• Journal of Korean society of Dental Hygiene
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• v.16 no.5
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• pp.783-790
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• 2016

Objectives: The purpose of this study is to evaluate the non-enzymatic antioxidants stabilities in dentifrices by ascorbic acid and tocopherol according to the chemical condition. Methods: For the analysis of two antioxidants, HPLC UV detector system was used. HPLC was performed using sodium sulfate, acetonitrile(ACN), methanol(MeOH) and measuring absorbance at 240-295 nm. To confirm general pH reaction of two compounds, buffer solution was prepared for the analysis. The dentifrice was titrated by pH so as to examine the change of elapsed time in dentifrice. Linearity of calibration curve of two antioxidants was measured. Results: Each compound showed good linearity at optimized wavelength as well as showing good precision. General pH reaction of two antioxidants was examined. Ascorbic acid showed the highest residue(63.23%) at pH 10 and the lowest residue(2.77%) at pH 4. Tocopherol showed the highest residue(55.70%) at pH 7 and the lowest residue(3.31%) at pH 4. As a result of changing elapsed time of antioxidants in dentifrice by pH, components were remained stably at low temperature($39.2^{\circ}F$) and pH 7. Conclusions: It is necessary to keep dentifrice including ascorbic acid and tocopherol, and non-enzymatic antioxidants at pH 7 and low temperature for improving chemical stability.

• Journal of the Korean Wood Science and Technology
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• v.27 no.3
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• pp.63-72
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• 1999

For the purpose of improving the wet strength properties of paper, cellulosic fibers were modified by the processes of carbarmoylethylation and N-chlorocarbamoylethylation. Carbamoylethylated cellulose was prepared by the reaction of acrylamide with cellulosic fibers under the alkali catalyst, and N-chlorocarbamoylethylated cellulose was prepared by the addition of sodium hypochlorite into the carbamoylethylated cellulose. In carbamoylethylation reaction, the conditions of NaOH concentration, temperature and acrylamide addition rate were considered to be important factors. An initial reactivity and degree of substitution(DS) in carbamoylethylation of cellulosic fibers were effective according to increasing the addition rates of alkali, acrylamide and the temperature condition of $40^{\circ}C$. The effective wet strength properties by N-chlorocarbamoylethylation of cellulosic fibers were indicated under the conditions of DS 0.06. The wet strength of sheet was improved to 85% at the 100% basis of dry strength. From the photograph of scanning electron microscopy, fiber cuttings on the edge of sheet sample used in tensile strength testing were found in the N-chlorocarbamoylethylated sheet, due to the improvement of fiber bonding strength. The hypochlorite treatment was effective in the recycling of N-chlorocarbamoylethylated sheet, and was reduced the wet strength of sheet to be able to reslush.

• Journal of Korean Biological Nursing Science
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• v.10 no.1
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• pp.96-104
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• 2008

Purpose: We had executed the 3 3 5 5 walking club program for 12 weeks for one hour three times per week to evaluate the effect of the program on health of the elderly. Methods: A pre and post measurement tool of the program was applied to measure obesity, rate of body fat, blood pressure, vital capacity, standard vital capacity, intake capacity of maximum oxygen, grasping power, reaction of whole body, pulse, body mass index (BMI), total bodily score, age of bodily strength, age of health. Data collected from this tool was analyzed by SPSS in paired t-test. Results: The 3 3 5 5 walking club program has affected the weight control of the participants. The participants of 3 3 5 5 walking club program reduced their weight from 61.7 kg to 61.25 kg, rate of body fat from 21.89 kg to 21.22 kg, standard vital capacity from 2,393.56 ml to 2,380.44 ml, reaction of whole body from 475.38 msec to 439.33 msec, and increased grasping power from 22.06 to 23.16 ml (p<.05), total bodily score 68.91 points to 71.38 points significantly (p<.05). Conclusion: The result indicated that the 3.3.5.5 Walking club program has an positive effect on improving health care of the elderly without special exercise tools.

• Transactions of the Korean hydrogen and new energy society
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• v.29 no.3
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• pp.260-266
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• 2018

To enhance catalyst activity of the palladium (Pd) towards oxygen reduction reaction (ORR), iridium (Ir) and yttrium (Y) were alloyed by polyol method. Due to the low reduction potential of Y, it is hard to reduce Y ion completely by polyol method. In XPS spectra, the binding energy of the Pd is shifted to a lower value, which indicates the d-electron of Pd is filled by the electron from the Y. And other phases of Y are observed by the XPS. Among the catalysts, the $Pd_4IrY_{0.1}/C$ showed the best activity towards ORR, which indicates the metallic Y is effective for improving the catalytic activity. Thus, for further enhancing ORR activity, the novel method for complete reduction of Y is needed.

• Korean Chemical Engineering Research
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• v.51 no.4
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• pp.432-437
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• 2013

The CO preferential oxidation reaction (PROX) has been done using Cu catalytic active species supported on some of mesoporous silica materials which can facilitate the diffusion of the reactants in order to prevent the poisoning of anode active materials by CO molecules during driving polymer electrolyte fuel cells (PEMFC) in this study. As a result when SBA-15 with large pore used as a support showed excellent CO oxidation activity, especially the activity increased in proportion to the amount of supported Cu. Ti components which was inserted to increase the degree of dispersion of Cu, contributed to improving the performance for CO oxidation at low-temperature. The degree of dispersion of Cu ingredients was the best in the catalyst inserted 20 mol-% Ti into the framework of SBA-15, and CO oxidation activity was also improved.

• Korean Chemical Engineering Research
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• v.60 no.1
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• pp.7-11
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• 2022

In the membrane forming process of a proton exchange membrane fuel cell (PEMFC), drying and annealing heat treatment processes are required for performance and durability. In this study, the optimal annealing temperature for improving the durability of the polymer membrane was studied. It was annealed in the temperature range of 125~175 ℃, and thermal stability and hydrogen permeability were measured as basic data of durability at each annealing temperature. The electrochemical durability was analyzed by Fenton reaction and open circuit voltage (OCV) holding. The annealing temperature of 165 ℃ was the optimal temperature in terms of thermal stability and hydrogen permeability. In the Fenton reaction, the fluorine emission rate of the membrane annealed at 165 ℃ was the lowest, and the lifespan of the membrane annealed at 165 ℃ was the longest in the OCV holding experiment, confirming that 165 ℃ was the optimal temperature for the durability of the polymer membrane.

• Korean Journal of Materials Research
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• v.34 no.3
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• pp.175-183
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• 2024

Geopolymer, also known as alkali aluminum silicate, is used as a substitute for Portland cement, and it is also used as a binder because of its good adhesive properties and heat resistance. Since Davidovits developed Geopolymer matrix composites (GMCs) based on the binder properties of geopolymer, they have been utilized as flame exhaust ducts and aircraft fire protection materials. Geopolymer structures are formed through hydrolysis and dehydration reactions, and their physical properties can be influenced by reaction conditions such as concentration, reaction time, and temperature. The aim of this study is to examine the effects of silica size and aging time on the mechanical properties of composites. Commercial water glass and kaolin were used to synthesize geopolymers, and two types of silica powder were added to increase the silicon content. Using carbon fiber mats, a fiber-reinforced composite material was fabricated using the hand lay-up method. Spectroscopy was used to confirm polymerization, aging effects, and heat treatment, and composite materials were used to measure flexural strength. As a result, it was confirmed that the longer time aging and use of nano-sized silica particles were helpful in improving the mechanical properties of the geopolymer matrix composite.

• Journal of the korean academy of Pediatric Dentistry
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• v.23 no.3
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• pp.640-658
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• 1996

The purpose of this study was to examine the mechanism of improving acid resistance of Nd-YAG laser irradiated tooth enamel and determine the most effective energy density for improving acid resistance. The bovine tooth enamel were lased with a pulsed Nd-YAG laser. The energy densities of exposed laser beam were varied from 10 to $70\;J/cm^2$. To investigate the degree of improving acid resistance by irradiation, all the samples were submerged to demineralize in 0.5 N $HClO_4$ solution for 1 minute. After 1 minute, 0.05 % $LaCl_3$ was added to the solution for interrupting the demineralization reaction. The amounts of dissolved calcium and phosphate in the solution were measured by using an atomic absorption spectrophotometer and the UV/VIS spectrophotometer, respectively. To examine the mechanism of improving acid resistance, X-ray diffraction analysis, infrared spectroscopy, and scanning electron microscopy were taken. The X-ray diffraction pattern of the samples were obtained in the $10^{\circ}{\sim}80^{\circ}2{\theta}$ range with $Cu-K{\alpha}$ radiation using M18HF(Mac Science Co.) with X-ray diffractometer operating at 40 KV and 300 mA. The infra-red spectra of the ground samples in 300 mg KBr pellets 10 mm diameter were obtained in the $4000cm^{-1}\;to\;400cm^{-1}$ range using JASCO 300E spectrophotometer. The scanning electron microscopy was carried out using JSM6400(JEOL Co.) with $500{\sim}2000$ times magnification. The results were as follow 1. The concentration of calcium dissolved from laser irradiated enamel with $50J/cm^2$ was significantly lesser than that of unlased control group (p<0.05) 2. From the result of the X-ray diffraction analysis, $\beta$-TCP, which increases acid solubility, was identified in lased enamel but the diffraction peaks of (002) and (004) became sharp with increasing energy density of laser irradiation. This means that the crystals in lased samples were grown through the c-axis and subsequently, the acid solubility of enamel decreased. 3. The a-axis parameter was slightly increased by laser irradiation, whereas the c-axis parameter was almost constant except for a little decrease at $50J/cm^2$. 4. In the infra-red spectra of lased enamels, phosphate bands ($600{\sim}500cm^{-1}$), B-carbonate bands (870, $1415{\sim}1455cm^{-1}$), and A-carbonate band ($1545cm^{-1}$) were observed. The amounts of phosphate bands and the B-carbonate bands were reduced, on the other hand, the amount of the A-carbonate band was increased by increase the energy density. 5. The SEM experiments reveal that the surface melting and recrystallization were appeared at $30J/cm^2$ and the cracks were observed at $70J/cm^2$. From above results, It may be suggested that the most effective energy density for improving acid resistance of tooth enamel with the irradiation of Nd-YAG laser was $50J/cm^2$. The mechanism of improving acid resistance were reduction of permeability due to surface melting and recrystallization of lased enamel and reduction of acid solubility of enamel due to decrease of carbonate content and growth of crystal.

• Journal of Korean society of Dental Hygiene
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• v.11 no.2
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• pp.275-289
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• 2011

Objectives : The recognition rate for issues and improving resolution for the recuperation income expense claim policy was examined. Methods : 1,135 copies of survey have been sent to the group of people who have claimed the dental recuperation income expense to dental recuperation institutions in Daejeon, Chungcheong Do that are registered to the health insurance evaluation and estimation office as of the May 2010 and 207 surveys that were regarded to be sincere for answering were analyzed. Results : Majority of respondence were belonged to the dentist institutions with more than 5 years of claim experiences as well as 10~50% of claim rate. The recognition of medical fee evaluation guideline was normal level, and negative recognition was higher to the health center with daily charge policy compare to the dental hospital and university affiliated dental center with treatment charge policy, Highest opinion for inappropriateness of dentist with significance was found (p<0.05). The openness of evaluation cases are regarded to be discharged through the transparent evaluation and most of the opinions for insurance claim evaluation adjustment are within the both 'Do not understand the evaluation guideline and program error of disease category, code and program' with significance(p<0.05). The reaction after the evaluation adjustment was high in reflection on the claim process after examining the reason for the evaluation adjustment through the evaluation and estimation office and university affiliated dental institution and dental center was regarded to be most active and deputy reclaimment was seemed to be most actively discharge the objection registration task (p<0.05). The claim error improving resolution recognition was highly prioritized to the accurate charting for the disease title and treatment description, improving the setting of claim program, and most highly recognized by the university affiliated dental hospital/dental center and comparably low by health center(p<0.05). and although the most of the responds of treatment description and browsing the medical fee was positive, 50% of dentists disagreed the idea so that this was creating a significant discrepancy with other groups(p<0.05). Conclusions : From this research, the recognition of medical fee evaluation guideline for dental (university) hospital and dentists were negative and high adjustment experience was examined as lacking of evaluation guideline understanding and error of disease name, code and programs and deputy reclaimment, university affiliated dental hospital/dental center were most actively handle the objection registration tasks and dentists have objection on the treatment description and browsing the treatment fee so that if these indexes can be referred to implement into the recuperation income claim process, this can be regarded to be a opportunity to create mutual credibility between recuperation institution, treatment pensioner and the evaluation institutions.

• Journal of the Microelectronics and Packaging Society
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• v.24 no.4
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• pp.59-63
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• 2017

The n-type GaN semiconductor has excellent properties as a photoelectrode, but it has disadvantage that its reliability is deteriorated due to the photocorrosion because the oxygen reaction occurs on the surface. For this reason, there are fundamental attempts to avoid photocorrosion reaction of GaN surfaces by using the p-type GaN as a photoelectrode where hydrogen generation reaction occurs on the surface. However, p-type GaN has a problem of low efficiency because of its high resistivity and low hole mobility. In this study, we try to improve the photocurrent efficiency by activation process for the p-type GaN. The p-type GaN was annealed for 1 min. at $500^{\circ}C$ in $N_2$ atmosphere. Hall effect measurement system was used for the electrical properties and potentiostat (PARSTAT4000) was used to measure the photoelectrochemical (PEC) characteristics. Consequently, the photocurrent density was improved more than 1.5 times by improving the activation process for the p-type GaN. Also, its reliability was maintained for 3 hours.