. At higher temperatures above 773 K, the influence of the diffusional creep increases and the stress exponent of the creep rate decreases.

• 한국지진공학회논문집
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• 제16권5호
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• pp.1-11
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• 2012

본 연구에서는 주기하중에 대하여 거시적 모델링 방법을 다르게 적용하여 철근콘크리트 벽체의 비선형 해석을 수행하고 기존에 나타난 실험 연구와 비교/분석하였다. ASCE41-06에서 제시하는 높이-길이 비에 따른 벽체의 파괴유형을 참고하여 기존에 수행된 실험연구 중에서 높이-길이비가 3.0을 초과하는 세장한 벽체와 높이-길이비가 1.5인 낮은 벽체를 선택하였다. 각 실험체에 대하여 거시적 모델을 다르게 고려하여 비선형 해석을 수행하였다. 본 연구에서 적용한 거시적 모델은 휨에 대한 거동을 정확히 묘사할 수 있는 방법과 벽체의 복부에서 발생되는 대각 전단을 고려할 수 있는 방법이다. 세장한 벽체는 거시적 모델에 따른 실험과 해석의 결과 차이가 거의 없는 것으로 나타났지만 낮은 벽체는 모델링 방법에서 고려할 수 있는 요소에 의해 이력 거동이 크게 달라지는 것으로 조사되었다. 또한, 높이-길이 비가 1.5인 철근콘크리트 벽체가 건축물에 적용된 경우 정확한 횡 저항능력을 평가하기 위해서 복부의 대각 압축 전단을 고려할 수 있는 모델을 사용하는 것이 타당하다.