619 research outputs found
The Formation of Networks with Side Payments
We examine the formation of networks among a set of players whose payoffs depend on the structure of the network. We focus on games where players may promise or demand transfer payments when forming links. If players may only make such transfers on the links they are directly involved with, then there are many settings where inefficient networks are the only equilibrium outcomes, and we fully characterize the supportable networks. If externalities are nonpositive and a convexity condition is satisfied, then efficient networks are supportable as equilibria with such direct transfers. If players can also make positive transfers to pay for links they are not involved with, then a convexity condition alone is sufficient for an efficient network to be supportable as an equilibrium. In cases where transfers can be made contingent on the network, then any efficient network is supportable as an equilibrium. We also consider a refinement of equilibrium that allows pairs of players to coordinate their promises and demands on a link. If players can make payments to prevent the formation of a link as well as to form it, then all efficient networks are supportable via the pairwise equilibrium refinementnetwork formation, side-payments
Aqueduct Metadata Document, Aqueduct Global Maps 2.0
This document describes the specific characteristics of the indicator data and calculations for the Aqueduct Water Risk Atlas Global Maps. Complete guidelines and processes for data collection, calculations, and mapping techniques are described fully in the Aqueduct Water Risk Framework. The Aqueduct Water Risk Atlas makes use of a Water Risk Framework, that includes 12 global indicators grouped into three categories of risk and one overall score
Voting for Committees in Agreeable Societies
We examine the following voting situation. A committee of people is to be
formed from a pool of n candidates. The voters selecting the committee will
submit a list of candidates that they would prefer to be on the committee.
We assume that . For a chosen committee, a given voter is said to
be satisfied by that committee if her submitted list of candidates is a
subset of that committee. We examine how popular is the most popular committee.
In particular, we show there is always a committee that satisfies a certain
fraction of the voters and examine what characteristics of the voter data will
increase that fraction.Comment: 11 pages; to appear in Contemporary Mathematic
TB163: Insect Predation of Seeds and Plant Population Dynamics
This review provides a framework for understanding the mechanisms of insect seed predation, the diversity of insects that prey on seeds, and the ecological and evolutionary consequences of insect seed predation. Insect seed predation can play significant roles in reducing plant population growth, modifying intraspecific and interspecific competition, shifting spatial and temporal distribution, affecting species evolution, and plant community structure, both in natural and agricultural ecosystems.https://digitalcommons.library.umaine.edu/aes_techbulletin/1039/thumbnail.jp
The BeppoSAX view of the hard X-ray background
First results on a medium-deep X-ray survey in the "new" 5-10 keV band
carried out with the MECS detectors onboard BeppoSAX are presented. The High
Energy Llarge Area Survey (HELLAS) is aimed to directly explore a band where
the energy density of the X-ray background is more than twice than that in the
soft (0.5-2.0 keV) band. The optical identification follow-up of the first ten
HELLAS hard X-ray sources indicate that Active Galactic Nuclei are the dominant
population at 5-10 keV fluxes of the order of 10e-13 cgs. We discuss the
implications of these findings for the AGN synthesis models for the XRB.Comment: 6 pages, 4 figures, uses psfig.sty. Accepted for publication in
Advances in Space Research, Proceedings of the 32nd Scientific Assembly of
COSPA
A long, hard look at MCG-6-30-15 with XMM-Newton II: detailed EPIC analysis and modelling
The bright Seyfert 1 galaxy MCG-6-30-15 has provided some of the best
evidence to date for the existence of supermassive black holes in active
galactic nuclei. Observations with ASCA revealed an X-ray iron line profile
shaped by strong Doppler and gravitational effects. In this paper the shape of
the iron line, its variability characteristics and the robustness of this
spectral interpretation are examined using the long XMM-Newton observation
taken in 2001. A variety of spectral models, both including and excluding the
effects of strong gravity, are compared to the data in a uniform fashion. The
results strongly favour models in which the spectrum is shaped by emission from
a relativistic accretion disc. It is far more difficult to explain the 3-10 keV
spectrum using models dominated by absorption (either by warm or partially
covering cold matter), emission line blends, curved continua or additional
continuum components. These provide a substantially worse fit to the data and
fail to explain other observations (such as the simultaneous BeppoSAX
spectrum). This reaffirms the veracity of the relativistic `disc line'
interpretation. The short term variability in the shape of the energy spectrum
is investigated and explained in terms of a two-component emission model. Using
a combination of spectral variability analyses the spectrum is successfully
decomposed into a variable power-law component (PLC) and a reflection dominated
component (RDC). The former is highly variable while the latter is
approximately constant throughout the observation, leading to the well-known
spectral variability patterns. (Abridged)Comment: 25 pages. 24 figures. Accepted for publication in MNRA
The variable X-ray spectrum of Markarian 766 - I. Principal components analysis
Aims: We analyse a long XMM-Newton spectrum of the narrow-line Seyfert 1
galaxy Mrk 766, using the marked spectral variability on timescales >20ks to
separate components in the X-ray spectrum. Methods: Principal components
analysis is used to identify distinct emission components in the X-ray
spectrum, possible alternative physical models for those components are then
compared statistically. Results: The source spectral variability is
well-explained by additive variations, with smaller extra contributions most
likely arising from variable absorption. The principal varying component,
eigenvector one, is found to have a steep (photon index 2.4) power-law shape,
affected by a low column of ionised absorption that leads to the appearance of
a soft excess. Eigenvector one varies by a factor 10 in amplitude on
time-scales of days and appears to have broad ionised Fe K-alpha emission
associated with it: the width of the ionised line is consistent with an origin
at about 100 gravitational radii. There is also a strong component of
near-constant emission that dominates in the low state, whose spectrum is
extremely hard above 1 keV, with a soft excess at lower energies, and with a
strong edge at Fe K but remarkably little Fe K-alpha emission. Although this
component may be explained as relativistically-blurred reflection from the
inner accretion disc, we suggest that its spectrum and lack of variability may
alternatively be explained as either (i) ionised reflection from an extended
region, possibly a disc wind, or (ii) a signature of absorption by a disc wind
with a variable covering fraction. Absorption features in the low state may
indicate the presence of an outflow.Comment: 14 pages, accepted for publication in Astronomy & Astrophysic
Barriers and facilitators to COVID-19 vaccine uptake among Australian health professional students during the pandemic: a nationwide study
Using a cross-sectional online survey we investigated knowledge, attitudes, and risk perception about COVID-19 vaccination and identified factors influencing vaccine uptake among Australian health professional students from October 2021 to January 2022. We analysed data from 1114 health professional students from 17 Australian universities. Most participants were enrolled in nursing programs (nâ=â958, 86.8%), and 91.6% (nâ=â858) of the participants received COVID-19 vaccination. Approximately 27% believed COVID-19 was no more serious than seasonal influenza and that they had a low risk of acquiring COVID-19. Nearly 20% disagreed that COVID-19 vaccines in Australia were safe and perceived they were at higher-risk of acquiring COVID infection than the general population. Higher-risk perception viewing vaccination as their professional responsibility, and vaccine mandate strongly predicted vaccination behaviour. Participants consider COVID-19 information from health professionals, government websites, and World Health Organization as the most trusted information sources. The findings highlight that healthcare decision-makers and university administrators need to monitor studentsâ hesitancy with vaccination to improve studentsâ promotion of the vaccination to the general population
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