6,981 research outputs found
Theoretical and experimental study of AC loss in HTS single pancake coils
The electromagnetic properties of a pancake coil in AC regime as a function
of the number of turns is studied theoretically and experimentally.
Specifically, the AC loss, the coil critical current and the voltage signal are
discussed. The coils are made of Bi2Sr2Ca2Cu3O10/Ag (BiSCCO) tape, although the
main qualitative results are also applicable to other kinds of superconducting
tapes, such as coated conductors. The AC loss and the voltage signal are
electrically measured using different pick up coils with the help of a
transformer. One of them avoids dealing with the huge coil inductance. Besides,
the critical current of the coils is experimentally determined by conventional
DC measurements. Furthermore, the critical current, the AC loss and the voltage
signal are simulated, showing a good agreement with the experiments. For all
simulations, the field dependent critical current density inferred from DC
measurements on a short tape sample is taken into account.Comment: 22 pages, 15 figures; contents extended (sections 3.2 and 4); one new
figure (figure 5) and two figures replaced (figures 3 and 8); typos
corrected; title change
Magnetic structure and orbital ordering in BaCoO3 from first-principles calculations
Ab initio calculations using the APW+lo method as implemented in the WIEN2k
code have been used to describe the electronic structure of the
quasi-one-dimensional system BaCoO3. Both, GGA and LDA+U approximations were
employed to study different orbital and magnetic orderings. GGA predicts a
metallic ground state whereas LDA+U calculations yield an insulating and
ferromagnetic ground state (in a low-spin state) with an alternating orbital
ordering along the Co-Co chains, consistent with the available experimental
data.Comment: 8 pages, 9 figure
On the representation of simple Riesz groups
In this paper we answer Open Problem 2 of Goodearl's book on
partially ordered abelian groups in the case of partially ordered sim-
ple groups. As a consequence, we obtain a version of the Theorem of
structure of dimension groups in the case of simple Riesz groups. Also,
we give a method for constructing torsion-free strictly perforated simple
Riesz groups of rank one, and we see that every dense additive subgroup
of Q can be obtained using this method
High-J v=0 SiS Maser Emission in IRC+10216: A New Case of Infrared Overlaps
We report on the first detection of maser emission in the J=11-10, J=14-13
and J=15-14 transitions of the v=0 vibrational state of SiS toward the C-rich
star IRC+10216. These masers seem to be produced in the very inhomogeneous
region between the star and the inner dust formation zone, placed at 5-7 R*,
with expansion velocities below 10 km/s. We interpret the pumping mechanism as
due to overlaps between v=1-0 ro-vibrational lines of SiS and mid-IR lines of
C2H2, HCN and their 13C isotopologues. The large number of overlaps found
suggests the existence of strong masers for high-J v=0 and v=1 SiS transitions,
located in the submillimeter range. In addition, it could be possible to find
several rotational lines of the SiS isotopologues displaying maser emission.Comment: 4 pages, 1 figure, published in the ApJ Letter
3D Modeling of the Magnetization of Superconducting Rectangular-Based Bulks and Tape Stacks
In recent years, numerical models have become popular and powerful tools to
investigate the electromagnetic behavior of superconductors. One domain where
this advances are most necessary is the 3D modeling of the electromagnetic
behavior of superconductors. For this purpose, a benchmark problem consisting
of superconducting cube subjected to an AC magnetic field perpendicular to one
of its faces has been recently defined and successfully solved. In this work, a
situation more relevant for applications is investigated: a superconducting
parallelepiped bulk with the magnetic field parallel to two of its faces and
making an angle with the other one without and with a further constraint on the
possible directions of the current. The latter constraint can be used to model
the magnetization of a stack of high-temperature superconductor tapes, which
are electrically insulated in one direction. For the present study three
different numerical approaches are used: the Minimum Electro-Magnetic Entropy
Production (MEMEP) method, the -formulation of Maxwell's equations and the
Volume Integral Method (VIM) for 3D eddy currents computation. The results in
terms of current density profiles and energy dissipation are compared, and the
differences in the two situations of unconstrained and constrained current flow
are pointed out. In addition, various technical issues related to the 3D
modeling of superconductors are discussed and information about the
computational effort required by each model is provided. This works constitutes
a concrete result of the collaborative effort taking place within the HTS
numerical modeling community and will hopefully serve as a stepping stone for
future joint investigations
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