• Korean Journal of Metals and Materials
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• v.48 no.4
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• pp.335-341
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• 2010

High-quality single-walled carbon nanotubes (SWCNTs) were synthesized by catalytic decomposition of $C_2H_2$ using Fe-Mo/MgO catalyst at $800^{\circ}C$. The as-synthesized SWCNTs typically occurred in the form of a bundle with a diameter of 10~20 nm together with amorphous carbon and catalytic impurities, which were removed by a two-step purification process consisting of oxidation and an acid treatment. The oxidation step, using an $O_2$-Ar mixture at $380^{\circ}C$ for 5 hr in a vertical-type furnace and a $HNO_3$ treatment at $100^{\circ}C$ for one hour, was utilized to remove the amorphous carbon particles. Subsequently, metallic catalysts were removed in HCl at room temperature for 5 hr under magnetic stirring. The SWCNT suspension was prepared by dispersing the purified SWCNTs in an aqueous sodium dodecyl benzene sulfonate solution with horn-type sonication. This was then air-sprayed on glass to fabricate CNT field emitters. The samples had a turn-on field value of 4 V/${\mu}m$ and a current density of 0.67 mA/$cm^2$ at 9 V/${\mu}m$. Increasing the HCl treatment time improved the field emission properties.

• Proceedings of the Korean Vacuum Society Conference
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• 2000.02a
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• pp.173-173
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• 2000

Multilayered films (MLF) consisting of transition metals and semiconductors have drawn a great deal of interest because of their unique properties and potential technological applications. Fe/Si MLF are a particular topic of research due to their interesting antiferromagnetic coupling behavior. although a number of experimental works have been done to understand the mechanism of the interlayer coupling in this system, the results are controversial and it is not yet well understood how the formation of an iron silicide in the spacer layers affects the coupling. The interpretation of the coupling data had been hampered by the lack of knowledge about the intermixed iron silicide layer which has been variously hypothesized to be a metallic compound in the B2 structure or a semiconductor in the more complex B20 structure. It is well known that both magneto-optical (MO0 and optical properties of a metal depend strongly on their electronic structure that is also correlated with the atomic and chemical ordering. In order to understand the structure and physical properties of the interfacial regions, Fe/Si multilayers with very thin sublayers were investigated by the MO and optical spectroscopies. The Fe/si MLF were prepared by rf-sputtering onto glass substrates at room temperature with a totall thickness of about 100nm. The thicknesses of Fe and Si sublayers were varied from 0.3 to 0.8 nm. In order to understand the fully intermixed state, the MLF were also annealed at various temperatures. The structure and magnetic properties of Fe/Si MLF were investigated by x-ray diffraction and vibrating sample magnertometer, respectively. The MO and optical properties were measured at toom temperature in the 1.0-4.7 eV energy range. The results were analyzed in connection with the MO and optical properties of bulk and thin-film silicides with various structures and stoichiometries.

• The Journal of Advanced Prosthodontics
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• v.16 no.2
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• pp.77-90
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• 2024

PURPOSE. The study aims to investigate the influence of the ferrule effect and types of posts on the stress distribution in three morphological types of the maxillary central incisor. MATERIALS AND METHODS. Nine models were created for 3 maxillary central incisor morphology types: "Fat" type - crown 12.5 mm, root 13 mm, and buccolingual cervical diameter 7.5 mm, "Medium" type - crown 11 mm, root 14 mm, and buccolingual cervical diameter 6.5 mm, and "Slim" type - crown 9.5 mm, root 15 mm, and buccolingual cervical diameter 5.5 mm. Each model received an anatomical castable post-and-core or glass-fiber post with resin composite core and three ferrule heights (nonexistent, 1 mm, and 2 mm). Then, a load of 14 N was applied at the cingulum with a 45° slope to the long axis of the tooth. The Maximum Principal Stress and the Minimum Principal Stress were calculated in the root dentin, crown, and core. RESULTS. Higher tensile and compression stress values were observed in root dentin using the metallic post compared to the fiber post, being higher in the slim type maxillary central incisor than in the medium and fat types. Concerning the three anatomical types of maxillary central incisors, the slim type without ferrule height in mm presented the highest tensile stress in the dentin, for both types of metal and fiber posts. CONCLUSION. Post system and tooth morphology were able to modify the biomechanical response of restored endodontically-treated incisors, showing the importance of personalized dental treatment for each case.

• Journal of the Korean Society for Nondestructive Testing
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• v.24 no.5
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• pp.508-517
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• 2004

We described a near-field scanning microwave microscope which uses a high-quality dielectric resonator with a tunable screw. The operating frequency is f=4.5 5GHz. The probe tip is mounted in a cylindrical resonant cavity coupled to a dielectric resonator We developed a hybrid tip combining a reduced length of the tapered part with a small apex. In order to understand the function of the probe, we fabricated three different tips using a conventional chemical etching technique and observed three different NSMM images for patterened Cr films on glass substrates. We measured the reflection coefficient of different metal thin film samples with the same thickness of 300m and compared with theoretical impedance respectly. By tuning the tunable screw coming through the top cover, we could improve sensitivity, signal-to-noise ratio, and spatial resolution to better than $1{\mu}m$. To demonstrate the ability of local microwave characterization, the surface resistance of metallic thin films has been mapped.

• The Journal of Korean Academy of Prosthodontics
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• v.40 no.3
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• pp.287-295
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• 2002

Statement of Problem. Endodontically treated teeth frequently required posts and cores to provide retention and resistance form for crowns. In spite of excellent mechanical properties of metal post and core, its metallic color can be detected through all ceramic restorations occasionally. To solve esthetic problems of metal post and core zirconia post system has been introduced recently. Purpose. The purpose of this study was to examine the fracture strength and mode of resin root analogs restored with zirconia, gold and titanium posts with resin, ceramic and metal cores after cementation with metal crowns. Materials and methods. To avoid the morphological variations of natural teeth, 40 root analogs were fabricated with composite resin. Forty resin root analogs were randomly assigned to four groups according to post and core materials: Group A: cast gold post and core and complete cast crowns, as control. Group B: titanium posts (Parapost, Coltent/Whaledent Inc., NJ, USA) and composite resin cores. Group C: zirconia posts (Cosmopost, Ivoclar AG, Schaan/Liechtenstein) and composite resin cores Group D: zirconia posts and heat-pressed ceramic cores (IPS Empress Cosmo Ingots, Ivoclar AG) After thermocycling ($5^{\circ}C{\sim}55^{\circ}C$, 30 sec.), cyclic loading was applied at 3mm below the incisal edge on the palatal surfaces at an angle of 135 degree to the long axis (2Hz, 50N, 50000cycles). Fracture strength was measured by universal testing machine (Instron, High Wycombe, UK) and fracture pattern of restored resin root analogs was also evaluated. Results and conclusion. Within the limitations of this study following results were drawn. 1. Resin root analogs restored with zirconia posts and composite resins demonstrated lowest fracture strength among tested groups. 2. There was no significant difference in the fracture strength between zirconia posts and heat pressed glass ceramic cores and cast gold posts and cores 3. The fracture strength of resin root analogs restored with titanium posts and composite resin cores was lower than that of gold posts and cores. 4. The deep oblique fracture lines were dominantly observed in root analogs restored with cast gold post and core and zirconia post and heat-pressed ceramic core groups.

• Journal of Conservation Science
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• v.30 no.2
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• pp.111-122
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• 2014

In Bongseon-ri site, the central type and the local type of the Baekje tombs co-exist together. Many swords with ring pommel which to regional leaders in Seocheon the Beekje government granted are excavated from these tombs. These represent that the regional leaders were controlled by the Baekje government gradually. Four swords with ring pommel and one simple sword are investigated metallurgically and we seek what swords have a function of weapon or what sword produce for grave goods. The simple sword is made by solid carburizing technology and quenching of heat treatment so it's possibly used as a weapon. In contrast, four swords with ring pommel has little chance of weapon because the blade of swords consists of microstructure that have low hardness and the back of swords don't have microstructure can absorb the shock. The most identical characteristic of the simple sword and swords with ring pommel is that they are possible to classify clearly into practical/non-practical tools. Additionally, according to non-metallic inclusion analysis result of these swords, w$\ddot{u}$stite and glass phase are found together. Thus, it is able to say that reduction method in low temperature is applied during smelting process.

• Journal of the Korean Society for Nondestructive Testing
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• v.28 no.1
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• pp.16-24
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• 2008

Near-field scanning microwave microscope (NSMM) has been used to characterize the electromagnetic properties of samples based on a cavity perturbation technique. We used a NSMM using a waveguide cavity to couple a metallic probe tip as a point like evanescent field emitter. We explained the quality of our NSMM system by applying the cavity perturbation theory. First, to make a shape perturbation, we inserted linear and loop probes in the waveguide resonator. To check up electric and magnetic field distribution inside the waveguide resonator by shape perturbation, we confirmed the field distribution by using a HFSS simulation. Second, to make material perturbation, we located a dielectric sample in front of the probe tip and measured reflection coefficient $(S_{11})$. We found that the resonance frequency$(f_r)$ was changed linearly as the dielectric constant of resonator$({\varepsilon}_r)$ increased when ${\Delta}{\varepsilon}\;and\;{\Delta}{\mu}$ were small.

• Journal of Nuclear Fuel Cycle and Waste Technology(JNFCWT)
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• v.14 no.2
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• pp.169-178
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• 2016

The properties of wastes for melting need to be considered to minimize the maintenance of refractory and to discharge the molten slags smoothly from a plasma torch melter. When the nonflammable wastes from nuclear facilities such as concrete debris, glass, sand, etc., are melted, they become acid slags with low basicity since the chemical composition has much more acid oxides than basic oxides. A molten slag does not have good characteristics of discharge and is mainly responsible for the refractory erosion due to its low liquidity. In case of a stationary plasma torch melter with a slant tapping port on the wall, a fixed amount of molten slags remains inside of tapping hole as well as the melter inside after tapping out. Nonmetallic slags keep the temperature higher than melting point of metal because metallic slags located on the bottom of melter by specific gravity difference are simultaneously melted when dual mode plasma torch operates in transferred mode. In order to minimize the refractory erosion, the compatible refractories are selected considering the temperature inside the melter and the melting behavior of slags whether to contact or noncontact with molten slags. An acidic refractory shall not be installed in adjacent to a basic refractory for the resistibility against corrosion.

• Journal of Sensor Science and Technology
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• v.8 no.2
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• pp.115-123
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• 1999

A micro-gas sensor with heater and sensing electrode on the same plane was fabricated on phosphosilicate glass(PSG, 800nm)/$Si_3N_4$ (150nm) dielectric membrane. PSG film was provided by atmospheric pressure chemical vapor deposition(APCVD), and $Si_3N_4$ film by low pressure chemical vapor deposition (LPCVD). Total area of the fabricated device was $3.78{\times}3.78mm^2$. The area of diaphragm was $1.5{\times}1.5mm^2$, and that of the sensing layer was $0.24{\times}0.24mm^2$. Finite-element simulation was employed to estimate temperature distribution for a square-shaped diaphragm. The power consumption of Pt heater was about 85mW at $350^{\circ}C$. Tin thin films were deposited on the silicon substrate by thermal evaporation at room temperature and $232^{\circ}C$, and tin oxide films($SnO_2$) were prepared by thermal oxidation of the metallic tin films at $650^{\circ}C$ for 3 hours in oxygen ambient. The film analyses were carried out by SEM and XRD techniques. Effects of humidity and ambient temperature on the resistance of the sensing layer were found to be negligible. The fabricated micro-gas sensor exhibited high sensitivity to butane gas.

• Korean Journal of Optics and Photonics
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• v.28 no.1
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• pp.9-15
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• 2017

We precisely measured and analyzed the dynamics of peptide-antibody interactions, using an ellipsometric biosensor based on a silicon substrate. To reduce the signal error due to the imperfect flatness of the substrate for extremely low concentrations of peptide, we fabricated the biosensor with a silicon substrate coated with Dextran SAM, instead of a glass prism coated with a thin metallic thin film. At an injection speed of $100{\mu}l/min$ of buffer liquid, we detected the dynamics of antibody-Dextran SAM or peptide-antibody fixed on biosensor, respectively. We detected the dynamics of antibody-Dextran SAM interactions down to a low concentration of 5 ng per liter, and we precisely measured the dynamics of association and dissociation of peptide and antibody down to 100 nM of peptide. We obtained the rate constants for association and dissociation from fitting the data by using deduced dynamical equation. As a result, we obtained an equilibrium constant for dissociation of 97 nM of peptide-antibody complex, which belongs to Class I.