4,135 research outputs found
Doping dependent Irreversible Magnetic Properties of Ba(Fe1-xCox)2As2 Single Crystals
We discuss the irreversible magnetic properties of self-flux grown
Ba(Fe1-xCox)2As2 single crystals for a wide range of concentrations covering
the whole phase diagram from the underdoped to the overdoped regime, x=0.038,
0.047, 0.058, 0.071, 0.074, 0.10, 0.106 and 0.118. Samples were characterized
by a magneto-optical method and show excellent spatial uniformity of the
superconducting state. The overall behavior closely follows classical Bean
model of the critical state. The field-dependent magnetization exhibits second
peak at a temperature and doping - dependent magnetic field, Hp. The evolution
of this fishtail feature with doping is discussed. Magnetic relaxation is
time-logarithmic and unusually fast. Similar to cuprates, there is an apparent
crossover from collective elastic to plastic flux creep above Hp. At high
fields, the field dependence of the relaxation rate becomes doping independent.
We discuss our results in the framework of the weak collective pinning and show
that vortex physics in iron-based pnictide crystals is much closer to high-Tc
cuprates than to conventional s-wave (including MgB2) superconductors.Comment: for the special issue of Physica C on iron-based pnictide
superconductor
Commensurate Itinerant Antiferromagnetism in BaFe2As2: 75As-NMR Studies on a Self-Flux Grown Single Crystal
We report results of 75As nuclear magnetic resonance (NMR) experiments on a
self-flux grown single crystal of BaFe2As2. A first-order antiferromagnetic
(AF) transition near 135 K was detected by the splitting of NMR lines, which is
accompanied by simultaneous structural transition as evidenced by a sudden
large change of the electric field gradient tensor at the As site. The NMR
results lead almost uniquely to the stripe spin structure in the AF phase. The
data of spin-lattice relaxation rate indicate development of anisotropic spin
fluctuations of the stripe-type with decreasing temperature in the paramagnetic
phase.Comment: 7 pages, 7 figures, accepted for publication in J. Phys. Soc. Jp
Pressure-induced superconductivity in EuCaFeAs : FeAs-based superconductivity hidden by antiferromagnetism of Eu sublattice
To clarify superconductivity in EuFe2As2 hidden by antiferromagnetism of
Eu2+, we investigated a Ca-substituted sample, Eu0.5Ca0.5Fe2As2, under high
pressure. For ambient pressure, the sample exhibits a spin-density-wave (SDW)
transition at TSDW = 191 K and antiferromagnetic order at TN = 4 K, but no
evidence of superconductivity down to 2 K. The Ca-substitution certainly
weakens the antiferromagnetism. With increasing pressure, TSDW shifts to lower
temperature and becomes more unclear. Above 1.27 GPa, pressure-induced
superconductivity with zero resistivity is observed at around Tc = 20 K. At
2.14 GPa, Tc reaches a maximum value of 24 K and the superconducting transition
becomes the sharpest. These features of emergence of the superconductivity are
qualitatively similar to those observed in AFe2As2 (A = Ba, Ca).Comment: 4 pages, 4 figure
2-Azido-2-deoxy-3,4-O-isopropylidene-2-C-methyl-d-talono-1,5-lactone
The relative stereochemistry of the title compound, C10H15N3O5, was confirmed by the crystal structure determination. The absolute configuration was determined from the use of d-lyxonolactone as the starting material. The six-membered ring adopts a boat conformation with the larger azide group, rather than the methyl group, in the bowsprit position. In the crystal structure, a bifurcated intermolecular O—H⋯O/O—H⋯N hydrogen bond links molecules into chains running parallel to the b axis
Critical properties of superconducting Ba1-xKxFe2As2
Magnetisation and magnetoresistance measurements have been carried out on
superconducting Ba1-xKxFe2As2 samples with x=0.40 and 0.50. From low field
magnetization data carried out at different temperatures below TC, HC1 has been
extracted. The plot of HC1 versus temperature shows an anomalous increase at
low temperatures. From high field magnetization hysterisis measurements carried
out in fields up to 16 T at 4.2 K and 20 K, the critical current density has
been evaluated using the Bean critical state model. The JC determined from the
high field data is >104A/cm2 at 4.2 K and 5 T. The superconducting transitions
were also measured resistively in increasing applied magnetic fields up to 12
Tesla. From the variation of the TC onset with applied field, dHC2/dT at TC was
obtained to be -7.708 T/K and -5.57 T/K in the samples with x=0.40 and 0.50.Comment: 14 pages; 7 figure
BLADE-ON-PETIOLE proteins act in an E3 ubiquitin ligase complex to regulate PHYTOCHROME INTERACTING FACTOR 4 abundance.
Both light and temperature have dramatic effects on plant development. Phytochrome photoreceptors regulate plant responses to the environment in large part by controlling the abundance of PHYTOCHROME INTERACTING FACTOR (PIF) transcription factors. However, the molecular determinants of this essential signaling mechanism still remain largely unknown. Here, we present evidence that the <i>BLADE-ON-PETIOLE</i> ( <i>BOP</i> ) genes, which have previously been shown to control leaf and flower development in Arabidopsis, are involved in controlling the abundance of PIF4. Genetic analysis shows that <i>BOP2</i> promotes photo-morphogenesis and modulates thermomorphogenesis by suppressing <i>PIF4</i> activity, through a reduction in PIF4 protein level. In red-light-grown seedlings PIF4 ubiquitination was reduced in the <i>bop2</i> mutant. Moreover, we found that BOP proteins physically interact with both PIF4 and CULLIN3A and that a CULLIN3-BOP2 complex ubiquitinates PIF4 in vitro. This shows that BOP proteins act as substrate adaptors in a CUL3 <sup>BOP1/BOP2</sup> E3 ubiquitin ligase complex, targeting PIF4 proteins for ubiquitination and subsequent degradation
The layered iron arsenides Sr2CrO3FeAs and Ba2ScO3FeAs
Polycrystalline samples of the layered iron arsenides Sr2CrO3FeAs and
Ba2ScO3FeAs were synthesized by high temperature solid state reactions and
their crystal structures determined by the X-ray powder diffraction. Their
structures are tetragonal (P4/nmm; Sr2CrO3FeAs: a = 391.12(1) pm, c =
1579.05(3) pm; Ba2ScO3FeAs: a = 412.66(5) pm, c = 1680.0(2) pm, Z = 2) and
isotypic to Sr2ScO3CuS. Iron arsenide layers are sandwiched between
perowskite-like oxide blocks and separated by ~1600 pm, which is much larger
compared to the 1111 iron arsenide superconductors. The bond length and angles
within the FeAs layers are adapted to the space requirements of the oxide
blocks. Measurements of the magnetic susceptibility and electrical resistivity
show no hint for a SDW-like anomaly in both compounds. Sr2CrO3FeAs shows
Curie-Weiss paramagnetism above 160 K with an effective magnetic moment of
3.83(3) muB in good agreement with the theoretical value of 3.87 muB for Cr3+.
Antiferromagnetic ordering was detected below TN ~ 31 K. 57Fe Moessbauer
spectra of Sr2CrO3FeAs show a single signal that broadens below the magnetic
ordering temperature due to a small transferred hyperfine field induced by the
magnetic ordering of the chromium atoms. 57Fe-Moessbauer spectra of Ba2ScO3FeAs
show single signals at 298, 77, and 4.2 K which are only subject to weak
quadrupole splitting.Comment: substantial addititions and corrections, references updated 19 pages,
7 figure
Review: optical fiber sensors for civil engineering applications
Optical fiber sensor (OFS) technologies have developed rapidly over the last few decades, and various types of OFS have found practical applications in the field of civil engineering. In this paper, which is resulting from the work of the RILEM technical committee “Optical fiber sensors for civil engineering applications”, different kinds of sensing techniques, including change of light intensity, interferometry, fiber Bragg grating, adsorption measurement and distributed sensing, are briefly reviewed to introduce the basic sensing principles. Then, the applications of OFS in highway structures, building structures, geotechnical structures, pipelines as well as cables monitoring are described, with focus on sensor design, installation technique and sensor performance. It is believed that the State-of-the-Art review is helpful to engineers considering the use of OFS in their projects, and can facilitate the wider application of OFS technologies in construction industry
Early Childhood Education: A Curriculum Review and Critical Analysis
In a more contemporary approach, th
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