• Journal of the Korea Concrete Institute
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• v.26 no.3
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• pp.315-321
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• 2014

Concrete as a construction material is widely used in nuclear vessel and plant for excellent radiation shielding. However the isolation characteristics in concrete may affect adversely in the case of fire and melt-down in nuclear vessel since temperature cooling down is very difficult from outside. This study is for development of high thermal conductive concrete, and its mechanical and thermal properties are evaluated. Magnetite aggregates with volume ratio of 42.3% (maximum) and steel powder of 1.5% are replaced with normal aggregates and thermal properties are evaluated. Thermal conductivity little increases by 30% addition of magnetite but rapidly increases afterwards. Finally thermal conductivity is magnified to 2.5 times in the case of 42.3% addition of magnetite. Steel powder has a positive effect on high thermal conduction to 106~113%. Several models for thermal conduction like ACI, DEMM, and MEM are compared with test results and they are verified to reasonably predict the thermal conductivity with increasing addition of magnetite aggregates and steel powder.

• Journal of the Korean Ceramic Society
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• v.42 no.3 s.274
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• pp.155-164
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• 2005

The characteristics of sintering for Mullite-Cordierite (MC) composites and the effect of $TiO_2$ addition were studied. The MC composites were manufactured by a solution-polymerization method using PVA as a polymer carrier, and $TiO_2$ was used as a sintering agent. They were calcined at $1300^{\circ}C$, planetary milled for 4 h and sintered at $1450^{\circ}C$. As cordierite content increased, relative density of materials was increased up to $98\%$ and sinterability was improved. In case of $50\;wt\%$ mullite/$5\;wt\%$ cordierite composition sintered for 16 h, the flexural strength and thermal expansion coefficient were 190 MPa and $3.07{\times}0^{-6}/^{\circ}C$, respectively. However, mechanical properties were decreased with the cordierite contents higher than $50\;wt\%$ because of the excess liquid-phase amount. As the addition of $TiO_2$ is increased, columnar crystal of mullite and liquid-phase contents were increased. In particular, the flexural strength and thermal expansion coefficient decreased in case of $5\;wt\%\;TiO_2$ addition.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.27 no.5
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• pp.235-242
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• 2017

In order to prepare porous scaffolds capable of pore control, PMMA powder serving as a pore-forming agent was added to HA powder to synthesize a slurry containing TBA as a solvent. And then, porous HA scaffolds where pillarshaped pore channels interconnected with each other were fabricated by freeze-casting and sintering. The crystal structure of the HA scaffolds according to the addition amount of PMMA powder was measured by XRD and the surface and inner cross section of the scaffolds were analyzed through SEM. It was found that removal of PMMA during sintering affects the internal structure of the scaffolds and the crystallinity of the HA powder. Furthermore, through evaluating the physical and mechanical properties of the scaffolds, it was confirmed that the porosity, pore size and compressive strength can be controlled by controlling the addition amount of the pore-forming agent. It was also found that the HA scaffolds produced in this study were similar in structure and properties to the natural cancellous bone. This suggests that porous HA scaffolds with PMMA can be used as an alternative to autogenous bone for tissue engineering as an artificial bone scaffold.

• Journal of the Korea Concrete Institute
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• v.28 no.3
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• pp.299-308
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• 2016

This paper presents an investigation of the mechanical and microstructural properties on hardened samples that were synthesized using blended binder(fly ash(FA) and blast furnace slag cement(BFSC)), alkali activator and sea water or distilled water. Binders were prepared by mixing the FA and BFSC in different blend weight ratios of 6:4, 7:3 and 8:2. Sodium hydroxide and sodium silicate were used 5 wt% of binder, respectively, as an alkaline activator. The compressive strength and absorption were measured at the age of 3, 7 and 28 days, and the XRD, TGA and MIP tests were performed at the age of 28 days. An increase in the content of BFSC leads to an increase in the quantities of ettringite and C-S-H formed, regardless of the type of mixing water. And it also shows higher strength due to the reduction of pores larger than ~50 nm. All hardened samples in this study have common hydration products of C-S-H, $Ca(OH)_2$ and calcite. Hydrocalumite of all reaction products formed was only present in hardened sample mixed with sea water. For each FA/BFSC mixing ratio, the compressive strength of hardened sample mixed with sea water was similar to that mixed with distilled water. It is proposed that the slight increase of strength of samples mixed with sea water is mainly due to the presence of hydrocalumite phase containing chlorine ion, contributing to the change of total porosity and pore size distribution in samples.

• 전자공학회논문지 IE
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• v.49 no.2
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• pp.1-8
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• 2012

The effects of the addition of either monoclinic $ZrO_2(pure)$ or tetragonal $ZrO_2$ containing 5.35wt% $Y_2O_3(Y-TZP)$ on the mechanical properties and thermal shock resistance of $Al_2O_3$ ceramics were investigated. The addition of $ZrO_2$(m) and Y-TZP increased sintered density of $Al_2O_3$. The Vickers hardness also increased as the volume fraction of Y-TZP increased going through a maximum at 20wt%. The hardness of the specimens was found to be dependent on the sintered density. The higher volume fraction of either $ZrO_2(m)$ or Y-TZP resulted in the higher fracture toughness of the composite was. This result may be taken as evidence that toughening of $Al_2O_3$ can be achieved by not only the transformation toughening but microcrack toughening of $ZrO_2$. The thermal shock property for $Al_2O_3-ZrO_2$ composites was improved by increasing the volume fraction of monoclinic $ZrO_2(pure)$. The grain size increased as the volume fraction of $ZrO_2$ did.

• Journal of Dental Rehabilitation and Applied Science
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• v.26 no.3
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• pp.323-337
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• 2010

The objective of this study was to examine the availability of the new impression coping by comparing with conventional coping in implant pick-up impression technique. Five implant fixtures were installed on #14, 21, 23, 25, 27 in acrylic resin model. That model with 5 fixtures was standard model, which was divided 3 groups; using new flag type impression coping, conventional impression coping splinted with self-curing resin, conventional impression coping without splinting. We made metal circular cones for calculation 3-dimensional coordinates by attaching to implant fixtures or analogs. Three-dimensional relationships of each model were calculated. Data was analyzed by multiple ANOVA and Bonferroni. The accuracy of impression between using new flag type impression coping and conventional impression coping did not show differences in 3 - dimensional analysis.Within limitations of this study, the new flag type impression coping is available in implant pick-up impression technique.

• Journal of Periodontal and Implant Science
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• v.50 no.2
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• pp.106-120
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• 2020

Purpose: A new form of porous polyethylene, characterized by higher porosity and pore interconnectivity, was developed for use as a tissue-integrated implant. This study evaluated the effectiveness of porous polyethylene blocks used as an onlay bone graft in rabbit mandible in terms of tissue reaction, bone ingrowth, fibrovascularization, and graft-bone interfacial integrity. Methods: Twelve New Zealand white rabbits were randomized into 3 treatment groups according to the study period (4, 12, or 24 weeks). Cylindrical specimens measuring 5 mm in diameter and 4.5 mm in thickness were placed directly on the body of the mandible without bone bed decortication, fixed in place with a titanium screw, and covered with a collagen membrane. Histologic and histomorphometric analyses were done using hematoxylin and eosin-stained bone slices. Interfacial shear strength was tested to quantify graft-bone interfacial integrity. Results: The porous polyethylene graft was observed to integrate with the mandibular bone and exhibited tissue-bridge connections. At all postoperative time points, it was noted that the host tissues had grown deep into the pores of the porous polyethylene in the direction from the interface to the center of the graft. Both fibrovascular tissue and bone were found within the pores, but most bone ingrowth was observed at the graft-mandibular bone interface. Bone ingrowth depth and interfacial shear strength were in the range of 2.76-3.89 mm and 1.11-1.43 MPa, respectively. No significant differences among post-implantation time points were found for tissue ingrowth percentage and interfacial shear strength (P>0.05). Conclusions: Within the limits of the study, the present study revealed that the new porous polyethylene did not provoke any adverse systemic reactions. The material promoted fibrovascularization and displayed osteoconductive and osteogenic properties within and outside the contact interface. Stable interfacial integration between the graft and bone also took place.

• Journal of the Korean Electrochemical Society
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• v.2 no.2
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• pp.81-87
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• 1999

Poly-acrylonitrile (PAN) based carbon fibers were stabilized under various tensions in the presence of air at about $200^{\circ}C$ and sequentially carbonized under some different gas environments in the range of 700 to $1500^{\circ}C$. The prepared carbon fibers were used for rechargeable lithium ion battery anode to investigate preparation parameters effects on electrochemical characteristics. It was found that the tension during stabilization, carbonization temperature and gas atmospheres affect the carbon fiber properties such as conductivity, mechanical strength, surface morphology and diffusion coefficient of lithium ion, which are closely related to the on electrolchemical properties as well as the charge/discharge characteristics.

• Journal of Broadcast Engineering
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• v.14 no.6
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• pp.692-702
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• 2009

Real-time virtual studios which could run only on expensive workstations are now available for personal computers thanks to the recent development of graphics hardware. Nevertheless, graphics are rendered off-line in the post production stage in film or TV drama productions, because the graphics' quality is still restricted by the real-time hardware. Software-based camera tracking methods taking only the source video into account take much computation time, and often shows unstable results. To overcome this restriction, we propose a system that stores camera motion data from sensors at shooting time as common virtual studios and uses them in the post production stage, named as POVIS(post virtual imaging system). For seamless registration of graphics onto the camera video, precise zoom lens calibration must precede the post production. A practical method using only two planar patterns is used in this work. We present a method to reduce the camera sensor's error due to the mechanical mismatch, using the Kalman filter. POVIS was successfully used to track the camera in a documentary production and saved much of the processing time, while conventional methods failed due to lack of features to track.

• Progress in Medical Physics
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• v.20 no.3
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• pp.119-124
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• 2009

Stents are frequently used throughout the human body. They keep pathways open in vascular or nonvascular duct for a long time. Therefore its stability is very important factor. In recent years, aconsiderable amount of research has been carried out in order to estimate mechanical properties of the stent such as expansion pressure behavior, radial recoil and longitudinal recoil using FEM (Finite element analyses). However, published works on simulation of stent fatigue behavior using FEM are relatively rare. In this paper, a nonlinear finite-element methodwas employed to analyses the compression of a stent using external pressure and fatigue behavior. Finite element analyses for the stent system were performed using NASTRAN FX. In conclusion this paper shows how the stent is behaved in the body, and its fatigue behavior.