• Resources Recycling
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• v.33 no.3
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• pp.12-20
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• 2024

The global cement industry emits approximately 2.9 billion tons of greenhouse gases, of which 1.74-1.89 billion tons are emitted from limestone, which is the main raw material for clinkers. Therefore, the feasibility of using slag, a non-carbonated CaO-based raw material, must be investigated, and the physical properties of cement must be considered. In this study, the mixing ratios of the raw mix and properties of cement were analyzed. The CaCO₃ replacement ratio was limited when one type of slag was used; however, when the mixed slag was utilized, the CaCO₃ replacement ratio increased by more than 12 %. The compressive strength of the slag-incorporated cement was lower than that of Ordinary Portland Cement (OPC). Therefore, the lime saturation factor (LSF) of the raw mix and fineness of the cement were increased to improve the compressive strength. The compressive strength of cement with improved fineness was similar to that of OPC for a CaCO₃ replacement ratio of up to 6 %, and it decreased as the CaCO₃ replacement ratio was increased to 9 %. When both fineness and LSF were increased, the compressive strength and flow value of the cement with a CaCO₃ replacement ratio of 12 % were similar to that of OPC.

• Journal of the Korean Society of Marine Environment & Safety
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• v.30 no.4
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• pp.308-316
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• 2024

Maintaining the appropriate number of national seafarers is essential for securing the competitiveness of maritime industry and security in Korea. However, the number of national seafarers in Korea has been decreased continuously recently. The government recognizes the repercussion of this issue and has been attempting to solve it. One of the most significant reasons contributing to the rapid decrease in national seafarers is presumed to be the high initial turnover rate due to the decreased preference for maritime careers among people in the 20s and 30s. Therefore, plans have been devised to prepare various policies that allow young people to select long-term boarding. This study analyzed the determinants of long-term boarding decisions among students enrolled in the Maritime College of 'M' University and verifies the relationship with the desired boarding period. Additionally, the crew composition (CC), long-term planning (LP), work environment (WE), and family environment (FE) were derived as the determinants of long-term boarding recognized by prospective seafarers. Among them, LP and WE significantly affect the desired boarding period, thus suggesting that the stronger the perception toward long-term planning and the more insensitive one is to the work environment, the longer is the desired boarding period. In terms of group differences in the perception of long-term boarding, analysis results show that the several determinants of long-term boarding are recognized differently depending on gender. This study may facilitate the preparation of factors and group-specific policy measures to promote long-term boarding among prospective seafarers.

• Journal of Adhesion and Interface
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• v.25 no.2
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• pp.69-74
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• 2024

Soft actuators can be applied to various fields such as the medical industry and manufacturing industry due to the flexibility and smooth movement resulted from their constituent materials. Stimuli-responsive hydrogels are a class of materials that can show large volume changes due to various surrounding stimuli and thus is suitable as a soft actuator material. However, because the change in volume of the stimuli-responsive hydrogel depends on the rate of temperature change and the rate at which the solvent diffuses into the polymer network, in most typical operating conditions, the response time of the actuator is slow due to inefficient heat transfer and diffusion process. In this study, a conjugated polymer was introduced into polydiethylacrylamide, a thermoresponsive hydrogel, to implement a soft actuator driven by light, and the improvement in response time by the photothermal effect of the conjugated polymer was investigated. It was confirmed that the response time was improved by 41% by the introduction of the conjugated polymer, due to the improvement in heat transfer efficiency. Finally, a soft gripper using the hydrogel with improved response time was fabricated and the response time of the gripper was investigated.

• Food Science and Preservation
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• v.31 no.3
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• pp.444-451
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• 2024

This study aimed to investigate the characteristics of protein hydrolysates derived from defatted egg yolk using various proteolytic enzymes and compare the antioxidant activity of the resulting hydrolysates. The defatted egg yolk powder was subjected to enzymatic hydrolysis using four different proteases (alcalase, bromelain, flavourzyme and neutrase), and the resulting hydrolysates were evaluated for their antioxidant properties. Through analysis of available amino group contents and sodium dodecyl sulfate-polyacrylamide gel electrophoresis, it was observed that the defatted egg yolk powder treated with alcalase, flavourzyme, and neutrase for 12 h exhibited a high degree of hydrolysis value. Based on the RC₅₀ values obtained from two different antioxidant analyses, all hydrolysates showed comparable antioxidant activity, except for the alcalase hydrolysate, which demonstrated notably higher scavenging activity against hydrogen peroxide than the other hydrolysates. These findings suggest the potential of protein hydrolysates from defatted egg yolk, a by-product of lecithin extraction, as natural antioxidants.

• The Journal of the Convergence on Culture Technology
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• v.10 no.6
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• pp.421-428
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• 2024

This study critically explores the dynamics of discourse construction and propagation in the context of South Korea's National Pension Scheme (NPS) reform process, initiated in late 2022. It specifically interrogates the theoretical validity and empirical applicability of the dichotomous narratives encapsulated by the themes "Fiscal Sustainability" and "Old-age Income Security," which have polarized the discourse on pension reform. The analysis is structured as follows: to enhance accessibility, an overview is first provided of the NPS reform trajectory, including an outline of the existing system, the imperatives for reform, the stages of policy discourse, and the resulting reform proposal along with its attendant controversies. The study then delves into an examination of the discursive contestation over the 2024 reform proposal, employing media analysis of articles retrieved through the Korean Press Foundation's KINDS database (www.kinds.or.kr). Within this discursive framework, the "Fiscal Sustainability Discourse" underscores concerns of intergenerational equity and the long-term viability of the NPS based on fiscal projections. In contrast, the "Old-age Income Security Discourse" argues for the alleviation of elderly poverty, the welfare function of the NPS, and the state's duty to ensure a basic standard of living for seniors, supported by public sentiment expressed through deliberative forums. By analyzing the conceptual efficacy of fiscal sustainability and income security as paradigmatic lenses for understanding the objectives and operational rationale of South Korea's NPS, this study assesses their utility in distinguishing and contextualizing the complexities inherent in public pension systems.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.37 no.4
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• pp.267-274
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• 2024

Hydrogen embrittlement fracture poses a challenge in ensuring the structural integrity of materials exposed to hydrogen-rich environments. This study advances our comprehension of hydrogen-induced fracture through an integrated numerical modeling approach. In addition, it employs a ductile fracture model named the Gurson-cohesive model (GCM) and hydrogen diffusion analysis. GCM is employed as a fracture model that combines the Gurson model to illustrate the continuum damage evolution and the cohesive zone model to describe crack surface discontinuity and softening behavior. Moreover, porosity and stress triaxiality are considered as crack initiation criteria . A hydrogen diffusion analysis is also integrated with the GCM to account for hydrogen enhanced decohesion (HEDE) mechanisms and their subsequent impacts on crack initiation and propagation. This framework considers the influence of hydrogen on the softening behavior of the traction-separation relationship on the discontinuous crack surface. Parametric studies explore the sensitivity to diffusion properties and hydrogen-induced fracture properties. By combining numerical models of hydrogen diffusion and the ductile fracture model, this study provides an understanding of hydrogen-induced fracture and thereby contributes significantly to the ongoing efforts to design materials that are resilient to hydrogen embrittlement in practical engineering applications.

• Journal of the Korean Geotechnical Society
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• v.40 no.4
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• pp.33-47
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• 2024

Offshore wind structures are subject to long-term repeated horizontal loads from wind, waves, and currents, making it essential to consider these loads in the design of offshore foundations. In this respect, monopiles are large-diameter hollow steel pipes that are relatively simple to construct compared with piles used on onshore sites. They can provide stable support for wind structures and have well-established design codes, leading to their widespread use globally. The behavior of monopiles under lateral static loads is typically assessed using the p-y method proposed by the American Petroleum Institute (API). However, the applicability of p-y curves to large-diameter monopiles exposed to repeated cyclic horizontal loads, such as those experienced in offshore wind applications, must yet be evaluated. Thus, this study evaluated the behavior of monopiles under two-way cyclic horizontal loads in loose silty sand, a representative soil type of the southwestern coast of Korea, using centrifuge model tests. The results demostrated that the behavior of monopiles varied depending on the loading level, number of cycles, and direction of the cyclic loads. Furthermore, the p-y curve method proposed by the API overestimated the behavior of a large-diameter monopile installed in silty sand under two-way cyclic loads.

• Journal of the Institute of Convergence Signal Processing
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• v.25 no.2
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• pp.94-99
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• 2024

Recently, wind power has been gaining attention as a highly efficient renewable energy source, leading to various technological developments worldwide. Typically, wind power is operated in the form of large wind farms with many wind turbines installed in areas rich in wind resources. However, in developing countries or regions isolated from the power grid, off-grid small wind power systems are emerging as an efficient solution. To efficiently operate and expand off-grid small-scale power systems, the development of real-time monitoring systems is required. For the efficient operation of small wind power systems, it is essential to develop real-time monitoring systems that can actively respond to excessive wind speeds and various environmental factors, as well as ensure the stable supply of produced power to small areas or facilities through an Energy Storage System (ESS). The implemented system monitors turbine RPM, power generation, brake operation, and more to create an optimal operating environment. The developed small wind power system can be utilized in remote road lighting, marine leisure facilities, mobile communication base stations, and other applications, contributing to the development of the RE100 industry ecosystem.

• Journal of Korea Port Economic Association
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• v.40 no.3
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• pp.1-26
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• 2024

This study aims to examine the business diversification status of Global Container Terminal Operators(GTOs) and to determine the impact of business diversification on corporate performance using a quantitative index. To this end, a panel regression analysis was conducted using 10-year time series data of 12 GTOs. The results of the empirical analysis show that, first, the mean of the business diversification index of GTOs is rather low at 0.244; second, the business diversification of GTOs affects ROE and TobinsQ among corporate performance. In the case of the dependent variable ROE, we found that there is a non-linear relationship, with no effect in the early stage, a negative effect after a certain level, and a positive effect after a certain level, while the dependent variable TobinsQ has a positive linear relationship. As a result, it seems that GTOs with strong global influence should pursue business diversification in the direction of strengthening and expanding their core business capabilities, and efficient selection and focus at the corporate level are necessary to avoid excessive diversification due to indiscriminate business expansion.

• The Journal of the Convergence on Culture Technology
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• v.10 no.4
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• pp.437-442
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• 2024

The unification of the Korean Peninsula is not only a national aspiration but also holds significant economic implications. By maximizing the economic synergy between South and North Korea and reconstructing the North Korean economy, balanced development across the peninsula can be promoted. However, the unification process will face various economic challenges, including the substantial costs of unification, integrating different economic systems, and bridging the economic disparity between the two Koreas. This paper aims to analyze these anticipated economic issues and propose systematic and phased solutions. Specifically, it discusses the objective estimation of unification costs and funding strategies, suggests effective integration methods for the disparate economic systems of the two Koreas, and identifies policy tasks to reduce economic disparities. The paper reviews existing studies on unification costs, explores strategies for the balanced development of South and North Korean economies through industrial restructuring and gradual transition to a market economy, and proposes concrete measures such as the expansion of North Korea's social overhead capital (SOC) and the development of human capital. The goal is to establish a solid economic foundation for peaceful unification and create opportunities for the economic resurgence of the Korean Peninsula.