• The Journal of the Acoustical Society of Korea
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• v.35 no.3
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• pp.175-182
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• 2016

For application to several MHz photoacoustic imaging systems, a needle hydrophone was designed and fabricated by using PMN-PZT piezoelectric single crystal, and its characteristics were evaluated through comparison with a commercial PVDF(Polybinylidene Fluoride) hydrophone of which receiving sensitivity is known. The simulation using the KLM model results show that the peak receiving impulse response for $50{\Omega}$ terminating impedance of the fabricated hydrophone is -261.6 dB re $1V/{\mu}Pa$ and the frequency response is relatively flat over 2 ~ 12 MHz with fluctuation less than 5 dB. The measurement results using tone burst signals also show that it has higher (ave. 10.9 dB) sensitivity than the commercial hydrophone in 2 ~ 8 MHz, and the receiving sensitivity of $-255.8{\pm}2.8$ dB re $1V/{\mu}Pa$ was measured for the fabricated hydrophone. In addition, it is known that the photoacoustic signals and the image of a hair obtained by a mechanical scanned photoacoustic imaging system with the fabricated hydrophone were bigger and better than those obtained with the commercial hydrophone.

• Membrane Journal
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• v.27 no.3
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• pp.240-247
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• 2017

In this study, the heterogeneous ion exchange membranes prepared by the combination of the carbon electrode and mixed the cation and anion exchange polymers and polyvinylidene fluoride as the basic polymer together were made to recognize the efficiency of the salt removal for the application of the membrane capacitive deionization process. The mixing weight ratio of the solvent, basic polymer and ion exchange resin was 7 : 2 : 1 and this mixed solution was directly cast on the electrode. As for the operating conditions of the adsorption voltage and time, feed flow rate, desorption voltage and time of the feed solution NaCl 100 mg/L, the salt removal efficiencies (SRE) were measured. Apart from this NaCl, the $CaCl_2$ and $MgSO_4$ solutions were investigated in terms of SRE as well. Typically, SRE for NaCl 100 mg/L solution under the conditions of adsorption voltage/time, 1.5 V/3 min, desorption voltage/time -0.1 V/3 min, was shown 98%. And for the $CaCl_2$ and $MgSO_4$ solutions, the SREs of 70 and 59% were measured under the conditions of adsorption voltage/time, 1.2 V/3 min, desorption voltage/time -0.5 V/5 min, respectively.

• Journal of the Korean Society of School Health
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• v.13 no.2
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• pp.331-340
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• 2000

Primary school is regarded as an important period when many health-related behaviors and life-styles begin to be formed. Acquiring them through school heath education has a strong influence on the health promotion of not only the family but also the community. The objectives of this study were to evaluate current oral health care of elementary schools in Chungnam province and to provide information for further development in elementary school oral health. We performed a questionnaire survey to 280 health teachers and among them, 155 teachers answered. The result of this study were as follows: 1. Sixty five percent of the health teachers had little interest in oral health. Major information sources for teaching oral health were books in 58.1% of the 155 teachers and 83.2% of teachers spent 30 minutes to 1hour per day in oral health care practice for the students. 2. Contents of the oral health education were composed of regular and special curriculums, and an average of education time during a semester was 2.6 hours in 3rd grade, and 1.3 hours in first and second grade. 60.6% of the teachers made the children practice the proper method of tooth brushing during the education time. 3. Major problems in oral health education were insufficient time, lack of equipment and difficulty in teaching method. The educational media were tooth models among 91.0% and OHP among 85.2% of the teachers. The tooth model was usually used in first to fourth grades and OHP in fifth to sixth grades. But 63.9% health teachers need to develop stronger educational methods using multimedia. 4. Meanwhile the most important strategy of oral health in urban schools was health education, that of rural schools was fluoride mouth-rinsing programme. Fluoride mouth-rinsing programmes were performed by 60.0% of the elementary school. Periodic dental examination was performed in all elementary schools. 98.2% of the schools sent the results home through school notification letters, but post-examination management was performed in only 67.1% of them 64.5% of the health teachers do follow-ups on the oral disease of the children after the examination. Only 0.7% of the schools have oral health education plans for the students' parents. Considering these major strategies for elementary school oral health care were health education, practicing proper methods of tooth brushing, periodic dental examinations, and fluoride mouth-rinsing programmes. But health teachers need more time for oral health education, practicing and management, and developing education materials. With regard to the high demand for oral health education and poor follow-up after periodic examination, the oral health education in elementary school should be considered as a formal educational course for more proper management of oral health, including application of major strategies to the children in earlier grades and efforts for increasing recognition and participation of the parents.

• Journal of the korean academy of Pediatric Dentistry
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• v.35 no.3
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• pp.446-455
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• 2008

The aim of this study was to evaluate the effect of fluoride varnish application on enamel decalcification. Eighty bovine enamel blocks divided randomly into 4 groups. Group I is the control group. Group II was treated with the APF gel and washed after 4 minutes. Group III and IV was treated with Fluor $Protector^{(R)}$ and $CavityShield^{TM}$ and washed after 1 minutes. Decalcification were created by placing all specimen into artificial acidic solution(pH 4.0). Then the optical density of the lesions were measured by visible light fluorescence and the lesion depths were measured. The results were : 1. The optical density of group II was higher than group I but lower than group III, IV(p<0.05) and there was no difference between group III, IV(p>0.05) at 48 hours. 2. The optical density of group IV was highest at 72 hours(p<0.05). 3. Mean lesion depths were $205.36{\pm}42.85{\mu}m$ and $210.81{\pm}44.60{\mu}m$ in group I, II but no significant difference between two groups(p>0.05). 4. Mean lesion depths were $80.03{\pm}21.66{\mu}m$ and $77.46{\pm}27.72{\mu}m$ in group III, IV but no significant difference between two groups(p>0.05). Fluoride varnish treatment resulted in a significant reduction in lesion depth compared with APF gel. Fluor $Protector^{(R)}$ and $CavityShield^{TM}$ provided the similar effect.

• Journal of Korean Society of Environmental Engineers
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• v.33 no.11
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• pp.855-859
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• 2011

The main pollutants from zirconium alloy tubing manufacturing process in nuclear industry are nitrate ($NO_3-N$) and fluoride (F-)Nitric acid, and hydrofluoric acid is used for acid pickling. The process for the removal of nitrate and fluoride is composed of 1st chemical coagulation, SOD (Sulfur Oxidation Denitrification) process using sulfur-oxidizing denitrification, and 2nd chemical coagulation. The characteristic of the wastewater treatment is an application of SOD process. The SOD Process is highly received attention because it is significantly different from existing processes for sulfur denitrification. A JSC (JeonTech-Sulfur- Calcium) Pellet is unification of sulfur and alkalinity material. According to result of SOD process in wastewater treatment plant, the removal efficiency of T-N was over 91% and the average concentration of T-N from influent was 147.55 mg T-N/L and that from effluent was 12.72 mg T-N/L. Therefore, SOD process is a useful to remove nitrogen from inorganic industrial wastewater and a new development of microbial activator was shown to be stable for activation of autotrophic bacteria.

• Restorative Dentistry and Endodontics
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• v.23 no.1
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• pp.197-212
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• 1998

The purpose of this study was to evaluate the effects of fluoride application on the aspect of shear bond strength of three aesthetic restorative materials to dentin. One light-cured composite resin(Palfique Esterite) and two light-cured glass ionomer cements(Fuji II LC and Compoglass)were used in this study. 120 permanent molars were used for this study. The teeth were extracted due to the origin of periodontal disease. The crowns of all teeth were removed, and the remaining roots were embedded in epoxy resin. The mesial or distal surfaces of roots were ground flat to expose dentin and polished on wet 320-, 400-, and 600 grit SIC papers for a total of 120 prepared flat root dentin surfaces. The prepared samples were divided into six groups. Group 1, 3, and 5 were control groups and group 2, 4, and 6 were experimental groups. Sixty samples for experimental groups were treated with 2% NaF solution for 5 minutes. Group 1 and 2 were bonded with Plafique Esterite, group 3 and 4 were bonded with Fuji II LC, and group 5 and 6 were bonded with Compoglass. After 24 hours water storage at $37{\pm}1^{\circ}C$, all samples were subjected to a shear to fracture with Instron universal testing machine(No.4467) at 1.0 mm/min displacement rate. Dentin surfaces treated with each conditioners before bonding and interfacial layers between dentin and aesthetic restorative materials were observed under Scanning Electron Microscope(Hitachi S-2300) at 20Kvp. The data were evaluated statistically at the 95% confidence level with ANOVA test. The result were as follows; 1. Among the control groups, group 1 showed strongest bond strength and group 3 showed weakest. 2. Among the experimental groups, group 2 showed strongest bond strength and group 6 showed weakest. 3. Statistical analysis of the data showed that pretreatment of dentin with 2% NaF solution significantly decreased the bond strength of three aesthetic restorative materials to dentin(P<0.05). 4. SEM findings of fluoride treated dentin surfaces (2, 4, 6 group) demonstrated dentin surfaces covered with fluoridated reaction products. 5. Except group 4 and 6, resin tags were formed in all groups.

• Applied Chemistry for Engineering
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• v.32 no.6
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• pp.653-658
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• 2021

Polyvinylidene fluoride (PVDF) is a promising coating material because of its outstanding processability. The PVDF coating, however, has limitations in anti-corrosion application due to its weak hydrophobicity compared to that of other fluoropolymers. In this study, plasma fluorination was performed using carbon tetrafluoride (CF₄) gas to improve anti-corrosion properties of PVDF. The fluorine content and hydrophobicity of PVDF were investigated in different CF₄ flow rates, followed by the determination of anti-corrosion properties. The fluorine content on the surface of the PVDF film increased by up to 46.70%, but the surface free energy was independent of CF₄ flow rate. Meanwhile, the surface roughness of the PDVF film tended to increase by up to 150% and then decrease with increasing CF₄ flow rate. It is considered that the plasma fluorination affects the surface free energy due to the introduction of fluorine functional groups and surface etching. In addition, the degree of corrosion of the PVDF-coated Fe plate was significantly reduced from 49.2% to 19.0% compared to that of the uncoated Fe plate. In particular, the degree of corrosion of the fluorinated PVDF-coated Fe plate was 13.6%, which was 28.4% lower than that of the PVDF-coated Fe plate, showing improved anti-corrosion protection.

• Journal of Microbiology and Biotechnology
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• v.9 no.3
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• pp.260-264
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• 1999

The combined activities of dextranase and amylase(DXAMase) from Lipomyces starkeyi KSM 22 produced from starch fermentation inhibited or prevented dental plaque formation. The activities were stable in commercial mouthwash products; DXAMase activity retained over 93％ of original activity after 6 months at 23℃. We examined the effects of enzyme inhibitors and active ingredients in mouthwash on DXAMase activity. The DXAMase was stable with 0.29％(w/v) EDTA, 20％ (v/v) ethanol, 0.05％ (w/v) fluoride, and 0.05％ (w/v) SDS. Among the active ingredients of mouthwash, sodium benzoate (up to 1 ％, w/v) had no inhibitory effect on either dextranase or amylase activity. In the case of cetylpyridinium chloride, the addition of 0.05％ (w/v) inhibited 6％ of dextranase activity and 13％ of amylase activity. Propylene glycol (up to 1％, w/v) showed no inhibitory effect on either enzyme activity. DXAMase (5 IU/㎖) in mouthwash could remove pre-formed films of glucan-bound S. mutans cells. The addition of 0.1 IU/㎖ DXAMase in mouthwash prevented the formation of insoluble-glucan. These in vitro properties of L. starkeyi KSM 22 DXAMase are desirable for its application as a dental plaque control agent.

• Proceedings of the Korean Vacuum Society Conference
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• 2016.02a
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• pp.228.1-228.1
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• 2016

기존 산업에서 많이 쓰여져오고 있는 저압 플라즈마에 비해 여러가지 장점을 지닌 대기압 플라즈마는 수년 전부터 많은 연구가 되어 왔으며 폭넓은 응용분야에 있어서 활발히 이용되고 있고, 특히 온도가 거의 상온과 비슷하다는 장점으로 대기압 저온 플라즈마는 바이오메디컬 분야에서 활발하게 응용되어지고 있다. 본 연구에서는 대기압 저온 플라즈마 젯 장치를 사용하여 치아 표면에 불소를 도포하고 법랑질 표면의 불소 원소를 검출함으로써 플라즈마가 치아표면 불소도포에 있어서 어떠한 효과가 있는지 정량적으로 비교분석하였다. 또한 대기압 플라즈마 젯 장치의 방전개시전압과 가스유량에 따른 플라즈마젯 길이의 변화 및 OES(Optical Emission Spectroscopy) 장치를 사용하여 플라즈마에 대한 광학적 진단을 진행하였다. 치아표면에서 검출된 불소량은 플라즈마를 사용했을때가 그렇지 않을때에 비해 더 높게 관찰 되었다.

• Bulletin of the Korean Chemical Society
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• v.30 no.9
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• pp.2093-2097
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• 2009

Novel fluorescent anion chemosensors based on anthracene-isothiouronium derivatives were synthesized. Isomerism due to the intramolecular mobility in these isothiouronium salts was detected by $^1H$ NMR spectroscopy. The effect of the substituent, temperature and solvent on the isomerism was also examined. The anthracene-isothiouronium sensor showed significant fluorescent enhancement upon the addition of various anions such as fluoride, acetate, and dihydrogen phosphate, even in the presence of water.