• Polymer(Korea)
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• v.24 no.5
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• pp.701-712
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• 2000

The continuous fiber reinforced composites of GF/PA were fabricated using a pultrusion resin impregnation apparatus and cut into pellets of 6 mm length. GF/PA pellets were then melt-mixed with PP resin to prepare new types of ternary composites, GF/PA/PP. Mechanical and rheological properties of such composites revealed to be better than conventional ternary composites due to the longer average glass fibers. Measurements also showed that the mechanical properties of the composites prepared by direct injection molding were higher than those of the composites prepared by injection molding followed by extrusion. To improve adhesions of fiber surfaces and polymer matrix, PP-MAH (maleic anhydride) has been introduced in the GF/PA/PP composites as a compatibilizer. It was found that PP-MAH did indeed improve surface adhesion between fibers and polymer matrix and that, as a result, various mechanical properties were markedly enhanced. Visualization of the phase structure in the samples was done by means of SEM. The surfaces of glass fibers in GF/PA/PP composites revealed that the fibers remained to be encapsulated by PA resin. However, pre-encapsulation did not persist in GF/PA/PP/PP-MAH composites due to the improvement of surface adhesion between fibers and polymer matrix, although resin sticking to the fiber was observed.

• Journal of the Mineralogical Society of Korea
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• v.28 no.4
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• pp.333-341
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• 2015

As results of X-ray diffraction analysis, samples of asbestos and soil were composed maily of dolomite ($CaMg(Co_3)_2$, tremolite ($Ca_2Mg_5Si_{18}O_{22}(OH)_2$), actinolite ($Ca(Mg,\;Fe)_6Si_8O_{22}(OH)_2$), talc ($Mg_3Si_4O_{10}(OH)_2$), calcite ($CaCO_3$) and small amounts of quartz ($SiO_2$) and clay minerals. The average size of asbestos fibers was about $100{\mu}m$ and maximum of some asbestos was $250.0{\mu}m$ in length. The aspect ratio of asbestos fiber were over 3 : 1 and inclined extinction in the range of $8.0-19.5^{\circ}$. Single isolated fragments of asbestos are probably fiber and acicula form in crystal edge along the cleavage plane. Tremolite that composed main asbestos mineral in rock and soil around Dong-a mine is higher content of Fe than actinolite asbestos.

• Journal of the Korean Wood Science and Technology
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• v.48 no.2
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• pp.231-244
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• 2020

As a way of finding value-added materials from waste medium density fiberboard (MDF), this study characterized cellulose nanocrystals (CNCs) isolated by ammonium persulfate (APS) oxidation using recycled MDF fibers. Chemical composition of the recycled MDF fibers was done to quantify α-cellulose, hemicellulose, lignin, nitrogen, ash and extractives. The APS oxidation was performed at 60 ℃ for 16 h, followed by ultrasonication, which resulted in a CNC yield of 11%. Transmission electron microscope images showed that rod-like CNCs had an average length and diameter of 167±47 nm and 8.24±2.28 nm, respectively, which gave an aspect ratio of about 20. The conductometric titration of aqueous CNCs suspension resulted in a carboxyl content of 0.24 mmol/g and the degree of oxidation was 0.04. Attenuated total reflection Fourier transform infrared (ATR-FTIR) spectroscopy clearly showed the presence of carboxyl group on the CNCs prepared by the APS oxidation. The change of pH of the aqueous CNC suspension from 4 to 7 converted the carboxyl group to sodium carboxylate group. These results showed that the APS oxidation was facile and CNCs had a one-step preparation method, and thus suggested an optimization of the oxidation condition in future.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.23 no.11 s.170
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• pp.1886-1895
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• 1999

The delamination behavior of multidirectional carbon-fiber/epoxy composite laminates under 10NA intermediate and high rates of test, up to rate of about 11.4m s has been investigated using the double cantilever beam specimens. The mode I loading under rates above l.0m/s showed considerable dynamic effects on the load-time curves and thus higher values of the average crack velocity than that expected from a simple proportional relationship with the test rate. The modified beam analysis utilizing only the opening displacement and crack length exhibited an effective means for evaluating the dynamic fracture energy $G_{IC}$. Based on the assumption of constant flexural modulus, values of $G_{IC}$ at the crack initiation and arrest were decreased with an increase of the test rate up to 5.7m/s, but the maximum $G_{IC}$ was increased at 11.4m/s.

• Structural Engineering and Mechanics
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• v.50 no.6
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• pp.709-722
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• 2014

Ultra-High Performance Concrete (UHPC) is an innovative new material that, in comparison to conventional concretes, has high compressive strength and excellent ductility properties achieved through the addition of randomly dispersed short fibers to the concrete mix. This study presents the results of an experimental investigation on the behavior of axially loaded UHPC short circular columns wrapped with Carbon-FRP (CFRP), Glass-FRP (GFRP), and Aramid-FRP (AFRP) sheets. Six plain and 36 different types of FRP-wrapped UHPC columns with a diameter of 100 mm and a length of 200 mm were tested under monotonic axial compression. To predict the ultimate strength of the FRP-wrapped UHPC columns, a simple confinement model is presented and compared with four selected confinement models from the literature that have been developed for low and normal strength concrete columns. The results show that the FRP sheets can significantly enhance the ultimate strength and strain capacity of the UHPC columns. The average greatest increase in the ultimate strength and strain for the CFRP- and GFRP-wrapped UHPC columns was 48% and 128%, respectively, compared to that of their unconfined counterparts. All the selected confinement models overestimated the ultimate strength of the FRP-wrapped UHPC columns.

• Journal of Digital Convergence
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• v.20 no.4
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• pp.459-468
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• 2022

In medical area, very high resolution images, which is loss sensitive data, are used. Therefore, the use of optical internet with high bandwidth and the transmission of high realiability is required. However, according to the nature of the Internet, various data use the same bandwidth and a new scheme is needed to differentiate effectively these data. In order to achieve the differentiation, optical delay line buffers are used. However, these buffers is constructed based on some optimal values such as the average offered load, measured data burst length, and basic delay unit. Once the buffers are installed, they are impossible to reinstall new buffers. So, the scheme changing burst length dynamically was considered. However, this method is highly unstable. Therefore, in this article, in order to guarantee the stable operation of the scheme, the analysis of operation conditions is performed. With the analysis together with the scheme, high resolution medical data with the higher class can transmit stably without loss.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.36 no.12
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• pp.1591-1597
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• 2012

Adherend samples were made from unsaturated polyester and woven and mat glass fibers by the hand layup and vacuum methods. The mechanical properties of the adhesive, composite adherends, and terminal-joint and secondary-joint specimens were determined experimentally. Combinations of the experiment results and the bonding theory were used in this study. The maximum and average shear stresses were calculated based on the maximum tensile force and geometry parameters of the joint specimens. The results of the maximum and average shear stresses were compared and evaluated for six joints. The results showed that the grinding and grind/acetone joint had the highest strength among three types of terminal-joints. Similarly, the mat-mat and mat-woven joints had the highest strength among three types of secondary-joints with the same value. Conversely, no treatment and woven-woven bonding had very low strength. In each case, failure occurred always at two ends and then moved toward the middle area of the overlap length.

• Journal of The Korean Society of Grassland and Forage Science
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• v.41 no.1
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• pp.10-15
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• 2021

'Gwangyoung', a winter forage triticale cultivar (X Triticosecale Wittmack), was developed at the Department of Rice and Winter Cereal Crop, NICS, RDA in 2018. The cultivar 'Gwangyoung' has leaves of wide width, medium length, and green color, and spikes of medium length and yellowish-brown color, and a large grain of yellowish-brown color. The heading date of the cultivar 'Gwangyoung' was April 22 which was similar to check cultivar 'Shinyoung'. Its tolerance or resistance to cold, lodging, wet injury powdery mildew, and leaf rust were also similar to those of the check cultivar. The leaf blade ratio of 'Gwangyoung' (27.5%) was higher than that of 'Shinyoung' (21.2%). The average forage fresh and dry matter yield of cultivar 'Gwangyoung' at milk-ripe stages were 50.0 and 17.6 MT ha-1, respectively, which were higher than those (47.7 and 17.1 MT ha-1) of the check cultivar. The silage quality of 'Gwangyoung' was lower than that of the check cultivar 'Shinyoung' in crude protein content (5.3%) and total digestible nutrients (61.3%), while was higher than the check cultivar in neutral detergent fiber (58.2%) and acid detergent fiber (34.9%). 'Gwangyoung' showed the silage of 1 grade and a grain yield of 6.03 MT ha-1.

• Journal of The Korean Society of Grassland and Forage Science
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• v.39 no.2
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• pp.68-74
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• 2019

'Choyoung', a winter forage triticale cultivar (X Triticosecale Wittmack), was developed at the Department of Rice and Winter Cereal Crop, NICS, RDA in 2015. The cultivar 'Choyoung' has the leaves of medium width, long length and green color and a medium grain of brown color. The heading date of the cultivar 'Choyoung' was April 30 which was 2 days earlier than that of check cultivar 'Shinyoung'. Its tolerance or resistance to cold, wet injury, powdery mildew, and leaf rust was similar to those of the check cultivar. But the resistance to the lodging of cultivar 'Choyoung' was stronger than that of the check. The average forage fresh and dry matter yield of cultivar 'Choyoung' at milk-ripe stages were 40.5 and $15.7MT\;ha^{-1}$, respectively, which were similar to those (40.3 and $16.1MT\;ha^{-1}$) of the check cultivar. The silage quality of 'Choyoung' was higher than that of the check cultivar 'Shinyoung' in crude protein content (5.9%), while was similar to the check cultivar 'Shinyoung' in acid detergent fiber (33.9%), neutral detergent fiber (57.3%), and total digestible nutrients (62.2%). It showed a grain yield of $5.59MT\;ha^{-1}$, which was 38% higher than that of the check cultivar 'Shinyoung' ($4.05MT\;ha^{-1}$). This cultivar is recommended for fall sowing forage crops in areas in which average daily minimum mean temperatures in January are higher than $-10^{\circ}C$.

• Composites Research
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• v.15 no.6
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• pp.1-7
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• 2002

In VARTM process where a sacrificial medium is used to facilitate the resin flow, the velocity of resin varies drastically between the sacrificial medium and the fiber preform. Although the thickness-to-length ratio of a VARTM product is usually small, a 3-D analysis is prerequisite to analyze the lead-lag flow in the two different media. The problem associated with the full 3-D analysis is the CPU time. A full 3-D numerical mesh comprising large number of nodes requires an impractical CPU time on average computer platforms. In this study, a dual-scale analysis technique was developed. The flow analysis for the entire calculation domain was conducted in 2.5-D, and the 3-D analysis was performed for a small area of special concern. In some numerical examples, the local 3-D analysis could discover an eccentric flow pattern as well as the lead-lag flow that will inevitably be neglected in 2.5-D simulations. The global-local analysis technique practiced in this study can be used to analyze the intricate flow of resin through non-uniform media in affordable CPU times.