2,733 research outputs found
Chemical abundances of the metal-poor horizontal-branch stars CS 22186-005 and CS 30344-033
We report on a chemical-abundance analysis of two very metal-poor
horizontal-branch stars in the Milky Way halo: CS 22186-005 ([Fe/H]=-2.70) and
CS 30344-033 ([Fe/H]=-2.90). The analysis is based on high-resolution spectra
obtained at ESO, with the spectrographs HARPS at the 3.6 m telescope, and UVES
at the VLT. We adopted one-dimensional, plane-parallel model atmospheres
assuming local thermodynamic equilibrium. We derived elemental abundances for
13 elements for CS 22186-005 and 14 elements for CS 30344-033. This study is
the first abundance analysis of CS 30344-033. CS 22186-005 has been analyzed
previously, but we report here the first measurement of nickel (Ni; Z = 28) for
this star, based on twenty-two NiI lines ([Ni/Fe]=-0.210.02); the
measurement is significantly below the mean found for most metal-poor stars.
Differences of up to 0.5 dex in [Ni/Fe] ratios were determined by different
authors for the same type of stars in the literature, which means that it is
not yet possible to conclude that there is a real intrinsic scatter in the
[Ni/Fe] ratios. For the other elements for which we obtained estimates, the
abundance patterns in these two stars match the Galactic trends defined by
giant and turnoff stars well. This confirms the value of horizontal-branch
stars as tracers of the chemical properties of stellar populations in the
Galaxy. Our radial velocities measurements for CS 22186-005 differ from
previously published measurements by more than the expected statistical errors.
More measurements of the radial velocity of this star are encouraged to confirm
or refute its radial velocity variability
X-ray Doppler Imaging of 44i Boo with Chandra
Chandra High-Energy Transmission Grating observations of the bright eclipsing
contact binary 44i Boo show X-ray line profiles which are Doppler-shifted by
orbital motions. The X-ray emission spectrum contains a multitude of lines
superimposed on a weak continuum, with strong lines of O VIII, Ne X, Fe XVII,
and Mg XII. The profiles of these lines from the total observed spectrum show
Doppler-broadened widths of ~ 550 km s^{-1}. Line centroids vary with orbital
phase, indicating velocity changes of > 180 km s^{-1}. The first-order light
curve shows significant variability, but no clear evidence for either primary
or secondary eclipses. Flares are observed for all spectral ranges;
additionally, the light curve constructed near the peak of the emission measure
distribution (T_e = 5 to 8 X 10^6 K) shows quiescent variability as well as
flares. The phase-dependences of line profiles and light curves together imply
that at least half of the emission is localized at high latitude. A simple
model with two regions on the primary star at relatively high latitude
reproduces the observed line profile shifts and quiescent light curve. These
first clear X-ray Doppler shifts of stellar coronal material illustrate the
power of Chandra.Comment: 15 pages, 6 figures to be published in Astrophysical Journal Letter
Estimation and Bias Correction of Aerosol Abundance using Data-driven Machine Learning and Remote Sensing
Air quality information is increasingly becoming a public health concern, since some of the aerosol particles pose harmful effects to peoples health. One widely available metric of aerosol abundance is the aerosol optical depth (AOD). The AOD is the integrated light extinction coefficient over a vertical atmospheric column of unit cross section, which represents the extent to which the aerosols in that vertical profile prevent the transmission of light by absorption or scattering. The comparison between the AOD measured from the ground-based Aerosol Robotic Network (AERONET) system and the satellite MODIS instruments at 550 nm shows that there is a bias between the two data products. We performed a comprehensive analysis exploring possible factors which may be contributing to the inter-instrumental bias between MODIS and AERONET. The analysis used several measured variables, including the MODIS AOD, as input in order to train a neural network in regression mode to predict the AERONET AOD values. This not only allowed us to obtain an estimate, but also allowed us to infer the optimal sets of variables that played an important role in the prediction. In addition, we applied machine learning to infer the global abundance of ground level PM2.5 from the AOD data and other ancillary satellite and meteorology products. This research is part of our goal to provide air quality information, which can also be useful for global epidemiology studies
Bio-based polymer nanocomposites based on layered silicates having a reactive and renewable intercalant
Soybean oil-based polymer nanocomposites were synthesized from acrylated epoxidized soybean oil (AESO) combined with styrene monomer and montmorillonite (MMT) clay by using in situ free radical polymerization reaction. Special attention was paid to the modification of MMT clay, which was carried out by methacryl-functionalized and quaternized derivative of methyl oleate intercalant. It was synthesized from olive oil triglyceride, as a renewable intercalant. The resultant nanocomposites were characterized by X-ray diffraction (XRD) and transmission electron microscopy (TEM). The effect of increased nanofiller loading in thermal and mechanical properties of the nanocomposites was investigated by thermogravimetric analysis (TGA) and dynamic mechanical analysis (DMA). The nanocomposites exhibited improved thermal and dynamic mechanical properties compared with neat acrylated epoxidized soybean oil based polymer matrix. The desired exfoliated nanocomposite structure was achieved when the OrgMMT loading was 1 and 2 wt % whereas partially exfoliated nanocomposite was obtained in 3 wt % loading. It was found that about 400 and 500% increments in storage modulus at glass transition and rubbery regions, respectively were achieved at 2 wt % clay loading compared to neat polymer matrix while the lowest thermal degradation rate was gained by introducing 3 wt % clay loading. © 2013 Wiley Periodicals, Inc
Observations of Lick Standard Stars Using the SCORPIO Multi-Slit Unit at the SAO 6-m Telescope
We present Lick line-index measurements of standard stars from the list of
Worthey. The spectra were taken with the multi-slit unit of the SCORPIO
spectrograph at the 6-m Special Astrophysical observatory telescope. We
describe in detail our method of analysis and explain the importance of using
the Lick index system for studying extragalactic globular clusters. Our results
show that the calibration of our instrumental system to the standard Lick
system can be performed with high confidence.Comment: 12 pages, 3 figure
Reentrant Phase Transitions of the Blume-Emery-Griffiths Model for a Simple Cubic Lattice on the Cellular Automaton
The spin-1 Ising (BEG) model with the nearest-neighbour bilinear and
biquadratic interactions and single-ion anisotropy is simulated on a cellular
automaton which improved from the Creutz cellular automaton(CCA) for a simple
cubic lattice. The simulations have been made for several sets of parameters
and in the and parameter regions.
The re-entrant and double re-entrant phase transitions of the BEG model are
determined from the temperature variations of the thermodynamic quantities
(, and ). The phase diagrams characterizing phase transitions are
compared with those obtained from other methods.Comment: 12 pages 7 figure
The prognostic impact of comorbidity, nutritional and performance status on patients with diffuse large B cell lymphoma
Background: The aim of the study was to investigate the impact of nutritional status, comorbidity, and performance status on patients with diffuse large B-cell lymphoma (DLBCL). Methods: A retrospective study was conducted on 112 DLBCL patients who were diagnosed at our center between 2009 and 2018. Demographic and disease characteristics and laboratory test results were recorded. Assessments were made using the age-adjusted Charlson comorbidity index (CCI-A) for comorbidity, albumin level for nutritional status, and Eastern Cooperative Oncology Group (ECOG) score for performance status. Results: The mean age of the patients was found to be 62.63 ± 15.16 years. The ECOG score of 65 patients (69.1%) was in the range of 0-1. The mean follow-up time of the patients was determined to be 25.24 ± 25.11 months, and at the end of the follow-up period, 64 patients (57.1%) were survivors. The progression-free survival (PFS), overall survival (OS), and 5-year OS rates of those with CCI-A > 4 were found to be significantly lower than those with CCI-A score ≤4 (P < 0.05). As a result of the Cox-Regression (Backward: LR method) analysis, ECOG and albumin levels were found to be independent risk factors for both OS and PFS (P < 0.05). Conclusion: This study demonstrated that CCI-A, ECOG, and nutritional status are independent prognostic markers for DLBCL patients. Initial evaluation of these patients should include all these parameters, which are easily available at the time of diagnosis
Physical Parameters of Some Close Binaries: ET Boo, V1123 Tau, V1191 Cyg, V1073 Cyg and V357 Peg
With the aim of providing new and up-to-date absolute parameters of some
close binary systems, new BVR CCD photometry was carried out at the Ankara
University Observatory (AUG) for five eclipsing binaries, ET Boo, V1123 Tau,
V1191 Cyg, V1073 Cyg and V357 Peg between April, 2007 and October, 2008. In
this paper, we present the orbital solutions for these systems obtained by
simultaneous light and radial velocity curve analyses. Extensive orbital
solution and absolute parameters for ET Boo system were given for the first
time through this study. According to the analyses, ET Boo is a detached binary
while the parameters of four remaining systems are consistent with the nature
of contact binaries. The evolutionary status of the components of these systems
are also discussed by referring to their absolute parameters found in this
study.Comment: this accepted paper will be published in New Astronom
Influence of steps on the tilting and adsorption dynamics of ordered Pn films on vicinal Ag(111) surfaces
Here we present a structural study of pentacene (Pn) thin films on vicinal
Ag(111) surfaces by He atom diffraction measurements and density functional
theory (DFT) calculations supplemented with van der Waals (vdW) interactions.
Our He atom diffraction results suggest initial adsorption at the step edges
evidenced by initial slow specular reflection intensity decay rate as a
function of Pn deposition time. In parallel with the experimental findings, our
DFT+vdW calculations predict the step edges as the most stable adsorption site
on the surface. An isolated molecule adsorbs as tilted on the step edge with a
binding energy of 1.4 eV. In addition, a complete monolayer (ML) with
pentacenes flat on the terraces and tilted only at the step edges is found to
be more stable than one with all lying flat or tilted molecules, which in turn
influences multilayers. Hence our results suggest that step edges can trap Pn
molecules and act as nucleation sites for the growth of ordered thin films with
a crystal structure similar to that of bulk Pn.Comment: 4 pages, 4 figures, 1 tabl
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