• 한국의학물리학회지:의학물리
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• 제13권4호
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• pp.218-223
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• 2002

두개외 병소 즉, 척추 등에 발생한 종양 혹은 혈관기형 등의 병소에 대해 침습적 수술이 불가한 경우 정위적 방사선 수술이 임상에서 시도되고 있다. 본 연구는 실험적으로 팬텀에 대해 척추 정위 방사선수술을 시행하고 결과 분석을 통하여 두개외 수술 목표점에 대한 방사선수술 위치 정확도를 평가하고자 한다. 이 실험을 위하여 팬텀을 특별히 고안하였으며 수술실에서 방사선 수술 목표점의 위치는 광학적 추적 장치를 이용하여 결정하였고 3 mm 미세다엽시준기(mMLC; mcro Multi-Leaf Collimator)를 사용하여 시술하였다. 팬텀의 목표점에 대한 방사선수술 오차는 $\pm$1 mm 이내였으며 분할방사선 수술 경우도 $\pm$1 mm 이내였다. 결과적으로 광학적 위치추적 장치를 이용한 두개외 목표점의 방사선 수술은 매우 정확하고 유용한 방법으로 판단된다.

• 천문학회지
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• 제41권2호
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• pp.39-47
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• 2008

Spectral line profiles of filaments/prominences to be observed by the Fast Imaging Solar Spectrograph (FISS) are studied. The main spectral lines of interests are $H{\alpha}$, Ca II 8542, and Ca II K. FISS has a high spectral resolving power of $2{\times}10^5$, and supports simultaneous dual-band recording. This instrument will be installed at the 1.6m New Solar Telescope (NST) of Big Bear Solar Observatory, which has a high spatial resolution of 0.065" at 500nm. Adopting the cloud model of radiative transfer and using the model parameters inferred from pre-existing observations, we have simulated a set of spectral profiles of the lines that are emitted by a filament on the disk or a prominence at the limb. Taking into account the parameters of the instrument, we have estimated the photon count to be recorded by the CCD cameras, the signal-to-noise ratios, and so on. We have also found that FISS is suitable for the study of multi-velocity threads in filaments if the spectral profiles of Ca II lines are recorded together with $H{\alpha}$ lines.

• Advances in Energy Research
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• 제5권3호
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• pp.219-226
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• 2017

Electrochemical double layer capacitors (EDLCs) have received a tremendous interest due to their suitability for diverse applications. They have been fabricated using different carbon based electrodes including activated carbons, single walled/multi walled carbon nano tubes. But, graphite which is one of the natural resources in Sri Lanka has not been given a considerable attention towards using for EDLCs though it is a famous carbon material. On the other hand, EDLCs are well reported with various liquid electrolytes which are associated with numerous drawbacks. Gel polymer electrolytes (GPE) are well known alternative for liquid electrolytes. In this paper, it is reported about an EDLC fabricated with a nano composite polyethylene oxide based GPE and two Sri Lankan graphite based electrodes. The composition of the GPE was [{(10PEO: $NaClO_4$) molar ratio}: 75wt.% PC] : 5 wt.% $TiO_2$. GPE was prepared using the solvent casting method. Two graphite electrodes were prepared by mixing 85% graphite and 15% polyvinylidenefluoride (PVdF) in acetone and casting n fluorine doped tin oxide glass plates. GPE film was sandwiched in between the two graphite electrodes. A non faradaic charge discharge mechanism was observed from the Cyclic Voltammetry study. GPE was stable in the potential windows from (-0.8 V-0.8 V) to (-1.5 V-1.5 V). By increasing the width of the potential window, single electrode specific capacity increased. Impedance plots confirmed the capacitive behavior at low frequency region. Galvanostatic charge discharge test yielded an average discharge capacity of $0.60Fg^{-1}$.

• 한국의학물리학회지:의학물리
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• 제17권1호
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• pp.32-39
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• 2006

CT 검사에서 조영제의 혈관외유출을 예방하기 위해 EDA시스템을 증폭기, ADC, 스트레인 게이지로 구성하여 개발하였고, 스트레인 게이지의 신호의 수치를 나타내도록 프로그램을 설계하였다. 신호비율은 500/1000 sec, 분해능 값은 0에서 4,096범위로 표시하고, 입력범위 $0{\sim}5$ V이다. 혈관외유출 검출 문턱 값은 50으로 하였고, 10 간격으로 조정하도록 하였다. 개발된 EDA 시스템을 성인 50명을 대상으로 적용하였다. 2명의 환자에서 혈관외유출이 검출되었고, 조영제 주입속도는 2.0 mL/sec, 2.5 mL/sec, 압력은 137 psi, 158 psi, 혈관외유출된 조영제 용량은 22 mL, 25 mL였다. 설정된 주입 조영제에 비해 20% 정도의 적은 용량이 혈관외유출되었다. 개발된 EDA 시스템은 소량의 조영제를 검출하여 혈관외유출을 예방하는 효과가 있다.

• 천문학논총
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• 제30권2호
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• pp.405-407
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• 2015

We describe a survey of quasars in the early universe, beyond z ~ 5, which is one of the main science goals of the Infrared Medium-deep Survey (IMS) conducted by the Center for the Exploration of the Origin of the Universe (CEOU). We use multi-wavelength archival data from SDSS, CFHTLS, UKIDSS, WISE, and SWIRE, which provide deep images over wide areas suitable for searching for high redshift quasars. In addition, we carried out a J-band imaging survey at the United Kingdom InfraRed Telescope with a depth of ~23 AB mag and survey area of ${\sim}120deg^2$, which makes IMS a suitable survey for finding faint, high redshift quasars at z ~ 7. In addition, for the quasar candidates at z ~ 5.5, we are conducting observations with the Camera for QUasars in EArly uNiverse (CQUEAN) on the 2.1m telescope at McDonald Observatory, which has a custom-designed filter set installed to enhance the efficiency of selecting robust quasar candidate samples in this redshift range. We used various color-color diagrams suitable for the specific redshift ranges, which can reduce contaminating sources such as M/L/T dwarfs, low redshift galaxies, and instrumental defects. The high redshift quasars we are confirming can provide us with clues to the growth of supermassive black holes since z ~ 7. By expanding the quasar sample at 5 < z < 7, the final stage of the hydrogen reionization in the intergalactic medium (IGM) can also be fully understood. Moreover, we can make useful constraints on the quasar luminosity function to study the contribution of quasars to the IGM reionization.

• 천문학논총
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• 제30권2호
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• pp.219-221
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• 2015

We present our recent observations of SDSS J102102.25+174439.9, a new eclipsing white dwarf - main sequence WDMS binary with an orbital period of 0.14 days. This system belongs to the post common-envelope binary group as shown by the spectrum from the Sloan Digital Sky Survey. We obtained our data using the ULTRASPEC instrument installed on the 2.4-m telescope at the Thai National Observatory (TNO). Our multi-band observations reveal an unusual and persistent drop in brightness after the primary eclipse. These dips, which appear to show variations in amplitude, also have a complex shape that changes within days. Dips in WDMS systems have been observed on only one other occasion, in the light curve of QS Vir prior to the eclipse of the white dwarf. The dips in SDSS J1021+1744 are unique because they are present at different wavelengths and they occur approximately at similar phases. Hosting a DA white dwarf and an M4 companion star, this system is known to be the only WDMS to show these kind of dips in its light curve. It is possible that these dips are caused by ejected materials from an active companion star, such as in QS Vir. The light curve in the g' filter exhibits deep and narrow features, implying that the material which passes in front of the white dwarf in SDSS J1021 must be dense and small in size. Furthermore, we try to constrain the stellar and orbital parameters of SDSS J1021+1744 using the Binary Maker 3 software. We use g' and r' data for our light curve analysis to have a better approximation for the red dwarf star.

• 정보처리학회논문지:소프트웨어 및 데이터공학
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• 제6권10호
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• pp.479-486
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• 2017

최근 GPGPU를 이용하여 저하된 컴퓨터 성능 향상폭을 높일 수 있게 되었고, 이로 인하여 높은 연산을 요구로 하는 물리 기반의 실시간 시뮬레이션을 PC에서 구동할 수 있게 되었다. 물리 시뮬레이션에서 적용되는 물리 계산은 병렬 처리로 수행되어질 수 있으며, 최근 OpenGL 4.3 및 Unity4.0에서 지원되는 Compute shader를 통한 병렬 연산을 이용하면 효율적으로 구동할 수 있다. 본 논문에서는 다양한 플랫폼을 지원하는 디지털 콘텐츠 제작 툴인 Unity와 다양한 플랫폼에서 구동되어지는 OpenGL에서의 실시간 물리 시뮬레이션에서의 성능을 측정 및 비교한다. 본 논문에서 particle 시뮬레이션의 실험 결과 Unity를 이용한 particle 시뮬레이션이 OpenGL을 이용한 particle 시뮬레이션에 비해 최대 136.04% 빠른 성능을 보인다. 이를 통하여 추후 멀티 플랫폼을 지원하는 디지털 콘텐츠를 제작함에 있어 더 나은 개발 도구를 선정할 수 있을 것으로 기대된다.

• Nuclear Engineering and Technology
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• 제53권10호
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• pp.3275-3285
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• 2021

A Nuclear Power Plant (NPP) is a complex dynamic system-of-systems with highly nonlinear behaviors. In order to control the plant operation under both normal and abnormal conditions, the different systems in NPPs (e.g., the reactor core components, primary and secondary coolant systems) are usually monitored continuously, resulting in very large amounts of data. This situation makes it possible to integrate relevant qualitative and quantitative knowledge with artificial intelligence techniques to provide faster and more accurate behavior predictions, leading to more rapid decisions, based on actual NPP operation data. Data-driven models (DDM) rely on artificial intelligence to learn autonomously based on patterns in data, and they represent alternatives to physics-based models that typically require significant computational resources and might not fully represent the actual operation conditions of an NPP. In this study, a feed-forward backpropagation artificial neural network (ANN) model was trained to simulate the interaction between the reactor core and the primary and secondary coolant systems in a pressurized water reactor. The transients used for model training included perturbations in reactivity, steam valve coefficient, reactor core inlet temperature, and steam generator inlet temperature. Uncertainties of the plant physical parameters and operating conditions were also incorporated in these transients. Eight training functions were adopted during the training stage to develop the most efficient network. The developed ANN model predictions were subsequently tested successfully considering different new transients. Overall, through prompt prediction of NPP behavior under different transients, the study aims at demonstrating the potential of artificial intelligence to empower rapid emergency response planning and risk mitigation strategies.

• 한국의학물리학회지:의학물리
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• 제30권1호
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• pp.1-6
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• 2019

Purpose: This study conducts a comparative evaluation of the skin dose in CyberKnife (CK) and Helical Tomotherapy (HT) to predict the accurate dose of radiation and minimize skin burns in head-and-neck stereotactic body radiotherapy. Materials and Methods: Arbitrarily-defined planning target volume (PTV) close to the skin was drawn on the planning computed tomography acquired from a head-and-neck phantom with 19 optically stimulated luminescent dosimeters (OSLDs) attached to the surface (3 OSLDs were positioned at the skin close to PTV and 16 OSLDs were near sideburns and forehead, away from PTV). The calculation doses were obtained from the MultiPlan 5.1.2 treatment planning system using raytracing (RT), finite size pencil beam (FSPB), and Monte Carlo (MC) algorithms for CK. For HT, the skin dose was estimated via convolution superposition (CS) algorithm from the Tomotherapy planning station 5.0.2.5. The prescribed dose was 8 Gy for 95% coverage of the PTV. Results and Conclusions: The mean differences between calculation and measurement values were $-1.2{\pm}3.1%$, $2.5{\pm}7.9%$, $-2.8{\pm}3.8%$, $-6.6{\pm}8.8%$, and $-1.4{\pm}1.8%$ in CS, RT, RT with contour correction (CC), FSPB, and MC, respectively. FSPB showed a dose error comparable to RT. CS and RT with CC led to a small error as compared to FSPB and RT. Considering OSLDs close to PTV, MC minimized the uncertainty of skin dose as compared to other algorithms.

• 한국의학물리학회지:의학물리
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• 제31권4호
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• pp.135-144
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• 2020

Purpose: Gafchromic films for proton dosimetry are dependent on linear energy transfers (LETs), resulting in dose underestimation for high LETs. Despite efforts to resolve this problem for single-energy beams, there remains a need to do so for multi-energy beams. Here, a bimolecular reaction model was applied to correct the under-response of spread-out Bragg peaks (SOBPs). Methods: For depth-dose measurements, a Gafchromic EBT3 film was positioned in water perpendicular to the ground. The gantry was rotated at 15° to avoid disturbances in the beam path. A set of films was exposed to a uniformly scanned 112-MeV pristine proton beam with six different dose intensities, ranging from 0.373 to 4.865 Gy, at a 2-cm depth. Another set of films was irradiated with SOBPs with maximum energies of 110, 150, and 190 MeV having modulation widths of 5.39, 4.27, and 5.34 cm, respectively. The correction function was obtained using 150.8-MeV SOBP data. The LET of the SOBP was then analytically calculated. Finally, the model was validated for a uniform cubic dose distribution and compared with multilayered ionization chamber data. Results: The dose error in the plateau region was within 4% when normalized with the maximum dose. The discrepancy of the range was <1 mm for all measured energies. The highest errors occurred at 70 MeV owing to the steep gradient with the narrowest Bragg peak. Conclusions: With bimolecular model-based correction, an EBT3 film can be used to accurately verify the depth dose of scanned proton beams and could potentially be used to evaluate the depth-dose distribution for patient plans.