454 research outputs found
Low-Temperature X-ray Crystal Structure Analysis of the Cage-Structured Compounds MBe13 (M = La, Sm, and U)
The beryllides MBe13 (M = rare earths and actinides) crystallize in a
NaZn13-type cubic structure, which can be categorized as a cage-structured
compound. In this study, powder X-ray diffraction measurements have been
performed on LaBe13, SmBe13, and UBe13 in the temperature range between 7 and
300 K in order to investigate their crystallographic characteristics
systematically. They keep the NaZn13-type cubic structure down to the lowest
temperature. We estimated their Debye temperature to be 600 - 750 K from
analyses of the temperature dependence of a lattice parameter, being in good
agreement with the values reported previously. Rietveld refinements on the
obtained powder patterns revealed that the M atom in the 8a site is located in
an almost ideal snub cube formed by 24 Be atoms in the 96i site, whose caged
structure is unchanged even at the low temperatures. In addition, it is argued
from the temperature variation of an isotropic mean-square displacement
parameter that the MBe13 compounds commonly have a low-energy phonon mode,
which can be described by a model assuming an Einstein oscillation of the M
atom with a characteristic temperature of ~ 160 K.Comment: 8 pages with 6 figures and 2 table
Experiment and numerical simulation of the combined effect of winding, cool-down, and screening current induced stresses in REBCO coils
This paper overviews the combined effects of winding, cool-down, and screening current-induced stresses in REBCO coils. First, a simulation method to model the circumferential stress modification effect due to the screening-current is overviewed. The simulation includes coil winding, cooling down, and coil charge up to the operating current. Second, we will compare the numerical simulation results with the experimental results. The numerical simulations for a dry coil and an epoxy impregnated coil agree well with the experimental results. Third, the enhanced circumferential stress did not degrade the performance of a dry winding REBCO coil, but the improved increased compressive stress buckled the coil structure. Finally, it is demonstrated that epoxy impregnation has beneficial effects in reducing the stress modification effect. However, the circumferential stress is enormously enhanced at the coil ends, sometimes resulting in degradation of the coil performance
Reply to "Comment on 'Isotope effect in multi-band and multi-channel attractive systems and inverse isotope effect in iron-based superconductors'"
The Comment insists on the following: in our model it is assumed that the
effective interactions have specific energy ranges within the single band with
a cutoff at \omega_1 for the phononic part and a range from \omega_1 to
\omega_2 in the AF channel. Our reply is that we assume that V_i(k,k')\neq 0 if
|\xi_k|<\omega_i and |\xi_{k'}|<\omega_i, and otherwise V_i(k,k')= 0 (i=1,2),
as stated in our paper. This is the model of BCS type with two attractive
interactions, and this assumption is the characteristic of the BCS
approximation. The claim "the integration limits have been modified such that
the AF channel mediated pairing sets in where the ph-channel pairing terminates
and is limited at an energy given by \omega_j=\omega_{AF}" in the Comment is
wrong. We describe the model and the method to solve the gap equation in more
detail
Crystalline Electric Field and Kondo Effect in SmOs4Sb12
Our ultrasound results obtained in pulsed magnetic fields show that the
filled-skutterudite compound SmOsSb has the quartet
crystalline-electric-field ground state. This fact suggests that the multipolar
degrees of freedom of the quartet play an important role in the
unusual physical properties of this material. On the other hand, the elastic
response below 20 T cannot be explained using the localized
4-electron model, which does not take into account the Kondo effect or
ferromagnetic ordering. The analysis result suggests the presence of a
Kondo-like screened state at low magnetic fields and its suppression at high
magnetic fields above 20 T even at low temperatures.Comment: 4 pages, 4 figure
Molecular Dynamics Simulation of Grain Boundary Formation and Migration in Silicon
Molecular dynamics simulation using Tersoff potential was carried out to investigate the formation and the migration of (010) AE5 twist boundary in silicon. Effects of carbon atoms on the grain boundary formation and the grain boundary migration were also investigated. Amorphous thin layers remained at the twist boundary even after crystallization, and changes in the thickness of this layers caused grain boundary migration. When carbon atoms were segregated at the twist boundary, these atoms prevented shrinkage of an amorphous thin layer, and the grain boundary migration was retarded. Precipitated carbon atoms within the grain produces a strain field and this strain field possibly became driving force for the grain boundary migration
Inverse Iron Isotope Effect on the transition temperature of the (Ba,K)Fe2As2 superconductor
We report that (Ba,K)Fe2As2 superconductor (a transition temperature, Tc = 38
K) shows inverse Iron isotope effect (-0.18) (the sample including the larger
atomic weight of Fe depicts higher Tc). Measurements of both temperature
dependent magnetization and resistivity reveal a clear inverse shift by
systematic studies on Tc using three types of Fe-isotopes (Fe-54, natural Fe
and Fe-57). This indicates the first evidence of the inverse isotope effect in
high-Tc superconductors. This atomic mass dependence on Tc implies the exotic
coupling mechanism.Comment: 12 pages, 6 figure
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