• Journal of Mechanical Science and Technology
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• v.18 no.10
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• pp.1772-1781
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• 2004

The mechanical as well as tribological characteristics of coating films as thin as a few nm become more crucial as applications in micro-systems grow. Especially, the amorphous carbon film has a potential to be used as a protective layer for micro-systems. In this work, quantitative evaluation of nano-indentation, scratching, and wear tests were performed on the 7nm thick amorphous carbon film using an Atomic Force Microscope (AFM). It was shown that AFM-based nano-indentation using a diamond coated tip can be feasibly utilized for mechanical characterization of ultra-thin films. Also, it was found that the critical load where the failure of the carbon film occurred was about 18${\mu}$N by the ramp load scratch test. Finally, the wear experimental results showed that the quantitative wear rate of the carbon film ranged 10$\^$-9/～10$\^$-8/ ㎣ /N cycle. These experimental methods can be effectively utilized for a better understanding the mechanical and tribological characteristics at the nano-scale.

• Proceedings of the ESK Conference
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• 1997.10a
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• pp.152-159
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• 1997

인간공학을 적용하는데 있어 가장 기본적으로 다루어져야 할 것은 인간의 신체적, 심리적능력에 관한 연구이다. 특히 산업 현장에서 흔히 이루어지는 인간의 힘을 그 동력원으로 하는 수작업의 경우에 있어 서는 작업자가 직업적인 요인에 의해 피로가 누적되거나 신체적인 무리를 가져오지 않고 수행할 수 있는 안전한 작업기준의 설정이 필요하며 이를 위해서는 인간의 신체적 능격에관한 연구가 필수적이다. 특히 최근 들어 여성의 사회진출 기회가 다양해지고 있으며 많은 여성들이 육체적 노동을 필요로 하는 직업에 종사하고 있는 현실에서 한국여성들의 신체적 능력에 관한 자료가 절대적으로 부족한 상황이다. 따라서 본 연구에서는 현재 한국의 여성들이 활동하고 육체적 작업조건들이 적절하게 설정되어 있는지를 분석하기 위한 기초 자료로서 한국 여성들의 생리학적 작업능력(PWC:physiological work capacity)을 최대산소소모 능력(Maximal Oxygen Consumption: V0$_{2}$Max)의 관점에서 파악하고자 하였다. 또한 외국 여성의 생리 학적 작업능력과 한구 여성의 생리학적 작업능력을 비교 평가하여한국 여성에게 외국여성의 기준치를 적용 시키는 것이 적절한지를 분석해 보았다. 본 연구는 피실험자에게 위험부담을 주지 않는 Submaximal test의 연속적인 방법(continuous mathod)중 하나인 램프 테스트(Ramp test)를 사용하여 심박수(H.R)와 산소 소모 량(V0$_{2}$) 측정하여 최대심박수에서의 PWC를 추정하였다. 작업 부하는 자전거 에르고노미터와 트레드 밀을 사용하여부과하였다. 실험 결과로서 자전거 에르고미터의 경우 치대산소 소모량의 추정치 평균이 1818.79ml/min으로 나타 났고 트레드밀의 경우 2076.33ml/min으로 나타났다. 이 결과는 자전거 에르고 노미터의 결과는 자전거 에르고노미터의 결과가 트레드밀의 결과에 87.60%정도 나타났다.

• Journal of the Korean Society of Propulsion Engineers
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• v.23 no.3
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• pp.76-87
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• 2019

A direct connected test was conducted for a supersonic combustor with a cavity-type flame holder. Liquid hydro-carbon fuel was injected in different types of injectors: inclined and aeroramp injectors, for the flow condition of Mach 4 at an altitude of 20 km. The static pressure on the combustor wall along the axis and the total pressure at the exit of combustor were measured to analyze the combustion characteristics at various fuel flow rates.

• Journal of the Korean Society of Propulsion Engineers
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• v.22 no.5
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• pp.97-106
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• 2018

This paper summarizes the technical difficulties pertaining the double-compression ramp scramjet inlet model testing in a shock tunnel and their corresponding solutions. Four technical difficulties are identified: 1) test facility unstart, 2) flow disturbance and model damage due to the impact of diaphragm debris, 3) lack of fuel jet development due to multiple injection, and 4) short test time. After overcoming the identified technical difficulties, the improved results were confirmed through the results of shadowgraph images and shock tube end wall pressure.

• Nuclear Engineering and Technology
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• v.43 no.6
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• pp.499-508
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• 2011

The paper briefs a fuel performance code, COSMOS, which can be utilized for an analysis of the thermal behavior and fission gas release of fuel, up to a high burnup. Of particular concern are the models for the fuel thermal conductivity, the fission gas release, and the cladding corrosion and creep in $UO_2$ fuel. In addition, the code was developed so as to consider the inhomogeneity of MOX fuel, which requires restructuring the thermal conductivity and fission gas release models. These improvements enhanced COSMOS's precision for predicting the in-pile behavior of MOX fuel. The COSMOS code also extends its applicability to the instrumented fuel test in a research reactor. The various in-pile test results were analyzed and compared with the code's prediction. The database consists of the $UO_2$ irradiation test up to an ultra-high burnup, power ramp test of MOX fuel, and instrumented MOX fuel test in a research reactor after base irradiation in a commercial reactor. The comparisons demonstrated that the COSMOS code predicted the in-pile behaviors well, such as the fuel temperature, rod internal pressure, fission gas release, and cladding properties of MOX and $UO_2$ fuel. This sufficient accuracy reveals that the COSMOS can be utilized by both fuel vendors for fuel design, and license organizations for an understanding of fuel in-pile behaviors.

• Steel and Composite Structures
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• v.37 no.2
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• pp.117-136
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• 2020

Curved steel-concrete composite box girder has been widely adopted in urban overpasses and ramp bridges. In order to investigate its mechanical behavior under complicated and combined bending, shear and torsion load, two large-curvature composite box girders with interior angles of 25° and 45° were tested under static hogging moment. Based on the strain and deflection measurement on critical cross-sections during the static loading test, the failure mode, cracking behavior, load-displacement relationship, and strain distribution in the steel plate and rebar were investigated in detail. The test result showed the large-curvature composite box girders exhibited notable shear lag in the concrete slab and steel girder. Also, the constraint torsion and distortion effect caused the stress measured at the inner side of the composite beam to be notably higher than that of the outer side. The strain distribution in the steel web was approximately linear; therefore, the assumption that the plane section remains plane was approximately validated based on strain measurement at steel web. Furthermore, the full-process non-linear elaborate finite element (FE) models of the two specimens were developed based on commercial FE software MSC.MARC. The modeling scheme and constitutive model were illustrated in detail. Based on the comparison between the FE model and test results, the FE model effectively simulated the failure mode, the load-displacement curve, and the strain development of longitudinal rebar and steel girder with sufficient accuracy. The comparison between the FE model and the test result validated the accuracy of the developed FE model.

• International Journal of Highway Engineering
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• v.19 no.6
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• pp.129-137
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• 2017

PURPOSES : The purpose of this study is to develop bridge deck concrete materials based on ordinary Portland cement concrete, and to evaluate the applicability of the developed materials through material properties tests. METHODS : For field implementation, raw material (cement, fine aggregate, and coarse aggregate) properties, fresh concrete properties (slump and air content), strength (compressive, flexural and bond strength) gain, and durability (freeze-thaw resistance, scaling resistance, and rapid chloride penetrating resistance) performance were evaluated in the laboratory. RESULTS : For the selected binder content of $410kg/m^3$, W/B = 0.42, and S/a = 0.48, the following material performance results were obtained. Considering the capacity of the deck finisher, a minimum slump of 150 mm was required. At least 6 % of air content was obtained to resist freeze-thaw damage. In terms of strength, 51.28 MPa of compressive strength, 7.41 MPa of flexural strength, and 2.56 MPa of bond strength at 28 days after construction were obtained. A total of 94.9 % of the relative dynamic modulus of elasticity after 300 cycles of freeze-thaw resistance testing and $0.0056kg/m^2$ of weight loss in a scaling resistance test were measured. However, in a chloride ion penetration resistance test, the result of 3,356 Coulomb, which exceeds the threshold value of the standard specification (1000 Coulomb at 56 days) was observed. CONCLUSIONS : Instead of using high-performance modified bridge deck materials such as latex or silica fume, we developed an optimum mix design based on ordinary Portland cement concrete. A test construction was carried out at ramp bridge B (bridge length = 111 m) in Gim Jai City. Immediately after the concrete was poured, the curing compound was applied, and then wet mat curing was applied for 28 days. Considering the fact that cracks did not occur during the monitoring period, the applicability of the developed material is considered to be high.

• Tribology and Lubricants
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• v.39 no.5
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• pp.203-211
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• 2023

This study experimentally investigates the effects of angular acceleration on the friction and wear performances of a gas foil thrust bearing (GFTB) using a typical GFTB with six pads. The outer radius of the bearing is 31.5 mm, the total bearing area is 2,041 mm² , and the bump foil and incline (ramp) height are both 500 ㎛. The newly developed GFTB test rig for measuring the friction torque and coefficient measures the axial load, drag torque, lift-off speed, and touch-down speed. The experiment is conducted for angular accelerations of 78.5, 314.2, and 328.3 rad/s² at axial loads of 5, 10, and 15 N, respectively. The test shows that the start-up friction coefficient increases with increasing axial load at the same angular acceleration, and the friction coefficient decreases with increasing angular acceleration under the same axial load. As the angular acceleration increases, the lift-off speed at the motor start-up increases, and the touch-down speed at the motor stop decreases. The wear distance of the GFTB for a single on/off cycle increases with increasing axial load at the same angular acceleration and decreases nonlinearly with increasing angular acceleration under the same axial load. The test results suggest that adjusting the rotational angular acceleration helps reduce bearing friction and wear.

• Proceedings of the KIEE Conference
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• 1988.11a
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• pp.147-150
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• 1988

Since the integration level of VLSI circuits progresses very quickly, a highly reliable thin $SiO_2$ film is required to fabricate a small-geometry MOS device. In the present study we have attempted to eliminate the failure-causing defects that develop in thin oxide films during the oxidation step by performing a long-time preoxidation and postoxidation annealing. The TDDB test and the copper decoration method were used to calculate the oxide defects density of MOS device. The dielectric reliability of high-quality thin oxides have been studied by using the time-zero-dielectric-breakdown (ramp-voltage-stressed I-V) and time-dependent-dielectric -breakdown (Constant-stressed I-V) tests. Failure times against temperature and electric field are examined and acceleration factors are abtained for each parameter. Based on the data obtained, breakdown wearout limitation for thin oxide films is estimated.

• The Journal of the Institute of Internet, Broadcasting and Communication
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• v.13 no.6
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• pp.79-85
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• 2013

In this paper, we discussed the traditional methods of generating digital halftoning image and DCT transform. Then we propose a new and simple halftoning algorithm that is based on DCT transformation. We do the feasibility test to verify the proposed algorithm. So we assessed several images generated by adjusting weights of DCT coefficients. As a result, we got the better result for weights of the ramp function type than for weights of the step function type through experiment. As a simple application, we can apply our algorithm to the MPEG video for generating the halftoning video.