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.

Regulation of cancer cell death by a novel compound, C604, in a c-Myc-overexpressing cellular environment

Jo, M.J.,Paek, A.R.,Choi, J.S.,Ok, C.Y.,Jeong, K.C.,Lim, J.H.,Kim, S.H.,You, H.J. North-Holland ; Elsevier Science Ltd 2015 european journal of pharmacology Vol.769 No.-

<P>The proto-oncogene c-Myc has been implicated in a variety of cellular processes, such as proliferation, differentiation and apoptosis. Several c-Myc targets have been studied; however, selective regulation of c-Myc is not easy in cancer cells. Herein, we attempt to identify chemical compounds that induce cell death in c-Myc-overexpressing cells (STF-cMyc and STF-Control) by conducting MTS assays on approximately 4000 chemical compounds. One compound, C604, induced cell death in STF-cMyc cells but not STF-Control cells. Apoptotic proteins, including caspase-3 and poly(ADP-ribose) polymerase (PAPP), were cleaved in C604-treated STF-cMyc cells. In addition, 5W620, HCT116 and NCI-H23 cells, which exhibit higher basal levels of c-Myc, underwent apoptotic cell death in response to C604, suggesting a role for C604 as an inducer of apoptosis in cancer cells with c-Myc amplification. C604 induced cell cycle arrest at the G2/M phase in cells, which was not affected by apoptotic inhibitors. Interestingly, C604 induced accumulation of c-Myc and Cdc25A proteins. In summary, a chemical compound was identified that may induce cell death in cancer cells with c-Myc amplification specifically through an apoptotic pathway. (C) 2015 Elsevier B.V. All rights reserved.</P>

Chemical inhibitors of c-Met receptor tyrosine kinase stimulate osteoblast differentiation and bone regeneration

Kim, J.W.,Lee, M.N.,Jeong, B.C.,Oh, S.H.,Kook, M.S.,Koh, J.T. North-Holland 2017 European journal of pharmacology Vol.806 No.-

<P>The c-Met receptor tyrosine kinase and its ligand, hepatocyte growth factor (HGF), have been recently introduced to negatively regulate bone morphogenetic protein (BMP)-induced osteogenesis. However, the effect of chemical inhibitors of c-Met receptor on osteoblast differentiation process has not been examined, especially the applicability of c-Met chemical inhibitors on in vivo bone regeneration. In this study, we demonstrated that chemical inhibitors of c-Met receptor tyrosine kinase, SYN1143 and SGX523, could potentiate the differentiation of precursor cells to osteoblasts and stimulate regeneration in calvarial bone defects of mice. Treatment with SYN1143 or SGX523 inhibited HGF-induced c-Met phosphorylation in MC3T3-E1 and C3H10T1/2 cells. Cell proliferation of MC3T3-E1 or C3H10T1/2 was not significantly affected by the concentrations of these inhibitors. Co-treatment with chemical inhibitor of c-Met and osteogenic inducing media enhanced osteoblast-specific genes expression and calcium nodule formation accompanied by increased Runx2 expression via c-Met receptor-dependent but Erk-Smad signaling independent pathway. Notably, the administration of these c-Met inhibitors significantly repaired critical-sized calvarial bone defects. Collectively, our results suggest that chemical inhibitors of c-Met receptor tyrosine kinase might be used as novel therapeutics to induce bone regeneration.</P>

Pseudomonas sabulinigri sp. nov., isolated from black beach sand

Kim, K.-H.,Roh, S. W.,Chang, H.-W.,Nam, Y.-D.,Yoon, J.-H.,Jeon, C. O.,Oh, H.-M.,Bae, J.-W. Microbiology Society 2009 International journal of systematic and evolutiona Vol.59 No.1

<P>A novel Gram-negative, aerobic, motile, short rod-shaped bacterium, designated J64T, was isolated from black sand collected from Soesoggak, Jeju Island, Korea. Cells grew at 4-37 degrees C, at pH 5.5-10.0 and with 0-10 % NaCl. The strain was found to be oxidase- and catalase-positive. Phylogenetic analyses showed that strain J64T belongs to the genus Pseudomonas, forming a monophyletic group with Pseudomonas pachastrellae, Pseudomonas pertucinogena and 'Pseudomonas denitrificans'. The 16S rRNA gene sequence similarity between strain J64T and type strains of all Pseudomonas species with validly published names was below 96.6 %. Low levels of DNA-DNA relatedness were found with respect to type strains of P. pachastrellae and P. pertucinogena, supporting the classification of strain J64T within a novel species of the genus Pseudomonas. Strain J64T contained C(18 : 1)omega7c (37.2 %), C(16 : 0) (20.4 %), summed feature 3 (17.4 %; comprising iso-C(15 : 0) 2-OH and/or C(16 : 1)omega7c) and C(12 : 0) (7.6 %) as major cellular fatty acids. On the basis of the phenotypic and phylogenetic data, strain J64T represents a novel species of the genus Pseudomonas, for which the name Pseudomonas sabulinigri sp. nov. is proposed. The type strain is J64T (=KCTC 22137T =JCM 14963T).</P>

T_c and J_c distribution in in situ processed MgB₂ bulk superconductors with/without C doping

Kim, C.J.,Kim, Y.J.,Lim, C.Y.,Jun, B.H.,Park, S.D.,Choo, K.N. The Korea Institute of Applied Superconductivity a 2014 한국초전도저온공학회논문지 Vol.16 No.2

Temperature dependence of magnetic moment (m-T) and the magnetization (M-H) at 5 K and 20 K of the in situ processed $MgB_2$ bulk pellets with/without carbon (C) doping were examined. The superconducting critical temperature ($T_c$), the superconducting transition width (${\delta}T$) and the critical current density ($J_c$) were estimated for ten test samples taken from the $MgB_2$ bulk pellets. The reliable m-T characteristics associated with the uniform $MgB_2$ formation were obtained for both $MgB_2$ pellets. The $T_cs$ and ${\delta}Ts$ of all test samples of the undoped $MgB_2$ were the same each other as 37.5 K and 1.5 K, respectively. The $T_cs$ and ${\delta}Ts$ of the C-doped $MgB_2$ were 36.5 K and 2.5 K, respectively. Unlike the m-T characteristics, there existed the difference among the M-H curves of the test samples, which might be caused by the microstructure variation. In spite of the slight $T_c$ decrease, the C doping was effective in enhancing the $J_c$ at 5 K.

Effects of neutron irradiation on superconducting critical temperatures of in situ processed MgB₂ superconductors

Kim, C.J.,Park, S.D.,Jun, B.H.,Kim, B.G.,Choo, K.N.,Ri, H.C. 한국초전도저온공학회 2014 한국초전도저온공학회논문지 Vol.16 No.1

Effects of neutron irradiation on the superconducting properties of the undoped $MgB_2$ and the carbon(C)-doped $MgB_2$ bulk superconductors, prepared by an in situ reaction process using Mg and B powder, were investigated. The prepared $MgB_2$ samples were neutron-irradiated at the neutron fluence of $10^{16}-10^{18}n/cm^2$ in a Hanaro nuclear reactor of KAERI involving both fast and thermal neutron. The magnetic moment-temperature (M-T) and magnetization-magnetic field (M-H) curves before/after irradiation were obtained using magnetic property measurement system (MPMS). The superconducting critical temperature ($T_c$) and transition width were estimated from the M-T curves and critical current density ($J_c$) was estimated from the M-H curves using a Bean's critical model. The $T_cs$ of the undoped $MgB_2$ and C-doped $MgB_2$ before irradiation were 36.9-37.0 K and 36.6-36.8 K, respectively. The $T_cs$ decreased to 33.2 K and 31.6 K, respectively after irradiation at neutron fluence of $7.16{\times}10^{17}n/cm^2$, and decreased to 22.6 K and 24.0 K, respectively, at $3.13{\times}10^{18}n/cm^2$. The $J_c$ cross-over was observed at the high magnetic field of 5.2 T for the undoped $MgB_2$ irradiated at $7.16{\times}10^{17}n/cm^2$. The $T_c$ and $J_c$ variation after the neutron irradiation at various neutron fluences were explained in terms of the defect formation in the superconducting matrix by neutron irradiation.

Effect of oxygen partial pressure on the morphology and properties of Ce doped YBCO films fabricated by a MOCVD process

Kim, Y.H.,Kim, C.J.,Jun, B.H.,Sung, T.H.,Han, Y.H.,Han, S.C.,Paik, H.J.,Youn, J.S.,No, K. North-Holland 2009 Physica. C, Superconductivity Vol.469 No.15

Rare-earth (RE) (e.g. Sm, Dy, Ce, etc.) doping has been widely investigated to improve critical current density (J<SUB>c</SUB>) of YBa<SUB>2</SUB>Cu<SUB>3</SUB>O<SUB>7-X</SUB> (YBCO) coated conductors (CC). Oxygen partial pressure is known to be a key parameter in terms of affecting the J<SUB>c</SUB> of YBCO films. In this work, the effect of oxygen partial pressure on the microstructure and J<SUB>c</SUB> of a Ce doped YBCO film was examined. Ce doped YBCO films were deposited on (100) SrTiO<SUB>3</SUB> (STO) single crystal substrates at oxygen partial pressures of 2.5, 5.0, and 10.0Torr using a metal organic chemical vapor deposition (MOCVD) method. Due to the enhanced migration of surface adatoms under reduced oxygen partial pressure, a 1wt% Ce doped YBCO film had a stoichiometric, dense surface. In addition, the zero-field J<SUB>c</SUB> (at 77K) of the 1wt% Ce doped YBCO film deposited at reduced oxygen partial pressure was increased. Irrespective of the amount of Ce, the Ce doped YBCO film showed an increased zero-field J<SUB>c</SUB> (at 77K) under reduced oxygen partial pressure.

A search for 0νββ decay of ¹²⁴Sn with tin-loaded liquid scintillator

KIMS Collaboration,Hwang, M.J.,Kwon, Y.J.,Kim, H.J.,Kwak, J.W.,Kim, S.C.,Kim, S.K.,Kim, T.Y.,Kim, S.Y.,Lee, H.S.,Lee, M.J.,Myung, S.S.,Kim, Y.D.,Lee, J.I.,Kang, W.G.,Hahn, I.S.,Lee, M.H. North-Holland ; Elsevier Science Ltd 2009 Astroparticle physics Vol.31 No.6

<P>A search for the neutrinoless double-beta decay of Sn-124 was carried out using the tin-loaded liquid scintillator for an active source-detector technique. Tin (32.6%) in weight was successfully loaded into the liquid scintillator, and light output was as high as 57% of the unloaded liquid scintillator. A tin-loaded liquid scintillator with 1.1 l volume was installed at the 700 m underground laboratory in YangYang. and data were taken for 5285 h. No evidence for the O nu beta beta decay was found and a lower limit on the Sn-124 half-life was obtained to be 2.0 x 10(19) year with 90% C.L The new limit represents a significant improvement with respect to those previously available for Sn-124. (C) 2009 Elsevier B.V. All rights reserved.</P>

Angular dependences of SiO₂ etch rates at different bias voltages in CF₄, C₂F₆, and C₄F₈ plasmas

Kim, J.H.,Cho, S.W.,Park, C.J.,Chae, H.,Kim, C.K. Elsevier Sequoia 2017 THIN SOLID FILMS - Vol.637 No.-

The angular dependences of SiO<SUB>2</SUB> etch rates at different bias voltages for in CF<SUB>4</SUB>, C<SUB>2</SUB>F<SUB>6</SUB>, and C<SUB>4</SUB>F<SUB>8</SUB> plasmas were investigated using a Faraday cage system. When the bias voltage was -400V, the normalized etch yields (NEYs) reached a maximum at 70<SUP>o</SUP> in CF<SUB>4</SUB> and C<SUB>2</SUB>F<SUB>6</SUB> plasmas, while they decreased monotonically with ion-incident angle in a C<SUB>4</SUB>F<SUB>8</SUB> plasma. This was because the thickness of the steady-state fluorocarbon film formed on the SiO<SUB>2</SUB> surface was minimized at an ion incident angle of 70<SUP>o</SUP> in CF<SUB>4</SUB> and C<SUB>2</SUB>F<SUB>6</SUB> plasmas, while much thicker fluorocarbon films were deposited in a C<SUB>4</SUB>F<SUB>8</SUB> plasma. When the bias voltage was as high as -1200V, the thicknesses of the steady-state fluorocarbon films were very thin (less than 2A) and nearly unchanged at all ion-incident angles for CF<SUB>4</SUB> and C<SUB>2</SUB>F<SUB>6</SUB> plasmas, resulting in nearly the same shape of the NEY curves. In a C<SUB>4</SUB>F<SUB>8</SUB> plasma, the NEY showed a maximum at an ion-incident angle of 50<SUP>o</SUP> because the thickness of the steady-state fluorocarbon film was minimized at this angle.

Mechanical properties of (W,Ti)C and (W,Ti)C-NiAl₃ cermet consolidated by the high-frequency induction-heating method

Kim, W.,Suh, C.Y.,Roh, K.M.,Cho, S.W.,Na, K.I.,Shon, I.J. Elsevier Sequoia 2013 Journal of alloys and compounds Vol.568 No.-

In the case of cemented (W,Ti)C, Co is added as a binder for the formation of composite structures. However, the high cost of Co and the low corrosion resistance of the (W,Ti)C-Co cermet have generated interest in recent years for alternative binder phases. In this study, NiAl<SUB>3</SUB> was used as a binder and consolidated by the high-frequency induction heated sintering (HFIHS) method. The densification of both monolithic (W,Ti)C and (W,Ti)C-NiAl<SUB>3</SUB> cermet was accomplished within 3min. Highly dense (W,Ti)C and (W,Ti)C-NiAl<SUB>3</SUB> with a relative density of upto 99% were obtained within 3min by HFIHS under a pressure of 80MPa. The method was found to enable not only the rapid densification but also the prohibition of grain growth preserving the nano-scale microstructure. The average grain sizes of the sintered (W,Ti)C and (W,Ti)C-NiAl<SUB>3</SUB> were lower than 100nm. The addition of NiAl<SUB>3</SUB> to (W,Ti)C enhanced the toughness at the expense of the slight decrease in hardness. The hardness of (W,Ti)C and (W,Ti)C-NiAl<SUB>3</SUB> was significantly higher than that of (W,Ti)C-Co or (W,Ti)C-Ni. The fracture toughness and hardness values of (W,Ti)C, (W,Ti)C-5vol.%NiAl<SUB>3</SUB>, and (W,Ti)C-10vol.%NiAl<SUB>3</SUB> consolidated by HFIHS with a pressure of 80MPa and a induced current were 7.6+/-0.4MPam<SUP>½</SUP> and 2850+/-35kg/mm<SUP>2</SUP>, 8.5+/-0.3MPam<SUP>½</SUP> and 2610+/-37kg/mm<SUP>2</SUP>, 9.7+/-0.5MPam<SUP>½</SUP> and 2520+/-26kg/mm<SUP>2</SUP>, respectively.