• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 1996.11a
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• pp.320-325
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• 1996

The influences of ZrB$_2$additives to the SiC and pulse width on electrical discharge machining of SiC-ZrB$_2$electroconductive ceramic composites were investigated. IIigher-flexural strength materials show a trend toward smaller crater volumes, leaving a soother surface; the average surface roughness of the SiC-ZrB$_2$15 Vol.% Composite with the flexural strength of 375㎫ was 3.2${\mu}{\textrm}{m}$,whereas the SiC-ZrB$_2$30 Vol.% composite of 457㎫ was 1.35${\mu}{\textrm}{m}$. In the SEM micrographs of the fracture surface of SiC-ZrB$_2$composites, the SiC-ZrB$_2$two phaes are distinct; the white phase is the ZrB$_2$. In the micrograph of the EDM surface, however, these phases are no longer distinct because of thicker recast layer of resolidified-melt-formation droplets present.

• The Journal of Society for e-Business Studies
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• v.10 no.2
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• pp.1-19
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• 2005

Due to the phenomenal growth in mobile internet users, mobile business as a type of applications of mobile internet has attracted the related industries' and academic researchers' attentions. However, most researchers focus on the issues of Mobile B2C collecting survey questions from consumers or internet users. This paper points out that Mobile B2B has distinct service sector and analyzes the current trend and demand of Mobile B2B in Korea by collecting survey questionnaire from specialists in mobile industries and people in universities and research institutes. Survey fields include business, market, contents/application, research and development and legal system. According to the survey results, Mobile B2B business will rise in distribution, finance, sales, and logistics industries from the beginning of 2005 using wireless PDA and the important preconditions will be security, certification, and standardization.

• Proceedings of the KIEE Conference
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• 2009.07a
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• pp.1254_1255
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• 2009

The composites were fabricated by adding 30, 35, 40, 45[vol.%] Zirconium Diboride(hereafter, $ZrB_2$) powders as a second phase to Silicon Carbide(hereafter, SiC) matrix. The physical, mechanical and electrical properties of electroconductive SiC ceramic composites by Spark Plasma Sintering(hereafter, SPS) were examined. Reactions between $\beta$-SiC and $ZrB_2$ were not observed in the XRD analysis. The relative density of SiC+30[vol.%]$ZrB_2$, SiC+35[vol.%]$ZrB_2$, SiC+40[vol.%]$ZrB_2$ and SiC+45[vol.%]$ZrB_2$ composites are 88.64[%], 76.80[%], 79.09[%] and 88.12[%], respectively. The XRD phase analysis of the electroconductive SiC ceramic composites reveals high of SiC and $ZrB_2$ and low of $ZrO_2$ phase. The electrical resistivity of SiC+30[vol.%]$ZrB_2$, SiC+35[vol.%]$ZrB_2$, SiC+40[vol.%]$ZrB_2$ and SiC+45[vol.%]$ZrB_2$ composites are $6.74{\times}10^{-4}$, $4.56{\times}10^{-3}$, $1.92{\times}10^{-3}$ and $4.95{\times}10^{-3}[{\Omega}{\cdot}cm]$ at room temperature, respectively. The electrical resistivity of SiC+30[vol.%]$ZrB_2$, SiC+35[vol.%]$ZrB_2$, SiC+40[vol.%]$ZrB_2$ and SiC+45[vol.%]$ZrB_2$ are Positive Temperature Coefficient Resistance(hereafter, PTCR) in temperature ranges from 25[$^{\circ}C$] to 500[$^{\circ}C$]. It is convinced that SiC+40[vol.%]$ZrB_2$ composite by SPS can be applied for heater or electrode.

• Progress in Superconductivity and Cryogenics
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• v.21 no.1
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• pp.18-24
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• 2019

This study was carried out to investigate the effect of milling of boron (B), which is one of raw materials of $MgB_2$, on the critical current density ($J_c$) of $MgB_2$. B powder used in this study is semi-amorphous B (Pavezyum, Turkey, 97% purity, 1 micron). The size of B powder was reduced by planetary milling using $ZrO_2$ balls (a diameter of 2 mm). The B powder and balls with a ratio of 1:20 were charged in a ceramic jar and then the jar was filled with toluene. The milling time was varied from 0 to 8 h. The milled B powders were mixed with Mg powder in the composition of (Mg+2B), and the powder mixtures were uniaxially pressed at 3 tons. The powder compacts were heat-treated at $700^{\circ}C$ for 1 h in flowing argon gas. Powder X-ray diffraction and FWHM (Full width at half maximum) were used to analyze the phase formation and crystallinity of $MgB_2$. The superconducting transition temperature ($T_c$) and $J_c$ of $MgB_2$ were measured using a magnetic property measurement system (MPMS). It was found that $B_2O_3$ was formed by B milling and the subsequent drying process, and the volume fraction of $B_2O_3$ increased as milling time increased. The $T_c$ of $MgB_2$ decreased with increasing milling time, which was explained in terms of the decreased volume fraction of $MgB_2$, the line broadening of $MgB_2$ peaks and the formation of $B_2O_3$. The $J_c$ at 5 K increased with increasing milling time. The $J_c$ increase is more remarkable at the magnetic field higher than 3 T. The $J_c$ at 5 K and 4 T was the highest as $4.37{\times}10^4A/cm^2$ when milling time was 2 h. The $J_c$ at 20 K also increased with increasing milling time. However, The $J_c$ of the samples with the prolonged milling for 6 and 8 h were lower than that of the non-milled sample.

• Tuberculosis and Respiratory Diseases
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• v.55 no.5
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• pp.488-498
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• 2003

Background : Activation of the transcription factor NF-${\kappa}B$ has been shown to protect cells from tumor necrosis factor-alpha, chemotherapy, and radiation-induced apoptosis. NF-${\kappa}B$-dependent cIAP expression is a major antiapoptotic mechanism for that. NF-${\kappa}B$ activation and cIAP expression in A549 lung cancer cells which is relatively resistant to radiation-induced cell death were investigated for the mechanism of radioresistance. Materials and methods : We used A549 lung cancer cells and Clinac 1800C linear accelerator for radiation. Cell viability test was done by MTT assay. NF-${\kappa}B$ activation was tested by luciferase reporter gene assay, Western blot for $I{\kappa}B{\alpha}$ degradation, and electromobility shift assay. For blocking ${\kappa}B$, MG132 and transfection of $I{\kappa}B{\alpha}$-superrepressor plasmid construct were used. cIAP expression was analyzed by RT-PCR and cIAP2 promoter activity was performed using luciferase assay system. Results : MTT assay showed that cytotoxicity even 48 hr after radiation in A549 cells were less than 20%. Luciferas assay demonstrated weak NF-${\kappa}B$ activation of $1.6{\pm}0.2$ fold compared to PMA-induced $3.4{\pm}0.9$ fold. Radiation-induced $I{\kappa}B{\alpha}$ degradation was observed in Western blot and NF-${\kappa}B$ DNA binding was confirmed by EMSA. However, blocking NF-${\kappa}B$ using MG132 and $I{\kappa}B{\alpha}$-superrepressor transfection did not show any sensitizing effect for radiation-induced cell death. The result of RT-PCR for cIAP1 & 2 expression was negative induction while TNF-${\alpha}$ showed strong expression for cIAP1 & 2. The cIAP2 promoter activity also did not show any change compared to positive control with TNF-${\alpha}$. Conclusion : We conclude that activation of NF-${\kappa}B$ does not determine the intrinsic radiosensitivity of cancer cells, at least for the cell lines tested in this study.

• Progress in Superconductivity and Cryogenics
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• v.19 no.1
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• pp.36-41
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• 2017

The effects of $MgB_4$ addition on the superconducting properties and the microstructure of in situ processed $MgB_2$ bulk superconductors were studied. $MgB_4$ powder of 1-20 wt.% was mixed with (Mg + 2B) powder and then pressed into pellets. The pellets of (Mg + 2B + $xMgB_4$) were heat-treated at $650^{\circ}C$ for 1 h in flowing argon. The powder X-ray diffraction (XRD) analysis for the heat-treated samples showed that the major formed phase in all samples was $MgB_2$ and the minor phases were $MgB_4$ and MgO. The full width at half maximum (FWHM) values showed that the grain size of $MgB_2$ decreased as the amount of $MgB_4$ addition increased. $MgB_4$ particles included in a $MgB_2$ matrix is considered to suppress the grain growth of $MgB_2$. The onset temperatures ($T_{c,onset}$) of $MgB_2$ with $MgB_4$ addition (0-10 wt.%) was between 37-38 K. The 20 wt.% $MgB_4$ addition slightly reduced the $T_{c,onset}$ of $MgB_2$ to 36.5 K. This result indicates that $MgB_4$ addition did not influence the superconducting transition temperature ($T_c$) of $MgB_2$ significantly. On the other hand, the small additions of 1-5 wt.% $MgB_4$ increased the critical current density ($J_c$) of $MgB_2$. The $J_c$ enhancement by $MgB_4$ addition is attributed not only to the grain size refinement but also to the possible flux pinning of $MgB_4$ particles dispersed in a $MgB_2$ matrix.

• The Korean Journal of Physiology and Pharmacology
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• v.27 no.5
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• pp.427-436
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• 2023

Mitotic arrest deficient 2 like 2 (Mad2L2, also known as Mad2B), the human homologue of the yeast Rev7 protein, is a regulatory subunit of DNA polymerase ζ that shares high sequence homology with Mad2, the mitotic checkpoint protein. Previously, we demonstrated the involvement of Mad2B in the cisplatin-induced DNA damage response. In this study, we extend our findings to show that Mad2B is recruited to sites of DNA damage in human cancer cells in response to cisplatin treatment. We found that in undamaged cells, Mad2B exists in a complex with Polζ-Rev1 and the APC/C subunit Cdc27. Following cisplatin-induced DNA damage, we observed an increase in the recruitment of Mad2B and Cdc20 (the activators of the APC/C), to the complex. The involvement of Mad2B-Cdc20-APC/C during DNA damage has not been reported before and suggests that the APC/C is activated following cisplatin-induced DNA damage. Using an in vitro ubiquitination assay, our data confirmed Mad2B-dependent activation of APC/C in cisplatin-treated cells. Mad2B may act as an accelerator for APC/C activation during DNA damage response. Our data strongly suggest a role for Mad2B-APC/C-Cdc20 in the ubiquitination of proteins involved in the DNA damage response.

• Polymer(Korea)
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• v.36 no.5
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• pp.643-650
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• 2012

In order to improve the thermal stability of polyurethane, we synthesized poly(adipate urethane) (PAU) and three PAU composites, PAU/30B (2.7 wt% 30B), PAU/MP (2.2 wt% MP), PAU/30B/MP (2.2 wt% 30B and 2.2 wt% MP), from poly(oxydiethylene adipate)-diol (PAD), 4,4'-methylene diphenyl diisocyanate (MDI), Cloisite 30B (30B), and melamine phosphate (MP). 30B and MP were introduced into the reactant mixture at the initial stage of the esterification between adipic acid and diethylene glycol, so 30B and MP were evenly dispersed in the PAU composites for long period. At temperatures lower than $250^{\circ}C$, the PAU composites were degraded faster than pristine PAU, mainly due to the decomposition of 30B and MP. At higher temperatures, the 30B and MP enhanced the thermal stability of the PAU composites. Compared with the pristine PAU, the thermal decomposition rates of the PAU composites decreased by 13~17%. In air, the residual weights of PAU/30B, PAU/MP, and PAU/30B/MP were 2.4, 2.3, and 7.3 wt% at $700^{\circ}C$, respectively.

• Proceedings of the KIEE Conference
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• 2007.07a
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• pp.1303-1304
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• 2007

The composites were fabricated, respectively, using 61[vol.%]SiC-39[vol.%]$TiB_2$ and using 61[vol.%]SiC-39[vol.%]$ZrB_2$ powders with the liquid forming additives of 12[wt%] $Al_{2}O_{3}+Y_{2}O_{3}$ by hot pressing annealing at $1650[^{\circ}C]$ for 4 hours. Reactions between SiC and transition metal $TiB_2$, $ZrB_2$ were not observed in this microstructure. ${\beta}{\rightarrow}{\alpha}$-SiC phase transformation was occurred on the SiC-$TiB_2$ and SiC-$ZrB_2$ composite. The relative density, the flexural strength and Young's modulus showed the highest value of 98.57[%], 226.06[Mpa] and 86.38[Gpa] in SiC-$ZrB_2$ composite at room temperature respectively. The electrical resistivity showed the lowest value of $7.96{\times}10^{-4}[{\Omega}{\cdot}cm]$ for SiC-$ZrB_2$ composite at $25[^{\circ}C]$. The electrical resistivity of the SiC-$TiB_2$ and SiC-$ZrB_2$ composite was all positive temperature coefficient resistance (PTCR) in the temperature ranges from $25[^{\circ}C]$ to $700[^{\circ}C]$. The resistance temperature coefficient of composite showed the value of $6.88{\times}10^{-3}/[^{\circ}C]$ and $3.57{\times}10^{-3}/[^{\circ}C]$ for SiC-$ZrB_2$ and SiC-$TiB_2$ composite in the temperature ranges from $25[^{\circ}C]$ to $700[^{\circ}C]$.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.56 no.9
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• pp.1602-1608
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• 2007

The composites were fabricated, respectively, using 61[vol.%] SiC-39[vol.%] $TiB_2$ and using 61[vol.%] SiC-39[vol.%] $ZrB_2$ powders with the liquid forming additives of 12[wt%] $Al_2O_3+Y_2O_3$ by hot pressing annealing at $1650[^{\circ}C]$ for 4 hours. Reactions between SiC and transition metal $TiB_2$, $ZrB_2$ were not observed in this microstructure. The result of phase analysis of composites by XRD revealed SiC(6H, 3C), $TiB_2$, $ZrB_2$ and $YAG(Al_5Y_3O_{12})$ crystal phase on the Liquid-Phase-Sintered(LPS) $SiC-TiB_2$, and $SiC-ZrB_2$ composite. $\beta\rightarrow\alpha-SiC$ phase transformation was occurred on the $SiC-TiB_2$ and $SiC-ZrB_2$ composite. The relative density, the flexural strength and Young's modulus showed the highest value of 98.57[%], 249.42[MPa] and 91.64[GPa] in $SiC-ZrB_2$ composite at room temperature respectively. The electrical resistivity showed the lowest value of $7.96{\times}10^{-4}[\Omega{\cdot}cm]$ for $SiC-ZrB_2$ composite at $25[^{\circ}C]$. The electrical resistivity of the $SiC-TiB_2$ and $SiC-ZrB_2$ composite was all positive temperature coefficient resistance (PTCR) in the temperature ranges from $25[^{\circ}C]$ to $700[^{\circ}C]$. The resistance temperature coefficient of composite showed the lowest value of $1.319\times10^{-3}/[^{\circ}C]$ for $SiC-ZrB_2$ composite in the temperature ranges from $100[^{\circ}C]$ to $300[^{\circ}C]$ Compositional design and optimization of processing parameters are key factors for controlling and improving the properties of SiC-based electroconductive ceramic composites.