• 대한조선학회논문집
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• 제38권4호
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• pp.1-10
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• 2001

비 압축성 점성 유동에 대한 RANS 방정식의 수치 해법을 사용해서 4상한(four quadrant) 조건에서 작동하는 박용 프로펠러 주위의 난류 유동과 프로펠러 단독 성능을 계산하였다. 4상한 조건의 단독 성능에 대한 실험결과가 존재하는 모형 프로펠러 P4381에 대하여 계산된 유동은 다양한 조건에서 프로펠러에 발생하는 3차원 유동박리를 포함한 복잡한 점성유동 특성을 잘 보여주었으며, 계산된 프로펠러 추력과 토크는 실험에서 캐비테이션이 심하게 발생된 일부 경우를 제외하고는 실험 결과와 잘 일치하였다.

• 조명전기설비학회논문지
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• 제23권11호
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• pp.22-27
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• 2009

This paper presents a two-paralleled four quadrant DC chopper type PWM power conversion circuit in order to generate a gradient magnetic field in the Magnetic Resonance Imaging (MRI) system. This circuit has 8-IGBTs at their inputs/outputs to realize further high-power density, high speed current tracking control, and to get a low switching ripple amplitude in a controlled current in the Gradient Coils (GCs). Moreover, the power conversion circuit has to realize quick rise/fall response characteristics in proportion to various target currents in GCs. It is proposed in this paper that a unique control scheme can achieve the above objective DSP-based control system realize a high control facility and accuracy. It is proved that the new control system will greatly enlarge the diagnostic target and improve the image quality of MRI.

• Journal of Electrical Engineering and Technology
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• 제3권1호
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• pp.68-78
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• 2008

This paper introduces a complete package for SRM drive on Power System Computer-Aided Design/Electromagnetic Transients (PSCAD/EMTDC). A three-phase SRM drive is modeled and simulated on PSCAD. The motor is modeled using an accurate nonlinear analytical model that takes into consideration the machine nonlinearities. A current control algorithm is applied for torque ripple minimization to achieve a smooth output torque which is necessary for high performance applications. The motor drive is tested for four-quadrant operations. The modeled SRM is capable of operating as a motor or generator during clockwise and counterclockwise motions. The proposed package helps in understanding the operational principles of switched reluctance motors, investigating the dynamic characteristics of SRM drives, and achieving a high performance dynamic control task.

• 전력전자학회논문지
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• 제8권3호
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• pp.285-291
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• 2003

스위치드 릴럭턴스 전동기는 고출력, 고효율 및 직권전동기 구동특성 등으로 견인구동용으로 주목받고 있다. 그러나 전동기를 4상한 구동하기 위한 발전영역에서 제어는 쉽지 않다. 본 논문은 전류제한법에 의해 안정된 발전제동이 가능한 제어방식을 제안하였다. 전동기 구동시는 기준전류제한방식과 위상각 제어방식으로 속도제어를 행하고, 발전제동모드에서는 상전류가 발산하지 않는 조건을 산정하여서 이 값을 기준전류로 한 전류제한방식을 채택하였다. 시뮬레이션과 실험에 의해 제안한 방식의 타당성을 확인하였다.

• 대한전기학회:학술대회논문집
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• 대한전기학회 1989년도 추계학술대회 논문집 학회본부
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• pp.240-244
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• 1989

This paper describes an electric vehicle DC-DC drive system capable of delivering motoring current and of generating braking current. The power transistor chopper Is adopted to operate a DC series motor. The transistor chopper adopted, a high chopping frequency and avoids additional inductance In series with the armature winding. The four-quadrant drive is applied to save the energy. The energy saving is critical in operating the Independent power source electric vehicle. Using software simulation, regeneration and braking characteristics are investigated. The microprocessor-based controller is used to operate the whole system.

• 한국IT서비스학회지
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• 제22권5호
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• pp.1-16
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• 2023

This study aimed to provide fundamental insights into the digital customer experience by identifying its components and analyzing their importance and satisfaction levels among youths. To achieve this objective, the components of digital customer experience were identified through a review of prior research and consultation with experts. Subsequently, a survey was conducted with 200 youths in Seoul and Gyeonggi-do. The main findings of the study are as follows: First, The components of the digital customer experience consisted of 12 items grouped into three categories. Second, an analysis of the disparity between the importance and satisfaction levels of digital customer experience revealed statistically significant differences across all items. Third, By utilizing IPA (Importance-Performance Analysis), the digital customer experience was categorized into four quadrant, each with its own characteristics and recommendations for management: The first quadrant, the "current level maintenance area," encompassed items related to "entertainment" and "recommended service." This area is currently functioning well but necessitates continuous attention and management. The second quadrant, the "area to be supported first," included items such as "personalization," "security," "inducing participation," "privacy," and "individuality expression." Intensive management and improvements are imperative in this quadrant. The third quadrant, the "long-term improvement area," consisted of items like 'consistency,' 'information quality,' and 'convenience.' These items require focus on long-term enhancement efforts. The fourth quadrant, the "areas where efforts have already been invested," encompassed items like 'accessibility' and 'deliberation.' It appears that excessive investment has been made in these areas relative to their importance, calling for selective investments while considering the specific issues associated with each factor. These research findings serve as essential data for managing the digital customer experiences of youths.

• Animal Systematics, Evolution and Diversity
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• 제19권1호
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• pp.111-117
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• 2003

경기도 시화호와 여수 및 대한해협에서 채집된 히드라해파리류는 관사르스해파리 (Sarsia tubujosa)와 네잎백합해파리 (Liriope tetraphylla)로 각각 동정되었다. 이들은 한국 미기록종으로 판명되어 재기재하여 보고한다. 관사르스해파리는 긴 관모양의 구병과 4개의 촉수를 가진다. 경해파리목 (Trachymedusae)에 속하는 네잎백합해파리는 내산의 중앙 표면에 위치한 삼각형의 생식선과 우산의 4분원 (quadrant)에 7개의 구심맹관 (blind centripetal canals)을 가지며 길고 굵은 구병과 구병 끝에 4개의 주름진 구엽을 가진다. 본 연구의 결과 지금까지 밝혀진 한국 해산 히드라해파리류는 5목 11과 12종이 된다.

• 한국지역사회생활과학회지
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• 제27권4호
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• pp.739-753
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• 2016

This study was performed to identify the tendency and benefits of outdoor recreation in rural areas. The preferences and importance of the benefits of outdoor recreation activities in rural areas were simultaneously compared and analyzed through the discussion of a four quadrants portfolio map using importance-performance analysis. The social benefits in quadrant i had the characteristics of 'sharing nice experiences with others', 'having contact/interchange with others', 'colleagueship/helping each other', 'being together with friends', and 'making new friends.' These social benefit types were perceived as very important characteristics, but the real level of achievement was rather low. Thus it seems necessary, in the process of program development, to apply the social benefit types to the characteristics of the participants. The experience of nature and relaxation benefits in quadrant ii had the characteristics of 'relaxation and recreation', 'understanding nature', 'nature experience', 'getting away from everyday life', and 'experiencing new things.' These benefits and experience of nature were regarded as very important characteristics by the participants in outdoor recreation and, at the same time, their real achievements were highly recognized, thus they seemed to be proper types for the goals involved in developing an outdoor recreation activity program in rural areas. The personal and challenge benefits in quadrant iv had the characteristics of 'training of mental ability', 'improvement of self-esteem', 'fitness', 'increase in determination', 'possible danger', 'achievement', 'excitement', and 'adventure.' These benefits had less importance to the participants, but had relatively high achievement, thus it might be important to make further suggestions for the direction of development according to the participants' tendency, seasons and facilities.

• 산업기술연구
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• 제14권
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• pp.3-17
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• 1994

This paper develops a design technique for approximating nonseparable frequency characteristics by sums and products of separable transfer functions. Therefore nonseparable frequency characteristics includes the four-quadrant symmetry filters. The desired filter with half plan symmetry is obtained by shifting a low pass characteristic in the frequency domain, and by combining these shifted characteristics. Also the paper develops the technique for designing recursive and nonrecursive two dimensional digital filters by the application of a complex transformation to one dimensional low pass filter.

• 대한전자공학회논문지SD
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• 제39권6호
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• pp.26-33
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• 2002

본 논문에서는 포화영역에서 동작하는 MOS트랜지스터의 제곱특성과 소오스를 결합한 차동회로의 뺄셈기능을 이용하여 구현한 quarter-square기술방식의 새로운 4상한 MOS아날로그 곱셈기를 제안하였다. 본 논문에서 제안된 회로는 p-well CMOS 공정으로 설계-제작되어 특성측정을 하였다. 제작된 곱셈회로의 입력에 공급전압의 50%의 크기를 기치는 신호를 인가하였을 때, 1%미만의 왜율을 갖는 -1.3V에서 1.3V크기의 출력신호를 얻었고, 0에서30㎒까지의 -3㏈ 주파수대역을 측정하였고, 81㏈의 출력유동범위와 40㎽의 전력을 소모하였으며, 0.54㎟의 칩면적을 차지하였다. 제안된 곱셈회로는 회로구성이 간단할 뿐만 아니라, 입력신호가 한 개의 트랜지스터를 통하여 출력에 전달되므로 고주파 응용에도 적합하다.