• Journal of the Korean Vacuum Society
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• v.19 no.6
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• pp.489-494
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• 2010

Enhance signal-to-noise ratio, slow positron coincidence Doppler Broadening method has been applied to study of characteristics of $Nb_3Ge$ superconductor film, which were performed from 20 K to 300 K sample temperature near Tc of it. In this investigation the numerical analysis of the Doppler spectra was employed to the determination of the shape parameter, S, defined as the ratio between the amount of counts in a central portion of the spectrum and the total counts of whole spectrum. The S-parameter values between 0.598 and 0.594 were decreased while the temperature were decreasing, that indicated the voids into the samples. The temperature dependence came from specific positron trapping rate into the vacancy-type defects. It is believed that the positrons annihilate with normal-electrons instead of super-electrons in the Nb3Ge superconductor.

• Proceedings of the Korea Association of Crystal Growth Conference
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• 1997.10a
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• pp.129-133
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• 1997

본 연구에서는 LiNbO$_3$ 단결정 소재의 광손상에 대한 저항성을 향상시키는 첨가물로 잘 알려져 이쓴 MgO 및 ZnO를 첨가하여 육성한 조화용융조성(congruent melting composition)의 LiNbO$_3$ 단결정의 domain 구조는 이들 dopants를 첨가함에 따라 single domain에서 ring 형태의 주기적인 domains으로 변화함을 확인하였고, 첨가된 이온이 domain 형성에 미치는 영향을 전자현미경(SEM-WDS)으로 관찰하였다. 또한, 육성한 [Li1-5xNb5(x-y)Mg(or Zn)5y]Nb1-4x+3yO3 단결정들의 유전율(전이온도) 변화 및 광학적 특성[광투과율, 굴절률]을 측정하여 undoped LiNbO$_3$단결정과 비교하였다. 첨가물을 첨가함에 따라 전이온도는 약 20~3$0^{\circ}C$정도 증가하였으며, 10-3 order의 굴절률 변동치를 나타내었다. 또한, 육성된 결정들의 투과율은 대체로 70~80%를 나타내었고, 첨가물을 첨가함에 따라 흡수단과 OH- 흡수 band는 단파장쪽으로 각각 약 5~10nm, 40nm이동됨을 확인하였다. 이는 LiNbO$_3$단결정의 광손상 저항성이 향상되었음을 간접적으로 보여주는 결과이다.

• Transactions of Materials Processing
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• v.26 no.1
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• pp.48-54
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• 2017

The dissolution and precipitation of Nb, which has been known as strong carbide-forming element, play a key role in controlling phase transformation kinetics of microalloyed steels. In this study, we analyzed both numerically and experimentally the precipitation behavior of Nb-microalloyed steel and its effect on the austenite decomposition during cooling. Nb precipitation in austenite matrix could be predicted by the thermo-kinetic software MatCalc, in which interfacial energy between precipitate and matrix is calculated. The simulated precipitation kinetics fairly well agrees with the experimental observations by TEM. Austenite decomposition, which is strongly affected by Nb precipitation during cooling, was measured by dilatometry and was modeled on the basis of a Johnson-Mehl-Avrami-Kolmorgorov(JMAK) equation. It was confirmed that the dissolved Nb delays the austenite decomposition, whereas, the precipitated Nb accelerates phase transformation during the austenite decomposition.

• Journal of Technologic Dentistry
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• v.28 no.1
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• pp.61-66
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• 2006

Titanium alloys have been used for dental materials due to it's very good biocompatibility. Ti-6Al-4V alloy instead of pure titanium is being widely used as biomaterials has some characteristics such as high fatigue strength, tensile strength and corrosion resistance. But it has been reported recently that the vanadium element expresses cytotoxicity and carcinogenicity and the aluminium element is related with dementia of Alzheimer type and neurotoxicity. The Ti-Nb alloys has designed and examined corrosion resistance. Ti-3wt.%Nb($\alpha$type), Ti-20wt.%Nb(${\alpha}+{\beta}$type) and Ti-40wt.%Nb($\beta$type) alloys were melted by vacuum arc furnace. The corrosion resistance of Ti alloys was evaluated by potentiodynamic polarization test in the solution of 0.9% NaCl and 5% HCl. The results can be summarized as follows: 1) For the corrosion test in the solution of 0.9% NaCl and 5% HCl, the corrosion behaviour of Ti-Nb alloys was similar to ASTM grade 2 CP Ti. 2) The corrosion resistance of Ti-20Nb alloy was better than that of CP-Ti, Ti-3Nb, Ti-40Nb alloy in 0.9% NaCl and 5% HCl, solutions.

• Proceedings of the KIEE Conference
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• 1997.07d
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• pp.1494-1496
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• 1997

The MRI Magnet is a most practical application of NbTi superconductor. In this paper, we present the main research results on superconducting wires for MRI magnet which we have developed. Cu/NbTi superconducting wires were fabricated by repeat of cold working and heat-treating process after that billets were extruded. We investigated the relation of superconductivities of wires and heat treatment condition. The correlation between cross section shape of wires and work inhomogeneity of NbTi rods was investigated by microscopic observation. The more repeatation number of cold working and heat-treating process, the higher critical current is achieved.

• Korean Journal of Materials Research
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• v.8 no.10
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• pp.956-960
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• 1998

The interfacial reaction between the CoINb bilayer and the $SiO_2$ substrate in the temperature range of $330^{\circ}C$-$800^{\circ}C$ in a vacuum has been investigated by X-ray photoelectron spectroscopy, glancing angle XRD, Auger Electron Spectroscopy and Atomic force microscopy. The Co and Nb were actively interdiffused at $600^{\circ}C$, and the layer inversion completed at $700^{\circ}C$. NbO was formed by interfacial reaction between the Nb interlayer and the $SiO_2$ substrate, while $Nb_20_5$ was formed on the surface by reaction of Nb with oxygen in the ambients. Free Si atoms obtained by the reaction between Nb and $SiO_2$ formed silicides like CoSi and $Nb_5Si_3$ by reacting with Co and Nb remnants. The sheet resistance of the Co/Nb bilayer increased substantially after annealing at $800^{\circ}C$. which is due to the agglomeration of the Co layer to reduce its surface energy.

• Proceedings of the Korean Magnestics Society Conference
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• 2007.05a
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• pp.81.1-81.1
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• 2007

• Proceedings of the Korean Vacuum Society Conference
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• 2014.02a
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• pp.353-353
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• 2014

본 연구에서는 Sputter를 이용하여 Room Temp.에서 증착된 NbOx 박막의 열처리에 따른 결정도를 분석하고, 이러한 결정도의 변화가 Metal Insulator Transition특성에 의한 Threshold switching에 어떠한 영향을 미치는 지에 대하여 연구하였다. NbOx 박막의 threshold switching 특성 분석을 위해, 1.4um의 TiN 위에 15nm의 NbOx를 증착하고 Top Electrode로 Pt를 증착하여 측정하였다. 증착된 NbOx는 Nb metal target으로 Reactive Sputter를 이용하여 Room Temp.에서 증착하였으며, 조성은 Partial Oxygen Pressure를 이용하여 조절하였다. 증착된 박막의 결정도는 TEM 및 XRD를 통하여 분석하였고 조성은 XPS를 이용하여 분석하였다. Sputter로 NbOx 증착 시 Partial Oxygen Pressure에 따른 조성을 XPS로 확인한 결과, Partial Oxygen Pressure 2%에서 NbOx의 조성을, 5%이상일 경우, Nb2O5의 조성을 가지는 것으로 확인되었다. Partial Oxygen Pressure 2%에서 증착한 NbOx 박막의 열처리에 따른 결정도를 분석한 결과, As-Dep상태에서는 amorphous상태였다가 600'C이상으로 1분간 열처리를 하였을 때 NbOx의 결정도가 증가함을 확인하였다. I-V 특성 측정 결과, 열처리 온도가 증가함에 따라 initial current가 점진적으로 증가하는 경향을 보이는데, 이는 열처리 시 amorphous상에서 poly-crystalline으로 미세구조의 변화가 일어나면서 grain boundary가 생성되며 생성된 grain boundary를 통해 leakage current가 증가하는 것으로 추측된다. 또한, 결정도가 증가함에 따라 electro-forming voltage가 감소하는 경향을 보이며 안정된 threshold switching 특성을 보이고 있다. 특히, 700'C 1분간 열처리 시에는 electro-forming 과정이 없이 threshold switching이 나타나는 현상이 관찰되었다. 이로 미루어 보아, threshold switching에서 나타나는 forming 현상은 local joule heating에 의해 박막이 결정화 되는 과정으로 추측된다. 결론적으로, 박막의 결정도가 initial current 및 Threshold switching 특성에 큰 영향을 미치는 것으로 예상된다.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.16 no.2
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• pp.53-58
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• 2006

When external field was applied to congruent $LiNbO_3$, it was investgated for domain formation and expansion of $LiNbO_3$. The domain wall velocities of 0.5 mm thickness $LiNbO_3$ were 28.70, 16.02 and $5.75{\mu}m/sec$ under poling field of 23.5, 22.0 and 21.0 kV/mm, respectively. As $1 M{\Omega}$ resistor was used in domain inversion system, harmonic domain inversion was not achieved by rapid domain expansion. And 50% duty cycle periodically poled $LiNbO_3$ have been fabricated by charge control using $10 M{\Omega}$ resistor.

• Journal of Korean Neurosurgical Society
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• v.63 no.6
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• pp.707-716
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• 2020

Objective : The function of B7H3, a member of the B7 family of proteins, in neuroblastoma (NB) remains poorly characterized. Here we examine the expression pattern of B7H3 in clinical NB specimens and characterize the phenotype of B7H3 knock-down in NB cell line. Methods : Immunohistochemical (IHC) staining was carried out to assess the expression of B7H3 in clinical NB specimens. Survival association was analyzed using five Gene Expression Omnibus (GEO) datasets (GSE85047, GSE45480, GSE62564, GSE16476, GSE49710). Clonogenic survival and flow cytometry were performed after B7H3 knockdown to assess the cellular proliferation and cell survival in vitro. Impact of B7H3 silencing on NB growth was examined in vivo using the SH-SY5Y xenograft model. Results : On IHC staining, B7H3 was widely expressed in clinical NB specimens. Analysis of the transcriptional profiles of five GEO datasets clinically annotated NB specimens revealed that decreased B7H3 expression was associated with improved overall survival. B7H3 knockdown suppressed the proliferation of the SH-SY5Y NB model in vitro and in vivo. Cell cycle analysis revealed that B7H3 silencing induced G1/S arrest. This arrest was associated with the suppression of E2F1 expression and induction of Rb expression. Conclusion : Our results demonstrate that B7H3 expression correlate with clinical survival in NB patients. Preliminary studies suggest that B7H3 may mediate the G1/S transition.