• Journal of Korea Foundry Society
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• v.21 no.2
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• pp.127-134
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• 2001

Misch metal (rare earth element, Ce, La, Nd, Pr) which has large influence on high-temperature stability and toughness was added to the Al-5%Ni-5%Mg alloy, and squeeze casting was used for Al-5%Ni-5%Mg-(Mm) alloys. The effect of applied pressure and misch metal additions on mechanical properties in Al-5%Ni-5%Mg alloy by direct squeeze casting has been investigated. The applied pressure were 0 MPa(gravity casting), 25, 50 and 75 MPa. Squeeze-cast Al-5%Ni-5%Mg-(Mm) alloys had better mechanical properties than those of non-pressurized cast alloys because of the increased cooling rate by the application of pressure during solidification. By the addition of misch metal in Al-5%Ni-5%Mg alloy, better combination of strength and elongation was obtained. The addition of 0.3%Mm in Al-5%Ni-5%Mg alloy improved the heat resistant property due to the formation of fine eutectic phases.

• Macromolecular Research
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• v.14 no.4
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• pp.438-442
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• 2006

Novel sulfonated poly(aryl ether ketones) containing benzoxazole were directly synthesized by aromatic nucleophilic polycondensation using various ratios of 2,2'-bi[2-( 4-flurophenyl)benzoxazol-6-yl]hexafluoropropane to sodium 5,5'-carbonylbis(2-fluorobenzenesulfonate). The copolymers were soluble in polar aprotic solvents such as N-methyl-2-pyrrolidone, N,N-dimethylacetamide, and N,N-dimethylformamide at a relatively high solid composition (>15 wt%) and formed tough, flexible and transparent membranes. The membranes exhibited a degradation temperature of above $290^{\circ}C$. The exact dissolution times of these membranes at $80^{\circ}C$ in Fenton's reagent (3 wt% $H_2O_2$ containing 2 ppm $FeSO_4$) were undetectable, confirming their excellent chemical stability in fuel cell application. The membranes showed a moderate increase in water uptake with respect to increasing temperature. The proton conductivities of the membranes were dependent on the composition and ranged from $1.10{\times}10^{-2}$ to $5.50{\times}10^{-2}Scm^{-1}$ at $80^{\circ}C$ and 95% relative humidity (RH). At $120^{\circ}C$ without externally humidified conditions, the conductivities increased above $10^{-2}Scm^{-1}$ with respect to increasing benzoxazole content, which suggested that the benzoxazole moieties contributed to the proton conduction.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.18 no.1
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• pp.43-49
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• 2005

Temperature stabilities of resonance frequencies of the substrates are very important in piezoelectric ceramics oscillators and fitters. In this study, it was investigated thermal resisting property of the length-extensional vibration mode of PZT ceramics. The mode can be utilized in fabricating ultra-small 55 kHz IF devices. We fabricated the ceramic specimens with x = 0.51, 0.52, 0.53, 0.54, and 0.55 in the Pb(Zr$\sub$x/Ti$\sub$1-x/)O$_3$ system. And their resonance frequencies were measured before 1st thermal aging, after 1st and 2nd thermal aging. In order to investigate the influence of thermal aging on thermal resisting properties, thermally aged specimens were once mote thermally aged. Before 1st thermal aging, the specimens of the compositions with morphotropic phase, x = 0.53 and rhombohedral phase, x = 0.54 have weak thermal resisting property of resonance frequency, while tetragonal phase, x = 0.51 has robust thermal resisting property of resonance frequency. 1st thermal aging improved thermal resisting property of resonance frequency in all specimens.

• Bulletin of the Korean Chemical Society
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• v.33 no.11
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• pp.3755-3760
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• 2012

Single crystals of lithium potassium phthalate (LiKP) were successfully grown from aqueous solution by solvent evaporation technique. The grown crystals were characterized by single crystal X-ray diffraction. The lithium potassium phthalate $C_{16}\;H_{12}\;K\;Li_3\;O_{11}$ belongs to triclinic system with the following unit-cell dimensions at 298(2) K;$a=7.405(5){\AA}$;$b=9.878(5){\AA}$;$c=13.396(5){\AA}$;${\alpha}=71.778(5)^{\circ}$;${\beta}=87.300(5)^{\circ}$;${\gamma}=85.405(5)^{\circ}$; having a space group P1. Mass spectrometric analysis provides the molecular weight of the compound and possible ways of fragmentations occurs in the compound. Thermal stability of the crystal was also studied by both simultaneous TGA/DTA analyses. The UV-Vis-NIR spectrum shows a good transparency in the whole of Visible and as well as in the near IR range. Third order nonlinear optical studies have also been studied by Z-scan technique. Nonlinear absorption and nonlinear refractive index were found out and the third order bulk susceptibility of compound was also estimated. The results have been discussed in detail.

• Journal of fish pathology
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• v.22 no.3
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• pp.335-342
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• 2009

The stability of immunoglobulin M (IgM) on different serum storage conditions and specific antibody response were tested using the serum collected from sevenband grouper Epinephelus septemfasciatus by enzyme-linked immunosorbent assay (ELISA). To test the effect of storage temperature and duration, sevenband grouper antiserum against bovine serum albumin (BSA) was stored at -80, -20 or 4${^{\circ}C}$ for 1, 34, 61 or 119 days. In addition, to test the effect of repeated freeze-thawing condition, the anti-BSA fish serum was frozen at -20 and -80${^{\circ}C}$ and then thawn and frozen for 1, 5 or 10 times repeatedly. Consequently, no significant difference was found in ELISA optical density (O.D.) values of sera for the above mentioned storage conditions: different temperatures (-80, -20 and 4${^{\circ}C}$), durations of storage (1, 34, 61 and 119 days), and repeated thaw-freeze cycles (1, 5, and 10 times), indicating that IgMs of test fish were stable. The specific antibody response of sevenband grouper was observed after BSA-immunization of the test fish reared at 20 ${^{\circ}C}$ or 25${^{\circ}C}$. At the rearing temperature of 20${^{\circ}C}$, the specific antibody against BSA first appeared at 14 days and maximum antibody titer was observed between 21 and 28 days, while at the rearing temperature of 25 ${^{\circ}C}$, specific antibody appeared at 7 days and maximum antibody titer was observed between 14 and 21 days. In conclusion, the rearing temperature at 25${^{\circ}C}$ gave a faster and higher specific antibody response than at 20${^{\circ}C}$ and the specific antibody response maintained for approximately 2 months at 20℃ and 25${^{\circ}C}$.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.22 no.12
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• pp.1681-1690
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• 1998

The aim of this paper is to investigate combustion characteristics of lean premixed mixture stabilized by catalytic surface reaction. The catalytic combustor consisted of a catalyst bed and a thermal combustor. The catalyst bed was made of two stage, Pd catalyst in the first stage and Pt catalyst in the second stage. Auto ignition of lean mixture took place in the thermal combustor. Ignition temperature was about $810{\sim}820^{\circ}C$ at the fuel-air ratio of 1.5~3.0 % and the mixture velocity of 11~18m/sec. The position of flame front in the thermal combustor moved toward back as preheat temperature increased and fuel-air ratio decreased. The f1ame supported by surface reaction was stabilized without any flame stabilizers. NOx emissions from the catalytic combustor were below 2.0 ppm ($O_2$ 15 %) when gas temperature was limited below $1350^{\circ}C$. This result demonstrates that NOx emission from the catalytic combustor is much low comparing with conventional combustors.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.13 no.8
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• pp.675-680
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• 2000

In this study the temperature coefficient of resonant frequency(TC $F_{r}$) dielectric and piezoelectric properties of Pb[(S $b_{1}$2//N $b_{1}$2/)$_{0.065}$)-(Z $r_{x}$, $Ti_{1-x}$ )$_{0.90}$] $O_3$ceramics were investigated with Zr/Ti ratio. The compositions near the morphotropic phase boundary (MPB) appeared when Zr/Ti ratio was 49.5/50.5 The dielectric constant and electromechanical coupling factor( $k_{p}$) also showed the highest values of 1,257, 0.653 respectively when the Zr/Ti ratio was 49.5/50.5 Moreover the mechanical quality factor( $Q_{m}$) showed th lowest value of 713 when the Zr/Ti ratio. The temperature coefficient of resonant frequency(TC $F_{r}$) abruptly change at the morphotropic phase boundary(MPB) which existed between the rhombohedral phase with highly negative TC $F_{r}$ of -106ppm/$^{\circ}C$ and the tetragonal phase with highly positive TC $F_{r}$ of +64pp $m^{\circ}C$ as Zr/Ti ratio varied from 50/50 to 49.5/50.5.50.5..50.5.

• 한국연소학회:학술대회논문집
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• 2006.10a
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• pp.60-64
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• 2006

Propagation rates ($U_{edge}$) of various premixed, twin edge-flames were measured as a function of global strain rate ($\sigma$), mixture strength, and Lewis number (Le). Using a counterflow slot-jet burner with electrical heaters at each end, both advancing (positive $U_{edge}$) and retreating (negative $U_{edge}$) edge-flames can be studied as they propagate along the long dimension of the burner. Experimental results are presented for premixed methane/air twin flames in terms of the effects of $\sigma$ on $U_{edge}$. Both low-$\sigma$ and high-$\sigma$ extinction limits were discovered for all mixtures tested. As a result, the domain of edge-flame stability was obtained in terms of heat loss factor and normalized flame thickness, and comparison with the numerical result of other researchers was also made. For low ($CH_4/O_2/CO_2$) and high ($C_3H_8$/air) Lewis number cases, propagation rates clearly show a strong dependence on Le.

• Bulletin of the Korean Chemical Society
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• v.34 no.10
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• pp.2865-2870
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• 2013

Ni-Ag core-shell nanoparticles were synthesized by polyol process and microemulsion technique successfully. In the polyol process, a chemical reduction method for preparing highly dispersed pure nickel and Ag shell formation have been reported. The approach involved the control of reaction temperature and reaction time in presence of organic solvent (ethylene glycol) as a reducing agent for Ag cation with poly(vinyl-pyrrolidone) (PVP. Mw = 40000) as a capping agent. In microemulsion method, the emulsion was prepared by water/cetyltrimetylammonium bromide (CTAB)/cyclohexane. The size of microemulsion droplet was determined by the molar ratio of water to surfactant (${\omega}_o$). The core-shell formation along with the change in structural phase and stability against oxidation at high temperature heat treatments of nanoparticles were investigated by X-ray diffraction and TEM analysis. Under optimum conditions the polyol process gives the Ni-Ag core-shell structures with 13 nm Ni core covered with 3 nm Ag shell, while the microemulsion method gives Ni core diameter of 8 nm with Ag shell of thickness 6 nm. The synthesized Ni-Ag core-shell nanoparticles were stable against oxidation up to $300^{\circ}C$.

• Korean Journal of Applied Biomechanics
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• v.32 no.2
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• pp.37-42
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• 2022

Objective: The aim of this study is to analyze the effect of the strength of the ankle support on the walking characteristics and ankle joints when men with flexible flat feet walk. Method: 13 adult male subjects (age: 23.9 ± 2.4 yrs, height: 173.0 ± 5.0 cm, weight: 76.9 ± 13.2 kg, Navicular Drop Test (NDT): 10.2 ± 0.8 mm) participated in this study. Each participant had to walk with the 3 conditions, barefoot, soft arch support and hard arch support, along a walkway while their kinematics was recorded at 100 Hz. Results: Based on the results of this study, it is considered that men with flexible flat feet should use hard arch support rather than bare feet to induce normal arch shape, relieve foot damage caused by excessive ankle joint abnormalities and improve stability. Conclusion: Our results for men with flat flexibility, there was a significant difference in the value of step length when walking was performed using two arch supports with different strengths. The angle of ankle dorsiflexion was significantly increased, and the ankle eversion angle was significantly decreased.