• Journal of the Korean Society of Food Science and Nutrition
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• v.31 no.3
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• pp.475-481
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• 2002

Blend films of poly(3-hydroxybutyric acid) (PHB) with chitosan were prepared, and their Physical properties and crystallization were investigated. The degree of crystallinity of PHB/chitosan films by X-ray diffraction decreased with increasing chitosan concentration. In the fourier-transformed infrared spectra, carbonyl peak of PHB became lower with increasing the amount of chitosan. The addition of chitosan to PHB film decreased thermal stability and crystallinity of the blend films. The granular sizes of the films were reduced with the addition of chitosan to the film in the microstructural observation by a scanning electron microscope. Mechanical properties, including tensile strength and percent elongation, of the blend films increased with increasing chitosan ratio in the films. For color of the films, L and b values generally decreased with increasing chitosan ratio, but transparency of the films increased.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2007.11a
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• pp.281-281
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• 2007

Low Temperature Co-fired Ceramic (LTCC) technology has been used in electronic device for various functions. LTCC technology is to fire dielectric ceramic and a conductive electrode such as Ag or Cu thick film below the temperature of $900^{\circ}C$ simultaneously. The glass-ceramic has been widely used for LTCC materials due to its low sintering temperature, high mechanical properties and low dielectric constants. To obtain the high strength, addition of filler, the microstructure should have various crystals and low pores in a composite. In this study, two glass frits were mixed with different alumina size(0.5, 2, 3.7um) and sintered at the range of $850{\sim}950^{\circ}C$. The microstructure, crystal phases, thermal and mechanical properties of the composites were investigated using FE-SEM, XRD, TG-DTA, Dilatomer. When the particle size of $Al_2O_3$ filler increased, the starting temperatures for the densification of the sintered bodies, onset point of crystallization, peak crystallization temperature in the glass-ceramic composites decreased gradually. After sintered at $900^{\circ}C$, the glass frits were crystallized as $CaAl_2Si_2O_8\;and\;CaMgSi_2O_6$. The purpose of our study is to understand the relationship between the $Al_2O_3$ particle size and thermal properties in composites.

• Proceedings of the Korea Society of Poultry Science Conference
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• 2003.11a
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• pp.99-100
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• 2003

This experiment was conducted to investigate the effect of restricted feeding to pullet on growth and laying Performance, e99 qualify and endocrine profile in brown layers. 1,080 brown-layer chicks divided to three diet treatments, conventional diet and two restricted diets, for 70 weeks. Conventional diets(C) was formulated by NRC recommendation, and one of restricted diet started from seven to seventeen week of age(T1), and the other started from twelve to seventeen(T2). Overall egg Production was the highest in T1 (P＜0.05) and there were not difference in C and T2. Average egg weight also showed similar to the tendency of egg production. Feed intake was higher in T1 during maximum production(P＜0.05), but there were not difference in all treatments after the peak. Overall feed conversion ratio improved in T1 compared to C and T1(p＜0.05). Egg shell thickness and egg shell strength tended to weak in aging, but there were not significant difference by treatments. Haugh unit also tended to similar to egg shell quality. Concentration of IGF-1 was influenced by feed intake. That of T1 maintained in low concentration compared to C during restriction period. The concentration of IGF-1 was decreased dramatically after the first egg. Estradiol concentration increased slightly at twelve week, and surged greatly near the first egg. Those of profile showed similar tendency of the first egg during laying period.

• International Journal of Highway Engineering
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• v.18 no.1
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• pp.57-62
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• 2016

PURPOSES : Reflection cracking has been one of the major causes of distress when asphalt pavement is laid on top of concrete pavement. This study evaluated the reflection cracking resistance of asphalt mixtures reinforced with asphalt embedded glass fiber and carbon fiber using a Texas Transportation Institute (TTI) overlay tester. METHODS : Different asphalt mixtures such as polymer-modified mastic asphalt (PSMA) and a dense graded asphalt mixture were reinforced with asphalt-embedded carbon fiber and glass fiber. For comparison purposes, two PSMA asphalt mixtures and one dense graded asphalt mixture were evaluated without fiber reinforcement. Two different overlay test modes, the repeated overlay test (R-OT) and monotonic overlay test (M-OT), were used to evaluate the reflection cracking resistance of asphalt mixtures at $0^{\circ}C$. In the R-OT test, the number of repeated load when the specimen failed was obtained. In the M-OT test, the tensile strength at the peak load and tensile strain were obtained. RESULTS : As expected, the fiber-reinforced asphalt mixture showed a higher reflection cracking resistance than the conventional nonreinforced asphalt mixtures based on the R-OT test and M-OT test. The dense graded asphalt mixture showed the least reflection cracking resistance and less resistance than the PSMA. CONCLUSIONS : The TTI overlay tester could be used to differentiate the reflection cracking resistance values of asphalt mixtures. Based on the R-OT and M-OT results, the carbon-fiber-reinforced asphalt mixture showed the highest reflection cracking resistance among the nonreinforced asphalt mixtures and glass-fiber-reinforced asphalt mixture.

• Proceedings of the Korean Vacuum Society Conference
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• 2000.02a
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• pp.211-211
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• 2000

Carbon nanotubes (CNTs) have been spotlighted as one of promising field emission displays(FEDs). For the first time, to authors knowledge, we have developed the 9" color CNT-FEDs with the resolution of 240x576 lines. The 9" CNT-FEDs with diode-type and triode-type structures are presented. The well-dispersed CNT paste was squeezed onto the metal-patterned cathode glass. For the anode plate, the Y2O2S:Eu, ZnS:Ag,Cl low-voltage phosphors were printed for red, green, and blue colors, respectively. The vacuum-packaged panel maintained the vacuum level of 1x10-7 Torr. The uniform moving images vacuum-packaged panel maintained the vacuum level of 1x10-7 Torr. The uniform moving images were demonstrated at 2 V/um. High brightness of 800, 200, and 150cd/m2 was observed on the green, red, and blue phosphors at V/um, respectively. Field emission characteristics of a triode-type CNT-FED were simulated using a finite element method. the resultant field strength on the cathode was modulated by gate bias and emitted electrons were focused on the anode. A relatively uniform emission image was experimentally achieved at the 800V anode. A relatively uniform emission image was experimentally achieved at the 800V anode and the 50-180 V gate biases. Energy distribution of electrons emitted from CNTs was measured using an energy analyzer. The maximum peak of energy curve corresponded to the Fermi energy level of CNTs. The whole fabrication processed of CNT-FEDs were fully scalable and reproducible. Our CNT-FEDs has demonstrated the high potential of large-area and full-color applications with very low cost fabrication and low power consumption.

• Proceedings of the Korean Vacuum Society Conference
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• 2000.02a
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• pp.64-64
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• 2000

Since its discovery in 1991, the carbon nanotube has attracted much attention all over the world; and several method have been developed to synthesize carbon nanotubes. According to theoretical calculations, carbon nanotubes have many unique properties, such as high mechanical strength, capillary properties, and remarkable electronical conductivity, all of which suggest a wide range of potential applications in the future. Here we report the synthesis in the catalytic decomposition of acetylene at ~65 $0^{\circ}C$ over Ni deposited on SiO2, For the catalyst preparation, Ni was deposited to the thickness of 100-300A using effusion cell. Different approaches using porous materials and HF or NH3 treated samples have been tried for synthesis of carbon nanotubes. It is decisive step for synthesis of carbon nanotubes to form a round Ni particles. We show that the formation of round Ni particles by heat treatment without any pre-treatment such as chemical etching and observe the similar size of Ni particles and carbon nanotubes. Carbon nanotubes were synthesized by chemial vapour deposition ushin C2H2 gas for source material on Ni coated Si substrate. Ni film gaving 20~90nm thickness was changed into Ni particles with 30~90nm diameter. Heat treatment of Ni fim is a crucial role for the growth of carbon nanotube, High-resolution transmission electron microscopy images show that they are multi-walled nanotube. Raman spectrum shows its peak at 1349cm-1(D band) is much weaker than that at 1573cm-1(G band). We believe that carbon nanotubes contains much less defects. Long carbon nanotubes with length more than several $\mu$m and the carbon particles with round shape were obtained by CVD at ~$650^{\circ}C$ on the Ni droplets. SEM micrograph nanotubes was identified by SEM. Finally, we performed TEM anaylsis on the caron nanotubes to determine whether or not these film structures are truly caron nanotubes, as opposed to carbon fiber-like structures.

• Korean Journal of Materials Research
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• v.20 no.3
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• pp.125-131
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• 2010

In this study, Ti powders were fabricated from Ti scrap by the Hydrogenation-Dehydrogenation (HDH) method. The Ti powders were prepared from the spark plasma sintering (SPS) and their microstructure was investigated. Hydrogenation reactions of Ti scrap occurred at near $450^{\circ}C$ with a sudden increase in the reaction temperature and the decreasing pressure of hydrogen gas during the hydrogenation process in the furnace. The dehydrogenation process was also carried out at $750^{\circ}C$ for 2 hrs in a vacuum of $10^{-4}$ torr. After the HDH process, deoxidation treatment was carried out with the Ca (purity: 99.5%) at $700^{\circ}C$ for 2 hrs in the vacuum system. It was found that the oxidation content of Ti powder that was deoxidized with Ca showed noticeably lower values, compared to the content obtained by the HDH process. In order to fabricate the Ti compacts, Ti powder was sintered under an applied uniaxial punch pressure of 40 MPa in the range of $900-1200^{\circ}C$ for 5 min under a vacuum of $10^{-4}$ torr. The relative density of the compact was 99.5% at $1100^{\circ}C$ and the tensile strength decreased with increasing sintering temperature. After sintering, all of the Ti compacts showed brittle fracture behavior, which occurred in an elastic range with short plastic yielding up to a peak stress. Ti improved the corrosion resistance of the Ti compacts, and the Pd powders were mixed with the HDH Ti powders.

• Transactions of the Korean Society of Mechanical Engineers
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• v.16 no.3
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• pp.598-607
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• 1992

The environment degradation of structural steel under high temperature is one of the key phenomena governing the availability and life of plant. This degradation resulted from the microstructural changes due to the long exposure at high temperature affect the mechanical properties such as creep strength and toughness. For instance, boiler tube materials usually tend to degrade, after long term operation, by precipitates, spherodizing, coarsening, and change in chemical composition of carbides. In this study, the material degradation under high temperature exposure was investigated by evaluating the carbide precipitation. The electrochemical polarization method was facilitated to investigate the precipitation and coarsening of carbides. It was shown by the modified electrochemical potentiokinetic reactivation (EPR) tests that the passivation of Mo-rich carbides did not occur even in the anodic peak current (Ip) which indicates the precipitation of Mo$_{6}$C was also observed. And it was assured that special electrolytic cell assembled in this research can be used for the detection of Mo$_{6}$C precipitation in the field.eld.

• Journal of the Korean Society of Food Culture
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• v.29 no.4
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• pp.355-363
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• 2014

The purpose of this study was to investigate the rheological characteristics of medium wheat flour mixed with bamboo leaf and lotus leaf powders. Rheological properties of the mixed flours were tested based on falling number, color, RVA, farinogram, and rheofermentometer analyses. Falling numbers increased with addition of bamboo leaf and lotus leaf powders. The L values of all mixed flours were less than that of control. The 1% mixed flour sample containing bamboo leaf and lotus leaf powders was not significantly different from 3% mixed flour. The a values of the mixed flour decreased as bamboo and lotus powders increased, whereas b values increased. Addition of bamboo leaf and lotus leaf powders to flour reduced peak viscosity, holding strength, and final viscosity. The set back values of mixed wheat flour containing bamboo leaf powder were lower than those of mixed wheat flour containing lotus leaf powder, suggesting that bamboo leaf powder suppressed retrogradation of flour compared to lotus leaf powder. In the farinogram, the water absorption and consistency of the flours containing bamboo and lotus leaf powders increased, whereas development time and stability decreased. The fermentation time of dough with lotus leaf powder was less than that of dough with bamboo leaf powder.

• Geomechanics and Engineering
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• v.22 no.5
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• pp.385-396
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• 2020

A uniaxial compression test was performed to analyse the mechanical properties and macroscale and mesoscale failure mechanisms of sandstone with pyrite concretions. The effect of the pyrite concretions on the evolution of macroscale cracks in the sandstone was further investigated through numerical simulations with Particle Flow Code in 2D (PFC2D). The results revealed that pyrite concretions substantially influence the mechanical properties and macroscale and mesoscale failure characteristics of sandstone. During the initial loading stage, significant stress concentrations occurred around the edges of the pyrite concretion accompanied by the preferential generation of cracks. Meanwhile, the events and cumulative energy counts of the acoustic emission (AE) signal increased rapidly because of friction sliding between the concretion and sandstone matrix. As the axial stress increased, the degree of the stress concentration remained relatively unchanged around the edges of the concretions. The cracks continued growing rapidly around the edges of the concretions and gradually expanded toward the centre of the sample. During this stage, the AE events and cumulative energy counts increased quite slowly. As the axial stress approached the peak strength of the sandstone, the cracks that developed around the edges of the concretion started to merge with cracks that propagated at the top-left and bottom-right corners of the sample. This crack evolution ultimately resulted in the shear failure of the sandstone sample around the edges of the pyrite concretions.