• 한국분말야금학회:학술대회논문집
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• 한국분말야금학회 2001년도 추계학술강연 및 발표대회
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• pp.7-7
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• 2001

The increasing interest in light weight materials coupled to the need for cost -effective processing have combined to create a significant opportunity for aluminum P/M. particularly in the automotive industry in order to reduce fuel emissions and improve fuel economy at affordable prices. Additional potential markets for Al PIM parts include hand tools. Where moving parts against gravity represents a challenge; and office machinery, where reciprocating forces are important. Aluminum PIM adds light weight, high compressibility. low sintering temperatures. easy machinability and good corrosion resistance to all advantages of conventional iron bm;ed P/rv1. Current commercial alloys are pre-mixed of either the AI-Si-Mg or AL-Cu-Mg-Si type and contain 1.5% ethylene bis-stearamide as an internal lubricant. The powder is compacted in closed dies at pressure of 200-500Mpa and sintered in nitrogen at temperatures between $580~630^{\circ}C$ in continuous muffle furnace. For some applications no further processing is required. although most applications require one or more secondary operations such as sizing and finishing. These sccondary operations improve the dimension. properties or appearance of the finished part. Aluminum is often considered difficult to sinter because of the presence of a stable surface oxide film. Removal of the oxide in iron and copper based is usually achieved through the use of reducing atmospheres. such as hydrogen or dissociated ammonia. In aluminum. this occurs in the solid st,lte through the partial reduction of the aluminum by magncsium to form spinel. This exposcs the underlying metal and facilitates sintering. It has recently been shown that < 0.2% Mg is all that is required. It is noteworthy that most aluminum pre-mixes contain at least 0.5% Mg. The sintering of aluminum alloys can be further enhanced by selective microalloying. Just 100ppm pf tin chnnges the liquid phase sintering kinetics of the 2xxx alloys to produce a tensile strength of 375Mpa. an increilse of nearly 20% over the unmodified alloy. The ductility is unnffected. A similar but different effect occurs by the addition of 100 ppm of Pb to 7xxx alloys. The lend changes the wetting characteristics of the sintering liquid which serves to increase the tensile strength to 440 Mpa. a 40% increase over unmodified aIloys. Current research is predominantly aimed at the development of metal matrix composites. which have a high specific modulus. good wear resistance and a tailorable coefficient of thermal expnnsion. By controlling particle clustering and by engineering the ceramic/matrix interface in order to enhance sintering. very attractive properties can be achicved in the ns-sintered state. I\t an ils-sintered density ilpproaching 99%. these new experimental alloys hnve a modulus of 130 Gpa and an ultimate tensile strength of 212 Mpa in the T4 temper. In contest. unreinforcecl aluminum has a modulus of just 70 Gpa.

• Steel and Composite Structures
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• 제34권5호
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• pp.681-698
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• 2020

The paper addresses contribution to the modeling and optimization of major machinability parameters (cutting force, surface roughness, and tool wear) in finish dry hard turning (FDHT) for machinability evaluation of hardened AISI grade die steel D₃ with PVD-TiN coated (Al₂O₃-TiCN) mixed ceramic tool insert. The turning trials are performed based on Taguchi's L₁₈ orthogonal array design of experiments for the development of regression model as well as adequate model prediction by considering tool approach angle, nose radius, cutting speed, feed rate, and depth of cut as major machining parameters. The models or correlations are developed by employing multiple regression analysis (MRA). In addition, statistical technique (response surface methodology) followed by computational approaches (genetic algorithm and particle swarm optimization) have been employed for multiple response optimization. Thereafter, the effectiveness of proposed three (RSM, GA, PSO) optimization techniques are evaluated by confirmation test and subsequently the best optimization results have been used for estimation of energy consumption which includes savings of carbon footprint towards green machining and for tool life estimation followed by cost analysis to justify the economic feasibility of PVD-TiN coated Al₂O₃+TiCN mixed ceramic tool in FDHT operation. Finally, estimation of energy savings, economic analysis, and sustainability assessment are performed by employing carbon footprint analysis, Gilbert approach, and Pugh matrix, respectively. Novelty aspects, the present work: (i) contributes to practical industrial application of finish hard turning for the shaft and die makers to select the optimum cutting conditions in a range of hardness of 45-60 HRC, (ii) demonstrates the replacement of expensive, time-consuming conventional cylindrical grinding process and proposes the alternative of costlier CBN tool by utilizing ceramic tool in hard turning processes considering technological, economical and ecological aspects, which are helpful and efficient from industrial point of view, (iii) provides environment friendliness, cleaner production for machining of hardened steels, (iv) helps to improve the desirable machinability characteristics, and (v) serves as a knowledge for the development of a common language for sustainable manufacturing in both research field and industrial practice.

• Journal of Radiation Protection and Research
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• 제38권2호
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• pp.91-99
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• 2013

사이클로트론은 그 자체의 수명에 의한 마모 파손뿐만 아니라 사용목적의 변경, 장소 이전, 업그레이드 등의 다양한 이유로 해체 또는 폐기를 경험하게 된다. 실제 미국과 유럽에서도 후자의 이유로 해체된 사례가 많고 또한 많은 양의 저준위 방사성 폐기물을 발생시켰으며 이에 따른 큰 해체 비용을 야기하였다. 유럽과 미국에서는 미래 해체 비용 감소 를 위해 많은 연구를 수행하였으며 미국에서는 허가시 해체 자금 계획(DFP, Decommissioning Funding Plan)을 제출 하도록 하고 있다. 사이클로트론 해체를 위해서는 기술적 측면(해체 절차, 제염 기술 등)과 안전성 측면(잔류 방사능, 예상선량 등)에서 해체 작업의 성취 정도를 예측함으로 해체 비용의 감소 및 방사성 폐기물관련 문제를 해결할 필요가 있다. 본 연구에서는 ANL (Argonne National Laboratory)과 벨기에(유럽위원회 주관)에서 수행된 사이클로트론 해체 사례를 분석하고 2012년 12월 수행된 국내 서울대학교병원 사이클로트론 해체 이전 사례를 살펴봄으로써 향후 사이클 로트론 해체 기준 수립을 위한 기초 자료를 제공하고자 하였다. 이를 위하여 IAEA (International Atomic Energy Agency)와 NRC (Nuclear Regulatory Commission)의 사이클로트론 해체 관련 기준을 분석하고 향후 방사성 폐기물 규제해제(이하 자체처분) 및 재사용과 해체 자금 계획(DFP)의 국내 도입 방안을 제시하였다. 도출된 자료는 사이클로 트론 해체시 방사화되는 정도를 예측하고 국내에 적용할 수 있는 효율적인 해체 요건과 기준들을 정립하는데 활용될 수 있을 것으로 판단된다.

• 한국산학기술학회논문지
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• 제10권9호
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• pp.2396-2401
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• 2009

본 연구는 건축자재로 널리 사용되는 PVC 바닥상재의 표면을 스크래치로부터 보호하기 위하여 기존에 사용하는 광경화형 우레탄-아크릴 수지에 내마모성을 향상시킨 광경화형 하드 코팅액 개발에 관한 것이다. PVC 바닥상재용으로 사용되는 내마모성이 없는 우레탄-아크릴 수지에 $Al_2O_3$(Al-160SG-3), $Al(OH)_3$(SH-8W) 및 $SiO_2$(KS-5000) 등 서로 다른 내마모성을 지닌 물질을 분말 형태로 수지의 양 대비 함량(wt%)을 $10{\sim}30%$로 변화하여 첨가한 후 링밀(Ring Mill)을 사용, 배합하여 수지의 내마모성을 향상시킨 하드 코팅액을 제조하였다. 제조한 하드 코팅액은 코팅층의 두께조절이 가능한 코팅(Bar-coating)을 사용하여 PVC 바닥상재에 코팅 한 후 내마모성, 연필경도, 부착력, 코팅두께 등의 코팅층 표면물성을 평가하였다. 연구결과, 수지에 $Al_2O_3$ 분말 30%를 혼합하여 제조한 하드 코팅액이 내마모성 1등급, 연필경도 H, 부착력 100%로 가장 좋은 물성을 보였으며, 전반적으로 입자크기가 작고, 분말 함량이 많을수록 또한 코팅두께가 두꺼워 질수록 경도 및 내마모성이 우수한 것으로 나타났다.

• 한국터널지하공간학회 논문집
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• 제22권3호
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• pp.323-335
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• 2020

본연구에서는 현행 도로터널의 환기설계기준의 적정성을 검토하기 위하여 사례조사를 수행하고, 5개 터널을 대상으로 입자상 및 가스상 물질의 농도를 현장측정 하였다. 사례조사 결과는 설계기준 대비 TSP (가시도)는 27.9%, CO는 1.6%, NOx는 3.4% 수준으로 분석되었고, 현장측정 결과는 각각 2.6%, 0.8%, 0.2%의 수준에 불과하였다. 또한 5개 터널에 대한 입자상물질(TSP)의 입경분석 결과, 타이어 마모, 재부유 분진 등의 입자라 할 수 있는 PM10 이상의 입경의 영역은 20.4%로 나타났다. 따라서 현행 도로터널 환기설계 기준으로 제시된 입자상물질은 엔진배출량 외에 비엔진배출량에 대한 고려가 반드시 필요하며, 최근의 연구결과를 통한 제작차 오염물질 배출량 및 경사속도 보정계수 등을 적용하여 대상오염물질에 대한 설계기준의 합리적인 개정이 요구되며 WRA (PIARC)에서도 환기설계 기준의 개정 필요성을 권고하고 있다. 현행 터널 내 낮은 환기설비(제트팬) 가동율을 고려할 경우 향후 터널 내 운영상 관리기준의 신설에 대한 필요성이 제기된다.

• 한국컴퓨터정보학회논문지
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• 제28권7호
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• pp.113-120
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• 2023

본 연구는 심폐소생술 시 착용하는 마스크의 유형에 따라 심장압박의 정확도, 피로도 및 생리학적 변화를 파악하고자 한다. 연구는 2022년 5월 9일부터 12일까지 D대학교 응급구조과 재학생 중 BLS provider를 소지하고 있는 학생 총 24명을 대상자로 선정하여 수술 마스크(Dental mask), 미세입자 94%차단마스크(KF94 mask)를 각각 12명씩 착용하고 총 7회에 걸쳐 2분간 심폐소생술을 실시하였다. 연구 결과, 마스크 유형에 따른 구조자의 가슴압박의 질 분석에는 KF94를 착용한 그룹에서 압박속도(F=24.91, p<.001),와 손의 위치불량(F=14.54, p=.024)에서 유의한 차이를 보였고, 피로도를 분석한 결과에서는 Dental mask그룹(F=51.16, p<.001)과 KF94그룹(F=63.49, p<.001) 모두에서 유의한 차이를 보였다. 생리학적 변화를 분석한 결과에서 심박동수를 살펴보면, Dental mask그룹(F=34.79, p<.001)과 KF94그룹(F=35.55, p<.001) 모두에서 유의한 차이를 보였고, 호흡수 측정결과에서도 Dental mask그룹(F=25.02, p=.001)과 KF94그룹(F=23.03, p=.002) 모두에서 유의한 차이를 보였다. 따라서 현장활동의 가장 중요한 심폐소생술시에는 효율적인 가슴압박의 정확도와 구조자의 피로도 및 생리학적 변화의 감소를 위해서는 구조자의 유형에 따른 개인보호장비를 착용하는 것이 필요할 것이다.

• 대한치과기공학회지
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• 제33권1호
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• pp.93-102
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• 2011

Purpose: The study aimed to evaluate working environment for dental technician by measuring dust level, ventilation conditions and the use of personal protective equipment and to provide basic information required to improve working environment and develop health education programs for dental technician. Methods: A total of 240 dental technician who are registered with the Daegu Association of Dental technician and working at 34 dental laboratories participated in the study. And the dust level was measured at 21 different spots in 16 dental laboratories out of 34. Results: Of 34 dental laboratories, 31 (91.2%) were equipped with a ventilator, but the remaining 3 (8.8%) did not have a ventilator. By the number of ventilator, 1 to 3 ventilators were found in 22 dental laboratories (71.0%), 4 to 6 ventilators were in 7 laboratories (22.5%) and more than 7 ventilators in 2 laboratories(6.5%). According to the frequence of changing filters in dust collector, 20 dental laboratories (58.9%) changed filters every four weeks, 10 laboratories (29.4%) changed them every six weeks and 4 laboratories (11.7%) changed them every eight weeks. Of total respondents, 114 (61.3%) said they wore a mask all the time while working, 56 (29.6%) said they frequently wore a mask, 19 (10.1%) said they did not wear a mask. As for the type of masks, 159 (84.1%) used a disposable mask, 25 (13.2%) used a cotton mask and 5 (2.7%) used an anti-dust mask. For dust sat on their outfits while working, 102 (54.0%) shook their uniforms inside workplace to keep dust off the uniforms, 64 (33.9%) did not anything until they wash their uniforms and 23 (12.1%) shook their uniforms outside workplace to keep dust off the uniforms. Of total respondents, 182 (96.3%) had a particle in their eyes while carrying out grinding work. Based on the measurement of floating dust at workplace, 3 dental laboratories showed dust concentration exceeding the minimum level of 10 mg/$m^3$ allowed under the permit for environment. Of those, 1 laboratory had the dust concentration that was more than 1.5 times higher than the minimum level. Dust concentration was higher in laboratories that used a dust collector with 0.5 horse power and changed filters more than 3 weeks ago. Dust comprised of nickel (more than 70%), chrome (9%) and others. The mean chrome concentration was more than twice higher than the minimum permissible level of 0.5 mg/$m^3$. There were two laboratories that showed chrome concentration exceeding the level of 0.4 mg/$m^3$. Like dust concentration, chrome level was higher in laboratories that used a dust collector with 0.5 horse power and changed filters more than 3 weeks ago. There were six laboratories that had nickel concentration exceeding the minimum permissible level of 1 mg/$m^3$. Of those, one laboratory had nickel concentration that was more than three times higher than the minimum permissible level. Nickel concentration was also higher in laboratories that used a dust collector with 0.5 horse power and changed filters more than 3 weeks ago. Conclusion: It is not likely that heavy metal concentrations found in the study constitute respiratory dust. It is however necessary for health of dental technician to apply the Industrial Safety and Healthy Law to dental laboratories and make recommendations for the use of personal protective equipment, installation of a proper number of ventilators, more frequent change of filters in dust collector and improved ventilation for polishing work. At the same time, dental technician need education on how to use personal protective equipment and how to efficiently remove dust from their uniforms.