7,273 research outputs found
Combining Contrast Invariant L1 Data Fidelities with Nonlinear Spectral Image Decomposition
This paper focuses on multi-scale approaches for variational methods and
corresponding gradient flows. Recently, for convex regularization functionals
such as total variation, new theory and algorithms for nonlinear eigenvalue
problems via nonlinear spectral decompositions have been developed. Those
methods open new directions for advanced image filtering. However, for an
effective use in image segmentation and shape decomposition, a clear
interpretation of the spectral response regarding size and intensity scales is
needed but lacking in current approaches. In this context, data
fidelities are particularly helpful due to their interesting multi-scale
properties such as contrast invariance. Hence, the novelty of this work is the
combination of -based multi-scale methods with nonlinear spectral
decompositions. We compare with scale-space methods in view of
spectral image representation and decomposition. We show that the contrast
invariant multi-scale behavior of promotes sparsity in the spectral
response providing more informative decompositions. We provide a numerical
method and analyze synthetic and biomedical images at which decomposition leads
to improved segmentation.Comment: 13 pages, 7 figures, conference SSVM 201
Magnetic metamaterials at telecommunication and visible frequencies
Arrays of gold split-rings with 50-nm minimum feature size and with an LC
resonance at 200-THz frequency (1500-nm wavelength) are fabricated. For normal
incidence conditions, they exhibit a pronounced fundamental magnetic mode,
arising from a coupling via the electric component of the incident light. For
oblique incidence, a coupling via the magnetic component is demonstrated as
well. Moreover, we identify a novel higher-order magnetic resonance at around
370 THz (800-nm wavelength) that evolves out of the Mie resonance for oblique
incidence. Comparison with theory delivers good agreement and also shows that
the structures allow for a negative magnetic permeability.Comment: 4 pages, 3 figure
The thermal QCD transition with two flavours of twisted mass fermions
We investigate the thermal QCD transition with two flavors of maximally
twisted mass fermions for a set of pion masses, 300 MeV \textless
\textless 500 MeV, and lattice spacings \textless 0.09 fm. We determine the
pseudo-critical temperatures and discuss their extrapolation to the chiral
limit using scaling forms for different universality classes, as well as the
scaling form for the magnetic equation of state. For all pion masses considered
we find resonable consistency with O(4) scaling plus leading corrections.
However, a true distinction between the O(4) scenario and a first order
scenario in the chiral limit requires lighter pions than are currently in use
in simulations of Wilson fermions.Comment: 11 pages, 11 figure
Optical microscopy via spectral modifications of a nano-antenna
The existing optical microscopes form an image by collecting photons emitted
from an object. Here we report on the experimental realization of microscopy
without the need for direct optical communication with the sample. To achieve
this, we have scanned a single gold nanoparticle acting as a nano-antenna in
the near field of a sample and have studied the modification of its intrinsic
radiative properties by monitoring its plasmon spectrum.Comment: 6 pages, 4 figures (color
Magnetic properties of single-crystalline CeCuGa3
The magnetic behavior of single-crystalline CeCuGa3 has been investigated.
The compound forms in a tetragonal BaAl4-type structure consisting of
rare-earth planes separated by Cu-Ga layers. If the Cu-Ga site disorder is
reduced, CeCuGa3 adopts the related, likewise tetragonal BaNiSn3-type
structure, in which the Ce ion are surrounded by different Cu and Ga layers and
the inversion symmetry is lost. In the literature conflicting reports about the
magnetic order of CeCuGa3 have been published. Single crystals with the
centrosymmetric structure variant exhibit ferromagnetic order below approx. 4 K
with a strong planar anisotropy. The magnetic behavior above the transition
temperature can be well understood by the crystal-field splitting of the 4f
Hund's rule ground-state multiplet of the Ce ions
Thermodynamic phase diagram and phase competition in BaFe2(As1-xPx)2 studied by thermal expansion
High-resolution thermal-expansion and specific-heat measurements were
performed on single crystalline BaFe2(As1-xPx)2 (0 < x < 0.33, x = 1). The
observation of clear anomalies allows to establish the thermodynamic phase
diagram which features a small coexistence region of SDW and superconductivity
with a steep rise of Tc on the underdoped side. Samples that undergo the
tetragonal-orthorhombic structural transition are detwinned in situ, and the
response of the sample length to the magneto-structural and superconducting
transitions is studied for all three crystallographic directions. It is shown
that a reduction of the magnetic order by superconductivity is reflected in all
lattice parameters. On the overdoped side, superconductivity affects the
lattice parameters in much the same way as the SDW on the underdoped side,
suggesting an intimate relation between the two types of order. Moreover, the
uniaxial pressure derivatives of Tc are calculated using the Ehrenfest relation
and are found to be large and anisotropic. A correspondence between
substitution and uniaxial pressure is established, i.e., uniaxial pressure
along the b-axis (c-axis) corresponds to a decrease (increase) of the P
content. By studying the electronic contribution to the thermal expansion we
find evidence for a maximum of the electronic density of states at optimal
doping
Svortices and the fundamental modes of the "snake instability": Possibility of observation in the gaseous Bose-Einstein Condensate
The connection between quantized vortices and dark solitons in a long and
thin, waveguide-like trap geometry is explored in the framework of the
non-linear Schr\"odinger equation. Variation of the transverse confinement
leads from the quasi-1D regime where solitons are stable to 2D (or 3D)
confinement where soliton stripes are subject to a transverse modulational
instability known as the ``snake instability''. We present numerical evidence
of a regime of intermediate confinement where solitons decay into single,
deformed vortices with solitonic properties, also called svortices, rather than
vortex pairs as associated with the ``snake'' metaphor. Further relaxing the
transverse confinement leads to production of 2 and then 3 vortices, which
correlates perfectly with a Bogoliubov-de Gennes stability analysis. The decay
of a stationary dark soliton (or, planar node) into a single svortex is
predicted to be experimentally observable in a 3D harmonically confined dilute
gas Bose-Einstein condensate.Comment: 4 pages, 4 figure
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