• Preventive Nutrition and Food Science
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• 제9권2호
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• pp.156-160
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• 2004

This study aims to investigate the changes in the lipid composition and angiotensin-converting enzyme activity in serum of rats exposed to microwave radiation, and to examine improving effects of green tea catechin to the lipid composition. The microwave-exposed rats received the normal and one of 3 diets: catechin free (MW-0C), 0.25% catechin (MW-0.25C) or 0.5% catechin (MW-0.5C). Rats were sacrificed 6th day after microwave radiation (2.45 ㎓, 15 min). The concentration of serum triglyceridein MW-0C group was increased by 85%, compared with the normal group, but that of MW-0.25C group with 0.25% catechin supplementation was to 17% lower, compared with the MW-0C group. There was no significant difference between normal group and MW-0.5C group. Total-cholesterol and LDL-cholesterol concentrations were increased by 21.4% and 38.6%, respectively, by microwave irradiation. The concentration of HDL-cholesterol in MW-0C group was lower to 29.3%, but it was maintained at the normal level by catechin supplementation. There was no significant difference among four groups in HLD-cholesterol/LDL-cholesterol. Atherogenic index in MW-0C group was increased by 56%, compared with the normal group. Angiotensin-converting enzyme (ACE) activity in lung tissue of MW-0C group was increased by 59 %, while that of MW -0.25C and MW -0.5C group were maintained at the normal level. ACE activity of MW-0C group in serum was increased by 122.8%, compared with the normal group. Catechin supplementation group was significantly reduced, compared with the MW-0C group ACE activity. In conclusion, microwave irradiation increased the serum triglyceride and cholesterol concentrations and ACE activity which are considered as the blood pressure increasing agents. However, catechin supplementation decreased the level of triglyceride, total cholesterol, LDL cholesterol, and ACE activity, which maybe consider catechin as being agent of lowering effect for blood lipid profile for athero-genesis.

• 대한기계학회논문집B
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• 제25권9호
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• pp.1157-1164
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• 2001

Centrifugal fans are widely used and the noise generated by these machines causes one of the most serious problems. In general, the centrifugal fan noise is often dominated by tones at BPF(blade passage frequency) and its higher harmonics. This is a consequence of the strong interaction between the flow discharged from the impeller and the cutoff in the casing. However, only a few research have been carried out on predicting the noise because of the difficulty in obtaining detailed information about the flow field and casing effects on noise radiation. The objective of this study is to understand the generation mechanism of sound and to develop a prediction method for the unsteady flow field and the acoustic pressure field of a centrifugal fan. We assume that the impeller rotates with a constant angular velocity and the flow field of the impeller is incompressible and inviscid. So, a discrete vortex method(DVM) is used to model the centrifugal fan and to calculate the flow field. The force of each element on the blade is calculated by the unsteady Bernoulli equation. Lowsons method is used to predict the acoustic source. In order to compare the experimental data, a centrifugal impeller and wedge introduced by Weidemann are used in the numerical calculation and the results are compared with the experimental data. Reasonable results are obtained not only for the peak frequencies but also for the amplitudes of the tonal.

• 대한조선학회논문집
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• 제30권2호
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• pp.43-53
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• 1993

부유체 강제동요문제를 수치해석하는 데에는 두가지 어려움이 따른다. 첫째는 교차점주위의 급격한 유동이고 둘째는 무한원방처리이다. 본 논문에서는 무한원방처리에 주안점을 두어, 자유표면의 Taylor 전개 및 F.F.T. 적용으로 계산시간을 단축시켜 수치해석하였다. 즉 Green 정리를 이용하여 해를 표현한 후, 축차방법에 의하여 해를 구한다. 축차단계에서는 계산식을 자유표면 기울기에 대하여 Taylor 전개하여 Convolution 형태로 변형한 후 F.F.T. 를 적용함으로써 계산시간을 O(Nlog N)으로 유지할 수 있었다. 수치검증을 위하여 부유체 선형문제와 압력장의 비선형 문제를 수치해석하여 비교하였고, 이를 확장하여 부유체의 강제동요문제를 수치해석하였는데, 계산시간을 O(Nlog N)으로 유지하면서 수치해석할 수 있었다.

• Imaging Science in Dentistry
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• 제42권4호
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• pp.237-242
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• 2012

Purpose: The objectives of this study were to survey the radiographic exposure parameters, to measure the patient doses for intraoral dental radiography nationwide, and thus to establish the diagnostic reference levels (DRLs) in intraoral dental X-ray examination in Korea. Materials and Methods: One hundred two intraoral dental radiographic machines from all regions of South Korea were selected for this study. Radiographic exposure parameters, size of hospital, type of image receptor system, installation duration of machine, and type of dental X-ray machine were documented. Patient entrance doses (PED) and dose-area products (DAP) were measured three times at the end of the exit cone of the X-ray unit with a DAP meter (DIAMENTOR M4-KDK, PTW, Freiburg, Germany) for adult mandibular molar intraoral dental radiography, and corrections were made for room temperature and pressure. Measured PED and DAP were averaged and compared according to the size of hospital, type of image receptor system, installation duration, and type of dental X-ray machine. Results: The mean exposure parameters were 62.6 kVp, 7.9 mA, and 0.5 second for adult mandibular molar intraoral dental radiography. The mean patient dose was 2.11 mGy (PED) and 59.4 $mGycm^2$ (DAP) and the third quartile one 3.07 mGy (PED) and 87.4 $mGycm^2$ (DAP). Doses at university dental hospitals were lower than those at dental clinics (p<0.05). Doses of digital radiography (DR) type were lower than those of film-based type (p<0.05). Conclusion: We recommend 3.1 mGy (PED), 87.4 $mGycm^2$ (DAP) as the DRLs in adult mandibular molar intraoral dental radiography in Korea.

• 방사선산업학회지
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• 제6권2호
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• pp.159-164
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• 2012

Bacterial cellulose (BC) is generated from citrus gel by Gluconacetobacter hansenii TL-2C. BC has good properties such as high-burst pressure, high-water contact and the ultrafine highly nanofibrous structure of mimic natural extracellular matrix (ECM) for tissue engineering. In this study, acrylic acid (AAc) was grafted onto BC surfaces under aqueous conditions using gamma-ray irradiation, and then immobilized gelatin onto AAc-g-BC. The characterization of scaffolds was performed by scanning electron microscopy (SEM), attenuated total reflectance-Fourier transform infrared spectroscopy (ATR-FTIR), toluidine blue O (TBO) assay. Morphology of gelatin and AAc incorporation onto BC nanofibers did not changed. Our study suggests that gelatin-immobilized BC nanofibers scaffold has a potentiality to fabricate 3D nanofibrous scaffolds for tissue engineering.

• Structural Engineering and Mechanics
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• 제72권4호
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• pp.421-432
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• 2019

In high-speed railway (HSR) system, the structure-borne noise inside viaduct at low frequency has been extensively investigated for its mitigation as a research hotspot owing to its harm to the nearby residents. This study proposed a novel acoustic optimization method for declining the structure-borne noise in viaduct-like structures by separating the acoustic contribution of each structural component in the measured acoustic field. The structural vibration and related acoustic sourcing, propagation, and radiation characteristics for the viaduct box girder under passing vehicle loading are studied by incorporating Finite Element Method (FEM) with Modal Acoustic Vector (MAV) analysis. Based on the Modal Acoustic Transfer Vector (MATV), the structural vibration mode that contributes maximum to the structure-borne noise shall be hereinafter filtered for the acoustic radiation. With vibration mode shapes, the locations of maximum amplitudes for being ribbed to mitigate the structure-borne noise are then obtained, and the structure-borne noise mitigation performance shall be eventually analyzed regarding to the ribbing conduction. The results demonstrate that the structural vibration and structure-borne noise of the viaduct box girder mainly occupy both in the range within 100 Hz, and the dominant frequency bands both are [31.5, 80] Hz. The peak frequency for the structure-borne noise of the viaduct box girder is mainly caused by $16^{th}$ and $62^{th}$ vibration modes; these two mode shapes mainly reflect the local vibration of the wing plate and top plate. By introducing web plate at the maximum amplitude of main mode shapes that contribute most to the acoustic modal contribution factors, the acoustic pressure peaks at the field-testing points are hereinafter obviously declined, this implies that the structure-borne noise mitigation performance is relatively promising for the viaduct.

• 한국군사과학기술학회지
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• 제24권2호
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• pp.211-218
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• 2021

This paper deals with the computational work to characterize the formation and pinching of a plasma in an X-pinch configuration. A resistive magnetohydrodynamic model of a single fluid and two temperature is adopted assuming a hollow conical structure in the (r,z) domain. The model includes the thermodynamic parameter of tungsten from the corrected Thomas-Fermi EOS(equation of state), determining the average ionization charge, pressure, and internal energy. The transport coefficients, resistivity and thermal conductivity, are obtained by the corrected Lee & More model and a simple radiation loss rate by recombination process is considered in the simulation. The simulation demonstrated the formation of a core-corona plasma and intense compression process near the central region which agrees with the experimental observation in the X-pinch device at Seoul National University. In addition, it confirmed the increase in radiation loss rate with the density and temperature of the core plasma.

• 한국경제지리학회지
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• 제24권2호
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• pp.163-180
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• 2021

원자력발전은 위험을 안고 있음에도 많은 국가에서 에너지 공급원으로 그리고 지구온난화 대응으로 중요하게 자리잡고 있다. 핵에너지는 방사능 오염의 위험과 핵무기의 위협 그리고 핵폐기물 처리의 문제를 가지고 있으나 효율적인 신기술로 안전 관리가 가능하다는 기술낙관주의가 전문가 그리고 정부 주도로 주류를 이루어 왔다. 그러나 체르노빌 그리고 후쿠시마 원전 사고는 전세계적으로 핵발전의 대안을 모색하는 관심과 노력은 확대되어 대안 모색으로 지속가능한 재생 에너지의 생산을 확대하는 노력, 에너지의 효율적 전달을 위한 스마트그리드와 환경친화적 소비 행태를 통한 에너지 사용 절감, 그리고 핵폐기물의 처리 등을 포함한 환경의 수용능력을 감안한 청지기 정신을 강조한다. 보다 근본적인 대안 운동으로는 대규모 원전 사고를 경험하며 기존 전문가와 정부가 중심이 되어 형성해온 기술주의가 배제했던 지역에서의 피해 사례와 이를 고려하지 못하는 접근에 대한 불만이 보다 광범위하게 피해자, 기술자, 일반인 등이 대안운동을 전개한다. 이들 비전문가들은 지역의 오염을 감지하고 대중의 일상생활에 심각하게 영향을 위험과 감정을 고려하는 능력을 가진 반전문가로 등장한다. 이들은 광범위한 지역에서 원자력에 대한 대안적 지식을 구성하고 합법화하는데 중요한 역할을 한다.

• 한국재난정보학회 논문집
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• 제19권3호
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• pp.582-596
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• 2023

연구목적: 본 연구는 원전사고 발생 시 임시 대피시설의 안전성을 강화할 수 있는 방안을 연구하였다. 연구방법: 본 연구에서는 과거의 체르노빌, 후쿠시마, 쓰리마일섬(TMI) 원전사고에 대한 사례연구를 활용하였다. 연구결과: 현재의 방사선 비상 대응 계획은 소개에 중점을 두고 있으며, 실내대피 개념은 단순히 주민 대피를 지원하는 수단으로 활용되고 있다. 그러나 사례연구를 통해 INES-5 이상의 사고의 경우, 소개보다 실내대피를 장려하는 것이 사상자 최소화에 효과적임을 확인하였다. 더 나은 실내대피를 보장하기 위해 아파트를 임시 대피소로 활용할 것을 권장하며, 아파트가 방사선 방호 기술을 갖추도록 개선사항을 제안한다. 결론: 더 나은 실내대피를 보장하기 위해 아파트를 임시 대피소로 활용할 것을 권장하며, 차폐, 양압, 밀폐기술을 이용해서 아파트의 성능을 보완하고자 한다.

• Nuclear Engineering and Technology
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• 제56권4호
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• pp.1310-1319
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• 2024

The reactor cavity cooling system (RCCS) is a passive reactor safety system commonly present in the designs of High-Temperature Gas-cooled Reactors (HTGR) that removes heat from the reactor pressure vessel by means of natural convection and radiation. It is one of the factors responsible for ensuring that the reactor does not melt down under any plausible accident scenario. For the simulation of accident scenarios, which are transient phenomena unfolding over a span of up to several days, intermediate fidelity methods and system codes must be employed to limit the models' execution time. These models can quantify radiation heat transfer well, but heat transfer caused by natural convection must be quantified with the use of correlations for the heat transfer coefficient. It is difficult to obtain reliable correlations for HTGR RCCS heat transfer coefficients experimentally due to such a system's size. They could, however, be obtained from high-fidelity steady-state simulations of RCCSs. The Rayleigh number in RCCSs is too high for using a Direct Numerical Simulation (DNS) technique; thus, a Reynolds-Averaged Navier-Stokes (RANS) approach must be employed. There are many RANS models, each performing best under different geometry and fluid flow conditions. To find the most suitable one for simulating an RCCS, the RANS models need to be validated. This work benchmarks various RANS models against three experiments performed on the HTTR RCCS Mockup by the Japanese Atomic Energy Agency (JAEA) in 1993. This facility is a 1/6 scale model of a vessel cooling system (VCS) for the High Temperature Engineering Test Reactor (HTTR), which is operated by JAEA. Multiple RANS models were evaluated on a simplified 2d-axisymmetric geometry. They were found to reproduce the experimental temperature profiles with errors of up to 22% for the lowest temperature benchmark and 15% for the higher temperature benchmarks. The results highlight that the pragmatic turbulence models need to be validated for high Rayleigh natural convection-driven flows and improved accordingly, more publicly available experimental data of RCCS resembling experiments is needed and indicate that a 2d-axisymmetric geometry approximation is likely insufficient to capture all the relevant phenomena in RCCS simulations.