Structural Features of Layered Iron Pnictide Oxides (Fe2As2)(Sr4M2O6)

Structural features of newly found perovskite-based iron pnictide oxide system have been systematically studied. Compared to REFePnO system, perovskite-based system tend to have lower Pn-Fe-Pn angle and higher pnictogen height owing to low electronegativity of alkaline earth metal and small repulsive force between pnictogen and oxygen atoms. As-Fe-As angles of (Fe2As2)(Sr4Cr2O6), (Fe2As2)(Sr4V2O6) and (Fe2Pn2)(Sr4MgTiO6) are close to ideal tetrahedron and those pnictogen heights of about 1.40 A are close to NdFeAsO with optimized carrier concentration. These structural features of this system may leads to realization of high Tc superconductivity.Comment: 3pages, 2figures, 1table, proceedings of M2S 200

Superconductivity at 38 K in Iron-Based Compound with Platinum-Arsenide Layers Ca10(Pt4As8)(Fe2-xPtxAs2)5

We report superconductivity in novel iron-based compounds Ca10(PtnAs8)(Fe2-xPtxAs2)5 with n = 3 and 4. Both compounds crystallize in triclinic structures (space group P-1), in which Fe2As2 layers alternate with PtnAs8 spacer layers. Superconductivity with a transition temperature of 38 K is observed in the n = 4 compound with a Pt content of x ~ 0.36 in the Fe2As2 layers. The compound with n = 3 exhibits superconductivity at 13 K.Comment: OPEN SELECT article, 11 pages, 5 figures, 2 table

Pressure Dependence of Superconducting Transition Temperature on Perovskite-Type Fe-Based Superconductors and NMR Study of Sr2VFeAsO3

We report the pressure dependences of the superconducting transition temperature (T_c) in several perovskite-type Fe-based superconductors through the resistivity measurements up to ~4 GPa. In Ca_4(Mg,Ti)_3Fe_2As_2O_y with the highest T_c of 47 K in the present study, the T_c keeps almost constant up to ~1 GPa, and starts to decrease above it. From the comparison among several systems, we obtained a tendency that low T_c with the longer a-axis length at ambient pressure increases under pressure, but high T_c with the shorter a-axis length at ambient pressure hardly increases. We also report the ^75As-NMR results on Sr_2VFeAsO_3. NMR spectrum suggests that the magnetic ordering occurs at low temperatures accompanied by some inhomogeneity. In the superconducting state, we confirmed the anomaly by the occurrence of superconductivity in the nuclear spin lattice relaxation rate 1/T_1, but the spin fluctuations unrelated with the superconductivity are dominant. It is conjectured that the localized V-3d moments are magnetically ordered and their electrons do not contribute largely to the Fermi surface and the superconductivity in Sr_2VFeAsO_3.Comment: 7 pages, 9 figure

Evolution of superconductivity by oxygen annealing in FeTe0.8S0.2

Oxygen annealing dramatically improved the superconducting properties of solid-state-reacted FeTe0.8S0.2, which showed only a broad onset of superconducting transition just after the synthesis. The zero resistivity appeared and reached 8.5 K by the oxygen annealing at 200\degree C. The superconducting volume fraction was also enhanced from 0 to almost 100%. The lattice constants were compressed by the oxygen annealing, indicating that the evolution of bulk superconductivity in FeTe0.8S0.2 was correlated to the shrinkage of lattice.Comment: 13 pages, 6 figure

Effects of metallic spacer in layered superconducting Sr2(Mgy_yTi1−y_{1-y})O3FeAs

The highly two-dimensional superconducting system Sr2(Mg$_y$Ti$_{1-y}$)O3FeAs, recently synthesized in the range of 0.2 < y < 0.5, shows an Mg concentration-dependent $T_c$. Reducing the Mg concentration from y=0.5 leads to a sudden increase in $T_c$, with a maximum $T_c$ ~40 K at y=0.2. Using first principles calculations, the unsynthesized stoichiometric y=0 and the substoichiometric y=0.5 compounds have been investigated. For the 50% Mg-doped phase (y=0.5), Sr2(Mg$_y$Ti$_{1-y}$)O3 layers are completely insulating spacers between FeAs layers, leading to the fermiology such as that found for other Fe pnictides. At y=0, representing a phase with metallic Sr2TiO3 layers, the $\Gamma$-centered Fe-derived Fermi surfaces (FSs) considerably shrink or disappear. Instead, three $\Gamma$-centered Ti FSs appear, and in particular two of them have similar size, like in MgB2. Interestingly, FSs have very low Fermi velocity in large fractions: the lowest being 0.6$\times10^6$ cm/s. Furthermore, our fixed spin moment calculations suggest the possibility of magnetic ordering, with magnetic Ti and nearly nonmagnetic Fe ions. These results indicate a crucial role of Sr2(Mg$_y$Ti$_{1-y}$)O3 layers in this superconductivity.Comment: 7 pages; Proceedings of ICSM-201

18q loss of heterozygosity in microsatellite stable colorectal cancer is correlated with CpG island methylator phenotype-negative (CIMP-0) and inversely with CIMP-low and CIMP-high

<p>Abstract</p> <p>Background:</p> <p>The CpG island methylator phenotype (CIMP) with widespread promoter methylation is a distinct epigenetic phenotype in colorectal cancer, associated with microsatellite instability-high (MSI-high) and <it>BRAF </it>mutations. 18q loss of heterozygosity (LOH) commonly present in colorectal cancer with chromosomal instability (CIN) is associated with global hypomethylation in tumor cell. A recent study has shown an inverse correlation between CIN and CIMP (determined by MINTs, p16, p14 and <it>MLH1 </it>methylation) in colorectal cancer. However, no study has examined 18q LOH in relation to CIMP-high, CIMP-low (less extensive promoter methylation) and CIMP-0 (CIMP-negative), determined by quantitative DNA methylation analysis.</p> <p>Methods:</p> <p>Utilizing MethyLight technology (real-time PCR), we quantified DNA methylation in 8 CIMP-specific promoters {<it>CACNA1G</it>, <it>CDKN2A </it>(p16), <it>CRABP1, IGF2</it>, <it>MLH1, NEUROG1, RUNX3 </it>and <it>SOCS1</it>} in 758 non-MSI-high colorectal cancers obtained from two large prospective cohorts. Using four 18q microsatellite markers (D18S55, D18S56, D18S67 and D18S487) and stringent criteria for 18q LOH, we selected 374 tumors (236 LOH-positive tumors with ≥ 2 markers showing LOH; and 138 LOH-negative tumors with ≥ 3 informative markers and no LOH).</p> <p>Results:</p> <p>CIMP-0 (0/8 methylated promoters) was significantly more common in 18q LOH-positive tumors (59% = 139/236, p = 0.002) than 18q LOH-negative tumors (44% = 61/138), while CIMP-low/high (1/8–8/8 methylated promoters) was significantly more common (56%) in 18q LOH-negative tumors than 18q LOH-positive tumors (41%). These relations persisted after stratification by sex, location, or the status of MSI, p53 expression (by immunohistochemistry), or <it>KRAS/BRAF </it>mutation.</p> <p>Conclusion:</p> <p>18q LOH is correlated positively with CIMP-0 and inversely with CIMP-low and CIMP-high. Our findings provide supporting evidence for relationship between CIMP-0 and 18q LOH as well as a molecular difference between CIMP-0 and CIMP-low in colorectal cancer.</p

Effects of Metal Hydride Coatings at the Electrodes on Neutron Production Rate in a Discharge-Type Fusion Neutron Source

A glow discharge (GD) fusion neutron source that utilizes nuclear fusion reactions of deuterium has been upgraded. The fusion reactions in this device mainly occur by collisions between the charged or neutral particles and the hydrogen isotopes trapped at the surface of electrodes. In addition, it is known that the metal hydride coating on the electrode enhances the neutron production rate (NPR). Therefore, the elemental distribution, including deuterium, in the depth direction on the electrode is an essential factor in neutron production. However, the distribution on the electrode has not been experimentally investigated. This study aims to analyze the distribution experimentally and indicate the effect of the metal hydride coatings. To achieve this purpose, we prepared the titanium (Ti)-coated cathode and the uncoated cathode, of which the base material was stainless steel. After that, the neutron production test was performed in the range of from 5-to 40-mA currents and from 20-to 60-kV applied voltage. This test indicated that the NPR was improved by coating the cathode with Ti than the uncoated cathode. In addition, depth profiling on the cathodes by glow discharge optical emission spectroscopy (GD-OES) was performed. While the analysis indicated that the concentration of deuterium on both cathodes was increased after the test, there was no significant difference in the concentration of deuterium between both cathodes. Furthermore, the concentration of Ti on the Ti-coated cathode was vastly decreased. The cause of these changes needs to be investigated

Evidence for Nodal superconductivity in Sr2_{2}ScFePO3_{3}

Point contact Andreev reflection spectra have been taken as a function of temperature and magnetic field on the polycrystalline form of the newly discovered iron-based superconductor Sr2ScFePO3. A zero bias conductance peak which disappears at the superconducting transition temperature, dominates all of the spectra. Data taken in high magnetic fields show that this feature survives until 7T at 2K and a flattening of the feature is observed in some contacts. Here we inspect whether these observations can be interpreted within a d-wave, or nodal order parameter framework which would be consistent with the recent theoretical model where the height of the P in the Fe-P-Fe plane is key to the symmetry of the superconductivity. However, in polycrystalline samples care must be taken when examining Andreev spectra to eliminate or take into account artefacts associated with the possible effects of Josephson junctions and random alignment of grains.Comment: Published versio

TGFBR2 and BAX Mononucleotide Tract Mutations, Microsatellite Instability, and Prognosis in 1072 Colorectal Cancers

Mononucleotide tracts in the coding regions of the TGFBR2 and BAX genes are commonly mutated in microsatellite instability-high (MSI-high) colon cancers. The receptor TGFBR2 plays an important role in the TGFB1 (transforming growth factor-β, TGF-β) signaling pathway, and BAX plays a key role in apoptosis. However, a role of TGFBR2 or BAX mononucleotide mutation in colorectal cancer as a prognostic biomarker remains uncertain.We utilized a database of 1072 rectal and colon cancers in two prospective cohort studies (the Nurses' Health Study and the Health Professionals Follow-up Study). Cox proportional hazards model was used to compute mortality hazard ratio (HR), adjusted for clinical, pathological and molecular features including the CpG island methylator phenotype (CIMP), LINE-1 methylation, and KRAS, BRAF and PIK3CA mutations. MSI-high was observed in 15% (162/1072) of all colorectal cancers. TGFBR2 and BAX mononucleotide mutations were detected in 74% (117/159) and 30% (48/158) of MSI-high tumors, respectively. In Kaplan-Meier analysis as well as univariate and multivariate Cox regression analyses, compared to microsatellite stable (MSS)/MSI-low cases, MSI-high cases were associated with superior colorectal cancer-specific survival [adjusted HR, 0.34; 95% confidence interval (CI), 0.20-0.57] regardless of TGFBR2 or BAX mutation status. Among MSI-high tumors, TGFBR2 mononucleotide mutation was associated with CIMP-high independent of other variables [multivariate odds ratio, 3.57; 95% CI, 1.66-7.66; p = 0.0011].TGFBR2 or BAX mononucleotide mutations are not associated with the patient survival outcome in MSI-high colorectal cancer. Our data do not support those mutations as prognostic biomarkers (beyond MSI) in colorectal carcinoma

Contrasting Pressure Effects in Sr2VFeAsO3 and Sr2ScFePO3

We report the resistivity measurements under pressure of two Fe-based superconductors with a thick perovskite oxide layer, Sr2VFeAsO3 and Sr2ScFePO3. The superconducting transition temperature Tc of Sr2VFeAsO3 markedly increases with increasing pressure. Its onset value, which was Tc{onset}=36.4 K at ambient pressure, increases to Tc{onset}=46.0 K at ~4 GPa, ensuring the potential of the "21113" system as a high-Tc material. However, the superconductivity of Sr2ScFePO3 is strongly suppressed under pressure. The Tc{onset} of ~16 K decreases to ~5 K at ~4 GPa, and the zero-resistance state is almost lost. We discuss the factor that induces this contrasting pressure effect.Comment: 5 pages, 4 figures, to be published in J. Phys. Soc. Jpn. No.12 (2009