10,875 research outputs found
Signal-to-Noise Eigenmode Analysis of the Two-Year COBE Maps
To test a theory of cosmic microwave background fluctuations, it is natural
to expand an anisotropy map in an uncorrelated basis of linear combinations of
pixel amplitudes --- statistically-independent for both the noise and the
signal. These -eigenmodes are indispensible for rapid Bayesian analyses of
anisotropy experiments, applied here to the recently-released two-year COBE
{\it dmr} maps and the {\it firs} map. A 2-parameter model with an overall
band-power and a spectral tilt describes well inflation-based
theories. The band-powers for {\it all} the {\it dmr} + GHz
and {\it firs} 170 GHz maps agree, , and
are largely independent of tilt and degree of (sharp) -filtering. Further,
after optimal -filtering, the {\it dmr} maps reveal the same
tilt-independent large scale features and correlation function. The unfiltered
{\it dmr} + index is ; increasing the
-filtering gives a broad region at (1.0--1.2)0.5, a jump to
(1.4--1.6)0.5, then a drop to 0.8, the higher values clearly seen to be
driven by -power spectrum data points that do not fit single-tilt models.
These indices are nicely compatible with inflation values (0.8--1.2), but
not overwhelmingly so.Comment: submitted to Phys.Rev.Letters, 4 pages, uuencoded compressed
PostScript; also bdmr2.ps.Z, via anonymous ftp to ftp.cita.utoronto.ca, cd to
/pub/dick/yukawa; CITA-94-2
Motivational, volitional and multiple goal predictors of walking in people with type 2 diabetes
Acknowledgment MNâs PhD scholarship was provided by Ministry of Health and Medical Education (Islamic Republic of Iran). This study was funded by the University of Aberdeen reference number: GP007RGC1618. FFS is funded by Fuse, the UK Clinical Research Collaboration Centre of Excellence for Translational Research in Public Health (grant number: MR/K02325X/1). The researchers gratefully acknowledge all the Type 2 diabetic patients and their household members who participated in the study for their contribution to this study; without them there would be no data. The researchers gratefully acknowledge the SDRN for providing the list of Type 2 diabetes and helping for sampling.Peer reviewedPublisher PD
Power Spectrum Estimators For Large CMB Datasets
Forthcoming high-resolution observations of the Cosmic Microwave Background
(CMB) radiation will generate datasets many orders of magnitude larger than
have been obtained to date. The size and complexity of such datasets presents a
very serious challenge to analysing them with existing or anticipated
computers. Here we present an investigation of the currently favored algorithm
for obtaining the power spectrum from a sky-temperature map --- the quadratic
estimator. We show that, whilst improving on direct evaluation of the
likelihood function, current implementations still inherently scale as the
equivalent of the cube of the number of pixels or worse, and demonstrate the
critical importance of choosing the right implementation for a particular
dataset.Comment: 8 pages LATEX, no figures, corrected misaligned columns in table
Structural model creation : the impact of data type and creative space on geological reasoning and interpretation
The authors would like to thank participants in the interpretation exercises. Bond was funded by Midland Valley Exploration and a Scottish Executive SCORE award whilst collecting the cohort 1 interpretation dataset. Midland Valley Exploration's Move software was used to create the geological model and borehole dataset. Fiji (Image J) software was used to create Figure 5a and c. ION GXT are thanked for creation of the synthetic seismic image dataset.Peer reviewedPublisher PD
Observational Constraints on Visser's Cosmological Model
Theories of gravity for which gravitons can be treated as massive particles
have presently been studied as realistic modifications of General Relativity,
and can be tested with cosmological observations. In this work, we study the
ability of a recently proposed theory with massive gravitons, the so-called
Visser theory, to explain the measurements of luminosity distance from the
Union2 compilation, the most recent Type-Ia Supernovae (SNe Ia) dataset,
adopting the current ratio of the total density of non-relativistic matter to
the critical density () as a free parameter. We also combine the SNe
Ia data with constraints from Baryon Acoustic Oscillations (BAO) and CMB
measurements. We find that, for the allowed interval of values for ,
a model based on Visser's theory can produce an accelerated expansion period
without any dark energy component, but the combined analysis (SNe Ia + BAO +
CMB) shows that the model is disfavored when compared with CDM model.Comment: 6 pages, 4 figure
The initial conditions of the universe: how much isocurvature is allowed?
We investigate the constraints imposed by the current data on correlated
mixtures of adiabatic and non-adiabatic primordial perturbations. We discover
subtle flat directions in parameter space that tolerate large (~60%)
contributions of non-adiabatic fluctuations. In particular, larger values of
the baryon density and a spectral tilt are allowed. The cancellations in the
degenerate directions are explored and the role of priors elucidated.Comment: 4 pages, 4 figures. Submitted to PR
Cosmological predictions from the Misner brane
Within the spirit of five-dimensional gravity in the Randall-Sundrum
scenario, in this paper we consider cosmological and gravitational implications
induced by forcing the spacetime metric to satisfy a Misner-like symmetry. We
first show that in the resulting Misner-brane framework the Friedmann metric
for a radiation dominated flat universe and the Schwarzschild or anti-de Sitter
black holes metrics are exact solutions on the branes, but the model cannot
accommodate any inflationary solution. The horizon and flatness problems can
however be solved in Misner-brane cosmology by causal and noncausal
communications through the extra dimension between distant regions which are
outside the horizon. Based on a semiclassical approximation to the
path-integral approach, we have calculated the quantum state of the
Misner-brane universe and the quantum perturbations induced on its metric by
brane propagation along the fifth direction. We have then considered testable
predictions from our model. These include a scale-invariant spectrum of density
perturbations whose amplitude can be naturally accommodated to the required
value 10, and a power spectrum of CMB anisotropies whose
acoustic peaks are at the same sky angles as those predicted by inflationary
models, but having much smaller secondary-peak intensities. These predictions
seem to be compatible with COBE and recent Boomerang and Maxima measurementsComment: 16 pages, RevTe
Kinetics of diffusion-limited catalytically-activated reactions: An extension of the Wilemski-Fixman approach
We study kinetics of diffusion-limited catalytically-activated
reactions taking place in three dimensional systems, in which an annihilation
of diffusive particles by diffusive traps may happen only if the
encounter of an with any of the s happens within a special catalytic
subvolumen, these subvolumens being immobile and uniformly distributed within
the reaction bath. Suitably extending the classical approach of Wilemski and
Fixman (G. Wilemski and M. Fixman, J. Chem. Phys. \textbf{58}:4009, 1973) to
such three-molecular diffusion-limited reactions, we calculate analytically an
effective reaction constant and show that it comprises several terms associated
with the residence and joint residence times of Brownian paths in finite
domains. The effective reaction constant exhibits a non-trivial dependence on
the reaction radii, the mean density of catalytic subvolumens and particles'
diffusion coefficients. Finally, we discuss the fluctuation-induced kinetic
behavior in such systems.Comment: To appear in J. Chem. Phy
2-Point Correlations in the COBE DMR 4-Year Anisotropy Maps
The 2-point temperature correlation function is evaluated from the 4-year
COBE DMR microwave anisotropy maps. We examine the 2-point function, which is
the Legendre transform of the angular power spectrum, and show that the data
are statistically consistent from channel to channel and frequency to
frequency. The most likely quadrupole normalization is computed for a
scale-invariant power-law spectrum of CMB anisotropy, using a variety of data
combinations. For a given data set, the normalization inferred from the 2-point
data is consistent with that inferred by other methods. The smallest and
largest normalization deduced from any data combination are 16.4 and 19.6 uK
respectively, with a value ~18 uK generally preferred.Comment: Sumbitted to ApJ Letter
Power Spectrum of Primordial Inhomogeneity Determined from the 4-Year COBE DMR Sky Maps
Fourier analysis and power spectrum estimation of the cosmic microwave
background anisotropy on an incompletely sampled sky developed by Gorski (1994)
has been applied to the high-latitude portion of the 4-year COBE DMR 31.5, 53
and 90 GHz sky maps. Likelihood analysis using newly constructed Galaxy cuts
(extended beyond |b| = 20deg to excise the known foreground emission) and
simultaneously correcting for the faint high latitude galactic foreground
emission is conducted on the DMR sky maps pixelized in both ecliptic and
galactic coordinates. The Bayesian power spectrum estimation from the
foreground corrected 4-year COBE DMR data renders n ~ 1.2 +/- 0.3, and
Q_{rms-PS} ~ 15.3^{+3.7}_{-2.8} microK (projections of the two-parameter
likelihood). These results are consistent with the Harrison-Zel'dovich n=1
model of amplitude Q_{rms-PS} ~ 18 microK detected with significance exceeding
14sigma (dQ/Q < 0.07). (A small power spectrum amplitude drop below the
published 2-year results is predominantly due to the application of the new,
extended Galaxy cuts.)Comment: 9 pages of text in LaTeX, 1 postscript Table, 4 postscript figures (2
color plates), submitted to The Astrophysical Journal (Letters
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