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Volumetric Calibration Refinement using masked back projection and image correlation superposition
This paper deals with a new, reconstruction based, approach of refining a volumetric calibration. The technique is based on a 2D cross-correlation between particle images on the sensor plane with a planar back projection from a tomographic reconstruction in the same sensor plane to determine potential disparities between the initial camera calibration and the measurement. Additive superposition of the correlation maps from different sets or particle images allows reducing the influence of noise and ghost particles such that the systematic errors in the calibration can be corrected. The different sections describe the theory, the principle processing steps and the convergence of the procedure. Furthermore, the concept is proven by simulating the entire process of the measurement chain, with the help of a synthetic comparison. The results show that disparities of over 9 pixels could be corrected to an average of below 0.1 pixels during the refinement steps. Finally, the technique demonstrates it´s potential to measured data, where the numbers of outliers in the raw results are reduced after the volumetric calibration refinement
Inverse Design of Perfectly Transmitting Eigenchannels in Scattering Media
Light-matter interactions inside turbid medium can be controlled by tailoring
the spatial distribution of energy density throughout the system. Wavefront
shaping allows selective coupling of incident light to different transmission
eigenchannels, producing dramatically different spatial intensity profiles. In
contrast to the density of transmission eigenvalues that is dictated by the
universal bimodal distribution, the spatial structures of the eigenchannels are
not universal and depend on the confinement geometry of the system. Here, we
develop and verify a model for the transmission eigenchannel with the
corresponding eigenvalue close to unity. By projecting the original problem of
two-dimensional diffusion in a homogeneous scattering medium onto a
one-dimensional inhomogeneous diffusion, we obtain an analytical expression
relating the intensity profile to the shape of the confining waveguide.
Inverting this relationship enables the inverse design of the waveguide shape
to achieve the desired energy distribution for the perfectly transmitting
eigenchannel. Our approach also allows to predict the intensity profile of such
channel in a disordered slab with open boundaries, pointing to the possibility
of controllable delivery of light to different depths with local illumination.Comment: 9 pages, 6 figure
Quantitative analysis of directional spontaneous emission spectra from light sources in photonic crystals
We have performed angle-resolved measurements of spontaneous-emission spectra
from laser dyes and quantum dots in opal and inverse opal photonic crystals.
Pronounced directional dependencies of the emission spectra are observed:
angular ranges of strongly reduced emission adjoin with angular ranges of
enhanced emission. It appears that emission from embedded light sources is
affected both by the periodicity and by the structural imperfections of the
crystals: the photons are Bragg diffracted by lattice planes and scattered by
unavoidable structural disorder. Using a model comprising diffuse light
transport and photonic band structure, we quantitatively explain the
directional emission spectra. This provides detailed understanding of the
transport of spontaneously emitted light in real photonic crystals, which is
essential in the interpretation of quantum-optics in photonic band-gap crystals
and for applications wherein directional emission and total emission power are
controlled.Comment: 10 pages, 10 figures, corrected pdf, inserted new referenc
What is the Nature of EUV Waves? First STEREO 3D Observations and Comparison with Theoretical Models
One of the major discoveries of the Extreme ultraviolet Imaging Telescope
(EIT) on SOHO were intensity enhancements propagating over a large fraction of
the solar surface. The physical origin(s) of the so-called `EIT' waves is still
strongly debated. They are considered to be either wave (primarily fast-mode
MHD waves) or non-wave (pseudo-wave) interpretations. The difficulty in
understanding the nature of EUV waves lies with the limitations of the EIT
observations which have been used almost exclusively for their study. Their
limitations are largely overcome by the SECCHI/EUVI observations on-board the
STEREO mission. The EUVI telescopes provide high cadence, simultaneous
multi-temperature coverage, and two well-separated viewpoints. We present here
the first detailed analysis of an EUV wave observed by the EUVI disk imagers on
December 07, 2007 when the STEREO spacecraft separation was .
Both a small flare and a CME were associated with the wave cadence, and single
temperature and viewpoint coverage. These limitations are largely overcome by
the SECCHI/EUVI observations on-board the STEREO mission. The EUVI telescopes
provide high cadence, simultaneous multi-temperature coverage, and two
well-separated viewpoints. Our findings give significant support for a
fast-mode interpretation of EUV waves and indicate that they are probably
triggered by the rapid expansion of the loops associated with the CME.Comment: Solar Physics, 2009, Special STEREO Issue, in pres
The morpho-kinematics of the circumstellar envelope around the AGB star EP Aqr
ALMA observations of CO(1-0) and CO(2-1) emissions of the circumstellar
envelope of EP Aqr, an oxygen-rich AGB star, are reported. A thorough analysis
of their properties is presented using an original method based on the
separation of the data-cube into a low velocity component associated with an
equatorial outflow and a faster component associated with a bipolar outflow. A
number of important and new results are obtained concerning the distribution in
space of the effective emissivity, the temperature, the density and the flux of
matter. A mass loss rate of (1.60.4)10 solar masses per year is
measured. The main parameters defining the morphology and kinematics of the
envelope are evaluated and uncertainties inherent to de-projection are
critically discussed. Detailed properties of the equatorial region of the
envelope are presented including a measurement of the line width and a precise
description of the observed inhomogeneity of both morphology and kinematics. In
particular, in addition to the presence of a previously observed spiral
enhancement of the morphology at very small Doppler velocities, a similarly
significant but uncorrelated circular enhancement of the expansion velocity is
revealed, both close to the limit of sensitivity. The results of the analysis
place significant constraints on the parameters of models proposing
descriptions of the mass loss mechanism, but cannot choose among them with
confidence.Comment: 26 pages, 31 figures, accepted for publication in MNRA
Temporal evolution of the Evershed flow in sunspots. I. Observational characterization of Evershed clouds
[Abridged] The magnetic and kinematic properties of the photospheric Evershed
flow are relatively well known, but we are still far from a complete
understanding of its nature. The evolution of the flow with time, which is
mainly due to appearance of velocity packets called Evershed clouds (ECs), may
provide information to further constrain its origin. Here we undertake a
detailed analysis of the evolution of the Evershed flow by studying the
properties of ECs. In this first paper we determine the sizes, proper motions,
location in the penumbra, and frequency of appearance of ECs, as well as their
typical Doppler velocities, linear and circular polarization signals, Stokes V
area asymmetries, and continuum intensities. High-cadence, high-resolution,
full vector spectropolarimetric measurements in visible and infrared lines are
used to derive these parameters. We find that ECs appear in the mid penumbra
and propage outward along filaments with large linear polarization signals and
enhanced Evershed flows. The frequency of appearance of ECs varies between 15
and 40 minutes in different filaments. ECs exhibit the largest Doppler
velocities and linear-to-circular polarization ratios of the whole penumbra. In
addition, lines formed deeper in the atmosphere show larger Doppler velocities,
much in the same way as the ''quiescent'' Evershed flow. According to our
observations, ECs can be classified in two groups: type I ECs, which vanish in
the outer penumbra, and type II ECs, which cross the outer penumbral boundary
and enter the sunspot moat. Most of the observed ECs belong to type I. On
average, type II ECs can be detected as velocity structures outside of the spot
for only about 14 min. Their proper motions in the moat are significantly
reduced with respect to the ones they had in the penumbra.Comment: Accepted for publication in A&
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