433 research outputs found
Probing non-Gaussianities on Large Scales in WMAP5 and WMAP7 Data using Surrogates
Probing Gaussianity represents one of the key questions in modern cosmology,
because it allows to discriminate between different models of inflation. We
test for large-scale non-Gaussianities in the cosmic microwave background (CMB)
in a model-independent way. To this end, so-called first and second order
surrogates are generated by first shuffling the Fourier phases belonging to the
scales not of interest and then shuffling the remaining phases for the length
scales under study. Using scaling indices as test statistics we find highly
significant signatures for both non-Gaussianities and asymmetries on large
scales for the WMAP data of the CMB. We find remarkably similar results when
analyzing different ILC-maps based on the WMAP five and seven year data. Such
features being independent from the map-making procedure would disfavor the
fundamental principle of isotropy as well as canonical single-field slow-roll
inflation - unless there is some undiscovered systematic error in the
collection or reduction of the CMB data or yet unknown foreground
contributions.Comment: 4 pages, 3 figures, to appear in the Proceedings of Moriond Cosmology
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Probing non-Gaussianities in the CMB on an incomplete sky using surrogates
We demonstrate the feasibility to generate surrogates by Fourier-based
methods for an incomplete data set. This is performed for the case of a CMB
analysis, where astrophysical foreground emission, mainly present in the
Galactic plane, is a major challenge. The shuffling of the Fourier phases for
generating surrogates is now enabled by transforming the spherical harmonics
into a new set of basis functions that are orthonormal on the cut sky. The
results show that non-Gaussianities and hemispherical asymmetries in the CMB as
identified in several former investigations, can still be detected even when
the complete Galactic plane (|b| < 30{\deg}) is removed. We conclude that the
Galactic plane cannot be the dominant source for these anomalies. The results
point towards a violation of statistical isotropy.Comment: 9 pages, 13 figures, accepted by Physical Review
A model-independent test for scale-dependent non-Gaussianities in the CMB
We present a model-independent method to test for scale-dependent
non-Gaussianities in combination with scaling indices as test statistics.
Therefore, surrogate data sets are generated, in which the power spectrum of
the original data is preserved, while the higher order correlations are partly
randomised by applying a scale-dependent shuffling procedure to the Fourier
phases. We apply this method to the WMAP data of the cosmic microwave
background (CMB) and find signatures for non-Gaussianities on large scales.
Further tests are required to elucidate the origin of the detected anomalies.Comment: accepted for publication in PRL, minor revisions, results unchanged,
l(cut)-dependency adde
Search for non-Gaussianities in the WMAP data with the Scaling Index Method
In the recent years, non-Gaussianity and statistical isotropy of the Cosmic
Microwave Background (CMB) was investigated with various statistical measures,
first and foremost by means of the measurements of the WMAP satellite. In this
Review, we focus on the analyses that were accomplished with a measure of local
type, the so-called Scaling Index Method (SIM). The SIM is able to detect
structural characteristics of a given data set, and has proven to be highly
valuable in CMB analysis. It was used for comparing the data set with
simulations as well as surrogates, which are full sky maps generated by
randomisation of previously selected features of the original map. During these
investigations, strong evidence for non-Gaussianities as well as asymmetries
and local features could be detected. In combination with the surrogates
approach, the SIM detected the highest significances for non-Gaussianity to
date.Comment: 19 pages, 15 figures, Review Article, Accepted for publication in
Advances in Astronom
Localization of Human RNase Z Isoforms: Dual Nuclear/Mitochondrial Targeting of the ELAC2 Gene Product by Alternative Translation Initiation
RNase Z is an endonuclease responsible for the removal of 3′ extensions from tRNA precursors, an essential step in tRNA biogenesis. Human cells contain a long form (RNase ZL) encoded by ELAC2, and a short form (RNase ZS; ELAC1). We studied their subcellular localization by expression of proteins fused to green fluorescent protein. RNase ZS was found in the cytosol, whereas RNase ZL localized to the nucleus and mitochondria. We show that alternative translation initiation is responsible for the dual targeting of RNase ZL. Due to the unfavorable context of the first AUG of ELAC2, translation apparently also starts from the second AUG, whereby the mitochondrial targeting sequence is lost and the protein is instead routed to the nucleus. Our data suggest that RNase ZL is the enzyme involved in both, nuclear and mitochondrial tRNA 3′ end maturation
Deleting edges to restrict the size of an epidemic in temporal networks.
Spreading processes on graphs are a natural model for a wide variety of real-world phenomena, including information or behaviour spread over social networks, biological diseases spreading over contact or trade networks, and the potential flow of goods over logistical infrastructure. Often, the networks over which these processes spread are dynamic in nature, and can be modeled with graphs whose structure is subject to discrete changes over time, i.e. with temporal graphs. Here, we consider temporal graphs in which edges are available at specified timesteps, and study the problem of deleting edges from a given temporal graph in order to reduce the number of vertices (temporally) reachable from a given starting point. This could be used to control the spread of a disease, rumour, etc. in a temporal graph. In particular, our aim is to find a temporal subgraph in which a process starting at any single vertex can be transferred to only a limited number of other vertices using a temporally-feasible path (i.e. a path, along which the times of the edge availabilities increase). We introduce a natural deletion problem for temporal graphs and we provide positive and negative results on its computational complexity, both in the traditional and the parameterised sense (subject to various natural parameters), as well as addressing the approximability of this problem
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A fast optics and orbit correction program
CEBAF is a large recirculating linear accelerator with approximately 1600 magnet power supplies in the beam transport system. The average beam power can be as great as 800 kW, concentrated into a spot of area less than 0.01 mm{sup 2}. Control of the transport is therefore quite critical, to avoid missteering the beam. To prevent dangerous beam losses and to prepare optics changes, the control programs must read the magnet power supplies and calculate the optics in a virtually real-time manner. A program named OLE (On-Line Envelope) has been developed at CEBAF to give a graphical display of the calculated machine {beta} function or, equivalently, the beam envelope. The time interval necessary to execute the program is somewhat less than one second, short enough that the operator can use it for setting up his lattice. Emphasis in the design was placed on speed of program execution at the expense of generality of application. As a result, the accelerator operator will be able to alter the magnetic field in any element in the machine, calculate the {beta} functions in both planes at the entrance and exit of each magnet, and display graphs of the functions, all within one second. The time that is required is short enough that the process approximates fairly well real-time operation
Constraints on f_nl and g_nl from the analysis of the N-pdf of the CMB large scale anisotropies
[Abridged] In this paper we explore a local non-linear perturbative model up
to third order as a general characterization of the CMB anisotropies. We focus
our analysis in large scale anisotropies. At these angular scales, the
non-Gaussian description proposed in this work defaults (under certain
conditions) to an approximated local form of the weak non-linear coupling
inflationary model. In particular, quadratic and cubic terms are governed by
the non-linear coupling parameters f_nl and g_nl, respectively. The extension
proposed in this paper allows us to directly constrain these non-linear
parameters. Applying the proposed methodology to WMAP 5-yr data, we obtain -5.6
x 10^5 < g_nl < 6.4 x 10^5, at 95% CL. This result is in agreement with
previous findings obtained for equivalent non-Gaussian models and with
different non-Gaussian estimators. A model selection test is performed,
indicating that a Gaussian model is preferred to the non-Gaussian scenario.
When comparing different non-Gaussian models, we observe that a pure f_nl model
is the most favoured case, and that a pure g_nl model is more likely than a
general non-Gaussian scenario. Finally, we have analyzed the WMAP data in two
independent hemispheres, in particular the ones defined by the dipolar pattern
found by Hoftuft et al. 2009. We show that, whereas g_nl is still compatible
with zero for both hemispheres, it is not the case for f_nl (with a p-value
0.04). However, if anisotropy of the data is assumed, the distance between the
likelihood distributions for each hemisphere is larger than expected from
Gaussian and anisotropic simulations, also for g_nl (with a p-value of 0.001 in
the case of this parameter). This result is an extra evidence for the CMB
asymmetries previously reported in WMAP data.Comment: 15 pages, 9 figures, accepted for publication in MNRAS. Corrections
made to match the final versio
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