• 한국철도학회:학술대회논문집
• /
• 한국철도학회 2008년도 추계학술대회 논문집
• /
• pp.1138-1144
• /
• 2008

To study the feasibility of applying wireless communication technology to the control of train for the effective control of train and for the reduction of cost and time to construct the necessary infra structure, we investigate into the application of the existing commercial WCDMA network to CBTC (communication-based train control) to grasp the obstacles and propose the solutions to circumvent them. The obstacles can be categorized into the hand-off problem, the interference problem near the stations, and the problem of radio shadow areas. We propose, as solutions, the cell overlap method and multi-terminal approach for the hand-off problem, the cell sectoring method for the interference problem, and establishment of new base stations along the railroad both to provide the wireless train control and communication service to the customers on the train which was otherwise impossible because of the shadowing effect.

• 한국진공학회:학술대회논문집
• /
• 한국진공학회 2011년도 제40회 동계학술대회 초록집
• /
• pp.310-310
• /
• 2011

Morphological evolution of amorphous carbon film is investigated by molecular dynamics simulation. Here, energetic carbon atoms (75 eV) are deposited on the diamond (001) substrate to find effect of incidence angles. At normal and near-normal incidences ($0^{\circ}{\sim}30^{\circ}$) atomically smooth surfaces are observed during their growth. However, rough surfaces emerge and develop into a ripple structure at grazing incidences ($60^{\circ}{\sim}70^{\circ}$). The different growth modes according to the incidence angles can be described by impact-induced displacements of atoms. Downhill transport along any sloped surfaces is predominant for the case of normal incidence. As the incidence angles become grazing, uphill transport is allowed along the surfaces, which have smaller slopes than incidence angle, so the surface features can be amplified. Impact-induced transport and self-shadowing effect can be responsible to the initial growth of seeding structures at a grazing incidence, which would be grown up as tilted columnar structures in further depositions.

• 한국통신학회논문지
• /
• 제23권4호
• /
• pp.901-913
• /
• 1998

본 논문에서는 CDMA 셀룰러 망에서 셀 간의 간섭이 불균일한 경우에 역방향 링크에서의 간섭을 계산하기 위한 새로운 해석 방법을 제시한다, 특히, 제안된 방식에서는 역방향 링크 전력 제어의 동적 특성을 반영함으로써 셀 간의 불균일한 통화량이 시스템 용량에 미치는 영향을 정확하게 정량화할 수 있으며, 셰도잉과 소프트 핸드 오프에 따른 영향을 고려한 분석이 가능하다. 이와 같이 셀 간의 불균일한 통화량을 고려한 상황에서 역방향 링크 전력 제어의 동적 특성을 반영한 간섭 계산 방식은 기존 연구에서 제시되지 않은 부분이다. 제안된 방식으로 계산된 결과를 살펴보면, 인접한 모든 셀들의 통화량이 두배가 될 때 계산된 가입자 수는 전력 제어의 동적 특성을 고려하지 않고 계산된 결과에 비해 27%까지 감소하는 것을 알 수 있다.

• 대한전자공학회논문지SD
• /
• 제37권12호
• /
• pp.24-28
• /
• 2000

본 논문에서는 레벨셋 방법을 이용한 표면 전진기를 사용하여 반도체 공정에서 3차원 증착 프로파일을 계산하는 방법을 보고한다. 레벨셋 방법을 이용하여 효율적으로 표면의 전진, 후퇴를 모델링 하기 위하여 반복법에 의한 초기화 방법을 새로이 개발하였다. 또한, 각각의 위치에서의 증착 및 식각률을 계산하기 위하여 소스에서 표면까지의 가시도 계산 방법과 표면 반사 모델을 개발하였다. 3차원 표면 전진기로 그림자 효과와 표면 반사가 고려된 계산을 수행하였다. 흡착 계수가 1인 경우와 0.3인 경우를 비교하여 반사, 스퍼터링에 의한 증착 프로파일의 변화를 비교하였다. 그리고 종횡비에 따른 증착률의 차이를 그림자 효과에 의한 가시각의 차이로 비교하였다.

• 한국통신학회논문지
• /
• 제32권6A호
• /
• pp.588-599
• /
• 2007

This paper presents the coexistence issues between M-WiMAX TDD and WCDMA FDD systems. To improve the M-WiMAX system performance and to reduce the adjacent channel interference to WCDMA FDD system, transmit and receive beamforming techniques are applied in the base stations of M-WiMAX system. Furthermore, we propose an adjacent channel interference modeling methodology, which captures the effect of transmit beamforming on the adjacent channel interference. Besides, we verify the performance improvement in the uplink of WCDMA system due to the transmit beamforming in M-WiMAX downlink based on the proposed adjacent channel interference modeling methodology. We also verify the performance enhancement due to the receive beamforming in the uplink of M-WiMAX system through system level Monte Carlo simulations, considering random user position, the effect of shadowing and multi-path fading channel. Discussions on the gain of applying transmit and receive beamforming in M-WiMAX system comparing the case of SISO system are also included. Furthermore, we present the performance of cosited M-WiMAX and WCDMA systems, considering commercial deployment, additional channel filter at base stations and the effects of TxBF and RxBF.

• Journal of Electrical Engineering and Technology
• /
• 제9권3호
• /
• pp.827-834
• /
• 2014

In order to meet the low voltage ride-through requirement in a grid code, a wind power plant (WPP) has to stay connected to a grid, supporting the voltage recovery for a grid fault. To do this, a plant-level controller as well as a wind generator (WG) controller is essential. The dynamic response of a WPP should be analyzed in order to design a plant-level controller. The dynamic response of a WPP for a grid fault is the collective response of all WGs, which depends on the wind speed approaching the WG. Thus, the dynamic response of a WPP should be analyzed by taking the wake effect into consideration, because different wind speeds at WGs will result in different responses of the WPP. This paper analyzes the response of a doubly fed induction generator (DFIG)-based offshore WPP with a grid fault taking into account the wake effect. To obtain the approaching wind speed of a WG in a WPP, we considered the cumulative impact of multiple shadowing and the effect of the wind direction. The voltage, reactive power, and active power at the point of common coupling of a 100 MW DFIG-based offshore WPP were analyzed during and after a grid fault under various wind and fault conditions using an EMTP-RV simulator. The results clearly demonstrate that not considering the wake effect leads to significantly different results, particularly for the reactive power and active power, which could potentially lead to incorrect conclusions and / or control schemes for a WPP.

• Journal of Chest Surgery
• /
• 제24권3호
• /
• pp.265-270
• /
• 1991

Since advent of the prosthetic cardiac valve replacement, much efforts for accurate assessing value function in-vivo have been attempted. To evaluate the postoperative functional and morphological status of the replaced cardiac valve prosthesis, 33 patients with valve replacement were studied by transthoracic and transesophageal 2-dimensional echocardiac imaging as well as by color Doppler flow velocity imaging. Twenty four patients had mitral valve replacement. 6 patients had aortic valve replacement and 3 patients had both mitral and aortic valve replacement. There were 34 mechanical and 2 biological prosthesis. Comparing to transthoracic echocardiography, transesophageal approach showed transvalvular regurgitant jet flow amid the prosthetic mitral valve ring during. systole and much clear visualization of cardiac chamber behind prosthesis which could give shadowing effect to ultrasound beam. According to the quantitative grading by the length and area of mitral regurgitant flow, 24 out of 27 mitral valves revealed mild degree regurgitation considered as physiological after prosthetic bileaflet valve replacement and the other 3 valves including 2 biological prosthesis had moderate degree regurgitation which was regarded as pathologic one. 2 cases of left atrial thromboses and 1 case of paravalvular leakage which were not visible by transthoracic approach were identified by transesophageal echocardiography in patients with mitral valve replacement and patients with aortic valve replacement respectively. We conclude that in patients with prosthetic mitral valve replacement, transesophageal 2-dimensional imaging with color Doppler can suggest reliable information beyond that available from the transthoracic access even though it gives patient some discomfort to proceed.

• 한국해양공학회지
• /
• 제24권1호
• /
• pp.47-52
• /
• 2010

This study presents a modified scheme for the radar image simulation of sea waves. A simulated radar image was obtained by taking into account the dot product of the directed vector from the radar and the normal vector of the sea surface. Moreover, to calculate the radar image, we used the radar received power and radar cross section. To demonstrate the effectiveness of the proposed scheme, the wave spectrum from field data was utilized to obtain the simulated sea waves. The radar image was simulated using numerically generated sea waves. The wave statistics from the simulation agrees comparatively with those of the original field data acquired by real radar measurements.

• 대한전자공학회논문지TC
• /
• 제42권6호
• /
• pp.33-40
• /
• 2005

본 논문에서는 광대역 무선 접속 시스템에서 동적 예약 접속 프로토콜의 메시지 지연시간을 해석적으로 분석한다. IEEE 802.16 BWA 와 ETSI HIPERLAN//2 와 같은 광대역 무선 접속 시스템은 무선 MAN 의 시스템 커버리지를 갖으며, 단말의 이동성을 지원하지 않는, 즉 단말이 고정되어 있는 시스템이다. 또한 광대역 무선 접속 시스템에서 사용하는 MAC 프로토콜은 트래픽별 QoS를 효율적으로 지원하기 위하여 경쟁 기반으로 동적 예약을 지원하는 TDMA 방식을 사용한다. 이와 같은 통신망을 분석하기 위하여 경쟁 기반 동적 예약 방식을 지원하는 TDMA 프로토콜의 성능을 해석적으로 분석한다.

• 한국임상수의학회지
• /
• 제22권4호
• /
• pp.444-449
• /
• 2005

An 11-year-old female, Golden retriever dog with a history of solid mass on the chest wall was referred to Veterinary Medical Teaching Hospital, Seoul National University. The mass was firm on palpation. A soft tissue opacity mass with calcified foci around the right 7th rib and extrapleural patterns around the right 5th rib and 7th rib was shown on thoracic radiographs. The mass of the 7th rib has a mixed-echo pattern with a strong acoustic shadowing and internal vascular signals on ultrasonography. On CT scan, the mass showed contrast enhancement effect, expansive pattern of intrathoracic and extrathoracic legion around costochondral junction. The 7th rib appeared mildly lytic. The mass of the 5th rib had a soft tissue swelling without bone lysis. The mass was diagnosed as a sarcoma by fine needle biopsy. Therefore, the mass was surgically removed. Subsequent histopathological study found the mass was chondrosarcoma.