10,546 research outputs found
Variability and polarization in the inner jet of 3C395
We present new results on the parsec-scale jet of the quasar 3C395, derived
from VLBI polarization sensitive observations made in 1995.91 and 1998.50 at
8.4, 15.4 and 22.2 GHz. The observations show a complex one-sided jet extending
up to 20 mas, with a projected magnetic field essentially aligned with the
radio jet. The emission is strongly dominated, in total intensity and
polarization, by the core and the inner jet region (of ~3 mas length). We have
studied the details of this dominant region finding clear structural variations
during this ~2.5 years period, in contrast with the apparent quietness of the
jet structure inferred from lower resolution VLBI observations. We observe the
ejection of a new component from the core and variations in the degree of
polarization of the inner jet components. We estimate a high Faraday Rotation
Measure close to the core, with a strong decrease along the inner jet.Comment: 7 pages, 4 figures, A&A in pres
Testing strong line metallicity diagnostics at z~2
High-z galaxy gas-phase metallicities are usually determined through
observations of strong optical emission lines with calibrations tied to the
local universe. Recent debate has questioned if these calibrations are valid in
the high-z universe. We investigate this by analysing a sample of 16 galaxies
at z~2 available in the literature, and for which the metallicity can be
robustly determined using oxygen auroral lines. The sample spans a redshift
range of 1.4 < z < 3.6, has metallicities of 7.4-8.4 in 12+log(O/H) and stellar
masses 10^7.5-10^11 Msun. We test commonly used strong line diagnostics (R23,
O3, O2, O32, N2, O3N2 and Ne3O2 ) as prescribed by four different sets of
empirical calibrations, as well as one fully theoretical calibration. We find
that none of the strong line diagnostics (or calibration set) tested perform
consistently better than the others. Amongst the line ratios tested, R23 and O3
deliver the best results, with accuracies as good as 0.01-0.04 dex and
dispersions of ~0.2 dex in two of the calibrations tested. Generally, line
ratios involving nitrogen predict higher values of metallicity, while results
with O32 and Ne3O2 show large dispersions. The theoretical calibration yields
an accuracy of 0.06 dex, comparable to the best strong line methods. We
conclude that, within the metallicity range tested in this work, the locally
calibrated diagnostics can still be reliably applied at z~2.Comment: 12 pages, 8 Figures, accepted for publication in MNRA
Characterizing the radial oxygen abundance distribution in disk galaxies
We examine the possible dependence of the radial oxygen abundance
distribution on non-axisymmetrical structures (bar/spirals) and other
macroscopic parameters such as the mass, the optical radius R25, the color g-r,
and the surface brightness of the galaxy. A sample of disk galaxies from the
CALIFA DR3 is considered. We adopted the Fourier amplitude A2 of the surface
brightness as a quantitative characteristic of the strength of non-axisymmetric
structures in a galactic disk, in addition to the commonly used morphologic
division for A, AB, and B types based on the Hubble classification. To
distinguish changes in local oxygen abundance caused by the non-axisymmetrical
structures, the multiparametric mass--metallicity relation was constructed as a
function of parameters such as the bar/spiral pattern strength, the disk size,
color index g-r in the SDSS bands, and central surface brightness of the disk.
The gas-phase oxygen abundance gradient is determined by using the R
calibration. We find that there is no significant impact of the
non-axisymmetric structures such as a bar and/or spiral patterns on the local
oxygen abundance and radial oxygen abundance gradient of disk galaxies.
Galaxies with higher mass, however, exhibit flatter oxygen abundance gradients
in units of dex/kpc, but this effect is significantly less prominent for the
oxygen abundance gradients in units of dex/R25 and almost disappears when the
inner parts are avoided. We show that the oxygen abundance in the central part
of the galaxy depends neither on the optical radius R25 nor on the color g-r or
the surface brightness of the galaxy. Instead, outside the central part of the
galaxy, the oxygen abundance increases with g-r value and central surface
brightness of the disk.Comment: 11 pages, 6 figures; accepted for publication in A&
The Broad Line Radio Galaxy J2114+820
In the frame of the study of a new sample of large angular size radio
galaxies selected from the NRAO VLA Sky Survey, we have made radio observations
of J2114+820, a low power radio galaxy with an angular size of 6'. Its radio
structure basically consists of a prominent core, a jet directed in north-west
direction and two extended S-shaped lobes. We have also observed the optical
counterpart of J2114+820, a bright elliptical galaxy with a strong unresolved
central component. The optical spectrum shows broad emission lines. This fact,
together with its low radio power and FR-I type morphology, renders J2114+820 a
non-trivial object from the point of view of the current unification schemes of
radio loud active galactic nuclei.Comment: 6 pages, 5 figures. To appear in the proceedings of EVN/JIVE
Symposium No. 4, New Astronomy Reviews (eds. Garrett et al.
Feminists really do count : the complexity of feminist methodologies
We are delighted to be presenting this special issue on the topic of feminism and quantitative methods. We believe that such an issue is exceptionally timely. This is not simply because of ongoing debates around quantification within the field of feminism and women‟s studies. It is also because of debates within the wider research community about the development of appropriate methodologies that take account of new technological and philosophical concerns and are fit-for-purpose for researching contemporary social, philosophical, cultural and global issues. Two areas serve as exemplars in this respect and both speak to these combined wider social science and specifically feminist methodological concerns. The first is the increasing concern amongst social scientists with how the complexity of social life can be captured and analysed. Within feminism, this can be seen in debates about intersectionality that recognise the concerns arising from multiple social positions/divisions and associated power issues. As Denis (2008: 688) comments in respect of intersectional analysis „The challenge of integrating multiple, concurrent, yet often contradictory social locations into analyses of power relations has been issued. Theorising to accomplish this end is evolving, and we are struggling to develop effective methodological tools in order to marry theorising with necessary complex analyses of empirical data.‟ Secondly, new techniques and new data sources are now coming on line. This includes work in the UK of the ESRC National Data Strategy which has been setting out the priorities for the development of research data resources both within and across the boundaries of the social sciences. This will facilitate historical, longitudinal, interdisciplinary and mixed methodological research. And it may be the case that these developments facilitate the achievement of a longstanding feminist aim not simply for interdisciplinarity but for transdisciplinarity in epistemological and methodological terms
Fostering Critical Thinking: Generative processing strategies to learn to avoid bias in reasoning
This dissertation focuses on fostering learning and transfer of critical thinking skills of higher education students. It has been investigated which instructional methods are effective in promoting an essential aspect of critical thinking, that is, the ability to avoid bias in reasoning and decision making
A Security Monitoring Framework For Virtualization Based HEP Infrastructures
High Energy Physics (HEP) distributed computing infrastructures require
automatic tools to monitor, analyze and react to potential security incidents.
These tools should collect and inspect data such as resource consumption, logs
and sequence of system calls for detecting anomalies that indicate the presence
of a malicious agent. They should also be able to perform automated reactions
to attacks without administrator intervention. We describe a novel framework
that accomplishes these requirements, with a proof of concept implementation
for the ALICE experiment at CERN. We show how we achieve a fully virtualized
environment that improves the security by isolating services and Jobs without a
significant performance impact. We also describe a collected dataset for
Machine Learning based Intrusion Prevention and Detection Systems on Grid
computing. This dataset is composed of resource consumption measurements (such
as CPU, RAM and network traffic), logfiles from operating system services, and
system call data collected from production Jobs running in an ALICE Grid test
site and a big set of malware. This malware was collected from security
research sites. Based on this dataset, we will proceed to develop Machine
Learning algorithms able to detect malicious Jobs.Comment: Proceedings of the 22nd International Conference on Computing in High
Energy and Nuclear Physics, CHEP 2016, 10-14 October 2016, San Francisco.
Submitted to Journal of Physics: Conference Series (JPCS
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