• Journal of the Korea Academia-Industrial cooperation Society
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• v.16 no.6
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• pp.3692-3697
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• 2015

A screw is a type of fastener characterized by a helical ridge known as thread. The demands for screws with the miniaturization and weight reduction are increasing for the trend of small size of mobile devices. The successful designs of mold and process are very important to obtain screws with good mechanical properties and high precision. In this study, the design of cold forging process of micro screw was carried out by using finite element method. In particular, in order to investigate the effects of die geometries and friction, design of experiment method was adopted and it was revealed that the friction was the dominant factor of folding defects. From these results, the design of die was modified and experiments were carried out with the modified die. From the experimental results, it was found that the folding defects disappeared.

• Tribology and Lubricants
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• v.37 no.3
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• pp.106-111
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• 2021

There are several studies on reducing the friction that occurs on the relative sliding contact surface of moving parts under extreme environments. In particular, a solid lubricated bearing is studied to solve the tribological problem with friction reduction and durability parts using solid lubricants (lead or silver) in a vacuum atmosphere. Galinstan is mainly used as a liquid metal lubricant, but it is inevitable to have limited tribological applications owing to its high coefficient of friction. Many researchers work on surface texturing for surface modification and precision processing methods. To increase durability and low friction, DLC coating with hydrophobicity is applied on the contact surface texture. Therefore, using an untextured specimen, a dimple specimen, and a DLC-coated dimple specimen under liquid metal lubrication, this paper presents the following experimental sliding friction characteristics in the sliding friction test. 1) The average coefficient of friction of the DLC-coated dimple specimen and dimple specimen are lower compared to that of a non-patterned specimen. 2) In the DLC-coated dimple specimens, the average coefficient of friction changes according to the change in the dimple density. 3) DLC-coated dimple specimens with a density of 12.5 have the lowest average coefficient of friction under 41.6 N of normal load and 143.3 RPM.

• Journal of Environmental Health Sciences
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• v.48 no.2
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• pp.123-129
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• 2022

Background: The Environmental Health Action Program was a national project carried out from 2012~2021. It was aimed at developing public technologies to protect people's health from various environmental hazards. Objectives: One of the final goals of the project was "creating health benefits worth more than 179.2 billion won by reducing the environmental burden of disease." This study aims to evaluate whether the program sufficiently achieved the planned benefits. Methods: In order to secure consistency in evaluation, we applied the same equation used in the goal-setting process. It is comprised of six parameters to estimate the benefit: 1. The amount of medical expenses for environmental diseases; 2. The attributable proportion of environmental risk factors' 3. The rate of reduction in medical expenses for environmental diseases; 4. R&D project contribution; 5. The proportion of successful policy reflection; and 6. The contributions of the project. The corresponding variables were estimated at the end of the project, and the health benefits of the project were recalculated using the newly estimated variables. Results: It was estimated that a total of 195 billion won in health benefits occurred or will occur from 2015 to 2026. The main contributors for achieving the target were an increase in medical expenses for environmental diseases, a high score in the R&D project contribution, and the proportion of successful policy reflection. Conclusions: Technically, the equation used in the project is about medical expenses for environmental diseases rather than about the environmental burden of disease. There are several benefits of using the environmental burden of disease in the evaluation of public health policies. In further studies, developing a policy evaluation framework using indicators such as population attributable fraction would be needed.

• Journal of The Korean Astronomical Society
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• v.55 no.4
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• pp.111-121
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• 2022

Based on the light an exoplanet blocks from its host star as it passes in front of it during a transit, the mid-transit time can be determined. Periodic variations in mid-transit times can indicate another planet's gravitational influence. We investigate 83 transits of TrES-1 b as observed from 6-inch telescopes in the MicroObservatory robotic telescope network. The EXOTIC data reduction pipeline is used to process these transits, fit transit models to light curves, and calculate transit midpoints. This paper details the methodology for analyzing transit timing variations (TTVs) and using transit measurements to maintain ephemerides. The application of Lomb-Scargle period analysis for studying the plausibility of TTVs is explained. The analysis of the resultant TTVs from 46 transits from MicroObservatory and 47 transits from archival data in the Exoplanet Transit Database indicated the possible existence of other planets affecting the orbit of TrES-1 and improved the precision of the ephemeris by one order of magnitude. We now estimate the ephemeris to be (2 455 489.66026 BJD_TDB ± 0.00044 d) + (3.0300689 ± 0.0000007) d × epoch. This analysis also demonstrates the role of small telescopes in making precise midtransit time measurements, which can be used to help maintain ephemerides and perform TTV analysis. The maintenance of ephemerides allows for an increased ability to optimize telescope time on large ground-based telescopes and space telescope missions.

• Structural Engineering and Mechanics
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• v.88 no.2
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• pp.159-168
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• 2023

Cost-effective high precision hybrid elements are presented in a hierarchical form for dynamic analysis of plates. The costs associated with controlling the vibrations of ferromagnetic plates can be minimized by adequate determination of the amount of electric current and magnetic field. In the present study, the effect of magnetic field and electric current on nonlinear vibrations of ferromagnetic plates is investigated. The general form of Lorentz forces and Maxwell's equations have been considered for the first time to present new relationships for electromagnetic interaction forces with ferromagnetic plates. In order to derive the governing nonlinear differential equations, the theory of third-order shear deformations of three-dimensional plates has been applied along with the von Kármán large deformation strain-displacement relations. Afterward, the nonlinear equations are discretized using the Galerkin method, and the effect of various parameters is investigated. According to the results, electric current and magnetic field have different effects on the equivalent stiffness of ferromagnetic plates. As the electric current increases and the magnetic field decreases, the equivalent stiffness of the plate decreases. This is a phenomenon reported here for the first time. Furthermore, the magnetic field has a more significant effect on the steady-state deflection of the plate compared to the electric current. Increasing the magnetic field and electric current by 10-times results in a reduction of about 350% and an increase of 3.8% in the maximum steady-state deflection, respectively. Furthermore, the nonlinear frequency decreases as time passes, and these changes become more intense as the magnetic field increases.

• The Korean Journal of Applied Statistics
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• v.37 no.4
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• pp.411-444
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• 2024

The objective of Phase I clinical trials is to ascertain the maximum tolerated dose (MTD) that is safe for human administration. Accurately determining the MTD within an acceptable safety margin is imperative, necessitating evaluations up to sufficiently high doses. To estimate the MTD, a plethora of methods have been developed, encompassing algorithm-based, model-based, and model-assisted techniques. In this paper, a new dose exploration method based on continual reassessment method (CRM) is proposed to address for the shortcomings of existing dose exploration methods. Through a comprehensive simulation study, this method's efficacy was compared against that of existing methodologies across a variety of scenarios. The findings from this study underscore its enhanced precision and safety in estimating the MTD, alongside a reduction in the number of subjects required for testing.

• Journal of the Korean Geosynthetics Society
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• v.23 no.3
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• pp.1-14
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• 2024

To better prepare for the increasing frequency of earthquakes, securing the seismic performance of coastal structures is more urgent than ever. Evaluating the stability of coastal structures precedes ensuring seismic performance. Methods for assessing stability during earthquakes include finite element analysis and model testing. However, these methods have the disadvantage of requiring significant cost and time. Therefore, this study aimed to propose a simplified method for quickly and easily predicting the horizontal displacement of caisson-type qual wall structures during earthquakes. Initially, existing simplified methods were compared and analyzed against numerical analysis. The results revealed limitations in predicting the displacement of caisson-type qual wall using existing simplified methods. To address this, correction coefficients related to the backfilled ground N value, velocity's PSI, and the W/H ratio were added to the existing simplified method. After the adjustments, a noticeable reduction in errors was observed, demonstrating high precision within the 200 gal range.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.32 no.6C
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• pp.295-304
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• 2012

In this study, a resonant column testing system which is the largest in Korea has been developed to evaluate the dynamic deformation characteristics of coarse granular geomaterials, and the performance and the applicability of the testing system have been verified. The system has been developed as a typical Stokoe type device whose boundary conditions are fixed bottom and free top with additional mass, and can adopt a large specimen with 200 mm in diameter and 400 mm in height. The driving and measurement instruments are configured as high performance and precision systems, hence the automated testing system is appropriate to drive enough stress and to measure the behavior precisely for the test in practical manner. The dynamic response of the mechanical components and the applicability of the system have been evaluated using metal specimens as well as polyurethane specimens, and its precision was verified by comparing its results with those from other equipment and/or methods. To confirm the applicability of the large system for coarse geomaterials, the resonant column test results from both large and normal scale apparatus for the same material were compared and it was found that the result can be partially affected by scale. Finally, the dynamic deformation characteristics of coarse geomaterial which is used for construction of large dam was evaluated using the large system and its practicality could be confirmed.

• Analytical Science and Technology
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• v.27 no.3
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• pp.161-166
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• 2014

Currently oxidation-reduction titration method for the assay method using the hazardous reagent, carbon tetrachloride, for cefroxadine capsules has been used in Korean Pharmaceutical Codex. We developed and validated an alternative HPLC assay method by substituting the use of the hazardous reagent, carbon tetrachloride, to the use of less toxic ones like acetonitrile. The linearity of the calibration curves in the desired concentration range was good ($r^2$ > 0.999). Relative standard deviations of intra-day precision were ranged between 0.30% and 0.69% and inter-day precision were ranged between 0.47% and 0.82%. Accuracy was obtained with recoveries in range of 100.20% and 100.56%. Developed method was applied to the determination of cefroxadine in commercial cefroxadine capsule and could be expected to become valuable tools for revising the Korean Pharmaceutical Codex.

• Journal of KIISE
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• v.41 no.9
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• pp.666-673
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• 2014

This paper proposes a scalable face recognition method for unconstrained face databases, and shows a simple experimental result. Existing face recognition research usually has focused on improving the recognition rate in a constrained environment where illumination, face alignment, facial expression, and background is controlled. Therefore, it cannot be applied in unconstrained face databases. The proposed system is face feature extraction algorithm for unconstrained face recognition. First of all, we extract the area that represent the important features(landmarks) in the face, like the eyes, nose, and mouth. Each landmark is represented by a high-dimensional LBP(Local Binary Pattern) histogram feature vector. The multi-scale LBP histogram vector corresponding to a single landmark, becomes a low-dimensional face feature vector through the feature reduction process, PCA(Principal Component Analysis) and LDA(Linear Discriminant Analysis). We use the Rank acquisition method and Precision at k(p@k) performance verification method for verifying the face recognition performance of the low-dimensional face feature by the proposed algorithm. To generate the experimental results of face recognition we used the FERET, LFW and PubFig83 database. The face recognition system using the proposed algorithm showed a better classification performance over the existing methods.