• 대한기계학회논문집B
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• 제30권2호
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• pp.110-116
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• 2006

A syringe pump or a device using high electric voltage has been used for controlling flows inside a LOC (lab-on-a-chip). Compared to LOC, however, these microfluidic devices are large and heavy that they are burdensome for a portable ${\mu}-TAS$ (micro total analysis system). In this study, a new flow control technique employing pressure regulators and pressure chambers was developed. This technique utilizes compressed air to control the micro-scale flow inside a LOC, instead of a mechanical actuator or an electric power supply. The pressure regulator controls the output air pressure by adjusting the variable resistor attached. We checked the feasibility of this system by measuring the flow rate inside a capillary tube of $100{\mu}m$ diameter in the Re numbers ranged from 0.5 to 50. In addition, the performance of this flow control system was compared with that of a conventional syringe pump. The developed flow control system was found to show superior performance, compared with the syringe pump. It maintains automatically the: air pressure inside a pressure chamber whether the flow inside the capillary tube is on or off. Since the flow rate is nearly proportional to the resistance, we can control flow in multiple microchannels precisely. However, the syringe pump shows large variation of flow rate when the fluid flow is blocked in the microchannel.

• 한국정보통신학회논문지
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• 제19권12호
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• pp.2963-2967
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• 2015

단일모드 광섬유를 사용한 WDM 시스템에서 CPM에 의한 성능저하를 이론적으로 분석하기 위해 펌프-프로브 구조에서 펌프신호가 주기적이라고 가정하였다. 주기적 펌프신호는 '0'과 '1'이 교대로 발생하는 경우를 모델링한 것으로 CPM에 의한 EOP를 이론적으로 예측할 수 있게 한다. 유도된 이론적 결과를 수치해석 결과와 비교하였으며, 그 결과 표준 단일모드 광섬유를 사용한 경우는 넓은 영역의 채널 간격 ${\Delta}f$에 대해 유도된 이론식이 수치해석의 결과와 잘 일치하고 분산천이 광섬유를 사용한 경우는 ${\Delta}f$>100GHz 에서 일치하였다. 분산천이 광섬유를 사용하여 ${\Delta}f$<100GHz 인 경우는 CPM뿐만 아니라 FWM에 의한 성능저하가 두드러지므로 이론적 결과와 수치 해석의 결과 사이의 편차가 증가한다. 펌브-프로브 구조가 광섬유의 비선형성중 CPM의 영향을 주로 분석하기 위한 것이므로 이 결과는 예상대로 이다.

• 한국기계가공학회지
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• 제15권5호
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• pp.8-17
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• 2016

While greenhouses have been utilized as a sustainable alternative to traditional soil farming, they are often powered by diesel boilers that necessitate vast amounts of non-renewable energy and emit toxic fumes. Thus, geothermal heat pumps have been proposed as a more energy-efficient substitution for diesel boilers. Currently, most horticultural facilities in the United States use shallow geothermal systems, and are often equipped with horizontal underground heat exchangers as well as heat pump equipment. These shallow geothermal systems require a large drilling site and heat pump to function, which results in high maintenance costs. The heat pump itself consumes a large amount of power, which degrades system performance. Conversely, high temperatures can be attained within a single borehole in deep geothermal vertical closing systems without using a heat pump. This setup can dramatically reduce the power consumption and improve system performance. In this study, we have modeled a circulation simulator after the circulation systems in deep geothermal facilities to analyze a 2000-meter borehole in Naju-Sanpo-myeon. The simulator is operated by manipulating various putative parameters affecting system performance to analyze the system's coefficient of performance.

• 한국추진공학회:학술대회논문집
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• 한국추진공학회 2008년도 제31회 추계학술대회논문집
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• pp.359-365
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• 2008

30톤급 액체로켓엔진용 터보펌프에 대하여 실매질을 사용하여 성능시험이 이루어졌다. 산화제펌프와 연료펌프에는 각각 액체산소, 케로신의 실매질을 사용하고 터빈에는 고압의 상온 수소가스가 사용되었다. 터보펌프는 설계점과 탈설계점의 전 영역에서 안정적으로 작동하였고 요구되는 성능 조건을 만족시켰으며 이로써 엔진 서브시스템 수준의 터보펌프 개발이 성능 측면에서 검증되었다고 볼 수 있다. 본 논문에서는 단일 운전으로 세 운용점에서 총 75초간 작동된 경우의 시험결과를 소개하였다. 펌프와 터빈의 성능 특성 관점에서 터보펌프 조립체의 실매질 성능시험 결과와 터보펌프 구성품의 상사 성능 시험 결과가 양호하게 일치하였다.

• Journal of Construction Engineering and Project Management
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• 제4권2호
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• pp.31-40
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• 2014

The management of vehicular supply of "perishable" construction material, such as concrete mixes, faces a series of uncertainties such as weather, daily traffic patterns and accidents. Presented in this paper is a logistics control model for managing a hauling fleet with interrelated processes at both ends and queue capacities. Discrete event simulation is used to model the complex interactions of production units and the randomness of the real world. Two alternative strategies for ready mix concrete delivery, with and without an off-site waiting queue, are studied to compare supply performance. Secondly, the paper discusses the effect of an agent-based GPS tracking system providing real-time travel data that lessens the uncertainty of trucking time. The results show that the combination of GPS information with off-site queuing reduces productivity loss and process wastes of concrete placement as well as the idleness of supply trucks when crew or pump experience an unexpected stoppage.

• 한국유체기계학회 논문집
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• 제19권6호
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• pp.34-42
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• 2016

The organic Rankine cycle (ORC) has been used to convert thermal energy to mechanical energy or electricity. The available thermal energy could be waste heat, solar energy, geothermal energy, and so on. However, these kinds of thermal energies cannot be provided continuously. Hence, the ORC can be operated at the off-design point. In this case, the performance of the ORC could be worse because the components of the ORC system designed based on a design point can be mismatched with the output power obtained at the off-design point. In order to improve the performance at the off-design point, a few components were replaced including generator, bearing, load bank, shaft, pump and so on. Experiments were performed on the same facility without including other losses in the experiment. The experimental results were compared with the results obtained with the previous model, and they showed that the system efficiency of the ORC was greatly affected by the losses occurred on the components.

• 대한의생명과학회지
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• 제17권4호
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• pp.337-345
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• 2011

It is well recognized that conventional coronary artery bypass grafting (ONCAB) often leads to major organ dysfunction including renal injury. Diabetes mellitus is a major cause of nephropathy and poor clinical outcomes. The aim of this retrospective study was to evaluate the occurrence of adverse outcomes including renal impairment between diabetic (n=75, DM group) and non-diabetic patients (n=72, Non-DM group) underwent off-pump coronary artery bypass grafting surgery (OPCAB). Fasting glucose, hemoglobin A1c, fructosamine, fibrinogen and serum osmolality levels in the DM group were higher than those of the Non-DM group at pre-operative (Pre-OP) period ($P$ <0.05). History of hypertension and renal impairment in the DM group was higher than that of the Non-DM group ($P$ <0.05). Potassium ($K^+$), blood urea nitrogen and creatinine levels were higher, whereas sodium ($Na^+$) and glomerular filtration rate (GFR) levels were lower in the DM group than the Non-DM group at peri-operative period ($P$ <0.05). Fasting glucose levels at Pre-OP period had positive correlations with blood urea nitrogen and creatinine levels at peri-operative period, but negative correlations with GFR levels at peri-operative period in the DM group ($P$ <0.05). Incidences of renal impairment, diuretic therapy or continuous renal replacement therapy and fever in the DM group were higher than those of the Non-DM group at post-operative period ($P$ <0.05). These results suggest that blood glucose level should be tightly controlled at peri-operative period to avoid renal dysfunction in diabetic patients.

• 한국정보전자통신기술학회논문지
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• 제9권6호
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• pp.553-558
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• 2016

본 논문은 바이오센서 칩에 사용하기 위해 3.3V CMOS 이미지 센서용 DC-DC 변환기 회로를 제안하였다. DC-DC 변환기 회로는 픽셀의 ON 전압인 PCP 전압과 OFF 전압인 NCP 전압으로 사용된다. 제안된 PCP 회로는 리플 전압이 45.35mV인 VPP (=5V) 양전하펌프 전압을 전압 레귤레이터를 이용하여 리플전압이 1.33mV 이내인 PCP 전압을 얻었다. 그리고 제안된 NCP 회로는 리플 전압이 62.8mV VNN (=-2V) 음전하펌프 전압을 전압 레귤레이터를 이용하여 리플전압을 0.05mV 이내로 설계하였다.

• Journal of Chest Surgery
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• 제46권4호
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• pp.265-273
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• 2013

Background: The safety and efficacy of arterial composite grafts for total arterial revascularization have been demonstrated. The saphenous vein (SV) is a widely used graft because of its accessibility, sufficient length, and ease of manipulation. Our aim was to compare mid-term outcomes of saphenous vein Y-grafts with radial artery Y-grafts joined by anastomosis to the left internal thoracic artery. Materials and Methods: Records of off-pump coronary artery bypass grafting with composite Y-grafts based on the left internal thoracic artery technique in 552 patients were analyzed retrospectively. After propensity score matching, 79 radial arterial (RA) composite grafts (RA group) and 79 saphenous vein composite grafts (SV group) were compared. The duration of mean follow-up was $24.6{\pm}14.6$ months (range, 1 to 55 months). Results: There were no differences in surgical mortality, all-cause mortality, or morbidity among the groups. Rates of 4-year survival were 91.7% and 96.3% in the RA and SV groups, respectively (p=0.519). The coronary reintervention-free survival rate and freedom from major adverse cardiovascular or cerebrovascular events were similar in the two groups (p=0.685, p=0.564). Conclusion: Construction of composite Y-grafts using the radial artery or saphenous vein showed similar mid-term results. Long-term follow-up and randomized trials will be needed to confirm our present conclusions.

• Journal of Chest Surgery
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• 제32권9호
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• pp.835-839
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• 1999

1974년에 말기 신부전증 환자에서 심폐바이패스를 이용한 관상동맥우회술이 처음 보고된 이래 고위 穩\ulcorner인 만성 신부전증 환자들에서의 관상동맥우회술에 대한 많은 연구 논문들이 발표되어 왔다. 만성 신부전증 환자들은 고혈압, 당뇨 등을 동반하는 경우가 종종 있으며, 이 질환들의 합병증 혹은 만성 신부전증 자체가 관상동맥우회술의 단기및 장기 생존율에 영향을 미칠수 있다. 개심술을 받은 말기 신부전증 환자들에서는 감염과 패혈증 등의 합병증의 발생률이 높으며, 수술전후의 수액량과 전해질 장애 등으로 수술 위험도가 증 가하는 것으로 알려져 왔다. 저자들은 3예의 만성 신부전증 환자들에서 심폐바이패스를 사용하지 않고 관상 동맥우회술을 시행하여 그 결과를 발표하고자 한다.