483 research outputs found
Non-pharmaceutical Interventions and the Infodemic on Twitter: Lessons Learned from Italy during the Covid-19 Pandemic
The COVID-19 pandemic changed expectations for information dissemination and use around the globe, challenging accepted models of communications, leadership, and social systems. We explore how social media discourse about COVID-19 in Italy was affected by the rapid spread of the virus, and how themes in postings changed with the adoption of social distancing measures and non-pharmaceutical interventions (NPI). We used topic modeling and social network analysis to highlight critical dimensions of conversations around COVID-19: 1) topics in social media postings about the Coronavirus; 2) the scope and reach of social networks; and 3) changes in social media content as the nation moved from partial to full social distancing. Twitter messages sent in Italy between February 11th and March 10th, 2020. 74,306 Tweets sent by institutions, news sources, elected officials, scientists and social media influencers. Messages were retweeted more than 1.2 million times globally. Non-parametric chi-square statistic with residual analysis to identify categories, chi-square test for linear trend, and Social Network Graphing. The first phase of the pandemic was dominated by social media influencers, followed by a focus on the economic consequences of the virus and placing blame on immigrants. As the crisis deepened, science-based themes began to predominate, with a focus on reducing the spread of the virus through physical distancing and business closures Our findings highlight the importance of messaging in social media in gaining the publicâs trust and engagement during a pandemic. This requires credible scientific voices to garner public support for effective mitigation. Fighting the spread of an infectious disease goes hand in hand with stemming the dissemination of lies, bad science, and misdirection
Recent cancer incidence trends in an observational clinical cohort of HIV-infected patients in the US, 2000 to 2011
Abstract Background In HIV-infected populations in developed countries, the most recent published cancer incidence trend analyses are only updated through 2008. We assessed changes in the distribution of cancer types and incidence trends among HIV-infected patients in North Carolina up until 2011. Methods We linked the University of North Carolina Center for AIDS Research HIV Clinical Cohort, an observational clinical cohort of 3141 HIV-infected patients, with the North Carolina Cancer registry. Cancer incidence rates were estimated across calendar years from 2000 to 2011. The distribution of cancer types was described. Incidence trends were assessed with linear regression. Results Across 15,022 person-years of follow-up, 202 cancers were identified (incidence rate per 100,000 person-years [IR]: 1345; 95% confidence interval [CI]: 1166, 1544). The majority of cancers were virus-related (61%), including Kaposi sarcoma (Nâ=â32) (IR: 213; 95%CI: 146, 301), non-Hodgkin lymphoma (Nâ=â34) (IR: 226; 95%CI: 157, 316), and anal cancer (Nâ=â16) (IR: 107; 95%CI: 61, 173). Non-Hodgkin lymphoma was observed to decrease from 2000 to 2011 (decline of 15 cases per 100,000 person-years per calendar year, 95%CI: -27, -3). No other changes in incidence or changes in incidence trends were observed for other cancers (all Pâ>â0.20). Conclusions We observed a substantial burden of a variety of cancers in this population in the last decade. Kaposi sarcoma and non-Hodgkin lymphoma were consistently two of the greatest contributors to cancer burden across calendar time. Cancer rates appeared stable across calendar years, except for non-Hodgkin lymphoma, which appeared to decrease throughout the study period
The role of feedback in shaping the structure of the interstellar medium
We present an analysis of the role of feedback in shaping the neutral hydrogen (H I) content of simulated disc galaxies. For our analysis, we have used two realizations of two separate Milky Way-like (similar to L star) discs - one employing a conservative feedback scheme (McMaster Unbiased Galaxy Survey), the other significantly more energetic [Making Galaxies In a Cosmological Context (MaGICC)]. To quantify the impact of these schemes, we generate zeroth moment (surface density) maps of the inferred H I distribution; construct power spectra associated with the underlying structure of the simulated cold interstellar medium, in addition to their radial surface density and velocity dispersion profiles. Our results are compared with a parallel, self-consistent, analysis of empirical data from The H I Nearby Galaxy Survey (THINGS). Single power-law fits (P proportional to k(gamma)) to the power spectra of the stronger feedback (MaGICC) runs (over spatial scales corresponding to similar to 0.5 to similar to 20 kpc) result in slopes consistent with those seen in the THINGS sample (gamma similar to -2.5). The weaker feedback (MUGS) runs exhibit shallower power-law slopes (gamma similar to -1.2). The power spectra of the MaGICC simulations are more consistent though with a two-component fit, with a flatter distribution of power on larger scales (i.e. gamma similar to -1.4 for scales in excess of similar to 2 kpc) and a steeper slope on scales below similar to 1 kpc (gamma similar to -5), qualitatively consistent with empirical claims, as well as our earlier work on dwarf discs. The radial H I surface density profiles of the MaGICC discs show a clear exponential behaviour, while those of the MUGS suite are essentially flat; both behaviours are encountered in nature, although the THINGS sample is more consistent with our stronger (MaGICC) feedback runs
Ram pressure drag - the effects of ram pressure on dark matter and stellar disk dynamics
We investigate the effects of ram pressure stripping on gas-rich disk
galaxies in the cluster environment. Ram pressure stripping principally effects
the atomic gas in disk galaxies, stripping away outer disk gas to a truncation
radius. We demonstrate that the drag force exerted on truncated gas disks is
passed to the stellar disk, and surrounding dark matter through their mutual
gravity. Using a toy model of ram pressure stripping, we show that this can
drag a stellar disk and dark matter cusp off centre within it's dark matter
halo by several kiloparsecs. We present a simple analytical description of this
process that predicts the drag force strength and its dependency on ram
pressures and disk galaxy properties to first order. The motion of the disk can
result in temporary deformation of the stellar disk. However we demonstrate
that the key source of stellar disk heating is the removal of the gas potential
from within the disk. This can result in disk thickening by approximately a
factor of two in gas-rich disks.Comment: Accepted by MNRAS (Oct 2011) 17 pages, 11 figures, 1 tabl
The dark matter halo shape of edge-on disk galaxies - I. HI observations
This is the first paper of a series in which we will attempt to put
constraints on the flattening of dark halos in disk galaxies. We observe for
this purpose the HI in edge-on galaxies, where it is in principle possible to
measure the force field in the halo vertically and radially from gas layer
flaring and rotation curve decomposition respectively. In this paper, we define
a sample of 8 HI-rich late-type galaxies suitable for this purpose and present
the HI observations.Comment: Accepted for publication by Astronomy & Astrophysics. For a higher
resolution version see
http://www.astro.rug.nl/~vdkruit/jea3/homepage/12565.pd
The M81 Group Dwarf Irregular Galaxy DDO 165. I. High Velocity Neutral Gas in a Post-Starburst System
We present new multi-configuration VLA HI spectral line observations of the
M81 group dIrr post-starburst galaxy DDO 165. The HI morphology is complex,
with multiple column density peaks surrounding a large region of very low HI
surface density that is offset from the center of the stellar distribution. The
bulk of the neutral gas is associated with the southern section of the galaxy;
a secondary peak in the north contains ~15% of the total HI mass. These
components appear to be kinematically distinct, suggesting that either tidal
processes or large-scale blowout have recently shaped the ISM of DDO 165. Using
spatially-resolved position-velocity maps, we find multiple localized
high-velocity gas features. Cross-correlating with radius-velocity analyses, we
identify eight shell/hole structures in the ISM with a range of sizes (~400-900
pc) and expansion velocities (~7-11 km/s). These structures are compared with
narrow- and broad-band imaging from KPNO and HST. Using the latter data, recent
works have shown that DDO 165's previous "burst" phase was extended temporally
(>1 Gyr). We thus interpret the high-velocity gas features, HI holes, and
kinematically distinct components of the galaxy in the context of the immediate
effects of "feedback" from recent star formation. In addition to creating HI
holes and shells, extended star formation events are capable of creating
localized high velocity motion of the surrounding interstellar material. A
companion paper connects the energetics from the HI and HST data.Comment: The Astrophysical Journal, in press. Full-resolution version
available on request from the first autho
Vehicle emissions and consumer information in car advertisements
This is an Open Access article distributed under the terms of the Creative Commons Attribution Licens
The spatial distribution of star and cluster formation in M51
Aims. We study the connection between spatially resolved star formation and
young star clusters across the disc of M51. Methods. We combine star cluster
data based on B, V, and I-band Hubble Space Telescope ACS imaging, together
with new WFPC2 U-band photometry to derive ages, masses, and extinctions of
1580 resolved star clusters using SSP models. This data is combined with data
on the spatially resolved star formation rates and gas surface densities, as
well as Halpha and 20cm radio-continuum (RC) emission, which allows us to study
the spatial correlations between star formation and star clusters. Two-point
autocorrelation functions are used to study the clustering of star clusters as
a function of spatial scale and age. Results. We find that the clustering of
star clusters among themselves decreases both with spatial scale and age,
consistent with hierarchical star formation. The slope of the autocorrelation
functions are consistent with projected fractal dimensions in the range of
1.2-1.6, which is similar to other galaxies, therefore suggesting that the
fractal dimension of hierarchical star formation is universal. Both star and
cluster formation peak at a galactocentric radius of 2.5 and 5 kpc, which we
tentatively attribute to the presence of the 4:1 resonance and the co-rotation
radius. The positions of the youngest (<10 Myr) star clusters show the
strongest correlation with the spiral arms, Halpha, and the RC emission, and
these correlations decrease with age. The azimuthal distribution of clusters in
terms of kinematic age away from the spiral arms indicates that the majority of
the clusters formed 5-20 Myr before their parental gas cloud reached the centre
of the spiral arm.Comment: 14 pages, 21 figures, accepted for publication in A&
The ISM in spiral galaxies: can cooling in spiral shocks produce molecular clouds?
We investigate the thermodynamics of the ISM and the formation of molecular
hydrogen through numerical simulations of spiral galaxies. The model follows
the chemical, thermal and dynamical response of the disc to an external spiral
potential. Self-gravity and magnetic fields are not included. The calculations
demonstrate that gas can cool rapidly when subject to a spiral shock. Molecular
clouds in the spiral arms arise through a combination of compression of the ISM
by the spiral shock and orbit crowding. These results highlight that local
self-gravity is not required to form molecular clouds. Self-shielding provides
a sharp transition density, below which gas is essentially atomic, and above
which the molecular gas fraction is >0.001. The timescale for gas to move
between these regimes is very rapid (<~1 Myr). From this stage, the majority of
gas generally takes between 10 to 20 Myr to obtain high H fractions (>50
%). Although our calculations are unable to resolve turbulent motions on scales
smaller than the spiral arm and do not include self-gravity. True cloud
formation timescales are therefore expected to be even shorter.
The mass budget of the disc is dominated by cold gas residing in the spiral
arms. Between 50 and 75 % of this gas is in the atomic phase. When this gas
leaves the spiral arm and drops below the self-shielding limit it is heated by
the galactic radiation field. Consequently, most of the volume in the interarm
regions is filled with warm atomic gas. However, some cold spurs and clumps can
survive in interarm regions for periods comparable to the interarm passage
timescale. Altogether between 7 and 40% of the gas in our disc is molecular,
depending on the surface density of the calculation, with approximately 20%
molecular for a surface density comparable to the solar neighbourhood.Comment: 16 pages, 19 figures, accepted for publication in MNRA
Calibration and Characterization of the IceCube Photomultiplier Tube
Over 5,000 PMTs are being deployed at the South Pole to compose the IceCube
neutrino observatory. Many are placed deep in the ice to detect Cherenkov light
emitted by the products of high-energy neutrino interactions, and others are
frozen into tanks on the surface to detect particles from atmospheric cosmic
ray showers. IceCube is using the 10-inch diameter R7081-02 made by Hamamatsu
Photonics. This paper describes the laboratory characterization and calibration
of these PMTs before deployment. PMTs were illuminated with pulses ranging from
single photons to saturation level. Parameterizations are given for the single
photoelectron charge spectrum and the saturation behavior. Time resolution,
late pulses and afterpulses are characterized. Because the PMTs are relatively
large, the cathode sensitivity uniformity was measured. The absolute photon
detection efficiency was calibrated using Rayleigh-scattered photons from a
nitrogen laser. Measured characteristics are discussed in the context of their
relevance to IceCube event reconstruction and simulation efforts.Comment: 40 pages, 12 figure
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