5,900 research outputs found
Si-induced superconductivity and structural transformations in DyRh4B4
DyRh4B4 has been known to crystallize in the primitive tetragonal
(pt)-structure and to exhibit a ferromagnetic transition at 12 K, the highest
magnetic transition temperature in the entire series of the RRh4B4 materials
[1]. We show here that our silicon-added samples of the nominal composition
DyRh4B4Si0.2 exhibit superconductivity below Tc ~ 4.5 K and an
antiferromagnetic transition below TN ~ 2.7 K. The 12 K transition observed in
the pt-DyRh4B4 is completely suppressed. Our annealed samples mainly consist of
domains of the chemical composition DyRh3.9B4.2Si0.08. These domains contain
two crystallographic phases belonging to the body-centred tetragonal
(bct)-structure and the orthorhombic (o)-structure. We have reasons to suggest
that superconductivity and antiferromagnetic ordering arise from bct- DyRh4B4
phase and, therefore, coexist below TN ~ 2.7 K.Comment: 11 pages, 6 figures, Accepted for publication in Journal of Alloys
and Compound
Search for vertical stratification of metals in atmospheres of blue horizontal-branch stars
The observed abundance peculiarities of many chemical species relative to the
expected cluster metallicity in blue horizontal-branch (BHB) stars presumably
appear as a result of atomic diffusion in the photosphere. The slow rotation
(typically 10 km s) of BHB stars with effective temperatures
11,500 K supports this idea since the diffusion mechanism is
only effective in a stable stellar atmosphere. In this work we search for
observational evidence of vertical chemical stratification in the atmospheres
of six hot BHB stars: B84, B267 and B279 in M15 and WF2-2541, WF4-3085 and
WF4-3485 in M13. We undertake an abundance stratification analysis of the
stellar atmospheres of the aforementioned stars, based on acquired Keck HIRES
spectra. We have found from our numerical simulations that three stars (B267,
B279 and WF2-2541) show clear signatures of the vertical stratification of iron
whose abundance increases toward the lower atmosphere, while the other two
stars (B84 and WF4-3485) do not. For WF4-3085 the iron stratification results
are inconclusive. B267 also shows a signature of titanium stratification. Our
estimates for radial velocity, and overall iron, titanium and
phosphorus abundances agree with previously published data for these stars
after taking the measurement errors into account. The results support the
hypothesis regarding the efficiency of atomic diffusion in the stellar
atmospheres of BHB stars with 11,500 K.Comment: 8 pages, 12 figures, accepted for publication in Astronomy and
Astrophysic
Electron-Phonon Coupling Origin of the resistivity in YNi_{2}B_{2}C Single Crystals
Resistivity measurements from 4.2 K up to 300 K were made on YNi_{2}B_{2}C
single crystals with Tc=15.5 K. The resulting rho(T) curve shows a perfect
Bloch-Grueneisen (BG) behavior, with a very small residual resistivity which
indicates the low impurity content and the high cristallographic quality of the
samples. The value lambda_{tr}=0.53 for the transport electron-phonon coupling
constant was obtained by using the high-temperature constant value of d(rho)/dT
and the plasma frequency reported in literature. The BG expression for the
phononic part of the resistivity rho_{ph}(T) was then used to fit the data in
the whole temperature range, by approximating alpha^{2}_{tr}F(Omega) with the
experimental phonon spectral density G(Omega) multiplied by a two-step
weighting function to be determined by the fit. The resulting fitting curve
perfectly agrees with the experimental points. We also solved the real-axis
Eliashberg equations in both s- and d-wave symmetries under the approximation
alpha^{2}F(Omega)= alpha^{2}_{tr}F(Omega). We found that the value of
lambda_{tr} here determined in single-band approximation is quite compatible
with Tc and the gap Delta experimentally observed. Finally, we calculated the
normalized tunneling conductance, whose comparison with break-junction tunnel
data gives indication of the possible s-wave symmetry for the order parameter
in YNi_{2}B_{2}C.Comment: 6 pages, 5 figures. Proceedings of SATT10 Conference, to be published
in Int. J. Mod. Phys.
Advertising and Product Confusion: A Case Study of Grapefruit Juice
Demand relationships for two closely related products -- grapefruit juice and grapefruit-juice cocktail -- were estimated from grocery-store scanner data to analyze the contention that consumer confusion exists between the two products. Results suggest confusion may exist, with grapefruit-juice advertising not only increasing the demand for grapefruit juice but also for grapefruit-juice cocktail.advertising, demand, grapefruit juice, cocktail, scanner data, Agribusiness, Consumer/Household Economics, Demand and Price Analysis,
Ballistic heat transport of quantum spin excitations as seen in SrCuO2
Fundamental conservation laws predict ballistic, i.e., dissipationless
transport behaviour in one-dimensional quantum magnets. Experimental evidence,
however, for such anomalous transport has been lacking ever since. Here we
provide experimental evidence for ballistic heat transport in a S=1/2
Heisenberg chain. In particular, we investigate high purity samples of the
chain cuprate SrCuO2 and observe a huge magnetic heat conductivity
. An extremely large spinon mean free path of more than a
micrometer demonstrates that is only limited by extrinsic
scattering processes which is a clear signature of ballistic transport in the
underlying spin model
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