514 research outputs found
Self-calibration and improving image fidelity for ALMA and other radio interferometers
This manual is intended to help ALMA and other interferometer users improve
images by recognising limitations and how to overcome them and deciding when
and how to use self-calibration. The images provided by the ALMA Science
Archive are calibrated using standard observing and data processing routines,
including a quality assurance process to make sure that the observations meet
the proposer's science requirements. This may not represent the full potential
of the data, since any interferometry observation can be imaged with a range of
resolutions and surface brightness sensitivity. The separation between phase
calibration source and target usually limits the target dynamic range to a few
hundred (or 50--100 for challenging conditions) but if the noise in the target
field has not reached the thermal limit, improvements may be possible using
self-calibration. This often requires judgements based on the target properties
and is not yet automated for all situations. This manual provides background on
the instrumental and atmospheric causes of visibility phase and amplitude
errors, their effects on imaging and how to improve the signal to noise ratio
and image fidelity by self-calibration. We introduce the conditions for
self-calibration to be useful and how to estimate calibration parameter values
for a range of observing modes (continuum, spectral line etc.). We also
summarise more general error recognition and other techniques to tackle imaging
problems. The examples are drawn from ALMA interferometric data processed using
CASA, but the principles are generally applicable to most similar cm to sub-mm
imaging.Comment: 76 pages, 55 figures, ALMA Memo serie
Sharenting: Pride, affect and the day to day politics of digital mothering
The coming together of parenting and routine posting on social networking sites has become a visible and recognisable theme and the term ‘sharenting’ has found a place in everyday talk to describe some forms of parental digital sharing practices. However, while social media has undoubtedly provided a space for parents to share experiences and receive support around parenting, sharenting remains a contestable issue. Thus, one reading of sharenting would be as a display of good parenting as mothers ‘show off’ their children as a marker of success. However, the term also can be used pejoratively to describe parental oversharing of child-focused images and content. In this paper we explore the practice of sharenting in terms of pride, affect, and the politics of digital mothering in a neoliberal context to conclude that sharenting can be best understood as a complex affective and intersectional accomplishment that produces motherhood and family as communicative activities within digital social practices
Towards Visual Feedback Loops for Robot-Controlled Additive Manufacturing
Robotic additive manufacturing methods have enabled the design and fabrication of novel forms and material systems that represent an important step forward for architectural fabrication. However, a common problem in additive manufacturing is to predict and incorporate the dynamic behavior of the material that is the result of the complex confluence of forces and material properties that occur during fabrication. While there have been some approaches towards verification systems, to date most robotic additive manufacturing processes lack verification to ensure deposition accuracy. Inaccuracies, or in some instances critical errors, can occur due to robot dynamics, material self-deflection, material coiling, or timing shifts in the case of multi-material prints. This paper addresses that gap by presenting an approach that uses vision-based sensing systems to assist robotic additive manufacturing processes. Using online image analysis techniques, occupancy maps can be created and updated during the fabrication process to document the actual position of the previously deposited material. This development is an intermediary step towards closed-loop robotic control systems that combine workspace sensing capabilities with decision-making algorithms to adjust toolpaths to correct for errors or inaccuracies if necessary. The occupancy grid map provides a complete representation of the print that can be analyzed to determine various key aspects, such as, print quality, extrusion diameter, adhesion between printed parts, and intersections within the meshes. This valuable quantitative information regarding system robustness can be used to influence the system’s future actions. This approach will help ensure consistent print quality and sound tectonics in robotic additive manufacturing processes, improving on current techniques and extending the possibilities of robotic fabrication in architecture
The High-redshift Clusters Occupied by Bent Radio AGN (COBRA) Survey: Investigating the Role of Environment on Bent Radio AGNs Using LOFAR
© 2023. The Author(s). Published by the American Astronomical Society. This is an open access article distributed under the terms of the Creative Commons Attribution License (CC BY), https://creativecommons.org/licenses/by/4.0/Bent radio active galactic nucleus (AGN) morphology depends on the density of the surrounding gas. However, bent sources are found inside and outside clusters, raising the question of how environment impacts bent AGN morphology. We analyze new LOw-Frequency Array the LOFAR Two-metre Sky Survey (LoTSS) Data Release II observations of 20 bent AGNs in clusters and 15 not in clusters from the high-z Clusters Occupied by Bent Radio AGN (COBRA) survey (0.35 1.2 Mpc) or bent AGNs in weaker groups rather than the field.Peer reviewe
Rapid evolution of Anguillicola crassusin Europe: species diagnostic traits are plastic and evolutionarily labile
The Mathematical Universe
I explore physics implications of the External Reality Hypothesis (ERH) that
there exists an external physical reality completely independent of us humans.
I argue that with a sufficiently broad definition of mathematics, it implies
the Mathematical Universe Hypothesis (MUH) that our physical world is an
abstract mathematical structure. I discuss various implications of the ERH and
MUH, ranging from standard physics topics like symmetries, irreducible
representations, units, free parameters, randomness and initial conditions to
broader issues like consciousness, parallel universes and Godel incompleteness.
I hypothesize that only computable and decidable (in Godel's sense) structures
exist, which alleviates the cosmological measure problem and help explain why
our physical laws appear so simple. I also comment on the intimate relation
between mathematical structures, computations, simulations and physical
systems.Comment: Replaced to match accepted Found. Phys. version, 31 pages, 5 figs;
more details at http://space.mit.edu/home/tegmark/toe.htm
The Massive and Distant Clusters of WISE Survey VI: Stellar Mass Fractions of a Sample of High-Redshift Infrared-selected Clusters
We present measurements of the stellar mass fractions () for a
sample of high-redshift () infrared-selected galaxy
clusters from the Massive and Distant Clusters of WISE Survey (MaDCoWS) and
compare them to the stellar mass fractions of Sunyaev-Zel'dovich (SZ)
effect-selected clusters in a similar mass and redshift range from the South
Pole Telescope (SPT)-SZ Survey. We do not find a significant difference in mean
between the two selection methods, though we do find an unexpectedly
large range in for the SZ-selected clusters. In addition, we measure
the luminosity function of the MaDCoWS clusters and find ,
similar to other studies of clusters at or near our redshift range. Finally, we
present SZ detections and masses for seven MaDCoWS clusters and new
spectroscopic redshifts for five MaDCoWS clusters. One of these new clusters,
MOO J1521+0452 at , is the most distant MaDCoWS cluster confirmed to
date.Comment: Accepted to Ap
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