270 research outputs found
Beliefs about Social Distancing During COVID-19 Stay-At-Home Orders: A Theory-Based Salient Belief Elicitation
Understanding the beliefs about social distancing behaviors is required to inform 2019 coronavirus disease (COVID-19) interventions that are based on theory, research, and evidence. This study investigated the salient beliefs related to social distancing. United States adults (n = 106) recruited from Amazon’s Mechanical Turk completed an online reasoned action approach belief elicitation from April 19 to April 25, 2020. Behavioral beliefs (advantages and disadvantages), normative beliefs (approvers and disapprovers), and control beliefs (facilitators and barriers) related to social distancing were elicited via open-ended questions. A content analysis was performed, and kappa statistics revealed high levels of interrater reliability (α = 0.86-0.96). Results revealed that a perceived salient advantage to social distancing was individual COVID-19 prevention, more so than community prevention. The most cited disadvantage was that social distancing could prevent participants from socially interacting with others, which could negatively impact mental health. Family and friends were the most mentioned approvers, while people who hold conservative ideologies and negative attitudes about COVID-19 were the most frequent disapprovers. Supply accessibility and store policies were the most listed facilitators. Results suggest three implications. First, pandemic-related public health and social marketing campaigns should focus more on individual health benefits than community health benefits. Second, digital public health interventions that address social connectedness and mental health outcomes are critical during pandemics. Third, public health scientists and practitioners should work with local and national media outlets and political leaders to create community-tailored and evidence-based information to increase adherence of mitigation strategies
Finding Galaxy Clusters using Voronoi Tessellations
We present an objective and automated procedure for detecting clusters of
galaxies in imaging galaxy surveys. Our Voronoi Galaxy Cluster Finder (VGCF)
uses galaxy positions and magnitudes to find clusters and determine their main
features: size, richness and contrast above the background. The VGCF uses the
Voronoi tessellation to evaluate the local density and to identify clusters as
significative density fluctuations above the background. The significance
threshold needs to be set by the user, but experimenting with different choices
is very easy since it does not require a whole new run of the algorithm. The
VGCF is non-parametric and does not smooth the data. As a consequence, clusters
are identified irrispective of their shape and their identification is only
slightly affected by border effects and by holes in the galaxy distribution on
the sky. The algorithm is fast, and automatically assigns members to
structures.Comment: 11 pages, 11 figures. It uses aa.cls (included). Accepted by A&
Mark correlations: relating physical properties to spatial distributions
Mark correlations provide a systematic approach to look at objects both
distributed in space and bearing intrinsic information, for instance on
physical properties. The interplay of the objects' properties (marks) with the
spatial clustering is of vivid interest for many applications; are, e.g.,
galaxies with high luminosities more strongly clustered than dim ones? Do
neighbored pores in a sandstone have similar sizes? How does the shape of
impact craters on a planet depend on the geological surface properties? In this
article, we give an introduction into the appropriate mathematical framework to
deal with such questions, i.e. the theory of marked point processes. After
having clarified the notion of segregation effects, we define universal test
quantities applicable to realizations of a marked point processes. We show
their power using concrete data sets in analyzing the luminosity-dependence of
the galaxy clustering, the alignment of dark matter halos in gravitational
-body simulations, the morphology- and diameter-dependence of the Martian
crater distribution and the size correlations of pores in sandstone. In order
to understand our data in more detail, we discuss the Boolean depletion model,
the random field model and the Cox random field model. The first model
describes depletion effects in the distribution of Martian craters and pores in
sandstone, whereas the last one accounts at least qualitatively for the
observed luminosity-dependence of the galaxy clustering.Comment: 35 pages, 12 figures. to be published in Lecture Notes of Physics,
second Wuppertal conference "Spatial statistics and statistical physics
The Apparent and Intrinsic Shape of the APM Galaxy Clusters
We estimate the distribution of intrinsic shapes of APM galaxy clusters from
the distribution of their apparent shapes. We measure the projected cluster
ellipticities using two alternative methods. The first method is based on
moments of the discrete galaxy distribution while the second is based on
moments of the smoothed galaxy distribution. We study the performance of both
methods using Monte Carlo cluster simulations covering the range of APM cluster
distances and including a random distribution of background galaxies. We find
that the first method suffers from severe systematic biases, whereas the second
is more reliable. After excluding clusters dominated by substructure and
quantifying the systematic biases in our estimated shape parameters, we recover
a corrected distribution of projected ellipticities. We use the non-parametric
kernel method to estimate the smooth apparent ellipticity distribution, and
numerically invert a set of integral equations to recover the corresponding
distribution of intrinsic ellipticities under the assumption that the clusters
are either oblate or prolate spheroids. The prolate spheroidal model fits the
APM cluster data best.Comment: 8 pages, including 7 figures, accepted for publication in MNRA
The intracluster magnetic field power spectrum in Abell 2382
The goal of this work is to put constraints on the strength and structure of
the magnetic field in the cluster of galaxies A2382. We investigate the
relationship between magnetic field and Faraday rotation effects in the
cluster, using numerical simulations as a reference for the observed
polarization properties. For this purpose we present Very Large Array
observations at 20 cm and 6 cm of two polarized radio sources embedded in
A2382, and we obtained detailed rotation measure images for both of them. We
simulated random three-dimensional magnetic field models with different power
spectra and thus produced synthetic rotation measure images. By comparing our
simulations with the observed polarization properties of the radio sources, we
can determine the strength and the power spectrum of intra-cluster magnetic
field fluctuations that best reproduce the observations. The data are
consistent with a power law magnetic field power spectrum with the Kolmogorov
index , while the outer scale of the magnetic field fluctuations is of
the order of 35 kpc. The average magnetic field strength at the cluster center
is about 3 G and decreases in the external region as the square root of
the electron gas density. The average magnetic field strength in the central 1
Mpc is about 1 G.Comment: Comments: 18 pages, 13 figures, accepted by A&A. For a version with
high quality figures, see http://erg.ca.astro.it/preprints/guidetti2007
The short GRB070707 afterglow and its very faint host galaxy
We present the results from an ESO/VLT campaign aimed at studying the
afterglow properties of the short/hard gamma ray burst GRB 070707. Observations
were carried out at ten different epochs from ~0.5 to ~80 days after the event.
The optical flux decayed steeply with a power-law decay index greater than 3,
later levelling off at R~27.3 mag; this is likely the emission level of the
host galaxy, the faintest yet detected for a short GRB. Spectroscopic
observations did not reveal any line features/edges that could unambiguously
pinpoint the GRB redshift, but set a limit z < 3.6. In the range of allowed
redshifts, the host has a low luminosity, comparable to that of long-duration
GRBs. The existence of such faint host galaxies suggests caution when
associating short GRBs with bright, offset galaxies, where the true host might
just be too dim for detection. The steepness of the decay of the optical
afterglow of GRB 070707 challenges external shock models for the optical
afterglow of short/hard GRBs. We argue that this behaviour might results from
prolonged activity of the central engine or require alternative scenarios.Comment: 6 pages, 5 figures, accepted by A&
Cosmological parameters from the clustering of AGN
We attempt to put constraints on different cosmological and biasing models by
combining the recent clustering results of X-ray sources in the local () and distant universe ().Comment: 9 pages, 3 figures, to be published in the proceedings of the ''2nd
Hellenic Cosmology Workshop'', Athens 2001, eds, Manolis Plionis & Spiros
Kotsaki
A2255: the First Detection of Filamentary Polarized Emission in a Radio Halo
A deep radio observation of the A2255 cluster of galaxies has been carried
out at 1.4 GHz with the Very Large Array synthesis telescope. Thanks to the
excellent (u,v) coverage and sensitivity achieved by our observation, the low
brightness diffuse extended sources in the cluster (radio halo and relic) have
been imaged with unprecedented resolution and dynamic range. We find that the
radio halo has filamentary structures that are strongly polarized. The
fractional linear polarization reaches levels of 2040% and the
magnetic fields appear ordered on scales of 400 kpc. This is the first
successful attempt to detect polarized emission from a radio halo and provides
strong evidence that in this cluster the magnetic field is ordered on large
scales.Comment: 4 pages, 3 figures, accepted for publication in Astronomy and
Astrophysics Letter
The scaling relation of early-type galaxies in clusters. II: Spectroscopic data for galaxies in eight nearby clusters
AIMS: We present in this work low and intermediate resolution spectroscopic
data collected for 152 early type galaxies in 8 nearby clusters with z
0.10.
METHODS: We use low resolution data to produce the redshift and the
K-correction for every individual galaxy, as well as to give their overall
spectral energy distribution, and some spectral indicators, including the
4000\AA break, the Mg strength, and the NaD equivalent width.We have also
obtained higher resolution data for early type galaxies in three of the
clusters, to determine their central velocity dispersion.
RESULTS: The effect of the resolution on the measured parameters is
discussed.
CONCLUSIONS: New accurate systemic redshift and velocity dispersion is
presented for four of the surveyed clusters, A98, A3125, A3330, and DC2103-39.
We have found that the K-correction values for E/S0 bright galaxies in a given
nearby clusters are very similar. We also find that the distribution of the
line indicators significantly differ from cluster to cluster.Comment: 16 pages, 9 figures, Accepted in A&
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