• Corrosion Science and Technology
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• v.5 no.1
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• pp.33-38
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• 2006

Current coating practice requires the thickness of anti-corrosion organic coatings to be over $250{\mu}m$ for immersion parts of ships and offshore structures and the corrosion resistance of these coatings has been evaluated by destructive and qualitative analysis. Recently, Electrochemical Impedance Spectroscopy(EIS) method has been employed, as an alternative, to evaluate corrosion resistance of organic coatings. This method is characterized as being nondestructive, reproducible, and quantitative in evaluating aging of organic coatings. In this study, EIS method was adopted to quantitatively and effectively select the coating systems having optimized protective performance. Evaluations of several epoxy and epoxy/polyurethane coating systems typically used for ships and offshore structures were carried out in wet($50^{\circ}C$, $90^{\circ}C$) and dry(room temp.) environments to accelerate the degradation of the organic coatings. These results were compared with the conventional scribed(scratched) test results. The plausible prediction model for determining the remaining life-time of coating systems was also proposed based on variations of impedance data, FT-IR and $T_g$ measurements results.

• Advances in aircraft and spacecraft science
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• v.4 no.2
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• pp.169-184
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• 2017

The optimum design of structures with frequency constraints is of great importance in the aeronautical industry. In order to avoid severe vibration, it is necessary to shift the fundamental frequency of the structure away from the frequency range of the dynamic loading. This paper develops a novel topology optimisation method for optimising the fundamental frequencies of structures. The finite element dynamic eigenvalue problem is solved to derive the sensitivity function used for the optimisation criteria. An alternative material interpolation scheme is developed and applied to the optimisation problem. A novel level-set criteria and updating routine for the weighting factors is presented to determine the optimal topology. The optimisation algorithm is applied to a simple two-dimensional plane stress plate to verify the method. Optimisation for maximising a chosen frequency and maximising the gap between two frequencies are presented. This has the application of stiffness maximisation and flutter suppression. The results of the optimisation algorithm are compared with the state of the art in frequency topology optimisation. Test cases have shown that the algorithm produces similar topologies to the state of the art, verifying that the novel technique is suitable for frequency optimisation.

• Journal of Information Processing Systems
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• v.16 no.6
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• pp.1293-1308
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• 2020

In fine-tuning-based transfer learning, the size of the dataset may affect learning accuracy. When a dataset scale is small, fine-tuning-based transfer-learning methods use high computing costs, similar to a large-scale dataset. We propose a mid-level feature extractor that retrains only the mid-level convolutional layers, resulting in increased efficiency and reduced computing costs. This mid-level feature extractor is likely to provide an effective alternative in training a small-scale medical image dataset. The performance of the mid-level feature extractor is compared with the performance of low- and high-level feature extractors, as well as the fine-tuning method. First, the mid-level feature extractor takes a shorter time to converge than other methods do. Second, it shows good accuracy in validation loss evaluation. Third, it obtains an area under the ROC curve (AUC) of 0.87 in an untrained test dataset that is very different from the training dataset. Fourth, it extracts more clear feature maps about shape and part of the chest in the X-ray than fine-tuning method.

• Journal of Positioning, Navigation, and Timing
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• v.11 no.1
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• pp.23-28
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• 2022

The eLoran system is a high-power terrestrial navigation system that is recognized as the most appropriate alternative to complement the GNSS's vulnerability to radio frequency interference. Accordingly, Korea has conducted eLoran technology development projects since 2016. The eLoran system developed in Korea provides 20 m positioning accuracy to maritime user in Incheon and Pyeongtaek harbor. To accurately calculate the position with the eLoran signal, it is necessary to apply a compensation method that mitigates the propagation delay. In this paper, we develop the compensation method to mitigate the eLoran signal propagation delay and evaluate the positioning performance in Incheon harbor. The propagation delay due to the terrain characteristics is pre-surveyed and stored in the user receiver. Real-time fluctuations in propagation delay compared to the pre-stored data are mitigated by the temporal correction generated at a nearby differential Loran station. Finally, two performance evaluation tests were performed to verify the positioning accuracy of the Korean eLoran system. The first test took place in December 2020 and the second in April 2021. As a result, the Korean eLoran service has been confirmed to provide 20 m location accuracy without GPS.

• Journal of Korean Society of Steel Construction
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• v.17 no.3 s.76
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• pp.375-384
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• 2005

The goal of this paper is to understand the stress-transfer mechanism of concrete-filled tubular column to H-beam connections with external T-stiffener through the finite element method and to offer basic data for the design of T-stiffener. To identify the problems of previous test results, the same shapes of the full-scale test specimens were modeled for the finite element analysis. Results of the analysis were compared with the test results. Several stress and strain indices were used to understand the stress-transfer mechanism of connection with various T-stiffeners parameters. The models of analysis with different T-stiffener are grouped into TS, TSD, and TSH series. An alternative plan that decreases the stress concentration of beam flange to horizontal stiffener connection is proposed through the elasto-plastic finite element method. The basic design idea and minimum sizes of T-stiffener were proposed based on the various indices in relation to the connection details.

• Transactions of the Korean Society of Automotive Engineers
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• v.22 no.6
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• pp.1-8
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• 2014

Safety performance of a new car is evaluated through USNCAP and their results in the star rating are provided to the consumers. It is very important to obtain high score of USNCAP to appeal their performance to consumers. Therefore the car companies have made the effort to improve their car safety performance. These efforts should satisfy the demand not only to get high score but also to pass the FMVSS, NHTSA regulations on safety. Huge numbers of car crash tests have been conducted on these bases by car companies. However physical tests spend too much cost and time, as an alternative way, the simulation on the car crash could be a solution to reduce the cost and time. Therefore the simulations have been widely conducted in car industry and various researches on this have been reported. In this study, restraint system had been optimized to minimize the injury of female passenger. Belted $5^{th}%ile$ female frontal crash test was selected from various test methods of USNCAP for the study. Initial velocity of the test was 56km/h. The combination injury probability of USNCAP was selected as an objective function and the injury limit value, which was defined in FMVSS, was set to an optimization constraint. Many researches that were similar to this study had been conducted, however most of them had limitation that interaction between airbag and safety belt had not been considered. Contrary to these researches, the interaction was considered in this study.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.13 no.5
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• pp.2382-2389
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• 2012

The retaining wall with the relieving platform can be constructed as an alternative to the concrete retaining wall in which the economic and stability are decreased as height increases. The relieving platform has the advantage of decreasing the total lateral earth pressure on the retaining wall and increasing the overall stability of the structure. In this study, model tests were performed to determine the distribution of the earth pressure on the retaining wall with and without the relieving platform which located at a depth of 0.4H from the ground surface. And model tests results were compared with analyzed results by 2-D finite element method and values driven from theoretical equation. As the result of this study, comparing model test results with those of numerical analysis and theoretical equation show that the reduction of the lateral earth pressure on wall was indicated clearly on the retaining wall with a relieving platform.

• The KIPS Transactions:PartC
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• v.13C no.4 s.107
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• pp.435-440
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• 2006

XML encryption is to provide confidentiality service, though not limited to, for web contents. XML encryption can be applied to entire data files as opaque objects, or more frequently to various parts of XML documents, supporting various encryption granularity. It is this characteristic that makes XML encryption a more efficient alternative for data confidentiality in various web applications than is possible with SSL/TLS, IPsec, PGP, or S/MIME. It is essential for successful deployment of XML encryption to achieve interoperability among the products implementing this technology, which requires the products to implement the XML encryption standards correctly. Conformance testing is to test if products implement the relevant standard correctly. In this paper we present a conformance testing method for XML encryption products and implement it. We will first look at XML encryption standards developed by W3C, and extract test criteria. Then we propose a testing method in which the encryption capability and the decryption capability of a product are tested separately. The proposed methody is actually implemented as a GUI-based testing tool and some test results are presented.

• School Mathematics
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• v.10 no.3
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• pp.401-422
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• 2008

In the current school curriculum, an alternative assessment method which focuses more on the problem solving process rather than the final solution is being investigated. The goal is to evaluate students' understanding of the subject. A descriptive evaluation is being suggested as a way of examining the thought process of the students by a structured analysis of the problem solving process. But currently, there are not enough descriptive problems available for teachers to effectively carry out the alternative assessment method in the elementary school mathematics curriculum. In this research, we surveyed 197 elementary school teachers in Seoul to determine the status of descriptive evaluation in elementary school mathematics and to understand the teachers perception about the new assessment method. The goal of the survey was to find an effective implication of the new assessment method in elementary mathematics classes. The research showed that the elementary teachers use this assessment method about 4 to 7 times per month in their classes. They give descriptive problem test anytime they think it is appropriate during the Instruction of the topic. More than 90% of the teachers were using this assessment method to improve students' creativity and mathematical thinking. The teachers in the survey also commented that the teachers' administrative responsibility should be reduced and that the school environment in general should be improved for the new assessment method to be successful. Finally the study also showed that development of more descriptive problems in each grade level is needed to progress the new assessment method.

• Toxicological Research
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• v.33 no.2
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• pp.107-118
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• 2017

Although alternative test methods based on the 3Rs (Replacement, Reduction, Refinement) are being developed to replace animal testing in reproductive and developmental toxicology, they are still in an early stage. Consequently, we aimed to develop alternative test methods in male animals using mouse spermatogonial stem cells (mSSCs). Here, we modified the OECD TG 489 and optimized the in vitro comet assay in our previous study. This study aimed to verify the validity of in vitro tests involving mSSCs by comparing their results with those of in vivo tests using C57BL/6 mice by gavage. We selected hydroxyurea (HU), which is known to chemically induce male reproductive toxicity. The 50% inhibitory concentration ($IC_{50}$) value of HU was 0.9 mM, as determined by the MTT assay. In the in vitro comet assay, % tail DNA and Olive tail moment (OTM) after HU administration increased significantly, compared to the control. Annexin V, PI staining and TUNEL assays showed that HU caused apoptosis in mSSCs. In order to compare in vitro tests with in vivo tests, the same substances were administered to male C57BL/6 mice. Reproductive toxicity was observed at 25, 50, 100, and 200 mg/kg/day as measured by clinical measures of reduction in sperm motility and testicular weight. The comet assay, DCFH-DA assay, H&E staining, and TUNEL assay were also performed. The results of the test with C57BL/6 mice were similar to those with mSSCs for HU treatment. Finally, linear regression analysis showed a strong positive correlation between results of in vitro tests and those of in vivo. In conclusion, the present study is the first to demonstrate the effect of HU-induced DNA damage, ROS formation, and apoptosis in mSSCs. Further, the results of the current study suggest that mSSCs could be a useful model to predict male reproductive toxicity.