19,360 research outputs found
Specific heat and thermal conductivity of ferromagnetic magnons in Yttrium Iron Garnet
The specific heat and thermal conductivity of the insulating ferrimagnet
YFeO (Yttrium Iron Garnet, YIG) single crystal were measured
down to 50 mK. The ferromagnetic magnon specific heat shows a
characteristic dependence down to 0.77 K. Below 0.77 K, a downward
deviation is observed, which is attributed to the magnetic dipole-dipole
interaction with typical magnitude of 10 eV. The ferromagnetic magnon
thermal conductivity does not show the characteristic
dependence below 0.8 K. To fit the data, both magnetic defect
scattering effect and dipole-dipole interaction are taken into account. These
results complete our understanding of the thermodynamic and thermal transport
properties of the low-lying ferromagnetic magnons.Comment: 5 pages, 5 figure
Nodeless superconductivity in Ca3Ir4Sn13: evidence from quasiparticle heat transport
We report resistivity and thermal conductivity measurements
on CaIrSn single crystals, in which superconductivity with K was claimed to coexist with ferromagnetic spin-fluctuations. Among
three crystals, only one crystal shows a small hump in resistivity near 20 K,
which was previously attributed to the ferromagnetic spin-fluctuations. Other
two crystals show the Fermi-liquid behavior at low temperature.
For both single crystals with and without the resistivity anomaly, the residual
linear term is negligible in zero magnetic field. In low fields,
shows a slow field dependence. These results demonstrate that
the superconducting gap of CaIrSn is nodeless, thus rule out
nodal gap caused by ferromagnetic spin-fluctuations.Comment: 5 pages, 4 figure
Persistent global power fluctuations near a dynamic transition in electroconvection
This is a study of the global fluctuations in power dissipation and light
transmission through a liquid crystal just above the onset of
electroconvection.
The source of the fluctuations is found to be the creation and annihilation
of defects. They are spatially uncorrelated and yet temporally correlated. The
temporal correlation is seen to persist for extremely long times. There seems
to be an especially close relation between defect creation/annihilat ion in
electroconvection and thermal plumes in Rayleigh-B\'enard convection
A time domain decentralized algorithm for two channel active noise control.
Due to their low computational complexity, reduced wiring cost, and flexibility of scaling up, decentralized multiple channel active control systems are attractive in many applications. In a decentralized multiple channel active control system, a number of small subsystems are constructed, which are updated independently with only the associated error signals. In this letter, a time domain two channel decentralized control algorithm is proposed to achieve the similar noise reduction performance as the centralized one. Auxiliary filters are introduced to filter the reference signal for control filter update and a unique design method is proposed to shape the frequency response of the auxiliary filters. The simulation results using the measured impulse responses demonstrate the efficacy of the proposed algorithm for broadband noise control
Quantum criticality and nodal superconductivity in the FeAs-based superconductor KFe2As2
The in-plane resistivity and thermal conductivity of
FeAs-based superconductor KFeAs single crystal were measured down to 50
mK. We observe non-Fermi-liquid behavior at =
5 T, and the development of a Fermi liquid state with when
further increasing field. This suggests a field-induced quantum critical point,
occurring at the superconducting upper critical field . In zero field
there is a large residual linear term , and the field dependence of
mimics that in d-wave cuprate superconductors. This indicates that
the superconducting gaps in KFeAs have nodes, likely d-wave symmetry.
Such a nodal superconductivity is attributed to the antiferromagnetic spin
fluctuations near the quantum critical point.Comment: 4 pages, 4 figures - replaces arXiv:0909.485
Nodeless superconductivity in IrPtTe with strong spin-orbital coupling
The thermal conductivity of superconductor IrPtTe
( = 0.05) single crystal with strong spin-orbital coupling was measured down
to 50 mK. The residual linear term is negligible in zero magnetic
field. In low magnetic field, shows a slow field dependence. These
results demonstrate that the superconducting gap of IrPtTe is
nodeless, and the pairing symmetry is likely conventional s-wave, despite the
existence of strong spin-orbital coupling and a quantum critical point.Comment: 5 pages, 4 figure
Configuring fixed-coefficient active control systems for traffic noise reduction
© 2018 Elsevier Ltd Practical implementation of active noise control (ANC) systems for outdoor traffic noise reduction remains rare. One challenge is the difficulty of configuring an ANC controller due to moving noise sources, which are typically located far from ANC systems. In this paper, a pseudo noise source method is proposed for configuring fixed-coefficient feedforward ANC systems for traffic noise control. First, a minimum of one pseudo noise source is placed near an ANC system to determine the control coefficients in the tuning stage. Second, the ANC systems are run to reduce the noise from far-field traffic noise sources using the optimal control coefficients in the cancelling stage. The feasibility and limitations of the proposed method are investigated by illustrating the effect of the pseudo noise source position on the noise reduction performance of the ANC system. The simulation results show that the performance of the ANC system increases with distance when the pseudo noise sources move farther from the system but approaches a constant when the pseudo noise sources are in the far field. The indoor experimental results are consistent with the simulation results. The outdoor experimental results of a six-channel coupled system show a noise reduction of 3 dB below 500 Hz at the position of a dummy head
The fractional quantum Hall effect in infinite layer systems
Stacked two dimensional electron systems in transverse magnetic fields
exhibit three dimensional fractional quantum Hall phases. We analyze the
simplest such phases and find novel bulk properties, e.g., irrational braiding.
These phases host ``one and a half'' dimensional surface phases in which motion
in one direction is chiral. We offer a general analysis of conduction in the
latter by combining sum rule and renormalization group arguments, and find that
when interlayer tunneling is marginal or irrelevant they are chiral semi-metals
that conduct only at T > 0 or with disorder.Comment: RevTeX 3.0, 4p., 2 figs with epsf; reference to the detailed
companion paper cond-mat/0006506 adde
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