• Journal of Adhesion and Interface
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• v.9 no.3
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• pp.7-13
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• 2008

The particulate type silicon carbide (SiC) and fiber type carbon fiber (CF) filler, of similar thermal conductivities, were mixed with polyetheretherketone (PEEK) to investigate the filler effects on the thermal diffusivity. The SiC and CF fillers had a good and uniform dispersion in PEEK matrix. Thermal diffusivities of PEEK composites were measured from ambient temperature up to $200^{\circ}C$ by laser flash method. The diffusivities were decreased as increasing temperature due to the phonon scattering between PEEK-filler and filler-filler interfaces. Thermal diffusivity of PEEK composites was increased with increasing filler content and the thermal conductivities of two-phase system were compared to the experimental results and it gave ideas on the filler dispersion, orientation, aspect ratio, and filler-filler interactions. Nielson equation gave a good prediction to the experimental results of PEEK/SiC. The easy network formation by CF was found to be substantially more effective than SiC and it gave a higher thermal diffusivities of PEEK/CF than PEEK/SiC.

• Composites Research
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• v.19 no.1
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• pp.29-35
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• 2006

The avoidance of enemy's radar detection is very important issue in the modem electronic weapon system. Researchers have studied to minimize reflected signals of radar. In this research, two types of radar absorbing structure (RAS), 'C'-type shell and 'U'-type shell, were fabricated using fiber-reinforced composite materials and their radar cross section (RCS) were evaluated. The absorption layer was composed of glass fiber reinforced epoxy and nano size carbon-black, and the reflection layer was fabricated with carbon fiber reinforced epoxy. During their manufacturing process, undesired thermal deformation (so called spring-back) was observed. In order to reduce spring-back, the bending angle of mold was controlled by a series of experiments. The spring-back of parts fabricated by using compensated mold was predicted by finite element analysis (ANSYS). The RCS of RAS shells were measured by compact range and predicted by physical optics method. The measured RCS data was well matched with the predicted data.

• Composites Research
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• v.37 no.3
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• pp.162-169
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• 2024

In this study, PAN(polyacrylonitrile)-based precursor fibers were produced through a wet-spinning process, and their morphologies and graphitization behavior were investigated in the presence of two graphitization catalysts (Ca, Ni). The graphitization catalysts were introduced into the formed pores during hot-water stretching of wet-spun PAN-based precursor fibers. The catalytic effects of graphitization catalysts were examined through crystal structure and Raman analysis. At a relatively low temperature of 1500℃, the graphitization was not significantly affected, whereas at a high temperature of 2400℃, the obtained I_D/I_G value of graphite fiber (GF-Ni100) was decreased by about twice (~0.28) compared to the untreated fibers (GF-AS~0.54). By comparing the I_D/I_G values (GF-Ca100~0.42: GF-Ni100~0.28) of Ca and Ni graphitization catalyst, it was found that the degree of graphitization of Ni graphitization catalyst showed higher influence than that of Ca graphitization catalyst. Moreover, 2D band was also observed, indicating that the graphite plane structures composed of multiple layers were developed. XRD results confirmed that the crystal inter-planar distance (d₀₀₂) of the graphite crystal was slightly decreased after the treatment with the graphitization catalyst, But, the crystal size of Ca-treated graphite fiber (GF-Ca100) was increased by up to ~5 nm.

• Korean Journal of Plant Resources
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• v.22 no.5
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• pp.365-380
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• 2009

Flora of vascular plants in mountains located at Wonju-si and Hoengseong-gun areas such as Chiak-san(1,288m), Taegi-san(1,261.4m), Obong-san(1,126.2m), Eungbong-san(1,094.9m), Eodab-san(789.4m), Deokgo-san(521.2m), Deokga-san(700.5m) and Seongji-bong(791m) was investigated from April, 2008 to May, 2009, and results from the previous researches in which voucher specimens had been presented from Balgyo-san(998.4m), Oeum-san(930.4m), Baekun-san(1,037.1m) and Chiak-san(1,288m) were included in the list of vascular plants from these areas. This investigations resulted in 804 taxa consisted of 680 species, 1 subspecies, 111 varieties, and 12 forms of 383 genera under 97 families, and totally in 973 taxa (21.14% of all vascular plants in Korea) of 818 species, 1 subspecies, 138 varieties and 16 forms of 418 genera under 105 families on addition of voucher specimens in the previous researches. Forests of the investigated areas were generally mixed of Pinus densiflora and deciduous trees. The areas with comparatively excellent vegetation were valley from Guryong-sa (temple) to Biro-bong (summit) via Seryeom-pokpo (fall) in Mt. Chiak-san, and Keunseong-gol (valley) and eastern slope from Taegibungyo-teo to Naksu-dae (fall) in Mt. Taegi-san. 10 families with abundantly collected species were Compositae, Graminae, Rosaceae, Ranunculaceae, Leguminosae, Cyperaceae, Liliaceae, Saxifragaceae, Umbelliferae and Labiatae in order, and they occuied 49.12% of all collected taxa. Endemic plants found in these areas were 38 taxa including Hanabusaya asiatica, Megaleranthis saniculifolia, and Pyrus ussuriensis var. diamantica, and rare and endangered ones were 24 taxa including Hanabusaya asiatica, Viola websteri, Viola diamantica, and Patrina saniculaefolia. Specially designated plants by the Ministry of Environment were 88 taxa including 12 taxa of 5th degree such as Woodsia intermedia, Hanabusaya asiatica, Equisetum pratense, Iris koreana, Lilium cernum, Trillium tschonoskii, Magnolia kobus(cultivated), Gastrodia elata, Polypodium virginianum, Cimicifuga heracleifolia, Megaleranthis saniculifolia and Viola websteri. 47 taxa of alien plants were found. As to 609 taxa (13.23% of all vascular plants in Korea) of useful plants, 334 taxa for the edible, 269 taxa for the medicinal, 127 taxa for the ornamental, 332 taxa for the forage, 3 taxa for the industrial raw material, 31 taxa for the timber and 13 taxa for the fiber were classified, respectively.

• Journal of Bio-Environment Control
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• v.27 no.2
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• pp.158-165
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• 2018

The effects of different kinds of supplementary lighting or heating lamps on the yield, cut flower life, and leaf color of cut rose were compared and analyzed. For this purpose, light emitting diode lamp (LED), metal halide lamps (MH), and high-pressure sodium lamps (HPS) as the supplementary lamps, and carbon fiber infrared lamp (NCFI) were installed on hydroponic cultivation bed in a cut rose farm. The yield of cut flower rose and the number of marketable flowers were greatly increased in spring and autumn by HPS treatment, but not in winter. The length of flower stalk was longer than that of control in the spring but decreased in winter. It seemed likely that the shorter flower stalk in winter was due to the shortened period of vegetative growth compared to the control because flowering was promoted by supplementary lighting. Vase life was not different among treatments in the autumn when the lighting time was short, but in winter, it was prolonged to 3 more days by only HPS, compared with the control. Leaf color was significantly affected by light treatment in winter rather than autumn. Leaf color was darkened in all supplementary lamps (LED, MH, HPS) treatment, whereas NCFI was similar to the control in leaf color. In conclusion, HPS is considered to be a very good supplementary lamp because it increases the length of flower stalk and the yield and prolongs vase life in cut roses. Even though NCFI could function as a heating lamp radiating a lot of heat, it was considered that the role as a supplementary light is unsatisfactory because the number of marketable flowers decreases and the quality index of cut rose deteriorates by NCFI.

• Membrane Journal
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• v.25 no.1
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• pp.48-59
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• 2015

This paper reports a fabrication of poly(L-lactic acid) (PLLA) scaffold membranes through phase separation process using pure and mixed solvents. Chloroform and 1,4-dioxane were used as pure solvents and mixed solvents were obtained by mixing the pure solvents together. Morphologies, mechanical properties and mass transfer characteristics of the scaffold membranes were investigated through SEM, stress-strain test and glucose diffusion test. Scaffold membranes from the solution with pure chloroform showed solid-wall pore structure. In contrast, nano-fibrous membranes were fabricated from the solution with pure 1,4-dioxane. In case of mixed solvents, the scaffold membranes showed various structures with changing composition of the solvents. When 1,4-dioxane content was lower than 20 wt% in the solvent, scaffold membrane showed solid-wall pore structure. When the content was 20 wt%, scaffold membranes with macropores with the maximum size of $100{\mu}m$ was obtained. In the concentration range of 1,4-dioxane over 25 wt%, the scaffold membranes showed nano-fibrous structures. In this range, the fibers showed different diameters with changing composition of the solvent. The minimum fiber diameter was about $15{\mu}m$, when 1,4-dioxane composition was 80 wt%. These results indicate that the composition of the solvent showed a significant effect on the structure of scaffold membrane.

• Journal of Korea Technical Association of The Pulp and Paper Industry
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• v.47 no.5
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• pp.91-97
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• 2015

Papermakers wish to increase the filler content of printing and writing grades because it allows saving in production cost through fiber replacement and improving the formation, and optical and printing properties of the paper. However, high filler loading in the base paper has negative side effects. It reduces the mechanical properties of paper and induces cracking at the fold after coating process. Fold cracking is one of the most frequent quality complaints for magazines, high quality books, etc. Two approaches were examined as methods to reduce fold cracking. One approach was to use preflocculated fillers, which was expected to reduce the fold cracking because it would decrease the interfiber bonding. The other approach was to use a new coating binder that gives greater binding power and thereby provides an opportunity of reducing the fold cracking of coated paper. When filler preflocculation was employed in producing the base paper, fold cracking becomes more severe than conventional filler loading condition. On the other hand, use of nano sized binder in coating improved the tensile properties of the coating layer and thereby decreased the crack area. It was shown that tensile properties of coating layer played an important role in fold cracking of coating.

• Polymer(Korea)
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• v.36 no.5
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• pp.612-616
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• 2012

In this work, the effect of chemical treatments of multi-walled carbon nanotubes (MWNTs) on the mechanical interfacial properties of carbon fiber fabric-reinforced composites was investigated. The surface properties of the MWNTs were determined by acid and base values, Fourier transform infrared spectroscopy (FTIR), and X-ray photoelectron spectroscopy (XPS) analyses. The mechanical interfacial properties of the composites were assessed by interlaminar shear stress (ILSS) and critical stress intensity factor ($K_{IC}$). The chemical treatments based on acid and base reactions led to a significant change of surface characteristics of the MWNTs, especially A-MWNTs/carbon fibers/epoxy composites had higher mechanical properties than those of B-MWNTs and non-treated MWNTs/carbon fibers/epoxy composites. These results were probably due to the improvement of interfacial bonding strength, resulting from the acid-base interaction and hydrogen bonding between the epoxy resins and the MWNT fillers.

• Advanced Composite Materials
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• v.17 no.1
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• pp.25-40
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• 2008

The research and development in soundproof materials for preventing noise have attracted great attention due to their social impact. Noise insulation materials are especially important in the field of soundproofing. Since the insulation ability of most materials follows a mass rule, the heavy weight materials like concrete, lead and steel board are mainly used in the current noise insulation materials. To overcome some weak points in these materials, fiber reinforced composite materials with lightweight and other high performance characteristics are now being used. In this paper, innovative insulation sheet materials with carbon and/or glass fabrics and nano-silica hybrid PU resin are developed. The parameters related to sound performance, such as materials and fabric texture in base fabric, hybrid method of resin, size of silica particle and so on, are investigated. At the same time, the wave analysis code (PZFlex) is used to simulate some of experimental results. As a result, it is found that both bundle density and fabric texture in the base fabrics play an important role on the soundproof performance. Compared with the effect of base fabrics, the transmission loss in sheet materials increased more than 10 dB even though the thickness of the sample was only about 0.7 mm. The results show different values of transmission loss factor when the diameters of silica particles in coating materials changed. It is understood that the effect of the soundproof performance is different due to the change of hybrid method and the size of silica particles. Fillers occupying appropriate positions and with optimum size may achieve a better effect in soundproof performance. The effect of the particle content on the soundproof performance is confirmed, but there is a limit for the addition of the fillers. The optimization of silica content for the improvement of the sound insulation effect is important. It is observed that nano-particles will have better effect on the high soundproof performance. The sound insulation effect has been understood through a comparison between the experimental and analytical results. It is confirmed that the time-domain finite wave analysis (PZFlex) is effective for the prediction and design of soundproof performance materials. Both experimental and analytical results indicate that the developed materials have advantages in lightweight, flexibility, other mechanical properties and excellent soundproof performance.

• Journal of the Korea Concrete Institute
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• v.26 no.1
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• pp.63-70
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• 2014

This experimental study was intended to improve the compressive strength of multi-walled CNT reinforced cementitious composites with efficiency. The variables considered are the degree of sonication, the amount of surfactant, the replacement ratio of silica fume, etc. Optical microscope informed that fiber dispersion of CNT was improved with the increase of sonication time, and the compressive strength was proved to be enhanced as the degree of sonication increased. When superplasticizer as a surfactant had SP/CNT ratio of 4~6, the best improvement in strength was obtained. Silica fume was shown to produce the highest compressive strength at 10% replacement. Microstructure of CNT composites was also analyzed; XRD and SEM results indicated that CNT addition hardly changed hydration products and microstructure, and MIP analysis found the reduction of total porosity as well as the increase of nano-pores with the size of tens of nm instead of the decrease of pore distribution in the region of around 10 ${\mu}m$ and 100 nm. The results of microstructure analysis explains that the strength improvement is closely related to physical contribution rather than chemical influence by adding CNT.