86 research outputs found
The equations of medieval cosmology
In Dantean cosmography the Universe is described as a series of concentric
spheres with all the known planets embedded in their rotation motion, the Earth
located at the centre and Lucifer at the centre of the Earth. Beyond these
"celestial spheres", Dante represents the "angelic choirs" as other nine
spheres surrounding God. The rotation velocity increases with decreasing
distance from God, that is with increasing Power (Virtu'). We show that, adding
Power as an additional fourth dimension to space, the modern equations
governing the expansion of a closed Universe (i. e. with the density parameter
\Omega_0>1) in the space-time, can be applied to the medieval Universe as
imaged by Dante in his Divine Comedy. In this representation the Cosmos
acquires a unique description and Lucifer is not located at the centre of the
hyperspheres.Comment: 3 pages, 1 figur
The Sagittarius Dwarf spheroidal Galaxy Survey (SDGS) II: The stellar content and constraints on the star formation history
A detailed study of the Star Formation History of the Sgr dSph galaxy is
performed through the analysis of the data from the Sagittarius Dwarf Galaxy
Survey (SDGS; Bellazzini, Ferraro & Buonanno 1999). Accurate statistical
decontamination of the SDGS Color - Magnitude diagrams allow us to obtain many
useful constraints on the age and metal content of the Sgr stellar populations
in three different region of the galaxy.
A coarse metallicity distribution of Sgr stars is derived, ranging from
[Fe/H]~ -2.0 to [Fe/H]~ -0.7, the upper limit being somewhat higher in the
central region of the galaxy. A qualitative global fit to all the observed CMD
features is attempted, and a general scheme for the Star Formation History of
the Sgr is derived. According to this scheme, star formation began at very
early time from a low metal content Inter Stellar Medium and lasted for several
Gyr, coupled with progressive chemical enrichment. The Star Formation Rate
(SFR) had a peak from 8 to 10 gyr ago when the mean metallicity was in the
range -1.3<= [Fe/H] <= -0.7. After that maximum, the SFR rapidly decreased and
very low rate star formation took place until ~1-0.5 Gyr ago.Comment: 21 pages, 12 figures, figg. 1,2,3,5,6,10 and 11 provided in lower
resolution format. For full resolution versions see
http://www.bo.astro.it/bap/BAPhome.html Accepted by MNRA
Enriching the Symphony of Gravitational Waves from Binary Black Holes by Tuning Higher Harmonics
For the first time, we construct an inspiral-merger-ringdown waveform model
within the effective-one-body formalism for spinning, nonprecessing binary
black holes that includes gravitational modes beyond the dominant mode, specifically . Our multipolar
waveform model incorporates recent (resummed) post-Newtonian results for the
inspiral and information from 157 numerical-relativity simulations, and 13
waveforms from black-hole perturbation theory for the (plunge-)merger and
ringdown. We quantify the improved accuracy including higher-order modes by
computing the faithfulness of the waveform model against the
numerical-relativity waveforms used to construct the model. We define the
faithfulness as the match maximized over time, phase of arrival,
gravitational-wave polarization and sky position of the waveform model, and
averaged over binary orientation, gravitational-wave polarization and sky
position of the numerical-relativity waveform. When the waveform model contains
only the mode, we find that the averaged faithfulness to
numerical-relativity waveforms containing all modes with 5 ranges
from to for binaries with total mass (using
the Advanced LIGO's design noise curve). By contrast, when the
modes are also included in the model, the
faithfulness improves to for all but four configurations in the
numerical-relativity catalog, for which the faithfulness is greater than
. Using our results, we also develop also a (stand-alone) waveform
model for the merger-ringdown signal, calibrated to numerical-relativity
waveforms, which can be used to measure multiple quasi-normal modes. The
multipolar waveform model can be extended to include spin-precession, and will
be employed in upcoming observing runs of Advanced LIGO and Virgo.Comment: 28 page
Response of Crime to Unemployment: An International Comparison
This article studies crime rates’ response to economic conditions. Using a longitudinal data set covering about 20 countries over the period 1970-2010, we investigate whether crime rates respond asymmetrically to increases in unemployment and recoveries in economic conditions. We find a positive response of crime rates on variation in unemployment rates, but we do not find compelling evidence of asymmetric responses to positive and negative variations in the economic cycle
How much should we trust crime statistics ? A comparison between UE and US
In this paper we take a cross-country perspective to study these issues. Our first objective is to investigate to which extent crime rates are declining in some major developed countries. Specifically, we look at the evolution of crime rates across the two sides of the Atlantic, namely United States and European countries between the 1970 and 2010. A crosscountry perspective is useful insofar we can learn if the apparent decline in crime rates is a global pattern. In doing this, we question the reliability of official crime statistics in assessing the trends in crime rates and some crucial factors impacting on criminal activity. A careful approach at the descriptive and inferential level has been suggested in the last years by several prominent scholars (Aebi, 2004; Dills et al., 2008; Goldberger and Rosenfeld, 2009; Durlauf et al., 2010): crime is a complex and by nature hidden social phenomenon and data need a careful inspection. While in other critical policy sectors data are collected systematically both at national and international level, descriptive information on crime trends across countries are not uniformly and systematically collected (...)
Spatial dependence of the Star Formation History in the Central Regions of the Fornax Dwarf Spheroidal Galaxy
We present the Star Formation History (SFH) and the age-metallicity relation
(AMR) in three fields of the Fornax dwarf spheroidal galaxy. They sample a
region spanning from the centre of the galaxy to beyond one core radius, which
allows studying galactocentric gradients. In all the cases, we found stars as
old as 12 Gyr, together with intermediate-age and young stellar populations.
The last star formation events, as young as 1 Gyr old, are mainly located in
the central region, which may indicate that the gas reservoir in the outer
parts of the galaxy would have been exhausted earlier than in the centre or
removed by tidal interactions. The AMR is smoothly increasing in the three
analyzed regions and similar to each other, indicating that no significant
metallicity gradient is apparent within and around the core radius of Fornax.
No significant traces of global UV-reionization or local SNe feedback are
appreciated in the early SFH of Fornax.
Our study is based on FORS1@VLT photometry as deep as I~24.5 and the
IAC-star/IAC-pop/MinnIAC suite of codes for the determination of the SFH in
resolved stellar populations.Comment: 13 pages, 8 figures, 4 table
Another Faint UV Object Associated with a Globular Cluster X-Ray Source: The Case of M92
The core of the metal poor Galactic Globular Cluster M92 (NGC 6341) has been
observed with WFPC2 on the Hubble Space Telescope through visual, blue and
mid-UV filters in a program devoted to study the evolved stellar population in
a selected sample of Galactic Globular Clusters. In the UV color magnitude diagram we have discovered a faint `UV-dominant'
object. This star lies within the error box of a Low Luminosity Globular
Cluster X-ray source (LLGCX) recently found in the core of M92. The properties
of the UV star discovered in M92 are very similar to those of other UV stars
found in the core of some clusters (M13, 47 Tuc, M80, etc)---all of them are
brighter in the UV than in the visible and are located in the vicinity of a
LLGCX. We suggest that these stars are a new sub-class of cataclysmic
variables.Comment: 21 pages, 4 figures. Astrophysical journal in pres
Blue Straggler Stars: a direct comparison of Star counts and population ratios in six Galactic Globular Clusters
The central regions of six Galactic Globular Clusters (GGCs) (M3, M80, M10,
M13, M92 and NGC 288) have been imaged using HST-WFPC2 and the ultraviolet (UV)
filters (F255W, F336W). The selected sample covers a large range in both
central density and metallicity ([Fe/H]). In this paper, we present a direct
cluster-to-cluster comparison of the Blue Stragglers Stars (BSS) population as
selected from (m_{255},m_{255}-m_{336}) Color Magnitude Diagrams (CMDs). We
have found:(a) BSS in three of the clusters (M3, M80, M92) are much more
concentrated toward the center of the cluster than the red giants; because of
the smaller BSS samples for the other clusters we can only note that the BSS
radial distributions are consistent with central concentration; (b) the
specific frequency of BSS varies greatly from cluster to cluster.
The most interesting result is that the two clusters with largest BSS
specific frequency are at the central density extremes of our sample: NGC 288
(lowest central density) and M80 (highest). This evidence together with the
comparison with theoretical collisional models suggests that both stellar
interactions in high density cluster cores and at least one other alternate
channel operating low density GGCs play an important role in the production of
BSS. We also note a possible connection between HB morphology and blue
straggler luminosity functions in these six clusters.Comment: 28 pages, 8 figures, in press in the Ap
PACE: A Probabilistic Atlas for Normal Tissue Complication Estimation in Radiation Oncology
In radiation oncology, the need for a modern Normal Tissue Complication Probability (NTCP) philosophy to include voxel-based evidence on organ radio-sensitivity (RS) has been acknowledged. Here a new formalism (Probabilistic Atlas for Complication Estimation, PACE) to predict radiation-induced morbidity (RIM) is presented. The adopted strategy basically consists in keeping the structure of a classical, phenomenological NTCP model, such as the Lyman-Kutcher-Burman (LKB), and replacing the dose distribution with a collection of RIM odds, including also significant non-dosimetric covariates, as input of the model framework. The theory was first demonstrated in silico on synthetic dose maps, classified according to synthetic outcomes. PACE was then applied to a clinical dataset of thoracic cancer patients classified for lung fibrosis. LKB models were trained for comparison. Overall, the obtained learning curves showed that the PACE model outperformed the LKB and predicted synthetic outcomes with an accuracy >0.8. On the real patients, PACE performance, evaluated by both discrimination and calibration, was significantly higher than LKB. This trend was confirmed by cross-validation. Furthermore, the capability to infer the spatial pattern of underlying RS map for the analyzed RIM was successfully demonstrated, thus paving the way to new perspectives of NTCP models as learning tools
- …