1,721,272 research outputs found
Rotation of Linear Polarization Plane and Circular Polarization from Cosmological Pseudoscalar Fields
No full textWe discuss the rotation of the linear polarization plane and the production of circular polarization generated by a cosmological pseudoscalar field. We compute analytically and numerically the propagation of the Stokes parameters from the last scattering surface for an oscillating and a monotonic decreasing pseudoscalar field. For the models studied in this paper, we show the comparison between the widely used approximation in which the linear polarization rotation angle is constant in time and the exact result. © 2009 The American Physical Society
Light Bending as a Probe of the Nature of Dark Energy
No full textWe study the bending of light for static spherically symmetric (SSS) space-times which include a dark energy contribution. Geometric dark energy models generically predict a correction to the Einstein angle written in terms of the distance to the closest approach, whereas a cosmological constant does not.
While dark energy is associated with a repulsive force in cosmological context, its effect on null geodesics in SSS space-times can be attractive as for the Newtonian term. This dark energy contribution may not be negligible with respect to the Einstein prediction in lensing involving clusters of galaxies. Strong lensing may therefore be useful to distinguish from other dark energy models
The impact of a stochastic background of primordial magnetic fields on scalar contribution to cosmic microwave background anisotropies
No full textThe scalar, vector and tensor contributions of a stochastic background of magnetic fields to cosmic microwave background anisotropies
No full textWe study the contribution of a stochastic background (SB) of primordial magnetic fields (PMFs) on the anisotropies in temperature and polarization of the cosmic microwave background (CMB) radiation. A SB of PMF modelled as a fully inhomogeneous component induces non-Gaussian scalar, vector and tensor metric linear perturbations. We give the exact expressions for the Fourier spectra of the relevant energy–momentum components of such a SB, given a power-law dependence parametrized by a spectral index nB for the magnetic field power spectrum cut at a damping scale kD. For all the values of nB considered here, the contribution to the CMB temperature pattern by such a SB is dominated by the scalar contribution and then by the vector one at higher multipoles. We also give an analytic estimate of the scalar contribution to the CMB temperature pattern
Impact of stochastic primordial magnetic fields on the scalar contribution to cosmic microwave background anisotropies
No full textWe study the impact of a stochastic background of primordial magnetic fields on the scalar contribution
of cosmic microwave background (CMB) anisotropies and on the matter power spectrum. We give the
correct initial conditions for cosmological perturbations and the exact expressions for the energy density
and Lorentz force associated to the stochastic background of primordial magnetic fields, given a powerlaw
for their spectra cut at a damping scale. The dependence of the CMB temperature and polarization
spectra on the relevant parameters of the primordial magnetic fields is illustrated
Impact of Soft Errors on High Performance Autoencoders for Cyberattack Detection
Full text linkDetecting anomalous messages generated by
cyberattacks is essential for IoT based critical applications (e.g.,
finance, healthcare, manufacturing, etc.), in order to guarantee
high levels of security and availability. Autoencoder-based
anomaly detection has been proven effective in detecting the
presence of messages altered by malicious attacks. To guarantee
low detection latency, autoencoders’ algorithms are typically
executed by HW accelerators implemented by nanotechnology.
However, such HW accelerators are susceptible to soft errors
(SEs), that may occur during their in-field operation. In this
paper, we analyze the impact of SEs on the effectiveness of
autoencoders in detecting anomalous messages generated by
cyberattacks. As an example, we consider autoencoders trained
to discriminate credit card legal and illegal transactions. We
show that SEs do not decrease system’s security, but may reduce
system’s availability of the 70%, so that proper solutions to
avoid the detrimental impact of SEs on system’s availability
should be devised for autoencoders implemented by high
performance HW accelerators
Improved WKB analysis of slow-roll inflation
No full textWe extend the WKB method for the computation of cosmological perturbations during inflation beyond leading order and provide the power spectra of scalar and tensor perturbations to second order in the slow-roll parameters. Our method does not require that the slow-roll parameters be constant. Although leading and next-to-leading results in the slow-roll parameters depend on the approximation technique used in the computation, we find that the inflationary theoretical predictions obtained may reach the accuracy required by planned observations. In two technical appendices, we compare our techniques and results with previous findings
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
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