• Journal of Korean Tunnelling and Underground Space Association
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• v.11 no.1
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• pp.71-83
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• 2009

Shotcrete is an important primary support for tunnelling in rock. The quality control of shotcrete is a core issue in the safe construction and maintenance of tunnels. Although shotcrete may be applied well initially onto excavated rock surfaces, it is affected by blasting, rock deformation and shrinkage and can debond from the excavated surface, causing problems such as corrosion, buckling, fracturing and the creation of internal voids. This study suggests an effective non-destructive evaluation method of the tunnel shotcrete bonding state applied onto hard rocks using the impact-echo (IE) method and ground penetration radar (GPR). To verify previous numerical simulation results, experimental study carried out. Generally, the bonding state of shotcrete can be classified into void, debonded, and fully bonded. In the laboratory, three different bonding conditions were modeled. The signals obtained from the experimental IE tests were analyzed at the time domain, frequency domain, and time-frequency domain (i.e., the Short- Time Fourier transform). For all cases in the analyses, the experimental test results were in good agreement with the previous numerical simulation results, verifying this approach. Both the numerical and experimental results suggest that the bonding state of shotcrete can be evaluated through changes in the resonance frequency and geometric damping ratio in a frequency domain analysis, and through changes in the contour shape and correlation coefficient in a time-frequency analysis: as the bonding state worsens in hard rock condition, the autospectral density increases, the geometric damping ratio decreases, and the contour shape in the time-frequency domain has a long tail parallel to the time axis. The correlation coefficient can be effectively applied for a quantitative evaluation of bonding state of tunnel shotcrete. Finally, the bonding state of shotcrete can be successfully evaluated based on the process suggested in this study.

• The Korean Journal of Applied Statistics
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• v.26 no.5
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• pp.835-845
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• 2013

Travel-time is considered the most typical and preferred traffic information for intelligent transportation systems(ITS). This paper proposes a real-time travel-time prediction method for a national highway. In this paper, the K-nearest neighbor(KNN) method is used for travel time prediction. The KNN method (a nonparametric method) is appropriate for a real-time traffic management system because the method needs no additional assumptions or parameter calibration. The performances of various models are compared based on mean absolute percentage error(MAPE) and coefficient of variation(CV). In real application, the analysis of real traffic data collected from Korean national highways indicates that the proposed model outperforms other prediction models such as the historical average model and the Kalman filter model. It is expected to improve travel-time reliability by flexibly using travel-time from the proposed model with travel-time from the interval detectors.

• Korean Journal of Cognitive Science
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• v.30 no.1
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• pp.51-83
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• 2019

Delay of immediate gains/losses brings on additional gaines/losses as much as waiting period. However, there are individual difference in evaluating the value of delayed time discounting on the person. In this study, to investigates the individual differences about valuating the delayed time, it is ascertained the correlation between decisions from intertemporal choice task and individual differences of risk taking/perception, emotion, regulatory focus, and HPSP and BELT, subjective period measuring task. In Addition, it is analyzed the individual differences after classifying good/bad performer of intertemporal tasks and person who perceive long/short about the future periods. As a result, good performers of intertemporal task have high openness and perceive longer about 12 hours, 15 days, 6 months and 5 years. Reconstruction about future temporal length plays an important role on intertemporal task, and it is discussed about necessity of follow up study.

• Journal of the Korea institute for structural maintenance and inspection
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• v.26 no.3
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• pp.64-71
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• 2022

In this study, fire and egress simulation was conducted for the egress safety evaluation of the nursing hospitals. A fire simulation was performed with or without the smoke exhaust system using the FDS, and the available safe egress time (ASET) of the nursing hospitals was calculated. In addition, an egress simulation considering the characteristics of occupants and egress delay time was performed using Pathfinder, and the required safe egress time (RSET) was calculated. By comparing the ASET and RSET, the egress safety of the nursing hospital with or without a smoke exhaust system was evaluated according to the number of egress guides and the egress delay time. The simulation results show that the number of casualties increased as the egress delay time increased, and the required safe egress time decreased as the number of egress guides increased. In addition, it was found that if a smoke exhaust system with the capacity specified in the KFPA is secured, the available safe egress time can be greatly increased and the number of casualties can be greatly reduced.

• Journal of the Korea institute for structural maintenance and inspection
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• v.21 no.2
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• pp.46-52
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• 2017

Recently durability design based on deterministic or probabilistic method has been attempted since service life evaluation in RC(Reinforced Concrete) structure exposed to chloride attack is important. The deterministic durability design contains a reasonable method with time effect on surface chloride content and diffusion coefficient, however the probabilistic design procedure has no consideration of time effect on both. In the paper, a technique on PDF(Probability of Durability Failure) evaluation is proposed considering time effect on diffusion and surface chloride content through equivalent surface chloride content which has same induced chloride content within a given period and cover depth. With varying period to built-up from 10 to 30 years and maximum surface chloride content from $5.0kg/m^3$ to $10.0kg/m^3$, the changing PDF and the related service life are derived. The proposed method can be reasonably applied to actual durability design with preventing conservative design parameters and considering the same analysis conditions of the deterministic method.

• Journal of the Korean Society for Nondestructive Testing
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• v.22 no.2
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• pp.149-154
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• 2002

An attempt was made to evaluate the changes of microstructures and mechanical properties with increasing aging time in 2.25Cr-1Mo steel. In this study, it was verified the feasibility of the evaluation for degraded 2.25Cr-1Mo steel by isothermal heat treatment at $630^{\circ}C$ up to 1,000 hours using surface SH wave and investigated the change of attenuation coefficient and propagation time. Attenuation coefficient had a tendency to increase according to degradation and propagation time drastically in the beginning of deterioration. A good correlation between ultrasonic attenuation coefficient and hardness was found, which made sure that attenuation coefficient is an potential parameter for evaluation of aging degradation. In addition, it has verified experimentally the frequency dependence of ultrasonic group velocity and attenuation coefficient using wavelet transform.

• Korean Journal of Clinical Laboratory Science
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• v.56 no.3
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• pp.217-227
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• 2024

In this paper, the factors affecting tissues during fixation on slides were determined by changing the tissue type, fixation time, and temperature. Also, stainability and DNA conservation were evaluated. The tissues selected were parenchymal and intestinal tissue. The stainability was evaluated using hematoxylin and eosin staining and a special stain suitable for the tissue. DNA conservation was evaluated using the DNA integrity number (DIN) for stability evaluation after purity measurement. The results showed that, at all temperatures, as time increased, there was no histomorphological difference and the stainability tended to intensify. The intestinal tissue tended to have less mucosal change and proper muscle layer degeneration. There was little difference in the purity. However, the longer the fixation time, the lower the DIN value for DNA. Significant differences were identified at 25℃ and 50℃. This means that fixation at 4℃ is the more safe for DNA. This experiment confirmed that, between the time and temperature conditions associated with fixation, time had a greater effect on both staining and DNA conservation. The results of this study are expected to provide basic data for future research on the setting appropriate conditions for fixation for histopathological examinations or diagnoses.

• Journal of the Microelectronics and Packaging Society
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• v.24 no.3
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• pp.41-46
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• 2017

In this study, rapid cooling method was proposed to improve the anti-scratch performance of anti-reflection film fabricated by nanoimprint lithography. Effects of cooling time on the mechanical properties and optical properties were evaluated. Pencil hardness measurements showed that anti-scratch performance enhanced as the cooling time increased while characterization on the optical property showed that reflectance on scratch increased as the cooling time increased. Therefore, it was concluded that the anti-scratch performance and optical properties are highly influenced by the cooling time. The observed results explained in terms of residual stress and free volume in polymeric materials.

• Proceedings of the Korea Concrete Institute Conference
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• 2008.11a
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• pp.161-164
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• 2008

It is played an important part in dam safety that KWATER is taken the responsibility of design, construction and maintenance about dam. It is considered that safety inspection of accumulated technology and knowledge of new evaluation method have developed. Thus this study is that instrumentation data is analyzed continually and dam's safety is evaluated about behavior property, in Chungju concrete dam. New evaluation method is that instrumentation data is analyzed reliability. It is suggested that suitability of management period and maintenance of instrument in dams.

• The Journal of The Korea Institute of Intelligent Transport Systems
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• v.2 no.2 s.3
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• pp.23-29
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• 2003

This study is the empirical research about application and evaluation of AVI that is an essential technology for calculating and providing the travel time. Travel time calculation and provision is one of the technique for information collecting and providing in the ITS. Through the field test on a national highway, we proposed the travel time calculation technique from the data by non-contact vehicle detecting method and validated field application performance with field data. We proposed the technique of evaluating field application performance, then using this, analyzed recognition rate, detection rate and travel time with field data.