• The Journal of Korean Academy of Prosthodontics
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• v.41 no.5
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• pp.626-639
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• 2003

Statement of problem : Recently, in attempts to reinforce the acrylic resin and to reduce the polymerization shrinkage, it has been reported that adding vinyloligo-silsesquioxane (vinyl-POSS) to PMMA significantly compensates for polymerization shrinkage and somewhat increases the fracture resistance. Purpose : There haven't been any studies on abrasion that can affect the adaptation of the denture in long-term use. In this study abrasion resistance was compared between acrylic resin with vinyl-POSS and commercialized acrylic resin for denture base. In addition, the difference in abrasion resistance according to molding methods was compared. Material and method : Using PaladentR 20 including vinyl-POSS. PaladentR 20, Lucitone 199R, SR IvocapR, denture bases were fabricated using compression molding technique and continuous-pressure injection technique. Surface hardness and abrasion were measured for each group, and the worn surfaces were observed under a scanning electron microscope. Results : 1. When surface hardness was measured for each material and molding technique, there was no statistically significant difference among the materials. (p<0.05) 2. When same denture base material and molding technique were used, the abrasion due to toothpaste solution was 5 times as severe as the abrasion due to soap solution. 3, When toothpaste solution was used, the abrasion decreased in the order of PaladentR20, PaladentR 20 including vinyl-POSS, SR IvocapR, and Lucitone 199R. However statistically significant difference was seen only among PaladentR 20, SR IvocapR, and Lucitone 199R. (p<0.05). 4. When soap solution was used, the abrasion was more severe in PaladentR 20 and including vinyl-POSS PaladentR 20 groups than in SR IvocapR and Lucitone 199R groups. (p<0.05). Conclusion : Addition of vinyl-POSS doesn't improve the abrasion resistance, and the abrasion resistance was similar to those of existing materials. Additional studies under different conditions are needed. For clinical application of vinyl-POSS, further investigations with different requirements and conditions are necessary.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.39 no.11
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• pp.885-890
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• 2015

Nanomaterials possess unique mechanical, physical, and chemical properties. They are small, and have an ultrahigh surface area, making them suitable for air filter applications. Electrospinning has been recognized as an efficient technique for fabricating polymer nanofibers. In order to determine the optimum manufacturing conditions, the effects of several electrospinning process parameters on the diameter, orientation, and distribution of polyacrylonitrile (PAN) nanofiber are analyzed. To improve interlaminar fracture toughness and suppress delamination in the form of laminated non-woven fibers by using a heat roller, the performances of filter efficiency and pressure drop achieved with PAN nanofiber air filter are evaluated experimentally.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.37 no.4
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• pp.467-473
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• 2013

In this study, two-dimensional finite element models were developed and experiments were conducted using an atomic force microscope to investigate the tribological characteristics of an SU-8 layer coated on a patterned wafer for microsystem applications. The results revealed that both the adhesion and the friction forces measured by the atomic force microscope were lower for the SU-8 coated surface than for the bare silicon surface. This is attributed to the hydrophobicity of SU-8. Another important result derived from the finite element analysis was the critical load required to fracture the SU-8 film with respect to the thickness. The critical loads for thicknesses of 200, 400, and 800 nm were approximately 13, 22, and 28 mN, respectively, which corresponded to a Hertzian contact pressure of 1.2-1.8 GPa. These results will aid in the design of a suitable SU-8 thickness for microsystem components that are in contact with one another.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.37 no.12
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• pp.1159-1165
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• 2013

Powder blasting, which is an efficient micromachining method for glass, silicon, and ceramics, has a critical disadvantage in that the surface finish is poor owing to the brittle fracture of materials. Low-pressure waterjet machining can be applied to smoothen the rough surface inside the blasted structure. In this study, the surface roughness and sectional dimension of micro-channels are observed during the repetitive application of a waterjet to blasted micro-channels. The asperities and subsurface cracks created by blasting are removed by waterjet machining. Along with the surface roughness, it is found that the sectional dimension increases and the edges of the finished micro-channel become slightly round. Finally, a microfluidic chip is machined by the blasting-waterjet process and a transparent microfluidic channel is obtained efficiently.

• Journal of the Korean Society for Precision Engineering
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• v.28 no.9
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• pp.1078-1085
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• 2011

Prediction of a minimum crack size for growth, which is defined as a crack size that grows fast enough to keep ahead of its removal by contact wear and periodic grinding, is the most demanding work to prevent rail from fatigue failure and develop cost effective railway maintenance strategy In this study, we investigated the wheel load increment due to a rail defect during a train ran over it, and its effect on the minimum crack size for growth. For this purpose, we developed simulation software based on the Fletcher and Kapoor's "2.5D" model and measured wheel load increment during a train passed over a defect. A maximum contact pressure and contact patch size were calculated by 3D FEM and crack growth analyses were performed by varying two of dominant contact contributors; surface friction coefficient(0.1, 0.2, 0.3 and 0.4) and crack aspect ratio. The minimum crack sizes for growth were calculated from 0.29 to 1.44mm depending on the contact conditions. They were decreasing with increasing surface friction coefficient and decreasing with crack aspect ratio(a/b).

• Tunnel and Underground Space
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• v.13 no.4
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• pp.304-315
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• 2003

In this paper, the DDA method with a new hydro-mechanical algorithm is used to study the effect of rock discontinuities on uplift and seepage in concrete gravity dam foundations. This paper presents an alternative method of predicting uplift and seepage at the base of concrete gravity dams. A sensitivity analysis was carried out to study the importance of several parameters on dam stability such as the orientation, spacing, and location of discontinuities. The study shows that joint water flow and adverse geological conditions could result in unusual uplift at the base of concrete gravity dams, well in excess of what is predicted with the classical linear or hi-linear pressure assumption. It is shown that, in general, the DDA program with the hydro-mechanical algorithm can be used as a practical tool in the design of gravity dams built on fractured rock masses.

• The Korean Journal of Pain
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• v.29 no.3
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• pp.185-188
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• 2016

The $12^{th}$ rib syndrome is a disease that causes pain between the upper abdomen and the lower chest. It is assumed that the impinging on the nerves between the ribs causes pain in the lower chest, upper abdomen, and flank. A 74-year-old female patient visited a pain clinic complaining of pain in her back, and left chest wall at a 7 on the 0-10 Numeric Rating scale (NRS). She had a lateral fixation at T12-L2, 6 years earlier. After the operation, she had multiple osteoporotic compression fractures. When the spine was bent, the patient complained about a sharp pain in the left mid-axillary line and radiating pain toward the abdomen. On physical examination, the $10^{th}$ rib was not felt, and an image of the rib-cage confirmed that the left $10^{th}$ rib was severed. When applying pressure from the legs to the $9^{th}$ rib of the patient, pain was reproduced. Therefore, the patient was diagnosed with $9^{th}$ rib syndrome, and ultrasound-guided $9^{th}$ and $10^{th}$ intercostal nerve blocks were performed around the tips of the severed $10^{th}$ rib. In addition, local anesthetics with triamcinolone were administered into the muscles beneath the $9^{th}$ rib at the point of the greatest tenderness. The patient's pain was reduced to NRS 2 point. In this case, it is suspected that the patient had a partial resection of the left $10^{th}$ rib in the past, and subsequent compression fractures at T8 and T9 led to the deformation of the rib cage, causing the tip of the remaining $10^{th}$ rib to impinge on the $9^{th}$ intercostal nerves, causing pain.

• Journal of the Korean Society for Heat Treatment
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• v.19 no.1
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• pp.30-36
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• 2006

Fretting fatigue behavior of SCM420 steel commonly used in the automotive industry for structural applications was investigated in this study. In addition, the effect of bridge pad on the fretting fatigue test was evaluated from different pad materials and following conclusions were drawn. Simple fatigue limit of SCM 420 steel was determined to be 350 MPa while this value was 225 MPa and 285.5 MPa with SCM420H and with SM45C pad, respectively. Reduction in fatigue limit was, thus found to be 35.7% and 17.9% with SCM 420H pad and SM45C pad, respectively. Results of fracture surface observation revealed that typical striation pattern of fatigue failure existed as well as dimpled and cleavage frature appearance was found in final fractured region. From the EDS compositional analysis, test sample and pad part all had high signals for oxygen and iron, suggesting that worn particles might be iron oxide, although exact chemical composition has to be confirmed. Considerable reduction in fatigue life was apparent in SCM 420 steel under fretting fatigue against simple fatigue. Such reduced fatigue life by fretting damage should be considered as an important factor not only in the viewpoint of repairing but also inevitably in the design stage of structural components.

• Geomechanics and Engineering
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• v.11 no.3
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• pp.345-359
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• 2016

In order to investigate the influence of the interfacial angel on failure characteristics and mechanism of combined coal-rock mass, 35 uniaxial/biaxial compressive simulation tests with 5 different interfacial angels of combined coal-rock samples were conducted by PFC2D software. The following conclusions are drawn: (1) The compressive strength and cohesion decrease with the increase of interfacial angle, which is defined as the angle between structure plane and the exterior normal of maximum principal plane, while the changes of elastic modulus and internal friction angle are not obvious; (2) The impact energy index $K_E$ decreases with the increase of interfacial angle, and the slip failure of the interface can be predicted based on whether the number of acoustic emission (AE) hits has multiple peaks or not; (3) There are four typical failure patterns for combined coal-rock samples including I (V-shaped shear failure of coal), II (single-fracture shear failure of coal), III (shear failure of rock and coal), and IV (slip rupture of interface); and (4) A positive correlation between interfacial angle and interface effect is shown obviously, and the interfacial angle can be divided into weak-influencing scope ($0-15^{\circ}$), moderate-influencing scope ($15-45^{\circ}$), and strong-influencing scope (> $45^{\circ}$), respectively. However, the confining pressure has a certain constraint effect on the interface effect.

• Proceedings of the Korean Radioactive Waste Society Conference
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• 2005.11a
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• pp.87-95
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• 2005

Laser sealing/cutting technique, one of the 4 core technologies to manufacture self-luminous glass tubes (SLGTs) has been developed. Through the analysis of commercial products it is found that Pyrex Is used for SLGTs. A CO2 laser, which is commonly used for glass work was used for the study The factors affecting the sealing/cutting were laser intensity, duration. Irradiation method, and pressure inside the tube. The whole Process is composed of 2 stages. In the first stage. both ends of the tubes are sealed while tritium is insected in the tubes. And the tritium sealed tubes are cut in the desired size in the second stage. Defocused beam was used for seal ing and focused beam was used for cutting. After the sealing/cutting, the tubes were heat treated to prevent fracture due to the residual heat stress.