• Journal of Radiation Protection and Research
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• 제41권3호
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• pp.260-267
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• 2016

Background: This study analyzes the differences in the annual averaged atmospheric dispersion factor and ground deposition factor produced using two classification methods of atmospheric stability, which are based on a vertical temperature difference and the standard deviation of horizontal wind direction fluctuation. Materials and Methods: Daedeok and Wolsong nuclear sites were chosen for an assessment, and the meteorological data at 10 m were applied to the evaluation of atmospheric stability. The XOQDOQ software program was used to calculate atmospheric dispersion factors and ground deposition factors. The calculated distances were chosen at 400 m, 800 m, 1,200 m, 1,600 m, 2,400 m, and 3,200 m away from the radioactive material release points. Results and Discussion: All of the atmospheric dispersion factors generated using the atmospheric stability based on the vertical temperature difference were shown to be higher than those from the standard deviation of horizontal wind direction fluctuation. On the other hand, the ground deposition factors were shown to be same regardless of the classification method, as they were based on the graph obtained from empirical data presented in the Nuclear Regulatory Commission's Regulatory Guide 1.111, which is unrelated to the atmospheric stability for the ground level release. Conclusion: These results are based on the meteorological data collected over the course of one year at the specified sites; however, the classification method of atmospheric stability using the vertical temperature difference is expected to be more conservative.

• 한국방재학회:학술대회논문집
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• 한국방재학회 2008년도 정기총회 및 학술발표대회
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• pp.799-802
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• 2008

General behaviors based on hydraulic characteristics of natural streams and channels have been recently analyzed and developed via various numerical models. However in the states of natural hydraulics, an experimental research must be performed simultaneously with the mathematical analysis due to effects of hydraulic properties such as meander, sediment, and so on. In this study based on 2-D advection-dispersion equation, flow and tracer experiments were performed in the S-curved meandering laboratory channel with a rectangular cross-section. The channel was equipped with instrument carriages which was equipped with an auto-traversing system to be used with velocity measuring sensors throughout the depth and breadth of the flow field. To measure concentration distribution of the salt solution was adjusted to that of the flume water by adding methanol and a red dye (KMnO4) was added to aid the visualization of the tracer cloud, the tracer was instantaneously injected into the flow as a full-depth vertical line source by the instantaneous injector and the initial concentration of the tracer was 100,000 mg/l. The secondary current as well as the primary flow pattern was analyzed to investigate the flow distribution in the meandering channels. The velocity distribution of the primary flow for all cases skewed toward the inner bank at the first bend, and was almost symmetric at the crossovers, and then shifted toward the inner bank again at the next alternating bend. Thus, one can clearly notice that the maximum velocity occurs taking the shortest course along the channel, irrespective of the flow conditions. The result of the tracer tests shows that pollutant clouds are spreading following the maximum velocity lines in each cases with various mixing patterns like superposition, separation, and stagnation of pollutant clouds. Flow characteristics in each cases performed in this study can be compared with tracer dispersion characteristics with using evaluation of longitudinal and transverse dispersion coefficients(LDC, TDC). As expected, LDC and TDC in meandering parts have been evaluated with increasing distribution and straight parts have effected to evaluate minimum of LDC and TDC due to symmetric flow patterns and attenuations of secondary flow.

• 한국콘텐츠학회논문지
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• 제20권12호
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• pp.537-546
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• 2020

본 연구에서는 오염물 사고에 대한 신속한 대응을 위하여 입자 분산 모형을 개발 및 개선하고 병렬 프로그램을 적용한 모의 속도 증가와 그 분석을 통하여 속도개선 결과를 평가하였다. 개발된 모형은 전단류 분산이론을 따르면서 수평 혼합 과정은 전단이송, 연직 혼합 과정은 연직배열 알고리즘을 이용한 난류 및 입자 확산을 구현하였다. 오염사고에 신속하게 대응하기 위해 모형 속도 개선을 위하여 OpenMP를 활용한 병렬 프로그래밍으로 멀티코어 적용 알고리즘을 적용하였다. 병렬 프로그래밍 적용 결과, 가상 사행수로에서 기준 소요시간 내로 모의가 가능한 입자 및 활용 코어 개수의 관계를 도출할 수 있었다. 이 연구 결과로 신속한 수질 오염사고 사고대응을 위한 적절한 모의 조건을 구성할 수 있게 되어 모형의 활용성을 증대할 수 있었다.

• 대한화장품학회지
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• 제33권2호
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• pp.105-110
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• 2007

제타전위를 이용하여 이산화티탄의 분산 안정성을 평가하고 이를 통하여 분산안정도 향상에 응용하고자 하였다. 본 연구에서는 제타전위와 관련된 전기이중층, 전기영동, 등전점 및 전기 침투에 대하여 설명하였으며 측정이론을 기술하였다. H-S equation을 이용하여 수계에 분산된 미립자 이산화티탄의 pH변화에 따른 제타전위 변화를 측정하였으며 제타전위는 pH $3.0{\sim}9.0$에서 음의 값으로 측정되었다. 제타전위 값은 pH값 상승에 따라 절대값이 증가하였으며 분산액의 pH 8.0과 9.0에서는 지속적으로 분산이 유지되었다. 이를 통하여 제타전위가 이산화티탄의 분산에 영향을 미치며 제타전위의 절대값 크기가 수계에서 이산화티탄의 분산안정도에 중요한 역할을 하는 것으로 생각된다.

• 한국섬유공학회:학술대회논문집
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• 한국섬유공학회 2007년도 학술발표회 논문집
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• pp.327-328
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• 2007

• 한국정밀공학회지
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• 제24권11호
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• pp.22-28
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• 2007

• 한국입자에어로졸학회지
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• 제9권4호
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• pp.231-238
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• 2013

Carbon nanotubes (CNTs) are one of the nanomaterials that were discovered by Iijima in 1991 for the first time. CNTs have long cylindrical and axi-symmetric structures. CNTs are made by rolling graphene sheets. Because of their large length-to-diameter ratio, they are called nanotubes. CNTs are categorized as single-walled carbon nanotubes (SWCNTs) or multi-walled carbon nanotubes (MWCNTs) based on the shell structures. CNTs are broadly used in various fields, such as scanning probe microscopy, ultra fine nano balance and medicine, due to their extraordinary thermal conductivity, electrical and mechanical properties. Because long, straight CNTs have the same shape as asbestos, which cause cancer in cells lining the lung, there have been many studies on the effects of MWCNTs on human health that have been conducted. Stable atomization of CNTs is very important for the estimation of inhalation toxicity. In the present study, electro-static assisted axial atomizer (EAAA), which is the instrument that uses MWCNTs and aerosolizes them by transforming the single fiber shape using ultrasonic dispersion and electric field, was invented. EAAA consists of a ultrasonic bath for dispersion of MWCNTs and a particle generator for atomizing single fibers. The performance evaluation was conducted in order to assess the possibilities of 6-hour straight atomization with stability, which is the suggested exposure time in a day for the estimation of inhalation toxicity.

• Composites Research
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• 제29권6호
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• pp.353-357
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• 2016

B-stage 레진 필름에 탄소나노튜브(CNT) 등을 균일하게 분포시킨 뒤에 기타의 보강섬유 층과 함께 여러 겹으로 적층하여 하이브리드 형태의 복합재료를 만드는 방법은 유용하다. 본 연구에서는 CNT가 포함된 에폭시 레진으로부터 shear mixing 및 Three-roll mill 공정을 이용하여 B-stage 레진 필름을 제작하였다. 두 공정을 통해 형성된 CNT/레진 복합재 필름의분산도를 파단면의 SEM 관찰을통해분석하였다. 보다 효율적인 공정을 위해 Calendering pass 횟수에 따른 분산도를 평가하였다. Pass의 횟수에 따른 샘플을 제조하고 CNT 분산도는 SEM 이미지를 통해 확인하고, 전기 전도도 측정을 통해 분석하였다. 추가적으로 gap mode, force mode를 통해 제작한 각각의 샘플의 전기 전도도를 측정하여 CNT 분산도를 분석하였고 이를 통해 최적공정을 도출하였다.

• 한국군사과학기술학회지
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• 제22권6호
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• pp.745-753
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• 2019

Recently, with the development of long-range / high-altitude guided weapon system for defense against ballistic missile, test range and firing altitude for guided weapons are increasing. Due to the increase in the test range and the intercepting altitude, it is expected to increase the range of safety area required for the firing test. Comparing to the foreign countries which have many desert or non-residence, in the domestic circumstances where the population is concentrated and distributed, it is more important to predict the falling area and to set the safety area for safely carry out the long-range / high-altitude intercept test. In this paper, we consider the following three points. The first is the booster fall trajectory modeling, the second is the shroud fall trajectory modeling, and finally, the debris dispersion modeling for the missile intercept. Especially, the AUTODYN model was used to predict debris falling area which produced in the high-speed guided missile intercepting test.

• Korean Journal of Radiology
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• 제23권2호
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• pp.237-245
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• 2022

Objective: Viscoelasticity is an essential feature of nerves, although little is known about their viscous properties. The discovery of shear wave dispersion (SWD) imaging has presented a new approach for the non-invasive evaluation of tissue viscosity. The present study investigated the feasibility of using SWD imaging to evaluate diabetic neuropathy using the sciatic nerve in a diabetic rat model. Materials and Methods: This study included 11 diabetic rats in the diabetic group and 12 healthy rats in the control group. Bilateral sciatic nerves were evaluated 3 months after treatment with streptozotocin. We measured the nerve cross-sectional area (CSA), nerve stiffness using shear wave elastography (SWE), and nerve viscosity using SWD imaging. The motor nerve conduction velocity (MNCV) was also measured. These four indicators and the histology of the sciatic nerves were then compared between the two groups. The performance of CSA, SWE, and SWD imaging in distinguishing the two groups was assessed using receiver operating characteristic (ROC) analysis. Results: Nerve CSA, stiffness, and viscosity in the diabetic group was significantly higher than those in the control group (all p < 0.05). The results also revealed a significantly lower MNCV in the diabetic group (p = 0.005). Additionally, the density of myelinated fibers was significantly lower in the diabetic group (p = 0.004). The average thickness of the myelin sheath was also lower in the diabetic group (p = 0.012). The area under the ROC curve for distinguishing the diabetic neuropathy group from the control group was 0.876 for SWD imaging, which was significantly greater than 0.677 for CSA (p = 0.030) and 0.705 for SWE (p = 0.035). Conclusion: Sciatic nerve viscosity measured using SWD imaging was significantly higher in diabetic rats. The viscosity measured using SWD imaging performed well in distinguishing the diabetic neuropathy group from the control group. Therefore, SWD imaging may be a promising method for the evaluation of diabetic neuropathy.