• Journal of the Korean Wood Science and Technology
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• 제48권4호
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• pp.431-449
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• 2020

Structural property of most hydrogels is soft, resulting in low mechanical performance that limits their usage in the biomedical applications. For overcoming the drawback, cellulose nanocrystals (CNCs) were adopted in this study. Effects of CNCs on characteristics and drug delivery performance of poly (vinyl alcohol) based hydrogels were explored. FT-IR results showed that the fabricated hydrogels had semi-IPN (semi-interpenetrating polymer network) by formation of acetal and aldehyde bridge. Water absorption and swelling ratio decreased with increasing CNCs content, and the hydrogels with CNCs showed better viscoelastic performance than the without CNCs. Also, CNCs mostly improved the ability of the hydrogel to absorb the drug and the sustainability of the drug release. These results demonstrated that incorporating CNCs into the hydrogel systems can be a good alternative to improve drug delivery performance and mechanical property of the hydrogels.

• Journal of the Korean Society for Nondestructive Testing
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• 제21권4호
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• pp.439-445
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• 2001

The destructive method is reliable and widely used lot the estimation of material degradation but, it have time-consuming and a great difficulty in preparing specimens from in-service industrial facilities. Therefore, the estimation of degraded structural materials used at high temperature by nondestructive evaluation such as electric resistance method, replica method, Barkhausen noise method, electro-chemical method and ultrasonic method are strongly desired. Ultrasonic nondestructive evaluation technique has been reported good to attain efficiency of measurement, high sensitivity of measurement, and rapidity and reliability of result interpretation. In this study, it was verified experimentally the feasibility of the evaluation of degraded 2.25Cr-1Mo steel specimens which were prepared by the isothermal aging heat treatment at $630^{\circ}C$ by high frequency longitudinal wave method investigating the change of attenuation coefficient by FFT analysis and wavelet transform. Because of carbide precipitation increase and spheroidization near grain boundary of microstructure to aging degradation, attenuation coefficient had a tendency to increase as degradation proceeded. It was identified possibly to evaluate degradation using the characteristics of high-frequency ultrasonics. Frequency dependence of ultrasonic attenuation coefficient to aging degradation appeared large, which made sure that attenuation coefficient is an important parameter for evaluation of aging degradation.

• Korean Journal of Materials Research
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• 제22권5호
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• pp.220-226
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• 2012

Pure zirconia and $x$ mol% calcia partially stabilized zirconia ($x$ = 1.5, 3, and 8) nanopowders were synthesized by hydrothermal method with various reaction temperatures for 24 hrs. The precipitated precursor of pure zirconia and $x$ mol% calcia doped zirconia was prepared by adding $NH_4OH$ to starting solutions; resulting sample was then put into an autoclave reactor. The optimal experimental conditions, such as reaction temperatures and times and amounts of stabilizer CaO, were carefully studied. The synthesized $ZrO_2$ and $x$ mol% CaO-$ZrO_2$ ($x$ = 1.5, 3, and 8) powders were characterized by XRD, SEM, TG-DTA, and Raman spectroscopy. When the hydrothermal temperature was as low as $160^{\circ}C$, pure $ZrO_2$ and $x$ mol% CaO-$ZrO_2$ ($x$ = 1.5 and 3) powders were identified as a mixture of monoclinic and tetragonal phases. However, a stable tetragonal phase of zirconia was observed in the 8 mol% calcia doped zirconia nanopowder at hydrothermal temperature above $160^{\circ}C$. To observe the phase transition, the 3 mol% CaO-$ZrO_2$ and 8 mol% CaO-$ZrO_2$ nanopowders were heat treated from 600 to $1000^{\circ}C$ for 2h. The 3 mol% CaO-$ZrO_2$ heat treated at above $1000^{\circ}C$ was found to undergo a complete phase transition from mixture phase to monoclinic phase. However, the 8 mol% calcia doped zirconia appeared in the stable tetragonal phase after heat treatment. The result of this study therefore should be considered as the preparation of 8 mol% CaO-$ZrO_2$ nanopowders via the hydrothermal method.

• Applied Biological Chemistry
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• 제38권2호
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• pp.111-117
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• 1995

In Escherichia coli, CRP forms a complex with cAMP and acts as a transcriptional regulator of many genes, including sugar metabolism operons. The E. coli MK2001, which is introduced the altered crp, is functional in the expression of lac, ara and man, in the absence of cAMP. However, the expression of mal gene is fully activated by the addition of cAMP or cGMP. The object of the study is cloning of the sfs (sugar fermentation stimulation) genes, which was involved in regulation of mal gene expression with the altered crp gene, and structural analysis and characterization of the genes at the molecular level. We have cloned 5 different E. coli genes which stimulate the maltose metabolism in a crp, cya::km (MK2001) background. Newly identified genes were designated as sfs. One of the sfs genes (pPC1), located at the 53.2 min map position on the E. coli chromosome, was further analyzed. Expression of the genes, which is involved in maltose metabolism, malQ (amylomaltase), was increased to 5.8-fold in the presence of a plasmid, pAP5, containing the subcloned sfs4 gene. The nucleotide seguence of a common 2,126 bp segment of the pPCM1 was determined and two open reading frames (ORF1 and ORF2) were detected. The ORF1 encodes the sfs4 gene and ORF2 encodes a truncated protein. Potential CRP binding site is located in the upstream of the putative promoter in the regulatory region. Expression of the cloned sfs4 gene was positively regulated by the cAMP-CRP complex.

• The Journal of Engineering Geology
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• 제21권4호
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• pp.381-391
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• 2011

Weathering can reduce rock strength and eventually affect the structural stability of a rock mass, which is important in the field of engineering geology. Several methods have been developed to evaluate the degree of weathering, including the chemical weathering index. In this study, we analyzed the weathering degree and characteristics of microtextures and pores in crystalline rocks (gneiss and granites) based on petrographic observations, the chemical weathering index, mineralogy by XRD, microtextural analysis by SEM/EDS, measurements of pore size and surface area by the BET method, and microporosity by X-ray CT. The formation of secondary minerals and microtexture in gneiss and granitic rocks are assumed to be affected by complex processes such as dissolution, precipitation, and fracturing. Hence, it is clear that some chemical weathering indices that are based solely on whole-rock chemistry (e.g., CIA and CWI) are unable to provide reliable assessments of the degree of weathering. Great care is needed to evaluate the degree of chemical weathering, including an understanding of the mineralogy and microtexture of the rock mass, as well as the characteristics of micropores.

• Applied Microscopy
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• 제31권1호
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• pp.49-57
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• 2001

In this study, the distribution of lectin receptors in culutured fibroblast was explored using colloidal gold label complexed with lectin WGA purified from wheat germ (Triticum vulgare). The lectin WGA gold complex, shown to recognize GlcNAc (N-acetylgalactosamine) and NeuNAc (N-acetylneuraminic acid) regions, was applied to detect binding sites in Lowicryl HM 20 sections viewed under electron microscope Labeled sections of the culutured fibroblast revealed gold particles specifically distributed on the cytoplasm and cell surface of the fibroblast. Labeling of 24 hours culutured fibroblast was then quantified and compared to that of 72 hours culutured fibroblast. 24 hours culutured fibroblast sections resulted in specific gold particle distribution on the cytoplasmic vesicle of the culutured fibroblast. These results indicate that lectin WGA receptors are located in the cytoplasmic vesicle and cell surface of the 24 hours culutured fibroblast, and on the cell surface of the 72 hours culutured fibroblast. Therefore, the GlcNAc and NeuNAc regions on the cell surface appear to be functionally associated with cell-recognition and protection from other cell of the tissue, and linked with secretion and exocytosis of the fibroblast cytoplasm.

• Journal of the Korean Ceramic Society
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• 제41권1호
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• pp.86-91
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• 2004

$LiCoO_2$ cathode powders with round particle shaped and nano grain sized of 70-300nm were synthesized by a mechanochemical method. The surface of Li-Co precursor prepared by freeze drying method was modified by $K_2SO_4$ coating and ball milling was used for the coating process. The precursor was crystallized to high temperature form of $LiCoO_2$ at $800^{\circ}C$ and the grain growth was inhibited by the $K_2SO_4$ coating effect. The $K_2SO_4$ coating was not decomposed at $800^{\circ}C$ and prevented the contact in the Li-Co precursor particles. The nano-sized $LiCoO_2$ powder had tetragonal phase and it affected the Li diffusion through the surface of particles. It means that the anode materials for hight performance battery should be satisfied not only small particle size but phase contol on the surface of particles. In this study, the powder characteristics and rate capabilities were compared with a commercial powder and the nano-sized $LiCoO_2$ powder fabricated by the mechanochemical method. And the crucial factor which affects on battery performance was also examined.

• Polymer(Korea)
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• 제35권5호
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• pp.378-384
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• 2011

Silk fibroin is a biocompatible and slowly biodegradable natural polymer. This natural polymer has excellent mechanical properties, non-toxicity, and non-immunogenic properties and has been demonstrated to support tissue regeneration. Also, gelatin is a natural material derived from collagen by hydrolysis and has an almost identical composition as that of collagen. Silk fibroin/gelatin scaffolds have been fabricated by using the freeze-drying method. To establish the scaffold manufacturing condition for silk fibroin and gelatin, we made scaffolds with various compositions of gelatin, glutaldehyde and silk fibroin. The silk fibroin/gelatin scaffolds were characterized using SEM, DSC, and water absorption ability tests. The cellular proliferation was evaluated by WST assay. These results suggested that a scaffold containing 8% of gelatin, 1% of glutaldehyde and 0.3 g of silk fibroin provided suitable characterstics for cell adhesion and proliferation. In conclusion, the silk fibroin/gelatin scaffold may serve as a potential cell delivery vehicle and a structural basis for tissue engineering.

• Journal of the Korean Wood Science and Technology
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• 제37권3호
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• pp.208-215
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• 2009

As a fundamental study to develop absorbing materials on harmful volatile organic compounds (VOC) such as formaldehyde, structural and crystalline characteristics of MDF carbonized at different temperatures were examined by a scanning electron microscope and an X-ray diffraction method. Fibers in surface layer of MDFs showed more compressed morphology than those in middle layer of MDFs, but the porosity of MDFs increased with increasing the carbonized temperature. The wrinkle shape was frequently surfaces of cell walls was more severe than that at the lumina of cells. The shape of pits in the fibers of carbonized MDFs were hardly changed. The cell walls of MDFs carbonized at $400^{\circ}C$ and over showed an amorphous-like structure without cell layering. X-ray diffratograms from the MDFs carbonized at $400^{\circ}C$ showed a trace of crystalline cellulose. On the other hand, an amorphous diffraction pattern from carbons was obtained with the MDFs carbonized at $1,000^{\circ}C$.

• Food Science of Animal Resources
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• 제36권5호
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• pp.665-670
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• 2016

The objectives of this study were conducted to characterize pepsin-soluble collagen (PSC) extracted from bones (PSC-B), skins (PSC-S), and tendons (PSC-T) of duck feet and to determine their thermal and structural properties, for better practical application of each part of duck feet as a novel source for collagen. PSC was extracted from each part of duck feet by using 0.5 M acetic acid containing 5% (w/w) pepsin. Electrophoretic patterns showed that the ratio between α₁ and α₂ chains, which are subunit polypeptides forming collagen triple helix, was approximately 1:1 in all PSCs of duck feet. PSC-B had slightly higher molecular weights for α₁ and α₂ chains than PSC-S and PSC-T. From the results of differential scanning calorimetry (DSC), higher onset (beginning point of melting) and peak temperatures (maximum point of curve) were found at PSC-B compared to PSC-S and PSC-T (p<0.05). Fourier transform infrared spectroscopy (FT-IR) presented that PSC-S and PSC-T had similar intermolecular structures and chemical bonds, whereas PSC-B exhibited slight difference in amide A region. Irregular dense sheet-like films linked by random-coiled filaments were observed similarly. Our findings indicate that PSCs of duck feet might be characterized similarly as a mixture of collagen type I and II and suggest that duck feet could be used for collagen extraction without deboning and/or separation processes.