• 한국자기학회지
• /
• 제16권1호
• /
• pp.1-5
• /
• 2006

결정구조는 같은 spinel 구조이나, 자기적으로는 각각 반강자성과 준강자성 특성을 띠고 있는 $Co_3O_4$와 자철광 $Fe_3O_4$의 혼성 Co-ferrite인 $Co_xFe_{1-x}O_4$ 박막을 sol-gel법으로 제조하여, Fe 이온에 대한 Co 이온 치환으로 발생된 양이온 거동이 Co-ferrite 박막의 결정구조 및 자기적 특성에 미치는 효과를 XRB 실험, VSM 측정, 그리고 Conversion Electron Mossbauer Spectroscopy (CEMS) 실험으로 조사하였다. 그 결과 $Co^{3+}$ 이온이 주로 $Fe^{3+}$ 이온을 치환하여 단위정의 크기가 감소를 가져오며, 결정구조는 inverse spinel 구조에서 normal spinel 구조로 변환된다. CEMS 분광실험을 통하여 확인된 Fe 이온의 site preference는 주로 $Fe^{3+}$ 이온이 $Co^{3+}$ 치환됨을 보여주고 있으며, 동시에 B-site의 $Co^{2+}$ 이온은 A-site로 이동된다. 자화곡선 측정결과 Co 조성값의 증가로 자기 moment값이 감소되는 것으로 나타났는데, 이것은 low spin상태의 $Co^{3+}$이 high spin상태의 $Fe^{3+}$이온을 치환하여 주로 발생한 것이다.

• 한국초전도ㆍ저온공학회논문지
• /
• 제7권4호
• /
• pp.1-3
• /
• 2005

Superconducting $MgB_2$ fibers are in-situ grown by a diffusion method. The fibers are prepared by exposing B filaments to Mg vapor inside a folded Ta foil over a wide range of temperature and growth time. The materials are sealed inside a quartz tube by gas welding. The as - grown fibers are characterized by scanning electron microscopy and energy dispersive x - ray analysis. The fibers have a diameter of about $110{\mu}m$. Surface morphology of the fibers looks dependent on growth temperature and mixing ratio of Mg and B. Radial distribution of Mg ions into B is observed and analyzed over the cross - sectional area. Transport properties of the $MgB_2$ fibers are examined by a physical property measurement system. The $MgB_2$ fibers grown at $900^{\circ}C$ for 2 hours show a superconducting transition at 39.8K with ${\Delta}T_c<$ 2.0 K. Resistance at room temperature $MgB_2$ is 3.745 $\Omega$ and residual resistivity ratio (RRR) is estimated as 4.723.

• Journal of Microbiology and Biotechnology
• /
• 제23권6호
• /
• pp.818-825
• /
• 2013

We isolated and functionally characterized the ${\alpha}$- and ${\beta}$-subunits (ApCpnA and ApCpnB) of a chaperonin from Aeropyrum pernix K1. The constructed vectors pET3d-ApCpnA and pET21a-ApCpnB were transformed into E. coli Rosetta (DE3), BL21 (DE3), or CodonPlus (DE3) cells. The expression of ApCpnA (60.7 kDa) and ApCpnB (61.2 kDa) was confirmed by SDS-PAGE analysis. Recombinant ApCpnA and ApCpnB were purified by heat-shock treatment and anion-exchange chromatography. ApCpnA and ApCpnB were able to hydrolyze not only ATP, but also CTP, GTP, and UTP, albeit with different efficacies. Purified ApCpnA and ApCpnB showed the highest ATPase, CTPase, UTPase, and GTPase activities at $80^{\circ}C$. Furthermore, the addition of ApCpnA and ApCpnB effectively protected citrate synthase (CS) and alcohol dehydrogenase (ADH) from thermal aggregation and inactivation at $43^{\circ}C$ and $50^{\circ}C$, respectively. In particular, the addition of ATP or CTP to ApCpnA and ApCpnB resulted in the most effective prevention of thermal aggregation and inactivation of CS and ADH. The ATPase activity of the two chaperonin subunits was dependent on the salt concentration. Among the ions we examined, potassium ions were the most effective at enhancing the ATP hydrolysis activity of ApCpnA and ApCpnB.

• 한국토양비료학회지
• /
• 제40권1호
• /
• pp.64-70
• /
• 2007

본 실험은 서로 다른 온도조건하에서 두 가지 Na 화합물을 이용하여 Ca-벤토나이트를 Na-벤토나이트 전환하였다. 두 가지 Na 화합물은 양이온 원으로 Na를 가지고 있는 5가지 화합물 중에서 선택하였다. 전환된 Na-벤토나이트의 팽창능은 Na의 농도가 높아질수록 증가하였으며 반면 온도가 증가할수록 최대 Na 농도는 감소하는 경향을 보였다. Na_2CO_3 은 조사된 Na-화합물 중에서 최대 팽창능을 보여주었으며 팽창지수는 처리온도가 최대 100 에 도달할 때까지 최고로 증가하였다. 동일 Na 처리농도에서는 팽창지수는 체류시간이 증가하거나 온도가 높아질 때 다소 감소하였다. 전환된 Na-벤토나이트의 흡착은 조사된 Pb나 Cd의 평형농도가 증가함에 따라 증가하는 경향을 보였으며 Pb의 흡착량이 Cd보다 다소 높은 것으로 조사되었다. 그리고 전환된 Na-벤토나이트에 Pb와 Cd의 흡착은 5 % $Na_2CO_3$. ${\approx}$ 5% $NaHCO_3$ > 3 % $NaHCO_3$ > 3 % $Na_2CO_3$ > 1 % $NaHCO_3$ > 1 % $Na_2CO_3$ > 원형 Na-B > 원형 Ca-B. 그러나 이러한 결과는 CEC에 따른 흡착의 결과와는 다소 상반되는 결과를 보여주고 있다.

• 한국재료학회지
• /
• 제18권12호
• /
• pp.678-682
• /
• 2008

This study investigates $Bi_2O_3$-$B_2O_3$-BaO-ZnO glass with variations of the $Co_3O_4$ content (0.25, 0.5, 1, and 2 wt%) and the interaction between transparent dielectric and Ag electrodes heat-treated at $500-560^{\circ}C$ for 30 min. The glass transition temperature, softening temperature and thermal expansion coefficient were $432^{\circ}C$, $460^{\circ}C$ and $81.4{\times}10^{-7}/^{\circ}C$, respectively. The transmittance of 0.25 wt% $Co_3O_4$ to which dielectric was added was highest and was decreased due to coloration with the addition of more than 0.25 wt%. However, without $Co_3O_4$, the transmittance of the transparent layer was decreased due to the formation of $Ba_5Bi_3$; however, the occurrence of the crystal phase decreased as a result of the addition of $Co_3O_4$. The amount of $Co^{2+}$ ions increased as the $Co_3O_4$ increased. With a maximum of $Co^{3+}$ ions, the highest transmittance was observed.

• KSBB Journal
• /
• 제19권2호
• /
• pp.159-163
• /
• 2004

$\AA$의 분해능을 가진 Bacillus macerans에서 분리 정제한 cyclodextrin glucanotransferase의 결정 구조를 X-ray를 이용하여 분자 대치법을 사용하여 밝혔다. 정확한 구조는 16.6% ( $R_{free}$ = 20.5%)의 결정학적 R-factor를 가지고 있다. 두 개의 $Ca^{2+}$$_{-}$/ 이온이 점유된 새로운 금속 결합자리는 활성 자리의 도달 채널에서 발견되었다. $Ca^{2+}$$_{-}$/ 이온에 결합하는 음의 하전을 띤 아미노산 잔기들이 많이 밀집되어 있고 이 때, domain A ($\alpha$H에서 아미노산 잔기 283-297)의 중심부에 연결 부분은 $\beta$ 13-$\alpha$G 이었다. $\beta$13-$\alpha$G 부분은 활성 자리의 입구에 위치한 subsite 1에서 -1 과 Tyr260 (subsite 2)사이에 있는 촉매 부위 Glu258을 포함하고 있다. 비록 $\alpha$-CGTase 부류에서 잘 보존되어 있지는 않으나, 새로운 $Ca^{2+}$$_{-}$/ 자리 3a,b가 이 $\alpha$-CGTase의 활성도와 생성물의 특이성에 중요한 역할을 하리라 추측된다.다.

• Corrosion Science and Technology
• /
• 제9권6호
• /
• pp.259-264
• /
• 2010

In continuous hot dip galvanizing process, oxide formation on steel surface has an influence on Zn wetting. High strength automotive steel contains high amount of Si and Mn, where Si-Mn composite oxides such as $Mn_2SiO_4$ or $MnSiO_3$ covers the surface after annealing. Zn wetting depends on how the aluminothermia reaction can reduce the Mn-Si composite oxides and then form inhibition layer such as $Fe_2Al_5$ on the steel surface. The outward diffusion of metallic ions such as $Mn^{2+}$, $Si^{2+}$ in the steel matrix is very important factor for the formation of the surface oxides on the steel surface. The surface state and grain boundaries provide an important role for the diffusion and the surface oxide reactions. Some elements such as P, Sb, and B have a strong affinity for the interface precipitation, and it influence the diffusivity of metallic ions on grain boundaries. B oxide forms very rapildly on the steel surface during the annealing, and this promote complex oxides with $SiO_2$ or MnO. P has inter-reacted with other elements on the grain boundaries and influence the diffusion through on them. Small addition of Sb could suppress the decarburization from steel surface and retards the formation of internal and external selective oxides on the steel surface. Interface control by the trace elements such as Sb could be available to improve the Zn wettability during the hot dip galvanizing.

• 한국진공학회:학술대회논문집
• /
• 한국진공학회 2000년도 제18회 학술발표회 논문개요집
• /
• pp.180-180
• /
• 2000

Plasma source ion implantation is a new doping technique for the formation of shallow junction with the merits of high dose rate, low-cost and minimal wafer charging damage. In plasma source ion implantation process, the wafer is placed directly in the plasma of the appropriate dopant ions. Negative pulse bias is applied to the wafer, causing the dopant ions to be accelerated toward the wafer and implanted below the surface. In this work, inductively couples plasma was generated by anodized Al antenna that was located inside the vacuum chamber. The outside wall of Al chamber was surrounded by Nd-Fe-B permanent magnets to confine the plasma and to enhance the uniformity. Before implantation, the wafer was pre-sputtered using DC bias of 300B in Ar plasma in order to eliminate the native oxide. After cleaning, B2H6 (5%)/H2 plasma and negative pulse bias of -1kV to 5 kV were used to form shallow p+/n junction at the boron dose of 1$\times$1015 to 5$\times$1016 #/cm2. The as-implanted samples were annealed at 90$0^{\circ}C$, 95$0^{\circ}C$ and 100$0^{\circ}C$during various annealing time with rapid thermal process. After annealing, the sheet resistance and the junction depth were measured with four point probe and secondary ion mass spectroscopy, respectively. The doping uniformity was also investigated. In addition, the electrical characteristics were measured for Schottky diode with a current-voltage meter.

• 대한화학회지
• /
• 제37권8호
• /
• pp.773-778
• /
• 1993

Tl$^+$이온 센서로서 크라운 에테르 B15C5와 DB18C6를 중성운반체로 한 PVC 액체막 이온 선택성 전극을 제작하였다. 막용매로는 DOA, NPPE 및 NPOE를 사용하였으며 친유성 염, KTClPB의 농도를 변화시킨 여러가지 조성의 막을 시험하였다. B15C5와 DB18C6 막 전극의 감응전위는 농도범위, 10$^{-1}$∼10$^{-5}$M에서 직선으로 나타났으며 최대 기울기는 전극에 따라서 40∼55 mV/decade였다. 선택계수는 분리용액법으로 결정하였으며 알카리금속 이온, 알칼리토금속 이온 및 일부 전이금속 이온에 대하여 좋은 선택성을 나타냈다. 제작된 액체막 전극은 Ph > 3 에서 안정한 감응전위를 보였다.

• BMB Reports
• /
• 제35권3호
• /
• pp.330-336
• /
• 2002

The lgtB genes that encode $\beta$-1,4-galactosyltransferases from Neisseria meningitidis ATCC 13102 and gonorrhoeae ATCC 31151 were isolated by a polymerase chain reaction using the pfu DNA polymerase. They were expressed under the control of lac and T7 promoters in Escherichia coli M15 and BL21 (DE3). Although the genes were efficiently expressed in E. coli M15 at $37^{\circ}C$ (33 kDa), most of the $\beta$-1,4-galactosyltransferases that were produced were insoluble and proteolysed into enzymatically inactive polypeptides that lacked C-terminal residues (29.5 kDa and 28 kDa) during the purification steps. When the temperature of the cell growth was lowered to $25^{\circ}C$, however, the solubility of the $\beta$-1,4-galactosyltransferases increased substantially. A stable N-terminal his-tagged recombinant enzyme preparation could be achieved with E. coli BL21 (DE3) that expressed lgtB. Therefore, the cloned $\beta$-1,4-galactosyltransferases were expressed under the control of the T7 promoter in E. coli BL21 (DE3), mostly to the soluble form at $25^{\circ}C$. The proteins were easily purified to homogeneity by column chromatography using Ni-NTA resin, and were found to be active. The galactosyltransferases exhibited pH optimum at 6.5-7.0, and had an essential requirement for the $Mn^{+2}$ ions for its action. The $Mg^{+2}$ and $Ca{+2}$ ions showed about half of the galactosyltransferase activities with the $Mn^{+2}$ ion. In the presence of the $Fe^{+2}$ ion, partial activation was observed with the $\beta$-1,4-galactosyltransferase from N. meningitidis(64% of the enzyme activity with the $Mn^{+2}$$Ni^{+2}$, $Zn^{+2}$, and $Cu^{+2}$ ions could not activate the $\beta$-1,4-galactosyltransferase activity. The inhibited enzyme activity with the $Ni^{+2}$ ion was partially recovered with the $Mn^{+2}$$Fe^{+2}$, $Zn^{+2}$, and $Cu^{+2}$ ions, the $Mn^{+2}$$\beta$-1,4-galactosyltransferase activity was 1.5-fold stimulated with the non-ionic detergent Triton X-100 (0.1-5%).