• 한국신뢰성학회지:신뢰성응용연구
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• 제16권4호
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• pp.356-363
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• 2016

Purpose: The purpose of this study is to propose efficiency of equipment testing the luminance degradation of OLED. Methods: The degradation model of Exponential model and Stretched exponential model is analyzed by goodness of fit test using calculated R-square. The degradation model having the higher R-square is finally selected. Scale parameter and Shape parameter using the selected degradation model is estimated. The activation energy and current density n using peck model among the accelerated model is estimated. the estimated parameters are analyzed by t-test. Results: The results of t-test show that the estimated parameters on chamber and hotplate are equal statistically. we can know the similarity of the luminance degradation rate and degradation pattern on chamber and hotplate. Conclusion: The result of the degradation test on chamber and hotplate is similar. when the accelerated degradation test on the panel of the OLED TV is performed, hotplate is requiring less samples, time and cost than chamber. so the accelerated degradation test on the panel of the OLED TV using the hoplate is efficient of time and cost.

• 한국식품과학회지
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• 제22권5호
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• pp.582-589
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• 1990

본 고에서는 Equivalent time과 Equivalent temperature를 활용하여 Kinetic parameters를 결정하는 새로운 방법을 제안하였다. 본 방법의 타당성을 두 가지의 kinetic data 즉, 계산치와 실험치를 이용하여 예시하였다. 계산치는 그 Kinetics가 잘 알려진 세 가지 화학반응에 대해 임의의 등온가열조건을 적용하여 계산하였고 실험치는 2% 설탕용액을 사용하여 0.0005N 염산용액을 사용하여 가수분해가 일어나는 정도를 효소반응을 이용하여 측정하였다. 본 방법에 의해 결정된 활성화 에너지와 Frequency factor는 각각 $104.74{\pm}1.87KJ/mol$과 $5.26{\times}10^{14)hr^{-1}$이었으며 이들 값은 보고된 결과와 잘 일치되었다.

• 대한금속재료학회지
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• 제48권1호
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• pp.85-89
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• 2010

The plastic deformation behavior of magnesium alloy is affected simultaneously by deformation temperature and strain rate under warm and/or hot working conditions. The soundness of deformation of AZ31-xCa (x=0. 0.7, 2.0 wt.%) extrudes during compression was strongly affected by processing variables including deformation temperature, strain rate. compression-loading direction, which was related to the activation of available deformation systems. The deformation behavior of AZ31-xCa extrudes was also affected by Ca content, which was related to the change of the sort and fraction of second phase. The complex effects of deformation temperature and strain rate on the deformation behavior of AZ31-xCa extrudes during compression under various conditions could be successfully described by Zener-Hollomon parameter.

• 한국산업융합학회 논문집
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• 제25권3호
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• pp.467-476
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• 2022

The Bank of Korea raised the benchmark interest rate by a quarter percentage point to 1.75 percent per year, and analysts predict that South Korea's policy rate will reach 2.00 percent by the end of calendar year 2022. Furthermore, because market volatility has been significantly increased by a variety of factors, including rising rates, inflation, and market volatility, many investors have struggled to meet their financial objectives or deliver returns. Banks and financial institutions are attempting to provide Robo-Advisors to manage client portfolios without human intervention in this situation. In this regard, determining the best hyper-parameter combination is becoming increasingly important. This study compares some activation functions of the Deep Deterministic Policy Gradient(DDPG) and Twin-delayed Deep Deterministic Policy Gradient (TD3) Algorithms to choose a sequence of actions that maximizes long-term reward. The DDPG and TD3 outperformed its benchmark index, according to the results. One reason for this is that we need to understand the action probabilities in order to choose an action and receive a reward, which we then compare to the state value to determine an advantage. As interest in machine learning has grown and research into deep reinforcement learning has become more active, finding an optimal hyper-parameter combination for DDPG and TD3 has become increasingly important.

• Toxicological Research
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• 제17권3호
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• pp.187-194
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• 2001

The oxidative stress causes the cell damage and death and thereby, stimulates membrane lipid peroxidation. In this study, the correlation between the lipid peroxidation product and the parameter of liver fibrosis (cirrhosis) was investigated in cholestasis induced rats. The Sprague-Dawley rats were divided into 3 groups (sham: sham operation, BDL/S-I and BDL/S-II : bile duct ligation/scission) and were observed for 2 or 4 weeks. After observation period, the organs were weighed and the ratio of organ weight/body weight was calculated. Sera and liver tissue were used for the measurement of malondealdehyde (MDA), parameter of clinical biochemistry, total collagen content and the staining. The ratio of organ weight/body weight in BDL/S-I and BDL/S-II was significantly increased compared to sham operated group. Serological parameters (Alanine transaminase, Aspartate transaminase, Alkaline phosphatase and Total bilirubin) in BDL/S-I and BDL/S-II group were significantly higher than those in sham operated group. Concentration of MDA in BDL/S-I (261%) and BDL/S-II(790%) was significantly increased compared to MDA in sham operated group. And the content of hydroxyproline (hyp) in BDL/S-I and BDL/S-II group was significantly increased 2~4 times than in sham operated group. The good correlations between hyp in liver tissue and MDA in sera of sham operated group and all operated group were found (r=0.825). The significantly higher value of MDA, hyp and serological parameters in BDL/S-I and BDL/S-II group suggests the stimulation of lipid peroxidation and chronic liver damage. Especially the activation of lipid peroxidation and the stimulation of liver fibrosis was stronger in BDL/S-II group than in BDL/S-I group. The stronger fibrosis, portal-portal septum formation, the more massive bile duct proliferation in portal triads and stroma, and hepatocytes swelling were observed in liver tissue of and BDL/S-II group compared to BDL/S-I group. Conclusively, a good correlation between MDA as a lipid peroxidation marker and hyp as a liver fibrotic parameter could be connected with the process of liver fibrosis. Moreover, cholestasis condition may cause jaundice, activation of lipid peroxidation, and collagen accumulation in liver. Additionally, optimal observation period of bile duct obstruction for the screening of antioxidant and antifibrotic effect in rats would be four weeks.

• 디지털콘텐츠학회 논문지
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• 제16권1호
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• pp.63-70
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• 2015

본 연구는 PACS의 영상저장부의 디스크 배열에 들어가는 하드디스크의 수명을 제조회사의 가속 수명시험 결과로 예측하고자 하였다. $50^{\circ}C$, $60^{\circ}C$의 고장시간 데이터로 Anderson-Darling 적합도 검증을 진행하여 와이블 분포를 채택하였다. 형상모수와 척도모수로 동일성 검증을 진행한 결과, 가속 수명 시험 $50^{\circ}C$ 조건과 가속 수명 시험 $60^{\circ}C$ 조건의 확률분포가 통계적으로 유의하지 않았다. 온도 가속인자를 포함한 와이블-아레니우스 모형으로부터 추정한 형상모수는 1.0409이며, 사용조건($30^{\circ}C$)의 특성수명은 24603.5 시간이었다. 또한 아레니우스 모델 식에 반영하여 활성화 에너지 0.5011 eV을 산출하였다. 그리고 가속시험의 정확성 확보차원에서 가속시험 불량시료와 시장 반품 시료로 고장 분석을 진행한 결과, 불량 모드별 점유율의 세부 차이는 있으나, 점유율 순서는 일치 하였다. 본 연구는 PACS 환경 하에서 하드디스크의 가속시험절차를 제안하며, 제조자와 사용자간에 수명예측에 도움을 주고자 한다.

• Journal of Korean Neurosurgical Society
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• 제58권3호
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• pp.242-247
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• 2015

Objective : The purpose of this study is to determine whether the changes of contralateral sensorimotor cortical activation on functional magnetic resonance imaging (fMRI) can predict the neurological outcome among spinal cord injury (SCI) patients when the great toes are stimulated without notice. Methods : This study enrolled a total of 49 patients with SCI and investigated each patient's preoperative fMRI, postoperative fMRI, American Spinal Injury Association (ASIA) score, and neuropathic pain occurrence. Patients were classified into 3 groups according to the change of blood oxygenation level dependent (BOLD) response on perioperative fMRI during proprioceptive stimulation with repetitive passive toe movements : 1) patients with a response of contralateral sensorimotor cortical activation in fMRI were categorized; 2) patients with a response in other regions; and 3) patients with no response. Correlation between the result of fMRI and each parameter was analyzed. Results : In fMRI data, ASIA score was likely to show greater improvement in patients in group A compared to those belonging to group B or C (p<0.001). No statistical significance was observed between the result of fMRI and neuropathic pain (p=0.709). However, increase in neuropathic pain in response to the signal change of the ipsilateral frontal lobe on fMRI was statistically significant (p=0.030). Conclusion : When there was change of BOLD response at the contralateral sensorimotor cortex on perioperative fMRI after surgery, relief of neurological symptoms was highly likely for traumatic SCI patients. In addition, development of neuropathic pain was likely to occur when there was change of BOLD response at ipsilateral frontal lobe.

• 열처리공학회지
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• 제14권4호
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• pp.220-227
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• 2001

The static creep behaviors of dispersion strengthened copper GlidCop were investigated over the temperature range of $650{\sim}690^{\circ}C$ (0.7Tm) and the stress range of 40~55 MPa (4.077~5.61 $kg/mm^2$). The stress exponents for the static creep deformation of this alloy was 8.42, 9.01, 9.25, 9.66 at the temperature of 690, 677, 663, and $650^{\circ}C$, respectively. The stress exponent, (n) increased with decreasing the temperature and became dose to 10. The apparent activation energy for the static creep deformation, (Q) was 374.79, 368.06, 361.83, and 357.61 kg/mole for the stress of 40, 45, 50, and 55 MPa, respectively. The activation energy (Q) decreased with increasing the stress and was higher than that of self diffusion of Cu in the dispersion strengthened copper. In results, it can be concluded that the static creep deformation for dispersion strengthened copper was controlled by the dislocation climb over the ranges of the experimental conditions. Larson-Miller parameter (P) for the crept specimens for dispersion strengthened copper under the static creep conditions was obtained as P=(T+460)(logtr+23). The failure plane observed for SEM slightly showed up transgranular at that experimental range, however, universally it was dominated by characteristic of the intergranular fracture.

• 한국안전학회지
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• 제8권4호
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• pp.27-40
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• 1993

High temperature tensile tests, steady state creep tests, Internal stress tests and creep rupture tests using A17075 alloy( $T_{6}$ ) were performed over the temperature range of 9$0^{\circ}C$~50$0^{\circ}C$ (0.4 $T_{m}$ ~0.85 $T_{m}$ ) and stress range of 0.64~17.2(kgf/$\textrm{mm}^2$). The main results obtained in this paper were as follows. (1) The activation energies for yielding at the temperature of 0.4 $T_{m}$ ~0.75 $T_{m}$ were calculated to be 25.7~36.5kcal/mol, which were nearly equal to the activation energies for creep. (2) At around the temperature of 9$0^{\circ}C$~12$0^{\circ}C$ and under the stress level of 10~17.2(kgf/$\textrm{mm}^2$), and at around the temperature of 200~41$0^{\circ}C$ and under the stress level of 1.53~9.55(kgf/$\textrm{mm}^2$) and again at around the temperature of 470~50$0^{\circ}C$ and under the stress level of 0.62~l.02(kgf/$\textrm{mm}^2$), the applied stress dependence of steady state creep rate $n_{measu}$ measured were, respectively, 3.15, 6.62 and 1.1, which were in good agreement the calculated stress dependence $n_{ealeu}$ obtained by the difference of the applied stress dependence of the Internal stress and the ratio of the internal stress to the applied stress. (3) At the temperature range of 0.4~0.43 $T_{m}$ , and at the temperature range of 0.52~0.75 $T_{m}$ and again at the temperature range of 0.82~0.85 $T_{m}$ , the activation energies $Q_{measu}$ obtained by steady state creep rate, respective, 26. 16, 34.9, 36.2 and 36.1kcal/mol, which were in good agreement with those obtained with the activation energies under constant effective stress and the temperature dependence of Internal stress. (4) At the temperature range of the 0.52~0.73 $T_{m}$ and under the stress level of 1.53~9.55(kgf/$\textrm{mm}^2$), the stress dependence of rupture life(n’) measured was 6.3~6.6, which was in good agreement with the stress dependence of steady state creep rate(n). And at the same condition the activation energy for rupture( $Q_{f}$ ) measured was 32.0~36.9kca1/mol, which was also in good agreement with the activation energy obtained by steady state creep rate ( $Q_{c}$ ). (5) The rupture life( $t_{f}$ ) might be represented by athermal process attributed to the difference of the applied stress dependence of the internal stress and the ratio of the internal stress to the applied stress, and the thermal activated process attributied to the temperature dependence of the internal stress as $t_{f}$ = A'$\sigma$$_{a}$ ｛n(1-d $\sigma$$_{i}$ /d $\sigma$$_{a}$ )/(1-$\sigma$$_{i}$ / $\sigma$$_{a}$ )｝.exp[｛ $Q_{c}$ $^{*}$-( $n_{o}$ R $T^2$/ $E_{(T)}$) (d $E_{(T)}$/dT) - ( $n_{0}$ R $T^2$/ $\sigma$$_{a}$ - $\sigma$$_{i}$ ) (d $\sigma$$_{i}$ /dT)｝/RT]. (6) The relationship betwween Larson-Miller rupture parameter and logarithmic stress was linearly decreased, so creep rupture life of Al 7075 alloy seemed to be predicted exactly with Larson-Miller parameter.meter.

• KSBB Journal
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• 제11권3호
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• pp.295-302
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• 1996

Rubisco의 parameter들을 측정하는 것은 광합성 연구에 대단히 중요한데, 본 연구에서는 방사성통위 원소를 사용하는 방법 이 아닌 photometric assay 방 법을 사용하여 parameter를 측정하였다. Rubisco 의 activation과 carbamylation에 미치는 고 CO2 놓도의 효과를 연구하기 위하여, 정상 $CO_2$ 농도 (350 ppm)와 고 $CO_2$ 농도(650 ppm)에서 기른 kidney bean (Phaseolus vulgaris L.) 잎을 각각 재료로 하여, dual beam(334 nm9-} 405 nm) spectro­p photometer를 사용하여 rubisco의 initial activity 와 total activity, carbamylation rate 및 量을 측정 비교하였으며, SDS-PAGE에 의해 rubisco의 전기 영통 profile을 분석하였다. 정상 $CO_2$ 농도에서의 initial activity와 total activity는 $41.2{\mu}M/m^2/s 와 52.2{\mu}M/m^2/s$이며, 고 $CO_2$ 농도에서는 $27.4{\mu}M/m^2/s 와 46.1{\mu}M/m^2/s$로서, 350 ppm에서 650 ppm으로 $CO_2$ 농도를 증가시키면 rubisco의 initial activity와 total activity가 갑소되었다. 또한 carbamylation율도 정상 $CO_2$ 농도에서는 79%이며, 고 $CO_2$ 농도에서는 58.9%로서, $CO_2$ 농도의 증가에 따라 감소되 었다. Rubisco 의 量은 정상 $CO_2$농도에서는 $1.94 {\mu}M/m^2$$ 임에 반해 고 $CO_2$ 농도에서는 $1.58{\mu}M/m^2$ 로서, $CO_2$2 농도는 증가되었는데 그 量은 감소되었다. 이와 같이 고 $CO_2$농도에셔 rubisco의 activity가 감소되는 것은 rubisco의 carbamylation에 기인되는 것으로 생각된다. SOS-PAGE 분석에서 50kO 분자량의 large s subunit와 14.5 kO의 분자량을 가지는 small subu n mt를 동정하였는데, 고 $CO_2$ 농도와 정상 $CO_2$ 농도 의 50kD와 14.5 kO band의 intensity를 비교하면 두 구 사이에 큰 차이가 발견되지 않았다. 고 CO2 농도에서 정상 $CO_2$ 농도로 switch한 rubisco의 parameter는 정상 $CO_2$ 농도에서의 pa­r rameter와 거의 비슷한 값을 나타내였는데, 이는 350 ppm의 정상 $CO_2$ 농도에 의해 rubisco의 acti­v vity가 회복되었음을 의미한다.