공중합에 의해 개질된 온도응답성 하이드로젤의 팽윤거동 및 체적 전이온도 변화

김형일 충남대학교 산업기술연구소 2003 산업기술연구논문집 Vol.18 No.1

The phase transition behavior of temperature-responsive N-isopropylacrylamide-based hydrogels depended on both the composition of hydrogel and the polymerization temperature. Photopolymerization was carried out in order to prepare hydrogels under the consistent condition without the effect of polymerization temperature. N-isopropylacrylamide-based hydrogels showed the improved optical transparency even for the thick slab gels as the polymerization temperature decreased. Poly(ethylene glycol) segments were grafted on the N-isopropylacrylamide-based hydrogels in order to modify the hydrogel to have enhanced hydrophilicity and biocompatibility. Increased hydrophilicity of hydrogel was responsible for the increase in both swelling ratio and volume transition temperature. The increase in the crosslinker content resulted to the higher crosslink density and less loading volume although the volume transition temperature remained unaffected. The release of r-aminobutyric acid from these temperature-responsive hydrogels had a close relation with the swelling ratio and the volume transition temperature.

특수교육교사 양성대학의 실무중심 교육과정 개선을 위한 재학생 및 현장교사 요구 분석

김형일,김희규,정동훈,채희태 나사렛대학교출판사 2007 지성과 창조 Vol.- No.10

본 연구는 대학의 교육이념과 특성화를 구현하면서 실무능력을 갖춘 특수교육 전문 인력을 배양하기 위하여 현재 특수교육과에 재학 중인 학생들과 현직 교사들을 대상으로 현행 교육과정에 대한 실태와 문제점을 파악하고 개선을 위한 요구를 조사하여 특수교육전공 교육과정을 개선하는데 그 기초적인 자료로 활용하고자 하였다. 개선된 교육과정을 통하여 예비특수교육교사 양성의 질을 높이고 교육과정을 보다 효율적이고 현장실무중심으로 운영할 수 있는 방안을 마련하고자 하였다. The present study surveyed the demands of 120 students of the department of special education and 70 field teachers to order to identify problems in the curriculums of the Department of Special Education and improving the curriculums for educating special teachers based on the opinions of field teachers and students at the Department of Special Education. The improved curriculums are expected to enhance the quality of education for the candidates of special education teachers and to be executed more effciently and practically in the field of education.

貴金屬을 포함하는 齒料鑄造用 代用合金의 特性 : EFFECT OF PALLADIUM ADDITION ON THE ATOMIC ORDERING AND AGE-HARDENING BEHAVIOR OF EQUIATOMIC AuCu ALLOY 等原子比 AuCu合金의 規則化와 時效硬化 擧動에 미치는 Pd添加의 影響

白石孝信,太田道雄,中川雅晴,金炯一 大韓齒科器材學會 1993 대한치과재료학회지 Vol.20 No.1

The effect of palladium addition up to 6at% to an equiatomic AuCu alloy on the atomic ordering and age-hardening behavior was studied by means of electrical resistivity measurements, X-ray diffraction and hardness test. The following results were obtained. 1. All alloys in the AuCu-Pd pseudo-binary system examined in this study exhibited a single phase with AuCu Ⅰ type ordered structure by the aging at 300℃, and the axial ratio(c/a) became larger than that of stoichiometric AuCu Ⅰ ordered lattice. 2. The order-disorder transition temperature(Tc) rose with increasing the palladium concentration. 3. With increasing the palladium concentration, age-hardening rate in the early stage of aging became slower and the onset of overaging delayed. This was attributed to the fact that ordering rate decreased with increasing the palladium concentration.

L929 및 CV1 세포를 사용한 한천중층법에서 치과용 합금의 독성 비교

조욱희,윤일,최석규,김형일 大韓齒科器材學會 1993 대한치과재료학회지 Vol.20 No.2

Biocompatability of pure gold, Au alloy, pure titanium, Ti alloy, Ni-Cr alloy, Co-Cr alloy and pure copper was assessed through the agar overlay test using L929 and CV1 cells. Pure gold, pure titanium and Ti alloy had none to mild cytotoxicity, Ni-Cr, Co-Cr and gold alloy had mild to moderate cytotoxicity and pure copper had severe cytotoxicity. Generally, L929 cells were more sensitive to toxic substances than CV1 cells. The application of human gingival fibroblast to the agar overlay method seemed not to be proper.

치과교정용 초탄성 Nitinol 선재의 피로특성

최석규,박익민,김형일 大韓齒科器材學會 1992 대한치과재료학회지 Vol.19 No.2

Nickel-titanium(NiTi) alloy wires are now widely used in the medical field because of their unique shape memory effect and superelasticity. The purpose of this study is to investigate the effects of mechanical fatigue and thermal cycling fatigue in orthodontics NiTi wire. The fatigue test was performed by three point bending fatigue test(No. of 4000, 8000, 12000, 16000) and tension-compression fatigue test(No. 1000, 2000, 3000, 4000) and thermal cycling fatigue test(No. 500, 1000). The results were as follows : 1. Strength, orthodontic force and transformation temperature(As, ??) were decreased with increasing number of fatigue cycle due to the coarsening of precipitations and increased density of dislocations. 2. Orthodontic force was slightly increased with number of cycle in thermal cycling fatigue due to the cohesion of precipitations and high density of dislocations.

치과 주조용 저금합금의 개발에 관한 연구

김교한,김형일 대한치과기재학회 1996 대한치과재료학회지 Vol.23 No.2

The purpose of this study was to develop the dental casting low carat gold alloys based upon Au-Ag-Cu ternary alloy. Three types of low carat gold alloy containing 46, 55 and 66wt. % of gold, content respectively, which were balanced with total amount of Au plus Ag of 74wt. %, were melted and casted to evaluate the mechanical properties, corrosion resistance, melting range and cytotoxicity. The obtained results were summarized follows : ·In mechanical properties, the type K-Ⅱalloys, which was increased in the amount of Pt component, showed 115MPa of yield strength, 400MPa of ultimate tensile strength and 150 of vicker's hardness value and these values are higher than those of K-Ⅰ, K-Ⅲ alloy of 30% in yield strength, 50% in ultimate tensile strength and 10% in hardness value. ·Age hardening effect was confirmed in all three alloys. ·Melting ranges of these alloys were in the range of 910-1050℃ ·Higher corrosion resistance was confirmed in the potential range of oral cavith. ·The cytotoxicity of alloys was evaluated by the cell growth and morphologic changes, Each alloy showed normal growth rate and cellular morphology.

국산화 개발한 치과용 저금합금의 시효경화 거동

김교한,권오원,김형일 대한치과기재학회 1997 대한치과재료학회지 Vol.24 No.1

To define the optimum heat treatment temperature and time of the developed three types of low karat gold alloys, hardness test, DTA and x-ray diffraction methods were used. The results were as follows. *The optimum temperature of heat treatment was at 400℃ in K-Ⅰ, K-Ⅱ and K-Ⅲ alloys. *The proper time of age-hardening was 10 minute in K-Ⅰ alloy, and 10-30-minutes in K-Ⅱ alloys. *The stable phases of three types of low karat gold alloys were Ag-rich α₁ phase, Cu-rich α₂ phase and AuCuⅠ phase in case of K-Ⅰ alloy, and α1 phase and AuCuⅠ phase were coexisted in K-Ⅱ and K-Ⅲ alloy. *The cause of the decrease of hardness by overageing was the α₁ phase and AuCu Ⅰ phase, which were precipitated in the grain boundary.

치과용 고카라트 금합금의 시효경화와 상변태 과정

배동화,설효정,이희경,김형일 대한치과기재학회 1999 대한치과재료학회지 Vol.26 No.1

The hardening behavior and phase transformation process of a dental high carat gold alloy by isothermal ageing treatment were investigated by means of hardness testing, X-ray diffraction study and scanning electron microscopic observations. The following results were obtained. The a single phase with a face centered cubic structure was finally transformed into the coexistence of the Ag-rich α₁phase with a face centered cubic structure and the AuCu I' type ordered phase with a face centered tetragonal superlattice structure by ageing of the solution-treated specimen at 400℃ and 500℃. By ageing at 500℃, the metastable Ag-rich α₁' and AuCu I' type ordered phases were formed prior to the final formation of the equilibrium Ag-rich α₁ and AuCu I type ordered phases . The hardening effect was more significant and the overageing with softening was slower by ageing at 400℃ than 500℃. By ageing at 500℃, the hardening was attributed to the formation of the metastable AuCu I' type ordered phases from the a phase, the overageing with softening was due to the formation of the AuCu I type ordered phase from the metastable Ag-rich α₁' and AuCu I' type ordered phases. By ageing at 500℃, the incubation period which limited the beginning of the hardening in the early stage of ageing existed, and the formation and growth of the precipitates which contributed the overageing with softening were observed concurrently at the grain boundaries and within grains. By ageing at 400℃, the hardening was attributed to the formation of the AuCu I type ordered phase from the a phase, the overageing with softening was due to the growth of the grain boundary precipitates of the lamellar structure composed of the Ag-rich α₁and AuCu I type ordered phases into the grain interior.

열처리가 Elgiloy 선재의 기계적 성질에 미치는 영향

이병태,허택,최석규,김형일 대한치과교정학회 1992 대한치과교정학회지 Vol.22 No.3

Heat treatment which removes internal stress enhances the mechanical properties of the orthodontic arch wire. The main purpose of this experiment was to investigate the effects of the heat treatment on the mechanical properties of the Elgiloy wire. The Elgiloy wire, 0.016"X0.022" and 0.018"X0.025", were heat treated in an electric oven for 5, 10 and 15 minutes at selected temperatures between 300 and 900℃. Tensile strength and load deflection rate were measured to reveal the changes of mechanical property at various conditions, and each specimen was observed under metallurgic microscope. Also to trace the precipitation material due to overheat treatment, a qualitative analysis was carried out with EDS system. It was found that heat treatment at a low temperature caused an increase in the tensile strength and bending resistance, and a maintenance in the fibrous in the tensile strength and bending resistance, and a maintenance in the fibrous structure of both sizes of wire. The changes observed in properties and appearance were probably due to the relief of internal stresses incurred in the metal during cold working. In both sizes of wire the tensile strength and the bending resistance continued to decrease at high temperature, and the fibrous structure continued to disappear then was not observed at 900℃. The carbide precipitation founded in grain boundary at 750℃ probably was other elements carbide (Ni, Ca) except Cr. The grain growth was observed at 1100℃. Optimum heat treatment for the 0.016"X0.022" Elgiloy wire was 10 minutes at 500℃, and for the 0.018"X0.025: Elgiloy wire it was 5 to 15 minutes at 500℃.

換率變動性推定의 時計列分析方法論 硏究

김형일 東亞大學校 大學院 1999 大學院論文集 Vol.24 No.-

Exchange rate volatility and its expectation have long been discussed since the free floating exchange rate system had been established in 1973. However nobody could have discovered the method of solving out the right equilibrium rates in the future. The purpose of this paper is to represent the time series analysis method of the estimation on the exchange rate volatility. Whether time series data are stable or not, depends on the existence of unit root. The unit root is tested in this purpose. The methods on testing the unit root such as Philips-Perron test and Dckey-Fuller test will be studied in the following paper.