• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2009.06a
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• pp.235-235
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• 2009

This paper describes the influence of a polycrystalline (poly) 3C-SiC buffer layer on the surface acoustic wave (SAW) properties of poly aluminum nitride (AlN) thin films by comparing the center frequency, insertion loss, the electromechanical coupling coefficient ($k^2$), andthetemperaturecoefficientoffrequency(TCF) of an IDT/AlN/3C-SiC structure with those of an IDT/AlN/Si structure, The poly-AlN thin films with an (0002)-preferred orientation were deposited on a silicon (Si) substrate using a pulsed reactive magnetron sputtering system. Results show that the insertion loss (21.92 dB) and TCF (-18 ppm/$^{\circ}C$) of the IDT/AlN/3C-SiC structure were improved by a closely matched coefficient of thermal expansion (CTE) and small lattice mismatch (1 %) between the AlN and 3C-SiC. However, a drawback is that the $k^2(0.79%)$ and SAW velocity(5020m/s) of the AlN/3C-SiC SAW device were reduced by appearing in some non-(0002)AlN planes such as the (10 $\bar{1}$ 2) and (10 $\bar{1}$ 3) AlN planes in the AlN/SiC film. Although disadvantages were shown to exist, the use of the AlN/3C-SiC structure for SAW applications at high temperatures is possible. The characteristics of the AlN thin films were also evaluated using FT-IR spectra, XRD, and AFM images.

• Bulletin of the Korean Mathematical Society
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• v.26 no.2
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• pp.159-164
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• 1989

Let M be a hypersurface of dimension n(.geq.2) in an (n+1)-dimensional real space form over bar M(c) with constant curvature c and H the second fundamental tensor of M. M is said to be birecurrent if here exists a covariant tensor field .alpha. of order 2 such that .del.$^{2}$H=H .alpha., where .del. is the connection of M. Also, M is said to be recurrent if there exists a 1-form .betha. such that .del.H=H .betha.. Matsuyama [2] recently proved that a recurrent hypersurface M in a real space form is locally symmetric and a complete irreducible birecurrent hypersurface M in a real space form is recurrent. The main purpose of this paper is to characterize the birecurrent or recurrent hypersurface M of a Riemannian manifold with constant curvature c and to prove that M is classified as a cylinder, $M^{n}$ (c) or ( $c_{1}$)* $M^{n-r}$ ( $c_{2}$) where 1/ $c_{1}$+1/ $c_{2}$=1/c.

• Korean Journal of Microbiology
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• v.32 no.2
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• pp.109-114
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• 1994

The Escherichia coli aroA and serC genes constitute a mixed-function operon which involves in two different amino acid biosynthetic pathways. The regulation of expression of serC-aroA operon was evaluated through the use of a serC-araA-lacZ fusion plasmid pWH2. The expression of the serC-aroA operon was decreased by aromatic amino acids such as tyrosine, tryptophan, and phenylalanine. The repressible effects were diminished in E. coli tyrR of trpR strain, indicating the involvemnt of TyrR of TrpR protein in the repression. Tyrosine was competitie with cAMP in the influence on the expression of the serC-AroA operon. From these data, it was suggested that the serC-aroA operon is controlled by aromatic amino acids in a negative manner.

• Journal of Sensor Science and Technology
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• v.16 no.3
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• pp.197-201
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• 2007

The magnetron reactive ion etching (RIE) characteristics of polycrystalline (poly) 3C-SiC grown on $SiO_{2}$/Si substrate by APCVD were investigated. Poly 3C-SiC was etched by $CHF_{3}$ gas, which can form a polymer as a function of side wall protective layers, with additive $O_{2}$ and Ar gases. Especially, it was performed in magnetron RIE, which can etch SiC at a lower ion energy than a commercial RIE system. Stable etching was achieved at 70 W and the poly 3C-SiC was undamaged. The etch rate could be controlled from $20\;{\AA}/min$ to $400\;{\AA}/min$ by the manipulation of gas flow rates, chamber pressure, RF power, and electrode gap. The best vertical structure was improved by the addition of 40 % $O_{2}$ and 16 % Ar with the $CHF_{3}$ reactive gas. Therefore, poly 3C-SiC etched by magnetron RIE can expect to be applied to M/NEMS applications.

• Korean Journal Plant Pathology
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• v.14 no.3
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• pp.240-246
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• 1998

A cDNA encoding desiccation-related protein was isolated from a flower bud cDNA library of Chinese cabbage (C-DH) and its nucleotide sequence was characterized. It contains 679 bp nucleotides with 501 bp open reading frame. The amino acid sequence of the putative protein showed the highest amino acid sequence homology (79 % identity) to dehydrin protein in Gossypium hirsutum. Also, the C-DH shares 48-52% amino acid sequence identity with the other typical dehydrin proteins in plant cells. When the amino acid sequence of their proteins were aligned, several peptide motifs were well conserved, of which function has to be solved. Particularly the C-DH contains 15 additional amino acids at its N-terminus. Genomic Southern blot analysis using the coding region of C-DH showed that the C-DH consists of a single copy gene in Chinese cabbage genome. The C-DH mRNA, whose transcript size is 0.7 kb, was expressed with a tissue-specific manner. It was highly expressed in seed, flower buds and low expression as detected in root, stem or leaf tissues of Chinese cabbage. And the transcript level of C-DH was significantly induced by the treatment of plant hormone, abscisic acid and water-deficit conditions.

• Journal of the Korean Society of Industry Convergence
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• v.20 no.2
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• pp.149-155
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• 2017

Mechanical properties of carbon coated $SiC_f/SiC$ composites have been investigated, in conjunction with a detailed analysis of microstructure. Especially, the fracture behavior of $SiC_f/SiC$ composites by the induction of carbon coating layers has been examined. The matrix region of $SiC_f/SiC$ composites with ultra-fine SiC powders were consolidated by a liquid phase sintering (LPS) process, using a sintering additive of $Al_2O_3-Y_2O_3$ powder compound. In this composite, plain and satin- woven Tyranno SA fabrics were also utilized as a reinforcing material. A carbon interfacial layer was coated around satin-woven SiC fabrics. The characterization of LPS-$SiC_f/SiC$ composites was investigated by means of SEM and three point bending test.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.20 no.9
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• pp.405-411
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• 2019

In this study, tensile tests were carried out on materials (A516-60, A283-C, A285-C, and SB410) for structural and pressure vessels at temperatures of $20^{\circ}C$, $-20^{\circ}C$, and $-40^{\circ}C$, and the changes in the mechanical properties were analyzed. Compared to the results at $20^{\circ}C$, the average yield stress increased by 6.4% and 7.5% at $-20^{\circ}C$ and $-40^{\circ}C$ for A516-60, while the average tensile stress increased by 1.3% and 4.1%, respectively. The average elongation decreased by 4.7% and 20.4% at these temperatures. In the case of A283-C, the average yield stress increased 8.8% and 9.8%, the average tensile stress increased by 4.1% and 5.9%, and the average elongation rate decreased by 7.4% and 9.9% at $-20^{\circ}C$ and $-40^{\circ}C$, respectively. For A285-C, the average yield stress increased by 1.8% and 8.6%, and the average tensile stress increased by 2.6% and 5.3%, respectively, but there was little change in the average elongation. Finally, for SB410, the average yield stress increased by 7.1% and 11.8%, the average tensile stress increased by 4.3% and 5.5%, but the average elongation rate decreased by 8.7% and 13.5%, respectively.

• Transactions on Electrical and Electronic Materials
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• v.12 no.3
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• pp.89-92
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• 2011

Hydrogenated amorphous carbon (a-C:H) films were deposited by plasma enhanced chemical vapor deposition on silicon substrates. a-C:H thin film was irradiated to a typical He-Cd laser to study its emitting properties. The photoluminescence (PL) intensity during the irradiation achieved a maximum value when 2,000 seconds elapsed. Fourier transform infrared measurement revealed a-C:H thin film suffered transformation from a polymer-like to graphite-like phase during laser irradiation. Thermal annealing was done at various temperatures, ranging from room temperature to $400^{\circ}C$ in the atmosphere, to investigate structural changes in a-C:H film by heat generation during the emission. PL intensity of a-C:H thin film increased 1.5 times without apparent structural change, as annealing temperature increased up to $200^{\circ}C$. However, a-C:H film above $200^{\circ}C$ exhibited significant decrease of PL accompanying dehydrogenation. This led to a red shift of the PL peak.

• THE INTERNATIONAL COMMERCE & LAW REVIEW
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• v.71
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• pp.245-265
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• 2016

A number of Chinese students who are studying in Korea have been gradually increasing since Korea and China established diplomatic relations. Many of them sale Korean products to China while studying for their degree programs in colleges. This kind of transactions can be named C2C overseas direct sales. C2C overseas direct sales which are being performed by Chinese student are good for exportation of Korean products. However Some of these transactions are not legal according to present law, First, Chinese student don't have legal status to make the transactions. Second, Chinese students usually make false declarations for evading the taxes, including tariff and VAT, Third, Chinese students can not offer the after-sale service for the goods for the Chinese consumers. Although C2C transactions have some legal matters, they should not be banned by a one-size-fits-all method. In this study, we highly recommend for the development of C2C transactions, First, Korean government should give Chinese students legal status. Second, China customs must strictly prohibit illegal activities of smuggling by taking advantage of postal route. Third, sellers in China can offer the after-sale service to consumers through some specialist A/S firms.

• Proceedings of the Korea Committee for Ocean Resources and Engineering Conference
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• 2006.11a
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• pp.158-161
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• 2006

SiC materials have been extensively studied for high temperature components in advanced energy conversion system and advanced gas turbine. However, the brittle characteristics of SiC such as law fracture toughness and law strain-to fracture impose a severe limitation on the practical applications of SiC materials. SiC/SiC composites can be considered as a promising candidate in various structural materials, because of their good fracture toughness. In this composite system, the direction of SiC fiber will give an effect to the mechanical properties. It is therefore important to control a properdirection of SiC fiber for the fabrication of high performance SiC/SiC composites. In this study, unidirection and two dimension woven structures of SiC/SiC composites were prepared starting from Tyranno SA fiber. SiC matrix was obtained by nano-powder infiltration and transient eutectoid (NITE) process. Effect of microstructure and density on the sintering temperature in NITE-SiC/SiC composites are described and discussed with the fiber direction of unidirection and two dimension woven structures.