• 전력전자학회논문지
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• 제11권6호
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• pp.520-528
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• 2006

동일한 변압기를 사용하는 공통암 타입의 절연형 다중레벨 인버터에서 스위칭 주파수를 저감하기 위해 새로운 위상변위제어기법을 제안 하였다. 제안된 스위칭 방식은 인버터의 각 암이 기본주파수당 한번만을 스위칭을 하는 스텝 펄스파 방식을 사용하여 동일한 스위칭 주파수를 유지할 수 있다. 제안된 스위칭 방식의 타당성을 검증하기 위해 기존의 동일변압기를 이용한 멀티레벨 인버터의 스위칭 패턴과 제안된 위상변위 제어방식을 이용한 멀티레벨 인버터의 스위칭 패턴을 시뮬레이션하고 실험을 통해 비교 하였다.

• 한국해양공학회지
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• 제28권1호
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• pp.55-63
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• 2014

In this paper, we propose an threshold-based Schur algorithm for estimating the media characteristics of sub-bottom multi-layers by using the signal generated by a parametric array transducer. We use the KZK model to generate a parametric array signal, and use the proposed threshold-based Schur algorithm for estimating the reflection coefficients of multiple sea bottom layers. Using computer simulation, we verify that the difference frequency component generated by the KZK model prevails over the signals of primary frequencies at long range. For the simulation, we use the transmit signal generated by the KZK and the reflected signal obtained from a lattice filter model for the seawater and sub-bottom of multi-level non-homogeneous layers. Through the simulation, we verify that the proposed threshold-based Schur algorithm can give much more accurate and efficient estimates of the reflection coefficients than methods using received signal, matched filter output signal, and normal Schur algorithm output.

• 대한전기학회:학술대회논문집
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• 대한전기학회 1987년도 전기.전자공학 학술대회 논문집(II)
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• pp.869-873
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• 1987

In this study, we have examined the multi-level QPRS system in point of error rate, which requires narrow bandwidth and has Little ISI. The generalized error rate equations of multi-level QPRS signal have been derived in the presence of Gaussian noise and co-channel CW interference. And the error rate performance of 9, 49, 225 QPRS system is investigated as parameters of carrier power-to-noise power, carrier power-to -interference power. Also, we have investigated the effect of carrier offset.

• 전력전자학회:학술대회논문집
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• 전력전자학회 2005년도 전력전자학술대회 논문집
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• pp.96-98
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• 2005

Proposed Multi-level PDP sustain Driver make use of element which has a low voltage rating instead of suggested method by the existing Webber and it passes through a second phase both rising and falling at sustaining voltage waveform In accordance with the change of timing phase(Tr1, Ti1, Tr2) performance comparison of a electric discharge characteristics in a PDP module has been carried out. At the conclusion of experimentation, the feature is extended by alteration of Ti1 and it has little to do with alteration of Tr1.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2007년도 제38회 하계학술대회
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• pp.1134-1135
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• 2007

In this paper, we proposed the isolated multi-level inverter using 3-phase transformers. It makes possible to use a single DC power source due to employing low frequency transformers. In this inverter, the number of transformer could be reduced comparing with an exiting 3-phase multi-level inverter using single phase transformer. Also, using phase angle control method with switching frequency equal to output fundamental frequency, harmonics component of output voltage and switching losses can be reduced. Finally, we made a prototype inverter to clarify the proposed electric circuit and reasonableness of control signal.

• Journal of Communications and Networks
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• 제10권2호
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• pp.127-136
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• 2008

For mobile wireless systems with full frequency reuse, co-channel interference near the cell coverage boundaries has a significant impact on the signal reception performance. This paper addresses an approach to efficiently mitigate the effect of downlink co-channel interference when multi-antenna terminals are used in cellular environments, by proposing a signal detection strategy combined with a system-level coordination for dynamic frequency reuse. We demonstrate the utilization of multi-antennas to perform spatial demultiplexing of both the desired signal and interfering signals from adjacent cells results in significant improvement of spectral efficiency compared to the maximal ratio combining (MRC) performance, especially when an appropriate frequency reuse based on the traffic loading condition is coordinated among cells. Both analytic expressions for the capacity and experimental results using the adaptive modulation and coding (AMC) are used to confirm the performance gain. The robustness of the proposed scheme against varying operational conditions such as the channel estimation error and shadowing effects are also verified by simulation results.

• 한국기계가공학회지
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• 제3권3호
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• pp.11-16
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• 2004

In this study, the characteristics of signals such as acoustic emission, vibration amplitude and noise level which are derived from the abnormal condition of compressor are investigated. The normal condition, vane stick sound and roller defect condition are chosen to analyze the signal in each cases. From the feature extraction of each signals, the dominant parameters of each signals which can identify the abnormal condition are suggested.

• Journal of Korean Neurosurgical Society
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• 제53권2호
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• pp.83-88
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• 2013

Objective : The authors reviewed their experiences of combined surgery (open door laminoplasty with unilateral screw fixation) for unstable multi-level cervical stenosis, to clarify the situation regarding the surgical approach most appropriate for the treatment of diffuse unstable multi-level cervical stenosis. Methods : From January 2011 to January 2012, combined surgery was performed for unstable multi-level cervical stenosis by one surgeon at our institution. The subjects of this study were 6 men of mean age 53.7 years (range, 48-71) with a mean follow-up of 9.3 (range, 3-14) months. All imaging studies showed severe multi-level cervical stenosis with spinal cord signal change, and instability or kyphotic deformity. A retrospective review of clinical, radiological, and surgical data was conducted. Results : Average laminoplasty level was 4.8 and the average screw fixation level was 5.0. Japanese Orthopedic Association score improved from an average of 5.2 to 11.2 points. According to Nurick's grades and Odom's criteria, symptom improvement was statistically significant. On the other hand, Cobb's angle changes were not significant. Average operation time was 5.86 hours with an average blood loss of 460 mL. No significant surgical complication was encountered. Conclusion : Despite the small cohort and the short follow-up duration, the present study demonstrates that laminoplasty with unilateral screw fixation is a safe and effective treatment for unstable multi-level cervical stenosis.

• 전력전자학회논문지
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• 제16권3호
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• pp.283-292
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• 2011

본 논문에서는 기존의 멀티레벨 인버터와는 달리 DC링크단에 스위치를 설치함으로써 성능을 향상시킨 새로운 형태의 H-브리지 멀티레벨 인버터를 제안한다. 제안된 방식은 계통 연계형 단상 멀티레벨 인버터로서 기존의 단상인버터에 비하여 출력 전압 파형이 정현파에 가깝고, 고압 대용량 시스템용 멀티레벨 인버터로의 확장도 용이할 뿐만 아니라 직렬연결을 통하여 간단히 전압레벨을 확장할 수 있다는 장점을 갖는다. 동일한 5레벨의 경우 기존의 H-브리지 직렬형이나 NPC형 멀티레벨 인버터는 가제어 스위치가 8개 사용되는 반면에 제안한 멀티레벨 인버터는 가제어 스위치가 6개 사용되기 때문에 회로 구성이 간단하여 신뢰도가 높고 경제적인 구현이 가능하고 스위칭 손실이 줄어서 효율이 향상되는 특징이 있다. POD 변조기법을 기반으로 하여 반송파 신호 하나만을 사용하는 새로운 PWM 방법을 제시하였으며 DC링크 커패시터 전압의 균형을 위한 스위칭 시퀀스에 대해서도 검토하였다. 제안된 토폴로지의 타당성을 시뮬레이션과 실험을 통하여 확인하였다.

• 대한원격탐사학회지
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• 제19권4호
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• pp.271-276
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• 2003

복합위성자료 신호처리기법을 사용해서 남인도양 지역을 중심으로 한 해수면변화와 사행 (meandering)을 연구하였다. 해수면변화는 아프리카 남부(46$^{\circ}$E)에서 크호제트 대지(Crozet basin)의 35$^{\circ}$~46$^{\circ}$S대를 걸쳐서 암스테르담-케르겔른 경로(Amsterdam-Kerguelen Passage)까지 확장된다. 이때 가장 강한 해수면변화(20~30cm)가 2개의 좁은 지역에서 발생하는데, 하나는 경도 49$^{\circ}$~57$^{\circ}$E(약 700Km) 및 위도 38$^{\circ}$~42$^{\circ}$S(약 450Km)나타났고 그리고 나머지 하나는 경도 58$^{\circ}$~64$^{\circ}$E(약 450Km) 및 위도 42$^{\circ}$~44$^{\circ}$S(약 200Km)에서 각각 나타났다. 이것은 해저지형과 관련된 강한 와동류의 형성 때문이다. 와동류 발생지역은 아규라스반류(Agulhas Return Current) 및 남극순환해류(Antarctic Circumpolar Current)와 관련하여 강한 흐름이 형성되는 지역에서 발생했다. 이때 복합위성자료(Topex/Poseidon, ERS1)는 표층순환과 해수면변동 특성을 잘 나타내었다.