• Korean Journal of Materials Research
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• v.32 no.11
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• pp.481-488
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• 2022

The Cu₂ZnSn(S_xSe_1-x)₄ (CZTSSe) absorbers are promising thin film solar cells (TFSCs) materials, to replace existing Cu(In,Ga)Se₂ (CIGS) and CdTe photovoltaic technology. However, the best reported efficiency for a CZTSSe device, of 13.6 %, is still too low for commercial use. Recently, partially replacing the Zn²⁺ element with a Cd²⁺element has attracting attention as one of the promising strategies for improving the photovoltaic characteristics of the CZTSSe TFSCs. Cd²⁺ elements are known to improve the grain size of the CZTSSe absorber thin films and improve optoelectronic properties by suppressing potential defects, causing short-circuit current (J_sc) loss. In this study, the structural, compositional, and morphological characteristics of CZTSSe and CZCTSSe thin films were investigated using X-ray diffraction (XRD), X-ray fluorescence spectrometer (XRF), and Field-emission scanning electron microscopy (FE-SEM), respectively. The FE-SEM images revealed that the grain size improved with increasing Cd²⁺ alloying in the CZTSSe thin films. Moreover, there was a slight decrease in small grain distribution as well as voids near the CZTSSe/Mo interface after Cd²⁺ alloying. The solar cells prepared using the most promising CZTSSe absorber thin films with Cd²⁺ alloying (8 min. 30 sec.) exhibited a power conversion efficiency (PCE) of 9.33 %, J_sc of 34.0 mA/cm², and fill factor (FF) of 62.7 %, respectively.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.50 no.11
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• pp.801-807
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• 2022

In this paper, we propose an ultra compact S-Band PCM/FM telemetry transmitter. The equipment is compact, so it can be applied to a limited space and capable of stable data transmission was designed and manufactured even with specifications set differently for each operating environment and system. RF direct conversion structure is used for the miniaturization of equipment, an RF transmission board, Power distribution board, and a signal processing board were implemented on a single PCB, so that the function of the transmitter could be performed with a minimum device. According to the target specification, variable output of 1~10W and variable data rate of 390kbps~12.5Mbps is possible in S-Band(2,200~2,400MHz) without degradation of performance. To verify the performance of the equipment, the RF performance test and BER measurement test were performed after the equipment was manufactured. It was confirmed that the OBW, null-to-null bandwidth, 1st IMD, Spurious emission, Phase noise specification of the PCM/FM modulated signal which is presented by the IRIG standard were satisfied, and we can confirm the data received using the transmitter inspection equipment were transmitted normally without distortion.

• Applied Chemistry for Engineering
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• v.34 no.4
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• pp.404-411
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• 2023

For the direct reforming of biogas, a three-phase gliding arc plasma reformer was designed to expand the plasma discharge region, and the operation conditions of the plasma reformer, such as the S/C ratio, the gas flow rate, and the plasma input power, were optimized. The H₂ production efficiency is increased at a lower specific plasma input energy density, but byproducts such as C_XH_Y and carbon soot are generated along with the increase in H₂ production efficiency. The formation of byproducts is decreased at higher specific plasma input energy densities and S/C ratios. The optimized operation conditions are 5.5 ~ 6.0 kJ/L for the specific plasma input energy density and 3 for the S/C ratio, considering the conversion efficiency, H₂ production, and byproduct formation. It is expected that the H₂ production efficiency will improve with the decrease in fuel consumption in biogas burners because the heat generated from plasma discharge heats up the feed gas to over 500 ℃.

• KIPS Transactions on Computer and Communication Systems
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• v.12 no.8
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• pp.253-262
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• 2023

E-voting is a concept that includes actions such as kiosk voting at a designated place and internet voting at an unspecified place, and has emerged to alleviate the problem of consuming a lot of resources and costs when conducting offline voting. Using E-voting has many advantages over existing voting systems, such as increased efficiency in voting and ballot counting, reduced costs, increased voting rate, and reduced errors. However, centralized E-voting has not received attention in public elections and voting on corporate agendas because the results of voting cannot be trusted due to concerns about data forgery and modulation and hacking by others. In order to solve this problem, recently, by designing an E-voting system using blockchain, research has been actively conducted to supplement concepts lacking in existing E-voting, such as increasing the reliability of voting information and securing transparency. In this paper, we proposed an electronic voting system that introduced hybrid blockchain that uses public and private blockchains in convergence. A hybrid blockchain can solve the problem of slow transaction processing speed, expensive fee by using a private blockchain, and can supplement for the lack of transparency and data integrity of transactions through a public blockchain. In addition, the proposed system is implemented as BaaS to ensure the ease of type conversion and scalability of blockchain and to provide powerful computing power. BaaS is an abbreviation of Blockchain as a Service, which is one of the cloud computing technologies and means a service that provides a blockchain platform ans software through the internet. In this paper, in order to evaluate the feasibility, the proposed system and domestic and foreign electronic voting-related studies are compared and analyzed in terms of blockchain type, anonymity, verification process, smart contract, performance, and scalability.

• Journal of Intelligence and Information Systems
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• v.27 no.2
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• pp.33-54
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• 2021

With the fourth industrial revolution and the arrival of the New Normal era due to Corona, the importance of Non-contact technologies such as artificial intelligence and big data research has been increasing. Convergent research is being conducted in earnest to keep up with these research trends, but not many studies have been conducted in the area of nuclear research using artificial intelligence and big data-related technologies such as natural language processing and text mining analysis. This study was conducted to confirm the applicability of data science analysis techniques to the field of nuclear research. Furthermore, the study of identifying trends in nuclear spent fuel recognition is critical in terms of being able to determine directions to nuclear industry policies and respond in advance to changes in industrial policies. For those reasons, this study conducted a media trend analysis of pyroprocessing, a spent nuclear fuel treatment technology. We objectively analyze changes in media perception of spent nuclear fuel dry treatment techniques by applying text mining analysis techniques. Text data specializing in Naver's web news articles, including the keywords "Pyroprocessing" and "Sodium Cooled Reactor," were collected through Python code to identify changes in perception over time. The analysis period was set from 2007 to 2020, when the first article was published, and detailed and multi-layered analysis of text data was carried out through analysis methods such as word cloud writing based on frequency analysis, TF-IDF and degree centrality calculation. Analysis of the frequency of the keyword showed that there was a change in media perception of spent nuclear fuel dry treatment technology in the mid-2010s, which was influenced by the Gyeongju earthquake in 2016 and the implementation of the new government's energy conversion policy in 2017. Therefore, trend analysis was conducted based on the corresponding time period, and word frequency analysis, TF-IDF, degree centrality values, and semantic network graphs were derived. Studies show that before the 2010s, media perception of spent nuclear fuel dry treatment technology was diplomatic and positive. However, over time, the frequency of keywords such as "safety", "reexamination", "disposal", and "disassembly" has increased, indicating that the sustainability of spent nuclear fuel dry treatment technology is being seriously considered. It was confirmed that social awareness also changed as spent nuclear fuel dry treatment technology, which was recognized as a political and diplomatic technology, became ambiguous due to changes in domestic policy. This means that domestic policy changes such as nuclear power policy have a greater impact on media perceptions than issues of "spent nuclear fuel processing technology" itself. This seems to be because nuclear policy is a socially more discussed and public-friendly topic than spent nuclear fuel. Therefore, in order to improve social awareness of spent nuclear fuel processing technology, it would be necessary to provide sufficient information about this, and linking it to nuclear policy issues would also be a good idea. In addition, the study highlighted the importance of social science research in nuclear power. It is necessary to apply the social sciences sector widely to the nuclear engineering sector, and considering national policy changes, we could confirm that the nuclear industry would be sustainable. However, this study has limitations that it has applied big data analysis methods only to detailed research areas such as "Pyroprocessing," a spent nuclear fuel dry processing technology. Furthermore, there was no clear basis for the cause of the change in social perception, and only news articles were analyzed to determine social perception. Considering future comments, it is expected that more reliable results will be produced and efficiently used in the field of nuclear policy research if a media trend analysis study on nuclear power is conducted. Recently, the development of uncontact-related technologies such as artificial intelligence and big data research is accelerating in the wake of the recent arrival of the New Normal era caused by corona. Convergence research is being conducted in earnest in various research fields to follow these research trends, but not many studies have been conducted in the nuclear field with artificial intelligence and big data-related technologies such as natural language processing and text mining analysis. The academic significance of this study is that it was possible to confirm the applicability of data science analysis technology in the field of nuclear research. Furthermore, due to the impact of current government energy policies such as nuclear power plant reductions, re-evaluation of spent fuel treatment technology research is undertaken, and key keyword analysis in the field can contribute to future research orientation. It is important to consider the views of others outside, not just the safety technology and engineering integrity of nuclear power, and further reconsider whether it is appropriate to discuss nuclear engineering technology internally. In addition, if multidisciplinary research on nuclear power is carried out, reasonable alternatives can be prepared to maintain the nuclear industry.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.25 no.6
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• pp.346-361
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• 2013

This article reviews the papers published in the Korean Journal of Air-Conditioning and Refrigeration Engineering during 2012. It is intended to understand the status of current research in the areas of heating, cooling, ventilation, sanitation, and indoor environments of buildings and plant facilities. The conclusions are as follows : (1) The research works on thermal and fluid engineering have been reviewed as groups of fluid machinery, pipes and valves, fuel cells and power plants, ground-coupled heat pumps, and general heat and mass transfer systems. Research issues are mainly focused on new and renewable energy systems, such as fuel cells, ocean thermal energy conversion power plants, and ground-coupled heat pump systems. (2) Research works on the heat transfer area have been reviewed in the categories of heat transfer characteristics, pool boiling and condensing heat transfer, and industrial heat exchangers. Researches on heat transfer characteristics included the results for natural convection in a square enclosure with two hot circular cylinders, non-uniform grooved tube considering tube expansion, single-tube annular baffle system, broadcasting LED light with ion wind generator, mechanical property and microstructure of SA213 P92 boiler pipe steel, and flat plate using multiple tripping wires. In the area of pool boiling and condensing heat transfer, researches on the design of a micro-channel heat exchanger for a heat pump, numerical simulation of a heat pump evaporator considering the pressure drop in the distributor and capillary tubes, critical heat flux on a thermoexcel-E enhanced surface, and the performance of a fin-and-tube condenser with non-uniform air distribution and different tube types were actively carried out. In the area of industrial heat exchangers, researches on a plate heat exchanger type dehumidifier, fin-tube heat exchanger, an electric circuit transient analogy model in a vertical closed loop ground heat exchanger, heat transfer characteristics of a double skin window for plant factory, a regenerative heat exchanger depending on its porous structure, and various types of plate heat exchangers were performed. (3) In the field of refrigeration, various studies were executed to improve refrigeration system performance, and to evaluate the applicability of alternative refrigerants and new components. Various topics were presented in the area of refrigeration cycle. Research issues mainly focused on the enhancement of the system performance. In the alternative refrigerant area, studies on CO2, R32/R152a mixture, and R1234yf were performed. Studies on the design and performance analysis of various compressors and evaporator were executed. (4) In building mechanical system research fields, twenty-nine studies were conducted to achieve effective design of mechanical systems, and also to maximize the energy efficiency of buildings. The topics of the studies included heating and cooling, HVAC system, ventilation, renewable energy systems, and lighting systems in buildings. New designs and performance tests using numerical methods and experiments provide useful information and key data, which can improve the energy efficiency of buildings. (5) In the fields of the architectural environment, studies for various purposes, such as indoor environment, building energy, and renewable energy were performed. In particular, building energy-related researches and renewable energy systems have been mainly studied, reflecting interests in global climate change, and efforts to reduce building energy consumption by government and architectural specialists. In addition, many researches have been conducted regarding indoor environments.

• Korean Journal of Labor Studies
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• v.17 no.1
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• pp.139-176
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• 2011

Non-regular workers came to the fore while working class formation was in retreat along with the democratic labor movement of regular workers. The formation of principal agents, however, is yet to occur. Then, why non-regular workers' struggles could not yield a consequence in that regard? What kind of factors are to determine the outcome of the struggles and how do they do it? It is the aim of this study to answer those questions. In contrast with regular workers' struggles, non-regular workers' struggles tend to break out in response to capitalist offensives, rely on atypical and, often, extreme measures of struggle rather than strike in the form of work stoppage, drag out for too long, and appeal for social solidarity outside when the solidarity of regular workers is not available. Non-regular workers' struggles tend to end up with failure rather than success, and with weakening rather than strengthening of their organizational strength. So as to overcome the tendency to fail, non-regular workers' struggles need regular workers' solidarity in addition to their own strong mobilization power, while social solidarity or positional power could substitute for regular workers' solidarity in some cases. So as to build up their organizational strength, non-regular workers' struggles should win victories in the struggles, while a victory could turn into a trap in the case of conversion. Both regular workers' solidarity and the internal integration of the struggles are two foremost important factors in achieving the victory of struggles and the building-up of organizational strength. Those who have got involved in struggles are from the best organized sector among all the non-regular workers. As they have gone through weakening of organizational strength, it becomes more difficult for non-regular workers to form principal agents. Without non-regular workers' struggles, however, the capitalist offensives must have carried the day. In that sense, non-regular workers' struggles did a role in at least detaining capitalist offensives, if not stopping them. The practical implication of non-regular workers' struggles is that, if non-regular workers redefine the ultimate goal of their struggles as the formation of their principal agents for working class formation, it would be a strategically rational choice to identify the strategic objective of struggles with the maintaining and strengthening of their organizational strength rather than the achievement of their immediate demands.

• The Journal of Fisheries Business Administration
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• v.34 no.2
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• pp.75-90
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• 2003

When we think of fundamental problems of the aquaculture industry, there are several strict conditions, and consequently the aquaculture industry is forced to change. Fish aquaculture has a structural supply surplus in production, aggravation of fishing grounds, stagnant low price due to recent recession, and drastic change of distribution circumstances. It is requested for us to initiate discussion on such issue as “how fish aquaculture establishes its status in the coastal fishery\ulcorner, will fish aquaculture grow in the future\ulcorner, and if so “how it will be restructured\ulcorner” The above issues can be observed in the mariculture of yellow tail, sea scallop and eel. But there have not been studied concerning seabream even though the production is over 30% of the total production of fish aquaculture in resent and it occupied an important status in the fish aquaculture. The objectives of this study is to forecast the future movement of sea bream aquaculture. The first goal of the study is to contribute to managerial and economic studies on the aquaculture industry. The second goal is to identify the factors influencing the competition between production areas and to identify the mechanisms involved. This study will examine the competitive power in individual producing area, its behavior, and its compulsory factors based on case study. Producing areas will be categorized according to following parameters : distance to market and availability of transportation, natural environment, the time of formation of producing areas (leaderㆍfollower), major production items, scale of business and producing areas, degree of organization in production and sales. As a factor in shaping the production area of sea bream aquaculture, natural conditions especially the water temperature is very important. Sea bream shows more active feeding and faster growth in areas located where the water temperature does not go below 13∼14$^{\circ}C$ during the winter. Also fish aquaculture is constrained by the transporting distance. Aquacultured yellowtail is a mass-produced and a mass-distributed item. It is sold a unit of cage and transported by ship. On the other hand, sea bream is sold in small amount in markets and transported by truck; so, the transportation cost is higher than yellow tail. Aquacultured sea bream has different product characteristics due to transport distance. We need to study live fish and fresh fish markets separately. Live fish was the original product form of aquacultured sea bream. Transportation of live fish has more constraints than the transportation of fresh fish. Death rate and distance are highly correlated. In addition, loading capacity of live fish is less than fresh fish. In the case of a 10 ton truck, live fish can only be loaded up to 1.5 tons. But, fresh fish which can be placed in a box can be loaded up to 5 to 6 tons. Because of this characteristics, live fish requires closer location to consumption area than fresh fish. In the consumption markets, the size of fresh fish is mainly 0.8 to 2kg.Live fish usually goes through auction, and quality is graded. Main purchaser comes from many small-sized restaurants, so a relatively small farmer and distributer can sell it. Aquacultured sea bream has been transacted as a fresh fish in GMS ,since 1993 when the price plummeted. Economies of scale works in case of fresh fish. The characteristics of fresh fish is as follows : As a large scale demander, General Merchandise Stores are the main purchasers of sea bream and the size of the fish is around 1.3kg. It mainly goes through negotiation. Aquacultured sea bream has been established as a representative food in General Merchandise Stores. GMS require stable and mass supply, consistent size, and low price. And Distribution of fresh fish is undertook by the large scale distributers, which can satisfy requirements of GMS. The market share in Tokyo Central Wholesale Market shows Mie Pref. is dominating in live fish. And Ehime Pref. is dominating in fresh fish. Ehime Pref. showed remarkable growth in 1990s. At present, the dealings of live fish is decreasing. However, the dealings of fresh fish is increasing in Tokyo Central Wholesale Market. The price of live fish is decreasing more than one of fresh fish. Even though Ehime Pref. has an ideal natural environment for sea bream aquaculture, its entry into sea bream aquaculture was late, because it was located at a further distance to consumers than the competing producing areas. However, Ehime Pref. became the number one producing areas through the sales of fresh fish in the 1990s. The production volume is almost 3 times the production volume of Mie Pref. which is the number two production area. More conversion from yellow tail aquaculture to sea bream aquaculture is taking place in Ehime Pref., because Kagosima Pref. has a better natural environment for yellow tail aquaculture. Transportation is worse than Mie Pref., but this region as a far-flung producing area makes up by increasing the business scale. Ehime Pref. increases the market share for fresh fish by creating demand from GMS. Ehime Pref. has developed market strategies such as a quick return at a small profit, a stable and mass supply and standardization in size. Ehime Pref. increases the market power by the capital of a large scale commission agent. Secondly Mie Pref. is close to markets and composed of small scale farmers. Mie Pref. switched to sea bream aquaculture early, because of the price decrease in aquacultured yellou tail and natural environmental problems. Mie Pref. had not changed until 1993 when the price of the sea bream plummeted. Because it had better natural environment and transportation. Mie Pref. has a suitable water temperature range required for sea bream aquaculture. However, the price of live sea bream continued to decline due to excessive production and economic recession. As a consequence, small scale farmers are faced with a market price below the average production cost in 1993. In such kind of situation, the small-sized and inefficient manager in Mie Pref. was obliged to withdraw from sea bream aquaculture. Kumamoto Pref. is located further from market sites and has an unsuitable nature environmental condition required for sea bream aquaculture. Although Kumamoto Pref. is trying to convert to the puffer fish aquaculture which requires different rearing techniques, aquaculture technique for puffer fish is not established yet.

• Microbiology and Biotechnology Letters
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• v.40 no.4
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• pp.414-418
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• 2012

The quantity of research on microbial fuel cells has been rapidly increasing. Microbial fuel cells are unique in their ability to utilize microorganisms and to generate electricity from sewage, pig excrement, and other wastewaters which include organic matter. This system can directly produce electrical energy without an inefficient energy conversion step. However, with MFCs maximum power production is limited by several factors such as activation losses, ohmic losses, and mass transfer losses in cathodes. Therefore, electron acceptors such as nitrate and ferric ion in the cathodes were utilized to improve the cathode reaction rate because the cathode reaction is very important for electricity production. When 100 mM nitrate as an electron acceptor was fed into cathodes, the current in single-cathode and dual-cathode MFCs was noted as $3.24{\pm}0.06$ mA and $4.41{\pm}0.08$ mA, respectively. These values were similar to when air-saturated water was fed into the cathodes. One hundred mM nitrate as an electron acceptor in the cathode compartments did not affect an increase in current generation. However, when ferric ion was used as an electron acceptor the current increased by $6.90{\pm}0.36$ mA and $6.67{\pm}0.33$ mA, in the single-cathode and dual-cathode microbial fuel cells, respectively. These values, in single-cathode and dual-cathode microbial fuel cells, represent an increase of 67.1% and 17.6%, respectively. Furthermore, when supplied with ferric ion without air, the current was higher than that of only air-saturated water. In this study, we attempted to reveal an inexpensive and readily available electron acceptor which can replace platinum in cathodes to improve current generation by increasing the cathode reaction rate.

• Korean Chemical Engineering Research
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• v.54 no.6
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• pp.863-870
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• 2016

We investigated the physical/chemical phenomena that a slow loss of $CO_2$ inventory into sodium after the sodium-$CO_2$ boundary failure in printed circuit heat exchangers (PCHEs), which is considered for the supercritical $CO_2$ Brayton cycle power conversion system of a sodium-cooled fast reactor (SFR). The first phenomenon is plugging inside narrow sodium channels by micro cracks and the other one is damage propagation referred to as wastage combined with the corrosion/erosion effect. Experimental results of plugging shows that sodium flow immediately stopped as $CO_2$ was injected through the nozzle at $300{\sim}400^{\circ}C$ in 3 mmID sodium channels, whereas sodium flow stopped about 60 min after $CO_2$ injection in 5 mmID sodium channels. These results imply that if pressure boundary of sodium-$CO_2$ fails a narrow sodium channel would be plugged by reaction products in a short time whereas a relatively wider sodium channel would be plugged with higher concentration of reaction products. Wastage by the erosion effect of $CO_2$ (200~250 bar) hardly occurred regardless of the kinds of materials (stainless steel 316, Inconel 600, and 9Cr-1Mo steel), temperature ($400{\sim}500^{\circ}C$), or the diameter of the $CO_2$ nozzle (0.2~0.8 mm). Velocities at the $CO_2$ nozzle were specified as Mach 0.4~0.7. Our experimental results are expected to be used for determining the design parameters of PCHEs for their safeties.