12,458 research outputs found
Calorimetric Evidence of Strong-Coupling Multiband Superconductivity in Fe(Te0.57Se0.43) Single Crystal
We have investigated the specific heat of optimally-doped iron chalcogenide
superconductor Fe(Te0.57Se0.43) with a high-quality single crystal sample. The
electronic specific heat Ce of this sample has been successfully separated from
the phonon contribution using the specific heat of a non-superconducting sample
(Fe0.90Cu0.10)(Te0.57Se0.43) as a reference. The normal state Sommerfeld
coefficient gamma_n of the superconducting sample is found to be ~ 26.6 mJ/mol
K^2, indicating intermediate electronic correlation. The temperature dependence
of Ce in the superconducting state can be best fitted using a double-gap model
with 2Delta_s(0)/kBTc = 3.92 and 2Delta_l(0)/kBTc = 5.84. The large gap
magnitudes derived from fitting, as well as the large specific heat jump of
Delta_Ce(Tc)/gamma_n*Tc ~ 2.11, indicate strong-coupling superconductivity.
Furthermore, the magnetic field dependence of specific heat shows strong
evidence for multiband superconductivity
A 1.3 cm line survey toward IRC +10216
IRC +10216 is the prototypical carbon star exhibiting an extended molecular
circumstellar envelope. Its spectral properties are therefore the template for
an entire class of objects. The main goal is to systematically study the
1.3 cm spectral line characteristics of IRC +10216. We carried
out a spectral line survey with the Effelsberg-100 m telescope toward IRC
+10216. It covers the frequency range between 17.8 GHz and 26.3 GHz (K-band).
In the circumstellar shell of IRC +10216, we find 78 spectral lines, among
which 12 remain unidentified. The identified lines are assigned to 18 different
molecules and radicals. A total of 23 lines from species known to exist in this
envelope are detected for the first time outside the Solar System and there are
additional 20 lines first detected in IRC +10216. The potential orgin of "U"
lines is also discussed. Assuming local thermodynamic equilibrium (LTE), we
then determine rotational temperatures and column densities of 17 detected
molecules. Molecular abundances relative to H are also estimated. A
non-LTE analysis of NH shows that the bulk of its emission arises from
the inner envelope with a kinetic temperature of 7020 K. Evidence for
NH emitting gas with higher kinetic temperature is also obtained, and
potential abundance differences between various C-bearing isotopologues
of HCN are evaluated. Overall, the isotopic C/C ratio is
estimated to be 499. Finally, a comparison of detected molecules in the
1.3 cm range with the dark cloud TMC-1 indicates that
silicate-bearing molecules are more predominant in IRC +10216.Comment: 32 pages, 9 figures, Accepted by A&
Tick-borne encephalitis virus induces chemokine RANTES expression via activation of IRF-3 pathway.
BACKGROUND: Tick-borne encephalitis virus (TBEV) is one of the most important flaviviruses that targets the central nervous system (CNS) and causes encephalitides in humans. Although neuroinflammatory mechanisms may contribute to brain tissue destruction, the induction pathways and potential roles of specific chemokines in TBEV-mediated neurological disease are poorly understood. METHODS: BALB/c mice were intracerebrally injected with TBEV, followed by evaluation of chemokine and cytokine profiles using protein array analysis. The virus-infected mice were treated with the CC chemokine antagonist Met-RANTES or anti-RANTES mAb to determine the role of RANTES in affecting TBEV-induced neurological disease. The underlying signaling mechanisms were delineated using RANTES promoter luciferase reporter assay, siRNA-mediated knockdown, and pharmacological inhibitors in human brain-derived cell culture models. RESULTS: In a mouse model, pathological features including marked inflammatory cell infiltrates were observed in brain sections, which correlated with a robust up-regulation of RANTES within the brain but not in peripheral tissues and sera. Antagonizing RANTES within CNS extended the survival of mice and reduced accumulation of infiltrating cells in the brain after TBEV infection. Through in vitro studies, we show that virus infection up-regulated RANTES production at both mRNA and protein levels in human brain-derived cell lines and primary progenitor-derived astrocytes. Furthermore, IRF-3 pathway appeared to be essential for TBEV-induced RANTES production. Site mutation of an IRF-3-binding motif abrogated the RANTES promoter activity in virus-infected brain cells. Moreover, IRF-3 was activated upon TBEV infection as evidenced by phosphorylation of TBK1 and IRF-3, while blockade of IRF-3 activation drastically reduced virus-induced RANTES expression. CONCLUSIONS: Our findings together provide insights into the molecular mechanism underlying RANTES production induced by TBEV, highlighting its potential importance in the process of neuroinflammatory responses to TBEV infection
Weak anisotropy of the superconducting upper critical field in Fe1.11Te0.6Se0.4 single crystals
We have determined the resistive upper critical field Hc2 for single crystals
of the superconductor Fe1.11Te0.6Se0.4 using pulsed magnetic fields of up to
60T. A rather high zero-temperature upper critical field of mu0Hc2(0) approx
47T is obtained, in spite of the relatively low superconducting transition
temperature (Tc approx 14K). Moreover, Hc2 follows an unusual temperature
dependence, becoming almost independent of the magnetic field orientation as
the temperature T=0. We suggest that the isotropic superconductivity in
Fe1.11Te0.6Se0.4 is a consequence of its three-dimensional Fermi-surface
topology. An analogous result was obtained for (Ba,K)Fe2As2, indicating that
all layered iron-based superconductors exhibit generic behavior that is
significantly different from that of the high-Tc cuprates.Comment: 4 pages, 4 figures, submit to PR
Coupling of electronic and magnetic properties in Fe1+y(Te1-xSex)
We have studied the coupling of electronic and magnetic properties in
Fe1+y(Te1-xSex) via systematic specific heat, magnetoresistivity, and Hall
coefficient measurements on two groups of samples with y = 0.02 and 0.1. In the
y = 0.02 series, we find that the 0.09 < x < 0.3 composition region, where
superconductivity is suppressed, has large Sommerfeld coefficient Gamma (~55-65
mJ/mol K^2), positive Hall coefficient R_H and negative magnetoresistance MR at
low temperature, in sharp contrast with the x=0.4-0.5 region where Gamma drops
to ~ 26 mJ/mol K^2 and R_H / MR becomes negative/positive at low temperature.
Dramatic changes of Gamma, as well as sign reversal in low-temperature RH and
MR, are also observed across the x~0.1 boundary where the long-range
antiferromagnetic order is suppressed. However, for the system with rich
interstitial excess Fe (y = 0.1), where bulk superconductivity is suppressed
even for x=0.4-0.5, the variations of Gamma, R_H and MR with x are distinct
from those seen in y = 0.02 system: Gamma is ~40 mJ/mol K^2 for 0.1 < x < 0.3,
and drops to ~ 34 mJ/mol K^2 for x = 0.4-0.5; R_H and MR does not show any sign
reversal as x is increased above 0.3. We will show that all these results can
be understood in light of the evolution of the incoherent magnetic scattering
by (pi,0) magnetic fluctuations with Se concentration. In addition, with the
suppression of magnetic scattering by magnetic field, we observed the
surprising effect of a remarkable increase in the superconducting volume
fraction under moderate magnetic fields for x=0.3-0.4 samples in the y = 0.02
system.Comment: To be appeared in PR
A 1.3 cm Line Survey toward Orion KL
Orion KL has served as a benchmark for spectral line searches throughout the
(sub)millimeter regime. The main goal is to systematically study spectral
characteristics of Orion KL in the 1.3 cm band. We carried out a spectral line
survey (17.9 GHz to 26.2 GHz) with the Effelsberg-100 m telescope towards Orion
KL. We find 261 spectral lines, yielding an average line density of about 32
spectral features per GHz above 3. The identified lines include 164
radio recombination lines (RRLs) and 97 molecular lines. A total of 23
molecular transitions from species known to exist in Orion KL are detected for
the first time in the interstellar medium. Non-metastable 15NH3 transitions are
detected in Orion KL for the first time. Based on the velocity information of
detected lines and the ALMA images, the spatial origins of molecular emission
are constrained and discussed. A narrow feature is found in SO2
(), possibly suggesting the presence of a maser line. Column
densities and fractional abundances relative to H2 are estimated for 12
molecules with LTE methods. Rotational diagrams of non-metastable 14NH3
transitions with J=K+1 to J=K+4 yield different results; metastable 15NH3 is
found to have a higher excitation temperature than non-metastable 15NH3,
indicating that they may trace different regions. Elemental and isotopic
abundance ratios are estimated: 12C/13C=63+-17, 14N/15N=100+-51,
D/H=0.0083+-0.0045. The dispersion of the He/H ratios derived from
H/He pairs to H/He pairs is very small, which
is consistent with theoretical predictions that the departure coefficients bn
factors for hydrogen and helium are nearly identical. Based on a non-LTE code
neglecting excitation by the infrared radiation field and a likelihood
analysis, we find that the denser regions have lower kinetic temperature, which
favors an external heating of the Hot Core.Comment: 70 pages, 26 figures, 12 tables, accepted for publication in A&A.
Figs. 1, 2, 8, 9 have been downsize
Field-Orientation Dependent Heat Capacity Measurements at Low Temperatures with a Vector Magnet System
We describe a heat capacity measurement system for the study of the
field-orientation dependence for temperatures down to 50 mK. A "Vector Magnet"
combined with a mechanical rotator for the dewar enables the rotation of the
magnetic field without mechanical heating in the cryostat by friction. High
reproducibility of the field direction, as well as an angular resolution of
better than 0.01 degree, is obtained. This system is applicable to other kinds
of measurements which require a large sample space or an adiabatic sample
environment, and can also be used with multiple refrigerator inserts
interchangeably.Comment: 7 pages, 8 figure
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