1,662 research outputs found
Interrupting the social amplification of risk process: a case study in collective emissions reduction
One of the main approaches we have for studying the progressive divergence of understandings around a risk issue is that of social risk amplification. This article describes a case study of a particular environmental contaminant, a chemical flame retardant that could be interpreted as having produced a risk amplifying process. It describes in particular how a group of industrial organizations acted collectively to reduce emissions of this contaminant, in an apparent attempt to avert regulation and boycottsâthat is, to intercept the social amplification process and avoid its secondary effects. The aim of the study was to investigate the constitutive qualities of this collective action: the qualities that defined it and made it effective in the eyes of those involved. These include institutionalisation and independence, the ability to confer individual as well as collective benefit, the capacity to attract (rather than avoid) criticism, and the âbrandingâ that helps communicate what otherwise appear to be a set of unconnected, local actions. Although the risk amplification framework has been criticised for implying that there is some externally given risk level that is subsequently amplified, it does appear to capture the mentality of actors involved in issues of this kind. They talk and act as though they believe they are participants in a risk amplification process
A Proper Motion Survey for White Dwarfs with the Wide Field Planetary Camera 2
We have performed a search for halo white dwarfs as high proper motion
objects in a second epoch WFPC2 image of the Groth-Westphal strip. We identify
24 high proper motion objects with mu > 0.014 ''/yr. Five of these high proper
motion objects are identified as strong white dwarf candidates on the basis of
their position in a reduced proper motion diagram. We create a model of the
Milky Way thin disk, thick disk and stellar halo and find that this sample of
white dwarfs is clearly an excess above the < 2 detections expected from these
known stellar populations. The origin of the excess signal is less clear.
Possibly, the excess cannot be explained without invoking a fourth galactic
component: a white dwarf dark halo. We present a statistical separation of our
sample into the four components and estimate the corresponding local white
dwarf densities using only the directly observable variables, V, V-I, and mu.
For all Galactic models explored, our sample separates into about 3 disk white
dwarfs and 2 halo white dwarfs. However, the further subdivision into the thin
and thick disk and the stellar and dark halo, and the subsequent calculation of
the local densities are sensitive to the input parameters of our model for each
Galactic component. Using the lowest mean mass model for the dark halo we find
a 7% white dwarf halo and six times the canonical value for the thin disk white
dwarf density (at marginal statistical significance), but possible systematic
errors due to uncertainty in the model parameters likely dominate these
statistical error bars. The white dwarf halo can be reduced to around 1.5% of
the halo dark matter by changing the initial mass function slightly. The local
thin disk white dwarf density in our solution can be made consistent with the
canonical value by assuming a larger thin disk scaleheight of 500 pc.Comment: revised version, accepted by ApJ, results unchanged, discussion
expande
Curvature energy effects on strange quark matter nucleation at finite density
We consider the effects of the curvature energy term on thermal strange quark
matter nucleation in dense neutron matter. Lower bounds on the temperature at
which this process can take place are given and compared to those without the
curvature term.Comment: PlainTex, 6 pp., IAG-USP Rep.5
Artificial Intelligence Approach to the Determination of Physical Properties of Eclipsing Binaries. I. The EBAI Project
Achieving maximum scientific results from the overwhelming volume of
astronomical data to be acquired over the next few decades will demand novel,
fully automatic methods of data analysis. Artificial intelligence approaches
hold great promise in contributing to this goal. Here we apply neural network
learning technology to the specific domain of eclipsing binary (EB) stars, of
which only some hundreds have been rigorously analyzed, but whose numbers will
reach millions in a decade. Well-analyzed EBs are a prime source of
astrophysical information whose growth rate is at present limited by the need
for human interaction with each EB data-set, principally in determining a
starting solution for subsequent rigorous analysis. We describe the artificial
neural network (ANN) approach which is able to surmount this human bottleneck
and permit EB-based astrophysical information to keep pace with future data
rates. The ANN, following training on a sample of 33,235 model light curves,
outputs a set of approximate model parameters (T2/T1, (R1+R2)/a, e sin(omega),
e cos(omega), and sin i) for each input light curve data-set. The whole sample
is processed in just a few seconds on a single 2GHz CPU. The obtained
parameters can then be readily passed to sophisticated modeling engines. We
also describe a novel method polyfit for pre-processing observational light
curves before inputting their data to the ANN and present the results and
analysis of testing the approach on synthetic data and on real data including
fifty binaries from the Catalog and Atlas of Eclipsing Binaries (CALEB)
database and 2580 light curves from OGLE survey data. [abridged]Comment: 52 pages, accepted to Ap
Relics of the Cosmological QCD Phase Transition
The abundance and size distribution of quark nuggets (QN), formed a few
microseconds after the big bang due to first order QCD phase transition in the
early universe, has been estimated. It appears that stable QNs could be a
viable candidate for cosmological dark matter. The evolution of baryon
inhomogeneity due to evaporated (unstable) QNs are also examined.Comment: To appear in Physical Review
Dynamical evolution of the Universe in the quark-hadron phase transition and possible nugget formation
We study the dynamics of first-order phase transition in the early Universe
when it was old with quarks and gluons condensing into hadrons.
We look at how the Universe evolved through the phase transition in small as
well as large super cooling scenario, specifically exploring the formation of
quark nuggets and their possible survival. The nucleation of the hadron phase
introduces new distance scales in the Universe, which we estimate along with
the hadron fraction, temperature, nucleation time etc. It is of interest to
explore whether there is a relic signature of this transition in the form of
quark nuggets which might be identified with the recently observed dark objects
in our galactic halo and account for the Dark Matter in the Universe at
present.Comment: LaTeX file with four postscript figure
Possible Cosmological Implications of the Quark-Hadron Phase Transition
We study the quark-hadron phase transition within an effective model of QCD,
and find that in a reasonable range of the main parameters of the model, bodies
with quark content between and 10 solar masses can have been formed
in the early universe. In addition, we show that a significant amount of
entropy is released during the transition. This may imply the existence of a
higher baryon number density than what is usually expected at temperatures
above the QCD scale. The cosmological QCD transition may then provide a natural
way for decreasing the high baryon asymmetry created by an Affleck-Dine like
mechanism down to the value required by primordial nucleosynthesis.Comment: 19 pages, LaTeX, 5 Postscript figures included. Submitted to Journal
of Physics
Early mortality outcomes of patients with fragility hip fracture and concurrent SARS-CoV-2 infection: a systematic review and meta-analysis
AimsHip fracture is a common condition of the older, frailer person. This population is also at risk from SARS-CoV-2 infection. It is important to understand the impact of coexistent hip fracture and SARS-CoV-2 for informed decision-making at patient and service levels.MethodsWe undertook a systematic review and meta-analysis of observational studies of older (> 60 years) people with fragility hip fractures and outcomes with and without SARS-CoV-2 infection during the first wave of the COVID-19 pandemic. The primary outcome was early (30-day or in-hospital) mortality. Secondary outcomes included length of hospital stay and key clinical characteristics known to be associated with outcomes after hip fracture.ResultsA total of 14 cohort and five case series studies were included (692 SARS-CoV-2 positive, 2,585 SARS-CoV-2 negative). SARS-CoV-2 infection was associated with an overall risk ratio (RR) for early mortality of 4.42 (95% confidence interval (CI) 3.42 to 5.82). Early mortality was 34% (95% CI 30% to 38%) and 9% (95% CI 8% to 10%) in the infected and noninfected groups respectively. Length of stay was increased in SARS-CoV-2 infected patients (mean difference (MD) 5.2 days (3.2 to 7.2)). Age (MD 1.6 years (0.3 to 2.9)); female sex (RR 0.83 (95% CI 0.65 to 1.05)); admission from home (RR 0.51 (95% CI 0.26 to 1.00)); presence of dementia (RR 1.13 (95% CI 0.94 to 1.43)); and intracapsular fracture (RR 0.89 (95% CI 0.71 to 1.11)) were not associated with SARS-CoV-2 infection. There were statistically, but not clinically, significantly greater Nottingham Hip Fracture Scores in infected compared with non-infected patients (MD 0.7 (0.4 to 0.9)).ConclusionSARS-CoV-2 infection is associated with worse outcomes after hip fracture. This is not explained by differences in patient characteristics. These data can be used to support informed decision-making and may help track the impact of widespread adoption of system-level and therapeutic changes in management of the COVID-19 pandemic
Baryon number segregation at the end of the cosmological quark-hadron transition
One of the most interesting questions regarding a possible first order
cosmological quark--hadron phase transition concerns the final fate of the
baryon number contained within the disconnected quark regions at the end of the
transition. We here present a detailed investigation of the hydrodynamical
evolution of an evaporating quark drop, using a multi-component fluid
description to follow the mechanisms of baryon number segregation. With this
approach, we are able to take account of the simultaneous effects of baryon
number flux suppression at the phase interface, entropy extraction by means of
particles having long mean-free-paths, and baryon number diffusion. A range of
computations has been performed to investigate the permitted parameter-space
and this has shown that significant baryon number concentrations, perhaps even
up to densities above that of nuclear matter, represent an inevitable outcome
within this scenario.Comment: 33 pages, Latex file, 6 postscript figures included in the text
(psfig.tex). To appear in Phys. Rev. D1
Strange Star Heating Events as a Model for Giant Flares of Soft Gamma-ray Repeaters
Two giant flares were observed on 5 March 1979 and 27 August 1998 from the
soft gamma-ray repeaters SGR 0526-66 and SGR 1900+14, respectively. The
striking similarity between these remarkable bursts strongly implies a common
nature. We show that the light curves of the giant bursts may be easily
explained in the model where the burst radiation is produced by the bare quark
surface of a strange star heated, for example, by impact of a massive
comet-like object.Comment: 5 pages, 4 figures, accepted for publication in Phys. Rev. Letter
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