• Journal of Korean Society of Steel Construction
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• v.20 no.3
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• pp.399-407
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• 2008

The clamping of torque shear bolt is based on KS B 2819. It was misunderstood that the tension force of the TS bolt was induced generally at the break of pin-tail specified. However, the clamping forces on slip critical connections do not often meet the intended tension, as it considerably varies due to torque coefficient dependent on temperature variables despite the break of the pin tail. In this study, the tension of torque shear bolts were compared with two types of high-strength hexagon bolts by temperature parameters from ${-10^{\circ}C}$ to ${50^{\circ}C}$. Torque shear bolts showed that the average clamping force increased to 20kN as the temperature increased. In case of galvanized high-strength hexagon bolts, the average clamping forces at $0^{\circ}C$, $20^{\circ}C$, $50^{\circ}C$ were recorded over standard bolt tension, 178kN, and the worst standard deviation was 50kN. In case of high-strength hexagon bolts, ave rage clamping forces increased as the temperature went up, and the worst standard deviation was 33kN lower than that of galvanized high-strength hexagon bolts. As for the turn-of-the-nut method, at nut rotation of ${90^{\circ}}$, two types of high-strength hexagon bolts did not met the intended design bolt in tension, 162kN.it is neccessary to re-evaluate the range of turn of nut, ${120^{\circ}{\pm}30^{\circ}}$.

• Korean Journal of Materials Research
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• v.7 no.10
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• pp.871-871
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• 1997

(1-x)CaTiO/sub 3/-xLa(Zn/sub 1/2/Ti/sub 1/2/)O/sub 3/의 마이크로 유전특성을 조사하였다. x가 증가함에 따라 비유전율과 공진주파수의 온도계수는 감소하였으며, Qㆍf/sub 0/는 증가하였다. 그 결과 x=0.5인 (Ca/sub 0.5/La/sub 0.5/)(Ti/sub 0.75/Zn/sub 0.25/)O/sub 3/의 조성에서 ε/sub r/=51, Qㆍf/sub 0/=38,000 (at 7 GHz), τ/sub f/=+5ppm/℃의 유전특성이 나타났다. (Ca/sub 0.5/La/sub 0.5/)(Ti/sub 0.75/Zn/sub 0.25/) O/sub 3/조성의 소결온도를 저하시키기 위하여 Bi/sub 2/O/sub 3/를 주조성으로한 소결체를 첨가하여 소결 및 유전특성을 조사하였다. 1wt% 0.76Bi/sub 2/O/sub 3/-0.24NiO가 첨가된 경우 소결온도는 150℃ 낮아졌으며, 비유전율 (ε/sub r/), 공진주파수의 온도계수(τ/sub f), Qㆍf/sub 0/가 각각 50+5ppm/℃, 35,000인 마이크로파 유전특성이 얻어졌다. 또한 3wt%의 0.76Bi/sub 2/O/sub 3/-0.24NiO가 첨가된 경우 소결온도는 200℃ 저하되었고, 비유전율 (ε/sub r/)과 공진주파수의 온도계수 (τ/sub f)는 변하기 않았으나, Qㆍf/sub 0/값이 38,000에서 25,000으로 저하되었다.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.10 no.1
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• pp.32-38
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• 2009

In this paper, cycle performance analysis for cooling capacity, compression work and COP of R744($CO_2$) transcritical vapor compression refrigeration system is presented to offer the basic design data for the operating parameters of the system. The operating parameters considered in this study include superheating degree, outlet temperature of gas cooler and evaporating temperature in the R744 vapor compression cycle. The main results were summarized as follows : The cooling capacity of R744 increases with superheating degree, but decreases with the increasing evaporating temperature and outlet temperature of gas cooler. The compression work increases with superheating degree and cooling pressure of R744, but decreases with the increasing evaporating temperature. And, The COP increases with outlet temperature and evaporating temperature of R744 gas cooler, but decreases with the increasing superheating degree. Therefore, superheating degree, outlet temperature and evaporating temperature of R744 vapor compression refrigeration system have an effect on the cooling capacity, compression work and COP of this system. With a thorough grasp of these effect, it is necessary to design the compression refrigeration cycle using R744.

• Journal of Korean Society for Geospatial Information Science
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• v.17 no.4
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• pp.39-44
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• 2009

To analysis the LST distribution of Jeju island, remote sensing techniques using Landsat TM band 6 data were used. In this study, we made the LST distribution map based on the NASA. The study areas are the Jeju and Seogwipo cities of the Jeju Island. And we analyzed the correlation between the LST and NDVI which was calculated from the Landsat TM band 3 and ban 4. From the result, we found that the coefficients of the correlation were -0.77 and -0.74 on the Jeju and the Seogwipo cities, respectively. Finally, from the correlation between the land cover and LST, we also found that an inverse relationship between the LST and NDVI was exist.

• The Korean Journal of Rheology
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• v.7 no.3
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• pp.181-191
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• 1995

점탄성유체의 물성치들 중 정압열팽창계수 및 밀도는 자연대류 열전달 연구에 전단 속도 0에서의 점도는 점탄성유체에 대한 모델들 사용 시 필요하다. 본 연구에서는 점탄성유 체이며 마찰 감소 첨가제, 유전자 분리용액동으로 사용하는 Separan AP-273 용액의 정압열 팽창계수, 밀도 및 전단속도 0에서의 점도에대한 농도 및 온도의 영향을 조사하였다. 작동유 체의 물성치들은 10~6$0^{\circ}C$의 온도범위와 100~20,000wppm의 농도범위에서 측정되었다. 작 동유체의 물성치들에 미치는 열주기와 노화의 영향을 조사하기 위해서 정압열팽창계수와 전 단속도 0에서의 점도를 교대로 두 번씩 측정했다. 정압열팽창계수 및 밀도를 측정하는 장치 의 측정 정밀도는 증류수에 대한 측정치와 문헌에 나타난 자료를 비교하여 얻었고 이는 $\pm$ 2%이내였다. Separan AP-273용액의 정압열팽창계수 및 밀도는 증류수의 값들로 대치될수 있다. 작동유체의 정압열팽창계수와 밀도는 열주기와 노화의 영향을 받지 않았다. 낙하식 점 도계를 사용해 측정한 겉보기점도 값들을 나타내느 flow curve에서 전단속도가 0이 되는방 향으로 겉보기점도를 외삽시켜 Separan AP-273용액에 대한 전단속도0에서의 점도를 얻었 다. 정압열팽창계수 측정 전후에 측정한 작동유체에 대한 전단속도 0에서의 점도는 열주기 와 노화로 인해 퇴화되었다.

• Journal of the Institute of Electronics Engineers of Korea SD
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• v.41 no.1
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• pp.9-14
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• 2004

In this paper, temperature dependence of effective ionization coefficient in Si is formulated as a single polynomial function of temperature, which allows analytical expressions for breakdown voltage of Si $p^+n$ junction as a function of temperature. The analytical breakdown voltages agree well with the simulation as well as the experimental ones reported within $3\%$ in error for the doping concentrations in the range of $10^{14}cm^{-3}{\~} 10^{17}cm^{-3}$ at 100K, 300K and 500K.

• Journal of the Korea Concrete Institute
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• v.17 no.4 s.88
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• pp.551-558
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• 2005

The setting and hardening of concrete is accompanied with nonlinear temperature distribution caused by development of hydration heat of cement. Especially at early ages, this nonlinear distribution has a large influence on the crack evolution. As a result, in order to predict the exact temperature history in concrete structures it is required to examine thermal properties of concrete. In this study, the convection heat transfer coefficient which presents thermal transfer between surface of concrete and air, was experimentally investigated with variables such as velocity of wind, curing condition and ambient temperature. At initial stage, the convection heat transfer coefficient is overestimated by the evaporation quantity. So it is essential to modify the thermal equilibrium considered with the boiling effect. From experimental results, the convection heat transfer coefficient was calculated using equations of thermal equilibrium. Finally, the prediction model for equivalent convection heat transfer coefficient including effects of velocity of wind, curing condition, ambient temperature and boiling effects was theoretically proposed. The convection heat transfer coefficient in the proposed model increases with velocity of wind, and its dependance on wind velocity is varied with curing condition. This tendency is due to a combined heat transfer system of conduction through form and convection to air. From comparison with experimental results, the convection heat transfer coefficient by this model was well agreed with those by experimental results.

• Proceedings of the KAIS Fall Conference
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• 2001.05a
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• pp.269-272
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• 2001

실리콘 마이크로머시닝 기술과 바이폴라 공정으로 집적화된 압력센서를 제작하고 동작특성 평가를 수행하였다. 센서부 보상파라미터를 추출하였고 트리밍 공정을 통하여 출력전압의 보상을 수행하였다. 센서 특성은 압저항 위치, 마스크 정렬 오차, 다이어프램 정밀두께제어 정도, 보호막의 과도식각 정도 등에 의하여 민감하게 좌우됨을 알 수 있었다. 웨이퍼별 샘플추출을 통하여 센서부 감도는 평균 0.653mV/kPa, 감도의 온도계수는 -2078.8ppm/℃, 옵셋 전압은 30.78mV, 옵셋전압의 온도계수는 32.11㎶/℃로 측정되었다. 추출된 샘플의 다이어프램 두께오차는 27±2.5㎛였다. 센서부 특성평가 결과를 통하여 신호처리회로의 옵셋 및 스팬보상, 온도보상을 위한 트리밍 공정을 수행한 결과 개발사양을 만족하는 결과를 얻을 수 있었다.

• Proceedings of the Korean Institute of Surface Engineering Conference
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• 2007.04a
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• pp.145-146
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• 2007

Cr-Si-N 박막은 하이브리드 코팅 시스템에 의해 온도와 바이어스의 변화에 따라 증착 되었다. 증착온도 $0{\sim}300^{\circ}C$ 범위에서, 경도와 탄성계수는 이온의 surface mobility의 증가 때문에 향상되었지만 $350^{\circ}C$ 이상의 증착 온도에서는 결정성장 때문에 경도는 다시 감소하였다. 바이어스 $0{\sim}-100V$까지 범위에서는, 경도와 탄성계수는 각각 46GPa, 600GPa의 최대값을 보여주었으며 바이어스 -100V에서 macro-particle과 surface molphology 감소가 발생하였다. 그러나 -100V이상의 바이어스에서 resputtering 현상에 의해 Si 의 양이 감소한다. 증착온도는 Si 함량에 많은 영향을 주지 못한다.

• Composites Research
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• v.36 no.5
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• pp.342-348
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• 2023

There has been increasing demand for real-time monitoring of body and ambient temperatures using wearable devices. Graphene-based thermistors have been developed for high-performance flexible temperature sensors. In this study, the temperature coefficient of resistance (TCR) of monolayer graphene was controlled by coating polyethylenimine (PEI) on graphene surfaces to enhance its temperature-sensing performances. Monolayer graphene grown by chemical vapor deposition (CVD) was wet-transferred onto a target substrate. To facilitate the interfacial doping by PEI, the hydrophobic graphene surface was altered to be hydrophilic by oxygen plasma treatments while minimizing defect generation. The effect of PEI doping on graphene was confirmed using a back-gated field-effect transistor (FET). The CVD-grown monolayer graphene coated with PEI exhibited an improved TCR of -0.49(±0.03) %/K in a temperature range of 30~50℃.