1,159 research outputs found
AC-Tolerant Multifilament Coated Conductors
We report the magnetization losses in an experimental multifilament coated
conductor. A 4 mm wide and 10 cm long YBCO coated conductor was subdivided into
eight 0.5 mm wide filaments by laser ablation and subjected to post-ablation
treatment. As the result, the hysteresis loss was reduced, as expected, in
proportion to the width of the filaments. However, the coupling loss was
reduced dramatically, and became practically negligible, in the range of a
sweep rate up to 20 T/s. This represents a drastic improvement on previous
multifilament conductors in which often the coupling losses became equal to the
hysteresis loss at a sweep rate as low as 3-4 T/s. These results demonstrate
that there is an effective and practical way to suppress coupling losses in
coated multifilament conductors.Comment: This paper is based on a talk given at 2006 Applied Superconductivity
Conference in Seattle, WA (August 27-September 1, 2006). To be published in
IEEE Trans. Appl. Superconductivit
Magnetization Losses in Multifilament Coated Superconductors
We report the results of a study of the magnetization losses in experimental
multifilament, as well as control (uniform), coated superconductors exposed to
time-varying magnetic field of various frequencies. Both the hysteresis loss,
proportional to the sweep rate of the applied magnetic field, and the coupling
loss, proportional to the square of the sweep rate, have been observed. A
scaling is found that allows us to quantify each of these contributions and
extrapolate the results of the experiment beyond the envelope of accessible
field amplitude and frequency. The combined loss in the multifilament conductor
is reduced by about 90% in comparison with the uniform conductor at full field
penetration at sweep rate as high as 3T/s
Hadron Physics and Confinement Physics in Lattice QCD
We are aiming to construct Quark Hadron Physics and Confinement Physics based
on QCD. Using SU(3) lattice QCD, we are investigating the three-quark
potential at T=0 and , mass spectra of positive and negative-parity
baryons in the octet and the decuplet representations of the SU(3) flavor,
glueball properties at T=0 and . We study also Confinement Physics
using lattice QCD. In the maximally abelian (MA) gauge, the off-diagonal gluon
amplitude is strongly suppressed, and then the off-diagonal gluon phase shows
strong randomness, which leads to a large effective off-diagonal gluon mass,
. Due to the large off-diagonal gluon mass in
the MA gauge, infrared QCD is abelianized like nonabelian Higgs theories. In
the MA gauge, there appears a macroscopic network of the monopole world-line
covering the whole system. From the monopole current, we extract the dual gluon
field , and examine the longitudinal magnetic screening. We obtain 0.5 GeV in the infrared region, which indicates the dual Higgs
mechanism by monopole condensation. From infrared abelian dominance and
infrared monopole condensation, low-energy QCD in the MA gauge is described
with the dual Ginzburg-Landau (DGL) theory.Comment: Invited talk given at International Symposium on Hadrons and Nuclei,
Seoul, Korea, 20-22 Feb 200
Noise invoked resonances near a homoclinic bifurcation in the glow discharge plasma
Stochastic Resonance (SR) and Coherence Resonance (CR) have been studied
experimentally in the discharge plasma close to a homoclinic bifurcation. For
the SR phenomena, it is observed that a superimposed subthreshold periodic
signal can be recovered via stochastic modulations of the discharge voltage.
Furthermore, it is realized that even in the absence of a subthreshold
deterministic signal, the system dynamics can be recovered and optimized using
noise. This effect is defined as CR in the literature. In the present
experiments, induction of SR and CR are quantified using the Absolute Mean
Difference (AMD) and Normalized Variance (NV) techniques respectively. AMD is a
new statistical tool to quantify regularity in the stochastic resonance and is
independent of lag.Comment: 6 pag
Numerical modelling of dynamic resistance in high-temperature superconducting coated-conductor wires
The use of superconducting wire within AC power systems is complicated by the dissipative interactions that occur when a superconductor is exposed to an alternating current and/or magnetic field, giving rise to a superconducting AC loss caused by the motion of vortices within the superconducting material. When a superconductor is exposed to an alternating field whilst carrying a constant DC transport current, a DC electrical resistance can be observed, commonly referred to as “dynamic resistance.” Dynamic resistance is relevant to many potential high-temperature superconducting (HTS) applications and has been identified as critical to understanding the operating mechanism of HTS flux pump devices.
In this paper, a 2D numerical model based on the finite-element method and implementing the H-formulation is used to calculate the dynamic resistance and total AC loss in a coated-conductor HTS wire carrying an arbitrary transport current and exposed to background AC magnetic fields up to 100 mT. The measured angular dependence of the superconducting properties of the wire are used as input data, and the model is validated using experimental data for magnetic fields perpendicular to the plane of the wire, as well as at angles of 30° and 60° to this axis.
The model is used to obtain insights into the characteristics of such dynamic resistance, including its relationship with the applied current and field, the wire’s superconducting properties, the threshold field above which dynamic resistance is generated and the flux-flow resistance that arises when the total driven transport current exceeds the field-dependent critical current, Ic(B), of the wire. It is also shown that the dynamic resistance can be mostly determined by the perpendicular field component with subtle differences determined by the angular dependence of the superconducting properties of the wire. The dynamic resistance in parallel fields is essentially negligible until Jc is exceeded and flux-flow resistance occurs
Effects of Gamma Ray Bursts in Earth Biosphere
We continue former work on the modeling of potential effects of Gamma Ray
Bursts on Phanerozoic Earth. We focus on global biospheric effects of ozone
depletion and show a first modeling of the spectral reduction of light by NO2
formed in the stratosphere. We also illustrate the current complexities
involved in the prediction of how terrestrial ecosystems would respond to this
kind of burst. We conclude that more biological field and laboratory data are
needed to reach even moderate accuracy in this modelingComment: Accepted for publication in Astrophysics & Space Scienc
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