• 대한전기학회:학술대회논문집
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• 대한전기학회 1993년도 하계학술대회 논문집 B
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• pp.546-549
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• 1993

The correlation between electrical conduct ion and dielectric relaxation properties of copper ion conducting glasses is discussed. The glasses were prepared in the system $CuI-Cu_2S-Cu_2O-MoO_3$ using rapid quenching technique. These glasses have high ionic conductivities at room temperature in the range of $10^{circ}$[S/m], and the conductivities increase with increasing CuI content. The activation energies for conduction are 0.26-0.57 eV. The dielectric relaxation times are 1-10uS, and the activation energy for ion jumping are 0.18-0.41eV. It is shown that the tendency of conduction properties depending on composition of the glass is similar those of dilectric relaxation.

• 한국소성가공학회:학술대회논문집
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• 한국소성가공학회 2005년도 춘계학술대회 논문집
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• pp.176-179
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• 2005

Spray casting of hypereutectic Al-Si based alloy has been reported to provide distinct advantages over ingot metallurgy (IM) or rapid solidification/powder metallurgy (RS/PM) process in terms of microstructure refinement. Hypereutectic Al-Si based alloys have been regarded attractive for automotive and aerospace application, due to high specific strength, good wear resistance, low coefficient of thermal expansion, high thermal stability, and good creep resistance. In this study, hypereutectic Al-25Si-2.0Cu-1.0Mg alloy was prepared by OSPREY spray casting process. High temperature deformation behavior of the hypereutectic Al-Si based alloy has been investigated by applying the internal variable theory proposed by Chang et al. The change of strain rate sensitivity and Creep transition were analyzed by using the load relaxation test and constant creep test.

• 대한치과교정학회지
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• 제21권2호
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• pp.433-446
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• 1991

The present study was performed to evaluate the relaxation patterns of rubber elastics, elastomeric modules and chains stored in the water bath. Initial loading profiles were established for extension of $100\%,\;200\%$ of their original length for elastomeric chains and of 21, 28, 35, 42, 49mm for rubber elastics and elastomeric modules. The tests were performed on materials stored in distilled water at $37^{\circ}C$ and extraoral elastics stored in dry state at room temperature, at 0 hour, 1 hour, 6 hours, 1 day, 1 week, 2 weeks, 3 weeks, and 4 weeks, respectively. The following results were drawn: 1. The relaxation of rubber elastics manifested no correlation with increments of the extension distances, but showed correlation with time lapse. Remaining forces of rubber elastics carne out $84.6-98.52\%$ after 1 day, $70.92-89.31\%$ after 3 weeks of period. 2. The relaxation of elastomers manifested no correlation with increments of the extension distances, however represented considerable relaxation with time lapse as rapid relaxation after 1 hour and then gradual relaxations with time lapse. Modules relaxed much more than chains. $60.58-67.05\%$ of remaining forces for chains and $37.77-65.17\%$ for modules after 1 hour were turned out, and $51.48-62.22\%$ for chains and $8.04-25.15\%$ for modules after 3 weeks as well. 3. Permanent deformation rates of rubber elastics could not be measured with present investigation, but elastomers underwent severe deformations. 4. $3-9\%$ of permanent deformations for chains, $3-10\%$ for modules at 0 hour were turned out, and $25-30\%$ for chains, $96-145\%$ for modules after 3 weeks as well.

• 한국강구조학회 논문집
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• 제16권5호통권72호
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• pp.519-528
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• 2004

대부분의 용접재는 용접 후 빠른 속도로 냉각하는 과정에서 재료조직의 변화, 즉 상변태(마르텐사이트변태)가 일어난다. 그리고 이러한 상변태에 의한 체적의 팽창은 특히 고강도강재의 용접시 용접부의 잔류응력완화에 기여한다. 따라서 고강도강을 적용한 강구조물 접합부의 잔류응력 특징을 파악하기 위해서는 고강도강 용접시 상변태가 잔류응력완화에 미치는 효과를 정량적으로 평가할 수 있는 수치적 모델을 확립해야 한다. 본 연구에서는 고강도강 용접시 상변태에 의한 체적의 팽창이 잔류응력 완화에 미치는 영향을 잔류응력 측정 실험을 통하여 조사하였고, 이를 바탕으로 상변태에 의한 잔류응력완화를 고려한 고강도강 및 이종강재 용접접합부의 잔류응력 특징을 3차원 열탄소성 해석기법 개발을 통하여 재현하였다.

• 대한기계학회논문집A
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• 제24권10호
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• pp.2552-2559
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• 2000

Most of ferrous b.c.c weld materials have martensitic transformation during rapid cooling after welding. It is well known that volume expansion due to the phase transformation could influence on the relaxation of welding residual stress. To apply this effect practically, it is necessary to establish a numerical model which is able to estimate the effect of phase transformation on residual stress relaxation quantitatively. For this purpose, the analysis is carried out in two regions, i.e., heating and cooling, because the variation of material properties following a phase transformation in cooling is different in comparison with the case in heating, even at the same temperature. The variation of material properties following phase transformation is considered by the adjustment of specific heat and thermal expansion coefficient, and the distribution of residual stress in analysis is compared with that of experiment by previous study. In this study, simplified numerical procedures considering phase transformation, which based on a commercial finite element package was established through comparing with the experimental data of residual stress distribution by other researcher. To consider the phase transformation effect on residual stress relaxation, the transition of mechanical and thermal property such as thermal expansion coefficient and specific heat capacity was found by try and error method in this analysis. In addition to, since the transformation temperature changes by the kind and control of alloying elements, the steel with many kinds of transformation temperature were selected and the effect of transformation on stress releasement was investigated by the numerical procedures considering phase transformation.

• 소성∙가공
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• 제14권6호
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• pp.502-508
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• 2005

Hypereutectic Al-Si alloys have been regarded attractive for automotive and aerospace application, due to high specific strength, good wear resistance, high thermal stability, low thermal expansion coefficient and good creep resistance. Spray casting of hypereutectic Al-Si alloy has been reported to provide distinct advantages over ingot metallurgy (IM) or rapid solidification/powder metallurgy (RS/PM) process in terms of microstructure refinement. In this study, hypereutectic Al-25Si-2.0Cu-1.0Mg alloy was prepared by OSPREY spray casting process. The change of strain rate sensitivity and Creep transition were analyzed by using the load relaxation test and constant creep test. High temperature deformation behavior of the hypereutectic Al-Si alloy has been investigated by applying the internal variable theory proposed by Chang et al. Especially, the creep resistance of spray casted hypereutectic Al-Si alloy can be enhanced considerably by the accumulation of prestrain.

• The Korean Journal of Physiology
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• 제24권1호
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• pp.91-102
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• 1990

토끼 흉부 대동맥을 이용하여 내피세포 의존성 혈관이완에 대한 세포외 $Ca^{2+}$과 여러가지 $Ca^{2+}$ 길항제의 효과를 분석하여 EDRF의 작용기전을 밝혀 보고자 하였다. 대동맥 횡단 절편의 등장성 수축은 $10^{-7}\;M$ 노에피네프린으로 유발시켰으며, $10^{-6}\;M$ 사세틸콜린으로 내피세포 의존성 혈관이완을 일으켰다. 내피세포는 작은 솜뭉치로 부드럽게 문질러서 제거하였으며, hemolysate를 사용하여 EDRF에 대한 헤모글로빈의 효과를 관찰하였다. 결과를 종합하면 다음과 같다. 1) 아세틸콜린에 의한 내피세포 의존성 혈관이완은 두 시기, 즉 초기급속이완기와 후기완만이완기로 나타났다. 2) 세포외 $Ca^{2+}$을 낮추면, 아세틸콜린에 의한 내피세포 의존성 혈관이완이 감소하였으며, 특히 후기완만이완기가 감소하였다. 3) Verapamil, nifedipine, $Mn^{2+}$ 및 $Cd^{2+}$은 내피세포 의존성 혈관이완에 영향이 없었던 반면 $La^{3+}$와 $Co^{2+}$는 억제시켰다. 4) 헤모글로빈을 투여하면 내피세포가 없는 절편에서는 기초긴장도의 변화가 없었으나 내피세포가 있는 절편에서는 기초긴장도가 증가하였고 아세틸콜린에 의한 내피세포 의존성 혈관이완도 완전히 억제되었다. 이상의 결과로부터 세포외 $Ca^{2+}$은 주로 후기완만이완기에 작용하며 이때 사용되는 $Ca^{2+}$ 유입 통로는 $Ca^{2+}$ 길항제로 억제되지 않는 것으로 결론지을 수 있다.

• Journal of Biosystems Engineering
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• 제39권4호
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• pp.345-351
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• 2014

Purpose: Rapid detection of bacteria is very important in agricultural and food industries to prevent many foodborne illnesses. The objective of this study was to develop a portable nuclear magnetic resonance (NMR)-based system to detect foodborne pathogens (E. coli). This study was focused on developing a method to detect low concentrations of magnetic nanoparticles using NMR techniques. Methods: NMR relaxometry was performed to examine the NMR properties of iron nanoparticle mixtures with different concentrations by using a 1 T permanent magnet magnetic resonance imaging system. Exponential curve fitting (ECF) and inverse Laplace transform (ILT) methods were used to estimate the NMR relaxation time constants, $T_1$ and $T_2$, of guar gum solutions with different iron nanoparticle concentrations (0, $10^{-3}$, $10^{-4}$, $10^{-5}$, $10^{-6}$, and $10^{-7}M$). Results: The ECF and ILT methods did not show much difference in these values. Analysis of the NMR relaxation data showed that the ILT method is comparable to the classical ECF method and is more sensitive to the presence of iron nanoparticles. This study also showed that the spin-spin relaxation time constants acquired by a Carr-Purcell-Meiboom-Gill (CPMG) pulse sequence are more useful for determining the concentration of iron nanoparticle solutions comparwith the spin-lattice relaxation time constants acquired by an inversion recovery pulse sequence. Conclusions: We conclude that NMR relaxometry that utilizes CPMG pulse sequence and ILT analysis is more suitable for detecting foodborne pathogens bound to magnetic nanoparticles in agricultural and food products than using inversion recovery pulse sequence and ECF analysis.

• Journal of Chest Surgery
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• 제24권3호
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• pp.229-244
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• 1991

A bioassay technique and organ bath study were performed to analyze the effects of extracellular $Ca^{2+}$ and $Ca^{2+}$-antagonists on endothelium-derived relaxing factor[s][EDRF] released from the endothelial cells of rabbit aorta. Transverse strips with intact endothelium or damaged endothelium were used for the mechanical contraction experiment using organ bath. Long segment including thoracic and abdominal aorta with endothelium [EDRF donor aorta] was perfused with Tyrode solution which was aerated with 95% $O_2-5%$ $CO_2$ mixed gas and kept at 35oC. The perfusate was bioassayed with a transverse strip of thoracic aorta with damaged endothelium. The test strip was contracted with nor-epinephrine and acetylcholine was used to stimulate the release of EDRF from endothelial cells. The results obtained were as follows; 1] The endothelium-dependent relaxation[EDR] induced by acetylcholine was biphasic; an initial rapid relaxation followed by a slow relaxation. 2] EDR induced by acetylcholine was reduced gradually with the decrease in the concentration of extracellular $Ca^{2+}$. The effect of extracellular $Ca^{2+}$ on EDR was more prominent in the late slow relaxation phase. 3] EDR to acetylcholine was not altered by acute exposure to organic $Ca^{2+}$-antagonists. Pretreatment with verapamil to the EDRF donor aortic segment did not alter the magnitude of EDR. 4] Among the inorganic $Ca^{2+}$-antagonists $Mn^{2+}$ and $Cd^{2+}$ did not inhibit EDR, whereas $Co^{2+}$ and $La^{3+}$ inhibited EDR. 5] The inhibitory response of $Co^{2+}$ to EDR developed when infused directly on the test strip. That of $La^{3+}$, however, was evoked when added to solution perfusing the donor aortic segment. The above results suggest that $Ca^{2+}$-antagonists do not affect EDR and the inhibitory effect of $Ca^{2+}$ results from influencing the action of EDRF on vascular smooth muscle, whereas that of $La^{3+}$ results from its action on the release of EDRF from endothelial cells.

• 한국재료학회:학술대회논문집
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• 한국재료학회 2003년도 춘계학술발표강연 및 논문개요집
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• pp.55-55
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• 2003

Recently, with the rapid development of the waveguide division multiplexing (WDM) systems for large capacity and flexibility of information network, the broad band 1.5$\mu\textrm{m}$ erbium-doped waveguide amplifier (EDWA) become important. The main factors affecting the performance of sol-gel-based waveguides are non-radiative relaxation channels due to rare-earth concentration quenching and to vibration of the OH groups Therefore, the sol-gel process has to be carefully controlled in order to minimize the residual OH content.