3,828 research outputs found
Concordance group of virtual knots
We study concordance of virtual knots. Our main result is that a classical
knot K is virtually slice if and only if it is classically slice. From this we
deduce that the concordance group of classical knots embeds into the
concordance group of long virtual knots
Profiling of fine and coarse particle mass : Case studies of Saharan dust and Eyjafjallajökull/Grimsvötn volcanic plumes
© Author(s) 2012. This work is distributed under the Creative Commons Attribution 3.0 LicenseThe polarization lidar photometer networking (POLIPHON) method introduced to separate coarse-mode and fine-mode particle properties of Eyjafjallajokull volcanic aerosols in 2010 is extended to cover Saharan dust events as well. Furthermore, new volcanic dust observations performed after the Grimsvotn volcanic eruptions in 2011 are presented. The retrieval of particle mass concentrations requires mass-specific extinction coefficients. Therefore, a review of recently published mass-specific extinction coefficients for Saharan dust and volcanic dust is given. Case studies of four different scenarios corroborate the applicability of the profiling technique: (a) Saharan dust outbreak to central Europe, (b) Saharan dust plume mixed with biomass-burning smoke over Cape Verde, and volcanic aerosol layers originating from (c) the Eyjafjallajokull eruptions in 2010 and (d) the Grimsvotn eruptions in 2011. Strong differences in the vertical aerosol layering, aerosol mixing, and optical properties are observed for the different volcanic eventsPeer reviewe
Quasiparticle Corrections to the Electronic Properties of Anion Vacancies at GaAs(110) and InP(110)
We propose a new method for calculating optical defect levels and
thermodynamic charge-transition levels of point defects in semiconductors,
which includes quasiparticle corrections to the Kohn-Sham eigenvalues of
density-functional theory. Its applicability is demonstrated for anion
vacancies at the (110) surfaces of III-V semiconductors. We find the (+/0)
charge-transition level to be 0.49 eV above the surface valence-band maximum
for GaAs(110) and 0.82 eV for InP(110). The results show a clear improvement
over the local-density approximation and agree closely with an experimental
analysis.Comment: 4 pages including 1 figure, RevTe
Optimal algorithms for global optimization in case of unknown Lipschitz constant
We consider a family of function classes which
allow functions with several minima and which
demand only Lipschitz continuity for smoothness.
We present an algorithm almost optimal for each of
these classes
Masses of double neutron star mergers
Aims. The mass discrepancy between the observed population of double neutron
star binaries by radio pulsar observations and gravitational-wave observation
requires an explanation.
Methods. Binary population synthesis calculations are performed, and their
results are compared with the radio and the gravitational-wave observations
simultaneously.
Results. Simulations of binary evolution are used to link different
observations of double neutron star binaries with each other. The progenitor of
GW190425 is investigated in more detail. A distribution of masses and merger
times of the possible progenitors is presented.
Conclusions. A mass discrepancy between the radio pulsars in the Milky Way
with another neutron star companion and the inferred masses from
gravitational-wave observations of those kind of merging systems is naturally
found in binary evolution.Comment: 5+2 pages, 3 figures, 3 tables, submitted to A&
Signatures of a Noise-Induced Quantum Phase Transition in a Mesoscopic Metal Ring
We study a mesoscopic ring with an in-line quantum dot threaded by an
Aharonov-Bohm flux. Zero-point fluctuations of the electromagnetic environment
capacitively coupled to the ring, with spectral density, can
suppress tunneling through the dot, resulting in a quantum phase transition
from an unpolarized to a polarized phase. We show that robust signatures of
such a transition can be found in the response of the persistent current in the
ring to the external flux as well as to the bias between the dot and the arm.
Particular attention is paid to the experimentally relevant cases of ohmic
() and subohmic () noise.Comment: 4 pages, 4 figures, realistic parameters estimated, reference update
Shielding superconductors with thin films
Determining the optimal arrangement of superconducting layers to withstand
large amplitude AC magnetic fields is important for certain applications such
as superconducting radiofrequency cavities. In this paper, we evaluate the
shielding potential of the superconducting film/insulating film/superconductor
(SIS') structure, a configuration that could provide benefits in screening
large AC magnetic fields. After establishing that for high frequency magnetic
fields, flux penetration must be avoided, the superheating field of the
structure is calculated in the London limit both numerically and, for thin
films, analytically. For intermediate film thicknesses and realistic material
parameters we also solve numerically the Ginzburg-Landau equations. It is shown
that a small enhancement of the superheating field is possible, on the order of
a few percent, for the SIS' structure relative to a bulk superconductor of the
film material, if the materials and thicknesses are chosen appropriately.Comment: 7 pages, 5 figure
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