• 대한화학회지
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• 제47권4호
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• pp.376-390
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• 2003

본 연구는 초등학교 자연교과서, 중등학교 과학교과서 및 대학의 일반화학 교재에 있는 화학반응 관련개념의 연계성을 고찰하였다. 화학반응에 관한 19개의 주제를 선정하여 각 주제별로 학교 급별에 따른 선행학습과 후속학습 간의 연계정도를 준거 기준에 따라 분석하였다. 연계성 판별을 위하여 5가지 준거를 수립하여 분석한 결과 초등학교에서 중학교 과정의 연계는 양호하였다. 그러나 중학교에서 고등학교 과정의 연계는 격차의 비율이 크게 나타났으며, 고등학교에서 대학으로의 연계는 반복과 격차의 비율이 높은 것으로 나타났다. 이 분석결과를 이용하여 화학반응에 대한 새로운 교과내용 구조도를 제시하였다.

• 한국태양에너지학회 논문집
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• 제26권3호
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• pp.25-32
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• 2006

The objective of this study is to investigate the effect of building integrated PV application method on power generation. PV modules were integrated to a hypothetical apartment building facade in Seoul, Korea. Three different design options of PV panel mounted on exterior wall were developed for the analysis of cooling effects through ventilation. Numerical simulations using TRNSYS coupled with COMIS were executed to evaluate the design options. Their facade configurations are such as vertically installed PV panels with or without air gap between PV rear surface and exterior wall surface, and the tilted PV panels attached to the exterior wall at an angle of to the horizontal. Parametric results show that there is little difference regardless of the air 9ap width between PV rear surface and exterior wall surface. Special strategies which could effectively cool a PV panel to increase the electric power are required if we prefer to a vertical facade configuration in a building integrated PV installation. Consequently, it is expected that there is no reason for architect to install vertically PV panels with air gap unless active strategies are considered.

• 한국화재소방학회논문지
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• 제16권1호
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• pp.30-38
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• 2002

가공 전력선로 아래에서 화재가 발생되면 전력선은 예기치 않은 섬락사고가 세계 여러나라에서 관측되고 있다. 본 연구에서는 화재의 발생으로 연소화염이 존재할 때, 주변 공기의 절연내력에 미치는 화염의 영향을 알아보기 위해 모의된 조건에서 여러 가지 실험을 행하였다. 침대평판, 구대평판 및 봉대평판 전극을 수직배치한 경우, 교류 및 직류 섬락전압 특성을 조사하였다. 실험결과, 구대평판 갭의 경우, d=1 cm 및 2cm일 때 교류섬락 전압의 상대값은 23.5% 및 30.4%이며, d=4cm인 경우는 37.8%인 것으로 나타났으며, 화염이 없는 경우에 비해 평균 33.0%인 것으로 나타났다. 직류전압 인가시는 화염이 없는 경우, 부극성의 섬락전압이 정극성보다 높았으나, 화염이 존재할 경우는 반대로 정극성이 부극성 전압보다 높은 것으로 나타났다.

• 설비공학논문집
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• 제19권6호
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• pp.441-446
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• 2007

An experimental study on the countercurrent two-phase flow in narrow rectangular channels has been peformed. Countercurrent flow limitation (CCFL) was investigated using air and water in 760mm long, 100mm wide, vertical test sections with 1 and 3mm channel gaps. Tests were systematically performed with downward liquid superficial velocities and upward gas velocities covering 0 to 0.125 and 0 to 3.5m/s ranges, respectively. As the gap width of rectangular channel increased the CCFL water superficial velocity decreased for the given air superficial velocity. Slight increase of the air superficial velocity resulted in the abrupt decrease of water velocity when $j_g=2{\sim}4m/s$. The critical superficial velocity of air, at which the downward flow of water was no longer allowed, also decreased with the increase of gap width. The experimental results were compared with the previous correlations, which were mainly for round tubes, and the qualitative trends were found to be partially acceptable. However the quantitative discrepancies were hardly neglected. New correlation of CCFL was developed and showed good agreement with the experimental data.

• 한국기계가공학회지
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• 제16권4호
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• pp.38-45
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• 2017

A finite element analysis-based approach which investigates the causes of the breakdown in the outer ring of the choke at hot rod rolling mill is presented. Two-dimensional drawings of the whole vertical-type mill stand are transformed into three-dimensional CAD models. Non-linear elasto-plastic deformation analysis of material at the roll gap is performed for computing roll force and torque of the work roll. Then, the reaction forces of the bearing rings together with a set of roller bearings that support the work roll are obtained by means of rigid body motion analysis. Finally, stress behaviors in the bearing rings together with a set of roller bearings that support the work roll are investigated by linear elastic analysis. Results reveal that stress at the contact area between the outer ring and roller bearing is extraordinary high when an internal gap between an external surface of the outer ring and the internal surface of the chock due to wear of the inside of the chock occurs.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2003년도 하계학술대회 논문집 Vol.4 No.1
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• pp.347-351
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• 2003

A p-$CdIn_2Te_4$ single crystal has been grown by the Bridgman method without a seed crystal in a tree-stage vertical electric furnace. From photocurrent measurements, it was found that three peaks, A, B, and C, corresponded to an intrinsic transition due to the band-to-band transition from the valence band states ${\Gamma}_7(A),\;{\Gamma}_6(B),\;and\;{\Gamma}_7(C)$ to the conduction band state ${\Gamma}_6$, respectively. Also, the valence band splitting of the $CdIn_2Te_4$ crystal has been confirmed by photocurrent spectroscopy. The crystal field splitting and the spin orbit splitting were obtained to be 0.2360 and 0.1119 eV, respectively. Also, the temperature dependence of the band gap energy of the $CdIn_2Te_4$ crystal has been driven as the following equation of $E_g(T)\;=E_g(0)\;-\;(9.43\;{\times}\;10^{-3})T^2/(2676\;+\;T)$. In this equation, the Eg(0) was estimated to be 1.4750, 1.7110, and 1.8229 eV at the valence band state A, B, and C, respectively. The band gap energy of the p-$CdIn_2Te_4$ at room temperature was determined to be 1.2023 eV.

• International Journal of Naval Architecture and Ocean Engineering
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• 제9권5호
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• pp.568-576
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• 2017

With an increase in the usage of LNG, there is a heightened interest about its safety aspects regarding the explosion of LNG carrier tank. The need for a cryogenic explosion-proof camera has increased. The camera has to work in cryogenic environment (below $-160^{\circ}C$) in LNG carrier. This study conducted design and heat transfer analysis of cryogenic camera to secure working time in limitation of heat source. The design with gap width of double pane windows was conducted based on simple vertical cavity model to insulate from cryogenic environment. The optimal gap width was 12.5 mm. For effective analysis considering convection within the camera, equivalent thermal conductivity method was adopted with ABAQUS. The working time of the camera predicted was over 10 h at warm-start condition. In cold-start condition, it required about 5 h of pre-warming time to work. The results of analysis were compared with the ones of the actual cryogenic test.

• Journal of Welding and Joining
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• 제16권2호
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• pp.100-110
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• 1998

In this paper, the laser weldability of thin gage steels for automobile application is discussed. Welding was carried out with a high power carbon dioxide laser system, and the laser energy was concentrated through a plano-convex lens. Test results showed that the joint gap in the butt welding proved to be one of the critical conditions for an acceptable weld. In the case where the ratio of the gap clearance to the material thickness was slightly bigger than optimal value, the weld strength was reduced showing weld metal fracture. It was possible to obtained a weld penetration ratio of 0.91 when the vertical offset ratio was controlled to be 0.4 or smaller. Results also demonstrated that the weld strength of the lap joint was influenced by travel speed. At the travel speeds lower than 37 mm/s, the weld strength indicated higher value than that of class A recommendation strength of a resistance spot weld based on the KS code. It was clear that the complicated effect of specimen alignment should be considered so as to make a sound weld with high integrity when the laser process was applied to the long weld line.

• Restorative Dentistry and Endodontics
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• 제22권2호
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• pp.792-800
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• 1997

The purpose of this study was to evaluate the adaptation of self-cured glass ionomer cement and resin-modified glass ionomer cement and polyacid-modified resin composite, which are light-cured giass ionomer cements, to dentin surface. Twelve extracted human maxillary and mandibular molar teeth were used in this study. The entire occlusal dentin surfaces of teeth were exposed with Diamond Wheel Saw and smoothed with sand papers (300, 600, 1200grits). They were randomly assigned into 3 groups according to glass ionomer cements used; Control group- Fuji II, Expeimental group 1 - Fuji II LC, Expeimental group 2 - Dyract. According to the manufacturer's directions, three glass ionomer cements were bonded to exposed dentin surfaces of the tooth crown and cured. Crowns and glass ionomers were trimmed after 24hrs and sectioned horizontally and vertically with diamond saw. The interface of glass ionomer cements and dentin was examined under SEM. The results were as follows : 1. Good adatation between glass ionomer cement and dentin on the horizontal section was showed in control and experimental group 1, but the gap of $20{\mu}m$, which was observed distinct separation between glass ionomer cement and dentin, was showed in experimental group 2. 2. Good adatation between glass ionomer cements and dentin on the vertical section was showed in control and experimental group 1, but the gap of 80-$100{\mu}m$ was showed in experimental group 2. 3. Cohesive fracture within glass ionomer cements in control and experimental group 1 was showed, but no cohesive fracture was showed in experimental group 2.

• 대한전기학회논문지:전기기기및에너지변환시스템부문B
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• 제54권12호
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• pp.592-600
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• 2005

In this paper, a low loss magnetic levitation(Maglev) system is suggested and tested. The suggested Maglev system includes four hybrid magnets which consist of permanent magnet and coil. In the steady state, the levitated module system can be supported by attraction force generated by permanent magnet. The coil current controls only dynamic loads due to external disturbances. The module systems are designed by using finite element method(FEM) software tools such as MAXWELL and ANSYS. Also, digital control systems are designed to keep the magnet airgap at a constant value. The control systems include a VME(versa module europa)-based CPU(central processing unit) board, AD(analog to digital) board, PWM(pulse width modulation) board, 4-quadrant chopper, and sensors. In order to estimate the vertical velocity of the magnet, we use second order state observer with acceleration and gap signals as input and output signals, respectively. The characteristics of the suggested low loss Maglev system are demonstrated by experimental results showing coil current of 0A in the steady state of 3m airgap and performance specifications are satisfied for reference gap and force disturbance.