5,210 research outputs found
Image restoration by selective short space spectral subtraction
Image restoration by short space spectral subtraction has been applied recursively to a photographic system in an attempt to increase the signal to noise ratio proportionally to the amount of optical density present. The image is smoothed in the frequency domain a small space at a time based on the power spectrum at a given density level. The method is a variable filter that is a function of photographic density
Statistical properties of the Disk Counterparts of Type II Spicules from simultaneous observations of RBEs in Ca II 8542 and H{\alpha}
Spicules were recently found to exist as two types when a new class of
so-called type II spicules was discovered at the solar limb with Hinode. The
type II spicules have been linked with on-disk observations of Rapid
Blue-shifted Excursions (RBEs) in the Ha and Ca 8542 lines. Here we analyze
observations optimized for the detection of RBEs in both Ha and Ca 8542
simultaneously at a high temporal cadence taken with CRISP at the SST. This
study used a high-quality time sequence for RBEs at different blue-shifts and
employed an automated detection routine to detect a large number of RBEs in
order to expand on the statistics of RBEs. We find that the number of detected
RBEs is dependent on the Doppler velocity of the images on which the search is
performed. Detection of RBEs at lower velocities increases the estimated number
of RBEs to the same order of magnitude expected from limb spicules. This shows
that RBEs and type II spicules are exponents of the same phenomenon. We provide
evidence that Ca 8542 RBEs are connected to Ha RBEs and are located closer to
the network regions with the Ha RBEs being the continuation, and show that RBEs
have an average lifetime of 83.9 s when observed in both spectral lines with
Doppler velocity ranges of 10-25 km/s in Ca 8542 and 30-50 km/s in Ha. In
addition, we determine the transverse motion of a much larger sample of RBEs
than previous studies and find that like type II spicules, RBEs undergo
significant transverse motions, 5-10 km/s. Finally, we find that the
intergranular jets discovered in BBSO are a subset of RBEs.Comment: Accepted for publication in the Astrophysical Journal, 15 pages, 10
figure
Compact star clusters of the LMC HII region N11C
Based on imaging and spectroscopy obtained at the ESO NTT telescope and using
an efficient image analysis algorithm, we study the core of the LMC OB
association LH13, particularly the two compact stellar clusters Sk-6641 and HNT
in the HII, region N11C. We resolve Sk-6641 into 15 components and for the
first time the HNT cluster into 70 stars, and derive photometry for the
members. Moreover, from medium resolution spectroscopy we determine the
spectral types for sixteen stars in N11C. We compare the color-magnitude
diagrams of the clusters with that of the field stars and discuss the cluster
ages. With an age of ~100 Myr, the HNT cluster appears significantly older than
the very young (< 5 Myr) Sk-6641 starburst. We suggest that most of the `field'
O-stars in the core of N11C have actually been ejected from Sk-6641 through
dynamical interactions in the compact cluster. The properties of the Sk-6641
and HNT clusters suggest that we are viewing different star formation regions
lying at different distances along the same line of sight.Comment: 12 pages, 8 figure
Acquisition and analysis of adaptive optics imaging polarimetry data
The process of data taking, reduction and calibration of near-infrared
imaging polarimetry data taken with the ESO Adaptive Optics System ADONIS is
described. The ADONIS polarimetric facility is provided by a rotating wire grid
polarizer. Images were taken at increments of 22.5 degrees of polarizer
rotation from 0 to 180 degrees, over-sampling the polarization curve but
allowing the effects of photometric variations to be assessed. Several
strategies to remove the detector signature are described. The instrumental
polarization was determined, by observations of stars of negligible
polarization, to be 1.7% at J, H and K bands. The lack of availability of
unpolarized standard stars in the IR, in particular which are not too bright as
to saturate current IR detectors, is highlighted. The process of making
polarization maps is described. Experiments at restoring polarimetry data, in
order to reach diffraction limited polarization, are outlined, with particular
reference to data on the Homunculus reflection nebula around Eta Carinae.Comment: 20 pages, A&A LaTeX2e, 11 figures. To appear in Astronomy &
Astrophysics, Supplement Serie
Lattice Quantum Gravity and Asymptotic Safety
We study the nonperturbative formulation of quantum gravity defined via
Euclidean dynamical triangulations (EDT) in an attempt to make contact with
Weinberg's asymptotic safety scenario. We find that a fine-tuning is necessary
in order to recover semiclassical behavior. Such a fine-tuning is generally
associated with the breaking of a target symmetry by the lattice regulator; in
this case we argue that the target symmetry is the general coordinate
invariance of the theory. After introducing and fine-tuning a nontrivial local
measure term, we find no barrier to taking a continuum limit, and we find
evidence that four-dimensional, semiclassical geometries are recovered at long
distance scales in the continuum limit. We also find that the spectral
dimension at short distance scales is consistent with 3/2, a value that could
resolve the tension between asymptotic safety and the holographic entropy
scaling of black holes. We argue that the number of relevant couplings in the
continuum theory is one, once symmetry breaking by the lattice regulator is
accounted for. Such a theory is maximally predictive, with no adjustable
parameters. The cosmological constant in Planck units is the only relevant
parameter, which serves to set the lattice scale. The cosmological constant in
Planck units is of order 1 in the ultraviolet and undergoes renormalization
group running to small values in the infrared. If these findings hold up under
further scrutiny, the lattice may provide a nonperturbative definition of a
renormalizable quantum field theory of general relativity with no adjustable
parameters and a cosmological constant that is naturally small in the infrared.Comment: 69 pages, 25 figures. Revised discussion of target symmetry
throughout paper. Numerical results unchanged and main conclusions largely
unchanged. Added references and corrected typos. Conforms with version
published in Phys. Rev.
Visualizing characteristics of ocean data collected during the Shuttle Imaging Radar-B experiment
Topographic measurements of sea surface elevation collected by the Surface Contour Radar (SCR) during NASA's Shuttle Imaging Radar (SIR-B) experiment are plotted as three dimensional surface plots to observe wave height variance along the track of a P-3 aircraft. Ocean wave spectra were computed from rotating altimeter measurements acquired by the Radar Ocean Wave Spectrometer (ROWS). Fourier power spectra computed from SIR-B synthetic aperture radar (SAR) images of the ocean are compared to ROWS surface wave spectra. Fourier inversion of SAR spectra, after subtraction of spectral noise and modeling of wave height modulation, yields topography similar to direct measurements made by SCR. Visual perspectives on the SCR and SAR ocean data are compared. Threshold distinctions between surface elevation and texture modulations of SAR data are considered within the context of a dynamic statistical model of rough surface scattering. The result of these endeavors is insight as to the physical mechanism governing the imaging of ocean waves with SAR
Probing dense and hot matter with low-mass dileptons and photons
Results on low-mass dileptons, covering the very broad energy range from the
BEVALAC up to SPS are reviewed. The emphasis is on the open questions raised by
the intriguing results obtained so far and the prospects for addressing them in
the near future with the second generation of experiments, in particular HADES,
NA60 and PHENIX.Comment: 6 pages, 8 figures, Proceedings of Hard Probes 2004 Conference,
Ericeira, November 4-10, 2004. Caption of Figure 2 corrected. To be published
in Eur. Phys. J. C. The orginal version is available at www.springerlink.co
Morphological analysis of the cm-wave continuum in the dark cloud LDN1622
The spectral energy distribution of the dark cloud LDN1622, as measured by
Finkbeiner using WMAP data, drops above 30GHz and is suggestive of a Boltzmann
cutoff in grain rotation frequencies, characteristic of spinning dust emission.
LDN1622 is conspicuous in the 31 GHz image we obtained with the Cosmic
Background Imager, which is the first cm-wave resolved image of a dark cloud.
The 31GHz emission follows the emission traced by the four IRAS bands. The
normalised cross-correlation of the 31 GHz image with the IRAS images is higher
by 6.6sigma for the 12um and 25um bands than for the 60um and 100um bands:
C(12+25) = 0.76+/-0.02 and C(60+100) = 0.64+/-0.01.
The mid-IR -- cm-wave correlation in LDN 1622 is evidence for very small
grain (VSG) or continuum emission at 26-36GHz from a hot molecular phase. In
dark clouds and their photon-dominated regions (PDRs) the 12um and 25um
emission is attributed to stochastic heating of the VSGs. The mid-IR and
cm-wave dust emissions arise in a limb-brightened shell coincident with the PDR
of LDN1622, where the incident UV radiation from the Ori OB1b association heats
and charges the grains, as required for spinning dust.Comment: accepted for publication in ApJ - the complete article with
uncompressed figures may be downloaded from
http://www.das.uchile.cl/~simon/ftp/l1622.pd
Maximum Entropy Analysis of the Spectral Functions in Lattice QCD
First principle calculation of the QCD spectral functions (SPFs) based on the
lattice QCD simulations is reviewed. Special emphasis is placed on the Bayesian
inference theory and the Maximum Entropy Method (MEM), which is a useful tool
to extract SPFs from the imaginary-time correlation functions numerically
obtained by the Monte Carlo method. Three important aspects of MEM are (i) it
does not require a priori assumptions or parametrizations of SPFs, (ii) for
given data, a unique solution is obtained if it exists, and (iii) the
statistical significance of the solution can be quantitatively analyzed.
The ability of MEM is explicitly demonstrated by using mock data as well as
lattice QCD data. When applied to lattice data, MEM correctly reproduces the
low-energy resonances and shows the existence of high-energy continuum in
hadronic correlation functions. This opens up various possibilities for
studying hadronic properties in QCD beyond the conventional way of analyzing
the lattice data. Future problems to be studied by MEM in lattice QCD are also
summarized.Comment: 51 pages, 17 figures, typos corrected, discussions on the boundary
conditions and renormalization constants added. To appear in Progress in
Particle and Nuclear Physics, Vol.4
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