• Earthquakes and Structures
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• 제4권6호
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• pp.607-627
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• 2013

The application of shape memory alloys (SMAs) to the seismic response reduction of civil engineering structures has attracted growing interest due to their self-centering feature and excellent fatigue performance. The loading rate dependence of SMAs raises a concern in the seismic analysis of SMA-based devices. However, the implementation of micromechanics-based strain-rate-dependent constitutive models in structural analysis software is rather complicated and computationally demanding. This paper investigates the feasibility of replacing complex rate-dependent models with rate-independent constitutive models for superelastic SMA elements in seismic time-history analysis. Three uniaxial constitutive models for superelastic SMAs, including one rate-dependent thermomechanical model and two rate-independent phenomenological models, are considered in this comparative study. The pros and cons of the three nonlinear constitutive models are also discussed. A parametric study of single-degree-of-freedom systems with different initial periods and strength reduction factors is conducted to examine the effect of the three constitutive models on seismic simulations. Additionally, nonlinear time-history analyses of a three-story prototype steel frame building with special SMA-based damping braces are performed. Two suites of seismic records that correspond to frequent and design basis earthquakes are used as base excitations in the seismic analyses of steel-braced frames. The results of this study show that the rate-independent constitutive models, with their parameters properly tuned to dynamic test data, are able to predict the seismic responses of structures with SMA-based seismic response modification devices.

• 한국전자파학회논문지
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• 제13권9호
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• pp.898-906
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• 2002

송신 전력이 비교적 높은 5 dBm인 광 펄스를 최적 펌프 전력 조건 하에서의 MSSI(Mid-Span Spectral Inversion) 보상 기법을 통해 전송할 때 다양한 주파수 첩(chirp)을 갖는 광 펄스의 전송 거리가 어느 정도 개선되는지를 다양한 전송 속도와 분산 계수에 따라 살펴보았고, 광 펄스의 주파수 첩과 Kerr효과에 의한 위상 변화의 상호 관계가 다양한 비트율에서의 광섬유 분산 계수 변화에 따라 MSSI 보상에 어떠한 영향을 주는 지를 시뮬레이션을 통해 분석해 보았다. 우선 광 펄스가 광섬유를 전파하면서 겪게 되는 자기 위상 변조에 의한 위상 변화가 광 변조 과정에서 인가된 광 펄스의 초기 첩에 의한 위상 변화와 어우러져 상쇄되는 정도가 광섬유의 분산 계수 값에 따라 달라지게 되어 MSSI 기법을 통해 광 펄스가 보상되는 정도에도 변화가 있는 것을 확인할 수 있었다. 또한 동일한 보상 특성을 얻을 수 있는 비트율에 따른 분산 천이 광섬유의 분산 계수 값은 전송비트율 증가 비율을 k라고 하면 2$^{k}$ 의 관계로 줄어들어야 하는 것을 알 수 있었다.

• Tuberculosis and Respiratory Diseases
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• 제76권6호
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• pp.276-283
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• 2014

Background: We aimed to investigate the role of the physician in practice and the factors that influence the success rate of smoking cessation. Methods: This study retrospectively analyzed 126 adult smokers who had visited the outpatient department of pulmonology, and received motivational interviewing with or without supplement drugs. The findings include continuous smoking abstinence rate, which was evaluated at 6, 12 and 24 weeks, and the factors associated with continuous abstinence for 6 months or longer. Results: The patients with only motivational interviewing accounted for 57.9%, while the nicotine patch therapy was applied to 30.2%; and varenicline was prescribed to 11.9%. The smoking cessation success rates of at 6, 12, and 24 weeks were 55.6%, 47.6%, and 33.3%, respectively. However, even in the failure group at six months, tobacco consumption was decreased under 10 cigarettes per day in 42.1% (53/126). In multivariate logistic regression analysis, degree of Fagerst$\ddot{o}$m Test for Nicotine Dependence (p=0.034; odds ratio, 3.607; 95% confidence interval [CI], 1.102-1.807), the absence of smoking-related lung disease (p=0.008; odds ratio, 4.693; 95% CI, 1.497-14.707), and education level (p=0.001; odds ratio, 181.420; 95% CI, 8.414-3,911.502) were the predictors of successful smoking cessation. Conclusion: An improved continuous smoking abstinence rate can be obtained by motivational interviewing, regardless of the association with pharmacotherapy.

• 한국초전도ㆍ저온공학회논문지
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• 제17권3호
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• pp.9-12
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• 2015

NbN thin films were deposited on thermally oxidized Si substrate at room temperature by using reactive magnetron sputtering in an $Ar-N_2$ gas mixture. Total sputtering gas pressure was fixed while varying $N_2$ flow rate from 1.4 sccm to 2.9 sccm. X-ray diffraction pattern analysis revealed dominant NbN(200) orientation in the low $N_2$ flow rate but emerging of (111) orientation with diminishing (200) orientation at higher flow rate. The dependences of the superconducting properties on the $N_2$ gas flow rate were investigated. All the NbN thin films showed a small negative temperature coefficient of resistance with resistivity ratio between 300 K and 20 K in the range from 0.98 to 0.89 as the $N_2$ flow rate is increased. Transition temperature showed non-monotonic dependence on $N_2$ flow rate reaching as high as 11.12 K determined by the mid-point temperature of the transition with transition width of 0.3 K. On the other hand, the upper critical field showed roughly linear increase with $N_2$ flow rate up to 2.7 sccm. The highest upper critical field extrapolated to 0 K was 17.4 T with corresponding coherence length of 4.3 nm. Our results are discussed with the granular nature of NbN thin films.

• 한국항공우주학회지
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• 제38권2호
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• pp.129-134
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• 2010

변형률-속도에 따른 형상기억합금의 열-기계적 특성 변화를 수치적으로 살펴보았다. 변형률 효과를 고려한 형상기억합금 수학 모델을 유도하였고, 해석 알고리즘을 ABAQUS 상용 프로그램에 적용하여 형상기억합금의 열-기계적 특성을 예측하였다. 마르텐사이트 상 변화량과 온도 변화사이의 연성된 열역학적 방정식을 적용하여, 변형률-속도에 따른 형상기억합금의 거동 특성을 살펴보았다. 변형률 효과를 고려함에 따라 형상기억합금의 의탄성 이력 특성이 크게 영향을 받음을 수치해석 결과를 통하여 알 수 있었다.

• 한국재료학회지
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• 제12권1호
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• pp.68-74
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• 2002

The lead has to be removed for the recycling of copper alloy. The lead cannot be removed from the copper alloy by oxidation. It can be removed by the evaporation because of its high vapor pressure. However, rare information is found on removal of lead from copper alloy. The purpose of present work is to provide a fundamental knowledges on the removal of lead from the copper alloy by evaporation. Gas injection was made in molten copper alloy, and the evaporation rate of lead was measured. The influence of Ar gas flow rata(2~4 L/min), initial contents of lead(2~4wt%Pb), temperature(1200~140$0^{\circ}C$) was investigated based on the thermodynamic and the kinetics. The rate constant is increased with increasing flow rate of Ar and temperature. Though amount of lead removed is increased with higher initial lead concentration, the rate constant is not changed significantly. The activation energy is estimated from the temperature dependence of the rate constant. Also removal of lead from the copper by adding chloride was made for the comparison.

• 대한기계학회논문집A
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• 제27권7호
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• pp.1152-1158
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• 2003

The mechanical behavior of a commercially pure titanium (CP-Ti) is investigated at high temperature Split Hopkinson Pressure Bar (SHPB) compression test with high strain-rate. Tests are performed over a temperature range from room temperature to 1000$^{\circ}C$ with interval of 200$^{\circ}C$ and a strain-rate range of 1900 ∼ 2000/sec. The true flow stress-true strain relations depending on temperature are achieved in these tests. For construction of constitutive equation from the true flow stress-true strain relation, parameters for the Johnson-Cook constitutive equation is determined. And the modified Johnson-Cook equation is used for investigation of behavior of flow stress in vicinity of recrystalization temperature. The Modified Johnson-Cook constitutive equation is more suitable in expressing the dynamic behavior of a CP-Ti at high temperature, i.e. about recrystalization temperature.

• Corrosion Science and Technology
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• 제7권2호
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• pp.130-133
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• 2008

Corrosion of silver by outgassed sulfur species from rubber has been investigated by means of quartz crystal microbalance technique (QCM) and cathodic reduction technique. Silver specimens were placed together with a rubber of predefined quantity in an enclosed environment. Corrosion progressed linearly with time and silver sulfide was found as the corrosion product during all the tests. No significant dependence on RH was observed, while the corrosion rate increased as temperature rose. Furthermore the corrosion rate increased logarithmically with the quantity of the rubber placed in the exposure environment. It may be suggested that the corrosion rate of silver is determined by the amount of outgassed sulfur species which is a function of temperature and the quantity of rubber contained in the exposure environment.

• 소성∙가공
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• 제4권2호
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• pp.159-168
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• 1995

The torsion tests in the range of $550~800^{\circ}C$, $5.0{\times}10^{-3}~5.0{\times}10^0/sec$ were performed to study the effects of strain rate$(\.{\varepsilon})$ and temperature(T) on the hot strength of Cu-Zn alloy. High temperature flow stresses of this alloy increased with increasing $\.{\varepsilon}$ and/or decreasing T, and than the more grain refinement could be obtained. The flow curves exhibited a peak followed by a steady steady state regime as a result of dynamic recrystallization. The hot strength dependence of $\.{\varepsilon}$ and T was described by a hyperbolic sine law, $\.{\varepsilon}=A(sinh0.017{\sigma})^4.81$exp(-216KJ/mol). Hot strength could be reduced at the arbitary condition, $\.{\varepsilon}$ and T, by constitutive parameter Z(Zenner-Hollomon parameter), $Z=A(sinh{\alpha}{\sigma})^n=\.{\varepsilon}$exp(Q/RT).

• 한국광학회지
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• 제8권4호
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• pp.353-355
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• 1997

공초점 형광 현미경과 단일 광자 계수기로 구성되어 있는 단일 분자 검출장치를 사용하여, 색소 농도에 따른 광자 계수율의 변화를 관측하였다. 농도가 증가함에 따라 계수율이 포화하는 경향을 보였으며, 광검출기의 죽은 시간을 고려하여 측정 결과를 설명하였다. 계수율과 검출 부피, 광검출기의 양자효율, 입사 광량 사이의 관계를 나타내는 관계식을 제시하였다. 또한 신호대 잡음비에 대해서도 간략하게 논하였다.