• Journal of Environmental Science International
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• v.19 no.2
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• pp.237-245
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• 2010

The relationship between air temperatures and the fraction of urban areas (FUA) and their linear regression equation were estimated using land-use data provided by the water management information system (WAMIS) and air temperatures by the Korea Meteorology Administration (KMA) in the Seoul metropolitan area (SMA) during 1975 through 2000. The future FUA in the SMA (from 2000 to 2030) was also predicted by the urban growth model (i.e., SLEUTH) in conjunction with several dataset (e.g., urban, roads, etc.) in the WAMIS. The estimated future FUA was then used as input data for the linear regression equation to estimate an annual mean minimum air temperature in the future (e.g., 2025 and 2030). The FUA in the SMA in 2000 simulated by the SLEUTH showed good agreement with the observations (a high accuracy (73%) between them). The urban growth in the SMA was predicted to increase by 16% of the total areas in 2025 and by 24% in 2030. From the linear regression equation, the annual mean minimum air temperature in the SMA increased about $0.02^{\circ}C$/yr and it was expected to increase up to $8.3^{\circ}C$ in 2025 and $8.7^{\circ}C$ in 2030.

• Journal of Ocean Engineering and Technology
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• v.11 no.4
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• pp.61-75
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• 1997

The social demand urges us to use some equipments and structures in high temperature environment. By this occasion, the necessity of studying the fatigue crack growth is an important aspect of new materials. However, the present situation is rarely to accumulate the fatigue data. Especially, 1Cr-1Mo-0.25V steel and 304 stainless steel have been increased to be used under the severe condition of high temperature. And so, the fatigue estimation of those materials is important and appropriate. Fatigue tests have been carried out to examine the crack initiation, growth behaviour for the small fatigue crack of 1Cr-1Mo-0.25V steel and 304 stainless steel at room temperature and 538^{\circ}C$. The remote measurement system which has many merits of checking and saving the image for detailed examination was applied to closely detect the crack length. Generally, the fatigue crack initiated in the form of multiple cracks and grew each other. And then it coalesced to become a major crack. The major crack governed the rest of the fatigue life. In the growing process, each peripheral cracks interact and grow for a certain period. After then, it coalesced and fractured. On the basis of the above experimental data for the small crack, a simulation program was developed to predict the residual life time and to estimate the integrity of machine elements and structures. At the same time, the simulation was extended to 1Cr-1Mo-0.25V steel. The simulation results have shown a good agreement to those of the experimental ones for both materials of 1Cr-1Mo-0.25V steel and 304 stainless steel with small cracks. The NASCRAC has applied to compare the fatigue life with the experimental results. And so, it can be said that the simulation program is valuable tools to the industrial fields.

• Journal of the Korean Institute of Gas
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• v.16 no.1
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• pp.26-32
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• 2012

The autoignition temperature is one of the most important physical properties used to determine the flammability characteristics of chemical substances. Despite the needs of the experimental autoignition temperature data for the design of chemical plants, it is not easy to get the data. This study have built and compared partial least squares (PLS) and support vector machine (SVM) models to predict the autoignition temperatures of 503 organic compounds out of DIPPR 801. As the independent variables of the models, 59 functional groups were chosen based on the group contribution method. The prediction errors calculated from cross-validation were employed to determine the optimal parameters of two models. And, particle swarm optimization was used to get three parameters of SVM model. The PLS and SVM results of the average absolute errors for the whole data range from 58.59K and 29.11K, respectively, indicating that the predictive ability of the SVM is much superior than PLS.

• Geomechanics and Engineering
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• v.22 no.4
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• pp.339-348
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• 2020

The uncertain geotechnical properties of frozen soil are important evidence for the design, operation and maintenance of the frozen ground. The complex geological, environmental and physical effects can lead to the spatial variations of the frozen soil, and the uncertain mechanical properties are the key factors for the uncertain analysis of frozen soil engineering. In this study, the elastic modulus, strength and Poisson ratio of warm frozen soil were measured, and the statistical characteristics under different temperature conditions are obtained. The autocorrelation distance (ACD) and autocorrelation function (ACF) of uncertain mechanical properties are estimated by random field (RF) method. The results show that the mean elastic modulus and mean strength decrease with the increase of temperature while the mean Poisson ratio increases with the increase of temperature. The average values of the ACD for the elastic modulus, strength and Poisson ratio are 0.64m, 0.53m and 0.48m, respectively. The standard deviation of the ACD for the elastic modulus, strength and Poisson ratio are 0.03m, 0.07m and 0.03m, respectively. The ACFs of elastic modulus, strength and Poisson ratio decrease with the increase of ratio of local average distance and scale of fluctuation. The ACF of uncertain mechanical properties is different when the temperature is different. This study can improve our understanding of the spatial autocorrelation variations of uncertain geotechnical properties and provide a basis and reference for the uncertain settlement analysis of frozen soil foundation.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.20 no.9
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• pp.2819-2832
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• 1996

The estimation of the remaining life for the aged components in power plant as well as chemical and petroleum plants has been recently concerned. The raw materials used in this study are the 1Cr-1Mo-0.25V steel which intensified P and S compositions along with the nominal compositions of ASTM A 470 standard. Five kinds of specimens with the different degradation levels were prepared by isothermal aging heat treatment at 630.deg.C. The mechanical properties and rotated bending fatigue strength of virgin and aged 1Cr-1Mo-0.25V steel have been investigated through the hardness, tensile, fatigue test, SEM fractograph and EDS analysis at 538.deg.C and room temperature, respectively. Thus the data of aged specimens were compared with those of virgin specimen to evaluate the aging effects. The main results obtained in this study are as follows ; The decrease of the yield and tensile strength due to degradation was distinguished until 50, 000hrs simulated service time. And it was confirmed that the considerable amount of P, Mn, Cr and S was precipitated at the grain boundary of aged material through the SEM and EDS analysis. The rotated bendingd fatigue strength at 538.deg.C of virgin, 25, 000, 50, 000, 75, 000 and 100, 000 hrs aged material was decreased 44.6 %, 49.6 %, 51.5 %, 52.4% and 53.8% than that of virgin material at 10$_{7}$cycles of room temperature, respectively. The major cracks of virgin and aged materials mainly initiated at the inclusions including Si, P and Mn compositions which were located at the outer periphery of the specimen.n.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.44 no.5
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• pp.455-462
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• 2016

Output Characteristics of the spaceborn image sensor such as infrared(IR) sensor are varied according to time elapses and sensor repetition on/off operation. As a result, the quality of IR sensor image is decreased. Therefore, spaceborne image sensor require a periodic calibration using a black body system by correcting a non-uniformity of the sensor. In this paper, we proposed a MEMS-based black body system that can implement the high temperature uniformity at various standard temperatures ranging from low to high temperature and easily estimate the representative surface temperature. In addition, it has advantages lightweight, low-power and high accuracy. The feasibility of the proposed MEMS-based black body system was verified through the thermal analysis.

• 한국해양학회지
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• v.26 no.2
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• pp.108-116
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• 1991

A production model was constructed by combining the production rate and biomass of Sargassum confusum measured at monthly intervals on the coast of Ohori, Korea, to estimate the algal production for a given period. The production for a certain period, e.g., for a year (P/SUB yr/), was calculated from the equation: P/SUB yr/ = .int.P/SUB t/$.$B/SUB t/dt, where pl and Bl are the production rate and biomass at time t. P/SUB l/ was considered as a function of temperature and light. Photosynthesis-Irradiance curves obtained from the in situ experiments were applied for P/SUB l/ Temperature and light intensity can be expressed as periodic functions of time (T, L=f(t)). Diurnal values of water temperature and light intensity at 3 m depth where S. confusum mainly found were substituted into the equation of P/SUB l/. Simulations using our models show that temperature was one of the most sensitive factors operating on the primary production. Thirty percent decrease of light intensity by cloud cover was estimated to decrease the annual production by 5%.

• Journal of the Korean Society for Nondestructive Testing
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• v.20 no.5
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• pp.424-430
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• 2000

In order to develop an ultrasonic evaluation method for properties degradation of high temperature materials, a number of Cr-Mo-V steel samples were heat-treated and their damage mechanism was examined. Ultrasonic parameters such as velocity, attenuation, and more recently developed nonlinear acoustic parameter were measured. The nonlinear acoustic parameter was found to be most sensitive to material degradation mainly attributed to the precipitation of impurities in grain boundaries. When compared to the electrical resistivity results, the nonlinear parameters showed similar behavior. There existed a relatively good correlation between the nonlinear parameter and the fracture appearance transition temperature (FATT) obtained by Charpy V-notch impact test. Based on the relationship between the FATT and the fracture toughness ($K_{IC}$), correlation between the nonlinear parameter and $K_{IC}$ was established.

• Tunnel and Underground Space
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• v.9 no.1
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• pp.27-35
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• 1999

The characteristics of heat conduction for the heat source boundary like an arch shape cavern are different from those for the semi-infinite or circular boundary which can be driven theoretically. A new form of transient heat conduction equation in rock mass around the arch shape cavern is evaluated with analyzing the pattern of the rock temperature distribution measured at the cold storage pilot plant. The new equation, which is driven by adopting a shape function, $SF=\sqrt{logx_0/log(x_0+x)}$ to the solution for a semi-infinite boundary, has the semi-radial form of temperature variation with distance. And, thermal properties of rock mass are estimated by comparing the rock temperature distributions by this equation with those by measurement. Thermal conductivity and specific heat of rock mass are estimated as giving the difference of 20~25% compared to those of laboratory scale. This difference seems to be caused by discontinuity like joint and water content in rock mass.

• Journal of Korea Water Resources Association
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• v.37 no.6
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• pp.479-485
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• 2004

This study presents the calculation of evapotranspiration using estimated daily incoming solar radiation based on maximum daily temperature and minimum daily temperature. The Thornton and Running method(1999) was used to estimate daily incoming solar radiation and then the resulting solar radiation was compared with the measurements. It showed that the estimated daily solar radiation was within reasonable accuracy. In turn, the estimated daily solar radiation was applied to calculate the daily evapotranspiration using the Priestly-Taylor equation and Penman equation and the general results were that evapotranspiration was overestimated in the Priestly-Taylor equation but that Penman was a good estimator with this approach. It is encouraging that it is possible to use this approach, because the required historical data for its estimation are not extensively available and it is not easy to access the meteorological stations in most areas. The calculated eyapotranspiration was compared with that of Hargreaves which was based on daily temperature, and gives us some intuition in terms of engineering.