• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2008.03a
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• pp.115-121
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• 2008

A core engine for pre-cooled turbojet engines is designed and its component performances are examined both by CFD analyses and experiments. The engine is designed for a flight demonstration of precooled turbojet engine cycle. The engine uses gas hydrogen as fuel. The external boundary including measurement devices is set within $23cm{\times}23cm$ of rectangular cross section, in order to install the engine downstream of the air intake. The rotation speed is 80000 rpm at design point. Mixed flow compressor is selected to attain high pressure ratio and small diameter by single stage. Reverse type main combustor is selected to reduce the engine diameter and the rotating shaft length. The temperature at main combustor is determined by the temperature limit of non-cooled turbine. High loading turbine is designed to attain high pressure ratio by single stage. The firing test of the core engine is conducted using components of small pre-cooled turbojet engine. Gas hydrogen is injected into the main burner and hot gas is generated to drive the turbine. Air flow rate of the compressor can be modulated by a variable geometry exhaust nozzle, which is connected downstream of the core engine. As a result, 75% rotation speed is attained without hazardous vibration and heat damage. Aerodynamic performances of both compressor and turbine are obtained and evaluated independently.

• Elastomers and Composites
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• v.38 no.3
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• pp.273-280
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• 2003

Elastic responses on both pure natural rubber melts with different molecular weights and the rubber compounds mixed with various types of carbon blacks were investigated in this study. Furthermore, the degree of bound rubber was measured for various carbon blacks with different sizes and structures in order to study the interaction between the rubber and carbon blacks, and to study the correlation between the interaction and the elastic responses. As a loading amount of carbon black increased, the degree of bound rubber became higher, particularly far carbon-black particles with smaller sizes and higher structures. The elastic responses of the rubber melt filled with carbon black remarkably improved, as compared with those of unfilled rubber melt, specially in carbon black showing higher contents of bound rubber. Stress relaxation was more delayed and recovery behavior became more elastic, as the molecular weight of the rubber melt increased and the size of carbon-black particles was decreased. Permanent set became higher, as the molecular weight of the rubber melts decreased and the size of carbon-black particles increased.

• Nuclear Engineering and Technology
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• v.51 no.1
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• pp.228-237
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• 2019

The crack growth responses of as-received and as-welded Alloy 600/182 and Alloy 690/152 welds to constant loading were measured by a direct current potential drop method using compact tension specimens in primary water at $325^{\circ}C$ simulating the normal operating conditions of a nuclear power plant. The as-received Alloy 600 showed crack growth rates (CGRs) between $9.6{\times}10^{-9}mm/s$ and $3.8{\times}10^{-8}mm/s$, and the as-welded Alloy 182 had CGRs between $7.9{\times}10^{-8}mm/s$ and $7.5{\times}10^{-7}mm/s$ within the range of the applied loadings. These results indicate that Alloys 600 and 182 are susceptible to cracking. The average CGR of the as-welded Alloy 152 was found to be $2.8{\times}10^{-9}mm/s$. Therefore, Alloy 152 was proven to be highly resistant to cracking. The as-received Alloy 690 showed no crack growth even with an inhomogeneous banded microstructure. The cracking mode of Alloys 600 and 182 was an intergranular cracking; however, Alloy 152 was revealed to have a mixed (intergranular + transgranular) cracking mode. It appears that the Cr concentration and the microstructural features significantly affect the cracking resistance and the cracking behavior of Ni-base alloys in PWR primary water.

• Korean Journal of Metals and Materials
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• v.56 no.12
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• pp.870-877
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• 2018

Cyanex 272 shows the highest separation factor for the rare earth elements from hydrochloric acid solution among the organophosporus acidic extractants, D2EHPA and PC 88A. Solvent extraction of Tb(III) from weak hydrochloric acid solution with an initial pH 3 to 6 was compared with Cyanex 272, its mixture with Alamine 336, and ionic liquid with Aliquat 336. The solvent extraction reaction of Tb(III) using Cyanex 272 was the same as that of light rare earth elements. Synergism was observed for the extraction of Tb(III) by the mixture with Alamine 336 when the initial concentration ratio of Cyanex 272 to Alamine 336 was higher than 5. Use of the ionic liquid led to a great increase in the extraction percentage of Tb(III) from the same initial extraction conditions. While the equilibrium pH of the mixture was always lower than the initial pH, under some conditions extraction with the ionic liquid resulted in a higher equilibrium pH than the initial pH. The loading capacity of the mixture and the ionic liquid was the same and 2.6 times larger than that using Cyanex 272 alone. Ionic liquid was recommended as a suitable extractant for the extraction of Tb(III) from hydrochloric acid solution based on the ease of handling and higher extraction percentage.

• The Korea Journal of Herbology
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• v.32 no.5
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• pp.39-46
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• 2017

Objective : This study was designed to evaluate the hypoglycemic effects of Helianthus tuberosi Rhizoma extracts and its optimum Heat processing conditions Methods : We investigated the Salivary ${\alpha}$-amylase, pancreas ${\alpha}$-amylase and ${\alpha}$-glucosidase inhibitory activities of extracts from Steam Heated Helianthus tuberosi Rhizoma Ext. The inhibitory activities of a 50% EtOH extract of Steam Heated Helianthus tuberosi Rhizoma Ext against ${\alpha}$-glucosidases were evaluated in this study. Inhibiting these enzymes involved in the absorption of disaccharides significantly decreases the postprandial increase in blood glucose level after a mixed carbohydrate diet. Furthermore, the postprandial blood glucose lowering effect of Steam Heated Helianthus tuberosi Rhizoma Ext. was compared to a known type 2 diabetes drug(Acarbose(R)) in a mice model. Steam Heated Helianthus tuberosus L. Ext significantly reduced the blood glucose increase after glucose loading. Results : The results were confirmed by real-time PCR that after treated with Streptozotocin in L6 cells, induced expression of GLUT4, after the steamed Helianthus tuberosus L. Ext. treated, observed its expression was increased. Steam Heated Helianthus tuberosus L Ext treated 4 hours in L6 cells, cytotoxicity was measured in MTT assay. Its toxicity were 5.7%, 9% and 11.3% at the treatment concentration $12.5{\mu}g/m{\ell}$, $25{\mu}g/m{\ell}$, the $50{\mu}g/m{\ell}$ respectively. Conclusions : Overall, the results of this study indicate that Hypoglycemic effect of Helianthus tuberosi Rhizoma caused by the Steam heat treatment, the optimum Heat processing condition is steamming at $121^{\circ}C$ for 30 min, and it will provide the basis for developing a useful dietary supplement for controlling postprandial hyperglycemia.

• Journal of the Korea Society for Simulation
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• v.18 no.2
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• pp.19-27
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• 2009

This paper addresses the berth allocation problem in naval ports. Navy vessels need various services such as emergency repair, missile loading, oil supply and many others while commercial vessels only unload and load container at the port. Furthermore, naval vessels have to shift frequently due to a limited capacity of the port. The objective of this paper is to minimize the total number of nesting vessels at the naval port. In other word, the objective is to maximize the total number of naval battleships engaging in the sea. A mixed integer programming(MIP) model is developed and experiments are conducted with ILOG CPLEX 11.0. We compare the computational results of the MIP model to the current scheduling approach by the ROK Navy. The results showed that MIP model performed well by minimizing the number of nesting vessels. and avoiding unnecessary shifts.

• Composites Research
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• v.19 no.2
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• pp.7-12
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• 2006

Graphite particle/carbon fiber hybrid conductive polymer composites were fabricated by the compression molding technique. Graphite particles were mixed with an epoxy resin to impart the electrical conductivity in the composite materials. In this study, graphite reinforced conductive polymer composites with high filler loadings were manufactured to accomplish high electrical conductivity above 100S/cm. Graphite particles were the main filler to increase the electrical conductivity of composites by direct contact between graphite particles. While high filler loadings are needed to attain good electrical conductivity, the composites becomes brittle. So carbon fiber was added to compensate weakened mechanical property. With increasing the carbon fiber loading ratio, the electrical conductivity gradually decreased because non-conducting regions were generated in the carbon fiber cluster among carbon fibers, while the flexural strength increased. In the case of carbon fiber 20wt.% of the total system, the electrical conductivity decreased 27%, whereas the flexural strength increased 12%.

• Composites Research
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• v.20 no.6
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• pp.1-7
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• 2007

Expanded graphite/carbon fiber hybrid conductive polymer composites were fabricated by the preform molding technique. The conductive fillers were mechanically mixed with a phenol resin to provide an electrical property to composites. The conductive filler loading was fixed at 60wt.% to accomplish a high electrical conductivity. Expanded graphites were excellent in forming a conductive networking by direct contacts between them while it was hard to get the high flexural strength over 40MPa with using only expanded graphite and phenol resin. In this study, carbon fibers were added in composites to compensate the weakened flexural strength. The effect of carbon fibers on the mechanical and electrical properties was examined according to the weight ratio of carbon fiber. As the carbon fiber ratio increased, the flexural strength increased until the carbon fiber ratio of 24wt.%, and then decreased afterward. The electrical conductivity gradually decreased as the increase of the carbon fiber ratio. This was attributed to the non-conducting regions generated among the carbon fibers and the reduction of the direct contact areas between expanded graphites.

• Computers and Concrete
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• v.31 no.5
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• pp.433-442
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• 2023

This study presents the visually observed behavior of fibers embedded in concrete samples that were subjected to a flexural bending test. Three types of fibers such as macro polypropylene, macro polyethylene, and the hybrid of steel and polyvinyl alcohol were mixed with cement by a designated mix ratio to prepare a total of nine specimens of each. The bending test was conducted by following ASTM C1609 with a net deflection of 2, 4, and 7 mm. The X-ray computed tomography (XCT) was carried out for 7 mm-deflection specimens. The original XCT images were post-processed to denoise the beam-hardening effect. Then, fiber, crack, and void were semi-manually segmented. The hybrid specimen showed the highest toughness compared to the other two types. Debonding based on 2D XCT sliced images was commonly observed for all three groups. The cement matrix near the crack surface often involved partially localized breakage in conjunction with debonding. The pullout was predominant for steel fibers that were partially slipped toward the crack. Crack bridging and rupture were not found presumably due to the image resolution and the level of energy dissipation for poly-fibers, while the XCT imaging was advantageous in evaluating the distribution and behavior of various fibers upon bending for fiber-reinforced concrete beam elements.

• Journal of the Korean Wood Science and Technology
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• v.50 no.2
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• pp.93-103
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• 2022

Currently, biofibers are used as a reinforcement in polymer composites for structural elements and construction materials instead of the synthetic fibers which cause environmental problems and are expensive. One of the chemicals with a pH close to neutral that can be potentially used as a modified fiber material is sodium chloride (NaCl). Therefore, this study aims to investigate the characteristics of a composite board made from NaCl-treated kenaf fiber. A completely randomized design method was used with consideration of two factors: the content of NaCl in the treatment solution (1 wt%, 3 wt%, and 5 wt%) and the duration of immersion of fibers in the solution (1 h, 2 h, and 3 h). The NaCl treatment was conducted by soaking the fibers in the solution for different durations. The fibers were then rinsed with water until the pH of the water reached 7 and subsequently dried inside an oven at 80℃ for 6 h. Kenaf fiber and epoxy were mixed manually with the total loading of 20 wt% based on the dry weight of the fiber. Physical and mechanical properties of the fibers were then evaluated based on JIS A 5908 particleboard standards. The results showed that increasing NaCl content in the fiber treatment solution can increase the physical and mechanical properties of the composite board. The properties of fibers treated with 5 wt% NaCl for 3 h were superior with a modulus of elasticity of 2.085 GPa, modulus of rupture of 19.77 MPa, internal bonding of 1.8 MPa, thickness swelling of 3%, and water absorption of 10.9%. The contact angle of untreated kenaf fibers was 104°, which increased to 80° and 73° on treatment with 1 wt% and 5 wt% NaCl for 3 h, respectively.