31,289 research outputs found
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
A novel fast fractal image compression method based on distance clustering in high dimensional sphere surface
Fractal encoding method becomes an effective image compression method because of its high compression ratio and short decompressing time. But one problem of known fractal compression method is its high computational complexity and consequent long compressing time. To address this issue, in this paper, distance clustering in high dimensional sphere surface is applied to speed up the fractal compression method. Firstly, as a preprocessing strategy, an image is divided into blocks, which are mapped on high dimensional sphere surface. Secondly, a novel image matching method is presented based on distance clustering on high dimensional sphere surface. Then, the correctness and effectiveness properties of the mentioned method are analyzed. Finally, experimental results validate the positive performance gain of the method
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
Properties of superconducting MgB_2 wires: "in-situ" versus "ex-situ" reaction technique
We have fabricated a series of iron-sheathed superconducting wires prepared
by the powder-in-tube technique from (MgB_2)_{1-x}:(Mg+2B)_x initial powder
mixtures taken with different proportions, so that x varies from 0 to 1. It
turned out that "ex-situ" prepared wire (x = 0) has considerable disadvantages
compared to all the other wires in which "in-situ" assisted (0 < x < 1) or pure
"in-situ" (x = 1) preparation was used due to weaker inter-grain connectivity.
As a result, higher critical current densities J_c were measured over the
entire range of applied magnetic fields B_a for all the samples with x > 0.
Pinning of vortices in MgB_2 wires is shown to be due to grain boundaries.
J_c(B_a) behavior is governed by an interplay between the transparency of grain
boundaries and the amount of "pinning" grain boundaries. Differences between
thermo-magnetic flux-jump instabilities in the samples and a possible threat to
practical applications are also discussed.Comment: To be published in Supercond. Sci. Technol. (2003), in pres
Hurst parameter analysis of radio pulsar timing noise
We present an analysis of timing residual (noise) of 54 pulsars obtained from
25-m radio telescope at Urumqi Observatory with a time span of 5~8 years,
dealing with statistics of the Hurst parameter. The majority of these pulsars
were selected to have timing noise that look like white noise rather than
smooth curves. The results are compared with artificial series of different
constant pairwise covariances. Despite the noise like appearance, many timing
residual series showed Hurst parameters significantly deviated from that of
independent series. We concluded that Hurst parameter may be capable of
detecting dependence in timing residual and of distinguishing chaotic behavior
from random processes.Comment: 7 pages, 3 figures, 2 tables, Submitted to MNRA
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