269 research outputs found
Deployment of national criteria for prevention of infection in surgical site in Ponta Grossa, Parana, Brazil
The nature of Long-GRB host galaxies from chemical abundances
Gamma-ray bursts (GRBs) are the most energetic events after the Big Bang and
they have been observed up to very high redshift. By means of measures of
chemical abundances now available for the galaxies hosting such events,thought
to originate from the explosion of very powerful supernovae (Type Ib/c), we
have the opportunity to study the nature of these host galaxies. The aim of
this paper is to identify the hosts of Long GRBs (LGRBs) observed both at low
and high redshift to see whether the hosts can be galaxies of the same type
observed at different cosmic epochs. We adopt detailed chemical evolution
models for galaxies of different morphological type (ellipticals, spirals,
irregulars) which follow the time evolution of the abundances of several
chemical elements (H, He, -elements, Fe), and compare the results with
the observed abundances and abundance ratios in galaxies hosting LGRBs. We find
that the abundances and abundance ratios predicted by models devised for
typical irregular galaxies can well fit the abundances in the hosts both at
high and low redshift. We also find that the predicted Type Ib/c supernova rate
for irregulars is in good agreement with observations. Models for spirals and
particularly ellipticals do not fit the high-redshift hosts of LGRBs (DLA
systems) nor the low redshift hosts: in particular, ellipticals cannot possibly
be the hosts of gamma-ray-bursts at low redshift since they do not show any
star formation, and therefore no supernovae Ib/c. We conclude that the observed
abundance and abundance ratios in LGRBs hosts suggest that these hosts are
irregular galaxies both at high and low redshift thus showing that the host
galaxies belong to in an evolutionary sequence.Comment: 8 pages, 9 figures, two references adde
The Richness and Beauty of the Physics of Cosmological Recombination: The Contributions from Helium
The physical ingredients to describe the epoch of cosmological recombination
are amazingly simple and well-understood. This fact allows us to take into
account a very large variety of processes, still finding potentially measurable
consequences. In this contribution we highlight some of the detailed physics
that were recently studied in connection with cosmological hydrogen and helium
recombination. The impact of these considerations is two-fold: (i) the
associated release of photons during this epoch leads to interesting and unique
deviations of the Cosmic Microwave Background (CMB) energy spectrum from a
perfect blackbody, which, in particular at decimeter wavelength, may become
observable in the near future. Despite the fact that the abundance of helium is
rather small, it also contributes a sizeable amount of photons to the full
recombination spectrum, which, because of differences in the dynamics of the
helium recombinations and the non-trivial superposition of all components, lead
to additional distinct spectral features. Observing the spectral distortions
from the epochs of hydrogen and helium recombination, in principle would
provide an additional way to determine some of the key parameters of the
Universe (e.g. the specific entropy, the CMB monopole temperature and the
pre-stellar abundance of helium), not suffering from limitations set by cosmic
variance. Also it permits us to confront our detailed understanding of the
recombination process with direct observational evidence. (ii) with the advent
of high precision CMB data, e.g. as will be available using the Planck Surveyor
or CMBpol, a very accurate theoretical understanding of the ionization history
of the Universe becomes necessary for the interpretation of the CMB temperature
and polarization anisotropies. (abridged)Comment: 16 pages, 11 figures, proceedings of the conference: "A Century of
Cosmology: Past, Present and Future
Perspectives on metaphyseal conservative stems
Total hip replacement is showing, during the last decades, a progressive evolution toward principles of reduced bone and soft tissue aggression. These principles have become the basis of a new philosophy, tissue sparing surgery. Regarding hip implants, new conservative components have been proposed and developed as an alternative to conventional stems. Technical and biomechanical characteristics of metaphyseal bone-stock-preserving stems are analyzed on the basis of the available literature and our personal experience. Mayo, Nanos and Metha stems represent, under certain aspects, a design evolution starting from shared concepts: reduced femoral violation, non-anatomic geometry, proximal calcar loading and lateral alignment. However, consistent differences are level of neck preservation, cross-sectional geometry and surface finishing. The Mayo component is the most time-tested component and, in our hands, it showed an excellent survivorship at the mid-term follow-up, with an extremely reduced incidence of aseptic loosening (partially reduced by the association with last generation acetabular couplings). For 160 implants followed for a mean of 4.7 years, survivorship was 97.5% with 4 failed implants: one fracture with unstable stem, 1 septic loosening and 2 aseptic mobilizations. DEXA analysis, performed on 15 cases, showed a good calcar loading and stimulation, but there was significant lateral load transfer to R3âR4 zones, giving to the distal part of the stem a function not simply limited to alignment. Metaphyseal conservative stems demonstrated a wide applicability with an essential surgical technique. Moreover, they offer the options of a âconservative revisionâ with a conventional primary component in case of failure and a âconservative revisionâ for failed resurfacing implants
The role of dedicated instrumentation in total hip arthroplasty
Tissue-sparing surgery is a surgical strategy aimed to reduce tissue damage in joint replacement. This can be achieved by reducing soft tissue trauma, performing minimally invasive access routes and limiting bone removal with implantation of conservative prostheses. In order to facilitate mini-approaches, special instrumentation was developed to avoid impingement of the soft tissues and provide an easier and more correct placement of the components. We performed an analysis of the literature and a research of the instrumentation available today, to evaluate the actual utility of dedicated tools
The Age of Cluster Galaxies from Continuum Colors
We determine the age of 1,104 early-type galaxies in eight rich clusters ( to ) using a new continuum color technique. We find that
galaxies in clusters divide into two populations, an old population with a mean
age similar to the age of the Universe (12 Gyrs) and a younger population with
a mean age of 9 Gyrs. The older population follows the expected relations for
mass and metallicity that imply a classic monolithic collapse origin. Although
total galaxy metallicity is correlated with galaxy mass, it is uncorrelated
with age. It is impossible, with the current data, to distinguish between a
later epoch of star formation, longer duration of star formation or late bursts
of star formation to explain the difference between the old and young
populations. However, the global properties of this younger population are
correlated with cluster environmental factors, which implies secondary
processes, post-formation epoch, operate on the internal stellar population of
a significant fraction of cluster galaxies. In addition, the mean age of the
oldest galaxies in a cluster are correlated with cluster velocity dispersion
implying that galaxy formation in massive clusters begins at earlier epochs
than less massive clusters.Comment: 35 pages, 10 figures, accepted by Ap
The Ages, Metallicities and Alpha Element Enhancements of Globular Clusters in the Elliptical NGC 5128: A Homogeneous Spectroscopic Study with Gemini/GMOS
We present new integrated light spectroscopy of globular clusters (GCs) in
NGC 5128 in order to measure radial velocities and derive ages, metallicities,
and alpha-element abundance ratios. Using Gemini-S 8-m/GMOS, we obtained
spectroscopy in the range of ~3400-5700 AA for 72 GCs with S/N > 30 /AA and we
have also discovered 35 new GCs within NGC 5128 from our radial velocity
measurements. We measured and compared the Lick indices from HdeltaA through
Fe5406 with the single stellar population (SSP) models of Thomas et
al.(2003,2004). We also measure Lick indices for 41 Milky Way GCs from Puzia et
al. (2002) and Schiavon et al. (2005) with the same methodology for direct
comparison. Our results show that 68% of the NGC 5128 GCs have old ages (> 8
Gyr), 14% have intermediate ages (5-8 Gyr), and 18% have young ages (< 5 Gyr).
However, when we look at the metallicity of the GCs as a function of age, we
find 92% of metal-poor GCs and 56% of metal-rich GCs in NGC 5128 have ages > 8
Gyr, indicating that the majority of both metallicity subpopulations of GCs
formed early, with a significant population of young and metal-rich GCs forming
later. Our metallicity distribution function generated directly from
spectroscopic Lick indices is clearly bimodal, as is the color distribution of
the same set of GCs. Thus the metallicity bimodality is real and not an
artifact of the color to metallicity conversion. The [alpha/Fe] values are
supersolar with a mean value of 0.14pm0.04, indicating a fast formation
timescale. However, the GCs in NGC 5128 are not as [alpha/Fe] enhanced as the
Milky Way GCs also examined in this study. Our results support a rapid, early
formation of the GC system in NGC 5128, with subsequent major accretion and/or
GC and star forming events in more recent times (abridged).Comment: Accepted to The Astrophysical Journal, 36 pages, 14 figures, 7 table
UVES/VLT high resolution spectroscopy of GRB 050730 afterglow: probing the features of the GRB environment
We analyze high resolution spectroscopic observations of the optical
afterglow of GRB050730, obtained with UVES@VLT about hours after the GRB
trigger. The spectrum shows that the ISM of the GRB host galaxy at z = 3.967 is
complex, with at least five components contributing to the main absorption
system. We detect strong CII*, SiII*, OI* and FeII* fine structure absorption
lines associated to the second and third component. For the first three
components we derive information on the relative distance from the site of the
GRB explosion. Component 1, which has the highest redshift, does not present
any fine structure nor low ionization lines; it only shows very high ionization
features, such as CIV and OVI, suggesting that this component is very close to
the GRB site. From the analysis of low and high ionization lines and fine
structure lines, we find evidences that the distance of component 2 from the
site of the GRB explosion is 10-100 times smaller than that of component 3. We
evaluated the mean metallicity of the z=3.967 system obtaining values about
0.01 of the solar metallicity or less. However, this should not be taken as
representative of the circumburst medium, since the main contribution to the
hydrogen column density comes from the outer regions of the galaxy while that
of the other elements presumably comes from the ISM closer to the GRB site.
Furthermore, difficulties in evaluating dust depletion correction can modify
significantly these values. The mean [C/Fe] ratio agrees well with that
expected by single star-formation event models. Interestingly the [C/Fe] of
component 2 is smaller than that of component 3, in agreement with GRB dust
destruction scenarios, if component 2 is closer than component 3 to the GRB
site.Comment: 11 pages, 15 postscript figures, accepted for pubblication in A&
The Initial Mass Function in disc galaxies and in galaxy clusters: the chemo-photometric picture
The observed brightness of the Tully-Fisher relation suggests a low stellar
M/L ratio and a "bottom-light" IMF in disc galaxies, but the corresponding
efficiency of chemical enrichment tends to exceed the observational estimates.
Either suitable tuning of the IMF slope and mass limits or metal outflows from
disc galaxies must then be invoked.
A standard Solar Neighbourhood IMF cannot explain the high metallicity of the
hot intra-cluster medium: a different IMF must be at work in clusters of
galaxies. Alternatively, if the IMF is universal and chemical enrichment is
everywhere as efficient as observed in clusters, substantial loss of metals
must occur from the Solar Neighbourhood and from disc galaxies in general; a
"non-standard" scenario challenging our understanding of disc galaxy formation.Comment: 6 pages, 4 figures; in Proceedings of IMF@50: the Initial Mass
Function 50 years later; Corbelli, Palla and Zinnecker (eds.
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