• 한국표면공학회:학술대회논문집
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• 한국표면공학회 2018년도 춘계학술대회 논문집
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• pp.23-23
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• 2018

In this study, new titanium alloys were prepared by adding elements such as tantalum (Ta), zirconium (Zr) and the like to complement the biological, chemical and mechanical properties of titanium alloys. The Ti-40Ta-xZr ternary alloy was formed on the basis of Ti-40Ta alloy with the contents of Zr in the contents of 0, 3, 7 and 15 wt. %. Plasma electrolytic oxidation (PEO), which combines high-voltage sparks and electrochemical oxidation, is a novel method to form ceramic coatings on light metals such as Ti and its alloys. These oxide film produced by the electrochemical surface treatment is a thick and uniform porous form. It is also composed of hydroxyapatite and calcium phosphate-based phases, so it has the characteristics of bone inorganic, non-toxic and very high bioactivity and biocompatibility. Ti-40Ta-xZr alloys were homogenized in an Ar atmosphere at $1050^{\circ}C$ for 1 hour and then quenched in ice water. The electrochemical oxide film was applied by using a power supply of 280 V for 3 minutes in 0.15 M calcium acetate monohydrate ($Ca(CH_3COO)_2{\cdot}H_2O$) and 0.02 M calcium glycerophosphate ($C_3H_7CaO_6P$) electrolyte. A small amount of 0.0075M zinc acetate and magnesium acetate were added to the electrolyte to enhance the bioactivity. The mechanical properties of the coated surface of Ti-40Ta-xZr alloys were evaluated by Vickers hardness, roughness test, and elastic modulus using nano-indentation, and the surface wettability was evaluated by measuring the contact angle of the coated surface. In addition, cell activation and differentiation were examined by cell culture of HEK 293 (Human embryonic kidney 293) cell proliferation. Surface properties of the alloys were analyzed by scanning electron microscopy(FE-SEM), EDS, and X-ray diffraction analysis (XRD).

• Restorative Dentistry and Endodontics
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• 제44권3호
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• pp.28.1-28.10
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• 2019

Objectives: The aim of this study was to evaluate the influence of different concentrations of nanofillers on the chemical and physical properties of ethanol-solvated and non-solvated dental adhesives. Materials and Methods: Eight experimental adhesives were prepared with different nanofiller concentrations (0, 1, 2, and 4 wt%) and 2 solvent concentrations (0% and 10% ethanol). Several properties of the experimental adhesives were evaluated, such as water sorption and solubility (n = 5, 20 seconds light activation), real-time degree of conversion (DC; n = 3, 20 and 40 seconds light activation), and stability of cohesive strength at 6 months (CS; n = 20, 20 seconds light activation) using the microtensile test. A light-emitting diode (Bluephase 20i, Ivoclar Vivadent) with an average light emittance of $1,200mW/cm^2$ was used. Results: The presence of solvent reduced the DC after 20 seconds of curing, but increased the final DC, water sorption, and solubility of the adhesives. Storage in water reduced the strength of the adhesives. The addition of 1 wt% and 2 wt% nanofillers increased the polymerization rate of the adhesives. Conclusions: The presence of nanofillers and ethanol improved the final DC, although the DC of the solvated adhesives at 20 seconds was lower than that of the non-solvated adhesives. The presence of ethanol reduced the strength of the adhesives and increased their water sorption and solubility. However, nanofillers did not affect the water sorption and strength of the tested adhesives.

• 대한의용생체공학회:의공학회지
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• 제25권3호
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• pp.201-206
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• 2004

뼈의 형성과 재형정은 조골세포에 의한 골기질의 합성과 파골세포에 의한 재흡수에 의해 조절된다. 최근에는 골형성세포의 활성화를 통한 골조직의 재생 및 치유에 대한 연구가 활발히 이루어지고 있다. 골형성 세포의 활성화는 생물학적 자극뿐만 아니라 물리적 자극에 의해서도 영향을 받는 것으로 알려져 있다. 본 연구에서는 물리적 자극 가운데에서 연구가 거의 되지 않은 저강도 초음파가 골형성 세포의 활성에 미치는 영향을 조사하였다. 이를 위하여 우선 다양한 특성의 초음파를 사용함으로써 세포활성에 미치는 최적의 초음파 조건을 결정하였다 본 연구 결과 전체 duty cycle에서 초음파 강도가 0.3W/$\textrm{cm}^2$일 경우가 세포활성에 가장 적합하며 duty cycle 50%인 경우 최고의 세포수 증가율을 나타내었다. 이와 같이 골조직의 재생에 적합한 초음파의 특성을 결정하여 골절 및 골다공증의 치료에 초음파를 활용할 수 있을 것으로 사료된다.

• 한국전기전자재료학회논문지
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• 제15권5호
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• pp.441-448
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• 2002

The electrical properties of the GaN-based green light emitting diodes(LEDs) with the Mg-doped p-GaN layer activated in $N_2$ or $O_2$ ambient have been compared. For the $N_2$ -ambient activation the current-voltage behavior of LEDs has been found to be improved when the Mg dopants activation was performed in the higher temperature. However, for the $O_2$-ambient activation the current-voltage characteristic has been observed to be enhanced when the Mg dopants activation was carried out in the lower temperature. The minimum forward voltage at 20mA was obtained to be 4.8 V for LEDs with the p-GaN layer activated at $900^{\circ}C$ in the $N_2$ ambient and 4.5V for LEDs with the p-GaN layer treated at $700^{\circ}C$ in the $O_2$ambient, repectively. The forward voltage reduction of the LEDs treated in the $O_2$-ambient may be related to the oxygen co-doping of the p-GaN layer during the activation process. The $O_2$ -ambient activation process is useful for the enhancement of the LED performance as well as the fabrication process since this process can activate the Mg dopants in the low temperature.

• Korean Chemical Engineering Research
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• 제52권2호
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• pp.166-174
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• 2014

본 연구에서는 점화제로 사용되는 $B-KNO_3$의 가속노화 실험에 따른 특성변화를 고찰하였다. 점화제는 보관 방법이나 보관기간에 따라 점화 효율이 저하되는 경향이 있으며 안정된 사용을 위해서는 이에 대한 명확한 이해가 필요하다. 따라서 노화에 대한 원인 규명을 위해 가속화 시험 시편의 미세구조와 결정구조 및 열분석을 수행하였으며 점화 특성에 끼치는 영향성을 규명하고자 하였다. 산화제로 첨가된 $KNO_3$의 결정구조를 분석함으로써 노화에 끼치는 산화제 영향을 해석하였다. 결론적으로 산화제의 결정구조가 안정한 구조로 변화되었으며 활성화 에너지변화에 영향을 끼쳤다.

• 한국철도학회논문집
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• 제13권4호
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• pp.357-362
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• 2010

1899년에 철도가 부설된 이후 철도관련시설은 근대화의 상징이다. 그러나 증기기관차의 운행이 중단된 후 급수탑은 방치된 시설이었다. 근대문화유산의 가치를 살린 급수탑 주변 요소에 따른 활성화 방안은 다음과 같다. 1)근대사의 현장성과 예술 작품의 배경 지역을 이용 2)주변 장소와 연계한 공원화 3)산업유산의 전시시설 4)지역의 역사유적 5)급수설비의 재생이 필요하다. 지방 자치단체의 기획 단계부터 전문가 집단의 조언과 지역주민의 활발한 참여가 필요하며, 급수탑 활성화가 도시정비차원에서 이루어져야 한다.

• 대한의용생체공학회:의공학회지
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• 제9권1호
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• pp.47-60
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• 1988

N-n-Propylacrylamide는 n-propyl bromide와 acrylamide로 부터 합성하였고, 합성된 N-n-propylacrylamide를 THF용매속에서 개시제로 AIBN을 사용하여 $60^{\circ}C$에서 acrylamide와 공중합시켰다. 그리고 합성된 단량체와 공중합체는 NMR과 IR에 의하여 확인하였다.

• Nuclear Engineering and Technology
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• 제49권8호
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• pp.1748-1751
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• 2017

Reduced activation ferritic/martensitic (RAFM) steels are widely applied as structural materials in the nuclear industry. To investigate hydrogen's effect on RAFM steels' elastic properties and the mechanism of that effect, a procedure of first principles simulation combined with experiment was designed. Density functional theory models were established to simulate RAFM steels' elastic status before and after hydrogen's insertion. Also, experiment was designed to measure the Young's modulus of RAFM steel samples with and without hydrogen charging. Both simulation and experiment showed that the solubility of hydrogen in RAFM steels would decrease the Young's modulus. The effect of hydrogen on RAFM steels' Young's modulus was more significant in water-quenched steels than it was in tempering steels. This indicated that defects inside martensite, considered to be hydrogen traps, could decrease the cohesive energy of the matrix and lead to a decrease of the Young's modulus after hydrogen insertion.

• 한국지능시스템학회:학술대회논문집
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• 한국퍼지및지능시스템학회 1998년도 The Third Asian Fuzzy Systems Symposium
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• pp.399-403
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• 1998

In this paper, we proposed a new fuzzy supervised learning algorithm. We construct, and train, a new type fuzzy neural net to model the linear activation function. Properties of our fuzzy neural net include : (1) a proposed linear activation function ; and (2) a modified delta rule for learning algorithm. We applied this proposed learning algorithm to exclusive OR,3 bit parity using benchmark in neural network and pattern recognition problems, a kind of image recognition.

• Carbon letters
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• 제12권2호
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• pp.70-80
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• 2011

Two pitches with different average molecular structures were electrospun and compared in terms of the properties of their fibers after oxidative stabilization, carbonization, and activation. The precursor with a higher molecular weight and greater content of aliphatic groups (Pitch A) resulted in better solubility and spinnability compared to that with a lower molecular weight and lower aliphatic group content (Pitch B). The electrical conductivity of the carbon fiber web from Pitch A of 67 S/cm was higher than that from Pitch B of 52 S/cm. The carbon fiber web based on Pitch A was activated more readily with lower activation energy, resulting in a higher specific surface area compared to the carbon fiber based on Pitch B (Pitch A, 2053 $m^2/g$; Pitch B, 1374 $m^2/g$).