659 research outputs found
The Stellar Population Histories of Early-Type Galaxies. II. Controlling Parameters of the Stellar Populations
We analyze single-stellar-population (SSP) equivalent parameters for 50 local
elliptical galaxies as a function of their structural parameters. These
galaxies fill a two-dimensional plane in the four-dimensional space of [Z/H],
log t, log , and [E/Fe]. SSP age and velocity dispersion can be taken
as the two independent parameters that specify a galaxy's location in this
``hyperplane.'' The hyperplane can be decomposed into two sub-relations: (1) a
``Z-plane,'' in which [Z/H] is a linear function of log and log t; and
(2) a relation between [E/Fe] and in which [E/Fe] is larger in
high- galaxies. Cluster and field ellipticals follow the same
hyperplane, but their (,t) distributions within it differ. Nearly all
cluster galaxies are old; the field ellipticals span a large range in SSP age.
The tight Mg-- relations of these ellipticals can be understood as
two-dimensional projections of the metallicity hyperplane showing it edge-on;
the tightness of these relations does not necessarily imply a narrow range of
ages at fixed . The relation between [E/Fe] and is consistent
with a higher effective yield of Type II SNe elements at higher . The
Z-plane is harder to explain and may be a powerful clue to star formation in
elliptical galaxies if it proves to be general. Present data favor a
``frosting'' model in which low apparent SSP ages are produced by adding a
small frosting of younger stars to an older base population. If the frosting
abundances are close to or slightly greater than the base population, simple
two-component models run along lines of constant in the Z-plane, as
required. This favors star formation from well-mixed pre-enriched gas rather
than unmixed low-metallicity gas from an accreted object. (Abridged)Comment: To be published in the June 2000 issue of the Astronomical Journal.
28 pages, 13 figures, uses emulateap
Optically variable active galactic nuclei in the 3 yr VST survey of the COSMOS field
The analysis of the variability of active galactic nuclei (AGNs) at different
wavelengths and the study of possible correlations among different spectral
windows are nowadays a major field of inquiry. Optical variability has been
largely used to identify AGNs in multivisit surveys. The strength of a
selection based on optical variability lies in the chance to analyze data from
surveys of large sky areas by ground-based telescopes. However the
effectiveness of optical variability selection, with respect to other
multiwavelength techniques, has been poorly studied down to the depth expected
from next generation surveys. Here we present the results of our r-band
analysis of a sample of 299 optically variable AGN candidates in the VST survey
of the COSMOS field, counting 54 visits spread over three observing seasons
spanning > 3 yr. This dataset is > 3 times larger in size than the one
presented in our previous analysis (De Cicco et al. 2015), and the observing
baseline is ~8 times longer. We push towards deeper magnitudes (r(AB) ~23.5
mag) compared to past studies; we make wide use of ancillary multiwavelength
catalogs in order to confirm the nature of our AGN candidates, and constrain
the accuracy of the method based on spectroscopic and photometric diagnostics.
We also perform tests aimed at assessing the relevance of dense sampling in
view of future wide-field surveys. We demonstrate that the method allows the
selection of high-purity (> 86%) samples. We take advantage of the longer
observing baseline to achieve great improvement in the completeness of our
sample with respect to X-ray and spectroscopically confirmed samples of AGNs
(59%, vs. ~15% in our previous work), as well as in the completeness of
unobscured and obscured AGNs. The effectiveness of the method confirms the
importance to develop future, more refined techniques for the automated
analysis of larger datasets.Comment: 21 pages, 10 figures; accepted for publication in A&
Towards closing the gap between hygroscopic growth and activation for secondary organic aerosol: Part 1 â Evidence from measurements
Secondary Organic Aerosols (SOA) studied in previous laboratory experiments generally showed only slight hygroscopic growth, but a much better activity as a CCN (Cloud Condensation Nucleus) than indicated by the hygroscopic growth. This discrepancy was examined at LACIS (Leipzig Aerosol Cloud Interaction Simulator), using a portable generator that produced SOA particles from the ozonolysis of <i>α</i>-pinene, and adding butanol or butanol and water vapor during some of the experiments. The light scattering signal of dry SOA-particles was measured by the LACIS optical particle spectrometer and was used to derive a refractive index for SOA of 1.45. LACIS also measured the hygroscopic growth of SOA particles up to 99.6% relative humidity (RH), and a CCN counter was used to measure the particle activation. SOA-particles were CCN active with critical diameters of e.g. 100 nm and 55 nm at super-saturations of 0.4% and 1.1%, respectively. But only slight hygroscopic growth with hygroscopic growth factors &le;1.05 was observed at RH<98% RH. At RH>98%, the hygroscopic growth increased stronger than would be expected if a constant hygroscopicity parameter for the particle/droplet solution was assumed. An increase of the hygroscopicity parameter by a factor of 4â6 was observed in the RH-range from below 90% to 99.6%, and this increase continued for increasingly diluted particle solutions for activating particles. This explains an observation already made in the past: that the relation between critical super-saturation and dry diameter for activation is steeper than what would be expected for a constant value of the hygroscopicity. Combining measurements of hygroscopic growth and activation, it was found that the surface tension that has to be assumed to interpret the measurements consistently is greater than 55 mN/m, possibly close to that of pure water, depending on the different SOA-types produced, and therefore only in part accounts for the discrepancy between hygroscopic growth and CCN activity observed for SOA particles in the past
Monitoring international migration flows in Europe. Towards a statistical data base combining data from different sources
The paper reviews techniques developed in demography, geography and statistics that are useful for bridging the gap between available data on international migration flows and the information required for policy making and research. The basic idea of the paper is as follows: to establish a coherent and consistent data base that contains sufficiently detailed, up-to-date and accurate information, data from several sources should be combined. That raises issues of definition and measurement, and of how to combine data from different origins properly. The issues may be tackled more easily if the statistics that are being compiled are viewed as different outcomes or manifestations of underlying stochastic processes governing migration. The link between the processes and their outcomes is described by models, the parameters of which must be estimated from the available data. That may be done within the context of socio-demographic accounting. The paper discusses the experience of the U.S. Bureau of the Census in combining migration data from several sources. It also summarizes the many efforts in Europe to establish a coherent and consistent data base on international migration.
The paper was written at IIASA. It is part of the Migration Estimation Study, which is a collaborative IIASA-University of Groningen project, funded by the Netherlands Organization for Scientific Research (NWO). The project aims at developing techniques to obtain improved estimates of international migration flows by country of origin and country of destination
Fulguraçao e radiofreqĂŒĂȘncia na taquicardia ventricular
Durante um perĂodo de 10 anos, 89 casos de taquicardia ventricular (TV) resistentes aos antiarrĂtmicos foram tratados pelo mĂ©todo da fulguraçao. A sĂ©rie foi composta por: 37 casos de enfarte do miocĂĄrdio, com fraçao de ejeçao mĂ©dia de 30%, onde o acompanhamento mĂ©dio dos sobreviventes foi de 61 meses e a eficĂĄcia clĂnica foi de 87,9%; 23 casos de displasia arritmogĂȘnica do ventrĂculo direito, em que a mĂ©dia de idade foi de 40 anos e a fraçao de ejeçao mĂ©dia de 57%, acompanhados durante 71 meses em mĂ©dia, com eficĂĄcia clĂnica de 83%; 12 pacientes que apresentavam TV sensĂveis ao verapamil (fasciculares), com idade mĂ©dia de 30 anos e fraçao de ejeçao mĂ©dia de 65%, sendo o seu acompanhamento mĂ©dio de 55 meses e eficĂĄcia clĂnica de 100%; 10 pacientes portadores de cardiomiopatia idiopĂĄtica dilatada, idade mĂ©dia de 35 anos e fraçao de ejeçao mĂ©dia de 23% que, acompanhados por 38 meses, permitiram constatar uma eficĂĄcia clĂnica de 80%; 4 outros pacientes, com idade mĂ©dia de 21 anos, doenças congĂȘnitas operadas e com fraçao de ejeçao mĂ©dia de 60%, em que um acompanhamento de 36 meses demonstrou eficĂĄcia clĂnica de 100%. Por fim, 3 pacientes com taquicardias ventriculares idiopĂĄticas infundibulares, idade mĂ©dia de 36 anos e fraçao de ejeçao mĂ©dia de 62%, acompanhados durante um perĂodo de 72 meses, com uma eficĂĄcia clĂnica de 67%. Complicaçoes nao letais foram observadas em 16% dos casos, notadamente o hemopericĂĄrdio, observado em 4,5% dos casos, tendo implicado em pericardiocentese. A mortalidade operatĂłria no mĂȘs posterior Ă ablaçao foi de 9,2%, sendo principalmente observada durante a fase de aprendizagem. Em conclusao, ainda que nao seja isenta de riscos, em maos experientes a fulguraçao obteve resultados notĂĄveis na maioria dos casos. Continua a ser indicada nas TV resistentes Ă radiofrequĂȘncia, o que foi observado em mais da metade dos casos numa sĂ©rie preliminar de 41 pacientes
ERCC1 expression and RAD51B activity correlate with cell cycle response to platinum drug treatment not DNA repair
Background: The H69CIS200 and H69OX400 cell lines are novel models of low-level platinum-drug resistance. Resistance was not associated with increased cellular glutathione or decreased accumulation of platinum, rather the resistant cell lines have a cell cycle alteration allowing them to rapidly proliferate post drug treatment. Results: A decrease in ERCC1 protein expression and an increase in RAD51B foci activity was observed in association with the platinum induced cell cycle arrest but these changes did not correlate with resistance or altered DNA repair capacity. The H69 cells and resistant cell lines have a p53 mutation and consequently decrease expression of p21 in response to platinum drug treatment, promoting progression of the cell cycle instead of increasing p21 to maintain the arrest.
Conclusion: Decreased ERCC1 protein and increased RAD51B foci may in part be mediating the maintenance of the cell cycle arrest in the sensitive cells. Resistance in the H69CIS200 and H69OX400 cells may therefore involve the regulation of ERCC1 and RAD51B independent of their roles in DNA repair. The novel mechanism of platinum resistance in the H69CIS200 and H69OX400 cells demonstrates the multifactorial nature of platinum resistance which can occur independently of alterations in DNA repair capacity and changes in ERCC1
Patterns of eukaryotic diversity from the surface to the deep-ocean sediment
Remote deep-ocean sediment (DOS) ecosystems are among the least explored biomes on Earth. Genomic assessments of their biodiversity have failed to separate indigenous benthic organisms from sinking plankton. Here, we compare global-scale eukaryotic DNA metabarcoding datasets (18S-V9) from abyssal and lower bathyal surficial sediments and euphotic and aphotic ocean pelagic layers to distinguish plankton from benthic diversity in sediment material. Based on 1685 samples collected throughout the world ocean, we show that DOS diversity is at least threefold that in pelagic realms, with nearly two-thirds represented by abundant yet unknown eukaryotes. These benthic communities are spatially structured by ocean basins and particulate organic carbon (POC) flux from the upper ocean. Plankton DNA reaching the DOS originates from abundant species, with maximal deposition at high latitudes. Its seafloor DNA signature predicts variations in POC export from the surface and reveals previously overlooked taxa that may drive the biological carbon pump
The Mass Function of an X-Ray Flux-Limited Sample of Galaxy Clusters
A new X-ray selected and X-ray flux-limited galaxy cluster sample is
presented. Based on the ROSAT All-Sky Survey the 63 brightest clusters with
galactic latitude |bII| >= 20 deg and flux fx(0.1-2.4 keV) >= 2 * 10^{-11}
ergs/s/cm^2 have been compiled. Gravitational masses have been determined
utilizing intracluster gas density profiles, derived mainly from ROSAT PSPC
pointed observations, and gas temperatures, as published mainly from ASCA
observations, assuming hydrostatic equilibrium. This sample and an extended
sample of 106 galaxy clusters is used to establish the X-ray
luminosity--gravitational mass relation. From the complete sample the galaxy
cluster mass function is determined and used to constrain the mean cosmic
matter density and the amplitude of mass fluctuations. Comparison to
Press--Schechter type model mass functions in the framework of Cold Dark Matter
cosmological models and a Harrison--Zeldovich initial density fluctuation
spectrum yields the constraints OmegaM = 0.12^{+0.06}_{-0.04} and sigma8 =
0.96^{+0.15}_{-0.12} (90% c.l.). Various possible systematic uncertainties are
quantified. Adding all identified systematic uncertainties to the statistical
uncertainty in a worst case fashion results in an upper limit OmegaM < 0.31.
For comparison to previous results a relation sigma8 = 0.43 OmegaM^{-0.38} is
derived. The mass function is integrated to show that the contribution of mass
bound within virialized cluster regions to the total matter density is small,
i.e., OmegaCluster = 0.012^{+0.003}_{-0.004} for cluster masses larger than
6.4^{+0.7}_{-0.6} * 10^{13} h_{50}^{-1} Msun.Comment: 35 pages; accepted for publication in The Astrophysical Journal; this
and related papers, supplementary information, as well as electronic files of
the tables given in this paper are available at
http://www.astro.virginia.edu/~thr4f
Spectroscopic study of MATLAS-2019 with MUSE:An ultra-diffuse galaxy with an excess of old globular clusters
The MATLAS deep imaging survey has uncovered a plethora of dwarf galaxies in
the low density environment it has mapped. A fraction of them are unusually
extended and have a low-surface brightness. Among these so-called ultra-diffuse
galaxies, a few seem to host an excess of globular clusters. With the
integral-field unit spectrograph MUSE we have observed one of these galaxies -
MATLAS J15052031+0148447 (MATLAS-2019) - located towards the nearby group NGC
5846 and measured its systemic velocity,age, and metallicity, and that of its
globular clusters candidates. For the stellar body of MATLAS-2019 we derive a
metallicity of -1.33+0.19-0.01 dex and an age of 11.2+1.8-0.8 Gyr. For some of
the individual GCs and the stacked GC population, we derive consistent ages and
metallicities. From the 11 confirmed globular clusters and using a Markov Chain
Monte Carlo approach we derived a dynamical mass-to-light ratio of
4.2+8.6-3.4M/L. This is at the lower end of the luminosity-mass scaling
relation defined by the Local Group dwarf galaxies. Furthermore, we couldn't
confirm nor reject the possibility of a rotational component of the GC system.
If present, this would further modify the inferred mass. Follow-up observations
of the globular cluster population and of the stellar body of the galaxy are
needed to assess whether this galaxy is lacking dark matter like it was
suggested for the pair of dwarf galaxies in the field of NGC 1052, or if this
is a miss-interpretation arising from systematic uncertainties of the method
commonly used for these systems and the large uncertainties of the individual
globular cluster velocities.Comment: 10 pages, 9 figures, 2 tables, accepted for publication in A&
Measurements of the Sensitivity of Aerosol Hygroscopicity and the kappa Parameter to the O/C Ratio
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