2,139 research outputs found
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
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
Food Webs: Experts Consuming Families of Experts
The question what determines the structure of natural food webs has been
listed among the nine most important unanswered questions in ecology. It arises
naturally from many problems related to ecosystem stability and resilience. The
traditional view is that population-dynamical stability is crucial for
understanding the observed structures. But phylogeny (evolutionary history) has
also been suggested as the dominant mechanism. Here we show that observed
topological features of predatory food webs can be reproduced to unprecedented
accuracy by a mechanism taking into account only phylogeny, size constraints,
and the heredity of the trophically relevant traits of prey and predators. The
analysis reveals a tendency to avoid resource competition rather than apparent
competition. In food webs with many parasites this pattern is reversed.Comment: 16 pages, 3 figures, 1 table + Appendix of 36 pages, 18 figures.
movie available from http://ag.rossberg.net/matching.mp
Transport Coefficients of Quark Gluon Plasma for Pure Gauge Models
The transport coefficients of quark gluon plasma are calculated on a lattice
16**3X8, with the pure gauge models. Matsubara Green's functions of energy
momentum tensors have very large fluctuations and about a few million MC sweeps
are needed to reduce the errors reasonably small in the case of the standard
action. They are much suppressed if Iwasaki's improved action is employed.
Preliminary results show that the transport coefficients roughly depend on the
coupling constant as a**(-3)(g) in the case of SU(2).Comment: Talk presented at LATTICE96(finite temperature), 3 pages in latex, 4
Postscript figure
Ferromagnetism induced in anisotropic stacked kagome-lattice antiferromagnet CsCuCeF
The magnetic properties of CsCuCeF were investigated through
magnetization and specific heat measurements. CsCuCeF is
composed of a buckled kagome lattice of Cu, which is stacked along the b
axis. The exchange network in the buckled kagome lattice is strongly
anisotropic. Consequently, CsCuCeF can be divided into two
subsystems: alternating Heisenberg chains with strong antiferromagnetic
exchange interactions and dangling spins. The dangling spins couple with one
another via effective exchange interactions, which are mediated by chain spins.
The dangling spins are further divided into two subsystems, DS1 and DS2. The
dangling spins in DS1 undergo three-dimensional ferromagnetic ordering at 3.14
K, while those in DS2 remain paramagnetic down to 0.35 K. The effective
interaction between the DS1 spins is approximately expressed by the
ferromagnetic model with the direction parallel to the
crystallographic c axis. A magnetic phase diagram for was
obtained and was analyzed within the framework of the molecular field
approximation. With increasing magnetic field, the dangling spins are polarized
and the magnetization curve exhibits a wide plateau at one-third of the
saturation magnetization.Comment: 10 pages, 12 figure
Quark Confinement Physics from Quantum Chromodynamics
We show the construction of the dual superconducting theory for the
confinement mechanism from QCD in the maximally abelian (MA) gauge using the
lattice QCD Monte Carlo simulation. We find that essence of infrared abelian
dominance is naturally understood with the off-diagonal gluon mass induced by the MA gauge fixing. In the MA gauge, the
off-diagonal gluon amplitude is forced to be small, and the off-diagonal gluon
phase tends to be random. As the mathematical origin of abelian dominance for
confinement, we demonstrate that the strong randomness of the off-diagonal
gluon phase leads to abelian dominance for the string tension. In the MA gauge,
there appears the macroscopic network of the monopole world-line covering the
whole system. We investigate the monopole-current system in the MA gauge by
analyzing the dual gluon field . We evaluate the dual gluon mass as 0.5GeV in the infrared region, which is the lattice-QCD evidence of
the dual Higgs mechanism by monopole condensation. Owing to infrared abelian
dominance and infrared monopole condensation, QCD in the MA gauge is
describable with the dual Ginzburg-Landau theory.Comment: Invited talk given at KEK-Tanashi International Symposium on Physics
of Hadrons and Nuclei, Tokyo, Japan, 14-17 Dec 199
Screening in Hot SU(2) Gauge Theory and Propagators in 3d Adjoint Higgs model
We investigate the large distance behavior of the electric and magnetic
propagators of hot SU(2) gauge theory in different gauges using lattice
simulations of the full 4d theory and the effective, dimensionally reduced 3d
theory. A comparison of the 3d and 4d data for the propagators suggests that
dimensional reduction works surprisingly well down to temperatures T=2 T_c. A
detailed study of the volume dependence of magnetic propagators is performed.
The electric propagators show exponential decay at large distances in all
gauges considered and a possible gauge dependence of the electric screening
mass turns out to be statistically insignificant.Comment: Submitted to Proceedings of Lattice 2000 and Workshop "Strong and
Electroweak Matter 2000". LaTeX uses espcrc2.st
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
Behavior of bulk high-temperature superconductors of finite thickness subjected to crossed magnetic fields
Crossed magnetic field effects on bulk high-temperature superconductors have
been studied both experimentally and numerically. The sample geometry
investigated involves finite-size effects along both (crossed) magnetic field
directions. The experiments were carried out on bulk melt-processed Y-Ba-Cu-O
(YBCO) single domains that had been pre-magnetized with the applied field
parallel to their shortest direction (i.e. the c-axis) and then subjected to
several cycles of the application of a transverse magnetic field parallel to
the sample ab plane. The magnetic properties were measured using orthogonal
pick-up coils, a Hall probe placed against the sample surface and
Magneto-Optical Imaging (MOI). We show that all principal features of the
experimental data can be reproduced qualitatively using a two-dimensional
finite-element numerical model based on an E-J power law and in which the
current density flows perpendicularly to the plane within which the two
components of magnetic field are varied. The results of this study suggest that
the suppression of the magnetic moment under the action of a transverse field
can be predicted successfully by ignoring the existence of flux-free
configurations or flux-cutting effects. These investigations show that the
observed decay in magnetization results from the intricate modification of
current distribution within the sample cross-section. It is also shown that the
model does not predict any saturation of the magnetic induction, even after a
large number (~ 100) of transverse field cycles. These features are shown to be
consistent with the experimental data.Comment: 41 pages, 9 figures, accepted in Phys. Rev. B Changes : 8 references
added, a few precisions added, some typos correcte
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