716 research outputs found
Seismotomography of the crust in the transition zone between the southern Tyrrhenian and Sicilian tectonic domains
A crustal tomography of seismic wave velocity was performed in the contact zone between the southern Tyrrhenian, Sicilian and Ionian tectonic units, a zone where the lithospheric structure can be expected to furnish evident signatures of dynamics related to the Tyrrhenian subduction process. A dataset of 10241 P and 5597 S readings from 932 local earthquakes recorded between 1978 and 2001 by stations operating in Sicily and Calabria was inverted by the SIMULPS12 algorithm for simultaneous computation of hypocenter parameters and Vp and Vp/Vs three dimensional distributions. The study brought significant improvement in the knowledge of the local velocity structure, furnishing new information useful to better identify the local tectonic units. The results appear to be compatible with the most recent hypotheses regarding the geodynamics of the study region
The Star Formation History of IZw18
The star formation history in IZw18 has been inferred from HST/WFPC2 archival
data. This is done by comparing the derived V, B-V and V, V-I color-magnitude
diagrams and luminosity functions with synthetic ones, based on various sets of
stellar evolutionary tracks. At a distance of 10 Mpc, the stars resolved in the
field of IZw18 allow for a lookback time up to 1 Gyr. We find that the main
body is not experiencing its first episode of star formation. Instead, it has
been forming stars over the last 0.5-1 Gyr, at a rate of ~ 1-2 * 10**(-2) Msol
per year per kpc**2. A more intense activity of 6-16 * 10**(-2) Msol per year
per kpc**2 has taken place between 15 and 20 Myr ago. For the secondary body,
the lookback time is 0.2 Gyr at most and the uncertainty is much higher, due to
the shallower diagrams and the small number of resolved stars. The derived
range of star formation rate is 3-10 * 10**(-3) Msol per year per kpc**2. The
IMF providing the best fit to the observed stellar populations in the main body
has a slope 1.5, much flatter than in any similar galaxy analyzed with the same
method. In the secondary body, it is peaked at 2.2, closer to Salpeter's slope
(2.35).Comment: 70 pages including 18 figures, to be published in The Astronomical
Journa
Recurrent mini-outbursts and a magnetic white dwarf in the symbiotic system FN Sgr
AIMS: We investigated the optical variability of the symbiotic binary FN Sgr,
with photometric monitoring during 55 years and with a high-cadence
Kepler light curve lasting 81 days. METHODS: The data obtained in the V and I
bands were reduced with standard photometric methods. The Kepler data were
divided into subsamples and analyses with the Lomb-Scargle algorithm. RESULTS:
The V and I band light curves showed a phenomenon never before observed with
such recurrence in any symbiotic system, namely short outbursts, starting
between orbital phase 0.3 and 0.5 and lasting about a month, with a fast rise
and a slower decline, and amplitude of 0.5-1 mag. In the Kepler light curve we
discovered three frequencies with sidebands. We attribute a stable frequency of
127.5 d (corresponding to an 11.3 minutes period) to the white dwarf
rotation. We suggest that this detection probably implies that the white dwarf
accretes through a magnetic stream, like in intermediate polars. The small
outbursts may be ascribed to the stream-disc interaction. Another possibility
is that they are due to localized thermonuclear burning, perhaps confined by
the magnetic field, like recently inferred in intermediate polars, albeit on
different timescales. We measured also a second frequency around 116.9 d
(corresponding to about 137 minutes), which is much less stable and has a
drift. It may be due to rocky detritus around the white dwarf, but it is more
likely to be caused by an inhomogeneity in the accretion disk. Finally, there
is a third frequency close to the first one that appears to correspond to the
beating between the rotation and the second frequency.Comment: Accepted for publication in Astronomy and Astrophysic
LEGUS and Halpha-LEGUS Observations of Star Clusters in NGC 4449: Improved Ages and the Fraction of Light in Clusters as a Function of Age
We present a new catalog and results for the cluster system of the starburst
galaxy NGC 4449 based on multi-band imaging observations taken as part of the
LEGUS and Halpha-LEGUS surveys. We improve the spectral energy fitting method
used to estimate cluster ages and find that the results, particularly for older
clusters, are in better agreement with those from spectroscopy. The inclusion
of Halpha measurements, the role of stochasticity for low mass clusters, the
assumptions about reddening, and the choices of SSP model and metallicity all
have important impacts on the age-dating of clusters. A comparison with ages
derived from stellar color-magnitude diagrams for partially resolved clusters
shows reasonable agreement, but large scatter in some cases. The fraction of
light found in clusters relative to the total light (i.e., T_L) in the U, B,
and V filters in 25 different ~kpc-size regions throughout NGC 4449 correlates
with both the specific Region Luminosity, R_L, and the dominant age of the
underlying stellar population in each region. The observed cluster age
distribution is found to decline over time as dN/dt ~ t^g, with g=-0.85+/-0.15,
independent of cluster mass, and is consistent with strong, early cluster
disruption. The mass functions of the clusters can be described by a power law
with dN/dM ~ M^b and b=-1.86+/-0.2, independent of cluster age. The mass and
age distributions are quite resilient to differences in age-dating methods.
There is tentative evidence for a factor of 2-3 enhancement in both the star
and cluster formation rate ~100 - 300 Myr ago, indicating that cluster
formation tracks star formation generally. The enhancement is probably
associated with an earlier interaction event
Epstein-Barr virus persistence and infection of autoreactive plasma cells in synovial lymphoid structures in rheumatoid arthritis.
OBJECTIVES:
Rheumatoid arthritis (RA) is associated with an increased Epstein-Barr virus (EBV) blood DNA load, a robust immune response to EBV and cross-reactive circulating antibodies to viral and self-antigens. However, the role of EBV in RA pathogenesis remains elusive. Here, we investigated the relationship between synovial EBV infection, ectopic lymphoid structures (ELS) and immunity to citrullinated self and EBV proteins.
METHODS:
Latent and lytic EBV infection was investigated in 43 RA synovial tissues characterised for presence/absence of ELS and in 11 control osteoarthritis synovia using RT-PCR, in situ hybridisation and immunohistochemistry. Synovial production of anti-citrullinated protein (ACPA) and anti-citrullinated EBV peptide (VCP1/VCP2) antibodies was investigated in situ and in vivo in the severe combined immunodeficiency (SCID)/RA chimeric model.
RESULTS:
EBV dysregulation was observed exclusively in ELS+ RA but not osteoarthritis (OA) synovia, as revealed by presence of EBV latent (LMP2A, EBV-encoded small RNA (EBER)) transcripts, EBER+ cells and immunoreactivity for EBV latent (LMP1, LMP2A) and lytic (BFRF1) antigens in ELS-associated B cells and plasma cells, respectively. Importantly, a large proportion of ACPA-producing plasma cells surrounding synovial germinal centres were infected with EBV. Furthermore, ELS-containing RA synovia transplanted into SCID mice supported production of ACPA and anti-VCP1/VCP2 antibodies. Analysis of CD4+ and CD8+ T-cell localisation and granzyme B expression suggests that EBV persistence in ELS-containing synovia may be favoured by exclusion of CD8+ T cells from B-cell follicles and impaired CD8-mediated cytotoxicity.
CONCLUSIONS:
We demonstrated active EBV infection within ELS in the RA synovium in association with local differentiation of ACPA-reactive B cells
The role of immune PSA complex (iXip) in the prediction of prostate cancer
Purpose: To analyse the performance of iXip in the prediction of prostate cancer (PCa) and high-grade PCa. Methods: A consecutive series of men undergoing MRI/FUSION prostate biopsies were enrolled in one centre. Indications for prostate biopsy included abnormal prostate-specific antigen (PSA) levels (PSA>4 ng/ml) and/or abnormal digital rectal examination (DRE) and/or abnormal MRI. All patients underwent the evaluation of serum PSA-IgM concentration and the iXip ratio was calculated. Accuracy iXip for the prediction of PCa was evaluated using multivariable binary regression analysis and receiver operator characteristics (ROC) curves. Results: Overall 160 patients with a median age of 65 (62/73) years were enrolled. Overall, 42% patients were diagnosed with PCa and 75% of them had high-grade cancer (Epstein ≥ 3). Patients with PCa were older and presented higher PSA levels, higher PIRADS scores and lower prostate volumes (PVs). On ROC analysis iXip presented an area under the curve (AUC) of 0.57 in the prediction of PCa and of 0.54 for the prediction of high-grade PCa. Conclusions: In our experience, immune PSA complexes are not predictors of PCa. iXip analysis should not be included in the diagnostic pathway of patients at increased risk of PCa
The VO: A Powerful Tool for Global Astronomy
Since its inception in the early 2000's, the Virtual Observatory (VO), developed as a collaboration of many national and international projects, has become a major factor in the discovery and dissemination of astronomical information worldwide. The International Virtual Observatory Alliance (IVOA) has been coordinating all these efforts worldwide to ensure a common VO framework that enables transparent access to and interoperability of astronomy resources (data and software) around the world. The VO is not a magic solution to all astronomy data management challenges but it does bring useful solutions in many areas borne out by the fact that VO interfaces are broadly found in astronomy's major data centres and projects worldwide. Astronomy data centres have been building VO services on top of their existing data services to increase interoperability with other VO-compliant data resources to take advantage of the continuous and increasing development of VO applications. VO applications have made multi-instrument and multi-wavelength science, a difficult and fruitful part of astronomy, somewhat easier. More recently, several major new astronomy projects have been directly adopting VO standards to build their data management infrastructure, giving birth to ‘VO built-in' archives. Embracing the VO framework from the beginning brings the double gain of not needing to reinvent the wheel and ensuring from the start interoperability with other astronomy VO resources. Some of the IVOA standards are also starting to be used by neighbour disciplines like planetary sciences. There is still quite a lot to be done on the VO, in particular tackling the upcoming big data challenge and how to find interoperable solutions to the new data analysis paradigm of bringing and running the software close to the data. We report on the current status and also desire to encourage others to adopt VO technology and engage them in the effort of developing the VO. Thus, we wish to ensure that the VO standards fit new astronomy projects requirements and needs
Searching for an Intermediate Mass Black Hole in the Blue Compact Dwarf galaxy MRK 996
The possibility is explored that accretion on an intermediate mass black hole
contributes to the ionisation of the interstellar medium of the Compact Blue
Dwarf galaxy MRK996. Chandra observations set tight upper limits (99.7 per cent
confidence level) in both the X-ray luminosity of the posited AGN,
Lx(2-10keV)<3e40erg/s, and the black hole mass, <1e4/\lambda Msolar, where
\lambda, is the Eddington ratio. The X-ray luminosity upper limit is
insufficient to explain the high ionisation line [OIV]25.89\mu m, which is
observed in the mid-infrared spectrum of the MRK996 and is proposed as evidence
for AGN activity. This indicates that shocks associated with supernovae
explosions and winds of young stars must be responsible for this line. It is
also found that the properties of the diffuse X-ray emission of MRK996 are
consistent with this scenario, thereby providing direct evidence for shocks
that heat the galaxy's interstellar medium and contribute to its ionisation.Comment: Submitted to MNRA
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