• Journal of Radiation Protection and Research
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• 제34권1호
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• pp.25-30
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• 2009

Micro-columnar CsI(Tl) is the most popular scintillator material which is used for many indirect digital X-ray imaging detectors. The light scattering at the surface of micro-columnar CsI(Tl) scintillator was studied to find the correlation between the surface roughness and the resultant image resolution of indirect X-ray imaging detectors. Using a commercially available optical simulation program, Light Tools, MTF (Modulation Transfer Function) curves of the CsI(Tl) film thermally evaporated on glass substrate with different thickness were calculated and compared with the experimental estimation of MTF values by the edge X-ray image method and CCD camera. It was found that the standard deviation value of Gaussian scattering model which is determined by the surface roughness of micro-columns could certainly change the MTF value of image sensors. This model and calculation methodology will be beneficial to estimate the overall performance of indirect X-ray imaging system with CsI(Tl) scintillator film for optimum design depending on its application.

• 소성∙가공
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• 제14권8호통권80호
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• pp.681-688
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• 2005

The high-temperature deformation mechanisms of a ${\alpha}+{\beta}$ titanium alloy (Ti-6Al-4V), near-a titanium alloy (Ti-6.85Al-1.6V) and a single-phase a titanium alloy (Ti-7.0Al-1.5V) were deduced within the framework of inelastic-deformation theory. For this purpose, load relaxation tests were conducted on three alloys at temperatures ranging from 750 to $950^{\circ}C$. The stress-versus-strain rate curves of both alloys were well fitted with inelastic-deformation equations based on grain matrix deformation and grain-boundary sliding. The constitutive analysis revealed that the grain-boundary sliding resistance is higher in the near-${\alpha}$ alloy than in the two-phase ${\alpha}+{\beta}$ alloy due to the difficulties in relaxing stress concentrations at the triple-junction region in the near-${\alpha}$ alloy. In addition, the internal-strength parameter (${\sigma}^*$) of the near-${\alpha}$ alloy was much higher than that of the ${\alpha}+{\beta}$ alloy, thus implying that dislocation emission/ slip transfer at ${\alpha}/{\alpha}$ boundaries is more difficult than at ${\alpha}/{\beta}$ boundaries.

• 한국정보통신학회논문지
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• 제16권6호
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• pp.1266-1272
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• 2012

게이트 길이와 폭이 다른 InGaZnO 박막 트랜지스터를 제작하고 소자의 크기에 따른 문턱전압과 음의 게이트 전압 스트레스 후의 소자 특성 저하에 관한 연구를 수행하였다. 게이트 길이가 짧은 소자는 문턱전압과 문턱전압 아래의 기울기 역수가 감소하였고 채널 폭이 작은 소자는 문턱전압이 증가 하였다. 음의 게이트 전압 스트레스 후에는 전달특성 곡선이 왼쪽으로 이동하였고 문턱전압은 감소하였으며 문턱전압 아래의 기울기 역수는 변화가 거의 없었다. 이러한 결과는 게이트 유전체에 포획된 홀 때문으로 사료된다. 게이트에 음의 스트레스 전압을 인가한 후에 게이트 길이가 짧을수록 그리고 게이트 폭이 증가할수록 문턱전압의 변화가 적은 것은 홀 주입이 적기 때문으로 사료된다.

• Archives of Plastic Surgery
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• 제45권5호
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• pp.395-402
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• 2018

Increased emphasis on competency-based learning modules and widespread departure from traditional models of Halstedian apprenticeship have made surgical simulation an increasingly appealing component of medical education. Surgical simulators are available in numerous modalities, including virtual, synthetic, animal, and non-living models. The ideal surgical simulator would facilitate the acquisition and refinement of surgical skills prior to clinical application, by mimicking the size, color, texture, recoil, and environment of the operating room. Simulation training has proven helpful for advancing specific surgical skills and techniques, aiding in early and late resident learning curves. In this review, the current applications and potential benefits of incorporating simulation-based surgical training into residency curriculum are explored in depth, specifically in the context of plastic surgery. Despite the prevalence of simulation-based training models, there is a paucity of research on integration into resident programs. Current curriculums emphasize the ability to identify anatomical landmarks and procedural steps through virtual simulation. Although transfer of these skills to the operating room is promising, careful attention must be paid to mastery versus memorization. In the authors' opinions, curriculums should involve step-wise employment of diverse models in different stages of training to assess milestones. To date, the simulation of tactile experience that is reminiscent of real-time clinical scenarios remains challenging, and a sophisticated model has yet to be established.

• 한국신재생에너지학회:학술대회논문집
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• 한국신재생에너지학회 2009년도 춘계학술대회 논문집
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• pp.373-373
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• 2009

Relative humidity, membrane conductivity and water activity are critical parameters of polymer electrolyte membrane fuel cells (PEMFC) for high performance and reliability. These parameters are closely related with temperature. Moreover, the ideal values of these parameters are not always identical along the channels. Therefore, the cooling channel design and its operating condition should be well optimized along the all location of the channels. In the present study, we have performed a numerical investigation on the effects of cooling channels on performance of a PEMFC. Three-dimensional Navier-Stokes equations are solved with the energy equation including heat generated by the electrochemical reactions in the fuel cell. The present numerical model includes the gas diffusion layers (GDL) and serpentine channels for both anode and cathode gas flows, as well as cooling channels. To accurately predict the water transport across the membrane, the distribution of water content in the membrane is calculated by solving a nonlinear differential equation with a nonlinear coefficient, i.e., the water diffusivity which is a function of water content as well as temperature. Main emphasis is placed on the heat transfer between the solid bipolar plate and coolant flow. The present results show that local current density is affected by cooling channels due to the change of the oxygen concentration and the membrane conductivity as well as the water content. It is also found that the relative humidity is influenced by the generated water and the gas temperature and thus it affects the distribution of fuel concentration and the conductivity of the membrane, ultimately fuel cell performance. Unit-cell experiments are also carried out to validate the numerical models. The performance curves between the models and experiments show reasonable results.

• 한국진공학회:학술대회논문집
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• 한국진공학회 2013년도 제44회 동계 정기학술대회 초록집
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• pp.221-221
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• 2013

Striving to replace the well known silicon nanocrystals embedded in oxides with solution-processable charge-trapping materials has been debated because of large scale and cost effective demands. Herein, a silicon quantum dot-polystyrene nanocomposite (SiQD-PS NC) was synthesized by postfunctionalization of hydrogen-terminated silicon quantum dots (H-SiQDs) with styrene using a thermally induced surface-initiated polymerization approach. The NC contains two miscible components: PS and SiQD@PS, which respectively are polystyrene and polystyrene chains-capped SiQDs. Spin-coated films of the nanocomposite on various substrate were thermally annealed at different temperatures and subsequently used to construct metal-insulator-semiconductor (MIS) devices and thin film field effect transistors (TFTs) having a structure p-$S^{++}$/$SiO_2$/NC/pentacene/Au source-drain. C-V curves obtained from the MIS devices exhibit a well-defined counterclockwise hysteresis with negative fat band shifts, which was stable over a wide range of curing temperature ($50{\sim}250^{\circ}C$. The positive charge trapping capability of the NC originates from the spherical potential well structure of the SiQD@PS component while the strong chemical bonding between SiQDs and polystyrene chains accounts for the thermal stability of the charge trapping property. The transfer curve of the transistor was controllably shifted to the negative direction by chaining applied gate voltage. Thereby, this newly synthesized and solution processable SiQD-PS nanocomposite is applicable as charge trapping materials for TFT based memory devices.

• Journal of Electrical Engineering and Technology
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• 제9권6호
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• pp.2070-2078
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• 2014

In this work, the frequency response of gate-all-around (GAA) Ge/GaAs heterojunction tunneling field-effect transistor (TFET) with hetero-gate-dielectric (HGD) and pnpn channel doping profile has been analysed by technology computer-aided design (TCAD) device-circuit mixed-mode simulations, with comparison studies among ppn, pnpn, and HGD pnpn TFET devices. By recursive tracing of voltage transfer curves (VTCs) of a common-source (CS) amplifier based on the HGD pnpn TFET, the operation point (Q-point) was obtained at $V_{DS}=1V$, where the maximum available output swing was acquired without waveform distortion. The slope of VTC of the amplifier was 9.21 V/V (19.4 dB), which mainly resulted from the ponderable direct-current (DC) characteristics of HGD pnpn TFET. Along with the DC performances, frequency response with a small-signal voltage of 10 mV has been closely investigated in terms of voltage gain ($A_v$), unit-gain frequency ($f_{unity}$), and cut-off frequency ($f_T$). The Ge/GaAs HGD pnpn TFET demonstrated $A_v=19.4dB$, $f_{unity}=10THz$, $f_T=0.487$ THz and $f_{max}=18THz$.

• 해양환경안전학회지
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• 제18권3호
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• pp.267-272
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• 2012

에너지 생성에 따른 탄소배출문제로 국제 에너지 기구는 세계 주요국의 에너지 효율을 15~30[%]이상 향상시키도록 권고하고 있으며, 국내 에너지 정책 동향도 에너지 절감 및 탄소 배출에 대해 정부에서 인센티브 및 페널티 프로그램을 제고하는 방향으로 가고 있다. 각국의 산업 현장에서 유체 이송용 펌프가 전기에너지의 20[%]를 소비하고 있는 실정으로, 주요 에너지 낭비 요인으로는 장시간 운전에 따른 효율 저하, 부적절한 설계 및 설비 등이 있다. 이러한 낭비를 줄이기 위해 펌프의 효율을 측정하여 펌프의 운전 상태를 진단하고자, 본 논문에서는 열역학적 방법으로 온도와 압력센서만을 활용하여 펌프의 최고 효율점을 측정할 수 있는 방법을 제시하고 실제 펌프의 효율을 계산하여 펌프제조사에서 제공한 성능곡선과 비교한 결과 유사한 성능곡선을 얻어 그 유효성을 확인하였다.

• 한국환경보건학회지
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• 제37권1호
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• pp.50-56
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• 2011

The adsorption capacity of charcoal is a function of the airborne concentration of the target chemical. To evaluate the adsorption capacity of charcoal packed in the cartridges of air purifying respirators, breakthrough tests were conducted with carbon tetrachloride for three commercial cartridges (3M models #7251, #6000 and AX) at 25, 50, 100, 250 and 500 ppm. Adsorption capacities were calculated using a mass transfer balance equation derived from the curve fitting to the breakthrough curves obtained experimentally. Carbon micropore volumes were estimated by iteration to fit the Dubinin/Radushkevich (D/R) adsorption isotherm. They were 0.6566, 0.5727 and 0.3087 g/cc for #7251, #6000 and the AX cartridge, respectively. Above 100 ppm (at high challenge concentrations), #7251 and #6000 showed higher adsorption capacities. However, as the challenge concentration decreased, the adsorption capacities of #7251 and #6000 sharply dropped. On the other hand, the adsorption capacity of the AX cartridge showed little change with the decrease of the challenge concentration. Thus, the AX showed a higher adsorption capacity than #7251 and #6000 at the 5-50 ppm level. It is concluded that service-life tests of cartridges and adsorption capacity tests of charcoal should be conducted at challenge concentration levels reflecting actual working environmental conditions. Alternatively, it is recommended to use the D/R adsorption isotherm to extrapolate adsorption capacity at low concentration levels from the high concentration levels at which breakthrough tests are conducted, at a minimum of two different concentration levels.

• 한국환경과학회지
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• 제5권5호
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• pp.593-603
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• 1996

용응탄산염 연료전지의 산소전극성능모사를 위한 이중기공구조의 filmed agglomerate model을 연구하였다. 이 모델에서는 전극과 전해질 계면의 물리, 화학적인 현상 및 전극반응기구를 고려하여 정상상태 에서 전극의 특성을 조업조건에 따라 표시할 수있다. 기존의 연구에서 기하학적인 구조를 가정하여 전극반응면적을 이론적으로 계산한 반면에 본 연구에서는 porosimeter를 이용한 기공도와 기공구조 분포 측정자료를 이용한 방법을 제시하였다. 계산결과는 전극재질, 기체조성, 전극두께, agglomerate 기공도 및 전해질 막의 두께에 따른 영향을 전류밀도와 과전압의 관계로 표시하였다. 또한 전극 재질로 perovskite (La0.8Sr0.2CoO3)와 NiO를 사용하여 실제전지를 이용한 성능을 측정하여 이론치와 비교하였다. 두전 극의 반쪽전지 실험에서 유사한 성능을 나타내었다. Perovskite 전극은 전극 기공도 65%, agglomerate 기공도 12% 그리고 전극두께 1.5~2mm에서 최적의 결과를 보여주었다. NiO전극의 경우 peroxide 반응기구에서 superoxide 반응기구의 계산결과보다 실험치와 일치하는 좋은 결과를 보였다.