• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.37 no.4
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• pp.347-357
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• 2024

Oxide semiconductor gas sensors are widely used for detecting toxic, explosive, and flammable gases due to their simple structure, cost-effectiveness, and potential integration into compact devices. However, their reliable gas detection is hindered by a longstanding issue known as humidity dependence, wherein the sensor resistance and gas response change significantly in the presence of moisture. This problem has persisted since the inception of oxide semiconductor gas sensors in the 1960s. This paper explores the root causes of humidity dependence in oxide semiconductor gas sensors and presents strategies to address this challenge. Mitigation strategies include functionalizing the gas-sensing material with noble metal/transition metal oxides and rare-earth/rare-earth oxides, as well as implementing a moisture barrier layer to prevent moisture diffusion into the gas-sensing film. Developing oxide semiconductor gas sensors immune to humidity dependence is expected to yield substantial socioeconomic benefits by enabling medical diagnosis, food quality assessment, environmental monitoring, and sensor network establishment.

• Journal of dental hygiene science
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• v.16 no.4
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• pp.317-322
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• 2016

Mineral trioxide aggregate (MTA) is widely used in endodontic therapy as a pulp-capping material, root or furcal perforation repair material, and for apexification and obturation of the root canal system. The purpose of this study was to formally document cases of MTA application in South Korean children and adolescents. Through this research, the practice of using MTA will be introduced and familiarized to the clinical practitioners. This study involved endodontic treatment using MTA for fractured crowns in 11- and 12-year-old. The children were followed up for 12 months until the pulp vitality was confirmed; in young permanent teeth with immature roots, the pulp is integral to the process of apexogenesis. These observational results regarding the use of MTA as an apexification material in non-vital immature permanent incisors appear to provide promising results in the search for new materials to meet existing endodontic needs.

• Journal of Periodontal and Implant Science
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• v.31 no.1
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• pp.225-232
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• 2001

The aim of this study was to recommend the optimal age for prevention of periodontal disease and to investigate the trend of treatment modality according to different period. From the chart recordings of the patients who had been treated periodontally from Jan. 1981 to Dec. 1995 in the dept .of periodontics, Chosun University Dental Hospital, those of the periodontally treated patients on more than 4 sixtants were selected for the present study. The distribution of the patients was counted according to the age group and the gender. And they were divided into 3 groups(group 1: 1987-1958, group 2: 1985-1990, group 3: 1991-1995) by 5 year interval according to the treated year. The periodontal treatment modalities were classified into non-surgical therapy, pocket elimination surgery, regenerative periodontal surgery, mucoginigival surgery, clinical crown lengthening, and others. The results were as follows; 1.In the distribution of the periodontally treated patients according to the age group, 40's age group was the highest, and 30's, 40's, and 50's age groups occupied more than two thirds(73%). 2.The sexual distribution of the periodontally treated patients showed that males(53.4%) were a little more than females(46.6%). Within 20's group female was higher, but within 40's male was higher. 3.Regardless of the age group and the gender, pocket elimination surgery was the most frequent treatment modality. 4.In group 1 and 2(1987-1990) the main treatment modality was pocket elimination surgery and non-surgical therapy, but in group 3(1991-1995) it was regenerative periodontal surgery and pocket elimination surgery. The above results suggest that the prevention of periodontal disease should be initiated from early twenties, and the most frequent treatment modality may be closely related with development of new material and method.

• Journal of Periodontal and Implant Science
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• v.25 no.2
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• pp.407-417
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• 1995

In order to evaluate the effect of platelet-derived growth factor(PDGF-BB) and guided tissue regeneration(GTR) technique on the regeneration of destructed periodontal tissue,intentional through-and-through furcation defects(4mm in height) were made on both mandibular 2nd and 4th premolars of 8 adult male dogs(30-40lb). Experimental group 1 was composed of the premolars that were treated by only topical application of PDGF-BB with 0.05M acetic acid without any barrier membrane. Experimental group 2 was composed of the premolars that were treated by GTR with expanded polytetrafluoroethylene membrane(ePTFE : Gore-tex periodontal material, USA). Experimental group 3 was composed of the premolars that were treated by GTR with ePTFE after topical application of PDGFBE. Control group was composed of the premolars that were treated by coronally positioned flap operation only without use of PDGF-BB and ePTFE membrane. All ePTFE membranes were carefully removed 4 weeks after regenerative surgery, and all experimental animals were sacrificed 8 weeks after regenerative surgery. The light microscopic findings were as follows ; (1) In experimental group 1, rapid new bone formation along the-root surface with multiple ankylosis and root resorption by multinucleated giant cells, and dense connective tissue in the central portion of the furcation defects were observed. (2) In experimental group 2, it was observed that the furcation defects were filled with newly formed bone, Sharpey's fibers were embedded into new cementum on root dentin of furcation fornix area, but the central portion and the area under furcation fornix were still filled with dense connective tissue. (3) In experimental group 3, the furcation defects were regenerated with newly formed dense bone and regular periodontal ligament with Sharpey's fibers embedded into newly formed cementum and bone underneath fornix area. (4) In control group, unoccupied space, apical migration of epithelium, dense infiltration of inflammatory cells in subepithelial connective tissue in relation to heavy plaque accumulation, and root resorption by inflammatory reaction were shown, but any new cementum formation on resorbed dentin surface could not be observed. The present study demonstrated that the combined therapy of PDGF-BB and GTR could enhance the regeneration of destructed periodontal tissue.

• Korean Journal of Materials Research
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• v.31 no.7
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• pp.420-426
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• 2021

Graphene, a new material with various advantageous properties, has been actively used in various fields in recent years. Applications of graphene oxide are increasing in combination with other materials due to the different properties of graphene oxide, depending on the number of single and multiple layers of graphene. In this study, single-layer graphene oxide and multi-layer graphene oxide are spray coated on polystyrene, and the physicochemical properties of the coated surfaces are characterized using SEM, Raman spectroscopy, AFM, UV-Vis spectrophotometry, and contact angle measurements. In single-layer graphene oxide, particles of 20 ㎛ are observed, whereas a 2D peak is less often observed, and the difference in surface height increases according to the amount of graphene oxide. Adhesion increases with an increase in graphene oxide up to 0.375 mg, but decreases at 0.75 mg. In multi-layer graphene oxide, particles of 5 ㎛ are observed, as well as a 2D peak. According to the amount of graphene oxide, the height difference of the surface increases and the adhesive strength decreases. Both materials are hydrophilic, but single-layer graphene oxide has a hydrophilicity higher than that of multi-layer graphene oxide. We believe that multi-layer graphene oxide and single-layer graphene oxide can be implemented based on the characteristics that make them suitable for application.

• Journal of the Korean Applied Science and Technology
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• v.41 no.2
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• pp.292-304
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• 2024

This study compared and evaluated the antioxidant activities of Symphoricarpos albus(S. albus) extract and fermented extract. Antioxidant activity was measured by DPPH radical scavenging, FRAP, and ABTS. Concentrations were measured at 200, 100, 50, and 10 ㎍/mL, and antioxidant activity increased in a concentration-dependent manner. S. albus leaves fermented extracts had the highest antioxidant activity. And this study evaluated the safety and tail regeneration of S. albus extract using zebrafish model embryos. Zebrafish are in the spotlight as an alternative animal and can be used for cosmetic research. Zebrafish embryos were collected and evaluated for coagulation rate, hatching rate, and cardiotoxicity. As a result, it was toxic at concentrations above 100 ㎍/ml. The tail was cut and the regenerative effect was observed for 3 days. As a result, from 72 hours, S. albus 200ug/ml leaf extract showed a 17% regenerative effect compared to the control group. These results suggest that S. albus can be used as a natural material for antioxidant and regeneration for skin improvement.

• Biomedical Science Letters
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• v.19 no.1
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• pp.32-40
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• 2013

Pluripotent stem cells (PSCs) have enormous potential in the biomedical sciences because they can grow continuously and differentiate into any kind of cell in the body. However, for future application in regenerative medicine, it is still a challenge to control the differentiation of PSCs without using genetic materials. To control the differentiation of PSCs, small molecules might be the best substitute for genetic materials considering the following advantages: small size, which enables penetration of plasma membrane; easy-to-modify structure; and low chance of genetic recombination in treated cells. Herein, we introduce small molecules that induce the neuroectodermal differentiation of mouse embryonic stem cells (ESCs). The small molecules were identified via ESC-based consecutive screenings of small-molecule libraries composed of 324 natural compounds or 93 selected drugs. The natural compounds discovered in the first screening were used to select 93 structurally similar drugs out of 1,200 approved drugs. In the second screening, among the 93 compounds, we found 4 drugs that induced the neuroectodermal differentiation of ESCs. These drugs were progesteroneor corticoid-derivatives. Our results suggest that small molecules targeting the progesterone receptor or glucocorticoid receptor could be used as chemical tools to induce the differentiation of PSCs into a specific germ lineage.

• Journal of the Korean Association of Oral and Maxillofacial Surgeons
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• v.39 no.3
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• pp.103-111
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• 2013

With successful extraction of growth factors and bone morphogenic proteins (BMPs) from mammalian teeth, many researchers have supported development of a bone substitute using tooth-derived substances. Some studies have also expanded the potential use of teeth as a carrier for growth factors and stem cells. A broad overview of the published findings with regard to tooth-derived regenerative tissue engineering technique is outlined. Considering more than 100 published papers, our team has developed the protocols and techniques for processing of bone graft material using extracted teeth. Based on current studies and studies that will be needed in the future, we can anticipate development of scaffolds, homogenous and xenogenous tooth bone grafts, and dental restorative materials using extracted teeth.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.33 no.4
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• pp.310-314
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• 2020

Although waste oil derived fuel (WDF) production technology was developed under a government initiative ~10 years ago, it became stagnant owing to the small size of participating companies, residents' rejection of foul odor, and the nature of the technology for recycling waste that was avoided. However, this subject is under the spotlight again because of recent developments, such as garbage crisis. In particular, plastic is the most difficult waste to dispose of, with more than 4 million tons of plastic waste produced every year according to statistics from the Ministry of Environment. The most effective method for treating plastic waste is to produce WDF through low temperature thermal decomposition. The WDF includes several volatile ingredients that mostly limit the use of fuel for boilers, owing to safety concerns. In particular, flash point is legally stipulated because of secondary contamination in the distribution process and the risk of fire and explosion. It is required that external shipments (distribution) should be maintained in the range of at least 30~60℃ (excluding explosion prevention facilities) for diesel power generation. Therefore, this study seeks to find the flash point that is best suited to WDFs produced from plastic waste.

• Proceedings of the KSR Conference
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• 2011.05a
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• pp.619-626
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• 2011

In this paper, while electric multiple unit is moving on the rail, the content of measuring and analysing electric power consumption is mentioned. In order to measure the electric power consumption, we developed the power record analysis equipment and installed it the inside of the converter and inverter system to record the electric power consumption measured by voltage sensor and current sensor. Moving on the rail, we analysed traction power used up and regenerative power by using the measuring instrument. We expect that the measured and analysed data will offer basic research material to devise a energy reduction plan and introduce a new EMU system with high efficiency.