865 research outputs found
Applications of Wavelets to the Analysis of Cosmic Microwave Background Maps
We consider wavelets as a tool to perform a variety of tasks in the context
of analyzing cosmic microwave background (CMB) maps. Using Spherical Haar
Wavelets we define a position and angular-scale-dependent measure of power that
can be used to assess the existence of spatial structure. We apply planar
Daubechies wavelets for the identification and removal of points sources from
small sections of sky maps. Our technique can successfully identify virtually
all point sources which are above 3 sigma and more than 80% of those above 1
sigma. We discuss the trade-offs between the levels of correct and false
detections. We denoise and compress a 100,000 pixel CMB map by a factor of
about 10 in 5 seconds achieving a noise reduction of about 35%. In contrast to
Wiener filtering the compression process is model independent and very fast. We
discuss the usefulness of wavelets for power spectrum and cosmological
parameter estimation. We conclude that at present wavelet functions are most
suitable for identifying localized sources.Comment: 10 pages, 6 figures. Submitted to MNRA
CMB Polarization Experiments
We discuss the analysis of polarization experiments with particular emphasis
on those that measure the Stokes parameters on a ring on the sky. We discuss
the ability of these experiments to separate the and contributions to
the polarization signal. The experiment being developed at Wisconsin university
is studied in detail, it will be sensitive to both Stokes parameters and will
concentrate on large scale polarization, scanning a degree ring. We will
also consider another example, an experiment that measures one of the Stokes
parameters in a ring. We find that the small ring experiment will be able
to detect cosmological polarization for some models consistent with the current
temperature anisotropy data, for reasonable integration times. In most
cosmological models large scale polarization is too small to be detected by the
Wisconsin experiment, but because both and are measured, separate
constraints can be set on and polarization.Comment: 27 pages with 12 included figure
Cosmic Microwave Background Anisotropies from Scaling Seeds: Fit to Observational Data
We compute cosmic microwave background angular power spectra for scaling seed
models of structure formation. A generic parameterization of the energy
momentum tensor of the seeds is employed. We concentrate on two regions of
parameter space inspired by global topological defects: O(4) texture models and
the large-N limit of O(N) models. We use fitting to compare these
models to recent flat-band power measurements of the cosmic microwave
background. Only scalar perturbations are considered.Comment: LaTeX file 4 pages, 4 postscript figs. revised version, to appear in
PR
The Dipole Observed in the COBE DMR Four-Year Data
The largest anisotropy in the cosmic microwave background (CMB) is the
mK dipole assumed to be due to our velocity with respect to the
CMB. Using the four year data set from all six channels of the COBE
Differential Microwave Radiometers (DMR), we obtain a best-fit dipole amplitude
mK in the direction , where the first
uncertainties are statistical and the second include calibration and combined
systematic uncertainties. This measurement is consistent with previous DMR and
FIRAS resultsComment: New and improved version; to be published in ApJ next mont
Repeated Intracarotid Amobarbital Tests
Rationale:Our goal was to determine the frequency of repeated intracarotid amobarbital test (IAT) at our center and to estimate the retest reliability of the IAT for both language and memory lateralization.
Methods: A total of 1,249 consecutive IATs on 1,190 patients were retrospectively reviewed for repeat tests.
Results: In 4% of patients the IAT was repeated in order to deliver satisfactory information on either language or memory lateralization. Reasons for repetition included obtundation and inability to test for memory lateralization, inability to test for language lateralization, no hemiparesis during first test, no aphasia during first test, atypical vessel filling, and bleeding complications from the catheter insertion site. Language lateralization was reproduced in all but one patient. Repeated memory test results were less consistent across tests, and memory lateralization was unreliable in 63% of the patients.
Discussion: In spite of test limitations by a varying dose of amobarbital, crossover of amobarbital from one side to the other, testing of both hemispheres on the same day, practice effects, unblinded observers, fluctuating cooperation of the patients, and a biased sample of patients language lateralization was reproduced in all but one patient. In contrast, repeated memory test results were frequently contradictory. Memory results on IAT therefore seem much less robust than the results of language testing. Gain of reliable information versus the risks of complications and failed tests has to be considered when a patient is subjected to an IAT
Testing the CMB Data for Systematic Effects
Under the assumption that the concordance Lambda cold dark matter (CDM) model
is the correct model, we test the cosmic microwave background (CMB) anisotropy
data for systematic effects by examining the band pass temperature residuals
with respect to this model. Residuals are plotted as a function of l, galactic
latitude, frequency, calibration source, instrument type and several other
variables that may be associated with potential systematic effects. Linear
fitting to the residuals indicates no significant identifiable systematic
errors associated with these variables, except for the case of galactic
latitude. We find evidence for a trend associated with the absolute galactic
latitude range at more than the 2-sigma level. This may be indicative of
galactic contamination and may require a 2% reduction in the normalisation of
low galactic latitude observations.Comment: 47 pages, 20 figures, 4 tables, ApJ submitted, uses aastex.cl
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