526 research outputs found
How You Can Write More Inclusive Data Practitioner Job Postings
The principles of equity, diversity, and inclusion have long been incorporated into many aspects of the data practitioner profession. The hiring process is an exception; it is opaque, stress-inducing, and ultimately reinforces a homogeneous workforce. Job postings are important both as a window into the profession and as the first way that candidates interact with your institution. This Commentary article provides concrete and actionable recommendations on how you can start writing more equitable, diverse, and inclusive job postings at your institution.
The substance of this article is based upon a panel presentation at RDAP Summit 2019
The Linear-Size Evolution of Classical Double Radio Sources
Recent investigations of how the median size of extragalactic radio sources
change with redshift have produced inconsistent results. Eales compared the
radio and optical properties of a bright 3C and faint 6C sample and concluded
that (), with being the median
size of the radio sources at a given epoch and z the redshift. Oort, Katgert,
and Windhorst, on the other hand, from a comparison of the properties of a
number of radio samples, found much stronger evolution, with
. In this paper we attempt to resolve the
difference. We have repeated the analysis of Eales using the virtually complete
redshift information that now exists for the 6C sample. Confining our analysis
to FR2 sources, which we argue is the best-understood class of radio sources
and the least likely to be affected by selection effects, we find
() and
(). Our complete redshift information allows us to gain insight
into our result by plotting a radio luminosity-size (P-D) diagram for the 6C
sample. The most obvious difference between the 3C and 6C P-D diagrams is the
clump of sources in the 6C diagram at . These clump sources have similar sizes to the emission-line
regions found around high-redshift radio galaxies, suggesting that the presence
of dense line-emitting gas around high-redshift radio galaxies is responsible
for the size evolution. We show that this explanation can quantitatively
explain the observed size evolution, as long as there is either little X-ray
emitting gas around these objects or, if there is, it is distributed in a
similar way to the emission-line gas: highly anisotropic and inhomogeneous.Comment: compressed and uuencoded postscript file. 33 pages including 5
figures (441951 bytes). Accepted for publication in September Ap
Readout Concepts for DEPFET Pixel Arrays
Field effect transistors embedded into a depleted silicon bulk (DEPFETs) can
be used as the first amplifying element for the detection of small signal
charges deposited in the bulk by ionizing particles, X-ray photons or visible
light. Very good noise performance at room temperature due to the low
capacitance of the collecting electrode has been demonstrated. Regular two
dimensional arrangements of DEPFETs can be read out by turning on individual
rows and reading currents or voltages in the columns. Such arrangements allow
the fast, low power readout of larger arrays with the possibility of random
access to selected pixels. In this paper, different readout concepts are
discussed as they are required for arrays with incomplete or complete clear and
for readout at the source or the drain. Examples of VLSI chips for the steering
of the gate and clear rows and for reading out the columns are presented.Comment: 8 pages, 9 figures, submitted to Nucl. Instr. and Methods as
proceedings of the 9th European Symposium on Semiconductor Detectors, Elmau,
June 23-27, 200
A panoramic VISTA of the stellar halo of NGC 253
Outskirts of large galaxies contain important information about the galaxy
formation and assembly process, and resolved star count studies can probe the
extremely low surface brightness of the outer halos. We use images obtained
with the VISTA telescope to construct spatially resolved J vs Z-J
colour-magnitude diagrams (CMDs) of NGC 253, a nearly edge-on disk galaxy in
the Sculptor group. The very deep photometry, down to J ~ 23.5, and the wide
area covered allows us to trace the red giant branch (RGB) and asymptotic giant
branch (AGB) stars that belong to the outer disk and the halo of NGC 253, out
to 50 kpc along the galaxy minor axis. We confirm the existence of an extra
planar stellar component of the disk, with a very prominent southern shelf and
a symmetrical feature on the north side. The only additional visible
sub-structure is an overdensity in the north-west part of the halo at about 28
kpc from the plane and extending over ~ 20 kpc parallel with the disk of the
galaxy. From the stellar count profile along the major axis we measure the
transition from the disk to the halo at a radial distance of about 25 kpc,
where a clear break appears in the number density profile. The isodensity
contours show that the inner halo is a flattened structure that blends with a
more extended, diffuse, rounder outer halo. Such external structure can be
traced to the very edge of our image out to 50 kpc from the disk plane. The
number density profile of the stars in the stellar halo follows a power law
with index -1.6, as function of radius. The CMD shows a very homogeneous
stellar population across the whole field; by comparison with theoretical
isochrones we conclude that the RGB stars are ~ 8 Gyr old or more, while the
AGB stars trace a population of about 2 x 10^8 Mo, formed from ~ 0.5 to a few
Gyr ago. Surprisingly, part of this latter population appears scattered over a
wide area.Comment: To appear on Astronomy and Astrophysic
The NIR structure of the barred galaxy NGC253 from VISTA
[abridged] We used J and Ks band images acquired with the VISTA telescope as
part of the science verification to quantify the structures in the stellar disk
of the barred Sc galaxy NGC253. Moving outward from the galaxy center, we find
a nuclear ring within the bright 1 kpc diameter nucleus, then a bar, a ring
with 2.9 kpc radius. From the Ks image we obtain a new measure of the
deprojected length of the bar of 2.5 kpc. The bar's strength, as derived from
the curvature of the dust lanes in the J-Ks image, is typical of weak bars.
From the deprojected length of the bar, we establish the corotation radius
(R_CR=3 kpc) and bar pattern speed (Omega_b = 61.3 km /s kpc), which provides
the connection between the high-frequency structures in the disk and the
orbital resonances induced by the bar. The nuclear ring is located at the inner
Lindblad resonance. The second ring does not have a resonant origin, but it
could be a merger remnant or a transient structure formed during an
intermediate stage of the bar formation. The inferred bar pattern speed places
the outer Lindblad resonance within the optical disk at 4.9 kpc, in the same
radial range as the peak in the HI surface density. The disk of NGC253 has a
down-bending profile with a break at R~9.3 kpc, which corresponds to about 3
times the scale length of the inner disk. We discuss the evidence for a
threshold in star formation efficiency as a possible explanation of the steep
gradient in the surface brightness profile at large radii. The NIR photometry
unveils the dynamical response of the NGC253 stellar disk to its central bar.
The formation of the bar may be related to the merger event that determined the
truncation of stars and gas at large radii and the perturbation of the disk's
outer edge.Comment: Accepted for publication in Astronomy & Astrphysics. High resolution
pdf file is available at the following link:
https://www.dropbox.com/s/4o4cofs1lyjrtpv/NGC253.pd
A Comparison of Statistical and Geometric Reconstruction Techniques: Guidelines for Correcting Fossil Hominin Crania
The study of human evolution centres, to a large extent, around the study of fossil morphology, including the comparison and interpretation of these remains within the context of what is known about morphological variation within living species. However, many fossils suffer from environmentally caused damage (taphonomic distortion) which hinders any such interpretation: fossil material may be broken and fragmented while the weight and motion of overlaying sediments can cause their plastic distortion. To date, a number of studies have focused on the reconstruction of such taphonomically damaged specimens. These studies have used myriad approaches to reconstruction, including thin plate spline methods, mirroring, and regression-based approaches. The efficacy of these techniques remains to be demonstrated, and it is not clear how different parameters (e.g., sample sizes, landmark density, etc.) might effect their accuracy.
In order to partly address this issue, this thesis examines three techniques used in the virtual reconstruction of fossil remains by statistical or geometrical means: mean substitution, thin plate spline warping (TPS), and multiple linear regression. These methods are compared by reconstructing the same sample of individuals using each technique. Samples drawn from Homo sapiens, Pan troglodytes, Gorilla gorilla, and various hominin fossils are reconstructed by iteratively removing then estimating the landmarks. The testing determines the methods' behaviour in relation to the extant of landmark loss (i.e., amount of damage), reference sample sizes (this being the data used to guide the reconstructions), and the species of the population from which the reference samples are drawn (which may be different to the species of the damaged fossil).
Given a large enough reference sample, the regression-based method is shown to produce the most accurate reconstructions. Various parameters effect this: when using small reference samples drawn from a population of the same species as the damaged specimen, thin plate splines is the better method, but only as long as there is little damage. As the damage becomes severe (missing 30% of the landmarks, or more), mean substitution should be used instead: thin plate splines are shown to have a rapid error growth in relation to the amount of damage. When the species of the damaged specimen is unknown, or it is the only known individual of its species, the smallest reconstruction errors are obtained with a regression-based approach using a large reference sample drawn from a living species. Testing shows that reference sample size (combined with the use of multiple linear regression) is more important than morphological similarity between the reference individuals and the damaged specimen.
The main contribution of this work are recommendations to the researcher on which of the three methods to use, based on the amount of damage, number of reference individuals, and species of the reference individuals
Automated data reduction workflows for astronomy
Data from complex modern astronomical instruments often consist of a large
number of different science and calibration files, and their reduction requires
a variety of software tools. The execution chain of the tools represents a
complex workflow that needs to be tuned and supervised, often by individual
researchers that are not necessarily experts for any specific instrument. The
efficiency of data reduction can be improved by using automatic workflows to
organise data and execute the sequence of data reduction steps. To realize such
efficiency gains, we designed a system that allows intuitive representation,
execution and modification of the data reduction workflow, and has facilities
for inspection and interaction with the data. The European Southern Observatory
(ESO) has developed Reflex, an environment to automate data reduction
workflows. Reflex is implemented as a package of customized components for the
Kepler workflow engine. Kepler provides the graphical user interface to create
an executable flowchart-like representation of the data reduction process. Key
features of Reflex are a rule-based data organiser, infrastructure to re-use
results, thorough book-keeping, data progeny tracking, interactive user
interfaces, and a novel concept to exploit information created during data
organisation for the workflow execution. Reflex includes novel concepts to
increase the efficiency of astronomical data processing. While Reflex is a
specific implementation of astronomical scientific workflows within the Kepler
workflow engine, the overall design choices and methods can also be applied to
other environments for running automated science workflows.Comment: 12 pages, 7 figure
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