Effects of nano-carbon doping and sintering temperature on microstructure and properties of MgB₂

Lim, J.H.,Shim, J.H.,Choi, J.H.,Park, J.H.,Kim, W.,Joo, J.,Kim, C.J. North-Holland 2009 Physica. C, Superconductivity Vol.469 No.15

We fabricated nano-carbon (NC) doped MgB<SUB>2</SUB> bulks using an in situ process in order to improve the critical current density (J<SUB>c</SUB>) under a high magnetic field and evaluated the correlated effects of the doped carbon content and sintering temperature on the phase formation, microstructure and critical properties. MgB<SUB>2-x</SUB>C<SUB>x</SUB> bulks with x=0 and 0.05 were fabricated by pressing the powder into pellets and sintering at 800<SUP>o</SUP>C, 900<SUP>o</SUP>C, or 1000<SUP>o</SUP>C for 30min. We observed that NC was an effective dopant for MgB<SUB>2</SUB> and that part of it was incorporated into the MgB<SUB>2</SUB> while the other part remained (undoped), which reduced the grain size. The actual C content was estimated to be 68-90% of the nominal content. The NC doped samples exhibited lower T<SUB>c</SUB> values and better J<SUB>c</SUB>(B) behavior than the undoped samples. The doped sample sintered at 900<SUP>o</SUP>C showed the highest J<SUB>c</SUB> value due to its high doping level, small amount of second phase, and fine grains. On the other hand, the J<SUB>c</SUB> was decreased at a sintering temperature of 1000<SUP>o</SUP>C as a result of the formation of MgB<SUB>4</SUB> phase.

여자 대학생의 저출산에 대한 인식 : 서울 지역 중심으로

김연주,김주예,김혜,민지유,박현영,이송,이혜심,주연진,최지희,함연화,강숙정,김부연,김윤정 이화여자대학교 간호과학대학 2019 이화간호학회지 Vol.- No.53

Purpose: The purpose of this study is to understand the perception of low birth rate within female college students. Methods: After obtaining approval from online community and several acquaintance, data were collected from August 10 to September 11. A total of eight students participated in the study. Semi-structured in-depth interview were conducted and the data subsequently analyzed. Results: This study extracted three themes: Fragmentary perception about low birth rate limited to social level problem; Avoidance about sacrifice from delivery and Lack of effectiveness in fertility incentives of present government. Conclusion: This study is meaningful that can explore the perception about low birth rates of female college students who are the subjects of future birth. They recognize low birth rates as a social problem, but do not recognize as individual problem. In addition, this study was able to identify the participants' perception of the low birth rate. It can be suggested as meaningful opinion for some follow-up study.

Superconducting properties of MgB₂ superconductors in-situ processed using various boron powder mixtures

Kang, M.O.,Joo, J.,Jun, B.H.,Kim, C.J. The Korean Society of Superconductivity and Cryoge 2021 한국초전도저온공학회논문지 Vol.23 No.3

In this study, the effect of the size of B powder on the critical current density (J_c) of MgB₂ prepared by an in situ reaction process was investigated. Various combinations of B powders were made using a micron B, ball-milled B and nano B powders. Micron B powder was reduced by ball milling and the milled B powder was mixed with the micron B or nano B powder. The mixing ratios of the milled B and micron or nano B were 100:0, 50:50 and 0:100. Non-milled micron B powder was also mixed with nano powder in the same ratios. Pellets of (2B+Mg) prepared with various B mixing ratios were heat-treated to form MgB₂. T_c of MgB₂ decreased slightly when the milled B was used, whereas the J_c of MgB₂ increased with increasing amount of the milled B or the nano powder. The used of the milled B and nano B power promoted the formation MgB₂ during heat treatment. In addition to the enhanced formation of MgB₂, the use of the powders reduced the grain size of MgB₂. The use of the milled and nano B powder increased the J_c of MgB₂. The highest J_c was achieved when 100% nano B powder was used. The J_c enhancement is attributed to the high volume fraction of the superconducting phase (MgB₂) and the large grain boundaries, which induces the flux pinning at the magnetic fields.

Fabrication of ex situ processed MgB₂ wires using nano carbon doped powder

Lee, C.M.,Park, J.H.,Hwang, S.M.,Lim, J.H.,Joo, J.,Kang, W.N.,Kim, C.J. North-Holland 2009 Physica. C, Superconductivity Vol.469 No.15

We fabricated ex situ MgB<SUB>2</SUB> wires using C-doped MgB<SUB>2</SUB> powder as a precursor in order to improve the core density of the wires and their C doping content. The C-doped powder was prepared with Mg, B, and nano carbon (NC) powders by the in situ technique and then MgB<SUB>2-x</SUB>C<SUB>x</SUB> (x=0, 0.01, and 0.03) wires were fabricated by the ex situ technique using the powder-in-tube method. The phase formation, lattice change, and microstructure were characterized and correlated with the T<SUB>c</SUB> and J<SUB>c</SUB> variations. We observed that the ex situ wire had a higher core density than the in situ wire, however its morphology consisted of agglomerated particles, indicating that sintering and grain growth did not occur completely, even though the sintering was conducted at high temperature (1000<SUP>o</SUP>C). As the C content increased, T<SUB>c</SUB> decreased, while the decrease of J<SUB>c</SUB> with increasing magnetic field became smaller. The J<SUB>c</SUB> of MgB<SUB>1.97</SUB>C<SUB>0.03</SUB> wire made by the ex situ technique was 3.34kA/cm<SUP>2</SUP> at 6.6T and 5K which is comparable to that of the in situ wire (4.81kA/cm<SUP>2</SUP> at 6.6T and 5K).

Improvement of high-field J_c of MgB₂ wires by polymethyl-methacrylate doping

Park, G.C.,Hwang, S.M.,Lee, C.M.,Choi, J.H.,Joo, J.,Lim, J.H.,Kang, W.N.,Kim, C.J. North-Holland 2010 Physica. C, Superconductivity Vol.470 No.suppl1

We applied polymethyl-methacrylate (PMMA) as a new doping material for MgB<SUB>2</SUB> and fabricated C-doped MgB<SUB>2</SUB> wires by in situ powder-in-tube (PIT) process. With increasing PMMA doping level, the transition temperature (T<SUB>c</SUB>) decreased and the MgO content increased, whereas the magnetic field dependence of the critical current density (J<SUB>c</SUB>) weakened. The MgB<SUB>2</SUB> wires doped with 3-10wt.% PMMA showed significantly higher J<SUB>c</SUB> by more than one order of magnitude than that of the undoped wire at 5K and 6.6T. These results confirmed the potential of PMMA as a promising material for the effective substitution of B by C in MgB<SUB>2</SUB>.

O-free polyacrylonitrile doping to improve the J_c(B) and H_c2 of MgB₂ wires

Hwang, S.M.,Sung, K.,Choi, J.H.,Kim, W.,Joo, J.,Lim, J.H.,Kim, C.J.,Park, Y.S.,Kim, D.H. North-Holland 2010 Physica. C, Superconductivity Vol.470 No.20

We selected polyacrylonitrile (PAN, -[C<SUB>3</SUB>H<SUB>3</SUB>N]-) as an O-free organic dopant and fabricated C-doped MgB<SUB>2</SUB> wires by in situ and powder-in-tube techniques. 0-5 wt.% PAN powders were uniformly mixed with B powder using a liquid mixing method. The precursor powders were mixed with Mg powder, filled into Fe tubes, and then drawn into wires. Sintering was performed at 900<SUP>o</SUP>C for 1h in a flowing Ar gas. The PAN doping decreased the critical temperature (T<SUB>c</SUB>) and a-axis lattice parameter, but significantly improved the critical current density (J<SUB>c</SUB>) in high fields, upper critical field (H<SUB>c2</SUB>), and irreversibility field (H<SUB>irr</SUB>) performances. These results are attributed to the replacement of B sites with C by the PAN doping. Furthermore, as expected, the MgO amount did not increase as the doping content increased. The J<SUB>c</SUB> of the PAN-doped MgB<SUB>2</SUB> wires was more than one order of magnitude higher than that of the undoped MgB<SUB>2</SUB> wire at 5K and 6.6T (1.46-3.82kA/cm<SUP>2</SUP> vs. 0.11kA/cm<SUP>2</SUP>).

Investigation of lauric acid dopant as a novel carbon source in MgB₂ wire

Lee, C.M.,Lee, S.M.,Park, G.C.,Joo, J.,Lim, J.H.,Kang, W.N.,Yi, J.H.,Jun, B.H.,Kim, C.J. North-Holland 2010 Physica. C, Superconductivity Vol.470 No.20

We fabricated lauric acid (LA) doped MgB<SUB>2</SUB> wires and investigated the effects of the LA doping. For the fabrication of the LA-doped MgB<SUB>2</SUB> wires, B powder was mixed with LA at 0-5wt.% of the total amount of MgB<SUB>2</SUB> using an organic solvent, dried, and then the LA-treated B and Mg powders were mixed stoichiometrically. The powder mixture was loaded into an Fe tube and the assemblage was drawn and sintered at 900<SUP>o</SUP>C for 3h under an argon atmosphere. We observed that the LA doping induced the substitution of C for the B sites in MgB<SUB>2</SUB> and that the actual content of C increased monotonically with increasing LA doping level. The LA-doped MgB<SUB>2</SUB> wires exhibited a lower critical temperature (T<SUB>c</SUB>), but better critical current density (J<SUB>c</SUB>) behavior in a high magnetic field: the 5wt.% LA-doped sample had a J<SUB>c</SUB> value of 5.32x10<SUP>3</SUP>A/cm<SUP>2</SUP>, which was 2.17 times higher than that of the pristine sample (2.45x10<SUP>3</SUP>A/cm<SUP>2</SUP>) at 5K and 6T, suggesting that LA is an effective C dopant in MgB<SUB>2</SUB> for enhancing the high-field J<SUB>c</SUB> performance.

Induction of nucleolin translocation by acharan sulfate in A549 human lung adenocarcinoma

Joo, Eun Ji,Yang, Hui,Park, Youmie,Park, Nam Young,Toida, Toshihiko,Linhardt, Robert J.,Kim, Yeong Shik Wiley Subscription Services, Inc., A Wiley Company 2010 Journal of cellular biochemistry Vol.110 No.5

<P>Acharan sulfate (AS), isolated from the giant African snail Achatina fulica, is a novel glycosaminoglycan, consisting primarily of the repeating disaccharide structure α-D-N-acetylglucosaminyl (1 → 4) 2-sulfoiduronic acid. AS shows anti-tumor activity in vitro and in vivo. Despite this activity, AS is only weakly cytotoxic towards cancer cells. We examine the interactions between AS and cell-surface proteins in an effort to explain this anti-tumor activity. Using flow cytometry and affinity column chromatography, we confirm that AS has strong affinity to specific cell-surface proteins including nucleolin (NL) in A549 human lung adenocarcinomas. Surprisingly, we found the translocation of NL from nucleus to cytoplasm under the stimulation of AS (100 µg/ml) in vitro. Also, as NL exits the nucleus, the levels of growth factors such as bFGF and signaling cascade proteins, such as p38, p53, and pERK, are altered. These results suggest that the communication between AS and NL plays a critical role on signal transduction in tumor inhibition. J. Cell. Biochem. 110: 1272–1278, 2010. Published 2010 Wiley-Liss, Inc.</P>

胎兒가 生存한 帝王切開瘢痕破裂의 1例

朱商源,金明濟,丘秉參,李智宰,李明秀 大韓産婦人科學會 1967 大韓産婦人科學會雜誌 Vol.10 No.11

유화형 Sausage의 품질특성에 식물성유와 동물성유 CLA 첨가가 미치는 영향

이정일,이진희,곽석준,하영주,정재두,이진우,이제룡,주선태,박구부 한국동물자원과학회 2003 한국축산학회지 Vol.45 No.2

CLA-식물성유와 CLA-동물성유가 대체가 유화형 sausage의 품질특성에 미치는 영향을 조사하기 위해 3개의 시험구를 배치하였다. CLA-CO는 돼지 등지방 함량 중 30%를 CLA-corn oil로 대체시켰으며, CLA-SSO는 30% CLA-safflower seed oil, CLA-LD는 30% CLA-lard을 각각 대체하여 유화형 sausage를 제조한 후 1, 7, 14, 21 그리고 28일 동안 4℃의 냉장고에 저장하면서 이화학적 특성, 조직감, 지방산패도, 지방산 조성 및 CLA 함량의 변화를 조사하였다. CLA-식물성유와 CLA-동물성유를 첨가한 sausage의 pH는 전 저장기간동안 대조구에 비하여 유의적으로 낮게 나타났으며(p<0.05), 모든 처리구가 저장 14일째에 유의적으로 가장 낮은 pH를 보였다(p<0.05). Sausage의 L*과 a*값은 모든 처리구간에 큰 차이는 없었으나, b*값의 경우 CLA-처리구가 대조구에 비해 전 저장기간 동안 유의적으로 높은 경향을 나타내었다(p<0.05). CLA 처리구가 대조구에 비하여 모든 지방산 조성이 감소하는 결과를 보인 반면에 linolenic acid 함량은 대조구에 비하여 CLA 처리구인 CLA-CO와 CLA-SSO 처리구가 유의적으로 높은 함량을 보였다(p<0.05). 모든 처리구가 저장기간 경과에 따른 지방산 조성의 변화는 없었다. 조직감에서는 CLA-LD 처리구가 대조구나 다른 처리구에 비하여 응집성, 탄력성, 고무성 및 파쇄성 등이 유의적으로 높았다(p<0.05). 유화형 sausage의 지방산패도는 저장기간이 경과함에 따라 처리구 모두 유의적으로 높게 나타났고(p<0.05), CLA-CO 처리구가 대조구 보다 유의적으로 낮은 경향을 보였다(p<0.05). 이상의 결과 유화형 sausage 제조시 CLA 첨가는 이화학적 특성과 조직감에 영향을 미치지 않으며, 제품의 저장기간을 연장 및 CLA를 축적시키는 것이 가능하여 고급 sausage 생산이 가능하다고 사료된다. Emulsion-type sausages were manufactured to investigate the effects of CLA-vegetable oils and CLA-lard on quality characteristics of emulsion-type sausage. Each treatments replaced pork back fat with CLA-corn oil (CLA-CO), CLA-safflower seed oil (CLA-SSO) and CLA-lard (CLA-LD) were stored during 1, 7, 14, 21 and 28 days at 4℃. The changes in physico-chemical properties, texture, thiobarbituric acid reactive substances (TBARS), fatty acid composition and CLA content of each treatments were measured during 1, 7, 14, 21 and 28 days at 4℃. During storage, pH of control showed higher pH value than that of CLA-vegetable and CLA-lard treatments. The pH values of all treatments was significantly low at storage 14 days (p<0.05). The color L^* and a^*-value of all the treatments was not significantly changed with the storage periods. Color b^*-value of CLA-treatments was higher than that of control during the storage period. Fatty acids composition was changed by addition of CLA-vegetable oils and CLA-lard. All kinds of fatty acids composition were decreased with CLA replacements than that of the control. Whereas linolenic acid content extremely increased by replacement of CLA-vegetable. CLA content of CLA-treatments was extremely increased than that of the control. The cohesiveness, springness, gumminess and brittleness of CLA-LD treatment was significantly higher (P<0.05) than that of the other treatments. The TBARS value of all treatments were significantly increased (P<0.05) as the storage period was passed. TBARS of sausage products containing CLA-CO was the lowest. Summing up the a forementioned results, emulsion-type sausage manufacturing with CLA-vegetable oil and CLA-lard was not affected in physico-chemical properties and texture characteristics. Also, it may be assumed that the high quality sausage can be manufactured with the extent of storage period and CLA accumulation.