2,132 research outputs found
Positronium collisions with rare-gas atoms
We calculate elastic scattering of positronium (Ps) by the Xe atom using the
recently developed pseudopotential method [I. I. Fabrikant and G. F. Gribakin,
Phys. Rev. A 90, 052717 (2014)] and review general features of Ps scattering
from heavier rare-gas atoms: Ar, Kr, and Xe. The total scattering cross section
is dominated by two contributions: elastic scattering and Ps ionization
(breakup). To calculate the Ps ionization cross sections we use the
binary-encounter method for Ps collisions with an atomic target. Our results
for the ionization cross section agree well with previous calculations carried
out in the impulse approximation. Our total Ps-Xe cross section, when plotted
as a function of the projectile velocity, exhibits similarity with the
electron-Xe cross section for the collision velocities higher than 0.8 a.u.,
and agrees very well with the measurements at Ps velocities above 0.5 a.u.Comment: 7 pages, 7 figures, submitted to J. Phys.
Renyi generalizations of the conditional quantum mutual information
The conditional quantum mutual information of a tripartite state
is an information quantity which lies at the center of many
problems in quantum information theory. Three of its main properties are that
it is non-negative for any tripartite state, that it decreases under local
operations applied to systems and , and that it obeys the duality
relation for a four-party pure state on systems . The
conditional mutual information also underlies the squashed entanglement, an
entanglement measure that satisfies all of the axioms desired for an
entanglement measure. As such, it has been an open question to find R\'enyi
generalizations of the conditional mutual information, that would allow for a
deeper understanding of the original quantity and find applications beyond the
traditional memoryless setting of quantum information theory. The present paper
addresses this question, by defining different -R\'enyi generalizations
of the conditional mutual information, some of which we can
prove converge to the conditional mutual information in the limit
. Furthermore, we prove that many of these generalizations
satisfy non-negativity, duality, and monotonicity with respect to local
operations on one of the systems or (with it being left as an open
question to prove that monotoniticity holds with respect to local operations on
both systems). The quantities defined here should find applications in quantum
information theory and perhaps even in other areas of physics, but we leave
this for future work. We also state a conjecture regarding the monotonicity of
the R\'enyi conditional mutual informations defined here with respect to the
R\'enyi parameter . We prove that this conjecture is true in some
special cases and when is in a neighborhood of one.Comment: v6: 53 pages, final published versio
A Feynman-Kac Formula for Anticommuting Brownian Motion
Motivated by application to quantum physics, anticommuting analogues of
Wiener measure and Brownian motion are constructed. The corresponding Ito
integrals are defined and the existence and uniqueness of solutions to a class
of stochastic differential equations is established. This machinery is used to
provide a Feynman-Kac formula for a class of Hamiltonians. Several specific
examples are considered.Comment: 21 page
Revealing hot tear formation dynamics in Al–Cu alloys with X-ray radiography
Hot tears can arise during the late part of alloy solidification because of the shrinkage of isolated liquid as it turns to solid and may have a catastrophic effect on cast tensile properties. Although there are correlations to suggest alloy hot tear sensitivity to casting conditions, they do not capture the influence of microstructure on tearing, such as second-phase particles or intermetallic compounds (IMCs) commonly present in engineering alloys. We use in situ X-ray radiography to quantify the formation and growth behaviour of hot tears in Al-5Cu and Al-5Cu-1Fe alloys during solidification. An automated hot tear detection, tracking and merging algorithm is developed and applied to reveal the role of Fe-rich IMC particles, typical of recycled alloys, on hot tear behaviour. These defects are termed hot tears here on the basis of their complex, extended inter-connected morphology, distinct from more rounded shrinkage porosity. We also visualise and quantify the velocity of interdendritic flow driven by solidification shrinkage, and estimate the pressure changes due to shrinkage. Hot tearing starts at lower solid fraction when IMCs are present due to reduced interdendritic flow, and hot tear formation is more spatially homogeneous, less clustered and more numerous. We show that the largest, most damaging hot tears form from many merging events, that is enhanced by the presence of IMCs
Adsorption of potassium on Cr<sub>2</sub>O<sub>3</sub>(0001) at ionic and metallic coverages and uv-laser-induced desorption
Translational energy distributions of neutral potassium atoms are reported as a function of potassium coverage after uv-laser-induced desorption from well-characterized adsorption sites on an epitaxial film of Cr2O3(0001)/Cr(110). Measurements using x-ray photoelectron spectroscopy, low-energy electron diffraction, and work-function measurements revealed that potassium adsorbs in a nonmetallic phase for deposition temperatures around 280–300 K allowing only a maximal saturation coverage to be grown for moderate growth rates. Aggregates are observed after deposition at 90 K; at this temperature any layer thickness is obtainable. The uv-laser-induced desorption for these two different phases was studied using excitation energies of 3.5 eV, 5.0 eV, and 6.4 eV and (1+1)-resonantly enhanced multiphonon ionization via the 6p2P state for detection. Desorption of potassium atoms from the nonmetallic phase proves to be ten times [σ(6.4eV)=(2±1)×10−19cm2] more efficient than desorption from metallic potassium aggregates. The mechanism of desorption from the nonmetallic phase appears to be the inverse harpooning process starting with an ion pair followed by a transfer of hot electrons from the substrate to unoccupied potassium states to neutralize the initially positively charged potassium. The maximum of the translational energy distribution (starting at 0.65 eV for low coverages) decreases with increasing potassium coverage and is by a factor of approximately 4 smaller for desorption from large potassium aggregates (0.16 eV). The decrease of the translational energy with increasing coverages for isolated atoms is ascribed to an increasing lateral interaction between the adsorbates and a concomittant smooth change of the ionicity of the atoms from partially ionic to neutral
Vortex lattice structures of SrRuO
The vortex lattice structures of SrRuO for the odd parity
representations of the superconducting state are examined for the magnetic
field along the crystallographic directions. Particular emphasis is placed upon
the two dimensional representation which is believed to be relevant to this
material. It is shown that when the zero-field state breaks time reversal
symmetry, there must exist two superconducting transitions when there is a
finite field along a high symmetry direction in the basal plane. Also it is
shown that a square vortex lattice is expected when the field is along the
-axis. The orientation of the square lattice with respect to the underlying
ionic lattice yields information as to which Ru 4d orbitals are relevant to the
superconducting state.Comment: 5 pages, 2 figure
GENCOR:a national registry for patients and families suffering from a familial heart disease in the Netherlands
GENCOR:a national registry for patients and families suffering from a familial heart disease in the Netherlands
GENCOR:a national registry for patients and families suffering from a familial heart disease in the Netherlands
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