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김충현,안효석,정태형,Kim, Chung-Hyeon,An, Hyo-Seok,Jeong, Tae-Hyeong 대한기계학회 2000 大韓機械學會論文集A Vol.24 No.3
Nylon, Polyacetal and PTFE were studied to gain a better understanding of their tribological behavior. Wear tests were conducted with reciprocating motion under dry sliding conditions. Friction coefficient and specific wear rate were measured as a function of sliding distance. The worn surfaces were examined with a Scanning Electron Microscope(SEM). Polyacetal showed lowest specific wear rates and PTFE exhibited lowest friction coefficient. The dominant wear mechanism found were adhesion and abrasion.
김충현,안효석,정태형,Kim, Chung-Hyeon,An, Hyo-Seok,Jeong, Tae-Hyeong 대한기계학회 2001 大韓機械學會論文集A Vol.25 No.11
Wear characteristics of Nylon and acetal pinions against steel gears for different pitch line velocities was studied with a power circulating gear test rig under unlubricated condition. Specific wear rate was measured as a function of tooth number, module, tooth width and total revolution. The worn tooth surfaces were examined with a profile projector. The Nylon pinion showed lower specific wear rate than the acetal pinion. However, the Nylon pinion was fractured at high tooth loads, whereas the acetal pinion exhibited a steady wear behavior. The wear characteristics of Nylon pinion varied significantly with the Pitch line velocity. Wear occurred most severely at the tooth tip and the region immediately below the pitch line of pinion. The dominant wear mechanisms were adhesion and abrasion.
김충현,이성철,안효석,정태형,Kim, Chung-Hyeon,Lee, Seong-Cheol,An, Hyo-Seok,Jeong, Tae-Hyeong 대한기계학회 2000 大韓機械學會論文集A Vol.24 No.9
Wear and operation characteristics of Nylon and Acetal pinion against steel gear were studied to gain a better understanding of their tribological and mechanical behavior. Tests were conducted with power circulating gear test rig under unlubricated conditions. Specific wear rates were measured as a function of applied load and total revolution. The worn tooth surfaces were examined with a profile projector and camera. Nylon pinion showed lower specific wear rates than Acetal pinion, but it revealed breakage at high load. Principal wear depths were developed at tooth tip and below the pitch line of pinion. Life estimation for the Nylon pinion was made by taking into account steel gear equivalent Hertz stress and average sliding velocity. The dominant wear mechanisms were adhesion and abrasion.
김충현,안효석,정태형,Kim, Chung-Hyeon,An, Hyo-Seok,Jeong, Tae-Hyeong 대한기계학회 2002 大韓機械學會論文集A Vol.26 No.9
Operating test of power-transmission plastic spur gears were performed inspecting both characteristics of friction-wear and endurance, and suggesting endurance improvement method that either drills internal holes of tooth or inserts metallic pin in the internal hole of tooth and verifying this newly-provided method. In case of acetal gears, amount of friction-wear is observed to increase by development of plastic deformation and increase of tooth stiffness due to brittle material property of acetal. To the contrary, in case of nylon gears, suggested method is shown to drop down the tooth temperature for about 3∼10$^{\circ}C$ than original gear, thus amount of wear is reduced by over 30% and operating lift prolonged by more than 200%. Hence, suggested method is proved to be practically applicable to the plastic gears made by soft polymers such as Nylon.
장생도라지 (Platycodon grandiflorum)의 항산화 활성 평가
김충현(Chung Hyeon Kim),정봉용(Bong Yong Jung),정선기(Sun Ki Jung),이철호(Chul Ho Lee),이현선(Hyun Sun Lee),김봉희(Bong-Hee Kim),김상겸(Sang Kyum Kim) 환경독성보건학회 2010 환경독성보건학회지 Vol.25 No.1
Platycodon grandiflorum, Doraji as Korean name, is one of the most widely used traditional oriental medicine for bronchial diseases and also used as a folk remedy for geriatric diseases and inflammatory diseases. In recent studies, it has been reported that some effect of P. grandijlorum is derived from its antioxidant activity, although there is still a lack of evidence to establish its oxy-radical scavenging activity. In this study, total oxy-radical scavenging capacity (TOSC) assay was used to evaluate antioxidant activity of total extracts (T-PG), polysaccharide fraction (Po-PG), and saponin fraction (Sa-PG) isolated from P. grandiflorum against peroxyl radicals and peroxynitrites. And MTT assay was taken to assess cyto-protective effects of T-PG, Po-PG and Sa-PG in H4IIE cells treated with hydrogen peroxide and tert-butylhydroperoxide. In the TOSC assay, Sa-PG showed strong oxy-radical scavenging capacity compared with T-PG and Po-PG. In cell-based assay, T-PG and Po-PG protected cells from oxidative stress, but Sa-PG did not protect cells because of cytotoxicity of Sa-PG. These results suggest that the saponin components of P. grandiflorum have relatively strong antioxidant capacity and cytotoxicity in rat hepatoma cells.
김충현(Chung-Hyeon Kim),은종호(Jong Ho Eun),김배성(Bae-Sung Kim),고성보(Seong-Bo Ko) 한국산학기술학회 2015 한국산학기술학회 학술대회 Vol.2015 No.1
본 연구는 한국양식광어의 중장기 수급분석이 가능하도록 한국 양식광어의 중장기 수급전망모형을 구축하였으며, 분석결과 2017년의 양식광어의 생산량은 약 42,561톤, 수출량은 2,823톤, 산지가격은 제주산 1kg기준 10,191원이 될 것으로 전망되었다.