3,440 research outputs found
BVRcIc photometric evolution and flickering during the 2010 outburst of the recurrent nova U Scorpii
CCD BVRcIc photometric observations of the 2010 outburst of the recurrent
nova U Scorpii are presented. The light-curve has a smooth development
characterized by t2(V)=1.8 and t3(V)=4.1 days, close to the t2(V)=2.2 and
t3(V)=4.3 days of 1999 outburst. The plateau phase in 2010 has been brighter,
lasting shorter and beginning earlier than in the 1999 outburst. Flickering,
with an amplitude twice larger in than in band, was absent on
day +4.8 and +15.7, and present on day +11.8, with a time scale of about half
an hour.Comment: published March 1
R-Matrix Formulation of the Quantum Inhomogeneous Groups Iso_qr(N) and Isp_qr(N)
The quantum commutations and the orthogonal (symplectic) conditions
for the inhomogeneous multiparametric -groups of the type are
found in terms of the -matrix of . A consistent
Hopf structure on these inhomogeneous -groups is constructed by means of a
projection from . Real forms are discussed: in
particular we obtain the -groups , including the quantum
Poincar\'e group.Comment: 14 pages, latex, no figure
RR Lyrae variables in M5 as a test of pulsational theory
We present B and V CCD photometry for variables in the cluster central
region, adding new data for 32 variables and giving suitable light curves, mean
magnitudes and corrected colors for 17 RR Lyrae. Implementing the data given in
this paper with similar data already appeared in the literature we discuss a
sample of 42 variables, as given by 22 RRab and 20 RRc, to the light of recent
predictions from pulsational theories. We find that the observational evidence
concerning M5 pulsators appears in marginal disagreement with predictions
concerning the color of the First Overtone Blue Edge (FOBE), whereas a clear
disagreement appears between the ZAHB luminosities predicted through
evolutionary or pulsational theories.Comment: 7 pages, 7 postscript figures, accepted for publication on MNRA
Pulsational M_V versus [Fe/H] relation(s) for globular cluster RR Lyrae variables
We use the results from recent computations of updated non-linear convective
pulsating models to constrain the distance modulus of Galactic globular
clusters through the observed periods of first overtone RRc pulsators. The
resulting relation between the mean absolute magnitude of RR Lyrae stars
and the heavy element content [Fe/H] appears well in the range of
several previous empirical calibrations, but with a non linear dependence on
[Fe/H] so that the slope of the relation increases when moving towards larger
metallicities. On this ground, our results suggest that metal-poor
([Fe/H]-1.5) variables follow two different
linear -[Fe/H] relations. Application to RR Lyrae stars in the
metal-poor globular clusters of the Large Magellanic Cloud provides a LMC
distance modulus of the order of 18.6 mag, thus supporting the "long" distance
scale. The comparison with recent predictions based on updated stellar
evolution theory is shortly presented and discussed.Comment: 8 pages, 4 postscript figures, accepted for publication on MNRA
Stellar populations in the dwarf spheroidal galaxy Leo I
We present a detailed study of the color magnitude diagram (CMD) of the dwarf
spheroidal galaxy Leo I, based on archival Hubble Space Telescope data. Our
photometric analysis, confirming previous results on the brighter portion of
the CMD, allow us to obtain an accurate sampling of the stellar populations
also at the faint magnitudes corresponding to the Main Sequence. By adopting a
homogeneous and consistent theoretical scenario for both hydrogen and central
helium-burning evolutionary phases, the various features observed in the CMD
are interpreted and reliable estimations for both the distance modulus and the
age(s) for the main stellar components of Leo I are derived. More in details,
from the upper luminosity of the Red Giant Branch and the lower luminosity of
the Subgiant Branch we simultaneously constrain the galaxy distance and the age
of the oldest stellar population in Leo I. In this way we obtain a distance
modulus (m-M)_V=22.000.15 mag and an age of 10--15 Gyr or 9--13 Gyr,
adopting a metallicity Z=0.0001 and 0.0004, respectively. The reliability of
this distance modulus has been tested by comparing the observed distribution of
the Leo I anomalous Cepheids in the period-magnitude diagram with the predicted
boundaries of the instability strip, as given by convective pulsating models.Comment: 19 pages, 3 tables, 14 figures To be published in A
Surviving on Mars: test with LISA simulator
We present the biological results of some experiments performed in the Padua
simulators of planetary environments, named LISA, used to study the limit of
bacterial life on the planet Mars. The survival of Bacillus strains for some
hours in Martian environment is shortly discussed.Comment: To be published on Highlights of Astronomy, Volume 15 XXVIIth IAU
General Assembly, August 2009 Ian F Corbett, ed. 2 pages, 1 figur
Theoretical insights into the RR Lyrae K-band Period-Luminosity relation
Based on updated nonlinear, convective pulsation models computed for several
values of stellar mass, luminosity and metallicity, theoretical constraints on
the K-band Period-Luminosity (PLK) relation of RR Lyrae stars are presented. We
show that for each given metal content the predicted PLK is marginally
dependent on uncertainties of the stellar mass and/or luminosity. Then, by
considering the RR Lyrae masses suggested by evolutionary computations for the
various metallicities, we obtain that the predicted infrared magnitude M_K over
the range 0.0001< Z <0.02 is given by the relation
MK=0.568-2.071logP+0.087logZ-0.778logL/Lo, with a rms scatter of 0.032 mag.
Therefore, by allowing the luminosities of RR Lyrae stars to vary within the
range covered by current evolutionary predictions for metal-deficient (0.0001<
Z <0.006) horizontal branch models, we eventually find that the infrared
Period-Luminosity- Metallicity (PLZK) relation is
MK=0.139-2.071(logP+0.30)+0.167logZ, with a total intrinsic dispersion of 0.037
mag. As a consequence, the use of such a PLZK relation should constrain within
+-0.04 mag the infrared distance modulus of field and cluster RR Lyrae
variables, provided that accurate observations and reliable estimates of the
metal content are available. Moreover, we show that the combination of K and V
measurements can supply independent information on the average luminosity of RR
Lyrae stars, thus yielding tight constraints on the input physics of stellar
evolution computations. Finally, for globular clusters with a sizable sample of
first overtone variables, the reddening can be estimated by using the PLZK
relation together with the predicted MV-logP relation at the blue edge of the
instability strip (Caputo et al. 2000).Comment: 8 pages, including 5 postscript figures, accepted for publication on
MNRA
Spectral properties of incommensurate charge-density wave systems
The concept of frustrated phase separation is applied to investigate its
consequences for the electronic structure of the high T_c cuprates. The
resulting incommensurate charge density wave (CDW) scattering is most effective
in creating local gaps in k-space when the scattering vector connects states
with equal energy. Starting from an open Fermi surface we find that the
resulting CDW is oriented along the (10)- and (or) (01)-direction which allows
for a purely one-dimensional or a two-dimensional ``eggbox type'' charge
modulation. In both cases the van Hove singularities are substantially
enhanced, and the spectral weight of Fermi surface states near the M-points,
tends to be suppressed. Remarkably, a leading edge gap arises near these
points, which, in the eggbox case, leaves finite arcs of the Fermi surface
gapless. We discuss our results with repect to possible consequences for
photoemission experiments
Presence of multiple bacterial markers in clinical samples might be useful for presumptive diagnosis of infection in cirrhotic patients with culture-negative reports
Bacterial infections in cirrhotic patients with ascites are associated with a severe prognosis and an increased risk of death. The microbiological standard tests for the diagnosis of suspected infection, based on culture test of blood and ascitic fluid, are, in many cases (30-40 %), negative, even when patients show symptoms of infection. A multiple culture-independent protocol was applied and evaluated as a diagnostic and prognostic tool for the detection of bacterial infection in cirrhotic patients. Sixty-four culture-negative samples obtained from 34 cirrhotic patients, with PMN < 250 cells/μl of ascitic fluid, were screened for the presence of bacterial DNA, endotoxin, peptidoglycan/β-glucan and microscopically visible bacterial cells. Correlations between the presence of multiple markers and various clinical and laboratory parameters were evaluated. Bacterial DNA was detected in 23 samples collected from 16 patients; a large part of these samples also showed the presence of other bacterial markers, which was associated with a worsening of liver functionality, a higher incidence of infections during the follow-up and a higher mortality rate in our cohort of cirrhotic patients. We believe that the detection of additional bacterial markers in bacterial DNA-positive clinical samples makes the bacterial presence and its clinical significance more realistic and might be useful as early markers of an ongoing bacterial infection and in establishing a clinical prognosis
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