• 한국진공학회:학술대회논문집
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• 한국진공학회 2013년도 제44회 동계 정기학술대회 초록집
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• pp.277-277
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• 2013

The epitaxial graphene on the 4H- or 6H-SiC(0001) surface has been intensively studied due to the possibility of wafer-scale growt. However the existence of interface layer (zero layer graphene) and its influence on the upper graphene layer have been considered as one of the main obstarcles for the industrial application. Among various methods tried to overcome the strong interaction with the substrate through the interface layer, it has been proved that the hydrogen intercalation successfully passivate the Si dangling bond of the substrate and can produce the quasi-free standing epitaxial graphene (QFEG) layers on the siC(0001) surface. In this study, we report the results of the angle-resolved photoemission spectroscopy (ARPES) and Raman spectroscopy for the QFEG layers produced by ex-situ and in-situ hydrogen intercalation.From the ARPES measurement, we confirmed that the Dirac points of QFEG layers exactly coincide with the Fermi level. The band structure of QFEG layer are sustainable upon thermal heating up to 1100 K and robust against the deposition of several metals andmolecular deposition. We also investigated the strain of the QFEG layers by using Raman spectroscopy measurement. From the change of the 2D peak position of graphene Raman spectrum, we found out that unlike the strong compressive strain in the normal epitaxial graphene on the SiC(0001) surface, the strain of the QFEG layer are significantly released and almost similar to that of the mechanically exfoliated graphene on the silicon oxide substrate. These results indicated that various ideas proposed for the ideal free-standing graphene can be tested based on the QFEG graphene layers grown on the SiC(0001) surface.

• Asian-Australasian Journal of Animal Sciences
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• 제21권6호
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• pp.818-823
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• 2008

The interaction of fibre degrading microbes and methanogens was studied using two forages, lucerne (Medicago sativa) hay and maize (Zea mays) hay, as substrate and 2-bromoethanesulphonic acid (BES) as an additive in an in vitro gas production test. Gas and methane production (ml/g dry matter) were significantly higher (p<0.05) on lucerne as compared to maize hay. Inclusion of BES in the incubation medium significantly suppressed methane emission irrespective of substrate. The population density of total bacteria, fungi, Ruminococcus flavefaciens and Fibrobacter succinogenes was higher, whereas that of methanogens was lower with maize hay as compared to lucerne as substrate. BES suppressed methanogen population by 7 fold on lucerene and by 8.5 fold on maize at 24 h incubation as estimated by real time-PCR. This suppression was accompanied by almost complete (>98% of control) inhibition of methanogenesis. The proportion of acetate decreased, whereas that of propionate increased significantly by inclusion of BES, resulting in narrowing of acetate to propionate ratio. In vitro true digestibility (IVTD) of lucerne was significantly higher as compared to maize but BES inclusion did not affect IVTD.

• BMB Reports
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• 제31권2호
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• pp.149-155
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• 1998

The N199H variant of the EcoRI endonuclease has about twice the catalytic activity of the wild-type. A comparison of their biochemical characteristics, using synthetic oligonucleotides 5'-dAAAACTTAAGAAAAAAAAAAA-3' (KA) and 5'-dTTTTTGAATTCTTTTTTTTTT-3' (KT), helps to define the cleavage reaction pathway of these enzymes. Both EcoRI and EcoRI variant N199H were found to cleave singlestranded KA or KT about three times faster than the double-stranded forms, although the KT oligonucleotide was more susceptible. Using the ssDNA substrate in kinetic analyses, lower $K_m$ values were obtained for the N199H variant than for the wild-type at low (50 mM), as well as high (200 mM), sodium chloride concentrations. This difference between the endonucleases is attributed to a grealter accessibility for tbe substrate by the variant, and also a higher affinity for the DNA backbone. It also appears that the relative activities of the two enzymes, particularly at high ionic strength, are proportional to their populations in the monomeric enzyme form. That is, according to gel filtration data, half of the N199H molecules exist as monomers in 200 mM NaCl, whereas those of the wild-type are mainly dimeric. Consequently, the Asp199 residue of the EcoRI endonuclease may be implicated in the protein-protein interaction leading to dimerization, as well as in coupling to DNA substrates. In summary, it is proposed that active monomeric endonuclease molecules, derived from the dimeric enzyme, recognize and form a complex with a single stranded form of the DNA substrate, which then undergoes nucleophilic substitution and cleavage.

• 한국재료학회지
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• 제8권10호
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• pp.956-960
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• 1998

XPS와 glancing angle XRD, AES 및 AFM을 사용하여 $330^{\circ}C$-$800^{\circ}C$사이의 진공분위기에서 열처리할 때, Co/Nb이중층과 $SiO_2$기판 사이의 계면반응을 조사하였다. $600^{\circ}C$에서 Co와 Nb는 서로 활발하게 확산하여, $700^{\circ}C$이상에서는 두 층사이의 충역전이 완전히 일어났다. 그 때 Nb 중간층과 $SiO_2$기판 사이의 반응에 의하여 계면에 일부 NbO가 형성되었으며, 표면에서는 분위기 중의 산소에 의하여 $Nb_2O_5$가 생성되었다. Nb와 기판간의 반응에 의하여 유리된 Si는 $600^{\circ}C$이상에서 잔류 Co 및 Nb와 반응하여 실리사이드를 형성하였다. Co/Nb 이중층 구조는 $800^{\circ}C$에서 열처리한 후 면저항이 급증하기 시작하였는데, 이것은 Co층이 기판과 바로 접하게 되어 계면에너지를 줄이기 위해 응집되기 때문이다.

• 한국진공학회:학술대회논문집
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• 한국진공학회 2012년도 제43회 하계 정기 학술대회 초록집
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• pp.382-382
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• 2012

Nanostructures have a larger surface/volume ratio as well as unique mechanical, physical, chemical properties compared to existing bulk materials. Materials for biomedical implants require a good biocompatibility to provide a rapid recovery following surgical procedure and a stabilization of the region where the implants have been inserted. The biocompatibility is evaluated by the degree of the interaction between the implant materials and the cells around the implants. Recent researches on this topic focus on utilizing the characteristics of the nanostructures to improve the biocompatibility. Several studies suggest that the degree of the interaction is varied by the relative size of the nanostructures and cells, and the morphology of the surface of the implant [1, 2]. In this paper, we fabricate the nanowires on the Ti substrate for better biocompatible implants and other biomedical applications such as artificial internal organ, tissue engineered biomaterials, or implantable nano-medical devices. Nanowires are fabricated with two methods: first, nanowire arrays are patterned on the surface using e-beam lithography. Then, the nanowires are further defined with deep reactive ion etching (RIE). The other method is self-assembly based on vapor-liquid-solid (VLS) mechanism using Sn as metal-catalyst. Sn nanoparticle solutions are used in various concentrations to fabricate the nanowires with different pitches. Fabricated nanowries are characterized using scanning electron microscopy (SEM), x-ray diffraction (XRD), and high resolution transmission electron microscopy (TEM). Tthe biocompatibility of the nanowires will further be investigated.

• 한국결정성장학회지
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• 제1권1호
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• pp.51-59
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• 1991

GaAs를 Si 웨이퍼에 성장시킬 때 초기단계의 핵생성에 대하여 computer simulation을 통해 이론적으로 고찰하였다. 기존의 핵생성이론과는 달리 초기의 미세한 핵의 경우 핵을 구성하는 ledge와 ledge간의 상호작용은 핵의 크기 및 모양에 의하여 결정되는 ledge간의 거리에 따라 변화함을 알 수 있었다. 따라서 여러 형태의 핵에 대하여 분석하여 본 결과 다층의 피라미드 형태로 GaAs 핵이 생성될 때 가장 낮은 excess에너지가 요구되었고 이와 같은 결과는 이러한 형태가 필연적으로 포함하게 되는 에너지가 낮은 Ga(111) facet 때문인 것으로 밝혀졌다. 그러므로 GaAs/Si에서 가장 문제가 되고 있는 전위결함도 초기의 핵생성에 크게 기인함을 알 수 있다.

• Bulletin of the Korean Chemical Society
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• 제24권8호
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• pp.1135-1140
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• 2003

The kinetics and mechanism of the pyridinolysis $(XC_5H_4N)$ of Y-aryl phenyl isothiocyanophosphates (1;$(YC_6H_4O)\;(C_6H_5O)$P(=O)NCS) are investigated in acetonitrile at 55.0 ℃. The Hammett plots for substituent (Y) variations in the substrate (log k₂ vs σY) exhibit a convex upward biphasic type with breaks at Y = H. For electron-donating Y groups the Hammett coefficients, ρY, are positive and cross-interaction constant ρXY is negative, while those for electron-withdrawing Y groups ρY values are negative with a positive ρXY. These results are interpreted to indicate mechanistic change at the breakpoint (σY = 0) from a concerted to a stepwise mechanism with rate-limiting expulsion of the $^-NCS$ group from a trigonal bipyramidal pentacoordinated (TBP-5C) intermediate. Biphasic plots of log k₂ vs σX or $pK_a$(X) with steeper slopes for the more basic nucleophiles are obtained suggesting an equatorial nucleophilic attack in contrast to an apical attack for the less basic nucleophiles with smaller magnitude of ρX or βx.

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 2005년도 춘계학술대회 논문집
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• pp.641-644
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• 2005

The study on the interaction forces of some biological materials is important to understanding biological phenomena and their application to practical purpose. This paper introduces a measuring technique for biological adhesive forces using the AFM(Atomic Force Microscope). Since no standardized thesis on adhesive forces exist, the adhesive forces is defined as adhesive forces against a hardened surface of biological materials. To grant the results are meaningful, which is based on the understanding the surface characteristics of biological materials using the AFM, a nominal value of average adhesive force per unit area should be measured. Therefore the modified AFM probe with small micro glass bead was proposed so that it can guarantee the required contact area for measuring the average adhesive forces. A pyrex glass substrate with circular patterns, which was fabricated by micromachining technique, is introduced in order to controll the contact area. The two types of mussel adhesive proteins, Celltak and recombinant-MGFP5, were tested by the proposed measuring method. The test results show that the adhesive force of the mussel adhesive proteins can be reliably measured by use of this method.

• 약학회지
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• 제40권2호
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• pp.193-201
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• 1996

In order to study the role of C-terminal aromatic region of T4 endonuclease V in the interaction with substrate DNA, NMR and Fluorescence spectrum were recorded. Analysis of flu orescence emission spectra showed that C-terminal region of T4 endonuclease V is in or very near the binding site. In the HSQC spectrum of $^{15}N$-Tyr-labeled T4 endonuclease V*DNA complex, the broadening of a peak was observed. It is presumed that this peak corresponds to one among three tyrosine residues which belong to the WYKYY segment of C-terminal region of T4 endonuclease V. Interactions of peptide fragments consisting of C-terminal residues of T4 endonuclease V with DNAs(TT-, T^T-DNA) were investigated by NMR and Fluorescence experiment. The results suggest that two peptide fragments themselves bind to DNAs and their binding pattern is not an intercalation mode.

• 펄프종이기술
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• 제35권3호
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• pp.21-28
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• 2003

It is essential to use base papers having proper surface characteristics in coating operation for improving coated paper quality and coater runnability. To fulfill these purposes surface sizing of coating base stock with anionic oxidized starch is commonly practiced. It is suggested that use of cationic starch for surface sizing rather than conventional oxidized starch will improve coated paper quality since cationic starch penetrates less into paper structure because of its strong electrostatic interaction with anionically charged paper surface. Strong interaction of cationic surface sizing starch with anionic coating color is expected to promote rapid immobilization of the coating color and improve coating holdout and optical property. The immediate objective of this study was to examine the influence of surface sizing starches on the properties of coated papers. Structural characteristics of the coatings formed on the substrate surface sized with cationic and anionic starches were examined. To enhance the efficiency of cationic surface sizing starch on coated paper properties, strongly charged cationic polymers were added to the surface sizing starch and its effect on coated paper properties was evaluated. Results showed that opacity and light scattering coefficient of coated paper were higher when base paper surface sized with cationic starch was used. Addition of less than 1% of cationic poly-DADMAC to the cationic surface sizing starch improved the opacity of coated paper significantly.