• Journal of Powder Materials
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• v.15 no.3
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• pp.221-226
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• 2008

Silver coated copper composite powders were prepared by electroless plating method by controlling the activation and deposition process variables such as feeding rate of silver ions solution, concentration of reductant and molar ratio of activation solution $(NH_4OH/(NH_4)_2SO_4)$ at room temperature. The characteristics of the product were verified by using a scanning electron microscopy (SEM), X-ray diffraction (XRD) and atomic absorption (A.A.). It is noted that completely cleansing the copper oxide layers and protecting the copper particles surface from hydrolysis were important to obtain high quality Ag-Cu composite powders. The optimum conditions of Ag-Cu composite powder synthesis were $NH_4OH/(NH_4)_2SO_4$ molar ratio 4, concentration of reductant 15g/l and feeding rate of silver ions solution 2 ml/min.

• Composites Research
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• v.28 no.3
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• pp.124-129
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• 2015

CNT and GNP have several excellent mechanical properties including, high strength, Young's modulus, thermal conductivity, corrosion resistance, electronic shielding and so on. In this study, CF/CNT, GNP/epoxy composites were manufactured by varying the CNT weight ratio at 2wt% and 3wt%, GNP weight ratio at 0.5wt% and 1 wt%. The composites were manufactured by mechanical method (3-roll-mill). Tensile, impact and wear tests were performed according to ASTM standards D638, D256 and D3181 respectively. The results showed that, CF/GNP0.5 wt%/epoxy composites gave good mechanical property in all composites, e.g., tensile strength, impact and were resistance.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 2013.05a
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• pp.503-506
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• 2013

The shielding coefficient of a conductive length structure is calculated by a ratio of induced voltage with that structure to without that structure. The environments are different between with a structure and without a structure. Beside the corresponding structure, all the parameters related to induced voltage should be normalized to a presumable same environment conditions. Basically each parameter must be compensated, which is a bottom-up type method. In this case, some parameter is not possible to be so because of its unknowing function. Then as a calculated voltage already has all characteristics of parameters, seeking a ratio of calculated induction voltages themselves will include the compensation of all parameters automatically. This is a top-down method.

• Journal of Welding and Joining
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• v.32 no.2
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• pp.22-28
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• 2014

To enhance productivity and provide high quality production material in a GMA welding process, weld quality, productivity and cost reduction affects the number of process variables. In addition, a reliable welding process and conditions must be implemented to reduce weld structure failure. In various industries the welding process mathematical model is not fully formulated for the process parameter and on the welding conditions, therefore only partial variables can be predicted. The research investigates the interaction between the welding parameters (welding speed, distance between electrodes, and flow rate of shielding gas) and bead geometry for predicting the weld bead geometry (bead width, bead height). Taguchi techniques are applied to bead shape to develope curve equation for predicting the optimized process parameters and quality characteristics by analyzing the S/N ratio. The experimental results and measured error is within the range of 10% presenting satisfactory accuracy. The curve equation was developed in such a way that you can predict the bead geometry of constructed machinery that can be used for making tandem welding process.

• Nuclear Engineering and Technology
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• v.54 no.7
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• pp.2614-2624
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• 2022

Monte Carlo simulations were used to model a portable Neutron backscattering (NBT) sensor suitable for detecting plastic anti-personnel mines (APMs) buried in dry and moist soils. The model consists of a 100 MBq ²⁵²Cf source encapsulated in a neutron reflector/shield assembly and centered between two ³He detectors. Multi-parameter optimization was performed to investigate the efficiency of Be/Zr(BH₄)₄ and Be/Be(BH₄)₂ assemblies in terms of increasing the signal-to-background (S/B) ratio and reducing the total dose equivalent rate. The MCNP results showed that 2 cm Be/3 cm Zr(BH₄)₄ and 2 cm Be/3 cm Be(BH₄)₂ are the optimal configurations. However, due to portability requirements and abundance of Be, the ²⁵²Cf-2 cm Be/3 cm Be(BH₄)₂ NBT model was selected to scan the center of APM buried 3 cm deep in dry and moist soils. The selected NBT model has positively identified the APM with a S/B ratio of 886 for dry soils of 1 wt% hydrogen content and with S/B ratios of 615, 398, 86, and 12 for the moist soils containing 4, 6, 10, and 14 wt% hydrogen, respectively. The total dose equivalent rate reached 0.0031 mSv/h, suggesting a work load of 8 h/day for 806 days within the permissible annual dose limit of 20 mSv.

• Nuclear Engineering and Technology
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• v.53 no.6
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• pp.2000-2010
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• 2021

Mechanical moduli, such as Young's modulus (E), Bulks modulus (B), Shear modulus (S), longitudinal modulus (L), Poisson's ratio (σ) and micro Hardness (H) were theoretically calculated for (100-x)TeO₂+x MgO glasses, where x = 10, 20, 30, 40 and 45 mol%, based on the Makishima-Mackenzie model. The estimated results showed that the mechanical moduli and the microhardness of the glasses were improved with the increase of the MgO contents in the TM glasses, while Poisson's ratio decreased with the increase in MgO content. Moreover, the radiation shielding capacity was evaluated for the studied TM glasses. Thus, the linear attenuation coefficient (LAC), mass attenuation coefficient (MAC), transmission factor (TF) and half-value thickness (𝚫_0.5) were simulated for gamma photon energies between 0.344 and 1.406 MeV. The simulated results showed that glass TM10 with 10 mol % MgO possess the highest LAC and varied in the range between 0.259 and 0.711 cm^-1, while TM45 glass with 45 mol % MgO possess the lowest LAC and vary in the range between 0.223 and 0.587 cm^-1 at gamma photon energies between 0.344 and 1.406 MeV. Furthermore, the BXCOM program was applied to calculate the effective atomic number (Z_eff), equivalent atomic number (Z_eq) and buildup factors (EBF and EABF) of the glasses. The effective removal cross-section for the fast neutrons (ERCSFN, ∑_R) was also calculated theoretically. The received data depicts that the lowest ∑_R was achieved for TM10 glasses, where ∑_R = 0.0193 cm² g^-1, while TM45 possesses the highest ERCSFN where ∑_R = 0.0215 cm² g^-1.

• Nuclear Engineering and Technology
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• v.55 no.5
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• pp.1587-1592
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• 2023

Time-encoded imagers (TEI) are important class of instruments to search for potential radioactive sources to prevent illicit transportation and trafficking of nuclear materials and other radioactive sources. The energy of the radiation cannot be known in advance due to the type and shielding of source is unknown in practice. However, the response function of the time-encoded imagers is related to the energy of neutrons or gamma-rays. An improved image reconstruction method based on MLEM was proposed to correct for the energy induced response difference. In this method, the count vector versus time was first smoothed. Then, the preset response function was adaptively corrected according to the measured counts. Finally, the smoothed count vector and corrected response were used in MLEM to reconstruct the source distribution. A one-dimensional dual-particle time-encode imager was developed and used to verify the improved method through imaging an Am-Be neutron source. The improvement of this method was demonstrated by the image reconstruction results. For gamma-ray and neutron images, the angular resolution improved by 17.2% and 7.0%; the contrast-to-noise ratio improved by 58.7% and 14.9%; the signal-to-noise ratio improved by 36.3% and 11.7%, respectively.

• Applied Chemistry for Engineering
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• v.9 no.3
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• pp.342-347
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• 1998

Light-weight conductive polymer composites were prepared by incorporating polyheterocycles such as polypyrrole and polythiophene into pores of a highly porous cross-linked polystyrene, host polymer, to form a conductive network. The highly hydrophobic and porous host polymer was synthesized by concentrated emulsion polymerization method. Polypyrrole-based composites, prepared by employing ferric chloride-methanol system, showed a conductivity as high as 0.82 S/cm. Conductivity of polythiophene-based composites, prepared from ferric chloride-acetonitrile system, was 6.05 S/cm. Conductivity of compositivity was influenced by the initial molar ratio of oxidant to monomer as well. SEM micrographs of the composites showed that conducting polymer coated uniformly the inside wall of the porous host polymer. Shielding effectiveness of the polypyrrole-based composites and of the polythiophene-based composites were 15.2 dB and 22.5 dB at 2.0 GHz, respectively. In the temperature range from 20 to 300K, a polypyrrole impregnated composite exhibited seimiconducting behavior and followed the variable range hopping(VRH) model for charge transport.

• Journal of Korean Neurosurgical Society
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• v.41 no.2
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• pp.111-117
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• 2007

Objective : The objective of this study was to validate the effects of a titanium mesh cage and dynamic plating in anterior cervical stabilization after corpectomy. Methods : A retrospective study was performed on 31 consecutive patients, who underwent anterior cervical reconstruction with a titanium mesh cage and dynamic plating, from March 2004 to February 2006. Twenty-four patients had 1-level and 7 had 2-level corpectomies. Ten patients underwent surgery with a cage of 10-mm diameter and 21 with 13-mm diameter. Neurological status and outcomes were assessed according to Odom's criteria. Sagittal angle, coronal angle, settling ratio, sagittal displacement, and cervical lordosis were used to evaluate the radiological outcomes. Results : In overall, 26 [83.9%] of 31 showed excellent or good outcomes. Thirteen percent [4 cases] of the patients developed surgical complications, such as hoarseness, transient dysphagia, or nerve root palsy. Seven [22.6%] patients had reconstruction failure:5 [20.8%] in the 1-level corpectomy group and 2 [28.5%] in the 2-level corpectomy group. Revisions were required in 2 patients with plate pullout due to significant instability. However, none of 5 patients who demonstrated cage displacement or screw pullout, underwent a revision. Radiographs revealed bony consolidation in 96.3% of the patients, including 6 patients with implantation failure during the follow-up period. Conclusion : Based on our preliminary results, the titanium mesh cage and dynamic plating was effective for cervical reconstruction after corpectomy. The anterior cervical reconstruction performed with dynamic plates is considered to reduce stress shielding and greater graft compression that is afforded by the unique plate design.

• Wind and Structures
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• v.30 no.6
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• pp.547-558
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• 2020

With the development of economy and construction technology, more and more bridges are built in complex mountainous areas. Accurate assessment of wind parameters is important in bridge construction at complex terrain. In order to investigate the wind characteristics in the high-altitude difference area, a complex mountain terrain model with the scale of 1:2000 was built. By using the method of wind tunnel tests, the study of wind characteristics including mean wind characteristics and turbulence characteristics was carried out. The results show: The wind direction is affected significant by the topography, the dominant wind direction is usually parallel to the river. Due to the sheltering effect of the mountain near the bridge, the wind speed and wind attack angle along the bridge are both uneven which is different from that at flat terrain. In addition, different from flat terrain, the wind attack angle is mostly negative. The wind profiles obey exponential law and logarithmic law. And the fitting coefficient is consistent with the code which means that it is feasible to use the method of wind tunnel test to simulate complex terrain. As for turbulence characteristics, the turbulence intensity is also related to the topography. Increases sheltering effect of mountain increases the degree of breaking up the large-scale vortices, thereby increasing the turbulence intensity. Also, the value of turbulence intensity ratio is different from the recommended values in the code. The conclusions of this study can provide basis for further wind resistance design of the bridge.