• Proceedings of the Korean Vacuum Society Conference
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• 1998.06a
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• pp.33-33
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• 1998

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2007.06a
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• pp.279-280
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• 2007

• Journal of Dental Rehabilitation and Applied Science
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• v.36 no.1
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• pp.1-11
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• 2020

Purpose: The purpose was to compare shear bond strength (SBS) of three types of resin for temporary restoration to polyetherketoneketone (PEKK) depending on surface modification. Materials and Methods: Sixty disks made from PEKK were air-abraded with 110 ㎛ alumina particles (Cobra, Renfert GmbH, Hilzinge, Germany) and thirty specimens were divided into two groups each: PEKK without Visio.link (Bredent, Senden, Germany)(U) and with Visio.link (P). Resins for temporary restoration (polymethylmethacrylate; PMMA, polyethylmethacrylate; PEMA, bis-acryl composite resin) in the shape of a square with one side 3.2 mm were bonded to PEKK twenty respectively and classified into six groups (UM, UE, UC, PM, PE and PC). All specimens were stored in distilled water at 37℃ for 24 hours. SBS of each group was measured at a crosshead speed of 2 mm/min in universal testing machine. SBS was compared using one-way ANOVA and a Tukey HSD test (P = 0.05). Results: Group UM and group UE showed a significant difference in SBS with group UC (P < 0.05). Group PC showed a significant increase in SBS than group UC (P < 0.05). Conclusion: It is recommended to apply Visio.link to PEKK for adhering bis-acrylic composite resin, but not for PMMA and PEMA in clinical practice.

• Transactions of the Korean Society of Mechanical Engineers
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• v.18 no.5
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• pp.1288-1300
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• 1994

Mathematical modeling and numerical calculation on the flow and thermal characteristics induced by fire in a partial enclosure are performed. The solution procedures include the Shvab-Zeldovich approximation for the physical transport equations, low Reynolds number k-.epsilon. model for the turbulent fluid flow and Discrete Ordinate method(DOM) to calculate the radiative heat transfer. PMMA(Polymethylmethacrylate) is adopted as a solid fuel. Two different cases are considered : combustions with and without gas radiation occuring in a open cavity for variable pyrolyzing location of PMMA. When the fire source is located at the left-wall, the flow region of flame gas is limited at the left-wall and ceiling and recirculation region of inlet gas is formulated at neat the floor. In case of neglecting the radiative heat transfer, more large flame size and higher temperature is predicted. It is essential to consider the radiative heat transfer for analysis of fire phenomenon.

• 제어로봇시스템학회:학술대회논문집
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• 1996.10b
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• pp.1000-1003
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• 1996

Nonlinear unified predictive control(UPC) algorithm was applied to the temperature control of a batch polymerization reactor for polymethylmethacrylate(PMMA). Before the polymerization reaction is initiated, the parameters of the process model are determined by the recursive least squares(RLS) method. During the reaction, nonlinearities due to generation of heat of reaction and variation of heat transfer coefficients are predicted through the nonlinear model developed. These nonlinearities are added to the process output from the linear process model. And then, the predicted process output is used to calculate the control output sequence. The performance of nonlinear control algorithm was verified by simulation and compared with that of the linear unified predictive control algorithm. In the experiment of a batch PMMA polymerization, nonlinear unified predictive control was implemented to regulate the temperature of the reactor, and the validity of the nonlinear model was verified through the experimental results. The performance of the nonlinear controller turned out to be superior to that of the linear controller for tracking abrupt changes in setpoint.

• Journal of radiological science and technology
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• v.42 no.6
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• pp.455-460
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• 2019

This study compared the radiation transmission and image quality of polymethylmethacrylate (PMMA), polycarbonate (PC), and carbon, which are common components of the compression plates currently used during breast imaging. In addition to measuring the transmitted dose and the intensity without the use of a compression paddle, the four different compression paddles were evaluated according to the material and thickness of each paddle. Radiation transmittance, maximum intensity, and plot profile type w ere all evaluated for each material, and for each factor evaluated the follow ing order w as noted, from best to w orst: carbon 4 mm, PMMA 3 mm, PMMA 4 mm, and PC 4 mm. It is necessary to study a variety of materials and thicknesses in order to find the optimal combination of material and thickness, because not only does the material have a large influence in reducing the radiation exposure during mammography, but the thickness of the compression plate also has a great influence.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2005.07a
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• pp.655-656
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• 2005

In the future, plastic based system will play a crucial role in modem life, for examples, transparent display or disposable electronics and so on. In this paper, we introduced a new method to fabricate the metal line on the plastic substrate. Metal lines were fabricated by hot embossing and CMP process on PMMA (polymethylmethacrylate) substrates. A Si mold was made by wet etching process and a PMMA wafer was cut off from I mm thick PMMA sheet. A 100 nm thick Al was deposited on PMMA wafers. The Al deposited PMMA wafer and the Si mold carefully sandwiched which was directly imprinted by hot embossing. After imprinting process, a residual Al layer was removed by CMP process. Finally, we found the entire process may be very useful to fabricate the metal line on plastic substrates.

• Journal of Technologic Dentistry
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• v.41 no.3
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• pp.203-209
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• 2019

Purpose: The purpose of this study was to investigate the mechanical properties of polymer prosthetic and restorative materials for dental CAD/CAM using two test method; surface characteristics and shear bond strength. Methods: Commercialized CAD/CAM polymer blanks were investigated; One kinds of PMMA, and one PEKK blanks. A total of 20 PMMA and PEKK specimens were prepared, and each group was divided into 10 specimens. Average surface roughness was observed under surface profilometer. The contact angle was measured with a surface electrooptics. The bond strength was evaluated by a universal testing machine at a crosshead speed of 5mm/min. The data were statistically analyzed using independent t-test and Fisher's exact test(P<0.05). Results: The PMMA and PEKK group showed a significant difference in the shear bond strength with the composite resin(P<0.05). The surface roughness of the PEKK group was higher than that of the PMMA group. The fracture mode were observed in PEKK groups with 50% showing adhesive remnant index score. Conclusion: PEEK is used as substructure material and composite veneering material is applied. PEKK resins will contribute to the development of successful products that will provide structural and aesthetic satisfaction.

• Journal of the Korean Chemical Society
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• v.33 no.4
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• pp.431-435
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• 1989

The refractive index, refractive-index distribution, birefringence, and the attenuation of the plastic fiber prepared from the transparent PMMA prerod were measured in accordance with continuous heat drawing temperature($T_d$). The refractive indices were decreased with $T_d$ elevation but the refractive-index distribution from the center of fiber to periphery was higher at lower $T_d$. The steep decrease of gradient index was only at the periphery of higher $T_d$. Birefringence was observed only below $220^{\circ}C$ and ranged $5{\times}10^{-4}$ to $6{\times}10^{-4}$. No birefringence was observed above $220^{\circ}C$. An elevation of $T_d$ brought about a monotonous decrease in the attenuation of the fiber.

• Journal of Korean Neurosurgical Society
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• v.46 no.4
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• pp.305-311
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• 2009

Objective : The purpose of this study was to determine the efficacy, radiological findings, clinical outcomes and complications in patients with lumbar stenosis and osteoporosis after the use of polymethylmethacrylate (PMMA) augmentation of a cannulated pedicle screw. Methods : Thirty-seven patients with degenerative spinal stenosis and osteoporosis (T-score < -2.5) underwent lumbar fusion using the Dream Technology Pedicle Screw ($DTPS^{TM}$, Dream Spine Total Solutions, Dream STS, Seoul. Korea) between 2005 and 2007. The clinical outcomes were evaluated by using the visual analog scale (VAS) and the Prolo scale. Radiologic findings were documented through computed tomography (CT) and plain films. Results : Thirty-seven patients were evaluated and included, 2 males and 35 females with an average bone mineral density (BMD) of $0.47g/cm^2$. The average age of the patients was 68.7 (range, 57-88). The preoperative VAS for low back and leg pain ($7.87{\pm}0.95$ and $8.82{\pm}0.83$) were higher as compared with postoperative VAS ($2.30{\pm}1.61$ and $1.42{\pm}0.73$) with statistical significance (p = 0.006, p = 0.003). According to the Prolo scale, 11, 22, one and three patients were in excellent, good, fair and poor conditions, respectively. The average amount of the injected cement per one cannulated screw was $1.83{\pm}0.11\;mL$. Conclusion : The results show favorable outcome both clinically and radiographically for 37 patients who underwent lumbar fusion using $DTPS^{TM}$ and PMMA. Based on the results, the use of this surgical method can be a safe and effective option for the operation on the osteoporotic spine.