• Journal of electromagnetic engineering and science
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• 제11권3호
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• pp.161-165
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• 2011

In this paper, a high-efficiency DC-AC converter is used for wireless energy transmission. The DC-AC convertter is implemented by combining the oscillator and power amplifier. Given that the conversion efficiency of a DC-AC converter is strongly affected by the efficiency of the power amplifier, a high-efficiency power amplifier is implemented using a class-E amplifier structure. Also, because of the low output power of the oscillator connected to the input stage of the power amplifier, a high-gain two-stage power amplifier using a drive amplifier is used to realize a high-output power DC-AC converter. The high-efficiency DC-AC converter is realized by connecting the oscillator to the input stage of the high-gain high-efficiency two-stage class-E power amplifier. The output power and the conversion efficiency of the DC-AC converter are 40.83 dBm and 87.32 %, respectively, at an operation frequency of 13.56 MHz.

• 동력기계공학회지
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• 제7권4호
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• pp.12-18
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• 2003

Various measures have been tried to reduce the NOx emission from diesel engine, but with partial success because the mechanisms of NOx and PM formations appear to have trade-off relation between each other. Therefore it has been known to be difficult to reduce NOx emission and PM emission simultaneously. Two stage combustion method i,e. a combustion process which has rich combustion stage and lean combustion stage one by one, has been developed successfully to reduce NOx formation in the continuous combustion chambers such as in the boilers. But until yet it is not successful to apply the same method in intermittent combustion chamber like in the diesel engine cylinder, as it was, only several research works were carried out. In this study, devised was a uniquely shaped combustion chamber with reformed piston crown intended to keep fuel-rich condition during early stage of combustion and fuel-lean condition during next stage. It was found that the NOx emission decreased significantly at various conditions of operation with the two stage combustion type engines of PR20 type, but other values such as smoke, CO and specific fuel consumption deteriorated as usual.

• Journal of Chest Surgery
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• 제29권3호
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• pp.337-341
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• 1996

A 40-year-old male patient who had ascending aortic pseudoaneurysm Involving right coronary artery obstruction and thoracic descending aortic pseudoaneurysm was successfully managed by two-stage operation. Repair of intimal tear of ascending aortic pseudoaneurysm with a patch of woven dacron vascular graft and right coronary artery bypass graft with great saphenous vein were performed in first stage operation. On 28 days postoperatively, Repair of intimal tear of descending aortic pseudoaneurysm with a patch of woven dacron vascular graft was done under the femorofemoral partial cardiopulri!onary bypass in second stage operation. The patient was discharged at postoperative 13th days without any evident.

• Journal of Medicine and Life Science
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• 제15권1호
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• pp.23-26
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• 2018

The most common surgical repair method for fingertip injuries are replantation, flap coverage, and skin graft. In fingertip injury cases, acellular dermal matrix (ADM) is generally used in a two-stage operation. In the present case, only ADM was used in a 67-year-old male patient with a right fifth fingertip injury. The patient was undergoing chemotherapy after surgery for colon cancer, preventing prolonged hospitalization. In addition, wound healing was likely to be problematic. As a typical surgical method might have been difficult to apply in such a patient, we performed a one-stage operation, using only ADM on the injured area. Postoperative followup for 3 months showed good wound healing. Accordingly, we report a successful treatment outcome using ADM alone for a fingertip injury.

• 한국유체기계학회 논문집
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• 제5권1호
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• pp.55-61
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• 2002

The feasibility of an oil-free, motor-driven, two-stage centrifugal compressor supported by air bump bearings is investigated. This centrifugal compressor is driven by a 75 kW motor at an operating speed of 39,000 RPM, and a pressure ratio of the compressor is set up to 4. The analysis is performed by using bearing equilibrium position, heaving stillness, Campbell diagram, unbalance response, and stability. It is demonstrated in this paper that air bump bearings can be adopted well to an oil-free, motor-driven, centrifugal compressor. Specially, Cu-coated bump bearings have enough damping force to reduce a synchronous unbalance for rigid modes of the two-stage compressor. Futhermore, this concept may be applied to the flexible rotor system such as high speed turbomachinery with a super critical speed.

• 대한전기학회:학술대회논문집
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• 대한전기학회 1996년도 추계학술대회 논문집 학회본부
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• pp.279-281
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• 1996

This paper deals with the two stage surge protection device by using varistor and LC low pass filter. Recently varistor alone has been used with overvoltage protection devices for the AC power mains and has same problems associated with high remnant voltage and noise. In this work, in order to improve the cutoff performance of surge protection device, the lightning surge protection device having two stage hybrid circuit for an AC single phase mains was designed and fabricated. Operation characteristics and surge clamping performance of the surge protection device in an $8/20{\mu}s$ surge current are investigated. As a consequence, it is found that the proposed two stage surge protective device for AC power mains has a variety of advantages such as a smaller clamping voltage, high frequency noise reduction and large clamping capacity.

• 대한전기학회논문지:전기기기및에너지변환시스템부문B
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• 제49권8호
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• pp.509-513
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• 2000

This paper deals with the parallel operation of space vector PWM for large capacity inverter system. To enlarge the capacity of inverter system and to reduce the current ripples on inverter output side, two or more inverters are operated in parallel. In this paper, a new parallel operation strategy which minimizes the harmonic distortion of the output stage is described. The proposed method is developed on the basis of the space-vector PWM in order to increase the linearly controllable voltage range. With the help of the proposed voltage synthesis method, the total harmonic distortion of the output stage can be greatly reduced in compared with that of conventional method with sinusoidal PWM or that of the single inverter operation case. The experimental results with reduced scale test show the feasibility of the proposed voltage synthesis method.

• Journal of Chest Surgery
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• 제30권3호
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• pp.263-269
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• 1997

1987년 4월부터 1996년 5월까지 복잡 선천성 심기형을 가진 13명의 환자에서 Norwood술식을적용 하였다. 진단별 분포로는 좌심형성부전증후군이 7례이었고, 상행대동맥과 대동맥궁의 형성부전이 있으 면서 심실중격결손증 및 대동맥하 협착증을 동반한 승모판 협착증, 심실중격결손증, 대동맥축착 및 대 동맥하 헙착증을 동반한 승모판 폐쇄증, 심실중격결손증 및 대동맥하 협착증을 동반한 대동맥궁 단절, 대혈관전위를 동반한 삼첨판 폐쇄증이 각각 1례씩 있었으며 이중입구부 좌심실이 2례 있었다 수술 당 시 나이는 3일에서 8.7개월 (평균 60.5 $\pm$ 71.6일, 중앙값 i9일)이었다. 수술 사망율( <30일)은 46% (6명) 이었으며 만기 사망율은 15% (2명)였다. 모든 수술사망은 술후 24시간 이내에 발생하였으며 체외순환으 로부터 이탈에 실패한 경우가 5례, 술후 갑작스런 혈역학적 불안정으로 사망한 경우가 1례 있었고, 만기 사망은모두 흡인성 폐렴에 의한 것이었다. 5명의 장기 생존자에 대한추후술식으로는2명의 환자에서 Norwood술식 후 각각 12, 17개월에 변형 Fontan수술을 하였으며 1명에서 4.5개월 후에 완전 대정맥폐동맥 단락술을 시행하였고 수술 사망은 없었다. 나머지 2명의 환자에서는 Fontan 술식전의 중간단계 로 양방향성 상대정맥-폐동맥 단락술을 각각 3, 5.5개휠 후에 시행하였으며 수술사망이 1례 있었다. 수 술 사망 및 만기 사망을 포함한 모든 환자에서 1년 생존율은 30.8%였다. 결론적으로 본원에서 경험한 Norwood 술식의 사망율이 다른 주요 심장기 형의 사망율과 비교하여 높지만 이에 대한 경험이 축적되면서 더 좋은 성적을 기대할 수 있을 것으로 생각된다.

• 대한족부족관절학회지
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• 제24권1호
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• pp.25-30
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• 2020

Purpose: Generally, the treatment of ankle trimalleolar open fractures is divided into two stages: external fixation and debridement; and secondary internal fixation. On the other hand, this two-stage operation takes considerable treatment time and is challenging in procedures requiring reduction. The purpose of this study was to evaluate the radiologic and clinical results of an immediate one-stage internal fixation operation considering the wound conditions to overcome two stage operation disadvantages. Materials and Methods: From September 2009 to January 2018, 24 cases of ankle trimalleolar open fractures, who underwent immediate internal fixation and were followed up for at least one year, were studied retrospectively. The open wound was divided into the Gustilo-Anderson classification. Open reduction and internal fixation were performed on every medial and lateral malleolar fracture. On the other hand, with posterior malleolar fractures, surgical or conservative treatment was performed depending on the fragment size. The radiologic outcome was evaluated using the Burwell and Charnley criteria and American Orthopaedic Foot and Ankle Society (AOFAS) scores, and complications, such as infection and posttraumatic arthritis, were used for the clinical evaluation. Results: The wound was classified into eight cases (33.3%) of type I, 11 cases (45.8%) of type II, and five cases (20.8%) of type IIIa. The degree of reduction was anatomical, fair, and poor in 16 cases (66.7%), six cases (25.0%), and two cases (8.3%), respectively. The mean AOFAS score was 79 points, and there were complications, such as infection in three cases (12.5%) and post-traumatic arthritis in two cases (8.3%). Conclusion: Satisfactory results were obtained through immediate surgical treatment in ankle trimalleolar open fractures of types I, II, and IIIa.

• Journal of Chest Surgery
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• 제55권1호
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• pp.37-43
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• 2022

Background: The surgical strategy for single-stage resection of primary colorectal cancer (CRC) and synchronous pulmonary metastases remains a matter of debate. Methods: Perioperative data of patients who underwent single-stage resection of primary CRC and synchronous pulmonary metastases were compared to those of patients who underwent 2-stage resections. The demographic data, number of metastases, type of pulmonary and colorectal resections, operation time, blood loss, postoperative complications, morbidities, mortality, medical costs, and length of hospital stay were analyzed. Results: Twenty-two patients underwent single-stage resection of primary CRC and pulmonary metastases, while 27 patients underwent 2-stage resection. Tumor size and the number of pulmonary metastases were not significantly different between the 2 groups. The extent of pulmonary metastasectomy and abdominal procedures were similar in both groups, as was the thoracic surgical approach (video-assisted thoracic surgery vs. thoracotomy). However, open laparotomy was performed more frequently in the 2-stage group than in the single-stage group (p=0.045), which also had a longer total anesthetic time (p=0.013). The operation time, medical costs, estimated blood loss, complication rates, and severity were similar in both groups, but the length of hospital stay was shorter in the single-stage group (p<0.001). Conclusion: Single-stage colorectal and pulmonary resection shortened the overall hospital stay, with no significant changes in operation time, medical costs, hospital mortality, and morbidity. Therefore, single-stage resection could be a good surgical strategy in selected patients.