• Maxillofacial Plastic and Reconstructive Surgery
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• 제33권4호
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• pp.363-367
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• 2011

Genioplasy with osteotomy is a flexible and useful procedure. However, osteotomy can cause different types of morbidity. Chin augmentation with porous polyethylene ($Medpor^{(R)}$) has become popular in the recent years. Porous polyethylene ($Medpor^{(R)}$) is an excellent biomaterial for reconstructing facial deformities. $Medpor^{(R)}$ has a porous architecture, which prevents capsule formation and decreases the degree of foreign-body reaction. In addition, it can be easily cut with scissors and molded, and it also maintains its shape. We report here on a satisfactory case of chin augmentation with using porous polyethylene ($Medpor^{(R)}$).

• 대한기계학회:학술대회논문집
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• 대한기계학회 2003년도 춘계학술대회
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• pp.1730-1735
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• 2003

The plume-induced shock wave is a complex phenomenon, consisting of plume-induced boundary layer separation, separated shear layer, multiple shock waves, and their interactions. The knowledge base of plume interference effect on powered missiles and flight vehicles is not yet adequate to get an overall insight of the flow physics. Computational studies are performed to better understand the flow physics of the plume-induced shock and separation particularly at high plume to exit pressure ratio. Test model configurations are a simplified missile model and two rounded and porous afterbodies to simulate moderately and highly underexpanded exhaust plumes at the transonic/supersonic speeds. The result shows that the rounded afterbody and porous wall attached at the missile base can alleviate the plume-induced shock wave phenomenon, and improve the control of the missile body.

• 대한기계학회논문집
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• 제11권3호
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• pp.368-375
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• 1987

본 연구에서는 이러한 기하형태의 불규칙성을 쉽게 고려할 수 있는 윤곽좌표계 (body fitted coordinate systems)를 이용하여 다공성 물질의 유효열전도율을 결정하 는 방법을 제시하였다.기공의 형상을 원형으로 가정하고 기공율과 기공 내부기체와 고체의 열전도율비 등의 변수가 유효열전도율과 이들 변수의 상관관계식을 제안하였으 며, 또한 핵연료 소결체와 같은 실제적인 다공성 물질의 유효열전도율을 해석하는데 좀 더 타당한 타원형 형상의 기공 가정방법을 제시하였다.

• 한국결정성장학회지
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• 제25권5호
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• pp.218-224
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• 2015

최근 세라믹 다공체를 이용하여 적조 생물을 여과, 제거하려는 연구가 시도되고 있다. 하지만 해양 환경에서 1개월 이상이 경과하면 다공체 표면에 해양 생물 오손(biofouling)이 발생하여 기능이 저하되는 문제가 나타난다. 본 논문에서는 세라믹 다공체의 특성 변화 또는 표면 개질을 통하여 해양 생물 오손을 억제하는 방법에 대하여 연구하였다. 6 종류의 세라믹 다공체를 시험한 결과, 기공율과 흡수율이 낮을수록 생물 오손량이 낮게 나타났다. 또한 다공체 표면에 실리카 입자를 결합시켜 표면 거칠기를 증가시키면, 따개비 등의 대형 해양 생물로 인한 오손량을 감소시킬 수 있었다. 한편 세라믹 다공체 표면에 유리분말을 융착 코팅시키면 오히려 생물 오손량이 증가하였는데, 이는 유리에서 용출되어 나오는 무기질 성분 이온들이 미생물의 생육을 촉진했기 때문이다. 본 연구로부터 세라믹 다공체의 물리적 성질 및 표면 거칠기를 제어하면 위험 물질을 사용하지 않고도 친환경적으로 해양 생물 오손량을 줄일 수 있음을 확인하였으며, 따라서 본 결과를 향후 해양 구조물 등에 적용할 수 있을 것으로 기대된다.

• Earthquakes and Structures
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• 제14권4호
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• pp.313-322
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• 2018

The present study is dedicated to investigate the SH body-as well as Love-waves propagation effects in porous media with uncertain porosity and permeability. A unified formulation of the governing equations for one-dimensional (1-D) wave propagation in anisotropic porous layered media is presented deterministically. The uncertainties around the above two cited parameters are taken into account by random fields with the help of Monte Carlo Simulations (MCS). Random samples of the porosity and the permeability are generated according to the normal and lognormal distribution functions, respectively, with a mean value and a coefficient of variation for each one of the two parameters. After performing several thousands of samples, the mathematical expectation (mean) of the solution of the wave propagation equations in terms of amplification functions for SH waves and in terms of dispersion equation for Love-waves are obtained. The limits of the Love wave velocity in a porous soil layer overlaying a homogeneous half-space are obtained where it is found that random variations of porosity change the zeros of the wave equation. Also, the increase of uncertainties in the porosity (high coefficient of variation) decreases the mean amplification function amplitudes and shifts the fundamental frequencies. However, no effects are observed on both Love wave dispersion and amplification function for random variations of permeability. Lastly, the present approach is applied to a case study in the Adapazari town basin so that to estimate ground motion accelerations lacked in the fast-growing during the main shock of the damaging 1999 Kocaeli earthquake.

• 한국분말재료학회지
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• 제22권3호
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• pp.197-202
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• 2015

In this study, porous stainless steel (STS316L) sintered body was fabricated by powder metallurgy method and its properties such as porosity, compressive yield strength, hardness, and permeability were evaluated. 67.5Fe-17Cr- 13Ni-2.5Mo (wt%) powder was produced by a water atomization. The atomized powder was classified into size with under $45{\mu}m$ and over $180{\mu}m$, and then they were compacted with various pressures and sintered at $1210^{\circ}C$ for 1 h in a vacuum atmosphere. The porosities of sintered bodies could be obtained in range of 20~53% by controlling the compaction pressure. Compressive yield strength and hardness were achieved up to 268 MPa and 94 Shore D, respectively. Air permeability was obtained up to $79l/min{\cdot}cm^2$. As a result, mechanical properties and air permeability of the optimized porous body having a porosity of 25~40% were very superior to that of Al alloy.

• 한국재료학회지
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• 제23권6호
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• pp.339-343
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• 2013

Porous Ti-systems with unidirectionally aligned channels were synthesized by freeze-drying and a heat treatment process. $TiH_2$ powder and camphene were used as the source materials of Ti and sublimable vehicles, respectively. Camphene slurries with $TiH_2$ content of 10 and 15 vol% were prepared by milling at $50^{\circ}C$ with a small amount of oligomeric polyester dispersant. Freezing of the slurry was done in a Teflon cylinder attached to a copper bottom plate cooled at $-25^{\circ}C$ while unidirectionally controlling the growth direction of the camphene. Pores were generated subsequently by sublimation of the camphene during drying in air for 48 h. The green body was heat-treated at $1100^{\circ}C$ for 1 h in a nitrogen and air atmosphere. XRD analysis revealed that the samples composed of TiN and $TiO_2$ phase were dependent on the heat-treatment atmosphere. The sintered samples showed large pores of about 120 mm which were aligned parallel to the camphene growth direction. The internal wall of the large pores had relatively small pores with a dendritic structure due to the growth of camphene dendrite depending on the degree of nucleation and powder rearrangement in the slurry. These results suggest that a porous body with an appropriate microstructure can be successfully fabricated by freeze-drying and a controlled sintering process of a camphene/$TiH_2$ slurry.

• 한국분말재료학회지
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• 제28권3호
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• pp.216-220
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• 2021

The effect of tert-butyl alcohol (TBA) as a freezing solvent on the pore structure of a porous tungsten body prepared by freeze-drying is analyzed. TBA slurries with a WO3 content of 10 vol% are prepared by mixing with a small amount of dispersant and binder at 30℃. The slurries are frozen at -25℃, and pores are formed in the frozen specimens by the sublimation of TBA during drying in air. After hydrogen reduction at 800℃ and sintering at 1000℃, the green body of WO₃ is completely converted to porous W with various pore structures. Directional pores from the center of the specimen to the outside are observed in the sintered bodies because of the columnar growth of TBA. A decrease in pore directionality and porosity is observed in the specimens prepared by long-duration drying and sintering. The change in pore structure is explained by the growth of the freezing solvent and densification.

• 한국분말재료학회지
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• 제18권2호
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• pp.105-111
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• 2011

This study investigated the effect of wire diameter and applied voltage on the fabrication of Ni-free Fe-based alloy nano powders by employing the PWE (pulsed wire evaporation) in liquid, for high temperature oxidation-resistant metallic porous body for high temperature particulate matter (or soot) filter system. Three different diameter (0.1, 0.2, and 0.3 mm) of alloy wire and various applied voltages from 0.5 to 3.0 kV were main variables in PWE process, while X-ray diffraction (XRD), field emission scanning microscope (FE-SEM), and transmission electron microscope (TEM) were used to investigate the characteristics of the Fe-Cr-Al nano powders. It was controlled the number of explosion events, since evaporated and condensed nano-particles were coalesced to micron-sized secondary particles, when exceeded to the specific number of explosion events, which were not suitable for metallic porous body preparation. As the diameter of alloy wire increased, the voltage for electrical explosion increased and the size of primary particle decreased.

• 한국분말재료학회지
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• 제28권4호
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• pp.331-335
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• 2021

The effects of drying temperature on the microstructure of porous W fabricated by the freeze-casting process of tert-butyl alcohol slurry with WO₃ powder was investigated. Green bodies were hydrogen-reduced at 800℃ for 1 h and sintered at 1000℃ for 6 h. X-ray diffraction analysis revealed that WO₃ powders were completely converted to W without any reaction phases by hydrogen reduction. The sintered body showed pores aligned in the direction of tert-butyl alcohol growth, and the porosity and pore size decreased as the amount of WO₃ increased from 5 to 10vol%. As the drying temperature of the frozen body increased from -25℃ to -10℃, the pore size and thickness of the struts increased. The change in microstructural characteristics based on the amount of powder added and the drying temperature was explained by the growth behavior of the freezing agent and the degree of rearrangement of the solid powder during the solidification of the slurry.