• Transactions of the Korean Society of Mechanical Engineers A
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• v.40 no.9
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• pp.815-820
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• 2016

An elastic polymer (e.g., PDMS) blended with EFG particles is a promising conductive composite for fabricating soft sensors that can detect an object's deformation up to or more than 50%. Here, we develop large-strain, sprayable soft sensors using a mixture of PDMS and EFG particles, which are used as a host elastomer and electrically conductive particles, respectively. A solution for a conductive composite mixture is prepared by the microwave-assisted graphite exfoliation, followed by ultrasonication-induced fragmentation of the exfoliated graphite and ultrasonic blending of PDMS and EFG. Using the prepared solutions for composite and pure PDMS, 1-, 2-, and 3-axis soft sensors are fabricated by airbrush stencil technique where composite mixture and pure PDMS are materials for sensing and insulating layers, respectively. We characterize the soft strain sensors after investigating the effect of PDMS/EFG wt% on mechanical compliance and electrical conductance of the conductive composite.

• Journal of Dental Rehabilitation and Applied Science
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• v.28 no.4
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• pp.327-337
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• 2012

The object of this study was to find out the effect of various reinforcing materials including Quarts Splint$^{TM}$ Mesh on the transverse strength of the denture resin. QC-20 and Lucitone199$^{(R)}$ were used as the denture resin, and polyethylene fiber Ribbond$^{(R)}$, light curing quarts fiber Quarts Splint$^{TM}$ Mesh, metal mesh were used as the reinforcing materials. Ten specimens were fabricated for each group and the size of specimens was $2.0{\times}10.0{\times}65.0mm$. To compare the effect of resin thickness, additional specimens of $2.5{\times}10.0{\times}65.0mm$, $3.0{\times}10.0{\times}65.0mm$ were fabricated. In the control group, the transverse strength of Lucitone199$^{(R)}$ was significantly higher than that of QC-20(p<0.05). Among the specimens of 2.0 mm thickness fabricated with $Lucitone199^{(R)}$ and QC-20, they showed high transverse strength in the order of metal mesh, Quarts Splint$^{TM}$ Mesh, Ribbond$^{(R)}$, and control group. In the specimens of 2.0 mm, 2.5 mm thickness, the transverse strength of Quarts Splint$^{TM}$ Mesh were significantly higher than that of QC-20(p<0.05). But in the specimens of 3.0 mm thickness, there was no significant difference.

• Polymer(Korea)
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• v.32 no.3
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• pp.230-238
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• 2008

The thermal and optical properties of cellobiose octa(cholestryloxycarbonyl)alkanoates CCCBn, $n=2{\sim}8$,10, the number of methylene units in the spacer) were investigated. All the samples formed monotropic cholesteric phases with left-handed helical structures. CCBn with n=2 or 10, in contrast with CCBn with $3{\leq}n{\leq}8$, did not display reflection colors over the full cholesteric range, suggesting that the helical twisting power of the cholesteryl group highly depends on the length of the spacer connecting the cholesteryl group to the cellobiose chain. The isotropic-cholestropic transition ($T_{ic}$) and glass transition temperatures decreased with increasing n and showed no odd-even effect. The transition entropy at $T_{ic}$ increased with increasing n from 2 up 6, but at n=7 it drops significantly and then increased again with increasing n from 8 to 10. The sharp change at n=7 may be attributed to a difference in arrangement of the side groups. The thermal stability and degree of order in the mesophase and the temperature dependence of the optical pitch observed for CCBn were significantly different from those reported for the cellulose tri(cholesteryloxycarbonyl)alkanoates and glucose penta(cholesteryloxycarbonyl)alkanoates. The results were discussed in terms of the differences in the degree of polymerization, the number of the mesogenic units per mole-glucose unit, and the conformation of the molecules.

• Restorative Dentistry and Endodontics
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• v.35 no.6
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• pp.486-491
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• 2010

Objectives: This study examined the effect of 2% chlorhexidine on the ${\mu}TBS$ of a direct composite restoration using one-step self-etch adhesives on human dentin. Materials and Methods: Twenty-four extracted permanent molars were used. The teeth were assigned randomly to six groups (n = 10), according to the adhesive system and application of chlorhexidine. With or without the application of chlorhexidine, each adhesive system was applied to the dentin surface. After the bonding procedure, light-cure composite resin buildups were produced. The restored teeth were stored in distilled water at room temperature for 24 hours, and then cut and glued to the jig of the microtensile testing machine. A tensile load was applied until the specimen failed. The failure mode was examined using an operating microscope. The data was analyzed statistically using one-way ANOVA, Student's t-test (p < 0.05) and Scheffet's test. Results: Regardless of the application of chlorhexidine, the Clearfil $S^3$ Bond showed the highest ${\mu}TBS$, followed by G-Bond and Xeno V. Adhesive failure was the main failure mode of the dentin bonding agents tested with some samples showing cohesive failure. Conclusions: The application of 2% chlorhexidine did not affect the ${\mu}TBS$ of the resin composite to the dentin using a one-step self-etch adhesive.

• Journal of Digital Convergence
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• v.17 no.10
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• pp.373-379
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• 2019

Polymethyl methacrylate (PMMA), a self-polymerizing resin for removable orthodontic devices, has been used as a dental orthodontic device for many years because of its advantages such as color stability, volume stability, and tissue compatibility. However, such a removable orthodontic device has a disadvantage that the longer the use in the oral cavity due to the low strength of the PMMA fracture of the orthodontic device resin in use. In this study, zinc nanoparticles (ZNP) were mixed with orthodontic PMMA to introduce strength effect. Rectangular samples ($1.4{\times}3.0{\times}19.0mm$) of orthodontic PMMA (0, 0.5, 1.0, 2.0 and 4.0%) containing ZNP were prepared. The finished specimen was tested for three-point bending strength at a speed of 1 mm / min, and the Vickers hardness was measured three times using a hardness tester. The surface roughness was measured with a surface roughness. As a result, the 3-point bending strength did not change significantly (p>0.05). Surface energy increased significantly. As a result, we successfully synthesized ZNP in this study and prepared the dispersed resin specimen for calibration. It will be possible to develop high-density dental orthodontic resins.

• Journal of the Korea Convergence Society
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• v.12 no.7
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• pp.125-131
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• 2021

Blue light with strong energy is required for light-curing resin treatment, which is being used more frequently in dentistry. To reduce the risk of exposure to scattered light, we tried to use colored lenses. The tips for light curing machine and a commercially available yellow-type blue-light blocking lens and a yellow lens colored with yellow dye, which are expected to be effective in blocking blue light, were placed in a UV-Vis spectrometer device, and transmission and blocking of blue light were tested respectively. As a result, the average blue light blocking rate of the light curing machine tips was 99.49%, and the C lens with the highest color density among commercially available lenses showed a high blue light blocking rate of 99.54%. In the case of lenses tinted with yellow, the yellow tinted C lens with the highest tint concentration showed 87.57% of blue light blocking rate. It is judged that the side effects related to the eyes caused by blue light can be reduced if a yellow-type commercially available or colored lens is worn along with a light curing machine tip during resin treatment.

• The Korean journal of helicobacter and upper gastrointestinal research
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• v.18 no.4
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• pp.277-279
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• 2018

전 세계적으로 Helicobacter pylori의 항생제 내성률은 지속적으로 증가하고 있으며, 기존의 제균 치료에 실패한 H. pylori 감염 환자들에 대한 효과적인 구제요법(rescue therapy)의 필요성 역시 증가하고 있다. 이 연구는 두 개 기관, 공개, 평행 그룹, 무작위 배정 연구로서 불응성 H. pylori 감염 환자들의 구제요법으로 유전자형 내성을 기반한 치료(genotype resistance-guided therapy)와 경험적 치료(empirical therapy) 중 어느 것이 보다 효과적인지를 비교하고자 하였다. 2012년 10월부터 2017년 9월까지 20세 이상의 불응성 H. pylori 감염 환자들을 대상으로 하였으며, 불응성 H. pylori 감염은 과거 두 종류 이상의 H. pylori 제균 치료를 받았음에도 불구하고 H. pylori 제균에 실패한 환자들로 정의하였다. 이들에게서 한 군은 14일간의 유전자형 내성을 기반한 순차 치료(n=21 in trial 1, n=205 in trial 2)를, 다른 한 군은 환자들의 과거 제균 치료 종류를 감안한 14일간의 경험적 순차 치료(n=20 in trial 1, n=205 in trial 2)를 시행하였다. 순차 치료법은 첫 7일은 esomeprazole 40 mg과 amoxicillin 1 g을 하루 두 번 복용한 다음, 나머지 7일은 esomeprazole 40 mg과 metronidazole 500 mg, 그리고 1) levofloxacin 250 mg 또는 2) clarithromycin 500 mg 또는 3) tetracycline 500 mg을 하루 두 번 복용하는 것으로 구성하였다. 23S ribosomal RNA (rRNA)나 gyrase A에 대한 내성 관련 돌연변이 여부는 direct sequencing을 통한 중합효소연쇄반응(polymerase chain reaction, PCR) 검사를 이용하였고, 제균 성공 여부는 요소호기검사를 통해 확인하였다. 일차 결과 지표는 치료 방법에 따른 제균율로 정하였다. Trial 1에서는 tetracycline 대신 doxycycline 100 mg을 사용하였는데, 제균 성공률이 유전자형 내성을 기반한 치료군에서는 17명(81%), 경험적 치료군에서는 12명(60%)으로 나타났다(P=0.181). 하지만, 다른 순차 치료군들과 비교하였을 때, doxycycline을 포함한 순차 치료군의 제균율이 현저히 낮은 것으로 나타나서(15/26, 57.7%) doxycycline을 포함한 순차 치료법은 종결하기로 하고, trial 2부터는 doxycycline 대신 tetracycline으로 교체하여 연구를 지속하였다. Trial 2의 intention-to-treat (ITT) 분석 결과, 유전자형 내성을 기반한 치료군에서는 160/205명(78%), 경험적 치료군에서는 148/205명(72.2%)으로 두 그룹 간의 통계적인 제균율의 차이는 보여주지 못하였다(P=0.170). 부작용 및 환자 순응도에서도 양 군 간의 의미 있는 차이는 없었다. 따라서, 두 종류 이상 H. pylori 제균 치료에 실패한 환자들이라고 할지라도 기존의 제균 치료력을 바탕으로 적절한 경험적 치료를 시행하는 것은 유전자형 내성을 기반한 치료 정도의 효과는 있으며 접근성, 비용, 환자들의 선호도 등의 여러 가지 부가적인 사항들을 고려할 때, 제균 치료력을 고려한 경험적 치료는 간단한 수준의 유전자형 내성을 기반한 치료의 대안으로 받아들여질 수 있을 것으로 제안하였다.

• Composites Research
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• v.35 no.3
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• pp.127-133
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• 2022

Polypropylene (PP) has been received great attention as a next-generation high-voltage power cable insulation material that can replace cross-linked polyethylene (XLPE). However, the PP cannot be used alone as an insulation material because of its high elastic modulus and vulnerability to impact, and thus is mainly utilized as a form of a copolymer with rubber phases included in the polymerization step. In this paper, a soft PP-based blend was prepared through melt-mixing of impact PP, polyolefin elastomer, and propylene-ethylene random copolymer. The elastic modulus and impact strength of the blend could properly be decreased or increased, respectively, by introducing elastomeric phases. Furthermore, the blends showed a high storage modulus even at a temperature of 100℃ or higher at which the XLPE loses its mechanical properties. In addition, the blend was found to be effective in suppressing the space charge compared to the pristine PP as well as XLPE.

• Journal of Adhesion and Interface
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• v.23 no.2
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• pp.44-52
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• 2022

Epoxy resin has the disadvantage of being easily destroyed by instantaneous impact due to its high crosslinking density despite its high glass transition temperature (T_g) and excellent properties. To compensate for this, in this study, polyol was synthesized by ring opening polymerization of propylene glycol (PPG) diamine, Jeffamine D 2000 and propylene carbonate, and urethane modified epoxy was synthesized using this. The properties of the synthesized urethane modified epoxy were confirmed by FT-IR, H-NMR. To confirm the degree of improvement in impact resistance as an adhesive, a urethane modified epoxy adhesive was prepared by mixing a digylcidyl ether bisphenol A (DGEBA) with curing agent and curing accelerator. Properties test of urethane modified epoxy were shear strength, tensile strength and impact strength. As a result, excellent results were obtained in all test when the ratio of DGEBA : urethane modified epoxy was 8:2.

• Journal of the Korea Convergence Society
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• v.13 no.1
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• pp.119-129
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• 2022

Cervical cytology has been widely used as a screening tool for cervical cancer. However, Human papillomavirus (HPV) detection and subtype testing are suggested to overcome the high false-negative rate associated with cytology. We aimed to investigate the clinical usefulness and infection rate in the HPV polymerase chain reaction (PCR) test performed in hospitals. HPV PCR data from 217 patients were analyzed. Analysis of variance revealed a significant difference in the infection rate among different age groups (P=0.015). The biopsy results showed that epithelial cell abnormalities and high HPV-positivity rate was observed in 1 (100%) subject aged <29 years, in 4 out of 5 (80%) patients in their 30s, and in 3 out of 4 (75%) patients aged ≥70 years. The prevalence of HPV infection was very high (46.1%). The highest prevalence (87.5%) was observed among patients in their <29, followed by those in their 30s (67.7%) and those in their 40s (31.9%).A high rate of epithelial cell abnormalities (≥ cervical intraepithelial neoplasia type 1, mild dysplasia) was observed in HPV-infected women aged<30 years. Therefore, extensive research and prevention activities are needed in this age group. HPV PCR testing is recommended to complement cervical cytology