• Asia-Pacific Journal of Business Venturing and Entrepreneurship
• /
• v.17 no.5
• /
• pp.237-250
• /
• 2022

On September 28, 2020, the Korea Fair Trade Commission introduced a proposed bill entitled the "Fair Online Platform Intermediary Transactions Act." We quantify the impact of this proposed act on Naver, Korea's major digital platform. Finding a proper control unit is not an easy task in social science studies. We overcome this caveat by constructing a synthetic version of Naver using Abadie & Gardeazabal's (2003) synthetic control method. It appears that the economic cost of the proposed act is not negligible at all. Naver's opportunity loss amounted to 16.18% of its market capitalization (approximately 8.5 trillion won in comparison with its pre-regulation market capitalization). Any regulation-based approaches to resolving digital platform issues have both promises and pitfalls. The results highlight that regulatory bodies should carefully gauge the impact of such regulations, as we have seen with Naver's case.

• Journal of the Society of Disaster Information
• /
• v.20 no.2
• /
• pp.329-338
• /
• 2024

Purpose: This study verified the safety of the improved box-type girder behavior by comparing and evaluating the bending behavior results of a full-scale specimen based on the analytical behavior of the splice element PSC U-shaped girder with integrated tensioning systems. Method: Based on the results of the service and strength limit state design using the bridge design standard(limit state design method), the applied load of a 40m full-scale specimen was calculated and a static loading experiment using the four-point loading method was performed. Result: When the design load, crack load, and ultimate load were applied, the specimen deflection occurred at 97.1%, 98.5%, and 79.0% of the analytical deflection value. When the design load, crack load, and ultimate load were applied, the crack gauge was measured at 0.009~0.035mm, 0.014~0.050mm, and 6.383~5.522mm at each connection. Conclusion: The specimen behaved linear-elastically until the crack load was applied, and after cracks occurred, it showed strainhardening up to the ultimate load, and it was confirmed that the resistance of bending behavior was clearly displayed against the applied load. The cracks in the dry joints were less than 25% of grade B based on the evaluation of facility condition standard. The final residual deformation after removing the ultimate load was 0.114mm, confirming the stable behavior of the segment connection.

• Journal of the Korea institute for structural maintenance and inspection
• /
• v.23 no.7
• /
• pp.9-15
• /
• 2019

The purpose of present study is to assess the maximum width of the surface cracks using the histogram analysis of image processing techniques in concrete structures. For this purpose, the concrete crack image is acquired by the camera. The image is Grayscale coded and Binary coded. After Binary coded image is Dilate and Erode coded, the image is then recognized as separated objects by applying Labeling techniques. Over time, dust and stains may occur naturally on the surface of concrete. The crack image of concrete may include shadows and reflections by lighting depending on a surrounding conditions. In general, concrete cracks occur in a continuous pattern and noise of image appears in the form of shot noises. Bilateral Blurring and Adaptive Threshold apply to the Grayscale image to eliminate these effects. The remaining noises are removed by the object area ratio to the Labeled area. The maximum numbers of pixels and its positions in the crack objects without noises are calculated in x-direction and y-direction by Histogram analysis. The widths of the crack are estimated by trigonometric ratio at the positions of the pixels maximum numbers for the Labeled objects. Finally, the maximum crack width estimated by the proposed method is compared to the crack width measured with the crack gauge. The proposed method by the present study may increase the reliability for the estimation of maximum crack width using image processing techniques in concrete surface images.

• Journal of Korea Water Resources Association
• /
• v.38 no.12 s.161
• /
• pp.1061-1072
• /
• 2005

A hydrological grey model is developed to forecast short-term river runoff from the Naju watershed located at upstream of the Youngsan estuary dam in Korea. The runoff of the Naju watershed is measured in real time at the Naju streamflow gauge station, which is a key station for forecasting the upstream inflow and operating the gates of the estuary dam in flood period. The model's governing equation is formulated on the basis of the grey system theory. The model parameters are reparameterized in combination with the grey system parameters and estimated with the annealing-simplex method In conjunction with an objective function, HMLE. To forecast accurately runoff, the fifth order differential equation was adopted as the governing equation of the model in consideration of the statistic values between the observed and forecast runoff. In calibration, RMSE values between the observed and simulated runoff of two and six Hours ahead using the model range from 3.1 to 290.5 $m^{3}/s,\;R^2$ values range from 0.909 to 0.999. In verification, RMSE values range from 26.4 to 147.4 $m^{3}/s,\;R^2$ values range from 0.940 to 0.998, compared to the observed data. In forecasting runoff in real time, the relative error values with lead-time and river stage range from -23.4 to $14.3\%$ and increase as the lead time increases. The results in this study demonstrate that the proposed model can reasonably and efficiently forecast runoff for one to six Hours ahead.

• Korean Journal of Animal Reproduction
• /
• v.17 no.2
• /
• pp.103-111
• /
• 1993

These experiments were undertaken to establish the optimal culture systems for in vitro maturation, fertilization and subsequently embryonic development of porcine immature follicular oocytes isolated from the ovary of slaughtered pigs. Porcine ovaries were brought to the laboratory from local slaughter house within 1 hour after slaughtering and cumulus oocytes complexes were recovered from antral follicles (3~5mm) with 23 gauge needle. To maturate follicular oocytes, cumulus oocytes complexes were washed three times with TCM-199 containing 25mM HEPES and incubated (39$^{\circ}C$, 5% CO2 in air) for 42hrs. Ejaculated and liquid storaged boar spermatozoa capacitated with different sperm capacitation methods and media were prepared forfertilizaing of matured follicular oocytes in vitro. Fertilization was performed by adding 5~10${mu}ell$ of capacitated spermatozoa containing 1~5$\times$105 sperm/ml to droplets. Eighteen to twenty-eight hours after sperm insemination, fertilized eggs were washed three times with culture media and transferred to the culture media. The fertilization rates of in vitro matured follicular oocytes cultured in B. O., TCM-HEPES, m-KRB, and TALP-II media were 61.3%, 83.0%, 88.9% and 89.2%, respectively. In addition, the polyspermy rates were 60.7%, 66.5%, 53.8%, and 43.9%, respectively. These data indicated that the highest of fertilization and the lowest of polyspermy rate was shown in TALP-II medium. Spermatozoa capacitated by caffeine, heparin, and percoll density gradient treatment in the 4 different media, the fertilization rates were 33.0~57.2%, 39.9~90.2%, and 52.6~92.8%, respectively, showing the lowest rate in caffeine treatment. The development rate of follicular oocytes, fertilized with the spermatozoa capacitated by caffeine, heparin, and percoll gradient in the TALP-II medium, upto 2 to 4-cell stages were 32.6%, 74.5% and 70.9%, respectively. Finally, fertilization rates of follicular oocytes cultured with follicular fluid containing medium from 10 to 100% were 61.2~94.1% and the rates (90~94%) with 10~20% follicular fluids were significantly higher than those (85.3%) of cultured in the media without follicular fluid. In addition, the rates of pronucleus formation were also higher in follicular fluid treated group (73.1~83.0%) than those (64.7%) of oocytes cultured without follicular fluid. The highest fertilization and pronucleus formation rates was found in oocytes cultured with 10% follicular fluid. These results suggest that the addition of heparin or percoll density gradient method is better capacitation method. Furthermore, the addition of porcine follicular fluid to the fertilization medium may improve the fertilization rates and formation of pronucleus.

• Clinical and Experimental Reproductive Medicine
• /
• v.30 no.3
• /
• pp.241-248
• /
• 2003

Objective: The purpose of this study was to evaluate the survival rate of vitrified blastocyst according to the freezing vessels, equilibration time in cryoprotectant and artificial dehydration method. Methods: Human blastocysts were vitrified after loading onto the plastic straw, open-pulled straw (OPS), electron microscopy grid (EM grid) for 1.5 min or 3 min. They also were directly plunged into LN2 within 30sec. For artificial shrinkage of blastocysts, 36 gauge fine needle was pushed at the cellular junction of the trophectoderm into the blstocoele cavity until it shrank without damage of inner cell mass. Results: The survival rate of vitrified blastocysts on plastic straw, OPS, EM grid as freezing vessels were 26.7, 13.0 and 60.5%, respectively. The survival rate of EM grid was significantly higher than that of plastic straw and OPS (p<0.05). For 1.5 min equilibrium, the survival rates of early blastocyst (EB), middle blastocyst (MB) and late blastocyst (LB) were 64.4, 81.0, and 20.0% respectively. For 3 min equilibrium, the survival rates of EB, MB, and LB were 69.9, 50.0 and 57.5% respectively. The survival rates of EB and MB were significantly higher than that of LB in 1.5 min equilibrium group (p<0.05), however, the significance was not observed in 3 min equilibrium groups. In cytoplasmic shrinkage before vitrification, the survival rates of EB, MB and LB were 92.9, 100 and 75.9% respectively. The survival rate of MB was significantly higher than that of LB (p<0.05). The survival rates of vitrified blastocysts by artificial dehydration and slow-frozen blastocysts were not significantly different as 88.9 and 66.7%, respectively. Conclusion: This study showed that the vitrification of human blastocysts using EM grid and artificial dehydration is an effective method. Therefore, these methods would be an useful techniques for blastocyst cryopreservation.

• Journal of Preventive Medicine and Public Health
• /
• v.18 no.1
• /
• pp.59-71
• /
• 1985

During a period from February 1st to November 30th in 1983, measurements were made twice a month on dustfalls and concentrations of various cations ana anions in their filtrates in an urban (Heuksuk-dong, Seoul) and in a rural (Ansung) districts. Standard British Deposit Gauge method was applied for collection of dustfalls and ion chromatographic method using Ion Chromatograph 10 (Dionex, U.S.A.) for determination of cation and anion concentrations. The results obtained were as follows: 1. Annual mean values of dustfalls were $8.30{\pm}5.09tons/km^2/month$ in an urban and $6.20{\pm}0.82tons/km^2/month$ in a rural districts. And annual mean values of pH of filtrates of the collected samples were $5.3{\pm}0.76$ in an urban and $6.0{\pm}0.82$ in a rural districts. 2. Annual mean concentrations of common cations and anions in their filtrates were as follows: urban rural (unit: ppm) $$Na^{+}\;1.7{\pm}1.30\;1.9{\pm}1.86$$ $$NH^{+}_{4}\;2.4{\pm}1.60\;1.3{\pm}1.59$$ $$K^{+}\;0.7{\pm}0.47\;1.5{\pm}3.79$$ $$Ca^{++}\;5.3{\pm}0.95\;3.4{\pm}2.58$$ $$Mg^{++}\;0.7{\pm}0.89\;0.5{\pm}0.83$$ $$Cl^{-}\;2.0{\pm}1.31\;4.0{\pm}2.35$$ $$NO^{-}_{3}\;4.0{\pm}2.35\;2.7{\pm}1.31$$ $$So^{--}_{4}\;16.9{\pm}17.40\;6.8{\pm}8.00$$ Some of anions such as $Br^{-},\;{PO_4}^{-3}\;and\;{NO_2}^{-}$ were scarecely detected and $F^{-}$ was measured at very low concentrations ranging from 0.1 to 0.5 ppm in Feb., Oct. and Nov. in an urban and in Feb. in a rural districts. 3. By two-way analysis of variance with 4 replications for dustfalls, pH and concentrations of various ion by district and month of a year, statistically significant differences were noted in dustfalls (p<0.01), pH (p<0.01) and concentrations of various ion (p<0.01) by month of a year, and in dustfalls (p<0.05) and concentrations of various ion such as ${NH_4}^{+},\;Ca^{++},\;{NO_{3}}^{-}\;and\;{SO_4}^{--}$ (p<0.01) by district. 4. There were statistically significant differences pH in Spring (Feb., Mar and Apr.) (p<0.01) and in ${SO_4}^{--}$ in Autumn (Aug., Sept., Oct. and Nov.) (p<0.05) between the two districts.

• Journal of Korea Water Resources Association
• /
• v.41 no.8
• /
• pp.807-823
• /
• 2008

This paper presents a technique for estimating discharge rating curve parameters. In typical practical applications, the original non-linear rating curve is transformed into a simple linear regression model by log-transforming the measurement without examining the effect of log transformation. The model of pseudo-likelihood estimation is developed in this study to deal with heteroscedasticity of residuals in the original non-linear model. The parameters of rating curves and variance functions of errors are simultaneously estimated by the pseudo-likelihood estimation(P-LE) method. Simulated annealing, a global optimization technique, is adapted to minimize the log likelihood of the weighted residuals. The P-LE model was then applied to a hypothetical site where stage-discharge data were generated by incorporating various errors. Results of the P-LE model show reduced error values and narrower confidence intervals than those of the common log-transform linear least squares(LT-LR) model. Also, the limit of water levels for segmentation of discharge rating curve is estimated in the process of P-LE using the Heaviside function. Finally, model performance of the conventional log-transformed linear regression and the developed model, P-LE are computed and compared. After statistical simulation, the developed method is then applied to the real data sets from 5 gauge stations in the Geum River basin. It can be suggested that this developed strategy is applied to real sites to successfully determine weights taking into account error distributions from the observed discharge data.

• Journal of the Korea institute for structural maintenance and inspection
• /
• v.20 no.3
• /
• pp.111-121
• /
• 2016

In this study, measurements were conducted by image processing to do an in-depth evaluation of strain of rebar in a uniaxial tension test. The distribution of strain and the necking region were evaluated. The image processing is used to analyze the color information of a colored image, so that the parts consistent with desired targets can be distinguished from the other parts. After this process, the image was converted to a binary one. Centroids of each target region are obtained in the binary images. After repeating such process on the images from starting point to the finishing point of the test, elongation between targets is calculated based on the centroid of each target. The tensile test were conducted on grade 60 #7(D22) and #9(D29) rebars fabricated in accordance with ASTM A615 standards. Strain results from image processing were compared to the results from a conventional strain gauge, in order to see the validity of the image processing. With the image processing, the measuring was possible in not only the initial elastic region but also the necking region of more than 0.5(50%) strain. The image processing can remove the measuring limits as long as the targets can be video recorded. It also can measure strain at various spots because the targets can easily be attached and detached. Thus it is concluded that the image processing helps overcome limits in strain measuring and will be used in various ways.

• Journal of Korea Water Resources Association
• /
• v.47 no.2
• /
• pp.119-133
• /
• 2014

The study adopted extended Kalman filter technique in an effort to predict Z-R relationship parameter as a stable value in real-time. Toward this end, a parameter estimation model was established based on extended Kalman filter in consideration of non-linearity of Z-R relationship. A state-space model was established based on a study that was conducted by Adamowski and Muir (1989). Two parameters of Z-R relationship were set as state variables of the state-space model. As a result, a stable model where a divergence of Kalman gain and state variables are not generated was established. It is noteworthy that overestimated or underestimated parameters based on a conventional method were filtered and removed. As application of inappropriate parameters might cause physically unrealistic rain rate estimation, it can be more effective in terms of quantitative precipitation estimation. As a result of estimation on radar rainfall based on parameters predicted with the extended Kalman filter, the mean field bias correction factor turned out to be around 1.0 indicating that there was a minor difference from the gauge rain rate without the mean field bias correction. In addition, it turned out that it was possible to conduct more accurate estimation on radar rainfall compared to the conventional method.