• Proceedings of the Korean Powder Metallurgy Institute Conference
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• 2001.11a
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• pp.30-30
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• 2001

$Bi_2Te_3$계 열전재료는 200~400K 정도의 저온에서 네어지 변환효율이 가장 높은 재료로써 열전냉각, 바런재로 등에 응요하기 위하여ㅠ 제조법 및 특서에 관한 많은 연구가 진행되어 왔다. $Bi_2Te_3$계 화합물은 rhombohedral의 결정 구조를 가지는 층상 화 ;물로 결정대칭성으로 인해 연전기적으로 큰 이방성을 나타낸다. 현재는 일반향용고법에 의해서 입자를 a축 방향으로 성장시켜 큰 결정립을 가진 다결정재료를 사용하고 있으나, c면이 매우 취약하기 때문에 가공서이 나쁘다. 따라서 이와같은 단점을 개선하기 위하여 기계적 강도를 높일 수 있는 가공공정 및 합금설계에 대한 연구가 활발히 진행되고 있다. 측히 열간 압출법으로 제조된 열전재료는 결정립의 미세화와 높은 이방성으로 성능지수와 기계적 강도를 향상시킬 수 있다는 연구결과가 보고되고 있다 또한 Schultz드의 연구결과에 의하면 $Bi_2Te_3$ 계 열전재료는 소성변형에 의하여 발생한 점결함에 의하여 캐리어 농도가 변화되며 이로 인하여 재료의 전기적 성질이 결정된다고 하였다. 따라서 상당히 큰 소성가공량과 열전측성과의 관계를 규명하는 것은 매우 중요하다. 이에 본 연구에서는 압출변수 중 소성가공량에 중요한 변수로 작요아는 압출비를 변화시켜 최적의 열간 소성가공량을 검토하고, 이에 따른 열전측성과 압출비와의 상관관계에 대하여 연구하는 것을 목적으로 하였다. 연구에 사용된 N형의 조성은$Bi_2Te_{2.75}Se_{0.15}$로서 순도 99.99를 사용하였고, dopant로 0.1wt%의 $SbI_3$를 사용하였다. $Bi_2Te_{2.75}Se_{0.15}$ 분말은 가스분사법(Gas atomization Process)를 이용하여, 용탕제조시 아르곤가스로 산화를 방지하였고, 냉매로는 질소가스를 이용하였다. 제조된 분말을 기ㅖ적 분급법을 이용하여 분급하였고, 냉매로는 질소가스를 이용하였다. 제조된 분말을 기계적 분급ㅂ법을 이용하여 분급하였고, 압출에 이용된 분말은 250$\mu\textrm{m}$이하의 크기를 사용하였다. 또한 분말제조과정 중 형성되는 표면산화층을 제거하기 위하여 36$0^{\circ}C$에서 4시간동안 수소 환원처리를 행하였다. 제조된 분말은 열간 압출을 위하여 Aㅣcan에 넣고 냉간성형체를 만들고, 진공처리를 한 후 밀봉하여 탈가스처리를 하였다. 압출다이는 압출비가 각각 28:1과 16:1인 평다이(9$0^{\circ}C$)를 사용하여 각각 내경이 9, 12cm이고, 길이가 50, 30cm인 압출재를 제조하였다. 열간압출한 후의 미세조직을 광학현미경으로 압출방향에 평행한 방향과 수직방향으로 관찰하였고, 열간 압출재 이방성을 검토하기 위하여 X선 회절분석을 실실하여 결정방위를 확인하였다. 전기 비저항 및 Seebeck 계수 측정을 위하여 각각 2$\times$2$\times$10$mm^3$ 그리고 5$\times$5$\times$10$mm^3$ 크기의 시편을 준비하였다.준비하였다.

• Resources Recycling
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• v.24 no.2
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• pp.13-22
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• 2015

$CO_2$ emitted from building materials and construction materials industry reaches about 67 million tons, which occupy about 30 % of $CO_2$ emitted from the construction field. Controls on the use of consumed fossil fuels and reduction of emission gases are essential for the reduction of $CO_2$ in the construction area as we reduce the second and third curing to emit $CO_2$ in the construction materials industry. Accordingly, this study applied the low energy curing admixture (hereinafter "LA") to the extruded panels to observe the physical properties, depending on the mixing amount of fiber, type of fiber and mixing ratio of fiber. The type of fiber did not appear to be a main factor to affect strength, while the LA mixing ratio and mixing amount of fiber appeared to be major factors to affect strength. Especially, the highest strength was developed when the LA mixing ratio was 40%, whereas the test object with the mixing ratio of 50% resulted in the decrease of strength. In addition, it appeared that the mixing ratio of fiber greatly affected flexural strength and strength increased as the mixing ratio increased.

• Journal of the korean academy of Pediatric Dentistry
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• v.25 no.2
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• pp.352-367
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• 1998

Intracellular pH (pHi) plays an important role in the regulation of cellular processes by influencing the acitivity of various enzymes in cells. Therefore, almost every type of mammalian cell possesses an ability to regulate its pHi. One of the most prominent mechanisms in the regulation of pHi is $Na^+/H^+$ exchanger. This exchanger has been known to be activated when cells are stimulated by the binding of agonist to the muscarinic receptors. Therefore, the aims of this study were to compare the rates of $H^+$ extrusion through $Na^+/H^+$ exchanger before and during muscarinic stimulation and to investigate the possible existence of $HCO_3^-$ transporter which is responsible for the continuous supply of $HCO_3^-$ ion to saliva. Acinar cells were isolated from the rat mandibular salivary glands and loaded with pH-sensitive fluoroprobe, 2', 7'-bis(2-carboxyethyl)-5(6)-carboxyfluorescein(BCECF), for 30min at room temperature. Cells were attached onto the coverglass in the perfusion chamber and the changes in pHi were measured on the iverted microscope using spectrofluorometer. 1. By switching the perfusate from $HCO_3^-$-free to $HCO_3^-$-buffered solution, pHi decreased by $0.39{\pm}0.02$ pH units followed by a slow increase at an initial rate of $0.04{\pm}0.007$ pH units/min. The rate of pHi increase was reduced to $0.01{\pm}0.002$ pH units/min by the simultaneous addition of 1 mM amiloride and $100{\mu}M$ DIDS. 2. An addition and removal of $NH_4^+$ caused a decrease in pHi which was followed by an increase in pHi. The increase of pHi was almost completely blocked by 1mM amiloride in $HCO_3^-$-free perfusate which implied that the pHi increase was entired dependent on the activation of $Na^+/H^+$ exchanger in $HCO_3^-$-free condition. 3. An addition of $10{\mu}M$ carbachol increased the initial rate of pHi recovery from $0.16{\pm}0.01$ pH units/min to $0.28{\pm}0.03pH$ units/min. 4. The initial rate of pHi decrease induced by 1mM amiloride was also increased by the exposure of the acinar cells to $10{\mu}M$ carbachol ($0.06{\pm}0.008pH$ unit/min) compared with that obtained before carbachol stimulation ($0.03{\pm}0.004pH$ unit/min). 5. The intracellular buffering capacity ${\beta}1$ was $14.31{\pm}1.82$ at pHi 7.2-7.4 and ${\beta}1$ increased as pHi decreased. 6. The rate of $H^+$ extrusion through $Na^+/H^+$ exchanger was greatly enhanced by the stimulation of the cells with $10{\mu}M$ carbachol and there was an alkaline shift in the activity of the exchanger. 7. An intrusion mechanism of $HCO_3^-$ was identified in rat mandibular salivary acinar cells. Taken all together, I observed 3-fold increase in $Na^+/H^+$ exchanger by the stimulation of the acinar cells with $10{\mu}M$ carbachol at pH 7.25. In addition, I have found an additional mechanism for the regulation of pHi which transported $HCO_3^-$ into the cells.

• Korean Journal of Food Science and Technology
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• v.29 no.1
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• pp.77-81
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• 1997

In order to develop a new type of natural seasoning material combining fish meat with seaweed, a processing method of the mixture of enzyme treated mackerel meat and Laminaria powder was studied. Mackerel meat previously boiled and deboned was treated with proteolytic enzyme to enhance taste of meat by proper hydrolysis. The enzyme-treated meat was dried at $100{\pm}2^{\circ}C$ for 4 hrs, and finally mixed with kelp power, moistened in advance, plus binding agents (0.02% calcium carbonate) to aid the formation of pellets by extrusion. Boiled mackerel meat of enzyme treated (0.03% Protease-A) at $50^{\circ}C$ for 90 min was adequate to result an increase in 6 times of total free amino acid content and about 10% increase of taste-enhancing amino acids such as glutamic acid, glycine, arginine, lysine.

• Proceedings of the Korean Powder Metallurgy Institute Conference
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• 2001.11a
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• pp.29-29
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• 2001

열전재료는 열전현상을 가지고 있어 열전발전과 열선냉각이 가능하기 때분에 해저용, 우주용, 군사용의 특수 전원으로 이미 실용화되어있고, 반도체, 레이저 다이오드, 적외선 검출소자 등의 냉각기로 쓰여지고 있어 많은 연구자들이 이들 재료에 대한 연구에 관을 갖고 열전특성을 향상시키기 위하여 많은 연구를 진행하고 있다 이들 열전재료는 사용 온도구역에 따라 3종류로 구분하고 있으며, 실온부근의 저온 영역(20$0^{\circ}C$)이하에서는 $Bi_2Te_3$계 재료, 중온영역(20$0^{\circ}C$~50$0^{\circ}C$)에서sms (Pb,Ge) Te계 재료, 고온영역(50$0^{\circ}C$~lOoo$^{\circ}C$)에서는 Si-Ge계 Fe Si계 재료가 이용되고 있다. 본 연구에서는 실온에서 성능지수가 높은 Bi_2(Te,Se)_3$에 대한 연구를 진행하였다. Bi_2(Te,Se)_3$계 열전재료는 기존의 공법인 Zone melting법을 이용하는 경우 성능지수가 높으나, 단위정이 Rhombohedral 구조파 기저면(basal plane)에 벽개성이 있는 관계로 재료의 적지 않은 손실과 가공상의 어려움이 있다. 또한 사료전체에 걸쳐 화학적으로 균질한 고용체를 얻는 것도 어려운 문제점으보 부각되고 있디 따라서 이와같은 문제점을 보완하기 위하여 용질원자의 편석감소, 고용도의 증가, 균일 고용체 형성, 결정립의 미세화등의 장점이 있는 급속응고법을 본 연구에 응용하였다. 본 연구에서는 위에서와 같은 급속응고의 장점과 대량 가공이 능늪한 연간압출공정을 이용하여 제조된 분말을 성형화 하였다. 특히 열간압출 가공에 있어서 압축다이 각 변화는 재료의 소성유동에 매우 중요한 역하을 하게되며, 이와 갇은 소성유동은 본 재료의 열전특성에 중요한 영향을 미치는 C 면 배양에 중요한 역할을 한 것으 로 기대된다. 이에 본 연구에서는 압출다이 각도 변화에 따른 미세조직변화와 이들 조직이 강도와 열전특성에 미치는 영향을 석하고자 한다. 압출재의 미세조직은 XRD(X Ray Diffraction), SEM(Scanning Electron Microscopy)으로 분석하였으며, 열전특성인 Seebeck계수($\alpha$)와 전기비저항( $\rho$ )은 열전측정장치로, 기계적 강도는 MTS장비를 이용하여 이루어졌다. 또한 압축다이각도 변화에 따른 결정방위 해석은 모노크로미터가 장착된 X RD장비감 이용하여 분석되었다.

• Journal of the korean academy of Pediatric Dentistry
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• v.38 no.3
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• pp.290-295
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• 2011

During tooth formation, tooth development can be affected by physical action or metabolic changes around dental follicle. Especially trauma to primary dentition is the most representative physical factor that can cause development disorders of succedaneous tooth. Enamel hypoplasia and crown discoloration of succedaneous tooth are common complications of trauma. And impaction, ectopic eruption, arrest of root formation and root dilaceration of succedaneous tooth are rare. In this case, a 6-year and 5-month-old female patient visited for dental evaluation after trauma. She was diagnosed with alveolar bone fracture near upper front teeth, extrusion of the upper right and left primary central incisors, intrusion of the upper right primary lateral incisor, and palatal luxation of the upper left primary lateral incisor. Upper right and left primary central incisors with severe mobility were extracted, with gingival suture on the day of the visit. During 24 months check up, root dilacerations were found near the cemento enamel junction in the upper lateral incisors and arrests of root formation were found on the coronal 1/3 of the root in the upper central incisors. Although alveolar bone fracture is rare type of trauma in children, a thorough examination of alveolar bone is essential for prognosis and following treatment in patients with trauma.

• Journal of the Korea institute for structural maintenance and inspection
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• v.26 no.5
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• pp.20-29
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• 2022

In this study, in order to improve the durability of the cement composite printed with the ME type 3D printer, PDMS, sodium silicate, and a surface hardener were employed. Post-treatment was performed on 3D-printed cement composite by coating after immersion, and the degree of improvement in durability was evaluated. As a result, in all evaluations, the durability performances of the post-processed specimens were improved compared to those of the plain specimens. Water absorption resistance, chloride penetration resistance, and carbonation resistance of the PDMS treated specimens were improved by 36.3 %, 77.1 %, and 50.4 % when compared to plain specimens. Freeze-thaw resistance of the specimens treated with sodium silicate was found to be the most excellent, with an average enhancement of 47.5% compared to plain specimens. It was found that PDMS was the most efficient post-treatment materials for 3D-printed cement composite. However, as suggested in this study, the post-treatment method by coating after immersion may not be applicable to cement composite structures printed with a 3D printer in field. Therefore, a follow-up study needs to be preformed on the durability enhancing materials suitable for 3D printing.

• Korean Journal of Animal Reproduction
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• v.23 no.3
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• pp.271-278
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• 1999

This study was conducted to investigate the cytogenetic properties, in vitro development, and their relationship in the bovine reconstituted embryos following cell cycle-controlled nuclear transfer. Sixteen-cell stage embryos were treated by nocodazole, and after release from nocodazole treatment, their blastomeres were separated and allowed to subsequent cleavage. Blastomeres within 1.5 h post cleavage(hpc) and at 3hpc were transferred to enucleated oocytes at MII-phase or S-phase. Donor nuclei transferred into M II-phase recipients underwent various nuclear remodeling, such as extrusion of a polar body(PB)-like structure, premature chromosome condensation(PCC) and chromatin modifications. These nuclear remodeling patterns varied by the time post cleavage of donor blastomeres. Developmental rate to the blastocyst stage differed with time post cleavage of donor blastomeres and existence of a PB-like structure. Whereas do-nor nuclei transferred into S-phase oocytes did not undergo PCC and other major modifications, and their developmental potentials less depended on the nuclei types. This result confirms that the nuclear remodeling type differs with donor and recipient cell cycle stage, which affect the development of reconstituted bovine embryos.

• Journal of the korean academy of Pediatric Dentistry
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• v.28 no.4
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• pp.600-612
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• 2001

The purpose of this study is concerned with an investigation of the actual condition of traumatic injuries of teeth and supporting structures in children to set up possible criteria for prevention and treatment of injured teeth. The materials consisted of the clinical records of 431 traumatically injured teeth of 212 children, accumulated during two years from the first of April in 1998 to the end of March in 2000, supplied from the Dept. of Pediatric Dentistry, Chonbuk National University Hospital. The incidence of injuries in boys was extremely high for permanent teeth, twice as high as in girls. Accidents to primary teeth were most common from 1 to 2 years of age and to permanent teeth were most from 8 to 9 years of age. The most common cause of trauma was a fall for both primary and permanent teeth, followed by collision. The anterior teeth in maxilla was most frequently affected by trauma in both the primary and permanent teeth. The most common type of trauma were loosening for the primary teeth, followed by luxation types which included the intrusion, displacement and extrusion and complete avulsion types. For the permanent teeth, the most common type of trauma were tooth fracture. The most common trauma of soft tissue was laceration of upper lip, lower lip and gingiva of maxilla Concerning treatment at the first visit, primary teeth with only loosening and concussion were not usually treated. Permanent teeth were often treated by crown restorations for crown fractures and by endodontic procedures for pulpal exposure. Though we could elucidate actual condition of traumatic injuries of teeth in children, we should make a follow-up survey to ensure the prognosis of injured teeth and establish the most desirable criteria for traumatized teeth in children.

• Applied Biological Chemistry
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• v.29 no.4
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• pp.407-415
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• 1986

To obtain informations on the development of the combined granular pesticides for the simultaneous control of rice insect pests and diseases which often occur at the same time or in overlapping experiments were carried out on twelve mixture pesticides of granular type formulated by extrusion method with two fungicides and three insecticides. Each of 12 mixtures was tested for physico-chemical properties and efficacy against to rice leaf blast and brown planthoppers under the laboratory conditions. All of the mixture pesticides showed acceptable physico chemical properties as granular formulation. Most of the compounds in mixture pesticides showed a tendency to have lower stabilities than those of pesticide alone, therefore, it was necessary to add stabilizer in formulation process. Isoprothiolane combinations were found very effective against leaf blast but their control effects were similar to that of isoprothiolane alone due to its high efficacy, while probenazole-carbofuran combinations showed synergistic effects for the control of leaf blast. All of the combinations showed synergistic effects to brown planthoppers. But fenthion and 3% propoxur combinations resulted comparatively low efficacies. In the consideration of their physico-chemical properties and efficacies to rice pests, carbofuran and 6% propoxur combinations were promising combined granular pesticides for the simultaneous control of leaf blast and brown planthoppers, while fenthion and 3% propoxur combinations were not available because of their low efficacies for brown planthoppers.