9,882 research outputs found
Constraints on a strong X-ray flare in the Seyfert galaxy MCG-6-30-15
We discuss implications of a strong flare event observed in the Seyfert
galaxy MCG-6-30-15 assuming that the emission is due to localized magnetic
reconnection. We conduct detailed radiative transfer modeling of the
reprocessed radiation for a primary source that is elevated above the disk. The
model includes relativistic effects and Keplerian motion around the black hole.
We show that for such a model setup the observed time-modulation must be
intrinsic to the primary source. Using a simple analytical model we then
investigate time delays between hard and soft X-rays during the flare. The
model considers an intrinsic delay between primary and reprocessed radiation,
which measures the geometrical distance of the flare source to the reprocessing
sites. The observed time delays are well reproduced if one assumes that the
reprocessing happens in magnetically confined, cold clouds.Comment: 4 pages, 2 figures, proceedings of a talk given at the symposium 238
at the IAU General Assembly 200
DPA on quasi delay insensitive asynchronous circuits: formalization and improvement
The purpose of this paper is to formally specify a flow devoted to the design
of Differential Power Analysis (DPA) resistant QDI asynchronous circuits. The
paper first proposes a formal modeling of the electrical signature of QDI
asynchronous circuits. The DPA is then applied to the formal model in order to
identify the source of leakage of this type of circuits. Finally, a complete
design flow is specified to minimize the information leakage. The relevancy and
efficiency of the approach is demonstrated using the design of an AES
crypto-processor.Comment: Submitted on behalf of EDAA (http://www.edaa.com/
Power Allocation Games in Wireless Networks of Multi-antenna Terminals
We consider wireless networks that can be modeled by multiple access channels
in which all the terminals are equipped with multiple antennas. The propagation
model used to account for the effects of transmit and receive antenna
correlations is the unitary-invariant-unitary model, which is one of the most
general models available in the literature. In this context, we introduce and
analyze two resource allocation games. In both games, the mobile stations
selfishly choose their power allocation policies in order to maximize their
individual uplink transmission rates; in particular they can ignore some
specified centralized policies. In the first game considered, the base station
implements successive interference cancellation (SIC) and each mobile station
chooses his best space-time power allocation scheme; here, a coordination
mechanism is used to indicate to the users the order in which the receiver
applies SIC. In the second framework, the base station is assumed to implement
single-user decoding. For these two games a thorough analysis of the Nash
equilibrium is provided: the existence and uniqueness issues are addressed; the
corresponding power allocation policies are determined by exploiting random
matrix theory; the sum-rate efficiency of the equilibrium is studied
analytically in the low and high signal-to-noise ratio regimes and by
simulations in more typical scenarios. Simulations show that, in particular,
the sum-rate efficiency is high for the type of systems investigated and the
performance loss due to the use of the proposed suboptimum coordination
mechanism is very small
Double-Peaked Broad Emission Lines in NGC 4450 and Other LINERs
Spectra taken with HST reveal that NGC 4450 emits Balmer emission lines with
displaced double peaks and extremely high-velocity wings. This characteristic
line profile, previously seen in a few nearby LINERs and in a small fraction of
broad-line radio galaxies, can be interpreted as a kinematic signature of a
relativistic accretion disk. We can reproduce the observed profile with a model
for a disk with a radial range of 1000-2000 gravitational radii and inclined by
27 degrees along the line of sight. The small-aperture HST data also allow us
to detect, for the first time, the featureless continuum at optical wavelengths
in NGC 4450; the nonstellar nucleus is intrinsically very faint, with M_B =
-11.2 mag for D = 16.8 Mpc. We have examined the multiwavelength properties of
NGC 4450 collectively with those of other low-luminosity active nuclei which
possess double-peaked broad lines and find a number of common features. These
objects are all classified spectroscopically as "type 1" LINERs or closely
related objects. The nuclear luminosities are low, both in absolute terms and
relative to the Eddington rates. All of them have compact radio cores, whose
strength relative to the optical nuclear emission places them in the league of
radio-loud active nuclei. The broad-band spectral energy distributions of these
sources are most notable for their deficit of ultraviolet emission compared to
those observed in luminous Seyfert 1 nuclei and quasars. The double-peaked
broad-line radio galaxies Arp 102B and Pictor A have very similar attributes.
We discuss how these characteristics can be understood in the context of
advection-dominated accretion onto massive black holes.Comment: To appear in The Astrophysical Journal. Latex, 15 pages, embedded
figures and tabl
Some energy conservative schemes for vibro-impacts of a beam on rigid obstacles
Caused by the problem of unilateral contact during vibrations of satellite solar arrays, the aim of this paper is to better understand such a phenomenon. Therefore, it is studied here a simplified model composed by a beam moving between rigid obstacles. Our purpose is to describe and compare some families of fully discretized approximations and their properties, in the case of non-penetration Signorini’s conditions. For this, starting from the works of Dumont and Paoli, we adapt to our beam model the singular dynamic method introduced by Renard. A particular emphasis is given in the use of a restitution coefficient in the impact law. Finally, various numerical results are presented and energy conservation capabilities of the schemes are investigated
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