202,936 research outputs found
Real-Space Inversion and Super-Resolution of Ultrafast Scattering using Natural Scattering Kernels
Directly resolving in real-space multiple atomic motions using ultrafast
x-ray or electron scattering is generally limited by the finite detector range.
As a result, signal interpretation mostly relies on modeling and simulations of
specific excitation pathways. Here, we introduce an approach to resolve
ultrafast diffuse scattering signals in real space below the diffraction limit,
and recover multiple atomic motions de-novo, using a scattering basis
representation that is composed of the measurement parameters and constraints,
and the subsequent inversion analysis. We leverage signal priors, such as
smoothness and sparsity to deconvolve the spatially transformed signals using
convex optimization. We validate the approach on simulated and experimental
data, demonstrate super-resolution in real space, and discuss the recovery
accuracy and resolution limits vs signal fidelity.Comment: 6 pages, 4 figure
Beyond the current noise limit in imaging through turbulent medium
Shift-and-add is an approach employed to mitigate the phenomenon of
resolution degradation in images acquired through a turbulent medium. Using
this technique, a large number of consecutive short exposures is registered
below the coherence time of the atmosphere or other blurring medium. The
acquired images are shifted to the position of the brightest speckle and
stacked together to obtain high-resolution and high signal-to-noise frame. In
this paper we present a highly efficient method for determination of frames
shifts, even if in a single frame the object cannot be distinguished from the
background noise. The technique utilizes our custom genetic algorithm, which
iteratively evolves a set of image shifts. We used the maximal energy of
stacked images as an objective function for shifts estimation and validate the
efficiency of the method on simulated and real images of simple and complex
sources. Obtained results confirmed, that our proposed method allows for the
recovery of spatial distribution of objects even only 2% brighter than their
background. The presented approach extends significantly current limits of
image reconstruction with the use of shift-and-add method. The applications of
our algorithm include both the optical and the infrared imaging. Our method may
be also employed as a digital image stabilizer in extremely low light level
conditions in professional and consumer applications.Comment: 8 pages, 4 figure
Dynamic super-resolution in particle tracking problems
Particle tracking in biological imaging is concerned with reconstructing the
trajectories, locations, or velocities of the targeting particles. The standard
approach of particle tracking consists of two steps: first reconstructing
statically the source locations in each time step, and second applying tracking
techniques to obtain the trajectories and velocities. In contrast, the dynamic
reconstruction seeks to simultaneously recover the source locations and
velocities from all frames, which enjoys certain advantages. In this paper, we
provide a rigorous mathematical analysis for the resolution limit of
reconstructing source number, locations, and velocities by general dynamical
reconstruction in particle tracking problems, by which we demonstrate the
possibility of achieving super-resolution for the dynamic reconstruction. We
show that when the location-velocity pairs of the particles are separated
beyond certain distances (the resolution limits), the number of particles and
the location-velocity pair can be stably recovered. The resolution limits are
related to the cut-off frequency of the imaging system, signal-to-noise ratio,
and the sparsity of the source. By these estimates, we also derive a stability
result for a sparsity-promoting dynamic reconstruction. In addition, we further
show that the reconstruction of velocities has a better resolution limit which
improves constantly as the particles moving. This result is derived by an
observation that the inherent cut-off frequency for the velocity recovery can
be viewed as the total observation time multiplies the cut-off frequency of the
imaging system, which may lead to a better resolution limit as compared to the
one for each diffraction-limited frame. It is anticipated that this observation
can inspire new reconstruction algorithms that improve the resolution of
particle tracking in practice
Seven-Year Wilkinson Microwave Anisotropy Probe (WMAP) Observations: Power Spectra and WMAP-Derived Parameters
(Abridged) We present the angular power spectra derived from the 7-year maps
and discuss the cosmological conclusions that can be inferred from WMAP data
alone. The third acoustic peak in the TT spectrum is now well measured by WMAP.
In the context of a flat LambdaCDM model, this improvement allows us to place
tighter constraints on the matter density from WMAP data alone, and on the
epoch of matter-radiation equality, The temperature-polarization (TE) spectrum
is detected in the 7-year data with a significance of 20 sigma, compared to 13
sigma with the 5-year data. The low-l EE spectrum, a measure of the optical
depth due to reionization, is detected at 5.5 sigma significance when averaged
over l = 2-7. The BB spectrum, an important probe of gravitational waves from
inflation, remains consistent with zero. The upper limit on tensor modes from
polarization data alone is a factor of 2 lower with the 7-year data than it was
using the 5-year data (Komatsu et al. 2010). We test the parameter recovery
process for bias and find that the scalar spectral index, ns, is biased high,
but only by 0.09 sigma, while the remaining parameters are biased by < 0.15
sigma. The improvement in the third peak measurement leads to tighter lower
limits from WMAP on the number of relativistic degrees of freedom (e.g.,
neutrinos) in the early universe: Neff > 2.7 (95% CL). Also, using WMAP data
alone, the primordial helium mass fraction is found to be YHe = 0.28+0.14-0.15,
and with data from higher-resolution CMB experiments included, we now establish
the existence of pre-stellar helium at > 3 sigma (Komatsu et al. 2010).Comment: 22 pages, 14 figures, version accepted to Astrophysical Journal
Supplement Series, added high-l EE detection, consolidated parameter recovery
simulation
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