• Journal of the Korean Society of Safety
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• v.39 no.2
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• pp.38-43
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• 2024

Recently, with the expanding market for electronic devices and electric vehicles, secondary battery usage has been on the rise. Lithium-ion batteries are particularly popular due to their fast charging times and lightweight nature compared to other types of batteries. A secondary battery consists of four components: anode, cathode, electrolyte, and separator. Generally, the positive and negative electrode materials of secondary batteries are composed of an active material, a binder, and a conductive material. Acetylene Black (AB) is utilized to enhance conductivity between active material particles or metal dust collectors, preventing the binder from acting as an insulator. However, when recycling waste batteries that have been subject to high usage, there is a risk of fire and explosion accidents, as accurately identifying the characteristics of Acetylene Black dust proves to be challenging. In this study, the lower explosion limit for Acetylene Black dust with an average particle size of 0.042 ㎛ was determined to be 153.64 mg/L using a Hartmann-type dust explosion device. Notably, the dust did not explode at values below 168 mg, rendering the lower explosion limit calculation unfeasible. Analysis of explosion delay times with varying electrode gaps revealed the shortest delay time at 3 mm, with a noticeable increase in delay times for gaps of 4 mm or greater. The findings offer fundamental data for fire and explosion prevention measures in Acetylene Black waste recycling processes via a predictive model for lower explosion limits and ignition delay time.

• Journal of Korean Foot and Ankle Society
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• v.4 no.2
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• pp.83-86
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• 2000

A vascular necrosis of the talus has frequently been reported following trauma because talus has no muscle insertions, sixty percent of the surface of the talus is covered by hyaline cartilage, takes only a small area for entrance of a blood supply. Osteonecrosis is also associated with a variety of nontraumatic disorders. There are many indications for steroid usage, patient with rheumatoid arthritis, systemic lupus erythematosus, chronic obstructive pulmonary disease, and status- post renal or cardiac transplantation may be on long- term steroid usage, osteonecrosis may develop. A vascular necrosis of the talus secondary to chronic steroid usage is an unusual case. Delay in detection of osteonecrosis may lead to fragmentation and collapse of the talar body. When pain on range of motion is present and conservative treatment have been exhausted, surgical treatment is indicated, that is, fusion of the ankle joint. However it is important that conservative treatment may prevent its various sequelae with early diagnosis because steroid - treated patients have a more operative risk and increased risk for postoperative infection. We report a rare case of corticosteroid induced avascular necrosis of talus after cardiac transplantation.

• The Transactions of the Korean Institute of Power Electronics
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• v.21 no.6
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• pp.486-496
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• 2016

The voltage unbalance of an LVDC bipolar distribution system was controlled for high power quality. Voltage unbalance may occur in a bipolar distribution system depending on the operation of the converter and load usage. Voltage unbalance can damage sensitive load and lead to converter accidents. The conditions that may cause voltage unbalance in a bipolar distribution system are as follows. First, three-level AC/DC converters in bipolar distribution systems can lead to voltage unbalance. Second, bipolar distribution systems can be at risk for voltage unbalance because of load usage. In this paper, the output DC link of a three-level AC/DC converter was analyzed for voltage unbalance, and the bipolar voltage was controlled with algorithms. In the case of additional voltage unbalance according to load usage, the bipolar voltage was controlled using the proposed converter. The proposed converter is a dual half-bridge converter, which was improved from the secondary circuit of a dual half-bridge converter. A control algorithm for bipolar voltage control without additional converters was proposed. The balancing control of the bipolar distribution system with distributed power was verified through experiments.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 2010.10a
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• pp.141-144
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• 2010

OSA(Opportunistic Spectrum Access) allows secondary users not having a license for spectrum usage to opportunistically occupy an idle spectrum owned by a licensee named primary users. We propose two OSA schemes for un-slotted secondary users exploiting spectrum opportunities in un-slotted primary networks. We provide mathematical analysis and simulation results to reveal the impact of various system parameters.

• The Mathematical Education
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• v.52 no.2
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• pp.163-174
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• 2013

This study conducted a survey to examine the knowledge formation and utilization of computer among beginning teachers of secondary school mathematics. We found that beginning teachers who had more experiences of taking computer utilization classes at teacher education institutes showed more interest in computer and saw the necessity and effectiveness of computer usage for teaching students. Teachers chose GSP the most among computer utilization knowledge learned in pre-service teachers program, and GSP is used the most in mathematics classes. However, they answered that computer is not so much available in class due to lack of hours and the relevant resources. Lastly, beginning teachers answered that the computer knowledge learned in in-service teacher program was more useful than that in pre-service. Thus, the professional development in utilizing computer should be improved through diversifying teacher training contents for beginning teachers as well as for pre-service teachers in teacher education institutes.

• Journal of Plant Biotechnology
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• v.48 no.3
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• pp.186-192
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• 2021

The roots of Korean ginseng (Panax ginseng) have a long history of usage as a medicinal drug. Ginsenosides, a group of triterpenioid saponins in ginseng, have been reported to show important pharmacological effects. Many studies have attempted to identify the ginsenoside synthesis pathways of P. ginseng and to increase crop productivity. Recent studies have shown that exogenous gibberellin (GA) treatments promote storage root secondary growth by integration of the modulating cambium stem cell homeostasis with a secondary cell wall-related gene network. However, the dynamic regulation of ginsenoside synthesis-related genes and their contents by external signaling cues has been rarely evaluated. In this study, we confirmed that GA treatment not only enhanced the secondary growth of P. ginseng storage roots, but also significantly enriched the terpenoid biosynthesis process in RNA-seq analysis. Consistently, we also found that the expression of most genes involved in the ginsenoside synthesis pathways, including those encoding methylerythritol-4-phosphate (MEP) and mevalonate (MVA), and the saponin content in both leaves and roots was increased by exogenous GA application. These results can be used in future development of biotechnology for ginseng breeding and enhancement of saponin content.

• International Journal of Computer Science & Network Security
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• v.22 no.5
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• pp.245-249
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• 2022

This paper explored gifted students' perspectives on using educational technologies in their schools in the Saudi context. Adopting a descriptive research approach, a questionnaire was used to collect information from a sample of 196 gifted secondary school students in Jeddah. Findings showed that educational technology was used to a high degree, with an overall mean of 3.74 and 4.06 for the degree of importance of technological usage. Based on the findings, the researcher forwards some recommendations for effectively using such technologies to promote gifted students' abilities and talents.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.36 no.4A
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• pp.356-368
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• 2011

While most of the public radio spectrum bands are allocated to licensed users, cognitive radio has been considered as a promising technology for the efficient spectrum utilization. In this new technology, secondary users opportunistically use the temporally underutilized licensed bands as long as they do not give the harmful interference to primary users. In this paper, we focus on the infra-structured network condition in which the cognitive radio network consists of a cognitive radio base station and multiple secondary users. Upon detecting a primary user, the entire cognitive radio network generally switches to another available channel, even if most of the on-going communications still does not interfere with the primary user. Moreover, the network re-entry process on a new channel causes the service disruption of the on-going communications. For this reason, in this paper, we propose a relaying scheme for efficient frequency usage, in which the secondary user out of the interference range of a primary user performs as a relaying node for the secondary user possibly interfering with a primary user. The entire spectrum switching is not required, and thus, we can avoid the service disruption of the on-going communications as much as possible.

• Journal of the Korean Society of Tobacco Science
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• v.33 no.1
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• pp.8-15
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• 2011

Genus Nicotiana has 76 species including N. tabacum. These plants are used not only as a material for cigarette manufacturing but also as ornamental plant, medicinal plant, poisonous substance plant, and bug repellent plant. N. tabacum is used as a main material for cigarette manufacturing with N. rustica. N. sylvestris and N. alata is used as ornamental plants because of their beautiful flowers and N. rustica is used for bug repellent or pesticide because of its high concentration of nicotine. N. glauca, a tree tobacco, is used for bio-fuel production. N. tabacum is used as a popular model plant system for degeneration, regeneration, and transformation. N. benthamiana is also used as a model system for foreign gene expression by agroinfiltration. The transformation ability of tobacco plant is a good target for molecular farming. Hepatitis B virus envelop protein, E. coli heat-labile enterotoxin, diabetes autoantigen, and cholera toxin B subunit were produced using tobacco plants. Secondary metabolites of tobacco include nicotine, anabasine, nornicotine, anatabine, cembranoid, solanesol, linoleic acid, rutin, lignin and sistosterol, and they are used for various medicine productions which cannot be produced by organic synthesis for their complicated structures. In conclusion, we have to understand the applicability of tobacco plant in detail and study to enlarge the usage of the plants.

• School Mathematics
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• v.10 no.2
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• pp.297-317
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• 2008

This study was designed to gain insight to adopt CAS into secondary level algebra education in Korea. Most inactive usage of calculators in math and most negative effects of calculators on their achievements of Korean students were shown in International studies such as TIMSS-R. A comparative study was carried out with consideration of mathematical backgrounds and technological environments. 8 Korean students and 26 US students in Grade 11 were participated in this study. Subjects' Problem solving process and their strategies of CAS usage in classical Box-problem with CAS were analyzed. CAS helped modeling by providing symbolic manipulation commands and graphs with students' mathematical knowledge. Results indicates that CAS requires shifts focus in algebraic contents: recognition of decimal & algebraic presentations of numbers; linking various presentations, etc. The extent of instrumentation effects on the selection of problem solving strategies among Korea and US students. Instrumentation