• 한국분말재료학회지
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• 제25권3호
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• pp.220-225
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• 2018

The microstructure and mechanical characteristics of SUS630 specimens fabricated using the direct energy deposition (DED) process are investigated. In DED, several process parameters such as laser scan speed, chamber gas flow, powder carrier gas flow, and powder feed rate are kept fixed; the laser power is changed as 150 W, 180 W, and 210 W. As the laser power increases, the surface becomes smooth, the thickness uniformity improves, and the size and number of pores decreases. With the increase in laser power, the hardness deviation decreases and the average hardness increases. The microstructure of the material is columnar; pores are formed preferentially along the columnar interface. The lath-martensite phase governs the overall microstructure. The volumetric fraction of the retained austenite phase is measured to increase with the increase of laser input power.

• 한국신뢰성학회지:신뢰성응용연구
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• 제15권4호
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• pp.270-275
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• 2015

Purpose : UHMWPE (Ultra-high-molecular-weight-polyethylene) is one of the most widely used material in knife protection clothes because of high strength, elasticity, and light weight. The purpose of this study is to develop the accelerated life test method and predict the lifetime for the knife protection fabric composed by UHMWPE. Methods : In this study, degradation characteristics of UHMWPE fibers and knife protection fabric for cut resistance were evaluated under the hydrolysis and photo-degradation conditions. It was found out that the degradation rate of retained tensile strength was more significant in the photo-degradation than hydrolysis. Therefore, the failure time was determined as the time that the retained tensile strength in photo-degradation is less than 50%. Considering an acceleration factor for irradiance and exposure time, the lifetime was predicted from the calculated failure time. Results : As a result of the accelerated life test, the $B_{10}$ lifetime of knife protection fabric composed by UHMWPE fibers is estimated as 2.8 years for a 90% statistical confidence level. Conclusion: Since the lifetime is predicted by the view-point of radiant exposure in this study, there is a possibility that the estimated lifetime may differ from the actual lifetime. However, it is considered as an useful methodology to estimate the long-term lifetime of knife protection fabrics.

• 한국생산제조학회지
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• 제8권1호
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• pp.81-88
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• 1999

This paper was carried out to know the influence of advanced austempered ductile cast iron (ADI) on the tool life and mechanical properties of drilling machinability. For manufactured method of ADI, the spheroidal graphite cast iron were austenized at 90$0^{\circ}C$ for 1 hour and then austempered for 2 hour at 37$0^{\circ}C$ in the salt bath. And interrelationship has been investigated between tool life and mechanical characteristics of specimen material on drilling condition when the ordinary and step-feed drilling are carried out to drill holes of specimens. Tensile strength and hardness of ADI decrease and elongation of ADI increases with the increase austempered temperature. It is known that about 2 times of tool life in the case of step-feed decreases compared with ordinary feed due to the high hardness of ADI and hardness ascribed to the fact that retained austenite became to martensite state due to cutting heat in drilling. Under the constant feed rate 0.1mm/rev relation between hardness and length of end tip after drilling can be formularized to Hv=$788.46L^{-0.096}$ for the cutting speed 6.1m/min.

• The Journal of Advanced Prosthodontics
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• 제12권1호
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• pp.38-48
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• 2020

PURPOSE. The objective of this literature review was to analyze the cumulative survival rates (CSRs) of rigid and non-rigid double-crown-retained removable dental prostheses. MATERIALS AND METHODS. Screening of the literature published from January 1995 to December 2019 was performed by using electronic data base (Pubmed) and manual search. The CSRs of rigid and non-rigid double crown removable dental prostheses were investigated. RESULTS. A total of 403 articles were reviewed and 56 relevant articles of them were selected. Subsequently, 25 articles were included for data extraction. These articles were classified according to rigid and non-rigid type double crowns and further subdivided into teeth, implants, and teeth-implant combination types. The CSRs of rigid type double crown ranged from 68.9% to 95.1% of 5 to 10 years in tooth abutments, 94.02% to 100% over a 3-year mean observation periods in implant abutments, and 81.8% to 97.6% in tooth-implant combination. Non-rigid type double crowns had various CSR ranges from 34% to 94% maximum during 10 years observation in teeth abutment. The CSRs of non-rigid type had over 98% in implant abutments, and ranged from 85% to 100% in tooth-implant combination. CONCLUSION. The CSRs of double crowns varies according to types. With accurate evaluation of the remaining teeth and plan of the strategic implant placement, it could be successful treatment alternatives for partially or completely edentulous patients.

• 생명과학회지
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• 제20권11호
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• pp.1656-1661
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• 2010

난황단백질 가수분해를 위한 알칼리성 단백질분해효소를 5가지 담체 Duolite A568, Celite R640, Dowex-1, Dowex 50W 그리고 Silica gel R60 에 고정화하였다. Duolite A568의 경우에 24.7%의 최대 고정화 효율을 나타내었다. 자유 효소와 고정화 효소에 대한 최적의 pH는 각각 8과 9였고, 최적의 pH는 고정화에 의해 염기성으로 1만큼 증가하였다. 그러나 최적 온도는 자유 효소와 고정화 효소 모두 $50^{\circ}C$로 같았다. 고정화 효소가 자유 효소에 비해 높은 열 안정성을 보였다. 재사용 회분식 공정에서 10 cycle 동안 효소활성은 초기 활성의 86%를 유지하였다. 연속 공정을 위한 충진층 반응기에서 여러 유속에 대한 장기 조업에서 효소 활성의 안정성 평가하였는데 낮은 유속일수록 높은 활성을 유지하였다. 연속 조업에서 casein과 난황 단백질을 사용하여 원료에 대한 고정화 효소의 활성에 대한 영향을 조사하였다. 96시간 연속 조업에서 casein의 경우는 초기 활성의 83%를 유지하였고 난황 단백질의 경우는 초기 활성의 61%를 유지하였다.

• 열처리공학회지
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• 제4권1호
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• pp.1-12
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• 1991

This study has been performed to find out the effect of austenitizing temperature, austempering temperature and its holding time, and tempering cycle on the mechanical properties such as impact resistance, hardness etc. of AISI $M_2$ Mo series high speed tool steel austempered or tempered after austempering treatment. The results obtained from the experiment are as follows ; (1) Optical micrograph has revealed that the transformation rate of bainite is delayed as the austenitizing temperature increases and that bainite is most apparently transformed at an austempering temperature of $290^{\circ}C$. (2) The amount of retained austenite during austempering has been analysed to be increased by the X-ray diffraction technique as the transformation product of bainite is increased. It has also been shown that the longer the holding time of austempering, the more the transformation quantity of bainite is formed, exhibiting, however, that the rate of bainitic transformation is considerably retarded after a certain period of holding time elapses. (3) Hardness measurement has shown that hardness values obtained after austempering increase with decreasing the amount of retained austenite. (4) The austempering and then tempering cycle has been formed to give hardness values which are more greatly improved as austenitizing temperature is increased. (5) The mechanical property of the specimen primary-tempered for 1 hour at $550^{\circ}C$ after austempering for 2 hours at $290^{\circ}C$ from the austenitizing temperature range of $1180^{\circ}C$ to $1210^{\circ}C$ have been estimated to be good values.

• 무역학회지
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• 제41권3호
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• pp.177-198
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• 2016

중국은 1979년부터 본격적으로 시장경제체제를 도입함으로써 급격한 경제성장을 이루었는데, 본고는 저임금과 중국정부의 적극적인 외자유치정책을 활용하기 위해 밀려들어온 외국인투자에 어떤 요인들이 영향을 미쳤는지를 검토하기 위해 1979년부터 2013년까지의 패널데이터를 이용해서 각 성·시의 고유한 특성까지 활용하는 실증분석을 시도한다. 실증분석을 위해 본고는 확률효과모형, 고정효과모형, Pooled OLS, 그리고 확률계수모형을 사용하는데, Pooled OLS와 확률계수모형의 결과는 본 연구의 분석결과와 비교를 위해서 제시된다. Hausman' test 결과 Random Effect Model보다는 Fixed Effect Model이 더 효율적인 분석결과를 제시하는 것으로 나타나 이를 근거로 중국정부에 대한 정책적 시사점을 제시한다. 분석결과는 FDI유입에 각 성·시의 지역소득수준, 자본량, 통신비는 긍정적인 영향을 미치고 고속도로는 부정적인 영향을 미치는 것으로 나타난다.

• 생물환경조절학회지
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• 제14권3호
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• pp.182-189
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• 2005

본 연구는 혼합상토의 보수성 증가를 위하여 polyacrylamide 고흡수성 수지 Stocksorb C를 혼합할 경우 상토의 물리성에 미치는 영향을 밝히기 위하여 수행하였다. 네종류 혼합상토, 피트모쓰 + 버미큘라이트(1:1 , v/v; PV), 피트모쓰+부숙왕겨(1:1, v/v; PR), 피트모쓰+부숙톱밥(1:1, v/v; PS), 그리고 피트모쓰+부숙수피(1:1, v/v; PB)를 조제하는 과정에서 STSB를 혼합하고, 플라스틱 포트에 충전하였으며, 5주 후에 상토의 물리적 특성을 측정하였다. STSB의 혼합비율이 증가할수록 PV, PS 및 PB 상토의 공극률이 증가하여 $5{\%}$ 수준의 통계적인 차이가 인정되었고, 직선 또는 2차곡선회귀가 성립하여 경향을 찾을 수 있었다. STSB의 혼합비율 증가로 PS와 PB상토의 용기용수량이 뚜렷하게 증가하였으나 PV 및 PR상토에서는 STSB의 혼합비율에 따른 처리간 차이가 인정되지 않았다. 특히 STSB의 혼합은 PV PS및 PB 상토의 기상률을 뚜렷하게 증가시켜 처리간 통계적인 차이와 함께 직선 및 2차곡선회귀가 성립하여 경향이 뚜렷하였다. 고흡수성 수지의 혼합비율이 높아질수록 4.90 kPa, 9.81 kPa, 29.4 kPa및 1.5 MPa 토양 수분장력 하에서 존재하는 수분량이 많았다. 각 상토별로 29.4 kPa이나 1.5 MPa에서 존재하는 수분은 PV 혼합상토에서 적었고, PB와 PR 혼합상토에서 유사한 수준이었으며, PS 혼합상토에서 가장 많았다. 이는 고흡수성 수지의 혼합비율이 높아짐에 따라 상토가 보유하는 수분량이 증가하지만 식물이 쉽게 흡수할 수 있는 수분량이 증가하지 않음을 의미한다.

• Food Science and Biotechnology
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• 제18권2호
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• pp.330-335
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• 2009

The principal objective of this study was to investigate changes in ice dendrite size during the freezing of tuna, in order to formulate a mathematical model of ice dendrite size. The tuna was frozen via a uni-directional heat transfer. Thermogram analysis allowed us to determine the position of the freezing front versus time, which is referred to as the freezing front rate. The morphology of the ice dendrites was assessed via scanning electron microscopy after freeze-drying, and the retained pore size was measured as ice dendrites. We noted that the mean size of ice dendrites increased with the distance to the cooling plate; however, it decreased with reductions in the cooling rate and the cooling temperature. In addition, shorter durations of the freeze-drying process decreased the freezing front rate, resulting in a larger size of the ice dendrite pores that operate as water vapor sublimation channels. According to our results, we could derive a linear regression as an empirical mathematical model equation between the ice dendrite size and the inverse of the freezing front rate.

• 대한치과보철학회지
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• 제42권1호
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• pp.83-93
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• 2004

Statement of problem : Since the concept of osseointegrated dental implant by $Br{\aa}nemark$ et al was first applied to mandibular full edentulous patients. Recently it is considerated the first treatment option on missing teeth. A common problem associated with dental implant restorations is loosening of screws that retain the prosthesis to the abutment and the abutment to the implant fixture. Purpose : This study is to examine the influence on screw loosening of implant-abutment designs. Material and methods : External hex, cone screw, beveled hex, cam cylinder, cylinder hex by means of evaluating the loosening torques, with respect to a range of tightening torques after repeated loading. Result : 1. Cone screw, beveled hex groups are the highest initial tightening rate and cylinder hex, external hex groups are the lowest initial tightening rate (p < 0.05). 2. Cone screw groups are the highest after repeated loading tightening rate and cylinder hex groups are lowest after repeated loading tightening rate(p < 0.05). 3. Cone screw groups have the highest initial stability and anal stability. 4. All groups are decreased tightening rate after repeated loading.