59 research outputs found
Search for signatures of dust in the Pluto-Charon system using Herschel/PACS observations
In this letter we explore the environment of Pluto and Charon in the far
infrared with the main aim to identify the signs of any possible dust ring,
should it exist in the system. Our study is based on observations performed at
70 um with the PACS instrument onboard the Herschel Space Observatory at 9
epochs between March 14 and 19, 2012. The far-infrared images of the
Pluto-Charon system are compared to those of the point spread function (PSF)
reference quasar 3C454.3. The deviation between the observed Pluto-Charon and
reference PSFs are less then 1 sigma indicating that clear evidence for an
extended dust ring around the system was not found. Our method is capable of
detecting a hypothetical ring with a total flux of ~3.3 mJy at a distance of
~153 000 km (~8.2 Pluto-Charon distances) from the system barycentre. We place
upper limits on the total disk mass and on the column density in a reasonable
disk configuration and analyse the hazard during the flyby of NASAs New
Horizons in July 2015. This realistic model configuration predicts a column
density of 8.7x10^(-10) gcm^(-2) along the path of the probe and an impactor
mass of 8.7x10^(-5) g.Comment: 10 pages, 4 figures, 2 table
Self-organized current transport through low angle grain boundaries in YBaCuO thin films, studied magnetometrically
The critical current density flowing across low angle grain boundaries in
YBaCuO thin films has been studied magnetometrically.
Films (200 nm thickness) were deposited on SrTiO bicrystal substrates
containing a single [001] tilt boundary, with angles of 2, 3, 5, and 7 degrees,
and the films were patterned into rings. Their magnetic moments were measured
in applied magnetic fields up to 30 kOe at temperatures of 5 - 95 K; current
densities of rings with or without grain boundaries were obtained from a
modified critical state model. For rings containing 5 and 7 degree boundaries,
the magnetic response depends strongly on the field history, which arises in
large part from self-field effects acting on the grain boundary.Comment: 8 pages, including 7 figure
Flux flow of Abrikosov-Josephson vortices along grain boundaries in high-temperature superconductors
We show that low-angle grain boundaries (GB) in high-temperature
superconductors exhibit intermediate Abrikosov vortices with Josephson cores,
whose length along GB is smaller that the London penetration depth, but
larger than the coherence length. We found an exact solution for a periodic
vortex structure moving along GB in a magnetic field and calculated the
flux flow resistivity , and the nonlinear voltage-current
characteristics. The predicted dependence describes well our
experimental data on unirradiated and irradiated
bicrystals, from which the core size , and the intrinsic depairing
density on nanoscales of few GB dislocations were measured for the
first time. The observed temperature dependence of
indicates a significant order parameter suppression in current channels between
GB dislocation cores.Comment: 5 pages 5 figures. Phys. Rev. Lett. (accepted
Conductive Buffer Layers and Overlayers for the Thermal Stability of Coated Conductors
We analyze fundamental issues related to the thermal and electrical stability
of a coated conductor during its operation. We address the role of conductive
buffer layers in the stability of Ni-based coated conductors, and the effect of
a metallic cap layer on the electrical properties of Ni alloy-based
superconducting tapes. For the first case we report on the fabrication of a
fully conductive RABiTS architecture formed of bilayers of conductive oxides
SrRuO3 and LaNiO3 on textured Ni tapes. For the second case we discuss
measurements of current-voltage relations on Ag/YBa2Cu3O7-d and Cu/Ag/
YBa2Cu3O7-d prototype multilayers on insulating substrates. Limitations on the
overall tape structure and properties that are posed by the stability
requirement are presented.Comment: 4 pages, 5 figure
A possible cooling effect in high temperature superconductors
We show that an adiabatic increase of the supercurrent along a superconductor
with lines of nodes of the order parameter on the Fermi surface can result in a
cooling effect. The maximum cooling occurs if the supercurrent increases up to
its critical value. The effect can also be observed in a mixed state of a bulk
sample. An estimate of the energy dissipation shows that substantial cooling
can be performed during a reasonable time even in the microkelvin regime.Comment: 5 pages, to appear in Phys. Rev.
Anisotropic, non-monotonic behavior of the superconducting critical current in thin YBa2Cu3O7-d films on vicinal SrTiO3 surfaces
The critical current density of epitaxial YBCO films grown on vicinal SrTiO3
substrates was investigated by electrical transport measurements along and
across the steps of the SrTiO3 surface for a range of temperatures of 10 K to
85 K and in applied magnetic fields varying from 0 to 14 T. For vicinal angles
of 4 and 8 degrees, we found evidence of enhanced pinning in the longitudinal
direction at low magnetic fields for a wide region of temperatures and
attribute this phenomenon to anti-phase boundaries in the YBCO film. The
transverse Jc data showed a peak in the Jc(H) curve at low magnetic fields,
which was explained on the basis of magnetic interaction between Abrikosov and
Abrikosov-Josephson vortices. The in-plane Jc anisotropy observed for vicinal
angles of 0.4 degrees was reversed with respect to the 8 degree and 4 degree
samples. This phenomenon was interpreted on the basis of strain induced in the
YBCO film by the stepped substrate's surface.Comment: accepted for publication in Phys. Rev.
Influence of a low magnetic field on the thermal diffusivity of Bi-2212
The thermal diffusivity of a Bi-2212 polycrystalline sample has been measured
under a 1T magnetic field applied perpendicularly to the heat flux. The
magnetic contribution to the heat carrier mean free path has been extracted and
is found to behave as a simple power law. This behavior can be attributed to a
percolation process of electrons in the vortex lattice created by the magnetic
field.Comment: 10 pages, 3 figures; to be published in Phys. Rev.
SN 2016coi/ASASSN-16fp: An example of residual helium in a type Ic supernova?
The optical observations of Ic-4 supernova (SN) 2016coi/ASASSN-16fp, from
to days after explosion, are presented along with analysis
of its physical properties. The SN shows the broad lines associated with SNe
Ic-3/4 but with a key difference. The early spectra display a strong absorption
feature at \AA\ which is not seen in other SNe~Ic-3/4 at this
epoch. This feature has been attributed to He I in the literature. Spectral
modelling of the SN in the early photospheric phase suggests the presence of
residual He in a C/O dominated shell. However, the behaviour of the He I lines
are unusual when compared with He-rich SNe, showing relatively low velocities
and weakening rather than strengthening over time. The SN is found to rise to
peak d after core-collapse reaching a bolometric luminosity of Lp
\ergs. Spectral models, including the nebular epoch, show
that the SN ejected \msun\ of material, with \msun\ below
5000 \kms, and with a kinetic energy of erg. The
explosion synthesised \msun\ of 56Ni. There are significant
uncertainties in E(B-V)host and the distance however, which will affect Lp and
MNi. SN 2016coi exploded in a host similar to the Large Magellanic Cloud (LMC)
and away from star-forming regions. The properties of the SN and the
host-galaxy suggest that the progenitor had of \msun\
and was stripped almost entirely down to its C/O core at explosion.Comment: Accepted for publication in MNRAS. Updated to reflect the published
version, minor typographical changes onl
Inter- and intragrain transport measurements in YBa2Cu3O7−x deformation textured coated conductors
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