• 한국정보과학회:학술대회논문집
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• 한국정보과학회 2004년도 가을 학술발표논문집 Vol.31 No.2 (3)
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• pp.673-675
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• 2004

애드혹 네트워크지(ad hoc network)는 기존 유선 환경에서의 인프라가 없이도 각 무선 노드들이 필요한 상황에 맞게 동적으로 네트워크를 구성할 수 있는 무선 노드들의 집합을 말한다. 애드혹 네트워크는 제한된 파워 공급, 노드의 이동성으로 인한 잦은 경로 재설정 등으로 동적인 토폴로 구조를 갖는다. 유선 네트워크와 다른 이러한 특징들 때문에 기존의 라우팅 알고리즘을 수정한 다양한 라우팅 알고리즘이 등장 하였다. 그 중 multi-rate을 고려한 AODV 라우팅 기법은 기존의 single-rate을 이용하는 것보다 전송 연 시간의 감소, 패킷 처리율 증가와 같은 장점을 갖는다. 그러나 새로운 경로를 설정함에 있어서 네트워크 전반에 걸쳐 제어 메시 의 수가 증가하는 단점이 있다. 애드혹 네트워크에서 제어메시 는 데이터 패 킷보다 전송시 우선 순위를 가 기 때문에 제어메시 의 증가는 전체적인 패킷 처리율을 감소시킨다. 이러한 문제점을 해결하고자 본 논문에서는 경로 복구 매커니즘의 확장 및 검색지(expanding ring search)알고리즘에서 제어 메시 의 수를 효과적으로 줄일 수 있는 방법을 제안하였다. 기본 아이디어는 단절 이전의 정보를 이용하여 선택적으로 제어 메시 를 브로드 캐스트하는 것이다. NS-2로 제안 알고리즘을 시뮬레이션 한 결과. 기존방법에 비해 20%이상 제어 메시 가 감소하였고, 패킷 전송 연에 대해서는 최대 10%의 감소율을 보여 기존 방법보다 좋은 성능을 보임을 확인할 수 있었다.

• 한국소음진동공학회논문집
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• 제23권3호
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• pp.234-239
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• 2013

There are many types of speed reducer for industrial uses. However the cycloid speed reducer is widely used in manipulators based on excellent performance of low backlash, high reduction ratio and compact size. It is essential to use precision speed reducer for accuracy of position controls on robot systems and electric vehicles. The cycloid speed reducer has a eccentric rotating motion and offset to avoid some problem of assembly, so it has a disadvantage for vibration. In this paper, a multi-body dynamic model is developed for a cycloid speed reducer and the dynamic behaviors of the reducer are investigated. The cycloid speed reducer consists of cycloidal plate gears, housing gear, input shaft, output pin and shaft, and eccentric bearings. Using a CAD program, each component of cycloid reducer is modeled based on the offset and eccentric. Multi-body simulations using Recurdyn and test using a rig tester are performed. As a result, the pin reaction force and the amplitude of housing displacement are increased by the larger offset and smaller eccentric value of cycloid reducer.

• 대한기계학회논문집B
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• 제27권6호
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• pp.773-780
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• 2003

The three-dimensional spatial structures of impeller flow created by a six bladed Rushton turbine have identified based on the volumetric velocity information from multi-plane stereoscopic PIV measurements. A total of 10 planes with 2 mm space and a 50 mm by 64 mm size of the field of view were targeted. To reduce the depth of focus, we adopted an angle offset configuration which satisfied the Scheimpflug condition. The distortion compensation procedure was utilized during the in situ calibration. Phase-locked instantaneous data were ensemble averaged and interpolated in order to obtain mean 3-D. volumetric velocity fields on a 60 degree sector of a cylindrical ring volume enclosing the turbine blade. Using the equi-vorticity surface rendering, the spatial structure of the trailing vortices was clearly demonstrated. Detail flow characteristics of the radial jet reported in previous studies of mixer flows were easily identified.

• 전기학회논문지
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• 제63권10호
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• pp.1412-1416
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• 2014

We report thin-film organic moisture barriers based on polystyrene(PS) laminates deposition by PECVD for an encapsulation of OLEDs. The organic polystyrene thin-film has the benzene ring structure and high hydrophobic characteristics and it was polymerized by PECVD in dry process. Life time properties of Ca test were obtained 32 minutes at the RF 100W process conditions. From the AFM test, the roughness of multi-layer thin-film was more excellent rather than that of a single-layer thin-film. In addition, 5 layers of the multi-layer film properties were obtained 45 minutes. So that the optical and electrical properties were not affected with these plasma polymerized organic thin-film encapsulation. For life time improvement, the inorganic $Al_2O_3$ thin-film were deposited 5nm using ALD atomic layer deposition. The WVTR(Water Vaper Transmission Rate) value of hybrid thin-film encapsulation in the optimum process conditions was resulted by less than $10-3g/m^2/day$. From the results of experiment, plasma polymerized hybrid encapsulation was suggested as the flexible display applications.

• International Journal of Concrete Structures and Materials
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• 제9권2호
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• pp.185-206
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• 2015

This paper presents statistical models developed to study the influence of key mix design parameters on the properties of lightweight self-consolidating concrete (LWSCC) with expanded shale (ESH) aggregates. Twenty LWSCC mixtures are designed and tested, where responses (properties) are evaluated to analyze influence of mix design parameters and develop the models. Such responses included slump flow diameter, V-funnel flow time, J-ring flow diameter, J-ring height difference, L-box ratio, filling capacity, sieve segregation, unit weight and compressive strength. The developed models are valid for mixes with 0.30-0.40 water-to-binder ratio, high range water reducing admixture of 0.3-1.2 % (by total content of binder) and total binder content of $410-550kg/m^3$. The models are able to identify the influential mix design parameters and their interactions which can be useful to reduce the test protocol needed for proportioning of LWSCCs. Three industrial class ESH-LWSCC mixtures are developed using statistical models and their performance is validated through test results with good agreement. The developed ESH-LWSCC mixtures are able to satisfy the European EFNARC criteria for self-consolidating concrete.

• 한국군사과학기술학회지
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• 제4권1호
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• pp.246-254
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• 2001

The breech system can be considered as a pressure vessel with an internal plug under high explosive pressure. The system consists of a breech block(internal plug) whose front surface subjects to pressure, and a breech ring(pressure vessel). There is the geometric discontinuity around roots of connection parts and then stress concentration is introduced due to pressure, where contact effect may be ignored because contact plane between two equipments is parallel ideally, Generally high stress concentration phenomena shorten the life cycle of the mechanical system. It is well known that shock load is much more harmful on safety of the system than static load. In this present paper, several geometric design variables which may affect stress condition on the system are chosen and the parametric study on the design variables is carried using commercial FEM codes. Finally, the obtained results in the single lug breech system are applied to design the 3 lugs breech system. The 3 lugs breech system can reduce the maximum stress level.

• Bulletin of the Korean Chemical Society
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• 제35권6호
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• pp.1639-1646
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• 2014

A series of novel fused-ring spiro compounds, spiro[benzo[ij]tetraphene-7,9'-fluorene] (SBTF) derivatives containing an end-capping aryl substituent at both the C3 and C10-positions hasbeen designed and synthesized via multi-step Suzuki coupling reactions. 3-(1-Naphthyl)-10-phenylSBTF (1N-PSBTF), 3-(2-naphthyl)-10-phenylSBTF (2N-PSBTF) and 3-[4-(1-naphthyl)phenyl]-10-phenylSBTF (NP-PSBTF) showed improved glass transition temperatures ($T_g$) with good thermal stability. Their photophysical, electrochemical, and electroluminescent properties were investigated and were used to construct blue organic light emission diodes (OLEDs). The typical OLED devices showed excellent performance; the NP-PSBTF-based device exhibited highly efficient deep blue-light emission with a maximum efficiency of 5.27 cd/A (EQE, 4.63%) with CIE (x = 0.133, y = 0.144). According to these characteristics, these deep-blue light emitting materials have sufficient potential for fluorescent OLED applications.

• 한국정밀공학회지
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• 제28권3호
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• pp.301-307
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• 2011

In this paper, effects of major design parameters of cold forging dies on die mechanics are quantitatively investigated with emphasis on shrink fit using a thermoelastic finite element method. A ball-stud cold forging process found in a cold forging company is selected as a test process and the effects of die insert material, magnitude of shrink fit, dimension of shrink ring, number of shrink rings, partition of die insert and clamping force on effective stress and circumferential stress are analyzed. It has shown that the number of shrink rings, magnitude of shrink fit, and Young's modulus of die insert material have strong influence on compressive circumferential stress in die insert but that the influence of the other design parameters is relatively weak.

• 에너지공학
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• 제12권4호
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• pp.259-266
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• 2003

안전감압계통 작동시 수조에서 발생하는 공기 기포군의 진동 하중을 줄이기 위해 ABB-Atom sparger에 는 하중저감 링이 설치되어 있다. 하중저감 링이 압력장에 미치는 영향을 알아보기 위해, 본 연구에서는 하중저감 링이 없는 ABB-Atom sparger를 통해 수조 내로 방출되는 공기 기포군의 진동에 대한 수치해석을 상용 열수력 해석 코드인 FLUENT 4.5를 사용하여 수행하였다. 코드에 내재된 다상유동 모델 중 VOF(Volume Of Fluid)모델을 사용하여 물, 공기 및 증기 유동을 모의하였다. 해석결과를 기존의 해석결과와 비교하여 하중저감 링은 벽면 압력 하중을 줄이는 효과가 있음을 확인하였다. 아울러 배관내의 공기량과 배관 입구 조건이 벽면 압력 진동에 미치는 영향도 분석하였다.

• 한국전자통신학회논문지
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• 제12권1호
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• pp.75-84
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• 2017

초고속 환경에서 대용량 데이터에 대한 안정적 기록 및 효율적인 데이터 접근의 필요성은 갈수록 높아지고 있다. 이와 관련된 기초과학의 한 분야로 방대한 천체 관측 데이터를 생산하는 VLBI(: Very Long Baseline Interferometer)가 있는데 고분해능, 고감도 관측 연구를 수행하기 위해서는 고성능의 데이터 저장 시스템이 요구된다. 하지만 시장에 출시된 대다수 클라우드 기반 스토리지는 일반 IT, 금융, 행정 서비스 지원을 위한 저용량, 복수 스트림의 비정형 데이터에 최적화되어 있기 때문에 빅 스트림 데이터 기록을 위한 최적의 대안이 될 수 없다. 본 논문에서는 이를 극복하기 위한 방안으로 데이터 입출력 처리에 있어 고성능, 동시성에 최적화된 데이터 저장 시스템을 설계하고자 한다. 이를 위해 멀티 코어 CPU 환경에서 libpcap, pf_ring 등의 API 호출을 통해 패킷 입출력 모듈을 구현하였고 외부로부터 유입되는 데이터를 효율적으로 처리할 수 있도록 소프트웨어 RAID(: Redundant Array of Inexpensive Disks) 기반의 확장성 있는 스토리지를 구축하였다.