43,258 research outputs found
Confidence driven TGV fusion
We introduce a novel model for spatially varying variational data fusion,
driven by point-wise confidence values. The proposed model allows for the joint
estimation of the data and the confidence values based on the spatial coherence
of the data. We discuss the main properties of the introduced model as well as
suitable algorithms for estimating the solution of the corresponding biconvex
minimization problem and their convergence. The performance of the proposed
model is evaluated considering the problem of depth image fusion by using both
synthetic and real data from publicly available datasets
A Class of Nonperturbative Configurations in Abelian-Higgs Models: Complexity from Dynamical Symmetry Breaking
We present a numerical investigation of the dynamics of symmetry breaking in
both Abelian and non-Abelian Higgs models in three spatial
dimensions. We find a class of time-dependent, long-lived nonperturbative field
configurations within the range of parameters corresponding to type-1
superconductors, that is, with vector masses () larger than scalar masses
(). We argue that these emergent nontopological configurations are related
to oscillons found previously in other contexts. For the Abelian-Higgs model,
our lattice implementation allows us to map the range of parameter space -- the
values of -- where such configurations exist and to
follow them for times t \sim \O(10^5) m^{-1}. An investigation of their
properties for -symmetric models reveals an enormously rich structure
of resonances and mode-mode oscillations reminiscent of excited atomic states.
For the SU(2) case, we present preliminary results indicating the presence of
similar oscillonic configurations.Comment: 21 pages, 19 figures, prd, revte
Coordinated optimization of visual cortical maps : 2. Numerical studies
In the juvenile brain, the synaptic architecture of the visual cortex remains in a state of flux for months after the natural onset of vision and the initial emergence of feature selectivity in visual cortical neurons. It is an attractive hypothesis that visual cortical architecture is shaped during this extended period of juvenile plasticity by the coordinated optimization of multiple visual cortical maps such as orientation preference (OP), ocular dominance (OD), spatial frequency, or direction preference. In part (I) of this study we introduced a class of analytically tractable coordinated optimization models and solved representative examples, in which a spatially complex organization of the OP map is induced by interactions between the maps. We found that these solutions near symmetry breaking threshold predict a highly ordered map layout. Here we examine the time course of the convergence towards attractor states and optima of these models. In particular, we determine the timescales on which map optimization takes place and how these timescales can be compared to those of visual cortical development and plasticity. We also assess whether our models exhibit biologically more realistic, spatially irregular solutions at a finite distance from threshold, when the spatial periodicities of the two maps are detuned and when considering more than 2 feature dimensions. We show that, although maps typically undergo substantial rearrangement, no other solutions than pinwheel crystals and stripes dominate in the emerging layouts. Pinwheel crystallization takes place on a rather short timescale and can also occur for detuned wavelengths of different maps. Our numerical results thus support the view that neither minimal energy states nor intermediate transient states of our coordinated optimization models successfully explain the architecture of the visual cortex. We discuss several alternative scenarios that may improve the agreement between model solutions and biological observations
Coordinated optimization of visual cortical maps (II) Numerical studies
It is an attractive hypothesis that the spatial structure of visual cortical
architecture can be explained by the coordinated optimization of multiple
visual cortical maps representing orientation preference (OP), ocular dominance
(OD), spatial frequency, or direction preference. In part (I) of this study we
defined a class of analytically tractable coordinated optimization models and
solved representative examples in which a spatially complex organization of the
orientation preference map is induced by inter-map interactions. We found that
attractor solutions near symmetry breaking threshold predict a highly ordered
map layout and require a substantial OD bias for OP pinwheel stabilization.
Here we examine in numerical simulations whether such models exhibit
biologically more realistic spatially irregular solutions at a finite distance
from threshold and when transients towards attractor states are considered. We
also examine whether model behavior qualitatively changes when the spatial
periodicities of the two maps are detuned and when considering more than 2
feature dimensions. Our numerical results support the view that neither minimal
energy states nor intermediate transient states of our coordinated optimization
models successfully explain the spatially irregular architecture of the visual
cortex. We discuss several alternative scenarios and additional factors that
may improve the agreement between model solutions and biological observations.Comment: 55 pages, 11 figures. arXiv admin note: substantial text overlap with
arXiv:1102.335
Eigenspectra optoacoustic tomography achieves quantitative blood oxygenation imaging deep in tissues
Light propagating in tissue attains a spectrum that varies with location due
to wavelength-dependent fluence attenuation by tissue optical properties, an
effect that causes spectral corruption. Predictions of the spectral variations
of light fluence in tissue are challenging since the spatial distribution of
optical properties in tissue cannot be resolved in high resolution or with high
accuracy by current methods. Spectral corruption has fundamentally limited the
quantification accuracy of optical and optoacoustic methods and impeded the
long sought-after goal of imaging blood oxygen saturation (sO2) deep in
tissues; a critical but still unattainable target for the assessment of
oxygenation in physiological processes and disease. We discover a new principle
underlying light fluence in tissues, which describes the wavelength dependence
of light fluence as an affine function of a few reference base spectra,
independently of the specific distribution of tissue optical properties. This
finding enables the introduction of a previously undocumented concept termed
eigenspectra Multispectral Optoacoustic Tomography (eMSOT) that can effectively
account for wavelength dependent light attenuation without explicit knowledge
of the tissue optical properties. We validate eMSOT in more than 2000
simulations and with phantom and animal measurements. We find that eMSOT can
quantitatively image tissue sO2 reaching in many occasions a better than
10-fold improved accuracy over conventional spectral optoacoustic methods.
Then, we show that eMSOT can spatially resolve sO2 in muscle and tumor;
revealing so far unattainable tissue physiology patterns. Last, we related
eMSOT readings to cancer hypoxia and found congruence between eMSOT tumor sO2
images and tissue perfusion and hypoxia maps obtained by correlative
histological analysis
The Star Formation History of the Large Magellanic Cloud
We present the first-ever global, spatially-resolved reconstruction of the
star formation history (SFH) of the Large Magellanic Cloud (LMC), based on the
application of our StarFISH analysis software to the multiband photometry of
twenty million of its stars from the Magellanic Clouds Photometric Survey. The
general outlines of our results are consistent with previously published
results: following an initial burst of star formation, there was a quiescent
epoch from approximately 12 to 5 Gyr ago. Star formation then resumed and has
proceeded until the current time at an average rate of roughly 0.2 solar
masses/yr, with temporal variations at the factor-of-two level. The re-ignition
of star formation about 5 Gyr ago, in both the LMC and SMC, is suggestive of a
dramatic event at that time in the Magellanic system. Among the global
variations in the recent star formation rate are peaks at roughly 2 Gyr, 500
Myr, 100 Myr and 12 Myr. The peaks at 500 Myr and 2 Gyr are nearly coincident
with similar peaks in the SFH of the Small Magellanic Cloud, suggesting a joint
history for these galaxies extending back at least several Gyr. The chemical
enrichment history recovered from our StarFISH analysis is in broad agreement
with that inferred from the LMC's star cluster population, although our
constraints on the ancient chemical enrichment history are weak. We conclude
from the concordance between the star formation and chemical enrichment
histories of the field and cluster populations that the field and cluster star
formation modes are tightly coupled.Comment: 20 pages, with color figures. Accepted for publication in A
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