7,966 research outputs found
Focused-ion-beam-induced deposition of superconducting nanowires
Superconducting nanowires, with a critical temperature of 5.2 K, have been
synthesized using an ion-beam-induced deposition, with a Gallium focused ion
beam and Tungsten Carboxyl, W(CO)6, as precursor. The films are amorphous, with
atomic concentrations of about 40, 40, and 20 % for W, C, and Ga, respectively.
Zero Kelvin values of the upper critical field and coherence length of 9.5 T
and 5.9 nm, respectively, are deduced from the resistivity data at different
applied magnetic fields. The critical current density is Jc= 1.5 10^5 A/cm2 at
3 K. This technique can be used as a template-free fabrication method for
superconducting devices.Comment: Accepted for publication in Applied Physics Letter
Resonant recoil in extreme mass ratio binary black hole mergers
The inspiral and merger of a binary black hole system generally leads to an
asymmetric distribution of emitted radiation, and hence a recoil of the remnant
black hole directed opposite to the net linear momentum radiated. The recoil
velocity is generally largest for comparable mass black holes and particular
spin configurations, and approaches zero in the extreme mass ratio limit. It is
generally believed that for extreme mass ratios eta<<1, the scaling of the
recoil velocity is V {\propto} eta^2, where the proportionality coefficient
depends on the spin of the larger hole and the geometry of the system (e.g.
orbital inclination). Here we show that for low but nonzero inclination
prograde orbits and very rapidly spinning large holes (spin parameter
a*>0.9678) the inspiralling binary can pass through resonances where the
orbit-averaged radiation-reaction force is nonzero. These resonance crossings
lead to a new contribution to the kick, V {\propto} eta^{3/2}. For these
configurations and sufficiently extreme mass ratios, this resonant recoil is
dominant. While it seems doubtful that the resonant recoil will be
astrophysically significant, its existence suggests caution when extrapolating
the results of numerical kick results to extreme mass ratios and near-maximal
spins.Comment: fixed references; matches PRD accepted version (minor revision); 9
pages, 2 figure
Phenomenological local potentials for \pi^- + ^{12}C scattering from 120 to 766 MeV
Pion-nucleus scattering cross sections are calculated by solving a
Schr\"{o}dinger equation reduced from the Klein-Gordon equation. Local
potentials are assumed, and phenomenological potential parameters are searched
energy-dependently for C system so as to reproduce not only
elastic differential cross sections but also total elastic, reaction and total
cross sections at 13 pion incident energies from 120 to 766 MeV. The real and
imaginary parts of the local potentials thus obtained are shown to satisfy the
dispersion relation. The imaginary part of the potentials as a function of the
pion energy is found to peak near the (1232)-resonance energy. The
strong absorption radius of the pion projectile with incident energies near the
-resonance region is found to be about fm, which is
consistent with previous studies of the region where the decay of the
's takes place in nuclei. The phenomenological local potentials are
then compared with the local potentials exactly phase-shift equivalent to
Kisslinger potentials for pion energies near the -resonance
The Earth Effect in the MSW Analysis of the Solar Neutrino Experiments
We consider the Earth effect in the MSW analysis of the Homestake,
Kamiokande, GALLEX, and SAGE solar neutrino experiments. Using the
time-averaged data and assuming two-flavor oscillations, the large-angle region
of the combined fit extends to much smaller angles (to ) than when the Earth effect is ignored. However, the additional constraint
from the Kamiokande II day-night data excludes most of the parameter space
sensitive to the Earth effect independent of astrophysical uncertainties, and
leaves only a small large-angle region close to maximal mixing at 90\% C.L. The
nonadiabatic solution remains unaffected by the Earth effect and is still
preferred. Both theoretical and experimental uncertainties are included in the
analysis.Comment: (11 pages, Revtex 3.0 (can be changed to Latex), 3 postscript figures
included, UPR-0570T
Standard Model Contributions to the Neutrino Index of Refraction in the Early Universe
With the standard electroweak interactions, the lowest-order coherent forward
scattering amplitudes of neutrinos in a CP symmetric medium (such as the early
universe) are zero, and the index of refraction of a propagating neutrino can
only arise from the expansion of gauge boson propagators, from radiative
corrections, and from new physics interactions. Motivated by nucleosynthesis
constraints on a possible sterile neutrino (suggested by the solar neutrino
deficit and a possible neutrino), we calculate the standard model
contributions to the neutrino index of refraction in the early universe,
focusing on the period when the temperature was of the order of a few . We
find sizable radiative corrections to the tree level result obtained by the
expansion of the gauge boson propagator. For the leading log correction is about , while for
the correction is about
. Depending on the family mixing (if any), effects from different family
scattering can be dominated by radiative corrections. The result for
is zero at one-loop level, even if neutrinos are
massive. The cancellation of infrared divergence in a coherent process is also
discussed.Comment: 46pp, 13 figures (not included), UPR-0495
Possible Effects of Quantum Mechanics Violation Induced by Certain Quantum Gravity on Neutrino Oscillations
In this work we tried extensively to apply the EHNS postulation about the
quantum mechanics violation effects induced by the quantum gravity of black
holes to neutrino oscillations. The possibilities for observing such effects in
the neutrino experiments (in progress and/or accessible in the near future)
were discussed. Of them, an interesting one was outlined specially.Comment: 18 pages, 0 figure, (1 REVTeX file
Periodic Oscillations of Josephson-Vortex Flow Resistance in Oxygen-Deficient Y1Ba2Cu3Ox
We measured the Josephson vortex flow resistance as a function of magnetic
field applied parallel to the ab-planes using annealed Y1Ba2Cu3Ox intrinsic
Josephson junctions having high anisotropy (around 40) by oxygen content
reduction. Periodic oscillations were observed in magnetic fields above 45-58
kOe, corresponding to dense-dilute boundary for Josephson vortex lattice. The
observed period of oscillations, agrees well with the increase of one fluxon
per two junctions (\textit{=}\textit{/2Ls}), may correspond
to formation of a triangular lattice of Josephson vortices as has been reported
by Ooi et al. for highly anisotropic (larger than 200) Bi-2212 intrinsic
Josephson junctions.Comment: 5 pages, 4 figure
Relative velocity of dark matter and baryonic fluids and the formation of the first structures
At the time of recombination, baryons and photons decoupled and the sound
speed in the baryonic fluid dropped from relativistic to the thermal velocities
of the hydrogen atoms. This is less than the relative velocities of baryons and
dark matter computed via linear perturbation theory, so we infer that there are
supersonic coherent flows of the baryons relative to the underlying potential
wells created by the dark matter. As a result, the advection of small-scale
perturbations (near the baryonic Jeans scale) by large-scale velocity flows is
important for the formation of the first baryonic structures. This effect
involves a quadratic term in the cosmological perturbation theory equations and
hence has not been included in studies based on linear perturbation theory. We
show that the relative motion suppresses the abundance of the first bound
objects, even if one only investigates dark matter haloes, and leads to
qualitative changes in their spatial distribution, such as introducing
scale-dependent bias and stochasticity. We discuss the possible observable
implications for high-redshift galaxy clustering and reionization
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