• Proceedings of the KIEE Conference
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• 1993.07b
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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.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2005.05a
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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.

• The korean journal of orthodontics
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• v.21 no.2 s.34
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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.

• Journal of Korean Society of Steel Construction
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• v.16 no.5 s.72
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• pp.519-528
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• 2004

Most of ferrous b.c.c weld materials may experience martensitic transformation during rapid cooling after welding. And it is well known that volume expansion due to phase transformation could influence in the case of welding of high tensile strength steels on the relaxation of welding residual stress. To apply this effect practically, it is a prerequisite to establish a numerical model which is able to estimate the effect of phase transformation on residual stress relaxation quantitatively. In this study, we investigated the effect of phase transformation on the relaxation of welding residual stress through experiment. And three-dimensional thermal elastic-plastic FEM analysis is conducted to reproduce the effect of phase transformation on the relaxation of welding residual stress. Also we carried out the analysis of welding residual stress in welds of similar or dissimilar steels considering the effect of residual stress relaxation due to phase transformation.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.24 no.10 s.181
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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.

• Transactions of Materials Processing
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• v.14 no.6 s.78
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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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• v.24 no.1
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• pp.91-102
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• 1990

The effects of extracellular $Ca^{2+}$ and various $Ca^{2+}$ antagonists on endothelium-dependent relaxation to acetylcholine were studied in the isolated rabbit thoracic aorta in order to elucidate the control mechanism of endothelium derived relaxing factor (EDRF) release. Endothelium was removed from aortic strips by gentle rubbing with cotton ball. The effect of hemoglobin on basal tension was also observed with hemolysate. The results obtained were as follows: 1) Endothelium-dependent relaxation (EDR) to acetylcholine (ACh) showed biphasic pattern; the initial rapid relaxation phase and the late slow relaxation phase. 2) With the depletion of the extracellular $Ca^{2+}$, EDR was gradually suppressed, especially the late slow relaxation. 3) Verapamil, nifedipine, $Mn^{2+}$ and $Cd^{2+}$ had not any effect on EDR, while $La^{3+}$ and $Co^{2+}$ suppressed EDR completely. 4) The resting tension of the strips with rubbed endothelium was not altered by the addition of hemoglobin. That of the strips with intact endothelium, however, was enhanced and EDR to ACh was completely blocked From these results, we suggest that extracellular $Ca^{2+}$ is necessary for ACh-induced slow relaxation while $Ca^{2+}$ antagonists have not any effect on EDR.

• Journal of Biosystems Engineering
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• v.39 no.4
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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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• v.24 no.3
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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.

• Proceedings of the Materials Research Society of Korea Conference
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• 2003.03a
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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.