• Journal of the Korea Academia-Industrial cooperation Society
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• v.22 no.6
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• pp.499-506
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• 2021

The purpose of this study is to verify the effect of SNS addiction on cyber-bullying among adolescents, considering the adjustment effect of friendship on this relationship. This study involved 811 middle/high school students with a gender distribution of 391 males and 420 females. According to the analysis, the higher the level of SNS addiction, the higher the level of cyber-bullying. A hierarchical regression analysis was conducted to verify the moderating effect of friendship. The result shows that better peer communication and reliance lowers the impact of cyber-bullying from SNS addiction. Based on research results suggesting the popularization of proactive pre-diagnosis programs to solve SNS addiction, practical intervention plans and the limitations of research on SNS addiction and cyber-bullying in youth are suggested.

• Journal of Dental Anesthesia and Pain Medicine
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• v.21 no.3
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• pp.237-244
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• 2021

Background: This study aimed to analyze Twitter users' emotional tendencies regarding oral surgery procedures before and after the coronavirus disease 2019 (COVID-19) pandemic worldwide. Methods: Tweets posted in English before and after the COVID-19 pandemic were included in the study. Popular tweets in 2019 were searched using the keywords "tooth removal", "tooth extraction", "dental pain", "wisdom tooth", "wisdom teeth", "oral surgery", "oral surgeon", and "OMFS". In 2020, another search was conducted by adding the words "COVID" and "corona" to the abovementioned keywords. Emotions underlying the tweets were analyzed using CrystalFeel - Multidimensional Emotion Analysis. In this analysis, we focused on four emotions: fear, anger, sadness, and joy. Results: A total of 1240 tweets, which were posted before and after the COVID-19 pandemic, were analyzed. There was a statistically significant difference between the emotions' distribution before and after the pandemic (p < 0.001). While the sense of joy decreased after the pandemic, anger and fear increased. There was a statistically significant difference between the emotional valence distributions before and after the pandemic (p < 0.001). While a negative emotion intensity was noted in 52.9% of the messages before the pandemic, it was observed in 74.3% of the messages after the pandemic. A positive emotional intensity was observed in 29.8% of the messages before the pandemic, but was seen in 10.7% of the messages after the pandemic. Conclusion: Infectious diseases, such as COVID-19, may lead to mental, emotional, and behavioral changes in people. Unpredictability, uncertainty, disease severity, misinformation, and social isolation may further increase dental anxiety and fear among people.

• Atmosphere
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• v.31 no.2
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• pp.185-198
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• 2021

In this study, we examined a spatial downscaling method based on Gradient and Inverse Distance Squared (GIDS) weighting to produce high-resolution grid data from a numerical weather prediction model over Korean Peninsula with complex terrain. The GIDS is a simple and effective geostatistical downscaling method using horizontal distance gradients and an elevation. The predicted meteorological variables (e.g., temperature and 3-hr accumulated rainfall amount) from the Limited-area ENsemble prediction System (LENS; horizontal grid spacing of 3 km) are used for the GIDS to produce a higher horizontal resolution (1.5 km) data set. The obtained results were compared to those from the bilinear interpolation. The GIDS effectively produced high-resolution gridded data for temperature with the continuous spatial distribution and high dependence on topography. The results showed a better agreement with the observation by increasing a searching radius from 10 to 30 km. However, the GIDS showed relatively lower performance for the precipitation variable. Although the GIDS has a significant efficiency in producing a higher resolution gridded temperature data, it requires further study to be applied for rainfall events.

• Journal of Korean Neurosurgical Society
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• v.64 no.4
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• pp.505-513
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• 2021

Objective : The adaptive immune response following subarachnoid hemorrhage (SAH) is not well understood. We evaluated and compared the T cell receptor (TCR) immune repertoire of good-grade and poor-grade SAH patients to elucidate the T cell immunology after ictus. Methods : Peripheral blood from six SAH patients was collected at two different times, admission and at the 7-day follow-up. Composition and variation of the TCR β-chain (TCRB) complimentary determining regions (CDR) 3 repertoire was examined using high-throughput sequencing; the analysis was based on sampling time and disease severity (good vs. poor-grade SAH). Results : Clonality at admission and follow-up were 0.059 (0.037-0.038) and 0.027 (0.014-0.082) (median, 25th-75th percentile). Poor-grade SAH (0.025 [0.011-0.038]) was associated with significantly lower clonality than good-grade SAH (0.095 [0.079-0.101]). Poor-grade SAH patients had higher diversity scores than good-grade SAH patients. CDR length was shorter in good-grade SAH vs. poor-grade SAH. Differences in clonotype distribution were more prominent in TCRBV gene segments than TCRBJ segments. TCRBV19-01/TCRBJ02-04 and TCRBV28-01/TCRBJ02-04 were the most increased and the most decreased V-J pairs in the 7-day follow-up compared to admission in good-grade SAH. The most increased and decreased V-J pairs in poor-grade SAH patients were TCRBV28-01/TCRBJ02-06 and TCRBV30-01/TCRBJ02-04, respectively. Conclusion : The TCRB repertoire is dynamic in nature following SAH. TCRB repertoire may facilitate our understanding of adaptive immune response according to SAH severity.

• Journal of the Korean Society for Geothermal and Hydrothermal Energy
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• v.17 no.1
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• pp.14-22
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• 2021

Drilling equipment is an essential part used in various fields such as construction, mining, etc., and it has drawn increasing attention in recent years. The drilling method is generally divided into three types. There are a top hammer method that strikes on the ground, a DTH (Down-The-Hole) method that directly strikes a bit in an underground area, and a rotary method that drills by using rotational force. Among them, the DTH method is most commonly used because it enables efficient drilling compared to other drilling methods. In the conventional DTH hammer, the valve between the piston and the bit is opened and closed using a face to face method. In order to improve the power of the DTH hammer, a DTH hammer with foot valve which is capable of instantaneous opening and closing is used in the drilling field. In this study, we designed a lab-scale DTH hammer with the foot valve, and manufactured an evaluation device for the experiment of the DTH hammer. In addition, we analyzed the performance of the DTH hammer adopted with foot valve according to the pressure range of 3-10 bar. As a result, the internal pressure distribution in the DTH hammer was experimentally analyzed, and then, the movement of the piston according to the pressure was predicted. We believe that this study provides the useful results to explain the performance characteristics of the DTH hammer with the foot valve.

• International Area Studies Review
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• v.20 no.4
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• pp.37-56
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• 2016

The purpose of this research is to present the implication for Korean firms' entry into the power market in Myanmar. This study investigated the characteristics of the Myanmar power market and analyzed SWOT, focusing on energy policy, power supply and demand, energy relations with neighboring countries and climate change issue. Opportunity factors are changes in energy strategies, the launch of an energy integration organization, changes in the power energy portfolio, rapid economic and power demand growth, and a clean development mechanism. The threats are high nonfulfillment of a contract, high power loss rates and low electricity distribution rates, increased energy exports to neighboring countries, and vulnerability to climate change. We suggest the use of CHP (Combined Heat and Power), Clean Development Mechanism (CDM), and Multilateral Development Bank (MDB).

• Journal of The Geomorphological Association of Korea
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• v.25 no.2
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• pp.15-29
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• 2018

The sediment transport process in a river reflects the process of geomorphological change in the watershed, influencesthe river bed variation and the river channel migration, and is a parametric phenomenon that exhibits a dynamic self-adjusting process. Sediment load is divided into bedload and suspended load depending on the dominant mechanism. Quantitative sediment load is important information for solving river problems. Because it is difficult and time consuming to measure bedload, compared to that ofsuspended load, data on the sediment transport load and the research required for the gravel-bed rivers are insufficient. This study is to analyze the ratio of the bedload to the total sediment load in gravel-bed rivers. The sediment load ratio in gravel-bed rivers increases with the flow rate per unit width, and the rate of the bedload varies more rapidly than the suspended load. The sediment transport efficiency coefficient has been affected by the ratio of the flow depth to the mean diameter of particles and has been dependent on the shear velocity Reynolds number. So $A^{\ast}$ and $B^{\ast}$ are introduced to compensate for the uncertainties such as bed materials, sediment transport, and flow velocity distribution, and the coefficient of bedload ratio has been presented. For the sediment load data in experimental channels and rivers, A* was 3.1. The dominant variables of $B^{\ast}$ were $u_*d_m/{\nu}$ in the gravel-bed and h/dm in the sand-bed. When $B^{\ast}$ the is the same, in the experimental channels the coefficient of bedload ratio was affected by the bed forms, but in the rivers it was of little difference between the gravel-bed and sand-bed.

• Korean Journal of Metals and Materials
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• v.46 no.3
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• pp.182-188
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• 2008

Carbon nanotubes(CNTs) have outstanding mechanical, thermal, and electrical properties. Thus, by placing nanotubes into appropriate matrix, it is postulated that the resulting composites will have enhanced properties. Cold spray can produce thick metal-based composite coatings with very high density, low oxygen content, and phase purity, which leads to excellent physical properties. In this study, we applied cold spray coating process for the consolidation of Cu/CNT composite powder. The precursor powder mixture, in which CNTs were filled into copper particles, was prepared to improve the distribution of the CNT in copper matrix. Pure copper coating was also conducted by cold spraying as a reference. Annealing heat treatment was applied to the coating to examine its effect on the properties of the composite coating. The hardness of Cu/CNT composite coating represented similar value to that of pure copper coating. It was importantly found that the electrical conductivity of the Cu/CNT composite coating significantly increased from 53% for the standard condition to almost 55% in the optimized condition, taking annealed ($500^{\circ}C/1hr$.) copper coating as a reference (100%). The thermal conductivity of Cu/CNT composite coating layer was higher than that of pure Cu coating. It was also found that the electrical and thermal conductivities of Cu/CNT composite could be improved through annealing heat treatment. The microstructural evolution of Cu/CNT coating was also investigated and related to the macroscopic properties.

• Journal of the Korea Institute of Information Security & Cryptology
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• v.13 no.3
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• pp.101-110
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• 2003

Secure and reliable group communication is an increasingly active research area prompted by the growing popularity of many types of group-oriented and collaborative applications. The central challenge is secure and efficient group key management. While centralized methods are often appropriate for key distribution in large multicast-style groups, many collaborative group settings require distributed key agreement techniques. Most of prior group key agreement protocols have been focused on reducing the computational costs. One exception is STR protocol that optimizes communicational cost. On the other hand, it requires O(n) number of modular exponentiations. In this paper, we propose a new group key agreement protocol that modifies STR protocol by utilizing pairing based cryptography. The resulting protocol reduces computational cost of STR protocol while preserving the communication cost.

• Structural Engineering and Mechanics
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• v.77 no.2
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• pp.197-215
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• 2021

Under a severe environment of multiple hazards such as earthquakes and winds, the life-cycle performance of engineering structures may inevitably be deteriorated due to the fatigue effect caused by long-term exposure to wind loads, which would further increase the structural vulnerability to earthquakes. This paper presents a framework for evaluating the lifetime structural seismic performance under the effect of wind-induced fatigue considering different sources of uncertainties. The seismic behavior of a high-rise steel-concrete composite frame with buckling-restrained braces (FBRB) during its service life is systematically investigated using the proposed approach. Recorded field data for the wind hazard of Fuzhou, Fujian Province of China from Jan. 1, 1980 to Mar. 31, 2019 is collected, based on which the distribution of wind velocity is constructed by the Gumbel model after comparisons. The OpenSees platform is employed to establish the numerical model of the FBRB and conduct subsequent numerical computations. Allowed for the uncertainties caused by the wind generation and structural modeling, the final annual fatigue damage takes the average of 50 groups of simulations. The lifetime structural performance assessments, including static pushover analyses, nonlinear dynamic time history analyses and fragility analyses, are conducted on the time-dependent finite element (FE) models which are modified in lines with the material deterioration models. The results indicate that the structural performance tends to degrade over time under the effect of fatigue, while the influencing degree of fatigue varies with the duration time of fatigue process and seismic intensity. The impact of wind-induced fatigue on structural responses and fragilities are explicitly quantified and discussed in details.