• Proceedings of the Korean Vacuum Society Conference
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• 2016.02a
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• pp.397-397
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• 2016

Triboelectric nanogenerators (TENG) can produce power from ambient mechanical sources and have strong points of high output performance, light weight, low cost, and easy manufacturing process. It is expected that TENG can be utilized in the fields of wireless electronics and self-powered devices in the world which pays attention to healthcare and the IoT. In this work, we focus on scavenging ambient rotational energy by using a durably designed TENG. In previous studies regarding harvesting rotation mode energy, the devices were based on sliding mechanism and durability was not considered as a major issue. However friction by rotation causes reliability problems due to wear and tear. Therefore, in this study, we convert rotary motion to linear motion utilizing a cam by which we can then utilize contact-mode TENG and improve device reliability. In order to increase output performance, bumper springs were used below the TENG and the optimum value for the bumper spring constant was analyzed theoretically. Furthermore, the inserting a soft substrate was proposed and its effect on high output was determined to be due to an increase in the contact area. By increasing the number of cam noses, the output frequency was shown to increase linearly. For the purpose of maximum power transfer, the input impedance of the device was determined. Finally, to demonstrate the use of the C-TENG as a direct power source, it was installed on a commercial bicycle wheel and connected to 180 LEDs. In conclusion we present a rotational motion TENG energy scavenger system designed for enhanced durability and optimized output by appropriate choice of spring constants and substrate.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.26 no.2
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• pp.260-266
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• 2002

DLC films were deposited on Si wafer by RF plasma assisted CVD using CH4 gas. Tribological tests were conducted using rotating type ball on disk friction tester in dry air. Four kinds of mating balls were used. The mating balls were made with stainless steel but apply different annealing conditions to achieve different hardness conditions. Testing results in all load conditions showed that the harder the mating materials, the lower the friction coefficient among the three kind of martensite mating balls. In case of austenite balls, the friction coefficients were lower than fully annealed martensite ball. The high friction coefficient in soft martensite balls seems to be caused by the larger contact area between DLC film and ball. The wear tracks of DLC films and mating balls could have proven that effect. Measuring the wear track of both DLC films and mating balls have similar tendency comparing to the results of friction coefficients. Wear rate of austenite balls were also smaller than that of fully annealed martensite ball. The results of effect of applying load showed, the friction coefficients were become decrease when the applying loads exceed critical load conditions. The wear track of mating balls showed that some material transfer occurs from DLC film to mating ball during the high friction process. Raman spectra analysis showed that transferred material was a kind of graphite and contact surface of DLC film seems to undergo phase transition from carbon to graphite during the high friction process.

• The Journal of the Korea Contents Association
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• v.7 no.4
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• pp.184-191
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• 2007

Our objective was to develop and evaluate a non-invasive device for rigid immobilization and surface disease non-contact of the table in the lower extremity during CT angiography. The immobilization device consists of two components. The patient's lower limb device stabilizing elements made of polyethylene resin soft materials, and pelvis parts foam pad is used for non-contact surface. In a Prospective study the lower extremity device was used in patients who underwent a CT angiography of the lower limb. Immobilization with our device was well tolerated by all patients. The quality of the resulting images in the popliteal and infrapopliteal region was rated by five-point scale. The rigid immobilization resulted in a complete absence of motion artifacts. The new device is an effective, well tolerated and easily used immobilization that is suitable of use in 3D lower extremity CT angiography.

• Journal of the Semiconductor & Display Technology
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• v.9 no.1
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• pp.5-10
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• 2010

Among a variety of cleaning processes, the cryogenic carbon dioxide ($CO_2$) cleaning has merits because it is highly efficient in removing very fine particles, innoxious to humans and does not produce residuals after the cleaning, which enables us to extend its area of coverage in the semi-conductor fabrication society. However, the cryogenic carbon dioxide cleaning method has some technical research issues in aspect to particles' adhesion and removal. To resolve these issues, performing an analysis for the identification of particle adhesion mechanism is needed. In this study, a research was performed by a theoretical approach. To this end, we extended the G-T (Greenwood-Tripp) model by applying the JKR (Johnson-Kendall-Roberts) and Lennard-Jones potential theories and the statistical characteristics of rough surface to investigate and identify the contact, adhesion and deformation mechanisms of soft or hard particles on the rough substrate. The statistical characteristics of the rough surface were taken into account through the employment of the normal probability distribution function of the asperity peaks on the substrate surface. The effects of surface roughness on the pull-off force for these particles were examined and discussed.

• Journal of dental hygiene science
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• v.7 no.3
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• pp.201-205
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• 2007

This study was designed to compare the perception of dental hygiene students and general public with respect to minor variations in maxillary anterior tooth size, alignment and their relation to the surrounding soft tissues. Maxillary anterior teeth were intentionally diagrammed in varying degree of deviation with respect to one of three common anterior esthetic discrepancies including variations in crown length, shape of gingival margin, and length of interproximal contact. Seventeen images were generated to be preferentially selected by 2 groups consisting of dental hygiene students and lay people in Busan(total of 216). The obtained results were as follows; 1. Both group preferred gingival margin of lateral incisor to be 0.5mm lower than that of central incisor. 2. Both group preferred the gingival margin shape of central incisor has 1/9 horizontal component of the crown width. 3. Both group preferred length of the interproximal contact has 1/2 of the crown length. The results of this study may be considered to influence the decision making process by dental professionals with respect to designing the anterior esthetic gingival line.

• Elastomers and Composites
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• v.54 no.4
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• pp.359-367
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• 2019

Poly(2-hydroxyethyl methacrylate) (PHEMA) hydrogels modified with various co-monomers, such as N-vinyl pyrrolidone (NVP), glycidyl methacrylate (GMA), and glycerol monomethacrylate (GMMA), were prepared to investigate the effect of adding a co-monomer on the water contents, surface wettability, and tensile modulus. These polymers were synthesized by thermal- and photo-polymerization in the presence of azobisisobutyronitrile (AIBN) and diphenyl(2,4,6-trimethylbenzoyl)-phosphineoxide (TPO) as the initiators. The characteristics of the hydrogels were analyzed via FTIR and UV/Vis spectroscopies, contact angle measurements, and tensile modulus measurements with UTM. Regarding the properties of water in the hydrogels, the ratio between free to bound water was investigated using differential scanning calorimetry (DSC). The effects of adding the co-monomers on the water content, surface wettability, and tensile modulus for soft contact lenses were also investigated. In the case of p(HEMA-co-NVP) hydrogels, the increase in the equilibrium water content (EWC) was primarily due to the increase in the bound water content. For p(HEMA-co-GMMA) hydrogels, an increase in free water content was the main reason for the increased EWC. In contrast, in the case of p(HEMA-co-GMA) hydrogels, a decrease in bound water content was observed to be the main factor that reduced the EWC. Photo-polymerized PHEMA hydrogels showed enhanced surface wettability and tensile modulus as compared to those produced via thermal polymerization.

• Journal of the korean academy of Pediatric Dentistry
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• v.32 no.3
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• pp.537-542
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• 2005

Dentofacial trauma can result in tooth fracture, avulsion, facial bone fracture. The Unites states and Japan mandated the use of mouthguards for contact sports. But, Korean didn't. Mouthguards divided into ready-made type and custom-made type. Mouthguards protect the lips, intraoral soft tissues, teeth and provide the mandible with resilient support to prevent jaw fracture and dislocations. Sports-related accidents have been reported to be one of the most common causes of dentofacial trauma. Sports trauma of involving teeth with incomplete root formation cause long chair time, multiple visit, economic considerations, additional dental services. So, mouthguards can offer considerable protection against sports-related trauma.

• Journal of the Korean Vacuum Society
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• v.19 no.4
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• pp.300-306
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• 2010

Superhydrophobic micro-nano hybrid structures were fabricated by reactive ion etching of hydrophobic polymer micro patterns using gold nanoparticles as etch masks. Micro structures of perfluoropolyether bisurethane methacrylate (PFPE) were prepared by soft-lithographic technique using polydimethylsiloxane (PDMS) molds. Water contact angles on the surfaces of various PFPE micro structures and corresponding micro-nano hybrid structures were compared to examine the effects of micro patterning and nanostructure formation in the manifestation of superhydrophobicity. The PFPE micro-nano hybrid structures exhibited a very stable superhydrophobicity, while the micro-only structures could not reach the superhydrophobicity but only showed the unstable hydrophobicity.

• Journal of the Korean Applied Science and Technology
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• v.36 no.1
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• pp.305-311
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• 2019

The acrylic copolymer was designed and prepared for soft lens with high content. The copolymers were prepared using 2-hydroxyethyl methacrylate(HEMA) as a monomer and ethylene glycol dimethacrylate(EGDMA), glycerol dimethacrylate(GD), or glycerol 1,3-diglycerolate diacrylate (GDD) as a cross linking agent. The water content for high water content lens was 46%, which was higher compared to general purpose of 36%. The contact angle decreased from 38.6 to 34.4, which appears hydrophilic surface. The tensile strength decreased from 0.1 Mpato 0.08, then again to 0.05 as hydrophilic properties of cross linking agents increased. No phase separation was observed in the cross section of lens using scanning electron microscope. The real-time infrared technique was used in photo-polymerization. The initial polymerization rate increased from 0.6 to 0.9, depending on crosslinking agent.

• Journal of Korean Neurosurgical Society
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• v.66 no.4
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• pp.418-425
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• 2023

Objective : Deciphering the anatomy of posterior communicating artery (PCoA) aneurysms in relation to surrounding structures is essential to determine adjuvant surgical procedures. However, it is difficult to predict surgical structures through preoperative imaging studies. We aimed to present anatomical structures using preoperative high-resolution three-dimensional proton density-weighted turbo spin-echo magnetic resonance (PDMR) imaging with simple classification. Methods : From January 2020 to April 2022, 30 patients underwent PDMR before microsurgical clipping for unruptured PCoA aneurysms in a single tertiary institute. We retrospectively reviewed the radiographic images and operative data of these patients. The structural relationship described by PDMR and intraoperative findings were compared. Subsequently, we classified aneurysms into two groups and analyzed the rate of adjuvant surgical procedures and contact with the surrounding structures. Results : Correlations between preoperative PDMR predictions and actual intraoperative findings for PCoA aneurysm contact to the oculomotor nerve, temporal uncus, and anterior petroclinoid fold (APCF) reported a diagnostic accuracy of 0.90, 0.87, and 0.90, respectively. In 12 patients (40.0%), an aneurysm dome was located on the plane of the oculomotor triangle and was classified as the infratentorial type. Compared to the supratentorial type PCoA aneurysm, adjuvant procedures were required more frequently (66.7% vs. 22.2%, p=0.024) for infratentorial type PCoA aneurysm clipping. Conclusion : Preoperative PCoA aneurysm categorization using PDMR can be helpful for predicting surgical complexity and planning of microsurgical clipping.