730 research outputs found
CMB E/B decomposition of incomplete sky: a pixel space approach
CMB polarization signal may be decomposed into gradient-like (E) and
curl-like (B) mode. We have investigated E/B decomposition in pixel space. We
find E/B mixing due to incomplete sky is localized in pixel-space, and
negligible in the regions far away from the masked area. By estimating the
expected local leakage power, we have diagnosed ambiguous pixels. Our criteria
for ambiguous pixels (i.e. r_c) is associated with the tensor-to-scalar ratio
of B mode power spectrum, which the leakage power is comparable to. By setting
r_c to a lower value, we may reduce leakage level, but reduce sky fraction at
the same time. Therefore, we have solved \partial \Delta C_l/\partial r_c=0,
and obtained the optimal r_c, which minimizes the estimation uncertainty, given
a foreground mask and noise level. We have applied our method to a simulated
map blocked by a foreground (diffuse + point source) mask. Our simulation shows
leakage power is smaller than primordial (i.e. unlensed) B mode power spectrum
of tensor-to-scalar ratio r\sim 10^{-3} at wide range of multipoles (50\lesssim
l \lesssim 2000), while allowing us to retain sky fraction ~ 0.48.Comment: v2: the point of the method strengthened, v3: criteria for ambiguous
pixels rigorously derived, v4: matched with the accepted version in A&A
(minor change), v5: typos correcte
Brane Dynamics in the Randall-Sundrum model, Inflation and Graceful Exit
We study the averaged action of the Randall-Sundrum model with a time
dependent metric ansatz. It can be reformulated in terms of a Brans-Dicke
action with time dependent Newton's constant. We show that the physics of early
universe, particularly inflation, is governed by the Brans-Dicke theory. The
Brans-Dicke scalar, however, quickly settles to its equilibrium value and
decouples from the post-inflationary cosmology. The deceleration parameter is
negative to start with but changes sign before the Brans-Dicke scalar settles
to its equilibrium value. Consequently, the brane metric smoothly exits
inflation. We have also studied the slow-roll inflation in our model and
investigated the spectra of the density perturbation generated by the radion
field and find them consistent with the current observations.Comment: Revised version, Accepted in Class. Quant. Gravit
Digital Deblurring of CMB Maps II: Asymmetric Point Spread Function
In this second paper in a series dedicated to developing efficient numerical
techniques for the deblurring Cosmic Microwave Background (CMB) maps, we
consider the case of asymmetric point spread functions (PSF). Although
conceptually this problem is not different from the symmetric case, there are
important differences from the computational point of view because it is no
longer possible to use some of the efficient numerical techniques that work
with symmetric PSFs. We present procedures that permit the use of efficient
techniques even when this condition is not met. In particular, two methods are
considered: a procedure based on a Kronecker approximation technique that can
be implemented with the numerical methods used with symmetric PSFs but that has
the limitation of requiring only mildly asymmetric PSFs. The second is a
variant of the classic Tikhonov technique that works even with very asymmetric
PSFs but that requires discarding the edges of the maps. We provide details for
efficient implementations of the algorithms. Their performance is tested on
simulated CMB maps.Comment: 9 pages, 13 Figure
A Measurement of the Cosmic Ray Spectrum and Composition at the Knee
The energy spectrum and primary composition of cosmic rays with energy
between and 3\times10^{16}\unit{eV} have been studied using
the CASA-BLANCA detector. CASA measured the charged particle distribution of
air showers, while BLANCA measured the lateral distribution of Cherenkov light.
The data are interpreted using the predictions of the CORSIKA air shower
simulation coupled with four different hadronic interaction codes.
The differential flux of cosmic rays measured by BLANCA exhibits a knee in
the range of 2--3 PeV with a width of approximately 0.5 decades in primary
energy. The power law indices of the differential flux below and above the knee
are and .
We present our data both as a mean depth of shower maximum and as a mean
nuclear mass. A multi-component fit using four elemental species shows the same
composition trends given by the mean quantities, and also indicates that QGSJET
and VENUS are the preferred hadronic interaction models. We find that an
initially mixed composition turns lighter between 1 and 3 PeV, and then becomes
heavier with increasing energy above 3 PeV.Comment: 25 pages, 10 figures. Submitted to Astroparticle Physic
A bound on neutrino masses from baryogenesis
Properties of neutrinos, the lightest of all elementary particles, may be the
origin of the entire matter-antimatter asymmetry of the universe. This requires
that neutrinos are Majorana particles, which are equal to their antiparticles,
and that their masses are sufficiently small. Leptogenesis, the theory
explaining the cosmic matter-antimatter asymmetry, predicts that all neutrino
masses are smaller than 0.2 eV, which will be tested by forthcoming laboratory
experiments and by cosmology.Comment: 8 pages, 2 figure
Radio Sources from a 31 GHz Sky Survey with the Sunyaev-Zel'dovich Array
We present the first sample of 31-GHz selected sources to flux levels of 1
mJy. From late 2005 to mid 2007, the Sunyaev-Zel'dovich Array (SZA) observed
7.7 square degrees of the sky at 31 GHz to a median rms of 0.18 mJy/beam. We
identify 209 sources at greater than 5 sigma significance in the 31 GHz maps,
ranging in flux from 0.7 mJy to ~200 mJy. Archival NVSS data at 1.4 GHz and
observations at 5 GHz with the Very Large Array are used to characterize the
sources. We determine the maximum-likelihood integrated source count to be
N(>S) = (27.2 +- 2.5) deg^-2 x (S_mJy)^(-1.18 +- 0.12) over the flux range 0.7
- 15 mJy. This result is significantly higher than predictions based on 1.4-GHz
selected samples, a discrepancy which can be explained by a small shift in the
spectral index distribution for faint 1.4-GHz sources. From comparison with
previous measurements of sources within the central arcminute of massive
clusters, we derive an overdensity of 6.8 +- 4.4, relative to field sources.Comment: 13 pages, 5 figure
Ethical issues in the use of in-depth interviews: literature review and discussion
This paper reports a literature review on the topic of ethical issues in in-depth interviews. The review returned three
types of article: general discussion, issues in particular studies, and studies of interview-based research ethics. Whilst
many of the issues discussed in these articles are generic to research ethics, such as confidentiality, they often had particular
manifestations in this type of research. For example, privacy was a significant problem as interviews sometimes
probe unexpected areas. For similar reasons, it is difficult to give full information of the nature of a particular interview
at the outset, hence informed consent is problematic. Where a pair is interviewed (such as carer and cared-for) there are
major difficulties in maintaining confidentiality and protecting privacy. The potential for interviews to harm participants
emotionally is noted in some papers, although this is often set against potential therapeutic benefit. As well as
these generic issues, there are some ethical issues fairly specific to in-depth interviews. The problem of dual role is noted
in many papers. It can take many forms: an interviewer might be nurse and researcher, scientist and counsellor, or
reporter and evangelist. There are other specific issues such as taking sides in an interview, and protecting vulnerable
groups. Little specific study of the ethics of in-depth interviews has taken place. However, that which has shows some
important findings. For example, one study shows participants are not averse to discussing painful issues provided they
feel the study is worthwhile. Some papers make recommendations for researchers. One such is that they should consider
using a model of continuous (or process) consent rather than viewing consent as occurring once, at signature, prior
to the interview. However, there is a need for further study of this area, both philosophical and empirical
Visualising high-dimensional Pareto relationships in two-dimensional scatterplots
Copyright © 2013 Springer-Verlag Berlin Heidelberg. The final publication is availablevia the DOI in this recordBook title: Evolutionary Multi-Criterion Optimization7th International Conference on Evolutionary Multi-Criterion Optimization (EMO 2013), Sheffield, UK, March 19-22, 2013The codebase for this paper is available at https://github.com/fieldsend/emo_2013_vizIn this paper two novel methods for projecting high dimensional data into two dimensions for visualisation are introduced, which aim to limit the loss of dominance and Pareto shell relationships between solutions to multi-objective optimisation problems. It has already been shown that, in general, it is impossible to completely preserve the dominance relationship when mapping from a higher to a lower dimension – however, approaches that attempt this projection with minimal loss of dominance information are useful for a number of reasons. (1) They may represent the data to the user of a multi-objective optimisation problem in an intuitive fashion, (2) they may help provide insights into the relationships between solutions which are not immediately apparent through other visualisation methods, and (3) they may offer a useful visual medium for interactive optimisation. We are concerned here with examining (1) and (2), and developing relatively rapid methods to achieve visualisations, rather than generating an entirely new search/optimisation problem which has to be solved to achieve the visualisation– which may prove infeasible in an interactive environment for real time use. Results are presented on randomly generated data, and the search population of an optimiser as it progresses. Structural insights into the evolution of a set-based optimiser that can be derived from this visualisation are also discussed
Application of a Self-Similar Pressure Profile to Sunyaev-Zel'dovich Effect Data from Galaxy Clusters
We investigate the utility of a new, self-similar pressure profile for
fitting Sunyaev-Zel'dovich (SZ) effect observations of galaxy clusters. Current
SZ imaging instruments - such as the Sunyaev-Zel'dovich Array (SZA) - are
capable of probing clusters over a large range in physical scale. A model is
therefore required that can accurately describe a cluster's pressure profile
over a broad range of radii, from the core of the cluster out to a significant
fraction of the virial radius. In the analysis presented here, we fit a radial
pressure profile derived from simulations and detailed X-ray analysis of
relaxed clusters to SZA observations of three clusters with exceptionally high
quality X-ray data: A1835, A1914, and CL J1226.9+3332. From the joint analysis
of the SZ and X-ray data, we derive physical properties such as gas mass, total
mass, gas fraction and the intrinsic, integrated Compton y-parameter. We find
that parameters derived from the joint fit to the SZ and X-ray data agree well
with a detailed, independent X-ray-only analysis of the same clusters. In
particular, we find that, when combined with X-ray imaging data, this new
pressure profile yields an independent electron radial temperature profile that
is in good agreement with spectroscopic X-ray measurements.Comment: 28 pages, 6 figures, accepted by ApJ for publication (probably April
2009
Late time cosmic acceleration from vacuum Brans-Dicke theory in 5D
We show that the scalar-vacuum Brans-Dicke equations in 5D are equivalent to
Brans-Dicke theory in 4D with a self interacting potential and an effective
matter field. The cosmological implication, in the context of FRW models, is
that the observed accelerated expansion of the universe comes naturally from
the condition that the scalar field is not a ghost, i.e., . We
find an effective matter-dominated 4D universe which shows accelerated
expansion if . We study the question of whether
accelerated expansion can be made compatible with large values of ,
within the framework of a 5D scalar-vacuum Brans-Dicke theory with variable,
instead of constant, parameter . In this framework, and based on a
general class of solutions of the field equations, we demonstrate that
accelerated expansion is incompatible with large values of .Comment: In V2 the summary section is expanded. To be published in Classical
and Quantum Gravity
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