• Journal of Electrical Engineering and Technology
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• v.13 no.3
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• pp.1060-1068
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• 2018

Droop control schemes have been widely employed in the control strategies for Multi-Terminal Direct Current (MTDC) system for its high reliability. Under the conventional DC voltage-active power droop control, the droop slope applies a proportional relationship between DC voltage error and active power error for power sharing. Due to the existence of DC network impedance and renewable resource fluctuation, there is inevitably a DC voltage deviation from the droop characteristic, which in turn results in inaccurate control of converter's power. To tackle this issue, a piecewise droop control with DC voltage dead band or active power dead band is implemented into controller design. Besides, an advanced droop control scheme with versatile function is proposed, which enables the converter to regulate DC voltage and AC voltage, control active and reactive power, get participated into frequency control, and feed passive network. The effectiveness of the proposed control method has been verified by simulation results.

• New & Renewable Energy
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• v.20 no.3
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• pp.1-11
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• 2024

Livestock manure solid fuel has been studied as a promising domestic energy resource for reducing greenhouse gas emissions in agricultural fields. To successfully commercialize this technology, the environmental facilities require optimization in accordance with domestic environmental standards. In the present study, a computational analysis model of a livestock manure solid fuel boiler system was developed using Aspen Plus^® to investigate nitrogen oxides (NOx) emissions and NOx conversion efficiency using urea-based selective non-catalytic reduction (SNCR). All data were compared across different livestock species and simulated at various operating temperatures. The simulation showed that NOx emissions were the highest from chicken manure and the lowest from swine manure. However, when converted to an oxygen concentration of 12%, NOx emissions were the highest from cattle manure. Dominant factors influencing NOx emissions through a range of temperatures were analyzed, and the optimal operating temperature range (875-950℃) was derived.

• Korean Journal of Agricultural Science
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• v.39 no.1
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• pp.133-142
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• 2012

In this paper, animal welfare egg was focused in Korea. This study was built to establish marketing strategies for the animal welfare egg. Data were collected by consumer survey on November 4th, 2011 at Chuncheon Hanaromart in Chuncheon. 355 questionnaires were distributed and collected. SAS 9.1 and Excel 2007 were used as statistical packages and ranked logit model was used to analyze. From the results of the study the following improving plans were suggested for the consideration factors affecting to purchase for animal welfare egg. First, strategies using public relations are needed only for package design. The package design will be able to complements gaps for low advertisement. Moreover, when consumer will be provided information on packaging for consumers, the consumer will be able to reduce anxiety. Second, package design of identity strategies are needed. There are so many package designs in market. The package design of identity may give competition power to the animal welfare egg.

• Journal of Family Resource Management and Policy Review
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• v.23 no.2
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• pp.79-97
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• 2019

This study aimed for in-depth observation of the status quo of the youth generation's happiness utilizing the Better Life Index and the World Value Survey. To serve this purpose, the study selected 11 of the Organization for Economic Cooperation and Development(OECD) member countries (Australia, Estonia, Germany, Japan, Korea, Mexico, New Zealand, Poland, Sweden, Turkey, United States) that overlapped with the subject countries of the World Value Survey. The results of the observation first revealed that among the work-life balance levels of youth generations from across the 11 studied countries, the level for Korean youth was in a very poor state. Second, the happiness level of Korean youth also sat among the bottom ranks, with the aspects of politics, friendship, and career casting a heavy influence on importance to life; specifically, the youth generations of Turkey and Germany showed high levels of life purpose, while Korean youth displayed outstanding results in the challenge aspect. The third finding of this study reported that family, religion, power, benevolence, and challenge were commonly related to the happiness level of youth generations in countries with a higher work-life balance. The results of this study are expected to contribute to the much needed attention and support for improving the happiness level of the Korean youth generation, who will eventually play the leading role in our future society.

• International conference on construction engineering and project management
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• 2024.07a
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• pp.799-806
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• 2024

Construction planners for hard rock tunnel projects often encounter practical challenges caused by inherent uncertainties in ground conditions and resource constraints. Therefore, planners cannot rapidly generate optimal excavation schedules for the shortest project durations with a given equipment fleet by considering the uncertainties in ground conditions. Although some schedule optimization methods exist, they are not tailored for resource-constrained hard rock tunnel projects. To overcome these limitations, the authors specified a formal Q-learning-based schedule optimization methodology for resource-constrained hard rock tunnel projects. States are defined according to the locations of tunnel faces under excavation. Actions consist of multiple and comprehensive heuristic-based rules, which are efficient methods for resource allocation. Rewards are the time intervals required between current states and next states. After that, the methodology is validated using a case study. The generated Q tables indicate (1) best actions under different states and (2) the shortest remaining durations when the project starts from specific (state, action) pairs. The results demonstrate that the optimal schedules can be obtained by applying the proposed methodology. Furthermore, it is beneficial for planners to rapidly assign optimal rules for each state under one ground condition scenario. The results further show the potential to consider the uncertainties in ground conditions using the information of possible ground condition scenarios provided.

• Korean Journal of Medicinal Crop Science
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• v.25 no.1
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• pp.37-44
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• 2017

Background: The light emitting plasma (LEP) has recently attracted attention as a novel artificial light source for plant growth and functional component enhancement. We investigated the effects of LEP on whitening and antioxidant activities of the plant parts of perilla. Methods and Results: Previously germianted seeds of perilla were cultivated under different light conditions (fluoresce lamp, LED red, blue, white, green, and LEP) in a culture room for 2 months. Parts of perilla were harvested and extracted in 70% EtOH. The extracts were used to detect total phenolic contents, total flavonoid contents, 2,2-diphenyl-1-picrylhydrazyl (DPPH), 2,2'-azino-bis-3-ethylbenzothiazoline-6-sulfonic acid (ABTS), reducing power and tyrosinase inhibition activity as indicators of biological activity. Biological activity was highest in seedlings grown under LEP. The total phenolic content was highest in the stems and the total flavonoid content was highest in the roots of perilla exposed to LEP. The DPPH and ABTS radical activity in all the parts of perilla exposed to LEP were higher by approximately three-fold compared to that in the control (fluoresce lamp). The reducing power values of perilla significantly increased after treatment with LEP. In addition, all the extract of perilla plants exposed to LEP promoted the tyrosinase inhibitory activity. These results suggest that LEP can be an important artificial light source for enhancement of biological activity. Conclusions: LEP could promote whitening and antioxidant activity of perilla.

• Environmental and Resource Economics Review
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• v.27 no.2
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• pp.315-337
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• 2018

Korean government temporarily shut down the coal-fired power plants built before 30 years and more from 6/1/2017 to 6/31/2017. This treatment provides a credible natural experiment regarding the regional $PM_{2.5}$ concentration and coal-fired generators. Based on this feature of the treatment, this study analyzed the causality between the old coal-fired power plants and regional $PM_{2.5}$ concentration. To be specific, we categorized two pollution monitoring stations nearby coal-fired power plants in Yeongdong into a treatment station and a control station based on the distance from the power plants. The control station is similar to the treatment station geographically and topographically, but its $PM_{2.5}$ concentration would not be directly affected by coal-fired power plants in Yeongdong. A difference-in-difference method was applied to identify the effects of the old coal-fire power plants on regional $PM_{2.5}$ concentration. The results show that the temporary shutdown would decrease $PM_{2.5}$ concentration nearby coal-fired power plants in Yeongdong by $3.7{\sim}4.4{\mu}g/m^3$.

• Environmental and Resource Economics Review
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• v.30 no.4
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• pp.607-625
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• 2021

The objective of this study is to estimate the relationship between CO₂ emissions and both nuclear power and renewable energy generation, and compare the cost efficiencies of nuclear power and renewable energy generation in reducing CO₂ emissions in Korea. The results show that nuclear power and renewable energy generation should be increased by 1.344% and 7.874% to reduce CO₂ emissions by 1%, respectively. Using the estimated coefficients and the levelized costs of electricity by source including the external costs, if the current amount of electricity generation is one megawatt-hour, the range of generation cost of nuclear power generation to reduce 1% CO₂ emissions is $0.72~$1.49 depending on the level of external costs. In the case of renewable energy generation, the generation cost to reduce 1% CO₂ emissions is $6.49. That is, to mitigate 1% of CO₂ emissions at the total electricity generation of 353 million MWh in 2020 in Korea, the total generation costs range for nuclear power is $254 million~$526 million for the nuclear power, and the cost for renewable energy is $2.289 billion for renewable energy. Hence, we can conclude that, in Korea, nuclear power generation is more cost-efficient than renewable energy generation in mitigating CO₂ emissions, even with the external costs of nuclear power generation.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.32 no.7A
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• pp.686-693
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• 2007

In this paper, we describe how to set up/down step-size in open loop power control for WiBro reverse link. Since open loop power control does not use feedback information, it is difficult to efficiently use wireless resource with accurate power control. We also provides a method of estimating levels of noise and interference. With numerical investigation, asymmetric up/down power-control step-size is shown to be promising to achieve high sector throughput as well as low error rate.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.14 no.1
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• pp.20-39
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• 2020

This paper considers a downlink multi-carrier cooperative non-orthogonal multiple access (NOMA) transmission, where no direct link exists between the far user and the base station (BS), and the communication between them only relies on the assist of the near user. Firstly, the BS sends a superimposed signal of the far and the near user to the near user, and then the near user adopts simultaneous wireless information and power transfer (SWIPT) to split the received superimposed signal into two portions for energy harvesting and information decoding respectively. Afterwards, the near user forwards the signal of the far user by utilizing the harvested energy. A minimum data is required to ensure the quality of service (QoS) of the far user. We jointly optimize power allocation, subcarrier allocation, time allocation, the power allocation (PA) coefficient and the power splitting (PS) ratio to maximize the number of data bits received at the near user under the energy causality constraint, the minimum data constraint and the transmission power constraint. The block-coordinate descent method and the Lagrange duality method are used to obtain a suboptimal solution of this optimization problem. In the final simulation results, the superiority of the proposed NOMA scheme is confirmed compared with the benchmark NOMA schemes and the orthogonal multiple access (OMA) scheme.