• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.18 no.4
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• pp.313-320
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• 2005

Stick-slip friction is one of the material removal mechanisms in tribology. It occurs when the static friction force is larger than the dynamic friction force, and make the friction curve fluctuated. In the friction monitoring of chemical mechanical polishing(CMP), the friction force also vibrates just as stick-slip friction. In this paper, an attempt to show the similarity between stick-slip friction and the friction of CMP was conducted. The prepared hard pa(IC1000/Suba400 stacked/sup TM/) and soft pad(Suba400/sup TM/) were tested with SiO₂ slurry. The friction force was measured by piezoelectric sensor. According to this experiment, it was shown that as the head and table velocity became faster, the stick-slip time shortened because of the change of real contact area. And, the gradient of stick-slip period as a function of head and table speed in soft pad was more precipitous than that of hard one. From these results, it seems that the fluctuating friction force in CMP is stick-slip friction caused by viscoelastic behavior of the pad and the change of real contact area.

• Journal of Korean Ophthalmic Optics Society
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• v.19 no.1
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• pp.31-42
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• 2014

Purpose: The present study was conducted to investigate the effect of the physical properties of RGP lens induced by lens polishing on the actual wearer's subjective comfort, the tear film break-up time and the blinking rate as a follow-up study that revealed the relationship between the lens physical properties during lens manufacturing and lens wearer's factors. Methods: RGP lenses made from the three different polishing conditions (25, 50 and 100 seconds) were applied on 28 eyes of 17 subjects, aged 20 to 29 years, without any known disease and surgical history in the eyes. While the subjects were asked to wear the RGP lenses longer than a week, the questionnaire for the comfortability was administered everyday. Subjective and objective tear break-up time and blinking rate of the wearers were further measured. Results: The wearer's subjective comfortability showed some difference in the type of discomfort and satisfaction score according to the polishing status when wearing RGP lenses made from different polishing conditions longer than a week, and a bigger difference in satisfaction score induced by polishing condition was especially shown in experienced RGP lens wearer rather than un-experienced wearer. In the case of RGP lens wearer compared with the ones without the wearing experience, as the wearing time increased subjective and objective tear break-up time were increased and the blinking rate was decreased. However, subjective and objective tear break-up time were tended to decrease with even longer wearing time when wearing the RGP lens made from the polishment for 100 seconds. Conclusions: These results confirmed that the optimization of physical properties of the lens may not give the same effect on the wearer's subjective and objective symptoms and other factors when actual wearing. From the results, it can suggest that the success rate of RGP lens wear may be changed by physiological factors such as the stabilization of wearer's tear film, comfortability and lens wearing experience when wearing RGP lens based on 'The manufacturing standard for soft contact lens/hard contact lens' provided by Korea Food and Drug Administration.

• Journal of Chest Surgery
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• v.20 no.3
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• pp.458-472
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• 1987

A heart supplies bloods of about 15, 000 liters to each human organ in a day. A normal function of heart valves is necessary to this act of heart. The disease of heart valve develops to a narrowness of a closure, resulting in an abnormal circulation of bloods. In an attempt to eliminate the affliction of heart valves, the operation method to repair with artificial heart valves has been developed and saved numerous patients over past 30 years. This replacement operation has been performed since early 1960`s in Korea, but all the artificial heart valves used are imported from abroad with very high costs until recent years. The artificial heart valve using pyrolytic carbon has been developed at KAIST, which was proved to be stable in the mechanical performance and durability. Therefore, the in viva performance of this valve was examined through animal tests. The artificial heart valves used in this study are tilting disc type valves, in which the disc were made of graphite coated with pyrolytic carbon and the cages were made of titanium. In viva testings of these valves were performed in 12 dogs, in which right ventriculo-pulmonary arterial [Croup I] or inter-aortic [Croup IV] valved conduit was implanted using polytetrafluoroethylene conduits containing KAIST valve and aortic valve [Group II] or pulmonary valve [Croup III] was replaced by a KAIST valve with a 21mm or 19mm tissue annulus diameter. In group I and II, pre-and post-operative transvalvular pressure gradient was measured and compared with other prosthetic valves. During post operative period laboratory examination was performed including hemoglobin, hematocrit, red cell count, white cell, lactic acid dehydrogenase and platelet. The eight surviving dogs were sacrificed and autopsy was performed at 2, 6, and 8 weeks. KAIST valve has low transvalvular gradient and relatively high orifice area. Average ventriculo-aortic peak systolic transvalvular gradient was 14 mmHg in 21 mm valve and 19 mmHg in 19 mm valve. The valve has slight intravascular hemolysis effect. Thrombogenic effect of low polishing quality and eddy currents around small orifice is high. The valve has vulnerability of disc movement. These animal tests suggest that the improvement of the heart valve design, surface polishing state and prescription methods.

• Journal of Periodontal and Implant Science
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• v.48 no.5
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• pp.295-304
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• 2018

Purpose: This study was undertaken to evaluate the clinical and microbiological effects of an erythritol powder air-polishing device (EPAP) as a supplement to scaling and root planing (SRP) therapy in patients with moderate chronic periodontitis. Methods: Clinical and microbiological evaluations were performed at 21 sites treated with SRP (control) and 21 sites treated with SRP+EPAP (test). All examinations were performed before treatment, 1 month after treatment, and 3 months after treatment. Results: There were no significant clinical differences between the test group and the control group. Microbiological analysis revealed that the relative expression level of Porphyromonas gingivalis was significantly lower in the test group than in the control group at 1 month after treatment. Clinical and microbiological results showed improvements at 1 month compared to baseline; in contrast, the results at 3 months after treatment were worse than those at 1 month after treatment. Conclusions: In this study, both SRP and SRP+EPAP were clinically and microbiologically effective as non-surgical periodontal treatments. In particular, the SRP+EPAP group showed an antimicrobial effect on P. gingivalis, a keystone bacterium associated with the onset of chronic periodontitis, in a short-term period. Periodic periodontal therapy, at intervals of at least every 3 months, is important for sustaining the microbiological effects of this treatment.

• Korean Journal of Metals and Materials
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• v.50 no.4
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• pp.338-343
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• 2012

The early osseointegration of titanium (Ti) dental implants is related to the initial cell morphology. The morphology of the cells (mesenchymal stem cells, MSC) was observed on three different Ti disc surfaces, which were mechanically treated by polishing, blasting, and scratching. A non-directional surface (isotropic texture) was obtained by the blasting of HA grits on cp-Ti discs, and a unidirectional surface (anisotropic texture) was obtained by the scratching of SiC papers. The cell attachment and arrangement in the initial periods were quite similar, but those in the later periods were significantly affected by the texture of the cp-Ti discs. After 1 week, the blasted Ti discs showed non-directional arrangement or spreading of the cells, whereas the scratched cp-Ti discs showed unidirectional properties parallel to the direction of the scratched grooves on the surface. The surface roughness of the cp-Ti discs significantly affects cell proliferation. Cell proliferation on the blasted and scratched surfaces was about 60% and 40% higher compared to the control result (polishing group) after 1 week (P<0.05). Cell proliferation on the blasted and scratched surfaces after 1 week was slightly enhanced with increasing surface roughness. It is believed that the direction of cell attachment and arrangement is closely related to the surface texture of the substrate surfaces, but cell proliferation after a relatively long period of time is directly enhanced by the surface roughness, not by the surface texture.

• Journal of the Korean institute of surface engineering
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• v.32 no.3
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• pp.410-415
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• 1999

The adhesion strength of sputtered copper films to Inconel substrates has been studied using the scratch test. The effects of substrate treatments before deposition such as chemical or ion bombardment etching were investigated by means of a mean critical load derived from a Weibull-like statistical analysis. It was found that the mean critical load was very weak unless the amorphous layer produced by mechanical polishing on the substrate surface was eliminated. Chemical etching in a nitric-hydrochloric acid bath was shown to have practically no effect on the enhancement of the adhesion. In contrast, the addition in this bath of nickel and copper sulphates allowed removal of the amorphous layer and an increase in the values of the mean critical load. However, it was observed that excessive chemical etching could cancel out the mean critical load enhancement. The results obtained in the case of ion bombardment etching pretreatments could be far higher than those obtained with chemical etching. Moreover, for a sufficiently long period of ion bombardment etching, the adhesion strength was so high that it was impossible to observe evidence of an adhesion failure.

• Journal of the Korean Society for Precision Engineering
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• v.18 no.10
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• pp.69-75
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• 2001

Systems engineering has been utilized in system development primarily for large-scale projects or commercial large-scale systems during the last several decades. We can understand why it would be useful to apply systems engineering to the development of a relatively small system. However, it is difficult to effectively carry out a project due to the complexity in applying the methods of systems engineering. To apply systems engineering to the development of a small system, the system engineering processes should be tailored. We established a requirements driven system design process(RDSDP) that can effectively carry out the system design far a small system. RDSDP is a system design process that treats all the requirements thoroughly and effectively. This is applied by the designer according to a standardized and systematized process during the first phase in design, in which system specifications are made. By using RDSDP, we can affect a reduction of the number of redesign phases in the process of the system design, shorten the period for to make specification, which will then cause the system to succeed in the actual application.

• Journal of Periodontal and Implant Science
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• v.41 no.3
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• pp.131-134
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• 2011

Purpose: To test the plaque-removal efficacy of a single-tufted toothbrush on the posterior molars compared with a flat-trimmed toothbrush. Methods: Forty-nine subjects were selected. Professional instruction and written brushing instructions were given. After thorough supra-gingival scaling and polishing, all subjects were asked to abstain from oral hygiene procedures for 24 hours prior to the first experiment. The subjects were randomized to a treatment sequence. The modified Quigley and Hein plaque index was recorded pre- and post-tooth brushing, at 6 surfaces of the posterior molars. After a wash-out period, all the remaining plaque was removed professionally. Twenty-four hours of brushing abstinence was again performed. The plaque index was recorded pre- and post-tooth brushing after the subjects were given the second toothbrush in the cross-over sequence. Results: The percentage reductions in plaque scores achieved with the single-tufted brushes were significantly higher than those of the flat-trimmed brush at the maxillary buccal interproximal, marginal and mandibular lingual interproximal site. The other locations showed no significant difference. Conclusions: The results of the present study implied that the single-tufted brush could be an effective tool for the removal of plaque at some, but not all, sites of the posterior molars.

• Magazine of the Korean Society of Agricultural Engineers
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• v.45 no.7
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• pp.70-82
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• 2003

A pilot study was performed from July 1998 to December 2002, including winter performance, to examine seasonal performance of a constructed wetland and subsequent pond system for treatment of sewage in small communities of Korea. Pond was operated as a intermittent-discharge pond during winter period, and continuous flow system during growing season; its effects was evaluated from December 2001 to April 2003. The subsurface flow (SSF) wetland was satisfactory for treating sewage with good removal efficiency even during the winter period. The wetland effluent concentrations of $BOD_5$ and TSS were often higher in winter than in the growing season, but this was explained by the higher loading rates, rather than lower removal efficiency. The relatively poor-quality wetland effluent was further polished during winter in the pond. The upper layer of the pond water column became remarkably clear immediately after ice melt. In the growing season, ponds could be operated as a continuous flow system to remove nutrients and pathogens, and the effluent of pond could be reused as a supplemental irrigation water without risk of infection by sewage-borne pathogens as well as causing adverse effect on growth and yield. Overall, the wetland system was found to be adequate for treating sewage with stable removal efficiency, and the intermittent-discharge pond was found to be effective for further polishing if necessary. Therefore, the combination of a wetland and subsequent pond system and reuse of effluent as crop irrigation water is recommended as a practical alternative to treat sewage in Korean small communities, and partial discharge of pond water in March is suggested.

• Journal of Periodontal and Implant Science
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• v.29 no.2
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• pp.433-447
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• 1999

The objective of this study was to evaluate the effect a chewable tablet containing sodium flouride and lauroyl sodium sulfate on removing plaque and inhibiting gingival inflammation. A randomized parallel study was designed. 100 voluteers participated in the study. There were two test groups each with 30 subject. Test group A was instructed to brush once in the morning, and to use the tablet once in the afternoon and once in the evening. Test group B was instructed to use the tablet three times a day without brushing. There were two control groups each with 20 subjects. Control group A was instructed to brush once in the morning only. Control group B was instructed not to brush all. Two weeks before the test period, the subjects received through tooth cleaning and polishing. At baseline, GI, PI, BOP, and GCF of the Ramfjord teeth were measured in all groups. Bacteria culture was done with the plaque sampled from tooth with the deepest pocket. After 5 days, clinical indices were measured and the bacterial culture was repeated. Control group B was dropped from the study after this period. All the other groups remained and the indices and the culture was repeated after 2 weeks, and 3weeks. Also whether the oral mucosa showed signs of irritation was monitored throughout the test period. Test group A showed less PI, GI, BOP, probing depth, GCF than test group B or control group A. Especially, PI and the BOP was significantly less than that of the group that was instructed to brush once a day. This implies that the added use of this tablet aids in plaque removal in people who brush just once a day. Test group A showed increase of cocci, decrease of motile rods, and decrease of spirochetes after 14-21 days. And this was significantly different from the control group A. At no time of the test period did any of the subjects show signs of irritation of the oral mucosa or adverse reactions. Following conclusions could be obtained from this study. This chewable tablet for enhanced oral hygiene could be used as an adjunct to oral hygiene in people who do not brush adequately. The use of this tablet decreased the number of subgingival bacteria, and this could be effective in plaque removal and for prevention of gingival inflammation.