• Advanced Composite Materials
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• 제18권4호
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• pp.351-364
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• 2009

The thermal stability and elevated temperature mechanical properties of $SiC_P$/Al-11.7Fe-1.3V-1.7Si (Al-11.7Fe-1.3V-1.7Si reinforced with SiC particulates) composites sheets prepared by spray deposition (SD) $\rightarrow$ hot pressing $\rightarrow$ rolling process were investigated. The experimental results showed that the composite possessed high ${\sigma}_b$ (elevated temperature tensile strength), for instance, ${\sigma}_b$ was 315.8 MPa, which was tested at $315^{\circ}C$, meanwhile the figure was 232.6 MPa tested at $400^{\circ}C$, and the elongations were 2.5% and 1.4%, respectively. Furthermore, the composite sheets exhibited excellent thermal stability: the hardness showed no significant decline after annealing at $550^{\circ}C$ for 200 h or at $600^{\circ}C$ for 10 h. The good elevated temperature mechanical properties and excellent thermal stability should mainly be attributed to the formation of spherical ${\alpha}-Al_{12}(Fe,\;V)_3Si$ dispersed phase particulates in the aluminum matrix. Furthermore, the addition of SiC particles into the alloy is another important factor, which the following properties are responsible for. The resultant Si of the reaction between Al matrix and SiC particles diffused into Al matrix can stabilize ${\alpha}-Al_{12}(Fe,\;V)_3Si$ dispersed phase; in addition, the interface (Si layer) improved the wettability of Al/$SiC_P$, hence, elevated the bonding between them. Furthermore, the fine $Al_4C_3$ phase also strengthened the matrix as a dispersion-strengthened phase. Meanwhile, load is transferred from Al matrix to SiC particles, which increased the cooling rate of the melt droplets and improved the solution strengthening and dispersion strengthening.

• 대한가정학회지
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• 제28권2호
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• pp.37-45
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• 1990

The purpose of this study was to determine the foaming properties of two small red bean protein isolates at various conditions. Data concerning the effects of pH, temperature, MaCl concentration, sugar concentration and protein concentration on the properties such as solubility, foam expansion, foam stability were presented. The results were summarized as follows : 1. The crude protein contents of two small red beans were 26.14% and 22.71%. The percentage of nonpolar amino acid group was the highest and that of sulfur containing amino acid group was the lowest. 2. Protein solubility showed the minimum at pH 4.5 which is isoelectric point of small red bean protein isolate adn heat treatment lowered solubility(P<0.05). At pH 4.5, solubility increased sighificantly as 0.4M NaCl was added. However, the effect of sugar concentration in the solubility was not significant. 3. Foam expansion of two small red bean protein isolates was high at pH 4.5 and heat treatment at 10$0^{\circ}C$ lowered foam expansion(P<0.05). While addition of NaCl, sugar did not affect the foma expansion, gradual increment of the protein isolates concentration up to 9% decreased the foma expansion slightly. 4. Foam stability was significantly high at pH 4.5 and heat treatment at 10$0^{\circ}C$ lowered foam stability. Addition of sugar caused slight decrease in foam stability. From 1% to 9% suspension, foma stability increased significantly as protein concentration increased(P<0.05)

• 한국염색가공학회지
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• 제30권4호
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• pp.264-274
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• 2018

Immobilization of lysozyme on chitosan non-woven using glutaraldehyde(GA) was investigated. For this, 100 % chitosan non-woven was prepared as novel support for the enzyme immobilization. In addition, free lysozyme activity was examined depending on various pH and temperature by measuring time. Moreover, the optimum immobilization conditions depending on various pH, temperature, immobilization time and lysozyme concentration was evaluated. In addition, thermal stability and storage stability of immobilized lysozyme were measured. The characteristics of immobilized lysozyme was examined by FT-IR, surface morphology, and MTT assay. The results are follows: the optimal immobilization of lysozyme were pH 7.0, $25^{\circ}C$, lysozyme concentration 1.5 mg/ml, immobilization time 240 min. The immobilized lysozyme showed higher thermal stability than the free trypsin. The immobilized lysozyme activity was retained 80 % of its initial activity at $4^{\circ}C$ over 30 days of storage. The lysozyme was immobilized effectively on chitosan non-woven by observation of surface morphology.

• 한국응용약물학회:학술대회논문집
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• 한국응용약물학회 2001년도 추계학술대회 및 정기총회
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• pp.88-88
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• 2001

The effects of pH and temperature on the degradation of prokidn in various buffered aqueous solutions(pH 1.32~9.66) and temperatures (35, 45 and 6$0^{\circ}C$ were investigated. The effect of ionic strength on the degradation of prokidin was also measured by varying ionic strength (0.0466~1.5) at pH 1.35 and 45$^{\circ}C$ The effect of metal ions on the degradation of prokidin at pH 7.35 and 3.98 was observed. The degradation of prokidin followed the pseudo- first- order kinetics. The degradation rate of prokidin showed pH-dependent and temperature-dependent patterns. Prokidin was very stable at the pH below 3.95, where half-lives at 35, 45 and 6$0^{\circ}C$were 294, 206 and 107 day, respectively. However, it degraded very rapidly at pH above 6.49; the half-lives at 35, 45 and 6$0^{\circ}C$were 60, 25 and 13 day, respectively. As ionic strength increased, the degradation rate of prokidin increased. Some metal ions increased the degradation rate in the rank order of Mn > Fe > Cu >Fe On the other hand. other metal ions such as Bi, Ba. Zn, Ni, Co did not show unfavorable effect.

• Journal of Pharmaceutical Investigation
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• 제25권3호
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• pp.239-247
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• 1995

The physico-chemical stability of aucubin, a hepatoprotective iridoid glucoside, in buffered aqueous solutions was studied using a stability-indicating reversed-phase high performance liquid chromatography. The degradation of aucubin followed the pseudo-first-order kinetics. In strong acidic regions, aucubin was rapidly degraded by the specific acid catalysis, forming dark brown precipitates. From the rate-pH profiles, it was found that aucubin was most stable at the pH of about 10. From the temperature dependence of degradation, activation energies for aucubin at pH 2.1 and 4.9 were calculated to be 22.0 and 24.3 kcal/mole, respectively. The shelf-life $(t_{90%})$ for aucubin at pH 9.07 and $20^{\circ}C$ was predicted to be about 603 days. A higher ionic strength accelerated the degradation of aucubin at pH 4.01. The effect of metal ions on the degradation rate of aucubin at pH 7.16 was in the rank order of $Cu^{2+}\;>\;Fe^{3+}\;>\;Co^{2+}\;>\;Fe^{2+}\;>\;Mg^{2+}$. On the other hand, $Mn^{2+}\;and\;Ba^{2+}$ slowed the degradation rate.

• 약학회지
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• 제30권5호
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• pp.228-231
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• 1986

The effect of temperature and pH on the degrdation of minoxidil in the aqueous solution was investigated and the stability of pharmaceutical preparation for solution was also studied. The degradation of minoxidil in the aqueous solution was first order type reaction and the rate constant at $20^{\circ}C$ in pH 7.0 phosphate buffer solution was 9.464${\times]10^{-3} day^{-1}$ and calculated activation energy was 11.7 kcal/mol. The degradation of minoxidil was acid-base catalytic reaction and the most stable range of pH was about 5.0. The liquid pharmaceutical preparation was very stable in 3 months.

• 한국표면공학회:학술대회논문집
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• 한국표면공학회 2018년도 춘계학술대회 논문집
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• pp.33.1-33.1
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• 2018

pH is expressed mathematically as $pH=-{\log}[H^+]$, is a measure of the hydrogen ion concentration, [$H^+$] to specify the acidity or basicity of an aqueous solution. The pH scale usually ranges from 0 to 14. Every aqueous solution can be measured to determine its pH value. The pH values below 7.0 express the acidity, above 7.0 are alkalinity and pH 7.0 is a neutral solution. The solution pH can be determined by indicator or by measurement using pH sensor, which measuring the voltage generated between a glass electrode and a reference electrode according to the Nernst Equation. The pH value of solutions depends on the temperature and the activity of contained ions. In nickel electroless plating process, the controlled pH value in some limited ranges are extremely important to achieve optimal deposition rate, phosphorus content as well as solution stability. Basically, nickel electroless plating solution contains of $Ni^{2+}ions$, reducing agent, buffer and complexing agents. The plating processes are normally carried out at $82-92^{\circ}C$. However, the change of its pH values with temperatures does not follow any rule. Thus, the purpose of study is to understand the relationship between pH and temperature of some based solutions and electroless nickel plating solutions. The change of pH with changing temperatures is explained by view of the thermal dynamic and the practical measurements.

• Biomolecules & Therapeutics
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• 제8권4호
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• pp.332-337
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• 2000

Physicochemical properties of aspalatone (acetylsalicylic acid maltol ester, AM), which has been recently found to have an antithrombotic effect, were studied in terms of solubility, dissolution, partition coefficient (Pc) and stability. The solubility of AM at 37$^{\circ}C$ was about 1.2 mg/ml and the P$_{c}$ value for n-octanol/water and chloroform/water was 11.4 and 382.6, respectively. Dissolution rates of AM at pH 1.2 and 6.8 were more than 80% within 30 min. The degradation of AM followed apparent first-order kinetics, and was dependent on temperature, pH and ionic strength. From the pH-rate profile, the optimal pH was found to be at around 4.0. Half-lives at pH 1.2 and 6.8 were 33.5 and 44.4 hr, respectively. The degradation rate of AM at pH 1.2 was somewhat faster than that of aspirin, but at pH 7.0, the degradation rate of AM was slower than that of aspirin.n.

• KSBB Journal
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• 제19권3호
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• pp.221-225
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• 2004

Bacillus sp. 유래의 Bacillus polyfermenticus SCD를 Bisroo $t^{ⓡ}$라고 부르고, 이것은 생균제로서 산업적으로 매우 유용하다. 본 연구에서는 B. polyfermenticus SCD를 산업적으로 활용성을 증대시키기 위해 three layer coating법을 사용하여 인공위액의 pH 변화에 대한 안정성과 열안정성, glucose 농도에 따른 안정성을 연구하였다. 그 결과 코팅한 B. polyfermenticus SCD가 인공위액에 대한 내성에서는 배양 4시간을 기준으로 pH 2는 30%, pH 4는 20%, pH 6은 14% 상승효과가 있었음을 알 수 있었고, 온도변화에 대한 안정성에서는 코팅한 B. polyfermenticus SCD가 8$0^{\circ}C$에서 2시간 기준으로 안정성이 약 40% 증진됨을 확인할 수 있었다. 고농도 (30%)의 glucose에서 코팅한 B. polyfermenticus SCD는 안정하였으며, 코팅하지 않은 것보다 약 50% 안정성이 증대됨을 확인할 수 있었다. 그리고 pH 4.0에서는 코팅한 B. polyfermenticus SCD는 코팅을 하지 않은 B polyfermenticus SCD보다 전체적으로 생존율이 40% 이상, pH 6.0에서는 생존율이 42% 이상 증진됨을 알 수 있었다.

• Journal of Microbiology and Biotechnology
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• 제24권5호
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• pp.639-647
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• 2014

Laccases have a broad range of industrial applications. In this study, we immobilized laccase on $SiO_2$ nanoparticles to overcome problems associated with stability and reusability of the free enzyme. Among different reagents used to functionally activate the nanoparticles, glutaraldehyde was found to be the most effective for immobilization. Optimization of the immobilization pH, temperature, enzyme loading, and incubation period led to a maximum immobilization yield of 75.8% and an immobilization efficiency of 92.9%. The optimum pH and temperature for immobilized laccase were 3.5 and $45^{\circ}C$, respectively, which differed from the values of pH 3.0 and $40^{\circ}C$ obtained for the free enzyme. Immobilized laccase retained high residual activities over a broad range of pH and temperature. The kinetic parameter $V_{max}$ was slightly reduced from 1,890 to 1,630 ${\mu}mol/min/mg$ protein, and $K_m$ was increased from 29.3 to 45.6. The thermal stability of immobilized laccase was significantly higher than that of the free enzyme, with a half-life 11- and 18-fold higher at temperatures of $50^{\circ}C$ and $60^{\circ}C$, respectively. In addition, residual activity was 82.6% after 10 cycles of use. Thus, laccase immobilized on $SiO_2$ nanoparticles functionally activated with glutaraldehyde has broad pH and temperature ranges, thermostability, and high reusability compared with the free enzyme. It constitutes a notably efficient system for biotechnological applications.