4,954 research outputs found
Correlations and invariance of seismicity under renormalization-group transformations
The effect of transformations analogous to those of the real-space
renormalization group are analyzed for the temporal occurrence of earthquakes.
The distribution of recurrence times turns out to be invariant under such
transformations, for which the role of the correlations between the magnitudes
and the recurrence times are fundamental. A general form for the distribution
is derived imposing only the self-similarity of the process, which also yields
a scaling relation between the Gutenberg-Richter b-value, the exponent
characterizing the correlations, and the recurrence-time exponent. This
approach puts the study of the structure of seismicity in the context of
critical phenomena.Comment: Short paper. I'll be grateful to get some feedbac
GALEX measurements of the Big Blue Bump as a tool to study bolometric corrections in AGNs
Active Galactic Nuclei emit over the entire electromagnetic spectrum with the
peak of the accretion disk emission in the far-UV, a wavelength range
historically difficult to investigate. We use here the GALEX (Galaxy Evolution
Explorer) Near-UV and Far-UV measurements (complemented with optical data from
Sloan Digital Sky Survey (SDSS) and XMM-Newton X-ray spectra) of a sample of 83
X-ray selected type 1 AGN extracted from the XMM-Newton Bright Serendipitous
Survey to study their spectral energy distribution (SED) in the optical, Near
and Far-UV and X-ray energy bands. We have constrained the luminosity of the
accretion disk emission component and calculated the hard X-ray bolometric
corrections for a significant sample of AGN spanning a large range in
properties (z, L(x)).Comment: 2 pages, 2 figures, To appear in refereed Proceedings of "X-ray
Astronomy 2009: Present Status, Multi-Wavelength Approach and Future
Perspectives", Bologna, Italy, September 7-11, 2009, AIP, eds. A. Comastri,
M. Cappi, and L. Angelin
Compton Thick AGN in the 70 Month Swift-BAT All-Sky Hard X-ray Survey: a Bayesian approach
The 70-month Swift/BAT catalogue provides a sensitive view of the
extragalactic X-ray sky at hard energies (>10 keV) containing about 800 Active
Galactic Nuclei. We explore its content in heavily obscured, Compton-thick AGN
by combining the BAT (14-195 keV) with the lower energy XRT (0.3-10 keV) data.
We apply a Bayesian methodology using Markov chains to estimate the exact
probability distribution of the column density for each source. We find 53
possible Compton-thick sources (with probability 3 to 100%) translating to a
~7% fraction of the AGN in our sample. We derive the first parametric
luminosity function of Compton-thick AGN. The unabsorbed luminosity function
can be represented by a double power-law with a break at in the 20-40 keV band.Comment: 13 pages, 9 figure
Anomalous Transport in Conical Granular Piles
Experiments on 2+1-dimensional piles of elongated particles are performed.
Comparison with previous experiments in 1+1 dimensions shows that the addition
of one extra dimension to the dynamics changes completely the avalanche
properties, appearing a characteristic avalanche size. Nevertheless, the time
single grains need to cross the whole pile varies smoothly between several
orders of magnitude, from a few seconds to more than 100 hours. This behavior
is described by a power-law distribution, signaling the existence of scale
invariance in the transport process.Comment: Accepted in PR
The Challenges of the "Software Support for Industrial Controls" Contract
ST division is currently specifying a 'Software Support for Industrial Controls' contract. The application of this contract and its success will require several changes in our habits for specifying, designing, and maintaining control systems. This paper summarizes some key concepts which should be respected in order to obtain maximum benefits from the future contract and to optimize the software activities in the division. The contract concerns the maintenance and development of the monitoring and control systems used for supervising CERN's technical infrastructure (electrical distribution, cooling water, air conditioning, safety, and access control). The systems concerned consist of computer and communication hardware and software, tailored to provide specific functionalities for the remote operation, command, and monitoring of equipment. All these systems use commercially available software and hardware such as SCADA, PLCs and associated drivers, controllers, fieldbuses, and networks. It is intended to contract out these activities on a results-oriented basis
Software Support for Industrial Controls Contract
The contract covers the development and the operation and maintenance (O&M) of the monitoring and control systems used for supervising CERN's technical infrastructure. The contract involves those responsible for equipment in any current or future technical installation. We are outsourcing a complex activity which will require efforts on both preparing the specifications for new projects and setting clear definitions of tasks and procedures for O&M. It is a result-oriented contract in which performance will be continually evaluated by different methods and tools: project management plan and project follow-up, and CAMMS (Computerised Assets and Maintenance Management system). To be used effectively, this approach requires complete traceability of activities and documentation of the systems. Based on the analysis of the results measured and the shared (CERN and contractor) experience, the O&M activities will be reviewed and reorganised and operational procedures will be changed according to needs. A key issue of this contract is the challenge of establishing a good partnership with the contractor in order to reach the goals
Network of Earthquakes and Recurrences Therein
We quantify the correlation between earthquakes and use the same to
distinguish between relevant causally connected earthquakes. Our correlation
metric is a variation on the one introduced by Baiesi and Paczuski (2004). A
network of earthquakes is constructed, which is time ordered and with links
between the more correlated ones. Data pertaining to the California region has
been used in the study. Recurrences to earthquakes are identified employing
correlation thresholds to demarcate the most meaningful ones in each cluster.
The distribution of recurrence lengths and recurrence times are analyzed
subsequently to extract information about the complex dynamics. We find that
the unimodal feature of recurrence lengths helps to associate typical rupture
lengths with different magnitude earthquakes. The out-degree of the network
shows a hub structure rooted on the large magnitude earthquakes. In-degree
distribution is seen to be dependent on the density of events in the
neighborhood. Power laws are also obtained with recurrence time distribution
agreeing with the Omori law.Comment: 17 pages, 5 figure
The XMM spectral catalog of SDSS optically selected Seyfert 2 galaxies
We present an X-ray spectroscopic study of optically selected (SDSS) Seyfert
2 (Sy2) galaxies. The goal is to study the obscuration of Sy2 galaxies beyond
the local universe, using good quality X-ray spectra in combination with high
S/N optical spectra for their robust classification. We analyzed all available
XMM-Newton archival observations of narrow emission line galaxies that meet the
above criteria in the redshift range 0.05<z<0.35. We initially selected narrow
line AGN using the SDSS optical spectra and the BPT classification diagram. We
further modeled and removed the stellar continuum, and we analyzed the residual
emission line spectrum to exclude any possible intermediate-type Seyferts. Our
final catalog comprises 31 Sy2 galaxies with median redshift z~0.1. X-ray
spectroscopy is performed using the available X-ray spectra from the 3XMM and
the XMMFITCAT catalogs. Implementing various indicators of obscuration, we find
seven (~23%) Compton-thick AGN. The X-ray spectroscopic Compton-thick
classification agrees with other commonly used diagnostics, such as the X-ray
to mid-IR luminosity ratio and the X-ray to [OIII] luminosity ratio. Most
importantly, we find four (~13%) unobscured Sy2 galaxies, at odds with the
simplest unification model. Their accretion rates are significantly lower than
the rest of our Sy2 sample, in agreement with previous studies that predict the
absence of the broad line region below a certain Eddington ratio threshold.Comment: 12 pages, 6 figures, accepted for publication in A&
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