3,447 research outputs found
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
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
Effects of metallic spacer in layered superconducting Sr2(MgTi)O3FeAs
The highly two-dimensional superconducting system
Sr2(MgTi)O3FeAs, recently synthesized in the range of 0.2 < y <
0.5, shows an Mg concentration-dependent . Reducing the Mg concentration
from y=0.5 leads to a sudden increase in , with a maximum ~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(MgTi)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 -centered Fe-derived Fermi surfaces (FSs)
considerably shrink or disappear. Instead, three -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 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(MgTi)O3 layers in this superconductivity.Comment: 7 pages; Proceedings of ICSM-201
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-Ξ², TGF-Ξ²) 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; pβ=β0.0011].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
Comparative study on the thermoelectric effect of parent oxypnictides LaAsO ( = Fe, Ni)
The thermopower and Nernst effect were investigated for undoped parent
compounds LaFeAsO and LaNiAsO. Both thermopower and Nernst signal in iron-based
LaFeAsO are significantly larger than those in nickel-based LaNiAsO.
Furthermore, abrupt changes in both thermopower and Nernst effect are observed
below the structural phase transition temperature and spin-density wave (SDW)
type antiferromagnetic (AFM) order temperature in Fe-based LaFeAsO. On the
other hand, Nernst effect is very small in the Ni-based LaNiAsO and it is
weakly temperature-dependent, reminiscent of the case in normal metals. We
suggest that the effect of SDW order on the spin scattering rate should play an
important role in the anomalous temperature dependence of Hall effect and
Nernst effect in LaFeAsO. The contrast behavior between the LaFeAsO and LaNiAsO
systems implies that the LaFeAsO system is fundamentally different from the
LaNiAsO system and this may provide clues to the mechanism of high
superconductivity in the Fe-based systems.Comment: 6 pages, 6 figure
Field-Induced Magnetostructural Transitions in Antiferromagnetic Fe1+yTe1-xSx
The transport and structural properties of Fe1+yTe1-xSx (x=0, 0.05, and 0.10)
crystals were studied in pulsed magnetic fields up to 65 T. The application of
high magnetic fields results in positive magnetoresistance effect with
prominent hystereses in the antiferromagnetic state. Polarizing microscope
images obtained at high magnetic fields showed simultaneous occurrence of
structural transitions. These results indicate that magnetoelastic coupling is
the origin of the bicollinear magnetic order in iron chalcogenides.Comment: 5 pages, 5 figures, accepted for publication in Journal of the
Physical Society of Japa
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A prospective study of plasma inflammatory markers and risk of colorectal cancer in men
Background: Chronic inflammation may mediate risk of colorectal cancer (CRC); however, the association between circulating inflammatory markers and risk of CRC has been inconsistent. Methods: We prospectively evaluated the association of plasma C-reactive protein (CRP), interleukin-6 (IL-6), and the soluble tumour necrosis factor receptor 2 (sTNFR-2) with incident CRC among 274 cases and 532 matched controls nested in the Health Professionals Follow-up Study. Results: Multivariate relative risk (RR) of CRC comparing the extreme quartiles of plasma IL-6 was 1.54 (95% confidence interval (CI), 0.99β2.40; Ptrend=0.02). However, after excluding cases diagnosed within 2 years of blood draw, this association was not statistically significant (RR=1.26, 95% CI, 0.78β2.05; Ptrend=0.21). In analyses restricted to cases diagnosed at least 2 years after blood draw, the association of IL-6 with CRC appeared to differ by body mass index such that the significantly positive association was only present among lean individuals (Pinteraction=0.03). We did not observe any significant association between CRP or sTNFR-2 and CRC. Conclusion: Plasma inflammatory markers are not generally associated with risk of CRC among men. However, the possibility that plasma IL-6 is associated with increased risk of CRC among lean men requires further investigation
A Study of Thymidylate Synthase Expression as a Biomarker for Resectable Colon Cancer: Alliance (Cancer and Leukemia Group B) 9581 and 89803.
PurposeTumor levels of thymidylate synthase (TS), a target of 5-fluorouracil (5-FU)-based chemotherapy for colorectal cancer, have been studied as a predictive or prognostic biomarker with mixed results.Patients and methodsTumor TS levels were prospectively evaluated in two adjuvant therapy trials for patients with resected stage II or III colon cancer. TS expression was determined by standard immunohistochemistry and by automated quantitative analysis. Tumor mismatch repair deficiency (MMR-D) and BRAF c.1799Tβ>βA (p.V600E) mutation status were also examined. Relationships between tumor TS, MMR-D, and BRAF mutation status, overall survival (OS), and disease-free survival (DFS) were investigated in the subset of stage III patients.ResultsPatients whose tumors demonstrated high TS expression experienced better treatment outcomes, with DFS hazard ratio (HR)β=β0.67, 95% confidence interval (CI)β=β0.53, 0.84; and OS HRβ=β0.68, 95% CIβ=β0.53, 0.88, for high versus low TS expression, respectively. No significant interaction between TS expression and stage was observed (DFS: interaction HRβ=β0.94; OS: interaction HRβ=β0.94). Tumors with high TS expression were more likely to demonstrate MMR-D (22.2% vs. 12.8%; pβ=β .0003). Patients whose tumors demonstrated both high TS and MMR-D had a 7-year DFS of 77%, compared with 58% for those whose tumors had low TS and were non-MMR-D (log-rank pβ=β .0006). Tumor TS expression did not predict benefit of a particular therapeutic regimen.ConclusionThis large prospective analysis showed that high tumor TS levels were associated with improved DFS and OS following adjuvant therapy for colon cancer, although tumor TS expression did not predict benefit of 5-FU-based chemotherapy. The Oncologist 2017;22:107-114Implications for Practice: This study finds that measurement of tumor levels of thymidylate synthase is not helpful in assigning specific adjuvant treatment for colorectal cancer. It also highlights the importance of using prospective analyses within treatment clinical trials as the optimal method of determining biomarker utility
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