4,703 research outputs found
Chemical evolution of the Galactic bulge: different stellar populations and possible gradients
We compute the chemical evolution of the Galactic bulge to explain the
existence of two main stellar populations recently observed. After comparing
model results and observational data we suggest that the old more metal poor
stellar population formed very fast (on a timescale of 0.1-0.3 Gyr) by means of
an intense burst of star formation and an initial mass function flatter than in
the solar vicinity whereas the metal rich population formed on a longer
timescale (3 Gyr). We predict differences in the mean abundances of the two
populations (-0.52 dex for ) which can be interpreted as a metallicity
gradients. We also predict possible gradients for Fe, O, Mg, Si, S and Ba
between sub-populations inside the metal poor population itself (e.g. -0.145
dex for ). Finally, by means of a chemo-dynamical model following a
dissipational collapse, we predict a gradient inside 500 pc from the Galactic
center of -0.26 dex kpc^{-1} in Fe.Comment: 9 pages, 9 figures, accepted for publication in Section 5. of
Astronomy and Astrophysic
Metronomic Chemotherapy with Vinorelbine Produces Clinical Benefit and Low Toxicity in Frail Elderly Patients Affected by Advanced Non-Small Cell Lung Cancer
Lung cancer is the leading cause of death worldwide. The treatment choice for advanced stage of lung cancer may depend on histotype, performance status (PS), age, and comorbidities. In the present study, we focused on the effect of metronomic vinorelbine treatment in elderly patients with advanced unresectable non-small cell lung cancer (NSCLC). Methods. From January 2016 to December 2016, 44 patients affected by non-small cell lung cancer referred to our oncology day hospital were progressively analyzed. The patients were treated with oral vinorelbine 30 mg x 3/wk or 40 mg x 3/wk meaning one day on and one day off. The patients were older than 60, stage IIIB or IV, ECOG PS ≥ 1, and have at least one important comorbidity (renal, hepatic, or cardiovascular disease). The schedule was based on ECOG-PS and comorbidities. The primary endpoint was progression-free survival (PFS). PFS was used to compare patients based on different scheduled dosage (30 or 40 mg x3/weekly) and age (more or less than 75 years old) as exploratory analysis. We also evaluated as secondary endpoint toxicity according to Common Toxicity Criteria Version 2.0. Results. Vinorelbine showed a good safety profile at different doses taken orally and was effective in controlling cancer progression. The median overall survival (OS) was 12 months. The disease control rate (DCR) achieved 63%. The median PFS was 9 months. A significant difference in PFS was detected comparing patients aged below with those over 75, and the HR value was 0.72 (p<0.05). Not significant was the difference between groups with different schedules. Conclusions. This study confirmed the safety profile of metronomic vinorelbine and its applicability for patients unfit for standard chemotherapies and adds the possibility of considering this type of schedule not only for very elderly patients
Galactic and Cosmic Type Ia SN rates: is it possible to impose constraints on SNIa progenitors?
We compute the Type Ia supernova rates in typical elliptical galaxies by
varying the progenitor models for Type Ia supernovae. To do that a formalism
which takes into account the delay distribution function (DTD) of the explosion
times and a given star formation history is adopted. Then the chemical
evolution for ellipticals with baryonic initial masses , and
is computed, and the mass of Fe produced by each galaxy is
precisely estimated. We also compute the expected Fe mass ejected by
ellipticals in typical galaxy clusters (e.g. Coma and Virgo), under different
assumptions about Type Ia SN progenitors. As a last step, we compute the cosmic
Type Ia SN rate in an unitary volume of the Universe by adopting several cosmic
star formation rates and compare it with the available and recent observational
data. Unfortunately, no firm conclusions can be derived only from the cosmic
SNIa rate, neither on SNIa progenitors nor on the cosmic star formation rate.
Finally, by analysing all our results together, and by taking into account
previous chemical evolution results, we try to constrain the best Type Ia
progenitor model. We conclude that the best progenitor models for Type Ia SNe
are still the single degenerate model, the double degenerate wide model, and
the empirical bimodal model. All these models require the existence of prompt
Type Ia supernovae, exploding in the first 100 Myr since the beginning of star
formation, although their fraction should not exceed 15-20% in order to fit
chemical abundances in galaxies.Comment: 17 pages, 11 figures, Submitted to MNRA
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LGBTQ+ Health-a Novel Course for Undergraduate Students.
The concept of providing focused, competency-based LGBTQ+ health education outside the setting of health professional programs, specifically for undergraduates, is quite uncharted. However, the issue at the core of our rationale is one shared by those with and without clinical exposure: how to best support the development of cultural competence in providers who are or will be caring for LGBTQ+ patients. Traditional health professional education programs have enacted a number of curricular initiatives in this regard, designed for advanced learners. By focusing specifically on the undifferentiated learner, we offer a new perspective on the timing of LGBTQ+ health-related education. Our course is not intended to supplant the critical learning and application that must occur in the clinic or hospital room. Rather, we present a framework for cultivating understanding of the healthcare issues faced by the LGBTQ+ community that may help a learner to acquire and apply skills subsequently with greater cultural competence
Chemical evolution of the bulge of M31: predictions about abundance ratios
We aim at reproducing the chemical evolution of the bulge of M31 by means of
a detailed chemical evolution model, including radial gas flows coming from the
disk. We study the impact of the initial mass function, the star formation rate
and the time scale for bulge formation on the metallicity distribution function
of stars. We compute several models of chemical evolution using the metallicity
distribution of dwarf stars as an observational constraint for the bulge of
M31. Then, by means of the model which best reproduces the metallicity
distribution function, we predict the [X/Fe] vs. [Fe/H] relations for several
chemical elements (O, Mg, Si, Ca, C, N). Our best model for the bulge of M31 is
obtained by means of a robust statistical method and assumes a Salpeter initial
mass function, a Schmidt-Kennicutt law for star formation with an exponent
k=1.5, an efficiency of star formation of , and an
infall timescale of Gyr. Our results suggest that the bulge
of M31 formed very quickly by means of an intense star formation rate and an
initial mass function flatter than in the solar vicinity but similar to that
inferred for the Milky Way bulge. The [/Fe] ratios in the stars of the
bulge of M31 should be high for most of the [Fe/H] range, as is observed in the
Milky Way bulge. These predictions await future data to be proven.Comment: Accepted for publication by MNRA
The Air Littoral: Another Look
Assessing threats to the air littoral, the airspace between ground forces and high-end fighters and bombers, requires a paradigm change in American military thinking about verticality. This article explores the consequences of domain convergence, specifically for the Army and Air Force’s different concepts of control. It will assist US military and policy practitioners in conceptualizing the air littoral and in thinking more vertically about the air and land domains and the challenges of domain convergence
Metallogeny of Serpentinite-Hosted Magnetite Deposits : Hydrothermal Overgrowth on Chromite or Metamorphic Transformation of Chromite?
Peculiar and rare occurrences of serpentinite-hosted magnetite deposits with mineable sizes are found in the Mesozoic ophiolites of Greece (Skyros), Iran (Nain and Sabzevar) and Oman (Aniba). These deposits have diverse thickness (from a few centimeters up to 50 m) and length (2 to >500 m). Magnetite ores show variable textures, including massive, nodular and banded ores, veins, net and fine-grained disseminations in serpentinites. Intriguingly, the investigated magnetite deposits can be mistaken for chromitite pods. Serpentinite-hosted magnetite deposits show three modes of occurrences including: (i) boulders strewn across the serpentinites (i.e. Skyros Island) (ii) ore bodies along the nonconformity contacts between serpentinites and limestones (i.e. Aniba); (iii) irregular and discontinuous trails of massive and semi-massive ore bodies within highly sheared serpentinite masses (i.e. Nain; Sabzevar). In all of these magnetite ore bodies, relicts of chromian spinel grains are occasionally enclosed in magnetite crystals. The chemistry of Cr-spinel relics found in these magnetite bodies are comparable to those of accessory Cr-spinels in the surrounding serpentinized peridotites. BSE images and elemental mapping revealed that magnetite occurs as a nucleation on chromian spinels but not being involved in reaction either with chromite or ferritchromite. Low-grade metamorphic transformation of chromite into Fe-chromite is documented along the cracks and fractures of a few chromite grains. Generally, magnetite has typical hydrothermal compositions, characterized by low Cr, V and Ti and high Mg and Mn. It is crucial to note that a few magnetite grains with metamorphic origin are characterized by high Cr and low Ti and Ni. The potential source of iron is essentially the Fe-rich olivine, We believe that multi-episodic serpentinization of peridotite systems at high fluid-rock ratios is the main process responsible for precipitation of magnetite at ore levels whereas low-grade metamorphic transformation of chromite to magnetite has minor contribution. Cumulative factors in generation of these deposits are modal volume of mantle olivine, peridotite composition, fluid chemistry, fluid-rock ratio, mechanisms of transportation and precipitation, structural controls such as cracks and shear zones
Compartmentalized control of Cdk1 drives mitotic spindle assembly
During cell division, dramatic microtubular rearrangements driven by cyclin B-cdk1 (Cdk1) kinase activity mark the onset of mitosis leading to dismantling of the interphase microtubular cytoskeleton and assembly of the mitotic spindle. During interphase, Cdk1 accumulates in an inactive state, phosphorylated at inhibitory sites by Wee1/Myt1 kinases. At mitosis onset, Cdc25 phosphatase dephosphorylates and activates Cdk1. Once activated, Cdk1 clears cytoplasmic microtubules by inhibiting microtubule-stabilizing and growth-promoting microtubule-associated proteins (MAPs). Nevertheless, some of these MAPs are required for spindle microtubule growth and spindle assembly, creating quite a conundrum. We show here that a Cdk1 fraction bound to spindle structures escapes Cdc25 action and remains inhibited by phosphorylation (i-Cdk1) in mitotic human cells. Loss or restoration of i-Cdk1 inhibits or promotes spindle assembly, respectively. Furthermore, polymerizing spindle microtubules foster i-Cdk1 aggregating with Wee1 and excluding Cdc25. Our data reveal that spindle assembly relies on compartmentalized control of Cdk1 activity
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