• Microbiology and Biotechnology Letters
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• v.44 no.3
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• pp.324-332
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• 2016

A bacterial strain capable of hydrolyzing xylan was isolated from fermented soybean paste obtained from a domestic Buddhist temple, using enrichment culture with rice straw as a carbon source. The isolate, named YB-1301, was identified as Bacillus safensis on the basis of its DNA gyrase subunit B gene (gyrB) sequence. The xylanase productivity of strain YB-1301 was drastically increased when it was grown in the presence of wheat bran or various xylans. In particular, the maximum xylanase productivity reached above 340 U/ml in the culture filtrate from LB broth supplemented with only birchwood xylan at shake-flask level. The xylanase production was significantly induced by xylans at the stationary growth phase in LB medium containing xylan, whereas only a small amount of xylanase was constitutively produced from cells grown in LB medium with no addition of xylan. Furthermore, xylanase biosynthesis was induced more rapidly by the enzymatically hydrolyzed products of xylan than by the non-hydrolyzed xylan. In addition, the xylanase in the culture filtrate of B. safensis YB-1301 was found to have optimal activity at 55℃ and pH 6.5–7.0.

• 한국초전도학회:학술대회논문집
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• v.9
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• pp.71-74
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• 1999

We have fabricated high-T$_c$ superconducting YBa$_2Cu_3O_{7-{\delta}}\;/SrTiO_3/\;YBa_2Cu_3O_{7-{\delta}}$ (YBCO/STO/YBCO) multilayer structure on (001) $SrTiO_3$ substrate by using pulsed laser deposition technique for applying to ground plane of single flux quantum digital circuits. In this structure, the top and bottom YBCO layers were connected through the holes in the STO insulating layer. The critical temperature of the two YBCO layers connected each other was 86 K after annealing at 500 $^{\circ}C$ in $O_2$ atm for about 60 hr. This result shows that the annealing process is very important fabricating YBCO/STO/YBCO multilayer structure An experiment to optimize the fabrication process of YSCO/ST0/YBCO multilayer structure with good quality is in progress.

• Journal of the Korean Ceramic Society
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• v.53 no.4
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• pp.456-462
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• 2016

$NaCaGd(MoO_4)_3:Ho^{3+}/Yb^{3+}$ ternary molybdates were successfully synthesized by microwave sol-gel method for the first time. Well-crystallized particles formed after heat-treatment at $900^{\circ}C$ for 16 h showed a fine and homogeneous morphology with particle sizes of $3-5{\mu}m$. Under excitation at 980 nm, the UC intensities of the doped samples exhibited strong yellow emissions based on the combination of strong emission bands at the 520-nm and 630-nm emission bands in the green and red spectral regions, respectively. The strong 520-nm emission band in the green region corresponds to the $^5S_2/^5F_4{\rightarrow}^5I_8$ transition of $Ho^{3+}$ ions, while the strong 630-nm emission band in the red region appears to be due to the $^5F_5{\rightarrow}^5I_8$ transition of the $Ho^{3+}$ ions. The optimal $Yb^{3+}:Ho^{3+}$ ratio was found at 9:1, as indicated by the composition-dependent quenching effect of $Ho^{3+}$ ions. The pump power dependence of the upconversion emission intensity and the Commission Internationale de L'Eclairage chromaticity coordinates of the phosphors were evaluated in detail.

• Journal of the Korean Ceramic Society
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• v.54 no.1
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• pp.70-74
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• 2017

Up-conversion (UC) and down-conversion (DC) luminescence of $LuNbO_4:0.18Yb^{3+}$, $xEr^{3+}$ (x = 0.01-0.07) powders were investigated. Post-annealed powders were composed of a single $LuNbO_4$ phase with a monoclinic fergusonite structure, whereas as-calcined powders contained a small amount of the $Li_3NbO_4$ impurity phase. Under near infrared radiation, the UC spectra of the post-annealed powders exhibited the strong green and weak red emission peaks assigned to the transition of $^2H_{11/2}/^4S_{3/2}$ and $^4F_{9/2}$ to the ground state ($^4I_{15/2}$) of $Er^{3+}$ ions, respectively; the green and red emission intensities were approximately 330 and 270% stronger, respectively, than those of the as-calcined powders. A two-photon UC process was involved in the emission as a result of an energy transfer from $Yb^{3+}$ to $Er^{3+}$. Under ultraviolet radiation, the DC spectra exhibited broad blue and sharp green emission bands. The DC mechanism was explained using self-activated $[NbO_4]^{3-}$ niobates and an energy transfer from $[NbO_4]^{3-}$ to $Er^{3+}$.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2009.06a
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• pp.180-181
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• 2009

$(Ba_{0.6},Sr_{0.3}Ca_{0.1})TiO_3$ powders, which were prepared by sol-gel method using a solution of Ba-acetate, Sr-acetate and Ca-acetate and Ti iso-propoxide, $(Ba_{0.6},Sr_{0.3}Ca_{0.1})TiO_3$ array thick films doped with 0.1 mol% $MnCO_3$ and $Yb_2O_3$ (0.1~0.7 mol%) were fabricated by the screen printing method on the alumina substrate. And the structural and electrical properties as a function of $Yb_2O_3$ amount were investigated. The thickness of all (Ba,Sr,Ca)$TiO_3$ thick films was approximately 60mm. The Curie temperature of doped with 0.1 mol% $Yb_2O_3$ specimen was $45^{\circ}C$, and the dielectric constant and at this temperature was 1062.

• Current Optics and Photonics
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• v.2 no.1
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• pp.79-84
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• 2018

We present a novel and simple method to enable spatially selective $ZnAl_2O_4$ nanocrystal formation on the surface of $B_2O_3$-$Al_2O_3$-ZnO-CaO-$K_2O$ glass by employing localized laser heating. Optimized precipitation of glass-ceramics containing nanocrystals doped with $Eu^{3+}$ and $Yb^{3+}$ ions was performed by controlling $CO_2$ laser power and scan speed. Micro-x-ray diffraction and transmission electron microscopy revealed the mean size and morphology of nanocrystals, and energy dispersive x-ray spectroscopy showed the lateral distribution of elements in the imaged area. Laser power and scan speed controled annealing temperature for crystalization in the range of 1.4-1.8 W and 0.01-0.3 mm/s, and changed the size of nanocrystals and distribution of dopant ions. We also report more than 20 times enhanced downshift visible emission under ultraviolet excitation, and 3 times increased upconversion emission from $Eu^{3+}$ ions assisted by efficient sensitizer $Yb^{3+}$ ions in nanocrystals under 980 nm excitation. The confocal microscope revealed the depth profile of $Eu^{3+}$ ions by showing their emission intensity variation.

• Microbiology and Biotechnology Letters
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• v.44 no.3
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• pp.370-375
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• 2016

Two xylanase genes were cloned into Escherichia coli from Bacillus sp. YB-1401 and B. amyloliquefaciens YB-1402, which had been isolated as mannanase producer from home-made doenjang, respectively, and their nucleotide sequences were determined. Both xylanase genes consisted of 642 nucleotides, encoding polypeptides of 213 amino acid residues. The deduced amino acid sequences of the YB-1401 and YB-1402 xylanase, designated Xyn1401 and Xyn1402, differed from each other by single amino acid residue, Asn for Xyn1401 and Lys for Xyn1402, corresponding to amino acid position of 127. Their amino acid sequences were highly homologous to those of xylanases belonging to the glycosyl hydrolase family 11. The 28 amino acid stretch in the N-terminus of both enzymes was predicted as signal peptide by SignalP4.1 server. Both xylanases were localized at the level of 91−94% in culture filtrate of the recombinant E. coli cells, suggesting they were secreted efficiently in E. coli cells. The optimal reaction conditions were 50℃ and pH 6.0 for Xyn1401, and 55℃ and pH 6.5 for Xyn1402, respectively, indicating one amino acid difference from each other affected pH and temperature profiles of their activities. In addition, their thermostabilities were somewhat different from each other.

• Korean Journal of Materials Research
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• v.14 no.4
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• pp.270-275
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• 2004

Due to the luminescence by$ Er ^{ 3+}$ activator, Er-doped $LaPO_4$ powders can be applied for optical amplification materials. In this study, $LaPO_4$:Er nanoparticles were synthesized in solution system using a high-boiling coordinating solvent and their properties were investigated through various spectroscopic techniques. The nanoparticles were to take a single phase of monazite structure by a X-ray diffraction analysis and to have the 5-6 nm of particles size with narrow size distribution by a TEM. And it was confirmed by the EA and FT-IR analyses that the surfaces of nanoparticles are coordinated with the solvent molecules, which will possibly keep from agglomerating between LaPO$_4$:Er nanoparticles. In the emission spectrum of $LaPO_4$:Er nanoparticle at NIR region, on the other hand, it was measured that the emission intensity is very weak, which is due to the transition from $^4$$I_{(13/2)}$ to $^4$$I_{(15/2)}$ of $Er^{3+ }$ion. It was interpreted that the weak luminescence of $LaPO_4$:Er is originated from the hydroxyl groups adsorbed on the surfaces of the nanoparticles, because OH group acts as an efficient quencher for the $^4$$I_{(13/2)}$ \longrightarrow $^4$$I_{(15/2)}$ emission of $Er^{3+}$ activator. But the co-doping of Yb$^{3+}$ as a sensitizer in this nanoparticle results in the increase of the emission intensity at 1539 nm due to the effective energy transfer from $Yb^{3+}$ to $Er^{3+}$ . In addition, the synthesized nanoparticles exhibited good dispersibility with some polymers and effective luminescence at NIR region.n.

• Electrical & Electronic Materials
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• v.6 no.6
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• pp.514-522
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• 1993

본 연구에서는 Ag/ 첨가에 의한 YB $a_{2}$C $u_{3}$ $O_{7-{\delta}}$산화물의 초전도 특성 변화를 조사하였다. Ag가 첨가된 YB $a_{2}$C $u_{3-x}$A $g_{x}$ $O_{7-{\delta}}$ 산화물 시료를 만들고 이 시료들에 대한 X-ray 회절분석, IR흡수 스펙트럼분석, 임계온도(Tc)측정 및 자화(M-H)특성 측정등을 통하여 제조된 시료의 물리적 성질을 조사하였다. X-ray 회절실험 결과로 부터 x.leq.0.03인 경우에는 YB $a_{2}$C $u_{3-x}$A $g_{x}$ $O_{7-{\delta}}$가 단일상의 물질로 존재하고 x가 증가함에 따라 불순물상( $Y_{2}$ $O_{3}$, 순Ag)이 나타남을 알 수 있었다. IR흡수의 실험결과에서 Cu와 치환되어 들어간 Ag의 Ag-O 결합에 의한 흡수 스펙트럼(670$cm^{-1}$ /)이 관측되었다. 실험 결과로 부터 치환된 Ag의 양 x가 증가함에 따라 Tc가 조금씩 낮아지는 경향이 있었으며 자화의 세기 및 임계자장( $H_{C2}$)은 급격히 감소함을 알 수 있었고 또 M-H특성곡선에는 히스테리시스 특성이 나타났다.났다..났다.다.

• Electrical & Electronic Materials
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• v.7 no.4
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• pp.289-293
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• 1994

Thin films of YB $a_{2}$C $u_{3}$$O_{7-x}$ supercondYB $a_{2}$C $u_{3}$$O_{7-x}$uctor were prepared on (100) SrTi $O_{3}$ substrates by pulsed laser deposition using visible light laser. Q-switched Nd:YAG(532 nm, 30 ns) pulsed laser was used for deposition. The effects of substrate temperature and oxygen pressure during deposition on films were studied. Critical current density of 2.93*10$^{6}$ A/c $m^{2}$ at 77K and Tc(zero)=91.7K were obtained from the film prepared with Tsub=745.deg. C and $P_{02}$=200 mTorr. XRD analysis showed that the grown film has c-axis normal orientation to the substrate surface and has single phase. Surface morphology of the film has been improved by interfering the plume ejected from YB $a_{2}$C $u_{3}$$O_{7-x}$ target.arget.t.