• Fibers and Polymers
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• 제2권4호
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• pp.171-177
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• 2001

Change of tensile properties, electrical conductivity and microwave shielding of electrochemically synthesized polypyrrole films with time are presented. Highly doped films had good electrical stability, retaining high microwave reflectivity throughout the aging period. Lightly doped films were less stable and partially reflective and absorptive of microwaves. FT-IR spectral observations revealed a progressive increase in intensity of an unsaturated conjugated carbonyl peak, which was not observed in the highly doped films, suggesting that the concentration of the dopant had an influence on mechanism of degradation of conductivity.

• 한국세라믹학회지
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• 제41권6호
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• pp.464-470
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• 2004

ZnO-P $r_{6}$ $O_{11}$-CoO-C $r_2$ $O_3$- $Y_2$ $O_3$계 세라믹스로 구성된 ZPCCY계 바리스터의 소결시간별 DC 가속열화 스트레스에 대한 전기적 안정성을 조사하였다. 소결시간은 전기적 특성 및 안정성에 크게 영향을 미치는 것으로 나타났다. 소결시간이 증가함에 따라 비직선 지수는 51.2∼23.8의 범위로 감소하였으며, 누설전류는 1.3∼5.6 $\mu$A의 범위로 증가하였다. 1시간 소결된 바리스터는 비직선성은 우수하나 밀도가 낮은 관계로 안정성이 상대적으로 낮았으며, 3시간 소결된 바리스터는 안정성은 양호하나 비직선성이 다소 낮은 것으로 나타났다 2시간 소결된 바리스터는 비직선 지수가 38.6, 누설전류가 3.6 $\mu$A로 양호 하고, DC스트레스_0.95 $V_{1㎃}$15$0^{\circ}C$/12h에서 바리스터 전압, 비직선 지수, 누설전류, 손실계수 변화율이 각각 -0.8%, -1.8%, +74.4%, +0.9%를 나타냄으로서 안정성이 우수한 것으로 나타났다.다.

• 한국세라믹학회지
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• 제42권7호
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• pp.490-496
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• 2005

The electrical properties and stability of the varistors composed of ZnO-Pr$_{6}$O$_{11}$-CoO-Cr$_{2}$O$_{3}$-Dy$_{2}$O$_{3}$ system were investigated with sintering time in the range of 1$\~$3 h at 1350$^{\circ}C$ . As the sintering time was increased, the varistor voltage and leakage current increased, but the nonlinear exponent decreased. The varistors sintered for 1 h exhibited excellent nonlinearity, with a nonlinear exponent of 55.3 and a leakage current of 0.1 $\mu$A, whereas presented relatively low stability. The varistors sintered for 2 h exhibited not only high nonlinear exponent of 46.3, low leakage current of 0.3 $\mu$A, low dielectric dissipation factor of 0.0431, but also the highest stability, in which the variation rates of varistor voltage, nonlinear exponent, leakage current, dielectric constant, and dielectric dissipation factor were -3.0$\%$, -4.1$\%$, +3056.2$\%$, +5.1$\%$, and -12.5$\%$, respectively, after DC accelerated aging stress state of 0.95 V$_{1ma}$/150$^{\circ}C$/24 h. On the whole, the nonlinearity and stability of these varistors are greatly affected by the sintering time.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2004년도 하계학술대회 논문집 Vol.5 No.2
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• pp.1142-1145
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• 2004

ZnO surge arresters continuously endure the operating voltages during the operation course, and in the mean time, which need to withstand occasionally transient voltages of lightning and switching overvoltages. Under these voltages, the ZnO varistors inside arresters would have aging phenomena, one important result of aging phenomena is the increasing of resistive currents of varistors, which leads to the increasing of power losses of varistors. And the operating voltage is continuously applied on the ZnO varistors, there is a degradation phenomenon existing in ZnO varistors. When the degradation reaches a certain degree, then the arrester must stop operation. The degradation is related to the applied voltage ratio, the applied voltage ratio is high, the degradation is quickly. When the power loss is higher than the thermal dispersion ability of house of arrester, then the arrester will thermally breakdown. In this study the thermal stability characteristics of surge arresters for high power wil be discussed on the view point of watt losses and thermal breakdown.

• 한국분말재료학회지
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• 제2권3호
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• pp.247-254
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• 1995

The theoretical optimum quaternary composition for improving the thermal stability of Al-Ti alloy was recently proposed. On the basis of the suggestion, quaternary Al-Ti-V-Zr alloy powders corresponding to the optimum compositions, one of which belongs to the region of the smallest lattice misfit between the matrix and the precipitates and the other belongs to the region of the smallest rate constant of coarsening, were prepared by mechanical alloying and the powders were vacuum-hot-pressed at $430^{\circ}C$ under the pressure of 800 MPa. The thermal stability of the specimens was evaluated by hardness testing after isothermal aging up to 400 hrs at various temperatures. The decrease of hardness of Al-Ti-V-Zr alloys was smaller than that of Al-Ti alloys. It was considered to be due to the formation of $Al_3Zr$ type and$Al_3Ti$ type quaternary precipitates having smaller lattice misfit than $Al_3Ti$ and the increase of volume fraction of All0v during the isothermal aging. The quaternary Al-Ti-V-Zr alloys corresponding to the smallest lattice misfit showed the most improved thermal stablilty and it was mainly considered to be due to the formation of All0v.

• 한국재료학회지
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• 제18권5호
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• pp.277-282
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• 2008

The effects of the field emission property in relation to the surface morphology and adhesion force were investigated. The single-wall-nanotube-based cathode was obtained by use of an in-situ arc discharge synthesis method, a screen-printing method and a spray method. The morphologies of the formed emitter layers were very different. The emission stability and uniformity were dramatically improved by employing an in-situ arc discharge synthesis method. In this study, it was confirmed that the current stability and uniformity of the field emission of the cathode depend on the surface morphology and adhesion force of the emitters. The current stability of the field emission device was also studied through an electrical aging process by varying the current and electric field.

• Bulletin of the Korean Chemical Society
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• 제28권1호
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• pp.99-102
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• 2007

To prepare freeze-dried ascorbyl palmitate (AsP)-containing liposome which can protect the drug from moisture attack and be used instantly by mixing with water for anti-aging and skin whitening therapy, AsP was encapsulated into liposomes and freeze-dried with trehalose. The freeze-dried liposome formulations were characterized by measuring water contents, particle size, time required for complete reconstitution. With the freeze-dried liposomes, we performed the stability test under accelerated conditions, skin permeation and localization test. The measurement of the time to perfect reconstitution showed that the freeze-dried liposomes can be changed to their initial state rapidly and short term stability test of AsP in reconstituted liposomes under accelerated conditions confirmed that the stability of AsP was considerably enhanced as compared to freshly prepared liposomes. The skin permeation and localization properties of AsP in reconstituted liposomes were not significantly different, indicating that the liposomal structures were maintained before and after freezedrying. In conclusion, the freeze-drying method provided a possible way to overcome the instability issue of AsP induced by the moisture and reproduced similar skin permeation and localization properties as shown by freshly prepared liposomes.

• 대한화장품학회:학술대회논문집
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• 대한화장품학회 2003년도 IFSCC Conference Proceeding Book II
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• pp.303-306
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• 2003

Indonesia is a tropical country having a temperature range of 25-35$^{\circ}C$ which can affect the skin and causes damages like aging. This aging process is due, at least, to free radical reactions. For this reason, many attempts had been done to find out creams containing natural antioxidant compound which have a potential of free radical scavenger. Kluwek, a fermented form of foot ball fruit or picung (Pangium edule.Reinw), had been proved to contain antioxidant compound in its methanol fraction oil to which antiaging cream was formulated. Stability evaluation was conducted for cream with Kluwek oil compared to base cream, including organoleptic (colour and odour), pH, viscosity, particle size, centrifugation test and flow characteristics either in room temperature (27$^{\circ}C$) or stress condition (4$^{\circ}C$ and 5$0^{\circ}C$) for 8 weeks continuously, and six times cycling test at 4$^{\circ}C$ and 5$0^{\circ}C$ every 24 hours. The results showed that cream with Kluwek oil and base cream were stable at temperature 27 and 4$^{\circ}C$, cycling test and centrifugation test, but not stable at 5$0^{\circ}C$. Free radical evaluation was done by Electron Spin Resonance and the result showed that cream with Kluwek oil had less free radicals compared to base cream.

• 대한화장품학회:학술대회논문집
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• 대한화장품학회 1999년도 IFSCC . ASCS 학술대회 발표 논문
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• pp.145-154
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• 1999

A novel retinol derivative, polyethoxylated retinamide (Medimin A) was synthesized, as an anti-aging agent. Collagen synthesis, skin permeation, stability, and toxicity of Medimin A were evaluated and compared with those of retinol and retinyl palmitate. In vitro collagen synthesis was evaluated by quantitative assay of [$^3H$]-proline incorporation into collagenase sensitive protein in fibroblast cultures. For in vitro skin permeation experiments, Franz diffusion cells (effective diffusion area: $1, 766{\;}\textrm{cm}^2$) and the excised skin of female hairless mouse aged 8 weeks were used The stabilities of retlnoids were evaluated at two different temperature ($25{\;}^{\circ}C$ and $40{\;}^{\circ}C$) and under UV in solubilized state and in OW emulsion. To estimate the safety, acute oral toxicity, acute dermal toxicity, primary skin irritation, acute eye irritation and human patch test were performed The effect of Medimin A on collagen synthesis was similar to that of retinol. The skin permeability of Medimin A was higher than those of retinol and retinyl palmitate. The Medimin A was more stable than retinol and retinyl palmitate. Medimin A was nontoxic in various toxicological tests. These results suggest that Medimin A would be a good anti-aging agent for enhancing bioavailability and stability.

• 대한화장품학회지
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• 제25권4호
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• pp.145-154
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• 1999

A novel retinol derivative, polyethoxylated retinamide(Medimin A) was synthesized, as an anti-aging agent. Collagen synthesis, skin permeation, stability, and toxicity of Medimin A were evaluated and compared with those of retinol and retinyl palmitate. In vitro collagen synthesis was evaluated by quantitative assay of $[^3H]-proline$ incorporation into collagenase sensitive protein in fibroblast cultures. For in vitro skin permeation experiments, Franz diffusion cells(effective diffusion area: 1,766 $cm^2$) and the excised skin of female hairless mouse aged 8 weeks were used, The stabilities of retinoids were evaluated at two different temperature($25^{\circ}C\;and\;40^{\circ}C$) and under UV in solubilized state and in O/W emulsion. To estimate the safety, acute oral toxicity, acute dermal toxicity, primary skin irritation, acute eye irritation and human patch test were performed. The effect of Medimin A on collagen synthesis was similar to that of retinol. The skin permeability of Medimin A was higher than those of retinol and retinyl palmitate. The Medimin A was more stable than retinol and retinyl palmitate. Medimin A was nontoxic in various toxicological tests. These results suggest that Medimin A would be a good anti-aging agent for enhancing bioavailability and stability.