에세이 - 전문건축사제도

이정근,Lee, Jeong-Keun 대한건축사협회 1994 建築士 Vol.1994 No.11

저압주조품의 미세조직과 기계적 성질에 미치는 금형온도의 영향

이정근,박종성,김명호 ( Jeong Keun Lee,Chong Sung Park,Myung Ho Kim ) 한국주조공학회 1998 한국주조공학회지 Vol.18 No.3

N/A Microstructure and mechanical properties of the low pressure die-cast Al wheels were investigated by microscope, image analyzer, NDT (non-destructive test), and tensile test. The variation of SDAS (secondary dendrite arm spacing), porosity per unit area, quality grade, and tensile properties with the mold temperatures were examined. SDAS was gradually decreased with a decrease in temperature. However, the lowest value of porosity per unit area was observed at the mold temperature of 405˚C and the optimum mold temperature was found to be 405˚C. Besides, from the observation of pore morphology, it was also found that the pore formation was mainly caused by shrinkage during solidification. The tensile strength, elongation, and impact toughness were markedly decreased, however the yield strength was nearly constant. The decrease of mechanical properties is attributed to the increase of porosity. (Received January 23, 1998)

탄화 티타늄 금속기 복합재의 드릴가공 특성에 대한 경험적 고찰(1)

이정근,Lee, Jeong-Keun 한국분말야금학회 2006 한국분말재료학회지 (KPMI) Vol.13 No.6

The experimental data from the central composite design runs were utilized for mathematical models far the drilling characteristics containing linear, quadratic and interactive effects of the parameters such as volume fraction of TiC in the composites, drill speed, feed rate and drill diameter. The models were developed via stepwise selection where the insignificant effects were removed using t-test. The models were subjected to optimization of maximizing drill life and satisfying the other constraints.

텅스텐-15% 카파 사출성형체의 잔류 탄소량 분석에 대한 측정 불확도

이정근,Lee, Jeong-Keun 한국분말야금학회 2007 한국분말재료학회지 (KPMI) Vol.14 No.6

Carbon contamination from the binder resin is an inherent problem with the metal powder injection molding process. Residual carbon in the W-Cu compacts has a strong impact on the thermal and electric properties. In this study, uncertainty was quantified to evaluate determination of carbon in a W-15%Cu MIM body by the combustition method. For a valid generalization about this evaluation, uncertainty scheme applied even to the repeatability as well as the uncertainty sources of each analyse step and quality appraisal sources. As a result, the concentration of carbon in the W-Cu part were measured as 0.062% with expanded uncertainty of 0.003% at 95% level. This evaluation example may be useful to uncertainty evaluation for other MIM products.

수계 바인더를 이용한 W-Cu 합금의 새로운 사출성형법 연구

이정근,Lee Jeong-Keun 한국분말야금학회 2006 한국분말재료학회지 (KPMI) Vol.13 No.1

The present work illustrates the use of water-soluble cupric salts as ingredients of binder for injection molding of $W-10 wt\%$ Cu. Parts produced are dense, homogeneous and have good surface finish, compared to those produced using conventional binder system. This new binder system provides also process-simplification benefit. $CuCl_2\;and\;Cu(NO_3)_2$ with the purity of $98\%$ was selected for this study. Rapid sintering process involving thermal decomposing was successful in densification for 1h. Final density that is about $93\%$ of theoretical value could be obtained, and are distinguishable from conventionally processed W-Cu composites.

탄화 티타늄 금속기 복합재에 대한 상대재의 마모거동

이정근,Lee, Jeong-Keun 한국분말야금학회 2006 한국분말재료학회지 (KPMI) Vol.13 No.6

Wear of steel plate was measured during unlubricated sliding against TiC composites. These composites consist of round TiC grains and steel matrix. TiC grain itself exhibits low surface roughness and round shape, which does not bring its counterpart into severe damage from friction. In our work a classical experimental design was applied to find out a dominant factor in counterpart wear. The analysis of the data showed that only the applied load has a significant effect on the counterpart wear. Wear rate of counterpart increased non-linearly with applied load. Amount of wear was discrepant from expectation of being in proportion to the load by analogy with friction force. Our experimental result from treating matrix variously revealed bimodal wear behavior between the composites and counterpart where a mode seems to result from the special lubricant characteristic of TiC grains, and the other is caused by metal-to-metal contact. The two wear mechanisms were discussed.

주조용 A356 합금에서 Fe 계 금속간화합물의 형상에 미치는 Be 의 영향

이정근,박종성,김명호 ( Jeong Keun Lee,Chong Sung Park,Myung Ho Kim ) 한국주조공학회 1998 한국주조공학회지 Vol.18 No.4

N/A Microstructure of A356 aluminium alloys cast in a permanent mold was investigated by optical microscope and image analyzer, with particular respect to the shape and size distribution of iron intermetallics known as β-phase (Al_5,FeSi). Morphologies of the β-phase was found to change gradually with the Be:Fe ratio like these. In Be-free alloys, β-phase with needlelike morphology was well developed, but script phase was appeared when the Be:Fe ratio is above 0.2:1. With the Be:Fe ratios of 0.4:1-1:1, script phase as well as Be-rich phase was also observed. In case of higher Be addition, above 1:1, Be-rich phase was observed on all regions of the specimens, and increasing of the Be:Fe ratios gradually make the Be-rich phase coarse. It was also observed that the β-phase with needlelike morphology was coarsened with increase of the Fe content in Be-free alloys. However, in Be-added alloys, length and number of these β-phases were considerably decreased with the increased Be:Fe ratio. It was concluded that Fe impurity element to be crystallized into needlelike intermetallics was tied up by Be addition element, and new phases were crystallized into script or Be-rich intermetallics. (Received January 23, 1998)

온간성형용 분말의 고온 유동도와 겉보기 밀도 측정에 관하여

이정근,김순욱,Lee Jeong-Keun,Kim Soon-Wook 한국분말야금학회 2006 한국분말재료학회지 (KPMI) Vol.13 No.1

The aim of this work was to establish an optimal condition for determination of apparent density and flow rate for warm compacting powder. For this purpose it was evaluated uncertainty on them according to ISO Guide to the Expression of Uncertainty in Measurement. This evaluation example would be useful even in powder fluidity measurement at room temperature.

Improving RFID Anti-Collision Algorithms with Multi-Packet Reception

이정근,권태경,최양희,김경아,Lee, Jeong-Keun,Kwon, Taek-Young,Choi, Yang-Hee,Kim, Kyung-Ah The Korean Institute of Communications and Informa 2006 韓國通信學會論文誌 Vol.31 No.11A

One of the important performance issues in large-scale RFID systems is to resolve collisions among responses from RFID tags. Considering two do facto anti-collision solutions, namely the binary-tree splitting algorithm and the Slotted-Aloha algorithm, we propose to use multi-packet reception (MPR) capability to enhance the RFID tag reading rate (i.e., throughput). MPR allows an RFID reader to receive multiple reponses transmitted by tags at the same time. We analyze the effect of MPR capability in the above anti-collision algorithms, which is also validated by simulation. The analysis and simulation results show that RFID reader antenna design and signal separation techniques play an important role in improving RFID system performance with MPR capability. 다수의 MD 태그들로부터 발신된 메시지들 사이의 충돌을 빠르게 해소하는 일은 대규모 RFID 시스템의 성능을 결정짓는 중요한 문제이다. 본 논문에서는 충돌방지 (anti-collision) 알고리즘의 성능 향상을 위하여 다중 패킷 수신 (multi-packet reception) 기법을 사용할 것을 제안한다. 다중 패킷 수신 기법을 통해서 RFID 판독기는 동시에 전송된 다수의 태그를 충돌없이 수신 할 수 있다. 대표적인 충돌방지기법인 이진 트리 분리 (binary-tree-splitting) 알고리즘과 슬롯 알로하 (Slotted-Aloha) 알고리즘에 다중 패킷 수신 기법을 적용했을 경우의 성능향상을 분석하는 모델을 제안하고 제안된 분석모델의 정확성을 시뮬레이션을 통해서 비교 검증한다. 다중 패킷 수신기법 적용 시 큰 폭의 성능향상이 있음을 보이고, 다중 패킷 수신 기법의 이득을 최대화하기 위해서는 RFID 판독기 안테나 디자인과 수신 신호 분리 기술이 중요함을 보인다.

뼈이식재 족보 바로 알고 사용하기

이정근(Jeong Keun Lee) 대한치과의사협회 2010 대한치과의사협회지 Vol.48 No.4

bone grafting is indicated in the case of bony defects and is classified into autograft, allograft, and xenograft. Synthetic bone graft is contrasted with these three categories in that it has a different donor source. Autograft is most prominent as it is known as a gold standard of all grafting procedures. Its principles and practices are well established via accumulated informations and clinical experiences, which imposes no regulations or restrictions in its clinical use. On the other hand, other bone graft procedures are under tight control for the safety and effectiveness of each product. Food and Drug Administration of the United States has a system in which the information on the approvals and clearances of bone graft materials on their internet homepage. All the bone graft materials that are under the regulations of the United States are classified into the category of medical devices, which includes allogenic bone, xenogenic bone, and synthetic bone graft materials. Each bone graft material has its own indication and the FDA approvals and clearances of medical devices contain the item of ‘intended use’ to specify the indications of each bone graft materials. US dentists, as users of the specific bone graft materials, are provided with adequate information on the approved materials they are to utilize. As an user of these materials, Korean dentists are less provided with the information on the bone graft materials they want to use. Medical providers of the bone graft materials have to be able to provide their users with the essential information such as the intended use of the regulatory approval. Dentists must also be active in gathering informations on the material of their interest, and the system must be built in which both of the medical providers and users of bone graft materials can be satisfied in providing and getting the information, respectively.