4,273 research outputs found
Some Practical Applications of Dark Matter Research
Two practical spin-offs from the development of cryogenic dark matter
detectors are presented. One in materials research, the other in biology.Comment: 8 pages,4 figure
Towards a Soft Evaluation and Refinement of Tagging in Digital Humanities
In this paper we estimate the soundness of tagging in digital repositories
within the field of Digital Humanities by studying the (semantic) conceptual structure
behind the folksnonomy. The use of association rules associated to this conceptual
structure (Stem and Luxenburger basis) allows to faithfully (from a semantic
point of view) complete the tagging (or suggest such a completion).Ministerio de Economía y Competitividad TIN2013-41086-PJunta de Andalucía TIC-606
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&
Point-occurrence self-similarity in crackling-noise systems and in other complex systems
It has been recently found that a number of systems displaying crackling
noise also show a remarkable behavior regarding the temporal occurrence of
successive events versus their size: a scaling law for the probability
distributions of waiting times as a function of a minimum size is fulfilled,
signaling the existence on those systems of self-similarity in time-size. This
property is also present in some non-crackling systems. Here, the uncommon
character of the scaling law is illustrated with simple marked renewal
processes, built by definition with no correlations. Whereas processes with a
finite mean waiting time do not fulfill a scaling law in general and tend
towards a Poisson process in the limit of very high sizes, processes without a
finite mean tend to another class of distributions, characterized by double
power-law waiting-time densities. This is somehow reminiscent of the
generalized central limit theorem. A model with short-range correlations is not
able to escape from the attraction of those limit distributions. A discussion
on open problems in the modeling of these properties is provided.Comment: Submitted to J. Stat. Mech. for the proceedings of UPON 2008 (Lyon),
topic: crackling nois
A model for the distribution of aftershock waiting times
In this work the distribution of inter-occurrence times between earthquakes
in aftershock sequences is analyzed and a model based on a non-homogeneous
Poisson (NHP) process is proposed to quantify the observed scaling. In this
model the generalized Omori's law for the decay of aftershocks is used as a
time-dependent rate in the NHP process. The analytically derived distribution
of inter-occurrence times is applied to several major aftershock sequences in
California to confirm the validity of the proposed hypothesis.Comment: 4 pages, 3 figure
Simulating detection-censored movement records for home range analysis planning
Home range estimation is an important analytical method in applied spatial ecology, yet best practices for addressing the effects of spatial variation in detection probability on home range estimates remain elusive. We introduce the R package “DiagnoseHR,” simulation tools for assessing how variation in detection probability arising from landscape, animal behavior, and methodological processes affects home range inference. We demonstrate the utility of simulation methods for home range analysis planning by comparing bias arising from three home range estimation methods under multiple detection scenarios. We simulated correlated random walks in three landscapes that varied in detection probability and constructed home ranges from locations filtered through a range of sampling protocols. Home range estimates were less biased by reduced detection probability when sampling effort was increased, but the effects of sampling day distribution were minimal. Like others, we found that kernel density estimates were the least affected by variation in detection probability, while minimum convex polygons were most affected. Our results illustrate the value of quantifying uncertainty in home range estimates and suggest that field biologists working in environments with low detection may wish to weight sample-size greater than concerns about temporal autocorrelation when designing sampling protocols
Scaling and correlations in the dynamics of forest-fire occurrence
Forest-fire waiting times, defined as the time between successive events
above a certain size in a given region, are calculated for Italy. The
probability densities of the waiting times are found to verify a scaling law,
despite that fact that the distribution of fire sizes is not a power law. The
meaning of such behavior in terms of the possible self-similarity of the
process in a nonstationary system is discussed. We find that the scaling law
arises as a consequence of the stationarity of fire sizes and the existence of
a non-trivial ``instantaneous'' scaling law, sustained by the correlations of
the process.Comment: Not a long paper, but many figures (but no large size in kb
An Analysis of STIS HST UV Spectra of M33 early B Supergiants
We present terminal velocities of M33 B-supergiants, obtained from STIS HST
spectra as part of our programme to investigate the Wind Momentum -- Luminosity
Relationship (WLR) in the Local Group. Terminal velocities are derived from
their NV, CIV, and SiIV resonance lines in UV spectra. Comparing with IUE
spectra of Galactic B-supergiants we found evidence of low metallicity in three
of our objects. %%The terminal velocities are found to be consistent with the
%%values found for Galactic stars, except for B-133. For this The terminal
velocities are consistent with the corresponding values of Galactic stars,
except for B-133. For this star we find a very large vterm and a red SiIV
component deeper than the blue one, that might be an indication of binarity.
The average ratio between terminal and turbulent wind velocities is 0.25, well
above the value found for Galactic stars.Comment: 9 pages, 6 figure
- …