• Tribology and Lubricants
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• 제36권3호
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• pp.124-132
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• 2020

The effect of the stoichiometry on the sliding wear properties of NiAl coatings has been investigated. Three different powder mixtures with the compositions of Ni-50at%Al, Ni-54at%Al and Ni-42at%Al were diepressed respectively, and which were subsequently coated on mild steel through combustion synthesis in an induction heating system. Sliding wear behavior of the coatings was examined against an alloyed tool steel using a pin-on-disc type sliding wear test machine. As results, it could be seen that powder mixture(Ni-54at%Al) with displaying Al-rich deviations from the stoichiometry of NiAl(Ni-50at%Al) was promoted the most the synthetic reactivity. The microstructure of the coating layer with the compositions of Ni-54at%Al exhibits the porous NiAl single phase structure. However, the microstructure of the coating layer of the compositions of Ni-42at%Al exhibits the denser multi-phase structure containing several intermediate phases in addition to NiAl. Densification of the coating layer was enhanced by increasing the reacting temperature. On the other hand, the wear properties of the coating layers showed that the wear mode at speeds of around 1 m/s was severe wear, regardless of the stoichiometry and reacting temperature. However, wear properties of coating layer with the compositions of Ni-42at%Al were superior to those of coating layer with the compositions of Ni-54at%Al. This would be attributed by the fact that coating layer with the compositions of Ni-42at%Al develops little void and much intermediate phases with high strength.

• 소성∙가공
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• 제6권3호
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• pp.239-249
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• 1997

The behaviour of alloys in the semi-solid state strongly depends on the imposed stress state and on the morphology of the phase which can vary from dendritic to globular. To optimal net shape forging of semi-solid materials, it is important to investigate for filling phenomena in forging process of arbitrarily shaped dies. To produce a automotive part which has good mechanical property, the filling pattern according to die velocity and solid fraction distribution has to be estimated for arbitrarily shaped dies. Therefore, the estimation of filling characteristic in the forging simulation with arbitrarily shaped dies of semi-solid materials are calculated by finite element method with proposed algorithm. The proposed theoretical model and a various boundary conditions for arbitrarily shaped dies is investigated with the coupling calculation between the liquid phase flow and the solid phase deformation. The simulation process with arbitrarily shaped dies is performed to the isothermal conditions of two dimensional problems. To analysis of forging process by using semi-solid materials, a new stress-strain relationship is described, and forging analysis is performed by viscoelastic model for the solid phase and the Darcy's law for the liquid flow. The calculated results for forging force and filling limitations will be compared to experimental data. The filling simulation of simple products performed with the uniform billet temperature(584$^{\circ}C$) from the induction heating by the commercial package MAGMAsoft. The initial step of computation is the touching of semi-solid material with the end of die gate and the initial concept of proposed system just fit with the capability of MAGMAsoft.

• 조명전기설비학회논문지
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• 제28권1호
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• pp.16-28
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• 2014

This paper presents a novel high-power-factor circuit topology of AC to AC current-fed type high frequency resonant inverter which includes the function of power factor correction(PFC) in the proposed inverter to operate the AC input block with high power factor. The proposed circuit topology of AC to AC current fed type high resonant inverter removes DC link electrolytic capacitor and has also the one of power factor correction(PFC) in the inverter circuit without an additional PFC circuit since the input current by constituting it in parallel as an unit inverter, which assumes the class-E high frequency resonant inverter of conventional current-fed type, flows in the form of the resultant current flowing through each constant current reactor($L_{d1}$, $L_{d2}$). The circuit analysis of proposed inverter is generally described by adopting the normalized parameters and the evaluation of its operating characteristics are conducted by using the parameters such as the ratio of switching and resonant frequency(${\mu}$), coupling coefficient(k) and so on. An example of procedure for circuit design based on the characteristic values obtained from the theoretical analysis is presented. To confirm the validity of the theoretical analysis, the experimental results are also presented. In the future, the proposed inverter shows it can be practically used as power supply system for induction heating application, DC-DC converter etc.

• 대한의생명과학회지
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• 제11권3호
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• pp.343-347
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• 2005

Bambusae caulis in Liquamen is one of the important herbal medicine produced by heating bamboo indirectly and is used for treatment of stroke, hypertension, and diabetes etc. Recently the mechanism of clinical effects on Bambusae caulis in Liquamen has been studied. This experiment was conducted to confirm the clinical effects of Bambusae caulis in Liquamen on type 1 diabetes and its related mechanism. We divided C57BL/6 mice into 3 groups and induced them to be type 1 diabetes by injection of streptozocin into peritoneum. The dosage of each group was 150 mg/kg once only, 140 mg/kg once only and 40 mg/kg for 5 days respectively. The two groups injected streptozocin for once took orally Bambusae caulis in Liquamen after the induction of diabetes, and the other one group was given Bambusae caulis in Liquamen during the diabetes inducing period. As the result, the two diabetes-induced groups showed blood glucose decreasing effect by Bambusae caulis in Liquamen on an average, but they didn't show the signiftcant differences statistically. But Bambusae caulis in Liquamen showed the anti-diabetic effect suppressing blood sugar rising trend during the diabetes inducing peried (P<0.05). The anti-oxidative effect of Bambusae caulis in Liquamen was measured with the hypoxanthine/xanthine oxidase (HX/XOD) system. The quantity of ROS was measured using DCFDA reagent indirectly. As the result, $10\%$ solution of Bambusae caulis in Liquamen showed anti-oxidative effect by scavenging $93.4\%$ superoxide as compared with control group. It is suspected that the anti-oxidative effect of Bambusae caulis in Liquamen suppressed the increase of blood glucose in the diabetes-inducing group. These results could be useful data to understand the effect of Bambusae caulis in Liquamen on type 1 diabetes and type 1 diabetes developing because ROS were closely connected with the induction and complications of diabetes.

• 한국산업보건학회지
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• 제32권4호
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• pp.381-392
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• 2022

Objectives: Objective of this study is to review briefly exposure characteristics, monitoring instruments and threshold limit values for extremely low frequency-magnetic field (ELF-MF) methods. This study was undertaken through brief literature review. We performed a literature search in PubMed to identify ELF-MF studies conducted in workplaces. Initial search keywords such as 'extremely low frequency-magnetic field (ELF-MF)' and 'electromagnetic fields (EMF)' combined or singly. We limited our review to occupational rather than general nonworkplace environmental exposures. Methods: The contents we reviewed: key industry and occupations generating ELF-MF, several direct-reading instruments monitoring ELF-MF and threshold limit values (TLV) preventing health effects may be caused by the exposure to ELF-MF. Results: The industries related to the generation and supply of electricity, electrolytic installations, welding, and induction heating and more were regarded as high ELF-MF exposure industries. All jobs handling or employed performed in power cable lines, electrical wiring, and electrical equipment are found to be exposed to ELF-MF. Threshold or ceiling limit, 1,000 µT, is established to prevent acute effects of exposure to low-frequency EMFs on the nervous system: the direct stimulation of nerve and muscle tissues and the induction of retinal phosphenes. The International Agency for Research on Cancer (IARC) has classified ELF-MF as possibly carcinogenic to humans chiefly based on epidemiological studies on childhood leukemia. However, a causal relationship between magnetic fields and several types of cancer including childhood leukemia has not been established nor has any other long-term effects. Risk management using precautionary measures, has been initiated by the US and EU to prevent chronic health effects related to ELF-MF exposure in workplaces. Conclusion: This study recommends the implementation of various measures such as theestablishment of occupational exposure limit values for ELF-MF and precautionary principle to prevent potential chronic occupational health effects may be caused by ELF-MF in Korea.

• 방사성폐기물학회지
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• 제10권4호
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• pp.247-254
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• 2012

원전에서 발생되는 방사성폐기물에 대한 고화처리 방법 중 하나인 유리화기술이 일부 가연성폐기물에 대해 적용되고 있다. 국내외적으로 중저준위 방사성폐기물의 효과적인 감용과 안정적인 처분을 위해 다양한 폐기물에 대한 유리화기술 적용방안이 확대 연구되고 있으며, 최근에는 가연성폐기물 뿐만 아니라 알루미늄 금속과 같은 비가연성폐기물에도 유리화 연구가 활발하게 진행되고 있다. 공기조화계통 (HVAC)에는 주로 필터가 이용되고 있으며, 사용 후 필터는 여과재 (유리섬유 및 알루미늄)를 이용하여 배기체를 흡착하기 때문에 방사성폐기물로 처리가 되어야 한다. 본 연구는 필터에 대한 처리기술 연구를 위해 유도가열식 저온용융로 (Cold Crucible Induction Melter: CCIM)를 이용한 유리화 타당성 연구를 수행하였다. 사용후 필터에 대한 유리화 (Vitrification)는 먼저 유리섬유 및 알루미늄 함량을 고려한 최적의 유리조성을 개발 하였으며, 개발된 유리 조성을 이용하여 최적의 폐기물 저감을 위한 용융변수와 최종 생성된 유리고화체의 특성을 분석하였다. 사용후 필터 유리화용 조성유리는 주로 $SiO_2$와 $B_2O_3$로 구성되어 있다. 전기로를 이용한 용융물 특성시험에서는 폐기물 투입률 및 최종 생성물인 유리고화체의 특성이 검토되었다. 본 연구에서는 알루미늄 금속과 유리섬유로 구성된 필터에 대한 유리조성 개발과 이를 통해 생성된 유리고화체의 물리화학적 특성을 검토하고 유리화 타당성을 확인하였다.