1,361 research outputs found
Cross-Correlation Studies between CMB Temperature Anisotropies and 21 cm Fluctuations
During the transition from a neutral to a fully reionized universe,
scattering of cosmic microwave background (CMB) photons via free-electrons
leads to a new anisotropy contribution to the temperature distribution. If the
reionization process is inhomogeneous and patchy, the era of reionization is
also visible via brightness temperature fluctuations in the redshifted 21 cm
line emission from neutral Hydrogen. Since regions containing electrons and
neutral Hydrogen are expected to trace the same underlying density field, the
two are (anti) correlated and this is expected to be reflected in the
anisotropy maps via a correlation between arcminute-scale CMB temperature and
the 21 cm background. In terms of the angular cross-power spectrum,
unfortunately, this correlation is insignificant due to a geometric
cancellation associated with second order CMB anisotropies. The same
cross-correlation between ionized and neutral regions, however, can be studied
using a bispectrum involving large scale velocity field of ionized regions from
the Doppler effect, arcminute scale CMB anisotropies during reionization, and
the 21 cm background. While the geometric cancellation is partly avoided, the
signal-to-noise ratio related to this bispectrum is reduced due to the large
cosmic variance related to velocity fluctuations traced by the Doppler effect.
Unless the velocity field during reionization can be independently established,
it is unlikely that the correlation information related to the relative
distribution of ionized electrons and regions containing neutral Hydrogen can
be obtained with a combined study involving CMB and 21 cm fluctuations.Comment: 10 pages, 3 figure
Methodological considerations of integrating portable digital technologies in the analysis and management of complex superimposed Californian pictographs: From spectroscopy and spectral imaging to 3-D scanning
How can the utilization of newly developed advanced portable technologies give us greater understandings of the most complex of prehistoric rock art? This is the questions driving The Gordian Knot project analysing the polychrome Californian site known as Pleito. New small transportable devices allow detailed on-site analyses of rock art. These non-destructive portable technologies can use X-ray and Raman technology to determine the chemical elements used to make the pigment that makes the painting; they can use imaging techniques such as Highlight Reflective Transformation Imaging and dStretch© to enhance their visibility; they can use digital imagery to disentangle complex superimposed paintings; and they can use portable laser instruments to analyse the micro-topography of the rock surface and integrate these technologies into a 3-D environment. This paper outlines a robust methodology and preliminary results to show how an integration of different portable technologies can serve rock art research and management
The SDSS Coadd: A Galaxy Photometric Redshift Catalog
We present and describe a catalog of galaxy photometric redshifts (photo-z's)
for the Sloan Digital Sky Survey (SDSS) Coadd Data. We use the Artificial
Neural Network (ANN) technique to calculate photo-z's and the Nearest Neighbor
Error (NNE) method to estimate photo-z errors for 13 million objects
classified as galaxies in the coadd with . The photo-z and photo-z
error estimators are trained and validated on a sample of
galaxies that have SDSS photometry and spectroscopic redshifts measured by the
SDSS Data Release 7 (DR7), the Canadian Network for Observational Cosmology
Field Galaxy Survey (CNOC2), the Deep Extragalactic Evolutionary Probe Data
Release 3(DEEP2 DR3), the VIsible imaging Multi-Object Spectrograph - Very
Large Telescope Deep Survey (VVDS) and the WiggleZ Dark Energy Survey. For the
best ANN methods we have tried, we find that 68% of the galaxies in the
validation set have a photo-z error smaller than . After
presenting our results and quality tests, we provide a short guide for users
accessing the public data.Comment: 16 pages, 13 figures, submitted to ApJ. Analysis updated to remove
proprietary BOSS data comprising small fraction (8%) of original
spectroscopic training set and erroneously included. Changes in results are
small compared to the errors and the conclusions are unaffected. arXiv admin
note: substantial text overlap with arXiv:0708.003
Using a Diverse Seed Mix to Establish Native Plants on a Sonoran Desert Burn
Revegetating burned areas is a formidable challenge facing resource managers in southwestern United States arid lands. Natural revegetation of desert burns by native species may be slow, or dominated by exotic annual grasses that perpetuate a frequent-fire regime. Resource managers may have several reasons for actively revegetating burns with native species, such as for providing competition with exotic species, minimizing soil erosion and dust pollution, and improving aesthetics. The use of native species in revegetation has been limited by a lack of available seed and by findings that native desert species are difficult to establish (e.g., Bainbridge and Virginia 1990, Banjerjee et al. 2006). Seeding may be one of only a few feasible options for reintroducing propagules to large desert burns covering thousands of hectares. Our objective was to assess the outcome of a 28-species (all native) operational seeding project for revegetating a 2005 burn in the Arizona Upland Subdivision of the Sonoran Desert
Signal Intensity Analysis and Optimization for in Vivo Imaging of Cherenkov and Excited Luminescence.
During external beam radiotherapy (EBRT), in vivo Cherenkov optical emissions can be used as a dosimetry tool or to excite luminescence, termed Cherenkov-excited luminescence (CEL) with microsecond-level time-gated cameras. The goal of this work was to develop a complete theoretical foundation for the detectable signal strength, in order to provide guidance on optimization of the limits of detection and how to optimize near real time imaging. The key parameters affecting photon production, propagation and detection were considered and experimental validation with both tissue phantoms and a murine model are shown. Both the theoretical analysis and experimental data indicate that the detection level is near a single photon-per-pixel for the detection geometry and frame rates commonly used, with the strongest factor being the signal decrease with the square of distance from tissue to camera. Experimental data demonstrates how the SNR improves with increasing integration time, but only up to the point where the dominance of camera read noise is overcome by stray photon noise that cannot be suppressed. For the current camera in a fixed geometry, the signal to background ratio limits the detection of light signals, and the observed in vivo Cherenkov emission is on the order of 100× stronger than CEL signals. As a result, imaging signals from depths \u3c 15 mm is reasonable for Cherenkov light, and depths \u3c 3 mm is reasonable for CEL imaging. The current investigation modeled Cherenkov and CEL imaging of two oxygen sensing phosphorescent compounds, but the modularity of the code allows for easy comparison of different agents or alternative cameras, geometries or tissues
Countercurrent Chromatography Fractions of Plant Extracts with Anti-Tuberculosis Activity
Samples of numerous plant species were received from the southwestern part of the USA, from Richard Spjut, and plant samples were collected here in Illinois. All were extracted with typical solvents, giving crude residues, some of which were subjected to chromatographic methods. Some of the crude residues and some of the fractions were tested for anti-tuberculosis activity and/or antibacterial activity.
In a general way, bioactive natural products are dealt with very well by Liang & Fang. More specifically, the southwestern part of the United States has a large variety of indigenous plants many of which have not been investigated for their medicinal potential, and only very few have had their extracts separated into the individual compounds they may contain. But, some information is available for Native American herbal uses (Moerman,2003)
Binary Contamination in the SEGUE sample: Effects on SSPP Determinations of Stellar Atmospheric Parameters
Using numerical modeling and a grid of synthetic spectra, we examine the
effects that unresolved binaries have on the determination of various stellar
atmospheric parameters for SEGUE targets measured using the SEGUE Stellar
Parameter Pipeline (SSPP). To model undetected binaries that may be in the
SEGUE sample, we use a variety of mass distributions for the primary and
secondary stars in conjunction with empirically determined relationships for
orbital parameters to determine the fraction of G-K dwarf stars, as defined by
SDSS color cuts, that will be blended with a secondary companion. We focus on
the G-K dwarf sample in SEGUE as it records the history of chemical enrichment
in our galaxy. To determine the effect of the secondary on the spectroscopic
parameters, we synthesize a grid of model spectra from 3275 to 7850 K (~0.1 to
1.0 \msun) and [Fe/H]=-0.5 to -2.5 from MARCS model atmospheres using
TurboSpectrum. We analyze both "infinite" signal-to-noise ratio (S/N) models
and degraded versions, at median S/N of 50, 25 and 10. By running individual
and combined spectra (representing the binaries) through the SSPP, we determine
that ~10% of the blended G-K dwarf pairs with S/N>=25 will have their
atmospheric parameter determinations, in particular temperature and
metallicity, noticeably affected by the presence of an undetected secondary. To
account for the additional uncertainty from binary contamination at a S/N~10,
uncertainties of ~140 K and ~0.17 dex in [Fe/H] must be added in quadrature to
the published uncertainties of the SSPP. (Abridged)Comment: 68 pages, 20 figures, 9 table
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