• 대한기계학회논문집B
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• 제29권10호
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• pp.1092-1100
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• 2005

In the present study, characteristics of steady state laminar flows of a straight duct connected to a 180$^{o}$ curved duct were examined in the entrance region through experimental and numerical analyses. For the analysis, the governing equations of laminar flows in the Cartesian coordinate system were applied. Flow characteristics such as velocity profiles and secondary flows were investigated numerically and experimentally in a square cross-sectional straight duct by the PIV system and a CFD code(STAR CD). For the PIV measurement, smoke particles produced from mosquito coils. The experimental data were obtained at 9 points dividing the test sections by 400 3m. Experimental and numerical results can be summarized as follows. 1) Reynolds number, Re was increased, dimensionless velocity profiles at the outer wall were increased due to the effect of the centrifugal force and secondary flows. 2) The intensity of a secondary flow became stronger at the inner wall rather than the outer wall regardless of Reynolds number. Especially, fluid dynamic phenomenon called conner impact were observed at dimensionless axial position, x/D$_{h}$=50.

• 한국농촌건축학회논문집
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• 제12권3호
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• pp.19-26
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• 2010

This study is aimed to look into the craftsmanship non-educated constructors in Korean-style secondary stations(Gong-So) of Naepo region which is located in the northwestern Chungcheongnam-do. Although the area was persecuted as one of three cradles of Korean Catholicism, Catholic activities flourished there. The 13 cases of Korean-style secondary stations were selected through a survey report list about modern cultural assets of Chungcheongnam-do published in december 2004. This study examined the methods of plan layout and framework of Gong-So to look into craftsmanship of non-educated constructors, the results are as follows; The methods of plan layout are divided into three types according to existence and arrangement of inner column(Nae-Ju); 'Layout with Nae-Ju' is considered as the primary form of Korean-style Gong-So with using regular Nae-Ju. 'Layout with the different position of the center between Nae-Ju and exterior column(Oe-Ju)' and 'layout without Nae-Ju' is appeared in Korean-style Gong-So which is important to assembly and alter function. The methods of framework are appeared variously according to different plan layout for securing worship space. The unusal beam(Chung-Ryang) is used to solve different spans of altar and narthex. When space was formed widely without Nae-Ju, diagonal members and M letter type rafters are used, they are influenced by the technique of western wooden roof truss.

• 대한전자공학회:학술대회논문집
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• 대한전자공학회 2009년도 정보 및 제어 심포지움 논문집
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• pp.284-286
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• 2009

In this paper, we consider a cognitive radio system operating as secondary user. It uses an empty channel that is not currently used by primary users having the license to the channel. In the previous works, secondary user looks for an empty channel by choosing any channel in order or randomly and by sensing the channel to distinguish whether primary users are using. But if primary user is fixed type, we will find an empty channel faster than the mentioned channel selecting methods by using a method considering prior information about cases that primary user used the channel, since it is possible to analogize the channel access possibility of primary user according to regular time and position. Therefore, we propose a channel searching method based on the channel list for the purpose of reducing the channel searching time and improving throughput of secondary users. Firstly, we determine a weighting value of each channel based on the history of channel activities of primary users. This value is added to current channel state buffer and we search an empty channel from channel with smallest value to one with the biggest value. Finally, we compare the performances of the proposed method with those of the sequential channel searching and the random channel searching methods in terms of the average channel searching time and the average number of transmissions of secondary user.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2000년도 춘계학술대회논문집B
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• pp.453-458
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• 2000

The paper describes a study of the variation of the NO production emitted from turbulent propane flames established on a practical combustor where a primary and a secondary fuel lines are installed. The flowrate of the secondary fuel is pulsated or added in addition to that of the primary fuel which constrantly flows to the nozzle of the burner. Two modes depending on the positions of supplying the secondary fuel are performed; one is for its position to be placed at the center of the primary fuel tube and the other around the stabilization baffle. The mean concentrations of gas species, $O_2,\;Co\;CO_2,\;NO$, and HC(unburnt hydrocarbones) have been measured at the exit of the combustor. As equivalence ration $({\Phi})$ is increased the profile of the NO concentration on the latter mode rises slowly less than that on the former one. In the range of ${\Phi}=0.5$ to 0.54 the NO production is reduced by about 35% more on the latter mode than on the former one. The influence of pulsating the secondary fuel on the variation of the NO concentration doesn't appear at both modes.

• 설비공학논문집
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• 제23권8호
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• pp.562-570
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• 2011

In this research, an experimental study is performed to investigate the effects of system operating variables on the cooling and heating characteristics of heat pump system using geothermal heat source and carbon dioxide as a refrigerant. System variables analyzed include compressor frequency, electronic expansion valve opening, refrigerant charge, secondary fluid temperature and flow rate. Results show that optimum refrigerant charge and electronic expansion valve opening position exist at the maximum point of COP curve, and both cooling and heating capacity increase but COPs decrease with the increase of compressor frequency. The change of a secondary fluid temperature leads to variation of overheat area and enthalpy difference in the evaporator and gas cooler. which again results in considerable variations of cooling and heating capacity and COP. In the case of effects of secondary water fluid flow rate, both cooling capacity and COP increase with the increase of secondary flow in evaporator or gas cooler, whereas heating capacity and COP decrease with the increase of flow rate in gas cooler.

• 한국추진공학회지
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• 제4권1호
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• pp.13-21
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• 2000

2차 유동 분사에 의한 추력 방향 제어 방법은 기계적인 방법에 비해 복잡한 기계적 작동장치가 배제됨으로 무게를 줄일 수 있다. 본 연구에서는 압축성 유동 해석을 위해 개발한 코드를 이용하여 SITVC 의 최적 작동 조건을 구하였다. 수치 실험은 2차원 초음속 수축-팽창 노즐 유동에서 2차 유동의 분사 위치, 분사 유량 및 분사 각도 등이 추력 방향에 미치는 영향을 조사하였다. 유동 해석 결과 2차 유동의 분사 위치는 생성된 경사 충격파가 노즐 출구까지 분포되는 지점이 최대 전향각과 횡추력을 가지는 분사 위치임을 알 수 있었다.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2001년도 하계학술대회 논문집 B
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• pp.1154-1156
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• 2001

This paper presents the implementation of a positon sensorless vector control system of a PM linear synchronous motor by sliding mode observer based on TMS320F240 DSP controller. Sliding mode observer estimates the secondary velocity and position based on the measurement of current, and it shows very robust characteristic to parameter variation. Therefore, it improves the system performance deterioration caused by system parameter variations. Simulation and experimental considerations are presented to confirm the applicability of sliding mode observer to the sensorless position control of PMLSM.

• 제어로봇시스템학회:학술대회논문집
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• 제어로봇시스템학회 1990년도 한국자동제어학술회의논문집(국제학술편); KOEX, Seoul; 26-27 Oct. 1990
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• pp.1343-1348
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• 1990

The architecture and functions of a prototype free ranging AGV system are described in this paper. The system has single tricycle configuration - the front wheel is driven and steered simultaneously. The primary position measurement device of this system is the redundant encoder system - an absolute encoder for the steering angle measurement of the front wheel, two incremental encoders for the measurement of the rear wheel rotations. The secondary position measurement device is implemented to reduce the accumulatad error in encoder measurements. The extended Kalman filter is suggested to combine the conflict measurement data for the proper position estimation.

• 한국산학기술학회논문지
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• 제18권12호
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• pp.359-371
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• 2017

본 연구에서는 교원임용 시험을 준비하고 있는 기간제 교사들의 교직생활과 삶을 탐색하였다. 이를 위해 10명의 기간제 교사들을 대상으로 반구조화된, 일대일 면담을 진행하였고, 합의적 질적 연구 방법을 사용하여 자료를 분석하였다. 연구결과, 대부분의 참여자들은 경제적 필요를 충족시키고 자신의 꿈인 교사생활의 기쁨과 보람을 맛보며, 임용 시험에 실질적인 도움을 얻고자 기간제 교사직을 선택한 것으로 나타났다. 기간제 교사생활에서 경험하는 어려움으로는 학교 관리자로부터의 차별 대우가 가장 두드러졌으며, 이로 인한 자존감의 저하와 정체성의 혼란을 겪고 있는 것으로 파악되었다. 이러한 차별이 오히려 임용 시험 준비에 대한 강한 의지로 전환되어 참여자들은 안정되고 당당한 교사 신분을 얻기 위해 임용시험준비에 전념하고 있다고 진술하였다. 하지만, 시험준비 과정에서 부족한 공부시간, 끝없는 공부양, 다양한 삶의 역할 수행, 체력 저하, 난해한 시험 유형, 이전 실패경험에서 오는 불안감 등으로 상당한 스트레스를 경험하는 것으로 확인되었다. 연구결과를 토대로 향후 연구의 방향에 대해 제언하였다.

• Archives of Plastic Surgery
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• 제35권4호
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• pp.465-470
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• 2008

Purpose: Reduction malarplasty is a popular aesthetic surgery for contouring wide and prominent zygoma. However a few patients complain postoperative results and want to revise the midfacial contour. We analyzed the etiology of unfavorable results and treated unsatisfied midfacial contours after reduction malarplasty. Methods: Total 53 patients were performed secondary operation for correction of unfavorable results after primary reduction malarplasty from elsewhere. Midfacial contour was evaluated with plain films and three-dimensional computed tomography. Unfavorable midfacial contours were corrected by secondary malarplasty. Flaring of zygomatic arch was reduced with infracturing technique and prominent zygomatic body was reduced with shaving. Drooped or displaced zygoma complex has been suspended to higher position and fixed with interosseous wiring. As adjuvant procedure, autologous fat injection has been performed in the region of depressed zygomatic body region. Results: The etiology of unfavorable midfacial contour after reduction malarplasty was classified into 7 categories: undercorrection of zygomatic arch(n=8), undercorrection of zygomatic arch and undercorrection of zygomatic body(n=6), undercorrection of zygomatic arch and overcorrection of zygomatic body(n=28), overcorrection of zygomatic body(n=3), simple asymmetry(n=4), malunion(n=2) or nonunion(n=2). Slim and balanced malar contour was achieved with treatment. And most of the patients were satisfied with the results of the surgery. Conclusion: To prevent the unfavorable results after reduction malarplasty, complete analysis of facial contour, choice of appropriate operation technique, precise osteotomy under direct vision, and security of zygoma position are important.