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>).

Study on the improved J_c(B) performance of polyacrylic acid-doped MgB₂ bulks

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

We fabricated polyacrylic acid (PAA)-doped MgB<SUB>2</SUB> bulks by wet mixing and in situ reaction process and studied the relationships between the phase formation, lattice change, microstructure, and critical properties according to the PAA doping level. The PAA doping increased the MgO amount and grain boundary area but decreased the a-axis lattice constant and critical temperature (T<SUB>c</SUB>), which is indicative of the substitution of B sites by C in MgB<SUB>2</SUB>. Furthermore, the critical current density (J<SUB>c</SUB>) at high magnetic fields improved with the increasing PAA content to 5.99kA/cm<SUP>2</SUP> for the 7wt% PAA-doped sample, which was about 6-fold higher than that of the pure sample at 5K and 6.6T. This improvement was mainly attributed to the C substitution and the fine grain size due to PAA doping, suggesting that PAA is an effective dopant in improving J<SUB>c</SUB>(B) performance of MgB<SUB>2</SUB>.

Nm23-M5 mediates round and elongated spermatid survival by regulating GPX-5 levels

Choi, Y.J.,Cho, S.K.,Hwang, K.C.,Park, C.,kim, J.H.,Park, S.B.,Hwang, S.,Kim, J.H. North-Holland Pub ; Elsevier Science Ltd 2009 FEBS letters Vol.583 No.8

Nucleoside diphosphate (NDP) kinases are involved in numerous regulatory processes associated with proliferation, development, and differentiation. Previously, we cloned a new member of the NDPK family from mouse, Nm23-M5, which encodes a 211-amino acid protein and has 86% identity to the human Nm23-H5 [Hwang, K.C., Ok, D.W., Hong, J.C., Kim, M.O. and Kim, J.H. (2003) Cloning, sequencing, and characterization of the murine Nm23-M5 gene during mouse spermatogenesis and spermiogenesis. Biochem. Biophys. Res. Commun. 306, 198-207]. To better understand Nm23-M5 function, we generated transgenic mice with reduced Nm23-M5 levels in vivo using a short hairpin RNA (shRNA) knock-down system. Nm23-M5 expression was markedly reduced, as indicated by Northern and Western blot analysis. Nm23-M5 shRNA transgenic mice exhibited reduced numbers of haploid cells. Furthermore, the antioxidant enzyme glutathione peroxidase 5 (GPX-5) is regulated by Nm23-M5 at the level of both expression and activity. These results reveal that expression of Nm23-M5 plays a critical role in spermiogenesis by increasing the cellular levels of GPX-5 to eliminate reactive oxygen species.

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>.

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).

Novel dentin phosphoprotein frameshift mutations in dentinogenesis imperfecta type II

Lee, K‐,E,Kang, H‐,Y,Lee, S‐,K,Yoo, S‐,H,Lee, J‐,C,Hwang, Y‐,H,Nam, KH,Kim, J‐,S,Park, J‐,C,Kim, J‐,W Blackwell Publishing Ltd 2011 Clinical genetics Vol.79 No.4

<P>Lee K‐E, Kang H‐Y, Lee S‐K, Yoo S‐H, Lee J‐C, Hwang Y‐H, Nam KH, Kim J‐S, Park J‐C, Kim J‐W. Novel dentin phosphoprotein frameshift mutations in dentinogenesis imperfecta type II.</P><P>The dentin sialophosphoprotein (<I>DSPP</I>) gene encodes the most abundant non‐collagenous protein in tooth dentin and DSPP protein is cleaved into several segments including the highly phosphorylated dentin phosphoprotein (DPP). Mutations in the <I>DSPP</I> gene have been solely related to non‐syndromic form of hereditary dentin defects. We recruited three Korean families with dentinogenesis imperfecta (DGI) type II and sequenced the exons and exon–intron boundaries of the <I>DSPP</I> gene based on the candidate gene approach. Direct sequencing of PCR products and allele‐specific cloning of the highly repetitive exon 5 revealed novel single base pair (bp) deletional mutations (c.2688delT and c.3560delG) introducing hydrophobic amino acids in the hydrophilic repeat domain of the DPP coding region. All affected members of the three families showed exceptionally rapid pulp chambers obliteration, even before tooth eruption. Individuals with the c.3560delG mutation showed only mild, yellowish tooth discoloration, in contrast to the affected individuals from two families with c.2688delT mutation. We believe that these results will help us to understand the molecular pathogenesis of DGI type II as well as the normal process of dentin biomineralization.</P>

Construction of a pilot-scale continuous-flow intense pulsed light system and its efficacy in sterilizing sesame seeds

Hwang, H.J.,Cheigh, C.I.,Chung, M.S. ELSEVIER 2017 INNOVATIVE FOOD SCIENCE AND EMERGING TECHNOLOGIES Vol. No.

<P>The purpose of this study was to identify the decontamination level of a laboratory-scale intense pulsed light (IPL) system and compared with that of newly constructed pilot-scale system in our laboratory. Sesame seeds, in which the initial microbial load was 10(4)-10(5) CFU/g, were treated by laboratory-scale IPL treatment at a total fluence of 39.85 J/cm(2). 0.86 log microbial reduction was achieved and adding a mixing step increased this to a 1.02 log reduction. We concluded that combining a mixing process and powerful IPL is essential to decontaminate sesame seeds satisfactorily, and so a pilot-scale IPL device in which the sample is placed in a cyclonic flow was designed and constructed in our laboratory. The xenon lamp and power supply were also upgraded. This modified device achieved a 1.46 log reduction at a total fluence of 44.46 J/cm(2). Changing the material of the treatment chamber from acrylic to stainless steel induced light reflections that resulted in improvement of the decontamination efficiency. Although this study showed a potential of a pilot-scale IPL device for treating larger amount of sample at once, further studies of technical improvement are essential to achieve higher decontamination level. (C) 2016 Elsevier Ltd. All rights reserved.</P>

The Magnetic Entropy Change on La<SUB>0.7</SUB>Ba<SUB>0.3</SUB>Mn<SUB>1-x</SUB>Fe<SUB>x</SUB>O₃ Compound

J. S. Hwang,D. M. Jang,K. S. Kim,J. S. Lee,S. C. Yu 한국자기학회 2013 Journal of Magnetics Vol.18 No.1

The magnetocaloric effect and magnetization behavior have been analyzed in the double-perovskite La0.7Ba0.3Mn1-XFeXO₃ compound with the sintering temperature at 1273 K. Samples were fabricated by the conventional solid-state reaction method. X-ray diffraction measurement revealed that all the samples had a single phase in orthorhombic. Detailed investigations of the magnetic entropy behavior of the samples were discussed with the variation of TC. The magnetic entropy changes, ΔSM of approximately 0.36-1.14 J/㎏ K were obtained in the temperature range of 145-350 K for the La0.7Ba0.3Mn1-XFeXO₃ compound. The enhancement of the magnetic entropy change is believed to be due to changes in the microstructure, which changes the magnetic part of the entropy of a solid around the magnetic ordering temperature.

Lateral Calcaneal Flap을 이용한 발꿈치 피부 결손의 치험례

황오열,박정준,김용배,이종현 大韓成形外科學會 1986 Archives of Plastic Surgery Vol.13 No.2

The heel and sole are vital musculoskeketal structures, responsible for weight bearing, shock absoption, and locomotion. Many reports have been published on the method of reconstructing a skin defect of the posterior heel and plantar heel, that is, ways of skin graft, innervated skin graft, local skin flap, neurovascular skin island flap (local delayed medial plantar, lateral plantar and dorsalis pedis), muscle flap (flexor digitorum brevis), neurovascular free flap (free groin, free dorsalis, free deltoid, free scapular, free Post. arm). In repair of a defect of the posterior heel, a relatively small, sensory flap is desirable and the lateral calcaneal flap is suitable for this purpose. The lateral calcaneal flap provides another modality for soft-tissue coverage when there is exposed of the calcaneal tendon or Os calcis on the posterior and/or plantar heel. There is a short and long version of this flap We present 3 cases of defects of the posterior heel with a favorable result.

Leak behavior of SCC degraded steam generator tubings of nuclear power plant

Hwang, Seong Sik,Kim, Hong Pyo,Kim, Joung Soo,Kasza, Kenneth E.,Park, Jangyul,Shack, William J. Elsevier 2005 Nuclear engineering and design Vol.235 No.23

<P><B>Abstract</B></P><P>A forced outage due to a steam generator tube leak in a Korean nuclear power plant has been reported <ce:cross-ref refid='bib3'>[Kim, J.S., Hwang, S.S., et al., 1999. KAERI Internal Report (Korean). Destructive analysis on pulled tubes from Ulchin unit 1. Korea Atomic Energy Research Institute]</ce:cross-ref>. Primary water stress corrosion cracking has occurred in many tubes in the plant, and they were repaired using sleeves or plugs. In order to develop proper repair criteria, it is necessary to understand the leak behavior of the tubes containing stress corrosion cracks. Cracked specimens were prepared using a room temperature cracking technique, and the leak rates and burst pressures of the degraded tubes were determined both at room temperature and at a high temperature. Some tubes with 100% through wall cracks did not show a leakage at 10.8MPa, which is the typical pressure difference of the pressurized water reactors (PWRs) during a normal operation. In some tests, the leak rates of the tubes increased with time at a constant pressure. In a high temperature pressure test at 282°C one specimen showed a very small leakage at 18.6MPa, which stopped after a small increase in the test pressure. Because stress corrosion cracks can develop at relatively low stresses, even 100% through wall cracks can be so tight that they will not leak at a normal operating pressure.</P>