• Clean Technology
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• v.17 no.4
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• pp.306-313
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• 2011

Flux or solder is used in soldering process for manufacturing electronic parts such as printed circuit boards (PCB). After soldering process, residual flux and solder paste on the parts should be removed since their residuals could cause performance degradation or failure of parts due to their corrosion and electric leakage. Ozone depletion substances such as 1,1,1- trichloroethane (TCE) and HCFC-141b have widely been using for removal of residual flux and solder paste after soldering process In manufacturing of electronic parts until now. In this study, non-aqueous cleaning agents without flash point were developed and applied to industrial field for replacement of cleaning agents with ozone depletion. In order to develop non-aqueous cleaning agents without ethers, esters, fluoride- type solvents. And their physical properties and cleaning abilities were evaluated, and they were applied to industrial fields for cleaning of flux and solder on the PCB. And vacuum distillation apparatus were operated to determine their operating conditions and recycling yields for recycling of used cleaning agents formulated in this study. As a result of physical properties measurement of our formulated cleaning agents, they were expected to have good wetting and penetrating power since their surface tensions were relatively low as 18.0~20.4 dyne/$cm^2$ and their wetting indices are relatively large. And some cleaning agents holding fluoride-type solvents as their components did not have any flash point and they seemed to be safe in their handling and storage. The cleaning experimental results showed that some cleaning agents were better in their cleaning of flux and solder paste than 1,1,1-TCE and HCFC-141b. And industrial application results of the formulated cleaning agents for cleaning PCB indicated that they can be applicable to industry due to their good cleaning capability in comparison with HCFC-141b. The recycling experiments of the used formulated cleaning agents through a vacuum distillation apparatus also showed that their 91.9~97.5% could be recycled with its proper operating conditions.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.20 no.3
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• pp.513-519
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• 2019

Typically, contaminated sediments cause clogging of the drain pipe, which increases the residual water pressure in the drain pipe; this study constructed a system for improving drainage efficiency of tunnels by reducing physical and chemical obstructions through ultrasonic energy generated by a PVDF film. The developed hybrid drainage system utilized a PVDF material film fused with an existing drainage tunnel and maintenance system resulting in the ability to initialize the reverse piezoelectric effect, which was evaluated through an on site application. In order to investigate the maintenance performance of the tunnel drainage system, contaminated sediments were simulated in a drainage pipe to test the effect of ultrasonic conditions on drainage efficiency in the laboratory. As a result of applying the developed portable equipment, the ultrasonic energy was generated for about 20 minutes resulting in a reduction of 74.62% of the contaminated sediments and improving drainage efficiency. From the tunnel, acoustic pressure measurements were taken to calculate the response rate while taking into account the laboratory results. In addition, PVDF film was attached to the transverse and longitudinal side of the drainage pipes where contaminated sediments occur most often in the field tunnel. these calculations show contaminant removal was 90% effective.

• Journal of Korean Society of Occupational and Environmental Hygiene
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• v.32 no.1
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• pp.78-88
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• 2022

Objectives: To develop the smart sensor to protect worker's health from chemical exposure by adopting ICT (Information and Communications Technology) technologies. Methods: To develope real-time chemical exposure monitoring system, IoT (Internet of Things) sensor technology and regulations were reviewed. We developed and produced smart sensor. A smart sensor is a system consisting of a sensor unit, a communication unit, and a platform. To verify the performance of smart sensors, each sensor has been certified by the Korea Laboratory Accreditation Scheme (KOLAS). Results: Chemicals (TVOC; Total Volatile Organic Compounds, Cl₂: Chlorine, HF: Hydrogen fluoride and HCN: Hydrogen cyanide) were selected according to a priority logic (KOSHA Alert, acute poisoning statistics, literature review). Notifications were set according to OEL (occupational exposure limit). Sensors were selected based on OEL and the capabilities of the sensors. Communication is designed to use LTE (Long Term Evolution) and Wi-Fi at the same time for convenience. Electronic platform were applied to build this monitoring system. Conclusions: Real-time monitoring system for OEL of hazardous chemicals in workplace was developed. Smart sensor can detect chemicals to complement monitoring of traditional workplace environmental monitoring such as short term and peak exposure. Further research is needed to expand the scope of application, improve reliability, and systematically application.

• Composites Research
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• v.34 no.6
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• pp.357-372
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• 2021

The energy harvesting device is known to be promising as an alternative to solve the resource shortage caused by the depletion of petroleum resources. In order to overcome the limitations (environmental pollution and low mechanical properties) of piezoelectric elements capable of converting mechanical motion into electrical energy, many studies have been conducted on a polymer matrix-based composite piezoelectric energy harvesting device. In this paper, the output performance and related applications of the reported piezoelectric composites are reviewed based on the applied materials and processes. As for the piezoelectric fillers, zinc oxide, which is advantageous in terms of eco-friendliness, biocompatibility, and flexibility, as well as ceramic fillers based on lead zirconate titanate and barium titanate, were reviewed. The polymer matrix was classified into piezoelectric polymers composed of polyvinylidene fluoride and copolymers, and flexible polymers based on epoxy and polydimethylsiloxane, to discuss piezoelectric synergy of composite materials and improvement of piezoelectric output by high external force application, respectively. In addition, the effect of improving the conductivity or the mechanical properties of composite material by the application of a metal or carbon-based secondary filler on the output performance of the piezoelectric harvesting device was explained in terms of the structure of the composite material. Composite material-based piezoelectric harvesting devices, which can be applied to small electronic devices, smart sensors, and medicine with improved performance, can provide potential insights as a power source for wireless electronic devices expected to be encountered in future daily life.

• Journal of dental hygiene science
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• v.3 no.1
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• pp.45-50
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• 2003

In order to develop the program of oral hygiene education for elementary school senior-students, a questionnaire survey of elementary fourth, fifth and sixth students who are under continual control program of oral hygiene. (1) For tooth brushing time, after dinner is more than before. 73.7% of respondents brushed the teeth twice or more a day. (2) 62.1% of respondents took the cariogenic food twice or more a day. (3) 90.1% of respondents had visited a dental clinic. (4) Concerning fear for dental treatment, only 14.4% had a feeling of fear. (5) Regarding the experience with a preventive treatment, 39.7% had an experience with pit and fissure sealing, and 24.2% had an experience with the application of fluorides. (6) 46.2% of respondents had a preference for the fluoride mouth rinsing program, and 38.4% wanted that program to keep going on. As to the reason to favor the fluoride mouth rinsing program, 38.2% preferred it because of prevention of dental caries, and 43.0%, the largest percentage, didn't favor it because they found it too much trouble to do. (7) Comparing with the research result in 2000, we proved positively the educational effect of brushing frequency, positive understanding and preference to water school fluoridation program, and got the negative data of experience of visiting to oral clinic and preventive treatment.

• Polymer(Korea)
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• v.28 no.1
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• pp.24-34
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• 2004

Transient sorption experiments were conducted among several combinations of fluoropolymers and various organic solvents. Fully fluorinated polymer tended to exhibit ideal sorption behavior, while partially fluorinated polymers showed anomalous sorption behaviors with a drastic acceleration at the final stage of uptake. Minimization of least-squares of the measured and predicted fractional uptake, which indicated the increasing degree of deviation from Fickian diffusion, gave values of 3.0${\times}$10$\^$-4/, 1.75${\times}$10$\^$-3/, 8.68${\times}$10/sup-3/, 1.75${\times}$10$\^$-2/, respectively, for perfluoroalkoxy copolymer, poly(ethylene-co-tetrafluoroethylene), poly(vinylidene fluoride), poly(ethylene-co-chlorotrifluoroethylene). From stress-strain tests, it was confirmed that non-Fickian diffusion is closely related to the significant variation of mechanical properties (such as modulus and tensile strength) of swollen polymer. Anomalous sorption behavior stemmed from non-Fickian diffusion caused by nonlinear disruption of polar inter-segmental bonds due to solvent-induced plasticization. Thus, it is imperative to investigate the diffusion behavior of swelling solvents in partially fluorinated polymers, especially for the application to barrier materials or perm-selective membranes.

• Journal of Korean Society of Environmental Engineers
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• v.29 no.3
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• pp.325-331
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• 2007

This study was aimed to find out methods for preventing scale formation from the struvite treated water, and improving ammonium nitrogen removal efficiency in the application of struvite crystallization for ammonium fluoride wastewater wastement. During the struvite mystallization seeding effects varied with G.td value applied as mixing conditions in the experiment. The removal efficiency of ammonium nitrogen$(NH_4^+-N)$ and phosphorus$(PO_4^{3-}-P)$ increased over 90% in the condition of low $G{\cdot}t_d$ value. In the experiment with seeding, $G{\cdot}t_d$ value was shown to decease four times lower than the one without seeding. When adding over 2% seeding materials in the total water volume, ammonium nitrogen removal efficiencies gradually increased, of which observation was also revealed in a paired-sample T-test with 95% reliability.

• Journal of the korean academy of Pediatric Dentistry
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• v.36 no.1
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• pp.71-77
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• 2009

The objective of this study is to find the improvement in the dental health care of the children through oral hygiene education and TBI. In Taebaek public health care center, an oral hygiene education, TBI and fluoride gel application was conducted 2 times for about 631 preschool children living in Taebaek City. The ages of preschool children were from 4 to 7. To examine the changes, a questionnaire was written and distributed for the collecting the results after the education of the second half for children, parents and teachers. As a result, the children showed better understanding of the caries through oral hygiene education and reduction of fright and fears for dental treatment. Many children learned how to brush and there was a significant increase in the number of brushing. Children learned to be able to classify good food and bad food for teeth and showed the change in eating habits although in small part through the oral hygiene education. Through this study, it is judged that the oral hygiene education of the preschool children has effectiveness and it is in need for the expansion of oral hygiene education in homes, kindergartens and dental offices.

• The korean journal of orthodontics
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• v.31 no.6 s.89
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• pp.567-578
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• 2001

To investigate the difference of Texture exhibited on interproximal enamel surface with each different stripping method and the susceptibility of proximal enamel to demineralization after stripping and the application of a topical fluoride go] and sealant, one hundred human premolars, which were Previously extracted for orthodontic reasons were evaluated by means of Scanning electron microscopy and laser fluorescence. The results were as follows : 1. No matter what the initial stripping instrument was the furrows that resulted from all the stripping methods were not completely removed by careful polishing. 2. Among the enamel surfaces that were treated with three different initial abrasive instruments, followed by the same polishing method (Sof-$Lex^{(r)}$ disks), the enamel surfaces that were treated with 700 crosscut carbide bur showed the smoothest surfaces. 3. The stripped teeth, no matter what the initial stripping instrument was, were less resistant to initial demineralization than untreated teeth. But no difference in caries susceptibility according to differently stripped methods was found (p<(0.001). 4. Teeth treated with APF-gel or sealant were mote resistant to demineralization than those treated without other treatment after stripping (p<0.001). 5. Comparing groups treated with APF-gel to groups treated with sealant, the former was more resistant to demineralization than the tatter (p<0.05). In conclusion, enamel surfaces that were stripped jnterproximally were less resistant to demineralization even though various attempts were made to produce smooth, self-cleaning enamel surfaces. Therefore, additional treatment-sealant or calcifying/ fluoridating solution To the stripped enamel surfaces is recommended.

• Journal of Korean society of Dental Hygiene
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• v.3 no.1
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• pp.13-24
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• 2003

The researcher worked with a total of 158 high school girls visiting the scaling practice room at the department of dental hygiene in Jinju Health college from November 11, 2002 to December 4, 2002, having their teeth scaled, observing their teeth and interviewing them with the aid of questionnaires. The findings can be summarized as follows. 1. The survey on the understanding of dental health and the attitudes of the subjects shows the following results : "I have never learned how to brush teeth" (65.8%: 104 girls); "I brush my teeth twice a day" (57.0%: 90 girls) : "I brush my teeth for 2 minutes"(44.3%: 70 girls): "I brush my teeth vertically and horizontally" (53.2%: 84 girls): "( brush my teeth, gum and tongue" (462%: 73 girls): "I use one brush for two months" (40.5%: 64 girls); "I don't have any floss" (582%: 92 girls): "I have never had my teeth scaled" (84.2%: 133girls) : "Smoking is bad for the teeth" (77.8%: 123 girls): "Drinking is bad for the teeth" (48.7%: 77 girls): "I have ever visited dental clinics" (92.4%: 146 girls). 2. The study on part of the teeth most exposed to caries shows the following results : Mandibular right first molar(79.8%: 126 girls): Mandibular left first molar(77.5%: 124 girls), Mandibular left second molar(70.2%: 111 girls). Mandibular right second molar(65.7%: 104 girls). Maxillary left first molar(59.5%: 94 girls): Maxillary left second molar(59.5%: 94 girls): Maxillary right first molar(58.2%: 92 girls). Maxillary right second molar(50.7%: 80 girls) 3. The statistics on the subjects' caries show the following results: DMF rate: 943%: DMFT rate: 25.61%: DMFT index: 7.17 teeth : DT rate: 4651%: FT rate: 52.25%: MT rate: 124% 4. The survey on dental caries statistics, dental health, dental health behavior, and the subjects' attitudes shows the following results: The worse the subjects' dental health was(r=-327, p<.001), the more they visited dental clinics(r=.195, p<.05), the higher DMT rate, DMFT index were; The more the subjects visited dental clinics(r =.359, p<.001), the higher DT rate was; The worse the subjects teeth went(r=-.197, p<.05), the higher MT rate was. It is necessary that systematic and substantial dental health education for high school students should be carried out in regard to plaque control, fluoride application, diet control, pit & fissure sealant as a part of developing national health policies designed for the dental health of the teenagers.