• 한국안전학회지
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• 제18권2호
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• pp.50-55
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• 2003

Radiation degradation of crosslinked polyethylene(XLPE) was investigated using thermogravimetric analysis(TGA), The results of TGA were compared with FT-IR, melting temperature, oxidation induction time, and elongation at break on the XLPE exposed by $\gamma$-ray. 5% decomposition temperature of $\gamma$-ray irradiated XLPE showed similar tendencies with the case of elongation at break. Both properties agreed below 1000 KGy, however, did not show any remarkable characteristics above 1000 kGy, these properties can be useful to evaluate the radiation degradation of XLPE for only low irradiated region. Above 1000 kGy, the thermal decomposition activation energy showed decreased, on the contrary, increasing below 1000 kGy. Compared with FT-IR spectrum of irradiated XLPE, it was confirmed that the oxidation reaction was still occurring below 1000 kGy. Radiation degradation of XLPE was dependent upon the irradiation doses, TGA can be a useful tool to evaluate the degradation.

• 한국군사과학기술학회지
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• 제18권4호
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• pp.409-414
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• 2015

M125 booster is one of the reliable S&A device(safety and arming device) to determine the arming distance of fuze for gun ammunitions from 90 mm to 8 inch in diameter. And it is also well known that the arming distance of M125 booster is determined by the multiplication value of the gun tube property(traveled distance per turn of projectile) and the S&A device property(number of turns to arm), not by the projectile muzzle velocity. We have tried and succeeded in executing a proper analysis on M125 booster to figure out its characteristic constant of arming distance by considering only the gun tube properties and the S&A device properties. More detailed arming distance will be analyzed in the future by considering dynamic characteristics on all elements in the S&A device with vector analysis.

• 한국태양에너지학회 논문집
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• 제33권3호
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• pp.99-106
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• 2013

Recently, high-thermal-conductivity graphene and carbon nanotube nanoparticles have attracted particularly close attention from researchers. In the present study, the thermal conductivity and viscosity properties of two kinds of graphene and carbon nanotube nanofluids added to distilled water - two graphenes and carbon nanotubes of differing size - were compared and analyzed. The thermal conductivities of the nanofluids, formulated in the usual manner by adding graphene and carbon nanotube to distilled water and subjecting the mixture to ultrasonic dispersion, were measured by the transient hot-wire method, and the viscosities were determined using a rotational digital viscometer. As a result, we concluded that the nanofluid of small particle diameter of graphene have outstanding properties as heat transfer media, due to their excellent thermal conductivity and viscosity, compared with the other nanofluid.

• Safety and Health at Work
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• 제10권3호
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• pp.314-320
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• 2019

Background: Sitting posture may be related to risk factors, including inadequate weight-bearing support, particularly when maintained for long periods. Considering that body weight is loaded in a closed support system composed of the seat, backrest, floor and working surface, the aims of the present study were to describe the development of an ergonomic sitting workstation to continuously record weight-bearing at the seat, chair, backrest, work surface, and floor and to test its measurement properties: reproducibility, criterion-related validity, and sensitivity. Methods: Rigid bodies (1 to 30 kg) and participant weights were recorded to evaluate the workstation measurement properties. Results: Rigid body tests showed variation values less than 0.050 kg on reproducibility test and errors below 5% of measured value on criterion validity tests. Participant tests showed no statistically significant differences between repeated measures ($p{\geq}0.40$), errors were less than 2% of participant weights an sensitivity presented statistically significant changes (p = 0.007). Conclusion: The sitting workstation proposed showed to be reliable, valid and sensitive for use in future ergonomic studies to evaluate the sitting posture.

• Nuclear Engineering and Technology
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• 제53권6호
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• pp.1924-1930
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• 2021

By using miniature SENB specimens, the fracture properties of the materials in the region of welded metal, 321 stainless steel heat affected zone, 690 alloy heat affected zone of 321/690 dissimilar metal girth welded joints were tested. Both the J-resistance curves and critical fracture toughness of the three different materials are affected by the crack size because of the effect of crack tip constraint. Groups of constraint corrected J-resistance curves of the three materials are obtained according to J-Q-M approach. The welded metals exhibit the best fracture resistance but the worst fracture resistance is observed in the material of 690 alloy heat affected zone.

• Steel and Composite Structures
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• 제43권3호
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• pp.353-362
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• 2022

Bridge fire hazard has become a growing concern over the last decade due to the rapid increase of ground transportation of hazardous materials and resulting fire incidents. The lack of fire safety provisions in steel bridges can be a significant issue owing steel thermal properties that lead to fast degradation of steel properties at elevated temperatures. Alternatively, the development of composite action between steel girders and concrete decks can increase the fire resistance of steel bridges and meet fire safety requirements in some applications. This paper reviews the fire problem in steel bridges and the fire behavior of composite steel-concrete bridge girders. A numerical model is developed to trace the fire response of a typical bridge girder and is validated using measurements from fire tests. The selected bridge girder is composed by a hot rolled steel section strengthened with bearing stiffeners at midspan and supports. A concrete slab sitting on the top of the girder is connected to the slab through shear studs to provide full composite action. The validated numerical model was used to investigate the fire resistance of real scale bridge girders and the effect of the composite action under different scenarios (standard and hydrocarbon fires). Results showed that composite action can significantly increase the fire resistance of steel bridge girders. Besides, fire severity played an important role in the fire behavior of composite girders and both factors should be taken into consideration in the design of steel bridges for fire safety.

• 한국산학기술학회논문지
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• 제10권10호
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• pp.2609-2614
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• 2009

휴대용 초음파 탐지기(Ultrasonic Detector)는 전기설비에서 발생하는 부분방전, 코로나, 아킹, 트래킹 등과 같은 전기적 방전현상 탐지에 매유 유용하다. 그러나 초음파 탐지기는 측정음의 특성을 사용자가 듣고 판정함으로써 주관적 반응에 의해 그 결과가 좌우되거나 정확히 판정하기 곤란하게 된다. 따라서 초음파 음의 특성을 구별할 수 있는 새로운 분석적 방법이 요구된다. 본 연구에서는 초음파 탐지기에 의해 측정된 코로나, 아킹, 트래킹의 초음파 음을 시각화 할 수 있는 초음파 분석프로그램을 개발하였다. 개발된 프로그램에 의한 분석적 방법을 사용함으로써 초음파 음의 특성에 의존하던 기존의 방식보다 초음파 진단결과의 정확성을 높일 수 있게 된다.

• 한국식품위생안전성학회지
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• 제29권4호
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• pp.383-390
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• 2014

The safety of a new natural plant composition (ADP) was assessed on the genotoxicity study and 14-day repeat dose toxicity study. ADP contains a mixed water extract obtained from the mixture of Phellodendron cortex (Phellodendron amurense) and Anemarrhena rhizoma (Anemarrhena asphodeloides), and poses the contractile properties mediated by alpha-adrenoceptor of the prostate and urethra as well as antioxidant and anti-inflammatory properties. In order to evaluate genetic safety, in vivo micronucleus test was performed in ICR mice orally administered with three dose levels of 1250, 2500, 5000 mg/kg body weight, and vehicle and positive control. In the 14 days study, Sprague-Dawley rats were treated with ADP at the dose levels of 500, 1000, 2000 mg/kg once a day, and clinical signs, body weights, hematology, serum biochemistry, necropsy findings and organ weights were monitored and examined. In experimental results, ADP treatment, compared with vehicle control, did not induce the micronucleated erythrocytes from mouse bone marrow. In the 14 days study, any significant and toxicological differences in all measurements of parameters were not observed in ADP treatment groups of animals, compared with vehicle treatment. The No-Observed-Adverse-Effect-Level (NOAEL) of ADP in the 14 days study was determined to be greater than 2000 mg/kg/day in both sexes.

• 식품과학과 산업
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• 제50권2호
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• pp.52-59
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• 2017

나노포장은 나노물질 첨가에 따라 항균성, 가스 및 자외선 차단성과 같은 기능성이 향상된다는 장점이 부각되면서 오랫동안 개발되어 왔다. 하지만 최근들어 이러한 나노물질들이 식품과 직접적으로 접촉되면서 식품으로 이행되어 식품과 함께 섭취될 수 있기 때문에 안전하지 않을 수 있다는 논란이 있다. 독일, 스페인, 영국 등의 많은 유럽 국가들에서는 이러한 문제에 대한 빠른 대처를 위해 2000년대 중반부터 또한 우리나라에서는 2014년부터 나노물질 적용 포장재에서 나노물질의 이행에 대한 연구를 수행하고 있다. 나노물질별, 환경별(온도, 시간), 식품모사용매 또는 식품 유형별에 따른 나노물질의 이행에 대한 연구결과를 바탕으로 향후 안전관리를 위한 방안과 가이드라인 등이 마련되어야 한다.

• Journal of Mechanical Science and Technology
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• 제20권9호
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• pp.1323-1338
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• 2006

An analytical method to estimate the coupled frequencies of the circular plate submerged in fluid is developed using the finite Fourier-Bessel series expansion and Rayleigh-Ritz method. To verify the validity of the analytical method developed, finite element method is used and the frequency comparisons between them are found to be in good agreement. For the perforated plate submerged in fluid, it is almost impossible to develop a finite element model due to the necessity of the fine meshing of the plate and the fluid at the same time. This necessitates the use of solid plate with equivalent material properties. Unfortunately the effective elastic constants suggested by the ASME code are found to be not valid for the modal analysis. Therefore in this study the equivalent material properties of perforated plate are suggested by performing several finite element analyses with respect to the ligament efficiencies.