• Journal of Surface Science and Engineering
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• v.53 no.6
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• pp.271-279
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• 2020

Non-ferrous metals, widely used in the mechanical industry, are difficult to machine, particularly by drilling and tapping. Since non-ferrous metals have a strong tendency to adhere to the cutting tool, the tool life is greatly deteriorated. Diamond-like carbon (DLC) is one of the promising candidates to improve the performance and life of cutting tool due to their low frictional property. In this study, a sacrificial DLC layer is applied on the hard nitride coated drill tool to improve the durability. The DLC coatings are fabricated by controlling the acceleration voltage of the linear ion source in the range of 0.6~1.8 kV. As a result, the optimized hardness(20 GPa) and wear resistance(1.4 x 10-8 ㎣/N·m) were obtained at the 1.4 kV. Then, the optimized DLC coating is applied as an sacrificial layer on the hard nitride coating to evaluate the performance and life of cutting tool. The Vickers hardness of the composite coatings were similar to those of the nitride coatings (AlCrN, AlTiSiN), but the friction coefficients were significantly reduced to 0.13 compared to 0.63 of nitride coatings. The drilling test were performed on S55C plate using a drilling machine at rotation speed of 2,500 rpm and penetration rate of 0.25 m/rev. The result showed that the wear width of the composite coated drills were 200 % lower than those of the AlCrN, AlTiSiN coated drills. In addition, the cutting forces of the composite coated drills were 13 and 15 % lower than that of AlCrN, AlTiSiN coated drills, respectively, as it reduced the aluminum clogging. Finally, the application of the DLC sacrificial layer prevents initial chipping through its low friction property and improves drilling quality with efficient chip removal.

• Korean Journal of Mineralogy and Petrology
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• v.35 no.4
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• pp.457-467
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• 2022

Electron bombardment to silicate glass during electron probe microanalysis (EPMA) causes outward migration of Na from the excitation volume and subsequent decrease in the measured X-ray count rates of Na. To acquire precise Na₂O content of silicate glass, one should use proper analytical technique to avoid or minimize Na migration effect or should correct for decreases in the measured Na X-ray counts. In this study, we analyzed 8 silicate glass standard samples using automated Time Dependent Intensity (TDI) correction method of Probe for EPMA software that can calculate zero-time intercept by extrapolating X-ray count changes over analysis time. We evaluated an accuracy of TDI correction for Na measurements of silicate glasses with EPMA at 15 kV acceleration voltage and 20 nA probe current electron beam, which is commonly utilized analytical condition for geological samples. Results show that Na loss can be avoided with 20 ㎛-sized large beam (<0.1 nA/㎛²), thus silicate glasses can be analyzed without TDI correction. When the beam size is smaller than 10 ㎛, Na loss results in large relative errors up to -55% of Na₂O values without correction. By applying TDI corrections, we can acquire Na₂O values close to the reference values with relative errors of ~ ±10%. Use of weighted linear-fit can reduce relative errors down to ±6%. Thus, quantitative analysis of silicate glasses with EPMA is required for TDI correction for alkali elements such as Na and K.

• Journal of the Earthquake Engineering Society of Korea
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• v.27 no.1
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• pp.25-35
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• 2023

Considering the non-linear behavior of structure and soil when evaluating a nuclear power plant's seismic safety under a beyond-design basis earthquake is essential. In order to obtain the nonlinear response of a nuclear power plant structure, a time-domain SSI analysis method that considers the nonlinearity of soil and structure and the nonlinear Soil-Structure Interaction (SSI) effect is necessary. The Boundary Reaction Method (BRM) is a time-domain SSI analysis method. The BRM can be applied effectively with a Perfectly Matched Layer (PML), which is an effective energy absorbing boundary condition. The BRM has a characteristic that the magnitude of the response in far-field soil increases as the boundary interface of the effective seismic load moves outward. In addition, the PML has poor absorption performance of low-frequency waves. For this reason, the accuracy of the low-frequency response may be degraded when analyzing the combination of the BRM and the PML. In this study, the accuracy of the analysis response was improved by adjusting the PML input parameters to improve this problem. The accuracy of the response was evaluated by using the analysis response using KIESSI-3D, a frequency domain SSI analysis program, as a reference solution. As a result of the analysis applying the optimal PML parameter, the average error rate of the acceleration response spectrum for 9 degrees of freedom of the structure was 3.40%, which was highly similar to the reference result. In addition, time-domain nonlinear SSI analysis was performed with the soil's nonlinearity to show this study's applicability. As a result of nonlinear SSI analysis, plastic deformation was concentrated in the soil around the foundation. The analysis results found that the analysis method combining BRM and PML can be effectively applied to the seismic response analysis of nuclear power plant structures.

• Korean Chemical Engineering Research
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• v.61 no.1
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• pp.26-31
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• 2023

For durability improvement of polymer electrolyte membrane fuel cell (PEMFC) polymer membrane, accelerated durability evaluation methods that can evaluate durability in a short time have been researched and developed. However, the lifespan of fuel cells for large commercial vehicles such as trucks and buses is more than three times that of passenger cars, and the chemical accelerated stress test (AST) time is also longer, reaching 1,500 hours or more. Therefore, in this study, as a method to evaluate the chemical durability of a membrane within a short time, it was examined whether the durability could be predicted by the pristine membrane characteristics. Hydrogen crossover current density (HCCD) and short resistance (SR) were estimated as initial characteristics, and AST time was predicted through the Fenton experiment, which was possible as an out-of-cell experiment for 3 hours. As the HCCD and fluoride ion emission concentration increased, the AST time tended to be linearly shortened, but there was a deviation (R² ≒0.65). When the SR decreased, the AST time showed a linear increase, and the accuracy was high (R² =0.93), so the AST time could be predicted with the initial SR of the membrane.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.28 no.3C
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• pp.187-196
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• 2008

An earthquake of magnitude 5.0 occurred at Ssang-gye-sa, a Buddhist temple in Jirisan, located near the southern border of the Korean peninsula on 4 July 1936. It resulted in severe damage of several buildings and structures in Ssang-gye-sa. Particularly, the top component of a five-story stone pagoda in the temple was tipped over and fell down during the earthquake. This earthquake damage case would be usefully applied to estimating the intensity of ground motion in the Korean peninsula, a moderate seismicity region, where strong motion has never been recorded with the exception of historic seismic events. In order to estimate the local site effects and the corresponding ground motion at Ssang-gye-sa site, intensive site investigations including borehole drilling and in-situ seismic tests such as crosshole and SASW tests were performed in the temple area. Based on the site characteristics, site-specific seismic response analyses using various input motions were conducted for a representative Ssang-gye-sa site by means of both one-dimensional equivalent-linear and nonlinear methods with six input rock outcrop acceleration levels ranging from 0.044g to 0.220g. The resultant site-specific seismic responses indicated the amplified ground motions in the short-period range near the site period of Ssang-gye-sa. Furthermore, the intensity on rock outcrop of the 1936 Jirisan earthquake was estimated by making a comparison between the site responses analysis results in this study and the full-scaled seismic test of pagoda model in the prior study.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.28 no.1C
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• pp.63-74
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• 2008

Site response analyses were performed based on equivalent linear technique using the local geologic and dynamic site characteristics, which include soil profiles, shear wave velocity profiles and depth to bedrock for 125 sites collected in Korean Peninsula. From the results of site response analyses, 2-parameters site classification system based on the combination of mean shear wave velocity of soil and depth to bedrock was newly recommended for regions of shallow bedrock depth in Korea. First, as the borders of bedrock depth (H) for site classification were determined as 10m and 20m, the soil sites were divided into 3 classes as $H_1$, $H_2$ and $H_3$ sites. And then, the 3 site classes were subdivided into 7 classes based on the mean shear wave velocity of soil ($V_{s,soil}$). The feasibility of new site classification system was verified and the representative site coefficients ($F_a$ and $F_v$) and design response spectrum were suggested by analyzing uniform trend and dispersion of site coefficients for each site class. The suggested site coefficients and the regression curves present the nonlinear characteristics of soils according to the change of rock outcrop acceleration with uniform trend effectively. From the comparison between the mean values of response spectrum which was acquired from the site response analysis and the suggested design response spectrum, there was a little difference in some of site classes and it was verified to adjust the integration interval to make it more suitable for the site condition in Korea.

• International Area Studies Review
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• v.15 no.1
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• pp.341-365
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• 2011

This study used a non-parametric linear program, Data Envelopment Analysis to compare the efficiency of South Korean and Chinese banks from 2000 to 2008, which is said to be the reformation period of their financial structure. The sample banks were 10 commercial banks and 6 regional banks in Korea, and 4 state-owned commercial banks and 11 stock commercial banks in China. The main objective of our research is to compare their efficiency, as well as the changes in efficiency periodically according to the types of the banks. According to the periodical analysis, both of the countries showed steady increase in efficiency. This shows that finance restructure and merging were positive factors for bank's efficiency during the revolution of finance structure. The study showed that between Korea and China, the bank of Korea has higher efficiency than that of China. Although the reconstruction period happened around the same time, due to the earlier acceleration period to opening Korea's financial market, made the difference in efficiency.

• Structural Engineering and Mechanics
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• v.90 no.6
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• pp.551-568
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• 2024

The present study deals with static and dynamic behaviors including forced vibrations of an elastic rectangular nano plate on the two-parameter foundation. Firstly, the rectangular plate is assumed to be subjected to uniformly distributed and eccentrically applied concentrated loads. The governing equations of the problem are derived by considering the dynamic response of the plate, employing a series of the Chebyshev polynomials for the displacement function and applying the Galerkin method. Then, effects of the non-essential boundary conditions of the plate, i.e., the boundary conditions related to the shearing forces, the bending moments and the corner forces, are included in the governing equation of motion to compensate for the non-satisfied boundary conditions and increase the accuracy of the Galerkin method. The approximate numerical solution is accomplished using an iterative process due to the non-linearity of the unilateral property of the two-parameter foundation. The plate under static concentrated load is investigated in detail numerically by considering a wide range of parameters of the plate and the foundation stiffnesses. Numerical treatment of the problem in the time domain is carried out by assuming a stepwise variation of the concentrated load and the linear acceleration procedure is employed in the solution of the system of governing differential equations derived from the equation of motion. Time variations of the contact region and those of the displacements of the plate are presented in the figures for various numbers of the two-parameter of the foundation, as well as the classical and nano parameters of the plate particularly focusing on the non-linearity of the problem due to the plate lift-off from the unilateral foundation. The effects of classical and nonlocal parameters and loading are investigated in detail. Definition of the separation between the plate and the two-parameter foundation is presented and applied to the given problem. The effect of the lift-off on the static and dynamic behavior of the rectangular plate is studied in detail by considering various loading conditions. The numerical study shows that the effect of nonlocal parameters on the behavior of the plate becomes significant, when nonlinearity becomes more profound, due to the lift-off of the plate. It is seen that the size effects are significant in static and dynamic analysis of nano-scaled rectangular plates and need to be included in the mechanical analyses. Furthermore, the corner displacement of the plate is affected more significantly from the lift-off, whereas it is less marked in the time variation of the middle displacement of the plate. Several numerical examples are presented to examine the sensibility of various parameters associated with nonlocal parameters of the plate and foundation. Both stiffening and softening nonlocal parameters behavior of the plate are identified in the numerical solutions which show that increasing the foundation stiffness decreases the extent of the contact region, whereas the stiffness of the shear layer increases the contact region and reduces the foundation settlement considerably.

• Journal of Preventive Medicine and Public Health
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• v.17 no.1
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• pp.173-192
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• 1984

On the basis of the study intended to research by crosssectional study keeps pace with semilongitudinal study the growthaccelerating phenomena that Maximum Growth age in teenager's body-height. By the random sampling method, the subject of study are 12659 persons(male; 6355, female; 6304) that they are from 7 ages to 17 ages in the whole country including the rural community. The measurement period passed three month days, the statistical data became electronic data processing system with computer. The other side, body-height and MGA of Koreans who had been for during the period from 1925 to 1966 proved transition of the growth-accelerating phenomena by research data reported between 1913 and 1983. The results are as follows; 1. The Growth and Development-Value of Body-height An age bracket the growth and development-value of body-height were, respectively, male is $123.88{\pm}5.05cm$ and female is $123.29{\pm}5.54cm$ for 7 ages group. these indices increased with age. the top-value reach, respectively. $169.08{\pm}5.62cm$ and $157.57{\pm}6.13cm$. The intersecting ages of male and female were the age $8.5{\sim}12.5$, during these periods, female excelled male but after these periods, male excelled female again. In case of body-height, MGA's are 7.0cm for male between 12 and 13 ages, and 7.01cm for female between 8 and 9 ages. As a rule, body-height of male excelled female but intersection phenomena of male and female appeared between 8.5 and 12.5 ages. By reginal groups, it is most prevailing is Seoul, and medium size cities and rural community rome in order. By regional groups, intersection phenomena of male and female are. a region of Seoul; $$8.5{\sim}11.5$$ ages a region of Daejeon; $$7.5{\sim}9.5$$ ages rural community; $$11.5{\sim}14.5$$ ages the whole country's average; $$8.5{\sim}12.5$$ ages By regional groups, the rate of maximum increase in a year are a region of Seoul; male is 7.23cm as 13 ages female is 7.65cm as 9 ages. a region of Daejeon; male is 7.85cm as 11 ages. female is 8.39cm as 9 ages. rural community; male is 7.65cm as 14 ages. female is 6.25cm as 12 ages. the whole country's average; male is 7.0cm as 13 ages. female is 7.01 as 9 ages. 2. Maximum Growth Age (M.G.A.) By reginal groups, maximum Growth Age's are as below in a region of Seoul, MGA's are 12.63 for male and 9.01 for female, which shows that MGA for female appears about 3.5 years earlier than that for male. In a region of Daejeon, MGA's are 9.20 for male and 8.93 for female, which. show that they are all much the same in M.G.A. In rural community, MGA's are 14.00 for male and 11.89 for female, which shows that MGA for female apperars about 2 years earlier than that for male. In the whole average, MGA's are 13.01 for male and 8.97 for femal, which shows that for female appears about 4 years earlier than that for male. For boy, M.G.A. shows fastest-growing in Daejeon, and Seoul and rural commonly come in order. For girl, It shows equal growth in Seoul and Daejeon, rural community comes later. 3. The M.G.A's in body height of male are respectively the age 15.02 in 1913, 14.23 in 1956, 13.86 in 1967, 13.62 in 1975, and 12.82 in 1981, while those of female are the age 12.0 in 1940, 11.52 in 1965, 9.53 in 1975, and 11.16 in 1980; these data show that the MGA of the Koreans has been getting younger. 4. The equation of linear regression of all the MGA's in body height are as follow; Male: Y(M.G.A)=$-0.020{\times}$ (the year)+15.19: female:Y(MGA)=$-0.028{\times}$(the year)+13.2549. 5. The corelation of all the MGA's in body height are as below; male; r=-0.329 female;r=-0.252 6. From the transition of the growth-accelating phenomena in 1980 we can capture the fact that the MGA's has been getting younger by 0.2 year per 10 years. 7. The MGA's in bodyheight are shown in table 4... 8. The future growth-accelating phenomena in body height are expected to show the similar tendency like that of the past, in 1910's but it should by more precisely reviewed after investigating the phenomena of the years directly ahead.

• Korean Journal of Food Science and Technology
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• v.7 no.1
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• pp.51-56
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• 1975

The effects of various concentration of NaCI, i.e., 1, 2, 2. 5, 3, and 4%, on the rancidity development of samples of Ramyon, deep-fried instant noodles, were studied. Dough for the samples, which was composed of wheat flour, distilled water, and pure NaCI, was prepared at a commercial plant but the deep-frying p개cess for the dough was performed in the laboratory. The products thus obtained were incubated for 50 days at $45.0{\pm}1.0^{\circ}C$. Peroxide and TBA values were determined every 5 days throughout the storage period. The results obtained are as follows. 1) Control and the samples containing 1, 2, 2. 5, and 3% salt had POVs of 8. 7, 9. 1, 9. 0, 9. 2 and 9. 7 respectively after 25 days. The control showed a POV of 19.1 after 45 days whereas the sample Ramyons containing 1, 2, 2. 5, 3, and 4% salt had POVs of 12. 6, 13. 2, 14. 6, 15. 3, and 15. 8 respectively after 30 days. 2) TBA values of Control and the sample containing 1, 2, 2. 5, 3, and 4% salt were 5. 8, 6. 1, 6. 2, 6. 4, 6. 7, and 6. 6 respectively after 15 days. But the control developed a TBA value of 11. 4 after 40 days. The samples containing 1, 2, 2. 5, and 3% salt showed TBA values of 10. 2, 14. 3, 15. 8, and 15. 3 respectively after 30 days whereas the sample containing 4% salt had a TBA value of 13. 8 after 25 days. 3) The relationship between the POVs and the TBA values was linear. However, the regression curves of the POVs and the TBA values indicated progressive increase in the gradients(POV/TBA) with increase in the salt content. 4) From the results of the present study, it was found that although the acceleration of rancidity was not in proportion to the amount of NaCI, definite progressive increase in the rancidity development was observed with increase in the salt content of the sample Ramyons.