• 한국정보통신학회:학술대회논문집
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• 한국해양정보통신학회 2010년도 추계학술대회
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• pp.764-765
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• 2010

인체의 진단에 사용되는 의료용 X선 기기는 비 침습적인 방법으로 인체 내부의 진단이 가능하여 의료기관에서 진단에 매우 큰 비중을 차지하고 있다. X선의 발생에 가장 중요한 고전압 발생장치는 기존 변압기 식이 주로 사용되었으나 크고 무거우며 직류 고전압의 리플이 커서 발생효율이 낮다. 이러한 단점을 보완하기 위해 인버터를 사용하여 입력전원의 주파수를 고주파하는 인버터 방식의 고전압 발생장치가 주로 사용되고 있다. 본 연구에서는 펄스폭 변조 방식을 적용하여 관전압과 관전류의 동작을 제어 하였으며, 오실로 스코프를 이용하여 동작 결과를 확인하였다.

• 대한기계학회논문집
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• 제17권2호
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• pp.300-312
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• 1993

The material deterioration of service-exposed boiler tube steels in fossil power plant was evaluated by using the electrochemical technique namely, modified electrochemical potentiokinetic reactivation(EPR). It was focused that the passivation of Mo$_{6}$C carbide which governs the mechanical properties of Mo alloyed steels did not occur even in the passivity region of steel in sodium molybdate solution and the reactivation peak current (Ip) observed as the result of non-passivation indicating the precipitation of Mo$_{6}$C carbides. To obtain the optimal test conditions for the field test by using the specially designed electrochemical cell, the effects of scan rate, the surface roughness and the pH of electrolyte on Ip value were also investigated. Furthermore, the change of mechanical properties occurred during the long time exposure at high temperature was evlauated quantitatively by small punch(SP) tests and micro hardness test taking account of the metallurgical changes. It is known that reactivation peak current (Ip) has a good relationship with Larson-Miller Parameter(LMP) which represents the information about material deterioration occurred at high temperature environment. In addition it was possible to estimate the ductile-brittle transition temperature (DBTT) by means of the SP test. The Sp test could be, therefore, suggested as a reliable test method for evaluating the material degradation of boiler tube steels. From the good correaltion between the SP DBTT and Ip values shown in this study, it was knows that the change of mechanical properties could be evaluated non-destructively by measurring only Ip values.ues.

• 비파괴검사학회지
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• 제17권4호
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• pp.262-269
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• 1997

발전 설비중 열교환기 튜브와 같이 단면 형상이 원형인 부품의 원주 방향으로 마모, 침식 등에 의해 발생할 수 있는 단면 형상 변화를 검사(profilometry)하기 위한 와전류 탐촉자를 임피던스 등가회로이론을 적용하여 개발하였다. 본 연구에서는 외경 9.68mm, 벽두께 0.47mm인 SS304 튜브 외부에 발생할 수 있는 마모, denting 등의 결함을 모의한 시편을 제작하여 실험을 통해 검출 감도와 S/N비가 최적인 탐촉자의 코일치수, 전기적 특성, 적용 시험 주파수 등을 설정하였다. 이 결과에 따라 단면 형상 검사용 $8{\times}1$ 다중표면 탐촉자를 설계 제작하여 모의시편의 각 결함별 마모율을 검사한 결과 튜브 외부 발생 단면 형상 변화를 튜브외경의 ${\pm}0.2%$ (0.022mm) 측정 오차 범위로 측정이 가능함을 확인하였다.

• 비파괴검사학회지
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• 제32권1호
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• pp.56-63
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• 2012

본 연구에서는 가공된 오스테나이트계 STS 316L ASME 표준 교정시험편을 이용하여 튜브 두께 감소율과 잔존두께에 대한 와전류 신호와 IRIS 신호특성을 비교하여 리보일러 튜브의 현장 적용성을 평가하였다. 그 결과 두께감소율의 경우 와전류탐상검사는 $20%{\times}4$ 평저공, 10% 외면 그루브, IRIS는 80%홈, 10%외면 그루브에서 ${\pm}15%$ 이상의 편차가 발생하였다. 잔존두께의 경우 와전류탐상은 측정치가 모두 허용범위를 만족하였으나, IRIS는 80% 인공홈에서 ${\pm}15%$ 이상의 편차가 발생하였다. 따라서 와전류탐상검사 후 의사지시에 대한 해석, 두께감소율 측정을 위해 IRIS를 수행한다면 신뢰성이 향상될 것으로 판단된다.

• 한국의학물리학회지:의학물리
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• 제27권3호
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• pp.125-130
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• 2016

Dual energy computed tomography (DECT) is used to classify two materials and quantify the mass density of each material in the human body. An energy modulation filter based DECT could acquire two images, which are generated by the low- and high-energy photon spectra, in one scan, with one tube and detector. In the case of DECT using the energy modulation filter, the filter should perform the optimization process for the type of materials and thicknesses for generating two photon spectra. In this study, Geant4 Monte-Carlo simulation toolkit was used to execute the optimization process for determining the property of the energy modulation filter. In the process, various materials used for the energy modulation filter are copper (Cu, $8.96g/cm^3$), niobium (Nb, $8.57g/cm^3$), stannum (Sn, $7.31g/cm^3$), gold (Au, $19.32g/cm^3$), and lead (Pb, $11.34g/cm^3$). The thickness of the modulation filter varied from 0.1 mm to 1.0 mm. To evaluate the overlap region of the low- and high-energy spectrum, Geant4 Monte-Carlo simulation is used. The variation of the photon flux and the mean energy of photon spectrum that passes through the energy modulation filter are evaluated. In the primary photon spectrum of 80 kVp, the optimal modulation filter is a 0.1 mm lead filter that can acquire the same mean energy of 140 kVp photon spectrum. The lead filter of 0.1 mm based dual energy CBCT is required to increase the tube current 4.37 times than the original tube current owing to the 77.1% attenuation in the filter.

• Imaging Science in Dentistry
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• 제48권2호
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• pp.103-109
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• 2018

Purpose: To analyze cone-beam computed tomography (CBCT) use, indications, and exposure parameters in San $Jos{\acute{e}}$, Costa Rica. Materials and Methods: A cross-sectional study was performed. All CBCT examinations over a period of 6 months at 2 radiological centers in San $Jos{\acute{e}}$, Costa Rica were evaluated. The examinations were performed with Veraview EPOC X550 and Veraviewepocs 3D R100 equipment. The patients' age and sex, clinical indication for CBCT, region of interest (ROI), repeat examinations, specialty of the referring dentist, field-of-view (FOV), tube voltage (kV), tube current (mA), and radiation dose (${\mu}Gy$) were evaluated. Patients were classified by age as children (${\leq}12years$), adolescents(13-18 years), and adults(${\geq}19years$). Results: The mean age of the 526 patients was 49.4 years. The main indications were implant dentistry and dental trauma. The most frequent ROIs were posterior, while anterior ROIs were much less common. The highest percentage of repeat examinations was in children. Fifty-six percent of the referring dentists were specialists. The most commonly used FOV was small. The mean tube voltage and current were 79.8 kV and 7.4 mA for Veraview EPOC X550 and 89.9 kV and 6 mA for Veraviewepocs 3D R100, respectively. The mean doses for children, adolescents, and adults were $6.9{\mu}Gy$, $8.4{\mu}Gy$, and $7.8{\mu}Gy$, respectively. Conclusion: Although CBCT was most commonly used in adults for implant dentistry, most repeat examinations were in children, and the highest mean dose was in adolescents. Additional dose optimization efforts should be made by introducing low-dose protocols for children and adolescents.

• 분석과학
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• 제13권4호
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• pp.412-422
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• 2000

실리콘 웨퍼 산업계의 청정실에서 사용되는 에어샤워기중 고분자로 제작된 부품들을 $100^{\circ}C$에서 30분간 다이나믹 해드 스페이스에서 가스로 용출한 후 GC-MS로 분석 하였다. 에어샤워기가 가동중인 청정실의 대기를 흡착관 튜브방식으로 채취하였고, 이러한 흡착관 튜브에 흡착된 유기화합물은 쏙시렛 용출법을 이용하여 용출한 후 GC-MS로 분석하였다. 에어샤워기의 제조 부품(electric over current relay, acryl plate. polycarbonate window, filter, fan housing, steel galvanized cold plate and canvas buffer)들로 부터의 분석결과 대부분의 성분들은 제조부품의 고분자 성분들에서 유래되었음을 확인 할 수 있었으며, 에어샤워기가 가동중인 청정실의 대기분석 결과와 비교 분석되었다. 이러한 분석결과의 비교 연구는 청정실내에서의 유기오염물질이 에어샤워기의 고분자 제조부품으로부터 유래 되었는지를 확인하게 해준다.

• 소성∙가공
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• 제28권3호
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• pp.135-144
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• 2019

Electromagnetic impulse welding (EMIW) is a type of solid state welding using the Lorentz force generated by interaction between the magnetic field of the coil and the current induced in the workpiece. Although many experimental studies have been investigated on the expansion and compression welding of tube using the EMIW process, studies on the EMIW process of lap joint between flat sheets are uncommon. Since the magnetic field enveloped inside the tube can be controlled with ease, the electromagnetic technique has been widely used for tube welding. Conversely, it is difficult to control the magnetic field in the flat sheet welding so as to obtain the required welding velocity. The current study analyzed the effects of coil shape on the impulse velocity for suitable flat one-turn coil for the EMIW of the flat sheets. The finite element (FE) multi-physics simulation involving magnetic and structural field of EMIW were conducted with the commercial software LS-DYNA to evaluate the several shape variables, viz., influence of various widths, thicknesses, gaps and standoff distances of the flat one-turn coil on the impulse velocity. To obtain maximum impulse velocity, the flat one-turn coil was designed based on the FE simulation results. The experiments were performed using an aluminum alloy 1050 sheets of 1.0mm thickness using the designed flat one-turn coil. Through the microscopic interfacial analysis of the welded specimens, the interfacial connectivity was observed to have no defects. In addition, the single lap joint tests were performed to evaluate the welding strength, and a fracture occurred in the base material. As a result, a flat one-turn coil was successfully designed to guarantee welding with bond strength equal to or greater than the base material strength.

• 대한전기학회:학술대회논문집
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• 대한전기학회 1996년도 하계학술대회 논문집 C
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• pp.1660-1662
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• 1996

Superconducting current lead is one of the promising applications of the oxide high-Tc superconductors, because they have the advantage of decreasing heat conduction to low temperature region, comparing with a conventional cooper alloy lead. High critical current density is a key factor for the applications such as current lead. $(Bi,Pb)_{2}Sr_{2}Ca_{2}Cu_{3}O_{x}$ high Tc superconductor hase been investigated in terms of critical current density. Bi-2223 superconducting current lead made by CIP and solid state sintering process. Bi-2223 current lead that heat treated at $836\;^{\circ}C$ for 240 h in 1/13 $PO_2$ had over $500\;A/cm^2$ of critical current density at 77K. We knew that the superconducting properties of tube type current leads were better than rods type of them. And we investigated the relation of Bi-2223 formation and heat treatment condition by XRD and SEM analysis.

• 전기화학회지
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• 제6권4호
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• pp.250-254
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• 2003

본 연구는 전기화학적 실험측정으로 페라이트계 430스테인레스강 시험편에 인위적으로 틈을 형성시켰다. 부식용액은 IN $H_2SO_4+0.1N\;NaCl$ 전해액을 사용하였고, 각 시험편의 틈의 크기를 달리하였다. 전기화학적 평가방법은 -600mV/5CE에서 정방향으로 +1,200mV/SCE까지 주사속도 600mV/hr로 동전위 분극시험을 실시하여 부식전위, 부동태 전류밀도 등의 부식거동을 분석하였다. 그리고 정전위 분극시험을 실시하여 부동태 구간 전위 -200mV/SCE를 일정하게 인가 한 후, 틈내에 부동태 전류밀도와 틈부식 발생시간을 계측하였다 실험방법에 있어 Microcapillary tube(MCT)를 이용한 방법으로 틈내 각 지점의 전위를 틈 깊이에 따른 틈내부의 전위강하(IR Drop)에 주목하고, 575 430 스테인레스강 금속에 대한 분극특성과 연계하므로써 틈부식의 발생 원인을 '전위의 이동'의 관점에서 규명 하였다.