• Composites Research
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• v.20 no.5
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• pp.43-48
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• 2007

The absorption and the interference shielding of electromagnetic wave have been very important issues for commercial and military purposes. The stealth technique is one of the most typical applications of electromagnetic wave absorption technology. This study has started for the development of composite fillers containing dielectric and magnetic lossy materials. To improve the electromagnetic characteristics of conductive nano fillers, carbon nanofibers (CNFs) with nickel-phosphorous (Ni-P) or nickel-iron (Ni-Fe) have been fabricated by the electroless plating process. Observations by the electron microscopy (SEM/TEM) and element analyzer (EDS/ELLS) showed the uniform Ni-P and Ni-Fe coated CNFs. The compositions of the plating layers were about Ni-6wt%P and Ni-70wt%Fe, respectively. The average thicknesses of the plating layers were about $50\;{\sim}\;100\;nm$.

• The Journal of the Acoustical Society of Korea
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• v.43 no.1
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• pp.49-59
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• 2024

Recently, the electric vehicle market is gradually growing due to strengthened environmental regulations and high oil prices. also, in internal combustion engine vehicles, the sensitivity of Buzz, Squeak, Rattle (BSR) noise is increasing as engine Noise, Vibration, and Harshness (NVH)-related noise is reduced and technology for shielding noise coming from outside is developed. In this study, the stick-slip noise that occurs in Panoramic Curved Display (PCD) of automobile was analyzed for the correlation between the surface energy of polymer plastic and the polar component. For polar polymer materials, Acrylonitrile Butadiene Styrene (ABS) and PolyCarbonate-Acrylonitrile Butadiene Styrene (PC-ABS), compound materials were fabricated and evaluated. As a result, when the polar component of the polymer plastic was 3.86 mN/m or higher, stick-slip motion occurred, and as the absolute transition slope increased in the friction behavior over time, the possibility of stick-slip noise increased and the value of the friction coefficient The greater the difference, the greater the strength of the stick-slip noise.

• Journal of Radiation Industry
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• v.17 no.2
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• pp.173-181
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• 2023

3D printing is a technology that can transform and process computerized data obtained through modeling or 3D scanning via CAD. In the medical field, studies on customized 3D printing technology for clinical use or patients and diseases continue. The importance of research on filaments and molding methods is increasing, but research on manufacturing methods and available raw materials is not being actively conducted. In this study, we compare the characteristics of each material according to the manufacturing method of the phantom manufactured with 3D printing technology and evaluate its usefulness. We manufactured phantoms of the same size using poly methyl meta acrylate (PMMA), acrylonitrile butadiene styrene (ABS), and Poly Lactic Acid (PLA) based on the international standard phantom of aluminum step wedge. We used SITEC's radiation generator (DigiRAD-FPC R-1000-150) and compared the shielding rate and line attenuation coefficient through the average after shooting 10 times. As a result, in the case of the measured dose transmitted through each phantom, it was confirmed that the appearance of the dose measured for phantoms decreased linearly as the thickness increased under each condition. The sensitivity also decreased as the steps increased for each phantom and confirmed that it was different depending on the thickness and material. Through this study, we confirmed that 3D printing technology can be usefully used for phantom production in the medical field. If further development of printing technology and studies on various materials are conducted, it is believed that they will contribute to the development of the medical research environment.

• Journal of the Mineralogical Society of Korea
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• v.24 no.4
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• pp.289-300
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• 2011

Atomistic origins of carbon solubility into silicates are essential to understand the effect of carbon on the properties of silicates and evolution of the Earth system through igneous and volcanic processes. Here, we investigate the atomic structure and NMR properties of dissolved carbon in enstatite using Raman spectroscopy and quantum chemical calculations. Raman spectrum for enstatite synthesized with 2.4. wt% of amorphous carbon at 1.5 GPa and $1,400^{\circ}C$ shows vibrational modes of enstatite, but does not show any vibrational modes of $CO_2$ or ${CO_3}^{2-}$. The result indicates low solubility of carbon into enstatite at a given pressure and temperature conditions. Because $^{13}C$ NMR chemical shift is sensitive to local atomic structure around carbon and we calculated $^{13}C$ NMR chemical shielding tensors for C substituted enstatite cluster as well as molecular $CO_2$ using quantum chemical calculations to give insights into $^{13}C$ NMR chemical shifts of carbon in enstatite. The result shows that $^{13}C$ NMR chemical shift of $CO_2$ is 125 ppm, consistent with previous studies. Calculated $^{13}C$ NMR chemical shift of C is ~254 ppm. The current calculation will alllow us to assign potential $^{13}C$ NMR spectra for the enstatite dissolved with carbon and thus may be useful in exploring the atomic environment of carbon.

• Journal of radiological science and technology
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• v.26 no.3
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• pp.51-57
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• 2003

Mitigation of fast neutron irradiation damage on reactor vessel and improvement of mechanical integrity are desired for the successful plant life-time extension. In this study, the performance of metallic hydride for this application is reviewed and compared. First, selected prospective metallic hydrides are evaluated by MCNP code and put into the attenuation test using Cf-252 neutron source. Since for the reactor application high moderation and reflection with no absorption are favored, Z factor is introduced for the evaluation. According to the Z value estimation $ZrD_2$ and $TiD_2$ are turned out to be the most favorable fast neutron shielding materials. More thorough evaluation by computer simulation and experimentally, will be followed.

• The Journal of Korean Society for Radiation Therapy
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• v.25 no.1
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• pp.87-90
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• 2013

Purpose: Introducing CR (Computed Radiography) system created a process of printing therapy irradiation images and converting the degree of enlargement. This is to increase job efficiency and contribute to work improvement using a computerized method with home grown software to simplify this process, work efficiency. Materials and Methods: Microsoft EXCEL (ver. 2007) and VISUAL BASIC (ver. 6.0) have been used to make the software. A window for each shield block was designed to enter patients' treatment information. Distances on the digital images were measured, the measured data were entered to the Excel program to calculate the degree of enlargement, and printouts were produced to manufacture shield blocks. Results: By computerizing the existing method with this program, the degree of enlargement can easily be calculated and patients' treatment information can be entered into the printouts by using macro function. As a result, errors in calculation which may occur during the process of production or errors that the treatment information may be delivered wrongly can be reduced. In addition, with the simplification of the conversion process of the degree of enlargement, no copy machine was needed, which resulted in the reduction of use of paper. Conclusion: Works have been improved by computerizing the process of block production and applying it to practice which would simplify the existing method. This software can apply to and improve the actual conditions of each hospital in various ways using various features of EXCEL and VISUAL BASIC which has already been proven and used widely.

• Journal of the Korean Society of Radiology
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• v.15 no.7
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• pp.975-982
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• 2021

The purpose of this study is to evaluate the effect on the phantom for magnetic resonance imaging located nearby by partially shielding RF with a mesh made thinner than hair composed of copper, black metal, and polyester using metallic materials of titanium, which are commonly used for esophageal stents and implants in the body. Magnetic resonance images according to field of view (FOV) were analyzed in the Spin Echo T1 weighted images of TR 500 ms, TE 20 ms, NEX 1, and slice thickness 5mm using a Cardiac coil of 3T Achieva X-series. Aliasing artifact did not occur in FOV 304 mm × 304 mm, but it occurred in 250 mm × 250 mm and 170 mm × 170 mm. In FOV 170 mm × 170 mm, when a mesh was not used, the SNR was measured with 78.23, and when separated by standing a mesh in the middle, it was 215.05, and when completely shielded with a mesh, the SNR was 366.44. In addition, when completely shielded with a mesh, the aliasing artifact was also removed, and signal intensities on the left, middle and right of the image were also able to obtain homogeneous images compared to the previous two cases. In conclusion, if RF is partially shielded with a mesh, aliasing artifact can be removed, and magnetic resonance images with excellent image resolution and homogeneity can be obtained using a small FOV.

• Applied Chemistry for Engineering
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• v.22 no.6
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• pp.672-678
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• 2011

In this work, carbon fibers were electrolessly Ni-plated in order to investigate the effect of metal plating on the electromagnetic shielding effectiveness (EMI-SE) of Ni-coated carbon fibers-reinforced epoxy matrix composites. The surfaces of carbon fibers were characterized by scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS). Electric resistance of the composites was tested using a 4-point-probe electric resistivity tester. The EMI-SE of the composites was evaluated by means of the reflection and adsorption methods. From the results, it was found that the EMI-SE of the composites enhanced with increasing Ni plating time and content. In high frequency region, the EMI-SE didn't show further increasing with high Ni content (Ni-CF 10 min) compared to the Ni-CF 5 min sample. In conclusion, Ni content on the carbon fibers can be a key factor to determine the EMI-SE of the composites, but there can be an optimized metal content at a specific electromagnetic frequency region in this system.

• Corrosion Science and Technology
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• v.8 no.2
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• pp.62-67
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• 2009

Ti and Ti-alloys have good biocompatibility, appropriate mechanical properties and excellent corrosion resistance. However, the widely used Ti-6Al-4V is found to release toxic ions (Al and V) into the body, leading to undesirable long-term effects. Ti-6Al-4V has much higher elastic modulus (100 GPa) than cortical bone (20 GPa). Therefore, titanium alloys with low elastic modulus have been developed as biomaterials to minimize stress shielding. The electrochemical behavior of surface-modified and MC3T3-E1 cell-cultured Ti-30(Nb,Ta) alloys with low elastic modulus have been investigated using various electrochemical methods. Surfaces of test samples were treated as follows: $0.3{\mu}m$ polished; $25{\mu}m$, $50{\mu}m$ and $125{\mu}m$ sandblasted. Specimen surfaces were cultured with MC3T3-E1 cells for 2 days. Average surface roughness ($R_a$) and morphology of specimens were determined using a surface profilometer, OM, and FE-SEM. Corrosion behavior was investigated using a potentiostat(EG&G PARSTAT 2273), and electrochemical impedance spectroscopy was performed (10 mHz to 100 kHz) in 0.9% NaCl solution at $36.5{\pm}1^{\circ}C$. The microstructures of the Ti-30(Ta,Nb) alloys had a needle-like appearance. The $R_a$ of polished Ti-30Ta and Ti-30Nb alloys was lower than that of the sandblasted Ti alloy. Cultured cells displayed round shapes. For polished alloy samples, cells were well-cultured on all surfaces compared to sandblasted alloy samples. In sandblasted and cell-cultured Ti-30(Nb,Ta) alloy, the pitting potential decreased and passive current density increased as $R_a$ increased. Anodic polarization curves of cell-cultured Ti alloys showed unstable behavior in the passive region compared to non-cell-cultured alloys. From impedance tests of sandblasted and cell-cultured alloys, the polarization resistance decreased as $R_a$ increased, whereas, $R_a$ for cell-cultured Ti alloys increased compared to non-cell-cultured Ti alloys.

• Proceedings of the Korean Powder Metallurgy Institute Conference
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• 2002.07a
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• pp.25-37
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• 2002

The most important industrial application of gamma radiation in characterizing green compacts is the determination of the density. Examples are given where this method is applied in manufacturing technical components in powder metallurgy. The requirements imposed by modern quality management systems and operation by the workforce in industrial production are described. The accuracy of measurement achieved with this method is demonstrated and a comparison is given with other test methods to measure the density. The advantages and limitations of gamma ray densitometry are outlined. The gamma ray densitometer measures the attenuation of gamma radiation penetrating the test parts (Fig. 1). As the capability of compacts to absorb this type of radiation depends on their density, the attenuation of gamma radiation can serve as a measure of the density. The volume of the part being tested is defined by the size of the aperture screeniing out the radiation. It is a channel with the cross section of the aperture whose length is the height of the test part. The intensity of the radiation identified by the detector is the quantity used to determine the material density. Gamma ray densitometry can equally be performed on green compacts as well as on sintered components. Neither special preparation of test parts nor skilled personnel is required to perform the measurement; neither liquids nor other harmful substances are involved. When parts are exhibiting local density variations, which is normally the case in powder compaction, sectional densities can be determined in different parts of the sample without cutting it into pieces. The test is non-destructive, i.e. the parts can still be used after the measurement and do not have to be scrapped. The measurement is controlled by a special PC based software. All results are available for further processing by in-house quality documentation and supervision of measurements. Tool setting for multi-level components can be much improved by using this test method. When a densitometer is installed on the press shop floor, it can be operated by the tool setter himself. Then he can return to the press and immediately implement the corrections. Transfer of sample parts to the lab for density testing can be eliminated and results for the correction of tool settings are more readily available. This helps to reduce the time required for tool setting and clearly improves the productivity of powder presses. The range of materials where this method can be successfully applied covers almost the entire periodic system of the elements. It reaches from the light elements such as graphite via light metals (AI, Mg, Li, Ti) and their alloys, ceramics ($AI_20_3$, SiC, Si_3N_4, $Zr0_2$, ...), magnetic materials (hard and soft ferrites, AlNiCo, Nd-Fe-B, ...), metals including iron and alloy steels, Cu, Ni and Co based alloys to refractory and heavy metals (W, Mo, ...) as well as hardmetals. The gamma radiation required for the measurement is generated by radioactive sources which are produced by nuclear technology. These nuclear materials are safely encapsulated in stainless steel capsules so that no radioactive material can escape from the protective shielding container. The gamma ray densitometer is subject to the strict regulations for the use of radioactive materials. The radiation shield is so effective that there is no elevation of the natural radiation level outside the instrument. Personal dosimetry by the operating personnel is not required. Even in case of malfunction, loss of power and incorrect operation, the escape of gamma radiation from the instrument is positively prevented.