• 한국분말재료학회지
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• 제22권1호
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• pp.6-9
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• 2015

In this study, the behavior of densification of copper powders during high-pressure torsion (HPT) at room temperature is investigated using the finite element method. The simulation results show that the center of the workpiece is the first to reach the true density of copper during the compressive stage because the pressure is higher at the center than the periphery. Subsequently, whole workpiece reaches true density after compression due to the high pressure. In addition, the effective strain is increased along the radius during torsional stage. After one rotation, the periphery shows that the effective strain is increased up to 25, which is extensive deformation. These high pressure and severe strain do not only play a key role in consolidation of copper powders but also make the matrix harder by grain refinement.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 2006년도 춘계학술발표회 논문집(I)
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• pp.98-101
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• 2006

As an alternative of conventional prestressed concrete (PSC) girders, various types of PSC girders are being developed and applied in bridge structures. Incrementally prestressed concrete girder is one of these newly developed girders. According to design concept, these new types of PSC girders have considerable advantages to reduce their self-weight and make spans longer. However, dynamic interaction between bridge superstructures and passing trains would be sometimes one of critical issues in these more flexible railway bridges. Therefore, it is very important to evaluate modal parameters of newly designed bridges before conducting dynamic analyses. In the present paper, a 25 meters long full scale PSC girder was fabricated as a test specimen and modal testing was carried out to evaluate modal parameters including natural frequencies and modal damping ratios at every prestressing stage. In the modal testing, a digitally controlled vibration exciter as well as an impact hammer is applied to obtain frequency response functions more exactly and the modal parameters are evaluated varying with construction stages. Prestressed force effects on changes of modal parameters are analyzed at every incremental prestressing stage.

• 한국주거학회논문집
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• 제24권1호
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• pp.11-20
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• 2013

The purpose of the study was to develop a classification of management for the qualitative improvement of the management of multi-family housing. The date were analyzed using the Excel program in terms of frequency and, criticality analysis in order to draw items stage by stage. The process of research was as follows: The first process drew classification of types using the content analysis of the documented studies. The second process examined subcategories according to classification of types via interviews of supervisors. Further, the criticality analysis between the two items was examined. Additionally, when this study surveys and analyzes the satisfactions and importance of management on the basis of the classification, it can have an effect on management by reflecting the result. In conclusion, the classification of the management of multi-family housing will make up the improvement scheme of supplement education, certification related management and management regulations on the characteristics of multi-family housing by types of houses in the future.

• 한국정보통신학회논문지
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• 제17권4호
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• pp.996-1004
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• 2013

본 논문에서는 무선 센서 네트워크에서 센서 노드들 간의 에너지 소비 불균형을 개선하여 무선 센서 네트워크의 전체적인 수명을 연장할 수 있는 클러스터링 기법들을 제안한다. 무선 센서 네트워크의 생성 단계에서 무선 센서 네트워크의 에너지 소모를 줄이기 위해서 센서 노드들의 밀도에 따라 클러스터 헤더를 선출하여 클러스터를 형성한다. 그 이후 센서 네트워크가 활성화되는 동안 센서 노드들 간의 에너지 불균형을 개선하기 위하여 에너지 소모량을 추정한 후 릴레이 기반으로 다음 라운드의 클러스터 헤더를 선출한다.

• 대한전기학회:학술대회논문집
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• 대한전기학회 1999년도 추계학술대회 논문집 학회본부 C
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• pp.965-967
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• 1999

In order to solve to instability in air and to format dentrite, we used carbonized phenol resin electrode which is amorphous carbon. The structure and properties of deeply Li-doped carbonized phenol resin have been investigated in association with their utilization as electrodes in rechargeable batteries. Resol type phenol resin used as starting material. The doped lithium was found neither in metallic nor in ionic states even in the most deeply doped state($C_{2.2}$Li stage). It has also been confirmed that the carbonized phenol resin electrode has a large capacity with good stability and reversibility. These results strongly suggest that the carbonized phenol resin can make an excellent anode material for secondary batteries. Finally, we discuss that the carbonized phenol resin doped up to the $C_2Li$ stage can exhibit an energy density per volume as high as lithium metal. We know that carbonized phenol resin can used as cathode as well as anode by cyclic voltammogram.

• 한국수학교육학회지시리즈A:수학교육
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• 제49권3호
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• pp.353-373
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• 2010

This research was to help slow learners to be motivated and to make their outcome productive, using GSP based on the mathematization theory for learning mathematics, as a way of encouraging the learner-centered approach. With 2 of the second graders in a high school, who had not yet understood trigonometric functions in their first grade period, 7 units of lesson plans were designed for the research. The results showed that first, understanding real life contexts and analyzing properties by observation, and experiment using GSP, to build the concept of trigonometric functions could be a foothold on which learner's organization and outcome from a horizontal mathematization led to vertical mathematization. Despite the delay during the level-up-stage for a while, the learners could attain the vertical mathematization stage and moreover the applicative mathematization through effective use of GSP and the interaction between the learners or a teacher and the learners. Second, using GSP was a vertical tool of connecting horizontal mathematization with vertical mathematization in forming the concept of trigonometric functions and its meaning could be understood by their verbalizing and presenting the outcomes through their active performance. Using GSP is helpful for slow learners to overcome learning difficulties, based on the instructional materials designed by Realistic Mathematics Education.

• Journal of Welding and Joining
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• 제26권5호
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• pp.66-73
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• 2008

Welding work in pre-erection or erection stage of shipbuilding construction to be carried out in flat and vertical upward position mostly and Electrogas welding(EGW) is actively applied especially for vertical butt joint of thicker steel plate recently. In this study considered how to develope and improve mechanical properties of weld metal and HAZ in high heat input welding processes such as EGW and Electroslag welding(ESW) with its welding equipment in order to extend the application range to the longitudinal members and hatch coaming parts of container ship. Some components of welding system and parameters were modified to get the faster travel speed and reduce weld heat input, and also by adding additional filler rods or tubes increase the amount of deposited weld metal. With the test get some good date can apply to actual fabrication work and recommend items to manufacture welding materials make better. Above all things it's a fruition that to prepare the possibility of application of ESW to shipbuilding construction which fill up the gap of stoppage days of more than 20 years.

• 대한설비공학회:학술대회논문집
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• 대한설비공학회 2006년도 하계학술발표대회 논문집
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• pp.953-958
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• 2006

Perimeter zone has been reinforced by active systems, such as fan-coil units, because it causes an increase in heating and cooling loads, dew condensation in winter, or discomfort with cold-draft to residents in buildings, through poor insulation by light-weighed skin due to progressing multi-storied buildings and skyscrapers. However, because these active systems raise Its capacity so that fossil fuel is used as much as they are added, and ultimately, greenhouse effect is urged, we proposed BIPV system functioned as solar collector which can substitute active system. As an early stage, heat balance equation in steady-state by Fortran was used not only for pre-heating effect and electric power capacity during the day in winter, but also for electric power capacity during day in slimmer and sky radiation effect during night in summer. Especially, we should have considered shading on PV, since even a little bit of it makes the efficiency too low for the PV to work. Still, when the flux of pre-heated air was increased to make air-barrier, its temperature was not enough to make it because the speed of heat exchange was too fast to warm up the air, thus the capacity to meet the condition was evaluated, and electric power from PV was made used for it.

• 한국산학기술학회논문지
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• 제11권1호
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• pp.49-54
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• 2010

자동차의 A.C 제너레이터(alternating current generator) 부품으로 사용되는 로터폴(rotor pole)을 가공할 때는 트랜스퍼온간단조금형(transfer warm forging die)으로 성형한다. 소재를 온간가공 영역으로 가열한 후 즉시 금형안으로 이송시켜 제1스테이지(1st stage)에서 업세팅가공(upsetting work)하고 제2스테이지(2nd stage)로 이송하여 측방압출(lateral extrusion)가공을 한다. 이때 측방압출 스테이지의 금형에서 다이블록(die block), 다이부싱(die bushing), 센터펀치(center punch), 사이드펀치(side punch)의 접촉면이 압출시의 과혹(過酷)한 조건에 견디지 못하여 쉽게 마멸(abrasion)되어 금형수명(die life)을 단축시키고 있다. 이 때문에 생산량 감소로 인한 납기지연, 금형의 수리보수시간 과다, 제품의 정밀도 저하 등의 문제점이 발생되고 있다. 이러한 문제점을 해결하기 위하여 금형재질 선정과 열처리 작업 싸이클 개선, 방전가공시의 트러블 해소, 핵심부품의 구조변경 등을 연구하여 금형수명을 40~50% 연장 하고자 하였다.

• 한국통신학회논문지
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• 제27권7B호
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• pp.686-694
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• 2002

본 논문에서는 DS-CDMA 환경 하에서 일반적인 그룹형 간섭제거기(Groupwise Canceller) 중 초기단을 개선시킨 그룹형 간섭제거기(Improved initial-stage Grouping Interference Canceller)의 개선된 정렬기법을 소개한다. 비선형 간섭제거기 중 초기단을 개선시킨 그룹형 간섭제거기(IGIC)는 입력된 신호를 그룹으로 나누어 정렬기법을 통해 초기단 성능을 개선시킨 간섭제거기이다. 그러나, 이 시스템은 정렬기법에 의해서 각 그룹에 할당되는 사용자수가 항상 동일하기 때문에 동일 그룹내에서 신호세력의 차이가 생길 수 있다. 이 경우, 동일 그룹내에 작은 신호들은 큰 신호들로부터 많은 다중접속간섭의 영향을 받는다. 이와 같은 다중접속간섭의 영향을 줄이기 위해 본 논문에서는 개선된 정렬기법을 사용하여 각 그룹에 할당되는 신호들이 비슷한 신호전력분포를 가지도록 하였다. 따라서, 그룹내의 신호세력 차이를 줄여 다중접속간섭의 영향이 감소되었다. 성능 분석은 전력제어를 하였을 때와 하지 않았을 때를 다른 비선형 간섭제거기와 비교하여 분석하였다.