• Proceedings of the KSME Conference
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• 2003.04a
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• pp.1633-1638
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• 2003

In case that in-leakage through the valve disk occurs, a numerical study is performed to estimate on thermal stratification phenomenon in the Safety Injection piping connected with the Reactor Coolant System piping of Nuclear Power Plant. As the leakage flow rate increases, the temperature difference between top and bottom of horizontal piping has the inflection point. In the connection point of valve and piping, the maximum temperature difference between top and bottom was 185K and occurred in the condition of 10 times of standard leakage flow rate. In the connection point of elbow and horizontal piping, the maximum temperature difference was 145K and occurred in the condition of 15 times of standard leakage flow rate. In the vertical piping of Safety Injection piping, the near of connection point between elbow and vertical piping showed the outstanding thermal stratification phenomenon in comparison with another region because of turbulent penetration from Reactor Coolant System piping. In order to prevent damage of piping due to the thermal stratification when in-leakage through the valve disk occurs, the connection points between valve and piping, and the connection points between elbow and piping need to be inspected continually.

• Fire Science and Engineering
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• v.22 no.3
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• pp.234-238
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• 2008

Autoignition suppression of hydrogen/air premixed mixtures by $CF_3CHFCF_3(HFP)$ was investigated computationally. Numerical simulation was performed in isobaric and homogeneous system to evaluate the induction times. The detailed chemistry of 93 species and 817 reaction mechanism was introduced for hydrogen/air/HFP mixtures. The result of pure hydrogen/air mixture show that the resulting value of induction time depends relatively weakly on the definition used event though there are various criteria for defining the induction time such as the inflection of temperature, OH and $O_2$ concentrations generally. Also, the autoignition temperature of $H_2/air$ mixture is estimated to about 850K, which is corresponds to the literature value. In the case of HFP addition in $H_2/air$ mixture, the results shows that there are several inflection points of radical concentration, and hence it might be to use the temperature for defining ignition delay. When HFP is added to stoichiometric $H_2/air$ mixture, the effect of ignition delay is outstanding above 10% HFP concentration. As HFP concentration increases, both dilution and chemical effects contribute to delay the ignition. Also, the chemical effect on the ignition delay is more considerable with the higher HFP concentration.

• Wind and Structures
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• v.19 no.1
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• pp.1-14
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• 2014

Rail-mounted cranes can be easily damaged by a sudden gust of wind while working at a running speed, due to the large mass and high barycenter positions. In current designs, working rail-mounted cranes mainly depend on wheel braking torques to resist large wind load. Regular brakes, however, cannot satisfactorily stop the crane, which induces safety issues of cranes and hence leads to frequent crane accidents, especially in sudden gusts of wind. Therefore, it is necessary and important to study the braking performance of working rail mounted cranes under wind load. In this study, a simplified mechanical model was built to simulate the working rail mounted gantry crane, and dynamic analysis of the model was carried out to deduce braking performance equations that reflect the qualitative relations among braking time, braking distance, wind load, and braking torque. It was shown that, under constant braking torque, there existed inflection points on the curves of braking time and distance versus windforce. Both the braking time and the distance increased sharply when wind load exceeded the inflection point value, referred to as the threshold windforce. The braking performance of a 300 ton shipbuilding gantry crane was modeled and analyzed using multibody dynamics software ADAMS. The simulation results were fitted by quadratic curves to show the changes of braking time and distance versus windforce under various mount of braking torques. The threshold windforce could be obtained theoretically by taking derivative of fitted curves. Based on the fitted functional relationship between threshold windforce and braking torque, theoretical basis are provided to ensure a safe and rational design for crane wind-resistant braking systems.

• Journal of the Korea Convergence Society
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• v.12 no.9
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• pp.153-159
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• 2021

In this study, basic data that can be referenced for ventilation modeling was presented by analyzing the characteristics of wind pressure coefficients(Cp) according to wind direction angles under conditions of different building layouts and aspect ratios through CFD (Computational Fluid Dynamics) analysis for flat-type apartment complexes. In the case of a wind direction angle of 0°, Cp distribution in the form of an inverted S-shape was shown on the front of the building located on the windward side. And Cp corresponding to the lowest floor, the uppermost floor, and the two inflection points showed relatively close values regardless of the height of the building. The inflection point of the low-rise part was formed at a height of about 11m, and the height of the high-rise part could be calculated through a trend formula proportional to the height of the building. It was confirmed that the averaged Cp value can be applied in most conditions except for the wind direction angle of 45 degrees.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 1997.03a
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• pp.77-80
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• 1997

The torsion tests in the range of 900~110$0^{\circ}C$, 5.0$\times$10-2~5.0$\times$100/sec were performed to study the recry stallization behavior of 304 stainless steel in the high temperature multistage deformation. The no-recrystallization temperature(Tnr) and fractional softening(FS) were determined by the change of flow curves. The inflection points of stress slope were moved to lower temperature area as the strain rate and the interrupt time were increased. From the multipass flow curve, the intersection between pass stress and FS curve was corresponding to the pass which the FS dropped abruptly and it was shown that the recrystallization area could be determined by the FS measurement in multipass deformation.

• Bulletin of the Korean Chemical Society
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• v.6 no.1
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• pp.11-15
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• 1985

Electrical conductivites of polycrystalline yttrium sesquioxides containing 1.6 and 3.2 mol % of holmium sesquioxdes have been measured from 650 to $1050^{\circ}C$ under oxygen partial pressures of $1{\times}10^{-5}$ to $2{\times}10^{-1}$ atm. Plots of log conductivity vs. 1/T at constant oxygen partial pressures are found to be linear away from the two inflection points. The low- and high-temperature dependences of conductivity show different defect structures of yttrium sesquioxide. The plots of log conductivity vs. log $PO_2$ are found to be linear at $PO_{2'}$s of $10^{-5}$ to $10^{-1} atm. The electrical conductivity dependences on $PO_2$ are found to be $1}5.3$ at $950-1050^{\circ}C$, $\frac{6}{1}$ at $800-950^{\circ}C$ and ($\frac{6.2}{1}$) - ($\frac{6.5}{1}$) at $650-800^{\circ}C$, respectively. The defect structures and conduction mechanisms have been suggested.

• Communications of the Korean Mathematical Society
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• v.34 no.1
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• pp.333-349
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• 2019

The paper study the curvature theory of a line-trajectory of constant Disteli-axis, according to the invariants of the axodes of moving body in spatial motion. A necessary and sufficient condition for a line-trajectory to be a constant Disteli-axis is derived. From which new proofs of the Disteli's formulae and concise explicit expressions of the inflection line congruence are directly obtained. The obtained explicit equations degenerate into a quadratic form, which can easily give a clear insight into the geometric properties of a line-trajectory of constant Disteli-axis with the theory of line congruence. The degenerated cases of the Burmester lines are discussed according to dual points having specific trajectories.

• Proceedings of the Korea Information Processing Society Conference
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• 2020.11a
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• pp.1084-1086
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• 2020

동영상 공유 플랫폼의 발전으로 다양한 영상들이 업로드 되고 있는데, 영상에 사용된 음악의 저작권 행사를 위해서는 음악 검색 알고리즘의 역할이 매우 중요하다. 그러나, 커버곡과 같이 원곡을 변형하여 사용한 경우에는 단순한 음악 검색 알고리즘으로는 이러한 상황을 탐지하기가 쉽지 않다. 음악의 높낮이나 빠르기 등이 바뀌어도 검색 성능이 유지되어야 하지만, 현재까지 연구된 알고리즘들은 이러한 변화에 취약하기 때문이다. 이에 본 연구에서는 멜로디 라인의 변곡점을 활용한 커버곡 검색 알고리즘을 제안한다. 본 알고리즘은 멜로디 라인을 중심으로 하여 높낮이 변화에도 높은 성능을 유지하고, 변곡점을 이용하기 때문에 빠르기 변화에 강하고 사용되는 메모리 양은 적다는 장점이 있다.

• East Asian mathematical journal
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• v.39 no.4
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• pp.437-454
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• 2023

The core of the change in the era of the 4th industrial revolution is the change in the base of 'digital technology'. These changes are incomparably large and are expected to have a more important impact on our lives than ever before. One of the major inflection points in the transition to the digital era is the education field, and IT technology has become an essential element in the educational field. Accordingly, this study examines domestic research trends related to the educational environment based on digital technology. Then, we would like to provide implications for the establishment of a digital-based educational environment that will change in the future. To this end, Semantic network analysis has been conducted to quantitatively structure text data obtained from studies related to digital technology in the field of mathematics education over the past 10 years, and the discussion will continue based on the results.

• Journal of Animal Science and Technology
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• v.54 no.6
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• pp.395-400
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• 2012

This study was conducted to estimate the growth curve parameters for the body weight (BW) and body length (BL) of miniature pigs in Korea. Growth curve parameters were estimated through a nonlinear regression model using Gompertz, Logistic, and von Bertalanffy methods. A total of 25 piglets were measured monthly from birth up to 15 months of age to estimate both body weight and length. Results showed that the estimated average values for the body weight (body length) were 31.83 kg (58.77 cm) for the mature weight (A), 3.06 (1.74) for the growth ratio (${\beta}$), and 0.28 (0.52) for the maturing rate (${\kappa}$). Average inflection points showing maximum growth rate estimated each month for body weight were 3.97 kg and 11.70 cm, while for the body length were 1.06 kg and 21.61 cm. Moreover, the estimated maturation rates of the body weight and length for the group of Sire 1 were 0.22 and 0.40 respectively, whereas for the group of Sire 2 these values were 0.34 and 0.39. On the other hand, for the groups of Dam 1, Dam 2, and Dam 3, maturation rates for their body weights were 0.26, 0.28 and 0.33 respectively, while for their body lengths these values were 0.43, 0.37, and 0.38, respectively. The study also indicated a negative relationship between the values of mature weight and maturity rate for the body weight will result to a higher inflection point which is in contrast for the body length where results show that a positive relationship between the values of mature length and the maturity rate will result to a higher inflection point. Furthermore, the growth performance of miniature pig varies across stages but using these estimated growth curve parameters could improve the genetic traits of miniature pig.