• Bulletin of the Korean Chemical Society
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• v.26 no.12
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• pp.2007-2016
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• 2005

An artificial neural network (ANN) is successfully presented for prediction acidity constant (pKa) of various benzoic acids and phenols with diverse chemical structures using a nonlinear quantitative structure-property relationship. A three-layered feed forward ANN with back-propagation of error was generated using six molecular descriptors appearing in the multi-parameter linear regression (MLR) model. The polarizability term $(\pi_1)$, most positive charge of acidic hydrogen atom $(q^+)$, molecular weight (MW), most negative charge of the acidic oxygen atom $(q^-)$, the hydrogen-bond accepting ability $(\epsilon_B)$ and partial charge weighted topological electronic (PCWTE) descriptors are inputs and its output is pKa. It was found that properly selected and trained neural network with 205 compounds could fairly represent dependence of the acidity constant on molecular descriptors. For evaluation of the predictive power of the generated ANN, an optimized network was applied for prediction pKa values of 37 compounds in the prediction set, which were not used in the optimization procedure. Squared correlation coefficient $(R^2)$ and root mean square error (RMSE) of 0.9147 and 0.9388 for prediction set by the MLR model should be compared with the values of 0.9939 and 0.2575 by the ANN model. These improvements are due to the fact that acidity constant of benzoic acids and phenols in water shows nonlinear correlations with the molecular descriptors.

• Bulletin of the Korean Chemical Society
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• v.22 no.6
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• pp.559-564
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• 2001

A method for calculating the main characteristics of a potentiometric titration curve in a carboxylic ion exchanger has been investigated. The potentiometric titration curves of simple electrolyte and ion exchangers (polyelectrolytes) showed a great difference between them. The acidity parameters of the ion exchangers, the thermodynamic constant (pK0), apparent equilibrium constant (K), and correction for the apparent equilibrium constant (b), were introduced and used to express the characteristics of the carboxylic ion exchanger. A characteristic equation related to the acidity parameters of the ion exchangers systems was derived. A fibrous carboxylic cation exchanger was used and potentiometric titration curves at different concentrations of the supporting electrolyte were obtained . To prove the validity of the characteristic equation, the concentration of the supporting electroyte was varied. In the present study, good agreement between the data points and the fitted curves was found in all the cases. The g (number of moles of alkali to 1 g of ion exchanger) of carboxylic ion exchanger was calculated from the concentration of supporting electrolyte (C), pH of the solution, and degree of neutralization of ion exchanger (x).

• Korean Chemical Engineering Research
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• v.57 no.2
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• pp.164-171
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• 2019

The protonation parameters, dissociation constants ($pK_{BH^+}$) of conjugate acid, slope values (m, ${\phi}$ and $m^*$) and correlation coefficients (r) of hydroxamic acids were determined by Hammett acidity function method, Bunnett-Olsen method and excess acidity method in hydrochloric and perchloric acid solutions. Effect of acid concentration on partition and percentage protonation was also studied. $pK_{BH^+}$ values show that hydroxamic acids do not behave as Hammett bases, but hydroxamic acids behave as weak bases in strong acidic solutions. The values of $pK_{BH^+}$ obtained through Bunnett-Olsen method and excess acidity method were compared with the Hammett acidity function. ChemAxon's MarvinSketch 6.1.5 software was also used for determining $pK_a$, pI and microspecies distribution (%) of hydroxamic acids with pH. Hydrogen donor and acceptor values and logD were also obtained. The results show that N-p-chlorophenyl-4-bromobenzohydroxamic acid has the highest $pK_a$ and lowest logD values. On the contrary, N-phenyl-3,5-dinitrobenzohydroxamic acid has lowest the $pK_a$ and highest logD values.

• Journal of the Korean Society of Food Science and Nutrition
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• v.26 no.6
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• pp.1021-1027
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• 1997

$CO_2$production in fermentation of dongchimi was measured and interrelated with changes in pH and titratable acidity. The effects of salt content and temperature on $CO_2$production rate were analysed. Fermentation of dongchimi showed drastic pH decrease in early stage and subsequent levelling off around 3.9, with linearly increased acidity up to 0.3~0.4% optimum quality. $CO_2$production of dongchimi could be analysed to consist of two consecutive stages of constant rate. The first stage $CO_2$production of higher rate moved to the second stage of lower rate when acidity rose beyond 0.3%. When compared to those of 1 and 2% salt content, dongchimi of 3% salt showed lower $CO_2$production rate in the 1st stage and slower acidity change through the whole fermentation period. However, it resulted in the product of highest $CO_2$accumulation at optimal ripeness because of consistent $CO_2$production of longer 1st stage period and relatively high $CO_2$production rate in 2nd stage. $CO_2$production depended on temperature less compared to acidity change(activation energy: 57.3 and 44.3kJ/mol for $CO_2$production of 1st and 2nd stages, respectively; 79.3kJ/mol for acidity change), which means higher ratio of $CO_2$production rate relative to acidity increase at lower temperature. Slower increase in acidity at low temperature also was shown to extend the period of 1st stage $CO_2$production. Therefore, low temperature fermentation was effective in producing the high $CO_2$content dongchimi at adequate acidity, which is desirable organoleptically.

• Journal of Sericultural and Entomological Science
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• v.15 no.2
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• pp.45-53
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• 1973

1. The sericin solubility increased rapidly as the increase of water M-alkalinity. 2. The acidity of the treated water was nutralized at the over 25ppm of M-alkalinity. 3. The more M-alkalinity of the sample water is, the more M-alkalinity was found after cocoon treat. 4. The total hardness of sample water seemed to be droped as M-alkalinity increased. 5. The sericin solubility also seemed to be droped as the increase of water acidity. 6. In case of treat finish with cocoon, the acidity and total hardness seemed to increase as the acidity of the water increased, but M-alkalinity was nutralized at 20~40 ppm of water acidity or the M-alkalinity could not be found in case over 40ppm of acidity. 7. In case increase of iron component with sample water, sericin solubility seemed to drop down, and mangan component showed the same nature but dull drop. 8. After cocoon was treated with water, acidity, M-alkalinity and total hardness were increased by the extraction from cocoon shell because of pH and treating temperature but not because of iron componnent. Mangan component, however, affected as to increase of acidity and total hardness but to decrease for M-alkalinity. 9. In case change of M-alkalinity and total hardness, sericin solubility has increased also. 10. In case constant pH and total hardness, the more M-alkalinity is, the more sericin solubility was found. 11. In case constant pH, total hardness, and M-alkalinity, the more acidity is, the less sericin solubility was found. 12. In case constant pH(6.8) and M-alkalinity, the more total hardness is, the less sericin solubility was found. 13. Though the combination of water, high solubility water, medium solubility water and low solubility water were prepared. The high solubility water desolved sericin 2.2% more than low solubility water. And the medium solubility water desolved sericin as much as 2.4~2.9%. 14. It was found that the most important factors for filature water are pH, M-alkalinity, acidity and total hardness which may need more words for optimum filature water development. 15. In case of repeat use of water, the buffer action of water has increased so that the sericin solubility to be decreased.

• Tribology and Lubricants
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• v.37 no.6
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• pp.203-207
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• 2021

This study presents the development of dielectric constant sensors to measure lubricant properties. The lubricant oil sensor is used to measure oil properties and machine conditions. Various condition monitoring methods are applied to diagnose machine conditions. Machine condition monitoring using oil sensors has advantage over other machine condition monitoring methods. The fault conditions can be noticed at the early stages by the detection of wear particles using oil sensors. Therefore, it provides an early warning in the failure procedure. A variety of oil sensors are applied to check the machine condition. Among all oil sensors, only one sensor can measure the tendency of several properties such as acidity and water content. A dielectric constant sensor is also used to measure various oil properties; therefore, it is very useful. The dielectric constant is the ratio of the capacitance of a capacitor using that material as a dielectric to that of a similar capacitor using vacuum as its dielectric. The dielectric constant has an effect on water content, contaminants, base oil, additive, and so forth. In this study, the dielectric constant sensor is fabricated using MEMS process. In the fabrication process, the shape, gap of the electrode array, and thickness of the insulation material are considered to improve the sensitivity of the sensor.

• Journal of the Korean Chemical Society
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• v.46 no.4
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• pp.323-330
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• 2002

The protonation equilibrium of 5-substituted 2-furaldehydes is investigated spectrophotometrically in aqueous sulfuric acid at $25^{\circ}C$ and the basicity constants(p$K_{BH+}$) of the substrates is calculated by means of the excess acidity method. The basicity constant of 5-metyl-2-furaldehyde having electron donating group is larger than that of 5- nitro-2-furaldehyde having electron withdrawing group. Difference between the basicity constants(p$K_{BH+}$) of these two compounds was about 3.25 pK unit. The m value which is the degree of solvation of the protonated substrate is similar to that of acetophenone having same protonation site. The dependence of p$K_{BH+}$ on m value shows good linear cor-relation.

• The Korean Journal of Food And Nutrition
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• v.29 no.5
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• pp.801-807
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• 2016

In Western countries, kimchi, the Korean traditional fermented cabbage, is considered to be a healthy. However, it is one of the main sources of the high sodium content of the Korean diet. In order to decrease the sodium content, we manufactured a low-sodium kimchi (LK, salinity 1.0%) and 4 additional low-sodium kimchi starters in which each of 4 lactic acid bacteria (Lb. sakei 1, Lb. sakei 2, Lb. palntarum and W. koreensis) were added. The LKL1 to LKL4 samples were prepared by adding 4 single LAB starters, each with an inoculum size of $10^6CFU/g$, when the cabbage was mixed with kimchi sauce. The kimchi starters were fermented at $10^{\circ}C$ until reaching 0.5% acidity, and then stored at $-1.5^{\circ}C$ until reaching 0.75% acidity. The pH and acidity of the starter kimchi changed more rapidly in the early phase of fermentation (up to 0.75% acidity) than control low-sodium kimchi. After the acidity of the kimchi starters reached 0.75% it remained constant. As the fermentation progressed, the total aerobic and lactic acid bacteria concentrations in the kimchi starter with added Lb. sakei 1 were the same as in the control low-sodium kimchi. The low-sodium kimchi fermentation of the kimchi starter with added Lb. palntarum progressed differently due to a difference in acid resistance. The kimchi starter with added Lb. sakei 2 had an overall liking score that was slightly higher than that of the control low-sodium kimchi due to a lower off-flavor.

• Preventive Nutrition and Food Science
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• v.4 no.4
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• pp.246-250
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• 1999

This study was conducted to develop the fermentation kinetic modeling for the prediction of pH and acidity changes in kimchi at isothermal and nonisothermal fermentation temperatures(0~15$^{\circ}C$) and salt concentrations(1.5~4.0%) using the traditional two-step method and alternative one-step method. The calculations of the two-step method of pH and acidity change during fermentation followed the pattern of the first order and zero order, respectively. The reaction rate constant of pH by the first order was increased from 0.008 {TEX}$day^{-1}${/TEX} to 0.017 {TEX}$day^{-1}${/TEX} by increasing the temperature from $0^{\circ}C$ to 15$^{\circ}C$ at 2.75% of salt concentration, and was decreased from 0.013 {TEX}$day^{-1}${/TEX} to 0.010 {TEX}$day^{-1}${/TEX} by increasing the salt concentration from 1.5% to 4.0% at 5$^{\circ}C$. For the pH and acidity of Kimchi, the zero order had a higher correlation than the first order to the estimate of the kinetics parameters by the one-step method. The {TEX}$E_{a}${/TEX} ranges of pH and acidity were 61.057~66.086 and 62.417~68.772 kJ/mole with different temperatures and salt concentrations. This one-step method had smaller and more realistic estimates of error(p〈0.05). The effective temperatures, {TEX}$T_{eff}${/TEX}, with 0~15$^{\circ}C$ of square function type of 12 hr intervals were 12.85, 11.48 and 12.46$^{\circ}C$ as increasing the salt concentration, 1.50, 2.75 and 4.00%, respectively. The {TEX}$T_{eff}${/TEX} were higher values than the mean temperature(7.5$^{\circ}C$).

• Elastomers and Composites
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• v.12 no.1
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• pp.27-32
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• 1977

The kinetics of azo-coupling reaction of N-acetyl-H-acid (1-acetamino-8-hydroxynaphthalene-3, 6-disulfonic acid) with several heterocyclic diasonium compounds such as diazotiged 3-aminopyridine, 3-aminoquinoline, 8-aminoauinoline and aniline was studied. It was found that reactions proceeded at remarkably different rate. Reaction rate was in increasing order; 3-aminopyridine, 3-aminoquinoline, 8-aminoauinoline and aniline. And the activation energies were 9.62, 10.10, 10.39, 10.70 Kcal/mole, respectively. Especially, the rate constant of 3-aminopyridine was 100 times larger than that of benzene diasonium compound even in strong acidity. Hammett plot was also made of the rate constants obtained against the heterocyclic substituent constants reported in the literature. A good linear relationship was obtained and the reaction constant of N-acetyl H-acid was calculated to be 3.14.