5,981 research outputs found
Post-market infrastructures and financial stability.
Post-market infrastructures execute critical functions — clearing and delivery versus payment — for the performance of trades in financial assets. This makes them potential vectors for destabilisation of the financial system in the event of malfunctions. Their impact on systemic risk warrants the supervisory and oversight authorities' concern for analysing the various risks that such infrastructures may incur and the efforts to establish a comprehensive set of recommendations for mitigating these risks. This objective has now been achieved with the publication of the CPSS/IOSCO recommendations in November 2001. These recommendations are intended to be universal in scope. In addition to setting adequate standards, the relevant authorities, and central banks in particular, have extended the scope of their responsibility in the field of maintaining financial stability by including the oversight of post-market infrastructures. The statutes of the Banque de France have recently been amended in such terms. Securities clearing and settlement infrastructures are changing rapidly both in Europe, where consolidation and sweeping rationalisation are taking place, and on the wider international scene. Users expect greater functional integration of infrastructures, which should contribute to the expansion of low-cost cross-border transactions and greater efficiency in securities processing. These changes have prompted the relevant authorities to co-operate more closely in the regulation, prudential supervision and oversight of the cross-border infrastructures being developed in Europe. With the development of pan-European infrastructures in the Paris financial markets, the Banque de France has played a very active role in enhancing co-ordinated oversight in conjunction with the other relevant national authorities.
Testing the inversion of asteroids' Gaia photometry combined with ground-based observations
We investigated the reliability of the genetic algorithm which will be used
to invert the photometric measurements of asteroids collected by the European
Space Agency Gaia mission. To do that, we performed several sets of simulations
for 10 000 asteroids having different spin axis orientations, rotational
periods and shapes. The observational epochs used for each simulation were
extracted from the Gaia mission simulator developed at the Observatoire de la
C\^{o}te d'Azur, while the brightness was generated using a Z-buffer standard
graphic method. We also explored the influence on the inversion results of
contaminating the data set with Gaussian noise with different values.
The research enabled us to determine a correlation between the reliability of
the inversion method and the asteroid's pole latitude. In particular, the
results are biased for asteroids having quasi-spherical shapes and low pole
latitudes. This effect is caused by the low lightcurve amplitude observed under
such circumstances, as the periodic signal can be lost in the photometric
random noise when both values are comparable, causing the inversion to fail.
Such bias might be taken into account when analysing the inversion results, not
to mislead it with physical effects such as non-gravitational forces. Finally,
we studied what impact on the inversion results has combining a full lightcurve
and Gaia photometry collected simultaneously. Using this procedure we have
shown that it is possible to reduce the number of wrong solutions for asteroids
having less than 50 data points. The latter will be of special importance for
planning ground-based observations of asteroids aiming to enhance the
scientific impact of Gaia on Solar system science.Comment: Accepted in MNRA
Radio observations of active galactic nuclei with mm-VLBI
Over the past few decades, our knowledge of jets produced by active galactic
nuclei (AGN) has greatly progressed thanks to the development of
very-long-baseline interferometry (VLBI). Nevertheless, the crucial mechanisms
involved in the formation of the plasma flow, as well as those driving its
exceptional radiative output up to TeV energies, remain to be clarified. Most
likely, these physical processes take place at short separations from the
supermassive black hole, on scales which are inaccessible to VLBI observations
at centimeter wavelengths. Due to their high synchrotron opacity, the dense and
highly magnetized regions in the vicinity of the central engine can only be
penetrated when observing at shorter wavelengths, in the millimeter and
sub-millimeter regimes. While this was recognized already in the early days of
VLBI, it was not until the very recent years that sensitive VLBI imaging at
high frequencies has become possible. Ongoing technical development and wide
band observing now provide adequate imaging fidelity to carry out more detailed
analyses.
In this article we overview some open questions concerning the physics of AGN
jets, and we discuss the impact of mm-VLBI studies. Among the rich set of
results produced so far in this frequency regime, we particularly focus on
studies performed at 43 GHz (7 mm) and at 86 GHz (3 mm). Some of the first
findings at 230 GHz (1 mm) obtained with the Event Horizon Telescope are also
presented.Comment: Published in The Astronomy & Astrophysics Review. Open access:
https://link.springer.com/article/10.1007/s00159-017-0105-
Understanding the relationship between the environment of the black hole and the radio jet: optical spectroscopy of compact AGN
We aim to investigate the relationship between radio jet activity on
parsec-scales and the characteristics of both the bright active galactic nuclei
(AGN) and their broad line regions (BLR). For this purpose, we combine 2cm Very
Long Baseline Array observations of AGN with their optical spectral
observations. This would enable us to investigate the optical spectra of a set
of 172 relativistically beamed, flat-spectrum AGN with the nuclear disk
oriented near to the plane of sky. Here, we present first results from optical
spectroscopic observations of the brightest AGN from the 2 cm VLBA survey, and
show a diversity of their spectral morphologies.Comment: 2 pages, to be published in the Proceedings of "Multiwavelength AGN
Surveys", Cozumel, Dec 8 - 12, 200
A novel approach to security enhancement of chaotic DSSS systems
In this paper, we propose a novel approach to the enhancement of physical layer security for chaotic direct-sequence spread-spectrum (DSSS) communication systems. The main idea behind our proposal is to vary the symbol period according to the behavior of the chaotic spreading sequence. As a result, the symbol period and the spreading sequence vary chaotically at the same time. This simultaneous variation aims at protecting DSSS-based communication systems from the blind estimation attacks in the detection of the symbol period. Discrete-time models for spreading and despreading schemes are presented and analyzed. Multiple access performance of the proposed
technique in the presence of additional white Gaussian noise (AWGN) is determined by computer simulations. The increase in security at the physical layer is also evaluated by numerical results. Obtained results show that our proposed technique can protect the system against attacks based on the detection of the symbol period, even if the
intruder has full information on the used chaotic sequence.Peer ReviewedPostprint (author's final draft
Radio-optical scrutiny of the central engine in compact AGN
We combine Very-Long-Baseline Interferometry (VLBI) data for active
galactic nuclei (AGN) available from the Very Large Baseline Array (VLBA) 2 cm
imaging survey and optical spectroscopy to investigate the relationships in the
emission-line region--central engine--radio jet system. Here, we present the
diversity of spectral types among the brightest AGN in our sample. We also
discuss correlations between the mass of the central engine and properties of
the parsec-scale radio jet for 24 AGN selected by the presence of H
broad-emission lines in their spectra.Comment: 4 pages, 5 figures, to appear in the proceedings of the Workshop on
"Multiband Approach to AGN" held in Bonn (Germany), 30 September - 2 October
2004, to be published in "Memorie della Societa Astronomica Italiana
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