• Nuclear Engineering and Technology
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• 제47권6호
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• pp.712-718
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• 2015

Cast duplex stainless steels are susceptible to thermal aging during long-term service at temperatures ranging from $280^{\circ}C$ to $450^{\circ}C$. To analyze the effect of thermal aging on leak-before-break (LBB) behavior, three-dimensional finite element analysis models were built for circumferentially cracked pipes. Based on the elasticeplastic fracture mechanics theory, the detectable leakage crack length calculation and J-integral stability assessment diagram approach were carried out under different bending moments. The LBB curves and LBB assessment diagrams for unaged and thermally aged pipes were constructed. The results show that the detectable leakage crack length for thermally aged pipes increases with increasing bending moments, whereas the critical crack length decreases. The ligament instability line and critical crack length line for thermally aged pipes move downward and to the left, respectively, and unsafe LBB assessment results will be produced if thermal aging is not considered. If the applied bending moment is increased, the degree of safety decreases in the LBB assessment.

• Wind and Structures
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• 제29권2호
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• pp.87-98
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• 2019

As a regenerated turbulent wind field process, wind tunnel test has proven to be a promising approach for investigating the transmission tower-line system (TTLS) performance in view of experimental scaled models design, simulation techniques of wind field, and wind induced responses subjected to typhoon. However, the challenges still remain in using various wind tunnels to regenerate turbulent wind field with considerable progress having been made in recent years. This review paper provides an overview of the state-of-the-art of the wind tunnel based on active or passive controlled simulation techniques. Specific attention and critical assessment have been given to: (a) the design of experimental scaled models, (b) the simulation techniques of wind field, and (c) the responses of TTLS subjected to typhoon in wind tunnel. This review concludes with the research challenges and recommendations for future research direction.

• 한국철도학회:학술대회논문집
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• 한국철도학회 2011년도 정기총회 및 추계학술대회 논문집
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• pp.7-13
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• 2011

RAMS is the procedure to maximize the reliability and availability of systems with managing operation rate, the frequency of failure in the system and repair method. Recently, all system life-cycle focusing on RAMS process has been rapidly developing in the field of railway vehicles, for example, applying th reliability management techniques for procurement and disposal of EMU. In particular, global economic recession require to reasonable measures for the EMU maintenance costs under the circumstances therefore, an alternative solution based on RCM(Reliability Centered Maintenance) which is the optimal maintenance method is interested. In this study, the state of being critical of each component and a primary factors was analyzed to improve VVVF inverter of the line 7 EMU by applying FMECA process. Furthermore, this paper showed the impact of connecting between the main and sub system. Based on these data, critical components according to malfunction ratings were classified by screening measures and improvements for each components was summarized.

• 제어로봇시스템학회논문지
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• 제4권4호
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• pp.506-516
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• 1998

In this paper, an algorithm is proposed to detect the malfunction of plasma-etching characteristics using EPD signal trajectories. EPD signal trajectories offer many information on plasma-etching process state, so they must be considered as the most important data sets to predict the wafer states in plasma-etching process. A recent work has shown that EPD signal trajectories were successfully incorporated into process modeling through critical parameter extraction, but this method consumes much effort and time. So Principal component analysis(PCA) can be applied. PCA is the linear transformation algorithm which converts correlated high-dimensional data sets to uncorrelated low-dimensional data sets. Based on this reason neural network model can improve its performance and convergence speed when it uses the features which are extracted from raw EPD signals by PCA. Wafer-state variables, Critical Dimension(CD) and uniformity can be estimated by simulation using neural network model into which EPD signals are incorporated. After CD and uniformity values are predicted, proposed algorithm determines whether malfunction values are produced or not. If malfunction values arise, the etching process is stopped immediately. As a result, through simulation, we can keep the abnormal state of etching process from propagating into the next run. All the procedures of this algorithm can be performed on-line, i.e. wafer to wafer.

• Journal of Magnetics
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• 제16권1호
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• pp.15-18
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• 2011

We have studied the $TiO_2$ doping effects on the flux pinning behavior of an $MgB_2$ superconductor synthesized by the in-situ solid-state reaction. From the field-cooled and zero-field-cooled temperature dependences of magnetization, the reversible-irreversible transition of $TiO_2$-doped $MgB_2$ was determined in the H-T diagram (the temperature dependence of upper critical magnetic field and irreversibility line). For comparison, the similar measurements are also obtained from SiC-doped $MgB_2$. The critical current density was estimated from the width of hysteresis loops in the framework of Bean's model at different temperatures. The obtained results manifest that nano-scale $TiO_2$ inclusions served as effective pinning centers and lead to the enhanced upper critical field and critical current density. It was concluded that the grain boundary pinning mechanism was realized in a $TiO_2$-doped $MgB_2$ superconductor.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2000년도 추계학술대회 논문집 학회본부 A
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• pp.10-12
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• 2000

As power systems tend to be operated more closely to their ultimate ratings. the role of SCOPF is changed and the importance for real-time security inhancement will be more increased in the new and competitive electricity market. This paper deals with the application of the SCOPF which make possible the On-Line application. The security margin of power system truly is changed according to the conditions or configuration of power system, therefore, the sensitivity factor related to the security is recalculated and the application should be updated in accordance with the state of power system. The proposed mechnism has been tested on modified Woolenberg 18-bus system and the results show more secure conditions against critical contingencies.

• 한국진공학회:학술대회논문집
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• 한국진공학회 2010년도 제39회 하계학술대회 초록집
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• pp.172-172
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• 2010

$MgB_2$ doped with $TiO_2$ was prepared by the in-situ solid state reaction to study the effects of $TiO_2$ dopant on the flux pinning behavior of $MgB_2$ superconductor. From the field-cooled and the zero-field-cooled temperature dependences of magnetization, the realms of vortex-glass and vortex-liquid states of $TiO_2$-doped $MgB_2$ were determined in the H-T diagram (the temperature dependence of upper critical magnetic field and irreversibility line). The critical current density was estimated from the width of hysteresis loops in the framework of Beam's model at different temperatures. The results indicate that nano-scale $TiO_2$ inclusions play a role of the effective pinning centers and lead to the enhanced upper critical field and critical current density. It is suggested that the grain-boundary pinning mechanism is realized in $TiO_2$-doped $MgB_2$ superconductor.

• 한국초전도학회:학술대회논문집
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• 한국초전도학회 2000년도 High Temperature Superconductivity Vol.X
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• pp.41-44
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• 2000

The mixed-state Hall angle has been measured in Hg-based superconducting thin films as functions of magnetic fields (H) up to 18 T. The temperature dependence of the Hall angle shows a peak (T$^{\ast}$) at low temperature, which is consistent with a crossover point from the thermally activated flux flow (TAFF) to a critical region (CR). At low fields below 10 T, T$^{\ast}$ shifts to low temperature with increasing fields. Interestingly, however, we found that T$^{\ast}$ is independent of fields above 10 T, suggesting unusual vortex state. A physical implication of H - T$^{\ast}$ line will be discussed.

• Progress in Superconductivity
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• 제2권1호
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• pp.39-42
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• 2000

The mixed-state Hall angle has been measured in Hg-based superconducting thin films as functions of magnetic fields (H) up to 18 T. The temperature dependence of the Hall angle shows a peak (T*) at low temperature, which is consistent with a crossover point from the thermally activated flux flow (TAFF) to a critical region (CR). At low fields below 10 T, T* shifts to low temperature with increasing fields. Interestingly, however, we found that T* is independent of fields above 10 T, suggesting unusual vortex state. A physical implication of H-T* line will be discussed.

• 한국물환경학회지
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• 제34권3호
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• pp.270-284
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• 2018

Paldang is a river reservoir located in the Midwest of Korea, with a water volume of $244{\cdot}10^6m^3$ and a water surface area of $36.5km^2$. It has eutrophied since the construction of a dam at the end of 1973, and the phosphorus concentration has decreased since 2001. Average hydraulic residence time of the Paldang reservoir is about 10 days during the spring season and 5.6 days as an annual level. The hydraulics and water quality of the reservoir can differ greatly, both temporally and spatially. For the spring period (March to May) in 2001 ~ 2017, the reservoir mean total phosphorus concentration calculated from the budget model based on a plug-flow system (PF) and a continuous stirred-tank reaction system (CSTR) was 13 % higher and 10 % lower than the observed concentration, respectively. A composite flow system (CF) was devised by assuming that the transition zone was plug flow, and that the lacustrine zone was completely mixed. The mean concentration calculated from the model based on CF was not skewed from the observed concentration, and showed just 6 % error. The retention coefficient of the phosphorus derived from the CF was 0.30, which was less than those of the natural lakes abroad or river reservoirs in Korea. The apparent settling velocity of total phosphorus was estimated to be $93m\;yr^{-1}$, which was 6 ~ 9 times higher than those of foreign natural lakes. Assuming CF, the critical load line for the total phosphorus concentration showed a hyperbolic relation to the hydraulic load in the Paldang reservoir. This is different from the previously known straight critical load line. The trophic state of the Paldang reservoir has recently been estimated to be mesotrophic based on the critical-load curve of the phosphorus budget model developed in this study. Although there is no theoretical error in the newly developed budget model, it is necessary to verify the validity of the portion below the inflection point of the critical-load curve afterwards.