167 research outputs found
Evaluation of plant derivatives of Meliaceae family as a source of nitrogen for trees
Soil application of fresh organic matter is a way to increase soil organic matter and provide nutrients to trees. The effect of application of organic matter depends on the interaction among soil, root and microbial biomass. The aim of this research was to evaluate the potential release of N for hybrid GF677 (P. persica x P. dulcis) uptake, of 6 neemcakes available on the Italian market compared with fresh leaves of Melia azedarach, an ornamental tree that grows in the area of investigation. The release of N, and consequently root uptake was related to C:N ratio, the lower the ratio the higher the N concentration in plant tissues and plant growth. Using the 15N isotope technique, we found that up to 30% of the N applied with fresh Melia leaves, was accumulated in the tree, however the mineral N concentration in soil and plant and plant growth was not affected by the application of plant derivatives
Genderâspecific Issues in Traumatic Injury and Resuscitation: Consensusâbased Recommendations for Future Research
Traumatic injury remains an unacceptably high contributor to morbidity and mortality rates across the United States. Genderâspecific research in trauma and emergency resuscitation has become a rising priority. In concert with the 2014 Academic Emergency Medicine consensus conference âGenderâspecific Research in Emergency Care: Investigate, Understand, and Translate How Gender Affects Patient Outcomes,â a consensusâbuilding group consisting of experts in emergency medicine, critical care, traumatology, anesthesiology, and public health convened to generate research recommendations and priority questions to be answered and thus move the field forward. Nominal group technique was used for the consensusâbuilding process and a combination of faceâtoâface meetings, monthly conference calls, eâmail discussions, and preconference surveys were used to refine the research questions. The resulting research agenda focuses on opportunities to improve patient outcomes by expanding research in sexâ and genderâspecific emergency care in the field of traumatic injury and resuscitation.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/110065/1/acem12536.pd
The role of the Rayleigh-Taylor instability in ram pressure stripped disk galaxies
Ram pressure stripping, i.e. the removal of a galaxy's gas disk due to its
motion through the intracluster medium of a galaxy cluster, appears to be a
common phenomenon. Not every galaxy, however, is completely stripped of its gas
disk. If the ram pressure is insufficiently strong, only the outer parts of the
gas disk are removed, and the inner gas disk is retained by the galaxy. One
example of such a case is the Virgo spiral NGC 4402. Observations of NGC 4402
(Crowl et al. 2005) reveal structures at the leading edge of the gas disk,
which resemble the characteristic finger-like structures produced by the
Rayleigh-Taylor (RT) instability. We argue, however, that the RT instability is
unlikely to be responsible for these structures. We demonstrate that the
conditions under which a galaxy's disk gas experiences ram pressure stripping
are identical to those that lead to RT instability. If the galaxy's gravity
prevents ram pressure stripping of the inner disk, it also prevents the RT
instability. In contrast, the stripped gas could still be subject to RT
instability, and we discuss consequences for the stripped gas.Comment: accepted by A&
Dwarf spheroidals in the M81 Group - Metallicity distribution functions and population gradients
We study the dwarf spheroidal galaxies in the nearby M81 group in order to
construct their photometric metallicity distributions and to investigate the
potential presence of population gradients. We select all the dwarf spheroidals
with available Hubble Space Telescope / Advanced Camera for Surveys archival
observations, nine in total. We interpolate isochrones so as to assign a
photometric metallicity to each star within a selection box in the
color-magnitude diagram of each dwarf galaxy. We assume that the dwarf
spheroidals contain mainly an old stellar population. In order to search for
metallicity gradients, we examine the spatial distribution of two stellar
populations that we separate according to their metallicities. As a result, we
present the photometric metallicity distribution functions, the cumulative
histograms and smoothed density maps of the metal-poor and metal-rich stars as
well as of the intermediate-age stars. From our photometric data we find that
all the dwarf spheroidals show a wide range in metallicities, with mean values
that are typical for old and metal-poor systems, with the exception of one
dwarf spheroidal, namely IKN. Some of our dwarf spheroidals exhibit
characteristics of transition-type dwarfs. Compared to the Local Group
transition type dwarfs, the M81 group ones appear to have mean metallicity
values slightly more metal-rich at a given luminosity. All the dwarf
spheroidals considered here appear to exhibit either population gradients or
spatial variations in the centroids of their metal-poor and metal-rich
population. In addition, there are luminous AGB stars detected in all of them
with spatial distributions suggesting that they are well mixed with the old
stars.Comment: 15 pages, 11 figures; A&A accepte
Hubble Space Telescope Survey of the Perseus Cluster: II. Photometric scaling relations in different environments
We investigate the global photometric scaling relations traced by early-type
galaxies in different environments, ranging from dwarf spheroidals, over dwarf
elliptical galaxies, up to giant ellipticals (-8 mag > M_V > -24 mag). These
results are based in part on our new HST/ACS F555W and F814W imagery of dwarf
spheroidal galaxies in the Perseus Cluster. These scaling relations are almost
independent of environment, with Local Group and cluster galaxies coinciding in
the various diagrams. We show that at M_V ~ -14 mag, the slopes of the
photometric scaling relations involving the Sersic parameters change
significantly. We argue that these changes in slope reflect the different
physical processes that dominate the evolution of early-type galaxies in
different mass regimes. As such, these scaling relations contain a wealth of
information that can be used to test models for the formation of early-type
galaxies.Comment: accepted for publication by MNRA
Anticoagulant Reversal Strategies in the Emergency Department Setting: Recommendations of a Multidisciplinary Expert Panel
A close look at the Centaurus A group of galaxies: I. Metallicity distribution functions and population gradients in early-type dwarfs
We study dwarf galaxies in the Centaurus A group to investigate their
metallicity and possible environmental effects. The Centaurus A group (at ~4
Mpc from the Milky Way) contains about 50 known dwarf companions of different
morphologies and stellar contents, thus making it a very interesting target to
study how these galaxies evolve. Here we present results for the early-type
dwarf galaxy population in this group. We use archival HST/ACS data to study
the resolved stellar content of 6 galaxies, together with isochrones from the
Dartmouth stellar evolutionary models. We derive photometric metallicity
distribution functions of stars on the upper red giant branch via isochrone
interpolation. The 6 galaxies are moderately metal-poor (=-1.56 to
-1.08), and metallicity spreads are observed (internal dispersions of
sigma_[Fe/H]=0.10 to 0.41 dex). We also investigate the possible presence of
intermediate-age stars, and discuss how these affect our results. The dwarfs
exhibit flat to weak radial metallicity gradients. For the two most luminous,
most metal-rich galaxies, we find statistically significant evidence for at
least two stellar subpopulations: the more metal-rich stars are found in the
center of the galaxies, while the metal-poor ones are more broadly distributed
within the galaxies. We find no clear trend of the derived physical properties
as a function of (present-day) galaxy position in the group, which may be due
to the small sample we investigate. We compare our results to the early-type
dwarf population of the Local Group, and find no outstanding differences,
despite the fact that the Centaurus A group is a denser environment that is
possibly in a more advanced dynamical stage.Comment: 21 pages, 12 figures, accepted for publication in Astronomy and
Astrophysic
On the isolated dwarf galaxies: from cuspy to flat dark matter density profiles and metallicity gradients
The chemodynamical evolution of spherical multi-component self-gravitating
models for isolated dwarf galaxies is studied. We compare their evolution with
and without feedback effects from star formation processes. We find that
initially cuspy dark matter profiles flatten with time as a result of star
formation, without any special tuning conditions. Thus the seemingly flattened
profiles found in many dwarfs do not contradict the cuspy profiles predicted by
cosmological models. We also calculate the chemical evolution of stars and gas,
to permit comparisons with observational data.Comment: Accepted the 28/01/1
Polycyclic aromatic hydrocarbon processing in a hot gas
Context: PAHs are thought to be a ubiquitous and important dust component of
the interstellar medium. However, the effects of their immersion in a hot
(post-shock) gas have never before been fully investigated. Aims: We study the
effects of energetic ion and electron collisions on PAHs in the hot post-shock
gas behind interstellar shock waves. Methods: We calculate the ion-PAH and
electron-PAH nuclear and electronic interactions, above the carbon atom loss
threshold, in H II regions and in the hot post-shock gas, for temperatures
ranging from 10^3 to 10^8 K. Results: PAH destruction is dominated by He
collisions at low temperatures (T < 3x10^4 K), and by electron collisions at
higher temperatures. Smaller PAHs are destroyed faster for T < 10^6 K, but the
destruction rates are roughly the same for all PAHs at higher temperatures. The
PAH lifetime in a tenuous hot gas (n_H ~ 0.01 cm^-3, T ~ 10^7 K), typical of
the coronal gas in galactic outflows, is found to be about thousand years,
orders of magnitude shorter than the typical lifetime of such objects.
Conclusions: In a hot gas, PAHs are principally destroyed by electron
collisions and not by the absorption of X-ray photons from the hot gas. The
resulting erosion of PAHs occurs via C_2 loss from the periphery of the
molecule, thus preserving the aromatic structure. The observation of PAH
emission from a million degree, or more, gas is only possible if the emitting
PAHs are ablated from dense, entrained clumps that have not yet been exposed to
the full effect of the hot gas.Comment: 16 pages, 11 figures, 3 tables, typos corrected and PAH acronym in
the title substituted with full name to match version published in Astronomy
and Astrophysic
The Dynamical and Chemical Evolution of Dwarf Spheroidal Galaxies
We present a large sample of fully self-consistent hydrodynamical
Nbody/Tree-SPH simulations of isolated dwarf spheroidal galaxies (dSphs). It
has enabled us to identify the key physical parameters and mechanisms at the
origin of the observed variety in the Local Group dSph properties. The initial
total mass (gas + dark matter) of these galaxies is the main driver of their
evolution. Star formation (SF) occurs in series of short bursts. In massive
systems, the very short intervals between the SF peaks mimic a continuous star
formation rate, while less massive systems exhibit well separated SF bursts, as
identified observationally. The delay between the SF events is controlled by
the gas cooling time dependence on galaxy mass. The observed global scaling
relations, luminosity-mass and luminosity-metallicity, are reproduced with low
scatter. We take advantage of the unprecedentedly large sample size and data
homogeneity of the ESO Large Programme DART, and add to it a few independent
studies, to constrain the star formation history of five Milky Way dSphs,
Sextans, LeoII, Carina, Sculptor and Fornax. For the first time, [Mg/Fe] vs
[Fe/H] diagrams derived from high-resolution spectroscopy of hundreds of
individual stars are confronted with model predictions. We find that the
diversity in dSph properties may well result from intrinsic evolution. We note,
however, that the presence of gas in the final state of our simulations, of the
order of what is observed in dwarf irregulars, calls for removal by external
processes.Comment: 21 Pages, 19 figures ; Accepted for publication in A&A. Higher
resolution version may be downloaded here :
http://obswww.unige.ch/~revaz/publications/aa2009_1173
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